arXiv subjects

C. L. Tan

Publications and source records attributed to C. L. Tan.

5 recordsLinked to original sources

arXiv2009

Observations of two-fold shell filling and Kondo effect in a graphene nano-ribbon quantum dot device

A graphene nanoribbon (GNR) with orientation along its principle axis was obtained through a mechanical tearing process, and a quantum dot device was fabricated from the GNR. We have studied the transport property of the GNR quantum dot device down to dilution refrigerator temperatures. Two-fold charging periodicity was observed in the Coulomb-blockade measurement, signaling a shell-filling process with broken valley degeneracy. In one of the smaller Coulomb diamonds, Kondo-like resonance were observed, with two conductance peaks displaced symmetrically from the zero bias voltage. The splitting of Kondo resonance at zero magnetic field suggests spin-polarization of the quantum dot, possibly due to the edge states of a zigzag GNR.

cond-mat.mes-hall↗

arXiv2009

Ganga: a tool for computational-task management and easy access to Grid resources

In this paper, we present the computational task-management tool Ganga, which allows for the specification, submission, bookkeeping and post-processing of computational tasks on a wide set of distributed resources. Ganga has been developed to solve a problem increasingly common in scientific projects, which is that researchers must regularly switch between different processing systems, each with its own command set, to complete their computational tasks. Ganga provides a homogeneous environment for processing data on heterogeneous resources. We give examples from High Energy Physics, demonstrating how an analysis can be developed on a local system and then transparently moved to a Grid system for processing of all available data. Ganga has an API that can be used via an interactive interface, in scripts, or through a GUI. Specific knowledge about types of tasks or computational resources is provided at run-time through a plugin system, making new developments easy to integrate. We give an overview of the Ganga architecture, give examples of current use, and demonstrate how Ganga can be used in many different areas of science.

cs.DC↗

arXiv2009

Spontaneous and low-field magnetoimpedance in La0.7Sr0.3CoO3 and La1-xSrxMnO3 (x = 0.18-0.5)

We report ac electrical transport in La0.7Sr0.3CoO3 and La1-xSrxMnO3 (x = 0.18- 0.5) as a function of temperature and frequency in H = 0 and 60 mT. Both resistive (R) and reactive (X) components of impedance (Z = R+jX) were measured. It is shown that a smooth decrease of the resistance around the Curie temperautre in La0.7Sr0.3CoO3 transforms into an abrupt increase followed closely by a peak in R with increasing frequency. Similar behavior in R was also found in metallic compositions of the La-Sr-MnO3 series. The observed anomaly at TC is suppressed by a small dc magnetic field of H = 60 mT which rrsults in a huge ac magnetoreistance (= 30 % in manganite and =7 % in cobaltite at f = 2 MHz). The anomaly in R in zero field is also accompanied by a sudden incrases of X. While the ac magnetoresitance is negative as a function of field from 100 Hz to 30 MHz, we show that the sign of X changes and a new double peak structure develops in X for frequencies above 15 MHz.

cond-mat.mtrl-sci↗

arXiv2003

GANGA: a user-Grid interface for Atlas and LHCb

The Gaudi/Athena and Grid Alliance (GANGA) is a front-end for the configuration, submission, monitoring, bookkeeping, output collection, and reporting of computing jobs run on a local batch system or on the grid. In particular, GANGA handles jobs that use applications written for the Gaudi software framework shared by the Atlas and LHCb experiments. GANGA exploits the commonality of Gaudi-based computing jobs, while insulating against grid-, batch- and framework-specific technicalities, to maximize end-user productivity in defining, configuring, and executing jobs. Designed for a python-based component architecture, GANGA has a modular underpinning and is therefore well placed for contributing to, and benefiting from, work in related projects. Its functionality is accessible both from a scriptable command-line interface, for expert users and automated tasks, and through a graphical interface, which simplifies the interaction with GANGA for beginning and c1asual users. This paper presents the GANGA design and implementation, the development of the underlying software bus architecture, and the functionality of the first public GANGA release.

cs.SE↗

arXiv2003

ATLAS Commander: an ATLAS production tool

This paper describes the ATLAS production tool AtCom (for ATLAS Commander). The purpose of the tool is to automate as much as possible the task of a production manager: defining and submitting jobs in large quantities, following up upon their execution, scanning log files for known and unknown errors, updating the various ATLAS bookkeeping databases on successful completion of a job whilst cleaning up and resubmitting otherwise. The design of AtCom is modular, separating the generic basic job management functionality from the interactions with the various databases on the one hand, and the computing systems on the other hand. Given the near future reality of different flavors of computing systems (legacy and GRID) deployed concurrently at the various, or even a single ATLAS site, AtCom allows several of them to be used at the same time transparently.

hep-ex↗