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Search Results: 1 - 10 of 140862 matches for " T. Shi "
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An Energy-Efficient MAC Protocol for Ad Hoc Networks  [PDF]
Yongsheng SHI, T. Aaron GULLIVER
Wireless Sensor Network (WSN) , 2009, DOI: 10.4236/wsn.2009.15049
Abstract: A mobile ad hoc network (MANET) is a collection of nodes equipped with wireless communications and a networking capability without central network control. Nodes in a MANET are free to move and organize themselves in an arbitrary fashion. Energy-efficient design is a significant challenge due to the characteristics of MANETs such as distributed control, constantly changing network topology, and mobile users with limited power supply. The IEEE 802.11 MAC protocol includes a power saving mechanism, but it has many limitations. A new energy-efficient MAC protocol (EE-MAC) is proposed in this paper. It is shown that EE-MAC performs better than IEEE 802.11 power saving mode and exceeds IEEE 802.11 with respect to balancing network throughput and energy savings.
Quantum entanglement of two flux qubits induced by an auxiliary SQUID
T. Shi,Z. Song
Physics , 2006, DOI: 10.1088/0253-6102/48/6/009
Abstract: We revisit a theoretical scheme to create quantum entanglement of two three-levels superconducting quantum interference devices (SQUIDs) with the help of an auxiliary SQUID. In this scenario, two three-levels systems are coupled to a quantized cavity field and a classical external field and thus form dark states. The quantum entanglement can be produced by a quantum measurement on the auxiliary SQUID. Our investigation emphasizes the quantum effect of the auxiliary SQUID. For the experimental feasibility and accessibility of the scheme, we calculate the time evolution of the whole system including the auxiliary SQUID. To ensure the efficiency of generating quantum entanglement, relations between the measurement time and dominate parameters of the system are analyzed according to detailed calculations.
Two-photon transport through a waveguide coupling to a whispering gallery resonator containing an atom and photon-blockade effect
T. Shi,Shanhui Fan
Physics , 2012, DOI: 10.1103/PhysRevA.87.063818
Abstract: We investigate the two-photon transport through a waveguide side-coupling to a whispering-gallery-atom system. Using the Lehmann-Symanzik-Zimmermann (LSZ) reduction approach, we present the general formula for the two-photon processes including the two-photon scattering matrices, the wavefunctions and the second order correlation functions of the out-going photons. Based on the exact results of the second order correlation functions, we analyze the quantum statistics behaviors of the out-going photons for two different cases: (a) the ideal case without the inter-modal coupling in the whispering gallery resonator; (b) the case in the presence of the inter-modal coupling which leads to more complex nonlinear behavior. In the ideal case, we show that the system consists of two independent scattering pathways, a free pathway by a cavity mode without atomic excitation, and a "Jaynes-Cummings" pathway described by the Jaynes-Cummings Hamiltonian of a single-mode cavity coupling to an atom. The free pathway does not contribution to correlated two-photon processes. In the presence of intermodal mixing, the system no longer exhibit a free resonant pathway. Instead, both the single-photon and the two photon transport properties depend on the position of the atom. Thus, in the presence of intermodal mixing one can in fact tune the photon correlation properties by changing the position of the atom. Our formalism can be used to treat resonator and cavity dissipation as well.
Activation Kinetics and Off-Target Effects of Thymus-Initiated Cre Transgenes
Jianjun Shi, Howard T. Petrie
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0046590
Abstract: The bacteriophage enzyme Cre is a site-specific recombinase widely used to delete loxP-flanked DNA sequences in lineage-specific fashion. Several mouse lines that direct Cre expression to lymphoid progenitors in the thymus have been established, but a side-by-side comparison of when they first become active, and/or their relative efficiency at various developmental stages, has been lacking. In this study, we evaluated these in four common Cre transgenic strains with thymus-initiated promoters (Lck, Cd2, or Cd4). We found that while all of them eventually labeled nearly all thymocytes, their kinetics were dramatically different, and other than Cd4[Cre], did not faithfully recapitulate the expression pattern of the corresponding endogenous gene. Perhaps even more importantly, while thymuses from some strains compared favorably to thymuses from control (Cre-negative) mice, we found that Cre expression could also result in off-target effects, including moderate to severe decreases in thymic cellularity. These effects occurred in the absence of loxP-flanked DNA target genes, and were dose and copy number dependent. Loss of cellularity was attributable to a specific decrease in CD4+8+ immature cells, and corresponds to an increased rate of programmed cell death. In addition to a comprehensive analysis of activation kinetics in thymus-initiated Cre transgenes, our data show that Cre is toxic to CD4+8+ cells in a dose-dependent fashion, and emphasize that the choice of thymus-initiated Cre strain is critically important for minimizing off-target effects of Cre.
Recovering Unitarity of Lee Model in Bi-Orthogonal Basis
T. Shi,C. P. Sun
Physics , 2009,
Abstract: We study how to recover the unitarity of Lee model with the help of bi-orthogonal basis approach, when the physical coupling constant in renormalization exceeds its critical value, so that the Lee's Hamiltonian is non-Hermitian with respect to the conventional inner product. In a very natural fashion, our systematic approach based on bi-orthogonal basis leads to an elegant definition of inner product with a non-trivial metric, which can overcome all the previous problems in Lee model, such as non-Hermiticity of the Hamiltonian, the negative norm, the negative probability and the non-unitarity of the scattering matrix.
Two-Photon Scattering in One Dimension by Localized Two-Level System
T. Shi,C. P. Sun
Physics , 2009,
Abstract: We study two-photon scattering in a one-dimensional coupled resonator arrays (CRA) by a two-level system (TLS), which is localized as a quantum controller. The $S$-matrix is analytically calculated for various two-photon scattering processes by TLS, e.g., one photon is confined by TLS to form a bound state while the other is in the scattering state. It is discovered from the poles of the $S$-matrix that there exist two kinds of three-body bound states for describing two bound photons localized around TLS.
Lehmann-Symanzik-Zimmermann Reduction Approach to Multi-Photon Scattering in Coupled-Resonator Arrays
T. Shi,C. P. Sun
Physics , 2008, DOI: 10.1103/PhysRevB.79.205111
Abstract: We present a quantum field theoretical approach based on the Lehmann-Symanzik-Zimmermann reduction for the multi-photon scattering process in a nano-architecture consisting of the coupled resonator arrays (CRA), which are also coupled to some artificial atoms as the controlling quantum node. By making use of this approach, we find the bound states of single photon for an elementary unit, the T-type CRA, and explicitly obtain its multi-photon scattering S-matrix in various situations. We also use this method to calculate the multi-photon S-matrices for the more complex quantum network constructed with main T-type CRA's, such as a H-type CRA waveguide.
Topological Phenomena in Trapped Ion Systems
T. Shi,J. I. Cirac
Physics , 2012, DOI: 10.1103/PhysRevA.87.013606
Abstract: We propose and analyze a scheme to observe topological phenomena with ions in microtraps. We consider a set of trapped ions forming a regular structure in two spatial dimensions and interacting with lasers. We find phonon bands with non-trivial topological properties, which are caused by the breaking of time reversal symmetry induced by the lasers. We investigate the appearance of edge modes, as well as their robustness against perturbations. Long-range hopping of phonons caused by the Coulomb interaction gives rise to flat bands which, together with induced phonon-phonon interactions, can be used to produce and explore strongly correlated states. Furthermore, some of these ideas can also be implemented with cold atoms in optical lattices.
Solvability of Cubic Graphs - From Four Color Theorem to NP-Complete
Tony T. Lee,Qingqi Shi
Computer Science , 2013,
Abstract: Similar to Euclidean geometry, graph theory is a science that studies figures that consist of points and lines. The core of Euclidean geometry is the parallel postulate, which provides the basis of the geometric invariant that the sum of the angles in every triangle equals $\pi$ and Cramer's rule for solving simultaneous linear equations. Since the counterpart of parallel postulate in graph theory is not known, which could be the reason that two similar problems in graph theory, namely the four color theorem (a topological invariant) and the solvability of NP-complete problems (discrete simultaneous equations), remain open to date. In this paper, based on the complex coloring of cubic graphs, we propose the reducibility postulate of the Petersen configuration to fill this gap. Comparing edge coloring with a system of linear equations, we found that the postulate of reducibility in graph theory and the parallel postulate in Euclidean geometry share some common characteristics of the plane. First, they both provide solvability conditions on two equations in the plane. Second, the two basic invariants of the plane, namely the chromatic index of bridgeless cubic plane graphs and the sum of the angles in every triangle, can be respectively deduced from them in a straightforward manner. This reducibility postulation has been verified by more than one hundred thousand instances of Peterson configurations generated by computer. Despite that, we still don't have a logical proof of this assertion. Similar to that of the parallel postulate, we tend to think that describing these natural laws by even more elementary properties of the plane is inconceivable.
Associations of Education Level and Bone Density Tests among Cognitively Intact Elderly White Women in Managed Medicare
Di Shi,Michael T. Yin,Qiuhu Shi,Donald R. Hoover
Current Gerontology and Geriatrics Research , 2012, DOI: 10.1155/2012/179150
Abstract: Objectives. To examine associations between having bone density tests and level of education among white elderly women in managed Medicare. Method. Data from the ninth through twelfth cohort (2006–2009) of the Medicare Health Outcome Survey (HOS) of managed Medicare plans were analyzed; 239331 white elderly women were included. Respondents were grouped by education level and the percentages of respondents who had lifetime bone density testing done among each group were analyzed. Results. 62.7% of respondents with less than a high school education reported previously taking a bone density test. This was lower than the 73.8% for respondents who completed high school and the 81.0% for respondents with more than a high school education. When potential confounding factors such as age, body mass index, marital status, smoking history, year of HOS survey, and region were factored in, the odds ratios of having a bone density test when compared to respondents with less than a high school education were 1.61 and 2.39, respectively, for those with just a high school education and more than a high school education ( ). Conclusion. Higher education was independently associated with greater use of bone density test in these elderly white women. 1. Introduction In recent years, many studies have found a link between education level and the overall health of a person. Lower education was found worldwide to be correlated with increases in many areas of health risk including cardiac dysfunction [1], preterm birth [2], mortality [3], and others diseases [4, 5]. Furthermore, these effects of education disparity on greater disease prevalence [4] and lower life expectancy may be growing [6]. When treating patients with lower education levels, physicians spend less time discussing health related issues [7] which may lead to gaps in health awareness including the use of preventive services. For example, lower levels of education have been linked to lower use of public health services in Brazil [8] and lower use of HIV testing in Portugal’s immigrant population [9]. The goal of this paper is to see if lower education also effects use of bone mineral density test among a group that would benefit most from testing, elderly white women in the United States. Bone fractures can have devastating consequences including pain, loss of mobility function, and death. Among elderly, particularly postmenopausal women, deterioration in bone mass progressively increases the risk of fragility fractures compared to people with healthy bone [10]. While all elderly women in America are at higher
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