Dense-Plasma Research Using Ballistic Compressors

An introduction is given to research on dense (or nonideal) plasmas which can be generated to advantage by ballistic compressors. Some properties of ballistic compressors are discussed especially in comparison with shock tubes. A short review is given on the history of these devices for high-pressure plasma generation. The present state of the art is reported including research on the two ZIE ballistic compressors.     

Quantum interference and ballistic transmission in nanotube electron waveguides

The electron transport properties of well-contacted individual single-walled carbon nanotubes are investigated in the ballistic regime. Phase coherent transport and electron interference manifest as conductance fluctuations as a function of Fermi energy. Resonance with standing waves in finite-length tubes and localized states due to imperfections are observed for various Fermi energies. Two units of quantum conductance 2G(0) = 4e(2)/h are measured for the first time, corresponding to the maximum conductance limit for ballistic transport in two channels of a nanotube.     

有限长双壁碳纳米管的电子输运性质

基于Landauer公式，研究了有限长的非公度和公度双壁碳纳米管的电子输运性顾，结果表明 ，双壁管的几何结构对其电子输运性质有显著的影响：非公度的双壁碳管的电导随能量的不 同，既可以是弹道型的，也可以是非弹道型的；由armchair管组成的公度的双壁碳管的电导 随能量变化呈现快速的电导振荡，并且此快速振荡叠加在背景慢振荡上，而zigzag管组成的 公度双壁管的电导随能量变化只有快速振荡、没有规则的慢振荡背景. 关键词： 碳纳米管 电子输运性质     

Multiwalled carbon nanotubes are ballistic conductors at room temperature

Following the experiments of Frank et al. [1], which demonstrated quantum transport in multiwalled carbon nanotubes, there have been several experiments that appear to contradict the main conclusion of that paper, which is that the transport of a MWNT at room temperature is ballistic. Here we demonstrate that the intrinsic resistance of clean-arc-produced carbon nanotubes is at most 200 Ω/ μm, which implies that the momentum mean free path is greater than 30 μm, which in turn is much larger than the tube length. This implies that these tubes are ballistic, according to the standard definition of ballistic transport. We also show that the contact resistance with mercury is quite large: a nanotube in contact with Hg over 100 nm of its length still represents a 3000 Ω resistance. Received: 14 September 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Superconductor-insulator transition in a two-dimensional array of resistively shunted small josephson junctions

Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multiwall carbon nanotubes. We find that interwall interactions not only block some of the quantum conductance channels, but also redistribute the current nonuniformly over individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and noninteger conductance values reported for multiwall nanotubes by Stefan Frank et al. [Stefan Frank et al., Science 280, 1744 (1998)].     

Modeling and simulations of the behavior of glass particles in a rotating drum in heptane and water vapor atmospheres

We have performed noise measurements on suspended ropes of single wall carbon nanotubes (SWNT) between 1 and 300 K for different values of dc current through the ropes. We find that the shot noise is suppressed by more than a factor 100 compared to the full shot noise 2eI. We have also measured an individual SWNT and found a level of noise which is smaller than the minimum expected. Another finding is the very low level of 1/f noise, which is significantly lower than previous observations. We propose two possible interpretations for the strong shot noise reduction: i) Transport within a rope takes place through few nearly ballistic tubes within a rope and possibly involves non integer effective charges with e ^*∼ 0.3e. ii) A substantial fraction of the tubes conduct with a strong reduction of effective charge (by more than a factor 50). Received 25 January 2002 Published online 19 July 2002     

Can we achieve ultra-low resistivity in carbon nanotube-based metal composites?

A concept for creating a future ultra-low-resistivity material based on a carbon nanotube–metal composite is presented. Using a simple effective-medium model it is shown that a room-temperature resistivity 50% lower than Cu is achievable. This article sets a goal for future R&D activities, although a number of technical as well as scientific problems are to be solved before realising the suggested concept. The ultra-low resistivity is possible because the ballistic conducting carbon nanotubes have an electron mean free path several orders of magnitude longer than metals like Cu and Ag. This implies that a system with parallel-connected tubes can indeed have a room-temperature resistivity far below the resistivity of conventional metal conductors like Al, Cu and Ag. PACS 72.15.-v; 81.05.Zx     

Ballistic anisotropic magnetoresistance

Electronic transport in ferromagnetic ballistic conductors is predicted to exhibit ballistic anisotropic magnetoresistance-a change in the ballistic conductance with the direction of magnetization. This phenomenon originates from the effect of the spin-orbit interaction on the electronic band structure which leads to a change in the number of bands crossing the Fermi energy when the magnetization direction changes. We illustrate the significance of this phenomenon by performing ab initio calculations of the ballistic conductance in ferromagnetic Ni and Fe nanowires which display a sizable ballistic anisotropic magnetoresistance when magnetization changes direction from parallel to perpendicular to the wire axis.     

Ballistic transport and quantum interference in InSb nanowire devices

An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in In Sb nanowires grown by molecular-beam epitaxy contacted by superconductor electrodes. At an elevated temperature, clear conductance plateaus are observed at zero magnetic field and in agreement with calculations based on the Landauer formula. At lower temperature, we have observed characteristic Fabry–Pérot patterns which confirm the ballistic nature of charge transport.Furthermore, the magnetoconductance measurements in the ballistic regime reveal a periodic variation related to the Fabry–Pérot oscillations. The result can be reasonably explained by taking into account the impact of magnetic field on the phase of ballistic electron's wave function, which is further verified by our simulation. Our results pave the way for better understanding of the quantum interference effects on the transport properties of In Sb nanowires in the ballistic regime as well as developing of novel device for topological quantum computations.     

光电经纬仪测量精度指标的确定

光电经纬仪测量元素误差是外弹道测量中最主要的误差源。为了保证外弹道的测量精度，就应对光电经纬仪的测量精度进行合理设计。通过数学解析的方法，推导建立了2个简洁的公式：1）单站定位体制下弹道点位精度和光电经纬仪测角、测距精度以及目标斜距、高角之间的数学表达式；2）对称交会测量体制下弹道点位精度和光电经纬仪测角精度以及目标斜距、交会角之间的数学表达式。这2个公式为光电经纬仪精度指标的设计论证提供了理论依据。     

Sagnac effect and Ritz ballistic hypothesis (Review)

It is shown that the Ritz ballistic hypothesis, which is based on the vector summation of the speed of light with the velocity of the radiation source, contradicts the fact of existence of the Sagnac effect. Based on a particular example of a three-mirror ring interferometer, it is shown that the application of the Ritz ballistic hypothesis leads to an obvious calculation error, namely, to the appearance of a difference in the propagation times of counterpropagating waves in the absence of rotation. A review is given of experiments and of results of processing of astronomical observations and discussions devoted to testing the Ritz ballistic hypothesis. A number of other physical phenomena that refute the Ritz ballistic hypothesis are considered.     

Imaging Transparent Objects in a Turbid Medium Using a Femtosecond Optical Kerr Gate

A femtosecond optical Kerr gate time-gated ballistic imaging method is demonstrated to image a transparent object in a turbid medium. The shape features of the object are obtained by time-resolved selection of the ballistic photons with different optical path lengths, the thickness distribution of the object is mapped, and the maximum is less than 3.6%. This time-resolved ballistic imaging has potential applications in studying properties of the liquid core in the near field of the fuel spray.     

弹道相机白天工作能力的影响因素分析及提高途径

弹道相机通常是在夜间对飞行目标进行拍摄,在相机类型不改变的情况下要达到白天工作能力具有一定困难,主要障碍是拍摄后,底板上目标与背景的衬比(度)下降,难以达到判读要求.针对这一问题,本文详细叙述了各因素对判读要求的影响,提出了改善相机白天工作能力的可行方法.     

Effect of ballistic electrons on ultrafast thermomechanical responses of a thin metal film

The ultrafast thermomechanical coupling problem in a thin gold film irradiated by ultrashort laser pulses with different electron ballistic depths is investigated via the ultrafast thermoelasticity model. The solution of the problem is obtained by solving finite element governing equations. The comparison between the results of ultrafast thermomechanical coupling responses with different electron ballistic depths is made to show the ballistic electron effect. It is found that the ballistic electrons have a significant influence on the ultrafast thermomechanical coupling behaviors of the gold thin film and the best laser micromachining results can be achieved by choosing the specific laser technology(large or small ballistic range).In addition, the influence of simplification of the ultrashort laser pulse source on the results is studied, and it is found that the simplification has a great influence on the thermomechanical responses, which implies that care should be taken when the simplified form of the laser source term is applied as the Gaussian heat source.     

Phonon focusing of elastically scattered phonons in GaAs

The propagation of high-frequency phonons through crystals at low temperatures is characterized by both ballistic and diffusive processes. Ballistic propagation of heat pulses is highly anisotropic due to phonon focusing, while diffusive propagation is expected to be nearly isotropic in cubic crystals. By using phonon imaging techniques, we have attempted to identify the heat flux from ballistic and scattered phonons in GaAs. Comparison of this data to Monte Carlo calculations which incorporate elastic scattering shows that the flux from phonons scattered a few times in the bulk retains a significant degree of anisotropy. In particular, a sharp feature discovered by Stock, Ulbrich, and Fieseler and attributed to ballistic propagation of phonons with frequencies up to 1.5 THz is now identified with the scattering of sub-THz phonons. Our analysis provides insights into the evolution of heat propagation from the ballistic to diffusive regimes.     

Ballistic behavior of Heracron®-based composites: effect of fiber density and fabrication method

In this study, a Heracron^® aramid fiber-based helmet was made, and its ballistic properties were investigated. The effect of fiber density was studied in depth. For the same weight and number of plies, a helmet manufactured from the HT-2820-based composite showed improved ballistic properties compared with one made from the HT-15000-based composite. This result suggested that fiber density may strongly affect the ballistic properties of armor. HT-2820, containing more multifilament fibers, provides more efficient energy absorption and dissipation. The influence of fabrication method on the ballistic behavior of a helmet was studied. The V₅₀ of a helmet made by the film laminating method was 10% better than that for a helmet made by the resin dipping approach. Based on these findings, the film laminating method, which forms the composite by directly attaching aramid fabric to the matrix film, may be a good candidate for improving the ballistic behavior. The required composite interfacial strength will be application-dependent. Greater fiber-matrix adhesion may be advantageous in certain cases.     

Photovoltaic effect in submicron ballistic rings

Photovoltaic effect is investigated for ballistic AlGaAs/GaAs rings under microwave radiation. The comparison of microwave EMF versus magnetic field dependencies and magnetoresistance shows that in ballistic rings the photovoltaic effect is due to the absence of central symmetry in microstructure geometry.     

Interplay of Ehrenfest and dephasing times in ballistic conductors

Quantum interference corrections in ballistic conductors require a minimal time: the Ehrenfest time. In this Letter, we investigate the fate of the interference corrections to quantum transport in bulk ballistic conductors if the Ehrenfest time and the dephasing time are comparable.     

对用冲击电流计测定直螺线管磁场实验的改进

采用新旧冲击电流计测定直螺线管的原理，对实验电路和实验方法的改进。     

Flux-limited nonequilibrium electron energy transport in warm dense gold

An abrupt change in energy transport has been observed in femtosecond laser heated gold when the absorbed laser flux exceeds ~7×10(12) W/cm(2). Below this value, the absorbed flux is carried by ballistic motion of nonthermal electrons produced in interband excitation. Above this value energy transport appears to include ballistic transport by nonthermal electrons and heat diffusion by thermalized hot electrons. The ballistic component is limited to a flux of ~7×10(12) W/cm(2). This offers a unique benchmark for comparison with theory on nonequilibrium electron transport.