Dimer statistics on the M\"obius strip and the Klein bottle

Closed-form expressions are obtained for the generating function of close-packed dimers on a $2M \times 2N$ simple quartic lattice embedded on a M\"obius strip and a Klein bottle. Finite-size corrections are also analyzed and compared with those under cylindrical and free boundary conditions. Particularly, it is found that, for large lattices of the same size and with a square symmetry, the number of dimer configurations on a M\"obius strip is 70.2% of that on a cylinder. We also establish two identities relating dimer generating functions for M\"obius strips and cylinders.Comment: 12 pages, 2 figs included, accepted by Phys. Lett.

Ising model on nonorientable surfaces: Exact solution for the Moebius strip and the Klein bottle

Closed-form expressions are obtained for the partition function of the Ising model on an M x N simple-quartic lattice embedded on a Moebius strip and a Klein bottle for finite M and N. The finite-size effects at criticality are analyzed and compared with those under cylindrical and toroidal boundary conditions. Our analysis confirms that the central charge is c=1/2.Comment: 8 pages, 3 eps figure

Identification of sources of elevated concentrations of polycyclic aromatic hydrocarbons in an industrial area in Tianjin, China

The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography equipped with a mass spectrometry detector in 105 topsoil samples from an industrial area around Bohai Bay, Tianjin in the North of China. Results demonstrated that concentrations of PAHs in 104 soil samples from this area ranged from 68.7 to 5,590 ng g (-aEuro parts per thousand 1) dry weight with a mean of a16PAHs 814 +/- 813 ng g (-aEuro parts per thousand 1), which suggests that there exists mid to high levels of PAH contamination. The concentration of a16PAHs in one soil sample from Tianjin Port was exceptionally high (48,700 ng g (-aEuro parts per thousand 1)). Ninety-three of the 105 soil samples were considered to be contaminated with PAHs (> 200 ng g (-aEuro parts per thousand 1)), and 25 were heavily polluted (> 1,000 ng g (-aEuro parts per thousand 1)). The sites with high PAHs concentration are mainly distributed around chemical industry parks and near highways. Two low molecular weight PAHs, naphthalene and phenanthrene, were the dominant components in the soil samples, which accounted for 22.1% and 10.7% of the a16PAHs concentration, respectively. According to the observed molecular indices, house heating in winter, straw stalk combustion in open areas after harvest, and petroleum input were common sources of PAHs in this area, while factory discharge and vehicle exhaust were the major sources around chemical industrial parks and near highways. Biological processes were probably another main source of low molecular weight PAHs

Regional differences and sources of organochlorine pesticides in soils surrounding chemical industrial parks

Concentrations of organochlorine pesticides (OCPs; dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB)) were investigated in 105 soil samples collected in vicinity of the chemical industrial parks in Tianjin, China. OCP concentrations significantly varied in the study area, high HCH and DDT levels were found close to the chemical industrial parks. The intensity of agricultural activity and distance from the potential OCP emitters have important influences on the OCP residue distributions. Principal component analysis indicates that HCH pollution is a mix of historical technical HCH and current lindane pollution and DDT pollution input is only due to technical DDT sources. The significant correlations of OCP compounds reveal that HCHs, DDTs and HCB could have some similar sources of origin

An Efficient Sensitivity Analysis Method for Optimization of Vehicle Random Vibrations

AbstractAn efficient and accuracy sensitivity analysis method for optimal analysis of random vibration of vehicle-bridge coupled system is purposed. The pseudo-excitation method is used to transform random road surface roughness into a series of deterministic harmonic excitations, and then the precise integration method is adopted to compute vehicle/bridge system response. The pseudo-excitation method and the precise integration method are both accurate and efficient, so that the first and second order sensitivity information of the responses can be obtained very conveniently. Taking ride comfort as the objective function, an optimal analysis for a vehicle/bridge system is performed

Digital Manufacturing of Gradient Meshed SOFC Sealing Composites with Self-Healing Capabilities

Solid oxide fuel cells (SOFC) hold great promise for clean power generation. However, high temperature stability and long term durability of the SOFC components have presented serious problems in SOFC technological advancement and commercialization. The seals of the fuel cells are the most challenging area to address. A high temperature gas seal is highly needed which is durable against cracking and gas leakage during thermal cycling and extended operation. This project investigates a novel composite seal by integrating 3D printed shape memory alloy (SMA) wires into a glass matrix. The SMA we use is TiNiHf and the glass matrix we use is SrO-La{sub 2}O{sub 3}-Al{sub 2}O{sub 3}-B{sub 2}O{sub 3}-SiO{sub 2} (SLABS). Dilatometry shows to be an extremely useful tool in providing the CTEs. It pinpoints regions of different CTEs under simulated SOFC thermal cycles for the same glass. For the studied SLABS glass system, the region with the greatest CTE mismatch between the glass seal and the adjacent components is 40-500 C, the typical heating and cooling regions for SOFCs. Even for low temperature SOFC development, this region is still present and needs to be addressed. We have demonstrated that the proposed SLABS glass has great potential in mitigating the thermal expansion mismatch issues that are limiting the operation life of SOFCs. TiNiHf alloy has been successfully synthesized with the desired particle size for the 3DP process. The TiNiHf SMA shape memory effect very desirably overlaps with the problematic low CTE region of the glass. This supports the design intent that the gradient structure transition, phase transformation toughening, and self-healing of the SMA can be utilized to mitigate/eliminate the seal problem. For the 3DP process, a new binder has been identified to match with the specific chemistry of the SMA particles. This enables us to directly print SMA particles. Neutron diffraction shows to be an extremely useful tool in providing information regarding the austenite to martensite phase transformation, SMA alloy lattice constant change, and the corresponding thermal stress from the glass matrix. It pinpoints regions of SMA phase transformation and the thermal stress effect under simulated SOFC thermal cycles. The bilayer test shows that there is still much work to be done for the proper integration of the seal components. Large scale production should lower the cost associated with the proposed approach, especially on the raw material cost and 3D printing

Prioritizing Preferable Locations for Increasing Urban Tree Canopy in New York City

This paper presents a set of Geographic Information System (GIS) methods for identifying and prioritizing tree planting sites in urban environments. It uses an analytical approach created by a University of Vermont service-learning class called “GIS Analysis of New York City\u27s Ecology” that was designed to provide research support to the MillionTreesNYC tree planting campaign. These methods prioritize tree planting sites based on need (whether or not trees can help address specific issues in the community) and suitability (biophysical constraints and planting partners’ existing programmatic goals). Criteria for suitability and need were based on input from three New York City tree-planting organizations. Customized spatial analysis tools and maps were created to show where each organization may contribute to increasing urban tree canopy (UTC) while also achieving their own programmatic goals. These methods and associated custom tools can help decision-makers optimize urban forestry investments with respect to biophysical and socioeconomic outcomes in a clear and accountable manner. Additionally, the framework described here may be used in other cities, can track spatial characteristics of urban ecosystems over time, and may enable further tool development for collaborative decision-making in urban natural resource management

Biological, Social, and Urban Design Factors Affecting Young Street Tree Mortality in New York City

In dense metropolitan areas, there are many factors including traffic congestion, building development and social organizations that may impact the health of street trees. The focus of this study is to better understand how social, biological and urban design factors affect the mortality rates of newly planted street trees. Prior analyses of street trees planted by the New York City Department of Parks & Recreation between 1999 and 2003 (n=45,094) found 91.3% of those trees were alive after two years and 8.7% were either standing dead or missing completely. Using a site assessment tool, a randomly selected sample of 13,405 of these trees was surveyed throughout the City of New York during the summers of 2006 and 2007. Overall, 74.3% of the sample trees were alive when surveyed and the remainder were either standing dead or missing. Results of our initial analyses reveal that highest mortality rates occur within the first few years after planting, and that land use has a significant effect on street tree mortality. Trees planted in one- and two-family residential areas had the highest survival rates (82.7%), while young street trees planted in industrial areas, open space and vacant land had the lowest rates of street tree survival (60.3% -62.9%). Also significant in predicting street tree success and failure are species type, tree pit enhancements, direct tree care/stewardship, and local traffic conditions. These results are intended to inform urban forest managers in making decisions about the best conditions for planting new street trees

Selection and evaluation of materials for advanced water electrolyzers

The mechanism of dissolution of ruthenium anodes and of the time variation of overpotential on such electrodes have been elucidated using combined electrochemical-ellipsometric studies. Attempts are being made to stabilize ruthenium based electrocatalysts for SPE water electrolyzers by investigation of mixed oxides with the requisite characteristics for highly efficient oxygen electrodes. The following materials have been identified as the most attractive for advanced alkaline water electrolyzers operating at 120 to 150/sup 0/C: Anode Electrocatalyst--High Surface Area Nickel Cobalt Oxide; Cathode Electrocatalyst--High Surface Area Nickel Boride; Separator--Teflon Bonded Potassium Titanate or Nafion; and Cell Frame--Teflon or Teflon Based. The tests on barrier materials, electrodes and cell components have so far been carried out on a static basis in a pressure vessel. Teledyne Energy Systems (TES) has designed and fabricated an advanced alkaline water electrolysis test rig (5-cell stack). In a joint BNl--TES--University of Virginia program, the most promising materials will be tested for performance and/or life in this test-rig

Distribution and density of the partition function zeros for the diamond-decorated Ising model

Exact renormalization map of temperature between two successive decorated lattices is given, and the distribution of the partition function zeros in the complex temperature plane is obtained for any decoration-level. The rule governing the variation of the distribution pattern as the decoration-level changes is given. The densities of the zeros for the first two decoration-levels are calculated explicitly, and the qualitative features about the densities of higher decoration-levels are given by conjecture. The Julia set associated with the renormalization map is contained in the distribution of the zeros in the limit of infinite decoration level, and the formation of the Julia set in the course of increasing the decoration-level is given in terms of the variations of the zero density.Comment: 8 pages,8figure