Recommended values of the thermophysical properties of eight alloys, their major constituents and oxides

Reference work provides in tabular and graphical form the thermophysical properties of basic alloys, their constituents and oxides. This is useful for personnel who deal with extreme temperature environments

Particle In Cell Simulation of Combustion Synthesis of TiC Nanoparticles

A coupled continuum-discrete numerical model is presented to study the synthesis of TiC nanosized aggregates during a self-propagating combustion synthesis (SHS) process. The overall model describes the transient of the basic mechanisms governing the SHS process in a two-dimensional micrometer size geometry system. At each time step, the continuum (micrometer scale) model computes the current temperature field according to the prescribed boundary conditions. The overall system domain is discretized with a desired number of uniform computational cells. Each cell contains a convenient number of computation particles which represent the actual particles mixture. The particle-in-cell (discrete) model maps the temperature field from the (continuum) cells to the respective internal particles. Depending on the temperature reached by the cell, the titanium particles may undergo a solid-liquid transformation. If the distance between the carbon particle and the liquid titanium particles is within a certain tolerance they will react and a TiC particle will be formed in the cell. Accordingly, the molecular dynamic method will update the location of all particles in the cell and the amount of transformation heat accounted by the cell will be entered into the source term of the (continuum) heat conduction equation. The new temperature distribution will progress depending on the cells which will time-by-time undergo the chemical reaction. As a demonstration of the effectiveness of the overall model some paradigmatic examples are shown.Comment: submitted to Computer Physics Communication

How Stress Can Reduce Dissipation in Glasses

We propose that stress can decrease the internal friction of amorphous solids, either by increasing the potential barriers of defects, thus reducing their tunneling and thermal activation that produce loss, or by decreasing the coupling between defects and phonons. This stress can be from impurities, atomic bonding constraints, or externally applied stress. Externally applied stress also reduces mechanical loss through dissipation dilution. Our results are consistent with the experiments, and predict that stress could substantially reduce dielectric loss and increase the thermal conductivity.Comment: 9 pages, 7 figure

Temperature Dependent Mean Free Path Spectra of Thermal Phonons Along the c-axis of Graphite

Heat conduction in graphite has been studied for decades because of its exceptionally large thermal anisotropy. While the bulk thermal conductivities along the in-plane and cross-plane directions are well known, less understood are the microscopic properties of the thermal phonons responsible for heat conduction. In particular, recent experimental and computational works indicate that the average phonon mean free path (MFP) along the c-axis is considerably larger than that estimated by kinetic theory, but the distribution of MFPs remains unknown. Here, we report the first quantitative measurements of c-axis phonon MFP spectra in graphite at a variety of temperatures using time-domain thermoreflectance measurements of graphite flakes with variable thickness. Our results indicate that c-axis phonon MFPs have values of a few hundred nanometers at room temperature and a much narrower distribution than in isotropic crystals. At low temperatures, phonon scattering is dominated by grain boundaries separating crystalline regions of different rotational orientation. Our study provides important new insights into heat transport and phonon scattering mechanisms in graphite and other anisotropic van der Waals solids

Assessing the Performance of Recent Density Functionals for Bulk Solids

We assess the performance of recent density functionals for the exchange-correlation energy of a nonmolecular solid, by applying accurate calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid metals and non-metals. The functionals tested are the modified Perdew-Burke-Ernzerhof generalized gradient approximation (PBEsol GGA), the second-order GGA (SOGGA), and the Armiento-Mattsson 2005 (AM05) GGA. For completeness, we also test more-standard functionals: the local density approximation, the original PBE GGA, and the Tao-Perdew-Staroverov-Scuseria (TPSS) meta-GGA. We find that the recent density functionals for solids reach a high accuracy for bulk properties (lattice constant and bulk modulus). For the cohesive energy, PBE is better than PBEsol overall, as expected, but PBEsol is actually better for the alkali metals and alkali halides. For fair comparison of calculated and experimental results, we consider the zero-point phonon and finite-temperature effects ignored by many workers. We show how Gaussian basis sets and inaccurate experimental reference data may affect the rating of the quality of the functionals. The results show that PBEsol and AM05 perform somewhat differently from each other for alkali metal, alkaline earth metal and alkali halide crystals (where the maximum value of the reduced density gradient is about 2), but perform very similarly for most of the other solids (where it is often about 1). Our explanation for this is consistent with the importance of exchange-correlation nonlocality in regions of core-valence overlap.Comment: 32 pages, single pdf fil

Reduction of thermal fluctuations in a cryogenic laser interferometric gravitational wave detector

The thermal fluctuation of mirror surfaces is the fundamental limitation for interferometric gravitational wave (GW) detectors. Here, we experimentally demonstrate for the first time a reduction in a mirror's thermal fluctuation in a GW detector with sapphire mirrors from the Cryogenic Laser Interferometer Observatory at 17\,K and 18\,K. The detector sensitivity, which was limited by the mirror's thermal fluctuation at room temperature, was improved in the frequency range of 90\,Hz to 240\,Hz by cooling the mirrors. The improved sensitivity reached a maximum of $2.2 \times 10^{-19}\,\textrm{m}/\sqrt{\textrm{Hz}}$ at 165\,Hz.Comment: Accepted for publication in Physical Review Letters, 5 pages, 2 figure

Ultraviolet B radiation mediated generation of Platelet-activating factor agonists augments melanoma tumor growth

poster abstractPlatelet-activating factor (1-alkyl-2-acetyl-glycerophosphocholine; PAF) is a potent lipid mediator with diverse activities. Our previous studies have demonstrated that oxidized glycerophosphocholines (OxGPCs) that act as agonists for the Platelet-activating factor receptor (PAF-R) mediate ultraviolet B radiation (UVB) induced systemic immunosuppression in a process involving IL-10. However, the exact role of UVB-mediated systemic immunosuppression in pathophysiological processes remains unclear. The current studies sought to define whether UVB-induced systemic immunosuppression could modulate experimental murine melanoma tumor growth. Using a murine UVB model of systemic immunosuppression, we demonstrate that UVB exposure to a remote site from skin implanted with subcutaneous B16F10 melanoma results in enhanced tumor growth in C57BL/6 (wild-type) mice but not in PAF-R-deficient mice. We further show that intraperitoneal injection of the PAF agonist carbamoylPAF (CPAF) mimicked the UVB effect. Interestingly, neutralizing antibody against IL-10 blocked both CPAF- and UVB-mediated augmentation of B16F10 tumor growth. The next studies were designed to define whether the PAF-R effect was due to direct effects on B16F10 cells. Of note, B16F10 cells lack functional PAF-R expression. To address this question, we first generated PAF-R expressing B16F10 (B16-PAFR) and its vector control B16-MSCV cells by retroviral transduction and confirmed the presence of PAF-R in B16-PAF-R cells by intracellular Ca2+ flux in response to CPAF and qRT-PCR. Transplantation of B16-PAFR cells into mice did not result in an increased rate of tumor growth over control B16-MSCV cells either alone, or in response to UVB or CPAF. These studies provide a novel unreported effect of UVB-mediated PAF agonists, namely, that they can augment melanoma tumor growth via IL-10

Platelet-activating Factor-receptor agonists generated by chemotherapy thwart host anti-tumor immunity

poster abstractPrevious studies have established that pro-oxidative stressors suppress host immunity due to their ability to generate oxidized glycerophosphocholine (Ox-GPC) lipids with Platelet-activating Factor-receptor (PAF-R) agonist activity. Because many chemotherapeutic agents also induce reactive oxygen species, the present studies were designed to define if chemotherapeutic agents could thwart host anti-tumor immunity against melanoma via PAF-R activation. We demonstrate that treatment of melanoma cell lines in vitro and tumors in vivo with chemotherapeutic agents generates PAF-R-agonists in a process blocked by antioxidants, indicating the involvement of non-enzymatic PAF-R-agonists in this event. In a model system consisting of implantation of two tumors, we show that intratumoral chemotherapy with melphalan or etoposide of one tumor significantly augments the growth of the other (untreated) tumor in wild-type but not PAF-R-deficient hosts. Chemotherapeutic agents-mediated PAF-R-dependent increased tumor growth is blocked by systemic administration of antioxidants and cyclooxygenase-2 inhibitors. In addition, depleting antibodies against regulatory T cells (Tregs) significantly attenuated chemotherapy-mediated growth of untreated tumors, suggesting the role of Tregs in this process. Moreover, using FoxP3EGFP transgenic mice, we show that COX-2 inhibitor blocked intratumoral Tregs, indicating that Tregs are downstream to COX-2. Furthermore, PAF-R agonists were identified in perfusates of patients undergoing isolated limb chemoperfusion for melanoma with melphalan chemotherapy. Finally, various novel Ox-GPCs are identified after chemotherapy by mass spectrometry. These findings provide evidence for a novel and previously unappreciated pathway by which Ox-GPC PAF-R agonists produced as a by-product of chemotherapy modulate tumor growth via the inhibition of anti-tumor immunity. These studies might explain some instances of chemotherapy treatment failure and offer insights into potential therapeutic strategies that could enhance the overall anti-tumor effectiveness of chemotherapy

Thermal Conductivity of Isotopically Enriched 28Si Revisited

The thermal conductivity of isotopically enriched 28Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of 4 samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched 28Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 102 %. This finding is in disagreement with an earlier report by Ruf et al. At 26 K the thermal conductivity of 28Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of 8 for a 99.982% 28Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be 3% lower than the values recommended in the literature

Linear Contraction Behavior of Low-Carbon, Low-Alloy Steels During and After Solidification Using Real-Time Measurements

A technique for measuring the linear contraction during and after solidification of low-alloy steel was developed and used for examination of two commercial low-carbon and low-alloy steel grades. The effects of several experimental parameters on the contraction were studied. The solidification contraction behavior was described using the concept of rigidity in a solidifying alloy, evolution of the solid fraction, and the microstructure development during solidification. A correlation between the linear contraction properties in the solidification range and the hot crack susceptibility was proposed and used for the estimation of hot cracking susceptibility for two studied alloys and verified with the real casting practice. The technique allows estimation of the contraction coefficient of commercial steels in a wide range of temperatures and could be helpful for computer simulation and process optimization during continuous casting. © 2013 The Minerals, Metals & Materials Society and ASM International