Measurements of All-Particle Energy Spectrum and Mean Logarithmic Mass of Cosmic Rays from 0.3 to 30 PeV with LHAASO-KM2A

We present the measurements of all-particle energy spectrum and mean logarithmic mass of cosmic rays in the energy range of 0.3-30 PeV using data collected from LHAASO-KM2A between September 2021 and December 2022, which is based on a nearly composition-independent energy reconstruction method, achieving unprecedented accuracy. Our analysis reveals the position of the knee at 3.67±0.05±0.15  PeV. Below the knee, the spectral index is found to be -2.7413±0.0004±0.0050, while above the knee, it is -3.128±0.005±0.027, with the sharpness of the transition measured with a statistical error of 2%. The mean logarithmic mass of cosmic rays is almost heavier than helium in the whole measured energy range. It decreases from 1.7 at 0.3 PeV to 1.3 at 3 PeV, representing a 24% decline following a power law with an index of -0.1200±0.0003±0.0341. This is equivalent to an increase in abundance of light components. Above the knee, the mean logarithmic mass exhibits a power law trend towards heavier components, which is reversal to the behavior observed in the all-particle energy spectrum. Additionally, the knee position and the change in power-law index are approximately the same. These findings suggest that the knee observed in the all-particle spectrum corresponds to the knee of the light component, rather than the medium-heavy components.

[Correlation of 1p/16q loss of heterozygosity and 1p gain with clinicopathological characteristics and prognosis in Wilms tumor]

Objective: To investigate the relationship between 1p/16q loss of heterozygosity (LOH) and 1p gain in Wilms tumor and their clinicopathologic characteristics and prognosis. Methods: A total of 175 Wilms tumor samples received from the Department of Pathology, Beijing Children's Hospital from September 2019 to August 2022 were retrospectively analyzed. The histopathologic type and presence of lymph node involvement were evaluated by two pathologists. The clinical data including patients'gender, age, tumor location, preoperative chemotherapy, and tumor stage were summarized. Fluorescence in situ hybridization (FISH) was done to detect 1p/16q LOH and 1p gain and their correlation with the clinicopathological features and prognosis were analyzed. Results: Among the 175 samples, 86 cases (49.1%) were male and 89 (50.9%) were female. The mean age was (3.5±2.9) years, and the median age was 2.6 years. There were 26 (14.9%) cases with 1p LOH, 28 (16.0%) cases with 16q LOH, 10 (5.7%) cases of LOH at both 1p and 16q, and 53 (30.3%) cases with 1q gain. 1q gain was significantly associated with 1p LOH (P<0.01) and 16q LOH (P<0.01). There were significant differences (P<0.01) between 1q gain, 1p LOH and 16q LOH among different age groups. The rate of 16q LOH in the high-risk histopathological subtype (50.0%) was significantly higher than that in the intermediate-risk subtype (13.6%, P<0.05). The frequency of 1q gain, 1p LOH, and 16q LOH in children with advanced clinical stages (Ⅲ and Ⅳ) was significantly higher than that in children with early clinical stages (Ⅰ and Ⅱ). 1q gain, 1p LOH, and 16q LOH showed no significant correlation with gender, unilateral or bilateral disease, chemotherapy, or lymph node metastasis. The progression-free survival (PFS) time for patients with 1q gain and 1p LOH was significantly shorter than those without these aberrations (P<0.05). Additionally, the PFS time of patients with 16q LOH was slightly shorter than those with normal 16q, although the difference was not statistically significant. Patients with stage Ⅲ to Ⅳ disease exhibiting 1q gain or 1p LOH had a significantly higher relative risk of recurrence, metastasis, and mortality. Conclusions: 1p/16q LOH and 1q gain are associated with age, high-risk histological type, and clinical stage in Wilms tumor. 1q gain and 1p LOH are significantly correlated with the prognosis of Wilms tumor.

Measurement of Ultra-High-Energy Diffuse Gamma-Ray Emission of the Galactic Plane from 10 TeV to 1 PeV with LHAASO-KM2A

The diffuse Galactic γ-ray emission, mainly produced via interactions between cosmic rays and the interstellar medium and/or radiation field, is a very important probe of the distribution, propagation, and interaction of cosmic rays in the Milky Way. In this Letter, we report the measurements of diffuse γ rays from the Galactic plane between 10 TeV and 1 PeV energies, with the square kilometer array of the Large High Altitude Air Shower Observatory (LHAASO). Diffuse emissions from the inner (15°10  TeV). The energy spectrum in the inner Galaxy regions can be described by a power-law function with an index of -2.99±0.04, which is different from the curved spectrum as expected from hadronic interactions between locally measured cosmic rays and the line-of-sight integrated gas content. Furthermore, the measured flux is higher by a factor of ∼3 than the prediction. A similar spectrum with an index of -2.99±0.07 is found in the outer Galaxy region, and the absolute flux for 10≲E≲60  TeV is again higher than the prediction for hadronic cosmic ray interactions. The latitude distributions of the diffuse emission are consistent with the gas distribution, while the longitude distributions show clear deviation from the gas distribution. The LHAASO measurements imply that either additional emission sources exist or cosmic ray intensities have spatial variations.

A tera-electron volt afterglow from a narrow jet in an extremely bright gamma-ray burst

Some gamma-ray bursts (GRBs) have a tera-electron volt (TeV) afterglow, but the early onset of this has not been observed. We report observations with the Large High Altitude Air Shower Observatory of the bright GRB 221009A, which serendipitously occurred within the instrument field of view. More than 64,000 photons >0.2 TeV were detected within the first 3000 seconds. The TeV flux began several minutes after the GRB trigger, then rose to a peak about 10 seconds later. This was followed by a decay phase, which became more rapid ~650 seconds after the peak. We interpret the emission using a model of a relativistic jet with half-opening angle ~0.8°. This is consistent with the core of a structured jet and could explain the high isotropic energy of this GRB.

[Association of hs-CRP with frailty and its components among the elderly over 65 years old in 9 longevity areas of China]

Objective: To investigate the association of the levels of high sensitivity C-reactive protein (hs-CRP) with frailty and its components among the elderly over 65 years old in 9 longevity areas of China. Methods: Cross-sectional data from the Health Ageing and Biomarkers Cohort Study (HABCS, 2017-2018) were used and the elderly over 65 years old were included in this study. Through questionnaire interview and physical examination, the information including demographic characteristics, behavior, diet, daily activity, cognitive function, and health status was collected. The association between hs-CRP and frailty and its components in the participants was analyzed by multivariate logistic regression model and restrictive cubic spline. Results: A total of 2 453 participants were finally included, the age was (84.8±19.8) years old. The median hs-CRP level was 1.13 mg/L and the prevalence of frailty was 24.4%. Compared with the low-level group (hs-CRP<1.0 mg/L), the OR (95%CI) value of the high-level group (hs-CRP>3.0 mg/L) was 1.79 (1.35-2.36) mg/L. As for the components, the hs-CRP level was also positively associated with ADL disability, IADL disability, functional limitation and multimorbidity. After adjusting for confounding factors, compared with the low-level group, the OR (95%CI) values of the high-level group for the four components were 1.68 (1.25-2.27), 1.88 (1.42-2.50), 1.68 (1.31-2.14) and 1.39 (1.12-1.72), respectively. Conclusion: There is a positive association between the levels of hs-CRP and the risk of frailty among the elderly over 65 years old in 9 longevity areas of China. The higher hs-CRP level may increase the risk of frailty by elevating the risk of four physical functional disabilities, namely ADL disability, IADL disability, functional limitation and multimorbidity.

[Association between urinary arsenic level and serum testosterone in Chinese men aged 18 to 79 years]

Objective: To investigate the association between the urinary arsenic level and serum total testosterone in Chinese men aged 18 to 79 years. Methods: A total of 5 048 male participants aged 18 to 79 years were recruited from the China National Human Biomonitoring (CNHBM) from 2017 to 2018. Questionnaires and physical examinations were used to collect information on demographic characteristics, lifestyle, food intake frequency and health status. Venous blood and urine samples were collected to detect the level of serum total testosterone, urine arsenic and urine creatinine. Participants were divided into three groups (low, middle, and high) based on the tertiles of creatinine-adjusted urine arsenic concentration. Weighted multiple linear regression was fitted to analyze the association of urinary arsenic with serum total testosterone. Results: The weighted average age of 5 048 Chinese men was (46.72±0.40) years. Geometric mean concentration (95%CI) of urinary arsenic, creatinine-adjusted urine arsenic and serum testosterone was 22.46 (20.08, 25.12) μg/L, 19.36 (16.92, 22.15) μg/L and 18.13 (17.42, 18.85) nmol/L, respectively. After controlling for covariates, compared with the low-level urinary arsenic group, the testosterone level of the participants in the middle-level group and the high-level group decreased gradually. The percentile ratio (95%CI) was -5.17% (-13.14%, 3.54%) and -10.33% (-15.68%, -4.63). The subgroup analysis showed that the association between the urinary arsenic level and testosterone level was more obvious in the group with BMI<24 kg/m² group (P_interaction<0.05). Conclusion: There is a negative association between the urinary arsenic level and serum total testosterone in Chinese men aged 18-79 years.

Constraints on Heavy Decaying Dark Matter from 570 Days of LHAASO Observations

The kilometer square array (KM2A) of the large high altitude air shower observatory (LHAASO) aims at surveying the northern γ-ray sky at energies above 10 TeV with unprecedented sensitivity. γ-ray observations have long been one of the most powerful tools for dark matter searches, as, e.g., high-energy γ rays could be produced by the decays of heavy dark matter particles. In this Letter, we present the first dark matter analysis with LHAASO-KM2A, using the first 340 days of data from 1/2-KM2A and 230 days of data from 3/4-KM2A. Several regions of interest are used to search for a signal and account for the residual cosmic-ray background after γ/hadron separation. We find no excess of dark matter signals, and thus place some of the strongest γ-ray constraints on the lifetime of heavy dark matter particles with mass between 10^{5} and 10^{9}  GeV. Our results with LHAASO are robust, and have important implications for dark matter interpretations of the diffuse astrophysical high-energy neutrino emission.

[Association of lead exposure with stunting and underweight among children aged 3-5 years in China]

Objective: To evaluate the association of lead exposure with stunting and underweight among children aged 3-5 years in China. Methods: Data was collected from China National Human Biomonitoring (CNHBM) between January 2017 and December 2018. A total of 3 554 children aged 3-5 years were included. Demographic characteristic, lifestyle and nutritional status were collected through questionnaires. Height and weight were measured by standardized method. Stunting and underweight status were determined by calculating height for age Z-score and weight for age Z-score. Blood and urine samples were collected to detect the concentrations of blood lead, urinary lead and urinary creatinine. Children were stratified into 4 groups (Q₁ to Q₄) by quartiles of blood lead level and corrected urinary lead level, respectively. Complex sampling logistic regression models were applied to evaluate the association of the blood lead level, urinary lead level with stunting and underweight. Results: Among 3 554 children, the age was (4.09±1.06) years, of which 1 779 (80.64%) were female and 1 948 (55.84%) were urban residents. The prevalence of stunting and wasting was 7.34% and 2.96%, respectively. The M (Q₁, Q₃) for blood lead levels and urinary lead levels in children was 17.49 (12.80, 24.71) μg/L, 1.20 (0.61, 2.14) μg/g Cr, respectively. After adjusting for confounding factors, compared with the lowest blood lead concentration group Q₁, the risk of stunting gradually increased in the Q₃ and Q₄ group (P_trend=0.010), with OR (95%CI) values of 1.40 (0.80-2.46) and 1.80 (1.07-3.04), respectively. Compared with the lowest urinary lead concentration group Q₁, the risk of stunting still increased in the Q₃ and Q₄ group (P_trend=0.012), with OR (95%CI) values of 1.69 (1.01-2.84) and 1.79 (1.05-3.06), respectively. The correlation between the lead exposure and underweight was not statistically significant (P>0.05). Conclusion: Lead exposure is positively associated with the risk of stunting among children aged 3-5 years in China.

[Mediation effect of inflammatory biomarkers on the association between blood lead levels and blood pressure changes in Chinese adults]

Objective: To investigate the role of inflammatory biomarkers in the relationship between blood lead levels and blood pressure changes. Methods: A total of 9 910 people aged 18-79 years who participated in the China National Human Biomonitoring in 2017-2018 were included in this study. A self-made questionnaire was used to collect demographic characteristics, lifestyle and other information, and the data including height, weight and blood pressure were determined through physical examination. Blood and urinary samples were collected for the detection of blood lead and cadmium levels, urinary arsenic levels, white blood cells, neutrophils, lymphocytes, and hypersensitive C-reactive protein (hs-CRP). Weighted linear regression models were used to evaluate the associations between blood lead, inflammatory biomarkers and blood pressure. Mediation analysis was performed to investigate the role of inflammation in the relationship between blood lead levels and blood pressure changes. Results: The median (Q₁, Q₃) age of all participants was 45.4 (33.8, 58.4)years, including 4 984 males accounting for 50.3%. Multivariate logistic regression model analysis showed that after adjusting for age, gender, residence area, BMI, education level, smoking and drinking status, family history of hypertension, consumption frequency of rice, vegetables, and red meat, fasting blood glucose, total cholesterol, triglycerides, blood cadmium and urinary arsenic levels, there was a positive association between blood lead levels, inflammatory biomarkers and blood pressure (P<0.05). Each 2.71 μg/L (log-transformed) increase of the lead was associated with a 2.05 (95%CI: 0.58, 3.53) mmHg elevation in systolic blood pressure (SBP), 2.24 (95%CI: 1.34, 3.14) mmHg elevation in diastolic blood pressure (DBP), 0.25 (95%CI: 0.05, 0.46) mg/L elevation in hs-CRP, 0.16 (95%CI: 0.03, 0.29)×10⁹/L elevation in white blood cells, and 0.11 (95%CI: 0.02, 0.21)×10⁹/L elevation in lymphocytes, respectively. Mediation analysis showed that the levels of hs-CRP significantly mediated the association of blood lead with SBP, with a proportion about 3.88% (95%CI: 0.45%, 7.32%). The analysis also found that the levels of hs-CRP and neutrophils significantly mediated the association of blood lead with SBP, with a proportion about 4.10% (95%CI: 1.11%, 7.10%) and 2.42% (95%CI: 0.07%, 4.76%), respectively. Conclusion: This study suggests that inflammatory biomarkers could significantly mediate the association of blood lead levels and blood pressure changes.

[Effect of topical glucocorticoid in treating phimosis on urinary tract infection of vesicoureteral reflux in infants]

Objective: To evaluate the effect of topical glucocorticoid in treating phimosis on urinarytract infection(UTI) of vesicoureteral reflux(VUR) in infants. Methods: Clinical data of infants with UTI diagnosed as primary VUR admitted to our hospital from January 2016 to January 2021 were retrospectively analyzed. The children were divided into three groups:the effective group (topical glucocorticoid was effective in the treatment of phimosis), the ineffective group(topical glucocorticoid was ineffective in the treatment of phimosis), and the untreated group(phimosis was not treated). Age of onset, degree of reflux, side and other indicators were compared to understand the effectiveness of topical glucocorticoid in treating phimosis, and the clinical characteristics of repeated UTI with VUR in treated phimosis and untreated phimosis. Results: A total of 544 children were included. Among them, 59 cases were treated with topical glucocorticoid for phimosis, 48 cases in the effective group, and their age was (12.5±8.4) months;11 cases in the ineffective group,and their age was (11.2±8.9) months. There were 485 cases in the untreated group, and their age was (13.1±9.3) months.The effective rate of topical glucocorticoid in the treatment of phimosis was 81.36%. There were 12 cases(12/48) of recurrent UTI in the effective group and 213 cases (213/485)of recurrent UTI in the untreated group, and the difference between the two groups was statistically significant (P=0.008). Conclusion: Treatment of phimosis with topical glucocorticoid is an effective, easy to perform, and cost-effective method, and can effectively reduce the risk of recurrent UTI in infants with primary VUR.

An overview of array invariant for source-range estimation in shallow water

Traditional matched-field processing (MFP) refers to array processing algorithms, which fully exploit the physics of wave propagation to localize underwater acoustic sources. As a generalization of plane wave beamforming, the "steering vectors," or replicas, are solutions of the wave equation descriptive of the ocean environment. Thus, model-based MFP is inherently sensitive to environmental mismatch, motivating the development of robust methods. One such method is the array invariant (AI), which instead exploits the dispersion characteristics of broadband signals in acoustic waveguides, summarized by a single parameter known as the waveguide invariant β. AI employs conventional plane wave beamforming and utilizes coherent multipath arrivals (eigenrays) separated into beam angle and travel time for source-range estimation. Although originating from the ideal waveguide, it is applicable to many realistic shallow-water environments wherein the dispersion characteristics are similar to those in ideal waveguides. First introduced in 2006 and denoted by χ, the dispersion-based AI has been fully integrated with β. The remarkable performance and robustness of AI were demonstrated using various experimental data collected in shallow water, including sources of opportunity. Further, it was extended successfully to a range-dependent coastal environment with a sloping bottom, using an iterative approach and a small-aperture array. This paper provides an overview of AI, covering its basic physics and connection with β, comparison between MFP and AI, self-calibration of the array tilt, and recent developments such as adaptive AI, which can handle the dependence of β on the propagation angle, including steep-angle arrivals.

[Association of blood lead and blood selenium with serum high-sensitivity C-reactive protein among Chinese adults aged 19 to 79 years]

Objective: To investigate the association of blood lead and blood selenium with serum high-sensitivity C-reactive protein (hs-CRP) among Chinese adults aged 19 to 79 years. Methods: The participants were enrolled from the first wave of China National Human Biomonitoring (CNHBM) conducted from 2017 to 2018. 10 153 participants aged 19 to 79 years were included in this study. Fasting blood samples were obtained from participants. Lead and selenium in whole blood and hs-CRP in serum were measured. Individuals with hs-CRP levels above 3.0 mg/L were defined as elevated hs-CRP. Generalized linear mixed models and restricted cubic spline models were used to analyze the association of blood lead and blood selenium with elevated hs-CRP. Logistic regression models were used to analyze the multiplicative scale and additive scale interaction between blood lead and blood selenium on elevated hs-CRP. Results: The age of participants was (48.91±15.38) years, of which 5 054 (61.47%) were male. 1 181 (11.29%) participants were defined as elevated hs-CRP. After multivariable adjustment, results from generalized linear models showed that compared with participants with the lowest quartile of blood lead, the OR (95%CI) of elevated hs-CRP for participants with the second, third, and highest quartiles were 1.14 (0.94-1.37), 1.25 (1.04-1.52) and 1.38 (1.13-1.68), respectively. When compared with participants with the lowest quartile of blood selenium, the OR (95%CI) of elevated hs-CRP for participants with the second, third and highest quartiles were 0.86 (0.72-1.04), 0.91 (0.76-1.11), and 0.75 (0.61-0.92), respectively. Results from the interaction analysis showed no significant interaction between lead and selenium on elevated hs-CRP. Conclusion: Blood concentration of lead was positively associated with elevated serum hs-CRP, and blood concentration of selenium was inversely related to elevated hs-CRP, while blood lead and selenium did not present interaction on elevated hs-CRP.

Exploring Lorentz Invariance Violation from Ultrahigh-Energy γ Rays Observed by LHAASO

Recently, the LHAASO Collaboration published the detection of 12 ultrahigh-energy γ-ray sources above 100 TeV, with the highest energy photon reaching 1.4 PeV. The first detection of PeV γ rays from astrophysical sources may provide a very sensitive probe of the effect of the Lorentz invariance violation (LIV), which results in decay of high-energy γ rays in the superluminal scenario and hence a sharp cutoff of the energy spectrum. Two highest energy sources are studied in this work. No signature of the existence of the LIV is found in their energy spectra, and the lower limits on the LIV energy scale are derived. Our results show that the first-order LIV energy scale should be higher than about 10^{5} times the Planck scale M_{Pl} and that the second-order LIV scale is >10^{-3}M_{Pl}. Both limits improve by at least one order of magnitude the previous results.

The waveguide invariant for a Pekeris waveguide

A closed-form waveguide invariant β for a Pekeris waveguide is derived. It is based on the modal Wentzel-Kramers-Brillouin (WKB) dispersion equation and implicit differentiation, in conjunction with the concept of the "effective boundary depth," ΔH(θ), where θ is the propagation angle. First, an explicit formula for β(m,n) between mode pairs is obtained assuming an ideal waveguide of the effective waveguide depth, H+ΔH(θ), and provides an excellent agreement with the reference value for the Pekeris waveguide of depth H obtained using the normal mode program kraken. Then, a closed-form expression for a group of adjacent modes is derived: β=(H+ΔH(θ))/(H/ cos² θ-ΔH(θ)), which can be approximated by β=cos² θ as ΔH(θ)/H≪1, the analytical expression for an ideal waveguide.

Peta-electron volt gamma-ray emission from the Crab Nebula

The Crab Nebula is a bright source of gamma rays powered by the Crab Pulsar's rotational energy through the formation and termination of a relativistic electron-positron wind. We report the detection of gamma rays from this source with energies from 5 × 10^-4 to 1.1 peta-electron volts with a spectrum showing gradual steepening over three energy decades. The ultrahigh-energy photons imply the presence of a peta-electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron's size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. The production rate of peta-electron volt electrons, 2.5 × 10³⁶ ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta-electron volt protons to the production of the highest-energy gamma rays.

Extended Very-High-Energy Gamma-Ray Emission Surrounding PSR J0622+3749 Observed by LHAASO-KM2A

We report the discovery of an extended very-high-energy (VHE) gamma-ray source around the location of the middle-aged (207.8 kyr) pulsar PSR J0622+3749 with the Large High-Altitude Air Shower Observatory (LHAASO). The source is detected with a significance of 8.2σ for E>25  TeV assuming a Gaussian template. The best-fit location is (right ascension, declination) =(95.47°±0.11°,37.92°±0.09°), and the extension is 0.40°±0.07°. The energy spectrum can be described by a power-law spectrum with an index of -2.92±0.17_{stat}±0.02_{sys}. No clear extended multiwavelength counterpart of the LHAASO source has been found from the radio to sub-TeV bands. The LHAASO observations are consistent with the scenario that VHE electrons escaped from the pulsar, diffused in the interstellar medium, and scattered the interstellar radiation field. If interpreted as the pulsar halo scenario, the diffusion coefficient, inferred for electrons with median energies of ∼160  TeV, is consistent with those obtained from the extended halos around Geminga and Monogem and much smaller than that derived from cosmic ray secondaries. The LHAASO discovery of this source thus likely enriches the class of so-called pulsar halos and confirms that high-energy particles generally diffuse very slowly in the disturbed medium around pulsars.

[Association of cadmium internal exposure with chronic kidney disease in Chinese adults]

Objective: To analyze the association of the cadmium internal exposure with chronic kidney disease (CKD) in Chinese adults aged 18 and older. Methods: A total of 9 821 adults aged 18-79 from the China National Human Biomonitoring (CNHBM) from 2017 to 2018 were included. Blood and urine cadmium exposure levels were measured by inductively coupled plasma mass spectrometry (ICP-MS), and urine cadmium levels were adjusted with urine creatinine; CKD were defined by estimated glomerular filtration (eGFR) using the chronic kidney disease epidemiology collaboration (CKD-EPI). Weights were considered due to complex sampling process for in statistical analysis. Logistic regression is used to analyze the association of blood cadmium, urine cadmium, and urine cadmium adjusted with creatinine exposure levels with CKD, and restricted cube spline (RCS) was used to assess the exposure-response curve of blood cadmium, urine cadmium and urine cadmium adjusted with creatinine with CKD. Results: The weighted age was 44.75 and males accounted for 61.1%. The prevalence rate of CKD was 12.7%. The geometric mean values of blood cadmium, urine cadmium, and urine cadmium adjusted with creatinine were 0.96 μg/L, 0.61 μg/L, and 0.58 μg/g. After adjusting for confounding factors, the weighted logistic regression showed that the lowest quintile (Q1) was compared with the odds ratio (OR) of the highest quintile (Q5) of blood cadmium, urine cadmium, and urine cadmium adjusted with creatinine and the 95% confidence interval (CI) was 1.80 (1.02-3.20), 1.77 (0.94-3.31) and 1.94 (1.11-3.37) respectively. In the restricted cubic spline regression model, non-linear association of blood cadmium, urine cadmium, and urine cadmium adjusted with creatinine with CKD were observed after adjusting for related confounding factors (P<0.001, 0.018, 0.031 respectively). The risk of CKD increased with the increment of cadmium exposure without risk threshold, and the exposure response curve was steeper at low cadmium exposure. Conclusions: Among Chinese adults aged 18 and older, cadmium exposure is positively associated with the risk of chronic kidney disease.

Ultrahigh-energy photons up to 1.4 petaelectronvolts from 12 γ-ray Galactic sources

The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10¹⁵ electronvolts) indicates the existence of the so-called PeVatrons-cosmic-ray factories that accelerate particles to PeV energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays¹. The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref. ²). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane^3-6, unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators.

[A cohort study on plasma uric acid levels and the risk of type 2 diabetes mellitus among the oldest old in longevity areas of China]

Objective: To investigate the effect of plasma uric acid level on the incident risk of type 2 diabetes mellitus (T2DM) among the oldest old (those aged ≥80 years). Methods: Participants were recruited from the Healthy Aging and Biomarkers Cohort Study (HABCS), which conducted a baseline survey in 2008-2009 and follow-up of 3 times in 2011-2012, 2014, and 2017-2018, respectively. A total of 2 213 oldest old were enrolled in this study. The general demographic, socioeconomic, lifestyle and disease data of the oldest old were collected, and physical measurements were made for the oldest old. Fasting venous blood was collected for uric acid and blood glucose detection. Information on the incident and death of T2DM were collected through the follow-up. Cox proportional hazard regression model was used to explore the association of hyperuricemia and plasma uric acid level with the incidence of T2DM. Restricted cubic spline (RCS) function was used to explore the dose-response relationship of plasma uric acid levels with the risk of T2DM. Results: The age of participants was (93.2±7.6) years old, and 66.7% of the participants (1 475) were female. The plasma uric acid level at baseline was (289.1±88.0)μmol/L, and the prevalence of hyperuricemia was 13.3% (294 cases). During 9 years of cumulative follow-up of 7 471 person-years (average of 3.38 years for each), 122 new cases of T2DM occurred and the incidence density was 1 632.98/10⁵ person year. Cox proportional hazards regression analysis showed that per 10μmol/L increase in plasma uric acid level, the risk of T2DM increased by 1.1% [HR (95%CI): 1.011 (1.004, 1.017)]. Compared with the participants with the lowest quintile of plasma uric acid (Q₁), the risk of diabetes increased by 20.7 % among the oldest old with uric acid in the highest quintile (Q₅) [HR (95%CI):1.207 (1.029, 1.416)]. The risk of T2DM was 19.2% higher in the hyperuricemia group than that in the oldest old with normal plasma uric acid [HR (95%CI): 1.192 (1.033, 1.377)]. RCS function showed that the risk of T2DM increased with the increase in plasma uric acid levels in a nonlinear dose-response relationship (P=0.016). Conclusion: The incident risk of T2DM increases with the elevates of plasma uric acid levels in the oldest old.

Localization of a distant ship using a guide ship and a vertical array

A method is presented for estimating the range of a distant ship in shallow water using a vertical array and a guide ship at a known range close to the array. The method involves a combination of four different approaches: blind deconvolution, waveguide invariant, virtual receiver (VR), and array invariant. (1) Blind deconvolution extracts a time-domain Green's function from the broadband acoustic source (guide ship). (2) The Green's function is extrapolated into adjacent ranges using the waveguide invariant, generating a horizontal array of synthetic guide sources. (3) Each guide source then turns into a VR where the output approximates the signal that the distant (objective) ship will produce at the location of the guide source. (4) The horizontal virtual array around the guide ship applies the blind deconvolution again to estimate the Green's function for the objective source, followed by the array invariant to estimate the distance between the two ships. The proposed method is demonstrated using a ship of opportunity radiating broadband noise (100-500 Hz) and a 56.25-m long vertical array in approximately 100-m water.

Adaptive array invariant in range-dependent environments with variable bathymetry

The adaptive array invariant developed for source-range estimation in shallow water can incorporate the propagation-angle dependence of the waveguide invariant for an ideal waveguide (β=cos²θ) [Byun and Song, J. Acoust. Soc. Am. 148, 925-933 (2020)]. This paper extends the approach to weakly (adiabatic) range-dependent environments with variable bathymetry, wherein the waveguide invariant is a complex function of the bathymetry between source and receiver as well as the propagation angle in powers of sin²θ. For a given bathymetry, the adaptive array invariant can be implemented in an iterative fashion, and its remarkable performance is demonstrated using a short-aperture vertical array (2.8 m) for a broadband source (0.5-3.5 kHz) towed on a continental slope where the water depth varies from 87.5 to 55 m over a 5-km range.

Observations of scatter from surface reflectors with Doppler sensitive probe signals

Previous analyses of surface scatter from the at-sea KAM11 experiment were made with linear frequency modulated waveforms that emphasized a single slope direction for arrivals in time-varying impulse response estimates. This analysis of Doppler sensitive waveform transmissions, made in the same geometry, resolves additional scatter arrivals with opposite slope. The different Doppler shifts in scatter observations are related to dispersed, naturally occurring, sea surface features that reflect the transmitted waveform to the receiver. The positions of these surface reflectors are estimated from the delay and Doppler shift of the observed arrivals without needing a receiving array with high spatial resolution.

Extracting Green's functions between ships of opportunity using a vertical array

A theoretical method for estimating the Green's function between two points in an acoustic waveguide was proposed using a vertical source array that spans sufficient waveguide depth [Roux and Fink, J. Acoust. Soc. Am. 113, 1406-1416 (2003)]. This paper shows that by reversing the role of sources and receivers, the Green's function between two ships (sources) can be extracted using a vertical receiver array with a limited aperture. First, the Green's functions from each ship are estimated along the array via blind deconvolution. Then the Green's function between two ships is obtained by either correlation or convolution of the individual Green's functions summed over the array, depending on the array position with respect to the ships. The feasibility of extracting Green's functions between ships of opportunity radiating random broadband (100-500 Hz) noise is demonstrated using a 56.25-m aperture vertical array in approximately 100-m shallow water.

Adaptive array invariant

The array invariant (χ) developed for robust source-range estimation in shallow water is based on the broadband dispersion characteristics in ideal waveguides that can be summarized by the waveguide invariant, β=cos²θ, with propagation angle θ. The standard array invariant relies on the waveguide invariant being constant, e.g., β = 1, valid for small propagation angles (θ<20°). In this paper, the array invariant is extended to fully incorporate the angle dependence of the waveguide invariant (β=cos²θ), referred to as adaptive array invariant and denoted by χ_β=χ/β, which, in theory, provides a perfect range estimate without constraining the propagation angle. The superior performance of the adaptive array invariant is illustrated via numerical simulations in an ideal waveguide, and then demonstrated using experimental data from a ship of opportunity radiating broadband noise (200-900 Hz) and a vertical array in a shallow-water environment.

Extrapolating Green's functions using the waveguide invariant theory

The broadband interference structure of sound propagation in a waveguide can be described by the waveguide invariant, β, that manifests itself as striations in the frequency-range plane. At any given range (r), there is a striation pattern in frequency (ω), which is the Fourier transform of the multipath impulse response (or Green's function). Moving to a different range (r+Δr), the same pattern is retained but is either stretched or shrunken in ω in proportion to Δr, according to Δω/ω=β(Δr/r). The waveguide invariant property allows a time-domain Green's function observed at one location, g(r,t), to be extrapolated to adjacent ranges with a simple analytic relation: g(r+Δr,t)≃g(r,α(t-Δr/c)), where α=1+β(Δr/r) and c is the nominal sound speed of 1500 m/s. The relationship is verified in terms of range variation of the eigenray arrival times via simulations and by using real data from a ship of opportunity radiating broadband noise (200-900 Hz) in a shallow-water environment, where the steep-angle arrivals contributing to the acoustic field have β≈0.92.

Multiple constraint matched field processing tolerant to array tilt mismatch

A multiple constraint method (MCM) specifically designed to accommodate the uncertainty of array tilt is developed for matched field processing (MFP). Combining the MCM with the white noise gain constraint method results in a processor that is tolerant to both array tilt and environmental mismatch. Experimental results verify the robustness of the proposed MFP to localize and track a surface ship radiating broadband noise (200-500 Hz), using a 56-m long vertical array with tilt in approximately 100-m deep shallow water.

Localization of multiple ships using a vertical array in shallow water

The blind deconvolution employs conventional plane-wave beamforming using an array, selects a well-resolved angle of arrival for beam steering to estimate the phase component of an unknown source waveform, and then extracts the Green's function between the source and the array. In this letter, the approach is extended to multiple-ship scenarios in which the multipath arrivals from one ship are masked by other ships, adopting the basic concept of successive interference cancellation. Once individual Green's functions are available, the array invariant method based on the beam-time migration can be subsequently applied to estimate each source range. Simultaneous localization of two ships radiating broadband noise (200-900 Hz) is demonstrated using a 16-element, 56-m long vertical array in approximately 100-m deep shallow water.

Remote acoustic illumination using time reversal and a surface ship

Time-reversal (TR) transmission of the Green's function between a time-reversal mirror (TRM) and a probe source (PS) in an acoustic waveguide produces a spatio-temporal focus at the PS location. The TR focus then behaves as a virtual point source in the outbound direction with respect to the TRM. Further, a collection of adjacent TR focuses may constitute a virtual source array (VSA) that can serve as a remote platform, redirecting the focused field to a selected location beyond the VSA for which the Green's function is not available a priori. The practical limitation to the VSA implementation, however, is the requirement of a PS at multiple adjacent locations to obtain the Green's functions between TRM and VSA. Alternatively, this work proposes the use of a surface ship radiating broadband noise as a PS in conjunction with the waveguide invariant theory, instantly generating a horizontal VSA. The feasibility of remote acoustic illumination using a ship and a TRM is demonstrated using numerical simulations in shallow water.

Performance comparisons of array invariant and matched field processing using broadband ship noise and a tilted vertical array

This paper compares the localization performance of array invariant (AI) and matched field processing (MFP) using a ship of opportunity radiating random noise (200-900 Hz) and a tilted vertical array. AI is a deterministic approach to source-range estimation (i.e., depth-blind), exploiting the dispersion characteristics of broadband signals with minimal/no knowledge of the environment in shallow water. It involves time-domain plane-wave beamforming to separate multiple coherent arrivals (eigenrays) in beam angle and travel time, called "beam-time migration," from which the source range is directly estimated. In contrast, MFP is a model-based approach that requires accurate knowledge of the environment and array geometry (e.g., array tilt) to generate "replicas" for all possible source locations, finding the best match in the two-dimensional ambiguity surface of range and depth. While AI and MFP are both sensitive to array tilt, AI is equipped with self-calibration capability to estimate the array tilt and source range simultaneously. With the array tilt information from AI incorporated, the performance of MFP for range estimation can be comparable to that of AI to such an extent that the environmental knowledge is accurate.

Simultaneous localization of a surface ship and a submerged towed source (L)

The cascade of blind deconvolution and array invariant has been successful for localizing a single source, either a surface ship or a submerged source, using a vertical array without knowledge of the environment or source waveform in shallow water. In this letter, the blind deconvolution is extended to a two-source case where individual Green's functions are separately extracted by exploiting a distinct group of modes strongly excited at different source depths. The subsequent array invariant confirms that a surface ship and a towed source at 50-m depth can be simultaneously localized using a 56-m long vertical array in 100-m deep shallow water.

Real-time tracking of a surface ship using a bottom-mounted horizontal array

The cascade of blind deconvolution and array invariant has been successful to localize and track a surface ship radiating random waveforms, using a 56-m long vertical array in 100-m deep shallow water. In this paper, it is shown that a 60-m long, bottom-mounted horizontal array can be utilized for blind deconvolution to extract the Green's functions from the same ship (100-800 Hz), in conjunction with the array invariant for source-range estimation. The additional information obtained with a horizontal array is the source bearing (azimuth angle, ϕ) from the well-resolved ray angle identified for blind deconvolution to extract the phase component of the unknown source waveforms. The overall tracking performance shows good agreement with global positioning system (GPS) measurements to less than 11% in terms of standard deviation of relative range error at ranges of 0.3-1.5 km, except when the ship is around the broadside (e.g., | ϕ | < 25 ° ) of the horizontal array. On the other hand, the source bearings are in excellent agreement with the GPS data except near the endfire due to the lower angular resolution. The potential for simultaneous localization of multiple ships is also discussed.

Acoustic scattering comparison of Kirchhoff approximation to Rayleigh-Fourier method for sinusoidal surface waves at low grazing angles

The Fourier series method for implementing the Rayleigh hypothesis [Rayleigh-Fourier method (RFM)] is used as a reference solution to assess the Kirchhoff approximation of the Helmholtz integral [Helmholtz-Kirchhoff approximation (HKA)] for modeling broadband scatter from sinusoidal surfaces at low grazing angles. The HKA is a valuable solution because it has an eigen-ray interpretation without unbounded caustic amplitudes and discontinuous shadow zones. Plane wave studies of the HKA, however, show it becomes inaccurate at low grazing angles. This study quantifies how this limitation manifests with increasing transmission distance for time domain scattering simulations. Scattering results are compared over a complete surface wave cycle with parameters modeling sea surface-swell. The HKA agrees reasonably well with the RFM in point source calculations for limited extensions of transmission distances beyond where plane wave comparisons begin to diverge. Past these distances, HKA solutions begin to show significant over-prediction of the acoustic amplitude around late arrivals. This over-prediction is frequency dependent and eigen-ray interference offers an explanation of this behavior. Further extending the transmission range leads to a significant HKA error, and a range is found at which flat surface reflections have less error.

Calibration of vertical array tilt using snapping shrimp sound

Snapping shrimp are the dominant biological source of high-frequency (>2 kHz) ambient noise in warm coastal waters. In a recent experiment, the highly impulsive signals produced by shrimp snaps were recorded continually by a large-aperture vertical array (56 m) that was bottom-moored in 100-m deep shallow water. Assuming the array vertical, initial localization of individual snaps based on wavefront curvature along the array indicated that all snaps came from either above or beneath the flat seabed. By constraining all snaps to originate from the seabed, several hundred snaps within a radius of 500 m from the array over a 20-s window were detected successfully and localized in the three-dimensional space of time-of-arrival, range, and array tilt. Since the estimated array tilt for each snap is a projection of the absolute array tilt onto the nominal array-snap plane, the maximal tilt in the range and tilt domain corresponds to the absolute array tilt. Both simulations and data demonstrate that snapping shrimp can be exploited as a source of opportunity for calibration of vertical array tilt.

Array invariant-based calibration of array tilt using a source of opportunity

The array invariant, a robust approach to source-range estimation in shallow water, is based on the dispersion characteristics of broadband signals in ideal waveguides. It involves time-domain plane-wave beamforming using a vertical line array (VLA) to separate multiple coherent arrivals in beam angle and travel time. Typically, a probe signal (i.e., a cooperating source) is required to estimate the Green's function, but the array invariant has been recently extended to a ship of opportunity radiating random signals using a ray-based blind deconvolution [Byun, Kim, Cho, Song, and Byun, J. Acoust. Soc. Am. 142, EL286-EL291 (2017)]. Still, one major drawback is its sensitivity to the array tilt, shifting the beam angles and adversely affecting the array invariant parameter that determines the source range. In this paper, a simple optimization algorithm for simultaneous estimation of the array tilt and the source range is presented. The method is applied to a ship of opportunity (200-900 Hz) circling around a 56-m long VLA at a speed of 3 knots (1.5 m/s) at ranges of 1.8-3.6 km in approximately 100-m deep shallow water. It is found that the standard deviation of the relative range error significantly reduces to about 4%, from 14% with no compensation of the array tilt. The estimated tilt angle displayed as a function of the ship's azimuth angle reveals that the VLA is tilted about 3° towards the northwest, suggesting that the array invariant can serve as a remote sensing technique for calibration of the array tilt using a source of opportunity.

Tunable quantum dot arrays as efficient sensitizers for enhanced near-infrared electroluminescence of erbium ions

Under electrical pumping conditions, high-efficiency Si-based near-infrared light generation and amplification on a chip have long been pursued for future optical interconnection technology. However, the overall performance of Si-based near-infrared electroluminescence (EL) devices, including the overall efficiency, turn-on voltage and stability under operational conditions, can rarely meet the requirements of monolithic optoelectronic integration. In this work, we designed a confined crystallization growth strategy for fabricating metal oxide quantum dot (QD) arrays embedded in Si-based films as sensitizers of Er³⁺ ions. Through the precise control of particle size and number density of QD sensitizers, the near-infrared photoluminescence (PL) emission of Er³⁺ ions can be enhanced by more than three orders of magnitude. More significantly, such hierarchical control over the regular arrangement of QD arrays not only considerably enhances the resonance energy transfer efficiency, but also offers an effective conduction path for carrier transport. Therefore, the corresponding near-infrared EL device exhibits a decreased turn-on voltage of 4.5 V, a high external quantum efficiency of 0.7%, and a long operational lifetime of more than 1000 hours, making this device superior to most Si-based on-chip near-infrared EL devices. This well-controlled metal oxide QD array represents an ideal sensitizer to effectively promote the EL emission of rare earth ions and reduce the turn-on voltage. Meanwhile, the analysis of the carrier transport mechanism paves the way for future research into resonance energy transfer under electrical pumping conditions.

Performance comparisons of frequency-difference and conventional beamforming

Frequency-difference beamforming [Abadi, Song, and Dowling (2012b). J. Acoust. Soc. Am. 132, 3018-3029] is an unconventional beamforming method for use with sparse receiver arrays. It involves beamforming a quadratic product of complex field amplitudes, P(ω₂)P^*(ω₁), at the difference frequency, ω₂-ω₁, instead of beamforming the complex field amplitude P(ω) at frequencies ω within the signal bandwidth. Frequency-difference beamforming is readily implemented with ordinary transducer array recordings of non-zero bandwidth signals. Results for, and comparisons of, frequency-difference beamforming from simulations and experiments are reported herein. In particular, spherical-wave beamforming is investigated using 15 and 165 kHz pulse signals in a 1.07-m-diameter water tank with a linear array having 14 elements spaced 5.08 cm apart. Here, frequency-difference beamforming using the high-frequency pulses provides comparable results to conventional beamforming at 15 kHz. Plane-wave beamforming is investigated using 11.2-32.8 kHz frequency-sweep signals broadcast 3 km through a 106-m-deep ocean sound channel to a vertical array having 16 elements spaced 3.75 m apart. Here, frequency difference beamforming in the 1.7-2.3 kHz difference frequency band provides results comparable to conventional beamforming in this band.

Array invariant-based ranging of a source of opportunity

The feasibility of tracking a ship radiating random and anisotropic noise is investigated using ray-based blind deconvolution (RBD) and array invariant (AI) with a vertical array in shallow water. This work is motivated by a recent report [Byun, Verlinden, and Sabra, J. Acoust. Soc. Am. 141, 797-807 (2017)] that RBD can be applied to ships of opportunity to estimate the Green's function. Subsequently, the AI developed for robust source-range estimation in shallow water can be applied to the estimated Green's function via RBD, exploiting multipath arrivals separated in beam angle and travel time. In this letter, a combination of the RBD and AI is demonstrated to localize and track a ship of opportunity (200-900 Hz) to within a 5% standard deviation of the relative range error along a track at ranges of 1.8-3.4 km, using a 16-element, 56-m long vertical array in approximately 100-m deep shallow water.

Iterative range estimation in a sloping-bottom shallow-water waveguide using the generalized array invariant

The array invariant theory was generalized by incorporating the waveguide invariant β, referred to as the generalized array invariant. In this paper, the generalized array invariant is extended to mildly range-dependent environments with a sloping bottom where the waveguide invariant is variable in range. Assuming knowledge of the bottom slope, the array invariant can be applied iteratively to estimate the source range starting with β = 1 (i.e., range-independent), which converges toward the correct source range by updating β at the previously estimated range. The iterative array invariant approach is demonstrated using a short-aperture vertical array (2.8-m) in a sloping-bottom shallow-water waveguide from the Random Array of Drifting Acoustic Receivers 2007 experiment, where a high-frequency source (2-3.5 kHz) close to the surface (6-m) was towed between 0.5 and 5 km in range with the water depth varying from 80 to 50 m.

Cascade of blind deconvolution and array invariant for robust source-range estimation

The array invariant proposed for robust source localization in shallow water is based on the dispersion characteristics in ideal waveguides. It involves conventional plane-wave beamforming using a vertical array, exploiting multiple arrivals separated in beam angle and travel time, i.e., beam-time migration. The approach typically requires either a short pulse emitted by a source or the Green's function that can be estimated from a probe signal to resolve distinct multipath arrivals. In this letter, the array invariant method is extended to unknown source waveforms by extracting the Green's function via blind deconvolution. The cascade of blind deconvolution and array invariant for robust source-range estimation is demonstrated using a 16-element, 56-m long vertical array at various ranges (1.5-3.5 km) from a towed source broadcasting broadband communication waveforms (0.5-2 kHz) in approximately 100-m deep shallow water.

Impact of array tilt on source-range estimation in shallow water using the array invariant

The array invariant proposed for robust source-range estimation in shallow water is based on the dispersion characteristics in ideal waveguides for broadband signals. With minimal knowledge of the environment, the approach involves plane-wave beamforming using a vertical array, utilizing multiple arrivals (i.e., eigenrays) separated in beam angle and travel time. In the presence of array tilt, however, the beam angle estimates are shifted, which potentially affects the range estimation based on the array invariant. Conversely, the array tilt could be estimated for a known source range. In this paper, the sensitivity to array tilt is analyzed theoretically and examined using simulations and data. It is found that even a small tilt angle (e.g., <2°) of a 1.2 -m long vertical array near the surface, if not compensated for, can result in a relative range error of 20% or more, for a high-frequency source (7-19 kHz) at 3-km range in approximately 100 -m deep shallow water. Moreover, the power spectrum of the time-evolving array tilt estimated for 9 min shows a dominant period of 5.6 s, which is consistent with the surface wave period concurrently measured from a waverider buoy.

Time-domain Helmholtz-Kirchhoff integral for surface scattering in a refractive medium

The time-domain Helmholtz-Kirchhoff (H-K) integral for surface scattering is derived for a refractive medium, which can handle shadowing effects. The starting point is the H-K integral in the frequency domain. In the high-frequency limit, the Green's function can be calculated by ray theory, while the normal derivative of the incident pressure from a point source is formulated using the ray geometry and ray-based Green's function. For a corrugated pressure-release surface, a stationary phase approximation can be applied to the H-K integral, reducing the surface integral to a line integral. Finally, a computationally-efficient, time-domain H-K integral is derived using an inverse Fourier transform. A broadband signal scattered from a sinusoidal surface in an upwardly refracting medium is evaluated with and without geometric shadow corrections, and compared to the result from a conventional ray model.

Adaptive frequency-difference matched field processing for high frequency source localization in a noisy shallow ocean

Remote source localization in the shallow ocean at frequencies significantly above 1 kHz is virtually impossible for conventional array signal processing techniques due to environmental mismatch. A recently proposed technique called frequency-difference matched field processing (Δf-MFP) [Worthmann, Song, and Dowling (2015). J. Acoust. Soc. Am. 138(6), 3549-3562] overcomes imperfect environmental knowledge by shifting the signal processing to frequencies below the signal's band through the use of a quadratic product of frequency-domain signal amplitudes called the autoproduct. This paper extends these prior Δf-MFP results to various adaptive MFP processors found in the literature, with particular emphasis on minimum variance distortionless response, multiple constraint method, multiple signal classification, and matched mode processing at signal-to-noise ratios (SNRs) from -20 to +20 dB. Using measurements from the 2011 Kauai Acoustic Communications Multiple University Research Initiative experiment, the localization performance of these techniques is analyzed and compared to Bartlett Δf-MFP. The results show that a source broadcasting a frequency sweep from 11.2 to 26.2 kHz through a 106 -m-deep sound channel over a distance of 3 km and recorded on a 16 element sparse vertical array can be localized using Δf-MFP techniques within average range and depth errors of 200 and 10 m, respectively, at SNRs down to 0 dB.

Array invariant-based source localization in shallow water using a sparse vertical array

The array invariant proposed for robust source localization in shallow water exploits the beam-time migration of broadband signals. The approach requires minimal knowledge of the environment, but involves plane wave beamforming using a short-aperture vertical array in stratified acoustic waveguides. In this paper, the array invariant approach is extended to a large-aperture vertical array that is sparse with significant variation of the sound speed across the aperture for conventional beamforming. The extension is feasible because the array invariant in shallow water utilizes surface/bottom-reflected arrivals that behave like those in ideal waveguides. Robust source-range estimation is demonstrated using data from a 16-element, 56-m long vertical array at various ranges (1.5-3.5 km) from a broadband source (0.5-2 kHz) in approximately 100-m deep shallow water.

Numerical study of three-dimensional sound reflection from corrugated surface waves

When a sound wave propagates in a water medium bounded by a smooth surface wave, reflection from a wave crest can lead to focusing and result in rapid variation of the received waveform as the surface wave moves [Tindle, Deane, and Preisig, J. Acoust. Soc. Am. 125, 66-72 (2009)]. In prior work, propagation paths have been constrained to be in a plane parallel to the direction of corrugated surface waves, i.e., a two-dimensional (2-D) propagation problem. In this paper, the azimuthal dependence of sound propagation as a three-dimensional (3-D) problem is investigated using an efficient, time-domain Helmholtz-Kirchhoff integral formulation. When the source and receiver are in the plane orthogonal to the surface wave direction, the surface wave curvature vanishes in conventional 2-D treatments and the flat surface simply moves up and down, resulting in minimal temporal variation of the reflected signal intensity. On the other hand, the 3-D propagation analysis reveals that a focusing phenomenon occurs in the reflected signal due to the surface wave curvature formed along the orthogonal plane, i.e., out-of-plane scattering.

Comment on "Reconstructing surface wave profiles from reflected acoustic pulses" [J. Acoust. Soc. Am. 133(5), 2597-2611 (2013)]

A computationally efficient, time-domain Helmholtz-Kirchhoff (H-K) integral was derived and applied to reconstructing surface wave profiles from reflected acoustic pulses [Walstead and Deane, J. Acoust. Soc. Am. 133, 2597-2611 (2013)]. However, the final form of the integral equation incorporating a stationary phase approximation contained a complex phase term exp(iπ/4), which cannot be treated as a simple time delay. In this work, a real time-domain H-K integral is presented that includes an additional Hilbert transform of the time-derivative of the transmitted pulse. Numerical simulation with a sinusoidal surface shows good agreement between the real time-domain formulation and exact H-K integral, while achieving a significant improvement in computational speed (e.g., 2 orders of magnitude).

Current global and Korean issues in radiation safety of nuclear medicine procedures

In recent years, the management of patient doses in medical imaging has evolved as concern about radiation exposure has increased. Efforts and techniques to reduce radiation doses are focussed not only on the basis of patient safety, but also on the fundamentals of justification and optimisation in cooperation with international organisations such as the International Commission on Radiological Protection, the International Atomic Energy Agency, and the World Health Organization. The Image Gently campaign in children and Image Wisely campaign in adults to lower radiation doses have been initiated in the USA. The European Association of Nuclear Medicine paediatric dosage card, North American consensus guidelines, and Nuclear Medicine Global Initiative have recommended the activities of radiopharmaceuticals that should be administered in children. Diagnostic reference levels (DRLs), developed predominantly in Europe, may be an important tool to manage patient doses. In Korea, overexposure to radiation, even from the use of medical imaging, has become a public issue, particularly since the accident at the Fukushima nuclear power plant. As a result, the Korean Nuclear Safety and Security Commission revised the technical standards for radiation safety management in medical fields. In parallel, DRLs for nuclear medicine procedures have been collected on a nationwide scale. Notice of total effective dose from positron emission tomography-computed tomography for cancer screening has been mandatory since mid-November 2014.