Model-predictive control of hyperthermia treatments

A model-predictive controller (MPC) of the thermal dose in hyperthermia cancer treatments has been developed and evaluated using simulations with one-point and one-dimensional models of a tumor. The developed controller is the first effort in: 1) the application of feedback control to pulsed, high-temperature hyperthermia treatments; 2) the direct control of the treatment thermal dose rather than the treatment temperatures; and 3) the application of MPC to hyperthermia treatments. Simulations were performed with different blood flow rates in the tumor and constraints on temperatures in normal tissues. The results demonstrate that 1) thermal dose can be controlled in the presence of plant-model mismatch and 2) constraints on the maximum allowable temperatures in normal tissue and/or the pulsed power magnitude can be directly incorporated into MPC and met while delivering the desired thermal dose to the tumor. For relatively high blood flow rates and low transducer surface intensities--factors that limit the range of temperature variations in the tumor, the linear MPC, obtained by piece-wise linearization of the dose-temperature relationship, provides an adequate performance. For large temperature variations, the development of nonlinear MPC is necessary.     

A survey of digital computer memory systems

Many types of storage and memory systems have been proposed for use in digital computing systems. This survey paper discusses only the various systems whose reaction time is faster than human reaction time, employing a historical approach to the subject. Criteria for evaluation are discussed, and comparisons given among the different systems as to general applicability, ease of construction and use, speed of operation, latency time, memory span, and economy     

Structure of computer programs: A survey

A survey of reasons fog and methods of dividing large computer programs into parts is presented. The paper concentrates on over-all or external program structures (e.g., methods of sharing data among procedures) rather than on internal program structures, such as arrays, pointers, loops, and conditional statements. The paper classifies reasons for dividing programs as arising from 1) physical constraints such as limited memory space, and 2) human constraints such as division of programming responsibility. The principal tool fog organizing programs to meet human constraints is functional decomposition, i.e., dividing a program and its specifications according to (hopefully simple) functions of the program parts. Unfortunately, the various constraints which impose divisions upon a large program do not necessarily suggest the same program organisation. The central portion of the paper deals with mechanism for program compsition. These mechanisms are classified as 1) routines which are called by sequential process (a routine is any procedure-like software mechanism), 2) mechanisms for data sharing among routines (such as Fortran's common data blocks and Algol's scope rules), and 3) mechanisms for handling asynchronous interactions (such as requesting the scheduling of input/output operations). The paper also discusses techniques for folding programs to meet memory constraints (by overlaying, paging, and segmenting) and methods of linking separately compiled procedures.     

A few more analog computer simulations of RC voltage transfer functions

A new synthesis procedure is described to obtain additional analog computer simulations of RC voltage transfer functions.     

Signal processing aspects of computer music: A survey

The application of modern signal processing techniques to the production and processing of musical sound gives the composer and musician a level of freedom and precision of control never before obtainable. This paper surveys the use of analyis of natural sounds for synthesis, the use of speech and vocoder techniques, methods of artificial reverberation, the use of discrete summation formulae for highly efficient synthesis, the concept of the all-digital recording studio, and discusses the role of special-purpose hardware in digital music synthesis, illustrated with two unique digital music synthesizers.     

Building highway systems with computer graphic simulations

A number of computer applications generate perspective drawings of proposed highway designs as a means of design evaluation. The use of this capability is rare in the United States. Examples, developed in France, show computer-generated perspective drawings simulating several actual highway design situations. Highway construction costs are rapidly increasing in the United States prompting a need for design optimization including wider use of computer-generated perspectives and simulations. This is encouraging the development of network-supported intelligent interactive graphic terminals. Congressional testimony supports the need for better ways to communicate proposed highway and transportation system designs to citizen groups. Computer-generated dynamic simulations were used as a basis for Congressional testimony. Computer simulations have been proposed to evaluate alternate commercial signposting situations in the State of Oregon. Two techniques for producing color and landscape enhanced perspectives are available, and electronic microfilm recorders offer promise as a means of producing simulations. There is a growing need for computer-generated simulations for designing better highway systems, and the necessary experience and technology are available.     

人机交互中的语音情感识别研究进展

语音情感识别是当前信号处理、模式识别、人工智能、人机交互等领域的热点研究课题,其研究的最终目的是赋予计算机情感能力,使得人机交互做到真正的和谐和自然。本文综述了语音情感识别所涉及到的几个关键问题,包括情感表示理论、情感语音数据库、情感声学特征分析以及情感识别方法四个方面的最新进展,并指出了研究中存在的问题及下一步发展的方向。     

Multipoint temperature control during hyperthermia treatments:theory and simulation

A real-time multipoint feedback temperature control system has been designed and implemented with an ultrasound phased-array applicator for hyperthermia. The control parameters are the total power available from the supply and the dwell times at a sequence of preselected heating patterns. Thermocouple measurements are assumed for temperature feedback. The spatial operator linking available heating patterns to temperature measurements is measured at the outset of the treatment and can be remeasured on line an adaptive implementation. A significant advantage of this approach is that the controller does not require a priori knowledge of either the placement of the thermocouples or the power distribution of the ultrasound heating patterns. Furthermore, the control loop uses a proportional integral (PI) gain in conjunction with a singular value decomposition (SVD) of the spatial transfer operator. This approach is advantageous for robust implementation and is shown to properly balance the power applied to the individual patterns. The controller also deals with saturation in the inputs without integrator windup and, therefore, without temperature overshoot. Here, the authors present the theoretical formulation and representative simulation results of the proposed controller. The control algorithm has been verified experimentally, both in vitro and in vivo. A subsequent paper describing these results and the practical implementation of the controller will follow     

A survey of CW and pulsed Gunn oscillators by computer simulation

A computer simulation survey has been carried out on X-band CW and pulsed Gunn oscillators with a variety of contact conditions. It is shown that devices with a large cathode doping notch will have a nearly constant bias voltage-frequency product for optimum RF power generation. Such a relationship is not clear for devices with a smaller notch that is large enough to cause optimum injection of dipolar space charge. For both types of device there is an optimum ratio of transit frequency and cavity controlled frequency for optimum RF power generation. Several other detailed features of operation that cannot be explained by instantaneous-domain-formation models are dealt with, including the frequency dependence of the device conductance and capacity under conditions of optimum efficiency, and the bias current-voltage characteristics.     

A survey of systems approaches to green design with illustrationsfrom the computer industry

Increased recognition of the importance of sustainable development is posing new challenges for industry. A systems approach provides a framework for reconciling the needs of sustainable development with all of the other demands on industry. The computer industry has been chosen to illustrate the application of a systems approach to green design in industry on account of both its increasing economic importance and the increasing role of computers in society. A brief discussion of the current environmental impact of the computer lifecycle is presented to set the context for the discussion of systems approaches to green design, and a survey of existing systems-based design approaches and discussion of their application to the computer industry is given. A number of examples are presented to illustrate the advantages and application of a systems approach to green design, and the principles as well as some of the main issues in a systems approach to green design in the computer industry are discussed     

3-D computer simulations of resolution effects of multidetector point focusing SPECT imaging

The authors present an efficient algorithm and the results of its application in simulating the three-dimensional (3-D) projection data resulting from a 3-D distribution of radioactivity. The algorithm was applied to a series of geometrical mathematical phantoms and to a realistic mathematical brain phantom. The authors simulated the projection data from a multidetector single-photon emission computed tomography (SPECT) system with point focusing collimators. The simulated projection data were then reconstructed using the manufacturer's software. The objects simulated included simple geometrical solids such as spheres and sheets, as well as the distribution of muscarinic cholinergic receptors in a realistic brain slice. Spheres were chosen as a model for brain structures such as caudate nucleus, thalamus, and cerebellum; sheets were selected as representing lateral cortical gray matter regions. The results of these simulations indicate the existence of significant qualitative and quantitative artifacts in reconstructed human brain images.     

Perturbations in hyperthermia temperature distributions associated with counter-current flow: numerical simulations and empirical verification

Two numerical techniques are used to calculate the effect of large vessel counter-current flow on hyperthermic temperature distributions. One is based on the Navier-Stokes equation for steady-state flow, and the second employs a convective-type boundary condition at the interface of the vessel walls. Steady-state temperature fields were calculated for two energy absorption rate distributions (ARD) in a cylindrical tissue model having two pairs of counter-current vessels (one pair with equal diameter vessels and another pair with unequal diameters). The first assumed a uniform ARD throughout cylinder; the second ARD was calculated for a tissue cylinder inside an existing four antenna Radiofrequency (RF) array. A tissue equivalent phantom was constructed to verify the numerical calculations. Temperatures induced with the RF array were measured using a noninvasive magnetic resonance imaging technique based on the chemical shift of water. Temperatures calculated using the two numerical techniques are in good agreement with the measured data. The results show: 1) the convective-type boundary condition technique reduces computation time by a factor of ten when compared to the fully conjugated method with little quantitative difference (approximately 0.3 degree C) in the numerical accuracy and 2) the use of noninvasive magnetic resonance imaging (thermal imaging) to quantitatively access the temperature perturbations near large vessels is feasible using the chemical shift technique.     

Optimal fitting of computer model simulations to first transitcardiac radionuclide curves. II

A discrete-time, lumped-parameter mathematical model of the human cardiopulmonary circulation as it appears during a first-transit radionuclide study has been described. An optimal fitting process is used to match curves obtained from the model to curves obtained from first transit studies in order to estimate the parameters of the subject's heart. The development of the optimization technique is described in this paper. The results of testing the effects of overlapping compartments and errors in delay estimates are presented. A parameter determination analysis is performed by applying the optimization algorithm to simulated data. This analysis technique provides a method of estimating many parameters of heart function using a single, simple, rapid procedure. Results of clinical studies will be presented subsequently.     

Analytic results for the base region of bipolar transistors based on computer simulations

Empirical formulae for effective base Gummel number (including dopant dependent mobility and band-gap reduction effects), effective mobility (with integrated band-gap narrowing) and transit time as functions of the accessible parameters of pinched base sheet resistance and junction depths are studied. The results are verified using numerical analysis on a range of actual fabricated devices.     

计算机犯罪案件现场勘查中加密文件的破解

近年来,计算机犯罪案件已经呈现了急速上升的趋势,且更具有高智能的特性。多数犯罪分子都对其犯罪证据进行毁灭或加密,这给计算机犯罪案件的现场勘查和侦查带来了很大的难度。本文对经加密的犯罪信息和证据如何解密和还原进行了探讨,并给出了现场勘查中加密文件的几种破解方法。     

Embedding impedance of a millimeter wave Schottky mixer: Scaled model measurements and computer simulations

Using scaled model measurements at 2.5–12 GHz the embedding network of a 3 mm Schottky diode mixer has been developed. The noise performance of a cryogenic millimeter wave receiver was simulated by computer applying the developed equivalent circuit and diode parameters. The effects of impedance match at the fundamental frequency as well as at harmonic frequencies were studied. Also the effect of diode I-V-curve steepness was studied. The calculated results were compared with the experimental noise performance.     

A VLSI analog computer/digital computer accelerator

The design of a single-chip VLSI analog computer fabricated in a 0.25-/spl mu/m CMOS process is described. It contains 80 integrators, 336 other linear and nonlinear analog functional blocks, switches for their interconnection, and circuitry to enable the system's programing and control. The IC is controlled, programmed and measured by a PC via a data acquisition card. This arrangement has been used to simulate ordinary differential equations (ODEs), partial differential equations, and stochastic differential equations with moderate accuracy, significantly faster than a modern workstation. Techniques for using the digital computer to refine the solution from the analog computer are presented. Solutions from the analog computer have been used to accelerate a digital computer's solution of the periodic steady state of an ODE by more than 10/spl times/. The IC occupies 1 cm/sup 2/ and consumes 300 mW. An analysis has been done showing that the analog computer dissipates 0.02% to 1% of the energy of a general purpose digital microprocessor and about 2% to 20% of the energy of a digital signal processor, when solving the same differential equation.     

A dipole antenna for interstitial microwave hyperthermia

An improved interstitial microwave antenna design was investigated in static phantom experiments at 915 MHz and different insertion depths. Compared with conventional interstitial antennas, the presented dipole microwave antenna shows heating patterns which are concentrated on the dipole irrespective of the insertion depth. By analogy to interstitial radiotherapy, the microwave antenna allows a high concentration of energy in the target volume with as little damage as possible to the healthy surrounding tissue. The undesired heating of healthy tissue along the feeding line observed with conventional interstitial antennas is avoided. A λ/4 sleeve on the feeding line (which does not radiate microwave energy itself to the surrounding tissue) transforms an open end, i.e. a high impedance at the generator end of the dipole antenna. The current flowing back along the outside of the outer conductor of the feeding line in the direction of the generator is zero at this point. Both dipole sections have the same terminating impedance. Since the λ/4 sleeve is mounted outside the antenna, its mechanical length is not restricted by the mechanical length of the antenna. It can be charged with dielectric materials of low dielectricity constants     

A comparison of deep-heating electrode concepts for hyperthermia

There is mounting evidence that localized hyperthermia produced by electromagnetic waves may be useful in the treatment of cancer, and many innovative devices have been designed for this purpose. Most applicators employed for deep heating operate in the frequency region of 10-100MHz to provide greatest depth of penetration. Two basic categories of launching devices exist: E-field and H-field. The E-field applicators include conductive plates and fringing field devices; either may be used individually or in a multiple feed system. The H-field applicators include cylindrical and planar devices configured to produce specific heating patterns. We have analyzed and compared the performance of each of these devices, particularly in terms of engineering principles, design characteristics and their ability to transfer potentially therapeutic energy safely and at depth.