Analytical solution of the Gross-Neveu model at finite density

Recent numerical calculations have shown that the ground state of the Gross-Neveu model at finite density is a crystal. Guided by these results, we can now present the analytical solution to this problem in terms of elliptic functions. The scalar potential is the superpotential of the non-relativistic Lame Hamiltonian. This model can also serve as analytically solvable toy model for a relativistic superconductor in the Larkin-Ovchinnikov-Fulde-Ferrell phase.Comment: 5 pages, no figures, revtex; vs2: appendix with analytical proof of self-consistency adde

How to get from imaginary to real chemical potential

Using the exactly solvable Gross-Neveu model as theoretical laboratory, we analyse in detail the relationship between a relativistic quantum field theory at real and imaginary chemical potential. We find that one can retrieve the full information about the phase diagram of the theory from an imaginary chemical potential calculation. The prerequisite is to evaluate and analytically continue the effective potential for the chiral order parameter, rather than thermodynamic observables or phase boundaries. In the case of an inhomogeneous phase, one needs to compute the full effective action, a functional of the space-dependent order parameter, at imaginary chemical potential.Comment: revtex, 9 pages, 10 figures; v2: add more references, modify concluding sectio

Covariant boost and structure functions of baryons in Gross-Neveu models

Baryons in the large N limit of two-dimensional Gross-Neveu models are reconsidered. The time-dependent Dirac-Hartree-Fock approach is used to boost a baryon to any inertial frame and shown to yield the covariant energy-momentum relation. Momentum distributions are computed exactly in arbitrary frames and used to interpolate between the rest frame and the infinite momentum frame, where they are related to structure functions. Effects from the Dirac sea depend sensitively on the occupation fraction of the valence level and the bare fermion mass and do not vanish at infinite momentum. In the case of the kink baryon, they even lead to divergent quark and antiquark structure functions at x=0.Comment: 13 pages, 12 figures; v2: minor correction

A discontinuity in the low-mass initial mass function

The origin of brown dwarfs (BDs) is still an unsolved mystery. While the standard model describes the formation of BDs and stars in a similar way recent data on the multiplicity properties of stars and BDs show them to have different binary distribution functions. Here we show that proper treatment of these uncovers a discontinuity of the multiplicity-corrected mass distribution in the very-low-mass star (VLMS) and BD mass regime. A continuous IMF can be discarded with extremely high confidence. This suggests that VLMSs and BDs on the one hand, and stars on the other, are two correlated but disjoint populations with different dynamical histories. The analysis presented here suggests that about one BD forms per five stars and that the BD-star binary fraction is about 2%-3% among stellar systems.Comment: 14 pages, 11 figures, uses emulateapj.cls. Minor corrections and 1 reference added after being accepted by the Ap

Dietary nitrate-induced increases in human muscle power: High versus low responders

Maximal neuromuscular power is an important determinant of athletic performance and also quality of life, independence, and perhaps even mortality in patient populations. We have shown that dietary nitrate (NO3- ), a source of nitric oxide (NO), improves muscle power in some, but not all, subjects. The present investigation was designed to identify factors contributing to this interindividual variability. Healthy men (n = 13) and women (n = 7) 22-79 year of age and weighing 52.1-114.9 kg were studied using a randomized, double-blind, placebo-controlled, crossover design. Subjects were tested 2 h after ingesting beetroot juice (BRJ) either containing or devoid of 12.3 ± 0.8 mmol of NO3- . Plasma NO3- and nitrite (NO2- ) were measured as indicators of NO bioavailability and maximal knee extensor speed (Vmax ), power (Pmax ), and fatigability were determined via isokinetic dynamometry. On average, dietary NO3- increased (P < 0.05) Pmax by 4.4 ± 8.1%. Individual changes, however, ranged from -9.6 to +26.8%. This interindividual variability was not significantly correlated with age, body mass (inverse of NO3- dose per kg), body mass index (surrogate for body composition) or placebo trial Vmax or fatigue index (in vivo indicators of muscle fiber type distribution). In contrast, the relative increase in Pmax was significantly correlated (r = 0.60; P < 0.01) with the relative increase in plasma NO2- concentration. In multivariable analysis female sex also tended (P = 0.08) to be associated with a greater increase in Pmax. We conclude that the magnitude of the dietary NO3- -induced increase in muscle power is dependent upon the magnitude of the resulting increase in plasma NO2- and possibly female sex

The Role of Accelerated Testing in Reliability Prediction

Accepted© EWTEC 2015The transition from the early stages of marine renewable energy (MRE) device development towards pre-commercial status involves rigorous design validation before full-scale testing. The main aim of Technology Readiness Levels 4-6 is to prove that the concept can deliver the required power production performance and also that a level of system reliability is achieved to ensure sufficient availability. Both of these metrics are crucial to obtaining competitive levelised cost of energy. The current state of the MRE sector means that reliability data is sparse or commercially sensitive. Device developers are therefore forced to base reliability predictions on physical testing, detailed numerical analysis or in the absence of these, generic (and potentially unsuitable) failure rate databases. Generic data will only provide a crude estimate of component or subsystem reliability unless modified to suit the application. More accurate estimates of component and subsystem reliability are possible through accelerated testing. As part of the DTOcean (Optimal Design Tools for Ocean Energy Arrays) project, results from physical tests involving synthetic ropes and shackles are used to demonstrate how quantitative accelerated testing can be used to bridge the gap between generic failure rates and those which are applicable to MRE mooring applications

A validated BEM model to analyse hydrodynamic loading on tidal stream turbines blades

This is the author accepted manuscript. The final version is available from the link in this record.AWTEC 2016: 3rd Asian Wave and Tidal Energy Conference, 24-28 October 2016, SingaporeThis paper details a Blade Element Momentum (BEM) model for a 3 bladed, horizontal axis Tidal Stream Turbine (TST). The code capabilities are tested and validated by applying a range of different turbine parameters and operating conditions, where results are compared to numerous datasets. The model shows excellent agreement to performance and thrust measurements for 3 of the 4 datasets. Compared to other BEM models improved correlations are seen at higher rotational speeds. The fourth case shows over predictions of up to 30% in power at peak operating speed. In this case, CFD studies show better correlation due to the ability to capture detailed flow features around the blade as well as free surface effects, however require 3 to 4 orders of magnitude greater computational cost. Steady, non-uniform inflow functionality is incorporated into the model, where distributions of thrust and torque along the blade as well as cyclic loads are determined. These show the potential of the model to be used in combination with tools such as stress and fatigue analyses to improve the blade design process.This research is carried out as part of the Industrial Doctoral Centre for Offshore Renewable Energy (IDCORE) programme, funded by the Energy Technology partnership and the RCUK Energy programme (Grant number EP/J500847/1), in collaboration with EDF R&D

Phase transition in the 3-D massive Gross-Neveu model

We consider the 3-dimensional massive Gross-Neveu model at finite temperature as an effective theory for strong interactions. Using the Matsubara imaginary time formalism, we derive a closed form for the renormalized $T$-dependent four-point function. This gives a singularity, suggesting a phase transition. Considering the free energy we obtain the $T$-dependent mass, which goes to zero for some temperature. These results lead us to the conclusion that there is a second-order phase transition.Comment: 06 pages, 02 figures, LATE

Component reliability test approaches for marine renewable energy

Philipp R Thies University of Exeter Cornwall Campus College of Engineering, Mathematics and Physical Science Penryn Cornwall TR10 9FE United KingdomArticleThis version is the author’s manuscript of the published article. Please cite the published version as: Thies PR, Johanning L, Karikari-Boateng KA, Ng C, McKeever P. (2015). Component reliability test approaches for marine renewable energy. Proc IMechE Part O: Journal of Risk and Reliability, Spec. Issue, Vol. 229 (5), pp. 403-416, DOI:10.1177/1748006X15580837.An increasing number of marine renewable energy (MRE) systems are reaching the stage where a working prototype must be demonstrated in operation in order to progress to the next stage of commercial projects. This stage is often referred to as ‘valley of death’ where device developers face the challenge of raising capital needed to demonstrate the prototype. The dilemma is that investors understandably demand a proven track record and demonstrated reliability in order to provide capital. One way to resolve this dilemma is specific component reliability testing that not only satisfies investor expectations but holds the potential to improve and de-risk components for MRE. This paper gives an overview to different component reliability test approaches in established industries and for MRE, covering both wave and tidal energy technologies. There has been notable activity in the research community to develop and implement dedicated component reliability test rigs that allow the investigation and demonstration of component reliability under controlled, yet representative conditions. Two case studies of physical test rigs will illustrate the possible test approaches. The Nautilus Powertrain test rig, a facility at the Offshore Renewable Energy (ORE) Catapult, focuses on the demonstration and testing of drive train components including gearboxes, generators, mechanical couplings and bearings. The Dynamic Marine Component test rig (DMaC) at the University of Exeter aims to replicate the forces and motions for floating offshore applications and their subsystems, including mooring lines and power cables. This paper highlights the relevance of component testing and qualification prior to large-scale commercial deployments and gives an insight to some of the test capabilities available in the sector. Several case studies illustrate the component test approach for tidal energy (Nautilus) and wave energy (DMaC) applications.European Union’s European Regional Development Fund (ERDF)Department of Energy and Climate Change (DECC)Peninsula Research Institute for Marine Renewable Energy (PRIMaRE)Engineering and Physical Sciences Research Council (EPSRC)Energy Technoliogy Istitute (ETI)Research Councils UK (RCUK) Energy programmeIndustrial Doctorate Centre in Offshore Renewable Energy (IDCORE

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Whether BDs form as stars through gravitational collapse ("star-like") or BDs and some very low-mass stars constitute a separate population which form alongside stars comparable to the population of planets, e.g. through circumstellar disk ("peripheral") fragmentation, is one of the key questions of the star-formation problem. For young stars in Taurus-Auriga the binary fraction is large with little dependence on primary mass above ~0.2Msun, while for BDs it is <10%. We investigate a case in which BDs in Taurus formed dominantly through peripheral fragmentation. The decline of the binary frequency in the transition region between star-like and peripheral formation is modelled. A dynamical population synthesis model is employed in which stellar binary formation is universal. Peripheral objects form separately in circumstellar disks with a distinctive initial mass function (IMF), own orbital parameter distributions for binaries and a low binary fraction. A small amount of dynamical processing of the stellar component is accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. The binary fraction declines strongly between the mass-limits for star-like and peripheral formation. The location of characteristic features and the steepness depend on these mass-limits. Such a trend might be unique to low density regions hosting dynamically unprocessed binary populations. The existence of a strong decline in the binary fraction -- primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star forming region. It is a test of the (non-)continuity of star formation along the mass-scale, the separateness of the stellar and BD populations and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.Comment: accepted for publication in A&A, 11 pages, 4 figures, 1 tabl