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At least 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Effective Thermal Contact Resistance of Regularly Textured Bodies in the Presence of Intercontact Heat-Conducting Media and the Phenomenon of Thermal Rectification

We compute the effective thermal contact resistance of a pair of materials formed by AISI 304 stainless steel and 200 nickel alloy in the presence of a periodic array of gaps filled with a heat-conducting medium (argon, water, helium, oxygen, or air) on the interface of these materials. In the nondeformed state, the surface of AISI 304 stainless steel has a microtextured topography formed by regularly located grooves of identical shapes, while the surface of 200 nickel alloy is perfectly flat. We estimate the level of thermal rectification for structures of this kind for different values of the applied mechanical and thermal loads and the maximal height of the surface grooves.

42 ENGINEERING↗
DOE OSTI2019

Nonlinear Second Harmonics of Localized Shear Waves in an Anisotropic Layer Between Anisotropic Half Spaces Under the Conditions of Imperfect Contact

We construct a numerical-analytic solution of the problem of generation of the nonlinear second harmonics in the course of propagation of elastic symmetric localized shear waves in the crystalline layer of cubic system of the m3m class located between the crystalline half spaces of the same type and the same class of anisotropy under the conditions of imperfect sliding contact of components of the waveguide. We determine the analytic form of the functions of wave motions for nonlinear anharmonic perturbations in the form of longitudinal-shear-type waves. We also perform the numerical investigations of the amplitude-frequency characteristics of the second harmonics for monochromatic localized waves in a layer of a single crystal of germanium between the half spaces from the single crystal of silicon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Validating mass spectrometry measurements of nuclear materials via a non-contact volume analysis method of ion sputter craters

A combination of secondary ion mass spectrometry, optical profilometry and a statistically-driven algorithm was used to develop a non-contact volume analysis method to validate the useful yields of nuclear materials. The volume analysis methodology was applied to ion sputter craters created in silicon and uranium substrates sputtered by 18.5 keV O- and 6.0 keV Ar+ ions. Sputter yield measurements were determined from the volume calculations and were shown to be comparable to Monte Carlo calculations and previously reported experimental observations. Additionally, the volume calculations were used to determine the useful yields of Si+, SiO+ and SiO2+ ions from the silicon substrate and U+, UO+ and UO2+ ions from the uranium substrate under 18.5 keV O- and 6.0 keV Ar+ ion bombardment. This work represents the first steps toward validating the interlaboratory and cross-platform performance of mass spectrometry for the analysis of nuclear materials.

Secondary ion mass spectrometry, Sputter yield, Us↗
DOE OSTI2018

Numerical analysis of a thermal contact problem with adhesion

In this paper, we study a class of dynamic thermal problems involving a frictional normal compliance adhesive contact model and a non-clamped condition for visco-elastic materials. The variational formulation of the problem leads to a general system defined by a second-order quasi-variational evolution inequality on the displacement field coupled with the two first-order evolution equations describing the evolution of the temperature and adhesion. We establish an existence and uniqueness result of the solution on displacement, temperature and adhesion. Then we provide a fully discrete numerical scheme of approximation and derive an error estimate. Finally, various numerical computations are included.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

An AFM Dynamic Contact Model with Finite Thickness Correction to Study Micro-Rheology of Biological Cells

One of the major sources of error in Atomic Force Microscopy based Force Spectroscopic studies is bottom substrate effect, which comes due to assumption of infinite sample thickness. In the present work, anew experimentally validated mathematical correction for finite thickness of thesample is incorporated into a dynamic indentation model. This model is an extension of Sneddon’s static indentation contact model developed for conical tip indenters by incorporating the tip geometric effects, correction to hydrodynamic drag, viscoelastic nature of the sample and its finite thickness. The new model is applied to extract the viscoelastic properties of primary mesenchymal stem cells (MSC’s) extracted from human bone marrow and HCT-116 aggressive epithelial colorectal cancer cells. The micro-rheological studies indicated the presence of profound influence of infinite thickness assumption depending upon indentation depth and sample thickness at the point of indentation. The present model nullified this error and provided a better estimate of the rheological properties. The tests were conducted over a wide frequency bandwidth (0.5 to 126 Hz) and frequency dependent material properties were analyzed using power law structural damping model. It was found that MSC’s are stiffer and less viscous in nature compared to cancer cells.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Non-contact electrochemical evaluation of biofilms

Abstract Here, we demonstrate a non-contact technique for electrochemical evaluation of biofilms on surfaces in relation to corrosion. Electrochemical impedance spectrometry was employed, incorporating flat patterned electrodes positioned over the surfaces of aluminum and glass with and without biofilms. Signal communication from the working electrode to the counter electrode followed electric field lines passing tangentially through the biofilms. Electrochemical impedance parameters that were evaluated included complex impedance, phase angle, imaginary (out of phase) conductivity and Cole–Cole plots with a corresponding equivalent circuit. Changes in the impedance properties due to the presence of biofilms were monitored and correlated through microbiological, chemical and electrochemical assays. Impedance parameters associated with microbial activity correlated with biofilms on aluminum and glass surfaces. This technical approach provides impedance information about the biofilm without the signal traveling through the underlying conductive media or disrupting the biofilm. In this way, biological contributions to surface fouling can be evaluated with minimal contribution from the inorganic surface under the biofilm. In addition, this technique can be used to monitor biofilms on electrochemically inert surfaces as well as electrically conductive surfaces. Graphic abstract

Turick, Charles E. (ORCID:0000000307815846)↗
DOE OSTI2015

Modification of a Superficial X-Ray Therapy Machine for Rectal Contact Therapy

X-ray therapy of superficial rectal cancers using a hand-held 50 kV contact unit (Philips RT-50) in a technique first described by Papillon had reached a point of widening clinical acceptability when the manufacturer of this equipment discontinued its production. To pursue this endocavitary approach to rectal therapy, technical modifications have to be made to conventional superficial x-ray therapy machines. Advantages over the original Papillon method include remote viewing of the lesion through the proctoscopic cone and a lower radiation exposure for the operator. We have evaluated a Bucky Combination Therapy Unit under conditions in which the operating voltage (65 kV), target skin distance (23.6 cm), and added filtration (0.39 mm Al) were selected in order to match as closely as possible the beam penetration characteristics of the “standard” (Papillon) technique. With this equipment, the thermal characteristics of the tube anode and housing limit the amount of radiation that can be delivered before a “rest period” for the machine is needed. In practice, 3 minutes of irradiation at an exposure rate of 500 R/min can be performed followed by an interval of 3 minutes before irradiation can be resumed.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2021

Benchmarking the multiconfigurational Hartree method by the exact wavefunction of two harmonically trapped bosons with contact interaction

Highlights: • Comparison of exact and numerical single-particle density matrices. • Benchmark for multiconfigurational Hartree. • Convergence for large number of orbitals. We consider two bosons in a one-dimensional harmonic trap, interacting by a contact potential, and compare the exact solution of this problem to a self-consistent numerical solution by using the multiconfigurational time-dependent Hartree (MCTDH) method. We thereby benchmark the predictions of the MCTDH method with a few-body problem that has an analytical solution for the most commonly experimentally realized interaction potential in ultracold quantum gases. It is found that exact ground state energy and first order correlations are accurately reproduced by MCTDH up to the intermediate dimensionless coupling strengths corresponding to typical background scattering lengths of magnetically trapped ultracold dilute Bose gases. For larger couplings, established for example by (a combination of) Feshbach resonances and optical trapping, the MCTDH approach overestimates the depth of the trap-induced correlation dip of first order correlations in position space, as well as overestimates the fragmentation, defined as the average relative occupation of orbitals other than the energetically lowest one. We anticipate that qualitatively similar features in the correlation function may arise for larger particle numbers, paving the way for a quantitative assessment of the accuracy of MCTDH by experiments with ultracold atoms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

TCR-contacting residues orientation and HLA-DRβ* binding preference determine long-lasting protective immunity against malaria

Fully-protective, long-lasting, immunological (FPLLI) memory against Plasmodium falciparum malaria regarding immune protection-inducing protein structures (IMPIPS) vaccinated into monkeys previously challenged and re-challenged 60 days later with a lethal Aotus monkey-adapted P. falciparum strain was found to be associated with preferential high binding capacity to HLA-DRβ1* allelic molecules of the major histocompatibility class II (MHC-II), rather than HLA-DRβ3*, β4*, β5* alleles. Complete PPII{sub L} 3D structure, a longer distance (26.5 Å ± 1.5 Å) between residues perfectly fitting into HLA-DRβ1*PBR pockets 1 and 9, a gauche{sup −} rotamer orientation in p8 TCR-contacting polar residue and a larger volume of polar p2 residues was also found. This data, in association with previously-described p3 and p7 apolar residues having gauche{sup +} orientation to form a perfect MHC-II-peptide-TCR complex, determines the stereo-electronic and topochemical characteristics associated with FPLLI immunological memory. - Highlights: • Stereo-electronic and topochemical rules associated with FPLLI immunological memory. • Presence of very high long-lasting antibody titres against Plasmodium falciparum Spz. • Protective memory induction associated with a binding capacity to HLA-DRβ1*. • gauche{sup −} rotamer orientation in p8 polar residue is related to is related to immunological memory.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Anion-derived contact ion pairing as a unifying principle for electrolyte design

Enabling new electrochemical technologies requires systems that can operate under ever-more demanding conditions, and progress in energy storage applications reveals tantalizing opportunities to reimagine electrolyte design for performance at extreme potentials. Here, a common thread among these innovations is the formation of significant populations of contact ion pairs (CIPs) in the electrolyte, regardless of the specific cation chemistry or solvent system. The examples summarized in this review suggest that a set of general electrolyte design rules likely exists, where the purposeful selection of anion chemistry can yield CIP structures with tunable control over reaction thermodynamics, kinetics, and interphase chemistry. Identifying the relevant descriptors for high-performance, anion-derived CIP structures can be achieved utilizing a combined experimental and computational approach, aided by machine learning and artificial intelligence, to more rapidly survey the vast combinatorial space available and to enable a new generation of electrolytes for decarbonized electrochemical processes at scale.

electrochemistry↗
DOE OSTI2017

Sputter-deposited WO x and MoO x for hole selective contacts

Here, reactive sputter deposited tungsten and molybdenum oxide (WO x , MoO x ) thin films are tested for their ability to form a hole selective contact for Si wafer based solar cells. A characterization approach based on analyzing the band bending induced in the c-Si absorber and the external and implied open-circuit voltage of test structures was used. It is shown that the oxygen partial pressure allows to tailor the selectivity to some extent and that a direct correlation between induced band bending and hole selectivity exists. Although the selectivity of the sputtered films is inferior to the reference films deposited by thermal evaporation, these results demonstrate a good starting point for further optimizations of sputtered WO x and MoO x towards higher work functions to improve the hole selectivity.

14 SOLAR ENERGY↗
DOE OSTI2017

Physics of direct-contact ultrasonic cloth drying process

Existing methods of drying fabrics involve energy-intensive thermal evaporation of moisture from clothes. Drying fabrics using high-frequency vibrations of piezoelectric transducers can substantially reduce drying time and energy consumption. In this method, vibrational energy generates instability on the liquid-air interface and mechanically ejects water from a wet fabric. For the first time, the physics of the ultrasonic fabric drying process in direct-contact mode is studied. The kinematic and thermal responses of water droplets and fabrics on piezoelectric crystal transducers and metal mesh–based transducers are studied. The results suggest that on piezoelectric crystal transducers, the response of a droplet subjected to ultrasonic excitation is dictated by the relative magnitude of the surface tension and the ultrasonic excitation forces. The drying process for a fabric on the studied transducers consists of two regimes—vibrational and thermal. When the water content is high, the vibrational forces can eject bulk water rapidly. But the more strongly bound water within the smaller fabric pores evaporates by the thermal energy generated as a result of the viscous losses. Our study finds that a metal mesh–based transducer is more suitable for dewatering fabrics, as it facilitates the ejection of water from the fabric–transducer interface to the opposite side of the mesh. A demonstration unit developed consumes 10–20% of the water latent heat energy at water contents greater than 20%.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2026

Modeling and Experimental Validation of a Direct-Contact Counter-Flow Fluidized Bed Heat Exchanger for Thermal Energy Storage (TES) Applications

Particle-based thermal energy storage (TES) systems are an emerging energy storage technology. The technological advances have reduced costs, making TES more competitive and reliable in the marketplace but an efficient and reliable operation is heavily dependent on coherent heat transfer between air to particles or vice versa. The particle-based TES technologies provide an intermediate system that can store energy for short (0-10 h), long (10-200 h) and seasonal (> 200 h) timescales. The TES systems store energy by converting electricity to thermal energy; electricity can be directly sourced intermittent generation technologies and/or the grid, helping manage peak loads and other mismatches in supply and demand. The overall efficiency of the TES system depends on the performance of system components (particle storage silos and particle transfer mechanism etc.). The particle heat exchanger is one of the key system components that affects the system efficiency. The pressurized fluidized bed heat exchanger (PFB HX) performance is challenging to predict due to the chaotic behavior of particle and fluid interaction. This research presents a computational study of a novel direct-contact, counter-flow and air-to-particles PFB HX, that contributes in advancing the particle-based long-duration TES technologies. For the current analysis an unsteady Eulerian-Eulerian CFD model was developed and validated against experiments performed at the National Laboratory of the Rockies for two particle sizes (600 ..mu..m and 825 ..mu..m ). Following validation, parametric simulations were conducted to evaluate the effects of interphase drag models (Syamlal-O'Brien and Gidaspow), particle size, bed height and the influence of a frictional-viscosity term on hydrodynamics and heat transfer between the air & particles. The key findings from the analysis are: (1) for the studied operating window Syamlal-O'Brien provides superior agreement with measured gas temperatures (errors generally < 10%) while Gidaspow shows large deviations for the coarse particle case; (2) model predictions are most sensitive in the lower 0.2 m above the air distributor where bubble initiation and local mixing dominate interphase heat transfer; (3) representation of the distributor (number of inlet ports) materially affects predicted local mixing and temperature stratification; and (4) the Eulerian-Eulerian framework reproduces bulk thermal trends but shows regime dependent limitations for coarse particles, motivating mesoscale informed closures for scale-up analysis for future studies. These results provide validated guidance for drag selection and distributor design in particle-based thermal energy storage applications. Collectively, the validated model and parametric results quantify key drivers of PHB-HX performance and provide practical guidance for design and optimization. The results provide confidence in the model predictability and provide a step forward to improve on heat exchange performance. The demonstrated performance and modeling approach support the deployment and further development of this novel PHB-HX concept for robust, particle-based long-duration thermal energy storage systems.

25 ENERGY STORAGE↗
DOE OSTI2020

Tailoring the coefficient of thermal expansion of ternary nickel alloys through compositional control and non-contact measurements

The majority of microelectromechanical systems (MEMS) are made of silicon, however, future applications will be used in extreme environments, especially at elevated temperatures, and require materials with enhanced properties. Use of metal alloys in these applications will require microscale manufacturability, a balance of physical and mechanical properties and dimensional stability. Here in this paper, we emphasized dimensional stability by reducing the coefficient of thermal expansion (CTE) and present an optical non-contact method for measuring the thermal expansion of planar thin films. A combinatorial approach was employed to determine the CTE of nickel-molybdenum-tungsten (Ni-Mo-W) sputter deposited films over a range of compositions, and the addition of Mo and W is shown to significantly decrease and provide a route for tailoring the CTE with compositional control. Ni-Mo-W alloys were revealed to have CTE values ranging from 8–12 × 10 -6 /°C, matching that of commercial glass substrates that are employed in numerous MEMS devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Friction and wear behavior of nitrogen-doped ZnO thin films deposited via MOCVD under dry contact

Most researches on doped ZnO thin films are tilted toward their applications in optoelectronics and semiconductor devices. Research on their tribological properties is still unfolding. In this work, nitrogen-doped ZnO thin films were deposited on 304 L stainless steel substrate from a combination of zinc acetate and ammonium acetate precursor by MOCVD technique. Compositional and structural studies of the films were done using Rutherford Backscattering Spectroscopy (RBS) and X-ray Diffraction (XRD). The frictional behavior of the thin film coatings was evaluated using a ball-on-flat configuration in reciprocating sliding under dry contact condition. After friction test, the flat and ball counter-face surfaces were examined to assess the wear dimension and failure mechanism. In conclusion, both friction behavior and wear (in the ball counter-face) were observed to be dependent on the crystallinity and thickness of the thin film coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Mechanical and electrochemical performance of composite cathode contact materials for solid oxide fuel cells

The feasibility of adding glass or inorganic binder to conventional SOFC cathode contact materials (CCM) in order to improve bonding to adjacent materials in the cell stack is assessed. Two glasses (SEM-COM SCZ-8 and Schott GM31107) and one inorganic binder (Aremco 644A) are mixed with LSM particles to produce composite CCM pastes. These are used to bond Mn1.5Co1.5O4-coated stainless steel mesh current collectors to anode-supported button cells. The cells are operated at 800 C for about 1000 h. The cell with SCZ-8 addition to the CCM displays quite stable operation (3.9%/1000 h degradation), whereas the other additives lead to somewhat higher degradation rate. Bonding of the CCM to coated stainless steel coupons is also assessed. Interfacial fracture toughness is determined using a four-point bend test. The fracture toughness for LSM Schott glass (12.3 N mm 1), LSM SCZ-8 glass (6.8 N mm 1) and LSM 644A binder (5.4 N mm 1) are significantly improved relative to pure LSM (1.7 N mm 1). Indeed, addition of binder or glass is found to improve bonding of the CCM layer without sacrificing cell performance.

Tucker, Michael C.↗
DOE OSTI2015

Electron dose distributions caused by the contact-type metallic eye shield: Studies using Monte Carlo and pencil beam algorithms

A metallic contact eye shield has sometimes been used for eyelid treatment, but dose distribution has never been reported for a patient case. This study aimed to show the shield-incorporated CT-based dose distribution using the Pinnacle system and Monte Carlo (MC) calculation for 3 patient cases. For the artifact-free CT scan, an acrylic shield machined as the same size as that of the tungsten shield was used. For the MC calculation, BEAMnrc and DOSXYZnrc were used for the 6-MeV electron beam of the Varian 21EX, in which information for the tungsten, stainless steel, and aluminum material for the eye shield was used. The same plan was generated on the Pinnacle system and both were compared. The use of the acrylic shield produced clear CT images, enabling delineation of the regions of interest, and yielded CT-based dose calculation for the metallic shield. Both the MC and the Pinnacle systems showed a similar dose distribution downstream of the eye shield, reflecting the blocking effect of the metallic eye shield. The major difference between the MC and the Pinnacle results was the target eyelid dose upstream of the shield such that the Pinnacle system underestimated the dose by 19 to 28% and 11 to 18% for the maximum and the mean doses, respectively. The pattern of dose difference between the MC and the Pinnacle systems was similar to that in the previous phantom study. In conclusion, the metallic eye shield was successfully incorporated into the CT-based planning, and the accurate dose calculation requires MC simulation.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2017

Energy reconstruction of an n-type segmented inverted coaxial point-contact HPGe detector

We have characterized, for the first time, an n-type segmented Inverted Coaxial Point-Contact detector. This novel detector technology relys on a large variation in drift time of the majority charge carriers, as well as image and net charges observed on the segments, to achieve a potential γ-ray interaction position resolution of better than 1 mm. However, the intrinsic energy resolution in such a detector is poor (more than 20 keV at 1332 keV) because of charge (electron) trapping effects. We propose an algorithm that enables restoration of the resolution to a value of 3.44 0.03 keV at 1332 keV for events with a single interaction. The algorithm is based on a measurement of the azimuthal angle and the electron drift time of a given event; the energy of the event is corrected as a function of these two values.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

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