Transition from decelerated to accelerated cosmic expansion in braneworld universes

Braneworld theory provides a natural setting to treat, at a classical level, the cosmological effects of vacuum energy. Non-static extra dimensions can generally lead to a variable vacuum energy, which in turn may explain the present accelerated cosmic expansion. We concentrate our attention in models where the vacuum energy decreases as an inverse power law of the scale factor. These models agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameter. The redshift at which the vacuum energy can start to dominate depends on the mass density of ordinary matter. For _m = 0.3, the transition from decelerated to accelerated cosmic expansion occurs at z _T ≈ 0.48 ± 0.20, which is compatible with SNe data. We set a lower bound on the deceleration parameter today, namely > − 1 + 3 _m /2, i.e., > − 0.55 for _m = 0.3. The future evolution of the universe crucially depends on the time when vacuum starts to dominate over ordinary matter. If it dominates only recently, at an epoch z < 0.64, then the universe is accelerating today and will continue that way forever. If vacuum dominates earlier, at z > 0.64, then the deceleration comes back and the universe recollapses at some point in the distant future. In the first case, quintessence and Cardassian expansion can be formally interpreted as the low energy limit of our model, although they are entirely different in philosophy. In the second case there is no correspondence between these models and ours.     

Constraints on the time scale of nuclear breakup from thermal hard-photon emission

Measured hard-photon multiplicities from second-chance nucleon-nucleon collisions are used in combination with a kinetic thermal model to estimate the breakup times of excited nuclear systems produced in nucleus-nucleus reactions at intermediate energies. The obtained nuclear breakup time for the ¹²⁹Xe + ^natSn reaction at 50 A MeV is Δτ ≈ 100-300 fm/c for all reaction centralities. The lifetime of the radiating sources produced in seven other different heavy-ion reactions studied by the TAPS experiment is consistent with Δτ ≈ 100 fm/c, such relatively long thermal photon emission times do not seemingly support the interpretation of nuclear breakup as due to a fast spinodal process for the heavy nuclear systems studied.     

Carmeli's Cosmology Fits Data for an Accelerating and Decelerating Universe Without Dark Matter or Dark Energy

A new relation for the density parameter Ω is derived as a function of expansion velocity υ based on Carmeli's cosmology. This density function is used in the luminosity distance relation D _L. A heretofore neglected source luminosity correction factor (1 − (υ/c)²)^−1/2 is now included in D _L. These relations are used to fit type Ia supernovae (SNe Ia) data, giving consistent, well-behaved fits over a broad range of redshift 0.1 < z < 2. The best fit to the data for the local density parameter is Ω_m = 0.0401 ± 0.0199. Because Ω_m is within the baryonic budget there is no need for any dark matter to account for the SNe Ia redshift luminosity data. From this local density it is determined that the redshift where the universe expansion transitions from deceleration to acceleration is z _t = 1.095^+0.264 _−0.155. Because the fitted data covers the range of the predicted transition redshift z _t, there is no need for any dark energy to account for the expansion rate transition. We conclude that the expansion is now accelerating and that the transition from a closed to an open universe occurred about 8.54 Gyr ago.     

The high response organic ultraviolet photodetectors based on 2-TNATA as donor

Organic ultraviolet photodetectors (OUV-PDs) were fabricated utilizing 2-TNATA as an electron donor with Bphen and TPBi as electron acceptors. A high sensitivity of OUV-PDs to UV light was obtained in the range of 300–420 nm. The optimized OUV-PDs composed of Bphen as the acceptor offered a photocurrent density up to 336 µA/cm² at ?8 V with 365 nm UV light at a power of 1.2 mW/cm². The high response is attributed to the excellent electron transport ability of Bphen and the matched energy level between 2-TNATA and Bphen.     

A new direction in design and manufacture of co-sensitized dye solar cells: Toward concurrent optimization of power conversion efficiency and durability

A novel methodology was implemented in the present study to concurrently control power conversion efficiency (η) and durability (D) of co-sensitized dye solar cells. Applying response surface methodology (RSM) and Desirability Function (DF), the main influential assembling (dye volume ratio and anti-aggregation agent concentration) and operational (performance temperature) parameters were systematically changed to probe their main and interactive effects on the η and D responses. Individual optimization based on RSM elucidated that D can be solely controlled by changing the ratio of vat-based organic photosensitizers, whereas η takes both effects of dye volume ratio and anti-aggregation concentration into account. Among the studied factors, the performance temperature played the most vital role in η and D regulation. In particular, however, multi-objective optimization by DF explored the degree to which one should be careful about manipulation of assembling and operational parameters in the way maximization of performance of a co-sensitized dye solar cell.     

Tensor optimized antisymmetrized molecular dynamics for relativistic nuclear matter

We apply a newly developed many-body theory, tensor optimized antisymmetrized molecular dynamics (TOAMD), to nuclear matter using a relativistic bare nucleon-nucleon interaction in the relativistic framework. It becomes evident that the tensor interaction plays an important role in nuclear many-body system due to the role of the pion in a strongly interacting system. We take the relativistic nuclear matter (RNM) wave function as a basic state and add tensor and short-range correlation operators in the form of pion and omega-meson correlation functions acting on the RNM wave function using the concept of TOAMD. We use the Monte Carlo (Metropolis) method based on the Gaussian integration and the second quantization method for antisymmetrization to calculate all the matrix elements of the many-body Hamiltonian. We write the whole formula of the TOAMD method for numerical calculations of the nuclear binding and saturation properties of nuclear matter using one-boson exchange potential.     

改进的PNJL模型下QCD的相图

Polyakov-Nambu-Jona-Lasinio（PNJL）模型是研究强相互作用物质性质的使用最为广泛的有效模型之一。在PNJL模型的基础上考虑了手征凝聚和Polyakov圈之间的纠缠作用,并且引入了化学势修正的Polyakov有效势,由此得到了化学势依赖的entangled PNJL（μEPNJL）模型。在平均场框架下的计算结果表明:相较于原始的PNJL模型,由μEPNJL模型计算得到的临界点（CEP）朝着温度更高、化学势更小处移动,并且手征对称性恢复相变和退禁闭相变在较大的化学势范围内都重合得很好。通过与STAR合作组在相对论重离子对撞机（RHIC）上进行的净质子数分布的测量结果相比,可以发现,通过适当的参数调节,由μEPNJL模型计算得到的CEP更加靠近实验预言的CEP可能存在的区域。Polyakov-Nambu-Jona-Lasinio (PNJL) model is one of the most popular effective quark models to investigate the properties of strongly interacting matter. Based on the PNJL model, we consider the entanglement interactions between the chiral condensate and Polyakov-loop, as well as the chemical potential modification of Polyakov-loop potential simultaneously, which is named μEPNJL model. Compared with the original PNJL model, the calculations in the mean field approximation show that the critical end point (CEP) given in the μEPNJL model moves towards higher temperature and smaller chemical potential in the T-μ phase diagram. Besides, the chiral symmetry restoration and deconfinement phase transition coincide well in a wide range of chemical potential. Comparing our calculations with the measurement of the moments of net-proton multiplicity distributions at Relativistic Heavy-Ion Collider (RHIC) by STAR Collaboration, we find that the CEP given by μEPNJL model can be closer to the range predicted by the experiment through appropriate parameter adjustment.     

Timing in EPR correlations

Detecting the instants of absorption of two paired EPR particles, and varying independently the distances of the detectors to the source, will experimentally display the V-shaped causal link between the two correlated occurrences.     

镱的原子吸收分析进展

本文对近些年来用电热原子吸收和火焰原子吸收测定镱时,为提高镱的灵敏度而采用的各种方法进行总结评述。     

NPB/Alq3有机量子阱光电特性研究

利用热蒸发的方法制备了有机量子阱发光器件和Alq3单层发光器件,其中NPB(N,N′-Di-[(lnaphthalenyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine)作垒层,Alq3(Tris-(8-quinolinolato) aluminum)作阱层,量子阱结构类似于无机半导体的Ⅱ型量子阱结构.实验发现有机量子阱发光器件结构中存在垒层向阱层的F(o)rster无辐射共振能量转移,具有良好的电流-电压特性,光谱的窄化及蓝移,并且光谱的蓝移程度随电压的增大而逐渐增强.