Shape of a ponytail and the statistical physics of hair fiber bundles

A general continuum theory for the distribution of hairs in a bundle is developed, treating individual fibers as elastic filaments with random intrinsic curvatures. Applying this formalism to the iconic problem of the ponytail, the combined effects of bending elasticity, gravity, and orientational disorder are recast as a differential equation for the envelope of the bundle, in which the compressibility enters through an "equation of state." From this, we identify the balance of forces in various regions of the ponytail, extract a remarkably simple equation of state from laboratory measurements of human ponytails, and relate the pressure to the measured random curvatures of individual hairs.     

Recombination emissions and spectral blueshift of pump radiation from ultrafast laser induced plasma in a planar water microjet

We report spectroscopic investigations of an ultrafast laser induced plasma generated in a planar water microjet. Plasma recombination emissions along with the spectral blueshift and broadening of the pump laser pulse contribute to the total emission. The laser pulses are of 100 fs duration, and the incident intensity is around 10¹⁵ W/cm². The dominant mechanisms leading to plasma formation are optical tunnel ionization and collisional ionization. Spectrally resolved polarization measurements show that the high frequency region of the emission is unpolarized whereas the low frequency region is polarized. Results indicate that at lower input intensities the emission arises mainly from plasma recombinations, which is accompanied by a weak blueshift of the incident laser pulse. At higher input intensities strong recombination emissions are seen, along with a broadening and asymmetric spectral blueshift of the pump laser pulse. From the nature of the blueshifted laser pulse it is possible to deduce whether the rate of change of free electron density is a constant or variable within the pulse lifetime. Two input laser intensity regimes, in which collisional and tunnel ionizations are dominant respectively, have been thus identified.     

阳加速器水传输线D-dot的设计、标定和实验

应用D-dot探测器进行了阳加速器水传输线电压测量,利用探头与高压电极之间的结构电容获得脉冲电压的微分信号,通过RC积分取得电压信号。利用Pspice软件的瞬态分析功能模拟结合实验结果估算了探测器的杂散参数,进行了幅频响应特性分析;运用频响分析解释了测试结果。在加速器低电压短路实验状态下,用电阻分压器对其进行了在线标定。测量结果表明D-dot探测器获取了正确的电压波形,且工作稳定可靠。     

阳加速器水传输线D-dot的设计、标定和实验

 应用D-dot探测器进行了阳加速器水传输线电压测量,利用探头与高压电极之间的结构电容获得脉冲电压的微分信号,通过RC积分取得电压信号。利用Pspice软件的瞬态分析功能模拟结合实验结果估算了探测器的杂散参数,进行了幅频响应特性分析;运用频响分析解释了测试结果。在加速器低电压短路实验状态下,用电阻分压器对其进行了在线标定。测量结果表明D-dot探测器获取了正确的电压波形,且工作稳定可靠。     

惯性约束聚变软X射线在线标定系统概念设计

长期以来,惯性约束聚变（ICF）研究软X射线诊断科学仪器设备的元器件标定工作主要依赖同步辐射光源X射线辐射计量站进行。该类装置通常与用于开展ICF研究的大型激光装置分处两地,难以满足ICF研究软X射线元器件实时实地的标定应用需求。另外,由于同步辐射和ICF激光等离子体产生的X射线辐射特性存在较大差异,同步辐射计量站的标定结果事实上也不能完全反映元器件在ICF实验应用中的计量响应特性。本文首先介绍一种基于单光学元件的软X射线紧凑型无谐波光源单色化技术,以此为基础提出研制基于ICF激光等离子体X射线源的同源、同几何位形、双束比较校准的多能量通道光源单色化系统,用于ICF应用软X射线元器件的在线标定。新系统一方面可望满足ICF软X射线元器件实时实地的标定应用需求;另一方面,其提供的标定光束的技术特征将最大可能地接近ICF激光等离子体X射线辐射本身。配备相应的X射线二极管（XRD）和标准探测器之后,该系统将形成一套具有在线自校准功能的新型多通道δ能量响应软X射线能谱仪。     

Error analysis and optimal design of polarization calibration unit for solar telescope

Polarization calibration unit(PCU) has become an indispensable element for solar telescopes to remove the instrumental polarization; the polarimetric accuracy of calibration depends strongly on the properties of PCU. In the paper, we analyze the measurement errors induced by PCU based on polarized light theory and find that the imperfections of the waveplate generate the main calibration errors. An optimized calibration method is proposed to avoid the effects from waveplate imperfections, and a numerical simulation is given to evaluate the polarization accuracy by analyzing the relation between calibration error and intensity instability. The work is very important for solar telescopes with high polarization precision up to 10~(-4) I_c.     

Visualization of penetration of a high-speed focused microjet into gel and animal skin

Journal of Visualization - Realization of a needle-free drug delivery device can solve needle-caused problems. Recently, attention has been given to the use of a focused liquid jet instead of the...     

Acoustical, sensory, and psychological research data and procedures for their use in predicting effects of environmental noises

A demonstration field-research study reveals that aircraft noise measured at two one-story houses is approximately 9 dB less attenuated from measured outdoor levels than is street traffic noise, and, found in other studies, approximately 14 dB less than railway noise. Comparable differences are found between these noises from the application of basic acoustical formulas for quantifying attenuations that occur on site of one- and two-story houses. Reasonably consistent with those findings are results from attitude surveys showing that daily exposure levels of aircraft must be approximately 8 dB less than levels of street traffic noise, and approximately 13 dB less than levels of railway noise to be perceived as an equal cause of annoyance and related adverse effects. However, USA government guidelines recommend that equal exposure levels of noise measured outdoors from vehicles of transportation should be considered as being equally annoying. Changes in present USA noise-measurement procedures and noise-control guidelines are proposed that provide more accurate predictions of annoyance, related adverse effects, and criteria for setting "tolerable" limits of noise exposure in residential areas. Key acoustical and psycho-acoustical principles and data pertaining to predicting correlations between dosages of environmental noises and its effects on people and land noise zoning in residential communities are examined.     

Noise level, inner hair cell damage, audiometric features, and equal-energy hypothesis

Rabbits were exposed to 2- to 7-kHz noise either for a short duration at a high sound-pressure level (15 or 30 min at 115 dB SPL), or a long duration at a low level (512 h at 85 dB SPL). The high-level exposure produced a hearing loss in the frequency range 2-6 kHz, whereas the low-level exposure gave maximum hearing loss at 12-20 kHz. The 115-dB exposure caused significantly more damage to inner hair cells than the 85-dB exposure. The implications of the present results for evaluating audiograms, equal-energy hypothesis, risk criteria, and subjective auditory features are pointed out.     

LES-based evaluation of a microjet noise reduction concept in static and flight conditions

The Large-Eddy Simulation (LES) numerical system established since 2002 for jet-noise computation is first evaluated in terms of recent gains in accuracy with increased computer resources, and is then used to explore the relatively new “microjet” noise-reduction concept (injection of high-pressure microjets in the vicinity of the main jet nozzle exit), which currently attracts attention in the aeroacoustic community. The simulations, which are carried out with an emulation of the microjets by specially designed distributed sources of mass, momentum, and energy in the governing equations, are found to capture the essential features of the flow/turbulence and the far-field noise alteration by the microjets observed in experiments, and to reveal the subtle flow features responsible for the effect of injection on noise. They also confirm the experimental observation that in static conditions microjets provide a noise reduction comparable with that from chevrons in the low-frequency range, and probably have a less pronounced high-frequency penalty. This positive evaluation of the microjets concept is, however, mitigated by the far less favorable results of simulations in flight conditions, which were never studied experimentally. The latter results, which are awaiting an experimental verification, make a practical use of the concept in its current form rather unlikely.     

The dynamic range of inner hair cell and organ of Corti responses

Inner hair cell (IHC) and organ of Corti (OC) responses are measured from the apical three turns of the guinea pig cochlea, allowing access to regions with best, or most sensitive, frequencies at approximately 250, 1000, and 4000 Hz. In addition to measuring both ac and dc receptor potentials, the average value of the half-wave rectified response (AVEHR) is computed to better reflect the signal that induces transmitter release. This measure facilitates comparisons with single-unit responses in the auditory nerve. Although IHC ac responses exhibit compressive growth, response magnitudes at high levels depend on stimulus frequency. For example, IHCs with moderate and high best frequencies (BF) exhibit more linear responses below the BF of the cell, where higher sound-pressure levels are required to approach saturation. Because a similar frequency dependence is observed in extracellular OC responses, this phenomenon may originate in cochlear mechanics. At the most apical recording location, however, the pattern documented at the base of the cochlea is not seen in IHCs with low BFs around 250 Hz. In fact, more linear behavior is measured above the BF of the cell. These frequency-dependent features require modification of cochlear models that do not provide for longitudinal variations and generally depend on a single stage of saturation located at the synapse. Finally, behavior of dc and AVEHR responses suggests that a single IHC is capable of coding intensity over a large dynamic range [Patuzzi and Sellick, J. Acoust. Soc. Am. 74, 1734-1741 (1983); Smith et al., in Hearing--Physiological Bases and Psychophysics (Springer, Berlin, 1983); Smith, in Auditory Function (Wiley, New York, 1988)] and that information compiled over wide areas along the cochlear partition is not essential for loudness perception, consistent with psychophysical results [Viemeister, Hearing Res. 34, 267-274 (1988)].     

瞬态热量标定系统的太阳模拟器光学系统设计

设计了一种应用于瞬时热量标定系统的太阳模拟器光学系统,系统由短弧氙灯、椭球聚光镜和通道反射式积分器组成。介绍了椭球聚光镜的设计准则和限制要求,分析了积分器的工作原理和体均匀性,讨论了辐照面大小要求和安装空间的限制,最后,优化了系统设计并进行了仿真模拟。仿真结果表明,当选用近轴收大倍率为4．5、积分器管长为85mm时,若采用7000w氙灯,即能够获得3％的均匀性和4250食太阳常数的辐账“瞍;若采用5000W氙灯,则可在均匀性不变的情况下获得2980个太阳常数的辐照强度,两者均满足使用要求。     

The Krichever map,vector bundles over algebraic curves,and Heisenberg algebras

We study the GrassmannianGr _x ⁿ consisting of equivalence classes of rankn algebraic vector bundles over a Riemann surfaceX with an holomorphic trivialization at a fixed pointp. Commutative subalgebras ofgl(n, H ),H being the ring of functions holomorphic on a punctured disc aboutp, define flows on the Grassmannian, giving rise to classes of solutions to multi-component KP hierarchies. These commutative subalgebras correspond to Heisenberg algebras in the Kac-Moody algebra associated togl(n, H ₎. One can obtain, by the Krichever map, points ofGr _x ⁿ (and solutions of mcKP) from coveringsf: YX and other geometric data. Conversely for every point ofGr _x ⁿ and for every choice of Heisenberg algebra we construct, using the cotangent bundle ofGr _x ⁿ , an algebraic curve coveringX and other data, thus inverting the Krichever map. We show the explicit relation between the choice of Heisenberg algebra and the geometry of the covering space.The research was partially supported by US Army grant DAA L03-87-K-0110 and NSF grant DMS 9106938     

A calibration method for optical trap force by use of electrokinetic phenomena

An experimental method for calibration of optical trap force upon cells by use of electrokinetic phenomena is demonstrated.An electronkinetic sample chamber system (ESCS) is designed instead of a common sample chamber and a costly automatism stage,thus the experimental setup is simpler and cheaper.Experiments indicate that the range of the trap force measured by this method is piconewton and sub-piconewton,which makes it fit for study on non-damage interaction between light and biological particles with optical tweezers especially.Since this method is relevant to particle electric charge,by applying an alternating electric field,the new method may overcome the problem of correcting drag force and allow us to measure simultaneously optical trap stiffness and particle electric charge.     

A design for a cylindrical mirror analyser for use in auger spectroscopy

The design of a cylindrical mirror analyser for use in Auger spectroscopy is discussed. The main feature of the design is the use of hemicylinders in place of the usual full cylinders. Although there is a consequent loss in solid angle of collection the loss is offset by a relaxation in machining tolerances, greater access to the specimen, and a simpler method of construction. An analyser built to this design has been operated and found to have a resolution of 0.35% for a semiangular aperture of ± 6°. The limitation on resolution appears to be set by the size of the incident electron beam on the target.Auger and loss spectra obtained with the analyser are shown and compared with those for the same material obtained with a conventional retarding-field analyser.     

On the use of stimulated Brillouin scattering as a calibration method for group delay and differential group delay measurements

We propose a novel group delay and differential group delay calibration method for polarization-dependent optical spectral characterization measurements. The calibration method is based on the dispersive nature of stimulated Brillouin scattering and its polarization dependent spectral response. The main advantage of the calibration method is its tunability in wavelength, bandwidth and magnitude, what makes it suitable for different measurement setups.