15,636 research outputs found
Arbitrary distribution and nonlinear modal interaction in coupled nanomechanical resonators
We propose a general one-dimensional {\em continuous} formulation to analyze
the vibrational modes of antenna-like nanomechanical resonators consisting of
two symmetric arrays of cantilevers affixed to a central nano-beam. The
cantilever arrays can have arbitrary density and length profile along the beam.
We obtain the secular equation that allows for the determination of their
frequency spectrum and illustrate the results on the particular examples of
structures with constant or alternating cantilever length profiles. We show
that our analytical results capture the vibration spectrum of such resonators
and elucidate key relationships that could prove advantageous for experimental
device performance. Furthermore, using a perturbative approach to treat the
nonlinear and dissipative dynamics of driven structures, we analyze the
anharmonic coupling between two specific widely spaced modes of the
coupled-element device, with direct application to experiments.Comment: 8 pages, 5 figures, additional info can be found at
http://nano.bu.ed
Effect of UV Radiation on the Spectral Fingerprints of Earth-like Planets Orbiting M dwarfs
We model the atmospheres and spectra of Earth-like planets orbiting the
entire grid of M dwarfs for active and inactive stellar models with =
2300K to = 3800K and for six observed MUSCLES M dwarfs with UV
radiation data. We set the Earth-like planets at the 1AU equivalent distance
and show spectra from the VIS to IR (0.4m - 20m) to compare
detectability of features in different wavelength ranges with JWST and other
future ground- and spaced-based missions to characterize exo-Earths. We focus
on the effect of UV activity levels on detectable atmospheric features that
indicate habitability on Earth, namely: HO, O, CH, NO and
CHCl.
To observe signatures of life - O/O in combination with reducing
species like CH, we find that early and active M dwarfs are the best
targets of the M star grid for future telescopes. The O spectral feature at
0.76m is increasingly difficult to detect in reflected light of later M
dwarfs due to low stellar flux in that wavelength region. NO, another
biosignature detectable in the IR, builds up to observable concentrations in
our planetary models around M dwarfs with low UV flux. CHCl could become
detectable, depending on the depth of the overlapping NO feature.
We present a spectral database of Earth-like planets around cool stars for
directly imaged planets as a framework for interpreting future lightcurves,
direct imaging, and secondary eclipse measurements of the atmospheres of
terrestrial planets in the HZ to design and assess future telescope
capabilities.Comment: in press, ApJ (submitted August 18, 2014), 16 pages, 12 figure
Leptogenesis from Spin-Gravity Coupling Following Inflation
The energy levels of the left and the right handed neutrinos is split in the
background of gravitational waves generated during inflation which in presence
of lepton number violating interactions gives rise to a net lepton asymmetry at
equilibrium. Lepton number violation is achieved by the same dimension five
operator which gives rise to neutrino masses after electro-weak symmetry
breaking. A net baryon asymmetry of the same magnitude can be generated from
this lepton asymmetry by electroweak sphaleron processes.Comment: Journal version (accepted for publication in Phys. Rev. Lett.
Angular momentum evolution of young low-mass stars and brown dwarfs: observations and theory
This chapter aims at providing the most complete review of both the emerging
concepts and the latest observational results regarding the angular momentum
evolution of young low-mass stars and brown dwarfs. In the time since
Protostars & Planets V, there have been major developments in the availability
of rotation period measurements at multiple ages and in different star-forming
environments that are essential for testing theory. In parallel, substantial
theoretical developments have been carried out in the last few years, including
the physics of the star-disk interaction, numerical simulations of stellar
winds, and the investigation of angular momentum transport processes in stellar
interiors. This chapter reviews both the recent observational and theoretical
advances that prompted the development of renewed angular momentum evolution
models for cool stars and brown dwarfs. While the main observational trends of
the rotational history of low mass objects seem to be accounted for by these
new models, a number of critical open issues remain that are outlined in this
review.Comment: 22 pages, 8 figures, accepted for publication in Protostars & Planets
VI, 2014, University of Arizona Press, eds. H. Beuther, R. Klessen, K.
Dullemond, Th. Hennin
Particle Swarm Optimization and gravitational wave data analysis: Performance on a binary inspiral testbed
The detection and estimation of gravitational wave (GW) signals belonging to
a parameterized family of waveforms requires, in general, the numerical
maximization of a data-dependent function of the signal parameters. Due to
noise in the data, the function to be maximized is often highly multi-modal
with numerous local maxima. Searching for the global maximum then becomes
computationally expensive, which in turn can limit the scientific scope of the
search. Stochastic optimization is one possible approach to reducing
computational costs in such applications. We report results from a first
investigation of the Particle Swarm Optimization (PSO) method in this context.
The method is applied to a testbed motivated by the problem of detection and
estimation of a binary inspiral signal. Our results show that PSO works well in
the presence of high multi-modality, making it a viable candidate method for
further applications in GW data analysis.Comment: 13 pages, 5 figure
Nutritional disorders in rice due to infestation by Heterodera oryzicola and Meloidogyne graminicola
Exploring the QCD landscape with high-energy nuclear collisions
Quantum chromodynamics (QCD) phase diagram is usually plotted as temperature
(T) versus the chemical potential associated with the conserved baryon number
(\mu_{B}). Two fundamental properties of QCD, related to confinement and chiral
symmetry, allows for two corresponding phase transitions when T and \mu_{B} are
varied. Theoretically the phase diagram is explored through non-perturbative
QCD calculations on lattice. The energy scale for the phase diagram
(\Lambda_{QCD} ~ 200 MeV) is such that it can be explored experimentally by
colliding nuclei at varying beam energies in the laboratory. In this paper we
review some aspects of the QCD phase structure as explored through the
experimental studies using high energy nuclear collisions. Specifically, we
discuss three observations related to the formation of a strongly coupled
plasma of quarks and gluons in the collisions, experimental search for the QCD
critical point on the phase diagram and freeze-out properties of the hadronic
phase.Comment: Submitted to the New Journal of Physics focus issue "Strongly
Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD Plasmas
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