泵涨落对双模激光增益模型竞争效应的影响

研究了泵涨落对双模激光增益模型竞争效应的影响。通过线性稳定性分析得到一些很有意义的结论。     

Resonance suppression in a TEM cell

All TEmnp resonances in a TEM cell have been suppressed by cutting the cell walls longitudinally. The TMmnp resonances and propagating TEM mode were not affected. The suppressed resonances have a residual interaction with a biological body inside the cell. Because of this, the modified cell can only be used for bioeffects dosimetry studies at a small number of frequencies above the upper limit for the original cell. Where an accuracy of only +/- 5 dB is required, such as in some EMC studies, the effective bandwidth of the modified cell is twice that of the original cell.     

Bandwidth limitations of TEM cells due to resonances

The first eight to ten TEmnp resonances have been identified in one large (6.1 X 7.3 X 13.0 m) and one small (1.0 X 0.6 X 2.0 m) TEM cell. The resonant frequencies fit a new equivalent coaxial box model with the effective length of the box depending on the mode. Weakly propagating TEmn modes were also detected at frequencies above their respective first-resonance frequencies. A biological body or metal box at the center of the test zone interacts strongly with the TE10p and TE11p resonances, but not with the TE01p resonances. These interactions cause bandwidth limitations in the use of TEM cells for bioeffects dosimetry studies, EMC testing, and probe calibration work.     

Experimental models for the evaluation of microwave biological effects

The theoretical and empirical approaches to biological effects of microwaves are discussed. The bioeffects should be considered as a chain of events: primary interaction analyzed in terms of biophysics and early direct, early indirect, late (delayed) effects analyzed in terms of physiology. Thermal balance experiments are discussed pointing out the necessity to take unequal deep body heating by microwaves into account. The use of physiologic rhythms in microwave bioeffects experimentation is presented. Possible use of pharmacodynamic approaches (simultaneous use of drugs and microwave exposure) is outlined. Possible ways of developing biological response microwave dosimetry are indicated. Unexplained effects are pointed out and the necessity of further experiments to clarify these stressed. Some possible experimental models are presented.     

Is there a Biological Basis for Therapeutic Applications of Millimetre Waves and THz Waves?

Millimetre wave (MMW) and THz wave (THz) applications are already employed in certain industrial and medical environments for non-destructive quality control, and medical imaging, diagnosis, and therapy, respectively. The aim of the present study is to investigate if published experimental studies (in vivo and in vitro) provide evidence for “non-thermal” biological effects of MMW and THz. Such effects would occur in absence of tissue heating and associated damage and are the ones that can be exploited for therapeutic medical use. The investigated studies provide some evidence for both MMW and THz that can influence biological systems in a manner that is not obviously driven by tissue heating. However, the number of relevant studies is very limited which severely limits the drawing of any far-reaching conclusions. Furthermore, the studies have not addressed specific interaction mechanisms and do not provide hints for future mechanistic studies. Also, the studies do not indicate any specific importance regarding power density levels, frequencies, or exposure duration. It is also unclear if any specific biological endpoints are especially sensitive. Any therapeutic potential of MMW or THz has to be evaluated based on future high-quality studies dealing with physical, bio-physical, and biological aspects that have specific health-related perspectives in mind.     

Different Aspects of Using Ultrasound to Combat Microorganisms

Growing resistance of microorganisms to antibiotics due to their widespread use has led to multiple bacterial infections posing a serious threat to health and human life. Low-frequency ultrasound is one of physical methods for inactivation of pathogenic microbial cells. Application of ultrasound is safe, demonstrates good tissue penetration without significant attenuation of energy, and does not induce microbial resistance. Bactericidal effect of ultrasound is based on acoustic cavitation—the growth and collapse of microbubbles in a liquid medium, resulting in shock waves, shear forces, and microjets which cause irreversible damage and inactivation of microorganisms. The present review combines and analyzes literature data on in vitro and in vivo studies and summarizes works demonstrating the ability of ultrasound, alone or in combination with other methods, to combat pathogenic microorganisms. The results of various studies presented in this review show that low-frequency ultrasound has a noticeable antimicrobial effect on planktonic cells of microorganisms and biofilms. Ultrasound synergistically enhances the effectiveness of other antibacterial agents and activates molecules called sonosensitizers, resulting in the formation of compounds toxic to microbial cells. Ultrasound can also promote local release of antimicrobial drugs from liposomes, as well as from medical implants.     

Vibration mode imaging

A new method for imaging the vibration mode of an object is investigated. The radiation force of ultrasound is used to scan the object at a resonant frequency of the object. The vibration of the object is measured by laser and the resulting acoustic emission from the object is measured by a hydrophone. It is shown that the measured signal is proportional to the value of the mode shape at the focal point of the ultrasound beam. Experimental studies are carried out on a mechanical heart valve and arterial phantoms. The mode images on the valve are made by the hydrophone measurement and confirmed by finite-element method simulations. Compared with conventional B-scan imaging on arterial phantoms, the mode imaging can show not only the interface of the artery and the gelatin, but also the vibration modes of the artery. The images taken on the phantom surface suggest that an image of an interior artery can be made by vibration measurements on the surface of the body. However, the image of the artery can be improved if the vibration of the artery is measured directly. Imaging of the structure in the gelatin or tissue can be enhanced by small bubbles and contrast agents.     

Advanced Medical Displays: A Literature Review of Augmented Reality

The impressive development of medical imaging technology during the last decades provided physicians with an increasing amount of patient specific anatomical and functional data. In addition, the increasing use of non-ionizing real-time imaging, in particular ultrasound and optical imaging, during surgical procedures created the need for design and development of new visualization and display technology allowing physicians to take full advantage of rich sources of heterogeneous preoperative and intraoperative data. During 90's, medical augmented reality was proposed as a paradigm bringing new visualization and interaction solutions into perspective. This paper not only reviews the related literature but also establishes the relationship between subsets of this body of work in medical augmented reality. It finally discusses the remaining challenges for this young and active multidisciplinary research community.      

Ultrasound color-flow imaging on a programmable system

Color-flow imaging is a well-established ultrasound mode and very valuable for visualizing in real time the distribution of blood flow in a specific region of interest. However, it is computationally quite expensive. To meet the large computational need in color-flow imaging, most ultrasound systems have been designed using fixed-function hardware. In this paper, we present a system where all the color-flow processing is supported on a programmable platform. About 95% of the processing modules were programmed in C language. On a single processor, we were able to achieve 7.9 frames/s, when the input data consist of 192 x 512 x 8 (ensemble size) samples for color flow and 384 x 512 for B mode and the output image size is 600 x 420. Additional processors can be added to handle more input data and/or support higher frame rates. Our results demonstrate that a programmable ultrasound system can provide the same functionality for clinical use as conventional ultrasound systems. However, it is more flexible and efficient due to its programmability.     

Computation of optical resonator modes by the method of resonance excitation

A novel computational method is used to calculate the modes of an optical resonator. The method is a computer simulation of the physical experiment of exciting a resonator externally and adjusting its length to resonate the various modes; the output at each resonance is purified by means of mode filters consisting of suitably adjusted resonators in tandem. The method is powerful and useful, and is applicable to resonators of arbitrary configuration. Calculated results for a Fabry-Perot resonator with a Fresnel number of ten are presented.     

部分掺杂光纤掺杂半径的选择

掺杂半径的选择是部分掺杂光纤能够有效选模的关键.从模式的归一化模场分布出发,通过对模式场分布的比较,确定采用较小或较大的掺杂半径均不利于基模的选取.从饱和增益和功率分配两个角度详细分析了掺杂半径的变化对各模式的增益获取能力和功率提取能力的影响.纤芯掺杂半径的变化改变了模式场与增益粒子的相互作用机会,因而改变了各模式的增益获取能力及模式功率的输出大小.当掺杂分布与基模场分布达到最佳重叠并使得基模在强度上占据优势时,则基模获得的增益超过其他模式,输出功率达到最大.定量计算结果说明,阶跃光纤采用0.6左右的相对掺杂半径可以有利于提取基模.     

基于转移概率的多视点视频快速模式选择算法

针对多视点视频编码(MVC)中部分大宏块模式(SKI P/DIRECT模式,帧间16×16模式)相对于其它模式的计算复杂 度低,并且在编码所确定的最优模式中占有相当高比重的特点,本文提出一种基于转移概率 的多视点视频 快速模式选择算法。首先根据多视点视频当前编码宏块对应时间和视点间宏块及周围宏块的 位置几何关系, 建立宏块模式参考模型;其次比较参考模型中模式的时间相似度和视点间相似度;最后计算 模式之间的转 移概率,确定提前结束大宏块模式选择过程的阈值。实验结果表明,本文所提出的快速算法 平均节约MVC时间80.93%,编码质量平均下降0.04dB,码率平均增加0.27%。     

Generation of Laser Light via Ultrasonic Four-wave Mixing

On the basis of the interaction between phonons in ionic crystals with anharmonic lattice vibration, we present a laser model on acoustic nondegenerate four-wave mixing. Two beams of highfrequency ultrasound, incident on the acoustic cavity fulfilled with the medium of ionic crystal, play the role of pumping and one of the two side-band modes of the pumping frequency as an acoustic signal mode has a strong interaction with the optical cavity mode, the coupling-out of which wiIl be the light (far-infrared) output of a laser. The problem is treated with quantum-mechanics. The theory shows that there is the threshold phenomenon as usual lasers and a so called "phase-matching" condition is derived, which should be satisfied for stability of the system.     

A broadband MVDR beamforming core for ultrasound imaging

The Minimum Variance Distortion less Response (MVDR) beamformer is an attractive alternative to conventional delay and sum (DAS) beamformers in medical ultrasound imaging. However, it is not widely employed in medical ultrasound imaging due to its computational complexity. In this paper, we intend to present a novel broadband MVDR beamformer architecture and its implementation for up to 32 channel ultrasound imaging system. The proposed architecture is based on the subarray MVDR and Dichotomous Coordinate Descent (DCD) iteration based adaptive weight computation. A Field Programmable Gate Array (FPGA) based ultrasound system prototype set up is designed, and the proposed MVDR beamforming Core is emulated on the FPGA. The proposed beamforming core could achieve up to 65.5 fps for a 640 x 480 ultrasound frame. The ultrasound system prototype operates at 20 MHz sampling frequency, and the FPGA implementation resulted in approximately 35% of FPGA resources (Xilinx Kintex-7 410T). Image quality comparisons in terms of Contrast Ration (CR) and Contrast to Noise Ratio (CNR) were performed with MATLAB™ MVDR model ported on the Verasonics™ Vantage-64 ultrasound research platform.     

结合深度信息的多视点视频编码快速模式选择算法

多视点视频加深度(MVD,multi-view video plus depth)的编码格式包含多个纹理视频序列及其对应的深度图,深度图与对应的纹理视频具有相似的边缘信息。传统的编码模式不考虑两者的联系,单独编码导致复杂度高、编码时间过长。因此,合理利用深度图与纹理图的相似性进行编码,可以有效降低编码复杂度,同时应该确保编码质量不受影响。本文利用深度图的这一特点辅助纹理视频的编码,提出一种帧间快速模式选择算法,充分利用深度图与纹理图之间的相似性,建立一种联合复杂度模型,根据模型得到每个宏块的复杂度。对于复杂度低的宏块,在计算率失真代价之前跳过编码中一些不必要的模式,从而降低编码复杂度。实验表明,本文提出的快速模式选择算法,在保证率失真性能基本不变的情况下,能减少60.57%的编码复杂度,并最高能减少80.64%的编码时间。     

Design considerations for the mechanical integrity of airgaps in nano-interconnects under chip–package interaction; a numerical investigation

Airgaps can undermine the mechanical properties of nano-interconnects and lead to reliability issues such as back end of line (BEOL) fractures. In this context, interconnect delamination under chip–package interaction (CPI) induced loads is a major failure mode which benefits from in-depth investigation. In this computational study, models of airgaps fabricated using the etch-back approach are developed for 90 nm pitch interconnects and potential mechanical failure modes including the fracture energy release rate (ERR) at various material interfaces are investigated. In addition, capacitance benefits of airgap implementation compared to the mainstream low-k technology are calculated using a capacitance simulator. Subsequently, mechanically conscious airgap design strategies are proposed which allow taking advantage of the maximal capacitive benefits of airgaps and limit the CPI related reliability concerns.     

Leaky modes in graded fibres

Leaky modes, particularly tunnelling leaky modes, in step-index fibres are well known, but they are also present in graded fibres, in which case they are much more likely to cause errors in calculations and measurements, for example, transmission measurements, since they cannot be distinguished by any simple means from bound modes. The possible and probable extent of their effects are calculated by simple mode theory.     

Computational Complexity Reduction for Volumetric Cardiac Deformation Recovery

Cardiac deformation recovery is to estimate displacements and thus strains of the myocardium from patient’s medical measurements, which can then be used to locate possible areas of cardiac diseases such as infarction. In order to properly couple a priori cardiac physiological models with measurements from medical images, different state-space based filtering algorithms have been proposed for physically meaningful and statistically optimal estimations with promising results demonstrated. Nevertheless, as the filtering procedures include matrix multiplications and inversions of dense matrices which sizes increase exponentially with the number of nodes representing the heart, the computational complexities of these algorithms are very large and thus their scalability and practicability are limited. In order to alleviate the computational requirements while minimizing the loss of accuracy, the mode superposition approach is adopted in this paper. Mode superposition transforms the origin cardiac system dynamics into a mathematically equivalent space spanned by shape vectors of different modes, with each mode representing a particular frequency of the displacements. As only relatively few frequencies are required for a good approximation of the system, many shape vectors can be discarded and results in a space of much lower dimension. With the proper transformations of the filtering components derived in this paper, the filtering procedures can then be performed in this space with largely reduced computational complexity. Experiments have been performed on synthetic data to show the benefits and costs of using the proposed framework, and also on a magnetic resonance image sequence to show its effects and performance on real data.

     

Interaction of two different frequency photonic crystal waveguide modes through the resonant excitation of modes on off-channel Kerr nonlinear media

The properties of two photonic crystal waveguide modes at different frequencies that propagate down a straight photonic crystal waveguide are studied for cases in which the two modes interact with off-channel structures composed of Kerr nonlinear dielectric media. The optical nonlinearity of the off-channel structures mediates an interaction between the two modes that allows the modes to modulate the transmission of each other down the waveguide channel. This interaction and mutual modulation is shown to be pronounced in the case when either of the two waveguide modes resonantly excites a localized mode on the off-channel features formed of Kerr nonlinear media. Cases that are considered are a straight linear dielectric media waveguide with off-channel structures formed as: (a) a single off-channel Kerr site that supports a bound localized electromagnetic mode, (b) multiple off-channel Kerr sites that support a bound intrinsic localized electromagnetic mode, and (c) multiple off-channel Kerr sites that support an intrinsic localized mode that in turn interacts with a semi-infinite waveguide of linear dielectric media. In cases (a) and (b) the effects of resonant excitation of single site and intrinsic localized modes in the Kerr medium on the transmission characteristics are determined. In case (c) the effects of resonant excitation of intrinsic localized modes in the Kerr medium on the transmission characteristics of the two waveguide modes into the infinite and semi-infinite waveguides are studied.     

Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis

In this paper, we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in those fields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multimodes as function of the power angle spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the mean effective gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes.