Ultrafast carrier relaxation dynamics of photoexcited GaAs and GaAs/AlGaAs nanowire array

Femtosecond optical pump-probe spectroscopy is employed to elucidate the ultrafast carrier nonradiative relaxation dynamics of bare GaAs and a core-shell GaAs/AlGaAs semiconductor nanowire array. Different from the single nanowire conventionally used for the study of ultrafast dynamics, a simple spin coating and peeling off method was performed to prepare transparent organic films containing a vertical oriented nanowire array for transient absorption measurement. The transient experiment provides the direct observation of carrier thermalization, carrier cooling, thermal dissipation and band-gap energy evolutions along with the carrier relaxations. Carrier thermalization occurs within sub-0.5 ps and proceeds almost independently on the AlGaAs-coating, while the time constants of carrier cooling and thermal dissipation are increased by an order of magnitude due to the AlGaAs-coating effect. The concomitant band-gap evolutions in GaAs and GaAs/AlGaAs include an initial rapid red-shift in thermalization period, followed by a slow blue and/or red shift in carrier cooling, and then by an even slower blue shift in thermal dissipation. The evolution is explained by the competition of band-gap renormalization, plasma screening and band-filling. These findings are significant for understanding the basic physics of carrier scattering, and also for the development of flexible optoelectronic devices.

Tissue tracking MR to evaluate left ventricular global myocardial deformation in patients with cardiac amyloidosis of transmural late gadolinium enhancement

Purpose

Cardiac amyloidosis (CA) is a major cause of mortality in patients with amyloidosis because it leads to heart failure and lethal arrhythmia. The present study was aimed to evaluate left ventricular (LV) global myocardial deformation in patients with CA of transmural late gadolinium enhancement (LGE) using tissue tracking MRI.

Materials and methods

Thirty-nine patients with CA, confirmed by cardiac MRI, and a biopsy of at least one involved organ were enrolled. According to LV ejection fraction (LVEF), they were divided into reduced LVEF (CArEF) and preserved EF (CApEF) groups. Thirty-nine normal controls were recruited (NC). Tissue tracking analysis was done based on cine MRI sequences. LV global longitudinal strain (GLS), global circumferential strain (GCS), and global radial strain (GRS) were computed.

Results

GLS [CArEF vs. CApEF vs. NC: (−5.82±2.42) % vs. (−8.44±4.15) % vs. (−14.74±2.93)%], GCS [CArEF vs. CApEF vs. NC: (−9.47±2.96) % vs. (−15.01±1.81) % vs. (−19.86±2.30) %], and GRS [CArEF vs. CApEF vs. NC: (11.37±4.68) % vs. (20.61±6.27) % vs. (39.02±8.98) %] were all reduced in the CArEF and CApEF groups compared with healthy control subjects (all P<0.01). GCS and GRS in the CArEF group were reduced compared with the CApEF group (P<0.01). GLS, GCS, and GRS were also strongly correlated with LVEF (r=−0.77, −0.88, and 0.83, respectively; P<0.01). Furthermore, the optimal cutoff values to predict LVEF reduction were −9.31% (sensitivity 88%, specificity 97%) for GLS, −14.13% (sensitivity 96%, specificity 97%) for GCS, and 20.11% (sensitivity 90%, specificity 97%) for GRS.

Conclusion

MRI-based LV global deformation parameters could be a useful method to assess LV myocardial systolic function and predict LVEF reduction in patients with CA of transmural enhancement on LGE. The differences of GCS and GRS between the CArEF and CApEF groups may also reflect preserved contractile function of the mid- or/and subepicardial myocardium.

Figure 1. LV deformation parameters

Funding Acknowledgement

Type of funding source: None

Influence of the depletion region in GaAs/AlGaAs quantum well nanowire photodetector

In semiconductor nanowire (NW) photodetectors, the Schottky barrier formed by the contact between metal and semiconductor can act as a depletion layer. For NW structures with a smaller diameter, the depletion region is especially important to the carrier transport. We prepared a GaAs/AlGaAs quantum well NW photodetector with a two-dimensional electron-hole tube, in which the two-dimensional hole tube (2DHT) formed by the inner layer of GaAs and AlGaAs has the most important role in the regulation of carriers. By adjusting the bias voltage to vary the depth of the depletion region, we have confirmed the influence of the depletion region in a 2DHT. A significant inflection point was found in the responsivity-voltage curve at 1.5 V. By combining the depletion region and 2DHT, the responsivity of the fabricated device was increased by 18 times to 0.199 A W^-1 and the detectivity is increased by 5 times to 5.8 × 10¹⁰ Jones, compared to the pure GaAs NW photodetector. Reasonable combination of depletion layer and 2DHT was proved to promote high-performance NW photodetector.

Humidity sensor based on a graphene oxide-coated few-mode fiber Mach-Zehnder interferometer

A relative humidity sensor based on a graphene oxide-coated few-mode fiber Mach-Zehnder interferometer (MZI) is proposed in this paper. The MZI was made by splicing a segment of the few-mode fiber (FMF) between two segments of a no-core fiber (NCF) and two segments of a single mode fiber (SMF) located outside the two NCFs. The core and cladding of the FMF acted as interferometric arms, while the NCFs acted as couplers for splitting and recombining light due to mismatch of mode field diameter. The cladding of the FMF was corroded with hydrofluoric acid, and a layer of graphene oxide (GO) film was coated on the corroded cladding of FMF via the natural deposition method. The refractive index of GO varied upon absorption the water molecules. As a result, the phase difference of the MZI varied and the wavelength of the resonant dip shifted with a change in the ambient relative humidity (RH). High humidity sensitivity of 0.191 and 0.061 nm/%RH in the RH range of 30-55% and 55-95%, respectively, were achieved experimentally. The high sensitivity, compact size, and simple manufacturing of the proposed sensor could offer attractive applications in fields of chemical sensors and biochemical detection.

Surface modification of all-inorganic halide perovskite nanorods by a microscale hydrophobic zeolite for stable and sensitive laser humidity sensing

Perovskite materials are very sensitive to the environment which is beneficial for humidity sensing. However, the existing illuminating humidity sensor has low luminous efficiency and sensitivity. Besides, the stability of perovskite materials remains a key issue to be resolved. Compared to luminescence, lasing is much more sensitive to the surrounding environmental situation. However, humidity sensing based on perovskite lasing has not been reported so far. In this work, all-inorganic halide perovskite CsPbBr3 nanorods with an optical gain coefficient as high as 954 cm-1 were designed and fabricated. Moreover, a microscale hydrophobic zeolite was introduced to modify perovskites for improved stability. It is interesting to note that the hydrophobic zeolite introduces strong scattering which is beneficial for three-dimensional random lasing with a quality (Q) factor of 2263. Through the strategy of using lasing instead of luminescence, optical stability and sensitive laser humidity sensing were demonstrated, and it exhibits high sensitivity and good reliability. This work provides a new idea of improved stability of perovskites, which will promote the practical application of perovskite materials and devices.

CRISPR-dCas9-mediated knockdown of prtR, an essential gene in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a widely distributed non-fermentative Gram-negative opportunistic pathogen that is often responsible for nosocomial infections. Gene interference is a potentially valuable tool for investigating essential genes in P. aeruginosa. To establish a gene interference platform in P. aeruginosa, CRISPR system was used with an inactive Cas9 protein. The CRISPR-dCas9 system was cloned into pHERD20T, a shuttle vector with arabinose inducible promoter, and was further modified to target a regulatory gene prtR that is essential for the viability of P. aeruginosa. Cells expressing the prtR-targeting CRISPR interference (CRISPRi) showed growth defect in an arabinose dose-dependent manner. A high-throughput RNA sequencing analysis of bacterial cells with or without the CRISPRi-mediated prtR inhibition indicated that prtRis a global regulator affecting multiple biological processes. In conclusion, the CRISPR-dCas9-based gene knockdown system has been successfully implemented in P. aeruginosa and demonstrated to be an effective tool in the investigation of essential or difficult-to-inactivate genes in this species.

0714 Effect of One-Week Velopharyngeal-Task Training on Genioglossus Corticomotor Excitability and Sleep Apnea Severity

Introduction

The effectiveness of the contraction of the UA dilator muscles plays a crucial role in the maintenance of UA patency. This study aimed to assess the effects of one-week velopharyngeal-task training (VTT) on sleep apnea severity and its genioglossus (GG) corticomotor excitability.

Methods

Ten patients with sleep apnea underwent 1 h VTT on seven consecutive days. During the VTT protocol, subjects were asked to develop repetitive intra-oral positive pressure using cheek-bulging maneuvers while wearing a mouth piece to keep the jaw opened and maintaining an exclusive nasal breathing. They were encouraged to generate approximately 4% of Max pressure by maintaining the pressure inside the corresponding pre-set pressure target window for 2 sec every 10 sec. PSG recording and GG transcranial magnetic stimulation (TMS) response was obtained before and after the one-week VTT.

Results

One-week VTT was associated with a global AHI decrease by 33.8% (pre-VTT: 34.5±31.9 n/h; post-VTT: 25.5±26.7 n/h; p< 0.05) and progressed from moderate/severe to mild/moderate in 40% of patients. Although the bulging pressure remained unchanged (pre-VTT: 17.1±5.6 kPa, post-VTT: 19.4±5.4 kPa, p> 0.05), the amplitude of GG motor evoked potential in response to TMS significantly increased after the one-week VTT (pre-VTT: 639.4±380.9mV; post-VTT: 1128.5±623.9mV; p< 0.05).

Conclusion

One-week VTT is sufficient to confer clinical benefits on patients with sleep apnea. VTT protocol is not oriented toward strength gain, but rather toward an enhancement in the upper airway muscle cortical excitability and improvement in the coordination of their contraction. The authors consider these results to be potentially clinically relevant and worthy of further investigation in a large randomized trial.

Support

National Natural Science Foundation of China, Grant/Award Number: 81670085.

WD-3 inhibits the proliferation of breast cancer cells by regulating the glycolytic pathway

Number 3 Prescription (WD-3) is an herbal remedy used in traditional Chinese medicine that has been shown to improve the outcomes of patients with advanced colon and gastric cancers. This study aimed to investigate the effect of WD-3 on proliferation, glycolysis, and hexokinase 2 expression in breast cancer cells. Four breast cancer cell lines (MDA-MB-231, BT-549, MCF-7, and MCF-7/ADR-RES) were treated with different concentrations of WD-3 compared with blank control (phosphate-buffered saline). Each of the breast cancer cell lines was also divided into WD-3, paclitaxel, and blank control group. Cell proliferation and morphology were assessed by MTT assay, nuclear Hoechst 33258 staining, or immunofluorescence. Apoptosis was analyzed by flow cytometry. High performance liquid chromatography was used for measurement of ATP, ADP, and AMP. Hexokinase 2 expression was analyzed by Western blot and quantitative reverse transcription PCR. WD-3 inhibited proliferation and increased apoptosis in all four breast cancer cell lines, in a dose-dependent manner. ATP and EC (energy charge) were significantly decreased in WD-3-treated BT-549 and MDA-MB-231 cells. WD-3 significantly downregulated the protein and mRNA expression of hexokinase II in BT-549 cells, however, not in the other three breast cancer cell lines. Our findings indicate that WD-3 targets the glycolytic pathway in breast cancer cells to exert its antitumor activity.

Enhancing Performance of a GaAs/AlGaAs/GaAs Nanowire Photodetector Based on the Two-Dimensional Electron-Hole Tube Structure

Here, we design and engineer an axially asymmetric GaAs/AlGaAs/GaAs (G/A/G) nanowire (NW) photodetector that operates efficiently at room temperature. Based on the I-type band structure, the device can realize a two-dimensional electron-hole tube (2DEHT) structure for the substantial performance enhancement. The 2DEHT is observed to form at the interface on both sides of GaAs/AlGaAs barriers, which constructs effective pathways for both electron and hole transport in reducing the photocarrier recombination and enhancing the device photocurrent. In particular, the G/A/G NW photodetector exhibits a responsivity of 0.57 A/W and a detectivity of 1.83 × 10¹⁰ Jones, which are about 7 times higher than those of the pure GaAs NW device. The recombination probability has also been significantly suppressed from 81.8% to 13.2% with the utilization of the 2DEHT structure. All of these can evidently demonstrate the importance of the appropriate band structure design to promote photocarrier generation, separation, and collection for high-performance optoelectronic devices.

Bridging the van der Waals Interface for Advanced Optoelectronic Devices

Van der Waals (vdW) heterostructures exhibit excellent optoelectronic properties and novel functionalities. However, their applicability is impeded due to the common issue of the tunneling barrier, which arises from the vdW gap; this significantly increases the injection resistance of the photoexcited carriers. Herein, a generic strategy is demonstrated to eliminate the vdW gap in a broad class of heterostructures. It is observed that the vdW gap in the interface is bridged via strong orbital hybridization between the interface dangling bonds of nonlayered chalcogenide semiconductors and the artificially induced vacancies of transition metal chalcogenides (TMDCs). The photoresponse times of bridged PbS/ReS₂ , PbS/MoSe₂ , and PbS/MoS₂ are ≈30, 51, and 43 µs, respectively. The photon-triggered on/off ratio of the bridged PbS/MoS₂ , ZnSe/MoS₂ , and ZnTe/MoS₂ heterostructures exceed 10⁶ , 10⁵ , and 10⁵ , respectively. These are several orders of magnitude higher than common vdW heterostructures. The findings obtained in this study present a versatile strategy for overcoming the performance limitations of vdW heterostructures.

Microcatheter shaping using three-dimensional printed models for intracranial aneurysm coiling

Background and purpose

Microcatheterization is an important, but also difficult, technique used for the embolization of intracranial aneurysms. The purpose of this study was to investigate the application of three-dimensional (3D) printing technology in microcatheter shaping.

Methods

Nine cases of internal carotid artery posterior communicating artery aneurysm diagnosed by CT angiography were selected, and 3D printing technology was used to build a 3D model including the aneurysm and the parent artery. The hollow and translucent model had certain flexibility; it was immersed in water and the microcatheter was introduced into the water to the target position in the aneurysm, followed by heating the water temperature to 50°C. After soaking for 5 min, the microcatheter was taken out and the shaping was completed. After sterilization, the shaped microcatheter was used for arterial aneurysm embolization and evaluation was conducted.

Results

Nine cases of microcatheter shaping were satisfactory and shaping the needle was not necessary; no rebound was observed. The microcatheter was placed in an ideal position, and the stent-assisted method was used in three cases of wide-neck aneurysm. There were no complications related to surgery.

Conclusion

A new microcatheter shaping method using 3D printing technology makes intracranial artery aneurysm embolization more stable and efficient.

Improved Optical Property and Lasing of ZnO Nanowires by Ar Plasma Treatment

ZnO nanowires play a very important role in optoelectronic devices due to the wide bandgap and high exciton binding energy. However, for one-dimensional nanowire, due to the large surface to volume ratio, surface traps and surface adsorbed species acts as an alternate pathway for the de-excitation of carriers. Ar plasma treatment is a useful method to enhance the optical property of ZnO nanowires. It is necessary to study the optical properties of ZnO nanowires treated by plasma with different energies. Here, we used laser spectroscopy to investigate the plasma treatments with various energies on ZnO nanowires. Significantly improved emission has been observed for low and moderate Ar plasma treatments, which can be ascribed to the surface cleaning effects and increased neutral donor-bound excitons. It is worth mentioning that about 60-folds enhancements of the emission at room temperature can be achieved under 200 W Ar plasma treatment. When the plasma energy exceeds the threshold, high-ion beam energy will cause irreparable damage to the ZnO nanowires. Thanks to the enhanced optical performance, random lasing is observed under optical pumping at room temperature. And the stability has been improved dramatically. By using this simple method, the optical property and stability of ZnO nanowires can be effectively enhanced. These results will play an important role in the development of low dimensional ZnO-based optoelectronic devices.

Enhanced Photoresponsivity of a GaAs Nanowire Metal-Semiconductor-Metal Photodetector by Adjusting the Fermi Level

Metal-semiconductor-metal (MSM)-structured GaAs-based nanowire photodetectors have been widely reported because they are promising as an alternative for high-performance devices. Owing to the Schottky built-in electric fields in the MSM structure photodetectors, enhancements in photoresponsivity can be realized. Thus, strengthening the built-in electric field is an efficacious way to make the detection capability better. In this study, we fabricate a single GaAs nanowire MSM photodetector with superior performance by doping-adjusting the Fermi level to strengthen the built-in electric field. An outstanding responsivity of 1175 A/W is obtained. This is two orders of magnitude better than the responsivity of the undoped sample. Scanning photocurrent mappings and simulations are performed to confirm that the enhancement in responsivity is because of the increase in the hole Schottky built-in electric field, which can separate and collect the photogenerated carriers more effectively. The eloquent evidence clearly proves that doping-adjusting the Fermi level has great potential applications in high-performance GaAs nanowire photodetectors and other functional photodetectors.

Pathogenicity of fowl adenovirus (FAdV) serotype 4 strain SDJN in Taizhou geese

Hydropericardium hepatitis syndrome (HHS) is a fatal disease in chickens, mainly caused by fowl adenovirus serotype 4 (FAdV-4). Since June 2015, HHS has appeared in many provinces in China. The disease has spread from broilers to laying hens, breeders and Cherry Valley ducks, seriously endangering the health of the poultry industry in China. In July 2016, an infectious disease was noticed in a goose farm in Jinan, Shandong Province, China, and hydropericardium was the main finding in post mortem investigations. In the actual study, we isolated a FAdV-4 strain from the livers of naturally-infected goslings and designated it as SDJN. We first evaluated its pathogenicity by inoculating Taizhou geese at 10, 20, and 30 days of age with 10^-7.15EID₅₀/0.2 ml doses of the SDJN strain in 1 ml allantoic fluid via subcutaneous injection or oral infection. Clinical signs and pericardial effusion appeared in geese infected subcutaneously at 10 days of age, whereas 20- and 30-day-old geese were not susceptible to FAdV-4. The results of real-time PCR showed that the replication ability of FAdV-4 in geese correlated with the age. Furthermore, results from clinical chemistry showed that FAdV-4 damaged the liver and kidney in geese and the results paralleled viral load and gross lesions. Consequently, FAdV-4 was pathogenic in geese, and the pathogenicity was related to age and mode of infection. This study is the first experimental infection of FAdV-4 in geese, which will provide a basis for further understanding of the disease. RESEARCH HIGHLIGHTS Pathogenicity tests with a FAdV-4 were conducted in geese, which included data on clinical signs, gross pathology, histopathology, clinical chemistry and viral load. FAdV-4 could replicate in geese and HHS was successfully induced. Pathogenicity of FAdV-4 in geese was related to the age and routes of infection.

Graphene oxide-film-coated splitting ratio-adjustable Mach-Zehnder interferometer for relative humidity sensing

In this paper, a splitting ratio-adjustable Mach-Zehnder interferometer (MZI) for the measurement of relative humidity (RH) is proposed and experimentally demonstrated. The sensing head contains three sections of single mode fiber (SMF) and two sections of multimode fiber (MMF), in which the two MMFs are spliced among the three SMFs. The MMFs are corroded with hydrofluoric acid and act as mode couplers to split and recombine light owing to the core diameter mismatch with the SMF. A layer of graphene oxide (GO) is coated on the MMFs by dip-coating and natural evaporation. The effective refractive index of the GO will vary when it absorbs the water molecules. As a result, the intensity of the transmission light in the core and cladding of the single mode fiber can be adjusted. Thus, the intensity of the resonant dip will vary when the relative humidity changes. The experimental results show that a humidity sensitivity of 0.263 dB/RH% with a linear correlation coefficient of 99% can be achieved in a relative humidity range of 35% to 85%.

Optical characteristics of GaAs/GaAsSb/GaAs coaxial single quantum-well nanowires with different Sb components

III–V ternary alloy quantum-wells have become a hot topic in recent years. Especially, GaAs/GaAsSb quantum wells have attracted increasing attention due to their numerous applications in the field of near-infrared optoelectronic devices. With the further reduction of dimensions, GaAs/GaAsSb nanowires show many special properties compared to their quantum well structures. In this work, GaAs/GaAs_1−xSb_x/GaAs coaxial single quantum-well nanowires with different Sb composition were grown by molecular beam epitaxy. The band structure and the optical properties were investigated through power-dependent and temperature-dependent photoluminescence measurement. It has been found that a deeper quantum well is created with the increase of Sb component. Thanks to the deeper quantum well, more effective electron confinement has been realized, the emission from the sample can still be detected up to room temperature. The different trend of peak position and shape at various temperatures also supports the improved temperature stability of the samples. These results will be beneficial for the design of alloy quantum wells, and will facilitate the development of alloy quantum-well based devices.

GaAs/GaAs_1−xSb_x/GaAs coaxial single quantum-well nanowires with larger Sb content result in better electron confinement, which greatly improves their thermal stability.

Abnormal resting-state functional connectivity of amygdala subregions in patients with obstructive sleep apnea

Background: The amygdala is one of the core areas of the emotional circuits. Previous neuroimaging studies have revealed that patients with obstructive sleep apnea (OSA) have aberrant structure and function in several brain areas (including the amygdala). However, the resting-state functional connectivity (rs-FC) of amgydala subregions remains uncertain. Objective: To determine whether aberrant rs-FC exists between the amygdala subregions and other brain areas and whether such abnormalities are related to emotional disorders and cognitive impairment in OSA. Methods: The resting-state functional magnetic resonance imaging (rs-fMRI) data of 40 male severe OSA patients and 40 matched healthy controls (HCs) were collected. The rs-FC between the amygdala subregions and other brain areas was compared between the two groups. The correlations between aberrant rs-FC and clinical variables and neuropsychological assessments were evaluated. Results: Compared with the HCs, the OSA patients showed significantly increased rs-FC between the left dorsal amygdala (DA) and the anterior lobe of the cerebellum, among the left ventrolateral amygdala (VA), the left inferior frontal gyrus (IFG) and the left superior temporal gyrus (STG), and between the right VA and the left IFG. However, significantly decreased rs-FC was observed between the right DA and the right prefrontal cortex (PFC) in OSA patients. No regional differences in rs-FC were found between the OSA patients and HCs in the bilateral medial amygdala (MA). Conclusion: In this study, male severe OSA patients showed complex rs-FC patterns in the amygdala subregions, which may be the result of OSA-related selective damage to the amygdala, and abnormal rs-FC between the amygdala subregions and brain regions associated with emotional, cognitive and executive functions may partly explain the affective deficits and cognitive impairment observed in male severe OSA patients.

Structural and spectroscopy characterization of coaxial GaAs/GaAsSb/GaAs single quantum well nanowires fabricated by molecular beam epitaxy

Through the growth and characterization of GaAs/GaAs_0.75Sb_0.25/GaAs SQW nanowires, an emission wavelength of about 1.2 μm is achieved.

Linear and nonlinear optical characteristics of all-inorganic perovskite CsPbBr3 quantum dots modified by hydrophobic zeolites

All-inorganic perovskite quantum dots (QDs) have been considered as outstanding candidates for high-performance optoelectronic device applications. However, the chemical and optical stabilities restrict their device applications. In this paper, hydrophobic zeolites were proposed to modify CsPbBr3 QDs to prevent water influence while achieving good dispersion. These hybrid luminescent materials possess high internal quantum efficiency (IQE, ∼81%@3.52 W cm-2) and low dissociation levels that give rise to improved optical stability in terms of temperature and time. More interesting, it is found that this nanocomposite is able to maintain its optical limiting performance under intensive laser illumination. This paper discusses the linear and nonlinear optical characteristics of CsPbBr3 QDs, which would be of great importance for both fundamental physics investigation and practical multiphoton applications.

Effect of Post Thermal Annealing on the Optical Properties of InP/ZnS Quantum Dot Films

The enhancement of optical properties via thermal annealing on InP/ZnS core/shell quantum dot (QD) film was investigated in this work. The increase of emission intensities of the QD films was observed after thermal annealing at 180 °C for 5 min. Through temperature dependence photoluminescence (TDPL) and power dependence photoluminescence (PL) measurement, the peak located at the low-energy shoulder was confirmed to be localized state emission and the high energy one comes from free-carrier emission. Moreover, from the TDPL spectra of the sample annealed at 180 °C for 5 min, the full width at half maximum (FWHM) of localization state emission was nearly the same before which is 250 K and then decreased with increasing temperature. However, the FWHM was decreased significantly when temperature increased in the untreated sample. We conclude that the escape of localization states with increasing temperature contributes to this anomaly phenomenon. Our studies have significance on the application of QDs in electroluminescence devices and down-conversion light-emitting devices.