Improvement of conversion efficiency of atom-molecule Bose-Einstein condensate

We investigate the stimulated Raman adiabatic passage in two-color photoassociation for a atom-molecule Bose-Einstein condensate. By applying two time-varying Guassian laser pulses that fulfill generalized two-photon resonance condition, we obtain highly efficient atom-molecule conversion. The efficiency depends on the free-bound detuning and the delay time between the two pulses. By adjusting the parameters optimally, we achieve 92% conversion efficiency.Comment: 4 pages, 4 figures. To be appeared in J. Korean Phys. Society (JKPS

Edge mode based graphene nanomechanical resonators for high-sensitivity mass sensor

We perform both molecular dynamics simulations and theoretical analysis to study the sensitivity of the graphene nanomechanical resonator based mass sensors, which are actuated following the global extended mode or the localized edge mode. We find that the mass detection sensitivity corresponding to the edge mode is about three times higher than that corresponding to the extended mode. Our analytic derivations reveal that the enhancement of the sensitivity originates in the reduction of the effective mass for the edge mode due to its localizing feature

Storage of spin squeezing in a two-component Bose-Einstein condensate

Efficient control of spin squeezing in a two-component Bose-Einstein Condensate is studied by rapidly turning-off the external field at a time that maximal spin squeezing appears. We show that strong reduction of spin fluctuation can be maintained in a nearly fixed direction for a long time. We explain the underlying physics unambiguously, and present analytical expressions of the maximal-squeezing time.Comment: 10 pages, 5 figures. This version is slightly different from the one published in Phys. Rev. Let

Spin squeezing and maximal-squeezing time

Spin squeezing of a nonlinear interaction model with Josephson-like coupling is studied to obtain time scale of maximal squeezing. Based upon two exactly solvable cases for two and three particles, we find that the maximal-squeezing time depends on the level spacing between the ground state and its next neighbor eigenstate.Comment: 7 pages, 5 figures, 1 table. Resubmitted to Phys. Rev.

Investigation of the relationship between fuel injection nozzle roto flow and hydra flow and the engine torque of a diesel engine

The purpose of this study was to investigate the possibility of reducing diesel engine torque variation by optimizing fuel injection nozzle tip configuration. In order to reduce engine torque variation, test runs were conducted to determine whether fuel injection nozzles affected diesel engine torque. There was a further effort to determine whether a correlation existed between the fuel injection nozzle roto flow and hydra flow, and the engine torque at specified engine speeds. Engines installed in cotton pickers and tractors were used for this study. Engines, five from the cotton picker and five from the tractor group were chosen randomly from those which were produced by the same group of people under the same production conditions. These restrictions minimized variation associated with nozzles and pumps. These engines were then put into the screen tests to make sure they were quality engines. The experiments with the selected engines were conducted in the manufacturer\u27s test cell and data were gathered at seven different engine speeds.Three levels (higher limit, medium, and lower limit) of nozzle roto flow and hydra flow were employed in the diesel engine injection system during the experiment. The investigation consisted of two limited-time production style tests. One test was without restrictions and the other was with restrictions. Fifteen calibrations for the tractor engine group and 15 for the cotton picker engine group were recorded for the nozzle roto flow and hydra flow, and the corresponding engine torque. Two-way ANOVA and correlation statistical procedure were used to analyze the data derived from the experimental sequences. These statistical procedures were used for the following purposes: Investigate the effect of different levels of nozzle roto flow and hydra flow on engine torque. Identify the difference between the effect of nozzle roto flow and hydra flow on engine torque and that of chance variables. Determine the Pearson\u27s correlation coefficient r between nozzle roto flow and hydra flow and engine torque at each engine speed. Determine linear relation between nozzle roto flow and hydra flow and engine torque at each specified engine speed. The statistical analyses indicated that different levels of fuel injection nozzle roto flow and hydra flow significantly affected diesel engine torque. The data also revealed that the effect of nozzle roto flow and .hydra flow on torque was independent of engine speed. The collected test data from the nozzle roto flow and hydra flow study further confirmed that engine speed affected engine torque. There was a significant positive correlation which was greater than 0.94 at each tested engine speed between nozzle roto flow and hydra flow and diesel engine torque. Linear relations between nozzle roto flow and hydra flow and the engine torque at each specified engine speed were determined. For cotton picker and tractor engines, a precise prediction of engine torque from a specific fuel injection nozzle roto flow or hydra flow can be calculated directly from the equations developed in this study. The findings could also help engine manufacturers more effectively choose the optimum fuel injection nozzle roto flow or hydra flow for the nominal torque required of the engine. This will better control engine torque variation

Towards Spatial Queries over Phenomena in Sensor Networks

Today, technology developments enable inexpensive production and deployment of tiny sensing and computing nodes. Networked through wireless radio, such senor nodes form a new platform, wireless sensor networks, which provide novel ability to monitor spatiotemporally continuous phenomena. By treating a wireless sensor network as a database system, users can pose SQL-based queries over phenomena without needing to program detailed sensor node operations. DBMS-internally, intelligent and energyefficient data collection and processing algorithms have to be implemented to support spatial query processing over sensor networks. This dissertation proposes spatial query support for two views of continuous phenomena: field-based and object-based. A field-based view of continuous phenomena depicts them as a value distribution over a geographical area. However, due to the discrete and comparatively sparse distribution of sensor nodes, estimation methods are necessary to generate a field-based query result, and it has to be computed collaboratively ‘in-the-network’ due to energy constraints. This dissertation proposes SWOP, an in-network algorithm using Gaussian Kernel estimation. The key contribution is the use of a small number of Hermite coefficients to approximate the Gaussian Kernel function for sub-clustered sensor nodes, and processes the estimation result efficiently. An object-based view of continuous phenomena is interested in aspects such as the boundary of an ‘interesting region’ (e.g. toxic plume). This dissertation presents NED, which provides object boundary detection in sensor networks. NED encodes partial event estimation results based on confidence levels into optimized, variable length messages exchanged locally among neighboring sensor nodes to save communication cost. Therefore, sensor nodes detect objects and boundaries based on moving averages to eliminate noise effects and enhance detection quality. Furthermore, the dissertation proposes the SNAKE-based approach, which uses deformable curves to track the spatiotemporal changes of such objects incrementally in sensor networks. In the proposed algorithm, only neighboring nodes exchange messages to maintain the curve structures. Based on in-network tracking of deformable curves, other types of spatial and spatiotemporal properties of objects, such as area, can be provided by the sensor network. The experimental results proved that our approaches are resource friendly within the constrained sensor networks, while providing high quality query results