1,080 research outputs found
Computer-controlled vibration testing
System features quickly achieved steady state, increased accuracy of spectrum definition, and true Gaussian amplitude distribution of resulting signals. Controlled shock-tests might also be tried with this system
Escaping Antiangiogenic Therapy: Strategies Employed by Cancer Cells
Indexación: Web of ScienceTumor angiogenesis is widely recognized as one of the hallmarks of cancer. Consequently, during the last decades the development and testing of commercial angiogenic inhibitors has been a central focus for both basic and clinical cancer research. While antiangiogenic drugs are now incorporated into standard clinical practice, as with all cancer therapies, tumors can eventually become resistant by employing a variety of strategies to receive nutrients and oxygen in the event of therapeutic assault. Herein, we concentrate and review in detail three of the principal mechanisms of antiangiogenic therapy escape: (1) upregulation of compensatory/alternative pathways for angiogenesis; (2) vasculogenic mimicry; and (3) vessel co-option. We suggest that an understanding of how a cancer cell adapts to antiangiogenic therapy may also parallel the mechanisms employed in the bourgeoning tumor and isolated metastatic cells delivering responsible for residual disease. Finally, we speculate on strategies to adapt antiangiogenic therapy for future clinical uses.http://www.mdpi.com/1422-0067/17/9/148
Canard Cycles and Poincar\'e Index of Non-Smooth Vector Fields on the Plane
This paper is concerned with closed orbits of non-smooth vector fields on the
plane. For a subclass of non-smooth vector fields we provide necessary and
sufficient conditions for the existence of canard kind solutions. By means of a
regularization we prove that the canard cycles are singular orbits of singular
perturbation problems which are limit periodic sets of a sequence of limit
cycles. Moreover, we generalize the Poincar\'e Index for non-smooth vector
fields.Comment: 20 pages, 25 figure
Supercritical colliding wind binaries
Context. Particle-accelerating colliding-wind binaries (PACWBs) are systems
that are formed by two massive and hot stars and produce nonthermal (NT)
radiation. The key elements of these systems are fast winds and the shocks that
they create when they collide. Binaries with nonaccreting young pulsars have
also been detected as NT emitters, again as a consequence of the wind-wind
interaction. Black holes (BHs) might produce NT radiation by this mechanism if
they accrete at super-Eddington rates. In such cases, the disk is expected to
launch a radiation-driven wind, and if this wind has an equatorial component,
it can collide with the companion star yielding a PACWB. These systems are
supercritical colliding wind binaries (SCWBs).
Aims. We aim to characterize the particle acceleration and NT radiation
produced by the collision of winds in binary systems composed of a
superaccreting BH and an early-type star.
Methods. We estimated the terminal velocity of the disk-driven wind by
calculating the spatial distribution of the radiation fields and their effect
on disk particles. We then found the location of the wind collision region and
calculated the timescales of energy gain and losses of relativistic particles
undergoing diffusive acceleration. With this information, we were able to
compute the associated spectral energy distribution of the radiation.
Results. We find that the interaction of winds can produce NT emission from
radio up to tens of GeV, with luminosities in the range of , which for the most part are
contributed by electron synchrotron and inverse Compton radiation.
Conclusions. We conclude that SCWBs, such as some ultraluminous X-ray sources
and some Galactic X-ray binaries, are capable of accelerating cosmic rays and
producing NT electromagnetic emission from radio to -rays, in addition
to the thermal components.Comment: 13 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Group Strategyproof Pareto-Stable Marriage with Indifferences via the Generalized Assignment Game
We study the variant of the stable marriage problem in which the preferences
of the agents are allowed to include indifferences. We present a mechanism for
producing Pareto-stable matchings in stable marriage markets with indifferences
that is group strategyproof for one side of the market. Our key technique
involves modeling the stable marriage market as a generalized assignment game.
We also show that our mechanism can be implemented efficiently. These results
can be extended to the college admissions problem with indifferences
Lifetimes of Confined Acoustic Phonons in Ultra-Thin Silicon Membranes
We study the relaxation of coherent acoustic phonon modes with frequencies up
to 500 GHz in ultra-thin free-standing silicon membranes. Using an ultrafast
pump-probe technique of asynchronous optical sampling, we observe that the
decay time of the first-order dilatational mode decreases significantly from
\sim 4.7 ns to 5 ps with decreasing membrane thickness from \sim 194 to 8 nm.
The experimental results are compared with theories considering both intrinsic
phonon-phonon interactions and extrinsic surface roughness scattering including
a wavelength-dependent specularity. Our results provide insight to understand
some of the limits of nanomechanical resonators and thermal transport in
nanostructures
Supersymmetric exact sequence, heat kernel and super KdV hierarchy
We introduce the free N=1 supersymmetric derivation ring and prove the
existence of an exact sequence of supersymmetric rings and linear
transformations. We apply necessary and sufficient conditions arising from this
exact supersymmetric sequence to obtain the essential relations between
conserved quantities, gradients and the N=1 super KdV hierarchy. We combine
this algebraic approach with an analytic analysis of the super heat operator.We
obtain the explicit expression for the Green's function of the super heat
operator in terms of a series expansion and discuss its properties. The
expansion is convergent under the assumption of bounded bosonic and fermionic
potentials. We show that the asymptotic expansion when of the Green's
function for the super heat operator evaluated over its diagonal generates all
the members of the N=1 super KdV hierarchy.Comment: 20 pages, to be published in JM
- …