368 research outputs found
The role of beach state and the timing of pre-storm surveys in determining the accuracy of storm impact assessments
Dune erosion principally occurs when water level exceeds the elevation of the beach and predicting erosion is progressively becoming more important for management as coastal populations increase, sea level rises, and storms become more powerful. This study assesses storm impacts using a simple model from Stockdon et al. (2007) configured with oceanographic information from the ADCIRC + SWAN model and frequently collected beach profiles. We applied that model to barrier islands in North Carolina including: Core Banks with a more dissipative beach morphology and Shackleford Banks and Onslow Beach with intermediate beach morphologies. The study periods captured 10 events where wave collision with the dunes and/or overwash were either predicted or observed, including large multiple-day events caused by hurricanes and smaller events caused by onshore winds and high tide. Comparing model output with a time series of beach photographs shows the predictive power and sensitivity of the model was consistently high at the Core Banks Site with its wide and low-gradient beach, high-elevation dunes (2.58 m), and high resistance to overwash. Model predictive power and sensitivity was lowest at the Shackleford Banks Site because frequent and large changes to beach slope and intermediate dune elevation (0.54â1.25 m) caused small variations of modeled total water level to either overpredict or underpredict storm impacts. In addition, storm impacts were always overpredicted during hurricanes at the Shackleford Banks Site, which was likely due to storm waves decreasing the beach slope from what was measured prior to the event and used as model input. Like Shackleford Banks, the beach slope of the Onslow Beach Site was steep and variable, but the low-elevation dunes (0.24â0.28 m) made resistance to overwash low and the predictive power and sensitivity of the model higher than at the Shackleford Banks Site. Results suggest that storm impacts and the associated potential for dune erosion is predicted more accurately at beaches where the threshold for overwash is high or low because total water level during most events will commonly fall short of or exceed the overwash threshold, respectively. The accuracy of predicting the storm impact regime is sensitive to beach slope. The slope of intermediate beaches is more variable than dissipative beaches and requires frequent measurement if it is to be represented accurately in the model, but this can be impractical and costly even using the latest drone-surveying methods. To maximize the accuracy of predicting storm impacts, intermediate beach morphology should be constrained by surveying at seasonal or yearly time scales and used as input to numerical models that estimate beach slope over short time scales (hours during an event or daily), configured with the latest wave and water-level forecasts
Crossover and scaling in a nearly antiferromagnetic Fermi liquid in two dimensions
We consider two-dimensional Fermi liquids in the vicinity of a quantum
transition to a phase with commensurate, antiferromagnetic long-range order.
Depending upon the Fermi surface topology, mean-field spin-density-wave theory
predicts two different types of such transitions, with mean-field dynamic
critical exponents (when the Fermi surface does not cross the magnetic
zone boundary, type ) and (when the Fermi surface crosses the magnetic
zone boundary, type ). The type system only displays behavior at
all energies and its scaling properties are similar (though not identical) to
those of an insulating Heisenberg antiferromagnet. Under suitable conditions
precisely stated in this paper, the type system displays a crossover from
relaxational behavior at low energies to type behavior at high energies. A
scaling hypothesis is proposed to describe this crossover: we postulate a
universal scaling function which determines the entire, temperature-,
wavevector-, and frequency-dependent, dynamic, staggered spin susceptibility in
terms of 4 measurable, , parameters (determining the distance, energy, and
order parameter scales, plus one crossover parameter). The scaling function
contains the full scaling behavior in all regimes for both type and
systems. The crossover behavior of the uniform susceptibility and the specific
heat is somewhat more complicated and is also discussed. Explicit computation
of the crossover functions is carried out in a large expansion on a
mean-field model. Some new results for the critical properties on the ordered
side of the transition are also obtained in a spin-density wave formalism. The
possible relevance of our results to the doped cuprate compounds is briefly
discussed.Comment: 20 pages, REVTeX, 6 figures (uuencoded compressed PostScript file for
figures is appended
Bosonic Excitations in Random Media
We consider classical normal modes and non-interacting bosonic excitations in
disordered systems. We emphasise generic aspects of such problems and parallels
with disordered, non-interacting systems of fermions, and discuss in particular
the relevance for bosonic excitations of symmetry classes known in the
fermionic context. We also stress important differences between bosonic and
fermionic problems. One of these follows from the fact that ground state
stability of a system requires all bosonic excitation energy levels to be
positive, while stability in systems of non-interacting fermions is ensured by
the exclusion principle, whatever the single-particle energies. As a
consequence, simple models of uncorrelated disorder are less useful for bosonic
systems than for fermionic ones, and it is generally important to study the
excitation spectrum in conjunction with the problem of constructing a
disorder-dependent ground state: we show how a mapping to an operator with
chiral symmetry provides a useful tool for doing this. A second difference
involves the distinction for bosonic systems between excitations which are
Goldstone modes and those which are not. In the case of Goldstone modes we
review established results illustrating the fact that disorder decouples from
excitations in the low frequency limit, above a critical dimension , which
in different circumstances takes the values and . For bosonic
excitations which are not Goldstone modes, we argue that an excitation density
varying with frequency as is a universal
feature in systems with ground states that depend on the disorder realisation.
We illustrate our conclusions with extensive analytical and some numerical
calculations for a variety of models in one dimension
Vascular effects of apelin in vivo in man
ObjectivesThis study was designed to establish the direct vascular effects of apelin in vivo in man.BackgroundApelin is the endogenous ligand for the previously orphaned G-proteinâcoupled receptor, APJ. This novel pathway is widely expressed in the cardiovascular system and is emerging as an important mediator of cardiovascular homeostasis. In pre-clinical models, apelin causes venous and arterial vasodilation.MethodsVascular effects of apelin were assessed in 24 healthy volunteers. Dorsal hand vein diameter was measured by the Aellig technique during local intravenous infusions (0.1 to 3 nmol/min) of apelin-36, (Pyr1)apelin-13, and sodium nitroprusside (0.6 nmol/min). Forearm blood flow was measured by venous occlusion plethysmography during intrabrachial infusions of apelin-36 and (Pyr1)apelin-13 (0.1 to 30 nmol/min) and subsequently in the presence or absence of a ânitric oxide clampâ (nitric oxide synthase inhibitor, L-NG-monomethylarginine [8 Îźmol/min], coinfused with nitric oxide donor, sodium nitroprusside [90 to 900 ng/min]), or a single oral dose of aspirin (600 mg) or matched placebo.ResultsAlthough sodium nitroprusside caused venodilation (p < 0.0001), apelin-36 and (Pyr1)apelin-13 had no effect on dorsal hand vein diameter (p = 0.2). Both apelin isoforms caused reproducible vasodilation in forearm resistance vessels (p < 0.0001). (Pyr1)apelin-13âmediated vasodilation was attenuated by the nitric oxide clamp (p = 0.004) but unaffected by aspirin (p = 0.7).ConclusionsAlthough having no apparent effect on venous tone, apelin causes nitric oxideâdependent arterial vasodilation in vivo in man. The apelin-APJ system merits further clinical investigation to determine its role in cardiovascular homeostasis
Changes in adductor strength after competition in Academy Rugby Union Players
Š 2016 National Strength and Conditioning Association. This study determined the magnitude of change in adductor strength after a competitive match in academy rugby union players and examined the relationship between locomotive demands of match-play and changes in postmatch adductor strength. A withinsubject repeated measures design was used. Fourteen academy rugby union players (age, 17.4 ¹ 0.8 years; height, 182.7 ¹ 7.6 cm; body mass, 86.2 ¹ 11.6 kg) participated in the study. Each player performed 3 maximal adductor squeezes at 458 of hip flexion before and immediately, 24, 48, and 72 hours postmatch. Global positioning system was used to assess locomotive demands of match-play. Trivial decreases in adductor squeeze scores occurred immediately (21.3 ¹ 2.5%; effect size [ES] = 20.11 ¹ 0.21; likely, 74%) and 24 hours after match (20.7 ¹ 3%; ES = 20.06 ¹ 0.25; likely, 78%), whereas a small but substantial increase occurred at 48 hours (3.8 ¹ 1.9%; ES = 0.32 ¹ 0.16; likely, 89%) before reducing to trivial at 72 hours after match (3.1 ¹ 2.2%; ES = 0.26 ¹ 0.18; possibly, 72%). Large individual variation in adductor strength was observed at all time points. The relationship between changes in adductor strength and distance covered at sprinting speed (VO2max 81%) was large immediately postmatch (p = 0.056, r = 20.521), moderate at 24 hours (p = 0.094, r = 20.465), and very large at 48 hours postmatch (p = 0.005, r = 20.707). Players who cover greater distances sprinting may suffer greater adductor fatigue in the first 48 hours after competition. The assessment of adductor strength using the adductor squeeze test should be considered postmatch to identify players who may require additional rest before returning to field-based training
The spatio-relational nature of urban innovation systems: Universities, knowledge intensive business service firms, and collaborative networks
The need to better identify the spatio-relational nature of urban innovation systems and spaces is increasingly acknowledged. The aim of this paper, therefore, is to provide an enhanced understanding of the knowledge networks existing between urban Knowledge Intensive Business Services firms (KIBS) and universities, which are often key components of such systems and spaces. Drawing on an analysis of urban KIBS firms and universities in the UK, it is found that the nature of firms, the location in which they are based, and the research intensity of their university partners are important determinants of the spatiality and localisation of the networks they form. The results show that the smallest urban KIBS firms have the highest propensity to engage in local links with universities, suggesting that they rely most significantly on their own urban innovation system for collaborative network ties.
Keywords : innovation systems; urban innovation spaces; knowledge-based development; proximity; networks; KIBS; universities
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Summary for Policymakers - Marine Ecosystem Assessment for the Southern Ocean
i. The Antarctic Treaty System (beginning in 1959 with the Antarctic Treaty) and its emphasis on conservation and protection, exemplified in the Convention on the Conservation of Antarctic Marine Living Resources (1980) and its Protocol on Environmental Protection to the Antarctic Treaty (1991), provide the most recent articulation of the global interest in Antarctica and the Southern Ocean and the need for their protection.
ii. The Southern Ocean and its ecosystems play critical roles in the climate system. Ecosystem functions are at risk because of anthropogenic climate change.
iii.âGlobal policies and actions are urgently required to safeguard Southern Ocean ecosystems from the effects of climate change, ocean warming and acidification caused by greenhouse gas emissions.
iv. Regional human pressures on Southern Ocean species and ecosystems have been dominated by fisheries, with human presence (science and tourism) and pollution having localised, but increasing, impacts.
v. The Marine Ecosystem Assessment for the Southern Ocean (MEASO) has demonstrated the array of existing knowledge, data, tools and approaches available for informing decisions on conserving and sustaining the marine ecosystems in the region and the services they provide, and how implementation of those processes could be improved
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
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