The value of additional reviews in reputation systems: Evidence from a car review platform

Online reviews, especially additional reviews, have become an important channel for consumers to obtain information about product quality. Based on review data obtained from “AutoHome”, which is a most popular car review platform in China, this study explores the influence of additional review function on the initial reviews from both the reader and reviewer levels. At the reader-level, the introduction of the additional review function improves readers’ perceived usefulness of the reviews. At the reviewer-level, it can drive reviewers to write more initial reviews. In general, the introduction of such a function can be regarded as an improvement of the existing review mechanism. The findings of this study can not only enrich the research on online word-of-mouth, but also provide valuable reference for related practitioners

Thermal performance analysis of a solar energy storage unit encapsulated with HITEC salt/copper foam/nanoparticles composite

HITEC salt (40 wt. % NaNO2, 7 wt. % NaNO3, 53 wt. % KNO3) with a melting temperature of about 142 °C is a typical phase change material (PCM) for solar energy storage. Both aluminum oxide (Al2O3) nanopowder and metal foam were used to enhance pure HITEC salt, so as to retrieve the limitation of composite PCMs with single enhancement. The morphologies and thermo-physical properties of the composites were firstly characterized with Scanning Electron Microscope, Fourier-transform Infrared spectroscopy and Differential Scanning Calorimeter, respectively. A pilot test rig with a heater of 380 W located in the inner pipe was built, which was encapsulated with HITEC salt, nano-salt (HITEC salt seeded with 2 wt. % Al2O3 nanopowder) and salt/copper foam composite seeded with 2 wt. % Al2O3 nanopowder as storage media. Then heat storage and retrieval tests of the energy storage system were conducted both for pure HITEC salt and composite PCMs at various heating temperatures. The temperature evolutions and distributions of the PCMs at different locations were measured, including radial, angular, and axial locations, and the energy and volumetric mean powers during heat storage/retrieval processes were calculated subsequently. The results show that metal foam is generally compatible with the nano-salt. The maximum deviation of the melting/freezing phase change temperatures of the nano-salt/copper foam composite is 3.54 °C, whereas that of the nano-salt/nickel foam composite is 3.80 °C. The specific heats of the nano-salt are apparently enhanced with the addition of Al2O3 nanopowder both in solid and liquid states. The system encapsulated with the nano-salt/copper foam composite can be considerably enhanced, e.g. the time-duration of heat storage process at the heating temperature of 160 °C can be reduced by about 58.5%, compared to that of pure salt. The volumetric mean power of heat storage for the nano-salt/copper foam composite at the heating temperature of 180 °C increases to 109.32 kW/m3, compared with 53.01 kW/m3 of pure HITEC salt. The information will be helpful for solar system design, construction and application using molten salt for solar energy storage

Controlled polarization rotation of an optical field in multi-Zeeman-sublevel atoms

We investigate, both theoretically and experimentally, the phenomenon of polarization rotation of a weak, linearly-polarized optical (probe) field in an atomic system with multiple three-level electromagnetically induced transparency (EIT) sub-systems. The polarization rotation angle can be controlled by a circularly-polarized coupling beam, which breaks the symmetry in number of EIT subsystems seen by the left- and right-circularly-polarized components of the weak probe beam. A large polarization rotation angle (up to 45 degrees) has been achieved with a coupling beam power of only 15 mW. Detailed theoretical analyses including different transition probabilities in different transitions and Doppler-broadening are presented and the results are in good agreements with the experimentally measured results.Comment: 28pages, 12figure

Performance analysis and discussion on the thermoelectric element footprint for PV–TE maximum power generation

Geometrical optimisation is a valuable way to improve the efficiency of a thermoelectric element (TE). In a hybrid photovoltaic-thermoelectric (PV-TE) system, the photovoltaic (PV) and thermoelectric (TE) components have a relatively complex relationship; their individual effects mean that geometrical optimisation of the TE element alone may not be sufficient to optimize the entire PV–TE hybrid system. In this paper, we introduce a parametric optimisation of the geometry of the thermoelectric element footprint for a PV–TE system. A uni-couple TE model was built for the PV–TE using the finite element method and temperature-dependent thermoelectric material properties. Two types of PV cells were investigated in this paper and the performance of PV–TE with different lengths of TE elements and different footprint areas was analysed. The outcome showed that no matter the TE element's length and the footprint areas, the maximum power output occurs when An/Ap= 1. This finding is useful, as it provides a reference whenever PV–TE optimisation is investigated