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991.
Generalized connections and their calculus have been developed in the context of quantum gravity. Here we apply them to abelian Chern-Simons theory. We derive the expectation values of holonomies in U(1) Chern-Simons theory using Stokes’ theorem, flux operators and generalized connections. A framing of the holonomy loops arises in our construction, and we show how, by choosing natural framings, the resulting expectation values nevertheless define a functional over gauge invariant cylindrical functions.The abelian theory considered in the present article is the test case for our method. It can also be applied to the non-abelian theory. Results will be reported in a companion article. 相似文献
992.
Ablikim M Achasov MN Alberto D Ambrose DJ An FF An Q An ZH Bai JZ Baldini Ferroli RB Ban Y Becker J Berger N Bertani MB Bian JM Boger E Bondarenko O Boyko I Briere RA Bytev V Cai X Calcaterra AC Cao GF Chang JF Chelkov G Chen G Chen HS Chen JC Chen ML Chen SJ Chen Y Chen YB Cheng HP Chu YP Cronin-Hennessy D Dai HL Dai JP Dedovich D Deng ZY Denysenko I Destefanis M Ding Ding WL Ding Y Dong LY Dong MY Du SX Fang J Fang SS Feng CQ Fu CD Fu JL Gao Y Geng C Goetzen K Gong WX Greco M Gu MH Gu YT 《Physical review letters》2012,108(11):112003
A partial wave analysis of the ppˉ mass-threshold enhancement in the reaction J/ψ→γppˉ is used to determine its J(PC) quantum numbers to be 0(-+), its peak mass to be below threshold at M=1832(-5)(+19)(stat)(-17)(+18)(syst)±19(model) MeV/c(2), and its total width to be Γ<76 MeV/c(2) at the 90% C.L. The product of branching ratios is measured to be BR[J/ψ→γX(ppˉ)]BR[X(ppˉ)→ppˉ]=[9.0(-1.1)(+0.4)(stat)(-5.0)(+1.5)(syst)±2.3(model)]×10(-5). A similar analysis performed on ψ(3686)→γppˉ decays shows, for the first time, the presence of a corresponding enhancement with a production rate relative to that for J/ψ decays of R=[5.08(-0.45)(+0.71)(stat)(-3.58)(+0.67)(syst)±0.12(model)]%. 相似文献
993.
Ablikim M Achasov MN Alberto D Ambrose DJ An FF An Q An ZH Bai JZ Baldini Ferroli RB Ban Y Becker J Berger N Bertani MB Bian JM Boger E Bondarenko O Boyko I Briere RA Bytev V Cai X Calcaterra AC Cao GF Chang JF Chelkov G Chen G Chen HS Chen JC Chen ML Chen SJ Chen Y Chen YB Cheng HP Chu YP Cronin-Hennessy D Dai HL Dai JP Dedovich D Deng ZY Denysenko I Destefanis M Ding Ding WL Ding Y Dong LY Dong MY Du SX Fang J Fang SS Feng CQ Fu CD Fu JL Gao Y Geng C Goetzen K Gong WX Greco M Gu MH Gu YT 《Physical review letters》2012,108(18):182001
The decays J/ψ → γ π+ π- π0 and J/ψ → γ π0 π0 π0 are analyzed using a sample of 225×10(6) J/ψ events collected with the BESIII detector. The decay of η(1405) → f(0)(980)π0 with a large isospin violation is observed for the first time. The width of the f(0)(980) observed in the dipion mass spectra is anomalously narrower than the world average. Decay rates for three-pion decays of the η' are also measured precisely. 相似文献
994.
Radial impellers have several technical applications. Regarding their aerodynamic performance, they are well optimized nowadays, but this is in general not true regarding acoustics. This work was therefore concerned with analyzing the flow structures inside isolated radial impellers together with the far-field sound radiated from them in order to optimize the aerodynamic and acoustic performance. Both numerical and experimental techniques were applied in order to study the effect of varying wrap angle and otherwise identical geometric configuration on aerodynamics and acoustics of the radial impellers. The results give a detailed insight into the processes leading to sound generation in radial impellers. Measurements were performed using laser Doppler anemometry for the flow field and microphone measurements to analyze the radiated noise. In addition, unsteady aerodynamic simulations were carried out to calculate the compressible flow field. An acoustic analogy was employed to compute far-field noise. Finally, the phenomena responsible for tonal noise and the role of the wrap angle could be identified. Using this knowledge, design guidelines are given to optimize the impeller with respect to the radiated noise. This work shows that improved aerodynamic efficiency for isolated impellers does not automatically lead to a smaller flow-induced sound radiation. 相似文献
995.
M.A. Hussein S. Esterl R. Pörtner K. Wiegandt T. Becker 《International Journal of Computational Fluid Dynamics》2013,27(5):341-350
Mass and Impulse transport of oxygen enriched water in cartilage cell breeding reactor are simulated using the lattice Boltzmann method (LBM). The solver is attached with a shear stress and pressure calculator to quantify the load distribution on the cells. The solver was validated using the backward-facing step flow, which is a classical benchmark of similar discrete geometry for the bioreactor. This is achieved by comparing the qualitative and quantitative results obtained by LBM with the traditional solution and experimental approach for such a problem. The D2Q9 lattice model is used to carry out the calculations for the flow field, with a first order bounce-back boundary condition. Oxygen consumption efficiency levels in the bioreactor were reported. 相似文献
996.
A fibre-reinforced hyperelastic–viscoplastic model using a finite strain Finite Element (FE) analysis is presented to study the expansive growth of cell walls. Based on the connections between biological concepts and plasticity theory, e.g. wall-loosening and plastic yield, wall-stiffening and plastic hardening, the modelling of cell wall growth is established within a framework of anisotropic viscoplasticity aiming to represent the corresponding biology-controlled behaviour of a cell wall. In order to model in vivo growth, special attention is paid to the differences between a living cell and an isolated wall. The proposed hyperelastic–viscoplastic theory provides a unique framework to clarify the interplay between cellulose microfibrils and cell wall matrix and how this interplay regulates sustainable growth in a particular direction while maintaining the mechanical strength of the cell walls by new material deposition. Moreover, the effect of temperature is taken into account. A numerical scheme is suggested and FE case studies are presented and compared with experimental data. 相似文献
997.
P. Becker 《The European physical journal. Special topics》2009,172(1):343-352
An improved attempt of several national metrology institutes to replace the present definition of the kilogram with the mass
of a certain number of 12C atoms is described. This requires the determination of the Avogadro constant, N
A, via the silicon route with a relative uncertainty better than 2 ⋅ 10-8. Previously, the limiting factor is the measurement of the average molar mass. Consequently, a world-wide collaboration has
been set up, to produce, approximately, 5 kg of 28Si single-crystal with an enrichment factor greater than 99.985% to be used for an improved determination of N
A. The first successful tests of all technological steps (enrichment of SiF4, purification and synthesis of silane, deposition of polycrystalline 28Si, single crystal growth) for the production of high-purity 28Si are described. 相似文献
998.
We present a detailed analysis of the electronic and geometric bonding properties of the model alkene ethene on different mono- and bimetallic surfaces to establish the difference between adsorption energy and interaction energy and to elucidate the chemical character of a single platinum atom in different chemical environments. The adsorption of ethene on Pt(1 1 1) at 100 K leads to two adsorption states, which are commonly described as being of di-σ-type (bidentate, μ2η2) and π-type (monodentate, μ1η2). While the later is the minority species on Pt(1 1 1) it is of larger abundance on the platinum alloys. We have chosen π-bonded ethene for our study since it can be found on Pt(1 1 1), the Pt3Sn and Pt2Sn surface alloys, and Cu3Pt(1 1 1). Density functional theory calculations of the adsorption structures, site and decomposed densities of states, as well as partial charge densities in conjunction with vibrational spectroscopy show that the bonding, i.e. the interaction energy, of the π ethene is only weakly influenced by alloying. Even in a copper matrix – as in the case of Cu3Pt(1 1 1) – the bonding platinum atom essentially keeps its chemical identity and the interaction energy is reduced by only 14% compared to Pt(1 1 1). This observation suggests that bonding on surfaces is a strongly localized phenomenon. However, the adsorption energy decreases significantly due to alloying, which is attributed to the varying local relaxation of the different metal surfaces. 相似文献
999.
In this paper we consider compactifications of heterotic strings in the presence of background flux. The background metric is a T2 fibration over a K3 base times four-dimensional Minkowski space. Depending on the choice of three-form flux different amounts of supersymmetry are preserved (N=2,1,0). For supersymmetric solutions unbroken space–time supersymmetry determines all background fields except one scalar function which is related to the dilaton. The heterotic Bianchi identity gives rise to a differential equation for the dilaton which we discuss in detail for solutions preserving an N=2 supersymmetry. In this case the differential equation is of Laplace type and as a result the solvability is guaranteed. 相似文献
1000.
Robert F. Fischetti Shenglan Xu Derek W. Yoder Michael Becker Venugopalan Nagarajan Ruslan Sanishvili Mark C. Hilgart Sergey Stepanov Oleg Makarov Janet L. Smith 《Journal of synchrotron radiation》2009,16(2):217-225
The high‐brilliance X‐ray beams from undulator sources at third‐generation synchrotron facilities are excellent tools for solving crystal structures of important and challenging biological macromolecules and complexes. However, many of the most important structural targets yield crystals that are too small or too inhomogeneous for a `standard' beam from an undulator source, ~25–50 µm (FWHM) in the vertical and 50–100 µm in the horizontal direction. Although many synchrotron facilities have microfocus beamlines for other applications, this capability for macromolecular crystallography was pioneered at ID‐13 of the ESRF. The National Institute of General Medical Sciences and National Cancer Institute Collaborative Access Team (GM/CA‐CAT) dual canted undulator beamlines at the APS deliver high‐intensity focused beams with a minimum focal size of 20 µm × 65 µm at the sample position. To meet growing user demand for beams to study samples of 10 µm or less, a `mini‐beam' apparatus was developed that conditions the focused beam to either 5 µm or 10 µm (FWHM) diameter with high intensity. The mini‐beam has a symmetric Gaussian shape in both the horizontal and vertical directions, and reduces the vertical divergence of the focused beam by 25%. Significant reduction in background was achieved by implementation of both forward‐ and back‐scatter guards. A unique triple‐collimator apparatus, which has been in routine use on both undulator beamlines since February 2008, allows users to rapidly interchange the focused beam and conditioned mini‐beams of two sizes with a single mouse click. The device and the beam are stable over many hours of routine operation. The rapid‐exchange capability has greatly facilitated sample screening and resulted in several structures that could not have been obtained with the larger focused beam. 相似文献