Hydrogenation of carbon monoxide was studied over the face centered cubic (fcc) phases of molybdenum and tungsten carbides. Moderately high surface area unsupported molybdenum and tungsten carbides ...(95 and 52
m
2
g
−1, respectively) were prepared using a temperature programmed synthesis method. The starting oxides were first converted to a cubic nitride by reacting with ammonia, which are subsequently transformed to the carbide in a methane/hydrogen mixture. The presence of the face centered cubic structure was confirmed by X-ray diffraction. The catalysts were tested in a slurry continuously stirred tank reactor (CSTR) at
P=2
MPa, in the temperature range 494–573
K and space velocities that varied from 2.5 to
15
S
l
h
−1
g
cat
−1
. The production of large amounts of carbon dioxide instead of water in the case of molybdenum carbide indicates a high water gas shift activity. In both cases the main hydrocarbon product is methane.
The addition of water during Fischer−Tropsch synthesis over a 12.4 wt % Co/SiO2 catalyst led to a significant increase in CO conversion. A positive reversible impact of water on catalyst activity was ...observed at partial pressures of water of <25 vol % added H2O. The CO conversion recovered to the reference activity after the termination of water addition. Therefore, this enhanced reversible activity for Co/SiO2 catalysts seems to be due to a kinetic effect of water. The catalyst was characterized using different techniques, including temperature-programmed reduction (TPR), Brunauer−Emmett−Teller (BET) surface area analysis, and H2 chemisorption. The rate expression has been obtained over the catalyst, using a 1-L continuously stirred tank reactor (CSTR) that was operated at a temperature of 483 K, a pressure of 2.21 MPa (21.42 atm), H2/CO feed ratios of 1.0−2.4, and 10%−70% CO conversion over a range of reactant partial pressures. The data of this study are fitted by a power-law expression of the form r CO = /(1 + mP H 2 O/P H 2 ), where k = 0.89 mol h-1 gcat -1 and m = −0.155.
A large class of problems of sequential decision making under uncertainty, of which the underlying probability structure is a Markov process, can be modeled as stochastic dynamic programs (referred ...to, in general, as Markov decision problems or MDPs). However, the computational complexity of the classical MDP algorithms, such as value iteration and policy iteration, is prohibitive and can grow intractably with the size of the problem and its related data. Furthermore, these techniques require for each action the one step transition probability and reward matrices, and obtaining these is often unrealistic for large and complex systems. Recently, there has been much interest in a simulation-based stochastic approximation framework called reinforcement learning (RL), for computing near optimal policies for MDPs. RL has been successfully applied to very large problems, such as elevator scheduling, and dynamic channel allocation of cellular telephone systems.
In this paper, we extend RL to a more general class of decision tasks that are referred to as semi-Markov decision problems (SMDPs). In particular, we focus on SMDPs under the average-reward criterion. We present a new model-free RL algorithm called SMART (Semi-Markov Average Reward Technique). We present a detailed study of this algorithm on a combinatorially large problem of determining the optimal preventive maintenance schedule of a production inventory system. Numerical results from both the theoretical model and the RL algorithm are presented and compared.
Understanding of the chemical nature of the dioxygen moiety
of oxyhemoglobin is crucial for elucidation of its physiological
function. In the present work, direct Raman spectroscopic observation
of ...both the Fe—O
2
and O—O stretching modes
unambiguously establishes the vibrational characteristics of the
oxygen-bound heme moiety in the hemoglobins of
Chlamydomonas
eugametos
and
Synechocystis
PCC6803. In addition
to providing the resonance Raman assignment of the O—O stretching
mode (1136 cm
−1
for
Chlamydomonas
, 1133
cm
−1
for
Synechocystis
) in an oxyhemoglobin
with an iron-porphyrin, this study also reports unusually low
frequencies for the Fe—O
2
stretching modes (554
cm
−1
). The effect of strong hydrogen bonding to the bound
oxygen is confirmed by changes in the frequency of the
Fe—O
2
stretching mode on mutation of distal residues.
These findings suggest an enzymatic function rather than an oxygen
transport role for these hemoglobins.
This paper presents a methodology that, for the problem of scheduling of a single server on multiple products, finds a dynamic control policy via intelligent agents. The dynamic (state dependent) ...policy optimizes a cost function based on the WIP inventory, the backorder penalty costs and the setup costs, while meeting the productivity constraints for the products. The methodology uses a simulation optimization technique called Reinforcement Learning (RL) and was tested on a stochastic lot-scheduling problem (SELSP) having a state–action space of size 1.8
×
10
7. The dynamic policies obtained through the RL-based approach outperformed various cyclic policies. The RL approach was implemented via a multi-agent control architecture where a decision agent was assigned to each of the products. A Neural Network based approach (least mean square (LMS) algorithm) was used to approximate the reinforcement value function during the implementation of the RL-based methodology. Finally, the dynamic control policy over the large state space was extracted from the reinforcement values using a commercially available tree classifier tool.
In accordance with the long-term policy objectives of the government of India for rural electrification, an off-grid woodfuel-based power plant for generation of grid quality electricity has been ...installed in a remote island of West Bengal. The present study focuses on technical performance of the largest biomass gasifier based power plant in India. Sustainability of such a power plant has been reviewed with respect to diesel replacement, fuelwood supply, cost of electricity generation and pollution load.
The
devR-devS two-component system of
Mycobacterium tuberculosis was identified earlier and partially characterized in our laboratory. A
devR::kan mutant of
M. tuberculosis was constructed by allelic ...exchange. The
devR mutant strain showed reduced cell-to-cell adherence in comparison to the parental strain in laboratory culture media. This phenotype was reversed on complementation with a wild-type copy of
devR. The
devR mutant and parental strains grew at equivalent rates within human monocytes either in the absence or in the presence of lymphocytic cells. The expression of DevR was not modulated upon entry of
M. tuberculosis into human monocytes. However, guinea pigs infected with the mutant strain showed a significant decrease in gross lesions in lung, liver and spleen; only mild pathological changes in liver and lung; and a nearly 3 log lower bacterial burden in spleen compared to guinea pigs infected with the parental strain. Our results suggest that DevR is required for virulence in guinea pigs but is not essential for entry, survival and multiplication of
M. tuberculosis within human monocytes in vitro. The attenuation in virulence of the
devR mutant in guinea pigs together with DevR-DevS being a bona fide signal transduction system indicates that DevR plays a critical and regulatory role in the adaptation and survival of
M. tuberculosis within tissues.
The effect of water on the performance of narrow and wide-pore silica-supported cobalt catalysts was investigated during Fischer–Tropsch synthesis in a continuously stirred tank reactor (CSTR). In ...these studies the added water replaced an equivalent amount of inert gas so that all other reaction conditions remained the same before, during and after water addition. A low cobalt loading of 12.4
wt.% on wide-pore silica exhibited a beneficial effect on CO conversion with the addition of water up to 25
vol.% of the total feed. In contrast, the addition of up to 20
vol.% water to a 20
wt.% Co on narrow- or wide-pore silica did not significantly alter the CO conversion. It appears that the CO conversion mainly increases when cobalt clusters are small enough to fit inside the silica pores.
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