Linear Programming for Large-Scale Markov Decision Problems

We consider the problem of controlling a Markov decision process (MDP) with a large state space, so as to minimize average cost. Since it is intractable to compete with the optimal policy for large scale problems, we pursue the more modest goal of competing with a low-dimensional family of policies. We use the dual linear programming formulation of the MDP average cost problem, in which the variable is a stationary distribution over state-action pairs, and we consider a neighborhood of a low-dimensional subset of the set of stationary distributions (defined in terms of state-action features) as the comparison class. We propose two techniques, one based on stochastic convex optimization, and one based on constraint sampling. In both cases, we give bounds that show that the performance of our algorithms approaches the best achievable by any policy in the comparison class. Most importantly, these results depend on the size of the comparison class, but not on the size of the state space. Preliminary experiments show the effectiveness of the proposed algorithms in a queuing application.Comment: 27 pages, 3 figure

Comment on "Competition between helimagnetism and commensurate quantum spin correlations in LiCu2O2"

The microscopic origin of the recently observed helical structure in LiCu2O2 [1] is considered. It is shown that the frustrated antiferromagnetic double chain scenario adopted in Ref.1 is unrealistic. It should be replaced by a frustrated single-chain (CuO2) scenario proposed in Ref. 2 with ferromagnetic nearest neighbor and antiferromagnetic next nearest neighbor exchange integrals \. [1] T. Masuda et al. Phys. Rev. Lett. 92 (2004), 177201. [2] A. Gippius et al. Phys. Rev. B 70 (2004), R01426; cond-mat/0312576.Comment: one page, one figur

Deformation and Ductile Fracture of a Low Alloy Steel under High Strain Rate Loading

Ductile failure of metals always occurs after a specific amount of plastic deformation. Therefore, the investigation and characterization of the deformation behaviour is required to understand the damage process and to describe the failure by a suitable constitutive relation. The effects of temperature and strain rate on the mechanical properties are important for the description of the material behavior in many applications. The MTS model is used here to describe the material behavior of some low alloy steels in a wide range of temperature and strain rates. A new part of stress is added to the MTS model in order to consider the effect of the dynamic strain aging at low strain rate and high temperature. The determination of material data at high strain and high strain rate is needed to describe the real material behaviour, specially for the simulation of high deformation and fracture. A special technique is used here to stop the deformation of tension specimen at high strain rate in the necking zone to determine the true stress and true strain. Using FEM computations (LS-DYNA 3D), the stress triaxiality in the necking zone of a tensile specimen is calculated up to the crack initiation. It is shown that the strain hardening characteristics affect the development of stress triaxiality

Predicting Intermediate Storage Performance for Workflow Applications

Configuring a storage system to better serve an application is a challenging task complicated by a multidimensional, discrete configuration space and the high cost of space exploration (e.g., by running the application with different storage configurations). To enable selecting the best configuration in a reasonable time, we design an end-to-end performance prediction mechanism that estimates the turn-around time of an application using storage system under a given configuration. This approach focuses on a generic object-based storage system design, supports exploring the impact of optimizations targeting workflow applications (e.g., various data placement schemes) in addition to other, more traditional, configuration knobs (e.g., stripe size or replication level), and models the system operation at data-chunk and control message level. This paper presents our experience to date with designing and using this prediction mechanism. We evaluate this mechanism using micro- as well as synthetic benchmarks mimicking real workflow applications, and a real application.. A preliminary evaluation shows that we are on a good track to meet our objectives: it can scale to model a workflow application run on an entire cluster while offering an over 200x speedup factor (normalized by resource) compared to running the actual application, and can achieve, in the limited number of scenarios we study, a prediction accuracy that enables identifying the best storage system configuration

Validity of path thermodynamics in reactive systems

Path thermodynamic formulation of nonequilibrium reactive systems is considered. It is shown through simple practical examples that this approach can lead to results that contradict well established thermodynamic properties of such systems. Rigorous mathematical analysis confirming this fact is presented

Reply to "Comment on `Validity of path thermodynamic description of reactive systems: Microscopic simulations'

The Comment's author argues that a correct description of reactive systems should incorporate the explicit interaction with reservoirs, leading to a unified system-reservoirs entity. However, this proposition has two major flaws. Firstly, as we will emphasize, this entity inherently follows a thermodynamic equilibrium distribution. In the Comment, no indication is provided on how to maintain such a system-reservoirs entity in a non-equilibrium state. Secondly, contrary to the author's claim, the inclusion of system-reservoir interaction in traditional stochastic modeling of reactive systems does not automatically alter the limited applicability of path thermodynamics to problematic reactive systems. We will provide a simple demonstration to illustrate that certain elementary reactions may not involve any changes in reservoir components, which seems to have been overlooked by the author.Comment: To appear in Physical Review

Selection of a high yielding soybean variety: Binasoybean-1

Collected 201 soybean [Glycine max (L.) Merrill] germplasm were evaluated for selection of desirable germplasm for registration as variety and/or for future utilization as breeding materials. Among the germplasm, nine were selected on the basis of better field performance considering their seed yield, morphological characters and yield attributes. Results showed that BAU-S/80 produced higher number of pods/plant and its yield was 2516 kg/ha as against 2142 and 2108 kg/ha of the two control varieties, Sohag and BARISoybean-5, respectively. Yield trials of BAU-S/80 were carried out in both rabi and kharif seasons during the period from 2007 to 2010 in selected locations under soybean growing areas of Bangladesh and found to be suitable for cultivation in the farmers' field. BAU-S/80 was found to be moderately resistant to soybean yellow mosaic virus and collar rot diseases, and also showed lower insect infestation than control varieties. On the basis of superior performance of BAU-S/80, Bangladesh Institute of Nuclear Agriculture (BINA) applied for registration to the National Seed Board NSB of Bangladesh. Consequently, the NSB of Bangladesh registered BAU-S/80 as Binasoybean-1 in 2011 for commercial cultivation in Bangladesh

Studies on some morphological characters and yield attributes of synthetic Brassica hexaploids and their parents

Allopolyploidy plays an important role in plant evolution and confers better advantages on crop growth and breeding compared to low ploidy levels. The present investigation aimed to study the synthetic hexaploid Brassica (AABBCC genome) developed from Brassica cainata (BBCC genome) and Brassica rapa (AA genome) compared to their parental genotypes considering some morphological characters, yield attributes and yield. Increased vegetative growth in hexaploids over their parents was observed. Hexaploids exhibited wider ranges with higher coefficients of variations compared to the parents for all characters studied. Hexaploids had taller plants, higher number of siliqua and larger flowers than those of both parents. Though average pollen fertility in the hexaploids was lower than both parents but out of 420 hexaploids, seventeen had comparatively higher percentages of pollen fertility as well as siliqua setting. Number of seeds per siliqua and siliqua length were found to be lower than their parents. Mean seed weight per plant in the hexaploids was lower than the parents though the hexaploids had higher number of siliquae along with higher seed weight. Days to flowering and maturity in the hexaploids were in between the parents and closer to the B. carinata parent. Five hexaploid plants from BARIBatishak-1 × Carinata-1 and two from each of Carinata-1 × BARIBatishak-1 and Agrani × Carinata-1 were found to be promising because they have higher seed yield per plant than their parents. Those nine selected high yielding hexaploid plants could be evaluated in the subsequent generations to select the stable and desirable Brassica hexaploids.Keywords: Brassica hexaploid, morphological characters, yield attribute