Isolation of Machine Foundations by Barriers

Experimental investigation has been carried out to study the effects due to isolation of foundations subjected to vertical vibration on the displacement amplitude. Tests were conducted on an embedded footing of contact area 45 x 45cm. with different embedments and some on the surface of natural ground. Three isolation barriers viz. air gap, saw dust and sand of various depths were used. From the results of the investigation it was found that an open trench (air gap) around the foundation reduces the displacement amplitude around the footing considerably to an extent of about 75%. Saw dust as a barrier, although not as good as air gap, performs better when compared to sand. The coefficient of attenuation is not a constant for a soil medium but varies with static and dynamic loads. The resonant frequency decreases and resonant amplitude increases by providing isolating barriers

A survey of red stars in the direction of the large Magellanic Cloud. 2. Some regions around the bar

We have continued the survey for red stars in the direction of the large Magellanic Cloud using the technique of ultra-low dispersion spectroscopy. This paper which is the second one on the series lists 706 stars located around the bar region. Finding charts and coordinates on the Hodge-Wright Atlas charts are provided

Biotechnology of Coconut

Biotechnology of coconut (Cocos nucifera L.) is a relatively recent area compared to similar work in other crops. It started as tissue culture in the eighties, which led to the development of molecular markers in late nineties with the use of RAPDs. Since then, considerable research has been carried out and protocols for tissue culture regeneration almost perfected. Embryo culture is being very successfully applied to germplasm transfer. Molecular markers such as AFLP, SSR, etc., were used to develop QTL maps. The entire gamut of coconut biotechnology is under review in this paper

Optimization and Application of Jet-Freezing

Cryofixation is considered to be the best method for immobilizing biological material in its natural state. In jet-freezing, the specimen typically is sandwiched between two carriers and kept in place while a coolant is moved very rapidly against the opposite surfaces. The JFD 030 jet-freezing device has been used to optimize the operating parameters. The course of the temperature in place of a specimen was measured with thermocouples and recorded by an IBM-compatible personal computer using a specifically developed software program. Mean cooling rates, over the temperature range of 273K to 173K, achievable with different cryogens, including the non-flammable HCFC 124 (SUVA 124-CHClFCF3), were measured under a variety of conditions. The freezing capability of the JFD 030 was evaluated by analyzing transmission electron microscopic results obtained from freeze-substituted plant cells and freeze-fractured cosmetic emulsions. Jet-freezing, despite its limits in freezing thick specimens, can be applied to cell suspensions as well as to semi-thin sections by the use of thin Ti supports, a higher pressure of the nitrogen gas or by a brief pretreatment with a cryoprotectant (e.g., sucrose). In addition, with the non-flammable HCFC 124 in combination with the thin Ti supports, freezing rates similar to those achievable with propane and standard copper supports can be reached giving researchers the chance to use jet-freezing without the dangerous propane

Towards the solution of the CP/CAC_{P}/C_{A} anomaly in shell-model calculations of muon capture

Recently many authors have performed shell-model calculations of nuclear matrix elements determining the rates of the ordinary muon capture in light nuclei. These calculations have employed well-tested effective interactions in large scale shell-model studies. For one of the nuclei of interest, namely $^{28}$Si, there exists recent experimental data which can be used to deduce the value of the ratio $C_{P}/C_{A}$ by using the calculated matrix elements. Surprisingly enough, all the abovementioned shell-model results suggest a very small value ($\simeq 0$) for $C_{P}/C_{A}$, quite far from the PCAC prediction and recent data on muon capture in hydrogen. We show that this rather disturbing anomaly is solved by employing effective transition operators. This finding is also very important in studies of the scalar coupling of the weak charged current of leptons and hadrons.Comment: Revtex, 6 pages, 2 figs include

Birth and early evolution of a planetary nebula

The final expulsion of gas by a star as it forms a planetary nebula --- the ionized shell of gas often observed surrounding a young white dwarf --- is one of the most poorly understood stages of stellar evolution. Such nebulae form extremely rapidly (about 100 years for the ionization) and so the formation process is inherently difficult to observe. Particularly puzzling is how a spherical star can produce a highly asymmetric nebula with collimated outflows. Here we report optical observations of the Stingray Nebula which has become an ionized planetary nebula within the past few decades. We find that the collimated outflows are already evident, and we have identified the nebular structure that focuses the outflows. We have also found a companion star, reinforcing previous suspicions that binary companions play an important role in shaping planetary nebulae and changing the direction of successive outflows.Comment: 9 pages + 3 figures. To appear in Nature, 2 April 199

Capacity of Asynchronous Random-Access Scheduling in Wireless Networks

Abstract—We study the throughput capacity of wireless networks which employ (asynchronous) random-access scheduling as opposed to deterministic scheduling. The central question we answer is: how should we set the channel-access probability for each link in the network so that the network operates close to its optimal throughput capacity? We design simple and distributed channel-access strategies for random-access networks which are provably competitive with respect to the optimal scheduling strategy, which is deterministic, centralized, and computationally infeasible. We show that the competitiveness of our strategies are nearly the best achievable via random-access scheduling, thus establishing fundamental limits on the performance of randomaccess. A notable outcome of our work is that random access compares well with deterministic scheduling when link transmission durations differ by small factors, and much worse otherwise. The distinguishing aspects of our work include modeling and rigorous analysis of asynchronous communication, asymmetry in link transmission durations, and hidden terminals under arbitrary link-conflict based wireless interference models. I