Land utilization and ecological aspects in the Sylhet-Mymensingh Haor Region of Bangladesh: An analysis of LANDSAT data

The use of remote sensing data from LANDSAT (ERTS) imageries in identifying, evaluating and mapping land use patterns of the Haor area in Bangladesh was investigated. Selected cloud free imageries of the area for the period 1972-75 were studied. Imageries in bands 4, 5 and 7 were mostly used. The method of analysis involved utilization of both human and computer services of information from ground, aerial photographs taken during this period and space imageries

Anaerobic Digestion and Co-digestion of Thickened Waste Activated Sludge (TWAS) and Food Waste (FW)

This study aimed at assessing the impact of ultrasonication on the anaerobic digestibility of thickened waste activated sludge (TWAS) in anaerobic fluidized bed reactor (AnFBR), determining the unbiodegradable fraction of TWAS, and exploring co-digestion of food waste (FW) and TWAS. Two lab-scale AnFBRs treating TWAS were studied to explore the impact of ultrasonication (US) in the break down and reuse of scum for methane production. At an organic loading rate (OLR) of 4.7 kg COD/m3-d and 480 kJ of US energy, COD and VSS destruction efficiencies were 65% and 63%, respectively roughly 20% higher than the control reactor without US. To explore the specific methanogenic bacterial activity (SMA), the SMA test was conducted during OLR of 9.7 kg COD/m3-d and showed that the activity-based sludge retention time is higher for the ultrasonicated AnFBR (U-AnFBR) (7.1 days) compared to AnFBR (5.1 days). The investigation also indicated that the unbiodegradable fractions of PCOD and VSS were 0.28 based on PCOD and 0.26 based on VSS. However, to investigate the co-digestibility of FW as co-substrate, five semi-continuous flow anaerobic digesters were operated to explore the co-digestion performance treating a mixture of FW and municipal biosolids (primary sludge and TWAS) at an HRT of 20 days. Sixty days of steady-state operation at organic loading rates of 2.2 kgCOD/m3-d to 3.85 kgCOD/m3-d showed that COD removals were higher for the three co-digesters than for the two municipal biosolids digesters i.e. 61%-69% versus 47%-52%. Specific methane production per influent CODs were 1.3-1.8 folds higher in co-digestion than mono-digestion. Additional methane production through synergism accounted for the minimum 18%-20% of the overall methane production

Doping Dependence of Thermal Oxidation on n-type 4H-SiC

The doping dependence of dry thermal oxidation rates in n-type 4H-SiC was investigated. The oxidation was performed in the temperature range 1000C to 1200C for samples with nitrogen doping in the range of 6.5e15/cm3 to 9.3e18/cm3, showing a clear doping dependence. Samples with higher doping concentrations displayed higher oxidation rates. The results were interpreted using a modified Deal-Grove model. Linear and parabolic rate constants and activation energies were extracted. Increasing nitrogen led to an increase in linear rate constant pre-exponential factor from 10-6m/s to 10-2m/s and the parabolic rate constant pre-exponential factor from 10e9m2/s to 10e6m2/s. The increase in linear rate constant was attributed to defects from doping-induced lattice mismatch, which tend to be more reactive than bulk crystal regions. The increase in the diffusion-limited parabolic rate constant was attributed to degradation in oxide quality originating from the doping-induced lattice mismatch. This degradation was confirmed by the observation of a decrease in optical density of the grown oxide films from 1.4 to 1.24. The linear activation energy varied from 1.6eV to 2.8eV, while the parabolic activation energy varied from 2.7eV to 3.3eV, increasing with doping concentration. These increased activation energies were attributed to higher nitrogen content, leading to an increase in effective bond energy stemming from the difference in C-Si (2.82eV) and Si-N (4.26eV) binding energies. This work provides crucial information in the engineering of SiO2 dielectrics for SiC MOS structures, which typically involve regions of very different doping concentrations, and suggests that thermal oxidation at high doping concentrations in SiC may be defect mediated.Comment: 13 pages. 9 figures, accepted as a transiction in IEEE electron device. TED MS#8035

Distribution of dwell times of a ribosome: effects of infidelity, kinetic proofreading and ribosome crowding

Ribosome is a molecular machine that polymerizes a protein where the sequence of the amino acid residues, the monomers of the protein, is dictated by the sequence of codons (triplets of nucleotides) on a messenger RNA (mRNA) that serves as the template. The ribosome is a molecular motor that utilizes the template mRNA strand also as the track. Thus, in each step the ribosome moves forward by one codon and, simultaneously, elongates the protein by one amino acid. We present a theoretical model that captures most of the main steps in the mechano-chemical cycle of a ribosome. The stochastic movement of the ribosome consists of an alternating sequence of pause and translocation; the sum of the durations of a pause and the following translocation is the time of dwell of the ribosome at the corresponding codon. We derive the analytical expression for the distribution of the dwell times of a ribosome in our model. Whereever experimental data are available, our theoretical predictions are consistent with those results. We suggest appropriate experiments to test the new predictions of our model, particularly, the effects of the quality control mechanism of the ribosome and that of their crowding on the mRNA track.Comment: This is an author-created, un-copyedited version of an article accepted for publication in Physical Biology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at DOI:10.1088/1478-3975/8/2/02600

Weakly coupled, antiparallel, totally asymmetric simple exclusion processes

We study a system composed of two parallel totally asymmetric simple exclusion processes with open boundaries, where the particles move in the two lanes in opposite directions and are allowed to jump to the other lane with rates inversely proportional to the length of the system. Stationary density profiles are determined and the phase diagram of the model is constructed in the hydrodynamic limit, by solving the differential equations describing the steady state of the system, analytically for vanishing total current and numerically for nonzero total current. The system possesses phases with a localized shock in the density profile in one of the lanes, similarly to exclusion processes endowed with nonconserving kinetics in the bulk. Besides, the system undergoes a discontinuous phase transition, where coherently moving delocalized shocks emerge in both lanes and the fluctuation of the global density is described by an unbiased random walk. This phenomenon is analogous to the phase coexistence observed at the coexistence line of the totally asymmetric simple exclusion process, however, as a consequence of the interaction between lanes, the density profiles are deformed and in the case of asymmetric lane change, the motion of the shocks is confined to a limited domain.Comment: 14 pages, 15 figures, to appear in Phys. Rev.

The CWKB particle production and classical condensate in de Sitter spacetime

The complex time WKB approximation is an effective tool in studying particle production in curved spacetime. We use it in this work to understand the formation of classical condensate in expanding de Sitter spacetime. The CWKB leads to the emergence of thermal spectrum that depends crucially on horizons (as in de Sitter spacetime) or observer dependent horizons (as in Rindler spacetime). A connection is sought between the horizon and the formation of classical condensate. We concentrate on de Sitter spacetime and study the cosmological perturbation of $k=0$ mode with various values of $m/H_0$. We find that for a minimally coupled free scalar field for $m^2/H_0^2<2$, the one-mode occupation number grows more than unity soon after the physical wavelength of the mode crosses the Hubble radius and soon after diverges as $N(t)\sim O(1)[\lambda_{phys}(t)/{H_0^{-1}}]^{2\sqrt{\nu^2-1/4}}$, where $\nu\equiv (9/4 -m^2/{H_0^2})^{1/2}$. The results substantiates the previous works in this direction. We also find the correct oscillation and behaviour of $N(z)$ at small $z$ from a single expression using CWKB approximation for various values of $m/H_0$. We also discuss decoherence in relation to the formation of classical condensate. We also find that the squeezed state formalism and CWKB method give identical results.Comment: 19 pages, revtex, 5 figure

Chlorinated Pesticide Residue Status in Tomato, Potato and Carrot

A study was carried out to identify the bioaccumulation and the ascertain level of chlorinated pesticide residues in some vegetables collected from market baskets of New market, Dhaka, Bangladesh namely potato, tomato and carrot. The samples were randomly collected from different shops and analyzed by capillary column of Gas Chromatograph Mass Spectrometry (GCMS) with Electron Impact Ionization (EI) method for the detection of chlorinated pesticide. The results of the study revealed that collected samples of potato, tomato, red amaranth and spinach were contaminated with some chlorinated substances. But Indian spinach and carrot were free of contamination with organochlorine pesticide

Implications of ecotourism development in protected areas: A study from Rema-Kalenga Wildlife Sanctuary, Bangladesh

This article is based on visitors profile study of protected area based tourist spots of Rema-Kalenga Wildlife Sanctuary (RKWS), Bangladesh to ascertain the potential of ecotourism. Study findings shows that 69% male constitute the visitors group while the maximum number of visitors was found in the age of below 30 years. Most of the visitors were literate and among them 43% visitors were student. Most (53%) of visitors preferred to get recreation in holidays as they were employed. Visitors were highly preferred to come with friends group. About 92% respondents showed positive mind to come here in future while 89% respondents view that park has tourism potential. Most of the respondents reported the presence of wildlife (48%) most notable followed by plant diversity and tribal community as recreational. From χ2 test it is found that highly significance association present between tourism potentiality of the wildlife sanctuary and some demographic variable like income of tourists (χ2 = 49.138, p < 0.000), visiting pattern (χ2 = 19.344, p < 0.000), education of tourists (χ2 = 50.226, p < 0.000), travelling distance (Km - χ2 = 11.427, p < 0.022), duration of staying (χ2 = 12.867, p < 0.002), frequency of visit (χ2 = 8.456, p < 0.015), visiting time (χ2 = 6.530, p < 0.011), problem in the study area (χ2 = 14.962, p < 0.021), occupation of tourists (χ2 = 8.848, p < 0.031). If the problems addressed by the visitors were solved, RKWS would be a bright place of eco-tourism in Bangladesh