Comparison of Engineering Wake Models with CFD Simulations

The engineering wake models by Jensen [1] and Frandsen et al. [2] are assessed for different scenarios simulated using Large Eddy Simulation and the Actuator Line method implemented in the Navier-Stokes equations. The scenarios include the far wake behind a single wind turbine, a long row of turbines in an atmospheric boundary layer, idealised cases of an infinitely long row of wind turbines and infinite wind farms with three different spacings. Both models include a wake expansion factor, which is calibrated to fit the simulated wake velocities. The analysis highlights physical deficiencies in the ability of the models to universally predict the wake velocities, as the expansion factor can be fitted for a given case, but with not apparent transition between the cases. 1

A note on the primordial abundance of stau NLSPs

In scenarios with a gravitino LSP, there exist strong BBN constraints on the abundance of a possible stau NLSP. We find that in settings with substantial left-right mixing of the stau mass eigenstates these constraints can be evaded even for very long-lived staus.Comment: 17 pages, 5 figures, discussion on vacuum stability adde

Disequilibrium, adaptation and the Norse settlement of Greenland

This research was supported by the University of Edinburgh ExEDE Doctoral Training Studentship and NSF grant numbers 1202692 and 1140106.There is increasing evidence to suggest that arctic cultures and ecosystems have followed non-linear responses to climate change. Norse Scandinavian farmers introduced agriculture to sub-arctic Greenland in the late tenth century, creating synanthropic landscapes and utilising seasonally abundant marine and terrestrial resources. Using a niche-construction framework and data from recent survey work, studies of diet, and regional-scale climate proxies we examine the potential mismatch between this imported agricultural niche and the constraints of the environment from the tenth to the fifteenth centuries. We argue that landscape modification conformed the Norse to a Scandinavian style of agriculture throughout settlement, structuring and limiting the efficacy of seasonal hunting strategies. Recent climate data provide evidence of sustained cooling from the mid thirteenth century and climate variation from the early fifteenth century. Archaeological evidence suggests that the Norse made incremental adjustments to the changing sub-arctic environment, but were limited by cultural adaptations made in past environments.Publisher PDFPeer reviewe

Ionic liquids at electrified interfaces

Until recently, “room-temperature” (<100–150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)–(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of “first-generation” room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the “later generation” RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in “cocktails” of one’s choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost “universal” solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) “sister-systems”.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules

The Scale and Impact of Viking Settlement in Northumbria

Recent archaeological research, notably at the Viking winter camp at Torksey, has indicated that the armies that invaded Anglo-Saxon England in the late 9th century were much larger than has often been assumed and that a literal reading of the Anglo-Saxon Chronicle’s assessment of the size of Viking fleets may, after all, have been correct. Furthermore, study of the Torksey metalwork assemblage has allowed the identification of the archaeological signature of the Viking Great Army and, when applied to Cottam, it confirmed the identification of an initial phase of raiding by an element of the Army, followed shortly thereafter by settlement represented by the development of a hybrid Anglo-Scandinavian culture. Taken together, over 25 categories of non-ferrous artefacts are diagnostic of Viking or Anglo-Scandinavian activity in Northumbria. Applying this model to over 15 sites, largely known only from metal-detecting, we can observe a common pattern. At the majority of sites, a large and fairly standardised Middle Anglo-Saxon finds assemblage is succeeded by just a few Viking finds, which we attribute to raiding following Halfdan’s return to Northumbria with part of the Great Army in AD 876. At a much smaller number of sites there are also assemblages of Anglo-Scandinavian finds, relating to the establishment of new settlements by the new landowners. The overall picture is of major settlement disruption and dislocation of existing land holdings and populations in the late 9th century. This demonstrates, for the first time from archaeological evidence, the scale and impact of Viking activity in Northumbria

Charged-particle multiplicities in pp interactions at root s=900 GeV measured with the ATLAS detector at the LHC ATLAS Collaboration

The first measurements from proton–proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range |η|500 MeVpT>500 MeV. The measurements are compared to Monte Carlo models of proton–proton collisions and to results from other experiments at the same centre-of-mass energy. The charged-particle multiplicity per event and unit of pseudorapidity at η=0η=0 is measured to be 1.333±0.003(stat.)±0.040(syst.)1.333±0.003(stat.)±0.040(syst.), which is 5–15% higher than the Monte Carlo models predict

Racemic, S(+)- and R(-)-ketamine do not increase elevated intracranial pressure

Background: There is controversy regarding the influence of ketamine and its enantiomers on cerebral haemodynamics at increased intracranial pressure (ICP). This study was designed to compare cerebrovascular responses, with particular respect to ICP, to bolus injections of racemic, S(+)- and R(-)-ketamine in an experimental model of intracranial hypertension. Methods: Nine pigs were anaesthetised with fentanyl and vecuronium during mechanical normoventilation. The ICP was raised with extradural balloon catheters to 23 mmHg. The intra-arterial xenon clearance technique was used to determine cerebral blood flow (CBF). Three 60-s bolus injections of racemic ketamine (10 mg/kg), S-ketamine (5 mg/kg) and R-ketamine (20 mg/kg) were given in a randomised sequence. Cerebral and systemic haemodynamic responses were evaluated before and at 1, 5, 10, 15, 30 and 45 min after each injection. Results: Racemic ketamine decreased ICP (P = 0.026) by maximally 10.8%, whereas there was no effect on ICP of S- (P = 0.178) or R-ketamine (P = 0.15). All study drugs had similar biphasic effects on CBF, with maximal initial decreases by 25-29%, followed by transient increases by 7-15%, and a reduction of mean arterial pressure by maximally 22-37%. Conclusions: A decrease or a lack of an increase in ICP in response to intravenous bolus injections of racemic, S- or R-ketamine suggests that the administration of racemic or S-ketamine might be safe in patients with intracranial hypertension due to a space-occupying lesion. The ICP-lowering effect indicates that racemic ketamine might offer a therapeutic advantage over S-ketamine