Microwave photovoltage and photoresistance effects in ferromagnetic microstrips

We investigate the dc electric response induced by ferromagnetic resonance in ferromagnetic Permalloy (Ni80Fe20) microstrips. The resulting magnetization precession alters the angle of the magnetization with respect to both dc and rf current. Consequently the time averaged anisotropic magnetoresistance (AMR) changes (photoresistance). At the same time the time-dependent AMR oscillation rectifies a part of the rf current and induces a dc voltage (photovoltage). A phenomenological approach to magnetoresistance is used to describe the distinct characteristics of the photoresistance and photovoltage with a consistent formalism, which is found in excellent agreement with experiments performed on in-plane magnetized ferromagnetic microstrips. Application of the microwave photovoltage effect for rf magnetic field sensing is discussed.Comment: 16 pages, 15 figure

Thermal Performance of an Adobe Structure Integrated with an Earth-Air Heat Exchanger: An Experimental Study

In this paper an attempt has been made to study annual thermal performance of an adobe structure with an effective area of 53 m2 located at solar energy park at Indian Institute of Technology Delhi, New Delhi ( 280 35' N,770 12' E ), India. Such houses are suitable for rural areas for various reasons e.g. storage of grains, low energy consumption, thermal comfort, made by local materials and environmental friendly. Experiments have been conducted during June 2004-May 2005 to measure hourly variation of room air temperature of room with an earth-air heat exchanger, untreated room and room with cross ventilation. Hourly variation of solar intensity, ambient temperature, inlet-outlet temperature of an earth-air heat exchanger has been measured. Analysis has been done by calculating average and maximum\minimum temperature of each room in each month. It has been found that room equipped with an earth-air heat exchanger gives best comfort among all other. It is seen that temperature of room with an earthair heat exchanger is 6.5 oC more and 3.0 oC less than temperature of untreated room in December and May month. Experimental uncertainties for December and May for room with an earth-air heat exchanger have been found out 11.9 and 3.0 % respectively

The value of rapid functional assays of germline p53 status in LFS and LFL families

We have tested two rapid assays of p53 function, namely the apoptotic assay and the FASAY as means of detecting germline p53 mutations in members of Li–Fraumeni and Li–Fraumeni-like families. Results of the functional assays have been compared with direct sequencing of all 11 exons of the p53 gene. The results show good agreement between the two functional assays and between them and sequencing. No false-positives or negatives were seen with either functional assay although the apoptotic assay gave one borderline result for an individual without a mutation. As an initial screen the apoptotic assay is not only rapid but inexpensive and very simple to perform. It would be expected to detect any germline defect that leads to loss of p53 function. The apoptotic assay could be ideal as a means of prescreening large numbers of samples and identifying those that require further investigation. The FASAY detects mutations in exons 4–10, is rapid and distinguishes between functionally important and silent mutations. © 2000 Cancer Research Campaig

Magneto-electrodynamics at high frequencies in the antiferromagnetic and superconducting states of DyNi_2B_2C

We report the observation of novel behaviour in the radio frequency (rf) and microwave response of DyNi_2B_2C over a wide range of temperature (T) and magnetic field (H) in the antiferromagnetic (AFM) and superconducting (SC) states. At microwave frequencies of 10 GHz, the T dependence of the surface impedance Z_s=R_s+iX_s was measured which yields the T dependence of the complex conductivity \sigma_1-i\sigma_2 in the SC and AFM states. At radio frequencies (4 MHz), the H and T dependence of the penetration depth \lambda(T,H) were measured. The establishment of antiferromagnetic order at T_N=10.3 K results in a marked decrease in the scattering of charge carriers, leading to sharp decreases in R_s and X_s. However, R_s and X_s differ from each other in the AFM state. We show that the results are consistent with conductivity relaxation whence the scattering rate becomes comparable to the microwave frequency. The rf measurements yield a rich dependence of the scattering on the magnetic field near and below T_N. Anomalous decrease of scattering at moderate applied fields is observed at temperatures near and above T_N, and arises due to a crossover from a negative magnetoresistance state, possibly associated with a loss of spin disorder scattering at low fields, to a positive magnetoresistance state associated with the metallic nature. The normal state magnetoresistance is positive at all temperatures for \mu_0H>2T and at all fields for T>15K. Several characteristic field and temperature scales associated with metamagnetic transitions (H_M1(T), H_M2(T)) and onset of spin disorder H_D(T), in addition to T_c, T_N and H_c2(T) are observed in the rf measurements.Comment: 9 pages, Latex, Uses REVTeX, This and related publications also available at http://sagar.physics.neu.edu/ Submitted to Phys. Rev.

Excitation Theory for Space-Dispersive Active Media Waveguides

A unified electrodynamic approach to the guided-wave excitation theory is generalized to the waveguiding structures containing a hypothetical space-dispersive medium with drifting charge carriers possessing simultaneously elastic, piezoelectric and magnetic properties. Substantial features of our electrodynamic approach are: (i) the allowance for medium losses and (ii) the separation of potential fields peculiar to the slow quasi-static waves. It is shown that the orthogonal complementary fields appearing inside the external source region are just associated with a contribution of the potential fields inherent in exciting sources. Taking account of medium losses converts the usual orthogonality relation into a novel form called the quasi-orthogonality relation. It is found that the separation of potential fields reveals the fine structure of interaction between the exciting sources and mode eigenfields: in addition to the exciting currents interacting with the curl fields, the exciting charges and the double charge (surface dipole) layers appear to interact with the quasi-static potentials and the displacement currents, respectively.Comment: LaTeX 2.09, 28 pages with mathematical appendi