Design Verification Model of Rubidium Frequency Standard for Space

In this paper, we report the development of the design verification model (DVM) of Rb atomic frequency standard for the Indian Regional Navigational Satellite System (IRNSS) programme. Rb atomic clock is preferred for the space applications as it is light-weight and small in size with excellent frequency stability for the short and medium term. It has been used in all other similar navigation satellite systems including GPS, GLONASS Galileo etc. The Rb atomic frequency standard or clock has two distinct parts. One is the physics package where the hyperfine transitions produce the clock signal in the integrated filter cell or separate filter cell configuration and the other is the electronic circuits which include frequency synthesizer for generating the resonant microwave hyperfine frequency, phase modulator and phase sensitive detector. In this paper, the details of the Rb physics package and the electronic circuits are given. The reasons for the mode change in Rb lamp have been revisited. The effect of putting the photo detector inside the microwave cavity is studied and reported with its effect on the resonance signal profile. The Rb clock frequency stability measurements have also been discussed.

Comparative analysis of multi-criteria probabilistic FR and AHP models for forest fire risk(FFR)mapping in Melghat Tiger Reserve(MTR)forest

A comparative study of Frequency Ratio(FR)and Analytic Hierarchy Process(AHP)models are performed for forest fire risk(FFR)mapping in Melghat Tiger Reserve forest,central India.Identification of FFR depends on various hydrometeorological parameters altitude,slope,aspect,topographic position index,normalized differential vegetation index,rainfall,air temperature,land surface temperature,wind speed,distance to settlements,and distance by road are integrated using a GIS platform.The results from FR and AHP show similar trends.The FR model was significantly higher accurate(overall accuracy of 81.3%,kappa statistic 0.78)than the AHP model(overall accuracy 79.3%,kappa statistic 0.75).The FR model total forest fire risk areas were classified into five classes:very low(7.1%),low(22.2%),moderate(32.3%),high(26.9%),and very high(11.5%).The AHP fire risk classes were very low(6.7%),low(21.7%),moderate(34.0%),high(26.7%),and very high(10.9%).Sensitivity analyses were performed for AHP and FR models.The results of the two different models are compared and justified concerning the forest fire sample points(Forest Survey of India)and burn images(2010-2016).These results help in designing more effective fire management plans to improve the allocation of resources across a landscape framework.

Adaptive TCP: A Sender Side Mechanism with Dynamic Adjustment of Congestion Control Parameters for Performance Improvement in WLAN

This paper presents a sender side only TCP mechanism to prevent compromise for bandwidth utilization in IEEE 802.11 wireless networks. In absence of mechanism for accurate and immediate loss discrimination, the TCP sender unnecessarily reduces its Loss Window in response to the packet losses due to transmission errors. At the same time, frequent transmission losses and associated link retransmissions cause inaccuracy for available bandwidth estimate. The proposal, Adaptive TCP tackles the above issues using two refinements. First, sender estimates the degree of congestion by exploiting the statistics for estimated Round Trip Time (RTT). With this, it prevents unnecessary shrinkage of Loss Window and bandwidth estimate. Second, by concluding the uninterrupted evolution of its sending rate in recent past, the Adaptive TCP advances bandwidth estimate under favorable network conditions. This in turn, facilitates for quick growth in TCP’s sending rate after loss recovery and consequently alleviates bandwidth utilization. The authors implement the algorithm on top of TCP NewReno, evaluate and compare its performance with the wireless TCP variants deployed in current Internet. Through intensive simulations it is demonstrated that the Adaptive TCP outperforms other well-established TCP variants, and yields more than 100% of the throughput performance and more than 60% of improvement for bandwidth utilization, compared to TCP NewReno. The simulation results also demonstrated compatibility of Adaptive TCP in a shared wireless environment.

Electromagnetic Modeling of Metallic Elliptical Plates

This paper presents the evaluation of the capacitance of an isolated elliptical plate and two parallel elliptical plates. Integral equations are formed by relating the previously unknown charges on the elliptical plates and the potential on the metallic plates. The integral equations are solved by applying the method of moments based on the pulse function and point matching. The elements of the matrix in the method of moments are found by dividing the structure into triangular subsections. The matrix equation is solved in order to compute the unknown charges on each subsection. Numerical results on the capacitance as a function of the geometrical parameters of the ellipse are presented.

A comparative study of manglicolous lichens and their distribution inside Bhitarkanika National Park(Odisha),India

The manglicolous lichens are a specific group of lichens which occur in association with mangrove plants.Mangrove ecosystems have limited accessibility and the lichen study in mangrove forests are less studied and reported.The present study is the first-time report on lichen diversity,their distribution and its associated host mangrove species at eight different sites within the mangrove forests of Bhitarkanika Wildlife Sanctuary and National Park(Odisha),India.The study recorded a total of 49 lichen species which belongs to 26 genera and 14 families.The comparison of growth forms showed presence of 28 species of crustose,18 species of foliose and three species of fruticose type of lichens from the study sites.The analysis of host mangrove species showed Excoecaria agallocha as the most preferable mangrove species as it housed 38 lichen species on its surface(i.e.,45%crustose,47%foliose,and 8%fruticose).The comparison of growth forms of the total recorded lichen species from Bhitarkanika National Park,resulted 57%species crustose,37%foliose and 6%of fruticose type of lichens.The mangrove species,Avicennia officinalis and lichen of the genus Chrysothrix were found as common to all the study sites.The Jaccard similarity index study of lichen species between the study sites showed Kalibhanjadiya Island and Habelikhati as more similar in comparison of lichen species composition(i.e.,0.64).The occurrence of foliose and fruticose type of lichens showed the healthy and undisturbed mangrove forest conditions at many sites within Bhitarkanika National Park.