463 research outputs found
Unruh quantization in presence of a condensate
We have shown that the Unruh quantization scheme can be realized in Minkowski
spacetime in the presence of Bose-Einstein condensate containing infinite
average number of particles in the zero boost mode and located basically inside
the light cone. Unlike the case of an empty Minkowski spacetime the condensate
provides the boundary conditions necessary for the Fulling quantization of the
part of the field restricted only to the Rindler wedge of Minkowski spacetime.Comment: 4 page
An example of a uniformly accelerated particle detector with non-Unruh response
We propose a scalar background in Minkowski spacetime imparting constant
proper acceleration to a classical particle. In contrast to the case of a
constant electric field the proposed scalar potential does not create
particle-antiparticle pairs. Therefore an elementary particle accelerated by
such field is a more appropriate candidate for an "Unruh-detector" than a
particle moving in a constant electric field. We show that the proposed
detector does not reveal the universal thermal response of the Unruh type.Comment: 12 pages, 1 figur
Quantum field aspect of Unruh problem
It is shown using both conventional and algebraic approach to quantum field
theory that it is impossible to perform quantization on Unruh modes in
Minkowski spacetime. Such quantization implies setting boundary condition for
the quantum field operator which changes topological properties and symmetry
group of spacetime and leads to field theory in two disconnected left and right
Rindler spacetimes. It means that "Unruh effect" does not exist.Comment: LaTeX, 13 pages, 1 figur
Measuring Selection when Parents and Offspring Interact
Non-social and social selection gradients are key evolutionary parameters in systems where individuals interact. They are most easily obtained by regressing an individual's fitness on the trait values of the individual and its social partner. In the context of parental care it is more common to regress the trait value of the parents (i.e. the social partner) on a ‘mixed’ fitness measure that is a function of the parent's and offspring's fitness (for example, the number of recruits, which equals parental fecundity multiplied by offspring survival). For such an approach to yield correct estimates of net-selection, the trait must be sex-limited and not affect the parents’ own survival. When a trait is not sex-limited, the non-social selection should be weighted by one (because all individuals express the trait) and social selection should be weighted by a half (because the relatedness between parents and the offspring they care for is a half, usually). The ‘mixed’ fitness approach does not give estimates of both components of selection and so they cannot be weighted appropriately. We show that mixed fitness components are frequently used in place of direct fitness measures in the literature (37% of fecundity selection estimates use a mixed fitness approach), but that the frequency is much higher in some taxa, such as birds and mammals. We suggest alternative methods that could be used to estimate both social and non-social selection gradients, while at the same time assessing the importance of unmeasured traits
Shot noise in resonant tunneling through a zero-dimensional state with a complex energy spectrum
We investigate the noise properties of a GaAs/AlGaAs resonant tunneling
structure at bias voltages where the current characteristic is determined by
single electron tunneling. We discuss the suppression of the shot noise in the
framework of a coupled two-state system. For large bias voltages we observed
super-Poissonian shot noise up to values of the Fano factor .Comment: 4 pages, 4 figures, accepted for Phys. Rev.
Vacuum instability in external fields
We study particles creation in arbitrary space-time dimensions by external
electric fields, in particular, by fields, which are acting for a finite time.
The time and dimensional analysis of the vacuum instability is presented. It is
shown that the distributions of particles created by quasiconstant electric
fields can be written in a form which has a thermal character and seems to be
universal. Its application, for example, to the particles creation in external
constant gravitational field reproduces the Hawking temperature exactly.Comment: 36 pages, LaTe
Life path analysis: scaling indicates priming effects of social and habitat factors on dispersal distances
1. Movements of many animals along a life-path can be separated into repetitive ones within home ranges and transitions between home ranges. We sought relationships of social and environmental factors with initiation and distance of transition movements in 114 buzzards Buteo buteo that were marked as nestlings with long-life radio tags.
2. Ex-natal dispersal movements of 51 buzzards in autumn were longer than for 30 later in their first year and than 35 extra-natal movements between home ranges after leaving nest areas. In the second and third springs, distances moved from winter focal points by birds that paired were the same or less than for unpaired birds. No post-nuptial movement exceeded 2 km.
3. Initiation of early ex-natal dispersal was enhanced by presence of many sibs, but also by lack of worm-rich loam soils. Distances travelled were greatest for birds from small broods and with relatively little short grass-feeding habitat near the nest. Later movements were generally enhanced by the absence of loam soils and short grassland, especially with abundance of other buzzards and probable poor feeding habitats (heathland, long grass).
4. Buzzards tended to persist in their first autumn where arable land was abundant, but subsequently showed a strong tendency to move from this habitat.
5. Factors that acted most strongly in ½-km buffers round nests, or round subsequent focal points, usually promoted movement compared with factors acting at a larger scale. Strong relationships between movement distances and environmental characteristics in ½-km buffers, especially during early ex-natal dispersal, suggested that buzzards became primed by these factors to travel far.
6. Movements were also farthest for buzzards that had already moved far from their natal nests, perhaps reflecting genetic predisposition, long-term priming or poor habitat beyond the study area
Territorial defence in the speckled wood butterfly (Pararge aegeria): The resident always wins
Análise filogenética e implicações sistemáticas e evolutivas nos Cuculiformes (Aves) com base na osteologia, comportamento e ecologia
The Tutoring Role of Mentors Working with Adults and Elderly People with Learning Disabilities Using Virtual Environments
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