精密宽频开尔文电桥的研制

为了在直流到100 kHz的宽频范围内能精密测量、校准交流电阻国家标准中1Ω-10kΩ的交流标准电阻器,研制出一款交直流通用的开尔文电桥;并采用替代法,以考察100 Ω、1kΩ双螺旋线绕结构交流标准电阻器的频率特性为例,试验验证了所研制的电桥具有准确度高、操作简单及工作频带宽等优点,达到了所需的技术指标要求.     

采用偏振分光棱镜的光桥式补偿技术

介绍了一种使用偏振分光棱镜的新型光桥式补偿技术。研究了棱镜消光比变化引起的误差。使用该补偿结构的光纤压力传感器已实际应用于石油化工部门油罐储量计量，其现场运行长期稳定性优于０．２％。     

Modeling Kelvin Wave Cascades in Superfluid Helium

We study two different types of simplified models for Kelvin wave turbulence on quantized vortex lines in superfluids near zero temperature. Our first model is obtained from a truncated expansion of the Local Induction Approximation (Truncated-LIA) and it is shown to possess the same scalings and the essential behaviour as the full Biot-Savart model, being much simpler than the later and, therefore, more amenable to theoretical and numerical investigations. The Truncated-LIA model supports six-wave interactions and dual cascades, which are clearly demonstrated via the direct numerical simulation of this model in the present paper. In particular, our simulations confirm presence of the weak turbulence regime and the theoretically predicted spectra for the direct energy cascade and the inverse wave action cascade. The second type of model we study, the Differential Approximation Model (DAM), takes a further drastic simplification by assuming locality of interactions in k-space via using a differential closure that preserves the main scalings of the Kelvin wave dynamics. DAMs are even more amenable to study and they form a useful tool by providing simple analytical solutions in the cases when extra physical effects are present, e.g. forcing by reconnections, friction dissipation and phonon radiation. We study these models numerically and test their theoretical predictions, in particular the formation of the stationary spectra, and closeness of numerics for the higher-order DAM to the analytical predictions for the lower-order DAM.     

The Kelvin Hall fairground accident

'The spread of information about failures within the technical community is essential and it is a sad refection on society that legal and political constraints are doing so much to prevent this spread', Max S M Saltsman¹. Details of such a failure are described here.     

Smoothing of nanoscale roughness based on the Kelvin effect

A novel method of smoothing surfaces with nanoscale roughness is described, based on the Kelvin effect. The problem of vapor redistribution in cylindrical channels and over rough planar walls with nanoscale texture is posed and solved analytically. Vapor deposition (condensation) on the walls initially produces a deposit emulating the surface landscape. After a saturated state at the deposit surface is reached, the Kelvin effect should result in higher vapor pressure/ concentration near the convex sections of the wall and in lower vapor pressure/ concentration near the concave sections. As a result, local vapor fluxes should arise directed from the locally convex to the locally concave regions. Accordingly, the deposited layer at the wall should vaporize (or sublimate) at the convex sections due to depletion and vapor should condense at the concave sections, thus causing smoothing of physical surface unevenness. This mechanism of smoothing of nanoscale roughness has not been considered in detail or used before, even though the basic physics of the Kelvin effect is well known. In the present work, the smoothing kinetics is predicted and the characteristic timescales are calculated in the general case of axisymmetric and non-axisymmetric perturbations of the cylindrical channel walls, as well as for planar surfaces. In addition, experimental data are presented to show that the theoretically motivated approach is also practically realizable.     

Material symmetry optimization by Kelvin modes

Pointwise optimization of the material symmetry of an anisotropic elastic material with respect to fixed and specified stress (or strain) states is accomplished. The conceptual variables in this problem are the type of material symmetry and the orientation of the canonical symmetry axis for the material at a point in the material. The actual variables are the coefficients of the elasticity (or compliance) matrix. The results are presented in the form of the elasticity (or compliance) matrices that minimize the strain energy with respect to specified, but arbitrary, stress (or strain) states.     

Symmetries and Interaction Coefficients of Kelvin Waves

We considered symmetry restriction on the interaction coefficients of Kelvin waves and demonstrated that linear in small wave vector asymptotic, obtained analytically, is not forbidden, as one can expect by naive reasoning. Therefore now we have no reason to doubt in this asymptote, that results in the L’vov-Nazarenko energy spectrum of Kelvin waves.     

Open-loop band excitation Kelvin probe force microscopy

A multidimensional scanning probe microscopy approach for quantitative, cross-talk free mapping of surface electrostatic properties is demonstrated. Open-loop band excitation Kelvin probe force microscopy (OL BE KPFM) probes the full response-frequency-potential surface at each pixel at standard imaging rates. The subsequent analysis reconstructs work function, tip-surface capacitance gradient and resonant frequency maps, obviating feedback-related artifacts. OL BE KPFM imaging is demonstrated for several materials systems with topographic, potential and combined contrast. This approach combines the features of both frequency and amplitude KPFM and allows complete decoupling of topographic and voltage contributions to the KPFM signal.     

Electroviscoelastic stability of a Kelvin fluid layer

The electroviscoelastic stability of a Kelvin fluid layer under the effect of a constant tangential electric field is discussed. The linear perturbation is considered. The analysis includes all possible modes of perturbations. A fourth-order partial differential equation is introduced to control the fluid motion. Applications of the boundary conditions lead to two simultaneous ordinary differential equations. A transcendental dispersion equation is obtained. A case of large viscosity is considered in order to simplify the complexity of the dispersion relation. The growth rate with respect to the retardation time parameter is carried out. The necessary and sufficient conditions for stability are introduced. It is found that the retardation time parameter has a stabilizing effects as well as the viscosity parameter, in the presence of the field. It is also, shown that viscosity and elastic parameters play against the density destabilization effects. It is shown that the tangential electric field plays a dual role in the stability criteria.     

Identification of Kelvin Waves: Numerical Challenges

Kelvin waves are expected to play an essential role in the energy dissipation for quantized vortices. However, the identification of these helical distortions is not straightforward, especially in case of vortex tangle. Here we review several numerical methods that have been used to identify Kelvin waves within the vortex filament model. We test their validity using several examples and estimate whether these methods are accurate enough to verify the correct Kelvin spectrum. We also illustrate how the correlation dimension is related to different Kelvin spectra and remind that the 3D energy spectrum E(k) takes the form 1/k in the high-k region, even in the presence of Kelvin waves.     

Reply: On Role of Symmetries in Kelvin Wave Turbulence

In the Ref. (Lebedev and L’vov in J. Low Temp. Phys. 161, 2010, doi:10.1007/s10909-010-0215-2), this issue, two of us (VVL and VSL) considered symmetry restriction on the interaction coefficients of Kelvin waves and demonstrated that linear in small wave vector asymptotic, obtained analytically, is not forbidden, as Kosik and Svistunov (KS) expect by naive reasoning. Here we discuss this problem in additional details and show that theoretical objections by KS, presented in Ref. (Kozik and Svistunov in J. Low Temp. Phys. 161, 2010, doi:10.1007/s10909-010-0242-z), this issue, are irrelevant and their recent numerical simulation, presented in Ref. (Kozik and Svistunov in arXiv:1007.4927v1, 2010) is hardly convincing. There is neither proof of locality nor any refutation of the possibility of linear asymptotic of interaction vertices in the KS texts, Refs. (Kozik and Svistunov in J. Low Temp. Phys. 161, 2010, doi:10.1007/s10909-010-0242-z; arXiv:1006.0506v1, 2010). Therefore we can state again that we have no reason to doubt in this asymptote, that results in the L’vov–Nazarenko energy spectrum of Kelvin waves.     

Preparative Steps Towards the New Definition of the Kelvin in Terms of the Boltzmann Constant

The International Committee for Weights and Measures (CIPM) approved, in its Recommendation 1 of 2005, preparative steps towards new definitions of the kilogram, the ampere, the kelvin, and the mole in terms of fundamental constants. Within the Consultative Committee for Thermometry (CCT), a task group (TG-SI) has been formed to consider the implications of changing the definitions of the above-mentioned base units of the SI, with particular emphasis on the kelvin and the impact of the changes on metrology in thermometry. The TG-SI has presented the results of its deliberations to the CCT and to the Consultative Committee for Units, CCU, and worked with them to prepare a report to the CIPM. This contribution, authored by the members of TG-SI, solicits input from the wider scientific and technical community on this important matter at the TEMPMEKO 2007 conference. For this purpose, the main details of the report to the CIPM are presented. The unit of temperature T, the kelvin, can be defined in terms of the SI unit of energy, the joule, by fixing the value of the Boltzmann constant k, which is simply the proportionality constant between temperature and thermal energy kT. Currently, several experiments are underway to determine k. The TG-SI is monitoring closely the results of all experiments relevant to the possible new definition of the kelvin, and has identified conditions to be met before proceeding with the proposed redefinition. The TG-SI considers that these conditions will be fulfilled before the 24th General Conference on Weights and Measures in October 2011. Therefore, the TG-SI is recommending a redefinition of the kelvin by fixing the value of the Boltzmann constant. A new definition of the kelvin in terms of the Boltzmann constant does not require the replacement of ITS-90 with an improved temperature scale nor does it prevent such a replacement. H. Ugur is the President, Consultative Committee for Thermometry (CCT).     

Transient Growth of Kelvin Waves on Quantized Vortices

Quantized vortex lines in helium II can be destabilized by a sufficiently large normal fluid velocity which is parallel to the vortex lines (Donnelly–Glaberson instability). We study what happens if the driving normal fluid is not steady but oscillates periodically with time. We show that in certain situations, agthough individual perturbations decay for t→∞, a state of transient growth of Kelvin waves is possible, which may explain observations of a small and not reproducible longitudinal component of mutual friction.     

Force gradient sensitive detection in lift-mode Kelvin probe force microscopy

We demonstrate frequency modulation Kelvin probe force microscopy operated in lift-mode under ambient conditions. Frequency modulation detection is sensitive to force gradients rather than forces as in the commonly used amplitude modulation technique. As a result there is less influence from electric fields originating from the tip's cone and cantilever, and the recorded surface potential does not suffer from the large lateral averaging observed in amplitude modulated Kelvin probe force microscopy. The frequency modulation technique further shows a reduced dependence on the lift-height and the frequency shift can be used to map the second order derivative of the tip-sample capacitance which gives high resolution material contrast of dielectric sample properties. The sequential nature of the lift-mode technique overcomes various problems of single-scan techniques, where crosstalk between the Kelvin probe and topography feedbacks often impair the correct interpretation of the recorded data in terms of quantitative electric surface potentials.     

Revisiting the Trust-performance Link in Strategic Alliances

• We extend research on the trust-performance link in strategic alliances (SAs) by arguing that the traditional focus of research on the influence of trust on performance of SAs needs to be complemented with a more explicit acknowledgment and analysis of the role that SA performance plays in the development of trust.
• Drawing on existing theoretical arguments and empirical findings related to the consequences and determinants of trust we argue for the existence of a bidirectional causal relationship between trust and performance in SAs. We empirically test this bilateral relationship using 3-stage least square regression models on data from 110 strategic alliances.
• Our results support the positive effect of SA performance on trust, but not the commonly stressed positive effect of trust on SA performance. We discuss the relevance of this finding for the theory of inter-firm collaboration. We conclude by discussing the implications of our findings for practitioners and scholars interested in SAs.

     

Flaw Nucleation In A Brittle Open-Cell Kelvin Foam

Open-cell Kelvin foam is considered as a spatial lattice consisting of brittle elastic struts rigidly connected to each other at the nodal points. The lattice is subjected to remote uniaxial tensile loading, an initial imperfection is introduced and sequential break of the struts is observed. Different loading directions and material densities are examined and it is found that the broken struts form a plane flaw, which may be either a bridged or a usual crack. The possible crack propagation planes to be used in the fracture toughness analysis are determined.     

The Roles of the Mise en Pratique for the Definition of the Kelvin

The mise en pratique (“practical realization”) for the definition of the kelvin (MeP-K) was created by the Consultative Committee for Thermometry (CCT) in 2006 to give practitioners of thermometry a guide to the realization of the kelvin, i.e., measurement of temperature in kelvins, in accord with the International System of Units. In this article, the present and the future content of the MeP-K, the relationship of the MeP-K to other documents relevant to thermometry, the categorization of thermometry techniques in the MeP-K, and the benefits of proposed additions to the 2006 version of the MeP-K are discussed. The three categories of measurements within the MeP-K are: (1) primary methods for measuring thermodynamic temperature T; (2) formal approximations to T, in particular, the International Temperature Scale of 1990 (ITS-90) and the Provisional Low Temperature Scale from 0.9 mK to 1 K (PLTS-2000); and (3) indirect approximation methods that are neither primary nor defined on a temperature scale, yet capable of exceptionally low uncertainties or increased reliability. By providing a framework for primary methods and indirect methods, the MeP-K will foster development and application of new methods, such as the use of absolute radiometry or high-temperature fixed points. The MeP-K provides the CCT with a mechanism to update and to expand the thermometric methods in common use, without imposing on industry the high costs of changing the International Temperature Scale.