Assessing the Relative Importance of Satellite-Detected Methane Superemitters in Quantifying Total Emissions for Oil and Gas Production Areas in Algeria

Methane emissions from oil and gas production provide an important contribution to global warming. We investigate 2020 emissions from the largest gas field in Algeria, Hassi R'Mel, and the oil-production-dominated area Hassi Messaoud. We use methane data from the high-resolution (20 m) Sentinel-2 instruments to identify and estimate emission time series for 11 superemitters (including 10 unlit flares). We integrate this information in a transport model inversion that uses methane data from the coarser (7 km × 5.5 km) but higher-precision TROPOMI instrument to estimate emissions from both the 11 superemitters (>1 t/h individually) and the remaining diffuse area source (not detected as point sources with Sentinel-2). Compared to a bottom-up inventory for 2019 that is aligned with UNFCCC-reported emissions, we find that 2020 emissions in Hassi R'Mel (0.16 [0.11-0.22] Tg/yr) are lower by 53 [24-73]%, and emissions in Hassi Messaoud (0.22 [0.13-0.28] Tg/yr) are higher by 79 [4-188]%. Our analysis indicates that a larger fraction of Algeria's methane emissions (∼75%) come from oil production than national reporting suggests (5%). Although in both regions the diffuse area source constitutes the majority of emissions, relatively few satellite-detected superemitters provide a significant contribution (24 [12-40]% in Hassi R'Mel; 49 [27-71]% in Hassi Messaoud), indicating that mitigation efforts should address both. Our synergistic use of Sentinel-2 and TROPOMI can produce a unique and detailed emission characterization of oil and gas production areas.

Prognostic value of right ventricular systolic function by speckle tracking echocardiography beyond conventional echocardiography in significant tricuspid regurgitation

Background

Right ventricular (RV) systolic function is determinant in the evaluation of patients with significant tricuspid regurgitation (TR). Timely detection of RV dysfunction with conventional 2D echocardiography is limited by the geometry and position of the RV. RV strain has emerged as an accurate and sensitive tool for evaluation of RV function with the capability of detect subclinical RV dysfunction

Purpose

This study was aimed to evaluate the prognostic value of RV strain in consecutive patients with significant TR, in comparison with conventional parameters of RV systolic function.

Methods

Consecutive patients in stable clinical status with significant TR (severe, massive or torrential TR) evaluated in the Heart Valve Clinic were included. RV systolic function was measured with conventional echocardiographic parameters (RV fractional area change [FAC], tricuspid annular plane systolic excursion [TAPSE]), DTI S wave ('S) and with STE derived automatic peak global and free wall longitudinal strain (GLS, FW-LS respectively) using the EPIQ system. A combined endpoint of hospital admission due to heart failure or cardiovascular mortality was defined.

Results

A total of 100 patients were included (mean age was 76±10 years, 65% females, 84% in NYHA I/II, 86% functional TR). Mean values of RV function parameters are shown in the table. During a mean follow up of 24±10 months, 24% of the patients reached the combined endpoint. Patients with events showed impaired RV GLS and FW-LS (p<0.01). Both parameters were predictive of the combined endpoint (table 1). Conventional parameters of RV systolic function were not associated with outcomes (p>0.05 for all).

Conclusion

In patients with severe TR, RV strain values are superior to conventional parameters to detect RV dysfunction. Among different measurements of RV function, RV GLS and FW-LS were the only predictors of poor prognosis. These parameters should be included in the serial evaluation of these patients.

Funding Acknowledgement

Type of funding source: None

Beyond effective regurgitant orifice in quantitative assessment of tricuspid regurgitation: impact on clinical outcomes

Background

Quantification in tricuspid regurgitation has been poorly investigated. Recommended methods and thresholds are directly translated from mitral regurgitation; however, the anatomy, hemodynamics, and regurgitant orifice geometry are different in TR. Effective regurgitant orifice (ERO) calculation may be incorrect in very severe TR when right atrial and ventricular pressures could get equalized resulting in typically very low TR velocities.

Purpose

Our aim was to compare the prognostic value of different parameters for the evaluation of the tricuspid regurgitation (TR).

Methods

Consecutive patients with significant TR (≥ moderate echocardiographic grade) evaluated in the Heart Valve Clinic were included. TR severity was evaluated by TR radius, TR flow rate, ERO and TR regurgitant volume by PISA method and biplane vena contracta (VC) width using EPIQ system. End-point included cardiovascular mortality, tricuspid valve surgery or heart failure.

Results

A total of 100 patients were included (mean age: 76±10 years, 65% females, 86% functional TR, 84% in NYHA I/II). During a mean follow up of 24±10 months 36% of the patients reached the combined end-point. Patients with events showed more severe TR independently of the parameter applied (table). In univariate analysis, TR radius, TR flow rate, ERO and TR regurgitant volume were predictors of the combined endpoint (p<0.05 for all). Among all parameters, TR flow rate was the strongest and independent predictor of outcomes in multivariate and ROC analysis (HR per 1 ml/seg 1.02 [1.003–1.026], p=0.01). A value of TR flow rate of 109 ml/sec reached the best accuracy to predicted poor outcomes (p<0.01).

Conclusion

Among different parameters to graduate TR severity, TR flow rate was the strongest predictor of outcomes. Since it does not include the TR velocity in the calculation, its incremental benefit may be related to very severe cases of TR. In this scenario, right atrial and ventricular pressures are equalized and TR velocity calculation is not longer possible. New grading schemes for TR may include this parameter in the classification.

Funding Acknowledgement

Type of funding source: None

Comparison of neutron and secondary gamma dose assessment using polygon mesh and voxel computational phantoms

The newly developed mesh-type reference computational phantoms (MRCPs) represent the evolution of the previous reference phantoms and a more detailed description of the human body, addressing the voxel reference phantom limitations. These allow for a more accurate dose calculation in the human body, which in some cases results in a significant difference of the calculated quantities. In this work, the absorbed dose calculation due to neutrons and gammas was calculated using a voxel and a mesh-type computational phantom. The goal was to understand how a more accurate description of the human body affects the estimated neutron dose. The phantoms were tested in a real-case scenario: they were placed in front of a neutron Howitzer container model using PHITS. This model corresponds to the neutron Howitzer container at the Neutron Measurements Laboratory of the Energy Engineering Department of the Polytechnic University of Madrid (UPM), and at the time of measurement it was equipped with a ²⁴¹Am-Be neutron source of 74 GBq in its center. The container allows the source to be in either the irradiation or the storage position. Results show that when dealing with neutrons, the dose deviation when using GOLEM or the MRCP leads to a general 20%-30% deviation that goes up to above 400% in small thin structures such as the eye.

P727 Unexpected ventricular aneurysm: further ischemic aetiology

Introduction

Ventricular aneurysm is an infrequent complication of myocardial infarction. In absence of an ischemic event, alternative aetiologies include: thoracic trauma, hypertrophic cardiomyopathy, myocarditis, Chagas disease, cardiac sarcoidosis or arrythmogenic cardiomyopathy. In the absence of any of the previous, congenital aneurysm diagnosis is made.

Case

We present the case of 57-year-old man referred to cardiology department because a new onset of atrial fibrillation with left bundle branch block. Past medical history included high blood pressure and dyslipidaemia without any history or smoking, alcohol consumption or any other toxic abuse. No chest pain, shortness of breath or other significant symptoms were reported. Physical examination was unremarkable except for an arrhythmic pulse at 85-90 bpm.

Echocardiogram showed moderate dilated left ventricle with mild-moderate LV dysfunction (EF 40% ) with a septal aneurysm of 2.4x1cm (Picture A). A coronary CT was performed that ruled out coronary heart disease and confirmed the presence of the septal aneurysm (Picture B). To better characterize this image, a cardiac magnetic resonance (CMR) was performed. Moderate dilated LV with significant dysfunction (EF 31%) was reported. A septal aneurysm of 13 x 22 x 33 mm composed of a 2.8 m thin wall of true myocardial tissue was documented (picture C and D-late gadolinium enhance). No myocardial delayed enhancement was detected in any area of the LV. Moreover, no signs of myocardial non compaction, arrythmogenic cardiomyopathy, hypertrophic cardiomyopathy or myocarditis were seen. Chagas serology as well as sarcoidosis diagnosis work up were negative. Patient denied any thoracic traumatism. Congenital aneurysm diagnosis was finally established.

Electrical cardioversion was performed after 1 month of correct oral anticoagulation and heart failure treatment was started. Case was presented in the Heart Team session and a conservative management was decided based on asymptomatic status and absence of ventricular arrhythmias. After 3 years of clinical follow up, the patients is in good status, asymptomatic and in sinus rhythm. Discussion: Congenital ventricular aneurysm is a rare cardiac malformation that arises during the fourth embryonic week. Most frequently, left ventricular aneurysms are found in the apex and the perivalvular area, being the septal location an atypical one. Most patients are asymptomatic but when symptoms occur, they are mostly related to the presence of ventricular arrhythmias. Aneurysm rupture incidence is variable, ranging from 3.7% to 12 % according to the different series. For this reason, surgery is recommended in symptomatic patients. However, management of asymptomatic patients is not clear since prognosis studies are lacking.

Abstract P727 Figure. A.Echo B.-CT C.-CMR. D.-CMR gadolinium

Quantification of nitrogen oxides emissions from build-up of pollution over Paris with TROPOMI

Nitrogen dioxide (NO2) is a regulated air pollutant that is of particular concern in many cities, where concentrations are high. Emissions of nitrogen oxides to the atmosphere lead to the formation of ozone and particulate matter, with adverse impacts on human health and ecosystems. The effects of emissions are often assessed through modeling based on inventories relying on indirect information that is often outdated or incomplete. Here we show that NO2 measurements from the new, high-resolution TROPOMI satellite sensor can directly determine the strength and distribution of emissions from Paris. From the observed build-up of NO2 pollution, we find highest emissions on cold weekdays in February 2018, and lowest emissions on warm weekend days in spring 2018. The new measurements provide information on the spatio-temporal distribution of emissions within a large city, and suggest that Paris emissions in 2018 are only 5-15% below inventory estimates for 2011-2012, reflecting the difficulty of meeting NOx emission reduction targets.

P5566Prognostic value of quantitative assessment of tricuspid regurgitation. Correlation between echocardiography and cardiac magnetic resonance

Background

Significant tricuspid regurgitation (TR) is related to poor prognosis independently of the etiology. TR severity and right ventricular (RV) size and function are determinant in the evaluation of patients with RT and are independently related to outcomes. While TR severity is commonly evaluated with echocardiography (echo), cardiac magnetic resonance (CMR) is the gold standard to study the RV. The association between CMR and echocardiographic measures of quantitative TR is unknown.

Purpose

Our aim was to evaluate the association between the most commonly used methods in both techniques: biplane vena contracta (VC) and effective regurgitant orifice (ERO) parameters evaluated by echo and TR volume (TRV) and TR regurgitant fraction (TRF) by CMR; secondly we aimed to evaluate the prognostic value of each parameter.

Methods

Consecutive patients in stable clinical status with significant TR evaluated in the Heart Valve Clinic between 2015–2018 with a contemporaneous echo and CMR were included. TR severity was evaluated by VC and ERO method, using EPIQ system and by VRF and TRF using a 1.5 Tesla CMR Philips scanner. End-point included cardiovascular mortality, tricuspid valve surgery or heart failure.

Results

A total of 36 patients were included (mean age was 72±7 years, 72% females, 94% functional TR). Both VC and ERO showed moderate to strong and significant correlations with VRF and TRF (table). During a median follow up of 20 months [IQR: 10–29], 38% of the patients reached the combined end point (n=7 developed right heart failure, n=11 underwent tricuspid valve surgery, and n=2 died). Patients with events showed a larger ERO and higher VRF and TRF (p<0.01 for all) and a tendency to larger VC (p=0.06). PISA, VRF and TRF were prognostic factors of the combined endpoint (PISA per 0.1 cm2, HR: 282 [3.9–20362], p=0.01; VC per 1 mm, HR 1.27 [0.98–1.64] p=0.06; VRF per 1ml: HR: 1.02 [1.005–1.025], p=0.003; FRT per 1%, HR: 219.5 [4.8–9897], p=0.06). A value of PISA of 0.42, of VRF of 46 ml and FRV of 43% reached the best accuracy to predicted poor outcomes (p<0.01 for all).

Table 1. Bivariate correlations ERO VC Regurgitant volume by CMR R=0.57, p=0.004 R=0.55, p=0.003 Regurgitant fraction by CMR R=0.61, p<0.001 R=0.56, p=0.01

Conclusion

Validated echocardiographic parameters of TR are significantly correlated with quantitative measures by CMR. PISA by echo, and VRF and FRV by CMR are predictive of impaired prognosis. Further studies confirming our CMR cut-off values of poor outcomes are needed for clinical implementation.

P6488Prognostic value of right ventricular systolic function by speckle tracking echocardiography beyond conventional echocardiography in significant tricuspid regurgitation

Background

Right ventricular (RV) systolic function is determinant in the evaluation of patients with significant tricuspid regurgitation (TR). Timely detection of RV dysfunction with conventional 2D echocardiography is limited by the geometry of the RV. RV strain has emerged as an accurate and sensitive tool for evaluation of RV function that can allow detection of subclinical RV dysfunction

Purpose

This study was aimed to evaluate the prognostic value of RV strain in stable patients with significant TR, in comparison with conventional parameters of RV systolic function.

Methods

Consecutive patients in stable clinical status with significant TR evaluated in the Heart Valve Clinic between 2015–2018 were included. RV systolic function was measured with conventional echocardiographic parameters (RV fractional area change [FAC], tricuspid annular plane systolic excursion [TAPSE]), DTI S wave (`S) and with STE derived peak global and free wall longitudinal strain (GLS, FW-LS respectively) using the EPIQ system. End-point included cardiovascular mortality, tricuspid valve surgery or heart failure

Results

A total of 70 patients were included (mean age was 74±8 years, 71% females). 5 patients were excluded due to poor acoustic window. According to ethyology, 94% were functional TR (60% due to left valve disease, 27% due to tricuspid annulus dilatation, 13% others). Mean values of RV function parameters are shown in the table. During a median follow up of 18 months [IQR: 4–28], 37% of the patients reached the combined end point (n=15 developed right heart failure, n=17 underwent tricuspid valve surgery, and n=3 died). Patients with events showed impaired RV-GLS and FW-LS. Both parameters were predictive of the combined endpoint (table 1). Conventional parameters of RV systolic function were not associated with outcomes.

Mean ± SD Mean ± SD Mean ± SD HR (95% confidence interval) P value in Cox regression analysis in all patients in patients with events in patients without events TAPSE 20±5 20±7 21±5 0.97 (0.9–1.06) 0.56 DTI S wave 10.5±2 11±3 10±2 1.08 (0.87–1.35) 0.49 FAC 44±7 43±6 45±8 1.04 (0.97–1.1) 0.22 FW longitudinal strain (FW-LS) 18±5 −16±5* −20±5 0.91 (0.84–0.98) 0.02 Global longitudinal strain (GLS) 19±4 −16±4* −21±4 0.87 (0.81–0.95) 0.001

Conclusion

In patients with asymptomatic TR, RV strain values are superior to conventional parameters to detect RV dysfunction. Among different measurements of RV function, RV GLS and FW-LS were the only predictors of poor prognosis. These parameters may be included in the serial evaluation of these patients.

Short-term efficacy and safety of new biological agents targeting the interleukin-23-T helper 17 pathway for moderate-to-severe plaque psoriasis: a systematic review and network meta-analysis

A new generation of biologics targeting the interleukin-23-T helper 17 pathway has been developed. This study aimed to assess the short-term effectiveness and safety of these new agents using a network meta-analysis. Twenty-seven randomized clinical trials (10 629 patients) were identified by a comprehensive systematic literature review (PROSPERO 2015: CRD42015025472). Quality of evidence was assessed following Cochrane-compliant rules and the Grading of Recommendations, Assessment, Development and Evaluations approach. Efficacy and safety outcomes at weeks 10-16 were compared using a random-effects network meta-analysis within a frequentist framework to estimate pooled odds ratios (ORs) of direct and indirect comparisons among the therapeutic options. There were six direct drug-to-drug comparisons in the network, with a high degree of consistency between the direct and indirect evidence. From the available evidence, infliximab 5 mg kg^-1 every 8 weeks [OR 118·89, 95% confidence interval (CI) 60·91-232·04] and secukinumab 300 mg every 4 weeks (OR 87·07, 95% CI 55·01-137·82) are shown to be among the most effective short-term treatments, but are ranked as the biologics most likely to produce any adverse event or an infectious adverse event, respectively. Ustekinumab 90 mg every 12 weeks, the third most efficacious treatment (OR 73·67, 95% CI 46·97-115·56), was the only agent that did not show increased risk of adverse events compared with placebo. Treatment recommendations should also consider long-term outcomes and costs.

Analysis of occupant kinematics and dynamics in nearside oblique impacts

OBJECTIVE

The objective of this article is to analyze the kinematics and dynamics of restrained postmortem human surrogates (PMHS) exposed to a nearside oblique impact and the injuries that were found after the tests.

METHODS

Three male PMHS of similar age (64 ± 4 years) and anthropometry (weight: 61 ± 9.6 kg; stature: 172 ± 2.7 cm) were exposed to a 30° nearside oblique impact at 34 km/h. The test fixture approximated the seating position of a front seat occupant. A rigid seat was designed to match the pelvic displacement in a vehicle seat. Surrogates were restrained by a 3-point seat belt consisting of a 2 kN pretensioner (PT), 4.5 kN force-limiting shoulder belt, and a 3.5 kN PT lap belt. The shoulder belt PT was not fired in one of the tests. Trajectories of the head, shoulder, and hip joint (bilaterally) were recorded at 1,000 Hz by a 3D motion capture system. The 3D acceleration and angular rate of the head, T1, and pelvis, and the 3D acceleration of selected spinal locations was measured at 10,000 Hz. Seat belt load cells measured the belt tension at 4 locations. PMHS donation and handling were performed with the approval of the relevant regional ethics review board.

RESULTS

Activation of the shoulder PT reduced substantially the peak forward excursion of the head but did not influence the lateral displacement of the head center of gravity (CG). In all 3 subjects, the lateral excursion of the head CG (291.1, 290, 292.1 mm) was greater than the forward displacement (271.4, 216.7, 171.5 mm). The hip joint excursion of the PMHS that was not exposed to the shoulder PT seat belt was twice the magnitude observed for the other 2 subjects. The 3 PMHS sustained clavicle fractures on the shoulder loaded by the seat belt and 2 of them were diagnosed atlantoaxial subluxation in the radiologist examination. Avulsion fractures of the right lamina of T1, T2, T3, and T4 were found when the PT was not used. The 3 PMHS received multiple fractures spread over both aspects of the rib cage and involving the posterior aspect of it.

CONCLUSION

In this study of nearside oblique impact loading, the PMHS exhibited kinematics characterized by reduced torso pitching and increased lateral head excursion as compared to previous frontal impact results. These kinematics resulted in potential cervical and thoracic spinal injuries and in complete, displaced fractures of the lateral and posterior aspects of the rib cage. Though this is a limited number of subjects, it shows the necessity of further understanding of the kinematics of occupants exposed to this loading mode.

Evaluation of CdZnTe as neutron detector around medical accelerators

The operation of electron linear accelerators (LINACs) and cyclotrons can produce a mixed gamma-neutron field composed of energetic neutrons coming directly from the source and scattered lower energy neutrons. The thermal neutron detection properties of a non-moderated coplanar-grid CdZnTe (CZT) gamma-ray detector close to an 18 MV electron LINAC and an 18 MeV proton cyclotron producing the radioisotope (18)F for positron emission tomography are investigated. The two accelerators are operated at conditions producing similar thermal neutron fluence rates of the order of 10(4) cm(-2) s(-1) at the measurement locations. The counting efficiency of the CZT detector using the prompt 558 keV photopeak following (113)Cd thermal neutron capture is evaluated and a good neutron detection performance is found at the two installations.

Artificial neural networks technology for neutron spectrometry and dosimetry

Artificial Neural Network Technology has been applied to unfold neutron spectra and to calculate 13 dosimetric quantities using seven count rates from a Bonner Sphere Spectrometer with a (6)LiI(Eu). Two different networks, one for spectrometry and another for dosimetry, were designed. To train and test both networks, 177 neutron spectra from the IAEA compilation were utilised. Spectra were re-binned into 31 energy groups, and the dosimetric quantities were calculated using the MCNP code and the fluence-to-dose conversion coefficients from ICRP 74. Neutron spectra and UTA4 response matrix were used to calculate the expected count rates in the Bonner spectrometer. Spectra and H(10) of (239)PuBe and (241)AmBe were experimentally obtained and compared with those determined with the artificial neural networks.

Water-extended polyester neutron shield for a 252Cf neutron source

A Monte Carlo study to determine the shielding features to neutrons of water-extended polyester was carried out. During calculations, (252)Cf and shielding were modelled and the neutron spectra as well as the H(10) were calculated in four sites. The calculation was extended to include a water shielding, the source in vacuum and in air. Besides neutron shielding characteristics, the Kerma in air due to gammas emitted by (252)Cf and due to capture gamma rays in the shielding were included.

Neutron fluence rate measurement using prompt gamma rays

A gamma ray spectrometer, with a 3('') Ø X 3('') NaI(Tl) detector, with a moderator sphere has been utilised to measure the neutron fluence rate, with this value the H(10) was estimated. When a neutron is captured by the hydrogen-based moderator, a 2.22 MeV prompt gamma ray is produced. In a multichannel analyser the net area under the 2.22 MeV photopeak is proportional to the total neutron fluence rate. The features of this system were determined by a Monte Carlo study that includes 3-, 5- and 10-inches diameter, water and polyethylene moderators and a (239)Pu-Be source. The prompt gamma response was extended to monoenergetic neutron sources. To verify the response, a (239)Pu-Be source in combination with a 10('') polyethylene sphere having a gamma-ray spectrometer with NaI(Tl) was utilised to estimate the neutron fluence rate and the H(10). These results were compared with neutron fluence rate and H(10) obtained using a Bonner sphere spectrometer and with the H(10) measured using a neutron remmeter.

Artificial neural networks in neutron dosimetry

An artificial neural network (ANN) has been designed to obtain neutron doses using only the count rates of a Bonner spheres spectrometer (BSS). Ambient, personal and effective neutron doses were included. One hundred and eighty-one neutron spectra were utilised to calculate the Bonner count rates and the neutron doses. The spectra were transformed from lethargy to energy distribution and were re-binned to 31 energy groups using the MCNP 4C code. Re-binned spectra, UTA4 response matrix and fluence-to-dose coefficients were used to calculate the count rates in the BSS and the doses. Count rates were used as input and the respective doses were used as output during neural network training. Training and testing were carried out in the MATLAB environment. The impact of uncertainties in BSS count rates upon the dose quantities calculated with the ANN was investigated by modifying by +/-5% the BSS count rates used in the training set. The use of ANNs in neutron dosimetry is an alternative procedure that overcomes the drawbacks associated with this ill-conditioned problem.

Evidence for strange-quark contributions to the nucleon's form factors at Q2=0.108 (GeV/c)2

We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q(2)=0.108 (GeV/c)(2) and at a forward electron scattering angle of 30 degrees <theta(e)<40 degrees . The measured asymmetry is A(LR)(e-->p)=[-1.36+/-0.29(stat)+/-0.13(syst)]x10(-6). The expectation from the standard model assuming no strangeness contribution to the vector current is A(0)=(-2.06+/-0.14)x10(-6). We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be G(s)(E)+0.106G(s)(M)=0.071+/-0.036 at Q(2)=0.108 (GeV/c)(2). We again find the value for G(s)(E)+0.106G(s)(M) to be positive, this time at an improved significance level of two sigma.

Measurement of strange-quark contributions to the nucleon's form factors at Q(2) = 0.230 (GeV/c)(2)

We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.

Characteristics of the neutron field of the facility at DIN-UPM

A new source facility (241Am-Be) has been installed in a bunker-type room of large dimensions. To characterise the neutron fields in the facility, detailed calculations have been made with MCNP-4C, showing the different components of the neutron radiation reaching the reference points (direct, inscattered, backscattered). The contribution from neutrons scattered in the walls to the total ambient dose equivalent remains reasonably low (<10%) in the reference points. Additionally, spectra measurements have been performed with a Bonner spheres spectrometer with a 6LiI(Eu) scintillator (0.4 phi x 0.4 cm2), UTA4 response matrix and BUNKIUT unfolding code. The calculated and experimentally obtained spectra are compared, with small differences found in the epithermal and thermal region, attributable to the concrete composition used in the calculations. The H*(10) rate has been determined from the spectra, and then compared to the reading of an active dosemeter (LB6411), with differences found lower than 8%.

Response components of LiF:Mg,Ti around a moderated Am-Be neutron source

The responses of TLD-1010, TLD-700 and TLD-600 thermoluminescence dosemeters to the radiation field inside a water tank enclosing an isotopic 241Am-Be neutron source are analysed. Separate contributions coming from thermal neutrons, neutrons with energies above thermal and gamma rays to the total response of the three types of TLD are obtained. This is accomplished by assuming that the gamma responses for materials with different 6Li enrichments are identical and that the neutron response of TLD-700 is negligible compared to TLD-100 and TLD-600. The last assumption is tested by Monte Carlo simulations of the neutron energy spectrum at the points where the TLDs are irradiated.

Characterization of the visual performance with soft daily wear disposable contact lenses

We investigate the visual performance associated with adaptation to a daily wear soft contact lens on the human eye. For this purpose, we used four parameters, one of which was an objective parameter, while the rest were subjective parameters. The objective parameter was a single quality parameter, a Merit function (Mf) derived from the modulation transfer function (MTF) of the overall [eye + contact lens] system The subjective parameters were the visual acuity (VA), the contrast sensitivity function (CSF) and the standard adaptation criterion of Terry et al. (1993). The normality criterion for the MTF was determined by evaluating the fluctuations of the Mf over a day in five emmetropic observers. Fluctuations with no statistically significant differences in the merit function (p > 0.05) and their standard deviation (8%) defined our standard criterion. The CSF and the VA were similarly measured (for emmetropic observers). The results obtained with emmetropic observers allowed us to establish a standard criterion for the evaluation parameters we propose. When this criterion is applied to daily soft wear disposable contact lenses, their performance proves to be good, since both the objective (MTF) and the subjective parameters (CSF, VA, adaptation criterion) always lie within the range defined by our criterion.

Standard criterion for fluctuations of modulation transfer function in the human eye: application to disposable contact lenses

It is well known that the modulation transfer function (MTF) characterizes the optical quality of the eye. Recently, some objective techniques have been introduced in order to measure this function in vivo. These techniques could be employed to display the temporal fluctuations of the eye + compensation system and to isolate the effect of the compensation element provided that the standard fluctuations for a normal observer were known. In this work we carry out a study of the MTF of the human eye over a long period of time to quantify the standard fluctuations of the retinal image quality and to establish a standard criterion of normality. We have defined a single quality parameter from each measured MTF to simplify the analysis of the results. We have evaluated this merit function on normal observers three times a day for one month. As expected, random deviations from the mean value of the merit function have been obtained, although fluctuations with no statistical differences of the merit function (P value from ANOVA test P > 0.01) and the standard deviation of these fluctuations (5%) can be chosen as a standard criterion. We have used this result to study the behaviour of a time-varying compensation element: a disposable contact lens. The study of the eye + contact lens system has been carried out with four types of disposable contact lenses for one month. In spite of their generally good behaviour, statistically significant differences from the standard pattern can be observed. This superimposed continuous fluctuation can be due to lens-dependent processes.

Contact lenses: do they really change the opticalperformance?

In this investigation the quality of two types of optical correction, hydrogel contact lenses and ophthalmic lenses, was compared by measuring the modulation transfer function (MTF) of the correcting lens plus visual optics system using an objective method. A merit function was defined in order to allow the direct comparison between the optical performance with the two corrections. A study on 10 subjects was undertaken, measuring the MTF of both corrections by using the double pass method. The results show that the optical quality of contact lenses was higher than that with ophthalmic lenses. The contrast sensitivity function (CSF) and visual acuity (VA) were determined as subjective parameters of visual performance.

Influence of the tear film on optical quality of the eye

The optical quality of the tear film of the eye was tested by measuring the retinal image before and after the break-up time (BUT). An objective method was used based on the evaluation of the retinal image of a point test projected onto the fovea. The loss of an entire tear film would result in a decrease in the optical quality because of corneal irregularities and the formation of an irregular tear lens after the BUT. Our results confirm the expected loss both of non-contact lens wearers and contact lens wearers. Also, the fact that the optical deterioration found after the BUT is greater for contact lens wearers confirms that soft contact lens wear produces a disruption of the tears.