Estimation of Soil Erosion for a Himalayan Watershed Using GIS Technique

The fragile ecosystem of the Himalayas has been an increasing cause of concern to environmentalists and water resources planners. The steep slopes in the Himalayas along with depletedforest cover, as well as high seismicity have been major factors in soil erosion and sedimentation in river reaches. Prediction ofsoil erosion is a necessity if adequate provision is to be madein the design of conservation structures to offset the ill effects of sedimentation during their lifetime.In the present study, two different soil erosion models, i.e. theMorgan model and Universal Soil Loss Equation (USLE) model, have been used to estimate soil erosion from a Himalayan watershed.Parameters required for both models were generated using remotesensing and ancillary data in GIS mode. The soil erosion estimated by Morgan model is in the order of 2200 t km^-2 yr^-1 and is within the limits reported for this region.The soil erosion estimated by USLE gives a higher rate. Therefore, for the present study the Morgan model gives, for area located in hilly terrain, fairly good results.     

Improved implementation of search technique to find spanning trees

The authors have developed a set of algorithms to find the spanning trees, the minimal paths and minimal cutsets of a graph, starting from the incidence matrix of the graph [1,3]. All the above algorithms employ a unique tracing process based on search techniques. The above algorithms have a number of salient features. The arithmetic and logic operations are very simple, which makes it possible to design small desk top calculators capable of handling reasonably large and complex graphs. The major constraint of these equipments is the memory capacity vis à vis their capability of handling larger graphs. The authors designed a microprocessor based system [2] to find spanning trees. The end results were available in the form of code numbers of branches appearing in a spanning tree, which had to be noted down, every time a tree was generated. In the new system the end results are in a more compact form, i.e. the vectors (see definition), one vector for one tree. The user can easily note down the vectors and decode them later to obtain the branches of a tree. In the new system the user can reallocate the available working memory space to suit the problem. The memory requirement in the new approach is also less.     

The influence of heavy doping effects on the reverse recovery storage time of a diode

During the reverse recovery process in a modern Si p-n junction diode, the value of J_EO/J_BO (the ratio of emitter to base dark saturation currents) increases and the recombination of carriers in the emitter becomes important due to heavy doping effects. A theory is developed to take these effects into account. The emitter and the base components of the current during the reverse recovery phase are found to vary with time. However, their sum remains equal to the constant reverse current J_R, which flows in the external circuit. The ratio of the total quantity of charge present in the base to that present in the emitter is found to increase rapidly with time. Values of the storage time t_s for different values of J_EO/J_BO are calculated. In a typical case, the storage time is reduced by a factor 5 in a diode with J_EO/J_BO = 2. In such cases, the values of lifetime τ_B calculated using measured t_s values and the Kingston's formula, become inaccurate. Theoretical expression for the total charge Q_BS left in the base at t = t_s in a base dominated diode is derived.An earlier semi-empirical formula known as Kuno's formula is derived theoretically. It is found that the formula is valid both for the base dominated diode as well as in a diode with large contribution of the emitter but only when J_R/J_F is small. According to this formula t_s vs 1n(1 + J_F/J_R) plot is approximately a straight line with slope approximately equal to τ_B in both cases. For large values of J_R/J_F when t_s values are small, the correct formula shows that the plot is highly curved. An analysis of this part of the curve yields a value of J_EO/J_BO.     

The effect of built-in drift field and emitter recombinations on FCVD of a p-n junction diode

This paper discusses the Forward Current induced open circuit Voltage Decay (FCVD) of a p-n junction diode including the effects of recombinations in the emitter as well as the built-in drift fields in the base and in the emitter. The analysis is based on the quasi-static approximation (QSA) of the carrier profiles in the emitter. It is shown that the emitter effects on FCVD is completely determined by J_EO, the dark saturation current in the emitter. The value of J_EO in general, depends on the heavy doping effects in the emitter, the drift field in the emitter, emitter thickness and surface recombination velocity at the emitter surface. It is shown that for a diode with retarding drift field in the base, emitter recombinations play a very significant role in FCVD. The decay time constant for large values of time in this case is given by $\text{τ}{}_{\mathrm{<mtext>eff</mtext>}}\text{= τ}{}_{\mathrm{B}}\text{/[1 + ?}{}_{\mathrm{B}}{}^2\text{? (a ? ?}{}_{\mathrm{B}}\text{)}{}^2\text{],}\text{where}\text{a = J}{}_{\mathrm{EO}}\text{/J}{}_{\mathrm{BO}}\text{, ?}{}_{\mathrm{B}}$ is the drift field parameter in the base. The higher value of a, the faster is the voltage decay. For accelerating fields in the base, the time constant for large values of time is independent of emitter recombinations and is given by $\text{τ}{}_{\mathrm{<mtext>eff</mtext>}}\text{= τ}{}_{\mathrm{B}}\text{/(1 + ?}{}_{\mathrm{B}}{}^2\text{)}$. However, the decay rate for small values of time is strongly affected by emitter recombinations for both types of the field; the higher the emitter recombinations, the faster is the initial rate of the voltage decay. For extremely strong drift fields in the base, QSA in the emitter is not valid. The coupled continuity equations are solved with the conditions $\text{?}{}_{\mathrm{B}}{}^2\text{? τ}{}_{\mathrm{B}}\text{/τ}{}_{\mathrm{E}}$ and an analytic expression for FCVD is derived. It is seen that FCVD for strong base fields is determined solely by emitter lifetime τ_E except for small values of time of the order of a few τ_E.     

Surface distortion features on indented CaF2 cleavages

Surface distortion features around static indents on the cleavages of CaF₂ single crystals have been investigated by multiple beam interference technique. At room temperature microcracks around such indents nucleate at the sinking in regions. Fizeau fringe patterns (around indents at 200° C) revealed a transition from a three-fold to a six-fold material flow.     

Bandwidth compression of noisy images

The effect of additive noise on Discrete Fourier Transform of pictorial data (2DFT) must be considered in several important problems such as filtering, enhancement and bandwidth compression. This paper investigates the statistical properties of the corrupted 2DFT coefficients, and the error involved in reconstruction when a subset of these coefficients is employed for the purpose. The latter being often the case, the present analysis provides a rational basis for frequency selection and filter specification. Application of an F-test quantifies the reliability of filtering or bandwidth compression.