Quarkonium at nonzero isospin density

We calculate the energies of quarkonium bound states in the presence of a medium of nonzero isospin density using lattice QCD. The medium, created using a canonical (fixed isospin charge) approach, induces a reduction of the quarkonium energies. As the isospin density increases, the energy shifts first increase and then saturate. The saturation occurs at an isospin density close to that where previously a qualitative change in the behavior of the energy density of the medium has been observed, which was conjectured to correspond to a transition from a pion gas to a Bose-Einstein condensed phase. The reduction of the quarkonium energies becomes more pronounced as the heavy-quark mass is decreased, similar to the behavior seen in two-color QCD at nonzero quark chemical potential. In the process of our analysis, the eta(b)-pi and Upsilon-pi scattering phase shifts are determined at low momentum. An interpolation of the scattering lengths to the physical pion mass gives a(eta b,pi) = 0: 0025(8)(6) fm and a(Upsilon,pi) = 0.0030(9)(7) fm

Multi-meson systems from Lattice Quantum Chromodynamics

Systems of non-zero isospin chemical potential ( muI), where the chemical potential for up and down quarks is equal in magnitude but of opposite sign, do not suffer from the sign problem, and normal LQCD techniques can be successfully adapted to study such systems. From chiral perturbation theory (chiPT), in addition to the deconfined phase transition at high temperature at zero chemical potential, another phase transition from ordinary hadronic states to a Bose Einstein Condensate (BEC) state has been conjectured [1] at non-zero isospin chemical potential. Such a BEC phase is of phenomenological relevance in the interior of neutron stars.;In LQCD, one way to investigate non-zero isospin chemical potential system is from a grand canonical approach by directly working with fermion actions of targeted isospin chemical potentials. Another approach to isospin chemical potential is by explicitly constructing systems of fixed isospin density, and inferring the isospin chemical potential from its ground state energy. In Ref. [2], the first studies of nonzero isospin chemical potential system from this approach were presented, finding that the dependence of the isospin chemical potential on the isospin density agrees with predictions from Ref. [1] at low density. In this thesis, we studied systems with the quantum numbers of up to 72 pions with newly constructed algorithms, and clearly identified the conjectured phase transition from a pion gas to a BEC state at muI = 1.3 mpi at T ≈ 20 MeV for the first time.;Having numerically constructed a novel state of matter, a natural question to ask is how it can be investigated. The suppression of J/psi and Upsilon resonances [3] at non-zero temperature in heavy ion collision is an important diagnostic of the formation of a quark-gluon plasma. Such suppression effects have been experimentally observed at Super Proton Synchrotron (SPS), RHIC and LHC [3]. Heavy quarks are naturally also expected to be useful probes of phase transitions at non-zero baryon chemical potential and non-zero isospin chemical potential. In this thesis, we investigated both bottomonium and charmonium in media of non-zero isospin chemical potential.;The investigation of QCD at non-zero isospin density presented in this thesis provide a numerical window into a novel state of strongly interacting matter. This matter is difficult to create in experiment but may play an important role in dense astrophysical environments

Lattice QCD at non-zero isospin chemical potential (2013 ver.)

Systems of non-zero isospin chemical potential are studied from a canonical approach by computing correlation functions with the quantum numbers of N pi(+)\u27s (C-N pi). In order to reduce the number of contractions required in calculating C-N pi for a large N in the Wick\u27s theorem, we constructed a few new algorithms. With these new algorithms, systems with isospin charge up to 72 are investigated on three anisotropic gauge ensembles with a pion mass of 390 MeV, and with lattice spatial extents L similar to 2.0, 2.5, 3.0 fm. The largest isospin density of rho(I) approximate to 9 fm(-3) is achieved in the smallest volume, and the QCD phase diagram is investigated at a fixed low temperature at varying isospin chemical potentials, m(pi) \u3c mu(I) \u3c 4.5 m(pi). By investigating the behaviour of the extracted energy density of the system at different isospin chemical potentials, we numerically identified the conjectured transition to a Bose-Einstein condensation state at mu(I) \u3e= m(pi)

An Adaptive Rescheduling Strategy for Grid Workflow Applications

Scheduling is the key to the performance of grid workflow applications. Various strategies are proposed, including static scheduling strategies which map jobs to resources before execution time, or dynamic alternatives which schedule individual job only when it is ready to execute. While sizable work supports the claim that the static scheduling performs better for workflow applications than the dynamic one, it is questioned how a static schedule works effectively in a grid environment which changes constantly. This paper proposes a novel adaptive rescheduling concept, which allows the workflow planner works collaboratively with the run time executor and reschedule in a proactive way had the grid environment changes significantly. An HEFT-based adaptive rescheduling algorithm is presented, evaluated and compared with traditional static and dynamic strategies respectively. The experiment results show that the proposed strategy not only outperforms the dynamic one but also improves over the traditional static one. Furthermore we observed that it performs more efficiently with data intensive application of higher degree of parallelism.

Lattice QCD at non-zero isospin chemical potential

Quantum chromodynamics (QCD) at non-zero isospin chemical potential is studied in a canonical approach by analyzing systems of fixed isospin number density. To construct these systems, we develop a range of new algorithms for performing the factorially large numbers of Wick contractions required in multi-hadron systems. We then use these methods to study systems with the quantum numbers of up to 72 $\pi^+$'s on three ensembles of gauge configurations with spatial extents $L\sim$ 2.0, 2.5 and 3.0 fm, and light quark masses corresponding to a pion mass of {390 MeV}. The ground state energies of these systems are extracted and the volume dependence of these energies is utilized to determine the two- and three- body interactions amongst $\pi^+$'s. The systems studied correspond to isospin densities of up to $\rho_I\sim 9\ {\rm fm}^{-3}$ and probe isospin chemical potentials, $\mu_I$, in the range m_\pi\ \lsim \mu_I\ \lsim 4.5\ m_\pi, allowing us to investigate aspects of the QCD phase diagram at low temperature and for varying isospin chemical potential. By studying the energy density of the system, we provide numerical evidence for the conjectured transition of the system to a Bose-Einstein condensed phase at \mu_I\ \gsim m_\pi.Comment: 32 pages, 22 figure

Perovskite Quantum Dot Light-Emitting Diodes

Recently, lead halide perovskite quantum dots (QDs) have attracted much attention because of their excellent properties of high color purity, tunable emission wavelength covering the whole visible region, and ultrahigh photoluminescence (PL) quantum yield. They are expected to be promising candidates for the next-generation cost-effective lighting and display sources. Here, we introduced the recent development in the direct solution-processed synthesis and ion exchange-based reactions, leading to organic/inorganic hybrid halide perovskites (CH3NH3PbX3; X = Cl, Br, I) and all-inorganic lead halide perovskites (CsPbX3; X = Cl, Br, I), and studied their optical properties related to exciton-related emission and quantum confinement effect. Finally, we reviewed the recent progresses on the perovskite light-emitting diodes (LEDs) based on CH3NH3PbX3 and CsPbX3 quantum dots and provided a critical outlook into the existing and future challenges

Integration Methodology of Spare Parts Supply Network Optimization and Decision-making

In order to optimize the spare parts supply network, a multi-objective optimization model is established with the objectives of the shortest supply time, the lowest risk, and the minimum supply cost. A decomposition-based multi-objective evolutionary algorithm with differential evolution strategy is introduced to solve the multi-objective model. A series of non-dominated solutions, that is, representing the optimal spare parts supply schemes are obtained. In order to comprehensively measure the performance of these solutions, suitable quantitative metrics are selected, and the secondary goal-based cross-efficiency Data Envelopment Analysis (DEA) model has been used to evaluate the efficiency of the obtained optimal schemes. The improved DEA model overcomes the problems that the efficient units cannot be sorted and the optimal weight is not unique in traditional DEA model. Finally, the self-evaluation efficiency and cross-evaluation efficiency of each scheme are obtained, and the optimal supply scheme is found based on their cross-evaluation efficiency.</p

Deterministic Spin-Orbit Torque Switching of Mn3Sn with the Interplay between Spin Polarization and Kagome Plane

Previous studies have demonstrated spin-orbit torque (SOT) switching of Mn3Sn where the spin polarization lies in the kagome plane (configuration I). However, the critical current density ($J_{crit}$) is unrealistically large ($J_{crit}$=$10^{14}$ A/$m^2$) and independent on the external field ($H_{ext}$). The stabilized magnetic state also depends on the initial state. These features conflict with the ferromagnet (FM) switching scheme as claimed in those studies, and thus call for other explanations. Alternatively, the system with the spin polarization perpendicular to the kagome plane (configuration II) is more like the FM based system since the spin polarization is orthogonal to all magnetic moments. In this work, we show SOT switching of Mn3Sn in configuration II. Similar to the FM, Jcrit and Hext are in the order of $10^{10}$ A/$m^2$ and hundreds of Oersted, respectively. The switching result is also independent of the initial state. Interestingly, the unique spin structure of Mn3Sn also leads to distinct features from FM systems. We demonstrate that Jcrit increases linearly with Hext, and extrapolation gives ultralow $J_{crit}$ for the field-free switching system. In addition, the switching polarity is opposite to the FM. We also provide the switching phase diagram as a guideline for experimental demonstration. Our work provides comprehensive understanding for the switching mechanism in both configurations. The switching protocol proposed in this work is more advantageous in realistic spintronic applications. We also clearly reveal the fundamental difference between FM and noncollinear antiferromagnetic switching

Experimental investigations of quasi-coherent micro-instabilities in Ohmic plasmas

The ITG and TEM instabilities with quasi-coherent spectra have been identified experimentally, by the newly developed far-forward collective scattering measurements in J-TEXT tokamak Ohmical plasmas. The ITG mode has characteristic frequencies in the range of 30-100kHz and wavenumber of k_\theta\rho_s<0.3. After the plasma density exceeds at critical value, the ITG mode shows a bifurcation behavior, featured by frequency decrease and amplitude enhancement. Meanwhile, the ion energy loss enhancement and confinement degradation are also observed. It gives the direct experimental evidence for ion thermal transport caused by ITG instability