11,416 research outputs found
Fermi surface renormalization in Hubbard ladders
We derive the one-loop renormalization equations for the shift in the
Fermi-wavevectors for one-dimensional interacting models with four Fermi-points
(two left and two right movers) and two Fermi velocities v_1 and v_2. We find
the shift to be proportional to (v_1-v_2)U^2, where U is the Hubbard-U. Our
results apply to the Hubbard ladder and to the t_1-t_2 Hubbard model. The
Fermi-sea with fewer particles tends to empty. The stability of a saddle point
due to shifts of the Fermi-energy and the shift of the Fermi-wavevector at the
Mott-Hubbard transition are discussed.Comment: 5 pages, 4 Postscript figure
Recommended from our members
Seasonal cycle of precipitation variability in South America on intraseasonal timescales
The seasonal cycle of the intraseasonal (IS) variability of precipitation in South America is described through the analysis of bandpass filtered outgoing longwave radiation (OLR) anomalies. The analysis is discriminated between short (10--30 days) and long (30--90 days) intraseasonal timescales. The seasonal cycle of the 30--90-day IS variability can be well described by the activity of first leading pattern (EOF1) computed separately for the wet season (October--April) and the dry season (May--September). In agreement with previous works, the EOF1 spatial distribution during the wet season is that of a dipole with centers of actions in the South Atlantic Convergence Zone (SACZ) and southeastern South America (SESA), while during the dry season, only the last center is discernible. In both seasons, the pattern is highly influenced by the activity of the Madden--Julian Oscillation (MJO). Moreover, EOF1 is related with a tropical zonal-wavenumber-1 structure superposed with coherent wave trains extended along the South Pacific during the wet season, while during the dry season the wavenumber-1 structure is not observed. The 10--30-day IS variability of OLR in South America can be well represented by the activity of the EOF1 computed through considering all seasons together, a dipole but with the stronger center located over SESA. While the convection activity at the tropical band does not seem to influence its activity, there are evidences that the atmospheric variability at subtropical-extratropical regions might have a role. Subpolar wavetrains are observed in the Pacific throughout the year and less intense during DJF, while a path of wave energy dispersion along a subtropical wavetrain also characterizes the other seasons. Further work is needed to identify the sources of the 10--30-day-IS variability in South America
Early Science with the Large Millimeter Telescope: an energy-driven wind revealed by massive molecular and fast X-ray outflows in the Seyfert Galaxy IRAS 17020+4544
We report on the coexistence of powerful gas outflows observed in millimeter
and X-ray data of the Radio-Loud Narrow Line Seyfert 1 Galaxy IRAS 17020+4544.
Thanks to the large collecting power of the Large Millimeter Telescope, a
prominent line arising from the 12CO(1-0) transition was revealed in recent
observations of this source. The complex profile is composed by a narrow
double-peak line and a broad wing. While the double-peak structure may be
arising in a disk of molecular material, the broad wing is interpreted as the
signature of a massive outflow of molecular gas with an approximate bulk
velocity of -660 km/s. This molecular wind is likely associated to a
multi-component X-ray Ultra-Fast Outflow with velocities reaching up to ~0.1c
and column densities in the range 10^{21-23.9} cm^-2 that was reported in the
source prior to the LMT observations. The momentum load estimated in the two
gas phases indicates that within the observational uncertainties the outflow is
consistent with being propagating through the galaxy and sweeping up the gas
while conserving its energy. This scenario, which has been often postulated as
a viable mechanism of how AGN feedback takes place, has so far been observed
only in ULIRGs sources. IRAS 17020+4544 with bolometric and infrared luminosity
respectively of 5X10^{44} erg/s and 1.05X10^{11} L_sun appears to be an example
of AGN feedback in a NLSy1 Galaxy (a low power AGN). New proprietary
multi-wavelength data recently obtained on this source will allow us to
corroborate the proposed hypothesis.Comment: Accepted for publication on ApJ Letters, 9 pages, 4 figure
Magnetic order and disorder in nanomagnets probed by superconducting vortices
We have studied two nanomagnet systems with strong (Co/Pd multilayers) and
weak (NdCo alloy films) stray magnetic fields by probing the out-of-plane
magnetic states with superconducting vortices. The hybrid samples are made of
array of nanomagnets embedded in superconducting Nb thin films. The vortex
motion detects relevant magnetic state features, since superconducting vortices
are able to discriminate between different magnetic stray field strengths and
directions. The usual matching effect between the superconducting vortex
lattice and the periodic pinning array can be quenched by means of disorder
magnetic potentials with strong stray fields at random. Ordered stray fields
retrieve the matching effect and yield asymmetry and shift in the vortex
dissipation signal. Furthermore vortices can discriminate the sizes of the
nanomagnet magnetic domains, detecting magnetic domain sizes as small as 70 nm.
In addition, we observe that the vortex cores play the crucial role instead of
the supercurrents around the vortex.Comment: 22 pages, 8 figure
Biowaiver monographs for immediate release solid oral dosage forms: Aciclovir
Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing (biowaiver) for the approval of immediate release (IR) solid oral dosage forms containing aciclovir are reviewed. Aciclovir therapeutic use and therapeutic index, pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability (BA) studies were also taken into consideration in order to ascertain whether a biowaiver can be recommended. According to the Biopharmaceutics Classification System (BCS) and considering tablet strengths up to 400 mg, aciclovir would be BCS Class III. However, in some countries also 800 mg tablets are available which fall just within BCS Class IV. Aciclovir seems not to be critical with respect to a risk for bio in equivalence, as no examples of bio in equivalence have been identified. It has a wide therapeutic index and is not used for critical indications. Hence, if: (a) the test product contains only excipients present in aciclovir solid oral IR drug products approved in ICH or associated countries, for instance as presented in this article; and (b) the comparator and the test product both are very rapidly dissolving , a biowaiver for IR aciclovir solid oral drug products is considered justified for all tablet strengths. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:5061–5073, 2008Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/61316/1/21392_ftp.pd
Statistics of Q-Oscillators, Quons and Relation to Fractional Satistics
The statistics of -oscillators, quons and to some extent, of anyons are
studied and the basic differences among these objects are pointed out. In
particular, the statistical distributions for different bosonic and fermionic
-oscillators are found for their corresponding Fock space representations in
the case when the hamiltonian is identified with the number operator. In this
case and for nonrelativistic particles, the single-particle temperature Green
function is defined with -deformed periodicity conditions. The equations of
state for nonrelativistic and ultrarelativistic bosonic -gases in an
arbitrary space dimension are found near Bose statistics, as well as the one
for an anyonic gas near Bose and Fermi statistics. The first corrections to the
second virial coefficients are also evaluated. The phenomenon of Bose-Einstein
condensation in the -deformed gases is also discussed.Comment: 21 pages, Latex, HU-TFT-93-2
GIARPS: commissioning and first scientific results
GIARPS (GIAno \& haRPS) is a project devoted to have on the same focal
station of the Telescopio Nazionale Galileo (TNG) both high resolution
spectrographs, HARPS-N (VIS) and GIANO-B (NIR), working simultaneously. This
could be considered the first and unique worldwide instrument providing
cross-dispersed echelle spectroscopy at a resolution of 50,000 in the NIR range
and 115,000 in the VIS and over in a wide spectral range (m)
in a single exposure. The science case is very broad, given the versatility of
such an instrument and its large wavelength range. A number of outstanding
science cases encompassing mainly extra-solar planet science starting from
rocky planets search and hot Jupiters to atmosphere characterization can be
considered. Furthermore both instruments can measure high precision radial
velocities by means the simultaneous thorium technique (HARPS-N) and absorbing
cell technique (GIANO-B) in a single exposure. Other science cases are also
possible. GIARPS, as a brand new observing mode of the TNG started after the
moving of GIANO-A (fiber fed spectrograph) from Nasmyth-A to Nasmyth-B where it
was re-born as GIANO-B (no more fiber feed spectrograph). The official
Commissioning finished on March 2017 and then it was offered to the community.
Despite the work is not finished yet. In this paper we describe the preliminary
scientific results obtained with GIANO-B and GIARPS observing mode with data
taken during commissioning and first open time observations.Comment: 10 pages, 11 figures, Telescopes and Astronomical instrumentation,
SPIE Conf. 201
- …