Kasra Daneshvar

Laser rapid prototyping in nonlinear medium

We have measured the second harmonic generation (SHG) using a 1.06 μm Q-switched pump beam in powdered nonlinear crystals suspended in a photopolymeric solution. The powdered crystals used include lithium niobate, LiNbO3, and potassium titanyl phosphate. Measurements were made as a function of the grain size and the number of grains per unit volume. The photopolymeric solution is transparent at the pump beam frequency while it is highly absorbing at the SH and it is the SH which transforms the photopolymer from liquid to solid. The results show that relatively intense SH incoherent light is produced in powder after the pump intensity exceeds a certain threshold. SHG does not depend on the grain size up to a critical grain size beyond which SHG falls off rapidly. Furthermore, the emission increases linearly as a function of the number of grains per unit volume and eventually levels off and stays constant. A practical focus of these studies has been in the areas of laser induced rapid prototyping and three ...

Matrix and thermal effects on photoluminescence from PbS quantum dots

Lead sulfide nanoquantum dot samples were prepared with sol gel materials, a capping agent, and with various concentrations of PbS quantum dots. The –OH group absorption was significantly reduced during the heating process. The calculated quantum dot sizes were 1.2 nm for undoped sol gel and 0.97 nm for zirconium-doped sol gel. Without a capping agent, no photoluminescence was observed for a wide range of PbS particle concentrations. Strong photoluminescence was achieved with a capping agent when excited by a 480 nm wavelength xenon light source at room temperature. Luminescence quenching was observed with an extra –SH group from the matrix and excess H2S exposure. The quenching process typically broadened the spectra and blueshifted the peak when there was excess sulfur. The band gap energy was shifted from 1.64 to 1.68 eV for the zirconium-doped samples and 1.54–1.56 eV for the zirconium-free samples at room temperature. The thermal process significantly enhanced the luminescence intensity and redshifte...

CdS quantum dots in hybrid sol–gel matrix; absorption and room-temperature photoluminescence

Strong room-temperature luminescence spectra for cadmium sulfide (CdS) nanometer quantum dots (NQDs) were obtained using a xenon lamp. The samples were fabricated of various concentrations of semiconductor NQDs in the hybrid sol–gel matrix. Concentration dependent total absorption showed a linear relationship following the Beer–Lambert law. An excess H2S source reduced the luminescence intensity, shifted the spectra peak to the red, and broadened the spectra. These excess H2S phenomena disappeared after a certain period of time in ambient conditions. The result showed that strong luminescence in CdS in hybrid-sol–gel matrix can be achieved without any casing.

Wideband negative permeability metamaterial with non-Foster compensation of parasitic capacitance

The analysis and simulation of negative effective permeability of a magnetic metamaterial is presented, including parasitic effects. Beyond known issues of non-Foster circuit stability, such parasitics can limit bandwidth improvement. Based on the analysis, ideal non-Foster elements are added to split rings to achieve broadband negative effective permeability while compensating parasitic effects. Results indicate that both a negative capacitance and negative inductance are needed to achieve negative permeability from 0.5 to 4.5 GHz.

High current nanosecond pulse generator

A simple circuit that can generate current pulses with amplitudes ranging from 100 mA to 5 A and with pulse widths varying from 2 ns to 10 ns, is constructed. It is noted that this current pulser is ideal for driving low impedance loads under 10 Omega and uses only low-voltage power supplies. Current pulses are formed using a shunt-series type step recovery (charge storage) diode circuit in conjunction with several power MOSFETs. A unique biasing scheme has been used to store charge on the step recovery diodes, which eliminates the DC bias current normally used in this configuration.<<ETX>>

Electrical resistivity and Hall effect of TiSi2 thin films in the temperature range of 2–300 K

The electrical resistivity and Hall effect of TiSi2 thin films were measured systematically in the temperature range of 2–300 K. The results were compared with theory and other work. The TiSi2 films were formed by Ti/Si solid‐state interaction on crystalline silicon or polysilicon substrates. The temperature dependence of the electrical resistivity of TiSi2 was approximated by the Bloch–Gruneisen theory. The Hall‐effect data show a multicarrier conduction mechanism in TiSi2. At low temperatures the Hall coefficient is positive for both substrates, but is negative at room temperature. The temperature at which the change of sign occurs is approximately 180 K for the crystalline‐Si substrate, and approximately 90 K for the polysilicon substrate. This is discussed briefly in terms of scattering mechansims for a simple model of the electronic structure.

Integrating optical and electrical engineering courses

The expansion in the fields of optical engineering and optoelectronics has made it essential to introduce optical engineering concepts into undergraduate courses and curricula. Because of limits on the number of course requirements for the B.S. degree, it is not clear how these topics should be introduced without replacing some of the traditional requirements. This paper demonstrates how optical engineering concepts can be easily presented as an integral part of electrical engineering subjects, with a minimal amount of replacement, while enhancing the depth and understanding of both fields. Courses such as linear signals and systems, electricity and magnetism, and electronics which traditionally represent the core requirements of the undergraduate electrical engineering curriculum contain subjects that have direct correlations with optical engineering concepts. The major changes that are needed are the creation of textbooks that contain concepts and examples in areas of both optical and electrical engineering and some relearning and familiarization on the part of instructors. This approach allows for a fresh look at courses being offered in electrical engineering, while providing the necessary background in optical engineering for students.

Hall effect of the high‐Tc superconducting Bi‐Sr‐Ca‐Cu‐O thin film

The Hall effect of BiSrCaCuO thin film is studied in the temperature range of 2–300 K. In the normal state the Hall‐effect data show a holelike carrier conduction and the Hall coefficient decreases slowly with increasing temperature. The hole density obtained at room temperature is 3×1021 cm−3. Near the superconducting transition temperature (TMid =83 K), the Hall coefficient shows a rapid change and drops sharply from a positive value to a negative minimum value with decreasing temperature.The possible physical meaning of the obtained results is discussed.

Combining predictive capabilities of transcranial doppler with electrocardiogram to predict hemorrhagic shock

Hemorrhagic shock (HS) potentially impacts the chance of survival in most traumatic injuries. Thus, it is highly desirable to maximize the survival rate in cases of blood loss by predicting the occurrence of hemorrhagic shock with biomedical signals. Since analyzing one physiological signal may not enough to accurately predict blood loss severity, two types of physiological signals - electrocardiography (ECG) and transcranial Doppler (TCD) - are used to discover the degree of severity. In this study, these degrees are classified as mild, moderate and severe, and also severe and non-severe. The data for this study were generated using the human simulated model of hemorrhage, which is called lower body negative pressure (LBNP). The analysis is done by applying discrete wavelet transformation (DWT). The wavelet-based features are defined using the detail and approximate coefficients and machine learning algorithms are used for classification. The objective of this study is to evaluate the improvement when analyzing ECG and TCD physiological signals together to classify the severity of blood loss. The results of this study show a prediction accuracy of 85.9% achieved by support vector machine in identifying severe/non-severe states.

Electrical properties of conductive metal/insulating shell nanocluster array

We have investigated conduction in a closely packed nanocluster array of copper with a copper oxide nano shell as a function of temperature. The result is found to be nonlinear and shows a sudden increase in electrical conductivity above a critical temperature. An attempt has been made to explain this anomalous behavior in terms of electrical and physical properties of the metallic nanostructure.