arXiv subjects

J. Wei

Publications and source records attributed to J. Wei.

64 records · Page 4Linked to original sources

arXiv2006

Normal state electronic structure in the heavily overdoped regime of Bi1.74Pb0.38Sr1.88CuO6+delta single-layer cuprate superconductors

We explore the electronic structure in the heavily overdoped regime of the single layer cuprate superconductor Bi1.74Pb0.38Sr1.88CuO6+delta. We found that the nodal quasiparticle behavior is dominated mostly by phonons, while the antinodal quasiparticle lineshape is dominated by spin fluctuations. Moreover, while long range spin fluctuations diminish at very high doping, the local magnetic fluctuations still dominate the quasiparticle dispersion, and the system exhibits a strange metal behavior in the entire overdoped regime.

cond-mat.supr-con↗

arXiv2006

Microwave-Induced Dephasing in One-Dimensional Metal Wires

We report on the effect of monochromatic microwave (MW) radiation on the weak localization corrections to the conductivity of quasi-one-dimensional (1D) silver wires. Due to the improved electron cooling in the wires, the MW-induced dephasing was observed without a concomitant overheating of electrons over wide ranges of the MW power $P_{MW}$ and frequency $f$. The observed dependences of the conductivity and MW-induced dephasing rate on $P_{MW}$ and $f$ are in agreement with the theory by Altshuler, Aronov, and Khmelnitsky \cite{Alt81}. Our results suggest that in the low-temperature experiments with 1D wires, saturation of the temperature dependence of the dephasing time can be caused by an MW electromagnetic noise with a sub-pW power.

cond-mat.mes-hall↗

arXiv2005

Magnetic field asymmetry of nonlinear transport in carbon nanotubes

We demonstrate that nonlinear transport through a two-terminal nanoscale sample is not symmetric in magnetic field B. More specifically, we have measured the lowest order B-asymmetric terms in single-walled carbon nanotubes. Theoretically, the size of these terms can be used to infer both the strength of electron-electron interactions and the handedness of the nanotube. Consistent with theory, we find that at high temperatures the B-linear term is small and has a constant sign independent of Fermi energy, while at low temperatures it develops mesoscopic fluctuations. We also find significant magnetoresistance of nanotubes in the metallic regime which is unexplained.

cond-mat.mes-hall↗

arXiv2001

SNS Application Programming Plan

The architecture for Spallation Neutron Source accelerator physics application programs is presented. These high level applications involve processing and managing information from the diagnostic instruments, the machine control system, models and static databases; they will be used to investigate and control beam behavior. Primary components include an SNS global database and Java-based Application Toolkit, called XAL. A key element in the SNS application programs is time synchronization of data used in these applications, due to the short pulse length (1 ms), pulsed (60 Hz) nature of the device. The data synchronization progress is also presented.

physics.acc-ph↗

arXiv2001

A Prototype of the UAL 2.0 Application Toolkit

The paper presents a prototype of the accelerator commissioning and simulation application toolkit based on the Unified Accelerator Libraries (UAL) framework. The existing UAL 1.x environment has been implemented as an open collection of C++ and Perl packages that address various tasks of accelerator physics. The UAL 2.0 application toolkit has been developing on the top of the Java infrastructure for integrating it with distributed accelerator control systems. The core part of the toolkit is composed of the Common Accelerator Objects (such as Accelerator, Algorithms, etc.) that form the framework for developing project-specific applications. The toolkit environment is not only limited to Java applications, but also supports the development and integration of high-level scripting codes (e.g. Java Python scripts) and existing C/C++ libraries. The configuration and navigation of the project-specific application system is provided by the XML-based Application Manager.

physics.acc-ph↗

arXiv2001

Optical and radio variability of the BL Lac object AO 0235+16: a possible 5-6 year periodicity

New optical and radio data on the BL Lacertae object AO 0235+16 have been collected in the last four years by a wide international collaboration, which confirm the intense activity of this source. The optical data also include the results of the Whole Earth Blazar Telescope (WEBT) first-light campaign organized in November 1997. The optical spectrum is observed to basically steepen when the source gets fainter. We have investigated the existence of typical variability time scales and of possible correlations between the optical and radio emissions by means of visual inspection, Discrete Correlation Function analysis, and Discrete Fourier Transform technique. The major radio outbursts are found to repeat quasi-regularly with a periodicity of about 5.7 years; this period is also in agreement with the occurrence of some of the major optical outbursts, but not all of them.

astro-ph↗

arXiv2000

ROSAC: Studying the clustering properties of X-ray selected AGNs

We present the first ROSAC results of an AGN clustering analysis. This study comprises a sample of 200 AGNs, 75% of which being at low redshifts z<0.5, in the Ursa Major constellation. The spatial 2-point-correlation function (SCF) as well as the minimal spanning tree (MST) technique were applied. Some evidence for clustering is found in the SCF, although with low significance. Using the MST technique, we could find two AGN groups. This result is preliminary and the exact significance will be tested with careful simulations.

astro-ph↗

arXiv1999

Relativistic Spheres

By analyzing the Einstein's equations for the static sphere, we find that there exists a non-singular static configuration whose radius can approach its corresponding horizon size arbitrarily.

gr-qc↗

arXiv1998

Large-scale structures in the distribution of X-ray selected AGN

We are searching for large-scale structures in the distribution of AGN discovered by the ROSAT All-Sky Survey. The RASS detected > 60000 X-ray objects, of which approximately 35% are AGN at z < 0.5. The surface density in the extragalactic sky is approximately 0.5 AGN/deg^2, which has not been reached until now by any other survey for this redshift range. We efficiently single out the AGN among all the RASS sources using the Hamburg/RASS database of optical identifications, which contains presently 13867 entries. Follow-up spectroscopy of RASS AGN candidates identified in selected areas of the northern sky is underway to determine the spatial distribution of the AGN in these areas. In every area structures reminiscent of clusters and filaments are found on scales 50 - 100 h^{-1}Mpc. These structures have a similar size as the serendipitously discovered groups of AGN in optical surveys at higher redshifts. Samples of low redshift AGN drawn from the RASS are large enough to be used with samples of higher redshift to study evolutionary effects in the large-scale distribution of AGN.

astro-ph↗

arXiv1997

Quasars around the Seyfert Galaxy NGC3516

We report redshift measurements of 5 X-ray emitting blue stellar objects (BSO's) located less than 12 arc min from the X-ray Seyfert galaxy, NGC 3516. We find these quasars to be distributed along the minor axis of the galaxy and to show a very good correlation between their redshift and their angular distance from NGC 3516. Moreover the redshifts of these 5 quasars are: 0.33, 0.69, 0.93, 1.40 and 2.10 which are very near the peaks of the redshift periodicity distribution (i.e. z=0.3, 0.6, 0.96, 1.41 and 1.96). All these observed properties strikingly confirm, around this single example of a Seyfert, the composite picture derived from previous physical associations of quasars with low redshift, active galaxies.

astro-ph↗