Long-term measurements of particle number size distributions and the relationships with air mass history and source apportionment in the summer of Beijing

A series of long-term and temporary measurements were conducted to study the improvement of air quality in Beijing during the Olympic Games period (8–24 August 2008). To evaluate actions taken to improve the air quality, comparisons of particle number and volume size distributions of August 2008 and 2004–2007 were performed. The total particle number and volume concentrations were 14 000 cm−3 and 37 μm−3 cm−3 in August of 2008, respectively. These were reductions of 41% and 35% compared with mean values of August 2004–2007. A cluster analysis on air mass history and source apportionment were performed, exploring reasons for the reduction of particle concentrations. Back trajectories were classified into five major clusters. Air masses from the south direction are always associated with pollution events during the summertime in Beijing. In August 2008, the frequency of air mass arriving from the south was 1.3 times higher compared to the average of the previous years, which however did not result in elevated particle volume concentrations in Beijing. Therefore, the reduced particle number and volume concentrations during the 2008 Beijing Olympic Games cannot be only explained by meteorological conditions. Four factors were found influencing particle concentrations using a positive matrix factorization (PMF) model. They were identified as local and remote traffic emissions, combustion sources as well as secondary transformation. The reductions of the four sources were calculated to 47%, 44%, 43% and 30%, respectively. The significant reductions of particle number and volume concentrations may attribute to actions taken, focusing on primary emissions, especially related to the traffic and combustion sources

Theory of ac electrokinetic behavior of spheroidal cell suspensions with an intrinsic dispersion

The dielectric dispersion, dielectrophoretic (DEP) and electrorotational (ER) spectra of spheroidal biological cell suspensions with an intrinsic dispersion in the constituent dielectric constants are investigated. By means of the spectral representation method, we express analytically the characteristic frequencies and dispersion strengths both for the effective dielectric constant and the Clausius-Mossotti factor (CMF). We identify four and six characteristic frequencies for the effective dielectric spectra and CMF respectively, all of them being dependent on the depolarization factor (or the cell shape). The analytical results allow us to examine the effects of the cell shape, the dispersion strength and the intrinsic frequency on the dielectric dispersion, DEP and ER spectra. Furthermore, we include the local-field effects due to the mutual interactions between cells in a dense suspension, and study the dependence of co-field or anti-field dispersion peaks on the volume fractions.Comment: accepted by Phys. Rev.

The roles of sulfuric acid in new particle formation and growth in the mega-city of Beijing

Simultaneous measurements of gaseous sulfuric acid and particle number size distributions were performed to investigate aerosol nucleation and growth during CAREBeijing-2008. The analysis of the measured aerosols and sulfuric acid with an aerosol dynamic model shows the dominant role of sulfuric acid in new particle formation (NPF) process but also in the subsequent growth in Beijing. Based on the data of twelve NPF events, the average formation rates (2–13 cm−3 s−1) show a linear correlation with the sulfuric acid concentrations (R2=0.85). Coagulation seems to play a significant role in reducing the number concentration of nucleation mode particles with the ratio of the coagulation loss to formation rate being 0.41±0.16. The apparent growth rates vary from 3 to 11 nm h−1. Condensation of sulfuric acid and its subsequent neutralization by ammonia and coagulation contribute to the apparent particle growth on average 45±18% and 34±17%, respectively. The 30% higher concentration of sulfate than organic compounds in particles during the seven sulfur-rich NPF events but 20% lower concentration of sulfate during the five sulfur-poor type suggest that organic compounds are an important contributor to the growth of the freshly nucleated particles, especially during the sulfur-poor cases

Magnetic phase diagram in Eu1−x_{1-x}Lax_xFe2_2As2_2 single crystals

We have systematically measured resistivity, susceptibility and specific heat under different magnetic fields (H) in Eu$_{1-x}$La$_x$Fe$_2$As$_2$ single crystals. It is found that a metamagnetic transition from A-type antiferromagnetism to ferromagnetism occurs at a critical field for magnetic sublattice of $Eu^{2+}$. The jump of specific heat is suppressed and shifts to low temperature with increasing H up to the critical value, then shifts to high temperature with further increasing H. Such behavior supports the metamagnetic transition. Detailed H-T phase diagrams for x=0 and 0.15 crystals are given, and possible magnetic structure is proposed. Magnetoresistance measurements indicate that there exists a strong coupling between local moment of $Eu^{2+}$ and charge in Fe-As layer. These results are very significant to understand the underlying physics of FeAs superconductors.Comment: 5 pages, 4 figure

Does social contact lessen perceived cultural distance? Evidence from tourist–host social contact

2016-2017 > Academic research: refereed > Publication in refereed journal201804_a bcm

Effects of Exogenous Cellulase Source on In Vitro Fermentation Characteristics and Methane Production of Crop Straws and Grasses

In vitro fermentation experiments were conducted to investigate the effects of 3 sources of exogenous cellulase products (EC) at 4 dose rates (DR) (0, 12, 37 and 62 IU/g of DM) on degradation of forage and methane production by mixed rumen micro-organisms of goats. The maximum gas production (Vf) of grasses was higher (P<0.001) in Neocallimastix patriciarum (NP) group than those in Trichoderma reesei (TR) and Trichoderma longibrachiatum (TL) groups. Quadratic increases in dry matter degradation (DMD) of forage and neutral detergent fiber (NDFD) of straw were observed for all EC, with optimum DR in the low range. Supplementation of EC originated from TR and NP increased (P<0.001) DMD of forage compared to that from TL. Addition of EC originated from TR and NP also decreased pH value, ammonia nitrogen (NH3-N) and methane (CH4) production compared to that from TL. Quadratic decreases in pH value, NH3-N and CH4 of forage were noted for EC of TR and NP, and with optimum DR in the low range. For short chain fatty acid, the EC of NP increased total volatile fatty acid (TVFA) and acetate concentration and the ratio of acetate to propionate of forage compared with EC of TL and TR, and with optimum DR in the low to medium range. It was concluded that the source of EC differed in fiber degradation and methane emission, and with optimum DR of TR in the low range (from 12 to 37 U/g DM) in improving fiber degradation and decreasing methane emission

The flavor-changing bottom-strange quark production in the littlest Higgs model with T parity at the ILC

In the littlest Higgs model with T-parity (LHT) the mirror quarks induce the special flavor structures and some new flavor-changing (FC) couplings which could greatly enhance the production rates of the FC processes. We in this paper study some bottom and anti-strange production processes in the LHT model at the International Linear Collider (ILC), i.e., $e^+e^-\rightarrow b\bar{s}$ and $\gamma\gamma\rightarrow b\bar{s}$. The results show that the production rates of these processes are sizeable for the favorable values of the parameters. Therefore, it is quite possible to test the LHT model or make some constrains on the relevant parameters of the LHT through the detection of these processes at the ILC.Comment: 12 pages, 8 figure

Hai Di Lao Hot Pot: From Employee Stimulation to Service Innovation

The management of Chinese restaurant chains has for some time followed the western model while accommodating Chinese customers. The new Hai Di Lao Hot Pot Restaurant chain has established its own management style, pioneering chain catering management to help the Chinese restaurant industry establish a professional image, explore a local management model, and maintain high standards of food safety. The objectives of this case study are to introduce the Hai Di Lao managerial strategy, investigate the secrets of its success from a human resources management perspective, to explore its innovative service, and to assess why it has inspired both marketers and the catering industry. The results show that human resources management can change employees’ behavior and emotional states by addressing a wide variety of needs. In addition, attention to service quality can improve customer satisfaction and retention

Iron pnictides: Single crystal growth and effect of doping on structural, transport and magnetic properties

We demonstrate the preparation of large, free standing iron pnictide single crystals with a size up to 20 x 10 x 1 mm3 using solvents in zirconia crucibles under argon atmosphere. Transport and magnetic properties are investigated to study the effect of potassium doping on the structural and superconducting property of the compounds. The spin density wave (SDW) anomaly at Ts ~138 K in BaFe2As2 single crystals from self-flux shifts to Ts ~85 K due to Sn solvent growth. We show direct evidence for an incorporation of Sn on the Fe site. The electrical resistivity data show a sharp superconducting transition temperature Tc~38.5 K for the single crystal of Ba0.68K0.32Fe2As2. A nearly 100% shielding fraction and bulk nature of the superconductivity for the single crystal were confirmed by magnetic susceptibility data. A sharp transition Tc~25 K occurred for the single crystal of Sr0.85K0.15Fe2As2. There is direct evidence for a coexistence of the SDW and superconductivity in the low doping regime of Sr1-xKxFe2As2 single crystals. Structural implications of the doping effects as well as the coexistence of the two order parameters are discussed.Comment: 22 pages, 9 figure

Fully Gapped Single-Particle Excitations in the Lightly Doped Cuprates

The low-energy excitations of the lightly doped cuprates were studied by angle-resolved photoemission spectroscopy. A finite gap was measured over the entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This effect was observed to be generic to the normal states of numerous cuprates, including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to close with increasing carrier doping. We consider various scenarios to explain our results, including the possible effects of chemical disorder, electronic inhomogeneity, and a competing phase.Comment: To appear in Phys. Rev.