2,627 research outputs found
The Feshbach-Kerman-Koonin multistep direct reaction theory
The multistep direct reaction theory of Feshbach, Kerman and Koonin (1980) is described in detail and compared with other theories. The results of several analyses of experimental cross-sections are described, and the validity and usefulness of the theory assessed
Analytical study of coherence in seeded modulation instability
We derive analytical expressions for the coherence in the onset of modulation
instability, in excellent agreement with thorough numerical simulations. As
usual, we start by a linear perturbation analysis, where broadband noise is
added to a continuous wave (CW) pump; then, we investigate the effect of adding
a deterministic seed to the CW pump, a case of singular interest as it is
commonly encountered in parametric amplification schemes. Results for the
dependence of coherence on parameters such as fiber type, pump power,
propagated distance, seed signal-to-noise ratio are presented. Finally, we show
the importance of including higher-order linear and nonlinear dispersion when
dealing with generation in longer wavelength regions (mid IR). We believe these
results to be of relevance when applied to the analysis of the coherence
properties of supercontinua generated from CW pumps.Comment: 6 pages, 8 figure
The irreversible evolution of buildings
Buildings, which are in fact ecosystems (living and inanimate organisms interacting together), are nowadays conceived and operated on the base of energy assessments underpinned by the first law of thermodynamics, and design strategies work towards energy conservation. Different approaches, based on the second law of thermodynamics, exist in research; they use the thermodynamic function called exergy - a measure of energy quality obtained from the combination of first and second law - and their scope is still centred on conservation strategies, optimised through irreversibility reduction. However, irreversibility plays a key role in nature, as entropy production dictates direction and modality of all processes and real phenomena are actually irreversible. The main problem related to the forefront of high-efficiency buildings is their high cost and complexity, which contrast stridently with the needs of the largest part of the built environment: effective low-budget sustainable solutions, easy to raise and control by non-specialised users. This research, through a pragmatic methodology, mixes practical experiences from low-budget construction sites with concepts from the relatively new discipline of non-equilibrium thermodynamics, and proposes an alternative energy design approach based on the second law of thermodynamics. Thinking of buildings as evolving ecosystems, their ability to perceive and exploit useful gradients can be enhanced through a deeper understanding of the role of irreversibility as the driving force of spontaneous processes, and imperfection as an intrinsic characteristic of architecture
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Developing and evaluating interventions to reduce inappropriate prescribing by general practitioners of antibiotics for upper respiratory tract infections: a randomised controlled trial to compare paper-based and web-based modelling experiments
Background: Much implementation research is focused on full-scale trials with little evidence of preceding modelling work. The Medical Research Council Framework for developing and evaluating complex interventions has argued for more and better theoretical and exploratory work prior to a trial as a means of improving intervention development. Intervention modelling experiments (IMEs) are a way of exploring and refining an intervention before moving to a full-scale trial. They do this by delivering key elements of the intervention in a simulation that approximates clinical practice by, for example, presenting general practitioners (GPs) with a clinical scenario about making a treatment decision.
Methods: The current proposal will run a full, web-based IME involving 250 GPs that will advance the methodology of IMEs by directly comparing results with an earlier paper-based IME. Moreover, the web-based IME will evaluate an intervention that can be put into a full-scale trial that aims to reduce antibiotic prescribing for upper respiratory tract infections in primary care. The study will also include a trial of email versus postal invitations to participate.
Discussion: More effective behaviour change interventions are needed and this study will develop one such intervention and a system to model and test future interventions. This system will be applicable to any situation in the National Health Service where behaviour needs to be modified, including interventions aimed directly at the public.
Trial registration: ClinicalTrials (NCT): NCT0120673
Frequency modulation of spin torque oscillator pairs
The current controlled modulation of nano-contact based spin torque
oscillator (STO) pairs is studied in both the synchronized and non-synchronized
states. The synchronized state shows a well behaved modulation and demonstrates
robust mutual locking even under strong modulation. The power distribution of
the modulation sidebands can be quantitatively described by assuming a single
oscillator model. However, in the non-synchronized state, the modulation
sidebands are not well described by the model, indicating interactions between
the two individual nano-contact STOs. These findings are promising for
potential applications requiring the modulation of large synchronized STO
arrays
Non-linear frequency and amplitude modulation of a nano-contact spin torque oscillator
We study the current controlled modulation of a nano-contact spin torque
oscillator. Three principally different cases of frequency non-linearity
( being zero, positive, and negative) are investigated.
Standard non-linear frequency modulation theory is able to accurately describe
the frequency shifts during modulation. However, the power of the modulated
sidebands only agrees with calculations based on a recent theory of combined
non-linear frequency and amplitude modulation.Comment: 4 pages, 4 figure
Local-Field Theory of the BCS-BEC Crossover
We develop a self-consistent theory unifying the description of a quantum Fermi gas in the presence of a Fano-Feshbach resonance in the whole phase diagram ranging from BCS to BEC type of superfluidity and from narrow to broad resonances, including the fluctuations beyond mean field. Our theory covers a part of the phase diagram which is not easily accessible by Quantum Monte Carlo simulations and is becoming interesting for a new class of experiments in cold atoms
Universal decay law in charged-particle emission and exotic cluster radioactivity
A linear universal decay formula is presented starting from the microscopic
mechanism of the charged-particle emission. It relates the half-lives of
monopole radioactive decays with the -values of the outgoing particles as
well as the masses and charges of the nuclei involved in the decay. This
relation is found to be a generalization of the Geiger-Nuttall law in
radioactivity and explains well all known cluster decays. Predictions on the
most likely emissions of various clusters are presented.Comment: 2 figure
Huge Seebeck coefficients in non-aqueous electrolytes
The Seeebeck coefficients of the non-aqueous electrolytes tetrabutylammonium
nitrate, tetraoctylphosphonium bromide and tetradodecylammonium nitrate in
1-octanol, 1-dodecanol and ethylene-glycol are measured in a temperature range
from T=30 to T=45 C. The Seebeck coefficient is generally of the order of a few
hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here
we report huge values of 7 mV/K at 0.1M concentration for tetrabutylammonium
nitrate in 1-dodecanol. These striking results open the question of
unexpectedly large kosmotrope or "structure making" effects of
tetraalkylammonium ions on the structure of alcohols.Comment: Submitted to J. Chem. Phy
Thermoelectric energy recovery at ionic-liquid/electrode interface
A Thermally Chargeable Capacitor containing a binary solution of
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide (EMIMTFSI) in
acetonitrile is electrically charged by applying a tempera- ture gradient to
two ideally polarisable electrodes. The corresponding thermoelectric
coefficient is -1.7 mV/K for platinum foil electrodes and -0.3 mV/K for
nanoporous carbon electrodes. Stored electrical energy is extracted by
discharging the capacitor through a resistor. The measured capacitance of the
electrode/ionic- liquid interface is 5 micro F for each platinum electrode
while it becomes four orders of magnitude larger mF for a single
nanoporous carbon electrode. Reproducibility of the effect through repeated
charging-discharging cycles under a steady-state temperature gradient
demonstrates the robustness of the electrical charging pro- cess at the
liquid/electrode interface. The acceleration of the charging by convective
flows is also observed. This offers the possibility to convert waste-heat into
electric energy without exchanging electrons between ions and electrodes, in
contrast to what occurs in most thermogalvanic cells.Comment: 8 pages, 11 figure
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