8,808 research outputs found
Twist1 Inactivation in Dmp1-Expressing Cells Increases Bone Mass but Does Not Affect the Anabolic Response to Sclerostin Neutralization
Wnt signaling plays a major role in bone metabolism. Advances in our understanding of secreted regulators of Wnt have yielded several therapeutic targets to stimulate osteoanabolism—the most promising of which is the Wnt inhibitor sclerostin. Sclerostin antibody recently gained approval for clinical use to treat osteoporosis, but the biology surrounding sclerostin antagonism is still incompletely understood. Numerous factors regulate the efficacy of sclerostin inhibition on bone formation, a process known as self-regulation. In previous communications we reported that the basic helix-loop-helix transcription factor Twist1—a gene know to regulate skeletal development—is highly upregulated among the osteocyte cell population in mice treated with sclerostin antibody. In this communication, we tested the hypothesis that preventing Twist1 upregulation by deletion of Twist1 from late-stage osteoblasts and osteocytes would increase the efficacy of sclerostin antibody treatment, since Twist1 is known to restrain osteoblast activity in many models. Twist1-floxed loss-of-function mice were crossed to the Dmp1-Cre driver to delete Twist1 in Dmp1-expressing cells. Conditional Twist1 deletion was associated with a mild but significant increase in bone mass, as assessed by dual energy x-ray absorptiometry (DXA) and microCT (µCT) for many endpoints in both male and female mice. Biomechanical properties of the femur were not affected by conditional mutation of Twist1. Sclerostin antibody improved all bone properties significantly, regardless of Twist1 status, sex, or endpoint examined. No interactions were detected when Twist1 status and antibody treatment were examined together, suggesting that Twist1 upregulation in the osteocyte population is not an endogenous mechanism that restrains the osteoanabolic effect of sclerostin antibody treatment. In summary, Twist1 inhibition in the late-stage osteoblast/osteocyte increases bone mass but does not affect the anabolic response to sclerostin neutralization
Deep learning for synthetic microstructure generation in a materials-by-design framework for heterogeneous energetic materials
The sensitivity of heterogeneous energetic (HE) materials (propellants,
explosives, and pyrotechnics) is critically dependent on their microstructure.
Initiation of chemical reactions occurs at hot spots due to energy localization
at sites of porosities and other defects. Emerging multi-scale predictive
models of HE response to loads account for the physics at the meso-scale, i.e.
at the scale of statistically representative clusters of particles and other
features in the microstructure. Meso-scale physics is infused in
machine-learned closure models informed by resolved meso-scale simulations.
Since microstructures are stochastic, ensembles of meso-scale simulations are
required to quantify hot spot ignition and growth and to develop models for
microstructure-dependent energy deposition rates. We propose utilizing
generative adversarial networks (GAN) to spawn ensembles of synthetic
heterogeneous energetic material microstructures. The method generates
qualitatively and quantitatively realistic microstructures by learning from
images of HE microstructures. We show that the proposed GAN method also permits
the generation of new morphologies, where the porosity distribution can be
controlled and spatially manipulated. Such control paves the way for the design
of novel microstructures to engineer HE materials for targeted performance in a
materials-by-design framework
Neutrino Oscillations and R-parity Violating Collider Signals
R-parity and L violation in the MSSM would be the origin of the neutrino
oscillation observed in Super-Kamiokande. A distinctive feature of this
framework is that it can be tested in colliders by observing decay products of
the destabilized LSP. We examine all the possible decay processes of the
neutralino LSP assuming the bilinear contribution to neutrino masses dominates
over the trilinear one which gives rise to the solar neutrino mass. We find
that it is possible to probe neutrino oscillations through colliders in most of
the R-parity conserving MSSM parameter space.Comment: 23 pages, 8 figures, to appear in Phys. Rev.
New scalar resonances from sneutrino-Higgs mixing in supersymmetry with small lepton number (R-parity) violation
We consider new s-channel scalar exchanges in top quark and massive
gauge-bosons pair production in e+e- collisions, in supersymmetry with a small
lepton number violation. We show that a soft bilinear lepton number violating
term in the scalar potential which mixes the Higgs and the slepton fields can
give rise to a significant scalar resonance enhancement in e+e- -> ZZ, W+W- and
in e+e- -> t t(bar). The sneutrino-Higgs mixed state couples to the incoming
light leptons through its sneutrino component and to either the top quark or
the massive gauge bosons through its Higgs component. Such a scalar resonance
in these specific production channels cannot result from trilinear Yukawa-like
R-parity violation alone, and may, therefore, stand as strong evidence for the
existence of R-parity violating bilinears in the supersymmetric scalar
potential. We use the LEP2 measurements of the WW and ZZ cross-sections to
place useful constrains on this scenario, and investigate the expectations for
the sensitivity of a future linear collider to these signals. We find that
signals of these scalar resonances, in particular in top-pair production, are
well within the reach of linear colliders in the small lepton number violation
scenario.Comment: 22 pages in revtex, 10 figures embadded in the text using epsfi
Interaction-based quantum metrology showing scaling beyond the Heisenberg limit
Quantum metrology studies the use of entanglement and other quantum resources
to improve precision measurement. An interferometer using N independent
particles to measure a parameter X can achieve at best the "standard quantum
limit" (SQL) of sensitivity {\delta}X \propto N^{-1/2}. The same interferometer
using N entangled particles can achieve in principle the "Heisenberg limit"
{\delta}X \propto N^{-1}, using exotic states. Recent theoretical work argues
that interactions among particles may be a valuable resource for quantum
metrology, allowing scaling beyond the Heisenberg limit. Specifically, a
k-particle interaction will produce sensitivity {\delta}X \propto N^{-k} with
appropriate entangled states and {\delta}X \propto N^{-(k-1/2)} even without
entanglement. Here we demonstrate this "super-Heisenberg" scaling in a
nonlinear, non-destructive measurement of the magnetisation of an atomic
ensemble. We use fast optical nonlinearities to generate a pairwise
photon-photon interaction (k = 2) while preserving quantum-noise-limited
performance, to produce {\delta}X \propto N^{-3/2}. We observe super-Heisenberg
scaling over two orders of magnitude in N, limited at large N by higher-order
nonlinear effects, in good agreement with theory. For a measurement of limited
duration, super-Heisenberg scaling allows the nonlinear measurement to overtake
in sensitivity a comparable linear measurement with the same number of photons.
In other scenarios, however, higher-order nonlinearities prevent this crossover
from occurring, reflecting the subtle relationship of scaling to sensitivity in
nonlinear systems. This work shows that inter-particle interactions can improve
sensitivity in a quantum-limited measurement, and introduces a fundamentally
new resource for quantum metrology
Collider Signatures of Neutrino Masses and Mixing from R-parity Violation
R-parity violation in the supersymmetric standard model can be the source of
neutrino masses and mixing. We analyze the neutrino mass matrix coming from
either bilinear or trilinear R-parity violation and its collider signatures,
assuming that the atmospheric and solar neutrino data are explained by three
active neutrino oscillations. Taking the gauge mediated supersymmetry breaking
mechanism, we show that the lightest neutralino decays well inside the detector
and the model could be tested by observing its branching ratios in the future
colliders. In the bilinear model where only the small solar neutrino mixing
angle can be accommodated, the relation, BR()
BR() BR(), serves as a
robust test of the model. The large mixing angle solution can be realized in
the trilinear model which predicts BR() BR() BR(). In either case, the
relation, BR() BR() BR(), should hold to be
consistent with the atmospheric neutrino and CHOOZ experiments.Comment: 24pages, Late
Constraining an R-parity violating supersymmetric theory from the SuperKamiokande data on atmospheric neutrinos
The constraints on an R-parity violating supersymmetric theory arising from
the recent SuperKamiokande results on atmospheric neutrinos are studied, with
special reference to a scenario with bilinear R-parity violating terms.
Considering both the fermionic and scalar sectors, we find that a large area of
the parameter space is allowed, in terms of both the lepton-number violating
entries in the superpotential and the soft R-violating terms in the scalar
potential, and that no fine-tuning is required. However, the need to avoid
flavour changing neutral currents puts additional restrictions on the theory,
requiring either the R-violating terms in the superpotential to be smaller than
the R-conserving ones, or a hierarchy in the R-violating parameters for
different lepton flavours in the superpotential.Comment: 18 pages, LaTex including postscript figure
The K^*_0(800) scalar resonance from Roy-Steiner representations of pi K scattering
We discuss the existence of the light scalar meson K^*_0(800) (also called
kappa) in a rigorous way, by showing the presence of a pole in the pi K --> pi
K amplitude on the second Riemann sheet. For this purpose, we study the domain
of validity of two classes of Roy-Steiner representations in the complex energy
plane. We prove that one of them is valid in a region sufficiently broad in the
imaginary direction. From this representation, we compute the l=0 partial wave
in the complex plane with neither additional approximation nor model
dependence, relying only on experimental data. A scalar resonance with
strangeness S=1 is found with the following mass and width: E_kappa = 658 \pm
13 MeV and Gamma_kappa = 557 \pm 24 MeV.Comment: 16 pages, 8 figures. Domain of validity of a Roy-Steiner
representation corrected and enlarged, and features of the K^*_0(800) pole
discussed in more details. Conclusions unchange
Flavor changing Z-decays from scalar interactions at a Giga-Z Linear Collider
The flavor changing decay Z -> d_I \bar{d}_J is investigated with special
emphasis on the b \bar{s} final state. Various models for flavor violation are
considered: two Higgs doublet models (2HDM's), supersymmetry (SUSY) with flavor
violation in the up and down-type squark mass matrices and SUSY with flavor
violation mediated by R-parity-violating interaction. We find that, within the
SUSY scenarios for flavor violation, the branching ratio for the decay Z -> b
\bar{s} can reach 10^{-6} for large \tan\beta values, while the typical size
for this branching ratio in the 2HDM's considered is about two orders of
magnitudes smaller at best. Thus, flavor changing SUSY signatures in radiative
Z decays such as Z -> b \bar{s} may be accessible to future ``Z factories''
such as a Giga-Z version of the TESLA design.Comment: 27 pages, 15 figures, REVTeX4. A new section added and a few minor
corrections were made in the tex
Implication of Super-Kamiokande Data on R-parity Violation
R-parity violating bilinear (soft) terms in the supersymmetric standard model
would be the leading source for nonzero neutrino masses and mixing. We point
out that the mixing between neutralinos (charginos) and neutrinos (charged
leptons) driven by the bilinear terms take factorized forms, which may enable
us to probe the neutrino mixing parameters in a collider. It is then shown that
the Super-Kamiokande data on atmospheric neutrinos require all the baryon
number violating couplings to be substantially suppressed: .Comment: 11 pages, LaTeX, to appear in Phys. Rev.
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