A Decision Feedback Based Scheme for Slepian-Wolf Coding of sources with Hidden Markov Correlation

We consider the problem of compression of two memoryless binary sources, the correlation between which is defined by a Hidden Markov Model (HMM). We propose a Decision Feedback (DF) based scheme which when used with low density parity check codes results in compression close to the Slepian Wolf limits.Comment: Submitted to IEEE Comm. Letter

Degree Optimization and Stability Condition for the Min-Sum Decoder

The min-sum (MS) algorithm is arguably the second most fundamental algorithm in the realm of message passing due to its optimality (for a tree code) with respect to the {\em block error} probability \cite{Wiberg}. There also seems to be a fundamental relationship of MS decoding with the linear programming decoder \cite{Koetter}. Despite its importance, its fundamental properties have not nearly been studied as well as those of the sum-product (also known as BP) algorithm. We address two questions related to the MS rule. First, we characterize the stability condition under MS decoding. It turns out to be essentially the same condition as under BP decoding. Second, we perform a degree distribution optimization. Contrary to the case of BP decoding, under MS decoding the thresholds of the best degree distributions for standard irregular LDPC ensembles are significantly bounded away from the Shannon threshold. More precisely, on the AWGN channel, for the best codes that we find, the gap to capacity is 1dB for a rate 0.3 code and it is 0.4dB when the rate is 0.9 (the gap decreases monotonically as we increase the rate). We also used the optimization procedure to design codes for modified MS algorithm where the output of the check node is scaled by a constant $1/\alpha$. For $\alpha = 1.25$, we observed that the gap to capacity was lesser for the modified MS algorithm when compared with the MS algorithm. However, it was still quite large, varying from 0.75 dB to 0.2 dB for rates between 0.3 and 0.9. We conclude by posing what we consider to be the most important open questions related to the MS algorithm.Comment: submitted to ITW 0

Methyl Coenzyme M Reductase (mcrA) Gene Abundance Correlates with Activity Measurements of Methanogenic H2/CO2-Enriched Anaerobic Biomass

Biologically produced methane (CH4) from anaerobic digesters is a renewable alternative to fossil fuels, but digester failure can be a serious problem. Monitoring the microbial community within the digester could provide valuable information about process stability because this technology is dependent upon the metabolic processes of microorganisms. A healthy methanogenic community is critical for digester function and CH4 production. Methanogens can be surveyed and monitored using genes and transcripts of mcrA, which encodes the α subunit of methyl coenzyme M reductase – the enzyme that catalyses the final step in methanogenesis. Using clone libraries and quantitative polymerase chain reaction, we compared the diversity and abundance of mcrA genes and transcripts in four different methanogenic hydrogen/CO2 enrichment cultures to function, as measured by specific methanogenic activity (SMA) assays using H2/CO2. The mcrA gene copy number significantly correlated with CH4 production rates using H2/CO2, while correlations between mcrA transcript number and SMA were not significant. The DNA and cDNA clone libraries from all enrichments were distinctive but community diversity also did not correlate with SMA. Although hydrogenotrophic methanogens dominated these enrichments, the results indicate that this methodology should be applicable to monitoring other methanogenic communities in anaerobic digesters. Ultimately, this could lead to the engineering of digester microbial communities to produce more CH4 for use as renewable fuel

Clinical profile of patients with acute organophosphorus poisoning in a tertiary care hospital

Background: Organophosphorus compound poisoning episodes are relatively common in occurrence in this part of the world and are associated with high levels of morbidity as well as death, at times despite competent care. The present study was conducted to profile clinically the patients admitted with history of acute organophosphorus poisoning.Methods: This prospective observational study was conducted between September 2017 and October 2019 at four hospitals with intensive care units in a city in central-west India region, wherein clinically relevant details of patients admitted with history of acute organophosphorus poisoning were noted and analysed.Results: Out of 160 participants studied, males (58.75%) and those between 21-30 years age group (45.0%) were affected more. Suicidal attempt was the commonest mode (97.5%). Majority of the participants belonged to severity grade II (45%); with severity grades found directly related to longer hospital stay and death. Constriction of pupils (76.25%) was the commonest clinical sign observed. The death rate was calculated to be 21.25%, with monocrotophos (100%) and dicholorovas (66.63%) compounds being associated with very high mortality. Dimethoate was the commonest substance incriminated (18.75%).Conclusions: Organophosphorus poisoning has affected the young, productive males prominently. Higher severity of the disease process at presentation leads to significant mortality. Selective prohibition of the riskier compounds causing higher proportion of deaths is recommended

Transient Study of the Wetting Films in Porous Media Using 3D X-Ray Computed Micro-Tomography: Effect of Imbibition Rate and Pore Geometry

Imbibition in porous media is governed by the complex interplay between viscous and capillary forces, pore structure and fluid properties. Understanding and predicting imbibition is important in many natural and engineered applications; it affects the efficiency of oil production operations, the moisture and contaminant transport in soil science, and the formation of defects in certain types of composite materials. Majority of the studies published on the transient imbibition behavior in a porous medium were conducted in the simplified 2D transparent micromodels or the 2D projection visualization (X-ray or visible light) of the 3D porous medium. However, the pore level transient imbibition studies have not been reported on real three dimensional porous medium. The main challenge arises from the slowness of the present 3D imaging techniques in comparison with the speed of the pore filling events. To overcome these difficulties, we have developed a novel experimental technique using UV-induced polymerization, which allows the fluid phase distributions to be frozen in place during transient imbibition. Pore-scale structure of the front can then be examined in the 3D microscopic details using the X-ray Computed micro-Tomography (XCT). We have also developed a suite of advanced image segmentation programs to segment the grayscale XCT data. Image-based physically representative pore network generation techniques were unitized to quantify the geometry and topology of pore, wetting and nonwetting phase structure. Using UV initiated polymerization technique and image-based quantitative analysis tools; we have studied the effects of capillary number, pore structure and surface roughness on the structure of the transient imbibition front

Preservation of Methanogenic Cultures to Enhance Anaerobic Digestion

The use of anaerobic biotechnology is increasing as a sustainable process to treat various organic wastes. Methanogens convert organic COD into CH4 and play the key role to drive thermodynamically unfavorable biochemical fermentation reactions and keep the digestion process steady and efficient. Progressive understanding of anaerobic microbiology with digester functionality may help to develop efficient, customized methanogenic cultures to enhance anaerobic bioprocesses. Preservation of methanogenic cultures via drying would be a cost-effective option for research and practical applications. However, preservation of methanogenic cultures is challenging due to methanogen sensitivity to O2 toxicity and drying, and very limited work is reported on their preservation. The work described herein involves preservation and subsequent storage of various methanogenic cultures in oxic conditions as well as applications to improve performance of anaerobic digesters and standardize laboratory testing. Five methanogenic cultures were customized under different growth conditions. The cultures were preserved using freeze- and heat-drying, and subsequently stored for short and long periods in the presence of air. Their activity was then assayed by measuring specific methanogenic activity. The influences of growth conditions and protective agent addition were investigated to improve methanogenic activity after preservation. Clone library and qPCR techniques were used to identify and quantify methanogenic communities before and after drying. The usefulness of preserved cultures was examined to bioaugment transiently upset anaerobic digesters and as seed inocula for a standard laboratory test, the biochemical methane potential (BMP) assay. The effect of bioaugmentation was correlated with methanogenic community structure using the DGGE molecular fingerprinting technique. All customized methanogenic cultures were significantly active even after handling, drying and subsequent storage in the presence of air, suggesting methanogenic culture preservation and storage in air is feasible. Freeze-dried cultures maintained higher methanogenic activity than heat-dried cultures. The culture developed in the presence of limited O2 exhibited higher methanogenic activity than cultures developed in strict anaerobic conditions regardless of the drying method employed. Glucose as a protective agent resulted in higher methanogenic activity, more so in freeze drying than heat drying. Some methanogenic community members were found to be more tolerant to drying stress than others. Dried methanogenic cultures were found to be viable options to use as a bioaugment to improve treatment efficiency of anaerobic digesters after toxic upset and for the BMP assay