WLAN话音面临功耗挑战

VoIP必定会给电话系统带来革命性的变化,这种技术通过电话实现了话音和数据互联的融合,从而不再需要单独的数据和话音电缆系统,它还提高了网络效率并降低了每次呼叫的成本.     

Electrosteric stability of styrene/acrylic acid copolymer latices under emulsion polymerization reaction conditions

Acrylic acid (AA) is used in many emulsion polymerization formulations to improve the colloidal stability during and after the production of latex products. Theoretically, the improved stability originates from electrostatic repulsion complemented with steric repulsion. The objective of this work was to study the contribution of AA to the colloidal stability of polystyrene and styrene/AA copolymer latices under simulated reaction conditions. The strength of electrostatic and steric repulsion forces as a function of the electrolyte concentration, pH, and temperature was investigated via coagulation experiments with monomer‐swollen latices in stirred tank reactors. Transmission electron microscopy pictures and dynamic light scattering measurements provided an understanding of the conditions and mechanisms leading to coagulation. The experiments demonstrated that the presence of surface‐bound carboxylic groups only improved the colloidal stability if the carboxylic groups were charged, that is, at a high pH. At a low pH, the copolymer latices were even less stable than the homopolymer latex, and this indicated that the addition of AA did not improve the colloidal stability of a growing polystyrene latex. With respect to emulsion polymerization process operations, insufficient mixing and a highly concentrated electrolyte feed were found to be sources of fouling and enhanced macroscopic coagulation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 726–732, 2005     

Genetics of Vocal Quality Characteristics in Monozygotic Twins: A Multiparameter Approach

The main purpose of this study was to determine the vocal quality characteristics among the 45 monozygotic cotwins (MT). As the performance of the voice is related to several genetically determined anatomical and physiological factors, the authors hypothesized that the vocal characteristics and the overall vocal quality by means of the Dysphonia Severity Index (DSI) will be identical in MT. An additional objective of this study was to determine whether sex and age influence vocal similarities in MT and to compare the voice characteristics of MT with the normative data of unrelated peers. As more environmental factors influence the aging of the voice, age-related differences were expected. No sex-related differences were expected. Subjective and objective assessment techniques determined the vocal quality. No significant differences were obtained, and most comparisons resulted in significant correlation coefficients. For the acoustic parameters jitter and shimmer only, no significant correlation coefficients could be obtained. It is clear that the perceptual voice characteristics, the laryngeal aerodynamic measurements of maximum phonation time (MPT), the vocal performances, and the overall vocal quality by means of the DSI are similar in MT. These vocal characteristics are not influenced either by the subjects' age or sex and are situated within the normative range of unrelated peers. To what extent other aspects (environment, anxiety, tension, etc) might play a role in the acoustical dimensions regarding frequency and amplitude perturbation, which were in the normal range, is a subject of further research.     

Logarithmic residues, generalized idempotents, and sums of idempotents in Banach algebras

In a commutative Banach algebraB the set of logarithmic residues (i.e., the elements that can be written as a contour integral of the logarithmic derivative of an analyticB-valued function), the set of generalized idempotents (i.e., the elements that are annihilated by a polynomial with non-negative integer simple zeros), and the set of sums of idempotents are all the same. Also, these (coinciding) sets consist of isolated points only and are closed under the operations of addition and multiplication. Counterexamples show that the commutativity condition onB is essential. The results extend to logarithmic residues of meromorphicB-valued functions.     

Voice over WLAN的技术挑战-耗电量

VoIP正对电话产生革命性的影响,这项技术将语音与数据联机整合至电话网络中,让用户不须为数据与语音系统分别布线,同时提高网络效率并降低通话成本.此外,我们亦正目睹无线局域网络(WLAN)的迅速成长,这种网络技术让使用者能以无线管道连上因特网,并透过网络存取点设备传输毅据.     

An Analytical Approach to Obtain the Interdeparture Time Characteristics in a Multistage VoIP Network

In this paper, we investigate the evolution of the interarrival and interdeparture times between voice packets when they are proceeding through a number of network nodes. We model the arrival process in a node as the superposition of a single tagged stream and an independent background process that aggregates the remaining traffic sources. Because we assume that the load of a single voice stream is very low compared to the load of the aggregate traffic, we can represent the tagged voice packets as markers (packets with size zero). We will establish an expression for the probability generating function (pgf) of the interdeparture time of the voice packets after one stage and use this interdeparture-time pgf as the pgf of the interarrival time of the voice packets in the next stage, in order to assess the evolution of the interarrival-time characteristics throughout the network.     

An indicator for Wiener-Hopf integral equations with invertible analytic symbol

For Wiener-Hopf integral equations with an operator or matrix valued kernel and with an invertible symbol which is analytic on the real line and at infinity an indicator is introduced. In general this indicator is a bounded linear operator, but when the kernel is matrix valued and the symbol is rational it is a (possibly non-square) matrix. From the indicator the invertibility properties and Fredholm characteristics of the integral equation can be read off. The class of Wiener-Hopf equations studied here is also described in terms of growth conditions on the derivatives of the kernel.     

Rings of integral quaternions

A quaternion order derived from an integral ternary quadratic form f = Σa_ijx_ix_j of discriminant d = 4 det (a_ij) is m-maximal if m is not divisible by any prime p such that p² | d, or p 6; d and c_p = 1. If R is m-maximal and m is a product p₁ … p_r of primes, then any primitive element α of R has unique right-divisor ideals of each norm p₁ … p_k (k = 1, …, r). This generalizes Lipschitz's ninety-year-old theorem. We characterize m-maximal orders, study their ideals, and show how the preceding result yields formulas for the number of representations of integers by certain quaternary quadratic forms.