2,635 research outputs found
Time-resolved lidar fluorosensor for sea pollution detection
A contemporary time and spectral analysis of oil fluorescence is useful for the detection and the characterization of oil spills on the sea surface. Nevertheless the fluorosensor lidars, which were realized up to now, have only partial capability to perform this double analysis. The main difficulties are the high resolution required (of the order of 1 nanosecond) and the complexity of the detection system for the recording of a two-dimensional matrix of data for each laser pulse. An airborne system whose major specifications were: time range, 30 to 75 ns; time resolution, 1 ns; spectral range, 350 to 700 nm; and spectral resolution, 10 nm was designed and constructed. The designed system of a short pulse ultraviolet laser source and a streak camera based detector are described
The effects of tidally induced disc structure on white dwarf accretion in intermediate polars
We investigate the effects of tidally induced asymmetric disc structure on
accretion onto the white dwarf in intermediate polars. Using numerical
simulation, we show that it is possible for tidally induced spiral waves to
propagate sufficiently far into the disc of an intermediate polar that
accretion onto the central white dwarf could be modulated as a result. We
suggest that accretion from the resulting asymmetric inner disc may contribute
to the observed X-ray and optical periodicities in the light curves of these
systems. In contrast to the stream-fed accretion model for these periodicities,
the tidal picture predicts that modulation can exist even for systems with
weaker magnetic fields where the magnetospheric radius is smaller than the
radius of periastron of the mass transfer stream. We also predict that
additional periodic components should exist in the emission from low mass ratio
intermediate polars displaying superhumps.Comment: 9 pages, 5 figures, accepted for publication in MNRA
WD1953-011 - a magnetic white dwarf with peculiar field structure
We present H-alpha spectra of the magnetic white dwarf star WD1953-011 which
confirm the presence of the broad Zeeman components corresponding to a field
strength of about 500kG found by Maxted & Marsh (1999). We also find that the
line profile is variable over a timescale of a day or less. The core of the
H-alpha line also shows a narrow Zeeman triplet corresponding to a field
strength of of about 100kG which appears to be almost constant in shape. These
observations suggest that the magnetic field on WD1953-011 has a complex
structure and that the star has a rotational period of hours or days which
causes the observed variability of the spectra. We argue that neither an offset
dipole model nor a double-dipole model are sufficient to explain our
observations. Instead, we propose a two component model consisting of a high
field region of magnetic field strength of about 500kG covering about 10% of
the surface area of the star superimposed on an underlying dipolar field of
mean field strength of about 70kG. Radial velocity measurements of the narrow
Zeeman triplet show that the radial velocity is constant to within a few km/s
so this star is unlikely to be a close binary.Comment: Accpeted for publication in MNRAS. 4 pages, 2 figure
One-side forward-backward asymmetry at the LHC
Forward-backward asymmetry is an essential observable to study
the nature of coupling in the standard model and physics beyond the standard
model, as shown at LEP and Tevatron. As a proton-proton collider, the LHC does
not have the preferred direction contrary to her counterpart, namely, LEP and
Tevatron. Therefore is not applicable at the LHC. However for the
proton the momentum of valence quark is usually larger than that of the sea
quark. Utilizing this feature we have defined a so-called one-side
forward-backward asymmetry for the top quark pair production at
LHC in the previous work. In this paper we extend our studies to the charged
leptons and bottom quarks as the final states. Our numerical results show that
at the LHC can be utilized to study the nature of the couplings
once enough events are collected.Comment: 19 pages, 7 figures, 1 table, published versio
Sense and sensitivity of double beta decay experiments
The search for neutrinoless double beta decay is a very active field in which
the number of proposals for next-generation experiments has proliferated. In
this paper we attempt to address both the sense and the sensitivity of such
proposals. Sensitivity comes first, by means of proposing a simple and
unambiguous statistical recipe to derive the sensitivity to a putative Majorana
neutrino mass, m_bb. In order to make sense of how the different experimental
approaches compare, we apply this recipe to a selection of proposals, comparing
the resulting sensitivities. We also propose a "physics-motivated range" (PMR)
of the nuclear matrix elements as a unifying criterium between the different
nuclear models. The expected performance of the proposals is parametrized in
terms of only four numbers: energy resolution, background rate (per unit time,
isotope mass and energy), detection efficiency, and bb isotope mass. For each
proposal, both a reference and an optimistic scenario for the experimental
performance are studied. In the reference scenario we find that all the
proposals will be able to partially explore the degenerate spectrum, without
fully covering it, although four of them (KamLAND-Zen, CUORE, NEXT and EXO)
will approach the 50 meV boundary. In the optimistic scenario, we find that
CUORE and the xenon-based proposals (KamLAND-Zen, EXO and NEXT) will explore a
significant fraction of the inverse hierarchy, with NEXT covering it almost
fully. For the long term future, we argue that Xe-based experiments may provide
the best case for a 1-ton scale experiment, given the potentially very low
backgrounds achievable and the expected scalability to large isotope masses.Comment: 30 pages, 12 figures, 6 table
Tests of the Standard Model with Low-Energy Neutrino Beams
We discuss the possibility of using future high--intensity low--energy neutrino beams for precision tests of the Standard Model. In particular we consider the determination of the electroweak mixing angle from elastic and quasi--elastic neutrino--nucleon scattering at a superbeam or --beam
Statistical properties of stochastic 2D Navier-Stokes equations from linear models
A new approach to the old-standing problem of the anomaly of the scaling
exponents of nonlinear models of turbulence has been proposed and tested
through numerical simulations. This is achieved by constructing, for any given
nonlinear model, a linear model of passive advection of an auxiliary field
whose anomalous scaling exponents are the same as the scaling exponents of the
nonlinear problem. In this paper, we investigate this conjecture for the 2D
Navier-Stokes equations driven by an additive noise. In order to check this
conjecture, we analyze the coupled system Navier-Stokes/linear advection system
in the unknowns . We introduce a parameter which gives a
system ; this system is studied for any
proving its well posedness and the uniqueness of its invariant measure
.
The key point is that for any the fields and
have the same scaling exponents, by assuming universality of the
scaling exponents to the force. In order to prove the same for the original
fields and , we investigate the limit as , proving that
weakly converges to , where is the only invariant
measure for the joint system for when .Comment: 23 pages; improved versio
GCRT J1745-3009 as a Transient White Dwarf Pulsar
A transient radio source in the direction of the Galactic Center, GCRT
J1745-3009, exhibited 5 peculiar consecutive outbursts at 0.33 GHz with a
period of 77.13 minutes and a duration of ~10 minutes for each outburst. It has
been claimed to be the prototype of a hitherto unknown class of transient radio
sources. We interpret it as a transient white dwarf pulsar with a period of
77.13 minutes. The ~10-minute flaring duration corresponds to the epoch when
the radio beam sweeps our line of sight. The bursting epoch corresponds to the
episodes when stronger sunspot-like magnetic fields emerge into the white dwarf
polar cap region during which the pair production condition is satisfied and
the white dwarf behaves like a radio pulsar. It switches off as the pair
production condition breaks down.Comment: minor changes, ApJL, in pres
Evaluation of Breaking Force of Different Suture Materials Used in Dentistry: An In Vitro Mechanical Comparison
The success of surgical procedures is strictly related to the biomechanical properties of the suture. Mechanical comparisons are scarcely reported in the literature, so the purpose of the present study was to evaluate and compare the mechanical behavior of different sutures commonly used in oral surgery in terms of traction resistance. Sutures made of eight different materials were analyzed: silk (S), polyglycolide-co-caprolactone (PGCL), polypropylene (PP), rapid polyglycolide (rPGA), standard polyglycolide (PGA), polyamide (PA), polyester (PE), and polyvinylidene fluoride (PVDF). For each material, three different sizes were tested: 3-0, 4-0, and 5-0. The breaking force of each suture was assessed with a uniaxial testing machine after being immersed in artificial saliva at 37\u25e6 C. The outcomes analyzed were the breaking force, the needle\u2013thread detachment breaking-point and the node response after forward\u2013reverse\u2013forward (FRF) tying when subjected to a tensile force. The 3-0 rPGA provided the maximum resistance, while the lowest value was recorded for the 5-0 PGCL. In general, 3-0 and 4-0 gauges showed non-statistically significant differences in terms of needle\u2013thread detachment. The highest needle\u2013thread detachment was found for the 3-0 PGA, whereas the lowest value was observed for the 5-0 PGCL. After tying the knot with an FRF configuration, the thread that showed the highest resistance to tension was the 3/0 silk, while the thread with the lowest resistance was the 5/0 silk. These data should be considered so that the operator is aware of as many aspects as possible on the behavior of various materials to ensure successful healing
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