3,766 research outputs found
Analysis of the fraction of clear sky at the La Palma and Mt Graham sites
The fraction of available telescope time is one of the most important
requirements for selecting astronomical sites affecting the performance of
ground based telescopes. A quantitative survey of clouds coverage at La Palma
and Mt.Graham is presented using both ground and satellite based data. The aim
of this work is deriving clear nights for the satellite infrared channels and
verifying the results using ground based observations. At La Palma we found a
mean percentage of clear nights of 62.6% from ground and 71.9% from satellite.
Taking into account the fraction of common nights we found a concordance of
80.7% clear nights from ground and satellite.
At Mt.Graham we found a 97% of agreement between Columbine heliograph and
night time observing log. From Columbine heliograph and TOMS-OMI satellite we
found about 45% of clear nights, while satellite data (GOES, TOMS) are much
more dispersed than those ones of La Palma. Setting a statistical threshold we
retried a comparable seasonal trend between heliograph and satellite.Comment: 14 pages, 18 figures, 6 tables, MNRAS accepted on September 23 200
Fraction of clear skies above astronomical sites: a new analysis from the GOES12 satellite
Comparing the number of clear nights (cloud free) available for astronomical
observations is a critical task because it should be based on homogeneous
methodologies. Current data are mainly based on different judgements based on
observer logbooks or on different instruments. In this paper we present a new
homogeneous methodology on very different astronomical sites for modern optical
astronomy, in order to quantify the available night time fraction. The data are
extracted from night time GOES12 satellite infrared images and compared with
ground based conditions when available. In this analysis we introduce a wider
average matrix and 3-Bands correlation in order to reduce the noise and to
distinguish between clear and stable nights. Temporal data are used for the
classification. In the time interval 2007-2008 we found that the percentage of
the satellite clear nights is 88% at Paranal, 76% at La Silla, 72.5% at La
Palma, 59% at Mt. Graham and 86.5% at Tolonchar. The correlation analysis of
the three GOES12 infrared bands B3, B4 and B6 indicates that the fraction of
the stable nights is lower by 2% to 20% depending on the site
Coherent tunneling by adiabatic passage in an optical waveguide system
We report on the first experimental demonstration of light transfer in an
engineered triple-well optical waveguide structure which provides a classic
analogue of Coherent Tunnelling by Adiabatic Passage (CTAP) recently proposed
for coherent transport in space of neutral atoms or electrons among
tunneling-coupled optical traps or quantum wells [A.D. Greentree et al., Phys.
Rev. B 70, 235317 (2004); K. Eckert et al., Phys. Rev. A 70, 023606 (2004)].
The direct visualization of CTAP wavepacket dynamics enabled by our simple
optical system clearly shows that in the counterintuitive passage scheme light
waves tunnel between the two outer wells without appreciable excitation of the
middle well.Comment: submitted for publicatio
Plasmonic Sensors beyond the Phase Matching Condition: A Simplified Approach
The conventional approach to optimising plasmonic sensors is typically based entirely on ensuring phase matching between the excitation wave and the surface plasmon supported by the metallic structure. However, this leads to suboptimal performance, even in the simplest sensor configuration based on the Otto geometry. We present a simplified coupled mode theory approach for evaluating and optimizing the sensing properties of plasmonic waveguide refractive index sensors. It only requires the calculation of propagation constants, without the need for calculating mode overlap integrals. We apply our method by evaluating the wavelength-, device length- and refractive index-dependent transmission spectra for an example silicon-on-insulator-based sensor of finite length. This reveals all salient spectral features which are consistent with full-field finite element calculations. This work provides a rapid and convenient framework for designing dielectric-plasmonic sensor prototypes-its applicability to the case of fibre plasmonic sensors is also discussed
Platelet proteome and clopidogrel response in patients with stable angina undergoing percutaneous coronary intervention
Objectives: We analyzed the platelet proteome of circulating platelets during the onset of clopidogrel therapy in patients with stable angina underwent percutaneous coronary intervention in order to investigate the mechanisms that control platelet reactivity and clopidogrel response in this context.
Design & methods: Twenty patients were enrolled in this study. Blood samples were collected before coronary angiography (T0), 12 h after 600 mg of clopidogrel (T1) and 24 h after percutaneous coronary intervention (PCI) (T2). Platelet reactivity, Clopidogrel response and proteomic analysis were examined.
Results: Clopidogrel loading dose produced a significant inhibition in all markers of platelet activation in both flow cytometry and aggregation tests. Among the proteins found differentially expressed, eighteen were identified by MS/MS analysis and they resulted involved in the cytoskeleton rearrangement (profilin-1, calpain, α-soluble NSF attachment protein, thrombospondin), in the energetic metabolism (ubiquitin-like
modifier-activating enzyme 1, protein-L-isoaspartate-(D-aspartate) O-methyltransferase and nucleoside diphosphate kinase B) and in the oxidative stress (heat shock 70 kDa protein 5 and anti-stress induced phosphoprotein 1.
Conclusions: The present study provides novel information on platelet proteome changes associated with platelet activation and clopidogrel response. This investigation supports the development of further proteomic studies for the identification of novel platelet biomarkers
A Black Hole in the X-Ray Nova Velorum 1993
We have obtained 17 moderate-resolution (~2.5 A) optical spectra of the
Galactic X-ray Nova Velorum 1993 in quiescence with the Keck-II telescope. The
orbital period (P) is 0.285206 +/- 0.0000014 d, and the semiamplitude (K_2) is
475.4 +/- 5.9 km/s. Our derived mass function, f(M_1) = PK_2^3 /2 pi G = 3.17
+/- 0.12 M_sun, is close to the conventional absolute limiting mass for a
neutron star (~ 3.0-3.2 M_sun) -- but if the orbital inclination i is less than
80 degrees (given the absences of eclipses), then M_1 is greater than 4.2-4.4
M_sun for nominal secondary-star masses of 0.5 M_sun (M0) to 0.65 M_sun (K6).
The primary star is therefore almost certainly a black hole rather than a
neutron star. The velocity curve of the primary from H-alpha emission has a
semiamplitude (K_1) of 65.3 +/- 7.0 km/s, but with a phase offset by 237
degrees (rather than 180 degrees) from that of the secondary star. The nominal
mass ratio q = M_2/M_1 = K_1/K_2 = 0.137 +/- 0.015, and hence for M_2 =
0.5-0.65 M_sun we derive M_1 = 3.64-4.74 M_sun. An adopted mass M_1 ~ 4.4 M_sun
is significantly below the typical value of ~ 7 M_sun found for black holes in
other low-mass X-ray binaries.
Keck observations of MXB 1659-29 (V2134 Oph) in quiescence reveal a probable
optical counterpart at R = 23.6 +/- 0.4 mag.Comment: 16 pages, 9 figures, added references, revised per. referee's
comments Accepted for publication in August 1999 issue of PAS
Nonlinearity-induced broadening of resonances in dynamically modulated couplers
We report the observation of nonlinearity-induced broadening of resonances in
dynamically modulated directional couplers. When the refractive index of the
guiding channels in the coupler is harmonically modulated along the propagation
direction and out-of-phase in two channels, coupling can be completely
inhibited at resonant modulation frequencies. We observe that nonlinearity
broadens such resonances and that localization can be achieved even in detuned
systems at power levels well below those required in unmodulated couplers.Comment: 14 pages, 4 figures, to appear in Optics Letter
Probing electromagnetic-gravitational wave emission coincidence in type I binary-driven hypernova family of long GRBs at very-high redshift
Due to the technical time delay of the XRT instrument on board the Neil
Gehrels Swift Observatory satellite, we cannot observe the X-ray emission
occurring less than ~s after a gamma-ray burst (GRB) trigger time. We
here indicate a new strategy of using the cosmological time dilatation in high
redshift GRBs to observe the earliest X-ray emission by Swift/XRT in the GRB
cosmological rest-frame. We illustrate this procedure using GRBs with a
well-defined cosmological redshift selected from the Swift GRB catalog. We
compare and contrast the time delay between the trigger of the source and the
first observation by Swift/XRT as measured in the observer frame (OTD) and the
corresponding delay measured in GRBs' cosmological rest-frame (RTD). We
consider as specific prototypes three binary-driven hypernovae of type I (BdHNe
I): GRB 090423 at with an RTD of ~s, GRB 090429B at
with an RTD of ~s, as well as the GRB 220101A at with an RTD of
~s. This opens a new possibility for probing Episode (1) of BdHNe, linked
to the origin and early appearance of the newborn neutron star (NS) and
its transition from a Jacobi triaxial ellipsoid (JTE) to a Maclaurin spheroid
configuration that originates the GRB afterglow onset. We also present the
methodology to compute the sweeping frequencies and the energetics of the
associated conspicuous gravitational wave emission.Comment: submitted to Ap
GRB-SN Association within the Binary-Driven Hypernova Model
The observations of supernovae (SNe) Ic occurring after the prompt emission
of long gamma-ray bursts (GRBs) are addressed within the binary-driven
hypernova (BdHN) model where GRBs originate from a binary composed of a
carbon-oxygen (CO) star and a neutron star (NS). The CO core
collapse gives the trigger, leading to a hypernova with a fast-spinning newborn
NS (NS) at its center. The evolution depends strongly on the binary
period, . For min, BdHNe I occur with energies
--erg. The accretion of SN ejecta onto the NS leads to its
collapse, forming a black hole (BH) originating the MeV/GeV radiation. For
min, BdHNe II occur with energies --erg
and for hours, BdHN III occurs with energies below
erg. {In BdHNe II and III,} no BH is formed. The --ms NS
originates, in all BdHNe, the X-ray-optical-radio afterglows by synchrotron
emission. The hypernova follows an independent evolution, becoming an SN Ic,
powered by nickel decay, observable after the GRB prompt emission. We report
SNe Ic associated with BdHNe. Their optical peak luminosity and time of
occurrence are similar and independent of the associated GRBs. {From previously
identified BdHN I comprising redshifts up to , we analyze} four
examples with their associated hypernovae. By multiwavelength extragalactic
observations, we identify seven new Episodes, theoretically explained,
fortunately not yet detected in galactic sources, opening new research areas.
Refinement of population synthesis simulations is needed to map the progenitors
of such short-lived binary systems inside our galaxy.Comment: Accepted for publication in The Astrophysical Journa
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