12,472 research outputs found
Tunnel diode circuit used as nanosecond-range time marker
Simple tunnel diode time marker circuit determines the time at which an event occurs in a scintillation crystal. It is capable of triggering at voltages as low as the noise level of a 10-stage PM tube
Overview of the INEX 2009 Interactive Track
In the paper we present the organization of the INEX 2009 interactive track. For the 2009 experiments the iTrack has gathered data on user search behavior in a collection consisting of book metadata taken from the online bookstore Amazon and the social cataloguing application LibraryThing. Thus the data are more structured than in previous years’ experiments, consisting of traditional bibliographic metadata, user-generated tags and reviews and promotional texts and reviews from publishers and professional reviewers. Through monitoring searches based on three different task types the experiment aims at studying how users interact with highly structured data. We describe the methods used for data collection and the tasks performed by the participants. Some preliminary results of the interaction analysis are reported
Structural Refinement for the Modal nu-Calculus
We introduce a new notion of structural refinement, a sound abstraction of
logical implication, for the modal nu-calculus. Using new translations between
the modal nu-calculus and disjunctive modal transition systems, we show that
these two specification formalisms are structurally equivalent.
Using our translations, we also transfer the structural operations of
composition and quotient from disjunctive modal transition systems to the modal
nu-calculus. This shows that the modal nu-calculus supports composition and
decomposition of specifications.Comment: Accepted at ICTAC 201
Extraction efficiency of drifting electrons in a two-phase xenon time projection chamber
We present a measurement of the extraction efficiency of quasi-free electrons
from the liquid into the gas phase in a two-phase xenon time-projection
chamber. The measurements span a range of electric fields from 2.4 to 7.1 kV/cm
in the liquid xenon, corresponding to 4.5 to 13.1 kV/cm in the gaseous xenon.
Extraction efficiency continues to increase at the highest extraction fields,
implying that additional charge signal may be attained in two-phase xenon
detectors through careful high-voltage engineering of the gate-anode region
Calibration of a two-phase xenon time projection chamber with a Ar source
We calibrate a two-phase xenon detector at 0.27 keV in the charge channel and
at 2.8 keV in both the light and charge channels using a Ar source that
is directly released into the detector. We map the light and charge yields as a
function of electric drift field. For the 2.8 keV peak, we calculate the
Thomas-Imel box parameter for recombination and determine its dependence on
drift field. For the same peak, we achieve an energy resolution,
, between 9.8% and 10.8% for 0.1 kV/cm to 2 kV/cm electric
drift fields.Comment: 12 pages, 7 figure
Coupled Magnetic Excitations in Single Crystal PrBa2Cu3O6.2
The dispersion of the low-energy magnetic excitations of the Pr sublattice in
PrBa2Cu3O6.2 is determined by inelastic neutron scattering measurements on a
single crystal. The dispersion, which shows the effect of interactions with the
Cu spin-waves, is well described by a model of the coupled Cu-Pr magnetic
system. This enables values for the principal exchange constants to be
determined, which suggest that both Pr-Pr and Cu-Pr interactions are important
in producing the anomalously high ordering temperature of the Pr sublattice.
Measurements of the Cu optic spin wave mode show that the inter-layer Cu-Cu
exchange is significantly lower than in YBa2Cu3O6.2.Comment: To be published Phys. Rev. Let
Structure and Mass of a Young Globular Cluster in NGC 6946
Using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope,
we have imaged a luminous young star cluster in the nearby spiral galaxy NGC
6946. The cluster has an absolute visual magnitude M(V)=-13.2, comparable to
the brightest young `super-star clusters' in the Antennae merger galaxy. UBV
colors indicate an age of about 15 Myr. The cluster has a compact core (core
radius = 1.3 pc), surrounded by an extended envelope. We estimate that the
effective radius (Reff) = 13 pc, but this number is uncertain because the outer
parts of the cluster profile gradually merge with the general field. Combined
with population synthesis models, the luminosity and age of the cluster imply a
mass of 8.2x10^5 Msun for a Salpeter IMF extending down to 0.1 Msun, or
5.5x10^5 Msun if the IMF is log-normal below 0.4 Msun. Depending on model
assumptions, the central density of the cluster is between 5300 Msun pc^-3 and
17000 Msun pc^-3, comparable to other high-density star forming regions. We
also estimate a dynamical mass for the cluster, using high-dispersion spectra
from the HIRES spectrograph on the Keck I telescope. The velocity dispersion is
10.0 +/- 2.7 km/s, implying a total cluster mass within 65 pc of (1.7 +/- 0.9)
x 10^6 Msun. Comparing the dynamical mass with the mass estimates based on the
photometry and population synthesis models, the mass-to-light ratio is at least
as high as for a Salpeter IMF extending down to 0.1 Msun, although a turn-over
in the IMF at 0.4 Msun is still possible within the errors. The cluster will
presumably remain bound, evolving into a globular cluster-like object.Comment: 33 pages, including 10 figures and 3 tables. Accepted for publication
in the Astrophysical Journa
Spectroscopic Constraints on the Form of the Stellar Cluster Mass Function
This contribution addresses the question of whether the initial cluster mass
function (ICMF) has a fundamental limit (or truncation) at high masses. The
shape of the ICMF at high masses can be studied using the most massive young
(<10 Myr) clusters, however this has proven difficult due to low-number
statistics. In this contribution we use an alternative method based on the
luminosities of the brightest clusters, combined with their ages. If a
truncation is present, a generic prediction (nearly independent of the cluster
disruption law adopted) is that the median age of bright clusters should be
younger than that of fainter clusters. In the case of an non-truncated ICMF,
the median age should be independent of cluster luminosity. Here, we present
optical spectroscopy of twelve young stellar clusters in the face-on spiral
galaxy NGC 2997. The spectra are used to estimate the age of each cluster, and
the brightness of the clusters is taken from the literature. The observations
are compared with the model expectations of Larsen (2009) for various ICMF
forms and both mass dependent and mass independent cluster disruption. While
there exists some degeneracy between the truncation mass and the amount of mass
independent disruption, the observations favour a truncated ICMF. For low or
modest amounts of mass independent disruption, a truncation mass of 5-6*10^5
Msun is estimated, consistent with previous determinations. Additionally, we
investigate possible truncations in the ICMF in the spiral galaxy M83, the
interacting Antennae galaxies, and the collection of spiral and dwarf galaxies
present in Larsen (2009) based on photometric catalogues taken from the
literature, and find that all catalogues are consistent with having a
(environmentally dependent) truncation in the cluster mass functions.Comment: 6 pages, 5 figures, in press, A&A Research Note
Second Order Perturbations of a Macroscopic String; Covariant Approach
Using a world-sheet covariant formalism, we derive the equations of motion
for second order perturbations of a generic macroscopic string, thus
generalizing previous results for first order perturbations. We give the
explicit results for the first and second order perturbations of a contracting
near-circular string; these results are relevant for the understanding of the
possible outcome when a cosmic string contracts under its own tension, as
discussed in a series of papers by Vilenkin and Garriga. In particular, second
order perturbations are necessaary for a consistent computation of the energy.
We also quantize the perturbations and derive the mass-formula up to second
order in perturbations for an observer using world-sheet time . The high
frequency modes give the standard Minkowski result while, interestingly enough,
the Hamiltonian turns out to be non-diagonal in oscillators for low-frequency
modes. Using an alternative definition of the vacuum, it is possible to
diagonalize the Hamiltonian, and the standard string mass-spectrum appears for
all frequencies. We finally discuss how our results are also relevant for the
problems concerning string-spreading near a black hole horizon, as originally
discussed by Susskind.Comment: New discussion about the quantum mass-spectrum in chapter
Topology Optimization and 3D printing of Large Deformation Compliant Mechanisms for Straining Biological Tissues
This paper presents a synthesis approach in a density-based topology
optimization setting to design large deformation compliant mechanisms for
inducing desired strains in biological tissues. The modelling is based on
geometrical nonlinearity together with a suitably chosen hypereleastic material
model, wherein the mechanical equilibrium equations are solved using the total
Lagrangian finite element formulation. An objective based on least-square error
with respect to target strains is formulated and minimized with the given set
of constraints and the appropriate surroundings of the tissues. To circumvent
numerical instabilities arising due to large deformation in low stiffness
design regions during topology optimization, a strain-energy based
interpolation scheme is employed. The approach uses an extended robust
formulation i.e. the eroded, intermediate and dilated projections for the
design description as well as variation in tissue stiffness. Efficacy of the
synthesis approach is demonstrated by designing various compliant mechanisms
for providing different target strains in biological tissue constructs.
Optimized compliant mechanisms are 3D-printed and their performances are
recorded in a simplified experiment and compared with simulation results
obtained by a commercial software.Comment: 23 pages, 14 figure
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