495,025 research outputs found

    Cosmological model of the interaction between dark matter and dark energy

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    In this paper, we test the dark matter-dark energy interacting cosmological model with a dynamic equation of state wDE(z)=w0+w1z/(1+z)w_{DE}(z)=w_{0}+w_{1}z/(1+z), using type Ia supernovae (SNe Ia), Hubble parameter data, baryonic acoustic oscillation (BAO) measurements, and the cosmic microwave background (CMB) observation. This interacting cosmological model has not been studied before. The best-fitted parameters with 1σ1 \sigma uncertainties are δ=0.022±0.006\delta=-0.022 \pm 0.006, ΩDM0=0.213±0.008\Omega_{DM}^{0}=0.213 \pm 0.008, w0=1.210±0.033w_0 =-1.210 \pm 0.033 and w1=0.872±0.072w_1=0.872 \pm 0.072 with χmin2/dof=0.990\chi^2_{min}/dof = 0.990. At the 1σ1 \sigma confidence level, we find δ<0\delta<0, which means that the energy transfer prefers from dark matter to dark energy. We also find that the SNe Ia are in tension with the combination of CMB, BAO and Hubble parameter data. The evolution of ρDM/ρDE\rho_{DM}/\rho_{DE} indicates that this interacting model is a good approach to solve the coincidence problem, because the ρDE\rho_{DE} decrease with scale factor aa. The transition redshift is ztr=0.63±0.07z_{tr}=0.63 \pm 0.07 in this model.Comment: 6 pages, 6 figures, published in A&

    COTS simulation package (CSP) interoperability - A solution to synchronous entity passing

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    In this paper we examine Commercial-Off-The- Shelf (COTS) Simulation Package (CSP) interoperability for one type of distributed simulation problem, namely synchronous entity passing. Synchronous entity passing is also referred to as the bounded buffer interoperability reference model. It deals with the case where for entities passed between models the receiving queue is bounded or the receiving workstation has limited capacity. This means the sending model must check the status of the receiving model before it can send entities. Correspondingly, the receiving model should update the status information dynamically when it changes. Similar to the work done on asynchronous entity passing, the High Level Architecture is chosen as the underlying standard to support reuse and interoperability. To simplify the integration of the CSP and the HLA, a middleware layer called DSManager is provided. Some new problems generated for synchronous entity passing are discussed and solutions are proposed together with a description of their implementation. Two sets of experiments are conducted to evaluate the solutions using a CSP Emulator (CSPE) which supports both standalone and distributed simulation

    A scale-based approach to finding effective dimensionality in manifold learning

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    The discovering of low-dimensional manifolds in high-dimensional data is one of the main goals in manifold learning. We propose a new approach to identify the effective dimension (intrinsic dimension) of low-dimensional manifolds. The scale space viewpoint is the key to our approach enabling us to meet the challenge of noisy data. Our approach finds the effective dimensionality of the data over all scale without any prior knowledge. It has better performance compared with other methods especially in the presence of relatively large noise and is computationally efficient.Comment: Published in at http://dx.doi.org/10.1214/07-EJS137 the Electronic Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of Mathematical Statistics (http://www.imstat.org

    Improved thermal performance of a large laminated lithium-ion power battery by reciprocating air flow

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    The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Thermal safety issues are increasingly critical for large-size laminated Lithium-Ion Batteries (LIBs). Despite a number of investigations conducted on the Battery Thermal Management System (BTMS) with reciprocating air-flow cooling, large laminated power LIBs are still not sufficiently investigated, particularly in the view of battery thermal characteristics. The present study investigates the thermal behaviors of an air-cooled NCM-type LIB (LiNi1−x−yCoxMnyO2 as cathode) from an experimental and systematic approach. The temperature distribution was acquired from different Depth of Discharge (DOD) by the infrared imaging (IR) technology. A reciprocating air-flow cooling method was proposed to restrict the temperature fluctuation and homogenize temperature distribution. Results showed that there was a remarkable temperature distribution phenomenon during the discharge process, the temperature distribution was affected by direction of air-flow. Forward air-flow (from current collector side to lower part of battery) was always recommended at the beginning of the discharge due to the thermal characteristics of the battery. After comprehensive consideration on battery temperature limit and cooling effect, the desired initial reversing timing was about 50% DOD at 3 C discharge rate. Different reversing strategies were investigated including isochronous cycles and aperiodic cycles. It was found that the temperature non-uniformity caused by heat accumulation and concentration was mitigated by reciprocating air-flow with optimized reversing strategy

    Measuring dark energy with the EisoEpE_{\rm iso}-E_{\rm p} correlation of gamma-ray bursts using model-independent methods

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    In this paper, we use two model-independent methods to standardize long gamma-ray bursts (GRBs) using the EisoEpE_{\rm iso}-E_{\rm p} correlation, where EisoE_{\rm iso} is the isotropic-equivalent gamma-ray energy and EpE_{\rm p} is the spectral peak energy. We update 42 long GRBs and try to make constraint on cosmological parameters. The full sample contains 151 long GRBs with redshifts from 0.0331 to 8.2. The first method is the simultaneous fitting method. The extrinsic scatter σext\sigma_{\rm ext} is taken into account and assigned to the parameter EisoE_{\rm iso}. The best-fitting values are a=49.15±0.26a=49.15\pm0.26, b=1.42±0.11b=1.42\pm0.11, σext=0.34±0.03\sigma_{\rm ext}=0.34\pm0.03 and Ωm=0.79\Omega_m=0.79 in the flat Λ\LambdaCDM model. The constraint on Ωm\Omega_m is 0.55<Ωm<10.55<\Omega_m<1 at the 1σ\sigma confidence level. If reduced χ2\chi^2 method is used, the best-fit results are a=48.96±0.18a=48.96\pm0.18, b=1.52±0.08b=1.52\pm0.08 and Ωm=0.50±0.12\Omega_m=0.50\pm0.12. The second method is using type Ia supernovae (SNe Ia) to calibrate the EisoEpE_{\rm iso}-E_{\rm p} correlation. We calibrate 90 high-redshift GRBs in the redshift range from 1.44 to 8.1. The cosmological constraints from these 90 GRBs are Ωm=0.230.04+0.06\Omega_m=0.23^{+0.06}_{-0.04} for flat Λ\LambdaCDM, and Ωm=0.18±0.11\Omega_m=0.18\pm0.11 and ΩΛ=0.46±0.51\Omega_{\Lambda}=0.46\pm0.51 for non-flat Λ\LambdaCDM. For the combination of GRB and SNe Ia sample, we obtain Ωm=0.271±0.019\Omega_m=0.271\pm0.019 and h=0.701±0.002h=0.701\pm0.002 for the flat Λ\LambdaCDM, and for the non-flat Λ\LambdaCDM, the results are Ωm=0.225±0.044\Omega_m=0.225\pm0.044, ΩΛ=0.640±0.082\Omega_{\Lambda}=0.640\pm0.082 and h=0.698±0.004h=0.698\pm0.004. These results from calibrated GRBs are consistent with that of SNe Ia. Meanwhile, the combined data can improve cosmological constraints significantly, comparing to SNe Ia alone. Our results show that the EisoEpE_{\rm iso}-E_{\rm p} correlation is promising to probe the high-redshift universe.Comment: 10 pages, 6 figures, 4 table, accepted by A&A. Table 4 contains calibrated distance moduli of GRB
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