Natural convection heat transfer at reduced pressures

This paper experimentally studies the natural convection heat transfer characteristics on horizontal and vertical plates at pressures lower than atmospheric value. Eight different pressures ranging from 10Pa to 101.325kPa, and three heating loads were used in the experiments. It is found that natural convection heat transfer characteristics at reduced pressures are independent of the plate arrangements and present different behaviors in two pressure ranges, 10Pa < p < 1000Pa and p > 1000Pa. The experimental heat transfer results are correlated into a non-dimensional equation to help the thermal design of stratosphere aircrafts and airborne equipment.     

Studies of the protein and the energy metabolism in man during a wintering in Antarctica

During the 29th Soviet Antarctic Expedition in Novolazarevskaya from March 1984 to March 1985, the protein and energy metabolisms were studied in six expeditioners from the German Democratic Republic. The investigations were carried out at the beginning of the expedition (May), during the polar night (July) and during the polar day (December). The effect of a special stress situation (sledge trek in April 1984) was investigated in one subject. The stable nitrogen isotope ¹⁵N was used to study the protein metabolism. The assessment of the energy metabolism was based on the oxygen consumption, which was determined by means of a spirograph. In addition, the vital capacity, the breath minute volume, the blood pressure, etc. were measured. The following results were obtained: During the polar night, the utilisation of the dietary proteins and the whole body protein synthesis calculated by means of the ¹⁵N excretion of the total nitrogen in urine were greater (73.6±0.9 % and 3.48±0.17 g protein d^?1 kg^?1, n=3) than the respective values during the polar day (69.7±1.2, p<0.05, n=3 and 3.05±0.07, p<0.05, n=3) and at the beginning of the expedition (69.6±1.4, p<0.02, n=5 and 2.81±0.09, p<0.01, n=5). The lowest values (58.0 % and 2.43 g protein d^?1 kg^?1) were obtained in the subject after the trek. The resting metabolic rate (in kJ d^?1 m^?2) was decreased during the polar night (45.6±5.0, n=4) in comparison with the polar day (61.5±11.3, n=3) and the beginning of the expedition (52.3±9.6, n=4) with p<0.01 in both cases.     

Zur Druckabhängigkeit der Anodenfallspannung von Hochdrucklichtbögen

The dependence of the anode fall voltage of freely burning high pressure arcs was investigated on the basis of a simplified arc model. It was found that the anode fall voltage does not contribute to the observed increase of arc voltage with pressure. The analysis was based on experimental investigations carried out with an argon arc. Due to the self-magneticly produced plasma flow a stagnation point flow pattern developed at the anode. The experiments were conducted at currents of I = 100 A and I = 150 A. The pressure was varied between p = 1 atm and p = 50 atm. The applied method necessitated the determination of the anode energy balance. As a side result of the investigation it was found that radiation contributes at p = 1 atm with appr. 20% and at p = 50 atm with appr. 50% to the total arc energy balance.     

Effects of ergot alkaloids on liver function of piglets can be detected by the [13C]methacetin breath test irrespective of oral or intramuscular route of tracer administration

Ergot alkaloids (sum=total alkaloids, TA) originate from the phyto-pathogenic fungus Claviceps purpurea and might exert feed intake depressing and hepatotoxic effects on animals. The aim of the study was to evaluate TA effects on performance and liver function of piglets with the [¹³C]methacetin breath test and two routes of tracer administration (orally, p.o.; intramuscularly, i.m.). Two ergot batches were mixed into piglet diets resulting in 21 and 17 mg TA kg^?1 (Ergot-5 and -12, respectively) and compared with an ergot-free control diet. Feed intake was significantly depressed after feeding the ergot containing diets (p=<0.001). The time at maximum ¹³CO₂ exhalation (t _max) and the half-life (t _0.5) were not influenced by treatments and varied between 25 and 68 min after the p.o., and 28 and 62 min after the i.m. administration of [¹³C]methacetin, respectively. The cumulative ¹³C recovery (cPDR₃₀) was significantly lower due to feeding the diet Ergot-5 (6.6 %) compared with the Ergot-12 (8.8 %) and the control diet (9.7 %) irrespective of the route of tracer administration (p=0.044). As a discrimination of the diet effects through both tracer administration routes is possible, the i.m. application should be preferred in piglets as this causes less stress than the oral forced administration.     

Pulsed-periodic discharge in cesium as an effective source of light

The spectrum of visible radiation from an inhomogeneous cesium-plasma column is evaluated in the approximation of locally thermodynamically equilibrium plasma. The plasma parameters correspond to a pulsed-periodic low-power discharge at pressures of 0.1–1.0 atm and the axial temperature T=5500 K. Under these conditions, the visible spectrum of the cesium plasma changes from discrete (line) to continuous as the pressure varies from 0.1 to 1.0 atm. This is associated largely with an increase in the intensity of the 6P and 5D recombination continua and an appreciable shift of the thresholds of the continua toward larger wavelengths (by ≈100 nm for 6P and by ≈150 nm for 5D) when the plasma density rises to ≈4×10¹⁷ cm⁻³. In this case, the optical thickness of the plasma column approaches unity and the average luminous flux per unit length of the arc column is close to 6500 lm/cm at the column radius R=2 mm and a duty ratio of 0.1.     

Structure of self-implanted silicon annealed under enhanced hydrostatic pressure

Implantation of any ions at a sufficiently high dose and energy (E) into single-crystalline Si leads to the creation of amorphous Si (aSi), with damages peaking near the projected range (R _p) of implanted species. Enhanced hydrostatic pressure (HP) at a high temperature (HT) influences the recrystallization of aSi. The structure of self-implanted Czochralski silicon (Si⁺ dose, D=2×10¹⁶ cm^?2, E=150 keV, R _p=0.22 μm) processed for 5 h at 1400 or 1520 K under HPs up to 1.45 GPa was investigated by X-ray, secondary ion mass spectrometry and photoluminescence methods. The implantation of Si produces vacancies (V) and self-interstitials (Si_i). Vacancies and Si_is form complex defects at HT–HP, also with contaminants (e.g. oxygen, always present in Czochralski silicon). The mobility and recombination of V and Si_i as well as the kinetics of recrystallization are affected by HP, thus processing at HT–HP affects the recovery of aSi.     

L-[1-13C]phenylalanine breath test in patients with chronic liver disease of different etiologies

The aim of this study was to compare the oxidation of l-[1-¹³C]phenylalanine (¹³C-PheOx) in patients with chronic liver failure due to different etiologies using l-[1-¹³C]phenylalanine breath test. Breath samples were collected before the administration of 100 mg l-[1-¹³C]phenylalanine, and every 10 min thereafter until completion of 1 h. Control subjects (n=9) presented a larger cumulative percentage of ¹³C dose recovery (CPDR) than patients (n=124) with chronic liver disease, regardless of the etiology (7.5±0.7 vs. 4.2±0.2, p=0.001). No differences in CPDR were found considering the Child-Pugh (CP) class or etiology: alcoholic (CP A=7.7±0.7, CP B=4.1±0.5, CP C=2.0±0.3), hepatitis C virus (CP A=5.4±0.5, CP B=4.0±0.2, CP C=2.2±0.3), hepatocellular carcinoma (CP A=5.5±1.6, CP B=3.6±1.8, CP C=2.2±1.0); or cryptogenic cirrhotic patients (CP A=7.4±1.5, CP B=4.4±0.4, CP C=2.1±0.7). Results confirm that ¹³C-PheOx decreases in patients with cirrhosis with respect to controls, notwithstanding the etiology.     

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). II. Rheological Behavior at the Gel Point

Abstract

Isothermal time evolution measurements at different constant temperatures (170°C, 180°C, and 190°C) over a wide range of frequency for the thermal cross‐linking process of poly(vinyl methyl ether), PVME, have been investigated rheologically. At the onset of cross‐linking (t _onset) the elastic storage modulus, G′, increases abruptly. The magnitude of the elevation in G′ and the value of t _onset were found to be temperature‐dependent. Similar behavior was observed for both the viscous loss modulus, G″ and the complex dynamic viscosity, η*; however, the value of G″ shows a very low sensitivity to the cross‐linking process compared to G′ and η* at the same experimental conditions. The gel point, t _gel, was evaluated from the point of intersection in plots of tan δ vs. curing time for different constant shear frequencies. At the gel point tan δ is no longer frequency‐dependent, and all curves cross‐over, indicating the validity of the Winter–Chambon criterion. The value of t _gel obtained from the coincidence of G′ and G″ was about 10 min longer than that determined from tan δ vs. t, indicating that the crossover of G′ and G″ is not be considered as a general method for evaluation of t _gel. The value of the apparent activation energy of gelation determined from the temperature dependence of t _gel was 74 kJ mol^?1 in good agreement with literature values for other different systems. At the gel point G′ and G″ showed a power law with shear frequency, i.e., G′ ～ G″ ～ ω _n with critical exponents equal to 0.64 and 0.75, respectively, in close agreement with the percolation theory (n = 2/3). The zero shear viscosity, η₀, and the equilibrium shear modulus, G _eq, can also be expressed in power low scaling functions with the relative distance from the gel point, ? i.e., η₀ ～ ?^?k and G _eq ～ ? ^z with k = 1.3 and z = 2.4 in good agreement with the predicted values based on the percolation theory.     

Measurement of the lifetime and quenching rate of metastable 2S muonic helium ions

The lifetime of the 2S state in (μ^?4He)⁺ ions has been measured at He-gas pressures between 50 Torr and 6 atm (T=300 K). We observed both X-rays from the two-photon 2S→1S transitions as well as delayed K_α X-rays associated with radiative quenching. The quenching rate is strongly pressure dependent; it is predominantly a quadratic function of pressure with a measured three-body rate coefficient k=(5.9±0.8)×10^?32cm⁶/s. At 6 atm, we find τ_2S<250 ns because of the absence of two-photon transitions.     

Non-Intersecting Squared Bessel Paths at a Hard-Edge Tacnode

The squared Bessel process is a 1-dimensional diffusion process related to the squared norm of a higher dimensional Brownian motion. We study a model of n non-intersecting squared Bessel paths, with all paths starting at the same point a > 0 at time t = 0 and ending at the same point b > 0 at time t = 1. Our interest lies in the critical regime ab = 1/4, for which the paths are tangent to the hard edge at the origin at a critical time ${t^*\in (0,1)}$ . The critical behavior of the paths for n → ∞ is studied in a scaling limit with time t = t ^* + O(n ^?1/3) and temperature T = 1 + O(n ^?2/3). This leads to a critical correlation kernel that is defined via a new Riemann-Hilbert problem of size 4 × 4. The Riemann-Hilbert problem gives rise to a new Lax pair representation for the Hastings-McLeod solution to the inhomogeneous Painlevé II equation q′′(x) = xq(x) + 2q ³(x) ? ν, where ν = α + 1/2 with α > ?1 the parameter of the squared Bessel process. These results extend our recent work with Kuijlaars and Zhang (Comm Pure Appl Math 64:1305–1383, 2011) for the homogeneous case ν = 0.     

Region-Specific Susceptibilities to Cuprizone-Induced Demyelination of C57BL/6 Mouse: In vivo T2WI and DTI Studies at 7.0T

The cuprizone (CPZ) mouse model of demyelination was recognized and used to explore multiple sclerosis (MS)-like brain lesions. In this study, we assessed CPZ-treated mice using T₂-weighted imaging and diffusion tensor imaging (DTI). C57BL/6 mice treated with 2 weeks of 0.2 % CPZ-containing diet (n = 10) and regular chow diet (n = 10) were scanned with a 7.0 T MRI scanner (Agilent, USA), respectively, using fast spin-echo and fast spin-echo DTI sequences. The normalized T₂ signal intensity (normalized to the cerebrospinal fluid) was calculated and fractional anisotropy (FA value), mean diffusivity, axial diffusivity and radial diffusivity were measured in the brain region of the cerebral cortex (CTX), caudate putamen (CP), hippocampus (HP) and thalamus (TH). Compared with controls, increased normalized T₂ signal intensities and reduced FA values (p < 0.05) were observed in the CTX, HP and CP (p < 0.01), but not in TH in cuprizone-fed mice. In the regions of reduced FA values, an increase in mean diffusivity (p < 0.05) and radial diffusivity (p < 0.05) was also found. Significant decreased axial diffusivity was only observed in CTX (p < 0.05). DTI is sensitive to detecting cuprizone-induced demyelination of C57BL/6 mice. This study suggests that CTX, HP and CP are more susceptible to cuprizone-induced demyelination than TH. Our results also indicate that the decrease of FA value may be more likely due to increased radial diffusivity.     

Electrical characterization of gadolinia-doped ceria films grown by pulsed laser deposition

Electrical characterization of 10 mol% gadolinia doped ceria (CGO10) films of different thicknesses prepared on MgO(100) substrates by pulsed laser deposition is presented. Dense, polycrystalline and textured films characterized by fine grains (grain sizes < 18 nm and < 64 nm for a 20-nm and a 435-nm film, respectively) are obtained in the deposition process. Grain growth is observed under thermal cycling between 300 and 800°C, as indicated by X-ray-based grain-size analysis. However, the conductivity is insensitive to this microstructural evolution but is found to be dependent on the sample thickness. The conductivity of the nanocrystalline films is lower (7.0×10^?4  S/cm for the 20-nm film and 3.6×10^?3  S/cm for the 435-nm film, both at 500°C) than that of microcrystalline, bulk samples ( $6\times 10^{-3}$  S/cm at 500°C). The activation energy for the conduction is found to be 0.83 eV for the bulk material, while values of 1.06 and 0.80 eV are obtained for the 20-nm film and the 435-nm film, respectively. The study shows that the ionic conductivity prevails in a broad range of oxygen partial pressures, for example down to about 10 ^?26  atm at 500°C.     

Composition,temperature and geometric dependent hysteresis behaviours in Ising-type segmented nanowire with magnetic and diluted magnetic,and its soft/hard magnetic characteristics

Abstract

In this paper, a theoretical approach to evaluate the hysteresis behaviours of Ising-type segmented nanowire (ISN) comprising magnetic and diluted magnetic segments is defined. The dependency to the system parameters are calculated for optimising their performance in applications like magnetic sensors or recording media. The effects of the composition (p) and temperature (T) as well as crystal field on the hysteresis behaviours are investigated in detail. We studied the effect of the segment dimensions obtained from the exchange interactions. The coercivity (H_C) and remanence (M_r) of the ISN are derived from hysteresis loops. The phase diagrams are presented in the different planes as function of H_C and M_r to investigate the magnetic characteristics of the ISN. Under certain conditions, namely p = 0 and J_D = 0, we also examined the effect of temperature on the nanowire with magnetic and non-magnetic segments. The distinct hysteresis properties and soft/hard the magnetic characteristics depending upon these factors are observed. We found that the magnetic hardness decreases case as the temperatures increase as well as p and crystal field (Δ) decrease. Moreover, when the p increase and Δ decrease the triple hysteresis loop behaviour occurs in the system. Comparisons between the observed theoretical results and some experimental works of nanowire with hysteresis behaviours are made and a very good agreement is obtained.     

Importance of through-plane heart motion correction for the assessment of aortic regurgitation severity using phase contrast magnetic resonance imaging

PurposeTo elucidate the influence of through-plane heart motion on the assessment of aortic regurgitation (AR) severity using phase contrast magnetic resonance imaging (PC-MRI).ApproachA patient cohort with chronic AR (n = 34) was examined with PC-MRI. The regurgitant volume (RVol) and fraction (RFrac) were extracted from the PC-MRI data before and after through-plane heart motion correction and was then used for assessment of AR severity.ResultsThe flow volume errors were strongly correlated to aortic diameter (R = 0.80, p < 0.001) with median (IQR 25%;75%): 16 (14; 17) ml for diameter>40mm, compared with 9 (7; 10) ml for normal aortic size (p < 0.001). RVol and RFrac were underestimated (uncorrected:64 ± 37 ml and 39 ± 17%; corrected:76 ± 37 ml and 44 ± 15%; p < 0.001) and ~ 20% of the patients received lower severity grade without correction.ConclusionThrough-plane heart motion introduces relevant flow volume errors, especially in patients with aortic dilatation that may result in underestimation of the severity grade in patients with chronic AR.     

Stark-Effekt-Verbreiterung der Neon I-Übergänge mit schwacher Feldstärkeabhängigkeit (2p 5 3s-2p 5 3p)

The half widths of Stark-broadened Ne I spectral lines (2p ⁵ 3s-2p ⁵ 3p) were measured in wall stabilized arc plasmas (pressurep=1 atm, andp=3 atm) consisting of several gas components (Ar 68%, Ne 27%, He 3%, H₂ 2%). The theoretical half widths of two spectral lines (λ=6,266.50 Å,λ=6,163.59 Å) with known calculated broadening parameters according to Griem differ by a factor 1.8 to 1.9 from the measured widths. Within the errors of Griem's line broadening calculations of about 20% there was agreement between experimental and theoretical half widths regarding two other spectral lines (λ=5,881.90 Å,λ=5,852.49 Å). Calculated adiabatic widths are smaller than the widths according to Griem. Therefore in some cases the deviation of the adiabatic widths from the measured widths is smaller than the difference between Griem widths and experimental ones. Static quadratic coefficients of NeI transitions 2p ⁵ 3s-2p ⁵ 3p calculated from measured Stark-broadened lines showed wavelength displacements in the order of 0.005 Å referring to an electrical field of 100 kV/cm. The determined coefficients are 10² times smaller than those values measurable by known methods of emission spectroscopy.     

Autoignition of condensed hydrocarbon fuels in non-premixed flows at elevated pressures

Experimental and computational investigation is carried out to elucidate the fundamental mechanism of autoignition of n-heptane, n-decane, and n-dodecane in non-premixed flows at elevated pressures up to 6 bar. The counterflow configuration is employed. In this configuration, an axisymmetric flow of a gaseous oxidizer stream is directed over the surface of an evaporating pool of liquid fuel. The oxidizer stream is a mixture of oxygen and nitrogen. The experiments are conducted at a fixed value of mass fraction of oxygen and at a fixed low value of strain rate. The temperature of the oxidizer stream at autoignition, T_ig, is measured as a function of pressure, p. Computations are carried out using skeletal mechanisms constructed from a detailed mechanism and critical conditions of autoignition are predicted. The experimental data and predictions show that, for all fuels tested, T_ig decreases with increasing p. At a fixed value of p, T_ig for n-dodecane is the lowest, followed by n-decane and n-heptane. This indicates that n-dodecane is the most easily ignited, followed by n-decane and n-heptane. This is in agreement with previous experimental and computational studies at 1 atm, where a similar order of reactivities for these fuels was observed at low strain rates. Flame structures at conditions before and at conditions immediately after autoignition are calculated. A noteworthy finding is that low temperature chemistry is found to play a dominant role in promoting autoignition. The influence of low temperature chemistry is found to increase with increasing pressure.     

Elastic and thermodynamic properties in CdO at high pressures from first-principles calculations

In this study, we report first-principles calculations of the elastic and thermodynamic properties for CdO in both the B1 (rocksalt) phase and B2 (cesium chloride) phase. The calculations are performed within the framework of density functional theory, using the pseudopotential plane-wave method. From the theoretical results, we find that the high pressure structural phase transition of CdO from B1 structure to B2 structure is 90.31 GPa. The calculated values are, generally speaking, in good agreement with experiments and with similar theoretical calculations. According to the quasi-harmonic Debye model, we investigate the sound velocity and Debye temperature of CdO under pressures in the range of 0<P<150 GPa.     

Three-dimensional array structures associated with Richtmyer-Meshkov and Rayleigh-Taylor instability

A boundary separating adjacent gas or liquid media is frequently unstable. Richtmyer-Meshkov and Rayleigh-Taylor instability cause the growth of intricate structures on such boundaries. All the lattice symmetries [rectangular (pmm2), square (p4mm), hexagonal (p6mm), and triangular (p3m1) lattices] which are of interest in connection with the instability of the surface of a fluid are studied for the first time. They are obtained from initial disturbances consisting of one (planar case, two-dimensional flow), two (rectangular cells), or three (hexagons and triangles) harmonic waves. It is shown that the dynamic system undergoes a transition during development from an initial, weakly disturbed state to a limiting or asymptotic stationary state (stationary point). The stability of these points (stationary states) is investigated. It is shown that the stationary states are stable toward large-scale disturbances both in the case of Richtmyer-Meshkov instability and in the case of Rayleigh-Taylor instability. It is discovered that the symmetry increases as the system evolves in certain cases. In one example the initial Richtmyer-Meshkov or Rayleigh-Taylor disturbance is a sum of two waves perpendicular to one another with equal wave numbers, but unequal amplitudes: a ₁(t=0)≠a ₂(t=0). Then, during evolution, the flow has p2 symmetry (rotation relative to the vertical axis by 180°), which goes over to p4 symmetry (rotation by 90°) at t→∞, since the amplitudes equalize in the stationary state: a ₁(t=∞)=a ₂(t=∞). It is shown that the hexagonal and triangular arrays are complementary. Upon time inversion (t→−t), “rephasing” occurs, and the bubbles of a hexagonal array transform into jets of a triangular array and vice versa. Zh. éksp. Teor. Fiz. 116, 908–939 (September 1999)     

Vicious random walkers in the limit of a large number of walkers

The vicious random walker problem on a line is studied in the limit of a large number of walkers. The multidimensional integral representing the probability that thep walkers will survive a timet (denotedP _t ^(p) ) is shown to be analogous to the partition function of a particular one-component Coulomb gas. By assuming the existence of the thermodynamic limit for the Coulomb gas, one can deduce asymptotic formulas forP _t ^(p) in the large-p, large-t limit. A straightforward analysis gives rigorous asymptotic formulas for the probability that after a timet the walkers are in their initial configuration (this event is termed a reunion). Consequently, asymptotic formulas for the conditional probability of a reunion, given that all walkers survive, are derived. Also, an asymptotic formula for the conditional probability density that any walker will arrive at a particular point in timet, given that allp walkers survive, is calculated in the limittp.     

Enhancing the performance of thin film CdS/PbS photovoltaic solar cells

This work investigates dependence of the short-circuit current density, open-circuit voltage, fill factor and efficiency of a thin film CdS/PbS solar cell on thickness of transparent conductive oxide (TCO) layer, thickness of window layer (CdS), concentration of uncompensated acceptors (width of space-charge region), carrier lifetime in PbS and the reflectivity from metallic back contact. The effect of optical losses, front and rear recombination losses as well as the recombination losses on space-charge region are also considered in this study. As a result, by thinning the front contact layer indium tin oxide from 400 to 100 nm and window layer (CdS) from 200 to 100 nm it is possible to reduce the optical losses from 32 to 20%. The effect of electron lifetime on the internal and external quantum efficiency can be neglected at high width of the space-charge region. The maximum current density of 18.4 mA/cm² is achieved at wide space-charge region (concentration of uncompensated acceptors = 10¹⁵ cm^?3) and the longest lifetime (τ_n = 10^?6 s) where the optical and recombination losses are about 55%. The maximum efficiency of 5.17%, maximum open-circuit voltage of 417 mV and approximately fixed fill factor of 74% are yielded at optimum conditions such as: electron lifetime = 10^?6 s; concentration of uncompensated acceptors = 10¹⁶ cm^?3; thickness of TCO = 100 nm; thickness of CdS = 100 nm; velocity of surface and rear recombination = 10⁷ cm/s and thickness of absorber layer = 3 μm. When the reflectance from the back contact is 100%, the cell parameters improve and the cell efficiency records a value of 6.1% under the above conditions.