Stress bounds for bars in torsion

Upper bounds for the maximum shear stress in the St. Venant torsion problem are derived with the aid of the theory of subharmonic functions. The main result is a bound that is determined in a simple manner by the magnitude of the applied twisting moment and two parameters peculiar to the cross section: the radius of the largest circle contained in it and the minimum curvature of the curve that bounds it.

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Zusammenfassung Mit Hilfe subharmonischer Funktionen werden obere Grenzen in dem Torsionsproblem von St. Venant erhalten. Das Hauptergebnis ist eine Grenze, die auf einfache Weise vom Drehmoment und zwei nur vom Querschnitt abhängigen Parametern bestimmt ist, und zwar von dem Radius des grössten eingeschriebenen Kreises und von der Minimalkrümmung der Begrenzungskurve des Querschnitts.

     

Discontinuous buffer systems operative at pH 2.5 - 11.0, 0 degrees C and 25 degrees C, available on the Internet

This communication is an announcement of the availability on the Internet of a computer output of discontinuous buffer systems operative at pH 2.5-11.0, 0 degrees C and 25 degrees C, generated by the theory and program of T. M. Jovin. The output and instructions for its use can be accessed under http://www.buffers.nichd.nih.gov.     

Spontaneous macroscopic spin polarization in independent spinor Bose-Einstein condensates

We present experimental evidence for the spontaneous formation of a macroscopic spin polarization in overlapping regions of two independent Bose-Einstein condensates produced in different hyperfine states of 87Rb. The condensates are independent in the sense that we do not explicitly introduce a relative phase between them. A single "spin-tip" pulse maps the transverse spin polarization into longitudinal spin polarization, and the atomic density distributions are measured with a Stern-Gerlach imaging method. The resulting matter-wave interference patterns are anticorrelated.     

Programmable modification of cell adhesion and zeta potential in silica microchips

Spatial patterning of thin polyacrylamide films bonded to self-assembled monolayers on silica microchannels is described as a means for manipulating cell-adhesion and electroosmotic properties in microchips. Streaming potential measurements indicate that the zeta potential is reduced by at least two orders of magnitude at biological pH, and the adhesion of several kinds of cells is reduced by 80-100%. Results are shown for cover slides and in wet-etched silica microchannels. Because the polyacrylamide film is thin and transparent, this film is consistent with optical manipulation of cells and detection of cell contents. The spatial patterning technique is straightforward and has the potential to aid on-chip analysis of single adherent cells.     

Discontinuous Galerkin finite element methods for linear elasticity and quasistatic linear viscoelasticity

Summary. We consider a finite-element-in-space, and quadrature-in-time-discretization of a compressible linear quasistatic viscoelasticity problem. The spatial discretization uses a discontinous Galerkin finite element method based on polynomials of degree r—termed DG(r)—and the time discretization uses a trapezoidal-rectangle rule approximation to the Volterra (history) integral. Both semi- and fully-discrete a priori error estimates are derived without recourse to Gronwall's inequality, and therefore the error bounds do not show exponential growth in time. Moreover, the convergence rates are optimal in both h and r providing that the finite element space contains a globally continuous interpolant to the exact solution (e.g. when using the standard ^k polynomial basis on simplicies, or tensor product polynomials, ^k, on quadrilaterals). When this is not the case (e.g. using ^k on quadri-laterals) the convergence rate is suboptimal in r but remains optimal in h. We also consider a reduction of the problem to standard linear elasticity where similarly optimal a priori error estimates are derived for the DG(r) approximation. Mathematics Subject Classification (2000):65N36Shaw and Whiteman would like to acknowledge the support of the US Army Research Office, Grant #DAAD19-00-1-0421, and the UK EPSRC, Grant #GR/R10844/01. Whiteman would also like to acknowledge support from TICAM in the form of Visiting Research Fellowships.     

Localization of multiple sound sources with two microphones

This paper presents a two-microphone technique for localization of multiple sound sources. Its fundamental structure is adopted from a binaural signal-processing scheme employed in biological systems for the localization of sources using interaural time differences (ITD). The two input signals are transformed to the frequency domain and analyzed for coincidences along left/right-channel delay-line pairs. The coincidence information is enhanced by a nonlinear operation followed by a temporal integration. The azimuths of the sound sources are estimated by integrating the coincidence locations across the broadband of frequencies in speech signals (the "direct" method). Further improvement is achieved by using a novel "stencil" filter pattern recognition procedure. This includes coincidences due to phase delays of greater than 2pi, which are generally regarded as ambiguous information. It is demonstrated that the stencil method can greatly enhance localization of lateral sources over the direct method. Also discussed and analyzed are two limitations involved in both methods, namely missed and artifactual sound sources. Anechoic chamber tests as well as computer simulation experiments showed that the signal-processing system generally worked well in detecting the spatial azimuths of four or six simultaneously competing sound sources.     

荞麦花多糖的提取及含量测定

采用热水提取、乙醇沉淀的方法从荞麦花中提取出了水溶性多糖,采用硫酸-苯酚法在波长为497nm处进行了糖含量的测定,求得其校准曲线的回归方程为y=0.00508x 0.0294,相关系数为r=0.9978.平均回收率为99%-103%,RSD为0.74%.结果显示:荞麦花多糖的产率为2.5%.糖含量为41.63%.     

分光光度法测定蒙药中痕量铅

采用双硫腙显色分光光度法测定蒙药中痕量铅,该方法具有简单、快速、灵敏等特点,用以测定蒙药中的痕量铅,获得了满意的结果.该方法线性范围为0.00-0.40μg/mL Pb2 ,相关系数0.9993.回收率95%-ll0%.     

航空胶片冲洗机直流电机调速控制系统设计

针对航空胶片冲洗机控制困难表现其电机负载不均匀，低速运行情况下电机震动剧烈．研制了专用的反馈控制系统．以双89C51单片机为核心组成控制电路，编写了系统操作程序和数字PID控制程序．对PID参量对控制系统稳定性的影响进行了分析，得出适应于本系统的PID控制规律，并经过大量的试验，获得了能使各档速度稳定运行下的PID控制参量．实践表明，该控制系统运行稳定可靠，低速控制准确度在3％以内，中高速准确度达到1％．     

Gravitationally squeezed light

Normally, pure states of coherent light have equal uncertainties for pairs of conjugate variables. In recent years, however, it has become possible to produce and detect light in which fluctuations of one of the quadrature components are suppressed below the corresponding flutuations of a coherent state. Such radiation is said to be in a squeezed state. We explore the possibility that a strong gravitational field can produce a squeezed state of light. Such squeezing does in fact occur, and we derive an expression for the resulting uncertainties in a high frequency or long time limit. These results comprise a new, testable prediction of general relativity.