A comparative analysis of the sensitivity of CsI (Tl), ZnO(Ga), and YAG(Ce) scintillators to the plasma background radiation under operating conditions of the ITER tokamak reactor

Problems related to neutral particle flux measurements on the ITER tokamak reactor under intense plasma background radiation conditions are considered. The results of measuring a background sensitivity with respect to neutron and γ-radiation for the scintillation detector, which is based on three different crystals (CsI (Tl), ZnO(Ga), and YAG(Ce)), are presented. The scintillators are compared and conclusions about the possibility of their applications in detectors of neutral particle analyzers currently created at the Ioffe Institute for the ITER tokamak reactor, are drawn.     

Crosslinked phenol-formaldehyde sulphonates as cation exchangers

The suspension polycondensation of phenol sulphonic acid and its homologues with formaldehyde, to produce a satisfactory cation exchanger in the bead form in the presence of sulphuric acid catalyst, was investigated. The various reaction conditions for bead formation, using an organic liquid suspending medium in the presence of a suspension stabiliser, such as the nature and quantity of the suspension stabilisers, the quantity of water added, the nature and quantity of the organic suspending medium and the rate of mixing, were studied. o-Dichlorobenzene was the best organic suspending liquid and a chemically peptised colloidal kaolin suspension was a good suspension stabiliser in the presence of a wetting agent. The optimum reaction conditions were given. The best exchangers were obtained in good yields using a molar ratio of phenol: HCHO:H₂SO₄ of 1·0:2·5:1·5 or a mixture of equimolecular amounts of phenol and resorcinol in a molar ratio of mixed phenols: HCHO: H₂SO₄ of 1·0:1·0:1·5. The efficiency of all the products obtained was measured by determination of their total exchange capacity.     

Lipid metabolism and membrane composition are altered in the brains of type II diabetic mice

CBL/57 strain db/db mice exhibit type II (noninsulin-dependent) diabetes. The affected mice are markedly hyperinsulinemic, hyperglycemic, and hypercholesterolemic, and their serum K+ levels are decreased. The brains of the diabetic mice are significantly smaller than those of their lean, control littermates, but the protein concentration is normal. The low brain weight is accompanied by a loss of major fatty acid components within the whole brain, nerve endings, and mitochondrial membranes. Cholesterol levels are low in whole brain but are not significantly different from normal in the synaptosomal membranes. The phospholipid concentration is significantly decreased in whole brain homogenates, crude synaptosomal membranes, and crude mitochondrial membranes of the diabetic mice. In addition, the specific activities of membrane-bound synaptosomal acetylcholinesterase, Na+,K(+)-ATPase, and Mg(2+)-ATPase are decreased in crude synaptosomal membranes of the diabetic mice. The specific activities of carnitine palmitoyltransferase I and carnitine acetyltransferase are significantly increased in the crude mitochondrial fraction isolated from the brains of the type II diabetic mice, whereas the specific activity of pyruvate dehydrogenase complex is decreased. The specific activities of two other mitochondrial enzymes--monoamine oxidase B and citrate synthase--and a cytosolic enzyme--lactate dehydrogenase--are unaltered. The ability to synthesize cyclic AMP is markedly decreased in the brains of the diabetic mice. The concentrations of carnitine and of the amino acids, glutamate, aspartate, glutamine, and serine are unaltered, whereas glycine levels are significantly elevated in the brains of the db/db mice. The data suggest that in vivo the brains of the diabetic mice exhibit a decreased capacity for glucose oxidation and increased capacity for fatty acid oxidation. This hypothesis is supported by the finding that cerebral mitochondria isolated from the db/db mice oxidize [1-14C]palmitate to 14CO2 at a rate almost twice that of control mitochondria. The present findings emphasize the potentially serious alteration of brain metabolism in uncontrolled type II diabetes.     

The effect of drying method on ordinary Portland cement surfaces during the early stages of hydration

During the early stages of ordinary Portland cement (OPC) hydration, ettringite, calcium hydroxide and C–S–H form on the OPC surface while nanoscale pits are formed in the exposed surface areas. In order to study these features using high resolution electron microscopy, samples must be appropriately dried to remove unbound water. The work reported here compares the effects of freeze-drying to drying by solvent exchange using four different solvents on the surface features of OPC after four hours of hydration in order to determine whether the solvent exchange process produces nanoscale changes in the surface features that can be detected using high resolution scanning electron microscopy (SEM). A quantitative image analysis of secondary electron SEM images was performed and the results analyzed using small sample statistics. They suggest that all of the solvent exchange methods damage the OPC surface and produce surface structures not seen in the freeze-dried samples. Caution is therefore warranted in the use of solvent exchange in the preparation of samples for the study of the dissolution of OPC surfaces.     

Hierarchical multi-agent reinforcement learning

In this paper, we investigate the use of hierarchical reinforcement learning (HRL) to speed up the acquisition of cooperative multi-agent tasks. We introduce a hierarchical multi-agent reinforcement learning (RL) framework, and propose a hierarchical multi-agent RL algorithm called Cooperative HRL. In this framework, agents are cooperative and homogeneous (use the same task decomposition). Learning is decentralized, with each agent learning three interrelated skills: how to perform each individual subtask, the order in which to carry them out, and how to coordinate with other agents. We define cooperative subtasks to be those subtasks in which coordination among agents significantly improves the performance of the overall task. Those levels of the hierarchy which include cooperative subtasks are called cooperation levels. A fundamental property of the proposed approach is that it allows agents to learn coordination faster by sharing information at the level of cooperative subtasks, rather than attempting to learn coordination at the level of primitive actions. We study the empirical performance of the Cooperative HRL algorithm using two testbeds: a simulated two-robot trash collection task, and a larger four-agent automated guided vehicle (AGV) scheduling problem. We compare the performance and speed of Cooperative HRL with other learning algorithms, as well as several well-known industrial AGV heuristics. We also address the issue of rational communication behavior among autonomous agents in this paper. The goal is for agents to learn both action and communication policies that together optimize the task given a communication cost. We extend the multi-agent HRL framework to include communication decisions and propose a cooperative multi-agent HRL algorithm called COM-Cooperative HRL. In this algorithm, we add a communication level to the hierarchical decomposition of the problem below each cooperation level. Before an agent makes a decision at a cooperative subtask, it decides if it is worthwhile to perform a communication action. A communication action has a certain cost and provides the agent with the actions selected by the other agents at a cooperation level. We demonstrate the efficiency of the COM-Cooperative HRL algorithm as well as the relation between the communication cost and the learned communication policy using a multi-agent taxi problem.     

Reduction-Triggered Doxorubicin Delivery by Self-Assembled Nanospheres of Lipoylated Caffeine

This study reports a new amphiphilic bioconjugate (CAFF-LA) derived from the lipoylation of a hydroxyethyl derivative of caffeine. In water, CAFF-LA self-assembles into nanospheres with an average size of 155 nm, as evidenced from dynamic light scattering and electron microscopy studies. The nanospheres are stable in serum and could be disintegrated upon exposure to the reducing environment of dithiothreitol (DTT; 10 mM) and glutathione (GSH; 10 mM). These nanospheres easily encapsulate the chemotherapy medication, doxorubicin (DOX), and demonstrate an efficacious transport into doxorubicin-resistant cervical cancer (HeLa) cells, wherein a marked induction in apoptosis and significantly lower IC₅₀ have been observed when compared to that of free drug. The in vitro assessment of cell viability and hemocompatibility present these nanospheres as potentially safe and efficient intracellular reduction stimulus-responsive drug-delivery vehicles.