769 research outputs found
Fate of semi-natural grassland in England between 1960 and 2013: a test of national conservation policy
It is well documented that significant losses in semi-natural grassland occurred across
Europe during the second half of the twentieth century. However, comparatively few
studies have investigated and quantified the fate of large numbers of individual grassland
areas. This is important for understanding the causes of decline, and consequently
establishing new policies to conserve and restore lost habitats. This study addresses this
problem; GIS was used to compare historic survey data collected between 1960 and 1981
with two contemporary spatial datasets of habitats in England. The datasets included the
Priority Habitats Inventory 2013 and the Land Cover Map 2007 and this was undertaken for
different types of semi-natural grassland across England. Considerable decreases occurred
across the different grassland types, with a loss of 47% of studied semi-natural grasslands
sites in England over 32–53 years. Of this, the majority of grassland was lost to conversion to
agriculturally-improved grassland or arable cultivation, 45% and 43% respectively. Changes
to woodland and urban areas were also evident, but on a much smaller scale. Sites receiving
statutory protection as a Site of Special Scientific Interest were found to have retained
more grassland (91%), compared with non-protected sites (27%), thus highlighting the
effectiveness of this aspect of current conservation policy in England, and the need for this
to continue in the future
Proposed direct test of a certain type of noncontextuality in quantum mechanics
The noncontextuality of quantum mechanics can be directly tested by measuring
two entangled particles with more than two outcomes per particle. The two
associated contexts are "interlinked" by common observables.Comment: 9 pages 2 figure
Modelling a Particle Detector in Field Theory
Particle detector models allow to give an operational definition to the
particle content of a given quantum state of a field theory. The commonly
adopted Unruh-DeWitt type of detector is known to undergo temporary transitions
to excited states even when at rest and in the Minkowski vacuum. We argue that
real detectors do not feature this property, as the configuration "detector in
its ground state + vacuum of the field" is generally a stable bound state of
the underlying fundamental theory (e.g. the ground state-hydrogen atom in a
suitable QED with electrons and protons) in the non-accelerated case. As a
concrete example, we study a local relativistic field theory where a stable
particle can capture a light quantum and form a quasi-stable state. As
expected, to such a stable particle correspond energy eigenstates of the full
theory, as is shown explicitly by using a dressed particle formalism at first
order in perturbation theory. We derive an effective model of detector (at
rest) where the stable particle and the quasi-stable configurations correspond
to the two internal levels, "ground" and "excited", of the detector.Comment: 13 pages, references added, final versio
Hyperentangled States
We investigate a new class of entangled states, which we call
'hyperentangled',that have EPR correlations identical to those in the vacuum
state of a relativistic quantum field. We show that whenever hyperentangled
states exist in any quantum theory, they are dense in its state space. We also
give prescriptions for constructing hyperentangled states that involve an
arbitrarily large collection of systems.Comment: 23 pages, LaTeX, Submitted to Physical Review
This elusive objective existence
Zurek's existential interpretation of quantum mechanics suffers from three
classical prejudices, including the belief that space and time are
intrinsically and infinitely differentiated. They compel him to relativize the
concept of objective existence in two ways. The elimination of these prejudices
makes it possible to recognize the quantum formalism's ontological implications
- the relative and contingent reality of spatiotemporal distinctions and the
extrinsic and finite spatiotemporal differentiation of the physical world -
which in turn makes it possible to arrive at an unqualified objective
existence. Contrary to a widespread misconception, viewing the quantum
formalism as being fundamentally a probability algorithm does not imply that
quantum mechanics is concerned with states of knowledge rather than states of
Nature. On the contrary, it makes possible a complete and strongly objective
description of the physical world that requires no reference to observers. What
objectively exists, in a sense that requires no qualification, is the
trajectories of macroscopic objects, whose fuzziness is empirically irrelevant,
the properties and values of whose possession these trajectories provide
indelible records, and the fuzzy and temporally undifferentiated states of
affairs that obtain between measurements and are described by counterfactual
probability assignments.Comment: To appear in IJQI; 21 pages, LaTe
The Free Will Theorem
On the basis of three physical axioms, we prove that if the choice of a
particular type of spin 1 experiment is not a function of the information
accessible to the experimenters, then its outcome is equally not a function of
the information accessible to the particles. We show that this result is
robust, and deduce that neither hidden variable theories nor mechanisms of the
GRW type for wave function collapse can be made relativistic. We also establish
the consistency of our axioms and discuss the philosophical implications.Comment: 31 pages, 6figure
Resonances, Unstable Systems and Irreversibility: Matter Meets Mind
The fundamental time-reversal invariance of dynamical systems can be broken
in various ways. One way is based on the presence of resonances and their
interactions giving rise to unstable dynamical systems, leading to well-defined
time arrows. Associated with these time arrows are semigroups bearing time
orientations. Usually, when time symmetry is broken, two time-oriented
semigroups result, one directed toward the future and one directed toward the
past. If time-reversed states and evolutions are excluded due to resonances,
then the status of these states and their associated backwards-in-time oriented
semigroups is open to question. One possible role for these latter states and
semigroups is as an abstract representation of mental systems as opposed to
material systems. The beginnings of this interpretation will be sketched.Comment: 9 pages. Presented at the CFIF Workshop on TimeAsymmetric Quantum
Theory: The Theory of Resonances, 23-26 July 2003, Instituto Superior
Tecnico, Lisbon, Portugal; and at the Quantum Structures Association Meeting,
7-22 July 2004, University of Denver. Accepted for publication in the
Internation Journal of Theoretical Physic
Quantum mechanics and elements of reality inferred from joint measurements
The Einstein-Podolsky-Rosen argument on quantum mechanics incompleteness is
formulated in terms of elements of reality inferred from joint (as opposed to
alternative) measurements, in two examples involving entangled states of three
spin-1/2 particles. The same states allow us to obtain proofs of the
incompatibility between quantum mechanics and elements of reality.Comment: LaTeX, 12 page
The Free-movement pattern Y-maze:A cross-species measure of working memory and executive function
Numerous neurodegenerative and psychiatric disorders are associated with deficits in executive functions, such as working memory and cognitive flexibility. Progress in developing effective treatments for disorders may benefit from targeting these cognitive impairments, the success of which is predicated on the development of animal models with validated behavioural assays. Zebrafish offer a promising model for studying complex brain disorders, but tasks assessing executive function are lacking. The Free movement pattern (FMP) Ymaze combines aspects of the common Y-maze assay, which exploits the inherent motivation of an organism to explore an unknown environment, with analysis based on a series of sequential two-choice discriminations. We validate the task as a measure of working memory and executive function by comparing task performance parameters in adult zebrafish treated with a range of glutamatergic, cholinergic and dopaminergic drugs known to impair working memory and cognitive flexibility. We demonstrate the cross-species validity of the task by assessing performance parameters in adapted versions of the task for mice and Drosophila, and finally a virtual version in humans, and identify remarkable commonalities between vertebrate species’ navigation of the maze. Together, our results demonstrate that the FMP Y-maze is a sensitive assay for assessing working memory and cognitive flexibility across species from invertebrates to humans, providing a simple and widely applicable behavioural assay with exceptional translational relevance
Neurology
Contains reports on five research projects.United States Navy, Office of Naval Research (Nonr-609(39))United States Army Chemical Corps (DA-18-108-405-Cml-942)United States Air Force (Contract AF33(616)-7282)United States Public Health Service (B-3055, B-3090
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