12,812 research outputs found
Beat Em or Join Em: Export Subsidies versus International Research Joint Ventures in Oligopolistic Markets
This paper compares adversarial with cooperative industrial and trade policies in a dynamic oligopoly game in which a home and foreign firm compete in R&D and output and, because of spillovers, each firm benefits from the other's R&D. When the government can commit to an export subsidy, such a policy raises welfare relative to cooperation, except when R&D is highly effective and spillovers are near-complete. Without commitment, however, subsidisation may yield welfare levels much lower than cooperation and lower even than free trade, though qualifications to the dangers from no commitment are noted.
Virtual Meson Cloud of the Nucleon and Intrinsic Strangeness and Charm
We have applied the Meson Cloud Model (MCM) to calculate the charm and
strange antiquark distribution in the nucleon. The resulting distribution, in
the case of charm, is very similar to the intrinsic charm momentum distribution
in the nucleon. This seems to corroborate the hypothesis that the intrinsic
charm is in the cloud and, at the same time, explains why other calculations
with the MCM involving strange quark distributions fail in reproducing the low
x region data. From the intrinsic strange distribution in the nucleon we have
extracted the strangeness radius of the nucleon, which is in agreement with
other meson cloud calculations.Comment: 9 pages RevTex, 4 figure
Expanding direction of the period doubling operator
We prove that the period doubling operator has an expanding direction at the
fixed point. We use the induced operator, a ``Perron-Frobenius type operator'',
to study the linearization of the period doubling operator at its fixed point.
We then use a sequence of linear operators with finite ranks to study this
induced operator. The proof is constructive. One can calculate the expanding
direction and the rate of expansion of the period doubling operator at the
fixed point
Being Even Slightly Shallow Makes Life Hard
We study the computational complexity of identifying dense substructures, namely r/2-shallow topological minors and r-subdivisions. Of particular interest is the case r = 1, when these substructures correspond to very localized relaxations of subgraphs. Since Densest Subgraph can be solved in polynomial time, we ask whether these slight relaxations also admit efficient algorithms.
In the following, we provide a negative answer: Dense r/2-Shallow Topological Minor and Dense r-Subdivsion are already NP-hard for r = 1 in very sparse graphs. Further, they do not admit algorithms with running time 2^(o(tw^2)) n^O(1) when parameterized by the treewidth of the input graph for r > 2 unless ETH fails
Hanbury-Brown--Twiss Analysis in a Solvable Model
The analysis of meson correlations by Hanbury-Brown--Twiss interferometry is
tested with a simple model of meson production by resonance decay. We derive
conditions which should be satisfied in order to relate the measured momentum
correlation to the classical source size. The Bose correlation effects are
apparent in both the ratio of meson pairs to singles and in the ratio of like
to unlike pairs. With our parameter values, we find that the single particle
distribution is too distorted by the correlation to allow a straightforward
analysis using pair correlation normalized by the singles rates. An analysis
comparing symmetrized to unsymmetrized pairs is more robust, but nonclassical
off-shell effects are important at realistic temperatures.Comment: 21 pages + 9 figures (tarred etc. using uufiles, submitted
separately), REVTeX 3.0, preprint number: DOE/ER/40561-112/INT93-00-3
Analytic considerations in applying a general economic evaluation reference case to gene therapy
The concept of a reference case, first proposed by the US Panel on Cost-Effectiveness in Health and Medicine, has been used to specify the required methodological features of economic evaluations of health care interventions. In the case of gene therapy, there is a difference of opinion on whether a specific methodologic reference case is required. The aim of this paper is to provide a more detailed analysis of the characteristics of gene therapy and the extent to which these characteristics warrant modifications to the methods suggested in general reference cases for economic evaluation. We argue that a completely new reference case is not required, but propose a tailored checklist that can be used by analysts and decision-makers to determine which aspects of economic evaluation should be considered further, given the unique nature of gene therapy
Optical Fibre Based Real-Time Measurements During an LDR Prostate Brachytherapy Implant Simulation: Using a 3D printed anthropomorphic phantom
An optical fbre sensor based on radioluminescence, using the scintillation material terbium doped gadolinium oxysulphide (Gd2O2S:Tb) is evaluated, using a 3D printed anthropomorphic phantom for applications in low dose-rate (LDR) prostate brachytherapy. The scintillation material is embedded in a 700 µm diameter cavity within a 1 mm plastic optical fbre that is fxed within a brachytherapy needle. The high spatial resolution dosimeter is used to measure the dose contribution from Iodine-125 (I-125) seeds. Initially, the efects of sterilisation on the sensors (1) repeatability, (2) response as a function of angle, and (3) response as a function of distance, are evaluated in a custom polymethyl methacrylate phantom. Results obtained in this study demonstrate that the output response of the sensor, pre- and post-sterilisation are within the acceptable measurement uncertainty ranging from a maximum standard deviation of 4.7% pre and 5.5% post respectively, indicating that the low temperature sterilisation process does not damage the sensor or reduce performance. Subsequently, an LDR brachytherapy plan reconstructed using the VariSeed treatment planning system, in an anthropomorphic 3D printed training phantom, was used to assess the suitability of the sensor for applications in LDR brachytherapy. This phantom was printed based on patient anatomy, with the volume and dimensions of the prostate designed to represent that of the patient. I-125 brachytherapy seeds, with an average activity of 0.410 mCi, were implanted into the prostate phantom under transrectal ultrasound guidance; following the same techniques as employed in clinical practice by an experienced radiation oncologist. This work has demonstrated that this sensor is capable of accurately identifying when radioactive I-125 sources are introduced into the prostate via a brachytherapy needle
Interaction-powered supernovae: Rise-time vs. peak-luminosity correlation and the shock-breakout velocity
Interaction of supernova (SN) ejecta with the optically thick circumstellar
medium (CSM) of a progenitor star can result in a bright, long-lived shock
breakout event. Candidates for such SNe include Type IIn and superluminous SNe.
If some of these SNe are powered by interaction, then there should be a
relation between their peak luminosity, bolometric light-curve rise time, and
shock-breakout velocity. Given that the shock velocity during shock breakout is
not measured, we expect a correlation, with a significant spread, between the
rise time and the peak luminosity of these SNe. Here, we present a sample of 15
SNe IIn for which we have good constraints on their rise time and peak
luminosity from observations obtained using the Palomar Transient Factory. We
report on a possible correlation between the R-band rise time and peak
luminosity of these SNe, with a false-alarm probability of 3%. Assuming that
these SNe are powered by interaction, combining these observables and theory
allows us to deduce lower limits on the shock-breakout velocity. The lower
limits on the shock velocity we find are consistent with what is expected for
SNe (i.e., ~10^4 km/s). This supports the suggestion that the early-time light
curves of SNe IIn are caused by shock breakout in a dense CSM. We note that
such a correlation can arise from other physical mechanisms. Performing such a
test on other classes of SNe (e.g., superluminous SNe) can be used to rule out
the interaction model for a class of events.Comment: Accepted to ApJ, 6 page
Heterogeneous ice nucleation properties of natural desert dust particles coated with a surrogate of secondary organic aerosol
Ice nucleation abilities of surface collected mineral dust particles from the
Sahara (SD) and Asia (AD) are investigated for the temperature (T) range
253–233 K and for supersaturated relative humidity (RH) conditions in the
immersion freezing regime. The dust particles were also coated with a proxy
of secondary organic aerosol (SOA) from the dark ozonolysis of
α-pinene to better understand the influence of atmospheric coatings on
the immersion freezing ability of mineral dust particles. The measurements
are conducted on polydisperse particles in the size range
0.01–3 µm with three different ice nucleation chambers. Two of the
chambers follow the continuous flow diffusion chamber (CFDC) principle
(Portable Ice Nucleation Chamber, PINC) and the Colorado State University
CFDC (CSU-CFDC), whereas the third was the Aerosol Interactions and Dynamics
in the Atmosphere (AIDA) cloud expansion chamber. From observed activated
fractions (AFs) and ice nucleation active site (INAS)
densities, it is concluded within experimental uncertainties that
there is no significant difference between the ice nucleation ability of the
particular SD and AD samples examined. A small bias towards higher
INAS densities for uncoated versus SOA-coated dusts is found but
this is well within the 1σ (66 % prediction bands) region of the
average fit to the data, which captures 75 % of the INAS densities observed in this study. Furthermore, no systematic differences are
observed between SOA-coated and uncoated dusts in both SD and AD cases,
regardless of coating thickness (3–60 nm). The results suggest that any
differences observed are within the uncertainty of the measurements or
differences in cloud chamber parameters such as size fraction of particles
sampled, and residence time, as well as assumptions in using INAS densities to compare polydisperse aerosol measurements which may show
variable composition with particle size. Coatings with similar properties to
that of the SOA in this work and with coating thickness up to 60 nm are not
expected to impede or enhance the immersion mode ice nucleation ability of
mineral dust particles.</p
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