Sigma meson in QCD sum rules using a two quark current with derivatives

We study the $\sigma$ meson in QCD sum rules using a two quark interpolating field with derivatives. In the constituent quark model, the $\sigma$ meson is composed of a quark and an antiquark in the relative p-wave state and is thus expected to have a larger overlap with an interpolating field that measures the derivative of the relative quark wave-function. While the sum rule with a current without derivatives gives a pole mass of around 1 GeV, the present sum rule with a derivative current gives a mass of around 550 MeV and a width of 400 MeV, that could be identified with the $\sigma$ meson.Comment: 4 pages, 2 figure

Camera oscillation pattern for VSLAM: translational versus rotational

Visual SLAM algorithms exploit natural scene features to infer the camera motion and build a map of the environment landmarks. SLAM algorithm has two interrelated processes localization and mapping. For accurate localization, we need the features location estimates to converge quickly. On the other hand, to build an accurate map, we need accurate localization. Recently, a biologically inspired approach exploits deliberate camera oscillation has been used to improve the convergence speed of depth estimate. In this paper, we explore the effect of camera oscillation pattern on the accuracy of VSLAM. Two main oscillation patterns are used for distance estimation: translational and rotational. Experiments, using static and moving robot, are made to explore the effect of these oscillation patterns on the VSLAM performance

Optically monitored nuclear spin dynamics in individual GaAs quantum dots grown by droplet epitaxy

We report optical orientation experiments in individual, strain free GaAs quantum dots in AlGaAs grown by droplet epitaxy. Circularly polarized optical excitation yields strong circular polarization of the resulting photoluminescence at 4K. Optical injection of spin polarized electrons into a dot gives rise to dynamical nuclear polarization that considerably changes the exciton Zeeman splitting (Overhauser shift). We show that the created nuclear polarization is bistable and present a direct measurement of the build-up time of the nuclear polarization in a single GaAs dot in the order of one second.Comment: 7 pages, 3 figure

Dynamic feature detection using virtual correction and camera oscillations

Visual SLAM algorithms exploit natural scene features to infer the camera motion and build a map of a static environment. In this paper, we relax the severe assumption of a static scene to allow for the detection and deletion of dynamic points. A new "virtual correction" method is introduced which serves to detect the dynamic points by checking the re-projection error of the points before and after the virtual measurement update. It can also recover the erroneously excluded useful features, particularly the distant points which may be deleted because of the change in its position after new measurement observation. Deliberate camera oscillations are also used to improve the VSLAM accuracy and the camera observability. The simulation results showed the effectiveness of the virtual correction when combined with camera oscillation in recovering the misclassified features and detecting the dynamic features even in difficult scenarios

Analysis of a Data Center Using Liquid-Liquid CO2 Heat Pump for Simultaneous Cooling and Heating

Liquid–liquid CO2 heat pump systems are a promising technology for commercial building applications, which require simultaneous heating and cooling. This paper presents the investigation of a data center on the Purdue University, West Lafayette campus. The data center located in the Department of Mathematics is the most energy intensive data center on campus. The cooling load of the data center is approximately 750 kW/hour. The heating season in West Lafayette is 7 to 8 months and the heating load of the buildings is very high during the coldest months. The heating load of the Mathematics building can go to as high as 600 kW/hour during the coldest days of the year. To suffice this simultaneous cooling and heating demand, a liquid-liquid CO2 heat pump is proposed. Presently, the cooling load of the data center is met by eight electrically driven and four steam-driven chillers and the heating load is satisfied by two coal fired and two natural gas boilers. Simulations are performed to compare the proposed CO2 heat pump system with the present system. The assessment shows noteworthy fuel savings and reduction in the CO2 emissions with the system working with a coefficient of performance (COP) of 6.19. If the CO2 heat pump system is installed, 574.92m3/day of natural gas and 751.68 kg/day of coal could be saved on a cold day. The system has the potential to reduce CO2 emissions by 2980.76 kg/day

Cost Optimization of Thermoelectric Sub-Cooling in Air-cooled CO2 Air Conditioners

This paper presents a cost-effective enhancement of a trans-critical carbon dioxide (CO2) cycle in air-conditioning mode by utilizing a thermoelectric sub-cooler. It is well-documented that the cooling COP of the transcritical CO2 cycle decreases as the ambient air temperature significantly increases above the critical temperature of the refrigerant. A high gas cooler outlet temperature limits the enthalpy of evaporation so that the air-conditioning cooling performance is reduced. Sub-cooling is known as a mitigation method to this problem. However, adding a small-scale heat pump to a residential or light commercial air conditioner can be quite costly. Therefore, a thermoelectric solid-state sub-cooler is proposed. The thermoelectric cooling (TEC) devices utilized in small temperature differences ranging from 5 to 15 oC can be quite efficient since the intrinsic heat loss of the TEC by heat conduction in reverse direction of pumping heat is minimal. Based on the prior work, the optimum design for cost-per-performance shows that the cost for sub-cooling is dominated by the heat exchangers and it is not by the thermoelectric material itself. The TECs are compact and have a low thickness, which is in the range of a few mm. Hence the TEC modules can be integrated into the form factor of a plate heat exchanger. In this study, the cooling COP of the CO2 air conditioner is enhanced by approximately 12% using an optimally designed thermoelectric sub-cooler at an ambient temperature of 35 oC. This potential improvement is based on a figure-of-merit (ZT) of currently available thermoelectric materials (ZT~1). The seasonal primary energy efficiency and the cost performance of the optimized TE sub-cooled CO2 heat pump system will be presented in comparison to other compact sub-cooling technologies

Study on Energy-Saving Performance of a Novel CO2 Heat Pump with Applications in Dairy Processes

In dairy processes, there are significant simultaneous heating and cooling demands. A novel type of transcritical CO2 heat pump system is proposed, and its features and benefits are introduced. Bassed on the technical characteristics, primary energy-savings, and operating cost aspects, the CO2 heat pump system is simulated and compared to current heating and cooling systems used in dairy plants. The results show that the highest primary energy-saving rate of the CO2 heat pump is 51.5%. For fluid milk and cheese manufacturing processes, the primary energy-saving is 36.2% and 45.1%, respectively. In addition, the operating cost savings of fluid milk and cheese production are evaluated based on the cost structures in the states of Wisconsin, California and New York

A Systematic Survey of Protoclusters at z∼3−6z\sim3\mathrm{-}6 in the CFHTLS Deep Fields

We present the discovery of three protoclusters at $z\sim3\mathrm{-}4$ with spectroscopic confirmation in the Canada-France-Hawaii Telescope (CFHT) Legacy Survey Deep Fields. In these fields, we investigate the large-scale projected sky distribution of $z\sim3\mathrm{-}6$ Lyman break galaxies and identify 21 protocluster candidates from regions that are overdense at more than $4\sigma$ overdensity significance. Based on cosmological simulations, it is expected that more than $76\%$ of these candidates will evolve into a galaxy cluster of at least a halo mass of $10^{14}\,\mathrm{M_\odot}$ at $z=0$. We perform follow-up spectroscopy for eight of the candidates using Subaru/FOCAS, KeckII/DEIMOS, and Gemini-N/GMOS. In total we target 462 dropout candidates and obtain 138 spectroscopic redshifts. We confirm three real protoclusters at $z=3\mathrm{-}4$ with more than five members spectroscopically identified, and find one to be an incidental overdense region by mere chance alignment. The other four candidate regions at $z\sim5\mathrm{-}6$ require more spectroscopic follow-up in order to be conclusive. A $z=3.67$ protocluster, which has eleven spectroscopically confirmed members, shows a remarkable core-like structure composed of a central small region (Mpc}) and an outskirts region ($\sim1.0\,\mathrm{physical\>Mpc}$). The Ly$\alpha$ equivalent widths of members of the protocluster are significantly smaller than those of field galaxies at the same redshift while there is no difference in the UV luminosity distributions. These results imply that some environmental effects start operating as early as at $z\sim4$ along with the growth of the protocluster structure.Comment: 25 pages, 6 tables, 25 figures, accepted for publication in Ap

Experimental Study of a CO2 Thermal Battery for Simultaneous Cooling and Heating Applications

This paper presents experimental investigations of the dynamics of a transcritical CO2 heat pump system with two thermal storages for simultaneous cooling and heating application. The preliminary results of the thermal battery are provided using a small-scale test bed that shows the accelerated penetration of renewable energy sources for building heating and cooling applications. The experimental system consists of a CO2 heat pump system with a compressor of 3 kW (1.02x104 BTU/hr) cooling capacity and two water tanks. During operation, the compressor and expansion valve are considered quasi-static. Thermal sensors are located in each of the two tanks to monitor the temperature gradient of water along the vertical orientation of the tank which impacts the overall system performance. Experiments are carried out under different water circulation flow rates for both the gas cooler and the evaporator in the heat pump, as well as under various discharge pressure conditions controlled by different charging rates and expansion valve openings. The impacts of water circulation flow rate and valve opening are reported in an effort to find the optimum coefficient-of-performance (COP). The results show that increasing the water inlet temperature in the gas cooler raises the discharge pressure significantly and drops the COP, whereas increasing the water temperature of the evaporator raises the discharge pressure relatively moderately. Although a larger water flow rate enhances the heat exchanger capacity and system COP, a smaller water flow rate seems to be preferable to maintain the thermal profile of the water tanks and to provide a more stable COP. At higher gas cooler water inlet temperature, the COP tends to increase with closing expansion valve. In this particular setup, the best COP is found to be approximately 7.0 at a specific expansion valve opening and at a discharge pressure between 75 and 83 bars (1088 to 1204 psia). The heating COP negatively corresponds to the water temperature at the gas cooler inlet. Experiments suggest the need of a proper control strategy and a matched tank capacity design. Based on these results, a 20% power enhancement may be possible by controlling the hot and cold water flow rates