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91.
We start with a stochastic flow of diffeomorphisms of the space. Particles enter the space at random times and places. Each particle is carried by the flow for some random amount of time. We examine the point process formed by the particles at a fixed time, on the evolution of that point process as time varies, and on the equilibrium law of the point process. 相似文献
92.
The engineering of many modern electronic devices demands control over a crystal down to the thickness of a single layer of atoms—and future demands will be even more challenging. Such control is achieved by the method of crystal growth known as epitaxy, and that makes this method the subject of intense study. More than that, recent advances are revolutionizing our knowledge of how surfaces grow. In fact, growing surfaces show a beautifully rich variety of phenomena, many of which are only now beginning to be uncovered. In the past few years many surface imaging techniques have been used to give us a close look at how crystals grow—while they are growing. The purpose of this article will be to illustrate some of the ways real surfaces grow and change as revealed by some of the latest in situ microscopic imaging technologies.
It is often said that crystal growth is more of an art than a science. Here we will show that it is emphatically both. 相似文献
93.
Ryuhei Wakita Masanori Miyakoshi Yohji Nakatsuji Mitsuo Okahara 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):127-139
A series of noncyclic neutral ionophores has been synthesized by the reaction of oligoethylene glycol dihalides with 8-quinolinol. Complexation properties for alkali metal picrates were evaluated from solvent extraction and bulk liquid membrane transport experiments. Complexation profiles of the newly synthesized ionophores with a hexyl chain were similar to those of their homologues without the hexyl chain in the extraction experiments. Among them, the pentaethylene glycol derivatives showed the highest extraction efficiency and selectivity towards potassium ion. From the1H NMR spectra (400 MHz), the change in chemical shifts of the aromatic protons upon the addition of alkali metal thiocyanates suggested the existence of a stabilization effect which is caused by intramolecular stacking conformations between the quinoline rings during complexation. Aryl stacking interactions depend on the size of the cations and on the chain length of the oligoethylene glycol. The relationship between transport ability towards alkali metal cations and lipophilicity of these ionophores is also discussed. 相似文献
94.
M. Froese C. Champagne J. R. Crespo López-Urrutia S. Epp G. Gwinner A. Lapierre J. Pfister G. Sikler J. Ullrich J. Dilling 《Hyperfine Interactions》2006,173(1-3):85-92
The precision of atomic mass measurements in a Penning trap is directly proportional to the charge state q of the ion and,
hence, can be increased by using highly charged ions (HCI). For this reason, charge breeding with an electron beam ion trap
(EBIT) is employed at TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) on-line facility in Vancouver, Canada. By bombarding
the injected and trapped singly charged ions with an intense beam of electrons, the charge state of the ions is rapidly increased
inside the EBIT. To be compatible with the on-line requirements of short-lived isotopes, very high electron beam current densities
are needed. The TITAN EBIT includes a 6 Tesla superconducting magnet and is designed to have electron beam currents and energies
of up to 5 A and 60 keV, respectively. Once operational at full capacity, most species can be bred into a He-like configuration
within tens of ms. Subsequently, the HCI are extracted, pass a Wien filter to reduce isobaric contamination, are cooled, and
injected into a precision Penning trap for mass measurement. We will present the first results and current status of the TITAN
EBIT, which has recently been moved to TRIUMF after assembly and commissioning at the Max-Planck-Institute (MPI) for Nuclear
Physics in Heidelberg, Germany. 相似文献
95.
Kamil Walczak 《Central European Journal of Physics》2006,4(1):8-19
The rate-equation approach is used to describe sequential tunneling through a molecular junction in the Coulomb blockade regime.
Such device is composed of molecular quantum dot (with discrete energy levels) coupled with two metallic electrodes via potential
barriers. Based on this model, we calculate nonlinear transport characteristics (conductance-voltage and current-voltage dependences)
and compare them with the results obtained within a self-consistent field approach. It is shown that the shape of transport
characteristics is determined by the combined effect of the electronic structure of molecular quantum dots and by the Coulomb
blockade. In particular, the following phenomena are discussed in detail: the suppression of the current at higher voltages,
the charging-induced rectification effect, the charging-generated changes of conductance gap and the temperature-induced as
well as broadening-generated smoothing of current steps. 相似文献
96.
This paper presents detailed information on the experience gained during the attempts to model a set of transitional flows
due to boundary layer separation. These flows are developed on a flat plate with a semi-circular leading edge and they have
been coded by the ERCOFTAC Special Interest Group on Transition, as T3L flows. Different freestream velocities and turbulence
intensities configure these transitional flows and, by consequence, govern the transition mechanism, resulting in larger or
smaller transitional regions. The modeling of the T3L flows has been performed by adopting a low-Reynolds number second-moment
closure turbulence model. The results showed satisfactory agreement with the experimental measurements, although some difficulties
regarding successful convergence have been faced. The final conclusion is that turbulence modeling can present quite accurate
results for transitional flows without any additional use of ad-hoc modifications or additional equations based on various
transition models and intermittency transport modeling. 相似文献
97.
This paper is concerned with the spectral analysis of a one-velocity transport operator with Maxwell boundary condition in
L
1-space. After a detailed spectral analysis it is shown that the associated Cauchy problem is governed by a C
0-semigroup. Next, we discuss the irreducibility of the transport semigroup. In particular, we show that the transport semigroup
is irreducible. Finally, a spectral decomposition of the solutions into an asymptotic term and a transient one which will
be estimated for smooth initial data is given. 相似文献
98.
The study of bed-load transport is of great significance both in theory and in practice. This paper discusses the saltation
of bed-load solid grains in flowing water. Experiments and theoretic analysis have been made by means of high-speed photographing
and advanced data processing technique with a combined method based on mechanical and statistical theories. It indicates that
the saltation is the main form of the bed-load transport under ordinary flowing conditions. In the meantime, taking successive
saltation as the model of bed-load transport, systematic analysis has been made with regard to the kinematic properties and
mechanism of saltation. The statistical analysis shows that the probability density functions of the relative height and length
of saltation are in conformity with Γ-type distribution, while the probability density functions of the relative velocities
of saltation are in conformity with the Gaussian distribution.
The project supported by National Natural Science Foundation of China 相似文献
99.
Guido Momerency Karel Van Cauwenberghe Ernst A. De Bruijn Allan T. Van Oosterom Martin S. Highley Peter G. Harper 《Journal of separation science》1994,17(9):655-661
A method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC-MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2- and 3-dechloroethyliphosphamide, 4-ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3-oxazolidine-2-one. The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C18 adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield of ca 50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3-oxazolidine-2-one were isolated with high yield by liquid extraction with ethyl acetate at pH 10. Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per ml of original plasma. 相似文献
100.
The cross section of the 3s → 3p transition of sodium produced by electron impact has been calculated by performing a numerical integration of the coupled differential equations. The potential functions have been calculated exactly using the hydrogen‐like wave functions for the valence electron of the sodium with an effective charge adjusted to fit the experimental 3s → 3p line strength. The results compare very well with experimental data and with those obtained using more elaborate and sophisticated models. 相似文献