1,716 research outputs found
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
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
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
Recommended Values of the Thermophysical Properties of Eight Alloys, Major Constituents and Their Oxides, February 1, 1965 - January 31, 1966
Thermophysical properties of aluminum, beryllium, Inconel, stainless steel, and titanium alloys and primary oxide
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
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
Primary Teratoma of the Lesser Sac: Lesser Sac Teratoma
Germ cell tumors predominantly involve the gonads but may rarely be found outside of the gonads, primarily in midline structures. We describe the case of a 27-year-old male with an asymptomatic 8 cm teratoma located within the lesser sac of his omentum. This is the fourth case of a teratoma located within the lesser sac of the omentum, which provides the opportunity to make some comparisons. Finally, we discuss some of the etiologic theories behind extragonadal germ cell tumors and how they relate to teratomas in the lesser sac
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 at 165\,Hz.Comment: Accepted for publication in Physical Review Letters, 5 pages, 2
figure
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
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