4,585 research outputs found
Dissipative Preparation of Spin Squeezed Atomic Ensembles in a Steady State
We present and analyze a new approach for the generation of atomic spin
squeezed states. Our method involves the collective coupling of an atomic
ensemble to a decaying mode of an open optical cavity. We demonstrate the
existence of a collective atomic dark-state, decoupled from the radiation
field. By explicitly constructing this state we find that it can feature spin
squeezing bounded only by the Heisenberg limit. We show that such dark states
can be deterministically prepared via dissipative means, thus turning
dissipation into a resource for entanglement. The scaling of the phase
sensitivity taking realistic imperfections into account is discussed.Comment: 5 pages, 4 figure
Profiling of berries by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GCxGC/TOF-MS)
poster C149, Proceedings Annual Biomedical Research Conference for Minority Students (ABRCMS 2011), November 9 - 12, 2011, America’s Center, St. Louis, MO, US
Morphological, compositional, and geometrical transients of V-groove quantum wires formed during metalorganic vapor-phase epitaxy
We present a theoretical model of the formation of self-limited (Al) GaAs quantum wires within V-grooves on GaAs(001) substrates during metalorganic vapor-phase epitaxy. We identify the facet-dependent rates of the kinetic processes responsible for the formation of the self-limiting profile, which is accompanied by Ga segregation along the axis perpendicular to the bottom of the original template, and analyze their interplay with the facet geometry in the transient regime. A reduced model is adopted for the evolution of the patterned profile, as determined by the angle between the different crystallographic planes as a function of the growth conditions. Our results provide a comprehensive phenomenological understanding of the self-ordering mechanism on patterned surfaces which can be harnessed for designing the quantum optical properties of low-dimensional systems. (C) 2013 AIP Publishing LLC
Reconstructing the massive black hole cosmic history through gravitational waves
The massive black holes we observe in galaxies today are the natural
end-product of a complex evolutionary path, in which black holes seeded in
proto-galaxies at high redshift grow through cosmic history via a sequence of
mergers and accretion episodes. Electromagnetic observations probe a small
subset of the population of massive black holes (namely, those that are active
or those that are very close to us), but planned space-based gravitational-wave
observatories such as the Laser Interferometer Space Antenna (LISA) can measure
the parameters of ``electromagnetically invisible'' massive black holes out to
high redshift. In this paper we introduce a Bayesian framework to analyze the
information that can be gathered from a set of such measurements. Our goal is
to connect a set of massive black hole binary merger observations to the
underlying model of massive black hole formation. In other words, given a set
of observed massive black hole coalescences, we assess what information can be
extracted about the underlying massive black hole population model. For
concreteness we consider ten specific models of massive black hole formation,
chosen to probe four important (and largely unconstrained) aspects of the input
physics used in structure formation simulations: seed formation, metallicity
``feedback'', accretion efficiency and accretion geometry. For the first time
we allow for the possibility of ``model mixing'', by drawing the observed
population from some combination of the ``pure'' models that have been
simulated. A Bayesian analysis allows us to recover a posterior probability
distribution for the ``mixing parameters'' that characterize the fractions of
each model represented in the observed distribution. Our work shows that LISA
has enormous potential to probe the underlying physics of structure formation.Comment: 24 pages, 16 figures, submitted to Phys. Rev.
Perturbations of slowly rotating black holes: massive vector fields in the Kerr metric
We discuss a general method to study linear perturbations of slowly rotating
black holes which is valid for any perturbation field, and particularly
advantageous when the field equations are not separable. As an illustration of
the method we investigate massive vector (Proca) perturbations in the Kerr
metric, which do not appear to be separable in the standard Teukolsky
formalism. Working in a perturbative scheme, we discuss two important effects
induced by rotation: a Zeeman-like shift of nonaxisymmetric quasinormal modes
and bound states with different azimuthal number m, and the coupling between
axial and polar modes with different multipolar index l. We explicitly compute
the perturbation equations up to second order in rotation, but in principle the
method can be extended to any order. Working at first order in rotation we show
that polar and axial Proca modes can be computed by solving two decoupled sets
of equations, and we derive a single master equation describing axial
perturbations of spin s=0 and s=+-1. By extending the calculation to second
order we can study the superradiant regime of Proca perturbations in a
self-consistent way. For the first time we show that Proca fields around Kerr
black holes exhibit a superradiant instability, which is significantly stronger
than for massive scalar fields. Because of this instability, astrophysical
observations of spinning black holes provide the tightest upper limit on the
mass of the photon: mv<4x10^-20 eV under our most conservative assumptions.
Spin measurements for the largest black holes could reduce this bound to
mv<10^-22 eV or lower.Comment: v1: 29 pages, 9 figures, 3 appendices. v2: References added and
improved discussion. Matches the version to appear in Physical Review D.
Mathematica notebooks available here http://blackholes.ist.utl.pt/?page=Files
and http://www.phy.olemiss.edu/~berti/qnms.htm
Multifaceted Health Benefits of Mangifera indica L. (Mango): The Inestimable Value of Orchards Recently Planted in Sicilian Rural Areas
Historically, Mangifera indica L. cultivations have been widely planted in tropical areas
of India, Africa, Asia, and Central America. However, at least 20 years ago its spreading allowed
the development of some cultivars in Sicily, an island to the south of Italy, where the favourable
subtropical climate and adapted soils represent the perfect field to create new sources of production
for the Sicilian agricultural supply chain. Currently, cultivations of Kensington Pride, Keitt, Glenn,
Maya, and Tommy Atkins varieties are active in Sicily and their products meet the requirements
of local and European markets. Mango plants produce fleshy stone fruits rich in phytochemicals
with an undisputed nutritional value for its high content of polyphenolics and vitamins. This review
provides an overview of the antioxidant, anti-inflammatory, and anticancer properties of mango,
a fruit that should be included in everyone\u2019s diet for its multifaceted biochemical actions and
health-enhancing properties
Geodesic stability, Lyapunov exponents and quasinormal modes
Geodesic motion determines important features of spacetimes. Null unstable
geodesics are closely related to the appearance of compact objects to external
observers and have been associated with the characteristic modes of black
holes. By computing the Lyapunov exponent, which is the inverse of the
instability timescale associated with this geodesic motion, we show that, in
the eikonal limit, quasinormal modes of black holes in any dimensions are
determined by the parameters of the circular null geodesics. This result is
independent of the field equations and only assumes a stationary, spherically
symmetric and asymptotically flat line element, but it does not seem to be
easily extendable to anti-de Sitter spacetimes. We further show that (i) in
spacetime dimensions greater than four, equatorial circular timelike geodesics
in a Myers-Perry black hole background are unstable, and (ii) the instability
timescale of equatorial null geodesics in Myers-Perry spacetimes has a local
minimum for spacetimes of dimension d > 5.Comment: 13 pages, 2 Figs, RevTex4. v2: Minor corrections. v3: more minor
correction
Gravitational wave signatures of the absence of an event horizon. I. Nonradial oscillations of a thin-shell gravastar
Gravitational waves from compact objects provide information about their
structure, probing deep into strong-gravity regions. Here we illustrate how the
presence or absence of an event horizon can produce qualitative differences in
the gravitational waves emitted by ultra-compact objects. In order to set up a
straw-man ultra-compact object with no event horizon, but which is otherwise
almost identical to a black hole, we consider a nonrotating thin-shell model
inspired by Mazur and Mottola's gravastar, which has a Schwarzschild exterior,
a de Sitter interior and an infinitely thin shell with finite tension
separating the two regions. As viewed from the external space-time, the shell
can be located arbitrarily close to the Schwarzschild radius, so a gravastar
might seem indistinguishable from a black hole when tests are only performed on
its external metric. We study the linearized dynamics of the system, and in
particular the junction conditions connecting internal and external
gravitational perturbations. As a first application of the formalism we compute
polar and axial oscillation modes of a thin-shell gravastar. We show that the
quasinormal mode spectrum is completely different from that of a black hole,
even in the limit when the surface redshift becomes infinite. Polar QNMs depend
on the equation of state of matter on the shell and can be used to distinguish
between different gravastar models. Our calculations suggest that
low-compactness gravastars could be unstable when the sound speed on the shell
vs/c>0.92.Comment: 19 pages, 8 figures. In press in Physical Review D. We found a new
family of modes and improved the discussion of nonradial instabilit
The good and bad of nrf2: An update in cancer and new perspectives in COVID-19
Nuclear factor erythroid 2-related factor 2 (Nrf2) is a well-known transcription factor best recognised as one of the main regulators of the oxidative stress response. Beyond playing a crucial role in cell defence by transactivating cytoprotective genes encoding antioxidant and detoxifying enzymes, Nrf2 is also implicated in a wide network regulating anti-inflammatory response and metabolic reprogramming. Such a broad spectrum of actions renders the factor a key regulator of cell fate and a strategic player in the control of cell transformation and response to viral infections. The Nrf2 protective roles in normal cells account for its anti-tumour and anti-viral functions. However, Nrf2 overstimulation often occurs in tumour cells and a complex correlation of Nrf2 with cancer initiation and progression has been widely described. Therefore, if on one hand, Nrf2 has a dual role in cancer, on the other hand, the factor seems to display a univocal function in preventing inflammation and cytokine storm that occur under viral infections, specifically in coronavirus disease 19 (COVID-19). In such a variegate context, the present review aims to dissect the roles of Nrf2 in both cancer and COVID-19, two widespread diseases that represent a cause of major concern today. In particular, the review describes the molecular aspects of Nrf2 signalling in both pathological situations and the most recent findings about the advantages of Nrf2 inhibition or activation as possible strategies for cancer and COVID-19 treatment respectively
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