Cavitating propeller flows predicted by RANS solver with structured grid and small reynolds number turbulence model approach

Within the EU research project VIRTUE, a propeller is investigated in uniform and nonuniform inflow conditions by means of a RANS equation solver, FINFLO. The analyses are made in wetted and cavitating conditions. The propeller analyzed in this paper is the INSEAN E779A propeller. The paper contains calculations at three different grid resolutions in wetted conditions and at the two finest grid resolutions in cavitating conditions in uniform inflow. The mediumsize grid is used for the propeller in nonuniform inflow simulations. The simulations are conducted on a model scale and the results are compared with the measurements and cavitation tests performed by INSEAN. The nonuniform inflow is generated by modeling the geometry of the artificial wake generator used in the cavitation tests in the calculation domain. The experimental results are published in several papers, for example in [1] and [2]. The predicted propeller open water thrust and torque are found to be within 5 % of the measured ones. The pressure peak at the leading edge of a blade is found to be sensitive to the grid resolution. The predicted cavitation behavior of the propeller blades is in reasonable accordance with the cavitation test observations. In uniform inflow the vaporized region is overpredicted. Contrastingly, the vaporized region is Underpredicted in the nonuniform inflow calculations. Side entrant jets could be identified in the cavity region in the nonuniform inflow simulations. The predicted vaporized regions in several blade positions together with photographs of the cavitating propeller are shown for comparison. The cavitation behavior trends seemed to be similar in the simulations and observations in nonuniform inflow, except that the rollup of detached sheet cavitation into a tip vortex could not be captured in the calculations. The total wake is measured between the propeller plane and the wake generator. The predicted wake is found to be too strong, but the width of the wake is relatively close to the measurements. The propeller loading history is shown over one propeller revolution. It shows qualitatively reasonable trends. The loading histories of the wetted and cavitating propeller are almost the same due to the relative small cavitating region in the investigated conditions. The pressure distributions at several blade positions on the suction side of the propeller are shown in wetted and cavitating conditions for comparison.http://deepblue.lib.umich.edu/bitstream/2027.42/84244/1/CAV2009-final45.pd

Decomposition products of oxygen scavengers and their effect on corrosion of steam generator materials – I. Diethyl-hydroxylamine and carbohydrazide

Hydrazine used as oxygen scavenger in the secondary circuit of pressurized water reactors is hazardous to the environment and potentially carcinogenic, thus, suitable replacement chemicals for it are actively sought. In the present paper, decomposition products of two potential replacements – carbohydrazide and diethyl-hydroxylamine – are analyzed, and their effect on secondary water chemistry and corrosion of the main steam generator materials – carbon steel 22 K, stainless steel 0X18H10T and Alloy 690 – is studied by in-situ electrochemical techniques complemented by ex-situ analyses of the formed oxides by spectroscopic and microscopic methods. Quantitative interpretation of the electrochemical impedance data with the Mixed-Conduction Model allowed for the estimation of oxidation and corrosion release rates depending on scavenger formulation, alloy type and temperature. Conclusions on the extent of interaction of decomposition products with construction materials are drawn based on the experimental and calculational results.<br/

Influence of tooth loss on mandibular morphology : a cone-beam computed tomography study

Tooth loss adversely affects patients? health and psychosocial wellbeing. In addition, it changes mandibular morphology. Objective: To evaluate the effect of tooth loss, age, and gender on mandibular morphology. Cone-beam computed tomographic (CBCT) scans of 101 patients were examined to measure the gonial angle (GA), ramus height (RH) and condylar height (CH). Patients? age, gender, and dental status were recorded. Repeated measures analysis of variance (ANOVA) was used to assess the impact of gender, age, and tooth loss on the GA, RH and CH. The mean measurements of the GA, RH and CH were compared between dentate/edentulous patients after splitting by gender. The GA was larger in edentulous patients compared to dentate ones, in females than in males, and in older than in younger. RH on the right side was significantly longer than on the left side (P< 0.0001), and also longer in males and younger patients. CH was shorter in younger than in older patients and in dentate than in edentulous patients. Tooth loss is associated with changes in mandibular morphology and its prevention would avoid these irreversible changes

Deuterium fractionation in cold dense cores in the low-mass star forming region L1688

In this work, we study deuterium fractionation in four starless cores in the low-mass star-forming region L1688 in the Ophiuchus molecular cloud. We study how the deuterium fraction ($R_D$) changes with environment, compare deuteration of ions and neutrals, core centre and its envelope, and attempt to reproduce the observed results with a gas-grain chemical model. We chose high and low gas density tracers to study both core centre and the envelope. With the IRAM 30m antenna, we mapped N$_2$H$^+$(1-0), N$_2$D$^+$(1-0), H$^{13}$CO$^+$ (1-0) and (2-1), DCO$^+$(2-1), and $p$-NH$_2$D(1$_{11}$-1$_{01}$) towards the chosen cores. The missing $p$-NH$_3$ and N$_2$H$^+$(1-0) data were taken from the literature. To measure the molecular hydrogen column density, dust and gas temperature within the cores, we used the Herschel/SPIRE dust continuum emission data, the GAS survey data (ammonia), and the COMPLETE survey data to estimate the upper limit on CO depletion. We present the deuterium fraction maps for three species towards four starless cores. Deuterium fraction of the core envelopes traced by DCO$^+$/H$^{13}$CO$^+$ is one order of magnitude lower ($\sim$0.08) than that of the core central parts traced by the nitrogen-bearing species ($\sim$0.5). Deuterium fraction increases with the gas density as indicated by high deuterium fraction of high gas density tracers and low deuterium fraction of lower gas density tracers and by the decrease of $R_D$ with core radii, consistent with the predictions of the chemical model. Our model results show a good agreement with observations for $R_D$(N$_2$D$^+$/N$_2$H$^+$) and R$_D$(DCO$^+$/HCO$^+$) and underestimate the $R_D$(NH$_2$D/NH$_3$).Comment: 30 pages with 22 figures, accepted for publication in MNRA

Role of Dicer1-DependentFactors in the Paracrine Regulation of Epididymal Gene Expression

Dicer1 is an endoribonuclease involved in the biogenesis of functional molecules such as microRNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs). These small non-coding RNAs are important regulators of post-transcriptional gene expression and participate in the control of male fertility. With the knowledge that 1) Dicer1-dependent factors are required for proper sperm maturation in the epididymis, and that 2) miRNAs are potent mediators of intercellular communication in most biological systems, we investigated the role of Dicer1-dependent factors produced by the proximal epididymis (initial segment/caput)-including miRNAs-on the regulation of epididymal gene expression in the distal epididymis regions (i.e. corpus and cauda). To this end, we performed comparative microarray and ANOVA analyses on control vs. Defb41(iCre/wt); Dicer1(fl/fl) mice in which functional Dicer1 is absent from the principal cells of the proximal epididymis. We identified 35 and 33 transcripts that displayed significant expression level changes in the corpus and cauda regions (Fold change > 2 or 2 or < -2; p < 0.01). These miRNAs are secreted via extracellular vesicles (EVs) derived from the DC2 epididymal principal cell line, and their expression correlates with target transcripts involved in distinct biological pathways, as evidenced by in silico analysis. Albeit correlative and based on in silico approach, our study proposes that Dicer1-dependent factors trigger-directly or not-significant genes expression changes in distinct regions of this organ. The paracrine control of functions important to post-testicular sperm maturation by Dicer1-dependent factors may open new avenues for the identification of molecular targets important to male fertility control

Nuclear spin ratios of deuterated ammonia in prestellar cores. LAsMA observations of H-MM1 and Oph D

We determine the ortho/para ratios of NH2D and NHD2 in two dense, starless cores, where their formation is supposed to be dominated by gas-phase reactions, which, in turn, is predicted to result in deviations from the statistical spin ratios. The Large APEX sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama Pathfinder EXperiment (APEX) telescope was used to observe the prestellar cores H-MM1 and Oph D in Ophiuchus in the ground-state lines of ortho and para NH2D and NHD2. The fractional abundances of these molecules were derived employing 3D radiative transfer modelling, using different assumptions about the abundance profiles as functions of density. We also ran gas-grain chemistry models with different scenarios concerning proton or deuteron exchanges and chemical desorption from grains to find out if one of these models can reproduce the observed spin ratios. The observationally deduced ortho/para ratios of NH2D and NHD2 are in both cores within 10% of their statistical values 3 and 2, respectively, and taking 3-sigma limits, deviations from these of about 20% are allowed. Of the chemistry models tested here, the model that assumes proton hop (as opposed to full scrambling) in reactions contributing to ammonia formation, and a constant efficiency of chemical desorption, comes nearest to the observed abundances and spin ratios. The nuclear spin ratios derived here are in contrast with spin-state chemistry models that assume full scrambling in proton donation and hydrogen abstraction reactions leading to deuterated ammonia. The efficiency of chemical desorption influences strongly the predicted abundances of NH3, NH2D, and NHD2, but has a lesser effect on their ortho/para ratios. For these the proton exchange scenario in the gas is decisive. We suggest that this is because of rapid re-processing of ammonia and related cations by gas-phase ion-molecule reactions.Comment: accepted for publication in Astronomy & Astrophysic

Space charge in drift chambers operated with the Xe,CO2(15%) mixture

Using prototype modules of the ALICE Transition Radiation Detector we investigate space charge effects and the dependence of the pion rejection performance on the incident angle of the ionizing particle. The average pulse height distributions in the drift chambers operated with the Xe,CO2(15%) mixture provide quantitative information on the gas gain reduction due to space charge accumulating during the drift of the primary ionization. Our results demonstrate that the pion rejection performance of a TRD is better for tracks which are not at normal incidence to the anode wires. We present detailed simulations of detector signals, which reproduce the measurements and lend strong support to our interpretation of the measurements in terms of space charge effects.Comment: 18 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth. A. Data files available at http://www-alice.gsi.de/tr

Modelling deuterated isotopologues of methanol towards the pre-stellar core L1544

Context. In the extremely cold and dark environments of pre-stellar cores, methanol is formed on the surface of interstellar dust grains and released into the gas phase via non-thermal desorption mechanisms. Gaseous methanol constitutes the starting point for the formation of many massive complex organic molecules and is therefore of utmost importance for the build-up of chemical complexity. Aims. We aim to improve upon a previous model for the prediction of column densities and deuterium fractions of non-deuterated and singly deuterated methanol. Thereby, we try to identify crucial chemical and physical parameters for which the study of deuteration could provide valuable additional constraints. Methods. We employed a gas-grain chemical code to devise a model that is in agreement with the observed column density and deuterium fraction profiles of the innermost region of the pre-stellar core L1544. For that purpose, we developed a new treatment of reactive desorption, deriving an individual reactive desorption efficiency for every product species in a chemical reaction that depends on the reaction enthalpy and type of the underlying surface. Furthermore, we explored several options to promote the diffusion of hydrogen and deuterium atoms over the surface of interstellar dust grains in order to increase methanol formation. Results. Our fiducial model employs diffusion via the quantum tunnelling of hydrogen and deuterium atoms, resulting in CH3OH and CH2DOH column densities that are approximately an order of magnitude lower than the observed values, which is an improvement over the results of the previous model by a factor of 10. The N(CH2DOH)/N(CH3OH) ratio is reproduced within a factor of 1.2 for the centre and 1.8 for the position of the methanol peak. Given the large uncertainties that chemical models typically have, we consider our predictions to be in agreement with the observations. In general, we conclude that a diffusion process with a high diffusion rate needs to be employed to obtain methanol column densities that are in accordance with the observed values. Also, we find that the introduction of abstraction reactions into the methanol formation scheme suppresses deuteration when used in combination with a high diffusion rate. © The Authors 2023.Ministry of Science and Higher Education of the Russian Federation: FEUZ-2020-0038The work by A.V. is supported by the Russian Ministry of Science and Higher Education via the Project FEUZ-2020-0038