Optimal Locally Repairable Codes and Connections to Matroid Theory

Petabyte-scale distributed storage systems are currently transitioning to erasure codes to achieve higher storage efficiency. Classical codes like Reed-Solomon are highly sub-optimal for distributed environments due to their high overhead in single-failure events. Locally Repairable Codes (LRCs) form a new family of codes that are repair efficient. In particular, LRCs minimize the number of nodes participating in single node repairs during which they generate small network traffic. Two large-scale distributed storage systems have already implemented different types of LRCs: Windows Azure Storage and the Hadoop Distributed File System RAID used by Facebook. The fundamental bounds for LRCs, namely the best possible distance for a given code locality, were recently discovered, but few explicit constructions exist. In this work, we present an explicit and optimal LRCs that are simple to construct. Our construction is based on grouping Reed-Solomon (RS) coded symbols to obtain RS coded symbols over a larger finite field. We then partition these RS symbols in small groups, and re-encode them using a simple local code that offers low repair locality. For the analysis of the optimality of the code, we derive a new result on the matroid represented by the code generator matrix.Comment: Submitted for publication, a shorter version was presented at ISIT 201

Gradient Coding from Cyclic MDS Codes and Expander Graphs

Gradient coding is a technique for straggler mitigation in distributed learning. In this paper we design novel gradient codes using tools from classical coding theory, namely, cyclic MDS codes, which compare favorably with existing solutions, both in the applicable range of parameters and in the complexity of the involved algorithms. Second, we introduce an approximate variant of the gradient coding problem, in which we settle for approximate gradient computation instead of the exact one. This approach enables graceful degradation, i.e., the $\ell_2$ error of the approximate gradient is a decreasing function of the number of stragglers. Our main result is that normalized adjacency matrices of expander graphs yield excellent approximate gradient codes, which enable significantly less computation compared to exact gradient coding, and guarantee faster convergence than trivial solutions under standard assumptions. We experimentally test our approach on Amazon EC2, and show that the generalization error of approximate gradient coding is very close to the full gradient while requiring significantly less computation from the workers

NMR Line Shape Analysis of a Multi-state Ligand Binding Mechanism in Chitosanase

Chitosan interaction with chitosanase was examined through analysis of spectral line shapes in the NMR HSQC titration experiments. We established that the substrate, chitosan hexamer, binds to the enzyme through the three-state induced-fit mechanism with fast formation of the encounter complex followed by slow isomerization of the bound-state into the final conformation. Mapping of the chemical shift perturbations in two sequential steps of the mechanism highlighted involvement of the substrate-binding subsites and the hinge region in the binding reaction. Equilibrium parameters of the three-state model agreed with the overall thermodynamic dissociation constant determined by ITC. This study presented the first kinetic evidence of the induced-fit mechanism in the glycoside hydrolases

FOLLOW UP IN LARGE BOWEL RESECTIONS: WERNICKE-KORSAKOFF'S SYNDROME

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FOLLOW UP IN LARGE BOWEL RESECTIONS: WERNICKE-KORSAKOFF'S SYNDROME

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How does IPM 3.0 look like (and why do we need it in Africa)?

Open Access Article; Published online: 09 Aug 2022The concept of Integrated Pest Management (IPM) was introduced sixty years ago to curb the overuse of agricultural pesticides, whereby its simplest version (IPM 1.0) was aiming at reducing the frequency of applications. Gradually, agro-ecological principles, such as biological control and habitat management, were included in IPM 2.0. However, throughout this time, smallholder farmers did not improve their decision-making skills and continue to use hazardous pesticides as their first control option. We are therefore proposing a new paradigm — IPM 3.0 — anchored on 3 pillars: 1) real-time farmer access to decision-making, 2) pest-management options relying on science-driven and nature-based approaches, and 3) the integration of genomic approaches, biopesticides, and habitat-management practices. We are convinced that this new paradigm based on technological advances, involvement of youth, gender-responsiveness, and climate resilience will be a game changer. However, this can only become effective through redeployment of public funding and stronger policy support

Conical-emission and shock-front dynamics in femtosecond laser-pulse filamentation

We investigate both experimentally and numerically the space-time dynamics of an ultrashort laser pulse during self-focusing and nonlinear propagation in water by means of a time-gated angular-spectrum characterization. The results identify the formation of shock fronts on both trailing and leading edges of the wave packet that are due to the formation of subluminal and superluminal group velocity intensity peaks, sustained by conical emission

Farmers' perception of climate change and climate-smart agriculture in northern Benin, west Africa

Climate-Smart Agriculture (CSA) is an approach that identifies actions needed to transform and reorganize agricultural systems to effectively support agricultural development and ensure food security in the face of climate change. In this study, we assessed farmers’ perception of climate change, available CSA practices (CSAP) and the determinants of CSAP adoption in northern Benin. A list of CSAP was generated from a workshop with different stakeholders. Face-to-face interviews were then carried out with 368 farmers selected based on stratified random sampling in the study area. Binomial generalized mixed-effect models were run to analyze the relation between socio-demographic characteristics and the use of CSAP. CSAP were evaluated using a three-point Likert scale and the frequency of agreement with the statement that the selected practices meet the pillars of CSA. More than 60% of farmers had heard about climate change, and more than 80% had observed changes in temperature, rainfall amounts and distribution. Thirty-one CSAP were identified in the area, and only 11 were known by more than 50% of farmers. Out of the 12 selected CSAP for the assessment of adoption and evaluation, seven (7) were used by more than 50% of those who knew them. Farmers agreed with the statements that the evaluated practices improved farm productivity and adaptation to climate change but did not mitigate climate change. Ethnic group and education level were the two major factors that significantly determined the use of the evaluated CSAP

Impact of CS-IPM on key social welfare aspects of smallholder farmers' livelihoods

Open Access JournalAll stakeholders, especially households that depend on agriculture, must come up with every avenue available to improve farm productivity in order to raise yields due to the constraints posed by climate change on food production systems. Sufficient increments in yields will address the challenges of food insecurity and malnutrition among vulnerable households, especially smallholder ones. Yield increases can be achieved sustainably through the deployment of various Climate Smart Integrated Pest Management (CS-IPM) practices, including good agronomic practices. Therefore, CS-IPM practices could be essential in ensuring better household welfare, including food security and nutrition. With such impact empirically documented, appropriate policy guidance can be realized in favor of CS-IPM practices at scale, thus helping to achieve sustainable food security and food systems. However, to this end, there is yet limited evidence on the real impact of CS-IPM practices on the various core social welfare household parameters, for instance, food security, household incomes, gender roles, and nutrition, among others. We contribute to this body of literature in this paper by reviewing various empirical evidence that analyzes the impact of respective CS-IPM practices on key social welfare aspects of smallholder farm households in developing countries around the world. The review finds that CS-IPM practices do increase households’ adaptation to climate change, thus enhancing soil and crop productivity, thereby ensuring food and nutrition security, as well as increasing market participation of CS-IPM adopters, thus leading to increased household incomes, asset accumulation, and subsequently better household food and nutrition security via direct own-farm produce consumption and market purchases using income. CS-IPM practices also enhance access to climate-related information, reduce greenhouse gas emissions, conserve biodiversity, and enhance dietary diversity through improved crop and livestock varieties and also reduce variable farm production costs. Therefore, there would be multiple welfare gains if CS-IPM practices were scaled up