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排序方式: 共有188条查询结果,搜索用时 296 毫秒
81.
C. Asbach H. Fissan B. Stahlmecke T. A. J. Kuhlbusch D. Y. H. Pui 《Journal of nanoparticle research》2009,11(1):101-109
Nanoparticle Surface Area Monitor (NSAM, TSI model 3550 and Aerotrak 9000) is an instrument designed to measure airborne surface
area concentrations that would deposit in the alveolar or tracheobronchial region of the lung. It was found that the instrument
can only be reliably used for the size range of nanoparticles between 20 and 100 nm. The upper size range can be extended
to 400 nm, where the minimum in the deposition curves occurs. While the fraction below 20 nm usually contributes only negligibly
to the total surface area and is therefore not critical, a preseparator is needed to remove all particles above 400 nm in
cases where the size distribution extends into the larger size range. Besides limitations in the particle size range, potential
implications of extreme concentrations up to the coagulation limit, particle material (density and composition) and particle
morphology are discussed. While concentration does not seem to pose any major constraints, the effect of different agglomerate
shapes still has to be further investigated. Particle material has a noticeable impact neither on particle charging in NSAM
nor on the deposition curves within the aforementioned size range, but particle hygroscopicity can cause the lung deposition
curves to change significantly which currently cannot be mimicked with the instrument. Besides limitations, possible extensions
are also discussed. It was found that the tendencies of the particle deposition curves of a reference worker for alveolar,
tracheobronchial, total and nasal depositions share the same tendencies in the 20–400 nm size range and that their ratios
are almost constant. This also seems to be the case for different individuals and under different breathing conditions. By
means of appropriate calibration factors NSAM can be used to deliver the lung deposited surface area concentrations in all
these regions, based on a single measurement. 相似文献
82.
Coherent transitions of charge carriers between the conduction and valence bands of a semiconductor medium are essential for the operation of a semiconductor laser. In this paper, we study how such interband coherence can be set up by an injection current and a coherent pump-field. In the absence of the pump-field, the injection current is the only source to establish the interband coherence in a semiconductor laser system. A laser threshold is obtained, which shows that a strongly coupled high-Q microcavity has a low threshold value. However, when an external pump-field serving as another mechanism to create the interband coherence is applied, the threshold value of the injection current can be lowered and it vanishes for sufficiently strong field. Besides, if the pump-field exceeds a threshold value, it is even possible to achieve a bistability in the inversionless region. Some fundamental macroscopic properties, including polarization, absorption and dispersion for the semicoductor system, are also obtained analytically. 相似文献
83.
84.
85.
Determination of the shape of a binary object by means of chosen initial phases and Sayre's equation
Pui Sum Yuen 《Optik》2014
The binary object treated is a square. We first use a set of initial phases to determine the symmetry of the object. The result shows a well-shaped image, and preserves symmetry of the object. We then use another set of initial phases. The result has gross shape of a square with approximately correct dimensions. Sayre's equation is applied to refine the gross shape. After iterations, the result shows an image which is close to a square with sharp boundary and has approximately correct dimensions. The charge densities of the image are approximately evenly distributed, scattering about the value of 1, and has no negative charge density. The shape of the binary object is obtained. The initial phases or the gross shape can be used as starting phases or starting envelope in other iterative algorithms. 相似文献
86.
Pui Tak Kan Marcelo M. Santos Zhouping Xin 《Communications in Mathematical Physics》1997,186(3):701-730
This paper concerns the initial boundary value problems for some systems of quasilinear hyperbolic conservation laws in the
space of bounded measurable functions. The main assumption is that the system under study admits a convex entropy extension.
It is proved that then any twicely differentiable entropy fluxes have traces on the boundary if the bounded solutions are
generated by either Godunov schemes or by suitable viscous approximations. Furthermore, in the case that the weak interior
solutions are generated by Godunov schemes, any Lipschitz continuous entropy fluxes corresponding to convex entropies have
traces on the boundary and the traces are bounded above by computable numerical boundary values. This in particular gives
a trace formula for the flux functions in terms of the numerical boundary data. We also investigate the formulation of boundary
conditions for systems of hyperbolic conservation laws. It is shown that
the set of expected boundary values derived from the viscous approximation contains the one derived in terms of the boundary
Riemann problems, and the converse is not true in general. The general theory is then applied to some specific examples. First,
several new facts are obtained for convex scalar conservation laws. For example, we give example which show that Godunov schemes
produce numerical boundary layers. It is shown that any continuous functions of density have traces on the boundary (instead
of only entropy fluxes). We also obtain interior and boundary regularity of the weak solutions for bounded measurable initial
and boundary data. A generalized Oleinik entropy condition is also obtained. Next, we prove the existence of a weak solution
to the initial-boundary value problem for a family of × quadratic system with a uniformly characteristic boundary condition.
Received: 23 July 1996 / Accepted: 28 October 1996 相似文献
87.
Pharmaceutical cocrystals have rapidly emerged as a new class of API solids with great promise and advantages. Much work has been focused on exploring the crystal engineering and design strategies that facilitate formation of cocrystals of APIs and ligands/cocrystal formers. However, fewer attempts have been made to understand the equilibrium phase behavior and phase transition kinetics of the cocrystallizing solutions. This limited knowledge on the solution physical chemistry often leads to difficulty in screening for potential molecular pairs of API and ligand that form cocrystals effectively. In this study, the long-time self-diffusivities measured using pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) are used to characterize the particle interactions in solutions for pharmaceutical cocrystallizing systems. For the pairs of API and ligand that produce cocrystals, the heteromeric attractions between API and ligand are found to be stronger than the homomeric attractions between API molecules and between ligand molecules, suggesting that an energetically favorable condition is induced for the formation of cocrystals. To the best of our knowledge, this is the first report of using the pair contribution of the self-diffusivity as a screening tool for cocrystal formation. 相似文献
88.
Ma Y Chiu PL Serrano A Ali SR Chen AM He H 《Journal of the American Chemical Society》2008,130(25):7921-7928
We have found that the polymerization process was 4,500 times faster when a self-doped polyaniline nanocomposite was fabricated using in situ polymerization in the presence of single-stranded DNA-dispersed and -functionalized single-walled carbon nanotubes (ssDNA-SWNTs). More importantly, the quality of the composite was significantly improved: fewer short oligomers were produced, and the self-doped polyaniline backbone had a longer conjugation length and existed in the more stable and conductive emeraldine state. The functionality of the boronic acid group in the composite and the highly improved electronic performance may lead to broad applications of the composite in flexible electronic devices. Blending of preformed polymer with carbon nanotubes is straightforward and widely used to fabricate nanocomposites. We demonstrate that this simple mixing approach might not fully and synergistically combine the merits of each individual component. Surprisingly, these advantages also cannot be obtained using in situ polymerization with preoxidized ssDNA-SWNTs, which is renowned as the "seed" method for production of conducting-polymer nanowires. The electronic structures of the carbon nanotubes and the monomer-nanotube interaction during polymerization greatly impact the kinetics of nanocomposite fabrication and the electronic performance of the resulting composites. 相似文献
89.
Complete asymmetric amplification of ethylenediammonium sulfate using an abrasion/grinding technique
Cheung PS Gagnon J Surprenant J Tao Y Xu H Cuccia LA 《Chemical communications (Cambridge, England)》2008,(8):987-989
Complete asymmetric amplification of ethylenediammonium sulfate was achieved under continuous dissolution/crystallization conditions using an abrasion/grinding method. 相似文献
90.