46,119 research outputs found
Phosphine-Catalyzed Formation of Carbon−Sulfur Bonds: Catalytic Asymmetric Synthesis of γ-Thioesters
A method for catalytic asymmetric γ sulfenylation of carbonyl compounds has been developed. In the presence of an appropriate catalyst, thiols not only add to the γ position of allenoates, overcoming their propensity to add to the β position in the absence of a catalyst, but do so with very good enantioselectivity. Sulfur nucleophiles are now added to the three families of nucleophiles (carbon, nitrogen, and oxygen) that had earlier been shown to participate in catalyzed γ additions. The phosphine catalyst of choice, TangPhos, had previously only been employed as a chiral ligand for transition metals, not as an efficient enantioselective nucleophilic catalyst
Effective Simulation of Quantum Entanglement Based on A Single-photon Field Modulated with Pseudorandom Phase Sequences
We demonstrate that a single-photon field modulated with n different
pseudorandom phase sequences (PPSs) can constitute a 2^n-dimensional Hilbert
space that contains tensor product structure. By using the single photon field
modulated with PPSs, we discuss effective simulation of Bell states and GHZ
state, and apply both correlation analysis and von Neumann entropy to
characterize the simulation. We obtain similar results with the cases in
quantum mechanics and find that the conclusions can be easily generalized to n
quantum particles. The research on simulation of quantum entanglement may be
important, for it not only provides useful insights into fundamental features
of quantum entanglement, but also yields new insights into quantum computation.Comment: 5 pages, 3 figures, a major corrected version. Added an important
appendix in which we propose three theoretical prediction
Dynamically generated resonances from the vector meson-octet baryon interaction in the strangeness zero sector
The interaction potentials between vector mesons and octet baryons are
calculated explicitly with a summation of t-, s-, u-channel diagrams and a
contact term originating from the tensor interaction. Many resonances are
generated dynamically in different channels of strangeness zero by solving the
coupled-channel Lippman-Schwinger equations with the method of partial wave
analysis, and their total angular momenta are determined. The spin partners
N(1650)1/2^{-} and N(1700)3/2^-, N(1895)1/2^{-} and N(1875)3/2^-, and the state
N(2120)3/2^- are all produced respectively in the isospin I=1/2 sector. In the
isospin I=3/2 sector, the spin partners Delta(1620)1/2^- and Delta(1700)3/2^-
are also associated with the pole in the complex energy plane. According to the
calculation results, a J^P=1/2^- state around 2000 MeV is predicted as the spin
partner of N(2120)3/2^-. Some resonances are well fitted with their
counterparts listed in the newest review of Particle Data Group(PDG), while
others might stimulate the experimental observation in these energy regions in
the future.Comment: 28 pages, 12 figures, 8 tables. arXiv admin note: text overlap with
arXiv:0905.0973 by other author
Enantioselective carbon–sulfur bond formation: γ additions of aryl thiols to allenoates catalyzed by a chiral phosphepine
An effective phosphine-catalyzed method was developed for the enantioselective addition of aryl thiols to the γ position of allenoates, thereby providing ready access to aryl alkyl sulfides in very good ee. The array of mechanistic data are consistent with the addition of the chiral phosphine to the allenoate being the turnover-limiting step of the catalytic cycle. The optimized reaction conditions, as well as the mechanistic observations, differ markedly from an earlier report on asymmetric additions of alkylthiols to allenoates, which highlights the potential for divergent behavior between alkyl and aryl thiols when acting as nucleophiles
Study on the yields and polarizations of within the framework of non-relativistic QCD via at CEPC
Within the framework of the non-relativistic QCD (NRQCD), we make a
systematical study of the yields and polarizations of and
via in photon-photon collisions
at the Circular Electron Positron Collider (CEPC), up to . We find that this process at CEPC is quite "clean",
namely the direct photoproduction absolutely dominate over the single- and
double- resolved processes, at least 2 orders of magnitude larger. It is found
that the next-to-leading order (NLO) QCD corrections will significantly reduce
the results due to that the virtual corrections to is large and
negative. For , as increases, the color octet (CO) processes will
provide increasingly important contributions to the total NLO results. Moreover
the inclusion of CO contributions will dramatically change the polarizations of
from toally transverse to longitudinal, which can be regarded as a
distinct signal for the CO mechanism. However, for the case of , the
effects of the CO processes are negligible, both for yields and polarizations.
For , the dependence of the yields on the value of the renormalization
scale is moderate, while significant for the polarization. The impact
of the variation of is found to be relatively slight. As for
the case of , the uncertainties of and just
bring about negligible effects. The future measurements on this semi-inclusive
photoproductions of , especially on the polarization
parameters of , will be a good laboratory for the study of heavy
quarkonium production mechanism and helpful to clarify the problems of the
polarization puzzle
Achieve Higher Efficiency at Maximum Power with Finite-time Quantum Otto Cycle
The optimization of finite-time thermodynamic heat engines was intensively
explored recently, yet limited to few cycles, e.g. finite-time Carnot-like
cycle. In this paper, we supplement a new type of finite-time engine with
quantum Otto cycle and show the better performance. The current model can be
widely utilized benefited from the general \mathcal{C}/\tau^{2} scaling of
extra work for finite-time adiabatic process with long control time \tau. Such
scaling allows analytical optimization of the generic finite-time quantum Otto
cycle to surpass the efficiency at maximum power for the Carnot-like engine. We
apply the current perturbation method to the quantum piston model and calculate
the efficiency at maximum power, which is validated with exact solution.Comment: 14 pages, 10 figure
Coexistence of antiferromagnetism and topological superconductivity on honeycomb lattice Hubbard model
Motivated by the recent numerical simulations for doped - model on
honeycomb lattice, we study superconductivity of singlet and triplet pairing on
honeycomb lattice Hubbard model. We show that a superconducting state with
coexisting spin-singlet and spin-triplet pairings is induced by the
antiferromagnetic order near half-filling. The superconducting state we obtain
has a topological phase transition that separates a topologically trivial state
and a nontrivial state with Chern number two. Possible experimental realization
of such a topological superconductivity is also discussed.Comment: 20 pages, 10 figure
Direct Adaptive Controller for Uncertain MIMO Dynamic Systems with Time-varying Delay and Dead-zone Inputs
This paper presents an adaptive tracking control method for a class of
nonlinearly parameterized MIMO dynamic systems with time-varying delay and
unknown nonlinear dead-zone inputs. A new high dimensional integral
Lyapunov-Krasovskii functional is introduced for the adaptive controller to
guarantee global stability of the considered systems and also ensure
convergence of the tracking errors to the origin. The proposed method provides
an alternative to existing methods used for MIMO time-delay systems with
dead-zone nonlinearities
Quantum Version of Gauge Invariance and Nucleon Internal Structure
The conflict between cononical commutation relation and gauge invariance,
which both the momentum and angular momentum of quark and gluon should satisfy,
is clarified. The quantum version of gauge invariance is studied. The gauge
independence of the matrix elements of quark momentum and angular momentum
operators between physical states are proved. We suggest to use the canonical
quark momentum and angular momentum distributions to describe the nucleon
internal structure in order to establish an internal consistent description of
hadron spectroscopy and hadron structure. The same problem for the atomic
spectroscopy and structure is discussed.Comment: 3 pages, in revtex4, to be published in the Proceedings of the
International Conference on QCD and Hadronic Physics, Beijing, China, June
16-20, 200
Optical analogy to quantum computation based on classical fields modulated pseudorandom phase sequences
We demonstrate that a tensor product structure and optical analogy of quantum
entanglement can be obtained by introducing pseudorandom phase sequences into
classical fields with two orthogonal modes. Using the classical analogy, we
discuss efficient simulation of several typical quantum states, including
product state, Bell states, GHZ state, and W state. By performing quadrature
demodulation scheme, we propose a sequence permutation mechanism to simulate
certain quantum states and a generalized gate array model to simulate quantum
algorithm, such as Shor's algorithm and Grover's algorithm. The research on
classical simulation of quantum states is important, for it not only enables
potential beyond quantum computation, but also provides useful insights into
fundamental concepts of quantum mechanics.Comment: Modify the title and some errors of Eq.(1),(38) and Fig. 1; 28 pages,
13 figures, Welcome to comment! Major update version of arXiv:1003.603
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