1,812 research outputs found
Neutron star bulk viscosity, "spin-flip" and GW emission of newly born magnetars
The viscosity-driven "spin-flip" instability in newborn magnetars with
interior toroidal magnetic fields is re-examined. We calculate the bulk
viscosity coefficient () of cold, matter in neutron stars
(NS), for selected values of the nuclear symmetry energy and in the regime
where -equilibration is slower than characteristic oscillation periods.
We show that: i) is larger than previously assumed and the instability
timescale correspondingly shorter; ii) for a magnetically-induced ellipticity
, typically expected in newborn
magnetars, spin-flip occurs for initial spin periods ms, with
some dependence on the NS equation of state (EoS). We then calculate the
detectability of GW signals emitted by newborn magnetars subject to
"spin-flip", by accounting also for the reduction in range resulting from
realistic signal searches. For an optimal range of , and birth spin period ms, we estimate an horizon
of Mpc, and Mpc, for Advanced and third generation
interferometers at design sensitivity, respectively. A supernova (or a
kilonova) is expected as the electromagnetic counterpart of such GW events.
Outside of the optimal range for GW emission, EM torques are more efficient in
extracting the NS spin energy, which may power even brighter EM transients.Comment: 10 pages, 4 figures, accepted for publication in MNRA
NuSTAR J095551+6940.8: a highly magnetised neutron star with super-Eddington mass accretion
The identification of the Ultraluminous X-ray source (ULX) X-2 in M82 as an
accreting pulsar has shed new light on the nature of a subset of ULXs, while
rising new questions on the nature of the super-Eddington accretion. Here, by
numerically solving the torque equation of the accreting pulsar within the
framework of the magnetically threaded-disk scenario, we show that three
classes of solutions, corresponding to different values of the magnetic field,
are mathematically allowed. We argue that the highest magnetic field one,
corresponding to B G, is favoured based on physical
considerations and the observed properties of the source. In particular, that
is the only solution which can account for the observed variations in
(over four time intervals) without requiring major changes in , which
would be at odds with the approximately constant X-ray emission of the source
during the same time. For this solution, we find that the source can only
accomodate a moderate amount of beaming, 0.5 . Last, we show
that the upper limit on the luminosity, L erg s
from archival observations, is consistent with a highly-magnetized neutron star
being in the propeller phase at that time.Comment: 8 pages, 3 figures, accepted for publication on MNRA
Gravitational Radiation from Newborn Magnetars
There is growing evidence that two classes of high-energy sources, the Soft
Gamma Repeaters and the Anomalous X-ray Pulsars contain slowly spinning
``magnetars'', i.e. neutron stars whose emission is powered by the release of
energy from their extremely strong magnetic fields (>10^15 G. We show here that
the enormous energy liberated in the 2004 December 27 giant flare from
SGR1806-20 (~5 10^46 erg), together with the likely recurrence time of such
events, requires an internal field strength of > 10^16 G. Toroidal magnetic
fields of this strength are within an order of magnitude of the maximum fields
that can be generated in the core of differentially-rotating neutron stars
immediately after their formation, if their initial spin period is of a few
milliseconds. A substantial deformation of the neutron star is induced by these
magnetic fields and, provided the deformation axis is offset from the spin
axis, a newborn fast-spinning magnetar would radiate for a few weeks a strong
gravitational wave signal the frequency of which (0.5-2 kHz range) decreases in
time. The signal from a newborn magnetar with internal field > 10^16.5 G could
be detected with Advanced LIGO-class detectors up to the distance of the Virgo
cluster (characteristic amplitude h_c about 10^-21). Magnetars are expected to
form in Virgo at a rate approx. 1/yr. If a fraction of these have sufficiently
high internal magnetic field, then newborn magnetars constitute a promising new
class of gravitational wave emitters.Comment: Accepted for publication on ApJ Letter
Higgs pair production: Choosing benchmarks with cluster analysis
New physics theories often depend on a significant number of
parameters and the phenomenology of fundamental processes may vary drastically depending on their values. It is advantageous to categorize the resulting final state
kinematics such that the investigation of a few typical points yields knowledge on a large area of the parameter space. Here it is showed how this can be done effectively
with a cluster analysis, by considering as specific process the non-resonant Higgs boson pairs production in the context of Standard Model extensions to Higgs boson
anomalous couplings
Shelf Life Assessment of Fresh Poultry Meat Packaged in Novel Bionanocomposite of Chitosan Incorporated with ZnO nanoparticles synthesized using food industry by-products
Nel settore alimentare viene utilizzata un’elevata quantità di materie plastiche per conservare i prodotti e facilitarne la distribuzione. L’utilizzo di questi polimeri ha un costo ambientale piuttosto elevato, per questo trovare surrogati ecosostenibili diventa sempre più importante.
In questa tesi abbiamo testato l’efficacia del confezionamento di un prodotto altamente deperibile, quale carne di pollo, con un biofilm a base di chitosano. Il chitosano è polisaccaride largamente presente in natura, dotato di caratteristiche chimico-fisiche che permettono l’ottenimento di un film con proprietà meccaniche e di barriera simili ai polimeri tradizionali, oltre a possedere attività antibatterica. Abbiamo realizzato film contenenti chitosano e altri biocomposti, quali montmorillonite, nanoparticelle di ossido di zinco e olio essenziale di rosmarino, per un totale di 6 film con diversa composizione. Tramite analisi microbiologiche e chimico-fisiche abbiamo confrontato l’efficacia dei diversi film prodotti rispetto ad un controllo (carne conservata in un contenitore asettico). Le analisi sono state svolte in doppio, a 0, 3, 7, 10, 15 giorni di conservazione ad una temperatura di 4°C. In diversi film abbiamo ottenuto una riduzione significativa rispetto al controllo (p0,05), e quando presenti, è perché il campione era più ossidato del controllo (p<0,05). Invece, è stato ottenuto un miglioramento significativo (p<0,05) dello Hue angle tra i film e il controllo. I risultati ottenuti forniscono le basi per studi aggiuntivi
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