Influence of excitation amplitude on the characteristics of nonlinear butyl rubber isolators

The purpose of this study is to explore the advantages and characteristics of nonlinear butyl rubber (type IIR) isolators in vibratory shear by comparison with linear isolators. It is known that the mechanical properties of viscoelastic materials exhibit significant frequency and temperature dependence, and in some cases, nonlinear dynamic behavior as well. Nonlinear characteristics in shear deformation are reflected in mechanical properties such as stiffness and damping. Furthermore, even when the excitation amplitude is small the response amplitude may often be large enough that nonlinearities cannot be ignored. The treatment involves developing phenomenological models of the effective storage modulus and effective loss factor of a rubber isolator material as a function of excitation amplitude. The transmissibility of a nonlinear viscoelastic isolator is compared with that of a linear isolator using an equivalent linear damping coefficient. Forced resonance vibration and impedance tests are used to characterize nonlinear parameters and to measure the normalized transmissibility. It is found that as the excitation amplitude of the nonlinear viscoelastic isolator increases, the response amplitude decreases and the transmissibility is improved over that of the linear isolator for excitation frequency that exceeds a particular value governed by the temperature and excitation amplitude. The method of multiple scales and numerical simulations are used to predict the response characteristics of the isolator based on the phenomenological modeling under different values of system parameters.     

Seven nonsynonymous SNPs in the gene encoding human deoxyribonuclease II may serve as a functional SNP potentially implicated in autoimmune dysfunction

Many nonsynonymous SNPs in the human DNase II gene (DNASE2), potentially relevant to autoimmunity in conditions such as rheumatoid arthritis, have been identified, but only limited population data are available and no studies have evaluated whether such SNPs are functional. Genotyping of all the 15 nonsynonymous human DNase II SNPs was performed in three ethnic groups including 16 different populations using the PCR‐restriction fragment length polymorphism technique. A series of constructs corresponding to each SNP was examined. Fifteen nonsynonymous SNPs in the gene, except for p.Val206Ile in a Korean population, exhibited a mono‐allelic distribution in all of the populations. On the basis of alterations in the activity levels resulting from the corresponding amino acid substitutions, four activity‐abolishing and five activity‐reducing SNPs were confirmed to be functional. The amino acid residues in activity‐abolishing SNPs were conserved in animal DNase II. All the nonsynonymous SNPs that affected the catalytic activity of human DNase II showed extremely low genetic heterogeneity. However, a minor allele of seven SNPs producing a loss‐of‐function or extremely low activity‐harboring variant could serve as a genetic risk factor for autoimmune dysfunction. These functional SNPs in DNASE2 may have clinical implications in relation to the prevalence of autoimmune diseases.     

农田土壤流失对三沙湾水环境的影响研究

应用美国通用土壤流失方程(USLE),计算了三沙湾周边地区农田土壤的侵蚀量,并用0.3的输沙系数计算出每年由农田流入三沙湾的泥沙量为12.29万t。每年随土壤侵蚀进入湾内的N、P、CODcr的量分别占海洋对各污染物环境容量的10.18%、9.84%和1.05%,根据计算结果分析评价了土壤流失对湾内水环境的影响程度。     

矩阵损失下一个参数子集的线性MINIMAX估计

考虑带多余参数的线性模型ＥＹ＝Ｘβ＋Ｚγ，Ｃｏｖ（Ｙ）＝σ＾２Ｖ。其中Ｖ是已知的非负定对称矩阵，在适当和假设下，我们得到了可估函数Ｓβ的所有线性ＭＩＮＩＭＡＸ估计。     

Mechanical and thermodynamic properties of infrared transparent low melting chalcogenide glass

The properties of infrared (IR) transparent chalcogenide glass Se₅₇I₂₀As₁₈Te₃Sb₂ have been studied for the first time by dynamic mechanical analysis (DMA). This glass demonstrates both high transparency in a broad IR band (1–12 μm) and a particularly low softening point (near 50 °C). It is known as one of the best adhesives intended for the binding of IR optics elements. The DMA method gives valuable information about the complex Young’s modulus of the glass in its softening region. In parallel with the study of mechanical properties of the glass the character of its glass transition process has been investigated. Our results of DMA were then compared with our thermodynamic data obtained by scanning calorimetry. The peak of mechanical losses in DMA appears to be situated considerably higher than the calorimetrically determined glass transition temperature.     

飘逝与渐悟——评《占有》中的两段爱情

A．S．拜厄特在小说《占有》中讲述了两段动人的爱情故事：其一为百年前维多利亚时期的男、女诗人艾什和拉摩特“飘逝”的爱情悲剧；其二为当代英国男、女学者罗兰和莫德“渐悟”的爱情喜剧。它们在小说中交叉前行，构成了小说的叙述主线。艾什、拉摩特的爱情是罗兰、莫德爱情成功的主要推动力量。两段爱情故事虽相隔百年历史，但都生动地阐释了爱情的伟大和不可或缺性，其主人公在爱情追求和对待爱情的态度等方面都表现出相似和不同之处。     

Hölder continuity in time for SG hyperbolic systems

We investigate well posedness of the Cauchy problem for SG hyperbolic systems with non-smooth coefficients with respect to time. By assuming the coefficients to be Hölder continuous we show that this low regularity has a considerable influence on the behavior at infinity of the solution as well as on its regularity. This leads to well posedness in suitable Gelfand-Shilov classes of functions on Rn. A simple example shows the sharpness of our results.     

Predicting Web Users' Next Access Based on Log Data

This article considers models that describe how people browse the Web. We restrict our attention to navigation patterns within a single site, and base our study on standard Web server access logs. Given a visitor's previous activities on the site, we propose models that predict their next page request. If the prediction is reasonably accurate, we might consider “prefetching” the page before the visitor requests it. A more conservative use for such predictions would be to simply update the freshness records in a proxy or network cache, eliminating unnecessary If-Modified-Since requests. Using data from the Web site for the Computing and Mathematical Sciences Research Division of Lucent Technologies (cm.bell-labs.com) we first evaluate the predictive performance of low-order Markov models. We next consider mixtures of first-order Markov models, achieving a kind of clustering of Web pages in the site. This approach is shown to perform well, while significantly reducing the space required to store the model. Finally, we explore a Bayesian approach using a Dirichlet prior on the collection of links available to a user at each stage in their travels through the site. We show that the posterior probabilities derived under this model are fairly close to the cross-validation estimates of the probability of success.     

On the loss process in a batch arrival queue

In this paper, we investigate the loss process in a finite-buffer queue with batch arrivals and total rejection discipline. In such a model, if the buffer has insufficient capacity to accept all the customers included in an arriving batch, the whole batch is blocked and lost. This scheme is especially useful in performance evaluation of buffering processes in IP (internet protocol) networks. The main result of this paper is a closed-form formula for the joint distribution of the length of the first lost series of batches and the time of the first loss. Moreover, the limiting distribution (as the buffer size grows to infinity) is shown.     

Parametric oscillator based on a single-layer resonant metamaterial

We perform numerical simulations demonstrating parametric generation and oscillation processes in a single-layer of metamaterial composed of split ring resonators (SRRs). In general, a parametric resonance is achieved by introducing a time-modulation of one of the energy-storing parameters of a resonant system. An individual SRR is a resonant system that can be modeled as an RLC-circuit inductively coupled to an applied time-varying magnetic field. The relatively simple circuit model can be employed to establish the range of parameters providing the growth of parametric oscillations within the SRR medium. We relate the numerically predicted circuit parameters that ensure the buildup of parametric oscillations to those parameters expected to be available in a modified SRR medium, in which lumped element varactors integrated into the SRRs are used as modulable capacitance elements.