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 Fluor®647-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

Track A Basic Science

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd

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-fusées sont très dépendants des caractéristiques 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 cryogénique, en particulier lorsque les ergols sont injectés au moyen d'un injecteur coaxial dans des conditions sous critiques. L'étude de la granulométrie d'un tel spray à l'aide de méthodes lasers peut se révéler difficile du fait de la non sphéricité des particules et des forts gradients thermiques dans la flamme cryogénique. La granulométrie par imagerie haute cadence peut se révéler dans ces conditions comme une alternative aux diagnostics laser car elle est moins sensible aux problématiques de gradients d'indice optique et de non sphéricité des particules. Cette technique permet aussi, lorsque la cadence d'enregistrement est suffisamment élevée, un suivi des particules et ainsi obtenir la vitesse de la phase dispersée, qui est difficile à ensemencer. Des mesures de diamètres moyens dans la zone d'atomisation sont comparées entre un granulomètre phase Doppler [2] et le granulomètre par imagerie proposé. Des corrélations taille/vitesse obtenues par imagerie permettent de mettre en évidence des effets de la flamme sur la granulométrie. ……………………………

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