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211.
When the processive motor protein kinesin walks along the biopolymer microtubule it can occasionally make a backward step.
Recent single molecule experiments on moving kinesin have revealed that the forward-to-backward step ratio decreases exponentially
with the load force. Carter and Cross (Nature 435, 308-312, 2005) found that this ratio tightly followed 802 × exp[−0.95F], where F is the load force in piconewtons. A straightforward analysis of a Brownian step leads to L/(2k
B
T) as the factor in front of the load force, where L is the 8 nm stepsize, k
B
is the Boltzmann constant, and T is the temperature. The factor L/(2k
B
T) does indeed equal 0.95 pN−1. The same analysis shows how the 802 prefactor derives from the power stroke energy G as exp[G/(2k
B
T)]. There are indications that the power stroke derives from the entropically driven coiling of the 30 amino acid neck linker
that connects the two kinesin heads. This idea is examined and consequences are deduced. 相似文献
212.
213.
Gravimetry experiments in a well-controlled environment have been performed to investigate aging for a glassy PMMA/toluene
film. The temperature is constant and the control parameter is the solvent vapor pressure above the film (i.e. the activity). Several experimental protocols have been used, starting from a high activity where the film is swollen and
rubbery and then aging the film at different activities below the glass transition. Desorption and resorption curves have
been compared for the different protocols, in particular in terms of the softening time, i.e. the time needed by the sample
to recover an equilibrium state at high activity. Non-trivial behaviors have been observed, especially at small activities
(deep quench). A model is proposed, extending the Leibler-Sekimoto approach to take into account the structural relaxation
in the glassy state, using the Tool formalism. This model well captures some of the observed phenomena, but fails in describing
the specific kinetics observed when aging is followed by a short but deep quench. 相似文献
214.
G. Mazzarella 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(1):61-66
We study mixtures of spinless bosons and not spin-polarized
fermions loaded in two dimensional optical lattices. We approach the problem of
the ground state stability within the framework of the linear response theory; by the mean of an
iterative procedure, we are able to obtain a relation for the dependence of boson-boson effective interaction on the absolute
temperature of the sample.
Proceeding from such a formula, we write down analytical expressions for
supersolid (SS) and phase separation (PS) transition temperatures, and plot the phase diagrams. 相似文献
215.
Karine Chesnel Joshua J. Turner Mark Pfeifer Stephen D. Kevan 《Applied Physics A: Materials Science & Processing》2008,92(3):431-437
We motivate the use of coherent soft X-ray beams to study materials that exhibit complex nanoscale behaviors. A new beamline
and magnetic scattering end station that has been constructed and commissioned at the ALS will be described. Finally, we present
some initial results that indicate the performance of the beamline.
K. Chesnel now at Department of Physics, Brigham Young University, Provo, Utah, USA.
J.J. Turner now at Department of Physics, Stony Brook University, Stony Brook, New York, USA.
M. Pfeifer now at School of Physics La Trobe University, Melbourne, Australia. 相似文献
216.
Xinzheng Zhang Jingmin Zhang Li Chen Jun Xu Liping You Dapeng Yu 《Applied Physics A: Materials Science & Processing》2008,92(3):669-672
In order to well understand the growth mechanism of the diverse morphology of the ZnO nanostructures, in situ analysis of
the formation of different ZnO nanostructures, such as nanowires, nanocombs, and nanosheets, has been conducted in an environmental
scanning electron microscope (ESEM). It is found that both nanocombs and nanosheets grew in two-stage heating processes on
parent nanowires. The difference is that the nanocombs were synthesized in extremely high pressure of zinc vapor via a self-catalyzed
vapor-liquid-solid process, while the ZnO nanosheets were grown in relatively low pressure of zinc vapor. All the growth processes
were revealed in real time imaging. It is demonstrated that the change in the growth environments can influence the thickness
of the ZnO polycrystalline surface of the zinc powder, which alters the pressure of the zinc vapor and in turn determines
the morphology of the final nanostructures. 相似文献
217.
Teik-Cheng Lim 《Czechoslovak Journal of Physics》2004,54(9):947-963
Relationship among interatomic potential functions can be useful in shedding insight on the extent of similarity, and in obtaining
a potential function from parameters of another potential function. The 2-body portion of the Biswas-Hamann (BH) and the Kaxiras-Pandey
(KP) potential functions are related by equating both functions, as well as their corresponding derivatives up to the third
order at the equilibrium bond length. Validity of the parametric relationship is verified by plotting the loose form of the
2-body BH potential in terms of KP parameters and comparing it with the KP potential function. The parametric relationships
developed herein are then compared with those that concern other potential functions, with particular emphasis on the scaling
factors. 相似文献
218.
V. V. Rubish V. Yu. Lazur O. K. Reity S. Chalupka M. Salak 《Czechoslovak Journal of Physics》2004,54(9):897-919
The WKB approximation is developed for the Dirac equation with the spherically symmetrical vector and scalar potentials. The
relativistic wavefunctions are constructed, new quantization rule containing the spin-orbital interaction is obtained. For
spherically symmetrical model of the Stark effect the quasi-classical spectrum of relativistic hydrogen-like atom is calculated.
Application of the WKB method to the mass spectrum of the hydrogen-like quark systems was done. 相似文献
219.
The temperature dependence of photoluminescence in Europium tris[3-(trifluoro-methylhydroxymethylene)-(+)-camphorate] (EuTFC) embedded in polymer films has been examined from 40 K down to 4.2 K with the goal of preparing sensor films for low-temperature thermal imaging. The behavior of EuTFC showed significant difference when based on polystyrene compared to poly(n-alkyl methacrylate)s. In poly(n-alkyl methacrylate)s prepared by standard methods for imaging applications, the photoluminescence is fully saturated below 30 K, whereas in polystyrene films there is a strong temperature dependence even down to 4.2 K. By optimizing the preparation procedure for films made of poly(butyl methacrylate) (PBMA) and poly(methyl methacrylate), also these polymers became very sensitive down to liquid helium temperature. The maximum temperature sensitivity of EuTFC in PBMA is found to be 1.0%/K at 4.2 K. The problem of delamination and cracking of the polymer film at cryogenic temperature is also avoided by the special preparation method. 相似文献
220.
A new method to determine tropisetron hydrochloride with l-tryptophan in the medium with pH=9.0 was studied, which is based on the fluorescence quenching effect of tropisetron hydrochloride on l-tryptophan. The fluorescence quenching mechanism and various factors influencing fluorescence quenching were discussed. Under the optimum conditions, the linear range and detection limit were 0.03-12.0 and 0.01 μg/mL (correlation coefficient r=0.9970), respectively. The calibration curve equation was ΔF=6.17+12.56 C (μg/mL). RSD was 3.4% (c=4.0 μg/mL, n=5); the detection limit estimated (S/N=3) was 0.01 μg/mL. The proposed method had been successfully applied to determine tropisetron hydrochloride in real samples and the obtained results were in good agreement with the results of the official method. 相似文献