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31.
If the set of spreading models of a Banach space is countable (up to equivalence), then it cannot contain a strictly increasing infinite chain of spreading models generated by normalized weakly null sequences. Moreover, such a space must have a spreading model which is `close' to or for some .
32.
Esa Järvenpää Maarit Järvenpää Antti Käenmäki Tapio Rajala Sari Rogovin Ville Suomala 《Mathematische Zeitschrift》2010,266(1):83-105
Let X be a metric measure space with an s-regular measure μ. We prove that if A ì X{A\subset X} is r{\varrho} -porous, then dimp(A) £ s-crs{{\rm {dim}_p}(A)\le s-c\varrho^s} where dimp is the packing dimension and c is a positive constant which depends on s and the structure constants of μ. This is an analogue of a well known asymptotically sharp result in Euclidean spaces. We illustrate by an example that the
corresponding result is not valid if μ is a doubling measure. However, in the doubling case we find a fixed N ì X{N\subset X} with μ(N) = 0 such that
dimp(A) £ dimp(X)-c(log\tfrac1r)-1rt{{\rm {dim}_p}(A)\le{\rm {dim}_p}(X)-c(\log \tfrac1\varrho)^{-1}\varrho^t} for all r{\varrho} -porous sets A ì X\ N{A \subset X{\setminus} N} . Here c and t are constants which depend on the structure constant of μ. Finally, we characterize uniformly porous sets in complete s-regular metric spaces in terms of regular sets by verifying that A is uniformly porous if and only if there is t < s and a t-regular set F such that A ì F{A\subset F} . 相似文献
33.
Branko Sarić 《Czechoslovak Mathematical Journal》2010,60(4):1043-1048
Let [a, b] be an interval in ℝ Rand let F be a real valued function defined at the endpoints of [a, b] and with a certain number of discontinuities within [a, b]. Assuming F to be differentiable on a set [a, b] | E to the derivative f, where E is a subset of [a, b] at whose points F can take values ±∞ or not be defined at all, we adopt the convention that F and f are equal to 0 at all points of E and show that KH-vt ∝
a
b
f = F(b) − F(a), where KH-vt denotes the total value of the Kurzweil-Henstock integral. The paper ends with a few examples that illustrate the theory. 相似文献
34.
A novel speech communications system using a modulated laser beam has been developed for short-range applications in which
high directionality is an exploitable feature. Although it was designed for certain underwater applications, such as speech
communications between divers or between a diver and the surface, it may equally be used for air applications. With some modification
it could be used for secure diver-to-diver communications in the situation where untethered divers are swimming close together
and do not want their conversations monitored by intruders. Unlike underwater acoustic communications, where the transmitted
speech may be received at ranges of hundreds of metres omnidirectionally, a laser communication link is very difficult to
intercept and also obviates the need for cables that become snagged or broken. Further applications include the transmission
of speech and data, including the short message service (SMS), from a fixed installation such as a sea-bed habitat; and data
transmission to and from an autonomous underwater vehicle (AUV), particularly during docking manoeuvres. The performance of
the system has been assessed subjectively by listening tests, which revealed that the speech was intelligible, although of
poor quality due to the speech algorithm used.
PACS 42.55.Px; 42.60.By; 42.62.-b 相似文献
35.
Journal of Mathematical Chemistry - A new implicit-explicit local differential transform method (IELDTM) is derived here for time integration of the nonlinear (2?+?1)-dimensional... 相似文献
36.
Jani P. J. Turunen Tapani Venäläinen Sari Suvanto Tuula T. Pakkanen 《Journal of polymer science. Part A, Polymer chemistry》2007,45(17):4002-4012
Mesoporous aluminas with average pore sizes of 4.3–7.8 nm were prepared by anodization of an aluminum film (AAO), and by a sol–gel templating method (TPL). In addition to a commercial alumina and sulfated TPL, the aluminas were used as supports for cyclopentadienyl zirconocene dichloride (Cp2ZrCl2) and trimethyl(η5‐pentamethylcyclopentadienyl)zirconium (Cp*ZrMe3) and tested in the polymerization of ethylene. The metallocenes supported on the alumina prepared with the templating method and its sulfated modification exhibited polymerization activities of 440 and 350 kgPE/(molZr × h × bar), respectively, comparable to that obtained with silica‐supported metallocenes (390 kgPE/(molZr × h × bar)). The acid site distribution of the aluminas was studied with FTIR and temperature programmed desorption (TPD) of pyridine, and also the amount of medium and strong acid sites was determined gravimetrically from the adsorption of pyridine. Relative to the surface area, AAO with the highest amount of acid sites (2.10 μmolpy/m) adsorbed Cp2ZrCl2 and Cp*ZrMe3 the most. Study of the polymers' morphology with a scanning electron microscope revealed polyethylene nanofibers in all the polymer samples, also in those obtained from the reference polymerizations with homogeneous Cp2ZrCl2 and Cp*ZrMe3. This finding suggests that a catalyst support with a tubular pore structure is not a prerequisite for the formation of polymer nanofibers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4002–4012, 2007 相似文献
37.
Breathing noise and bubble noise are the main factors affecting the subjective quality of through-water speech signals in communications between divers wearing full-face masks or aural-nasal masks. Only breathing noise is considered here, which can be gated out by applying a combination of zero-crossing detection and energy measurements to noisy speech signals above predetermined threshold values. The signals are picked up by a microphone placed close to the diver's mouth in the air cavity of the mask. Results were obtained during diving trials with four different types of masks. 相似文献
38.
Munetaka Takeuchi Yasuo Kameda Yasuhiro Umebayashi Sari Ogawa Takaaki Sonoda Shin-ichi Ishiguro Miho Fujita Mitsuru Sano 《Journal of Molecular Liquids》2009,148(2-3):99-108
Self-diffusion coefficients of Li+ DLi+, PF6− DPF6− and solvent propylene carbonate (PC) DPC in LiPF6−PC solutions were determined at 298 K by the pulse gradient spin echo (PGSE) NMR technique over the salt concentration range of 0.1–3.0 M (M = mol dm– 3). The order of the diffusion coefficients was found to be DLi+ < DPF6− < DPC over the concentration range examined, and they were monotonically decreased with increasing the salt concentration. Haven ratio Λ/ΛNMR, where Λ and ΛNMR represent the ionic conductivity measured electrochemically and that estimated via the Nernst-Einstein equation using the diffusion coefficient, respectively, was evaluated as the measure of the ion–ion interaction in the LiPF6–PC solutions. Though Λ/ΛNMR values for LiPF6-solutions decrease with increasing the salt concentration, they were greater than those for LiBF4–PC solutions over the whole concentration range examined, which indicates that the ion pair formation ability of PF6– ion is weaker than that of the BF4– ion. The smaller value of the ionic conductivity for the highly concentrated LiPF6–PC solution (above 2.0 M) than that of the LiBF4-solutions can be attributed to the more rapidly increased viscosity relative to the LiBF4-solution. Classic molecular dynamics (MD) simulations for the respective LiPF6 and LiBF4-solution of 0.5 and 1.0 M were also carried out based on the effective pair potentials. Diffusion coefficients, ionic conductivity and Haven ratio for these solutions were calculated from MD trajectories, and they qualitatively agree with those evaluated by experiments. Pair correlation functions gLiO(r) (for Li+–O (PC) pair) and gLiPF6(r) (for Li+–PF6– pair) or gLiBF4(r) (for Li+–BF4– pair) revealed that the lithium ion weakly forms the contact ion pairs with PF6–, whilst strongly with BF4–, which supports the present experimental results. Moreover, the simulation results show that both anions in the contact ion pairs predominantly take the monodentate form, which is in contrast to the multidentate coordination predicted by ab initio calculation in gas phase. 相似文献
39.
In this study, we have investigated theoretically the binding energies of shallow donor impurities in modulation-doped GaAs/Al0.33Ga0.67As double quantum wells (DQWs) under an electric field which is applied along the growth direction for different doping concentrations as a function of the impurity position. The electronic structure of modulation-doped DQWs under an electric field has been investigated by using a self-consistent calculation in the effective-mass approximation. The results obtained show that the carrier density and the depth of the quantum wells in semiconductors may be tuned by changing the doping concentration, the electric field and the structure parameters such as the well and barrier widths. This tunability gives a possibility of use in many electronic and optical devices. 相似文献
40.
The diamagnetic susceptibility of a hydrogenic donor placed in Si, Ge and GaAs quantum wells with infinite confinement potential which have different effective mass anisotropy parameters (γ=m⊥/m∥) has been investigated as a function of the well sizes. The binding energies of the donor have also been computed using a trial wave function with two parameters in the framework of the effective mass approximation. It has been observed that the diamagnetic susceptibility of the donor in the anisotropic materials converges rapidly to the bulk limit as the well size increases. 相似文献