Transient Slope Research Articles

A Predictive-Adaptive, Multipoint Feedback Controller for Local Heat Therapy of Solid Tumors

Uniform heating of tumor tissue to therapeutic temperatures without damaging surrounding normal tissue is required for optimal local heat therapy of cancer. This paper describes an algorithm for on-line computer control that will allow the therapist to minimize the standard deviation of measured intratumoral temperatures. The method is applicable to systems incorporating multiple surface and/or interstitial applicators delivering microwave, radiofrequency, or ultrasonic power and operating under control of a small computer. The essential element is a novel predictive-adaptive control algorithm that infers relevant thermal parameters from the responses of multiple temperature sensors as each of the power applicators is briefly turned off. Applied power and effective perfusion are estimated from transient slope changes of the temperature-time curves for each sensor. By substituting these values into a system of linear equations derived from the bio-heat transfer equation, the small computer can calculate the optimal allocation of power among the various applicators (knob settings) to generate most uniform intratumoral temperature distribution with the desired mean, or minimum, tumor temperature.

Transient response of a string on an elastic base

The transient response of a stretched string resting on an elastic base and subjected to impulsive end loading is treated herein. The analysis is based on the concept of a wave as a carrier of discontinuities in the field variable and its derivatives. These discontinuities are determined from a recurrence relation which is in turn generated by using a time-harmonic asymptotic series solution to the equation of motion. Numerical examples are treated where the responses of the string to delta and step function boundary loads are obtained. The results confirm the influence of the base modulus on the transient displacement, velocity and slope distributions in the string. The distortion of the transients and the discontinuities in the velocity and slope are evident from the results presented. The transient response of the string due to other boundary conditions can be obtained by using the present results.

STRESS DEPENDENCE OF DEFECT LEVELS IN SEMICONDUCTORS

New criterion for symmetric properties of defect potential in semiconductors is presented. For a degenerate energy level Es, we introduce the average Es of energy splitling under stress. Es is invariant under symmetry operation of Hamiltonian. Therefore, it is straight foward to reduce the stress coefficient tensor of Es by group theoretical method. For instance, for cubic semiconductors, if the defect level ET is withdefect potential of T group symmetry, the uniaxial stress coefficient of (?(Ec-ET))/(?F) or (?(ET-Ev))/(?F) is isotropic and equal to one third of corresponding hydrostatic pressurecoefficient. The case of defect potential with C3v symmetry is also discussed.The electron (or hole) emission and capture processes of defect levels under energy splitting are analysed. The weighted average of emission rate en and capture rate cn satisfy the following relation: en=gTgc-1cnN′ce(-(Bc-BT)/kT) By measuring the stress dependence of en., various schemes for determining the symmetry property of defect potential are discussed. The transient processes under defect level splitting are also discussed. When transitions are al lowed between the splitting states, the transient is exporential with single decay time constant en-1. When transitions between different states are forbidden, the transient is decay with multi-exponential time constants. en is determined by the initial transient slope.

Meaning of the cardiac output-blood volume relationship in essential hypertension.

This study interprets the cardiac output-blood volume relationship in essential hypertension. Previous reports indicated that the chronic volume-flow slope (i.e., the regression coefficient alpha, cardiac output = alpha blood volume + beta, obtained from steady-state volume and flow) and the transient volume-flow slope observed during a dextran infusion were both steeper in essential hypertensives than in normotensives. By applying the Guyton-Coleman circulatory model to essential hypertension, this reports demonstrates that: 1) several alterations of the circulatory system may theoretically change the steady state of volume and flow and generate a chronic volume-flow relationship. However, only alterations of the kidney function and of the autonomic nervous system may produce a volume-flow curve compatible with the available data. 2) As hypertension develops, vascular resistance and compliance have the greatest influence on the slope of the chronic volume-flow curve. 3) To account for the observed increase of this slope in the transition from normotension to essential hypertension, not only must resistance be increased but also compliance must be reduced in essential hypertension. The same conclusions are drawn from the study of the transient volume-flow relationship observed during the dextran infusion.

Determination of minority-carrier lifetime in silicon solar cells from laser-transient photovoltaic effect

The minority-carrier lifetime in the base of silicon solar cells has been determined from the transient decay slope of the short-circuit current after pulsed-laser carrier excitation. Two series of solar cells with the same thickness (400 μm) and with base resistivities of 0.1 and 1 Ω cm, respectively, have been analyzed. The values for the lifetime are 2.4/6.0 μs for the 1-Ω cm resistivity cells and of 5.2/19.1 μs for the other ones. The extreme values correspond to back-surface recombination velocity S = 0 or S = ∞. The results are in reasonable agreement with those obtained by other authors with the surface photovoltage method.

Diurnal photosynthetic performance of seaweeds measured under natural conditions

Statements comparing photosynthetic performance characteristics of species rely upon empirical data, usually light-saturation curves (photosynthesis, P, versus incidentlight flux-density, I o, relationships) derived from instantaneous measurements. The specific comparative parameters are initial slope and maximum photosynthesis, P max. For phytoplankton, diurnal variation in specific productivity at maximum incident light, I max is typically asymmetrical, i.e., there is a morning maximum followed by an afternoon depression. Five seaweed species, numerical dominants from the Outer Banks of North Carolina, were examined for patterns of diurnal photosynthetic performance in sunlight of habitat equivalence. These were Codium decorticatum (Woodw.) Howe and Ulva curvata (Kutz.) De Toni in the Chlorophyceae, Dictyota dichotoma (Huds.) Lamour. and Petalonia fascia (O.F. Mull.) Kuntze in the Phaeophyceae, and Gracilaria foliifera (Forssk.) Borg. in the Rhodophyceae. Diurnal patterns of oxygen exchange were varied, some symmetrical about the midday axis, others asymmetrical, and were specific for (1) species, (2) derived habitat, (3) thallus absorptance (1-I/I o, where I is the transmitted light), (4) developmental stage, and (5) diurnal photosynthetically active radiation (PAR) history. All species show a depression in oxygen exchange rates at less than 0.1 I max, and show varying degrees of recovery when I o decreases from that value. Diurnal photosynthetic performance of some species at 0.03 I o (total diurnal maximum) exceeds several times that at 0.70 I o (total diurnal maximum), an observation not predicted by instantaneous measurements. Specific day-rate integrals of I o vary, producing transient initial slope and P max values. Thus, initial slope and P max values derived from instantaneous measurements in the laboratory bear little relationship to actual diurnal production. At this time there appears to be no substitute for direct measurement of diurnal photosynthesis.

Transient Response of a Shear Beam to Correlated Random Boundary Excitation

The transient mean-square displacement, slope, and relative motion of a viscously damped shear beam subjected to correlated random boundary excitation is presented. The effects of various system parameters including the spectral characteristics of the excitation, the delay time between the beam support motion, and the beam damping have been investigated. Marked amplifications in the mean-square response are shown to occur for certain dimensionless time delays.