7,434 research outputs found
Large Gravitational Wave Background Signals in Electroweak Baryogenesis Scenarios
The bubble wall velocity in an electroweak first order phase transition is a
key quantity both for electroweak baryogenesis and for the production of a
stochastic background of gravitational waves that may be probed in the future
through gravitational wave experiments like LISA or BBO. We show that, contrary
to the conclusion drawn from previous studies, it is actually possible to
generate a potentially large gravitational wave signal while satisfying the
requirements for viable electroweak baryogenesis, once the effects of the
hydrodynamics of bubble growth are taken into account. Then, the observation of
a large gravitational wave background from the electroweak phase transition
would not necessarily rule out electroweak baryogenesis as the mechanism having
generated the observed baryon asymmetry of the universe.Comment: 6 pages. References added. Accepted for publication in Phys. Rev.
Flight Tests, Performances and Flight Certification of a Twin-Engine Light Aircraft
This paper deals with flight test activities performed on P2006T, a twin-engine light aircraft recently designed and produced by Tecnam. Research activities and flight tests have been conducted during the flight certification of P2006T for the normal category under CS-23. All the acquired data and flight results presented have been focused on both aircraft certification and on aircraft performances, stability and flight qualities measurement. The data have been acquired through a light, accurate and reliable flight instrumentation available at DIAS (Department of Aerospace Engineering). Some flight data about aircraft leveled speed, stall speed, climb characteristics and ground performances (take-off and landing) will be presented. After preliminary flight tests, winglets have been designed and added to the final configuration in order to obtain good climb performances also in OEI (One Engine Inoperative) conditions. Accurate stall tests have been performed in all configurations and influence of both entry-rate and load factor on stall speed have been highlighted. Excellent ground performances have been measured with short take-off and landing distances compared with similar airplanes. All measured flight performances can be considered very good for this aircraft category and have been used to demonstrate aircraft safety and to obtain CS23 certification
Some Cosmological Implications of Hidden Sectors
We discuss some cosmological implications of extensions of the Standard Model
with hidden sector scalars coupled to the Higgs boson. We put special emphasis
on the conformal case, in which the electroweak symmetry is broken radiatively
with a Higgs mass above the experimental limit. Our refined analysis of the
electroweak phase transition in this kind of models strengthens the prediction
of a strongly first-order phase transition as required by electroweak
baryogenesis. We further study gravitational wave production and the
possibility of low-scale inflation as well as a viable dark matter candidate.Comment: 23 pages, 8 figures; some comments added, published versio
Sensory evaluation of wheat/cassava composite bread and effect of label information on acceptance and preference
The performance of 10, 20 and 30% cassava composite bread was carried out by evaluating the colour, aroma, texture, acceptability and buying preference. The samples were served to semi-trained panelists.The result showed that bread baked with 10 and 20% composite flour were not significantly different in all sensory attributes, acceptability and readiness to buy from the control. However, bread baked from30% composite flour showed low mean scores to all the attributes. There was a tendency for bread baked with 10 and 20% composite flour to be rated higher than the control especially in flavour, acceptability and desire to buy. Uniformity in the scores between all labeled and unlabelled sampleswas also observed. Values obtained for proximate composition of cassava composite bread samples were comparable to those obtained for whole wheat bread. Adoption of wheat/cassava flour for bread making is advocated in this work as an alternative to 100% wheat
Transition from Mott insulator to superconductor in GaNbSe and GaTaSe under high pressure
Electronic conduction in GaMSe (M=Nb;Ta) compounds with the fcc
GaMoS-type structure originates from hopping of localized unpaired
electrons (S=1/2) among widely separated tetrahedral M metal clusters. We
show that under pressure these systems transform from Mott insulators to a
metallic and superconducting state with T=2.9 and 5.8K at 13 and 11.5GPa
for GaNbSe and GaTaSe, respectively. The occurrence of
superconductivity is shown to be connected with a pressure-induced decrease of
the MSe octahedral distortion and simultaneous softening of the phonon
associated with MSe-bonds.Comment: 10 pages, 5 figure
Churg Strauss Syndrome: a Review
Churg Strauss syndrome is a medical condition of unknown aetiology characterized by asthma, eosinophilia and finally vasculitis involving small vessels in the limbs and nasal sinuses and the lungs. The purpose of this review is to highlight the natural history of this condition, the pathogenesis, clinical features and treatment modalities available and the prognosis. Literature on the subject was reviewed using manual library search, articles in journals, internet search and conference abstracts.Churg Strauss syndrome has been reported to be predominantly common in middle aged individuals in their middle age of life with a history of new onset or worsened asthma. The condition has a male predisposition. Prior to the advent of steroid therapy this condition invariably leads to death, but since the introduction of prednisolone therapy and other immunosuppressive therapy, the outlook has improved for sufferers and long term survival has been seen. Suspicion of this condition should be based on a good history, physical examination and laboratory investigations and diagnosis based on the criteria that has been drawn by the American College of Rheumatology.Keywords:Asthma, Churg Strauss syndrome, Eosinophilia, Vasculitis
Effect of temperature and illumination on the electrical characteristics of polymer-fullerene bulk-heterojunction solar cells
The current-voltage characteristics of ITO/PEDOT:PSS/OC1C10-PPV:PCBM/Al solar cells were measured in the temperature range 125-320 K under variable illumination, between 0.03 and 100 mW cm(-2) (white light), with the aim of determining the efficiency-limiting mechanism(s) in these devices, and the temperature and/or illumination range(s) in which these devices demonstrate optimal performance. (ITO: indium tin oxide; PEDOT:PSS: poly(styrene sulfonate)-doped poly(ethylene dioxythiophene); OC1C10-PPV: poly[2-methoxy-5-(3,7-dimethyl octyloxy)-1,4-phenylene vinylene]; PCBM: phenyl-C-61 butyric acid methyl ester.) The short-circuit current density and the fill factor grow monotonically with temperature until 320 K. This is indicative of a thermally activated transport of photogenerated charge carriers, influenced by recombination with shallow traps. A gradual increase of the open-circuit voltage to 0.91 V was observed upon cooling the devices down to 125 K. This fits the picture in which the open-circuit voltage is not limited by the work-function difference of electrode materials used. The overall effect of temperature on solar-cell parameters results in a positive temperature coefficient of the power conversion efficiency, which is 1.9% at T = 320 K and 100 mW cm(-2) (2.5% at 0.7 mW cm(-2)). The almost-linear variation of the short-circuit current density with light intensity confirms that the internal recombination losses are predominantly of monomolecular type under short-circuit conditions. We present evidence that the efficiency of this type of solar cell is limited by a light-dependent shunt resistance. Furthermore, the electronic transport properties of the absorber materials, e.g., low effective charge-carrier mobility with a strong temperature dependence, limit the photogenerated current due to a high series resistance, therefore the active layer thickness must be kept low, which results in low absorption for this particular composite absorber
Hydrodynamic obstruction to bubble expansion
We discuss a hydrodynamic obstruction to bubble wall acceleration during a
cosmological first-order phase transition. The obstruction results from the
heating of the plasma in the compression wave in front of the phase transition
boundary. We provide a simple criterion for the occurrence of the obstruction
at subsonic bubble wall velocity in terms of the critical temperature, the
phase transition temperature, and the latent heat of the model under
consideration. The criterion serves as a sufficient condition of subsonic
bubble wall velocities as required by electroweak baryogenesis.Comment: 18 pages, 4 figures; comments and reference added, published versio
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