4,926 research outputs found
On the theory of electric dc-conductivity : linear and non-linear microscopic evolution and macroscopic behaviour
We consider the Schrodinger time evolution of charged particles subject to a
static substrate potential and to a homogeneous, macroscopic electric field (a
magnetic field may also be present). We investigate the microscopic velocities
and the resulting macroscopic current. We show that the microscopic velocities
are in general non-linear with respect to the electric field. One kind of
non-linearity arises from the highly non-linear adiabatic evolution and (or)
from an admixture of parts of it in so-called intermediate states, and the
other kind from non-quadratic transition rates between adiabatic states. The
resulting macroscopic dc-current may or may not be linear in the field. Three
cases can be distinguished : (a) The microscopic non-linearities can be
neglected. This is assumed to be the case in linear response theory (Kubo
formalism, ...). We give arguments which make it plausible that often such an
assumption is indeed justified, in particular for the current parallel to the
field. (b) The microscopic non-linearitites lead to macroscopic
non-linearities. An example is the onset of dissipation by increasing the
electric field in the breakdown of the quantum Hall effect. (c) The macroscopic
current is linear although the microscopic non-linearities constitute an
essential part of it and cannot be neglected. We show that the Hall current of
a quantized Hall plateau belongs to this case. This illustrates that
macroscopic linearity does not necessarily result from microscopic linearity.
In the second and third cases linear response theory is inadequate. We
elucidate also some other problems related to linear response theory.Comment: 24 pages, 6 figures, some typing errors have been corrected. Remark :
in eq. (1) of the printed article an obvious typing error remain
REINVESTIGATION OF THE REACTION OF [ETA-5-C5ME5(CO)2MO]2-(MO=MO) WITH PHOSPHORUS LIGANDS - FORMATION OF (C5ME5)2MO2(CO)3PR3-(MO=MO=) (PR3=P(OME)3 - PHP(OCH2CH2)2NH) AND C5ME5(CO)2[P(OME)3]ME, AND THE CRYSTAL-STRUCTURE OF (C5ME5)2MO2(CO)3[PHP(OCH2CH2)2NHI
SALT: a Spectral Adaptive Light curve Template for Type Ia Supernovae
We present a new method to parameterize Type Ia Supernovae (SN Ia)
multi-color light curves. The method was developed in order to analyze the
large number of SN Ia multi-color light curves measured in current
high-redshift projects. The technique is based on empirically modeling SN Ia
luminosity variations as a function of phase, wavelength, a shape parameter,
and a color parameter. The model is trained with a sample of well measured
nearby SN Ia and then tested with an independent set of supernovae by building
an optimal luminosity distance estimator combining the supernova rest-frame
luminosity, shape parameter and color reconstructed with the model. The
distances we measure using B- and V-band data show a dispersion around the
Hubble line comparable or lower than obtained with other methods. With this
model, we are able to measure distances using U- and B-band data with a
dispersion around the Hubble line of 0.16 +- 0.05.Comment: Accepted in A&A, June 23, 2005 (printer friendly replacement version,
includes language corrections
Dark Energy Accretion onto a Black Hole in an Expanding Universe
By using the solution describing a black hole embedded in the FLRW universe,
we obtain the evolving equation of the black hole mass expressed in terms of
the cosmological parameters. The evolving equation indicates that in the
phantom dark energy universe the black hole mass becomes zero before the Big
Rip is reached.Comment: 7 pages, no figures, errors is correcte
Fractal Bubble Cosmology: A concordant cosmological model?
The Fractal Bubble model has been proposed as a viable cosmology that does
not require dark energy to account for cosmic acceleration, but rather
attributes its observational signature to the formation of structure. In this
paper it is demonstrated that, in contrast to previous findings, this model is
not a good fit to cosmological supernovae data; there is significant tension in
the best fit parameters obtained from different samples, whereas LCDM is able
to fit all datasets consistently. Furthermore, the concordance between galaxy
clustering scales and data from the cosmic microwave background is not achieved
with the most recent supernova compilations. The validity of the FB formalism
as a sound cosmological model is further challenged as it is shown that
previous studies of this model achieve concordance by requiring a value for the
present day Hubble constant that is derived from supernovae data containing an
arbitrary distance normalisation.Comment: 6 pages, 3 figures, revised version published in MNRAS letter
Using the Topology of Large Scale Structure to constrain Dark Energy
The use of standard rulers, such as the scale of the Baryonic Acoustic
oscillations (BAO), has become one of the more powerful techniques employed in
cosmology to probe the entity driving the accelerating expansion of the
Universe. In this paper, the topology of large scale structure (LSS) is used as
one such standard ruler to study this mysterious `dark energy'. By following
the redshift evolution of the clustering of luminous red galaxies (LRGs) as
measured by their 3D topology (counting structures in the cosmic web), we can
chart the expansion rate and extract information about the equation of state of
dark energy. Using the technique first introduced in (Park & Kim, 2009), we
evaluate the constraints that can be achieved using 3D topology measurements
from next-generation LSS surveys such as the Baryonic Oscillation Spectroscopic
Survey (BOSS). In conjunction with the information that will be available from
the Planck satellite, we find a single topology measurement on 3 different
scales is capable of constraining a single dark energy parameter to within 5%
and 10% when dynamics are permitted. This offers an alternative use of the data
available from redshift surveys and serves as a cross-check for BAO studies.Comment: 8 pages, 5 figures, 2 tables, Submitted to MNRAS, updated
acknowledgement
Cosmological parameter extraction and biases from type Ia supernova magnitude evolution
We study different one-parametric models of type Ia Supernova magnitude
evolution on cosmic time scales. Constraints on cosmological and Supernova
evolution parameters are obtained by combined fits on the actual data coming
from Supernovae, the cosmic microwave background, and baryonic acoustic
oscillations. We find that data prefer a magnitude evolution such that
high-redshift Supernova are brighter than would be expected in a standard
cosmos with a dark energy component. Data however are consistent with
non-evolving magnitudes at the one-sigma level, except special cases.
We simulate a future data scenario where SN magnitude evolution is allowed
for, and neglect the possibility of such an evolution in the fit. We find the
fiducial models for which the wrong model assumption of non-evolving SN
magnitude is not detectable, and for which at the same time biases on the
fitted cosmological parameters are introduced. Of the cosmological parameters
the overall mass density has the strongest chances to be biased due to the
wrong model assumption. Whereas early-epoch models with a magnitude offset ~z^2
show up to be not too dangerous when neglected in the fitting procedure, late
epoch models with magnitude offset ~sqrt(z) have high chances to bias the fit
results.Comment: 12 pages, 5 figures, 3 tables. Accepted for publication by A&A.
Revised version: Corrected Typos, reference added to section
Double-valuedness of the electron wave function and rotational zero-point motion of electrons in rings
I propose that the phase of an electron's wave function changes by when
the electron goes around a loop maintaining phase coherence. Equivalently, that
the minimum orbital angular momentum of an electron in a ring is
rather than zero as generally assumed, hence that the electron in a ring has
azimuthal zero point motion. This proposal provides a physical explanation for
the origin of electronic `quantum pressure', it implies that a spin current
exists in the ground state of aromatic ring molecules, and it suggests an
explanation for the ubiquitousness of persistent currents observed in
mesoscopic rings
Measuring Ejecta Velocity Improves Type Ia Supernova Distances
We use a sample of 121 spectroscopically normal Type Ia supernovae (SNe Ia)
to show that their intrinsic color is correlated with their ejecta velocity, as
measured from the blueshift of the Si II 6355 feature near maximum brightness,
v_Si. The SN Ia sample was originally used by Wang et al. (2009) to show that
the relationship between color excess and peak magnitude, which in the absence
of intrinsic color differences describes a reddening law, was different for two
subsamples split by v_Si (defined as "Normal" and "High-Velocity"). We verify
this result, but find that the two subsamples have the same reddening law when
extremely reddened events (E(B-V) > 0.35 mag) are excluded. We also show that
(1) the High-Velocity subsample is offset by ~0.06 mag to the red from the
Normal subsample in the (B_max - V_max) - M_V plane, (2) the B_max - V_max
cumulative distribution functions of the two subsamples have nearly identical
shapes, but the High-Velocity subsample is offset by ~0.07 mag to the red in
B_max - V_max, and (3) the bluest High-Velocity SNe Ia are ~0.10 mag redder
than the bluest Normal SNe Ia. Together, this evidence indicates a difference
in intrinsic color for the subsamples. Accounting for this intrinsic color
difference reduces the scatter in Hubble residuals from 0.190 mag to 0.130 mag
for SNe Ia with A_V < 0.7 mag. The scatter can be further reduced to 0.109 mag
by exclusively using SNe Ia from the Normal subsample. Additionally, this
result can at least partially explain the anomalously low values of R_V found
in large SN Ia samples. We explain the correlation between ejecta velocity and
color as increased line blanketing in the High-Velocity SNe Ia, causing them to
become redder. We discuss some implications of this result, and stress the
importance of spectroscopy for future SN Ia cosmology surveys, with particular
focus on the design of WFIRST.Comment: 9 pages, 8 figures, submitted to Ap
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