Improving the W Coating Uniformity by a COMSOL Model-Based CVD Parameter Study for Denser Wf/W Composites

Tungsten (W) has the unique combination of excellent thermal properties, low sputter yield, low hydrogen retention, and acceptable activation. Therefore, W is presently the main candidate for the first wall and armor material for future fusion devices. However, its intrinsic brittleness and its embrittlement during operation bears the risk of a sudden and catastrophic component failure. As a countermeasure, tungsten fiber-reinforced tungsten (Wf/W) composites exhibiting extrinsic toughening are being developed. A possible Wf/W production route is chemical vapor deposition (CVD) by reducing WF6 with H2 on heated W fabrics. The challenge here is that the growing CVD-W can seal gaseous domains leading to strength reducing pores. In previous work, CVD models for Wf/W synthesis were developed with COMSOL Multiphysics and validated experimentally. In the present article, these models were applied to conduct a parameter study to optimize the coating uniformity, the relative density, the WF6 demand, and the process time. A low temperature and a low total pressure increase the process time, but in return lead to very uniform W layers at the micro and macro scales and thus to an optimized relative density of the Wf/W composite. High H2 and low WF6 gas flow rates lead to a slightly shorter process time and an improved coating uniformity as long as WF6 is not depleted, which can be avoided by applying the presented reactor model.

Intraday Volatility and Volatility spill-over Effects in KTB and Won/Dollar Futures Markets

We analyze the dynamic behavior of the volatility of KTB futures price through GARCH models. In conducting this analysis we use two type data. Using dailly data we analyze the return and volatility spill-over effect between KTB spot and futures. Through 15-minute and 5-minute data we analyze return and volatility spill-over effect between KTB futures and won/dollar futures. We find that ARCH and GARCH effect exists in the volatility of KTB futures, but leverage effect does not exist in this data. Volatility spill-over effect was found only in 15-minute data. Lead and lag effect was found in 15-minute data of dollar and KTB futures where dollar return leads KTB futures and KTB volatility leads dollar volatility. In the daily data we found that KTB futures return lead KTB spot return while mutual spill-over existed between spot and futures in volatility data. Since conditional heteroscedasticity exists in KTB futures we need to consider the these effects in building up systems for arbitrage, valuation and risk management.

Hearing in insects: The nature of the response of certain receptors to auditory stimuli

The auditory receptors of the Orthoptera include tympanal organs and hair sensilla. The former have long been recognized as subserving an aural function, but the latter have, in this group, only recently been shown to respond to auditory stimuli (Pumphrey and Rawdon-Smith, 1936). Wever and Bray (1933), using an amplifier and telephones, have attempted to analyse the nervous response from the tympanal organs of the foreleg of crickets ( Lyogryllus campestris ). Their operational technique may be shortly described. Without previous dissection, a fine wire electrode was introduced into the leg of the experimental animal, the return lead consisting of a pad applied to the animal’s body. Owing to the fact that no direct contact was certainly made with the tympanal nerve and that the central ends of the leg nerves were not severed, responses of several kinds were obtained. Of these, an asynchronous response, described as producing a shushing noise in the telephones, was thought to arise from the tympanal organ; but no certain indication was given that this response was not partly or wholly of tactile origin. This point is of importance since, as we shall show in this paper, a response from certain types of tactile receptor may be readily elicited by an auditory stimulus. Similar criticisms apply to the recent results of Wever (1935) on the tympanic organ of the grasshopper (Arphea sulphurea).