779 research outputs found
Sensitivity of Neutrino Mass Experiments to the Cosmic Neutrino Background
The KATRIN neutrino experiment is a next-generation tritium beta decay
experiment aimed at measuring the mass of the electron neutrino to better than
200 meV at 90% C.L. Due to its intense tritium source, KATRIN can also serve as
a possible target for the process of neutrino capture, {\nu}e +3H \to 3He+ +
e-. The latter process, possessing no energy threshold, is sensitive to the
Cosmic Neutrino Background (C{\nu}B). In this paper, we explore the potential
sensitivity of the KATRIN experiment to the relic neutrino density. The KATRIN
experiment is sensitive to a C{\nu}B over-density ratio of 2.0x 10^9 over
standard concordance model predictions (at 90% C.L.), addressing the validity
of certain speculative cosmological models
Dryland salinity: a multi-disciplinary conceptual model designed for on-farm salinity control
Non-Peer Reviewe
Kinematic modelling of a 3-axis NC machine tool in linear and circular interpolation
Machining time is a major performance criterion when it comes to high-speed
machining. CAM software can help in estimating that time for a given strategy.
But in practice, CAM-programmed feed rates are rarely achieved, especially
where complex surface finishing is concerned. This means that machining time
forecasts are often more than one step removed from reality. The reason behind
this is that CAM routines do not take either the dynamic performances of the
machines or their specific machining tolerances into account. The present
article seeks to improve simulation of high-speed NC machine dynamic behaviour
and machining time prediction, offering two models. The first contributes
through enhanced simulation of three-axis paths in linear and circular
interpolation, taking high-speed machine accelerations and jerks into account.
The second model allows transition passages between blocks to be integrated in
the simulation by adding in a polynomial transition path that caters for the
true machining environment tolerances. Models are based on respect for path
monitoring. Experimental validation shows the contribution of polynomial
modelling of the transition passage due to the absence of a leap in
acceleration. Simulation error on the machining time prediction remains below
1%
Discovery of an old nova remnant in the Galactic globular cluster M 22
A nova is a cataclysmic event on the surface of a white dwarf in a binary
system that increases the overall brightness by several orders of magnitude.
Although binary systems with a white dwarf are expected to be overabundant in
globular clusters (GCs) compared to the Galaxy, only two novae from Galactic
globular clusters have been observed. We present the discovery of an emission
nebula in the Galactic globular cluster M 22 (NGC 6656) in observations made
with the integral-field spectrograph MUSE. We extract the spectrum of the
nebula and use the radial velocity determined from the emission lines to
confirm that the nebula is part of NGC 6656. Emission-line ratios are used to
determine the electron temperature and density. It is estimated to have a mass
of 1 to solar masses. This mass and the emission-line
ratios indicate that the nebula is a nova remnant. Its position coincides with
the reported location of a 'guest star', an ancient Chinese term for
transients, observed in May 48 BCE. With this discovery, this nova may be one
of the oldest confirmed extrasolar events recorded in human history.Comment: 7 pages, 3 figures; accepted for publication in Astronomy &
Astrophysic
Piecing together the puzzle of NGC 5253: abundances, kinematics and WR stars
We present Gemini-S/GMOS-IFU optical spectroscopy of four regions near the
centre of the nearby (3.8 Mpc) dwarf starburst galaxy NGC 5253. This galaxy is
famous for hosting a radio supernebula containing two deeply embedded massive
super star clusters, surrounded by a region of enhanced nitrogen abundance that
has been linked to the presence of WR stars. We detected 11 distinct sources of
red WR bump (CIV) emission over a 20" (~350 pc) area, each consistent with the
presence of ~1 WCE-type star. WC stars are not found coincident with the
supernebula, although WN stars have previously been detected here. We performed
a multi-component decomposition of the H\alpha\ line across all four fields and
mapped the kinematics of the narrow and broad (FWHM = 100-250 km/s) components.
These maps paint a picture of localised gas flows, as part of multiple
overlapping bubbles and filaments driven by the star clusters throughout the
starburst. We confirm the presence of a strong H\alpha\ velocity gradient over
~4.5" (~80 pc) coincident with the region of N/O enhancement, and high gas
density known from previous study, and interpret this as an accelerating
ionized gas outflow from the supernebula clusters. We measure the ionized gas
abundances in a number of regions in the outer IFU positions and combine these
with measurements from the literature to assess the radial abundance
distribution. We find that the O/H and N/H profiles are consistent with being
flat. Only the central 50 pc exhibits the well-known N/O enhancement, and we
propose that the unusually high densities/pressures in the supernebula region
have acted to impede the escape of metal-enriched hot winds from the star
clusters and allow them to mix with the cooler phases, thus allowing these
freshly processed chemicals to be seen in the optical.Comment: 16 pages, accepted to A&
Propagation of strangelets in the Earth's atmosphere
A new model for the description of the behaviour of strangelets in the
Earth's atmosphere is presented. Strangelet fission induced by collision with
air nuclei is included. It is shown that strangelets with certain parameters of
initial mass and energy may reach depths near sea level, which can be examined
by ground-based experiments.Comment: 10 pages, 6 figure
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