459 research outputs found
Ehrenfest relations at the glass transition: solution to an old paradox
In order to find out whether there exists a thermodynamic description of the
glass phase, the Ehrenfest relations along the glass transition line are
reconsidered. It is explained that the one involving the compressibility is
always satisfied, and that the one involving the specific heat is principally
incorrect.
Thermodynamical relations are presented for non-ergodic systems with a
one-level tree in phase space. They are derived for a spin glass model, checked
for other models, and expected to apply, e.g., to glass forming liquids. The
second Ehrenfest relation gets a contribution from the configurational entropy.Comment: 4 pages revtex, to appear in Phys. Rev. Let
Observation of Nonspreading Wave Packets in an Imaginary Potential
We propose and experimentally demonstrate a method to prepare a nonspreading
atomic wave packet. Our technique relies on a spatially modulated absorption
constantly chiseling away from an initially broad de Broglie wave. The
resulting contraction is balanced by dispersion due to Heisenberg's uncertainty
principle. This quantum evolution results in the formation of a nonspreading
wave packet of Gaussian form with a spatially quadratic phase. Experimentally,
we confirm these predictions by observing the evolution of the momentum
distribution. Moreover, by employing interferometric techniques, we measure the
predicted quadratic phase across the wave packet. Nonspreading wave packets of
this kind also exist in two space dimensions and we can control their amplitude
and phase using optical elements.Comment: 4 figure
Ellipsoidal primary of the RS CVn binary zeta And: Investigation using high-resolution spectroscopy and optical interferometry
We have obtained high-resolution spectroscopy, optical interferometry, and
long-term broad band photometry of the ellipsoidal primary of the RS CVn-type
binary system zeta And. Based on the optical interferometry the apparent limb
darkened diameter of zeta And is 2.55 +/- 0.09 mas using a uniform disk fit.
The Hipparcos distance and the limb-darkened diameter obtained with a uniform
disk fit give stellar radius of 15.9 +/- 0.8 Rsolar, and combined with
bolometric luminosity, it implies an effective temperature of 4665 +/- 140 K.
The temperature maps obtained from high resolution spectra using Doppler
imaging show a strong belt of equatorial spots and hints of a cool polar cap.
The equatorial spots show a concentration around the phase 0.75. This spot
configuration is reminiscent of the one seen in the earlier published
temperature maps of zeta And. Investigation of the Halpha line reveals both
prominences and cool clouds in the chromosphere. Long-term photometry spanning
12 years shows hints of a spot activity cycle, which is also implied by the
Doppler images, but the cycle length cannot be reliably determined from the
current data.Comment: 9 pages, 9 figures, accepted for A&
“SPLIT” Pancreaticojejunostomy in the Surgical Treatment of Chronic Pancreatitis
“Split” pancreaticojejunostomy is a procedure consisting of vertical transection of the pancreas
and anastomosis of both sides of the cut pancreatic duct with an interposed, Roux-en-Y jejunal
loop. In this paper we report the long term results of this procedure in the treatment of eight
patients with chronic pancreatitis (CP)
Multi-interaction mean-field renormalization group
We present an extension of the previously proposed mean-field renormalization
method to model Hamiltonians which are characterized by more than just one type
of interaction. The method rests on scaling assumptions about the magnetization
of different sublattices of the given lattice and it generates as many flow
equations as coupling constants without arbitrary truncations on the
renormalized Hamiltonian. We obtain good results for the test case of Ising
systems with an additional second-neighbor coupling in two and three
dimensions. An application of the method is also done to a morphological model
of interacting surfaces introduced recenlty by Likos, Mecke and Wagner [J.
Chem. Phys. {\bf{102}}, 9350 (1995)].
PACS: 64.60.Ak, 64.60.Fr, 05.70.JkComment: Tex file and three macros appended at the end. Five figures available
upon request to: [email protected], Fax: [+]39-40-224-60
HD 144432: a young triple system
We present new imaging and spectroscopic data of the young Herbig star HD
144432 A, which was known to be a binary star with a separation of 1.47 arcsec.
High-resolution NIR imaging data obtained with NACO at the VLT reveal that HD
144432 B itself is a close binary pair with a separation of 0.1 arcsec.
High-resolution optical spectra, acquired with FEROS at the 2.2m MPG/ESO
telescope in La Silla, of the primary star and its co-moving companions were
used to determine their main stellar parameters such as effective temperature,
surface gravity, radial velocity, and projected rotational velocity by fitting
synthetic spectra to the observed stellar spectra. The two companions, HD
144432 B and HD 144432 C, are identified as low-mass T Tauri stars of spectral
type K7V and M1V, respectively. From the position in the HRD the triple system
appears to be co-eval with a system age of 6+/-3 Myr.Comment: Accepted for publication in Astronomy & Astrophysics, 4 pages, 4
figure
U-dual fluxes and Generalized Geometry
We perform a systematic analysis of generic string flux compactifications,
making use of Exceptional Generalized Geometry (EGG) as an organizing
principle. In particular, we establish the precise map between fluxes, gaugings
of maximal 4d supergravity and EGG, identifying the complete set of gaugings
that admit an uplift to 10d heterotic or type IIB supegravity backgrounds. Our
results reveal a rich structure, involving new deformations of 10d supergravity
backgrounds, such as the RR counterparts of the -deformation. These new
deformations are expected to provide the natural extension of the
-deformation to full-fledged F-theory backgrounds. Our analysis also
provides some clues on the 10d origin of some of the particularly less
understood gaugings of 4d supergravity. Finally, we derive the explicit
expression for the effective superpotential in arbitrary N = 1 heterotic or
type IIB orientifold compactifications, for all the allowed fluxes.Comment: 58 pages, 6 table
Stimulus-preceding negativity in ADHD
Children with ADHD often show disrupted response preparation as indicated by attenuated stimulus-preceding negativity (SPN). This study examined response preparation in a relatively short cue-stimulus interval. No differences in SPN occurred between children with ADHD and their normal peers. A strong positive relationship was found between SPN and mean reaction time in both groups. Children with ADHD are able to mentally prepare themselves for upcoming events in short cue-stimulus intervals. © 2013 Springer-Verlag Wien
The VMC Survey. V. First results for Classical Cepheids
The VISTA Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting deep
Ks-band time-series photometry of the pulsating variable stars hosted by the
system formed by the two Magellanic Clouds (MCs) and the "bridge" connecting
them. In this paper we present the first results for Classical Cepheids, from
the VMC observations of two fields in the Large Magellanic Cloud (LMC). The VMC
Ks-band light curves of the Cepheids are well sampled (12-epochs) and of
excellent precision. We were able to measure for the first time the Ks
magnitude of the faintest Classical Cepheids in the LMC (Ks\sim17.5 mag), which
are mostly pulsating in the First Overtone (FO) mode, and to obtain FO
Period-Luminosity (PL), Period-Wesenheit (PW), and Period-Luminosity-Color
(PLC) relations, spanning the full period range from 0.25 to 6 day. Since the
longest period Cepheid in our dataset has a variability period of 23 day, we
have complemented our sample with literature data for brighter F Cepheids. On
this basis we have built a PL relation in the Ks band that, for the first time,
includes short period pulsators, and spans the whole range from 1.6 to 100 days
in period. We also provide the first ever empirical PW and PLC relations using
the (V-Ks) color and time-series Ks photometry. The very small dispersion
(\sim0.07 mag) of these relations makes them very well suited to study the
three-dimensional (3D) geometry of the Magellanic system. The use of "direct"
(parallax- and Baade-Wesselink- based) distance measurements to both Galactic
and LMC Cepheids, allowed us to calibrate the zero points of the PL, PW, and
PLC relations obtained in this paper, and in turn to estimate an absolute
distance modulus of (m-M)0=18.46\pm0.03 for the LMC. This result is in
agreement with most of the latest literature determinations based on Classical
Cepheids.Comment: 12 pages, 7 figures: MNRAS in pres
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