19,527 research outputs found
Viscosity of strongly interacting quantum fluids: spectral functions and sum rules
The viscosity of strongly interacting systems is a topic of great interest in
diverse fields.
We focus here on the bulk and shear viscosities of \emph{non-relativistic}
quantum fluids, with particular emphasis on strongly interacting ultracold
Fermi gases. We use Kubo formulas for the bulk and shear viscosity spectral
functions, and respectively, to derive exact,
non-perturbative results. Our results include: a microscopic connection between
the shear viscosity and the normal fluid density ; sum rules for
and and their evolution through the BCS-BEC
crossover; universal high-frequency tails for and the dynamic
structure factor . We use our sum rules to show that, at
unitarity, is identically zero and thus relate
to density-density correlations. We predict that frequency-dependent shear
viscosity of the unitary Fermi gas can be experimentally
measured using Bragg spectroscopy.Comment: Published versio
Applications of nanomaterials in mechano-sensitive tissues
Bone, cartilage and tendon defects have specific structural, chemical and biological compositions. The extracellular matrix (ECM) of these musculoskeletal tissues interacts with cells to guide tissue formation. Since the ECM of such tissues is at the nanoscale, scaffolds in development are being developed which can mimic these structure. The structural features of the scaffolds affects cell adhesion, proliferation and differentiation. In order to repair musculoskeletal defects of bone, cartilage or tendon, synthetic materials are widely used. It is important that such materials must mimic the natural environment and provide an optimal matrix environment, biological properties including appropriate chemical cues such as growth factors and optimal mechanical properties to guide tissue regeneration. This chapter provides an overview of the properties of nanomaterials for bone, cartilage and tendon regeneration. It covers the aspects of incorporating nanoparticles with scaffolds to improve mechanical properties and the biocompatibility of polymers. The design, fabrication, challenges and success of incorporating of growth factors, genetic cues and drugs to enhance mechano-sentesive tissue has been provided with concluding remarkes on the future challenges and directions of nanomaterials for musculoskeletal tissues
The reduced cost of providing a nationally recognised service for familial hypercholesterolaemia
OBJECTIVE: Familial hypercholesterolaemia (FH) affects 1 in 500 people in the UK population and is associated with premature morbidity and mortality from coronary heart disease. In 2008, National Institute for Health and Care Excellence (NICE) recommended genetic testing of potential FH index cases and cascade testing of their relatives. Commissioners have been slow to respond although there is strong evidence of cost and clinical effectiveness. Our study quantifies the recent reduced cost of providing a FH service using generic atorvastatin and compares NICE costing estimates with three suggested alternative models of care (a specialist-led service, a dual model service where general practitioners (GPs) can access specialist advice, and a GP-led service).METHODS: Revision of existing 3?year costing template provided by NICE for FH services, and prediction of costs for running a programme over 10?years. Costs were modelled for the first population-based FH service in England which covers Southampton, Hampshire, Isle of Wight and Portsmouth (SHIP). Population 1.95 million.RESULTS: With expiry of the Lipitor (Pfizer atorvastatin) patent the cost of providing a 10-year FH service in SHIP reduces by 42.5% (£4.88 million on patent vs £2.80 million off patent). Further cost reductions are possible as a result of the reduced cost of DNA testing, more management in general practice, and lower referral rates to specialists. For instance a dual-care model with GP management of patients supported by specialist advice when required, costs £1.89 million.CONCLUSIONS: The three alternative models of care are now <50% of the cost of the original estimates undertaken by NICE
Dielectronic recombination of W^20+ (4d^10 4f^8): addressing the half-open f-shell
A recent measurement of the dielectronic recombination (DR) of W^20+
[Schippers et al Phys. Rev. A83, 012711 (2011)] found an exceptionally large
contribution from near threshold resonances (<1eV). This still affected the
Maxwellian rate coefficient at much higher temperatures. The experimental
result was found to be a factor 4 or more than that currently in use in the
100-300eV range which is of relevance for modeling magnetic fusion plasmas. We
have carried-out DR calculations with AUTOSTRUCTURE which include all
significant single electron promotions. Our intermediate coupling (IC) results
are more than a factor of 4 larger than our LS-coupling ones at 1eV but still
lie a factor 3 below experiment here. If we assume complete (chaotic) mixing of
near-threshold autoionizing states then our results come into agreement (to
within 20%) with experiment below about 2eV. Our total IC Maxwellian rate
coefficients are 50-30% smaller than those based-on experiment over 100-300eV.Comment: 10 pages, 8 figures, submitted to Phys.Rev.
DNS++: Dynamic Name Resolution with Homomorphic Encryption Based Privacy
This paper presents DNS++, a re-design of the Internet's name resolution system that addresses dynamic information and privacy. DNS++ uses a pub/sub overlay to send updates about a given service to interested clients, allowing them to (re)select between replicas according to their requirements, as updates about services and their features dynamically change. Since third-party brokers in the overlay are not always trusted for the confidentiality of the content flowing through them, clients' privacy is preserved in DNS++ through homomorphic encryption. Brokers are prevented from accessing encrypted service information but can perform homomorphic match and forward service updates to relevant clients through the overlay accordingly. Assuming that forwarding tables in each broker are implemented via ordered data structures, the time required for adding a new client's subscription, and to perform homomorphic match between existing subscriptions and service updates, would grow logarithmically with the number of entries within a table. This is shown by our performance evaluation, which confirms that DNS++ is feasible to be deployed with an acceptable performance overhead
Cell surface localization of tissue transglutaminase is dependent on a fibronectin-binding site in its N-terminal beta-sandwich domain
Increasing evidence indicates that tissue transglutaminase (tTG) plays a role in the assembly and remodeling of extracellular matrices and promotes cell adhesion. Using an inducible system we have previously shown that tTG associates with the extracellular matrix deposited by stably transfected 3T3 fibroblasts overexpressing the enzyme. We now show by confocal microscopy that tTG colocalizes with pericellular fibronectin in these cells, and by immunogold electron microscopy that the two proteins are found in clusters at the cell surface. Expression vectors encoding the full-length tTG or a N-terminal truncated tTG lacking the proposed fibronectin-binding site (fused to the bacterial reporter enzyme β-galactosidase) were generated to characterize the role of fibronectin in sequestration of tTG in the pericellular matrix. Enzyme-linked immunosorbent assay style procedures using extracts of transiently transfected COS-7 cells and immobilized fibronectin showed that the truncation abolished fibronectin binding. Similarly, the association of tTG with the pericellular matrix of cells in suspension or with the extracellular matrix deposited by cell monolayers was prevented by the truncation. These results demonstrate that tTG binds to the pericellular fibronectin coat of cells via its N-terminal β-sandwich domain and that this interaction is crucial for cell surface association of tTG
Dynamic spin response of a strongly interacting Fermi gas
We present an experimental investigation of the dynamic spin response of a
strongly interacting Fermi gas using Bragg spectroscopy. By varying the
detuning of the Bragg lasers, we show that it is possible to measure the
response in the spin and density channels separately. At low Bragg energies,
the spin response is suppressed due to pairing, whereas the density response is
enhanced. These experiments provide the first independent measurements of the
spin-parallel and spin-antiparallel dynamic and static structure factors and
open the way to a complete study of the structure factors at any momentum. At
high momentum the spin-antiparallel dynamic structure factor displays a
universal high frequency tail, proportional to , where is the probe energy.Comment: Replaced with final versio
Multiobjective analysis for the design and control of an electromagnetic valve actuator
The electromagnetic valve actuator can deliver much improved fuel efficiency and reduced emissions in spark ignition (SI) engines owing to the potential for variable valve timing when compared with cam-operated, or conventional, variable valve strategies. The possibility exists to reduce pumping losses by throttle-free operation, along with closed-valve engine braking. However, further development is required to make the technology suitable for accept- ance into the mass production market. This paper investigates the application of multiobjective optimization techniques to the conflicting objective functions inherent in the operation of such a device. The techniques are utilized to derive the optimal force–displacement characteristic for the solenoid actuator, along with its controllability and dynamic/steady state performance
Single-particle and collective excitations in a charged Bose gas at finite temperature
The main focus of this work is on the predictions made by the dielectric
formalism in regard to the relationship between single-particle and collective
excitation spectra in a gas of point-like charged bosons at finite temperature
below the critical region of Bose-Einstein condensation. Illustrative
numerical results at weak coupling () are presented within the Random
Phase Approximation. We show that within this approach the single-particle
spectrum forms a continuum extending from the transverse to the longitudinal
plasma mode frequency and leading to a double-peak structure as increases,
whereas the density fluctuation spectrum consists of a single broadening peak.
We also discuss the momentum distribution and the superfluidity of the gas.Comment: 15 pages, 5 figure
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