Unsteady shock-flow characteristics in an over-expanded rocket nozzle

<正>A numerical investigation of transient side-loads in an axisymmetric over-expanded thrust optimized contour nozzle is presented.These nozzles experience side-loads during start-up and shut-down operations,because of the flow separation at nozzle walls.Two types of flow separations such as FSS and RSS shock structure occur.A two-dimension numerical simulation has been carried out over an axisymmetric TOC nozzle to validate present results and investigate oscillatory flow characteristics for start-up processes.Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme.Governing equations are solved by coupled implicit scheme.Reynolds Stress turbulence model is selected.Present computed pressure at the nozzle wall closely matched with experiment data.A hysteresis phenomenon has been observed between these two shock structures.The transition from FSS to RSS pattern during start-up process has shown maximum nozzle wall pressure.Nozzle wall pressure and shear stress values have shown fluctuations during the FSS to RSS transition. The oscillatory pressure has been observed on the nozzle wall for high pressure ratio.Present results have shown that magnitude of the nozzle wall pressure variation is high for the oscillatory phenomenon.     

Enhancing Thermopower and Nernst Signal of High-Mobility Dirac Carriers by Fermi Level Tuning in the Layered Magnet EuMnBi2

Dirac/Weyl semimetals hosting linearly dispersing bands have received recent attention for potential thermoelectric applications, since their ultrahigh-mobility carriers could generate large thermoelectric and Nernst power factors. To optimize these efficiencies, the Fermi energy needs to be chemically controlled in a wide range, which is generally difficult in bulk materials because of disorder effects from the substituted ions. Here it is shown that the Fermi energy is tunable across the Dirac point for layered magnet EuMnBi₂ by partially substituting Gd³⁺ for Eu²⁺ in the insulating block layer, which dopes electrons into the Dirac fermion layer without degrading the mobility. Clear quantum oscillation observed even in the doped samples allows to quantitatively estimate the Fermi energy shift and optimize the power factor (exceeding 100 µ W K⁻² cm⁻¹ at low temperatures) in combination with the first-principles calculation. Furthermore, it is shown that Nernst signal steeply increases with decreasing carrier density beyond a simple theoretical prediction, which likely originates from the field-induced gap reduction of the Dirac band due to the exchange interaction with the Eu moments. Thus, the magnetic block layer provides high controllability for the Dirac fermions in EuMnBi₂, which would make this series of materials an appealing platform for novel transport phenomena.     

Mechanism of mitochondrial dysfunction and cytotoxicity induced by tropolones in isolated rat hepatocytes

The hair cell orientation patterns present on the saccules of fishes may be important for encoding the direction of a sound source. This study was conducted to determine whether primary afferent projections to the medulla are organized by the best directions for the hair cells they innervate. The toadfish saccule has hair cells oriented primarily in the vertical plane: both the rostral and the caudal saccule have hair cell orientations sweeping from 0 degrees to 45 degrees, and the middle saccule has hair cells oriented at 90 degrees. Fluorescent dextran amines were used singly and in combination to label regions of the saccular nerve innervating rostral, middle, and caudal saccule. The projections of those afferents were examined in detail in the anterior and descending octaval nuclei, which are auditory nuclei in this species. There was no evidence of topographic projections based on location along the length of the saccule or based on hair cell orientation. There was some evidence that parallel inputs are present from each region of the saccule examined, which may be based on the 180 degrees opposition of hair cells found throughout the saccule; however, afferents from the rostral, middle, and caudal saccule appear to have overlapping projections to the anterior and descending octaval nuclei. These data suggest that in toadfish, calculations of the direction of the sound source may begin in either of these primary auditory nuclei by comparing afferent input from along the saccule.     

Estimating stochastic volatility models using daily returns and realized volatility simultaneously

Realized volatility, which is the sum of squared intraday returns over a certain interval such as a day, has recently attracted the attention of financial economists and econometricians as an accurate measure of the true volatility. In the real market, however, the presence of non-trading hours and market microstructure noise in transaction prices may cause bias in the realized volatility. On the other hand, daily returns are less subject to noise and therefore may provide additional information on the true volatility. From this point of view, modeling realized volatility and daily returns simultaneously based on the well-known stochastic volatility model is proposed. Empirical studies using intraday data of Tokyo stock price index show that this model can estimate realized volatility biases and parameters simultaneously. The Bayesian approach is taken and an efficient sampling algorithm is proposed to implement the Markov chain Monte Carlo method for our simultaneous model. The result of the model comparison between the simultaneous models using both naive and scaled realized volatilities indicates that the effect of non-trading hours is more essential than that of microstructure noise and that asymmetry is crucial in stochastic volatility models. The proposed Bayesian approach provides an estimate of the entire conditional predictive distribution of returns under consideration of the uncertainty in the estimation of both biases and parameters. Hence common risk measures, such as value-at-risk and expected shortfall, can be easily estimated.     

Charge-to-mass ratio and dendrite structure of diesel particulate matter charged by corona discharge

The electric charge of diesel particulate matter (DPM) from a corona discharge device is measured for understanding the electrical characteristics of the DPM; an electrostatic precipitator (ESP) is employed for trapping DPM. Exhaust gas from a diesel engine is sampled by isokinetic sampling, and DPM contained in the gas is charged by negative corona discharge. The charged DPM is collected by a Faraday cup, and its electric charge is measured by a Coulomb meter. In addition, the appearance of the collected DPM is observed using a scanning electron microscope. It is found that when the gas velocity is 0.28 m/s, the maximum charge-to-mass ratio of the DPM is −126 μC/g. The DPM appears to agglomerate into a large particle in the absence of corona discharge; however, the agglomerated DPM forms a dendrite structure in the presence of corona discharge. The dendrite structure causes an increase in the surface area of the agglomerated DPM. Therefore, the oxidation removal of the DPM trapped by the ESP by using ozone and nitrogen dioxide can be enhanced because an oxidation reaction occurs on the surface of the DPM.     

Effects of calcium stearate addition of ultrahigh molecular weight polyethylene in direct compression molding

The effects of calcium stearate addition in molding of ultrahigh molecular weight polyethylene (UHMWPE) were investigated by tensile testing, scanning electron microscope (SEM), Fourier transform infrared (FT‐IR) spectroscopy, and elemental analysis. Four types of UHMWPE specimens with varying contents of calcium stearate (<5, 50, 100, and 1000 ppm) were used in this study. SEM observation revealed that calcium stearate added specimens have smoother and more homogeneous microstructures. After accelerated aging, subsurface oxidative degeneration was observed in all specimens; however, calcium stearate added specimens had less oxidative degeneration in comparison with specimens without additives. Specimens showed better mechanical properties with increasing content of calcium stearate. Though all specimens aggravated their mechanical properties due to oxidation after accelerated aging, the specimens of 100 ppm of calcium stearate showed better properties at 3.7 MPa larger yield strength and four times larger value of elongation at fracture than the specimens without additives. These results indicate that calcium stearate addition produces dense packing of UHMWPE particles, which brings about stronger fusion among the particles and fewer structural defects, and results in better mechanical properties and better resistance to oxidative degeneration. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1602–1609, 2003     

Plasma Phosphatidylethanolamine and Triacylglycerol Fatty Acid Concentrations are Altered in Major Depressive Disorder Patients with Seasonal Pattern

Disturbances in peripheral and brain lipid metabolism, including the omega-3 fatty acid docosahexaenoic acid (DHA), have been reported in major depressive disorder (MDD). However, these changes have yet to be confirmed in MDD with seasonal pattern (MDD-s), a subtype of recurrent MDD. The present exploratory study quantified plasma plasmalogen and diacyl-phospholipid species, and fatty acids within total phospholipids, cholesteryl esters, triacylglycerols and free fatty acids in non-medicated MDD-s participants (n = 9) during euthymia in summer or fall, and during depression in winter in order to screen for potential high sensitivity lipid biomarkers. Triacylglycerol alpha-linolenic acid concentration was significantly decreased, and myristoleic acid concentration was significantly increased, during winter depression compared to summer-fall euthymia. 1-stearyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine, a diacyl-phospholipid containing stearic acid and DHA, was significantly decreased in winter depression. Concentrations of cholesteryl ester oleic acid and several polyunsaturated fatty acids between summer/fall and winter increased in proportion to the increase in depressive symptoms. The observed changes in lipid metabolic pathways in winter-type MDD-s offer new promise for lipid biomarker development.     

Kinetic Study of the Scavenging Reaction of the Aroxyl Radical by Eight Kinds of Vegetable Oils in Solution

A detailed kinetic study was performed for the reaction of the aroxyl radical (ArO?) with eight vegetable oils 1–8, which contain different concentrations of α‐, β‐, γ‐, and δ‐tocopherols and ‐tocotrienols (‐Tocs and ‐Toc‐3s). The second‐order rate constants (k_s) and aroxyl radical absorption capacity (ARAC) values for the reaction of ArO? with vegetable oils 1–8 (rice bran 1, perilla 2, rapeseed 3, safflower 4, grape seed 5, sesame 6, extra virgin olive 7, and olive oils 8) were measured in ethanol/chloroform/D₂O (50:50:1, v/v/v) solution at 25 °C using stopped‐flow spectrophotometry. The k_s value (16.1 × 10^?3 L g^?1 s^?1) of rice bran oil 1 with the highest activity was 8.0 times larger than that (2.02 × 10^?3) of olive oil 8 with the lowest activity. The concentrations (in mg 100 g^?1) of α‐, β‐, γ‐, and δ‐Tocs and ‐Toc‐3s contained in the vegetable oils 1–8 were determined using high performance liquid chromatography‐mass spectrometry/mass spectrometry (HPLC‐MS/MS). From these results, it was clarified that the ArO?‐scavenging rates (k_s) (i.e., the relative ARAC value) obtained for the vegetable oils 1–8 may be well explained as the sum of the product of the rate constant () and the concentration ([AOH‐i]/10⁵) of AOH‐i (Tocs and Toc‐3s) included in vegetable oils. The results suggest that the ARAC assay method might be used in the evaluation of antioxidant activity of general food extracts.     

Hydrothermal dewatering of brown coal and catalytic hydrothermal gasification of the organic compounds dissolving in the water using a novel Ni/carbon catalyst

Brown coals will continue to be important energy resources in the near future, but their high water contents, which sometimes exceed 50 wt%, and their low calorific values restrict their utilization. Development of an efficient treatment method for dewatering and upgrading is desired to utilize brown coals on a large scale. Hydrothermal treatment is believed to be a promising treatment method because it can not only remove water in liquid phase but also improve calorific value of brown coal. However, some organic compounds are inevitably leached out from the coal during the treatment to emit a huge amount of wastewater containing organic compounds in small concentration, which causes a loss of coal energy as well as a serious problem of wastewater treatment. In this paper, an Australian brown coal (Morwell) was hydrothermally treated for dewatering and upgrading at 250-300 °C. When treated at 300 °C, the water content decreased from 1.31 kg/kg on dry matter to 0.59 kg/kg on dry matter and the calorific value increased from 25.8 to 27.8 MJ/kg on dry matter, indicating that the hydrothermal treatment is really effective for dewatering and upgrading the brown coal. The reactivity to oxygen at low temperature was also reduced by the treatment, which will contribute to suppress the spontaneous combustion of the coal. On the other hand, the amount of organic compound dissolved in the recovered wastewater increased with increasing treatment temperature and it reached ca. 1.5% on carbon basis at 300 °C. The wastewater was treated using a novel Ni-supported carbon catalyst developed by the authors. The organic compounds in the wastewater were completely gasified at as low as 350 °C under 20 MPa at the liquid hourly space velocity of as large as 50, producing combustible gas rich in CH₄ and H₂. The proposed hydrothermal gasification process was found not only to be efficient for wastewater treatment but also to be effective for energy recovery from wastewater. The gasification process combined with the hydrothermal treatment process, which is operated under the conditions close to those of the gasification, will be a new and effective brown coal pretreatment process.     

A U-shaped actuation system for dual-stage actuators used in hard disk drives

In this paper, we propose an actuation system, called U-shaped actuation, for dual-stage actuator to suppress the arm mode flutter. We manufactured an actuator using this actuation method and measured the frequency response. We found that the frequency response had an in-phase arm mode frequency and that there was little difference between each head at arm sway and suspension sway mode. Next, we designed a controller and compared its sensitivity function with that of conventional actuation. By applying stabilizing control to the in-phase arm mode, NRRO of the arm flutter of the outer and inner arms was suppressed by 10.9 and 13.2?%, respectively.