2,127 research outputs found
Supersolidity in quantum films adsorbed on graphene and graphite
Using quantum Monte Carlo we have studied the superfluid density of the first
layer of He and H adsorbed on graphene and graphite. Our main focus has
been on the equilibrium ground state of the system, which corresponds to a
registered phase. The perfect solid phase of H shows
no superfluid signal whereas He has a finite but small superfluid fraction
(0.67%). The introduction of vacancies in the crystal makes the superfluidity
increase, showing values as large as 14% in He without destroying the
spatial solid order.Comment: 5 pages, accepted for publication in PR
Xe films on a decagonal Al-Ni-Co quasicrystal surface
The grand canonical Monte Carlo method is employed to study the adsorption of
Xe on a quasicrystalline Al-Ni-Co surface. The calculation uses a semiempirical
gas-surface interaction, based on conventional combining rules and the usual
Lennard-Jones Xe-Xe interaction. The resulting adsorption isotherms and
calculated structures are consistent with the results of LEED experimental
data. In this paper we focus on five features not discussed earlier (Phys. Rev.
Lett. 95, 136104 (2005)): the range of the average density of the adsorbate,
the order of the transition, the orientational degeneracy of the ground state,
the isosteric heat of adsorption of the system, and the effect of the vertical
cell dimension.Comment: 6 pages, 5 pic
Evolution of topological order in Xe films on a quasicrystal surface
We report results of the first computer simulation studies of a physically
adsorbed gas on a quasicrystalline surface, Xe on decagonal Al-Ni-Co. The grand
canonical Monte Carlo method is employed, using a semi-empirical gas-surface
interaction, based on conventional combining rules, and the usual Lennard-Jones
Xe-Xe interaction. The resulting adsorption isotherms and calculated structures
are consistent with the results of LEED experimental data. The evolution of the
bulk film begins in the second layer, while the low coverage behavior is
epitaxial. This transition from 5-fold to 6-fold ordering is temperature
dependent, occurring earlier (at lower coverage) for the higher temperatures
Possible role of 3He impurities in solid 4He
We use a quantum lattice gas model to describe essential aspects of the
motion of 4He atoms and of 3He impurities in solid 4He. This study suggests
that 3He impurities bind to defects and promote 4He atoms to interstitial sites
which can turn the bosonic quantum disordered crystal into a metastable
supersolid. It is suggested that defects and interstitial atoms are produced
during the solid 4He nucleation process where the role of 3He impurities (in
addition to the cooling rate) is known to be important even at very small (1
ppm) impurity concentration. It is also proposed that such defects can form a
glass phase during the 4He solid growth by rapid cooling.Comment: 4 two-column Revtex pages, 4 figures. Europhysics Letters (in Press
Flickering in FU Orionis
We analyze new and published optical photometric data of FU Orionis, an
eruptive pre-main sequence star. The outburst consists of a 5.5 mag rise at B
with an e-folding timescale of roughly 50 days. The rates of decline at B and V
are identical, 0.015 +- 0.001 mag per yr. Random fluctuations superimposed on
this decline have an amplitude of 0.035 +- 0.005 mag at V and occur on
timescales of 1 day or less. Correlations between V and the color indices U-B,
B-V, and V-R indicate that the variable source has the optical colors of a G0
supergiant. We associate this behavior with small amplitude flickering of the
inner accretion disk.Comment: 19 pages of text, 3 tables, and 6 figures to be published in the
Astrophysical Journal, 10 March 200
Irradiation study of a fully monolithic HV-CMOS pixel sensor design in AMS 180 nm
High-Voltage Monolithic Active Pixel Sensors (HV-MAPS) based on the 180 nm
HV-CMOS process have been proposed to realize thin, fast and highly integrated
pixel sensors. The MuPix7 prototype, fabricated in the commercial AMS H18
process, features a fully integrated on-chip readout, i.e. hit-digitization,
zero suppression and data serialization. It is the first fully monolithic
HV-CMOS pixel sensor that has been tested for the use in high irradiation
environments like HL-LHC. We present results from laboratory and test beam
measurements of MuPix7 prototypes irradiated with neutrons (up to
) and protons (up to ) and compare the performance with non-irradiated
sensors. Efficiencies well above 90 % at noise rates below 200 Hz per pixel are
measured. A time resolution better than 22 ns is measured for all tested
settings and sensors, even at the highest irradiation fluences. The data
transmission at 1.25 Gbit/s and the on-chip PLL remain fully functional
The MuPix Telescope: A Thin, high Rate Tracking Telescope
The MuPix Telescope is a particle tracking telescope, optimized for tracking
low momentum particles and high rates. It is based on the novel High-Voltage
Monolithic Active Pixel Sensors (HV-MAPS), designed for the Mu3e tracking
detector. The telescope represents a first application of the HV-MAPS
technology and also serves as test bed of the Mu3e readout chain. The telescope
consists of up to eight layers of the newest prototypes, the MuPix7 sensors,
which send data self-triggered via fast serial links to FPGAs, where the data
is time-ordered and sent to the PC. A particle hit rate of 1 MHz per layer
could be processed. Online tracking is performed with a subset of the incoming
data. The general concept of the telescope, chip architecture, readout concept
and online reconstruction are described. The performance of the sensor and of
the telescope during test beam measurements are presented.Comment: Proceedings TWEPP 2016, 8 pages, 7 figure
Changes in the sense of agency : Implications for the psychotherapy of bulimia nervosa- A case study
A sense of agency is a transtheoretical concept that increases our understanding of important processes in psychotherapy. Agency can be described in terms of how strongly the person believes that she can have an impact on her problematic experiences and behaviors. In this case study, a patient's sense of agency in relation to symptoms of bulimia nervosa was assessed during 3 years of psychotherapy. Five distinct phases of agency in relation to eating disorder symptoms were identified: A false sense of agency or no agency at all, a weak sense of agency, a nascent sense of agency, a wavering sense of agency, and a strong sense of agency. A better understanding of patient agency can facilitate adapting approaches and methods best suited for the patient's capacity for change throughout treatment.Peer reviewe
An International Ultraviolet Explorer Archival Study of Dwarf Novae in Outburst
We present a synthetic spectral analysis of nearly the entire far ultraviolet
International Ultraviolet Explorer (IUE) archive of spectra of dwarf novae in
or near outburst. The study includes 46 systems of all dwarf nova subtypes both
above and below the period gap. The spectra were uniformly analyzed using
synthetic spectral codes for optically thick accretion disks and stellar
photospheres along with the best-available distance measurements or estimates.
We present newly estimated accretion rates and discuss the implications of our
study for disk accretion physics and CV evolution.Comment: Accepted for publication in the ApJ, Part
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