6,583 research outputs found
Kodaira Dimension of Subvarieties
In this article we study how the birational geometry of a normal projective
variety is influenced by a normal subvariety One of the most
basic examples in this context is provided by the following situation. Let
be a surjective holomorphic map with connected fibers between
compact connected complex manifolds. It is well known that given a general
fiber of we have This article grew
out of the realization that this result should be true with replaced
by the codimension \cod_X A for a pair consisting of a normal
subvariety of a compact normal variety under weak semipositivity
conditions on the normal sheaf of and the weak singularity condition
\cod_A (A\cap\sing X)\ge 2. We shall now state our main results in the
special case of a submanifold in a projective manifold and we also
simplify the semipositivity notion
Finite-Difference and Pseudospectral Time-Domain Methods Applied to Backwards-Wave Metamaterials
Backwards-wave (BW) materials that have simultaneously negative real parts of
their electric permittivity and magnetic permeability can support waves where
phase and power propagation occur in opposite directions. These materials were
predicted to have many unusual electromagnetic properties, among them
amplification of the near-field of a point source, which could lead to the
perfect reconstruction of the source field in an image [J. Pendry, Phys. Rev.
Lett. \textbf{85}, 3966 (2000)]. Often systems containing BW materials are
simulated using the finite-difference time-domain technique. We show that this
technique suffers from a numerical artifact due to its staggered grid that
makes its use in simulations involving BW materials problematic. The
pseudospectral time-domain technique, on the other hand, uses a collocated grid
and is free of this artifact.
It is also shown that when modeling the dispersive BW material, the linear
frequency approximation method introduces error that affects the frequency of
vanishing reflection, while the auxiliary differential equation, the Z
transform, and the bilinear frequency approximation method produce vanishing
reflection at the correct frequency. The case of vanishing reflection is of
particular interest for field reconstruction in imaging applications.Comment: 9 pages, 8 figures, accepted by IEEE Transactions on Antennas and
Propagatio
A Study on the Efficacy of Sentiment Analysis in Author Attribution
The field of authorship attribution seeks to characterize an author’s writing style well enough to determine whether he or she has written a text of interest. One subfield of authorship attribution, stylometry, seeks to find the necessary literary attributes to quantify an author’s writing style. The research presented here sought to determine the efficacy of sentiment analysis as a new stylometric feature, by comparing its performance in attributing authorship against the performance of traditional stylometric features. Experimentation, with a corpus of sci-fi texts, found sentiment analysis to have a much lower performance in assigning authorship than the traditional stylometric features
COMPARISON OF MECHANICAL vs. MANUAL MANIPULATION METHODS FOR LOW BACK PAIN
ABSTRACT:Purpose and Study Design: Prospective cohort study to explore the clinical treatment effect of mechanical vs. manual manipulation for acute low back pain.Methods: 92 patients with a history of acute low back pain were recruited from three private chiropractic offices. Two of these offices utilized manual lumbar manipulation and one used mechanical instrument manipulation (Activator) as their primary modes of treatment. The chiropractors used a "treatment as usual" protocol with the participants for a maximum of eight visits or four weeks, which ever occurred first. Primary and secondary outcome measures were the differences in pain and Oswestry scores from baseline to four weeks, respectively. Results: Socio-demographic characteristics of the two cohorts at baseline were not found to show any significant differences between the groups except for age. The Activator cohort had a significantly higher utilization of adjunctive modalities and x-rays, with a mean number of office visits about twice that of the manual manipulation cohort at four weeks. The pain scores decreased in both groups with the manual manipulation group showing a slightly greater amount of pain reduction at four weeks, but this difference did not reach statistical significance after controlling for baseline pain. The manual manipulation group also showed a slightly greater reduction in Oswestry scores from baseline to four-weeks, but this difference was not statistically significant after adjusting for baseline Oswestry score.Conclusions: In this observational study of treatment-as-usual there was no significantly greater reduction in pain scores or Oswestry scores between the manipulation and Activator groups at four weeks. There were many differences between the Activator and manual manipulation groups with respect to treatment beliefs and expectations, modality usage, and frequency/duration of care, which are potential sources of confounding in the interpretation of these results. This study provides important pilot data and research issues for the design of a future randomized clinical trial that can control for these issues of confounding variables
Projections from Subvarieties
Let be an n-dimensional connected projective submanifold of
projective space. Let denote the projection from a
linear . Assuming that we have the induced
rational mapping . This article started as an
attempt to understand the structure of this mapping when has a lower
dimensional image. In this case of necessity we have is
nonempty. We have in this article studied a closely related question, which
includes many special cases including the case when the center of the
projection \pn q is contained in .
PROBLEM. Let be a proper connected k-dimensional projective submanifold
of an -dimensional projective manifold . Assume that . Let be a
very ample line bundle on such that is spanned by global
sections, where denotes the ideal sheaf of in . Describe the
structure of under the additional assumption that the image of
under the mapping associated to is lower dimensional
Adiabatic Preparation of a Heisenberg Antiferromagnet Using an Optical Superlattice
We analyze the possibility to prepare a Heisenberg antiferromagnet with cold
fermions in optical lattices, starting from a band insulator and adiabatically
changing the lattice potential. The numerical simulation of the dynamics in 1D
allows us to identify the conditions for success, and to study the influence
that the presence of holes in the initial state may have on the protocol. We
also extend our results to two-dimensional systems.Comment: 5 pages, 4 figures + Supplementary Material (5 pages, 6 figures),
published versio
The Collapse of the Wien Tail in the Coldest Brown Dwarf? Hubble Space Telescope Near-Infrared Photometry of WISE J085510.83-071442.5
We present Hubble Space Telescope (HST) near-infrared photometry of the
coldest known brown dwarf, WISE J085510.83071442.5 (WISE 08550714). WISE
08550714 was observed with the Wide Field Camera 3 (WFC3) aboard HST using
the F105W, F125W, and F160W filters, which approximate the , , and
near-infrared bands. WISE 08550714 is undetected at F105W with a
corresponding 2 magnitude limit of 26.9. We marginally detect
WISE 08550714 in the F125W images (S/N 4), with a measured magnitude
of 26.41 0.27, more than a magnitude fainter than the band magnitude
reported by Faherty and coworkers. WISE J08550714 is clearly detected in the
F160W band, with a magnitude of 23.90 0.02, the first secure detection of
WISE 08550714 in the near-infrared. Based on these data, we find that WISE
08550714 has extremely red F105WF125W and F125WF160W colors relative
to other known Y dwarfs. We find that when compared to the models of Saumon et
al. and Morley et al., the F105WF125W and F125WF160W colors of WISE
08550714 cannot be accounted for simultaneously. These colors likely
indicate that we are seeing the collapse of flux on the Wien tail for this
extremely cold object.Comment: Accepted for publication in ApJ Letter
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