Mathematical Modeling of Thermomechanical Processes under Intense Thermal Effect

Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type.     

Evanescently coupled photodiodes integrating a double-stage taper for 40-Gb/s applications-compared performance with side-illuminated photodiodes

The design, fabrication, and performance of double-stage taper photodiodes (DSTPs) are reported. The objective of this work is to develop devices compatible with 40-Gb/s applications. Such devices require high efficiency, ultrawide band, high optical power handling capability, and compatibility with low-cost module fabrication. The integration of mode size converters improves both the coupling efficiency and the responsivity with a large fiber mode diameter. Responsivity of 0.6 A/W and 0.45 A/W are achieved with a 6-/spl mu/m fiber mode diameter and cleaved fiber, respectively, providing relaxed alignment tolerances (/spl plusmn/1.6 /spl mu/m and /spl plusmn/2 /spl mu/m, respectively), compatible with cost-effective packaging techniques. DSTPs also offer a wide bandwidth greater than 40 GHz and transverse-electric/transverse-magnetic polarization dependence lower than 0.2 dB. Furthermore, a DSTP saturation current as high as 11 mA results in optical power handling greater than +10 dBm and a high output voltage of 0.8 V. These capabilities allow the photodiode to drive the decision circuit without the need of a broad-band electrical amplifier. The DSTP devices presented here demonstrate higher responsivities with large fiber mode diameter and better optical power handling capabilities and are compared with classical side-illuminated photodiodes.     

The measurement of solar array discharges in a simulated spaceenvironment

A spacecraft in a plasma builds up charge on all the dielectric surfaces and interfaces. Once the net charge exceeds the dielectric breakdown of the material, a discharge occurs. One of the more susceptible pieces of equipment is the antenna/receiver system. The radiated E-field may be strong enough to create an ambiguous signal which may be misinterpreted by the system electronics and cause a system malfunction. A technique is developed to monitor the radiated E-field of materials discharging in an electron environment, using vacuum chambers for measuring the material discharges which are made of highly reflective materials. These chambers affect the radiated E-field due to multiple reflections from the walls. The technique developed defines a method for correcting the effects caused by the measurement facilities. The methodology is: monitor the radiated E-field with a broadband dipole antenna, and digitize the radiated signal as a function of time. Determine the frequency response of the radiated E-field using an FFT algorithm. Measure the transmission and reflection characteristics of the two-port network inside the measurement chamber, and determine the impedance network from the measured E-parameters across the frequency band of interest. Transform the measured E-field frequency response through the impedance network to obtain the frequency response of the actual radiated discharge current. Find the inverse FFT of this response to obtain the actual radiated discharge current response. This technique aids in the prediction of the E-field coupling into receive antennas on-board actual satellites     

Non-resonant RF and microwave response: A novel technique for the characterization of superconducting materials

When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT _c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination of material parameters of interest such asJ _c andH _c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The details of these aspects are discussed.     

Effect of pulse time gate on CsI(T1) light output

The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval.     

A base-band NDS electrode configuration for HACT devices

Heterostructure Acoustic Charge Transport (HACT) devices have been fabricated with a new nondestructive sense (NDS) electrode structure that provides for the recovery of base-band signals without the use of an integrating capacitor. This electrode structure provides an output signal comprising an RF carrier at the SAW frequency, amplitude modulated by the sampled input signal which has been delayed by a period proportional to the output electrodes distance from the input diode. The output of the NDS electrode structure is subsequently demodulated to provide the base-band signal     

Endometrioid carcinoma arising from endometriosis of the sigmoid colon during estrogenic treatment

A case of endometrioid carcinoma arising from endometriosis of the sigmoid colon is reported. The patient had been treated with unopposed continuous estrogen injection for twenty years after bilateral salpingo-oophorectomy because of severe endometriosis. The pathology, pertinent literature and implications of the present case are discussed.