Solutions to the Jaynes-Cummings model without the rotating-wave approximation

By using extended bosonic coherent states, the solution to the Jaynes-Cummings model without the rotating-wave approximation can be mapped to that of a polynomial equation with a single variable. The solutions to this polynomial equation can give all eigenvalues and eigenfunctions of this model with all values of the coupling strength and the detuning exactly, which can be readily applied to recent circuit quantum electrodynamic systems operating in the ultra-strong coupling regime.Comment: 6 pages,3 figure

Quantum discord of two-qubit X-states

Quantum discord provides a measure for quantifying quantum correlations beyond entanglement and is very hard to compute even for two-qubit states because of the minimization over all possible measurements. Recently a simple algorithm to evaluate the quantum discord for two-qubit X-states is proposed by Ali, Rau and Alber [Phys. Rev. A 81, 042105 (2010)] with minimization taken over only a few cases. Here we shall at first identify a class of X-states, whose quantum discord can be evaluated analytically without any minimization, for which their algorithm is valid, and also identify a family of X-states for which their algorithm fails. And then we demonstrate that this special family of X-states provides furthermore an explicit example for the inequivalence between the minimization over positive operator-valued measures and that over von Neumann measurements.Comment: 5 pages, 4 figure

Mitochondrial Dysfunction Triggers Synaptic Deficits via Activation of p38 MAP Kinase Signaling in Differentiated Alzheimer’s Disease Trans-Mitochondrial Cybrid Cells

Loss of synapse and synaptic dysfunction contribute importantly to cognitive impairment in Alzheimer’s disease (AD). Mitochondrial dysfunction and oxidative stress are early pathological features in AD-affected brain. However, the effect of AD mitochondria on synaptogenesis remains to be determined. Using human transmitochondrial “cybrid” (cytoplasmic hybrid) neuronal cells whose mitochondria were transferred from platelets of patients with sporadic AD or age-matched non-AD subjects with relatively normal cognition, we provide the first evidence of mitochondrial dysfunction compromises synaptic development and formation of synapse in AD cybrid cells in response to chemical-induced neuronal differentiation. Compared to non-AD control cybrids, AD cybrid cells showed synaptic loss which was evidenced by a significant reduction in expression of two synaptic marker proteins: synaptophysin (presynaptic marker) and postsynaptic density protein-95, and neuronal proteins (MAP-2 and NeuN) upon neuronal differentiation. In parallel, AD-mediated synaptic deficits correlate to mitochondrial dysfunction and oxidative stress as well as activation of p38 MAP kinase. Notably, inhibition of p38 MAP kinase by pharmacological specific p38 inhibitor significantly increased synaptic density, improved mitochondrial function, and reduced oxidative stress. These results suggest that activation of p38 MAP kinase signaling pathway contributes to AD-mediated impairment in neurogenesis, possibly by inhibiting the neuronal differentiation. Our results provide new insight into the crosstalk of dysfunctional AD mitochondria to synaptic formation and maturation via activation of p38 MAP kinase. Therefore, blockade of p38 MAP kinase signal transduction could be a potential therapeutic strategy for AD by alleviating loss of synapses

Andreev bound states and π\pi -junction transition in a superconductor / quantum-dot / superconductor system

We study Andreev bound states and $\pi$-junction transition in a superconductor / quantum-dot / superconductor (S-QD-S) system by Green function method. We derive an equation to describe the Andreev bound states in S-QD-S system, and provide a unified understanding of the $\pi$-junction transition caused by three different mechanisms: (1) {\it Zeeman splitting.} For QD with two spin levels $E_{\uparrow}$ and $E_{\downarrow}$, we find that the surface of the Josephson current $I(\phi =\frac \pi 2)$ vs the configuration of $(E_{\uparrow},E_{\downarrow})$ exhibits interesting profile: a sharp peak around $E_{\uparrow}=E_{\downarrow}=0$; a positive ridge in the region of $E_{\uparrow}\cdot E_{\downarrow}>0$; and a {\em % negative}, flat, shallow plain in the region of $E_{\uparrow}\cdot E_{\downarrow}<0$. (2){\it \ Intra-dot interaction.} We deal with the intra-dot Coulomb interaction by Hartree-Fock approximation, and find that the system behaves as a $\pi$-junction when QD becomes a magnetic dot due to the interaction. The conditions for $\pi$-junction transition are also discussed. (3) {\it \ Non-equilibrium distribution.} We replace the Fermi distribution $f(\omega)$ by a non-equilibrium one $\frac 12[ f(\omega -V_c)+f(\omega +V_c)]$, and allow Zeeman splitting in QD where $$ The curves of $I(\phi =\frac \pi 2)$ vs $$ show the novel effect of interplay of non-equilibrium distribution with magnetization in QD.Comment: 18 pages, 8 figures, Late

Pressure-induced unconventional superconductivity near a quantum critical point in CaFe2As2

75As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe2As2 under pressure. At P = 4.7 and 10.8 kbar, the temperature dependences of nuclear-spin-lattice relaxation rate (1/T1) measured in the tetragonal phase show no coherence peak just below Tc(P) and decrease with decreasing temperature. The superconductivity is gapless at P = 4.7 kbar but evolves to that with multiple gaps at P = 10.8 kbar. We find that the superconductivity appears near a quantum critical point under pressures in the range 4.7 kbar < P < 10.8 kbar. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound.Comment: 5pages, 5figure

Distribution of Spectral Lags in Gamma Ray Bursts

Using the data acquired in the Time To Spill (TTS) mode for long gamma-ray bursts (GRBs) collected by the Burst and Transient Source Experiment on board the Compton Gamma Ray Observatory (BATSE/CGRO), we have carefully measured spectral lags in time between the low (25-55 keV) and high (110-320 keV) energy bands of individual pulses contained in 64 multi-peak GRBs. We find that the temporal lead by higher-energy gamma-ray photons (i.e., positive lags) is the norm in this selected sample set of long GRBs. While relatively few in number, some pulses of several long GRBs do show negative lags. This distribution of spectral lags in long GRBs is in contrast to that in short GRBs. This apparent difference poses challenges and constraints on the physical mechanism(s) of producing long and short GRBs. The relation between the pulse peak count rates and the spectral lags is also examined. Observationally, there seems to be no clear evidence for systematic spectral lag-luminosity connection for pulses within a given long GRB.Comment: 20 pages, 4 figure

Data-driven image color theme enhancement

Proceedings of the 3rd ACM SIGGRAPH Asia 2010, Seoul, South Korea, 15-18 December 2010It is often important for designers and photographers to convey or enhance desired color themes in their work. A color theme is typically defined as a template of colors and an associated verbal description. This paper presents a data-driven method for enhancing a desired color theme in an image. We formulate our goal as a unified optimization that simultaneously considers a desired color theme, texture-color relationships as well as automatic or user-specified color constraints. Quantifying the difference between an image and a color theme is made possible by color mood spaces and a generalization of an additivity relationship for two-color combinations. We incorporate prior knowledge, such as texture-color relationships, extracted from a database of photographs to maintain a natural look of the edited images. Experiments and a user study have confirmed the effectiveness of our method. © 2010 ACM.postprin

Statistical Study of the Relationship Between Ion Upflow and Field-Aligned Current in the Topside Ionosphere for Both Hemispheres During Geomagnetic Disturbed and Quiet Time

A statistical study of ion upflow and field‐aligned currents (FACs) has been performed in the topside ionosphere of both hemispheres for magnetic quiet and disturbed times by using DMSP satellite observations from 2010–2013. Distributions in MLT/MLat reveal that ion upflow occurrence shows a dawn‐dusk asymmetry distribution that matches well with the Region 1 FACs. In addition, there are highest occurrence regions near noon and within the midnight auroral disturbance area, corresponding to dayside cusp and nightside auroral disturbance regions, respectively. Both the ion upflow occurrence and FAC regions expand equatorward to a wider area during disturbed times.publishedVersio

Magnetic Sunyaev-Zel'dovich effect in galaxy clusters

This Letter explores influences of intracluster magnetic fields (\gsim 1\muG) submerged in the hot electron gas on classic Sunyaev-Zel'dovich effect (SZE) and thermal bremsstrahlung in X-ray emissions. As the Larmor frequency is much higher than all collision frequencies, the presence of magnetic field may lead to an anisotropic velocity distribution of hot electrons. For the two-temperature relativistic Maxwell-Boltzmann distribution, we compute modifications to the classical thermal SZE. Intracluster magnetic fields tend to enhance the SZE with steeper radial variations, which bear important consequences for cluster-based estimates of cosmological parameters. By applying the magnetic SZE theory to spectral observations of SZ and Chandra X-ray emissions from the galaxy cluster Abell 2163, a $\sim 30-40\mu$G central core magnetic field $B_0$ is predicted. For the SZ and Chandra X-ray spectral observations of the Coma cluster, our theoretical analysis is also consistent with an observationally inferred B_0\lsim 10\muG. As the magnetic SZE is redshift $z$ independent, this mechanism might offer a potentially important and unique way of probing intracluster magnetic fields in the expanding universe.Comment: 4 pages, 3 figures. submitted to ApJ

Parallel momentum distribution of the 28^{28}Si fragments from 29^{29}P

Distribution of the parallel momentum of $^{28}$Si fragments from the breakup of 30.7 MeV/nucleon $^{29}$P has been measured on C targets. The distribution has the FWHM with the value of 110.5 $\pm$ 23.5 MeV/c which is consistent quantitatively with Galuber model calculation assuming by a valence proton in $^{29}$P. The density distribution is also predicted by Skyrme-Hartree-Fock calculation. Results show that there might exist the proton-skin structure in $^{29}$P.Comment: 4 pages, 4 figure