Panel Data Models with Multiple Time-Varying Individual Effects

This paper considers a panel data model with time-varying individual effects. The data are assumed to contain a large number of cross-sectional units repeatedly observed over a fixed number of time periods. The model has a feature of the fixed-effects model in that the effects are assumed to be correlated with the regressors. The unobservable individual effects are assumed to have a factor structure. For consistent estimation of the model, it is important to estimate the true number of factors. We propose a generalized methods of moments procedure by which both the number of factors and the regression coefficients can be consistently estimated. Some important identification issues are also discussed. Our simulation results indicate that the proposed methods produce reliable estimates.panel data, time-varying individual effects, factor models

Scaling of the charm cross-section and modification of charm pTp_{T} spectra at RHIC

Charm production from the direct reconstruction of $D^0$ ($D^0\to K\pi$ up to 2 GeV/$c$) and indirect lepton measurements via charm semileptonic decays ($c\to e+X$ at 0.9\textless$p_T$\textless5.0 GeV/$c$ and $c\to \mu+X$ at 0.17\textless$p_{T}$\textless0.25 GeV/$c$) at $\sqrt{s_{_{NN}}}=200$ GeV Au+Au collisions are analyzed. The transverse momentum ($p_T$) spectra and the nuclear modification factors for $D^0$ and for leptons from heavy flavor decays is presented. Scaling of charm cross-section with number of binary collisions at $\sqrt{s_{_{NN}}}=200$ GeV from d+Au to Au+Au collisions is reported.Comment: 4 pages, 4 figures, proceedings for Quark Matter 200

Six degrees of freedom vibration isolation using electromagnetic suspension

Experimental data are presented for modeling an electromagnet. Control laws are considered with and without flux feedback and with position and orientation information of the suspended body. Base motion and sensor noise are the principal disturbances. Proper selection of the geometrical operating point minimizes the passive coupling above the bandwidth of the control and filtering can attenuate the high frequency content of sensor noise. Six electromagnets are arranged in a configuration which optimizes the load support and provides control over all six degrees of freedom of the suspended body. The design is based on experimental data generated with a specially designed test facility. Application for suspension of a gravity wave antenna is discussed

Information Technology as a Facilitator of Enhancing Dynamic Capability through Knowledge Management

Dynamic capability is an emergent field of firms encountering turbulent administrative environment. Eisenhardt and Martin (2000) point out that firms with dynamic capability are not guaranteed to enhancing organizational performance, but without dynamic capability it is impossible for firms to enhance organizational performance. Another research stream in current management thoughts is related to knowledge management that has been confirmed to be a major source of competitive advantage. Research question of this research is whether or not knowledge management contributes to the enhancement of dynamic capability, and thus to the enhancement of competitive advantage of a firm. Following previous research interest of knowledge management on the application of information technology (IT), this research incorporates knowledge management facilitated by IT to examine the effect on enhancement of dynamic capability. Based on a survey of top 1000 Taiwanese firms, the current empirical research tests relevant hypotheses with regression models. Empirical findings include management of both endogenous and exogenous knowledge through IT applications significantly affects the enhancement of dynamic capability. Results shed light to current strategic management issues

Non-saturating large magnetoresistance in semimetals

The rapidly expanding class of quantum materials known as {\emph{topological semimetals}} (TSM) display unique transport properties, including a striking dependence of resistivity on applied magnetic field, that are of great interest for both scientific and technological reasons. However, experimental signatures that can identify or discern the dominant mechanism and connect to available theories are scarce. Here we present the magnetic susceptibility ($\chi$), the tangent of the Hall angle ($\tan\theta_H$) along with magnetoresistance in four different non-magnetic semimetals with high mobilities, NbP, TaP, NbSb$_2$ and TaSb$_2$, all of which exhibit non-saturating large MR. We find that the distinctly different temperature dependences, $\chi(T)$ and the values of $\tan\theta_H$ in phosphides and antimonates serve as empirical criteria to sort the MR from different origins: NbP and TaP being uncompensated semimetals with linear dispersion, in which the non-saturating magnetoresistance arises due to guiding center motion, while NbSb$_2$ and TaSb$_2$ being {\it compensated} semimetals, with a magnetoresistance emerging from nearly perfect charge compensation of two quadratic bands. Our results illustrate how a combination of magnetotransport and susceptibility measurements may be used to categorize the increasingly ubiquitous non-saturating large magnetoresistance in TSMs.Comment: Accepted for publication at Proc. Natl. Acad. Sci., minor revisions, 6 figure

Synthesis of luminescent silicon clusters by spark ablation

The synthesis of luminescent nanometer-scale Si clusters by spark ablation from a crystalline Si substrate is described. The cluster source, described in the text, generates clusters in a flowing Ar stream at atmospheric pressure. Electron microscopy reveals that the clusters have diameters in the 2-4 nm size range. The luminescence spectra of the clusters, similar to that of porous Si, are presented