802 research outputs found
Measurement of the Higgs Boson Mass with a Linear e+e- Collider
The potential of a linear e+e- collider operated at a centre-of-mass energy
of 350 GeV is studied for the measurement of the Higgs boson mass. An
integrated luminosity of 500 fb-1 is assumed. For Higgs boson masses of 120,
150 and 180 GeV the uncertainty on the Higgs boson mass measurement is
estimated to be 40, 65 and 70 MeV, respectively. The effects of beam related
systematics, namely a bias in the beam energy measurement, the beam energy
spread and the luminosity spectrum due to beamstrahlung, on the precision of
the Higgs boson mass measurement are investigated. In order to keep the
systematic uncertainty on the Higgs boson mass well below the level of the
statistical error, the beam energy measurement must be controlled with a
relative precision better than 10-4.Comment: 19 pages, 10 Figure
Provenance of quartz grains from soils over Quaternary terraces along the Guadalquivir River, Spain
This work was supported by a grant from the Ministerio de EconomĂa, Industria y Competitividad de España (âMediterranean Soil Typologies versus Quartz. At the frontier of pedogenic knowledgeâ; Ref. CGL2016-80308-P). Alberto Molinero-GarcĂa acknowledges the PhD funding (BES-2017-080078) provided by MCIN/AEI /10.13039/501100011033 and FSE âEl FSE invierte en tu futuroâ. This work is part of the Doctoral Dissertation of Alberto Molinero-GarcĂa. We thank Dr. Mathieu Duval and an anonymous reviewer for their constructive criticism of the script and their valuable suggestions. We also acknowledge Tanya Shew for English proofreading. Funding for open access charge: Universidad de Granada / CBUA.The characterisation of quartz grainsâ chemical and mineralogical properties in sediments and sedimentary rocks is widely used in provenance studies. This paper analyses quartz grains from the coarse sand fraction in soils in Quaternary fluvial terraces (Guadalquivir River, southern Spain). The tentative soil ages are 0.3 ka (Haplic Fluvisol), 7 ka (Haplic Calcisol), 70 ka (Cutanic Luvisol), 300 ka (Lixic Calcisol) and 600 ka (Cutanic Luvisol). The quartz grains analyses shed light on the sedimentological history of these terraces. Scanning electron microscope cathodoluminescence (SEM-CL) characteristics, micro inclusion inventory established by Energy-dispersive X-ray spectroscopy (SEM-EDX) and trace element contents determined with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of quartz grains permitted distinguishing six types of grains in the soils studied: metamorphic quartz (type 1), undeformed granitic quartz (type 2), strongly altered granitic quartz (type 3), recrystallised (deformed) granitic quartz (type 4), sandstone-derived quartz (type 5) and hydrothermal quartz grains (type 6). Metamorphic quartz grains (type 1) come from the Sierra Morena (Iberian Massif) and Sierra Nevada (Internal Betic Zone). Granitic quartz grains (types 2 to 4) come from Los Pedroches batholith and its associated plutons (Santa Elena and Linares). The sandstone-derived quartz type 5 comes from the numerous sandstone outcrops scattered in the central catchment area of the Guadalquivir River. Finally, hydrothermal quartz grains (type 6) originate from hydrothermal veins associated with subvolcanic rocks of the Los Pedroches batholith. Variations were noted in the proportions of quartz types in soils of different ages, attributed to spatial and temporal changes in the catchment area. The most remarkable change occurred between 500 and 240 ka ago when the catchment area extended into Sierra NevadĂĄs metamorphic rocks, well reflected in type 1 content (lower in P2, P4, P5 and PM) and their characteristics (quartz with less healed fractures, less Al content, bigger mica microinclusions, smaller Al/Ti ratio) in the post-500â240 ka soils. Our study shows that the combined study of SEM-CL characteristics, micro inclusions (SEM-EDX), and trace element contents (LA-ICP-MS) of quartz grains is an efficient approach for characterising the provenance of quartz grains in the sand fraction of soils.CBUAMCINMediterranean Soil Typologies versus Quartz
BES-2017-080078Faculty of Science and Engineering, University of ManchesterUniversidad de GranadaMinisterio de EconomĂa, Industria y Competitividad, Gobierno de EspañaAgencia Estatal de InvestigaciĂł
Split-merge cycle, fragmented collapse, and vortex disintegration in rotating Bose-Einstein condensates with attractive interactions
The dynamical instabilities and ensuing dynamics of singly- and
doubly-quantized vortex states of Bose-Einstein condensates with attractive
interactions are investigated using full 3D numerical simulations of the
Gross-Pitaevskii equation. With increasing the strength of attractive
interactions, a series of dynamical instabilities such as quadrupole, dipole,
octupole, and monopole instabilities emerge. The most prominent instability
depends on the strength of interactions, the geometry of the trapping
potential, and deviations from the axisymmetry due to external perturbations.
Singly-quantized vortices split into two clusters and subsequently undergo
split-merge cycles in a pancake-shaped trap, whereas the split fragments
immediately collapse in a spherical trap. Doubly-quantized vortices are always
unstable to disintegration of the vortex core. If we suddenly change the
strength of interaction to within a certain range, the vortex splits into three
clusters, and one of the clusters collapses after a few split-merge cycles. The
vortex split can be observed using a current experimental setup of the MIT
group.Comment: 11 pages, 10 figure
Critical Collapse of the Massless Scalar Field in Axisymmetry
We present results from a numerical study of critical gravitational collapse
of axisymmetric distributions of massless scalar field energy. We find
threshold behavior that can be described by the spherically symmetric critical
solution with axisymmetric perturbations. However, we see indications of a
growing, non-spherical mode about the spherically symmetric critical solution.
The effect of this instability is that the small asymmetry present in what
would otherwise be a spherically symmetric self-similar solution grows. This
growth continues until a bifurcation occurs and two distinct regions form on
the axis, each resembling the spherically symmetric self-similar solution. The
existence of a non-spherical unstable mode is in conflict with previous
perturbative results, and we therefore discuss whether such a mode exists in
the continuum limit, or whether we are instead seeing a marginally stable mode
that is rendered unstable by numerical approximation.Comment: 11 pages, 8 figure
HDE 245059: A Weak-Lined T Tauri Binary Revealed by Chandra and Keck
We present the Chandra High Energy Transmission Grating Spectrometer (HETGS)
and Keck observations of HDE 245059, a young weak-lined T Tauri star (WTTS),
member of the pre-main sequence group in the Lambda Orionis Cluster. Our high
spatial resolution, near-infrared observations with Keck reveal that HDE 245059
a binary separated by 0.87". Based on this new information we have obtained an
estimate of the masses of the binary components; 3M_{sun} and 2.5M_{sun} for
the north and south components, respectively. We have estimated the age of the
system to be ~2-3 Myr. We detect both components of the binary in the zeroth
order Chandra image and in the grating spectra. Our fits to the spectrum of the
binary have shown that the emission is dominated by a plasma between 8 and 15
MK, a soft component at 4 MK and a hard component at 50 MK are also detected.
The value of the hydrogen column density was low, 8 x 10^{19} cm^{-2}, likely
due to the clearing of the inner region of the Lambda Orionis cloud. The
abundance pattern shows an inverse First Ionization Potential (FIP) effect for
all elements from O to Fe, the only exception being Ca. A 3-T model was fitted
to the individual zeroth order spectra using the abundances derived for the
binary. We have also obtained several lines fluxes from the grating spectra.
The fits to the triplets show no evidence of high densities. We conclude that
the X-ray properties of the weak-lined T Tau binary HDE 245059 are similar to
those generally observed in other weak-lined T Tau stars. Although its
accretion history may have been affected by the clearing of the interstellar
material around Lambda Ori, its coronal properties appears not to have been
strongly modified.Comment: 12 pages, 10 figures Accepted for publication in Ap
Unital Quantum Channels - Convex Structure and Revivals of Birkhoff's Theorem
The set of doubly-stochastic quantum channels and its subset of mixtures of
unitaries are investigated. We provide a detailed analysis of their structure
together with computable criteria for the separation of the two sets. When
applied to O(d)-covariant channels this leads to a complete characterization
and reveals a remarkable feature: instances of channels which are not in the
convex hull of unitaries can return to it when either taking finitely many
copies of them or supplementing with a completely depolarizing channel. In
these scenarios this implies that a channel whose noise initially resists any
environment-assisted attempt of correction can become perfectly correctable.Comment: 31 page
Investigating the nutritional advice and support given to colorectal cancer survivors in the UK: is it fit for purpose and does it address their needs?
Background
The present study assessed the quantity and quality of nutritional advice and support given to colorectal cancer survivors in the UK.
Methods
A descriptive crossâsectional survey was completed by 75 colorectal cancer survivors recruited through social media and bowel cancer support groups in the UK. The survey consisted of openâended and closed questions that aimed to explore the nutritional needs, nutritional advice given and other sources of information accessed by colorectal cancer survivors.
Results
Sixtyânine percent of respondents reported that they did not receive any nutritional advice or support from their healthcare team throughout diagnosis, treatment and postâtreatment. Colorectal cancer survivors accessed nutritional advice from a variety of sources, mainly cancer charity websites. Respondents expressed their desire for individualised advice relating to their nutritional problems.
Conclusions
The results obtained in the present study indicate that a high proportion of colorectal cancer patients are not receiving the nutritional support that they need to overcome nutritional difficulties. There is an urgent need to improve clinical practice to ensure colorectal patients receive nutritional advice that is both consistent between healthcare professionals and personalised throughout each stage of diagnosis, treatment and postâtreatment
New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation
(abridged) The heating mechanism at high densities during M dwarf flares is
poorly understood. Spectra of M dwarf flares in the optical and
near-ultraviolet wavelength regimes have revealed three continuum components
during the impulsive phase: 1) an energetically dominant blackbody component
with a color temperature of T 10,000 K in the blue-optical, 2) a smaller
amount of Balmer continuum emission in the near-ultraviolet at lambda 3646
Angstroms and 3) an apparent pseudo-continuum of blended high-order Balmer
lines. These properties are not reproduced by models that employ a typical
"solar-type" flare heating level in nonthermal electrons, and therefore our
understanding of these spectra is limited to a phenomenological interpretation.
We present a new 1D radiative-hydrodynamic model of an M dwarf flare from
precipitating nonthermal electrons with a large energy flux of erg
cm s. The simulation produces bright continuum emission from a
dense, hot chromospheric condensation. For the first time, the observed color
temperature and Balmer jump ratio are produced self-consistently in a
radiative-hydrodynamic flare model. We find that a T 10,000 K
blackbody-like continuum component and a small Balmer jump ratio result from
optically thick Balmer and Paschen recombination radiation, and thus the
properties of the flux spectrum are caused by blue light escaping over a larger
physical depth range compared to red and near-ultraviolet light. To model the
near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer
lines, we include the extra Balmer continuum opacity from Landau-Zener
transitions that result from merged, high order energy levels of hydrogen in a
dense, partially ionized atmosphere. This reveals a new diagnostic of ambient
charge density in the densest regions of the atmosphere that are heated during
dMe and solar flares.Comment: 50 pages, 2 tables, 13 figures. Accepted for publication in the Solar
Physics Topical Issue, "Solar and Stellar Flares". Version 2 (June 22, 2015):
updated to include comments by Guest Editor. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11207-015-0708-
Hydrodynamic excitations of trapped dipolar fermions
A single-component Fermi gas of polarized dipolar particles in a harmonic
trap can undergo a mechanical collapse due to the attractive part of the
dipole-dipole interaction. This phenomenon can be conveniently manipulated by
the shape of the external trapping potential. We investigate the signatures of
the instability by studying the spectrum of low-lying collective excitations of
the system in the hydrodynamic regime. To this end, we employ a time-dependent
variational method as well as exact numerical solutions of the hydrodynamic
equations of the system.Comment: 4 pages, 2 eps figures, final versio
Controlling collapse in Bose-Einstein condensates by temporal modulation of the scattering length
We consider, by means of the variational approximation (VA) and direct
numerical simulations of the Gross-Pitaevskii (GP) equation, the dynamics of 2D
and 3D condensates with a scattering length containing constant and
harmonically varying parts, which can be achieved with an ac magnetic field
tuned to the Feshbach resonance. For a rapid time modulation, we develop an
approach based on the direct averaging of the GP equation,without using the VA.
In the 2D case, both VA and direct simulations, as well as the averaging
method, reveal the existence of stable self-confined condensates without an
external trap, in agreement with qualitatively similar results recently
reported for spatial solitons in nonlinear optics. In the 3D case, the VA again
predicts the existence of a stable self-confined condensate without a trap. In
this case, direct simulations demonstrate that the stability is limited in
time, eventually switching into collapse, even though the constant part of the
scattering length is positive (but not too large). Thus a spatially uniform ac
magnetic field, resonantly tuned to control the scattering length, may play the
role of an effective trap confining the condensate, and sometimes causing its
collapse.Comment: 7 figure
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