5,747 research outputs found
Accurate evolutions of inspiralling and magnetized neutron-stars: equal-mass binaries
By performing new, long and numerically accurate general-relativistic
simulations of magnetized, equal-mass neutron-star binaries, we investigate the
role that realistic magnetic fields may have in the evolution of these systems.
In particular, we study the evolution of the magnetic fields and show that they
can influence the survival of the hypermassive-neutron star produced at the
merger by accelerating its collapse to a black hole. We also provide evidence
that even if purely poloidal initially, the magnetic fields produced in the
tori surrounding the black hole have toroidal and poloidal components of
equivalent strength. When estimating the possibility that magnetic fields could
have an impact on the gravitational-wave signals emitted by these systems
either during the inspiral or after the merger we conclude that for realistic
magnetic-field strengths B<~1e12 G such effects could be detected, but only
marginally, by detectors such as advanced LIGO or advanced Virgo. However,
magnetically induced modifications could become detectable in the case of
small-mass binaries and with the development of gravitational-wave detectors,
such as the Einstein Telescope, with much higher sensitivities at frequencies
larger than ~2 kHz.Comment: 18 pages, 10 figures. Added two new figures (figures 1 and 7). Small
modifications to the text to match the version published on Phys. Rev.
Superconducting resonators as beam splitters for linear-optics quantum computation
A functioning quantum computer will be a machine that builds up, in a
programmable way, nonclassical correlations in a multipartite quantum system.
Linear optics quantum computation (LOQC) is an approach for achieving this
function that requires only simple, reliable linear optical elements, namely
beam splitters and phase shifters. Nonlinear optics is only required in the
form of single-photon sources for state initialization, and detectors. However,
the latter remain difficult to achieve with high fidelity. A new setting for
quantum optics has arisen in circuit quantum electrodynamics (cQED) using
superconducting (SC) quantum devices, and opening up the way to LOQC using
microwave, rather than visible photons. Much progress is being made in SC
qubits and cQED: high-fidelity Fock state generation and qubit measurements
provide single photon sources and detection. Here we show that the LOQC toolkit
in cQED can be completed with high-fidelity (>99.92%) linear optical elements.Comment: 4 pages, 3 figure
The Magnetic Sensitivity of the Ba II D1 and D2 Lines of the Fraunhofer Spectrum
The physical interpretation of the spectral line polarization produced by the
joint action of the Hanle and Zeeman effects offers a unique opportunity to
obtain empirical information about hidden aspects of solar and stellar
magnetism. To this end, it is important to achieve a complete understanding of
the sensitivity of the emergent spectral line polarization to the presence of a
magnetic field. Here we present a detailed theoretical investigation on the
role of resonance scattering and magnetic fields on the polarization signals of
the Ba II D1 and D2 lines of the Fraunhofer spectrum, respectively at 4934 \AA\
and 4554 \AA. We adopt a three-level model of Ba II, and we take into account
the hyperfine structure that is shown by the Ba and Ba
isotopes. Despite of their relatively small abundance (18%), the contribution
coming from these two isotopes is indeed fundamental for the interpretation of
the polarization signals observed in these lines. We consider an optically thin
slab model, through which we can investigate in a rigorous way the essential
physical mechanisms involved (resonance polarization, Zeeman, Paschen-Back and
Hanle effects), avoiding complications due to radiative transfer effects. We
assume the slab to be illuminated from below by the photospheric solar
continuum radiation field, and we investigate the radiation scattered at 90
degrees, both in the absence and in the presence of magnetic fields,
deterministic and microturbulent. We show in particular the existence of a
differential magnetic sensitivity of the three-peak Q/I profile that is
observed in the D2 line in quiet regions close to the solar limb, which is of
great interest for magnetic field diagnostics.Comment: 40 pages, 1 table and 19 figures. Accepted for publication in The
Astrophysical Journal (ApJ
Far-Ultraviolet Activity Levels of F, G, K, and M dwarf Exoplanet Host Stars
We present a survey of far-ultraviolet (FUV; 1150 - 1450 Ang) emission line
spectra from 71 planet-hosting and 33 non-planet-hosting F, G, K, and M dwarfs
with the goals of characterizing their range of FUV activity levels,
calibrating the FUV activity level to the 90 - 360 Ang extreme-ultraviolet
(EUV) stellar flux, and investigating the potential for FUV emission lines to
probe star-planet interactions (SPIs). We build this emission line sample from
a combination of new and archival observations with the Hubble Space
Telescope-COS and -STIS instruments, targeting the chromospheric and transition
region emission lines of Si III, N V, C II, and Si IV.
We find that the exoplanet host stars, on average, display factors of 5 - 10
lower UV activity levels compared with the non-planet hosting sample; this is
explained by a combination of observational and astrophysical biases in the
selection of stars for radial-velocity planet searches. We demonstrate that UV
activity-rotation relation in the full F - M star sample is characterized by a
power-law decline (with index ~ -1.1), starting at rotation periods
>~3.5 days. Using N V or Si IV spectra and a knowledge of the star's bolometric
flux, we present a new analytic relationship to estimate the intrinsic stellar
EUV irradiance in the 90 - 360 Ang band with an accuracy of roughly a factor of
~2. Finally, we study the correlation between SPI strength and UV activity in
the context of a principal component analysis that controls for the sample
biases. We find that SPIs are not a statistically significant contributor to
the observed UV activity levels.Comment: ApJS, accepted. 33 pages in emulateapj, 13 figures, 10 table
Our Peculiar Motion Away from the Local Void
The peculiar velocity of the Local Group of galaxies manifested in the Cosmic
Microwave Background dipole is found to decompose into three dominant
components. The three components are clearly separated because they arise on
distinct spatial scales and are fortuitously almost orthogonal in their
influences. The nearest, which is distinguished by a velocity discontinuity at
~7 Mpc, arises from the evacuation of the Local Void. We lie in the Local Sheet
that bounds the void. Random motions within the Local Sheet are small. Our
Galaxy participates in the bulk motion of the Local Sheet away from the Local
Void. The component of our motion on an intermediate scale is attributed to the
Virgo Cluster and its surroundings, 17 Mpc away. The third and largest
component is an attraction on scales larger than 3000 km/s and centered near
the direction of the Centaurus Cluster. The amplitudes of the three components
are 259, 185, and 455 km/s, respectively, adding collectively to 631 km/s in
the reference frame of the Local Sheet. Taking the nearby influences into
account causes the residual attributed to large scales to align with observed
concentrations of distant galaxies and reduces somewhat the amplitude of motion
attributed to their pull. On small scales, in addition to the motion of our
Local Sheet away from the Local Void, the nearest adjacent filament, the Leo
Spur, is seen to be moving in a direction that will lead to convergence with
our filament. Finally, a good distance to an isolated galaxy within the Local
Void reveals that this dwarf system has a motion of at least 230 km/s away from
the void center. Given the velocities expected from gravitational instability
theory in the standard cosmological paradigm, the distance to the center of the
Local Void must be at least 23 Mpc from our position. The Local Void is large!Comment: Tentatively scheduled for Astrophysical Journal, 676 (March 20),
2008. 18 figures, 3 tables including web link for 2 tables, web links to 2
video
Functional assessment of cancer therapy questionnaire for breast cancer (FACT-B+4): Italian version validation
BACKGROUND:
Improvements in breast cancer diagnosis and treatment led to an increased incidence of survivors' rate. The healthcare system has to face new problems related not only to the treatment of the disease, but also to the management of the quality of life after the diagnosis. The aim of this study was to validate the Italian version of the Functional Assessment of Cancer Therapy - Breast (FACT-B+4) questionnaire and to evaluate its reliability.
METHODS:
The questionnaire was administered twice, with an interval of three days between each administration, to a cohort of women of the Breast Surgical Unit, PoliclincoUmberto I. Cronbach's alpha was used as a measure of the internal consistency of the Italian version.
RESULTS:
The Italian version of the tool was administered to 55 subjects. The Cronbach's alpha for most scores registered values >0.7, both at baseline and at the follow-up analysis, therefore the subscale showed good internal consistency.
CONCLUSIONS:
The Italian version of FACT-B+4 demonstrated acceptable reliability properties in the Breast Unit patients. The use of this questionnaire seemed to be effective and in line with the results derived from the English and Spanishversions. Internal consistency and validity had similar performance results
Extracellular vesicle microRNAs contribute to the osteogenic inhibition of mesenchymal stem cells in multiple myeloma
Osteolytic bone disease is the major complication associated with the progression of multiple myeloma (MM). Recently, extracellular vesicles (EVs) have emerged as mediators of MM-associated bone disease by inhibiting the osteogenic differentiation of human mesenchymal stem cells (hMSCs). Here, we investigated a correlation between the EV-mediated osteogenic inhibition and MM vesicle content, focusing on miRNAs. By the use of a MicroRNA Card, we identified a pool of miRNAs, highly expressed in EVs, from MM cell line (MM1.S EVs), expression of which was confirmed in EVs from bone marrow (BM) plasma of patients affected by smoldering myeloma (SMM) and MM. Notably,we found that miR-129-5p, which targets different osteoblast (OBs) differentiation markers, is enriched in MM-EVs compared to SMM-EVs, thus suggesting a selective packaging correlated with pathological grade. We found that miR-129-5p can be transported to hMSCs by MM-EVs and, by the use of miRNA mimics, we investigated its role in recipient cells. Our data demonstrated that the increase of miR-129-5p levels in hMSCs under osteoblastic differentiation stimuli inhibited the expression of the transcription factor Sp1, previously described as a positive modulator of osteoblastic differentiation, and of its target the Alkaline phosphatase (ALPL), thus identifying miR-129-5p among the players of vesicle-mediated bone disease
Variable stars in the Fornax dSph Galaxy. II. Pulsating stars below the horizontal branch
We have carried out an intensive survey of the northern region of the Fornax
dwarf spheroidal galaxy with the aim of detecting the galaxy's short--period
pulsating stars (P<0.25 days). Observations collected over three consecutive
nights with the Wide Field Imager of the 2.2m MPI telescope at ESO allowed us
to detect 85 high-amplitude (0.20-1.00 mag in B-light) variable stars with
periods in the range from 0.046 to 0.126 days, similar to SX Phoenicis stars in
Galactic metal-poor stellar populations. The plots of the observed periods vs.
the B and V magnitudes show a dispersion largely exceeding the observational
errors. To disentangle the matter, we separated the first-overtone from the
fundamental-mode pulsators and tentatively identified a group of subluminous
variables, about 0.35 mag fainter than the others. Their nature as either
metal-poor intermediate-age stars or stars formed by the merging of close
binary systems is discussed. The rich sample of the Fornax variables also led
us to reconstruct the Period-Luminosity relation for short-period pulsating
stars. An excellent linear fit, M(V)=-1.83(+/-0.08)-3.65(+/-0.07) log P(fund),
was obtained using 153 Delta Scuti and SX Phoenicis stars in a number of
different stellar systems.Comment: 11 pages plus 1 on-line figure and 1 on-line table; accepted for
publication in ApJ. Part of this work has been the subject of the Laurea
thesis of LDA. His supervisor and our colleague, Prof. Laura E. Pasinetti,
suddendly passed away on September 13, 2006. Several astronomers have been
trained under her tutelage and we gratefully honor her memor
Time Resolved Correlation measurements of temporally heterogeneous dynamics
Time Resolved Correlation (TRC) is a recently introduced light scattering
technique that allows to detect and quantify dynamic heterogeneities. The
technique is based on the analysis of the temporal evolution of the speckle
pattern generated by the light scattered by a sample, which is quantified by
, the degree of correlation between speckle images recorded at
time and . Heterogeneous dynamics results in significant
fluctuations of with time . We describe how to optimize TRC
measurements and how to detect and avoid possible artifacts. The statistical
properties of the fluctuations of are analyzed by studying their
variance, probability distribution function, and time autocorrelation function.
We show that these quantities are affected by a noise contribution due to the
finite number of detected speckles. We propose and demonstrate a method to
correct for the noise contribution, based on a extrapolation
scheme. Examples from both homogeneous and heterogeneous dynamics are provided.
Connections with recent numerical and analytical works on heterogeneous glassy
dynamics are briefly discussed.Comment: 19 pages, 15 figures. Submitted to PR
Search for the Optical Counterpart of the Vela Pulsar X-ray Nebula
Observations of the Vela pulsar region with the Chandra X-ray observatory
have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN),
which showed an overall similarity with the Crab PWN. However, contrary to the
Crab, no firm detection of the Vela PWN in optical has been reported yet. To
search for the optical counterpart of the X-ray PWN, we analyzed deep optical
observations performed with different telescopes. We compared the optical
images with those obtained with the Chandra ACIS to search for extended
emission patterns which could be identified as counterparts of the X-ray nebula
elements. Although some features are seen in the optical images, we find no
correlation with the X-ray structure. Thus, we conclude that the diffuse
optical emission is more likely associated with filaments in the host Vela SNR.
The derived upper limits on the optical flux from the PWN are compatibile,
within the uncertainties, with the values expected on the basis of the
extrapolations of the X-ray data.Comment: 19 pages, 6 figures. Accepted for publication in Ap
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