The optimum bandwidth of chirp signals in ultrasonic applications

A new formula for the pulse-compression ratio achievable with linear FM pulses (chirp signals) in ultrasonic applications is derived. The calculations take into account the frequently omitted effects of the transfer function of an ultrasonic transducer. For a squared-cosine type transducer spectrum, the optimum chirp signal bandwidth is 1.14 times the 6 dB bandwidth of the transducer. The pulse-compression ratio is 2.24 dB lower than in the case of an ideal broadband transducer. Measurements show a close agreement with the presented theory.     

Holovideo: Real-time 3D range video encoding and decoding on GPU

We present a 3D video-encoding technique called Holovideo that is capable of encoding high-resolution 3D videos into standard 2D videos, and then decoding the 2D videos back into 3D rapidly without significant loss of quality. Due to the nature of the algorithm, 2D video compression such as JPEG encoding with QuickTime Run Length Encoding (QTRLE) can be applied with little quality loss, resulting in an effective way to store 3D video at very small file sizes. We found that under a compression ratio of 134:1, Holovideo to OBJ file format, the 3D geometry quality drops at a negligible level. Several sets of 3D videos were captured using a structured light scanner, compressed using the Holovideo codec, and then uncompressed and displayed to demonstrate the effectiveness of the codec. With the use of OpenGL Shaders (GLSL), the 3D video codec can encode and decode in realtime. We demonstrated that for a video size of 512×512, the decoding speed is 28 frames per second (FPS) with a laptop computer using an embedded NVIDIA GeForce 9400 m graphics processing unit (GPU). Encoding can be done with this same setup at 18 FPS, making this technology suitable for applications such as interactive 3D video games and 3D video conferencing.     

Compression evaluation of surgery video recordings retaining diagnostic credibility (compression evaluation of surgery video)

Wider dissemination of medical digital video libraries is affected by two correlated factors, resource effective content compression that directly influences its diagnostic credibility. It has been proved that it is possible to meet these contradictory requirements halfway for long-lasting and low motion surgery recordings at compression ratios close to 100 (bronchoscopic procedures were a case study investigated). As the main supporting assumption, it has been accepted that the content can be compressed as far as clinicians are not able to sense a loss of video diagnostic fidelity (a visually lossless compression). Different market codecs were inspected by means of the combined subjective and objective tests toward their usability in medical video libraries. Subjective tests involved a panel of clinicians who had to classify compressed bronchoscopic video content according to its quality under the bubble sort algorithm. For objective tests, two metrics (hybrid vector measure and hosaka Plots) were calculated frame by frame and averaged over a whole sequence.     

Nonlinear Dynamics of a Two-Mode Wave Packet with Strong Linear Intermode

We investigate the dynamics of the wave packet formed by two codirected strongly interacting waves propagating in a medium with cubic nonlinearity. We obtain a soliton solution of the nonlinear Schrödinger equation in the degenerate case where the wave packet is described by a single partial momentum. In the nondegenerate case, we use the variational method to find the equation for the pulse duration, which turns out to be analogous to the equation for the coordinate in the Kepler problem. Solving it, we find the dependences of the pulse duration on the propagation distance in the cases of finite and infinite propagation regimes.     

The electronic properties and electron transport of sawtooth penta-graphene nanoribbon under uniaxial strain: ab-initio study

ABSTRACT

The electronic properties and electron transport of a sawtooth penta-graphene nanoribbon (SSPGNR) under uniaxial strains are theoretically studied by density-functional theory (DFT) in combination with the non-equilibrium Green's function formalism. We investigated the electronic structures and the current–voltage (I–V) characteristics of the SSPGNRs under a sequence of uniaxial strains in range from 10% compression to 10% stretch. In this strained range, carbon atoms still keep a pentagon network, but with the changing bond lengths. The C–C bond lengths change almost linearly with the tolerable strain. The value of the band gap of SSPGNRs can be depicted as a parabola under uniaxial strain. Our calculations show that the current is monotonous increase with compressive strain at the same applied bias voltage. In case of tensile strain, the variable rule of the current is different that it increases at first and decrease later. The fundamental physical properties (band structure, I–V characteristic) of SSPGNRs seem to be more sensitive to compressive strain than the stretch strain. The current intensity of the compressive-SSPGNR is by 2 orders of magnitude compared to that of the tensile-SSPGNR at the same strain in range from 6% to 10%. The results obtained from our calculations are beneficial to practical applications of these strained structures in SSPGNRs-based electromechanical devices.     

Generation of attosecond pulses in molecular nitrogen

We investigate the carrier-envelope phase dependence of the total ionization yield for single and double ionization of xenon. We compare our results to theoretical calculations and to the phase dependent asymmetry in photoelectron emission. We observe that the phase dependence of the photoion yields, regardless if single or double ionization, is at least 2-3 orders of magnitude below the photoelectron emission signal. We conclude that total photoionization yields are only very weakly dependent on the carrier envelope phase, and that they are not a useful means for measurement of the phase. It seems possible that the broad bandwidth of few-cycle pulses facilitates multiphoton ionization, which leads to a randomization of strong field ionization phase dependencies. Besides, we observe that the spatial asymmetry in photoelectron emission appears to be useful as an indicator for the laser pulse duration in the few cycle regime.     

Externally applied stress sign and film elastic properties effects on brittle film fracture

Rectangular stainless steel samples with TiN film deposited on the front lateral surface were loaded in three-point bending to the maximum normal strain of 6%. Scanning electron microscopy showed that vertical cracks appeared in the tension zone when the tensile strain exceeded 1.5%, while horizontal cracks appeared in the compression zone when the compressive strain exceeded –2.9%. Film cracks in the compressive zone originate from the tensile stress imposed by the plastically deformed substrate due to the Poisson’s expansion. Taking plastic deformation and Poisson’s expansion of the substrate in compression into account, theoretical analysis of normal stress distribution along the cracked film segment in compression is presented. Substrate strain and film elastic properties affect film cracking in the compressive zone. At larger compressive strain, some transverse cracks along with buckling cause the film spallation. The presented method is useful for studying brittle film fracture with variable strain levels in a single sample.     

Influences of nonlinear interactions of polaritons in uniaxial crystals

We have analysed theoretically the polarization and dielectric constant of uniaxial ionic crystals,including the effect of the nonlinear interactions between ions.The spectrum of polaritons(coupling modes of photons and optical phonons) under nonlinear interactions was developed.A new branch of dispersion relations emerges in the original frequency gap.     

单轴晶体包层啁啾光纤光栅中电光效应和弹光效应的理论研究

提出了以单轴晶体材料为包层,光轴平行于光栅主轴(z轴)的新型啁啾光纤光栅模型,应用耦合模理论和传输矩阵方法在理论上分析了该类光纤光栅中的电光效应和弹光效应,理论研究发现在包层施加沿光栅轴向的电场和应变场可以改变布拉格波长和反射谱。得到了3种不同单轴晶体为包层时布拉格波长λB和反射光谱随外加电场和应变场变化的曲线。研究结果表明当轴向外加电场从1×107V/m变化到8×107V/m时λB减小0.12nm,当外加应变场从0变化到0.04时,λB减小0.45nm。     

太阳能溴化锂吸收式制冷循环的改进

由于单效溴化锂吸收制冷循环受太阳能热源温度较低的限制,需要采用适当的辅助手段.本文对增压辅助型太阳能溴冷机循环流程提出了在冷凝器前加装隔离阀的改进方案,该方案可降低发生压力,以充分利用低温热源,并可有效回收压缩功.通过计算分析了改进循环的热力系数COP与热源温度和循环溶液质量分数差的关系.给出了在不同的热源温度下对应的最佳发生压力的调整范围.