Polytetrafluoroethylene Samples Research Articles

Development of electrostatic removal system for application in dust removal from Martian spacesuits

Dust removal from Martian spacesuits whilst on exploration activities is critically important for long-term Martian exploration missions. Martian dust is known to contain harmful particles which must be removed from Martian spacesuits to prevent entry into habitation zones on Mars, and prevent spacesuit wear. In this work, an Electrostatic Removal System was developed which utilised the phenomenon of dielectrophoresis to remove Martian dust from the outer layer of spacesuits. Dielectrophoretic forces were exerted on dust particles by an alternating electrostatic field which acted to remove the particles from a surface. The field was generated by applying high voltage square waves, produced by a MOSFET H-Bridge, across an array of parallel copper electrodes contained within an Electrostatic Removal Device. A theoretical model was derived to predict the effect of variables on the system performance, which was validated through experimental testing. This system demonstrated a high dust clearing performance of over 95% when the dust is in direct contact with the Electrostatic Removal Device’s surface. However, the system was not able to achieve dust removal from samples of Nomex, Teflon, and Kevlar, the three constituent materials of the outer layer of spacesuits. Further development is required for the system to become a viable option for the removal of Martian dust from spacesuits. Nonetheless, this system may prove effective in other applications such as dust removal from solar panels or optical devices, where the electrodes may be able to be integrated directly beneath the dust layer.

Enhancing gamma irradiation resistance by a‐C film treatment on polytetrafluoroethylene (PTFE) surface

Polytetrafluoroethylene (PTFE) solid self‐lubricating materials exhibit inferior tribological properties in the gamma‐irradiated environment. In this paper, amorphous hydrogen‐free carbon (a‐C) film was deposited on the PTFE polymer surface by magnetron sputtering, and the a‐C/PTFE samples were irradiated with gamma ray at a maximum dose of up to 5 MGy. The evolution of the structure and nanomechanical and tribological properties of a‐C/PTFE with different irradiation doses were investigated. The structural analyses reveal that the microstructure of a‐C films irradiated at 5 MGy doses is stable. Due to the covering of the a‐C film, significant cracks appear at the surface of the a‐C/PTFE sample only when the irradiation dose reaches 5 MGy. Before and after irradiation, the nanohardness and Young's modulus of the a‐C/PTFE are significantly higher than those of PTFE. The mechanical properties of PTFE are improved by a‐C film surface treatment. The friction experiments show that the average friction coefficients of both a‐C/PTFE and PTFE remain stable around 0.175 with increasing irradiation dose. When the irradiation dose is within 1 MGy, frictional behaviors occur only on the surface of a‐C films, and the wear rate of a‐C/PTFE is as low as 9.3 × 10−5 mm3/N.m, which is significantly lower than that of PTFE. The method of a‐C film treatment on the PTFE surface can dramatically improve the irradiation resistance of PTFE.

Analysis of micromechanical and tribotechnical properties of fluoropolymers during friction on 40Kh steel

The paper presents the results of micromechanical and tribotechnical tests of samples of polytetrafluoroethylene, radiation-modified (PTFE – RM according to modes A and B), coked in comparison with the PTFE standard (Fluoroplast -F4). The influence of the surface roughness of a 40Kh steel counter-tile on the coefficients of friction against time at a constant sliding speed is considered. Micromechanical tests were carried out using the method of instrumental indentation with a triangular Berkovich diamond pyramid. Tribotechnical tests were performed on a friction machine with a vertical axis of rotation of the spindle according to the scheme “the end of the sample of the fluoropolymer disk is the end of the counter-flange of the annular sleeve (steel 40Kh)” without lubrication and when the friction pair is lubricated with MGE-10A hydraulic oil. It was found that during friction without lubrication, PTFE samples had the maximum friction coefficients, and F4K20 samples had the minimum friction coefficients when working with 40X steel counter-tiles treated with P180 sandpaper. PTFE-RM (A) samples had the best wear resistance, followed by decreasing F4K20, PTFE – RM (B) and PTFE under friction without lubrication. In the presence of lubricant, the samples of the PTFE standard were inferior in wear resistance to the F4K20 samples, but were 5-7% better than the samples of PTFE-RM (B) and (A), respectively.

Singlet oxygen generation under optical excitation of polytetrafluoroethylene

Singlet oxygen together with radical reactions plays an important role in biochemistry of living organisms, and is one of the main active substances in photodynamic treatment of organs and body fluids. Along with traditional singlet oxygen photosensitizers based on biocompatible dyes, the singlet oxygen photogeneration ability of matrix materials such as organic solvents and metal oxide surfaces has recently been investigated. Despite a good compatibility with bio substances, polytetrafluoroethylene (also known under the trademark as Teflon®) remains unaddressed in these studies. Here we present our photoluminescence studies of singlet oxygen generation in polytetrafluoroethylene samples under ultraviolet and visible irradiation. We found a good singlet oxygen photogeneration with an efficiency no less and possibly exceeding it in carbon tetrachloride, a known singlet‑oxygen-retentive medium. Based on the results obtained, it is assumed that the phosphorescence of singlet oxygen is observed from the volume of polytetrafluoroethylene with direct optical excitation of oxygen adsorbed or dissolved in the structure of polytetrafluoroethylene by analogy with direct optical excitation of oxygen in the volume of various solvents. Cooling a PTFE sample down to −20 °C allows to enhance the singlet oxygen concentration in the polymer indicating the enthalpy of oxygen sorption of ΔHsorp = −1.51 kcal/mol. Our results can heighten medical interest to fluoropolymers and, in particular, to polytetrafluoroethylene making it a promising singlet oxygen generator for photodynamic uses.

Rational Design Strategy for Triboelectric Nanogenerators Based on Electron Back Flow and Ionic Defects: The Case of Polytetrafluoroethylene

AbstractThe lack of theoretical understanding of triboelectrification has hindered the development of energy harvesting technologies like triboelectric nanogenerators. Focusing on polytetrafluoroethylene, a material with a strong triboelectric output, a model predictive of its triboelectric behavior, driving the development of improved nanogenerators are formulated. With a combined computational‐experimental approach it is shown that defluorination enhances polytetrafluoroethylene nanoscale triboelectric charging. Then a model, explaining the macroscale triboelectric output as determined by the competition of two mechanisms is developed. Defluorination enhances charging while also reducing the interface gap, favoring the backflow of electrons, and possibly reducing charging. However, numerical analysis shows that backflow is negligible, aligning with the prediction of increased triboelectric output. By building triboelectric nanogenerators with defluorinated polytetrafluoroethylene samples, achieved by X‐ray irradiation, a one‐order‐of‐magnitude output increase is demonstrated. The predictive models, supported by experiments, lead to an improved strategy for designing effective energy harvesting devices and new applicative breakthroughs.

Stability assessment of organic sulfur and organosulfate compounds in filter samples for quantification by Fourier- transform infrared spectroscopy

Abstract. Organic sulfur and sulfate compounds, which are tracers for sources and atmospheric processes, are not currently measured in national monitoring networks such as the Interagency Monitoring of Protected Visual Environments (IMPROVE). The goal of this paper is to begin to assess the stability of organic sulfur and sulfate-containing compounds on polytetrafluoroethylene (PTFE) filters and the suitability of Fourier-transform infrared (FT-IR) spectroscopy to measure these compounds. Stability assessment is needed because PTFE samples collected by IMPROVE are typically stored 6–9 months prior to analysis. For this study, two organosulfur compounds, methanesulfonic acid (MSA) and hydroxymethanesulfonate ion (HMS), and two organosulfate compounds, methyl sulfate (MS) and 2-methyltetrol sulfate (2-MTS), are collected individually on PTFE filters. Gravimetric mass measurements are used to assess mass stability over time. FT-IR spectra are evaluated to assess the capability of measuring the compound from PTFE filters by assessing the compound stability or chemical changes over time. Ion chromatography (IC) and inductively coupled plasma optical emission spectroscopy (ICP-OES) are used as additional tools to assess stability or chemical changes over time. MS has the highest potential to be measured by FT-IR in IMPROVE samples. For MS, a simple organosulfate, the mass changes are within measurement uncertainty and FT-IR spectra indicate no compositional change over a 4-month period, suggesting that MS can be measured using FT-IR. IC and ICP-OES support the conclusion that MS is stable on the filter. However, for 2-MTS, the other organosulfate measured in this study, spectral changes after a month on the filter suggest that it decomposes into other organosulfates or an inorganic sulfate. MSA in IMPROVE samples can be measured, but only as a lower bound, due to volatility off the filter as indicated by FT-IR and gravimetry. FT-IR and IC both show that MSA does not chemically change over the course of the study. Measurements by all methods indicate that HMS is unstable on the PTFE filter, and IC and FT-IR indicate that it likely converts to inorganic sulfate. Future work includes the evaluation of these compounds in an ambient aerosol sample matrix to determine any differences in stability, identifying interference that could limit quantification, and developing calibrations to measure the compounds or functional groups in ambient samples.

Enhancing surface adhesion of polytetrafluoroethylene induced by two-step in-situ treatment with radiofrequency capacitively coupled Ar/Ar+CH4+NH3 plasma

Although some progress in plasma modification of the polytetrafluoroethylene (PTFE) surface has been made recently, its adhesion strength still needs to be further improved. In this work, the surface of a PTFE sample was treated with a two-step in-situ method. Firstly, the PTFE surface was treated with capacitively coupled Ar plasma to improve its mechanical interlocking performance; then, Ar+NH3+CH4 plasma was used to deposit an a-CN x :H cross-linking layer on the PTFE surface to improve the molecular bonding ability. After treatment, a high specific surface area of 2.20 and a low F/C ratio of 0.32 were achieved on the PTFE surface. Its surface free energy was increased significantly and its maximum adhesion strength reached 77.1 N·10 mm−1, which is 56% higher than that of the single-step Ar plasma-treated sample and 32% higher than that of the single-step Ar+CH4+NH3 plasma-treated sample.

Design of slot radiating RF planar sensor for homogeneity check of dielectric discontinuity

AbstractIn this paper, a 2.8‐GHz RF planar sensor with radiating slots is proposed for effective checking of discontinuity in homogeneous dielectric samples. The slots etched in the ground plane reduce the effective area for sample placement, which increases in the case of a conventional ring at the desired frequency. Several forms of discontinuity are analyzed and measured with the help of varying geometrical configurations of Teflon, wood, and polyethylene samples with varying permittivity. It is observed that due to the uniform distribution of fields among all the radiating slots any sort of configurational discontinuity is detected by the sensor in terms of the shift in resonant frequency and S21 transmission notch. The simulations are carried out using CST‐MWS and the equivalent model is developed using ADS. The numerical analysis is carried out using Origin software and the measurement is carried out using Taconic TLY‐5 substrate by photolithographic etching.

Mechanisms of the memory effect of clathrate hydrates

The memory effect in the nucleation of gas hydrates refers to the phenomenon that gas hydrates nucleate easier or faster in the water that has a history of gas hydrate formation than in fresh water that has no such history. Although several hypotheses have been proposed to explain the cause of the memory effect over the last several decades, it remains the longest-standing mystery in the nucleation of gas hydrates. Supersaturation of the guest gas has been considered to occur in a memory system, however, the extent of its impact on the memory effect has been unclear. In the current research, we used linear cooling ramp experiments under isobaric conditions to determine the nucleation curves of CO2 hydrate in quiescent water in a stainless-steel sample cell and in quiescent quasi-free water droplets supported by a bulk liquid of perfluoromethyldecalin contained in a Teflon sample cell. From systematically comparing the nucleation curves of both freshly prepared samples and samples with a history of CO2 hydrate formation in both the stainless-steel sample cell and the quasi-free water droplets, as well as the nucleation curves of methane – propane mixed gas hydrates previously reported, a coherent picture emerged. The impurity imprinting component, with the interfacial gaseous states as the entity of the “impurity”, and the guest supersaturation component, with or without nanobubbles in the bulk water, are comparable in size, albeit the former is the larger one.

Characterization of offline analysis of particulate matter with FIGAERO-CIMS

Abstract. Measurements of the molecular composition of organic aerosol (OA) constituents improve our understanding of sources, formation processes, and physicochemical properties of OA. One instrument providing such data at a time resolution of minutes to hours is the chemical ionization time-of-flight mass spectrometer with filter inlet for gases and aerosols (FIGAERO-CIMS). The technique collects particles on a filter, which are subsequently desorbed, and the evaporated molecules are ionized and analyzed in the mass spectrometer. However, long-term measurements using this technique and/or field deployments at several sites simultaneously require substantial human and financial resources. The analysis of filter samples collected outside the instrument (offline) may provide a more cost-efficient alternative and makes this technology available for the large number of particle filter samples collected routinely at many different sites globally. Filter-based offline use of the FIGAERO-CIMS limits this method, albeit to particle-phase analyses, which is likely at a reduced time resolution compared to online deployments. Here we present the application and assessment of offline FIGAERO-CIMS, using Teflon and quartz fiber filter samples that were collected in autumn 2018 in urban Beijing. We demonstrate the feasibility of the offline application with a “sandwich” sample preparation for the over 900 identified organic compounds with (1) high signal-to-noise ratios, (2) high repeatability, and (3) linear signal response to the filter loadings. Comparable overall signals were observed between the quartz fiber and Teflon filters for 12 and 24 h samples but with larger signals for semi-volatile compounds for the quartz fiber filters, likely due to adsorption artifacts. We also compare desorption profile (thermogram) shapes for the two filter materials. Thermograms are used to derive volatility qualitatively based on the desorption temperature at which the maximum signal intensity of a compound is observed (Tmax⁡). While we find that Tmax⁡ can be determined with high repeatability (±5.7 ∘C) from the duplicate tests for one filter type, we observe considerable differences in Tmax⁡ between the quartz and Teflon filters, warranting further investigation into the thermal desorption characteristics of different filter types. Overall, this study provides a basis for expanding OA molecular characterization by FIGAERO-CIMS to situations where and when deployment of the instrument itself is not possible.

Transient multilayer analytical model of a line heat source probe for in-pile thermal conductivity measurements

In-pile measurements of nuclear fuel properties is of critical importance for the design, performance, and safety considerations of next generation nuclear reactors and can be difficult due to the high temperature and high neutron flux environment. Real-time data for thermal conductivity is currently lacking due to the difficulty in deploying advanced instrumentation for thermal properties measurements in situ during nuclear operations. This limitation hinders our understanding of the mechanisms responsible for these changes. In this study, we have developed analytical models, utilizing the quadrupoles method, for in-pile thermal conductivity measurements using a novel line heat source. This probe uses Joule heating of a single wire to induce a temperature gradient and heat flow in surrogate fuel samples, while simultaneously leveraging the temperature dependent resistance of the wire as a thermometer to monitor the temperature rise of the sample for thermal conductivity extraction. The analytical models have been verified against more computationally intensive finite element models and experimental results were obtained from Teflon (PTFE) and aluminum samples. Coefficient of determination (R2) values for the measurements were 0.995, 0.987, and 0.992 for 10, 20, and 30 mm PTFE respectively and 0.983, 0.992, and 0.960 for 10, 20, and 30 mm aluminum respectively. Further complimenting the fits, sensitivity parameter studies were conducted on the 10 and 30 mm PTFE and aluminum highlighting the potential of our approach for rapid in-pile thermal conductivity measurements.

Crack propagation in viscoelastic finite-sized solids: theory and experiments

The problem of crack propagation in viscoelastic materials is of great interest given the numerous engineering applications of such materials. Due to viscoelasticity, even the study of the basic Mode I opening represents a tricky theoretical challenge. Indeed, existing theories adopt important approximations such as i) simplistic constitutive behaviour, ii) steady-state crack propagation, iii) infinite domain of the system. In this work, we revise the theory of Persson & Brener for systems of infinite domain; specifically, we propose a solution to take into account size effects in a viscoelastic plate. The theory allows to consider the realistic constitutive behaviour of viscoelastic materials and to predict the dependence of the energy release rate with the crack tip speed. Comprehensive experimental investigations are performed to corroborate our theoretical predictions. First, dynamic mechanical analysis (DMA) is performed to characterize the complex viscoelastic modulus of PolyTetraFluoroEthylene (PTFE). Second, tensile tests are carried out on cracked PTFE samples, and pictures are recorded with an image acquisition system. Moreover, a point tracking algorithm is developed to measure the crack length and opening displacement. Moving from small to high crack tip speeds, the fracture process becomes less ductile and an increase in the maximum load is observed. In addition, experimental data show that the inclusion of finite-size effects in the theory is crucial for accurately estimating the energy release rate.

Dyeable Hydrophilic Surface Modification for PTFE Substrates by Surface Fluorination.

Polytetrafluoroethylene (PTFE) is the most widely used fluoropolymer that has various functionalities such as heat resistance, chemical resistance, abrasion resistance, and non-adhesiveness. However, PTFE is difficult to dye because of its high water repellency. In this study, the PTFE surface was modified by a combination of gold sputtering and surface fluorination to improve dyeability. X-ray photoelectron spectroscopy indicated that, compared with the untreated sample, the gold-sputtered and acid-washed surface of PTFE had a negligible number of C-F terminals. Furthermore, the intensity of the C-C peak increased drastically. The polar groups (C=O and C-Fx) increased after surface fluorination, which enhanced the electronegativity of the surface according to the zeta potential results. Dyeing tests with methylene blue basic dye showed that the dye staining intensity on the surface of fluorinated PTFE samples was superior to other samples. It is due to the increased surface roughness and the negatively charged surface of fluorinated PTFE samples. The modified PTFE substrates may find broad applicability for dyeing, hydrophilic membrane filters, and other adsorption needs.

Gradient Index Metasurface Lens for Microwave Imaging.

This paper presents the design, simulation and experimental validation of a gradient-index (GRIN) metasurface lens operating at 8 GHz for microwave imaging applications. The unit cell of the metasurface consists of an electric-LC (ELC) resonator. The effective refractive index of the metasurface is controlled by varying the capacitive gap at the center of the unit cell. This allows the design of a gradient index surface. A one-dimensional gradient index lens is designed and tested at first to describe the operational principle of such lenses. The design methodology is extended to a 2D gradient index lens for its potential application as a microwave imaging device. The metasurface lenses are designed and analyzed using full-wave finite element (FEM) solver. The proposed 2D lens has an aperture of size 119 mm (3.17λ) × 119 mm (3.17λ) and thickness of only 0.6 mm (0.016λ). Horn antenna is used as source of plane waves incident on the lens to evaluate the focusing performance. Field distributions of the theoretical designs and fabricated lenses are analyzed and are shown to be in good agreement. A microwave nondestructive evaluation (NDE) experiment is performed with the 2D prototype lens to image a machined groove in a Teflon sample placed at the focal plane of the lens.

Assessing the effect of compaction pressure on the mechanical properties of polytetrafluoroethylene elaborated by field assisted sintering technique

We study the effect of compaction pressure on the mechanical properties of polytetrafluoroethylene (PTFE) synthesized by the field-assisted sintering technique (FAST). PTFE is a commonly polymer use material with various technological applications in the automotive, aerospace, and chemical industries. While the manufacture of PTFE is problematic due to its high molecular weight and hence a very high melt viscosity, FAST is an adequate process which can fix this problem by offering rapid densification (a few minutes). In this context, we explore the mechanical behavior of sintered PTFE produced with different compaction pressures, all other operating parameters being held constant. The stress-strain curves of PTFE investigated by uniaxial tension tests show a significant dependence of the compaction pressure on the elastic and plastic mechanical characteristics. An attempt is made to correlate the applied pressure during the sintering process to microstructural changes according to the de Gennes creep model. For plastic deformation, the stress-strain curves are compared to the predictive Hollomon's and Haward and Thackray's models and discussed in physical terms. We conclude that a better mechanical behavior of sintered PTFE materials can be achieved by using an optimum value of compaction pressure which is not necessary found above the yield flow. • PTFE samples produced by the field-assisted sintering technique are characterized. • Stress-strain curves show significant dependence on compaction pressure. • Hollomon's and HT analysis allow us to characterize the strain hardening behavior. • Optimal properties correspond to sintered samples at pressure less than 5 MPa.

A More Accurate Measurement Method of the Dielectric Material Properties With High Tolerance Using an Overmoded Waveguide

This article proposed an overmoded waveguide method (OWM) for more accurate measurement of dielectric properties in the subterahertz and terahertz band. Compared with the traditional standard waveguide method (SWM), the OWM is beneficial to alleviate the significant error caused by the air gap. Simulation predicts that for typical medium permittivity and loss materials, the relative errors of <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> and tan<inline-formula> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> can be reduced from 10&#x0025; to below 3&#x0025; using the OWM with an overmoded factor of 3 when the air gap is 0.02 mm at W-band. When extending the overmoded factor over 5, the relative error can be reduced below 1.5&#x0025;. The tolerance improvement was verified by measuring a polytetrafluoroethylene (PTFE) sample through SWM and OWM. Experimental results show the relative error of <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> is lower than 5&#x0025; even when there exists a 0.24-mm air gap in the OWM.

Molecular emission dynamics from a femtosecond filament induced plasma plume

In this study, we investigated the filament-induced plasma properties and the associated molecular emission features from three different non-metallic samples. Graphite, polymethyl methacrylate, and Teflon samples have been ablated using a tightly focused filament, and their emission spectra were analyzed using a time-integrated optical emission spectroscopy technique. The temporal responses and evolution dynamics of molecular species such as CN and C2 from these samples in ambient conditions are compared. The tightly focused filament was generated by focusing the Ti:Sapphire femtosecond pulses having a pulse duration of 29 fs using a short focal length external focusing system. The time-integrated intensified charge-coupled device images of air filament show that the filament survives up to a few nanosecond time duration after the onset of air plasma. The influence of physical and chemical properties of the samples during filament ablation has also been studied by characterizing the optical emission spectra. We find that the molecular signal intensity strongly depends on the sample properties and the position of the sample in the filament. The increase in molecular emission intensity from a graphite sample as a function of incident laser intensity suggests that the tightly focused filament surpasses the intensity clamping value.

Towards subpercentage uncertainty proton stopping-power mapping via dual-energy CT: Direct experimental validation and uncertainty analysis of a statistical iterative image reconstruction method.

To assess the potential of a joint dual-energy computerized tomography (CT) reconstruction process (statistical image reconstruction method built on a basis vector model (JSIR-BVM)) implemented on a 16-slice commercial CT scanner to measure high spatial resolution stopping-power ratio (SPR) maps with uncertainties of less than 1%. JSIR-BVM was used to reconstruct images of effective electron density and mean excitation energy from dual-energy CT (DECT) sinograms for 10 high-purity samples of known density and atomic composition inserted into head and body phantoms. The measured DECT data consisted of 90 and 140 kVp axial sinograms serially acquired on a Philips Brilliance Big Bore CT scanner without beam-hardening corrections. The corresponding SPRs were subsequently measured directly via ion chamber measurements on a MEVION S250 superconducting synchrocyclotron and evaluated theoretically from the known sample compositions and densities. Deviations of JSIR-BVM SPR values from their theoretically calculated and directly measured ground-truth values were evaluated for our JSIR-BVM method and our implementation of the Hünemohr-Saito (H-S) DECT image-domain decomposition technique for SPR imaging. A thorough uncertainty analysis was then performed for five different scenarios (comparison of JSIR-BVM stopping-power ratio/stopping power (SPR/SP) to International Commission on Radiation Measurements and Units benchmarks; comparison of JSIR-BVM SPR to measured benchmarks; and uncertainties in JSIR-BVM SPR/SP maps for patients of unknown composition) per the Joint Committee for Guides in Metrology and the Guide to Expression of Uncertainty in Measurement, including the impact of uncertainties in measured photon spectra, sample composition and density, photon cross section and I-value models, and random measurement uncertainty. Estimated SPR uncertainty for three main tissue groups in patients of unknown composition and the weighted proportion of each tissue type for three proton treatment sites were then used to derive a composite range uncertainty for our method. Mean JSIR-BVM SPR estimates deviated by less than 1% from their theoretical and directly measured ground-truth values for most inserts and phantom geometries except for high-density Delrin and Teflon samples with SPR error relative to proton measurements of 1.1% and -1.0% (head phantom) and 1.1% and -1.1% (body phantom). The overall root-mean-square (RMS) deviations over all samples were 0.39% and 0.52% (head phantom) and 0.43% and 0.57% (body phantom) relative to theoretical and directly measured ground-truth SPRs, respectively. The corresponding RMS (maximum) errors for the image-domain decomposition method were 2.68% and 2.73% (4.68% and 4.99%) for the head phantom and 0.71% and 0.87% (1.37% and 1.66%) for the body phantom. Compared to H-S SPR maps, JSIR-BVM yielded 30% sharper and twofold sharper images for soft tissues and bone-like surrogates, respectively, while reducing noise by factors of 6 and 3, respectively. The uncertainty (coverage factor k=1) of the DECT-to-benchmark values comparison ranged from 0.5% to 1.5% and is dominated by scanning-beam photon-spectra uncertainties. An analysis of the SPR uncertainty for patients of unknown composition showed a JSIR-BVM uncertainty of 0.65%, 1.21%, and 0.77% for soft-, lung-, and bony-tissue groups which led to a composite range uncertainty of 0.6-0.9%. Observed JSIR-BVM SPR estimation errors were all less than 50% of the estimated k=1 total uncertainty of our benchmarking experiment, demonstrating that JSIR-BVM high spatial resolution, low-noise SPR mapping is feasible and is robust to variations in the geometry of the scanned object. In contrast, the much larger H-S SPR estimation errors are dominated by imaging noise and residual beam-hardening artifacts. While the uncertainties characteristic of our current JSIR-BVM implementation can be as large as 1.5%, achieving<1% total uncertainty is feasible by improving the accuracy of scanner-specific scatter-profile and photon-spectrum estimates. With its robustness to beam-hardening artifact, image noise, and variations in phantom size and geometry, JSIR-BVM has the potential to achieve high spatial-resolution SPR mapping with subpercentage accuracy and estimated uncertainty in the clinical setting.

Reducing the Specular Properties of Metalized Teflon Coverings on Canadian Mobile Servicing Station on the International Space Station

A surface modification process was developed for the metalized Teflon coverings used for thermal protection of electronic equipment on the International Space Station [1]. The developed modification process of Teflon surfaces reduced substantially the specularity of Ag-Inconel coated Teflon thermal control films by changing the morphological appearance of their surfaces by ion-beam texturing in a controlled manner from a metallic-like and shiny to complete milky, white appearance without significantly affecting the thermal optical properties.&#x0D; A number of space hardware units covered with the textured Silver-Teflon were exposed to the open space environment between June 2002 and June 2006 and delivered back to Earth at the end of 2006. Remarkable performance was demonstrated by the treated Ag/Teflon, with the solar absorptance and total emittance values and the α/ε ratio remaining very close to the original values as measured before the flights [2].&#x0D; In an attempt to protect further the textured surfaces of Teflon from possible erosion by atomic oxygen and VUV in LEO environment, an additional novel surface modification process was developed that created an SixOyCzFn type of structure on the treated surface. The textured Teflon samples before and after surface treatments were tested in a space simulator facility under a combined atomic oxygen/vacuum ultraviolet exposure. A number of advanced characterization techniques were used to evaluate the properties of the modified films [3].

Chemical Composition and Source Apportionment of PM2.5 in a Border City in Southwest China

This paper studied the chemical characteristics and seasonal changes of PM2.5 in plateau cities on the southwest border of China. Urban air was sampled in Baoshan City during the rainy and dry seasons. Finally, 174 PM2.5 filters were collected (including 87 quartz and 87 Teflon samples for PM2.5). The mass concentrations, water-soluble inorganic ions, organic and inorganic carbon concentrations, and inorganic elements constituting PM2.5 were determined. Positive definite matrix factorization was used to identify potential sources of PM2.5, and the backward trajectory model was used to calculate the contribution of the long-distance transmission of air particles to the Baoshan area. It was found that in the wet season, most of the air masses come from the Indian Ocean and Myanmar. In the dry season, the air mass mainly comes from the China and Myanmar border area. The average concentration of PM2.5 in the wet and dry seasons was 23.17 ± 12.23 μg/m3. The daily mean value of OC/EC indicated that the measured SOC content was generated by the photochemical processes active during the sampling days. However, elements from anthropogenic sources (Na, Mg, Al, Si, P, K, Ca, Ti, Fe, Cu, Zn, Sb, Ba, and Pb) accounted for 99.51% and 99.40% of the total inorganic elements in the wet season and dry season, respectively. Finally, source apportionment showed that SIA, dust, industry, biomass burning, motor vehicle emissions, and copper smelting emissions constituted the major contributions of PM2.5 in Baoshan. Using combined data from three measurement sites provides a focus on the common sources affecting all locations.