High order Chin actions in path integral Monte Carlo

High order actions proposed by Chin have been used for the first time in path integral Monte Carlo simulations. Contrarily to the Takahashi-Imada action, which is accurate to fourth order only for the trace, the Chin action is fully fourth order, with the additional advantage that the leading fourth and sixth order error coefficients are finely tunable. By optimizing two free parameters entering in the new action we show that the time step error dependence achieved is best fitted with a sixth order law. The computational effort per bead is increased but the total number of beads is greatly reduced, and the efficiency improvement with respect to the primitive approximation is approximately a factor of ten. The Chin action is tested in a one-dimensional harmonic oscillator, a H$_2$ drop, and bulk liquid $^4$He. In all cases a sixth-order law is obtained with values of the number of beads that compare well with the pair action approximation in the stringent test of superfluid $^4$He.Comment: 19 pages, 8 figure

On the onset of surface condensation: formation and transition mechanisms of condensation mode

Financial supports from the National Natural Science Foundation of China (51406205), the Beijing Natural Science Foundation (3142021), China Scholarship Council Ph. D studentship and the Engineering and Physical Sciences Research Council (EPSRC) of the UK through research grant (EP/L001233/1) are acknowledged

Effect of Suspension Freeze-concentration Technology on the Quality of Wine

One of the factors that inhibits the development of the Chinese wine industry is that the sugar content ofthe grape feedstock is insufficient. In order to produce wine with better qualities using these materials,concentrating the grape juice could be a good alternative to adding sugars. In this study, suspension freezeconcentrationtechnology was applied to concentrating grape juice with a low sugar content. The freezeconcentratedgrape juice was made into red and white wines separately. In the control group, red andwhite wines were made from chaptalized (sugar-enriched) grape juice. The physical and chemical indexes,sensory evaluation results and polyphenolic content of the wine were analysed to evaluate the practicalityof applying the freeze-concentration technology in the wine industry. The results show that, after removingice every 30 min for approximately 14 h with a -18°C coolant, grape juice with an initial sugar content of14°Brix reached 23°Brix. Both the red wines and white wines made from freeze-concentrated grape juicewere of a higher quality than the wines made from chaptalised grape juice. Moreover, the phenolic contentwas concentrated, which may provide health benefits. Thus, suspension freeze-concentration technology isa promising alternative to traditional chaptalisation technology

Exposure to hazardous volatile organic compounds, PM 10 and CO while walking along streets in urban Guangzhou, China

Toxic air pollutants in street canyons are important issues concerning public health especially in some large Asian cities like Guangzhou. In 1998 <18% of Guangzhou citizens used public transportation modes, with a majority commuting on foot (42%) or by bicycle (22%). Of the pedestrians, 57% were either senior citizens or students. In the present study, we measured toxic air pollutants while walking along urban streets in Guangzhou to evaluate pedestrian exposure. Volatile organic compounds (VOCs) were collected with sorbent tubes, and PM 10 and CO were measured simultaneously with portable analyzers. Our results showed that pedestrian exposure to PM 10 (with an average of 303 μg m -3 for all samples) and some toxic VOCs (for example, benzene) was relatively high. Monocyclic aromatic hydrocarbons were found to be the most abundant VOCs, and 71% of the samples had benzene levels higher than 30 μg m -3. Benzene, PM 10 and CO in walk-only streets were significantly lower (p<0.05) than in traffic streets, and the differences in exposure levels between new urban streets and old urban streets were highly significant (p<0.01). Pedestrian exposure to toxic VOCs and PM 10 was higher than those reported in other public transportation modes (bus and subway). The good correlations between BTEX, PM 10 and CO in the streets indicated that automotive emission might be their major source. Our study also showed that the risk to pedestrians due to air pollution was misinterpreted by the reported air quality index based on measurement of SO 2, NO x and PM 10 in the government monitoring stations. An urban roadside monitoring station might be needed by air quality monitoring networks in large Asian cities like Guangzhou, in order to survey exposure to air toxics in urban roadside microenvironments. © 2004 Elsevier Ltd. All rights reserved

Dynamic and nonlinear magnetoconductance: Numerical analysis in two dimensions

We report theoretical investigations on the magnetoconductance of a two-probe two-dimensional mesoscopic conductor in the dynamic and weakly nonlinear transport regimes. Crucial to the investigation is the development of a viable numerical scheme for evaluating functional derivatives of a scattering matrix with respect to the scattering potential landscape in the presence of a magnetic field. The physical behavior of the local partial density of states, the sensitivity, the dynamic conductance, and the second order nonlinear dc conductance as functions of an external uniform magnetic field is revealed at two dimensions. Due to symmetry breaking the magnetic field adds very important effects to these physical quantities.published_or_final_versio

Dimensional crossover of thermal conductance in graphene nanoribbons: A first-principles approach

First-principles density-functional calculations are performed to investigate the thermal transport properties in graphene nanoribbons (GNRs). The dimensional crossover of thermal conductance from one to two dimensions (2D) is clearly demonstrated with increasing ribbon width. The thermal conductance of GNRs in a few nanometer width already exhibits an approximate low-temperature dependence of $T^{1.5}$, like that of 2D graphene sheet which is attributed to the quadratic nature of dispersion relation for the out-of-plane acoustic phonon modes. Using a zone-folding method, we heuristically derive the dimensional crossover of thermal conductance with the increase of ribbon width. Combining our calculations with the experimental phonon mean-free path, some typical values of thermal conductivity at room temperature are estimated for GNRs and for 2D graphene sheet, respectively. Our findings clarify the issue of low-temperature dependence of thermal transport in GNRs and suggest a calibration range of thermal conductivity for experimental measurements in graphene-based materials.Comment: 18 pages, 4 figure

Visualization of facet-dependent pseudo-photocatalytic behavior of TiO2 nanorods for water splitting using In situ liquid cell TEM

We report an investigation of the pseudo-photocatalytic behavior of rutile TiO2 nanorods for water splitting observed with liquid cell transmission electron microscopy (TEM). The electron beam serves as a “light” source to initiate the catalytic reaction and a “water-in-salt” aqueous solution is employed as the electrolyte. The observation reveals that bubbles are generated preferentially residing near the {110} facet of a rutile TiO2 nanorod under a low electron dose rate (9.3–18.6 e-/Å2·s). These bubbles are ascribed to hydrogen gas generated from the pseudo-photocatalytic water splitting. As the electron beam current density increases to 93 e-/Å2 ·s, bubbles are also found at the {001} and {111} facets as well as in the bulk liquid solution, demonstrating the dominant effects of water electrolysis by electron beam under higher dose rates. The facet-dependent pseudo-photocatalytic behavior of rutile TiO2 nanorods is further validated using density functional theory (DFT)calculation. Our work establishes a facile liquid cell TEM setup for the study of pseudo-photocatalytic water splitting and it may also be applied to investigation of other photo-activated phenomena occurring at the solid-liquid interfaces

Hybridization-induced magnetism in correlated cerium systems

There is a great change in the nature of the magnetic ordering on going from CeIn3, a local moment antiferromagnetic system, to CePb3, a heavy fermion itinerant antiferromagnetic system, both of which have Cu3Au crystal structure. We have applied ab initio electronic structure calculations, based on the linear-muffin-tin-orbital method, and a phenomenological theory of orbitally driven magnetic ordering, to study the effects of the band-f hybridization-induced interactions and the band-f exchange-induced interactions, pertinent to the magnetic behavior of these systems. The position of the Ce 4 f energy level relative to the Fermi energy and the intra-atomic Coulomb interaction are obtained from a sequence of three total-energy supercell calculations with two, one and zero f electrons in the Ce 4 f core. The calculations elucidate the origins in the electronic structure of the variation of the f-state resonance width characterizing the strength of the hybridization and the density of states at the Fermi energy characterizing the number and character of band states available for hybridization. We present results for the hybridization potential and the hybridization-induced exchange interactions on going from CeIn3 to CePb3, where the only obvious change is the addition of an anion p electron

Achieving economically sustainable subcontracting through the hotelling model by considering the spillover effect

In the process of internationalization of construction contractors, international enterprises as main contractors (IMC) need to consider whether part of the contract should be subcontracted to local subcontractors (LSC) to gain a competitive advantage when competing with local main contractors (LMC). The involvement of local subcontractors can usually help reduce cost through the cost spillover effect. However, it should be noted that the share of local subcontractors with local main contractors with an inferior quality may lead to quality spillover. The Hotelling model is therefore adopted to investigate the subcontracting decisions of main contractors considering both cost and quality spillover effects. Many scenarios are simulated and the results show that LMCs with inferior quality can always choose the subcontracting strategy to obtain increased profit regardless of the strategy that IMCs adopt. On the other hand, IMCs need to balance the cost spillover of subcontracting and the quality spillover for improving the quality level of LSCs. The results are useful for contractors to make decisions that are relevant to the adoption of subcontracting strategies to obtain competitive advantages