1,425 research outputs found
Vegetation structure and fire weather influence variation in burn severity and fuel consumption during peatland wildfires
Temperate peatland wildfires are of significant environmental concern but information on their environmental effects is lacking. We assessed variation in burn severity and fuel consumption within and between wildfires that burnt British moorlands in 2011 and 2012. We adapted the composite burn index (pCBI) to provide semi-quantitative estimates of burn severity. Pre- and post-fire surface (shrubs and graminoids) and ground (litter, moss, duff) fuel loads associated with large wildfires were assessed using destructive sampling and analysed using a generalised linear mixed model (GLMM). Consumption during wildfires was compared with published estimates of consumption during prescribed burns. Burn severity and fuel consumption were related to fire weather, assessed using the Canadian Fire Weather Index System (FWI System), and pre-fire vegetation type. pCBI varied 1.6 fold between, and up to 1.7 fold within, wildfires. pCBI was higher where moisture codes of the FWI System indicated drier fuels. Spatial variation in pre- and post-fire fuel load accounted for a substantial proportion of the variance in fuel loads. Average surface fuel consumption was a linear function of pre-fire fuel load. Average ground fuel combustion completeness could be predicted by the Buildup Index. Carbon release ranged between 0.36 and 1.00 kg C m−2. The flammability of ground fuel layers may explain the higher C release-rates seen for wildfires in comparison to prescribed burns. Drier moorland community types appear to be at greater risk of severe burns than blanket-bog communities
Unambiguous quantum state filtering
In this paper, we consider the generalized measurement where one particular
quantum signal is unambiguously extracted from a set of non-commutative quantum
signals and the other signals are filtered out. Simple expressions for the
maximum detection probability and its POVM are derived. We applyl such
unambiguous quantum state filtering to evaluation of the sensing of decoherence
channels. The bounds of the precision limit for a given quantum state of probes
and possible device implementations are discussed.Comment: 7 pages, 5 figure
The Schrodinger Wave Functional and Vacuum State in Curved Spacetime II. Boundaries and Foliations
In a recent paper, general solutions for the vacuum wave functionals in the
Schrodinger picture were given for a variety of classes of curved spacetimes.
Here, we describe a number of simple examples which illustrate how the presence
of spacetime boundaries influences the vacuum wave functional and how physical
quantities are independent of the choice of spacetime foliation used in the
Schrodinger approach despite the foliation dependence of the wave functionals
themselves.Comment: 26 pages, 4 figures, LATE
Stability estimates for resolvents, eigenvalues and eigenfunctions of elliptic operators on variable domains
We consider general second order uniformly elliptic operators subject to
homogeneous boundary conditions on open sets parametrized by
Lipschitz homeomorphisms defined on a fixed reference domain .
Given two open sets , we estimate the
variation of resolvents, eigenvalues and eigenfunctions via the Sobolev norm
for finite values of , under
natural summability conditions on eigenfunctions and their gradients. We prove
that such conditions are satisfied for a wide class of operators and open sets,
including open sets with Lipschitz continuous boundaries. We apply these
estimates to control the variation of the eigenvalues and eigenfunctions via
the measure of the symmetric difference of the open sets. We also discuss an
application to the stability of solutions to the Poisson problem.Comment: 34 pages. Minor changes in the introduction and the refercenes.
Published in: Around the research of Vladimir Maz'ya II, pp23--60, Int. Math.
Ser. (N.Y.), vol. 12, Springer, New York 201
Rayleigh Scattering in Rare Gas Liquids
The Rayleigh scattering length has been calculated for rare-gas liquids in
the ultraviolet for the frequencies at which they luminesce. The calculations
are based on the measured dielectric constants in the gas phase, except in the
case of xenon for which measurements are available in the liquid. The
scattering length mayplace constraints on the design of some large-scale
detectors, using uv luminescence, being proposed to observe solar neutrinos and
dark matter. Rayleigh scattering in mixtures of rare-gas mixtures is also
discussed.Comment: 8 pages, 4 tables; This version corrects erratum in table and has
expanded discussion in Section II. Accepred for publication in NIM
Testing timed systems modeled by stream X-machines
Stream X-machines have been used to specify real systems where complex data structures. They are a variety of extended finite state machine where a shared memory is used to represent communications between the components of systems. In this paper we introduce an extension of the Stream X-machines formalism in order to specify systems that present temporal requirements. We add time in two different ways. First, we consider that (output) actions take time to be performed. Second, our formalism allows to specify timeouts. Timeouts represent the time a system can wait for the environment to react without changing its internal state. Since timeous affect the set of available actions of the system, a relation focusing on the functional behavior of systems, that is, the actions that they can perform, must explicitly take into account the possible timeouts. In this paper we also propose a formal testing methodology allowing to systematically test a system with respect to a specification. Finally, we introduce a test derivation algorithm. Given a specification, the derived test suite is sound and complete, that is, a system under test successfully passes the test suite if and only if this system conforms to the specification
Interaction model for magnetic holes in a ferrofluid layer
Nonmagnetic spheres confined in a ferrofluid layer (magnetic holes) present
dipolar interactions when an external magnetic field is exerted. The
interaction potential of a microsphere pair is derived analytically, with a
precise care for the boundary conditions along the glass plates confining the
system. Considering external fields consisting of a constant normal component
and a high frequency rotating in-plane component, this interaction potential is
averaged over time to exhibit the average interparticular forces acting when
the imposed frequency exceeds the inverse of the viscous relaxation time of the
system. The existence of an equilibrium configuration without contact between
the particles is demonstrated for a whole range of exciting fields, and the
equilibrium separation distance depending on the structure of the external
field is established. The stability of the system under out-of-plane buckling
is also studied. The dynamics of such a particle pair is simulated and
validated by experiments.Comment: 15 pages, 11 figures (18 with subfigures). to appear in Phys. Rev.
Appointments, pay and performance in UK boardrooms by gender
This article uses UK data to examine issues regarding the scarcity of women in boardroom positions. The article examines appointments, pay and any associated productivity effects deriving from increased diversity. Evidence of gender-bias in the appointment of women as non-executive directors is found together with mixed evidence of discrimination in wages or fees paid. However, the article finds no support for the argument that gender diverse boards enhance corporate performance. Proposals in favour of greater board diversity may be best structured around the moral value of diversity, rather than with reference to an expectation of improved company performance
On the running coupling constant in QCD
We try to review the main current ideas and points of view on the running
coupling constant in QCD. We begin by recalling briefly the classic analysis
based on the Renormalization Group with some emphasis on the exact solutions of
the RG equation for a given number of loops, in comparison with the usual
approximate expressions. We give particular attention to the problem of
eliminating the unphysical Landau singularities, and of defining a coupling
that remains significant at the infrared scales. We consider various proposals
of couplings directly related to the quark-antiquark potential or to other
physical quantities (effective charges) and discuss optimization in the choice
of the scale parameter and of the RS. Our main focus is, however, on dispersive
methods, their application, their relation with non-perturbative effects. We
try also to summarize the main results obtained by Lattice simulations in
various MOM schemes. We conclude briefly recalling the traditional comparison
with the experimental data.Comment: 75 pages, 8 figures. Corrected typos, added references, replaced 1
figure. Accepted for publication in Progress in Particle and Nuclear Physic
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