1,117 research outputs found
New Perspectives in Sinographic Language Processing Through the Use of Character Structure
Chinese characters have a complex and hierarchical graphical structure
carrying both semantic and phonetic information. We use this structure to
enhance the text model and obtain better results in standard NLP operations.
First of all, to tackle the problem of graphical variation we define
allographic classes of characters. Next, the relation of inclusion of a
subcharacter in a characters, provides us with a directed graph of allographic
classes. We provide this graph with two weights: semanticity (semantic relation
between subcharacter and character) and phoneticity (phonetic relation) and
calculate "most semantic subcharacter paths" for each character. Finally,
adding the information contained in these paths to unigrams we claim to
increase the efficiency of text mining methods. We evaluate our method on a
text classification task on two corpora (Chinese and Japanese) of a total of 18
million characters and get an improvement of 3% on an already high baseline of
89.6% precision, obtained by a linear SVM classifier. Other possible
applications and perspectives of the system are discussed.Comment: 17 pages, 5 figures, presented at CICLing 201
Total Hadronic Cross Section and the Elastic Slope: An Almost Model-Independent Connection
An almost model-independent parametrization for the ratio of the total cross
section to the elastic slope, as function of the center of mass energy, is
introduced. The analytical result is based on the approximate relation of this
quantity with the ratio of the elastic to total cross section and empirical
fits to the data from proton-proton scattering above 10 GeV, under the
conditions of asymptotic unitarity and the black-disk limit. This
parametrization may be useful in studies of extensive air showers and the
determination of the proton-proton total cross section from proton-air
production cross section in cosmic-ray experiments.Comment: 15 pages, 4 figures, v4: few typos corrected, final version to be
published in Nucl. Phys.
Scaling violations: Connections between elastic and inelastic hadron scattering in a geometrical approach
Starting from a short range expansion of the inelastic overlap function,
capable of describing quite well the elastic pp and scattering data,
we obtain extensions to the inelastic channel, through unitarity and an impact
parameter approach. Based on geometrical arguments we infer some
characteristics of the elementary hadronic process and this allows an excellent
description of the inclusive multiplicity distributions in and
collisions. With this approach we quantitatively correlate the violations of
both geometrical and KNO scaling in an analytical way. The physical picture
from both channels is that the geometrical evolution of the hadronic
constituents is principally reponsible for the energy dependence of the
physical quantities rather than the dynamical (elementary) interaction itself.Comment: 16 pages, aps-revtex, 11 figure
Breather lattice and its stabilization for the modified Korteweg-de Vries equation
We obtain an exact solution for the breather lattice solution of the modified
Korteweg-de Vries (MKdV) equation. Numerical simulation of the breather lattice
demonstrates its instability due to the breather-breather interaction. However,
such multi-breather structures can be stabilized through the concurrent
application of ac driving and viscous damping terms.Comment: 6 pages, 3 figures, Phys. Rev. E (in press
Structural Invariance of Sunspot Umbrae Over the Solar Cycle: 1993-2004
Measurements of maximum magnetic flux, minimum intensity, and size are
presented for 12 967 sunspot umbrae detected on the NASA/NSO
spectromagnetograms between 1993 and 2004 to study umbral structure and
strength during the solar cycle. The umbrae are selected using an automated
thresholding technique. Measured umbral intensities are first corrected for a
confirming observation of umbral limb-darkening. Log-normal fits to the
observed size distribution confirm that the size spectrum shape does not vary
with time. The intensity-magnetic flux relationship is found to be steady over
the solar cycle. The dependence of umbral size on the magnetic flux and minimum
intensity are also independent of cycle phase and give linear and quadratic
relations, respectively. While the large sample size does show a low amplitude
oscillation in the mean minimum intensity and maximum magnetic flux correlated
with the solar cycle, this can be explained in terms of variations in the mean
umbral size. These size variations, however, are small and do not substantiate
a meaningful change in the size spectrum of the umbrae generated by the Sun.
Thus, in contrast to previous reports, the observations suggest the equilibrium
structure, as testified by the invariant size-magnetic field relationship, as
well as the mean size (i.e. strength) of sunspot umbrae do not significantly
depend on solar cycle phase.Comment: 17 pages, 6 figures. Published in Solar Physic
The emission regions in X-ray binaries: dipping as a diagnostic
X-ray dipping in the black hole binary Cygnus X-1, the Galactic jet source
GRO J1655-40 and in low mass X-ray binaries is discussed. It is shown that
spectral analysis strongly constrains emission models. Measurement of dip
ingress/egress times allows the sizes of extended emission regions to be
determined, notably for the Accretion Disk Corona which is responsible for
Comptonization in X-ray binaries. In LMXB, the radius of the ADC is shown to be
between ~ 10^9 and ~ 5x10^10 cm, an appreciable fraction of the accretion disk
radius. This is inconsistent with Comptonization models requiring a localized
Comptonizing region, for example, in the immediate neighbourhood of the neutron
star. Results from a survey of LMXB using ASCA and BeppoSAX reveal an
approximate equality between the height of the blackbody emission region on the
neutron star and the height of the inner radiatively-supported disk, suggesting
either that there is a direct causal link, such as a radial accretion flow
between the inner disk edge and the star, or an indirect link, as in the case
of accretion flow creep on the surface of the neutron star as suggested by
Inogamov & Sunyaev. Finally, the survey shows that the blackbody cannot
originate on the accretion disk as the required inner radii in many sources are
substantially less than the neutron star radius.Comment: solicited review paper presented at COSPAR 2000 "X-ray and Gamma-ray
Signatures of Black Holes and Weakly Magnetized Neutron Stars"; accepted for
publication in Advances in Space Research (2nd affiliation added
Dispersive properties of quasi-phase-matched optical parametric amplifiers
The dispersive properties of non-degenerate optical parametric amplification
in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary
grating profile are theoretically investigated in the no-pump-depletion limit.
The spectral group delay curve of the amplifier is shown to be univocally
determined by its spectral power gain curve through a Hilbert transform. Such a
constraint has important implications on the propagation of spectrally-narrow
optical pulses through the amplifier. In particular, it is shown that anomalous
transit times, corresponding to superluminal or even negative group velocities,
are possible near local minima of the spectral gain curve. A possible
experimental observation of such effects using a QPM Lithium-Niobate crystal is
suggested.Comment: submitted for publicatio
Clinical and molecular characterization of HER2 amplified-pancreatic cancer
<p>Background:
Pancreatic cancer is one of the most lethal and molecularly diverse malignancies. Repurposing of therapeutics that target specific molecular mechanisms in different disease types offers potential for rapid improvements in outcome. Although HER2 amplification occurs in pancreatic cancer, it is inadequately characterized to exploit the potential of anti-HER2 therapies.</p>
<p>Methods:
HER2 amplification was detected and further analyzed using multiple genomic sequencing approaches. Standardized reference laboratory assays defined HER2 amplification in a large cohort of patients (n = 469) with pancreatic ductal adenocarcinoma (PDAC).</p>
<p>Results:
An amplified inversion event (1 MB) was identified at the HER2 locus in a patient with PDAC. Using standardized laboratory assays, we established diagnostic criteria for HER2 amplification in PDAC, and observed a prevalence of 2%. Clinically, HER2- amplified PDAC was characterized by a lack of liver metastases, and a preponderance of lung and brain metastases. Excluding breast and gastric cancer, the incidence of HER2-amplified cancers in the USA is >22,000 per annum.</p>
<p>Conclusions:
HER2 amplification occurs in 2% of PDAC, and has distinct features with implications for clinical practice. The molecular heterogeneity of PDAC implies that even an incidence of 2% represents an attractive target for anti-HER2 therapies, as options for PDAC are limited. Recruiting patients based on HER2 amplification, rather than organ of origin, could make trials of anti-HER2 therapies feasible in less common cancer types.</p>
Bose condensates in a harmonic trap near the critical temperature
The mean-field properties of finite-temperature Bose-Einstein gases confined
in spherically symmetric harmonic traps are surveyed numerically. The solutions
of the Gross-Pitaevskii (GP) and Hartree-Fock-Bogoliubov (HFB) equations for
the condensate and low-lying quasiparticle excitations are calculated
self-consistently using the discrete variable representation, while the most
high-lying states are obtained with a local density approximation. Consistency
of the theory for temperatures through the Bose condensation point requires
that the thermodynamic chemical potential differ from the eigenvalue of the GP
equation; the appropriate modifications lead to results that are continuous as
a function of the particle interactions. The HFB equations are made gapless
either by invoking the Popov approximation or by renormalizing the particle
interactions. The latter approach effectively reduces the strength of the
effective scattering length, increases the number of condensate atoms at each
temperature, and raises the value of the transition temperature relative to the
Popov approximation. The renormalization effect increases approximately with
the log of the atom number, and is most pronounced at temperatures near the
transition. Comparisons with the results of quantum Monte Carlo calculations
and various local density approximations are presented, and experimental
consequences are discussed.Comment: 15 pages, 11 embedded figures, revte
Neutron scattering search for static magnetism in oxygen ordered YBa2Cu3O6.5
We present elastic and inelastic neutron scattering results on highly oxygen
ordered YBa2Cu3O6.5 ortho-II. We find no evidence for the presence of ordered
magnetic moments to a sensitivity of 0.003 Bohr magnetons, an order of
magnitude smaller than has been suggested in theories of orbital or
d-density-wave (DDW) currents. The absence of sharp elastic peaks, shows that
the d-density-wave phase is not present, at least for the superconductor with
the doping of 6.5 and the ordered ortho-II structure. We cannot exclude the
possibility that a broad peak may exist with extremely short-range DDW
correlations. For less ordered or more doped crystals it is possible that
disorder may lead to static magnetism. We have also searched for the large
normal state spin gap that is predicted to exist in an ordered DDW phase.
Instead of a gap we find that the Q-correlated spin susceptibility persists to
the lowest energies studied, 6 meV. Our results are compatible with the
coexistence of superconductivity with orbital currents, but only if they are
dynamic, and exclude a sharp phase transition to an ordered d-density-wave
phase.Comment: 6 pages 4 figures RevTex Submitted to Phys Rev B January 23, 200
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