http://nopr.niscair.res.in/handle/123456789/1819 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/1912 Title: Design, fabrication and characterization of microstrip square patch antenna array for X-band applications <br/> <br/>Authors: Sood, Deepak; Singh, Gurpal; Tripathi, Chander Charu; Sood, Suresh Chander; Joshi, Pawan <br/> <br/>Abstract: Microstrip patch antenna array to be used for X-band short-range microwave applications has been introduced. This antenna maintains a maximum gain of 14.6 dB for far field region w.r.t paraboloidal rectangular aperture antenna. It is actually a probe (coaxial) fed antenna with quarter wave sections that are fabricated as an arrangement for impedance matching with 50 Ω coaxial cable. This antenna works well in the frequency range 8.45-9.33 GHz with a maximum at 8.53 GHz. It is basically a low cost, lightweight, medium gain and narrowband antenna and suited for short-range microwave applications such as a feeding element for other antennas and in research institutes as a reference antenna. It can also be used at the output of signal conditioning circuit for receiving signals from micro electromechanical sensors. <br/> <br/>Page(s): 593-597 Tue, 29 Jul 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/1911 Title: Role of binding energy in the generation of photocurrent in bulk heterojunction organic materials <br/> <br/>Authors: Sharma, S K; Bothra, Chandra; Sharma, G D <br/> <br/>Abstract: The role of binding energy of electron hole pair in the generation of photocurrent has been studied using Braun’s model based on Onsager theory. For the study, two bulk heterojunction devices namely poly (2-methoxy-5-(3′,7′- dimethyloctyloxy)-p-phenylene vinylene)(OC₁C₁₀-PPV) and poly (2-methoxy-5-(3′, 7′-dimethyloctyloxy)-1-4-phenylene vinylene) (MDMO-PPV) have been chosen. These materials act as electron donor in the bulk hetero-junctions and are based on intermixing of conjugate polymers and fullerene derivatives. Photocurrent has been calculated theoretically for different values of exciton binding energies. The variation of photocurrent with binding energy shows that a constant value of photocurrent is obtained up to a threshold value of 0.6 eV. When binding energy exceeds the threshold value, photocurrent diminishes rapidly. Thus, binding energy plays an important role in the generation of photocurrent and can be used as a primary parameter for the characterization of organic semiconductors in solar cell applications. <br/> <br/>Page(s): 588-592 Tue, 29 Jul 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/1910 Title: Electric field dependent microwave losses in BaxSr₁₋xTiO₃ perovskites <br/> <br/>Authors: Kukreti, Ashish; Kumar, Ashok; Naithani, U C <br/> <br/>Abstract: The electric field dependent microwave loss of anharmonic BaxSr₁₋xTiO₃ perovskites has been calculated in its para electric phase from the Silverman Joseph Hamiltonoian augumented with fourth order phonon co-ordinates using double time Greens functions. The results are used to obtain an expression for the frequency and temperature dependence of dielectric loss at microwave frequencies due to impurity and anharmonic scattering. The loss tangent consists of a contribution which is quadratic in applied biasing and field independent. The variation of tan δ with applied field is noticeable in the vicinity of Curie temperature . In the higher temperature region, the electric field effect ceases and the increase in loss arises mainly due to higher order anharmonic terms. <br/> <br/>Page(s): 580-587 Tue, 29 Jul 2008 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/1909 Title: Superconducting transition temperature of co-doped Y₀․₉₅Pr₀․₀₅Ba₂(Cu₁₋xMnx)₃O₇₋δ superconductors for x ≤ 0.02 <br/> <br/>Authors: Gahtori, Bhasker; Lal, R; Agarwal, S K <br/> <br/>Abstract: Values of the superconducting transition temperature Tc extracted from the resistivity and ac susceptibility of Y₀․₉₅Pr₀․₀₅Ba₂(Cu₁₋xMnx)₃O₇₋δ (x ≤ 0.02) are found to follow the same qualitative variation with the Mn content. Both lead, in particular, to lower Tc for the x=0.005 sample than those of the x=0.0, 0.0075 and 0.01 samples. Comparing Tc with difference of resistivities with and without Pr for various x, it has been argued that electronic effects dominate over the potential scattering in suppressing Tc below x=0.02. Superconducting volume fraction fg (as deduced through imaginary part ϰ″ of the ac susceptibility at the peak temperature) when considered in conjunction with the average grain size for the x=0.005 sample, indicates that the smaller size of the grains in x=0.005 sample leads to stronger fluctuations. This is an additional source for the larger Tc degradation in the x=0.005 sample. <br/> <br/>Page(s): 575-579 Tue, 29 Jul 2008 22:58:59 GMT