17,486 research outputs found
The impact of a wave farm on large scale sediment transport
This study investigates the interactions of waves and tides at a wave farm in the southwest of England, in particular their effects on radiation stress, bottom stress, and consequently on the sediment transport and the coast adjacent to the wave-farm (the Wave Hub). In this study, an integrated complex numerical modelling system is setup at the Wave Hub site and is used to compute the wave and current fields by taking into account the wave-current interaction, as well as the sediment transport. Results show that tidal elevation and tidal currents have a significant effect on the wave height and direction predictions; tidal forcing and wind waves have a significant effect on the bed shear-stress, relevant to sediment transport; waves via radiation stresses have an important effect on the longshore and cross-shore velocity components, particularly during the spring tides. Waves can impact on bottom boundary layer and mixing in the water column. The results highlight the importance of the interactions between waves and tides when modelling coastal morphology with presence of wave energy devices
Wear and friction of TiAlN/VN coatings against Al2O3 in air at room and elevated temperatures
TiAlN/VN multilayer coatings exhibit excellent dry sliding wear resistance and low friction coefficient, reported to be associated with the formation of self-lubricating V2O5. To investigate this hypothesis, dry sliding ball-on-disc wear tests of TiAlN/VN coatings on flat stainless steel substrates were undertaken against Al2O3 at 25 C, 300 C and 635 C in air. The coating exhibited increased wear rate
with temperature. The friction coefficient was 0.53 at 25 C, which increased to 1.03 at 300 C and decreased to 0.46 at 635 C. Detailed investigation of the worn surfaces was undertaken using site-specific transmission electron microscopy (TEM) via focused ion beam (FIB) microscopy, along with Fourier transform infrared (FTIR) and Raman spectroscopy. Microstructure and tribo-induced chemical
reactions at these temperatures were correlated with the coatingâs wear and friction behaviour. The friction behaviour at room temperature is attributed to the presence of a thin hydrated tribofilm and the presence of V2O5 at high temperature
Structural Disorder, Octahedral Coordination, and 2-Dimensional Ferromagnetism in Anhydrous Alums
The crystal structures of the triangular lattice, layered anhydrous alums
KCr(SO4)2, RbCr(SO4)2 and KAl(SO4)2 are characterized by X-ray and neutron
powder diffraction at temperatures between 1.4 and 773 K. The compounds all
crystallize in the space group P-3, with octahedral coordination of the
trivalent cations. In all cases, small amounts of disorder in the stacking of
the triangular layers of corner sharing MO6 octahedra and SO4 tetrahedra is
seen, with the MO6-SO4 network rotated in opposite directions between layers.
The electron diffraction study of KCr(SO4)2 supports this model, which on
average can be taken to imply trigonal prismatic coordination for the M3+ ions;
as was previously reported for the prototype anhydrous alum KAl(SO4)2. The
temperature dependent magnetic susceptibilities for ACr(SO4)2 (A = K,Rb,Cs)
indicate the presence of predominantly ferromagnetic interactions. Low
temperature powder neutron diffraction reveals that the magnetic ordering is
ferromagnetic in-plane, with antiferromagnetic ordering between planes below 3
K.Comment: Accepted to the Journal of Solid State Chemistr
Mapping the Milky Way bulge at high resolution: the 3D dust extinction, CO, and X factor maps
Three dimensional interstellar extinction maps provide a powerful tool for
stellar population analysis. We use data from the VISTA Variables in the Via
Lactea survey together with the Besan\c{c}on stellar population synthesis model
of the Galaxy to determine interstellar extinction as a function of distance in
the Galactic bulge covering and . We adopted a
recently developed method to calculate the colour excess. First we constructed
the H-Ks vs. Ks and J-Ks vs. Ks colour-magnitude diagrams based on the VVV
catalogues that matched 2MASS. Then, based on the temperature-colour relation
for M giants and the distance-colour relations, we derived the extinction as a
function of distance. The observed colours were shifted to match the intrinsic
colours in the Besan\c{c}on model as a function of distance iteratively. This
created an extinction map with three dimensions: two spatial and one distance
dimension along each line of sight towards the bulge. We present a 3D
extinction map that covers the whole VVV area with a resolution of 6' x 6',
using distance bins of 0.5 kpc. The high resolution and depth of the photometry
allows us to derive extinction maps for a range of distances up to 10 kpc and
up to 30 magnitudes of extinction in . Integrated maps show the same
dust features and consistent values as other 2D maps. We discuss the spatial
distribution of dust features in the line of sight, which suggests that there
is much material in front of the Galactic bar, specifically between 5-7 kpc. We
compare our dust extinction map with high-resolution maps towards
the Galactic bulge, where we find a good correlation between and
. We determine the X factor by combining the CO map and our dust
extinction map. Our derived average value is consistent with the canonical
value of the Milky Way.Comment: 11 pages, 18 figures, accepted for publication in
Astronomy&Astrophysic
Thermionic charge transport in CMOS nano-transistors
We report on DC and microwave electrical transport measurements in
silicon-on-insulator CMOS nano-transistors at low and room temperature. At low
source-drain voltage, the DC current and RF response show signs of conductance
quantization. We attribute this to Coulomb blockade resulting from barriers
formed at the spacer-gate interfaces. We show that at high bias transport
occurs thermionically over the highest barrier: Transconductance traces
obtained from microwave scattering-parameter measurements at liquid helium and
room temperature is accurately fitted by a thermionic model. From the fits we
deduce the ratio of gate capacitance and quantum capacitance, as well as the
electron temperature
Unknowns after the SNO Charged-Current Measurement
We perform a model-independent analysis of solar neutrino flux rates
including the recent charged-current measurement at the Sudbury Neutrino
Observatory (SNO). We derive a universal sum rule involving SNO and
SuperKamiokande rates, and show that the SNO neutral-current measurement can
not fix the fraction of solar oscillating to sterile neutrinos. The
large uncertainty in the SSM B flux impedes a determination of the sterile
neutrino fraction.Comment: Version to appear in PRL; includes analysis with anticipated SNO NC
measuremen
Pancreatic cysts suspected to be branch duct intraductal papillary mucinous neoplasm without concerning features have low risk for development of pancreatic cancer.
BackgroundThe risk of developing pancreatic cancer is uncertain in patients with clinically suspected branch duct intraductal papillary mucinous neoplasm (BD-IPMN) based on the "high-risk stigmata" or "worrisome features" criteria proposed in the 2012 international consensus guidelines ("Fukuoka criteria").MethodsRetrospective case series involving patients referred for endoscopic ultrasound (EUS) of indeterminate pancreatic cysts with clinical and EUS features consistent with BD-IPMN. Rates of pancreatic cancer occurring at any location in the pancreas were compared between groups of patients with one or more Fukuoka criteria ("Highest-Risk Group", HRG) and those without these criteria ("Lowest-Risk Group", LRG).ResultsAfter exclusions, 661 patients comprised the final cohort (250 HRG and 411 LRG patients), 62% female with an average age of 67 years and 4 years of follow up. Pancreatic cancer, primarily adenocarcinoma, occurred in 60 patients (59 HRG, 1 LRG). Prevalent cancers diagnosed during EUS, immediate surgery, or first year of follow up were found in 48/661 (7.3%) of cohort and exclusively in HRG (33/77, 42.3%). Using Kaplan-Meier method, the cumulative incidence of cancer at 7 years was 28% in HRG and 1.2% in LRG patients (P<0.001).ConclusionsThis study supports using Fukuoka criteria to stratify the immediate and long-term risks of pancreatic cancer in presumptive BD-IPMN. The risk of pancreatic cancer was highest during the first year and occurred exclusively in those with "high-risk stigmata" or "worrisome features" criteria. After the first year all BD-IPMN continued to have a low but persistent cancer risk
AuNx stabilization with interstitial nitrogen atoms: A Density Functional Theory Study
Researchers have been studying 4d and 5d Series Transition Metal Nitrides lately as a result of the experimental production of AuN, PtN, CuN. In this paper, we used the Density Functional Theory (DFT) implementing a pseudopotential plane-wave method to study the incorporation of nitrogen atoms in the face-centered cube (fcc) lattice of gold (Au). First, we took the fcc structure of gold, and gradually located the nitrogen atoms in tetrahedral (TH) and octahedral (OH) interstitial sites. AuN stabilized in: 2OH (30%), 4OH and 4TH (50%), 4OH - 2TH (close to the wurtzite structure) and 6TH (60%). This leads us to think that AuN behaves like a Transition Metal Nitride since the nitrogen atoms look for tetrahedral sites. © Published under licence by IOP Publishing Ltd
Dipolar origin of the gas-liquid coexistence of the hard-core 1:1 electrolyte model
We present a systematic study of the effect of the ion pairing on the
gas-liquid phase transition of hard-core 1:1 electrolyte models. We study a
class of dipolar dimer models that depend on a parameter R_c, the maximum
separation between the ions that compose the dimer. This parameter can vary
from sigma_{+/-} that corresponds to the tightly tethered dipolar dimer model,
to R_c --> infinity, that corresponds to the Stillinger-Lovett description of
the free ion system. The coexistence curve and critical point parameters are
obtained as a function of R_c by grand canonical Monte Carlo techniques. Our
results show that this dependence is smooth but non-monotonic and converges
asymptotically towards the free ion case for relatively small values of R_c.
This fact allows us to describe the gas-liquid transition in the free ion model
as a transition between two dimerized fluid phases. The role of the unpaired
ions can be considered as a perturbation of this picture.Comment: 16 pages, 13 figures, submitted to Physical Review
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