6,041 research outputs found
Picosecond Internal Dynamics of Lysozyme as Affected by Thermal Unfolding in Nonaqueous Environment
AbstractA neutron-scattering investigation of the internal picosecond dynamics of lysozyme solvated in glycerol as a function of temperature in the range 200–410K has been undertaken. The inelastic contribution to the measured intensity is characterized by the presence of a bump generally known as “boson peak”, clearly distinguishable at low temperature. When the temperature is increased the quasielastic component of the spectrum becomes more and more intrusive and progressively overwhelms the vibrational bump. This happens especially for T>345K when the protein goes through an unfolding process, which leads to the complete denaturation. The quasielastic term is the superposition of two components whose intensities and linewidths have been studied as a function of temperature. The slower component describes motions with characteristic times of ∼4ps corresponding to reorientations of polypeptide side chains. Both the intensity and linewidth of this kind of relaxations show two distinct regimes with a crossover in the temperature range where the melting process occurs, thus suggesting the presence of a dynamical transition correlated to the protein unfolding. Conversely the faster component might be ascribed to the local dynamics of hydrogen atoms caged by the nearest neighbors with characteristic time of ∼0.3ps
Interface pinning and slow ordering kinetics on infinitely ramified fractal structures
We investigate the time dependent Ginzburg-Landau (TDGL) equation for a non
conserved order parameter on an infinitely ramified (deterministic) fractal
lattice employing two alternative methods: the auxiliary field approach and a
numerical method of integration of the equations of evolution. In the first
case the domain size evolves with time as , where is
the anomalous random walk exponent associated with the fractal and differs from
the normal value 2, which characterizes all Euclidean lattices. Such a power
law growth is identical to the one observed in the study of the spherical model
on the same lattice, but fails to describe the asymptotic behavior of the
numerical solutions of the TDGL equation for a scalar order parameter. In fact,
the simulations performed on a two dimensional Sierpinski Carpet indicate that,
after an initial stage dominated by a curvature reduction mechanism \`a la
Allen-Cahn, the system enters in a regime where the domain walls between
competing phases are pinned by lattice defects.
The lack of translational invariance determines a rough free energy
landscape, the existence of many metastable minima and the suppression of the
marginally stable modes, which in translationally invariant systems lead to
power law growth and self similar patterns. On fractal structures as the
temperature vanishes the evolution is frozen, since only thermally activated
processes can sustain the growth of pinned domains.Comment: 16 pages+14 figure
Voltage rectification effects in mesoscopic superconducting triangles: experiment and modelling
The interaction of externally applied currents with persistent currents
induced by magnetic field in a mesoscopic triangle is investigated. As a
consequence of the superposition of these currents, clear voltage rectification
effects are observed. We demonstrate that the amplitude of the rectified signal
strongly depends on the configurations of the current leads with the lowest
signal obtained when the contacts are aligned along a median of the triangle.
When the contacts are aligned off-centered compared to the geometrical center,
the voltage response shows oscillations as a function of the applied field,
whose sign can be controlled by shifting the contacts. These results are in
full agreement with theoretical predictions for an analogous system consisting
of a closed loop with a finite number of identical Josephson junctions.Comment: 5 pages, 4 figures, published in Phys. Rev.
Optical Spectroscopy of the IRAS 1-Jy Sample of Ultraluminous Infrared Galaxies
This paper discusses the optical spectroscopic properties of the IRAS 1-Jy
sample of ultraluminous infrared galaxies (ULIGs). One hundred and eight of the
118 1-Jy ULIGs have been observed at dlambda = 8.3 AA resolution over the
wavelength range ~4500 A -- 8900 A. These data are combined with large,
previously published sets of optical spectroscopic data of lower luminosity
infrared galaxies to look for systematic trends with infrared luminosity over
the luminosity range L_ir ~ 10^{10.5}-10^{13} L_sun. As found in previous
studies, the fraction of Seyfert galaxies among luminous infrared galaxies
increases abruptly above L_ir ~ 10^{12.3} L_sun --- about 50% of the galaxies
with L_ir > 10^{12.3} L_sun present Seyfert characteristics. Many of the
optical and infrared spectroscopic properties of the Seyfert galaxies are
consistent with the presence of a genuine active galactic nucleus (AGN). About
30% of these galaxies are Seyfert 1s with broad-line regions similar to those
of optical quasars. The percentage of Seyfert 1 ULIGs increases with infrared
luminosity, contrary to the predictions of the standard unification model for
Seyfert galaxies. Comparisons of the broad-line luminosities of optical and
obscured Seyfert 1 ULIGs with those of optically selected quasars of comparable
bolometric luminosity suggest that the dominant energy source in most of these
ULIGs is the same as in optical quasars, namely mass accretion onto a
supermassive black hole, rather than a starburst. These results are consistent
with recently published ISO, ASCA, and VLBI data. (abridged)Comment: Text and 23 figures (45 pages), Tables 1 - 6 (16 pages
The VMC survey - VIII : First results for anomalous Cepheids
The VISTA near-infrared YJKs survey of the Magellanic Clouds System (VMC, PI M.-R. L. Cioni) is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted in the system formed by the two Magellanic Clouds and the Bridge connecting them. In this paper, we present for the first time Ks-band light curves for anomalous Cepheid (AC) variables. In particular, we have analysed a sample of 48 Large Magellanic Cloud ACs, for which identification and optical magnitudes were obtained from the OGLE III and IV catalogues. The VMC Ks-band light curves for ACs are well sampled, with the number of epochs ranging from 8 to 16, and allowing us to obtain very precise mean Ks magnitudes with errors on average of the order of 0.01 mag. The values were used to build the first period-luminosity and period-Wesenheit relations in the near-infrared for fundamental mode and first overtone ACs. At the same time we exploited the optical (V, I) OGLE data to build accurate period-luminosity, period-luminosity-colour and period-Wesenheit relations both for fundamental mode and first overtone ACs. For the first time, these relations were derived from a sample of pulsators which uniformly cover the whole AC instability strip. The application of the optical period-Wesenheit relation to a sample of dwarf galaxies hosting a significant population of ACs revealed that this relation is a valuable tool for deriving distances within the Local Group. Due to its lower dispersion, we expect the Ks period-Wesenheit relations first derived in this paper to represent a valuable tool for measuring accurate distances to galaxies hosting ACs when more data in near-infrared filters become available.Peer reviewe
The host galaxies of low luminosity quasars at high redshift
We present VLT/ISAAC near-infrared imaging of the host galaxies of 15 low
luminosity quasars at 1 < z < 2. This work complements our studies to trace the
cosmological evolution of the host galaxies of high luminosity quasars. The
radio-loud (RLQ) and radio-quiet (RQQ) quasars have similar distribution of
redshift and luminosity, and together the high and low luminosity quasars cover
a large range of the quasar luminosity function. Both RLQ and RQQ hosts
resemble massive inactive ellipticals undergoing passive evolution. However,
RLQ hosts are systematically more luminous than RQQ hosts, as also found for
the high luminosity quasars. The difference in the host luminosity remains the
same from z = 2 to z = 0. For the entire set of quasars, we find a correlation
between the nuclear and the host luminosities, albeit with a large scatter. The
correlation is less apparent for the RQQs than for the RLQs.Comment: 6 pages, 3 figures, to appear in "QSO Hosts: Evolution and
Environment", P.D. Barthel, D.B. Sanders, eds., August 2005, Leiden
University, New Astr. Re
ISO-SWS spectroscopy of NGC 1068
We present ISO-SWS spectroscopy of NGC 1068 for the wavelength range 2.4 to
45um, detecting a total of 36 emission lines. Most of the observed transitions
are fine structure and recombination lines originating in the narrow line
region. We compare the line profiles of optical lines and reddening-insensitive
infrared lines to constrain the dynamical structure and extinction properties
of the NLR. The considerable differences found are most likely explained by two
effects. (1) The spatial structure of the NLR is a combination of a highly
ionized outflow cone and lower excitation extended emission. (2) Parts of the
NLR, mainly in the receding part at velocities above systemic, are subject to
extinction that is significantly suppressing optical emission. Line asymmetries
and net blueshifts remain, however, even for infrared fine structure lines
suffering very little obscuration. This may be either due to an intrinsic
asymmetry of the NLR, or due to a very high column density obscuring component
which is hiding part of the NLR even from infrared view. Mid-infrared emission
of molecular hydrogen in NGC 1068 arises in a dense molecular medium at
temperatures of a few hundred Kelvin that is most likely closely related to the
warm and dense components seen in the near-infrared H2 transitions, and in
millimeter wave tracers of molecular gas. Any emission of the putative pc-scale
molecular torus is likely overwhelmed by this larger scale emission.Comment: aastex (V4), 9 eps figures. Accepted by Ap
ALMA constraints on the faint millimetre source number counts and their contribution to the cosmic infrared background
We have analysed 18 ALMA continuum maps in Bands 6 and 7, with rms down to
7.8Jy, to derive differential number counts down to 60Jy and
100Jy at 1.3 mm and 1.1 mm, respectively. The area
covered by the combined fields is at 1.1mm and at 1.3mm. We improved the source extraction method by
requiring that the dimension of the detected sources be consistent with the
beam size. This method enabled us to remove spurious detections that have
plagued the purity of the catalogues in previous studies. We detected 50 faint
sources with S/N3.5 down to 60Jy, hence improving the statistics by a
factor of four relative to previous studies. The inferred differential number
counts are at a 1.1 mm flux Jy, and at a 1.3
mm flux Jy. At the faintest flux limits,
i.e. 30Jy and 40Jy, we obtain upper limits on the differential number
counts of and , respectively. Our results provide a new
lower limit to CIB intensity of 17.2 at 1.1mm and of
12.9 at 1.3mm. Moreover, the flattening of the integrated
number counts at faint fluxes strongly suggests that we are probably close to
the CIB intensity. Our data imply that galaxies with SFR
certainly contribute less than 50% to the CIB while more than 50% of the CIB
must be produced by galaxies with . The differential
number counts are in nice agreement with recent semi-analytical models of
galaxy formation even as low as our faint fluxes. Consequently, this supports
the galaxy evolutionary scenarios and assumptions made in these models.Comment: 11 pages, 9 figures, A&A accepte
Phase-space approach to dynamical density functional theory
We consider a system of interacting particles subjected to Langevin inertial
dynamics and derive the governing time-dependent equation for the one-body
density. We show that, after suitable truncations of the
Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, and a multiple time scale
analysis, we obtain a self-consistent equation involving only the one-body
density. This study extends to arbitrary dimensions previous work on a
one-dimensional fluid and highlights the subtelties of kinetic theory in the
derivation of dynamical density functional theory
Coarsening and Pinning in the Self-consistent Solution of Polymer Blends Phase-Separation Kinetics
We study analytically a continuum model for phase-separation in binary
polymer blends based on the Flory-Huggins-De Gennes free energy, by means of
the self-consistent large- limit approach. The model is solved for values of
the parameters corresponding to the weak and strong segregation limits. For
deep quenches we identify a complex structure of intermediate regimes and
crossovers characterized by the existence of a time domain such that phase
separation is pinned, followed by a preasymptotic regime which in the scalar
case corresponds to surface diffusion. The duration of the pinning is
analytically computed and diverges in the strong segregation limit. Eventually
a late stage dynamics sets in, described by scaling laws and exponents
analogous to those of the corresponding small molecule systems.Comment: 16 pages, 5 figures. Submitted to Phys. Rev.
- …