6,614 research outputs found
Nonlinear envelope equation for broadband optical pulses in quadratic media
We derive a nonlinear envelope equation to describe the propagation of
broadband optical pulses in second order nonlinear materials. The equation is
first order in the propagation coordinate and is valid for arbitrarily wide
pulse bandwidth. Our approach goes beyond the usual coupled wave description of
phenomena and provides an accurate modelling of the evolution of
ultra-broadband pulses also when the separation into different coupled
frequency components is not possible or not profitable
The Effect of Adding Features on Product Attractiveness: the Role of Product Perceived Congruity
This paper investigates the effect of adding more features on product evaluation. We argue that product evaluation as the number of
features increases depends on the congruity of the features added with the product. We show that adding features leads to increased
product attractiveness if these features are congruent with the product, but not if these features are moderately or extremely
incongruent. However, the manipulation of two factors, task involvement and temporal construal, has been shown to make product
evaluation increase as more moderately (but not extremely) incongruent features are added to the product
Investing in Italy: Key legal issues for investors in the Gulf
Recent market data and press reports seem to confirm a growing interest, including from the Gulf, for investments in private and listed companies in Italy. In taking advantage of the opportunities presented by the Italian market (including the disposal plans announced and in part already enacted by the Italian government), investors should be aware of some key legal issues and practical factors. This article briefly outlines some of these key legal issues and factors as they may apply to investors from the Gulf region. It first addresses some of the disclosure and mandatory tender offer obligations that may be triggered in connection with investments in companies listed in Italy. It then provides some legal and practical insights regarding shareholders’ agreements, including certain related merger control considerations. It also provides a general overview of the new foreign investment control regime applicable to investments in the sectors of defense and national security, and in certain assets in the sectors of energy, transport and communications. Finally, it makes brief reference to the potential regulatory-specific approvals that may be required for investments in certain sectors and industries or in respect of certain assets. This article condenses the presentations and discussions that took place at the seminars hosted on this topic by Cleary Gottlieb in Abu Dhabi and Dubai in May 2014
Ecological notes of the alien species godiva quadricolor (Gastropoda: Nudibranchia) occurring in Faro lake (Italy)
The first record from Sicily of the introduced facelinid nudibranch Godiva quadricolor allowed the detection of trophic relationships with the polycerid Polycera hedgpethi, another non-native nudibranch, and with two bryozoan species, namely the naturalized Cheilostomatida Bugula neritina and the cryptogenic Ctenostomatida Amathia verticillata. The settlement of both nudibranchs was presumably promoted by a trophic shift of P. hedgpethi from the natural prey B. neritina towards the largely available and not exploited A. verticillata. This short food web, without evident links with native fauna and having G. quadricolor as the top predator, is described. A DNA barcoding approach was used to confirm the identity of this facelinid species and to explore the possible genetic divergence occurring among the samples analysed
Dimensional crossover and incipient quantum size effects in superconducting niobium nanofilms
Superconducting and normal state properties of sputtered Niobium nanofilms
have been systematically investigated, as a function of film thickness in a
d=9-90 nm range, on different substrates. The width of the
superconducting-to-normal transition for all films remained in few tens of mK,
thus remarkably narrow, confirming their high quality. We found that the
superconducting critical current density exhibits a pronounced maximum, three
times larger than its bulk value, for film thickness around 25 nm, marking the
3D-to-2D crossover. The extracted magnetic penetration depth shows a sizeable
enhancement for the thinnest films, aside the usual demagnetization effects.
Additional amplification effects of the superconducting properties have been
obtained in the case of sapphire substrates or squeezing the lateral size of
the nanofilms. For thickness close to 20 nm we also measured a doubled
perpendicular critical magnetic field compared to its saturation value for d>33
nm, indicating shortening of the correlation length and the formation of small
Cooper pairs in the condensate. Our data analysis evidences an exciting
interplay between quantum-size and proximity effects together with
strong-coupling effects and importance of disorder in the thinnest films,
locating the ones with optimally enhanced critical properties close to the
BCS-BEC crossover regime
Liquid-vapor interface of a polydisperse fluid
We report a Grand Canonical Monte Carlo simulation study of the liquid-vapor
interface of a model fluid exhibiting polydispersity in terms of the particle
size . The bulk density distribution, , of the system
is controlled by the imposed chemical potential distribution . We
choose the latter such that assumes a Schulz form with
associated degree of polydispersity . By introducing a smooth
attractive wall, a planar liquid-vapor interface is formed for bulk state
points within the region of liquid-vapor coexistence. Owing to fractionation,
the pure liquid phase is enriched in large particles, with respect to the
coexisting vapor. We investigate how the spatial non-uniformity of the density
near the liquid-vapor interface affects the evolution of the local distribution
of particle sizes between the limiting pure phase forms. We find (as previously
predicted by density functional theory, Bellier-Castella {\em et al}, Phys.
Rev. {\bf E65}, 021503 (2002)) a segregation of smaller particles to the
interface. The magnitude of this effect is quantified for various via
measurements of the relative adsorption. Additionally, we consider the utility
of various estimators for the interfacial width and highlight the difficulties
of isolating the intrinsic contribution of polydispersity to this width.Comment: 9 pages, 10 Fig
Meaningful characterisation of perturbative theoretical uncertainties
We consider the problem of assigning a meaningful degree of belief to
uncertainty estimates of perturbative series. We analyse the assumptions which
are implicit in the conventional estimates made using renormalisation scale
variations. We then formulate a Bayesian model that, given equivalent initial
hypotheses, allows one to characterise a perturbative theoretical uncertainty
in a rigorous way in terms of a credibility interval for the remainder of the
series. We compare its outcome to the conventional uncertainty estimates in the
simple case of the calculation of QCD corrections to the e+e- -> hadrons
process. We find comparable results, but with important conceptual differences.
This work represents a first step in the direction of a more comprehensive and
rigorous handling of theoretical uncertainties in perturbative calculations
used in high energy phenomenology.Comment: 28 pages, 5 figures. Language modified in order to make it more
'bayesian'. No change in results. Version published in JHE
Expansion Around the Mean-Field Solution of the Bak-Sneppen Model
We study a recently proposed equation for the avalanche distribution in the
Bak-Sneppen model. We demonstrate that this equation indirectly relates
,the exponent for the power law distribution of avalanche sizes, to ,
the fractal dimension of an avalanche cluster.We compute this relation
numerically and approximate it analytically up to the second order of expansion
around the mean field exponents. Our results are consistent with Monte Carlo
simulations of Bak-Sneppen model in one and two dimensions.Comment: 5 pages, 2 ps-figures iclude
Predator recognition and anti-predatory behaviour in a recent aquatic invader, the killer shrimp (Dikerogammarus villosus)
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