排序方式: 共有34条查询结果,搜索用时 437 毫秒
11.
I. S. Shivakumara Jinho Lee N. Devaraju G. Gopalakrishna 《Transport in Porous Media》2011,87(2):485-501
A linear stability analysis is implemented to study thermal convective instability in a horizontal fluid-saturated rotating porous layer with throughflow in the vertical direction. The modified Forchheimer-extended Darcy equation that includes the time-derivative and Coriolis terms is employed as a momentum equation. The criterion for the occurrence of direct and Hopf bifurcations is obtained using the Galerkin method. It is shown that if a Hopf bifurcation is possible it always occurs at a lower value of the Darcy?CRayleigh number than the direct bifurcation. Increase in the throughflow strength and inertia parameter is to decrease the domain of Prandtl number up to which Hopf bifurcation is limited but opposite is the trend with increasing Taylor number. The effect of rotation is found to be stabilizing the system, in general. However, in the presence of both rotation and Forchheimer drag a small amount of vertical throughflow as well as inertia parameter show some destabilizing effect on the onset of direct bifurcation; a result of contrast noticed when they are acting in isolation. The existing results in the literature are obtained as limiting cases from the present study. 相似文献
12.
The compatibility of microfluidic devices with solvents and other chemicals is extremely important for many applications such as organic synthesis in microreactors and drug screening. We report the successful fabrication of microfluidic devices from a novel perfluoropolyether based polymer utilizing the Multilayer Soft Lithography? (MSL) technique with simple, straightforward processing. The perfluorinated polymer SIFEL X-71 8115 is a highly chemically resistant elastomeric material. We demonstrate fabrication of a microfluidic device using an off-ratio bonding technique to bond multiple SIFEL layers, each patterned lithographically. The mechanical properties of the SIFEL MSL valves (including actuation pressures) are similar to PDMS MSL valves of the same geometry. Chemical compatibility tests highlight SIFEL's remarkable resistance to organic solvents, acids and alkalis. 相似文献
13.
Monodispersed Li(2)MnSiO(4) nanoparticles are synthesized via a supercritical solvothermal method at 300 °C for 5 min reaction time. The as-synthesized nanoparticles are free from impurities and have 15-20 nm diameter. After coating with conductive polymer, a discharge capacity of 313 mA h g(-1) is obtained for the first time because of nearly 2Li(+) reaction. 相似文献
14.
Ai‐Xin Zhu Qing‐Yuan Yang Soumya Mukherjee Amrit Kumar Cheng‐Hua Deng Andrey A. Bezrukov Mohana Shivanna Michael J. Zaworotko 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(50):18380-18385
Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacities for gas‐storage applications than the related rigid porous coordination networks. To be of practical utility, the pressures at which switching occurs, the gate‐opening and gate‐closing pressures, must lie between the storage and delivery pressures. Here we study the effect of linker substitution to fine‐tune gate‐opening and gate‐closing pressure. Specifically, three variants of a previously reported pcu ‐topology MOF, X‐pcu‐5‐Zn , have been prepared: X‐pcu‐6‐Zn , 6 =1,2‐bis(4‐pyridyl)ethane (bpe), X‐pcu‐7‐Zn , 7 =1,2‐bis(4‐pyridyl)acetylene (bpa), and X‐pcu‐8‐Zn , 8 =4,4′‐azopyridine (apy). Each exhibited switching isotherms but at different gate‐opening pressures. The N2, CO2, C2H2, and C2H4 adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6 , afforded lower gate‐opening and gate‐closing pressures. This simple design principle enables a rational control of the switching behavior in adsorbent materials. 相似文献
15.
The linear and weakly nonlinear thermal convection in a rotating porous layer is investigated by constructing a simplified
model involving a system of fifth-order nonlinear ordinary differential equations. The flow in the porous medium is described
by Lap wood-Brinkman-extended Darcy model with fluid viscosity different from effective viscosity. Conditions for the occurrence
of possible bifurcations are obtained. It is established that Hopf bifurcation is possible only at a lower value of the Rayleigh
number than that of simple bifurcation. In contrast to the non-rotating case, it is found that the ratio of viscosities as
well as the Darcy number plays a dual role on the steady onset and some important observations are made on the stability characteristics
of the system. The results obtained from weakly nonlinear theory reveal that, the steady bifurcating solution may be either
sub-critical or supercritical depending on the choice of physical parameters. Heat transfer is calculated in terms of Nusselt
number. 相似文献
16.
Electrical resistivity measurements have been carried out on As-Te-In glasses up to a pressure of 8 GPa using an Opposed Anvil Cell. It is found that the electrical resistivity and conductivity activation energy decrease continuously with pressure and the samples become metallic at pressures in the range 1.5-2.5 GPa. The variation with composition of the normalized electrical resistivity at different pressures suggests the possibility of rigidity percolation and chemical thresholds occurring around the average coordination of 〈r〉=2.65 and 2.7 respectively. It is also observed that As-Te-In samples remain amorphous when they undergo metallization at high pressures, which is analogous to the threshold switching exhibited by these samples. 相似文献
17.
Dr. Quang Duc Truong Dr. Murukanahally Kempaiah Devaraju Dr. Yoshikazu Sasaki Dr. Hiroshi Hyodo Prof. Itaru Honma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16210-16215
Atomic‐resolution imaging of the crystal defects of cathode materials is crucial to understand their formation and the correlation between the structure, electrical properties, and electrode performance in rechargeable batteries. The polytype, a stable form of varied crystal structure with uniform chemical composition, holds promise to engineer electronic band structure in nanoscale homojunctions. 1 – 3 Analyzing the exact sites of atoms and the chemistry of the boundary in polytypes would advance our understanding of their formation and properties. Herein, the polytype and stacking faults in the lithium cobalt silicates are observed directly by aberration‐corrected scanning transmission electron microscopy. The atomic‐scale imaging allows clarification that the polytype is formed by stacking of two different close‐packed crystal planes in three‐dimensional space. The formation of the polytype was induced by Li–Co cation exchange, the transformation of one phase to the other, and their stacking. This finding provides insight into intrinsic structural defects in an important Li2CoSiO4 Li‐ion battery cathode. 相似文献
18.
Coriolis effect on thermal convection in a couple-stress fluid-saturated rotating rigid porous layer
I. S. Shivakumara S. Sureshkumar N. Devaraju 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(4):513-530
Both linear and weakly nonlinear stability analyses are performed to study thermal convection in a rotating couple-stress
fluid-saturated rigid porous layer. In the case of linear stability analysis, conditions for the occurrence of possible bifurcations are obtained.
It is shown that Hopf bifurcation is possible due to Coriolis force, and it occurs at a lower value of the Rayleigh number
at which the simple bifurcation occurs. In contrast to the nonrotating case, it is found that the couple-stress parameter
plays a dual role in deciding the stability characteristics of the system, depending on the strength of rotation. Nonlinear
stability analysis is carried out by constructing a set of coupled nonlinear ordinary differential equations using truncated
representation of Fourier series. Sub-critical finite amplitude steady motions occur depending on the choice of physical parameters
but at higher rotation rates oscillatory convection is found to be the preferred mode of instability. Besides, the stability
of steady bifurcating equilibrium solution is discussed using modified perturbation theory. Heat transfer is calculated in
terms of Nusselt number. Also, the transient behavior of the Nusselt number is investigated by solving the nonlinear differential
equations numerically using the Runge–Kutta–Gill method. It is noted that increase in the value of Taylor number and the couple-stress
parameter is to dampen the oscillations of Nusselt number and thereby to decrease the heat transfer. 相似文献
19.
Water Molecules in Hydrotalcite‐like Layered Double Hydroxides: Interplay between the Hydration of the Anions and the Metal Hydroxide Layer
下载免费PDF全文
![点击此处可从《无机化学与普通化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Layered double hydroxides comprise positively charged metal hydroxide layers and intercalated anions. These materials are obtained from aqueous medium both in nature and in the laboratory. Consequently the layered double hydroxides include a considerable amount of water. The presented study was designed to determine the proportion of water associated with the hydration sphere of the anion as opposed to that of the metal hydroxide slab. Among the two differently bound water species observed in all layered double hydroxides, the weakly bound water is associated with the metal hydroxide layer and is lost at 100 °C, whereas the strongly bound water is in the hydration sphere of the anion and is lost at higher temperatures (100 °C ≤ T ≤ 250 °C). This is in contrast to the better known cationic clays, wherein all the intercalated water is generally found to be in the hydration sphere of the cations. Further the water molecules in layered double hydroxides also bond to each other, leading to the incorporation of water in excess of what is predicted by the Miyata formula (Miyata, 1975) based on crystal chemical considerations. The excess water is one of the reasons for the poor crystallinity of layered hydroxides. 相似文献
20.
S. Devaraju M. R. Vengatesan A. Ashok Kumar M. Alagar 《Journal of Sol-Gel Science and Technology》2011,60(1):33-40
New type of Polybenzoxazine–silica (PBZ–SiO2) hybrid nanocomposites was prepared through in situ sol–gel method. Benzoxazine was synthesized using bisphenol-A, trans-4-aminocyclohexanol hydrochloride and formaldehyde solution through Mannich condensation reaction and was characterized by
FT-IR, 1HNMR and 13CNMR spectroscopy. The methodology adopted in the present study involves to formation of hydrogen bond interaction between
the benzoxazine monomer and the silica matrix, followed by the ring opening polymerization of benzoxazine monomer through
thermal curing to obtain a red brown transparent PBZ–SiO2 hybrid. The formation of hybrid nanocomposites was confirmed by FT-IR. Thermal and morphological properties of the hybrid
materials were investigated by the differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), scanning electron
microscopy (SEM). The PBZ–SiO2 hybrids show improved thermal properties and glass transition (Tg) temperature. The nitrogen porosimetry study was carried
out to confirm the nanometer level integration of polybenzoxazine in the PBZ–SiO2 hybrid nanocomposites. 相似文献