Search

We operated a p-type point contact high purity germanium (PPCGe) detector (CDEX-1B, 1.008 kg) in the China Jinping Underground Laboratory (CJPL) for 500.3 days to search for neutrinoless double beta ($0\nu\beta\beta$) decay of $^{76}$Ge. A total of 504.3 kg $\cdot$ day effective exposure data was accumulated. The anti-coincidence and the multi/single-site event (MSE/SSE) discrimination methods were used to suppress the background in the energy region of interest (ROI, $1989-2089$ keV for this work) with a factor of 23. A background level of 0.33 counts/(keV $\cdot$ kg $\cdot$ yr) was achieved. The lower limit on the half life of $^{76}$Ge $0\nu\beta\beta$ decay was constrained as $T_{1/2}^{0\nu}\ > \ {2.2}\times 10^{23}\ \rm yr\ (90\% \ C.L.)$, corresponding to the upper limits on the effective Majorana neutrino mass: $\langle m_{\beta\beta}\rangle < 2.3-5.2\ \mathrm{eV}$., Comment: 10 pages, 12 figures

Dark matter direct detection experiments mostly operate at deep underground laboratories. It is necessary to consider shielding effect of the Earth, especially for dark matter particles interacting with a large cross section. We analyzed and simulated the Earth shielding effect for dark matter at the China Jinping Underground Laboratory (CJPL) with a simulation package, CJPL Earth Shielding Simulation code (CJPL\_ESS), which is applicable to other underground locations. The further constraints on the $\chi$-N cross section exclusion regions are derived based on the studies with CDEX experiment data., Comment: 8 pages, 8 figures, 2 tables. Version updated to match PRD version

We present improved germanium-based constraints on sub-GeV dark matter via dark matter--electron ($\chi$-$e$) scattering using the 205.4 kg$\cdot$day dataset from the CDEX-10 experiment. Using a novel calculation technique, we attain predicted $\chi$-$e$ scattering spectra observable in high-purity germanium detectors. In the heavy mediator scenario, our results achieve 3 orders of magnitude of improvement for $m_{\chi}$ larger than 80 MeV/c$^2$ compared to previous germanium-based $\chi$-$e$ results. We also present the most stringent $\chi$-$e$ cross-section limit to date among experiments using solid-state detectors for $m_{\chi}$ larger than 90 MeV/c$^2$ with heavy mediators and $m_{\chi}$ larger than 100 MeV/c$^2$ with electric dipole coupling. The result proves the feasibility and demonstrates the vast potential of a new $\chi$-$e$ detection method with high-purity germanium detectors in ultralow radioactive background., Comment: 6 pages, 3 figures. Version updated to match PRL version

We present novel constraints on light dark matter (DM) from evaporating primordial black holes (PBHs), using the 205.4 kg$\cdot$day data from China Jinping Underground Laboratory's CDEX-10 p-type point contact germanium detector with 160 eVee analysis threshold. DM from PBHs with masses ranging from 1$\times$10$^{15}$ to 2$\times$10$^{16}$ g is searched in this work. In the presence of PBH abundance compatible with present bounds, our result excludes the DM-nucleon elastic scattering cross section region from 8.2$\times$10$^{-31}$ to 2.0$\times$10$^{-29}$ cm$^{2}$ for DM of 1 keV to 15 MeV from PBHs with masses of 5$\times$10$^{15}$ g, as well as, from 1.7$\times$10$^{-29}$ to 5.0$\times$10$^{-29}$ cm$^{2}$ for DM of 1 keV to 2 MeV from PBHs with masses of 1.8$\times$10$^{16}$ g. If the DM-nucleon elastic scattering cross section can be determined in the future, the abundance of PBH may be severely constrained by DM evaporation., Comment: 7 pages, 6 figures

A natural broad energy germanium (BEGe) detector is operated in the China Jinping Underground Laboratory (CJPL) for a feasibility study of building the next generation experiment of the neutrinoless double-beta (0{$\nu\beta\beta$}) decay of $^{76}$Ge. The setup of the prototype facility, characteristics of the BEGe detector, background reduction methods, and data analysis are described in this paper. A background index of 6.4$\times$10$^{-3}$ counts/(keV$\cdot$kg$\cdot$day) is achieved and 1.86 times lower than our previous result of the CDEX-1 detector. No signal is observed with an exposure of 186.4 kg$\cdot$day, thus a limit on the half life of $^{76}$Ge 0$\nu\beta\beta$ decay is set at T$_{1/2}^{0\nu}$ $>$ 5.62$\times$10$^{22}$ yr at 90% C.L.. The limit corresponds to an effective Majorana neutrino mass in the range of 4.6 $\sim$ 10.3 eV, dependent on the nuclear matrix elements., Comment: 10 pages, 15 figures

We report the first results of a light weakly interacting massive particles (WIMPs) search from the CDEX-10 experiment with a 10 kg germanium detector array immersed in liquid nitrogen at the China Jinping Underground Laboratory with a physics data size of 102.8 kg day. At an analysis threshold of 160 eVee, improved limits of 8 $\times 10^{-42}$ and 3 $\times 10^{-36}$ cm$^{2}$ at a 90\% confidence level on spin-independent and spin-dependent WIMP-nucleon cross sections, respectively, at a WIMP mass ($m_{\chi}$) of 5 GeV/${c}^2$ are achieved. The lower reach of $m_{\chi}$ is extended to 2 GeV/${c}^2$., Comment: 5 pages, 4 figures

We report the results of searches for solar axions and galactic dark matter axions or axion-like particles with CDEX-1 experiment at the China Jinping Underground Laboratory, using 335.6 kg-days of data from a p-type point-contact germanium detector. The data are compatible with the background model and no excess signals are observed. Limits of solar axions on the model independent coupling $g_{Ae}, 8 pages, 8 figures

We have carried out an extensive search for the SiC Bucky-diamond structure to confirm not only that a pair of Si and C atoms can form sp2- as well as sp3-type bonds but also that these two types of bonds can co-exist in the same SiC-based structure. The successful and surprising discovery of the SinCm Bucky-diamond structure at the specific composition of n=68 and m=79 is the result of the relaxation of the truncated bulk 3C-SiC network to yield a SinCm cluster with m +n=147. It highlights the important role played by the composition in determining the structure and hence other properties of SiC-based nano-structures. We have also shed light on the mechanism behind the formation of the Bucky-diamond structure. The formation process is initiated by the induced bonds between pairs of surface carbon atoms of the initial configuration of the Si68C79 cluster obtained by truncating bulk 3C-SiC network. This action then continuously incorporates atoms in the six outer shells of the Si68C79 clusters to form the 112-atom Fullerene shell through nearest neighbor Si-C interactions. Because the 35-atom inner core with five completely filled shells only interacts weakly with the Fullerene shell through the six atoms on its "surface", the diamond-like inner core is barely perturbed and is suspended inside the Fullerene shell. We have also suggested a likely route of synthesizing the SiC Bucky-diamond structure based on the result of our simulation., Comment: J. Chem. Phys. 2011

The spin Hamiltonian parameters for the two Cu$^{2+}$ centers $A1$ and $A2$ in the calcined catalysts CuO-ZnO are theoretically investigated using the high order perturbation formulas of these parameters for a $3d^{9}$ ion in tetragonally elongated octahedra. In the above formulas, the tetragonal field parameters $Ds$ and $Dt$ are determined from the superposition model, by considering the relative axial elongation of the oxygen octahedron around the Cu$^{2+}$ due to the Jahn-Teller effect. Based on the calculations, the relative elongation ratios of about 5% and 3% are obtained for the tetragonal Cu$^{2+}$ centers $A1$ and $A2$, respectively. The theoretical spin Hamiltonian parameters are in good agreement with the observed values for both systems. The larger axial elongation in center $A1$ is ascribed to the more significant low symmetrical (tetragonal) distortion of the Jahn-Teller effect. The local structures characterized by the above axial elongations are discussed., Comment: 6 pages

The structural optimization and energetics studies of SiC graphitic-like structures have been investigated theoretically in the context of formations of stable graphitic-like layer structures, single- and multi-walled nanotubes using the DFT-based Vienna ab-inito simulation package. The bonding nature of atoms in the optimized structures has been examined using a local analysis technique based on a self-consistent and environment-dependent semi-empirical Hamiltonian. Results of our studies reveal that stabilized SiC graphitic-like layer structures possess the sp2 bonding nature, different from the sp3 bonding nature in bulk SiC. Such flexibility in bonding configurations between Si and C atoms holds the possibility for a wide range of stable SiC-based structures, similar to those for carbon-based structures. In the case of SiC-based nanotubes, we have calculated quantities such as the strain energy, the degree of buckle in the cylindrical shell, and bond charges between Si and C atoms, to obtain an understanding of the optimized structures. The optimized interlayer spacing of SiC graphitic-like multilayer sheets has been found to depend on the ordering of atoms in different layers of the SiC graphitic-like structure (0.37 nm for the Si-C sequence of bilayer arrangement versus 0.48 nm for either the Si-Si or the C-C sequence of bilayer arrangement). These observations may be attributed to the Coulomb interactions due to the charge redistribution among Si and C atoms. On the other hand, the existence of two different ranges of interlayer separation in SiC double-walled nanotubes (0.38 nm for zigzag and 0.48 nm for armchair) is found to be related to whether the dominant interlayer neighbors are of the Si-C type or the Si-Si and C-C types., Comment: 29 pages with 6 figures

Methanofollis formosanus sp. nov. Description of Methanofollis formosanus sp. nov. Methanofollis formosanus (for.mo.sa'nus. N.L. masc. adj. formosanus from Formosa, the beautiful island of Taiwan). Irregularly coccoid cells, non-motile, 1 5-2 0 mmin diameter. Obligately anaerobic cells. Stains Gram-negative. Cell wall has an SDS-sensitive S-layer protein with an Mr of 138 800. Catabolic substrates used include H2/CO2 and formate, but not acetate, methanol, trimethylamine, dimethylamine, ethanol, 2-propanol, iso-butanol, 2-butanol or dimethylamine. Cells are mesophilic and grow at 20- 42��C, with optimal growth at 37��C. Cells grow at pH 5 6- 7-3, with optimal growth atpH 6-6. Cells grow well in 0-4 % NaCl, with optimal growth at 3 % NaCl. Addition ofacetate reduces the lag time and the trace element tungsten greatly promotes cell growth and extends the growth range. No growth is detected in minimal medium. Growth is completely inhibited by chloramphenicol and partly inhibited by tetracycline, but not by ampicillin, penicillin, kanamycin or spectinomycin. The G+C content of DNA of strain ML15T is 58 4 mol%. The type strain is strain ML15T (= OCM 789T = DSM 15483T), isolated from a marine water aquaculture fish pond near Wang-gong, Taiwan., Published as part of Wu, S. - Y., Chen, S. - C. & Lai, M. - C., 2005, Methanofollis formosanus sp. nov., isolated from a fish pond., pp. 837-842 in International Journal of Systematic and Evolutionary Microbiology 55 on page 5

Our study of the adsorption of oxygen molecules on individual semiconductiong single-walled carbon nanotubes at ambient conditions reveals that the adsorption is physisorption, that the resistance without O2 increases by ~two orders of magnitude as compared to that with O2, and that the sensitive response is due to the pinning of the Fermi level near the top of the valence band of the tube resulting from impurity states of O2 appearing above the valence band., Comment: 16 pages, 4 figures

A reliable semi-empirical Hamiltonian for materials simulations must allow electron screening and charge redistribution effects. Using the framework of linear combination of atomic orbitals (LCAO), a self-consistent and environment-dependent (SCED) Hamiltonian has been constructed for quantum mechanics based simulations of materials. This Hamiltonian contains environment-dependent multi-center interaction terms and electron-electron correlation terms that allow electron screening and charge-redistribution effects. As a case study, we have developed the SCED/LCAO Hamiltonian for silicon. The robustness of this Hamiltonian is demonstrated by scrutinizing a variety of different structures of silicon. In particular, we have studied the following: (i) the bulk phase diagrams of silicon, (ii) the structure of an intermediate-size Si71 cluster, (iii) the reconstruction of Si(100) surface, and (iv) the energy landscape for a silicon monomer adsorbed on the reconstructed Si(111)-7x7 surface. The success of the silicon SCED/LCAO Hamiltonian in the above applications, where silicon exists in a variety of different co-ordinations, is a testament to the predictive power of the scheme., Comment: 40 pages, 5 figures, 5 tables

A partial equilibrium model of stochastic crop production is used to analyze the environmental impacts of popular subsidized crop insurance programs. Land use is unchanged only when an actuarially fair, perfectly separating insurance contract is offered. For the more typical pooling equilibrium contracts, however, land with a minimum quality that is stricly lower than the minimum quality without insurance will be added to production. In such cases, the environment will be adversely effected. If economically marginal land is also environmentally marginal, pooling crop insurance policies disproportionately contribute to the degradation of the environment. Popular subsidies merely exacerbate the problem.

A new aerosol model, the Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (MADRID) has been developed to simulate atmospheric particulate matter (PM). MADRID and the Carnegie-Mellon University (CMU) bulk aqueous-phase chemistry have been incorporated into the three-dimensional Models-3/Community Multiscale Air Quality model (CMAQ). The resulting model, CMAQ-MADRID, is applied to simulate the August 1987 episode in the Los Angeles basin. Model performance for ozone and PM is consistent with current performance standards. However, organic aerosol was underpredicted at most sites owing to underestimation of primary organic PM emissions and secondary organic aerosol (SOA) formation. Nitrate concentrations were also sometimes underpredicted, mainly owing to overpredictions in vertical mixing, underpredictions in relative humidity, and uncertainties in the emissions of primary pollutants. Including heterogeneous reactions changed hourly O3 by up to 17% and 24-hour average PM2.5, sulfate2.5, and nitrate2.5 concentrations by up to 3, 7, and 19%, respectively. A SOA module with a mechanistic representation provides results that are more consistent with observations than that with an empirical representation. The moving-center scheme for particle growth predicts more accurate size distributions than a typical semi-Lagrangian scheme, which causes an upstream numerical diffusion. A hybrid approach that simulates dynamic mass transfer for coarse PM but assumes equilibrium for fine PM can predict a realistic particle size distribution under most conditions, and the same applies under conditions with insignificant concentrations of reactive coarse particles to a bulk equilibrium approach that allocates transferred mass to different size sections based on condensational growth law. In contrast, a simple bulk equilibrium approach that allocates transferred mass based on a given distribution tends to cause a downstream numerical diffusion in the predicted particle size distribution. Copyright 2004 by the American Geophysical Union.

Two headrace tunnels and the drainage tunnel were excavated by tunnel boring machines (TBMs) in Jinping II Hydropower Station. During TBM excavation, two types of slabbing failure were encountered in these deep buried marble tunnels. One is rock bursting and the other is non-violent slabbing. In order to study the rock burst and slabbing failure, a unique true triaxial rock burst test was carried out to simulate the rock burst process with different in situ stresses. Four rock samples in different marble layers were obtained in the site, and then four experiments are conducted under the same stressed conditions as the in situ field. The rock burst process and slabbing failure phenomena of the four experiments are in good accordance with the observations of corresponding excavation site. The failure modes of slabbing and rock burst in different rock groups can be predicted based on the experiments. The influence of the slabbing and rock burst failure on TBM excavation is analyzed in depth. Non-violent slabbing is beneficial to the rock breakage process. Rock burst with violent slabbing process greatly affects the tunnel support, cutter and cutterhead damage, gripper movement and force and so on.