73 research outputs found
Numerical investigation of high-pressure combustion in rocket engines using Flamelet/Progress-variable models
The present paper deals with the numerical study of high pressure LOx/H2 or
LOx/hydrocarbon combustion for propulsion systems. The present research effort
is driven by the continued interest in achieving low cost, reliable access to
space and more recently, by the renewed interest in hypersonic transportation
systems capable of reducing time-to-destination. Moreover, combustion at high
pressure has been assumed as a key issue to achieve better propulsive
performance and lower environmental impact, as long as the replacement of
hydrogen with a hydrocarbon, to reduce the costs related to ground operations
and increase flexibility. The current work provides a model for the numerical
simulation of high- pressure turbulent combustion employing detailed chemistry
description, embedded in a RANS equations solver with a Low Reynolds number
k-omega turbulence model. The model used to study such a combustion phenomenon
is an extension of the standard flamelet-progress-variable (FPV) turbulent
combustion model combined with a Reynolds Averaged Navier-Stokes equation
Solver (RANS). In the FPV model, all of the thermo-chemical quantities are
evaluated by evolving the mixture fraction Z and a progress variable C. When
using a turbulence model in conjunction with FPV model, a probability density
function (PDF) is required to evaluate statistical averages of chemical
quantities. The choice of such PDF must be a compromise between computational
costs and accuracy level. State- of-the-art FPV models are built presuming the
functional shape of the joint PDF of Z and C in order to evaluate
Favre-averages of thermodynamic quantities. The model here proposed evaluates
the most probable joint distribution of Z and C without any assumption on their
behavior.Comment: presented at AIAA Scitech 201
Micro-Hall Magnetometry Studies of Thermally Assisted and Pure Quantum Tunneling in Single Molecule Magnet Mn12-Acetate
We have studied the crossover between thermally assisted and pure quantum
tunneling in single crystals of high spin (S=10) uniaxial single molecule
magnet Mn12-acetate using micro-Hall effect magnetometry. Magnetic hysteresis
experiments have been used toinvestigate the energy levels that determine the
magnetization reversal as a function of magnetic field and temperature. These
experiments demonstrate that the crossover occurs in a narrow (~0.1 K) or broad
(~1 K) temperature interval depending on the magnitude and direction of the
applied field. For low external fields applied parallel to the easy axis, the
energy levels that dominate the tunneling shift abruptly with temperature. In
the presence of a transverse field and/or large longitudinal field these energy
levels change with temperature more gradually. A comparison of our experimental
results with model calculations of this crossover suggest that there are
additional mechanisms that enhance the tunneling rate of low lying energy
levels and broaden the crossover for small transverse fields.Comment: 5 pages, 5 figure
T-Cell Immune Responses Against Env from CRF12_BF and Subtype B HIV-1 Show High Clade-Specificity that Can Be Overridden by Multiclade Immunizations
BACKGROUND: The extreme genetic diversity of the human immunodeficiency virus type 1 (HIV-1) poses a daunting challenge to the generation of an effective AIDS vaccine. In Argentina, the epidemic is characterized by the high prevalence of infections caused by subtype B and BF variants. The aim of this study was to characterize in mice the immunogenic and antigenic properties of the Env protein from CRF12_BF in comparison with clade B, employing prime-boost schemes with the combination of recombinant DNA and vaccinia virus (VV) vectors. METHODOLOGY/PRINCIPAL FINDINGS: As determined by ELISPOT from splenocytes of animals immunized with either EnvBF or EnvB antigens, the majority of the cellular responses to Env were found to be clade-specific. A detailed peptide mapping of the responses reveal that when there is cross-reactivity, there are no amino acid changes in the peptide sequence or were minimal and located at the peptide ends. In those cases, analysis of T cell polifunctionality and affinity indicated no differences with respect to the cellular responses found against the original homologous sequence. Significantly, application of a mixed immunization combining both clades (B and BF) induced a broader cellular response, in which the majority of the peptides targeted after the single clade vaccinations generated a positive response. In this group we could also find significant cellular and humoral responses against the whole gp120 protein from subtype B. CONCLUSIONS/SIGNIFICANCE: This work has characterized for the first time the immunogenic peptides of certain EnvBF regions, involved in T cell responses. It provides evidence that to improve immune responses to HIV there is a need to combine Env antigens from different clades, highlighting the convenience of the inclusion of BF antigens in future vaccines for geographic regions where these HIV variants circulate
Human Macrophages and Dendritic Cells Can Equally Present MART-1 Antigen to CD8+ T Cells after Phagocytosis of Gamma-Irradiated Melanoma Cells
Dendritic cells (DC) can achieve cross-presentation of naturally-occurring
tumor-associated antigens after phagocytosis and processing of dying tumor
cells. They have been used in different clinical settings to vaccinate cancer
patients. We have previously used gamma-irradiated MART-1 expressing melanoma
cells as a source of antigens to vaccinate melanoma patients by injecting
irradiated cells with BCG and GM-CSF or to load immature DC and use them as
a vaccine. Other clinical trials have used IFN-gamma activated macrophage
killer cells (MAK) to treat cancer patients. However, the clinical use of
MAK has been based on their direct tumoricidal activity rather than on their
ability to act as antigen-presenting cells to stimulate an adaptive antitumor
response. Thus, in the present work, we compared the fate of MART-1 after
phagocytosis of gamma-irradiated cells by clinical grade DC or MAK as well
as the ability of these cells to cross present MART-1 to CD8+
T cells. Using a high affinity antibody against MART-1, 2A9, which specifically
stains melanoma tumors, melanoma cell lines and normal melanocytes, the expression
level of MART-1 in melanoma cell lines could be related to their ability to
stimulate IFN-gamma production by a MART-1 specific HLA-A*0201-restricted
CD8+ T cell clone. Confocal microscopy with Alexa FluorÂź647-labelled
2A9 also showed that MART-1 could be detected in tumor cells attached and/or
fused to phagocytes and even inside these cells as early as 1 h and up to
24 h or 48 h after initiation of co-cultures between gamma-irradiated melanoma
cells and MAK or DC, respectively. Interestingly, MART-1 was cross-presented
to MART-1 specific T cells by both MAK and DC co-cultured with melanoma gamma-irradiated
cells for different time-points. Thus, naturally occurring MART-1 melanoma
antigen can be taken-up from dying melanoma cells into DC or MAK and both
cell types can induce specific CD8+ T cell cross-presentation
thereafter
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Track A Basic Science
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd
PLIF Investigation of Reactive Flows in the Separation Region of an Over-Expanded Two-Dimensional Nozzle
Granulométrie et vélocimétrie par imagerie haute cadence dans une flamme cryogénique de moteur-fusée
International audienceLes processus physiques intervenant lors de la combustion d'ergols liquides dans les moteurs-fusĂ©es sont trĂšs dĂ©pendants des caractĂ©ristiques du spray produit au niveau de l'injection dans la chambre de combustion. L'atomisation est un processus dominant qui pilote le comportement d'une telle flamme cryogĂ©nique, en particulier lorsque les ergols sont injectĂ©s au moyen d'un injecteur coaxial dans des conditions sous critiques. L'Ă©tude de la granulomĂ©trie d'un tel spray Ă l'aide de mĂ©thodes lasers peut se rĂ©vĂ©ler difficile du fait de la non sphĂ©ricitĂ© des particules et des forts gradients thermiques dans la flamme cryogĂ©nique. La granulomĂ©trie par imagerie haute cadence peut se rĂ©vĂ©ler dans ces conditions comme une alternative aux diagnostics laser car elle est moins sensible aux problĂ©matiques de gradients d'indice optique et de non sphĂ©ricitĂ© des particules. Cette technique permet aussi, lorsque la cadence d'enregistrement est suffisamment Ă©levĂ©e, un suivi des particules et ainsi obtenir la vitesse de la phase dispersĂ©e, qui est difficile Ă ensemencer. Des mesures de diamĂštres moyens dans la zone d'atomisation sont comparĂ©es entre un granulomĂštre phase Doppler [2] et le granulomĂštre par imagerie proposĂ©. Des corrĂ©lations taille/vitesse obtenues par imagerie permettent de mettre en Ă©vidence des effets de la flamme sur la granulomĂ©trie. âŠâŠâŠâŠâŠâŠâŠâŠâŠâŠâŠ
Atomization of cryogenic rocket engines coaxial injectors. Modeling aspects and experimental investigations
International audienceEven if it has been extensively studied in the last decades, atomization remains a key point in the understanding and modeling of cryogenic rocket engines combustion chambers because the physical processes in the chamber are highly dependent on the characteristics of the spray produced by the injector. The parameters describing the spray, like the expansion angle, the penetration depth, the droplet size distribution, are usually given as input data in the numerical simulation codes of such engines. To overcome this difficulty, ONERA is developing in the CEDRE code [8] a fully eulerian coupling strategy between "separated" and "dispersed" two-phase flows solvers. To reach this crucial challenge, diffuse interface models are used for primary atomization while kinetic models are used to compute the combustion of the spray. The aim is to compute the spray produced by a coaxial injector directly from the upstream global parameters (injection pressures, mass flow rates ...) instead of imposing its characteristics as an input of the simulation. In parallel to this numerical work, an experimental investigation was started on the Mascotte cryogenic test facility [9], in order to improve existing measurements, with the objective to provide relevant experimental data to validate the model. Experiments were run at 1 MPa in a single element combustion chamber. The injector was fed with liquid oxygen (LOX) atomized by a co-flow of gas at room temperature. Both cold flow and hot fire tests were achieved. The hydrogen used in the combustion tests was replaced by helium for the cold flow experiment. Similarity between cold and hot conditions was obtained by keeping constant the geometry, the chamber pressure, the LOX mass flow rate and the momentum flux ratio in the injector exit plane. The spray was investigated with a high speed camera in a backlighting optical configuration
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