1,902 research outputs found
Signatures of Confinement in Axial Gauge QCD
A comparative dynamical study of axial gauge QED and QCD is presented.
Elementary excitations associated with particular field configurations are
investigated. Gluonic excitations analogous to linearly polarized photons are
shown to acquire infinite energy. Suppression of this class of excitations in
QCD results from quantization of the chromelectric flux and is interpreted as a
dual Meissner effect, i.e. as expulsion from the QCD vacuum of chromo-electric
fields which are constant over significant distances. This interpretation is
supported by a comparative evaluation of the interaction energy of static
charges in the axial gauge representation of QED and QCD.Comment: 22 pages (no figures
Competing mechanisms of chiral symmetry breaking in a generalized Gross-Neveu model
Chiral symmetry of the 2-dimensional chiral Gross-Neveu model is broken
explicitly by a bare mass term as well as a splitting of scalar and
pseudo-scalar coupling constants. The vacuum and light hadrons - mesons and
baryons which become massless in the chiral limit - are explored analytically
in leading order of the derivative expansion by means of a double sine-Gordon
equation. Depending on the parameters, this model features new phenomena as
compared to previously investigated 4-fermion models: spontaneous breaking of
parity, a non-trivial chiral vacuum angle, twisted kink-like baryons whose
baryon number reflects the vacuum angle, crystals with alternating baryons, and
appearance of a false vacuum.Comment: 8 pages, 7 figures; v2: typos correcte
Assessing Energy Transition Scenarios for Islands through Network Reliability and Power Flow Analysis
This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordThis paper presents a methodology for the reliability and power flow assessments of island/off grid power networks for situations of scarce data and information. This could be a useful tool to help decision makers replacing fossil fuel with renewable energy sources for the off grid/ Island power networks. The aim of the paper is to present and apply a general methodology, informing the decision making towards sustainable island communities. Ushant Island, a small French island, is considered as a case study. The assessment of the current power network status and the reliability analysis reliability are presented. The grid performance parameters are further compared for conventional diesel generator operation and renewable energy generation scenarios to emphasis the advantages of replacing the ordinary diesel units with renewable energy sources in terms of system reliability and network future structure plan. It provides recommendations for the system structure.Intelligent Community Energy (ICE) projec
Parathyroid localization
Twenty-nine consecutive patients with suspected primary hyperparathyroidism were examined preoperatively using ultrasound, sonographically guided fine needle aspiration, and aspirate immunostaining for PTH. In 25 patients, localization of enlarged parathyroid glands was successful. In 2 patients, the tumors were located retrosternally and, thus, could not be detected by ultrasound. One patient had a multinodular goiter which impeded localization. In 1 patient with renal osteodystrophy, 2 enlarged parathyroid glands in the neck were not visualized preoperatively. Cytology was not diagnostic, although some cytological features were suggestive of parathyroid cells. Immunostaining of the aspirated smears for PTH, however, correctly diagnosed all preoperatively localized lesions. Ultrasound should be the routine procedure of choice for preoperative localization of abnormal parathyroid glands in primary hyperparathyroidism. Fine needle aspiration and immunocytochemistry can supply confirmation, if necessary
From non-degenerate conducting polymers to dense matter in the massive Gross-Neveu model
Using results from the theory of non-degenerate conducting polymers like
cis-polyacetylene, we generalize our previous work on dense baryonic matter and
the soliton crystal in the massless Gross-Neveu model to finite bare fermion
mass. In the large N limit, the exact crystal ground state can be constructed
analytically, in close analogy to the bipolaron lattice in polymers. These
findings are contrasted to the standard scenario with homogeneous phases only
and a first order phase transition at a critical chemical potential.Comment: 12 pages, 7 figures, revtex; v2: improved readability, following
advice of PRD referee; accepted for publicatio
Are older people putting themselves at risk when using their walking frames?
Background Walking aids are issued to older adults to prevent falls, however, paradoxically their use has been identified as a risk factor for falling. To prevent falls, walking aids must be used in a stable manner, but it remains unknown to what extent associated clinical guidance is adhered to at home, and whether following guidance facilitates a stable walking pattern. It was the aim of this study to investigate adherence to guidance on walking frame use, and to quantify user stability whilst using walking frames. Additionally, we explored the views of users and healthcare professionals on walking aid use, and regarding the instrumented walking frames (‘Smart Walkers’) utilized in this study.
Methods This observational study used Smart Walkers and pressure-sensing insoles to investigate usage patterns of 17 older people in their home environment; corresponding video captured contextual information. Additionally, stability when following, or not, clinical guidance was quantified for a subset of users during walking in an Activities of Daily Living Flat and in a gait laboratory. Two focus groups (users, healthcare professionals) shared their experiences with walking aids and provided feedback on the Smart Walkers.
Results Incorrect use was observed for 16% of single support periods and for 29% of dual support periods, and was associated with environmental constraints and a specific frame design feature. Incorrect use was associated with reduced stability. Participants and healthcare professionals perceived the Smart Walker technology positively.
Conclusions Clinical guidance cannot easily be adhered to and self-selected strategies reduce stability, hence are placing the user at risk. Current guidance needs to be improved to address environmental constraints whilst facilitating stable walking. The research is highly relevant considering the rising number of walking aid users, their increased falls-risk, and the costs of falls.
Trial Registration Not applicable
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
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
Tau blocks traffic of organelles, neurofilaments, and APP vesicles in neurons and enhances oxidative stress
We studied the effect of microtubule-associated tau protein on trafficking of vesicles and organelles in primary cortical neurons, retinal ganglion cells, and neuroblastoma cells. Tau inhibits kinesin-dependent transport of peroxisomes, neurofilaments, and Golgi-derived vesicles into neurites. Loss of peroxisomes makes cells vulnerable to oxidative stress and leads to degeneration. In particular, tau inhibits transport of amyloid precursor protein (APP) into axons and dendrites, causing its accumulation in the cell body. APP tagged with yellow fluorescent protein and transfected by adenovirus associates with vesicles moving rapidly forward in the axon (∼80%) and slowly back (∼20%). Both movements are strongly inhibited by cotransfection with fluorescently tagged tau (cyan fluorescent protein–tau) as seen by two-color confocal microscopy. The data suggests a linkage between tau and APP trafficking, which may be significant in Alzheimer's disease
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