39,512 research outputs found
Measuring Dark Energy with Gamma-Ray Bursts and Other Cosmological Probes
It has been widely shown that the cosmological parameters and dark energy can
be constrained by using data from type-Ia supernovae (SNe Ia), the cosmic
microwave background (CMB) anisotropy, the baryon acoustic oscillation (BAO)
peak from Sloan Digital Sky Survey (SDSS), the X-ray gas mass fraction in
clusters, and the linear growth rate of perturbations at z=0.15 as obtained
from the 2dF Galaxy Redshift Survey. Recently, gamma-ray bursts (GRBs) have
also been argued to be promising standard candles for cosmography. In this
paper, we present constraints on the cosmological parameters and dark energy by
combining a recent GRB sample including 69 events with the other cosmological
probes. First, we find that for the LambdaCDM cosmology this combination makes
the constraints stringent and the best fit is close to the flat universe.
Second, we fit the flat Cardassian expansion model and find that this model is
consistent with the LambdaCDM cosmology. Third, we present constraints on
several two-parameter dark energy models and find that these models are also
consistent with the LambdaCDM cosmology. Finally, we reconstruct the dark
energy equation-of-state parameter w(z) and the deceleration parameter q(z). We
see that the acceleration could have started at a redshift from
z_T=0.40_{-0.08}^{+0.14} to z_T=0.65_{-0.05}^{+0.10}. This difference in the
transition redshift is due to different dark energy models that we adopt. The
most stringent constraint on w(z) lies in the redshift range z\sim 0.3-0.6.Comment: 28 pages, 13 figures, accepted for publication in ApJ. One reference
added, one minor change in the final paragraph of section
Reconsideration of Second Harmonic Generation from neat Air/Water Interface: Broken of Kleinman Symmetry from Dipolar Contribution
It has been generally accepted that there are significant quadrupolar and
bulk contributions to the second harmonic generation (SHG) reflected from the
neat air/water interface, as well as common liquid interfaces. Because there
has been no general methodology to determine the quadrupolar and bulk
contributions to the SHG signal from a liquid interface, this conclusion was
reached based on the following two experimental phenomena. Namely, the broken
of the macroscopic Kleinman symmetry, and the significant temperature
dependence of the SHG signal from the neat air/water interface. However,
because sum frequency generation vibrational spectroscopy (SFG-VS) measurement
of the neat air/water interface observed no apparent temperature dependence,
the temperature dependence in the SHG measurement has been reexamined and
proven to be an experimental artifact. Here we present a complete microscopic
analysis of the susceptibility tensors of the air/water interface, and show
that dipolar contribution alone can be used to address the issue of broken of
the macroscopic Kleinman symmetry at the neat air/water interface. Using this
analysis, the orientation of the water molecules at the interface can be
obtained, and it is consistent with the measurement from SFG-VS. Therefore, the
key rationales to conclude significantly quadrupolar and bulk contributions to
the SHG signal of the neat air/water interface can no longer be considered as
valid as before. This new understanding of the air/water interface can shed
light on our understanding of the nonlinear optical responses from other
molecular interfaces as well
Dynamics of Vortex Core Switching in Ferromagnetic Nanodisks
Dynamics of magnetic vortex core switching in nanometer-scale permalloy disk,
having a single vortex ground state, was investigated by micromagnetic
modeling. When an in-plane magnetic field pulse with an appropriate strength
and duration is applied to the vortex structure, additional two vortices, i.e.,
a circular- and an anti-vortex, are created near the original vortex core.
Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at
the annihilation point and propagated through the entire element; the relaxed
state for the system is the single vortex state with a switched vortex core.Comment: to appear in Appl. Phys. Let
Measurement of ultralow injection current to polymethyl-methacrylate film
2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Nodeless superconductivity in IrPtTe with strong spin-orbital coupling
The thermal conductivity of superconductor IrPtTe
( = 0.05) single crystal with strong spin-orbital coupling was measured down
to 50 mK. The residual linear term is negligible in zero magnetic
field. In low magnetic field, shows a slow field dependence. These
results demonstrate that the superconducting gap of IrPtTe is
nodeless, and the pairing symmetry is likely conventional s-wave, despite the
existence of strong spin-orbital coupling and a quantum critical point.Comment: 5 pages, 4 figure
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