Showing papers by "Yang Gao published in 2008"

The LHCb detector at the LHC

Abstract: The LHCb experiment is dedicated to precision measurements of CP violation and rare decays of B hadrons at the Large Hadron Collider (LHC) at CERN (Geneva). The initial configuration and expected performance of the detector and associated systems, as established by test beam measurements and simulation studies, is described.

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

Abstract: A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN.

Search for the highly suppressed decays B-→K +π-π- and B-→K -K-π+

Abstract: We report a search for the decays B- -> K+pi(-)pi(-) and B- -> K-K-pi(+), which are highly suppressed in the standard model. Using a sample of (467 +/- 5) x 10(6) B (B) over bar pairs collected with the BABAR detector, we do not see any evidence of these decays and determine 90% confidence level upper limits of B(B- -> K+pi(-)pi(-)) and K-K-pi(+)) and < 1.6 x 10(-7) on the corresponding branching fractions, including systematic uncertainties.

Study of Polarization in B ---> VT Decays

Abstract: In this paper, we examine B{yields}VT decays (V is a vector and T is a tensor meson), whose final-state particles can have transverse or longitudinal polarization. Measurements have been made of B{yields}{phi}K{sub 2}*, and it is found that f{sub T}/f{sub L} is small, where f{sub T} (f{sub L}) is the fraction of transverse (longitudinal) decays. We find that the standard model naively predicts that f{sub T}/f{sub L}<<1. The two extensions of the naive standard model which have been proposed to explain the large f{sub T}/f{sub L} in B{yields}{phi}K*--penguin annihilation and rescattering--make no firm predictions for the polarization in B{yields}{phi}K{sub 2}*. The two new-physics scenarios, which explain the data in B{yields}{pi}K and the {phi}({rho})K* polarization measurements, can reproduce the f{sub T}/f{sub L} data in B{yields}{phi}K{sub 2}* only if the B{yields}T form factors obey a certain hierarchy. Finally, we present the general angular analysis which can be used to get helicity information using two- and three-body decays.

Development Of Thermal, Sensors And Drilling Systems, For Application On Lunar Lander Missions

Abstract: The upcoming lunar lander missions, for example Chang’e 2 from CNSA and several mission proposals and studies currently under consideration at NASA (e.g. Neal et al., ROSES 2006 Proposal to NASA, 2006), ESA (e.g. Hufenbach, European Workshop on Lunar Landers, ESTEC, Noordwijk, The Netherlands, 2005; Foing, EPSC Abstracts, vol 2, EPSC2007-A-00422, European Planetary Science Congress, Potsdam, Germany, 2007) and JAXA, Japan (Matsumoto et al., Acta Astronautica, 59:68–76, 2006) offer new possibilities to measure the thermal properties of the lunar regolith and to determine the global lunar heat flow more accurately than it is hitherto known. Both properties are of high importance for the understanding of the lunar structure and the evolution of the Moon–Earth system. In this paper we present some work on new thermal sensors to be used for in situ investigations of the lunar soil in combination with novel drilling techniques applicable for the lunar regolith. Such systems may preferably be mounted on mobile stations like the lunar rover currently built for the Chinese Chang’e 2 mission. A general description of a presently tested prototype of the lunar rover is given and mounting possibilities for a drilling system and thermal sensors are shown. Then we discuss some options for thermal sensors and drills and how they could be combined into one compact instrument. Subsequently a tube-like sensor suitable for measuring the thermal conductivity of the material surrounding a borehole is described in more detail. Finally the performance of such a tube-shaped sensor when applied in a lunar borehole is investigated by thermal modelling and compared with the behaviour of a more conventional needle-shaped sensor.

A theory of general solutions of 3D problems in 1D hexagonal quasicrystals

Abstract: A theory of general solutions of three-dimensional (3D) problems is developed for the coupled equilibrium equations in 1D hexagonal quasicrystals (QCs), and two new general solutions, which are called generalized Lekhnitskii?Hu?Nowacki (LHN) and Elliott?Lodge (E?L) solutions, respectively, are presented based on three theorems. As a special case, the generalized LHN solution is obtained from our previous general solution by introducing three high-order displacement functions. For further simplification, considering three cases in which three characteristic roots are distinct or possibly equal to each other, the generalized E?L solution shall take different forms, and be expressed in terms of four quasi-harmonic functions which are very simple and useful. It is proved that the general solution presented by Peng and Fan is consistent with one case of the generalized E?L solution, while does not include the other two cases. It is important to note that generalized LHN and E?L solutions are complete in z-convex domains, while incomplete in the usual non-z-convex domains.

New general solutions of plane elasticity of one-dimensional quasicrystals

Abstract: A theory of general solutions of plane problems is developed for the coupled equations of plane elasticity of one-dimensional quasicrystals. By introducing a displacement function, very large numbers of complicated equations of the in-plane problem are simplified to a sixth-order partial differential governing equation, and then three general solutions are presented through an operator method. Since the displacement function is required to satisfy the sixth-order governing equation, it is still difficult to obtain rigorous analytic solutions from the higher-order equation directly and is not applicable in most cases. Therefore, a decomposition and superposition procedure is employed to replace the higher-order displacement function with three second-order displacement functions, and accordingly the general solutions are simplified in terms of these functions. In consideration of different cases of three characteristic roots, the general solutions involve three cases, but all are in simple forms that are conveniently applied. Furthermore, it is worth noting that the general solutions obtained here are complete in x3-convex domains. To illustrate the application of the general solutions obtained, the closed form solutions are obtained for wedge problems subjected to point phonon force and phason force at the apex. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A Theory of General Solutions of Plane Problems in Two-Dimensional Octagonal Quasicrystals

Abstract: A theory of general solutions of plane problems is developed for the coupled equations in plane elasticity of two-dimensional octagonal quasicrystals. In virtue of the operator method, the general solutions of the antiplane and inplane problems are given constructively with two displacement functions. The introduced displacement functions have to satisfy higher order partial differential equations, and therefore it is difficult to obtain rigorous analytic solutions directly and is not applicable in most cases. In this case, a decomposition and superposition procedure is employed to replace the higher order displacement functions with some lower order displacement functions, and accordingly the general solutions are further simplified in terms of these functions. In consideration of different cases of characteristic roots, the general solution of the antiplane problem involves two cases, and the general solution of the inplane problem takes three cases, but all are in simple forms that are convenient to be applied. Furthermore, it is noted that the general solutions obtained here are complete in x3-convex domains.

Performance study of a GEM-TPC prototype using cosmic rays

Abstract: Time projection chambers (TPCs) have been successfully used as the central tracking devices in a number of high-energy physics experiments. However, the performance requirements on TPCs for future high-energy physics experiments greatly exceed the abilities of traditional TPCs read out by multi-wire proportional chambers (MWPCs). Micro-pattern gas detectors (MPGDs), such as gas electron multipliers (GEMs) or micromegas, have great potential to improve TPC performance when used as readout detectors. In order to evaluate its feasibility, a GEM-based TPC prototype with a drift length up to 50 cm was designed. Measurements of the spatial resolution of cosmic-ray tracks without and with a magnetic field (B=1 T) are presented. A very good performance is achieved, matching the analytic formula for the spatial resolution of a MPGD-readout TPC. A dedicated study shows that the increase of GEM detector gain can improve the TPC's spatial resolution.

Boundary conditions for the bending of a piezoelectric beam

Abstract: For beam bending in transversely isotropic piezoelectric media, the reciprocal theorem and the general solution of piezoelasticity are applied in a novel way to obtain the appropriate stress and mixed boundary conditions accurate to all orders for the beam of general edge geometry and loadings. By generalizing the method developed by Gregory and Wan, a set of necessary conditions on the edge-data for the existence of a rapidly decaying solution is established. The prescribed edge-data of the beam must satisfy these conditions in order that they could generate a decaying state within the beam. When stress and mixed conditions are imposed on the beam edge, these decaying state conditions for the case of bending deformation of piezoelectric beam are derived explicitly. They are then used for the correct formulation of boundary conditions for the beam theory solution (or the interior solution). Besides, an analytical solution of elastic beam is formulated to verify validity of our boundary conditions. For the stress data, our boundary conditions coincide with those obtained in conventional forms of beam theories. More importantly, the appropriate boundary conditions with two sets of mixed edge-data are obtained for the first time.

Optical flow based techniques for ExoMars rover autonomous navigation

Abstract: In this paper, we have introduced the baseline design of ExoMars navigation system and proposed a scheme to implement an optical flow package to perform three major tasks, namely visual odometry, target tracking and on-the-fly obstacle avoidance. The proposed scheme could potentially improve the autonomy of a rover and enable it travel longer for each planned traverse.

Proton resonance properties in light nuclei with mean-field type potentials

Abstract: The properties of proton resonances in the p and sd shells are studied with a single-particle potential generated by self-consistent-mean field calculations. Besides, we also propose to calculate the proton-nucleus interaction by a double-folding procedure with the density of the daughter nucleus represented by the result of the same mean-field model. Without raising any adjustable parameter, these calculations provide reasonable estimates for the widths of observed proton resonances in light nuclei. The mean-field-based calculation is particularly useful for the predications of the properties of resonances in light exotic nuclei and the direct proton capture reactions of astrophysics.

An Update on MoonLITE

Abstract: MoonLITE is a proposed, UK led lunar science mission involving 4 scientific penetrators that will make in situ measurements at widely separated locations on the Moon. MoonLITE will create the first global lunar network with nodes near and far-side, and in permanently shaded crater(s). With such a network MoonLITE will be able to determine much about the interior of the Moon, including characterisation of its core. Penetrator(s) at the poles will seek and characterise frozen volatiles, possibly of cometary origin and of great importance both to human exploration and to astrobiology. MoonLITE penetrators will reach the Moon at ~300 m/s and so must be able to stand the forces associated with this impact. As part of a programme aimed to establish reliable penetrator technologies the first full-scale impact trials have been conducted and are described here.

The remarkable nature of one-dimensional quasicrystal

Abstract: A material is spherically uniform when its generalized Hooke's law at each material point referred to a spherical coordinate system is the same everywhere. We study a sphere of spherically uniform linear anisotropic one-dimensional quasicrystalline material subjected to radial phonon and phason strains on its surface. For a certain range of material parameters the phonon as well as the phason stress diverges at the center. The applied phason strain does not affect the phonon field but the phason field is disturbed by the phonon strain. "White hole" at the center may occur when the sphere is subjected to uniform tension while uniform pressure may cause a "black hole". This behavior depends only on a dimensionless material parameter and the kind of applied strain but not on its magnitude.

Method on holomorphic vector functions and applications in two-dimensional quasicrystals

Abstract: Generalization of the Stroh formalism to two-dimensional quasicrystal materials results in a ten-dimensional formalism for which there are five pairs of complex eigenvalues. By virtue of the generalized Stroh formalism, two-dimensional problems of quasicrystals elasticity are transferred into the boundary value problems of holomorphic vector functions in a given region. If the conformal mapping from an ellipse to a circle is known, a general method can be presented for solving the boundary value problems of holomorphic vector functions. Using the necessary and sufficient condition of boundary value problems of holomorphic vector functions, several basic two-dimensional problems in two-dimensional quasicrystals are solved.

The influence of GEM readout detector gain on the spatial resolution of a GEM-TPC prototype

Abstract: This paper investigated the influence of GEM detector gain on the spatial resolution of a GEM-TPC prototype Tests show that the x-resolution of the TPC prototype improves with the increase of the voltage of GEM readout detector The change tendencies of the effective number of electron and the relative gain match quite well

The decomposed form and boundary conditions of elastic beams with free faces

Abstract: From the decomposition theorem of elastic beams, two classes of exact stress states are investigated for the equations of three dimensional elasticity governing elastic beams in bending deformations with free faces. One of these is the analogue of the Levy solution for elastic plates and is designated as the interior state. The other complementary class corresponds to a decaying state and is designated as the Papkovich-Fadle state. The appropriate boundary conditions have been established recently for the prescribed data at the end edge of beams to induce only an exponentially decaying elastostatic state. The present paper describes how these conditions may be used to determine the boundary conditions of these two states. The decomposition theorem of beams effectively allows us to split the prescribed edge-data correctly into two parts, one for the interior solution components and the other for the decaying solution components. An analytical solution of the decaying state is formulated to verify the validity of our boundary conditions. The results in turn show that the necessary conditions for the Papkovich-Fadle state are also sufficient conditions. The boundary conditions obtained for the interior state show that the interior solution determined by these conditions is the correct solution in the beam interior up to exponentially small terms. Moreover, with the separate consideration of the interior and decaying solution components, a relatively simple analytical solution is often practical and desirable, and the numerical computation process is essentially simplified. As an illustrative example, the present results are applied to the end-loaded cantilever beam.

Edge conditions for piezoelectric semi-infinite strips with mixed edge-data

Abstract: For piezoelectric semi-infinite strips with mixed edge-data, the Betti-Rayleigh reciprocal theorem and the general solution of plane piezoelectricity are applied in a novel way to obtain the appropriate edge conditions accurate to all order. A decay analysis technique is used to establish necessary conditions which the prescribed data on the edge of the strips must satisfy in order that it should generate a decaying state within the strips. For the case of transverse bending of the strips, these decaying state conditions are obtained explicitly for the first time when the mixed conditions are imposed on the edge.