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1.
The critical exponent of degenerate parabolic systems 总被引:1,自引:0,他引:1
Yuan-Wei Qi H. A. Levine 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1993,44(2):249-265
The Cauchy problemu
t=u
+v
p
,v
t
=v
+u
q
is studied, wherex R
N
, 0 <t < and ,,p andq, are positive exponents. It is proved that ifp,q 1 and 1 <pq < 1 + 2 max(p + ,q + )/n then every nontrivial non-negative solution is not global in time; whereaspq > 1 + 2 max(p + , q + )/n then there exist both positive global solutions and non-global solutions. In addition, the decaying in time of solutions tou
t,=u
inR
n
× (0, ), an equation which occurs naturally in our study of above systems, is studied and solutions with the fastest decaying in time are constructed. 相似文献
2.
3.
Transmission Frequency Properties of Elastic Waves along a Hetero-Phononic Crystal Waveguide
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We investigate the propagation properties of hetero-phononic crystal waveguides by the improved eigen-mode matching theory, which can be used at same time to calculate both the transmission (reflection) coefficient and band structure. The numerical results show that the transmission frequency range is the same as the common range for two uniform waveguides composing the hereto-system, and the gap of any composite waveguide is also the gap of the hetero-phononic crystals waveguide. 相似文献
4.
Suzuki T Zhang YW Koyama T Sasaki DY Kurihara K 《Journal of the American Chemical Society》2006,128(47):15209-15214
The substrate-enzyme complexation of heptaprenyl diphosphate synthase was directly investigated using colloidal probe atomic force microscopy (AFM) and a quartz crystal microbalance (QCM) in order to obtain new insights into the molecular mechanism of the enzyme reaction. This enzyme is composed of two dissociable subunits that exhibit a catalytic activity only when they are associated together in the presence of a cofactor, Mg2+, and a substrate, farnesyl diphosphate (FPP). The QCM measurement revealed that FPP was preferentially bound to subunit II in the presence of Mg2+, while the AFM measurement showed that the adhesive force between the subunits was observed only in the presence of both Mg2+ and FPP. This is the first direct demonstration of the specific interaction involved in the enzyme reaction. The dependence of the Mg2+ concentration on the specific interaction between subunits I and II well agreed with that on the enzyme activity of heptaprenyl diphosphate synthase. This indicated that the observed adhesive forces were indeed involved in the catalytic reaction of this enzyme. On the basis of these results, we discussed the processes involved in the substrate-enzyme complexation. The first, the substrate FPP bound to subunit II using Mg2+, followed by the formation of the subunit I-FPP-Mg2+-subunit II complex. Our study showed a very useful methodology for examining the elemental processes of biological reactions such as an enzyme reaction. 相似文献
5.
Li-Xiang Han Yuan-Wei Yao Xin Zhang Fu-Gen Wu Hua-Feng Dong Zhong-Fei Mu Jing-bo Li 《Physics letters. A》2018,382(5):357-361
Here we present a design of a transmitted acoustic metasurface based on a single row of Helmholtz resonators with varying geometric parameters. The proposed metasurface can not only steer an acoustic beam as expected from the generalized Snell's law of refraction, but also exhibits various interesting properties and potential applications such as insulation of two quasi-intersecting transmitted sound waves, ultrasonic Bessel beam generator, frequency broadening effect of anomalous refraction and focusing. 相似文献
6.
7.
Ordered porous block copolymer films(PBCFs) have attracted much attention because of their potential applications in several fields. In this paper, we first reported a non-destructive, controllable, and efficient approach for preparation of β-cyclodextrin(β-CD)-functionalized PBCFs(β-CD-PBCFs). The key point of the approach is to incorporate β-CD units into the hydrophilic segment of amphiphilic block copolymers before the preparation of films. β-CD-PBCFs with structural integrity and controllable pore parameters were fabricated through combining of self-assembly and breath figure methods. And then, the effective adsorption capacity of β-CD-PBCFs toward Congo red was confirmed through UV-Vis spectroscopy and was found to be affected by β-CD content and solution p H values. Adsorption kinetic results showed that the adsorption behavior of β-CD-PBCFs was consistent with the pseudo-second-order kinetic model and the chemisorption mechanism. 相似文献
8.
Quantitative determination of ginsenoside Rh2 in rat biosamples by liquid chromatography electrospray ionization mass spectrometry 总被引:2,自引:0,他引:2
Gu Y Wang GJ Sun JG Jia YW Xie HT Wang W 《Analytical and bioanalytical chemistry》2006,386(7-8):2043-2053
Ginsenoside Rh2 is a “hot” natural compound with great potential as a new anti-cancer drug based on abundant pharmacological experiments.
However, no systemic pharmacokinetic study of Rh2 was reported because current analysis methods could not fully meet the requirements. Thus, we developed a simple LC/MS method
with highly improved sensitivities for the determination of Rh2 in rat plasma, bile, urine, feces and most tissues. The tissues and feces were firstly homogenized mechanically using buffer
and methanol as the media, respectively. Plasma, bile, urine and tissue homogenates were extracted with diethyl ether for
sample preparation. Feces homogenates were directly deproteinized with acetonitrile. The subsequent analysis procedures were
performed on a Shimadzu LCMS2010A system (electrospray ionization single quadrupole mass analyzer), with an ODS column (150 mm × 2.0-mm
i.d., 5 μm) plus a C18 guard column for separation and ammonium chloride (500 μmol) as mobile phase additive. The proportions
of mobile phase were changed timely according to gradient programs. Chlorinated adducts of molecular ions [M + Cl]− of Rh2 at m/z 657.35 and internal standard digitoxin at m/z 799.55 were monitored in selective ion monitoring mode of negative ions. The method was validated to be accurate, precise
and rugged with good linearity in all matrices, according to the FDA guidelines. The lower limits of quantitation in rat plasma,
urine and feces were 0.2, 0.2 and 20 ng/mL respectively. Stability studies were also performed, indicating that there were
no stability-related problems in the analytical procedure of Rh2. The proposed method was successfully applied to the preclinical pharmacokinetic research of Rh2 in rats, including plasma kinetics, tissue distribution and excretion studies. 相似文献
9.
Research on the thermal conduction in a single polymer chain is significant for the improvement of the thermal property of bulk polymer materials. We calculate the thermal conductivity of a single polyethylene (PE) chain by using both the Green-Kubo approach and a nonequilibrium molecular dynamics simulation method. The results suggest that the thermal conductivity of an individual polymer chain is very high although bulk PE is a thermal insulator, even divergent in our case. Moreover, the thermal conductivity of PE chains is observed to increase with the chain length. 相似文献
10.