arXiv subjects

J. Wang

Publications and source records attributed to J. Wang.

At least 433 records · Page 24Linked to original sources

arXiv2006

Evolutionary Implications from SDSSJ085338.27+033246.1: A Spectacular N arrow-Line Seyfert 1 Galaxy with Young Post-starburst

We analyze the physical properties of post-starburst AGN SDSS J085338.27+033246.1 according to its optical spectrum and discuss its implications on AGN's evolution. The spectra PCA method is developed to extract emission lines and absorption features from the total light spectrum. The emission-line analysis indicates that the object can be classified as a NLS1 with FeII/H$β_{\rm{B}}=2.4\pm0.2$, large Eddington ratio ($\sim0.34$), small black hole mass ($\sim1.1\times10^{7}M_{\odot}$) and intermediately strong radio emission. A simple SSP model indicates that the absorption features are reproduced by a $\sim$100 Myr old starburst with a mass of $\sim7\times10^{9}M_{\odot}$ rather well. The current SFR $\sim3.0M_{\odot}\rm{yr^{-1}}$ inferred from the [OII] emission is much smaller than the past average SFR$\sim70M_{\odot}\rm{yr^{-1}}$, however. The line ratio diagnosis using the BPT diagrams indicates that the narrow emission lines are almost entirely emitted from HII regions. We further discuss a possible evolutionary path that links AGN and starburst phenomena.

astro-ph↗

arXiv2006

Properties of the Initial Participant Matter Interaction Zone in Near Fermi-Energy Heavy Ion Collisions

The sizes, temperatures and free neutron to proton ratios of the initial interaction zones produced in the collisions of 40 MeV/nucleon $^{40}$Ar + $^{112}$Sn and 55 MeV/nucleon$^{27}$Al + $^{124}$Sn are derived using total detected neutron plus charged particle multiplicity as a measure of the impact parameter range and number of participant nucleons. The size of the initial interaction zone, determined from a coalescence model analysis, increases significantly with decreasing impact parameter. The temperatures and free neutron to proton ratios in the interaction zones are relatively similar for different impact parameter ranges and evolve in a similar fashion.

nucl-ex↗

arXiv2006

Angular distribution in two-photon double ionization of helium by intense attosecond soft X-ray pulses

We investigate two-photon double ionization of helium by intense ($10^{15} W/cm^2$) ultrashort ($\approx 300$ as) soft X-ray pulses (E = 91.6 eV). The time-dependent two-electron Schrödinger equation is solved using a coupled channel method. We show that for ultrashort pulses the angular distribution of ejected electrons depends on the pulse duration and provides novel insights into the role of electron correlations in the two-electron photoemission process. The angular distribution at energies near the ``independent electron'' peaks is close to dipolar while it acquires in the ``valley'' of correlated emission a significant quadrupolar component within a few hundred attoseconds.

physics.atom-ph↗

arXiv2005

Equilibrium spin current through the tunnelling junctions

We study equilibrium pure spin current through tunnelling junctions at zero bias. The two leads of the junctions connected via a thin insulator barrier, can be either a ferromagnetic metal (FM) or a nonmagnetic high-mobility two-dimensional electron gas (2DEG) with Rashba spin orbital interaction (RSOI) or Dresselhaus spin orbital interaction (DSOI). As a lead of a tunnelling junction, the isotropic RSOI or DSOI in 2DEG can give rise to an average effective planar magnetic field orthogonal or parallel to the current direction. It is found by the linear response theory that equilibrium spin current $\vec{J}$ can flow in the following three junctions, 2DEG/2DEG, 2DEG/FM, and FM/FM junctions, as a result of the exchange coupling between the magnetic moments, $\vec{h}_{l}$ and $\vec{h}_{r}$, in the two electrodes of the junction, i.e., $\vec{J}\sim\vec{h}_{l}\times\vec{h}_{r}$. An important distinction between the FM and 2DEG with RSOI (DSOI) lead is that in a strict one-dimensional case RSOI (DSOI) cannot lead to equilibrium spin current in the junction since the two spin bands are not spin-polarized as in a FM lead where Zeeman spin splitting occurs.

cond-mat.other↗

arXiv2005

A Sample of IRAS Infrared-Selected Seyfert 1.5 Galaxies: Infrared-Color $α(60,25)$ Dominated Eigenvector 1

The well-documented E1 relationships are first extended to infrared color $α(60,25)$ and flux ratio [OIII]/H$β_{\rm{n}}$ by comparing emission line properties to continuum properties in infrared wavelength. Both direct correlations and a principle component analysis are used in a sample of 50 IRAS IR-selected Seyfert 1.5 galaxies. In addition to confirm the correlations of E1 in Boroson & Green (1992), our Eigenvector 1 turns out to be dominated by mid-infrared color $α$(60,25), and most strongly effected by RFe, [OIII]/H$β_{\rm{n}}$, and EW(H$β_{\rm{b}}$). Our analysis indicate that the objects with large E1 tend to co-existent with relatively young nuclear stellar populations, which implies that the E1 is related with nuclear starformation history. The IR-dominated Eigenvector 1 can be, therefore, inferred to be interpreted as ``age'' of AGN. In confirmation of Xu et al. (2003), it is clear that the extreme Seyfert galaxies with both large RFe and large [OIII]/H$β_{\rm{n}}$ are rare in our Universe.

astro-ph↗

arXiv2005

Theory of carrier dynamics and time resolved reflectivity in InMnAs/GaSb heterostructures

We present detailed theoretical calculations of two color, time-resolved pump-probe differential reflectivity measurements. The experiments modeled were performed on InMnAs/GaSb heterostructures and showed pronounced oscillations in the differential reflectivity as well as a time-dependent background signal. Previously, we showed that the oscillations resulted from generation of coherent acoustic phonon wavepackets in the epilayer and were not associated with the ferromagnetism. Now we take into account not only the oscillations, but also the background signal which arises from photoexcited carrier effects. The two color pump-probe reflectivity experiments are modeled using a Boltzmann equation formalism. We include photogeneration of hot carriers in the InMnAs quantum well by a pump laser and their subsequent cooling and relaxation by emission of confined LO phonons. Recombination of electron-hole pairs via the Schockley-Read carrier trapping mechanism is included in a simple relaxation time approximation. The time resolved differential reflectivity in the heterostructure is obtained by solving Maxwell's equations and compared with experiment. Phase space filling, carrier capture and trapping, band-gap renormalization and induced absorption are all shown to influence the spectra.

cond-mat.stat-mech↗

arXiv2005

Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation

Time-resolved magneto-optical Kerr spectroscopy of ferromagnetic InMnAs reveals two distinct {\em demagnetization} processes -- fast ($<1$ ps) and slow ($\sim$100 ps). Both components diminish with increasing temperature and are absent above the Curie temperature. The fast component rapidly grows with pump power and saturates at high fluences ($>10$ mJ/cm$^2$); the saturation value indicates a {\em complete quenching} of ferromagnetism on a sub-picosecond time scale. We attribute this fast dynamics to spin heating through $p$-$d$ exchange interaction between photo-carriers and Mn ions while the $\sim$100 ps component is interpreted as spin-lattice relaxation.

cond-mat.mes-hall↗

arXiv2005

Propagating Coherent Acoustic Phonon Wavepackets in InMnAs/GaSb

We observe pronounced oscillations in the differential reflectivity of a ferromagnetic InMnAs/GaSb heterostructure using two-color pump-probe spectroscopy. Although originally thought to be associated with the ferromagnetism, our studies show that the oscillations instead result from changes in the position and frequency-dependent dielectric function due to the generation of coherent acoustic phonons in the ferromagnetic InMnAs layer and their subsequent propagation into the GaSb. Our theory accurately predicts the experimentally measured oscillation period and decay time as a function of probe wavelength.

cond-mat.mes-hall↗

arXiv2005

Electrical Properties of Carbon Fiber Support Systems

Carbon fiber support structures have become common elements of detector designs for high energy physics experiments. Carbon fiber has many mechanical advantages but it is also characterized by high conductivity, particularly at high frequency, with associated design issues. This paper discusses the elements required for sound electrical performance of silicon detectors employing carbon fiber support elements. Tests on carbon fiber structures are presented indicating that carbon fiber must be regarded as a conductor for the frequency region of 10 to 100 MHz. The general principles of grounding configurations involving carbon fiber structures will be discussed. To illustrate the design requirements, measurements performed with a silicon detector on a carbon fiber support structure at small radius are presented. A grounding scheme employing copper-kapton mesh circuits is described and shown to provide adequate and robust detector performance.

hep-ex↗

arXiv2005

Critical Behavior in Light Nuclear Systems: Experimental Aspects

An extensive experimental survey of the features of the disassembly of a small quasi-projectile system with $A \sim$ 36, produced in the reactions of 47 MeV/nucleon $^{40}$Ar + $^{27}$Al, $^{48}$Ti and $^{58}$Ni, has been carried out. Nuclei in the excitation energy range of 1-9 MeV/u have been investigated employing a new method to reconstruct the quasi-projectile source. At an excitation energy $\sim$ 5.6 MeV/nucleon many observables indicate the presence of maximal fluctuations in the de-excitation processes. The fragment topological structure shows that the rank sorted fragments obey Zipf's law at the point of largest fluctuations providing another indication of a liquid gas phase transition. The caloric curve for this system shows a monotonic increase of temperature with excitation energy and no apparent plateau. The temperature at the point of maximal fluctuations is $8.3 \pm 0.5$ MeV. Taking this temperature as the critical temperature and employing the caloric curve information we have extracted the critical exponents $β$, $γ$ and $σ$ from the data. Their values are also consistent with the values of the universality class of the liquid gas phase transition. Taken together, this body of evidence strongly suggests a phase change in an equilibrated mesoscopic system at, or extremely close to, the critical point.

nucl-ex↗

arXiv2005

Variability of Optical \ion{Fe}{ii} Complex in Narrow-Line Seyfert 1 Galaxy NGC 4051

The variability of optical FeII blends in NGC 4051 is examined from spectra extracted from the AGN Watch program.In our analysis, the FeII complex are subtracted and measured with the following results. Firstly, the FeII variations were detected in NGC 4051 during a 3-year period. The identified FeII variations followed the variations in continuum closely. Secondly, the EW of FeII is reported to increase with the rising continuum flux, which is consistent with previous claims that there is no convincing Baldwin Effect in optical FeII. Thirdly, by comparing the variations of H$β$ and FeII, we find that RFe scales with continuum flux as $\rm{R_{Fe}\propto (5.0\pm0.8) \log(L/M)}$, which is significantly different from the theoretical expectations. Finally, in six selected Seyferts, four out of five Narrow-Line Seyfert 1 galaxies present positive correlation between RFe and the continuum flux. The negative correlations are identified in the remaindng two objects that have relatively broad profiles of H$β$ ($\rm{FWHM>1500 km\ s^{-1}}$).We argue that the difference of electron density of broad line clouds and/or variability behavior of incident high-energy radiation can explain the dichotomy in variability behavior of RFe.

astro-ph↗

arXiv2005

Variability of Broad and Blueshifted Component of [OIII]$λ$5007 in IZWI

Although the existence of asymmetrical profile of [OIII]$λ$5007 has been discovered for ages, its filiation and physics are poorly understood. Two new spectra of I ZWI taken on Nov 16, 2001 and on Dec 3, 2002 were compared with the spectra taken by BG92. Following results are obtained. 1)The certain variations of broad [OIII] during about 10 years separating the observations are identified. The inferred length scale of broad [OIII] emitting region ranges from 0.3pc to 3pc. By assuming a Keplerian motion in emitting region, the material emitting broad [OIII] is likely to be located at transient emission line region, between BLR and NLR. 2)We find a positive relation between the FeII emission and flux of H$β$(or continuum). On the other hand, the parameter RFe decreases with ionizing continuum marginally. 3)We detect a low ionized NLR in I ZWI, because of the low flux ratios $\rm{[OIII]_{n}/Hβ_{n}}$($\sim1.7$).

astro-ph↗

arXiv2005

An overdensity of galaxies at z=5.9 +/-0.2 in the Ultra Deep Field confirmed using the ACS grism

We present grism spectra taken with the Advanced Camera for Surveys to identify 29 red sources with (i'-z') > 0.9 in the Hubble Ultra Deep Field (HUDF). Of these 23 are found to be galaxies at redshifts between z=5.4 and 6.7, identified by the break at 1216 angstrom due to IGM absorption; two are late type dwarf stars with red colors; and four are galaxies with colors and spectral shape similar to dust reddened or old galaxies at redshifts z~1-2. This constitutes the largest uniform, flux-limited sample of spectroscopically confirmed galaxies at such faint fluxes z'<27.5. Many are also among the most distant spectroscopically confirmed galaxies (at redshifts up to z=6.7). We find a significant overdensity of galaxies at redshifts z=5.9 +/- 0.2. Nearly two thirds of the galaxies in our sample (15/23) belong to this peak. Taking into account the selection function and the redshift sensitivity of the survey, we get a conservative overdensity of at least a factor of two along the line-of-sight. The galaxies found in this redshift peak are also localized in the plane of the sky in a non-random manner, occupying about half of the ACS chip. Thus the volume overdensity is a factor of four. The star-formation rate derived from detected sources in this overdense region is sufficient to reionize the local IGM.

astro-ph↗

arXiv2005

Tracing the Evolution of Temperature in Near Fermi Energy Heavy Ion Collisions

The kinetic energy variation of emitted light clusters has been employed as a clock to explore the time evolution of the temperature for thermalizing composite systems produced in the reactions of 26A, 35A and 47A MeV $^{64}$Zn with $^{58}$Ni, $^{92}$Mo and $^{197}$Au. For each system investigated, the double isotope ratio temperature curve exhibits a high maximum apparent temperature, in the range of 10-25 MeV, at high ejectile velocity. These maximum values increase with increasing projectile energy and decrease with increasing target mass. The time at which the maximum in the temperature curve is reached ranges from 80 to 130 fm/c after contact. For each different target, the subsequent cooling curves for all three projectile energies are quite similar. Temperatures comparable to those of limiting temperature systematics are reached 30 to 40 fm/c after the times corresponding to the maxima, at a time when AMD-V transport model calculations predict entry into the final evaporative or fragmentation stage of de-excitation of the hot composite systems. Evidence for the establishment of thermal and chemical equilibrium is discussed.

nucl-ex↗

arXiv2004

A Ghoshal-like Test of Equilibration in Near-Fermi-Energy Heavy Ion Collisions

Calorimetric and coalescence techniques have been employed to probe equilibration for hot nuclei produced in heavy ion collisions of 35 to 55 MeV/u projectiles with medium mass targets. Entrance channel mass asymmetries and energies were selected in order that very hot composite nuclei of similar mass and excitation would remain after early stage pre-equilibrium particle emission. Inter-comparison of the properties and de-excitation patterns for these different systems provides evidence for the production of hot nuclei with decay patterns relatively independent of the specific entrance channel.

nucl-ex↗

arXiv2004

Towards the critical behavior for the light nuclei by NIMROD detector

The critical behavior for the light nuclei with A$\sim 36$ has been investigated experimentally by the NIMROD multi-detectors. The wide variety of observables indicate the critical point has been reached in the disassembly of hot nuclei at an excitation energy of 5.6$\pm$0.5 MeV/u.

nucl-ex↗

arXiv2004

Measurements of the Branching Fractions and Decay Distributions for KL->πμνγand KL->πeνγ

We present measurements of R_Kl3rad = Gamma(KL->π\ellνγ; Egcm > 10 MeV)/Gamma(KL->π\ellν), where ell = mu or e, and Egcm is the photon energy in the kaon rest frame. These measurements are based on KL decays collected in 1997 by the KTeV (E832) experiment at Fermilab. With samples of 1385 KL->πμνγand 14221 KL->π\eνγcandidates, we find R_Km3rad = (0.530 +- 0.019)% and R_Ke3rad = (4.942 +- 0.062)%. We also examine distributions of photon energy and lepton-photon angle.

hep-ex↗

arXiv2004

Experimental studies of light propagation and storage

We report on an experimental study of light pulse propagation and storage in a Rb atomic vapor for different pulse durations, magnetic fields, and atomic densities, and for two different isotopes. The results have been analyzed and compared with previous studies.

quant-ph↗