208 research outputs found
On the stability of travelling waves with vorticity obtained by minimisation
We modify the approach of Burton and Toland [Comm. Pure Appl. Math. (2011)]
to show the existence of periodic surface water waves with vorticity in order
that it becomes suited to a stability analysis. This is achieved by enlarging
the function space to a class of stream functions that do not correspond
necessarily to travelling profiles. In particular, for smooth profiles and
smooth stream functions, the normal component of the velocity field at the free
boundary is not required a priori to vanish in some Galilean coordinate system.
Travelling periodic waves are obtained by a direct minimisation of a functional
that corresponds to the total energy and that is therefore preserved by the
time-dependent evolutionary problem (this minimisation appears in Burton and
Toland after a first maximisation). In addition, we not only use the
circulation along the upper boundary as a constraint, but also the total
horizontal impulse (the velocity becoming a Lagrange multiplier). This allows
us to preclude parallel flows by choosing appropriately the values of these two
constraints and the sign of the vorticity. By stability, we mean conditional
energetic stability of the set of minimizers as a whole, the perturbations
being spatially periodic of given period.Comment: NoDEA Nonlinear Differential Equations and Applications, to appea
Energy fluctuation relations and repeated quantum measurements
In this paper, we discuss the statistical description in non-equilibrium regimes of energy fluctuations originated by the interaction between a quantum system and a measurement apparatus applying a sequence of repeated quantum measurements. To properly quantify the information about energy fluctuations, both the exchanged heat probability density function and the corresponding characteristic function are derived and interpreted. Then, we discuss the conditions allowing for the validity of the fluctuation theorem in Jarzynski form 〈e−βQ〉=1, thus showing that the fluctuation relation is robust against the presence of randomness in the time intervals between measurements. Moreover, also the late-time, asymptotic properties of the heat characteristic function are analyzed, in the thermodynamic limit of many intermediate quantum measurements. In such a limit, the quantum system tends to the maximally mixed state (thus corresponding to a thermal state with infinite temperature) unless the system's Hamiltonian and the intermediate measurement observable share a common invariant subspace. Then, in this context, we also discuss how energy fluctuation relations change when the system operates in the quantum Zeno regime. Finally, the theoretical results are illustrated for the special cases of two- and three-levels quantum systems, now ubiquitous for quantum applications and technologies
A dimension-breaking phenomenon for water waves with weak surface tension
It is well known that the water-wave problem with weak surface tension has
small-amplitude line solitary-wave solutions which to leading order are
described by the nonlinear Schr\"odinger equation. The present paper contains
an existence theory for three-dimensional periodically modulated solitary-wave
solutions which have a solitary-wave profile in the direction of propagation
and are periodic in the transverse direction; they emanate from the line
solitary waves in a dimension-breaking bifurcation. In addition, it is shown
that the line solitary waves are linearly unstable to long-wavelength
transverse perturbations. The key to these results is a formulation of the
water wave problem as an evolutionary system in which the transverse horizontal
variable plays the role of time, a careful study of the purely imaginary
spectrum of the operator obtained by linearising the evolutionary system at a
line solitary wave, and an application of an infinite-dimensional version of
the classical Lyapunov centre theorem.Comment: The final publication is available at Springer via
http://dx.doi.org/10.1007/s00205-015-0941-
Influence of climatic variables on crown condition in pine forests of Northern Spain
Producción CientÃficaThe aim of this study was to find relationships between crown condition and
some climatic parameters to identify which are those having a main influence on
crown condition, and how this influence is shown in the tree (crown transparency),
and to contribute to the understanding of how these parameters will affect under
future climate change scenarios
Cancer mortality in a cohort of asbestos textile workers
A cohort of 889 men and 1077 women employed for at least 1 month between 1946 and 1984 by a former Italian leading asbestos (mainly textile) company, characterised by extremely heavy exposures often for short durations, was followed up to 1996, for a total of 53 024 person-years of observation. Employment data were obtained from factory personnel records, while vital status and causes of death were ascertained through municipality registers and local health units. We observed 222 cancer deaths compared with 116.4 expected (standardized mortality ratio, SMR=191). The highest ratios were found for pleural (SMR=4105), peritoneal (SMR=1817) and lung (SMR=282) cancers. We observed direct relationships with duration of employment for lung and peritoneal cancer, and with time since first employment for lung cancer and mesothelioma. Pleural cancer risk was independent from duration (SMR=3428 for employment <1 year, 7659 for 1–4 years, 2979 for 5–9 years and 2130 for ⩾10 years). Corresponding SMRs for lung cancer were 139, 251, 233 and 531. Nonsignificantly increased ratios were found for ovarian (SMR=261), laryngeal (SMR=238) and oro-pharyngeal (SMR=226) cancers. This study confirms and further quantifies the central role of latency in pleural mesothelioma and of cumulative exposure in lung cancer
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