151 research outputs found
The INGRID project: Development of Solutions for Sustainable and Highly Interconnected Grids
One of the current main challenges in green-power storage and smart grids is the lack of effective solutions for accommodating the unbalance between renewable energy sources - offering intermittent electricity supply - and a variable electricity demand. Integrating intermittent renewable energy sources by safe and cost-effective energy storage systems is today achievable. Coupled with electrolizers, high-capacity solid-state storage of green-hydrogen is practicable to sustain integration, monitoring and control of large quantity of GWh from renewable generation. The 23.9 MLN Euros INGRID European large demonstrative project started in July 2012 combines magnesium-based material solid-state hydrogen storage systems with advanced ICT technologies to intelligently interconnect miscellaneous energy networks (i.e. electricity and gas) and safely delivering green-hydrogen to various existing or forthcoming markets. One solution INGRID project addresses is an off-grid utility to store renewable electricity captured from wind sources to refill full-battery electric cars
Pairing of Cooper pairs in a Josephson junction network containing an impurity
We show how to induce pairing of Cooper pairs (and, thus,
superconductivity) as a result of local embedding of a quantum impurity in a
Josephson network fabricable with conventional junctions. We find that a
boundary double Sine-Gordon model provides an accurate description of the dc
Josephson current patterns, as well as of the stable phases accessible to the
network. We point out that tunneling of pairs of Cooper pairs is robust against
quantum fluctuations, as a consequence of the time reversal invariance, arising
when the central region of the network is pierced by a dimensionless magnetic
flux . We find that, for , a stable attractive finite
coupling fixed point emerges and point out its relevance for engineering a two
level quantum system with enhanced coherence.Comment: 5 Pages, 5 Figures. Small modifications, ref.[11] added. To appear in
EP
Low Energy Properties of the (n,n) Carbon Nanotubes
According to band theory, an ideal undoped (n,n) carbon nanotube is metallic.
We show that the electron-electron interaction causes it to become Mott
insulating with a spin gap. More interestingly, upon doping it develops
superconducting fluctuations.Comment: 5pages, 2eps figures, one reference added, final version, accepted to
PR
Unified analysis of terminal-time control in classical and quantum systems
Many phenomena in physics, chemistry, and biology involve seeking an optimal
control to maximize an objective for a classical or quantum system which is
open and interacting with its environment. The complexity of finding an optimal
control for maximizing an objective is strongly affected by the possible
existence of sub-optimal maxima. Within a unified framework under specified
conditions, control objectives for maximizing at a terminal time physical
observables of open classical and quantum systems are shown to be inherently
free of sub-optimal maxima. This attractive feature is of central importance
for enabling the discovery of controls in a seamless fashion in a wide range of
phenomena transcending the quantum and classical regimes.Comment: 10 page
Surface impedance anisotropy of YBaCuO single crystals: electrodynamic basis of the measurements
An electrodynamic technique is developed for determining the components of
surface impedance and complex conductivity tensors of HTSC single crystals on
the basis of measured quantities of a quality factor and a resonator frequency
shift. A simple formula is obtained for a geometrical factor of a crystal in
the form of a plate with dimensions in a microwave magnetic field
. To obtain the c-axis complex conductivity from
measurements at we propose a procedure which
takes account of sample size effects. With the aid of the technique involved
temperature dependences of all impedance and conductivity tensors components of
YBaCuO single crystal, grown in BaZrO crucible, are
determined at a frequency of GHz in its normal and superconducting
states. All of them proved to be linear at , and their extrapolation
to zero temperature gives the values of residual surface resistance
and m and
magnetic field penetration depth nm and
m.Comment: 9 pages, 7 figures. Submitted to Phys.Rev.B 05Jun2002; accepted for
publication 21Febr200
Fragility of the Free-Energy Landscape of a Directed Polymer in Random Media
We examine the sensitiveness of the free-energy landscape of a directed
polymer in random media with respect to various kinds of infinitesimally weak
perturbation including the intriguing case of temperature-chaos. To this end,
we combine the replica Bethe ansatz approach outlined in cond-mat/0112384, the
mapping to a modified Sinai model and numerically exact calculations by the
transfer-matrix method. Our results imply that for all the perturbations under
study there is a slow crossover from a weakly perturbed regime where rare
events take place to a strongly perturbed regime at larger length scales beyond
the so called overlap length where typical events take place leading to chaos,
i.e. a complete reshuffling of the free-energy landscape. Within the replica
space, the evidence for chaos is found in the factorization of the replicated
partition function induced by infinitesimal perturbations. This is the reflex
of explicit replica symmetry breaking.Comment: 29 pages, Revtex4, ps figure
Randomized controlled trial of a good practice approach to treatment of childhood obesity in Malaysia: Malaysian childhood obesity treatment trial (MASCOT)
Context. Few randomized controlled trials (RCTs) of interventions for the treatment of childhood obesity have taken place outside the Western world. Aim. To test whether a good practice intervention for the treatment of childhood obesity would have a greater impact on weight status and other outcomes than a control condition in Kuala Lumpur, Malaysia. Methods. Assessor-blinded RCT of a treatment intervention in 107 obese 7- to 11-year olds. The intervention was relatively low intensity (8 hours contact over 26 weeks, group based), aiming to change child sedentary behavior, physical activity, and diet using behavior change counselling. Outcomes were measured at baseline and six months after the start of the intervention. Primary outcome was BMI z-score, other outcomes were weight change, health-related quality of life (Peds QL), objectively measured physical activity and sedentary behavior (Actigraph accelerometry over 5 days). Results. The intervention had no significant effect on BMI z score relative to control. Weight gain was reduced significantly in the intervention group compared to the control group (+1.5 kg vs. +3.5 kg, respectively, t-test p < 0.01). Changes in health-related quality of life and objectively measured physical activity and sedentary behavior favored the intervention group. Conclusions. Treatment was associated with reduced rate of weight gain, and improvements in physical activity and quality of life. More substantial benefits may require longer term and more intensive interventions which aim for more substantive lifestyle changes
On the Application of the Non Linear Sigma Model to Spin Chains and Spin Ladders
We review the non linear sigma model approach (NLSM) to spin chains and spin
ladders, presenting new results. The generalization of the Haldane's map to
ladders in the Hamiltonian approach, give rise to different values of the
parameter depending on the spin S, the number of legs and
the choice of blocks needed to built up the NLSM fields. For rectangular blocks
we obtain or depending on wether , is even or
odd, while for diagonal blocks we obtain . Both
results agree modulo , and yield the same prediction, namely that even (
resp. odd) ladders are gapped (resp. gapless). For even legged ladders we show
that the spin gap collapses exponentially with and we propose a
finite size correction to the gap formula recently derived by Chakravarty using
the 2+1 NSLM, which gives a good fit of numerical results. We show the
existence of a Haldane phase in the two legged ladder using diagonal blocks and
finally we consider the phase diagram of dimerized ladders.Comment: 25 pages, Latex, 7 figures in postscript files, Proc. of the 1996 El
Escorial Summer School on "Strongly Correlated Magnetic and Superconducting
Systems". Some more references are adde
Coordinated optimization of visual cortical maps (II) Numerical studies
It is an attractive hypothesis that the spatial structure of visual cortical
architecture can be explained by the coordinated optimization of multiple
visual cortical maps representing orientation preference (OP), ocular dominance
(OD), spatial frequency, or direction preference. In part (I) of this study we
defined a class of analytically tractable coordinated optimization models and
solved representative examples in which a spatially complex organization of the
orientation preference map is induced by inter-map interactions. We found that
attractor solutions near symmetry breaking threshold predict a highly ordered
map layout and require a substantial OD bias for OP pinwheel stabilization.
Here we examine in numerical simulations whether such models exhibit
biologically more realistic spatially irregular solutions at a finite distance
from threshold and when transients towards attractor states are considered. We
also examine whether model behavior qualitatively changes when the spatial
periodicities of the two maps are detuned and when considering more than 2
feature dimensions. Our numerical results support the view that neither minimal
energy states nor intermediate transient states of our coordinated optimization
models successfully explain the spatially irregular architecture of the visual
cortex. We discuss several alternative scenarios and additional factors that
may improve the agreement between model solutions and biological observations.Comment: 55 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:1102.335
Self-rated health, work characteristics and health related behaviours among nurses in Greece: a cross sectional study
BACKGROUND: Previous studies on self-rated health among nurses have indicated an association of low job satisfaction and stress in relation to poor self-rated health. The relationship between self rated health and the specific work characteristics and health related behaviours of nurses to our knowledge have not been adequately studied. OBJECTIVE: To investigate the health profile of nurses working in hospitals in North West Greece and to examine the associations between self rated health (SRH) and health related behaviours and work characteristics in this group of hospital employees. METHODS: A self-administered questionnaire was distributed to a random sample of 443 nurses working in all the hospitals in North West Greece. Regression analysis was used to examine the relationship of health related behaviours and work characteristics with self rated health among the nurses. RESULTS: A total of 353 responded to the questionnaire (response rate 80%) of which 311 (88%) were female and 42 (12%) male. The mean age (standard deviation) of the respondents was 36 years (5.6) and their mean years of working as nurses were 13.5 years (5.9). Almost half of the nurses' smoked, and about one third were overweight or obese. About 58% (206) of the nurses reported having poor health while 42% (147) reported having good health. Self-rated health was independently associated with gender, effort to avoid fatty foods and physical activity, according to multiple logistic regression analysis. CONCLUSION: The population studied presented a relatively poor health profile, and a high proportion of poor SRH. Though female gender and effort to avoid fatty foods were associated with poor SRH, and exercise and white meat consumption with good SRH, specific work characteristics were not associated with SRH
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