26,673 research outputs found
Weak Scale Superstrings
Recent developments in string duality suggest that the string scale may not
be irrevocably tied to the Planck scale. Two explicit but unrealistic examples
are described where the ratio of the string scale to the Planck scale is
arbitrarily small. Solutions which are more realistic may exist in the
intermediate coupling or ``truly strong coupling'' region of the heterotic
string. Weak scale superstrings have dramatic experimental consequences for
both collider physics and cosmology.Comment: harvmac, 14 pages. References added, 3 typos fixed, Comments added at
beginning of section 4 emphasizing flaws of the toy example
Power spectra from an inflaton coupled to the Gauss-Bonnet term
We consider power-law inflation with a Gauss-Bonnet correction inspired by
string theory. We analyze the stability of cosmological perturbations and
obtain the allowed parameter space. We find that for GB-dominated inflation
ultra-violet instabilities of either scalar or tensor perturbations show up on
small scales. The Gauss-Bonnet correction with a positive (or negative)
coupling may lead to a reduction (or enhancement) of the tensor-to-scalar ratio
in the potential-dominated case. We place tight constraints on the model
parameters by making use of the WMAP 5-year data.Comment: 5 pages, 4 figures, RevTeX, references added, published versio
A Note on Marginally Stable Bound States in Type II String Theory
Spectrum of elementary string states in type II string theory contains
ultra-short multiplets that are marginally stable. -duality transformation
converts these states into bound states at threshold of -branes carrying
Ramond-Ramond charges, and wrapped around -cycles of a torus. We propose a
test for the existence of these marginally stable bound states. Using the
recent results of Polchinski and of Witten, we argue that the spectrum of bound
states of -branes is in agreement with the prediction of -duality.Comment: LaTeX file, 6 page
Kinematic and morphological modeling of the bipolar nebula Sa2-237
We present [OIII]500.7nm and Halpha+[NII] images and long-slit, high
resolution echelle spectra in the same spectral regions of Sa2--237, a possible
bipolar planetary nebula. The image shows a bipolar nebula of about 34" extent,
with a narrow waist, and showing strong point symmetry about the central
object, indicating it's likely binary nature. The long slit spectra were taken
over the long axis of the nebula, and show a distinct ``eight'' shaped pattern
in the velocity--space plot, and a maximum projected outflow velocity of
V=106km/s, both typical of expanding bipolar planetary nebulae. By model
fitting the shape and spectrum of the nebula simultaneously, we derive the
inclination of the long axis to be 70 degrees, and the maximum space velocity
of expansion to be 308 km/s. Due to asymmetries in the velocities we adopt a
new value for the system's heliocentric radial velocity of -30km/s. We use the
IRAS and 21cm radio fluxes, the energy distribution, and the projected size of
Sa2-237 to estimate it's distance to be 2.1+-0.37kpc. At this distance Sa2-237
has a luminosity of 340 Lsun, a size of 0.37pc, and -- assuming constant
expansion velocity -- a nebular age of 624 years. The above radial velocity and
distance place Sa2--237 in the disk of the Galaxy at z=255pc, albeit with
somewhat peculiar kinematics.Comment: 10pp, 4 fig
Structural and Electronic Properties of the Interface between the High-k oxide LaAlO3 and Si(001)
The structural and electronic properties of the LaAlO3/Si(001) interface are
determined using state-of-the-art electronic structure calculations. The atomic
structure differs from previous proposals, but is reminiscent of La adsorption
structures on silicon. A phase diagram of the interface stability is calculated
as a function of oxygen and Al chemical potentials. We find that an
electronically saturated interface is obtained only if dopant atoms segregate
to the interface. These findings raise serious doubts whether LaAlO3 can be
used as an epitaxial gate dielectric.Comment: 4 pages, 5 figure
Kaluza-Klein electrically charged black branes in M-theory
We present a class of Kaluza-Klein electrically charged black p-brane
solutions of ten-dimensional, type IIA superstring theory. Uplifting to eleven
dimensions these solutions are studied in the context of M-theory. They can be
interpreted either as a p+1 extended object trapped around the eleventh
dimension along which momentum is flowing or as a boost of the following
backgrounds: the Schwarzschild black (p+1)-brane or the product of the
(10-p)-dimensional Euclidean Schwarzschild manifold with the (p+1)-dimensional
Minkowski spacetime.Comment: 16 pages, uses latex and epsf macro, figures include
Therapeutic efficacy of anti-MMP9 antibody in combination with nab-paclitaxel-based chemotherapy in pre-clinical models of pancreatic cancer
Matrix metalloproteinase 9 (MMP9) is involved in the proteolysis of extracellular proteins and plays a critical role in pancreatic ductal adenocarcinoma (PDAC) progression, invasion and metastasis. The therapeutic potential of an anti-MMP9 antibody (αMMP9) was evaluated in combination with nab-paclitaxel (NPT)-based standard cytotoxic therapy in pre-clinical models of PDAC. Tumour progression and survival studies were performed in NOD/SCID mice. The mechanistic evaluation involved RNA-Seq, Luminex, IHC and Immunoblot analyses of tumour samples. Median animal survival compared to controls was significantly increased after 2-week therapy with NPT (59%), Gem (29%) and NPT+Gem (76%). Addition of αMMP9 antibody exhibited further extension in survival: NPT+αMMP9 (76%), Gem+αMMP9 (47%) and NPT+Gem+αMMP9 (94%). Six-week maintenance therapy revealed that median animal survival was significantly increased after NPT+Gem (186%) and further improved by the addition of αMMP9 antibody (218%). Qualitative assessment of mice exhibited that αMMP9 therapy led to a reduction in jaundice, bloody ascites and metastatic burden. Anti-MMP9 antibody increased the levels of tumour-associated IL-28 (1.5-fold) and decreased stromal markers (collagen I, αSMA) and the EMT marker vimentin. Subcutaneous tumours revealed low but detectable levels of MMP9 in all therapy groups but no difference in MMP9 expression. Anti-MMP9 antibody monotherapy resulted in more gene expression changes in the mouse stroma compared to the human tumour compartment. These findings suggest that anti-MMP9 antibody can exert specific stroma-directed effects that could be exploited in combination with currently used cytotoxics to improve clinical PDAC therapy
Self-Repairing Disk Arrays
As the prices of magnetic storage continue to decrease, the cost of replacing
failed disks becomes increasingly dominated by the cost of the service call
itself. We propose to eliminate these calls by building disk arrays that
contain enough spare disks to operate without any human intervention during
their whole lifetime. To evaluate the feasibility of this approach, we have
simulated the behavior of two-dimensional disk arrays with n parity disks and
n(n-1)/2 data disks under realistic failure and repair assumptions. Our
conclusion is that having n(n+1)/2 spare disks is more than enough to achieve a
99.999 percent probability of not losing data over four years. We observe that
the same objectives cannot be reached with RAID level 6 organizations and would
require RAID stripes that could tolerate triple disk failures.Comment: Part of ADAPT Workshop proceedings, 2015 (arXiv:1412.2347
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