scholarly journals Radon Progeny Recoil Effect in Retrospective Indoor Glass Dosimetry

2020 ◽  
Vol 7 (1) ◽  
pp. 35-41
Author(s):  
C.D. Tibambre-Heredia ◽  
H. Olaya-Dávila ◽  
A.C. Sevilla ◽  
R. Samasundaram ◽  
J.A. Lopez ◽  
...  
Keyword(s):  
Structural Modification ◽  
Atomic Displacement ◽  
Gas Diffusion ◽  
Recoil Energy ◽  
Recoil Effect ◽  
Radon Progeny ◽  
Significant Difference ◽  
Geant4 Code ◽  
Diffusion Speed ◽  
Ion Recombination

Radon gas diffusion and progeny transport in air, are mechanisms to be considered in retrospective glass dosimetry.   With the aim to contribute to the understanding of the Rn progeny recoil energy role in this dosimetry methodology, we carried out a simulation employing GEANT4 code. In that, we assumed the chemical compound of the glass that is used commonly in households.  Results are compared to experimentally measured 210Bi concentration to show that the recoil energy helps the progenies incrustation, mainly for the 218,214Po alpha emitters but do not influence bismuth-210 diffusion directly. A significant difference exists between our results and measured values; that is interpreted as due to atomic displacement by primary knock-on atoms. The SiO2 molecule binding energy breaks and the following ion recombination, induce a structural modification between the atom by e.g. cavities formation in such a way that reduces significantly the radon progeny diffusion speed.

Aerosol Properties and Unattached Fraction of Radon Daughters Close to the Human Face

1994 ◽  
Vol 56 (1-4) ◽  
pp. 133-135 ◽  
Author(s):  
P. Eklund ◽  
M. Bohgard
Keyword(s):  
Geometric Mean ◽  
Sampling Point ◽  
Radon Progeny ◽  
Human Face ◽  
Radon Exposure ◽  
Chamber Volume ◽  
Significant Difference ◽  
Radon Daughters ◽  
The Face ◽  
Unattached Fraction

Abstract A humanoid dummy inside a well controlled radon exposure chamber (volume=20m3) was used to investigate the properties of an aerosol close to, and far away from the human face, respectively. Rn222 and a NaCl aerosol (geometric mean diameter=86 nm, concentration ( 5000 cm-3 was added to the room. The size distribution of the passive aerosol and the unattached fraction of the radon progeny were measured in one sampling point during two different conditions: (1) with the face of the dummy close to the sampling point and (2) with the dummy placed 3 m from the sampling. The measured parameters show no significant difference in the two sampling situations, so it seems to be possible to characterise the inhaled air by measuring far away from the face, as is being done in most cases.

scholarly journals Gas-Transport Characteristics of PdCu–Nb–PdCu Membranes Modified with Nanostructured Palladium Coating

2021 ◽  
Vol 23 (1) ◽  
pp. 228
Author(s):  
Iliya Petriev ◽  
Polina Pushankina ◽  
Nikita Shostak ◽  
Mikhail Baryshev
Keyword(s):  
Hydrogen Transfer ◽  
Membrane Surface ◽  
Protective Layer ◽  
Gas Diffusion ◽  
Threshold Temperature ◽  
Functional Layer ◽  
Cu Doping ◽  
Associative Processes ◽  
Significant Difference ◽  
Cost Efficient

A method for obtaining composite gas-diffusion PdCu–Nb–PdCu membranes modified with a nanostructured crystalline coating was developed to increase the performance of Nb-based membranes. A modifying functional layer with a controlled size and composition was synthesized by electrochemical deposition, which made it possible to determine a certain geometric shape for palladium nanocrystallites. Developed PdCu–Nb–PdCu membranes have demonstrated flux values up to 0.232 mmol s−1 m−2 in the processes of diffusion purification of hydrogen at 400 °C. A very significant difference in the hydrogen fluxes through the modified and non-modified composite PdCu–Nb–PdCu membranes reached 1.73 times at the lower threshold temperature of 300 °C. Cu doping of protective layer did not affect the selective properties of the membranes, which was confirmed by the obtained high selectivity values up to 1323, and made it possible to reduce the noble metal content. The research data indicate that the modification of the membrane surface significantly accelerates the hydrogen transfer process at sufficiently low temperatures due to the acceleration of dissociative–associative processes on the surface. The reported approach demonstrates new possibilities for creating productive and cost-efficient membranes based on niobium.

scholarly journals Roles of Low-Molecular-Weight Penicillin-Binding Proteins in Bacillus subtilis Spore Peptidoglycan Synthesis and Spore Properties

1999 ◽  
Vol 181 (1) ◽  
pp. 126-132 ◽  
Author(s):  
David L. Popham ◽  
Meghan E. Gilmore ◽  
Peter Setlow
Keyword(s):  
Structural Modification ◽  
Cross Linking ◽  
Phenotypic Properties ◽  
Penicillin Binding Proteins ◽  
Peptidoglycan Synthesis ◽  
Bacillus Subtilis Spore ◽  
Growing Cell ◽  
Low Degree ◽  
Significant Difference ◽  
Peptidoglycan Structure

ABSTRACT The peptidoglycan cortex of endospores of Bacillusspecies is required for maintenance of spore dehydration and dormancy, and the structure of the cortex may also allow it to function in attainment of spore core dehydration. A significant difference between spore and growing cell peptidoglycan structure is the low degree of peptide cross-linking in cortical peptidoglycan; regulation of the degree of this cross-linking is exerted byd,d-carboxypeptidases. We report here the construction of mutant B. subtilis strains lacking all combinations of two and three of the four apparentd,d-carboxypeptidases encoded within the genome and the analysis of spore phenotypic properties and peptidoglycan structure for these strains. The data indicate that while thedacA and dacC products have no significant role in spore peptidoglycan formation, the dacB anddacF products both function in regulating the degree of cross-linking of spore peptidoglycan. The spore peptidoglycan of adacB dacF double mutant was very highly cross-linked, and this structural modification resulted in a failure to achieve normal spore core dehydration and a decrease in spore heat resistance. A model for the specific roles of DacB and DacF in spore peptidoglycan synthesis is proposed.

Measurement of Liquid Water Content Inside the Gas Diffusion Layer

2012 ◽  
Author(s):  
Siddiq Hussain Tahseen ◽  
Kehan Chen ◽  
Mehdi Shahraeeni ◽  
Samuel C. M. Yew ◽  
Mina Hoorfar
Keyword(s):  
Water Content ◽  
Capillary Pressure ◽  
Diffusion Layer ◽  
Liquid Water ◽  
Gas Diffusion Layer ◽  
Liquid Water Content ◽  
Gas Diffusion ◽  
Water Volume ◽  
Significant Difference ◽  
The Impact

The amount of the liquid water present at the gas diffusion layer (GDL) has an impact on the diffusivity, capillary pressure and the permeability which in turn influences convective and diffusive transport. A prodigious amount of research has been conducted to study and measure the different properties (time of breakthrough and capillary pressure versus saturation) associated with the breakthrough condition. However, most of the reported data ignored the impact of expansion of different components in the set-up (such as tubing) and the condition after the time of breakthrough. The focus of this study is to measure the breakthrough pressure and time of breakthrough and hence determine the liquid water content inside the GDL before the time of breakthrough. The measurements are performed for different samples to study the effect of the thickness and hydrophobic contents. The results show that expansion has significant difference in the determination of water volume inside the GDL.

scholarly journals Investigation on Mechanical Properties of a Carbon Paper Gas Diffusion Layer through a 3-D Nonlinear and Orthotropic Constitutive Model

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6341
Author(s):  
Yanqin Chen ◽  
Yuchao Ke ◽  
Yingsong Xia ◽  
Chongdu Cho
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Mechanical Performance ◽  
Polymer Electrolyte Membrane ◽  
Gas Diffusion ◽  
Carbon Paper ◽  
Operation Conditions ◽  
Significant Difference ◽  
Assembly Technology ◽  
Simulation Results

The mechanical loads that gas diffusion layers (GDLs) withstand in polymer electrolyte membrane fuel cell (PEMFC) stacks are sensitive to the assembly and working conditions. The mechanical properties of GDLs mostly depend on their composition materials, microstructural characteristics, operation conditions, etc. An accurate and comprehensive understanding of the mechanical performance of GDLs is significant for predicting the stress distribution and improving the assembly technology of PEMFC stacks. This study presented a novel 3-D nonlinear and orthotropic constitutive model of a carbon paper GDL to represent the material stiffness matrix with its compressive, tensile, and shear properties. Numerical simulations were performed based on the 3-D constitutive model, and the proposed 3-D model was validated against the experimental data reported previously. It is found that the simulation results of the 3-D constitutive model show a good agreement with the experimental results. Besides, the novel 3-D nonlinear and orthotropic model was applied in the overall stress simulation of a simplified PEMFC unit cell, compared to a conventional 3-D linear and isotropic model, and the simulation results of the two models show a significant difference.

scholarly journals Relativistic effect on atomic displacement damage for two-body inducing discrete reactions

2020 ◽  
Vol 239 ◽  
pp. 08004
Author(s):  
Shengli Chen ◽  
David Bernard ◽  
Cyrille De Saint Jean
Keyword(s):  
Elastic Scattering ◽  
Neutron Energy ◽  
Relativistic Effect ◽  
Relativistic Correction ◽  
Atomic Displacement ◽  
Recoil Energy ◽  
Incident Neutron ◽  
Incident Neutron Energy ◽  
Fusion Neutron ◽  
Atomic Recoil

The relativistic effect on two-body discrete reaction inducing atomic recoil energy and the sequent damage energy is studied for 6Li, 56Fe, 184W, and 238U. The relativistic correction is within 1% if incident neutron energy is below 20 MeV. For incident neutron energy up to 200 MeV or even 800 MeV, the relativistic effect should be taken into account for treating two-body kinematics. The relativistic correction is about 0.05Ein/MeV% for neutron elastic scattering for nuclei from 56Fe to 238U and smaller for (n,α) and (n,t) reactions. Analyses on damage energy show that the relativistic corrections are generally within 2% for incident neutron below 200 MeV for nuclei lighter than 56Fe because of the “saturation” of damage energy. However, the current damage theory cannot be applied for Primary Knock-on Atom (PKA) energy higher than 24.9ARZR4/3 keV, which is 10 times lower than the maximum PKA energy for D+T fusion neutron elastic scattering of 6Li.

Cristal-growth dynamics of n-doped gaAs

1992 ◽  
Vol 50 (2) ◽  
pp. 1544-1545
Author(s):  
Pham V. Huong ◽  
Stéphanie Bouchet ◽  
Jean-Claude Launay
Keyword(s):  
Crystal Growth ◽  
Spatial Resolution ◽  
Epitaxial Layer ◽  
Outer Surface ◽  
Gaas Substrate ◽  
Structural Modification ◽  
Growth Dynamics ◽  
Argon Laser ◽  
High Anisotropy ◽  
Crystal Gaas

Microstructure of epitaxial layers of doped GaAs and its crystal growth dynamics on single crystal GaAs substrate were studied by Raman microspectroscopy with a Dilor OMARS instrument equipped with a 1024 photodiode multichannel detector and a ion-argon laser Spectra-Physics emitting at 514.5 nm.The spatial resolution of this technique, less than 1 μm2, allows the recording of Raman spectra at several spots in function of thickness, from the substrate to the outer deposit, including areas around the interface (Fig.l).The high anisotropy of the LO and TO Raman bands is indicative of the orientation of the epitaxial layer as well as of the structural modification in the deposit and in the substrate at the interface.With Sn doped, the epitaxial layer also presents plasmon in Raman scattering. This fact is already very well known, but we additionally observed that its frequency increases with the thickness of the deposit. For a sample with electron density 1020 cm-3, the plasmon L+ appears at 930 and 790 cm-1 near the outer surface.

Compact and efficient gas diffusion electrodes based on nanoporous alumina membranes for microfuel cells and gas sensors

The Analyst ◽  
2020 ◽  
Vol 145 (1) ◽  
pp. 122-131 ◽  
Author(s):  
Wanda V. Fernandez ◽  
Rocío T. Tosello ◽  
José L. Fernández
Keyword(s):  
Response Times ◽  
Hydrogen Oxidation ◽  
Fast Response ◽  
Gas Diffusion ◽  
Limiting Current ◽  
Gas Diffusion Electrodes ◽  
Nanoporous Alumina ◽  
Alumina Membranes ◽  
Current Densities ◽  
Microfuel Cells

Gas diffusion electrodes based on nanoporous alumina membranes electrocatalyze hydrogen oxidation at high diffusion-limiting current densities with fast response times.

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