1,582 research outputs found
On Markov operators preserving polynomials
The paper is concerned with a special class of positive linear operators acting on the space C(K) of all continuous functions defined on a convex compact subset K of R^d, d \geq 1, having non-empty interior. Actually, this class consists of all positive linear operators T on C(K) which leave invariant the polynomials of degree at most 1 and which, in addition, map polynomials into polynomials of the same degree. Among other things, we discuss the existence of such operators in the special case where K is strictly convex by also characterizing them within the class of positive projections.
In particular we show that such operators exist if and only if ∂K is an ellipsoid.
Furthermore, a characterization of balls of R^d in terms of a special class of them is furnished. Additional results and illustrative examples are presented as well
Odd and Even Lidstone-type polynomial sequences. Part 1: basic topics
Abstract Two new general classes of polynomial sequences called respectively odd and even Lidstone-type polynomials are considered. These classes include classic Lidstone polynomials of first and second kind. Some characterizations of the two classes are given, including matrix form, conjugate sequences, generating function, recurrence relations, and determinant forms. Some examples are presented and some applications are sketched
Measurement crosstalk between two phase qubits coupled by a coplanar waveguide
We analyze the measurement crosstalk between two flux-biased phase qubits
coupled by a resonant coplanar waveguide cavity. After the first qubit is
measured, the superconducting phase can undergo damped oscillations resulting
in an a.c. voltage that produces a frequency chirped noise signal whose
frequency crosses that of the cavity. We show experimentally that the coplanar
waveguide cavity acts as a bandpass filter that can significantly reduce the
crosstalk signal seen by the second qubit when its frequency is far from the
cavity's resonant frequency. We present a simple classical description of the
qubit behavior that agrees well with the experimental data. These results
suggest that measurement crosstalk between superconducting phase qubits can be
reduced by use of linear or possibly nonlinear resonant cavities as coupling
elements.Comment: 4 pages, 3 figure
Circuit QED scheme for realization of the Lipkin-Meshkov-Glick model
We propose a scheme in which the Lipkin-Meshkov-Glick model is realized
within a circuit QED system. An array of N superconducting qubits interacts
with a driven cavity mode. In the dispersive regime, the cavity mode is
adiabatically eliminated generating an effective model for the qubits alone.
The characteristic long-range order of the Lipkin-Meshkov-Glick model is here
mediated by the cavity field. For a closed qubit system, the inherent second
order phase transition of the qubits is reflected in the intensity of the
output cavity field. In the broken symmetry phase, the many-body ground state
is highly entangled. Relaxation of the qubits is analyzed within a mean-field
treatment. The second order phase transition is lost, while new bistable
regimes occur.Comment: 5 pages, 2 figure
Synthesis and Biological Evaluation of Dantrolene-Like Hydrazide and Hydrazone Analogues as Multitarget Agents for Neurodegenerative Diseases
Dantrolene, a drug used for the management of malignant hyperthermia, had been recently evaluated for prospective repurposing as multitarget agent for neurodegenerative syndromes, including Alzheimer's disease (AD). Herein, twenty-one dantrolene-like hydrazide and hydrazone analogues were synthesized with the aim of exploring structure-activity relationships (SARs) for the inhibition of human monoamine oxidases (MAOs) and acetylcholinesterase (AChE), two well-established target enzymes for anti-AD drugs. With few exceptions, the newly synthesized compounds exhibited selectivity toward MAO B over either MAO A or AChE, with the secondary aldimine 9 and phenylhydrazone 20 attaining IC50 values of 0.68 and 0.81 μM, respectively. While no general SAR trend was observed with lipophilicity descriptors, a molecular simplification strategy allowed the main pharmacophore features to be identified, which are responsible for the inhibitory activity toward MAO B. Finally, further in vitro investigations revealed cell protection from oxidative insult and activation of carnitine/acylcarnitine carrier as concomitant biological activities responsible for neuroprotection by hits 9 and 20 and other promising compounds in the examined series
Decoherence, Autler-Townes effect, and dark states in two-tone driving of a three-level superconducting system
We present a detailed theoretical analysis of a multi-level quantum system
coupled to two radiation fields and subject to decoherence. We concentrate on
an effect known from quantum optics as the Autler-Townes splitting, which has
been recently demonstrated experimentally [M. A. Sillanpaa et al., Phys. Rev.
Lett. 103, 193601 (2009)] in a superconducting phase qubit. In the three-level
approximation, we derive analytical solutions and describe how they can be used
to extract the decoherence rates and to account for the measurement data.
Better agreement with the experiment can be obtained by extending this model to
five levels. Finally, we investigate the stationary states created in the
experiment and show that their structure is close to that of dark states.Comment: 16 pages, 8 figure
Parametric coupling between macroscopic quantum resonators
Time-dependent linear coupling between macroscopic quantum resonator modes
generates both a parametric amplification also known as a {}"squeezing
operation" and a beam splitter operation, analogous to quantum optical systems.
These operations, when applied properly, can robustly generate entanglement and
squeezing for the quantum resonator modes. Here, we present such coupling
schemes between a nanomechanical resonator and a superconducting electrical
resonator using applied microwave voltages as well as between two
superconducting lumped-element electrical resonators using a r.f.
SQUID-mediated tunable coupler. By calculating the logarithmic negativity of
the partially transposed density matrix, we quantitatively study the
entanglement generated at finite temperatures. We also show that
characterization of the nanomechanical resonator state after the quantum
operations can be achieved by detecting the electrical resonator only. Thus,
one of the electrical resonator modes can act as a probe to measure the
entanglement of the coupled systems and the degree of squeezing for the other
resonator mode.Comment: 15 pages, 4 figures, submitte
trans-rac-[1-Oxo-2-phenethyl-3-(2-thienyl)-1,2,3,4-tetrahydroisoquinolin-4-yl]methyl 4-methylbenzenesulfonate
The title compound, C29H27NO4S2, was synthesized by reaction of trans-rac-4-(hydroxymethyl)-2-phenethyl-3-(thiophen-2-yl)-3,4-dihydroisoquinolin-1(2H)-one and 4-methylbenzene-1-sulfonyl chloride in the presence of Et3N in CH2Cl2. The relative orientations of the benzene ring (A) of the 3,4-dihydroisoquinolinone ring system, the thiophene ring (B), the benzene ring (C) of the methylbenzene group and the phenyl ring (D) result in the following dihedral angles: A/B = 80.91 (16), A/C = 22.79 (18), A/D = 9.9 (2), B/C = 80.73 (19), B/D = 88.9 (2) and C/D = 29.9 (2)°. The crystal structure is stabilized by weak intermolecular C—H⋯O hydrogen bonds and C—H⋯π interactions
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