566 research outputs found
Vacuum Solutions of Einstein's Equations in Parabolic Coordinates
We present a simple method to obtain vacuum solutions of Einstein's equations
in parabolic coordinates starting from ones with cylindrical symmetries.
Furthermore, a generalization of the method to a more general situation is
given together with a discussion of the possible relations between our method
and the Belinsky-Zakharov soliton-generating solutions.Comment: 15 pages, version published in Class. Quantum Gra
Measurement of the electric dipole moments for transitions to rubidium Rydberg states via Autler-Townes splitting
We present the direct measurements of electric-dipole moments for
transitions with for Rubidium atoms. The
measurements were performed in an ultracold sample via observation of the
Autler-Townes splitting in a three-level ladder scheme, commonly used for
2-photon excitation of Rydberg states. To the best of our knowledge, this is
the first systematic measurement of the electric dipole moments for transitions
from low excited states of rubidium to Rydberg states. Due to its simplicity
and versatility, this method can be easily extended to other transitions and
other atomic species with little constraints. Good agreement of the
experimental results with theory proves the reliability of the measurement
method.Comment: 12 pages, 6 figures; figure 6 replaced with correct versio
Inflation for Bianchi IX model
The influence of Inflation on initial (i.e. at Planck's epoch) large
anisotropy of the Universe is studied, considering a more general metric than
the isotropic one: the locally rotationally symmetric (L.R.S.) Bianchi IX
metric. We find, then, a large set of initial conditions of intrinsic curvature
and shear allowing an inflationary epoch that make the anisotropy negligible.
These are not trivial because of the non-linearity of the Einstein's equations.Comment: 10 pages, Latex. To be published in Phisical Review
Two-dimensional array of microtraps with atomic shift register on a chip
Arrays of trapped atoms are the ideal starting point for developing registers
comprising large numbers of physical qubits for storing and processing quantum
information. One very promising approach involves neutral atom traps produced
on microfabricated devices known as atom chips, as almost arbitrary trap
configurations can be realised in a robust and compact package. Until now,
however, atom chip experiments have focused on small systems incorporating
single or only a few individual traps. Here we report experiments on a
two-dimensional array of trapped ultracold atom clouds prepared using a simple
magnetic-film atom chip. We are able to load atoms into hundreds of tightly
confining and optically resolved array sites. We then cool the individual atom
clouds in parallel to the critical temperature required for quantum degeneracy.
Atoms are shuttled across the chip surface utilising the atom chip as an atomic
shift register and local manipulation of atoms is implemented using a focused
laser to rapidly empty individual traps.Comment: 6 pages, 4 figure
Constraints on the [C II] luminosity of a proto-globular cluster at z ∼ 6 obtained with ALMA
We report on ALMA observations of D1, a system at z ∼ 6.15 with stellar mass M∼ 107M⊙ containing globular cluster (GC) precursors, stronglymagnified by the galaxy clusterMACS J0416.1-2403. Since the discovery of GC progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas through infrared observations. A careful analysis of our data set, performed with a suitable procedure designed to identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us to identify a 4σ tentative detection of [CII] emission with intrinsic luminosity L[C II] = (2.9 ± 1.4) 106 L⊙, one of the lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the L[C II]-SFR relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face value our estimate lies more than ∼1 dex below the values observed in local and high redshift systems. Our weak detection indicates a deficiency of [C II] emission, possibly ascribed to various explanations, such as a low-density gas and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection in the continuum, we derive constraints on the dust mass, with 3σ upper limit values as low as ∼ a few 104 M⊙, consistent with the values measured in local metal-poor galaxies
A MUSE view of the massive merging galaxy cluster ACT-CL J0102-4915 (El Gordo) at z = 0.87: robust strong lensing model and data release
We present a detailed strong lensing analysis of the massive and distant
() galaxy cluster ACT-CL J01024915 (ACT0102, also known as El
Gordo), taking advantage of new spectroscopic data from the Multi Unit
Spectroscopic Explorer (MUSE) on the Very Large Telescope, and archival imaging
from the Hubble Space Telescope. Thanks to the MUSE data, we measure secure
redshifts for 374 single objects, including 23 multiply lensed galaxies, and
167 cluster members of ACT0102. The observed positions of 56 multiple images,
along with their new spectroscopic redshift measurements, are used as
constraints for our strong lensing model. Remarkably, some multiple images are
detected out to a large projected distance of Mpc from the
brightest cluster galaxy, allowing us to estimate a projected total mass value
of within that radius. We
find that we need two extended cluster mass components, the mass contributions
from the cluster members and the additional lensing effect of a foreground
() group of galaxies, to predict the positions of all multiple images
with a root mean square offset of . The main cluster-scale mass
component is centered very closely to the brightest cluster galaxy and the
other extended mass component is located in the north-west region of the
cluster. These two mass components have very similar values of mass projected
within 300 kpc from their centers, namely
and
, in agreement with the major
merging scenario of ACT0102. We make publicly available the lens model,
including the magnification maps and posterior distributions of the model
parameter values, as well as the full spectroscopic catalogue containing all
redshift measurements obtained with MUSE.Comment: 12 pages, 9 figures, 4 tables + appendix. Submitted to A&
Jaynes-Cummings dynamics in mesoscopic ensembles of Rydberg-blockaded atoms
We show that Jaynes-Cummings dynamics can be observed in mesoscopic atomic ensembles interacting with a classical electromagnetic field in the regime of a Rydberg blockade where the time dynamics of the average number of Rydberg excitations in mesoscopic ensembles displays collapses and revivals typical of this model. As the frequency of Rabi oscillations between collective states of Rydberg-blockaded ensembles depends on the number of interacting atoms, for randomly loaded optical dipole traps, we predict collapses and revivals of Rabi oscillations. We have studied the effects of finite interaction strengths and a finite laser linewidth on the visibility of the revivals. We have shown that observation of collapses and revivals of Rabi oscillations can be used as a signature of the Rydberg blockade without the need to measure the exact number of Rydberg atoms
Rehabilitative treatment of patients with covid-19 infection: The p.a.r.m.a. evidence based clinical practice protocol
Background: The impact of the SARS-CoV-2 on the National Health System (NHS) required a reorganization of the various levels of care, which also involved the rehabilitation reality. Aim of the work: A clinical practice review of the literature was conducted to provide operational-rehabilitation guidelines adapt-ed to the local reality and to the recent corporate reorganization in the context of the COVID-19 emergency. Methods: A practice review of the available scientific evidence was regularly conducted from the start of the COVID-19 pandemic to periodically update the clinical practice guidelines. Articles that met the following inclusion criteria were included: studies conducted on human adult subjects with COVID-19 infection, un-dergoing rehabilitation in any hospitalization setting. Results: The results of this clinical practice update were periodically discussed with colleagues and collaborators in a multi-professional team, in order to guarantee a good clinical practice protocol, named P.A.R.M.A. Conclusions: The P.A.R.M.A. protocol is the result of a periodic review literature update, which has allowed us to take charge of patients affected by COVID-19 ac-cording to the most up-to-date clinical evidences, guaranteeing a shared and uniform treatment within a local reality in an era of health emergency. (www.actabiomedica.it)
Psychosocial assessment of families caring for a child with acute lymphoblastic leukemia, epilepsy or asthma: Psychosocial risk as network of interacting symptoms
The purpose of this study is to assess psychosocial risk across several pediatric medical conditions and test the hypothesis that different severe or chronic pediatric illnesses are characterized by disease specific enhanced psychosocial risk and that risk is driven by disease specific connectivity and interdependencies among various domains of psychosocial function using the Psychosocial Assessment Tool (PAT). In a multicenter prospective cohort study of 195 patients, aged 5-12, 90 diagnosed with acute lymphoblastic leukemia (ALL), 42 with epilepsy and 63 with asthma, parents completed the PAT2.0 or the PAT2.0 generic version. Multivariate analysis was performed with disease as factor and age as covariate. Graph theory and network analysis was employed to study the connectivity and interdependencies among subscales of the PAT while data-driven cluster analysis was used to test whether common patterns of risk exist among the various diseases. Using a network modelling approach analysis, we observed unique patterns of interconnected domains of psychosocial factors. Each pathology was characterized by different interdependencies among the most central and most connected domains. Furthermore, data-driven cluster analysis resulted in two clusters: patients with ALL (89%) mostly belonged to cluster 1, while patients with epilepsy and asthma belonged primarily to cluster 2 (83% and 82% respectively). In sum, implementing a network approach improves our comprehension concerning the character of the problems central to the development of psychosocial difficulties. Therapy directed at problems related to the most central domain(s) constitutes the more rational one because such an approach will inevitably carry over to other domains that depend on the more central function
Dynamical Compactification, Standard Cosmology and the Accelerating Universe
A cosmological model based on Kaluza-Klein theory is studied. A metric, in
which the scale factor of the compact space evolves as an inverse power of the
radius of the observable universe, is constructed. The
Freedmann-Robertson-Walker equations of standard four-dimensional cosmology are
obtained precisely. The pressure in our universe is an effective pressure
expressed in terms of the components of the higher dimensional energy-momentum
tensor. In particular, this effective pressure could be negative and might
therefore explain the acceleration of our present universe. A special feature
of this model is that, for a suitable choice of the parameters of the metric,
the higher dimensional gravitational coupling constant could be negative.Comment: 11 pages, uses revte
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