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排序方式: 共有202条查询结果,搜索用时 15 毫秒
61.
An exact single envelope soliton solution of the damped nonlinear Schrödinger equation in a medium with a parabolic density profile has been obtained. It is found that the condition of reflection of the soliton from the density hump is determined by its initial velocity and the scale lengths of the inhomogeneity. 相似文献
62.
Batch studies have been carried out in the removal of Hg(II) from aqueous solutions by using well-synthesized and -characterized hydrous manganese oxide (HMO) and hydrous tin oxide (HTO) employing a radiotracer technique. Results obtained reveal that increased sorptive concentration (10(-8)-10(-2) mol dm(-3)), temperature (298-328 K), and pH (ca. 2.0-10.5) enhance the removal efficiency of these solids. First-order uptake of Hg(II) on HMO and HTO follows the Freundlich adsorption isotherm for entire concentration range. Positive values of DeltaH0 for the uptake process on both solids indicate endothermic uptake and desorption experiments point to irreversible uptake. Radiation stability of the adsorbents has also been assessed using a 300-mCi (Ra-Be) neutron source having an integral neutron flux of 3.85 x 10(6) N cm(-2) s(-1) and associated with a nominal gamma-dose of ca. 1.72 Gy/h. 相似文献
63.
Theoretical studies have been carried out to investigate the convective heat transfer coefficients at different locations in the entrance region of a cylindrical duct with combined axial and tangential entry of time-independent power-law fluids. Investigations have been performed with uniform heat flux and uniform wall temperature boundary conditions. Theoretical model uses integral approach of hydrodynamic and thermal boundary layer theory to establish a functional relationship of local Nusselt number (Nu
z
) with the pertinent input parameters such as generalised Reynolds number based on tangential velocity of injection
, generalised Prandtl number based on inlet tangential velocity (Pr
G
), the ratio of axial-to-tangential velocity at the inlet to the duct (V
R), the flow behaviour index of the fluid (n) and the ratio of axial-distance-to-duct-diameter (z/D).
Nomenclature A E Area of the tangential entry ports - a 1 Area of the axial entry port - C p Specific heat of fluid - D Duct diameter - E A non-dimensional parameter defined by Eq. (10) - G A non-dimensional parameter defined by Eq. (10) - K Flow consistency index of the fluid - K t Thermal conductivity of the fluid - L Length of the duct - Axial mass flux at the inlet plane - Tangential mass flux at the inlet plane - Nu z Local Nusselt number, Nuz=hz D/Kt - n Flow behaviour index of the fluid - P Static pressure - Pr Prandtl number - Pr G Generalised Prandtl number - r I Radius of the duct - Generalised Reynolds number - r Radial distance from the axis - r c Radius of forced vortex core - t Temperature of fluid at any location - t 0 Free stream temperature of the fluid - t w Wall temperature - u 0 Uniform axial velocity at the inlet - V r Radial velocity component - V z Axial velocity component - V Ø Tangential velocity component - z Distance along the axis of the duct - Thermal diffusivity - Hydrodynamic boundary layer thickness - t Thermal boundary layer thickness - w Defined by Eq. (31), w= tw – t0 - Dynamic viscosity - Density - Circulation constant - Angular velocity in forced vortex core 相似文献
Konvektive Wärmeübertragung bei einer Drallströmung in einem zylindrischen Rohr
Zusammenfassung Es werden theoretische Untersuchungen des lokalen konvektiven Wärmeüberganges im Eintrittsbereich eines zylindrischen Rohres mit kombiniertem axialen und tangentialen Eintritt eines Fluids mit zeitunabhängigem Verhalten nach dem Potenzgesetz vorgestellt. Randbedingungen waren dabei konstanter Wärmestrom und konstante Wandtemperatur. Das theoretische Modell verwendet eine integrale Näherung der hydrodynamischen und thermischen Grenzschichttheorie. Es folgt eine funktionale Beziehung zwischen der lokalen Nusseltzahl (Nu z ) und den relevanten Eingangsparametern wie der verallgemeinerten Reynoldszahl und der verallgemeinerten Prandtlzahl (PrG), die mit der tangentialen Eintrittsgeschwindigkeit gebildet werden sowie dem Verhältnis der axialen und tangentialen Geschwindigkeiten am Rohreintritt (VR), der Kennzahl des Strömungsverhaltens des Fluids (n) und dem Verhältnis von axialer Länge zu Rohrdurchmesser (z/D).
Nomenclature A E Area of the tangential entry ports - a 1 Area of the axial entry port - C p Specific heat of fluid - D Duct diameter - E A non-dimensional parameter defined by Eq. (10) - G A non-dimensional parameter defined by Eq. (10) - K Flow consistency index of the fluid - K t Thermal conductivity of the fluid - L Length of the duct - Axial mass flux at the inlet plane - Tangential mass flux at the inlet plane - Nu z Local Nusselt number, Nuz=hz D/Kt - n Flow behaviour index of the fluid - P Static pressure - Pr Prandtl number - Pr G Generalised Prandtl number - r I Radius of the duct - Generalised Reynolds number - r Radial distance from the axis - r c Radius of forced vortex core - t Temperature of fluid at any location - t 0 Free stream temperature of the fluid - t w Wall temperature - u 0 Uniform axial velocity at the inlet - V r Radial velocity component - V z Axial velocity component - V Ø Tangential velocity component - z Distance along the axis of the duct - Thermal diffusivity - Hydrodynamic boundary layer thickness - t Thermal boundary layer thickness - w Defined by Eq. (31), w= tw – t0 - Dynamic viscosity - Density - Circulation constant - Angular velocity in forced vortex core 相似文献
64.
65.
Hee‐Jeong Cha Se‐Yeun Hwang Da‐Som Lee Akula Ravi Kumar Yong‐Uk Kwon Moritz Voß Eva Schuiten Uwe T. Bornscheuer Frank Hollmann Deok‐Kun Oh Jin‐Byung Park 《Angewandte Chemie (International ed. in English)》2020,59(18):7024-7028
Long‐chain aliphatic amines such as (S,Z)‐heptadec‐9‐en‐7‐amine and 9‐aminoheptadecane were synthesized from ricinoleic acid and oleic acid, respectively, by whole‐cell cascade reactions using the combination of an alcohol dehydrogenase (ADH) from Micrococcus luteus, an engineered amine transaminase from Vibrio fluvialis (Vf‐ATA), and a photoactivated decarboxylase from Chlorella variabilis NC64A (Cv‐FAP) in a one‐pot process. In addition, long chain aliphatic esters such as 10‐(heptanoyloxy)dec‐8‐ene and octylnonanoate were prepared from ricinoleic acid and oleic acid, respectively, by using the combination of the ADH, a Baeyer–Villiger monooxygenase variant from Pseudomonas putida KT2440, and the Cv‐FAP. The target compounds were produced at rates of up to 37 U g?1 dry cells with conversions up to 90 %. Therefore, this study contributes to the preparation of industrially relevant long‐chain aliphatic chiral amines and esters from renewable fatty acid resources. 相似文献
66.
M. A. P. Martins N. O. Santos M. M. Som 《International Journal of Theoretical Physics》1997,36(6):1457-1463
We consider a conformally flat, inhomogeneous solution of the Einstein equations for a dissipative fluid. The production of
entropy is found to depend on some arbitrary functions of time. By some subsidiary conditions, such a model is shown to evolve
into a homogeneous Friedmann-type universe. 相似文献
67.
Ahmad R Som S Kesselring E Kuppusamy P Zweier JL Potter LC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2010,207(2):322-331
A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramér-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration. 相似文献
68.
This paper reports the photoluminescence and thermoluminescence properties of gamma ray induced rare earth doped yttrium gadolinium mixed oxide phosphor. The europium (Eu3+) was used as rare earth dopant. The phosphor was prepared by chemical co-precipitation method according to the formula (Y2−x−yGdx) O3: Euy3+ (x=0.5; y=0.05). The photoluminescence emission spectrum of the prepared phosphor shows intense peaks in the red region at 615 nm for 5D0→7F2 transitions and the photoluminescence excitation spectra show a broad band located around 220–270 nm for the emission wavelength fixed at 615 nm. The thermoluminescence studies were carried out after irradiating the phosphor by gamma rays in the dose range from 100 Gy to 1 KGy. In the thermoluminescence glow curves, one single peak was observed at about 300 °C of which the intensity increases linearly in the studied dose range of gamma rays. The glow peak was deconvoluted by GlowFit program and the kinetic parameters associated with the deconvoluted peaks were calculated. The kinetic parameters were also calculated by various glow curve shape and heating rate methods. 相似文献
69.
70.
Jacques kagan Katrina Tadema-Wielandt Ging Chan Som N. Dhawan Jeffrey Jaworsky Indra Prakash Sudershan K. Arora 《Photochemistry and photobiology》1984,39(4):465-467
Abstract— Phenylheptatriyne (PHT) is a good singlet oxygen sensitizer in vitro. In vivo , its phototoxicity toward E. coli B has been proved unequivocally to depend on the presence of oxygen. The literature reports indicating that phenylheptatriyne was representative of a new class of sensitizers were probably based on experiments conducted under conditions which were not strictly anaerobic. 相似文献