3,793 research outputs found
How Dry Are Red Mergers?
The focus of current research in galaxy evolution has increasingly turned to
understanding the effect that mergers have on the evolution of systems on the
red sequence. For those interactions purported to occur dissipationlessly (so
called "dry mergers"), it would appear that the role of gas is minimal.
However, if these mergers are not completely dry, then even low levels of gas
may be detectable. The purpose of our study is to test whether early type
galaxies with HI in or around them, or "wet" ellipticals, would have been
selected as dry mergers by the criteria in van Dokkum (2005, AJ, 130, 2647). To
that end, we examine a sample of 20 early types from the HI Rogues Gallery with
neutral hydrogen in their immediate environs. Of these, the 15 brightest and
reddest galaxies match the optical dry merger criteria, but in each case, the
presence of HI means that they are not truly dry.Comment: 8 pages plus 1 table and 5 figures; accepted for publication in A
Anomalous optical absorption in overdoped cuprates near the charge-ordering instability
We propose an interpretation for the hump observed in the optical
conductivity at or below a few hundreds of cm, in overdoped cuprates
like the electron-doped Nd_{2-x}Ce_xCuO_{4-y} at x\gtrsim 0.15 and the
hole-doped Bi_2Sr_2CuO_6 and La_{2-x}Sr_xCuO_4. This interpretation is based on
the direct excitation of charge collective modes, which become nearly critical
in the proximity to a charge-ordering instability. The nearly critical
character of these excitations entails a peculiar temperature dependence and a
pseudo-scaling form of the lineshapes, which are in agreement with the
experimental data.Comment: 5 pages, 3 figure
Structures in magnetohydrodynamic turbulence: detection and scaling
We present a systematic analysis of statistical properties of turbulent
current and vorticity structures at a given time using cluster analysis. The
data stems from numerical simulations of decaying three-dimensional (3D)
magnetohydrodynamic turbulence in the absence of an imposed uniform magnetic
field; the magnetic Prandtl number is taken equal to unity, and we use a
periodic box with grids of up to 1536^3 points, and with Taylor Reynolds
numbers up to 1100. The initial conditions are either an X-point configuration
embedded in 3D, the so-called Orszag-Tang vortex, or an
Arn'old-Beltrami-Childress configuration with a fully helical velocity and
magnetic field. In each case two snapshots are analyzed, separated by one
turn-over time, starting just after the peak of dissipation. We show that the
algorithm is able to select a large number of structures (in excess of 8,000)
for each snapshot and that the statistical properties of these clusters are
remarkably similar for the two snapshots as well as for the two flows under
study in terms of scaling laws for the cluster characteristics, with the
structures in the vorticity and in the current behaving in the same way. We
also study the effect of Reynolds number on cluster statistics, and we finally
analyze the properties of these clusters in terms of their velocity-magnetic
field correlation. Self-organized criticality features have been identified in
the dissipative range of scales. A different scaling arises in the inertial
range, which cannot be identified for the moment with a known self-organized
criticality class consistent with MHD. We suggest that this range can be
governed by turbulence dynamics as opposed to criticality, and propose an
interpretation of intermittency in terms of propagation of local instabilities.Comment: 17 pages, 9 figures, 5 table
Understanding studentsâ motivation towards proactive career behaviours through goal-setting theory and the job demandsâresources model
The graduate labour market is highly competitive but little is known about why students vary in their development of employability. This study contributes to the literature by applying goal-setting theory and the job demandsâresources model to investigate how motivational processes influence studentsâ proactive career behaviours. We tested four hypotheses using structural equation modelling and moderation/mediation analysis using a nested model approach; 432 undergraduates from 21 UK universities participated in this cross-sectional study. The results showed that students higher in mastery approach had greater perceived employability mediated by two proactive career behaviours (skill development and network building). Studentsâ career goal commitment was associated with all four proactive career behaviours (career planning, skill development, career consultation and network building). Studentsâ academic and employment workloads did not negatively impact their proactive career behaviours. University tutors and career services should therefore encourage students to set challenging career goals that reflect mastery approach
Sensory imagery in craving: From cognitive psychology to new treatments for addiction
Sensory imagery is a powerful tool for inducing craving because it is a key component of the cognitive system that underpins human motivation. The role of sensory imagery in motivation is explained by Elaborated Intrusion (EI) theory. Imagery plays an important role in motivation because it conveys the emotional qualities of the desired event, mimicking anticipated pleasure or relief, and continual elaboration of the imagery ensures that the target stays in mind. We argue that craving is a conscious state, intervening between unconscious triggers and consumption, and summarise evidence that interfering with sensory imagery can weaken cravings. We argue that treatments for addiction can be enhanced by the application of EI theory to maintain motivation, and assist in the management of craving in high-risk situations
Type I D-branes in an H-flux and twisted KO-theory
Witten has argued that charges of Type I D-branes in the presence of an
H-flux, take values in twisted KO-theory. We begin with the study of real
bundle gerbes and their holonomy. We then introduce the notion of real bundle
gerbe KO-theory which we establish is a geometric realization of twisted
KO-theory. We examine the relation with twisted K-theory, the Chern character
and provide some examples. We conclude with some open problems.Comment: 23 pages, Latex2e, 2 new references adde
Lenticular galaxies with UV-rings
By using the public UV imaging data obtained by the GALEX (Galaxy Ultraviolet
Explorer) for nearby galaxies, we have compiled a list of lenticular galaxies
possessing ultraviolet rings - starforming regions tightly confined to
particular radial distances from galactic centers. We have studied large-scale
structure of these galaxies in the optical bands by using the data of the SDSS
(Sloan Digital Sky Survey): we have decomposed the galactic images into
large-scale disks and bulges, have measured the ring optical colours from the
residual images after subtracting model disks and bulges, and have compared the
sizes of the rings in the optical light and in the UV-band. The probable origin
of the outer starforming ring appearances in unbarred galaxies demonstrating
otherwise the regular structure and homogeneously old stellar population beyond
the rings is discussed.Comment: 9 pages plus one big colour figure in the Appendix; the slightly
expanded version of the paper accepted to Astronomy Letter
On-chain electrodynamics of metallic (TMTSF)_2 X salts: Observation of Tomonaga-Luttinger liquid response
We have measured the electrodynamic response in the metallic state of three
highly anisotropic conductors, (TMTSF)_2 X, where X=PF_6, AsF_6, or ClO_4, and
TMTSF is the organic molecule tetramethyltetraselenofulvalene. In all three
cases we find dramatic deviations from a simple Drude response. The optical
conductivity has two features: a narrow mode at zero frequency, with a small
spectral weight, and a mode centered around 200 cm^{-1}, with nearly all of the
spectral weight expected for the relevant number of carriers and single
particle bandmass. We argue that these features are characteristic of a nearly
one-dimensional half- or quarter-filled band with Coulomb correlations, and
evaluate the finite energy mode in terms of a one-dimensional Mott insulator.
At high frequencies (\hbar\omega > t_\perp, the transfer integral perpendicular
to the chains), the frequency dependence of the optical conductivity
\sigma_1(\omega) is in agreement with calculations based on an interacting
Tomonaga-Luttinger liquid, and is different from what is expected for an
uncorrelated one-dimensional semiconductor. The zero frequency mode shows
deviations from a simple Drude response, and can be adequately described with a
frequency dependent mass and relaxation rate.Comment: 12 pages, 7 figures, RevTeX; minor corrections to text and
references; To be published in Phys. Rev. B, 15 July 199
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