Operational Trans-Resistance Amplifier Based Tunable Wave Active Filter

In this paper, Operational Trans-Resistance Amplifier (OTRA) based wave active filter structures are presented. They are flexible and modular, making them suitable to implement higher order filters. The circuits implement the resistors using matched transistors, operating in linear region, making them well suited for IC fabrication. They are insensitive to parasitic input capacitances and input resistances due to the internally grounded input terminals of OTRA. As an application, a doubly terminated third order Butterworth low pass filter has been implemented, by substituting OTRA based wave equivalents of passive elements. PSPICE simulations are given to verify the theoretical analysis

Shallow Deep Transitions of Neutral and Charged Donor States in Semiconductor Quantum Dots

We carry out a detailed investigation of neutral ($D^0$) and charged ($D^-$) impurity states of hydrogen-like donors in spherical semiconductor quantum dots. The investigation is carried out within the effective mass theory (EMT). We take recourse to local density approximation (LDA) and the Harbola-Sahni (HS) schemes for treating many-body effects. We experiment with a variety of confining potentials: square, harmonic and triangular. We observe that the donor level undergoes shallow to deep transition as the dot radius ($R$) is reduced. On further reduction of the dot radius it becomes shallow again. We term this non-monotonic behaviour \textbf{SHADES}. This suggests the possibility of carrier {\textbf{\textit{``freeze out''}}} for both $D^0$ and $D^-$. Further, our study of the optical gaps also reveals a {\textbf{SHADES}} transition.Comment: 19 pages, 8 figures, Revised Versio

Response time correlations for platinum resistance thermometers in flowing fluids

The thermal response of two types of Platinum Resistance Thermometers (PRT's), which are being considered for use in the National Transonic Wind Tunnel Facility, were studied. Response time correlations for each PRT, in flowing water, oil and air, were established separately. A universal correlation, tau WOA = 2.0 + 1264, 9/h, for a Hy-Cal Sensor (with a reference resistance of 100 ohm) within an error of 20% was established while the universal correlation for the Rosemount Sensor (with a reference resistance of 1000 ohm), tau OA = 0.122 + 1105.6/h, was found with a maximum percentage error of 30%. The correlation for the Rosemount Sensor was based on air and oil data only which is certainly not sufficient to make a correlation applicable to every condition. Therefore, the correlation needs more data to be gathered in different fluids. Also, it is necessary to state that the calculation of the parameter, h, was based on the available heat transfer correlations, whose accuracies are already reported in literature uncertain within 20-30%. Therefore, the universal response constant correlations established here for the Hy-Cal and Rosemount sensors are consistent with the uncertainty in the input data and are recommended for future use in flowing liquids and gases

BVRI CCD photometric standards in the field of GRB 990123

The CCD magnitudes in Johnson $BV$ and Cousins $RI$ photometric passbands are determined for 18 stars in the field of GRB 990123. These measurements can be used in carrying out precise CCD photometry of the optical transient of GRB 990123 using differential photometric techniques during non--photometric sky conditions. A comparison with previous photometry indicates that the present photmetry is more precise.Comment: Tex file, 5 pages with 1 figure. Bull. Astron. Society India, Vol. 27 (accepted

Grassland Management in Wildlife Protected Areas (PA\u27s) in India

Ecological status of Indian grasslands had been a subject of conflicting opinion in the past. Existing grasslands are anthropogenic in origin except, Himalayan meadows in high altitudes. Extensive clearing of the forests for human settlements, agricultural cultivation and domestication of animals in the past have been resulted into opening of pockets/grasslands amidst the forest areas. Such tame grasslands are categorized as succession or rotational grasslands. There are four categories of PAs viz., National parks, wildlife sanctuaries, conservation reserves and community reserves. Thus, 683 PAs (102 national parks, 551 wildlife sanctuaries, 47 conservation reserves and 04 community reserves) spread over an area of 164985 sq km (about 5% of total geographic area) have been constituted in different biogeographic zones of the country, most of PAs are situated in the forest ecosystems. According to the report of the Forestry Commission (2006), nearly 40% of these PAs are suffering from livestock grazing and fodder extraction by the inhabitants of well-established villages. At the beginning, ‘Project Tiger’ was launched in the year 1972-73 for conservation of tiger and their habitats, consisting of entire food web in the natural ecosystem, including prey species. A step ahead, till 2005, 28 Tiger Reserves spread over 37,700 sq km in 17 States, have been established and representing to different bio regions of the country