Single atom impurity in a Single Molecular Transistor

The influence of an impurity atom on the electrostatic behaviour of a Single Molecular Transistor (SMT) was investigated through Ab-initio calculations in a double-gated geometry. The charge stability diagram carries unique signature of the position of the impurity atom in such devices which together with the charging energy of the molecule could be utilised as an electronic fingerprint for the detection of such impurity states in a nano-electronic device. The two gated geometry allows additional control over the electrostatics as can be seen from the total energy surfaces (for a specific charge state) which is sensitive to the positions of the impurity. These devices which are operational at room temperature can provide significant advantages over the conventional Silicon based single dopant devices functional at low temperature. The present approach could be a very powerful tool for the detection and control of individual impurity atoms in a single molecular device and for applications in future molecular electronics.Comment: 6 pages, 3 figure

Emergency egress requirements for caution and warning, logistics, maintenance, and assembly stage MB-6 of Space Station Freedom

The safety and survival of the crewmembers has been the prime concern of NASA. Previous studies have been conducted mainly for emergencies occurring during the operating mode of the fully assembled Station. The present study was conducted to evaluate the emergency requirements for the caution and warning, logistics, maintenance, and assembly stage MB-6 of the Station in space. Effective caution and warning is essential to achieve safe egress in emergencies. In order to survive a long period in space, the safety and emergency requirements for maintenance, logistics, and extravehicular assembly operation in space must be met

Strange stars at finite temperature

We calculate strange star properties, using large N_c approximation with built-in chiral symmetry restoration (CSM). We used a relativistic Hartree Fock mean field approximation method, using a modified Richardson potential with two scale parameters \Lambda and \Lambda^\prime, to find a new set of equation of states for strange quark matter. We take the effect of temperature (T) on gluon mass, in addition to the usual density dependence, and find that the transition T from hadronic matter to strange matter is 80 MeV. Therefore formation of strange stars may be the only signal for formation of QGP with asymptotic freedom and CSM.Comment: To be published in the proceedings of The Third 21COE Symposium, held at Department of Physics, Waseda University, Tokyo, Japan, September 1-3, 200

Emergency egress requirements for Space Station Freedom

An objective was to determine if the pressurized elements and hatchways of the Space Station Freedom support the emergency egress of crewmembers during operation of the station at the stage of Permanently Manned Capacity. Emergency egress was defined as the exit from a pressurized element when an event occurs which makes that element uninhabitable. The possible egress paths for four emergency scenarios considered were: (1) accident occurs in a module and crewmembers translate to the attached node; (2) accident occurs at a node and crewmembers translate through it to the safe node; (3) accident occurs at a module close to a node and crewmembers are not able to translate through the affected area; and (4) accident occurs at a node and crewmembers cannot translate through it. The structural design of the pressurized elements and the hatches studied is adequate for the emergence egress translation requirement. The current location of a few racks may cause some obstruction for egress to the orbiter. The egress time required in the worst situation is estimated to be about 3 mins. There is a chance of getting crewmembers trapped in a module in case of a severe accident. Aids are needed for emergency egress translation

Comments on the size of the simulation box in cosmological N-Body simulations

N-Body simulations are a very important tool in the study of formation of large scale structures. Much of the progress in understanding the physics of high redshift universe and comparison with observations would not have been possible without N-Body simulations. Given the importance of this tool, it is essential to understand its limitations as ignoring the limitations can easily lead to interesting but unreliable results. In this paper we study the limitations arising out of the finite size of simulation volume. This finite size implies that modes larger than the size of the simulation volume are ignored and a truncated power spectrum is simulated. If the simulation volume is large enough then the mass in collapsed haloes expected from the full power spectrum and from the truncated power spectrum should match. We propose a quantitative measure based on this approach that allows us to compute the minimum box size for an N-Body simulation. We find that the required box size for simulations of LCDM model at high redshifts is much larger than is typically used. We can also use this approach to quantify the effect of perturbations at large scales for power law models and we find that if we fix the scale of non-linearity, the required box size becomes very large as the index becomes small. The appropriate box size computed using this approach is also an appropriate choice for the transition scale when tools like MAP (Tormen and Bertschinger, 1996) that add the contribution of the missing power are used.Comment: 7 pages, 8 figures, Accepted for publication in the MNRA

Emergency egress requirements for Space Station Freedom

There is a real concern regarding the requirements for safe emergency egress from the Space Station Freedom (SSF). The possible causes of emergency are depressurization due to breach of the station hull by space debris, meteoroids, seal failure, or vent failure; chemical toxicity; and a large fire. The objectives of the current study are to identify the tasks required to be performed in emergencies, establish the time required to perform these tasks, and to review the human equipment interface in emergencies. It was found that a fixed time value specified for egress has shifted focus from the basic requirements of safe egress, that in some situations the crew members may not be able to complete the emergency egress tasks in three minutes without sacrificing more than half of the station, and that increased focus should be given to human factors aspects of space station design