7,459 research outputs found
Characterising the phenotypic diversity of Papilio dardanus wing patterns using an extensive museum collection
The history of 20th Century evolutionary biology can be followed through the study of mimetic butterflies. From the initial findings of discontinuous polymorphism through the debates regarding the evolution of mimicry and the step-size of evolutionary change, to the studies on supergene evolution and molecular characterisation of butterfly genomes, mimetic butterflies have been at the heart of evolutionary thought for over 100 years. During this time, few species have received as much attention and in-depth study as Papilio dardanus. To assist all aspects of mimicry research, we present a complete data-derived overview of the extent of polymorphism within this species. Using historical samples permanently held by the NHM London, we document the extent of phenotypic variation and characterise the diversity present in each of the subspecies and how it varies across Africa. We also demonstrate an association between âimperfectâ mimetic forms and the transitional race formed in the area where Eastern and Western African populations meet around Lake Victoria. We present a novel portal for access to this collection, www.mimeticbutterflies.org, allowing remote access to this unique repository. It is hoped that this online resource can act as a nucleus for the sharing and dissemination of other collections databases and imagery connected with mimetic butterflies
Reentrant stability of BEC standing wave patterns
We describe standing wave patterns induced by an attractive finite-ranged
external potential inside a large Bose-Einstein Condensate (BEC). As the
potential depth increases, the time independent Gross-Pitaevskii equation
develops pairs of solutions that have nodes in their wavefunction. We elucidate
the nature of these states and study their dynamical stability. Although we
study the problem in a two-dimensional BEC subject to a cylindrically symmetric
square-well potential of a radius that is comparable to the coherence length of
the BEC, our analysis reveals general trends, valid in two and three
dimensions, independent of the symmetry of the localized potential well, and
suggestive of the behavior in general, short- and large-range potentials. One
set of nodal BEC wavefunctions resembles the single particle n node bound state
wavefunction of the potential well, the other wavefunctions resemble the n-1
node bound-state wavefunction with a kink state pinned by the potential. The
second state, though corresponding to the lower free energy value of the pair
of n node BEC states, is always unstable, whereas the first can be dynamically
stable in intervals of the potential well depth, implying that the standing
wave BEC can evolve from a dynamically unstable to stable, and back to unstable
status as the potential well is adiabatically deepened, a phenomenon that we
refer to as "reentrant dynamical stability".Comment: 13 pages, 9 figures; revised discussion in Sec.
Zero sound in a single component fermion - Bose Einstein Condensate mixture
The resonant dynamics of mediated interactions supports zero-sound in a cold
atom degenerate mixture of a single component fermion gas and a Bose-Einstein
condensate (BEC). We characterize the onset of instability in the phase
separation of an unstable mixture and we find a rich collective mode structure
for stable mixtures with one undamped mode that exhibits an avoided crossing
and a Landau-damped mode that terminates.Comment: 4 pages, 2 figure
The Status of the Pion-Nucleon Coupling Constant
A review is given of the various determinations of the different piNN
coupling constants in analyses of the low-energy pp, np, pbarp, and pi-p
scattering data. The most accurate determinations are in the energy-dependent
partial-wave analyses of the NN data. The recommended value is f^2 = 0.075 . A
recent determination of f^2 by the Uppsala group from backward np cross
sections is shown to be model dependent and inaccurate, and therefore
completely uninteresting. We also argue that an accurate determination of f^2
using pp forward dispersion relations is not a realistic option.Comment: 19 pages, latex2e with a4wide.sty, more information is available at
http://NN-OnLine.sci.kun.nl . Invited talk at FBXV, Groningen, The
Netherlands, July 22-26, 1997. Invited talk at MENU97, Vancouver, B.C.,
Canada, July 28 - August 1, 199
Partial-Wave Analyses of all Proton-Proton and Neutron-Proton Data Below 500 MeV
In 1993 the Nijmegen group published the results of energy-dependent
partial-wave analyses (PWAs) of the nucleon-nucleon (NN) scattering data for
laboratory kinetic energies below Tlab=350 MeV (PWA93). In this talk some
general aspects, but also the newest developments on the Nijmegen NN PWAs are
reported. We have almost finished a new energy-dependent PWA and will discuss
some typical aspects of this new PWA; where it differs from PWA93, but also
what future developments might be, or should be.Comment: Presentation at the 19th European Conference on Few-Body Problems in
Physics, Groningen, The Netherlands, 23-27 August 2004. 4 pages REVTeX4, no
figure
Deconfinement and cold atoms in optical lattices
Despite the fact that by now one dimensional and three dimensional systems of
interacting particles are reasonably well understood, very little is known on
how to go from the one dimensional physics to the three dimensional one. This
is in particular true in a quasi-one dimensional geometry where the hopping of
particles between one dimensional chains or tubes can lead to a dimensional
crossover between a Luttinger liquid and more conventional high dimensional
states. Such a situation is relevant to many physical systems. Recently cold
atoms in optical traps have provided a unique and controllable system in which
to investigate this physics. We thus analyze a system made of coupled one
dimensional tubes of interacting fermions. We explore the observable
consequences, such as the phase diagram for isolated tubes, and the possibility
to realize unusual superfluid phases in coupled tubes systems.Comment: Proceedings of the conference on "Quantum Many Body Theories 13", to
be published by World Scientifi
Black rabbits on Lundy: Tudor treasures or post-war phonies?
Lundy is renowned for its feral black rabbits which, according to popular tradition, have inhabited the island since medieval times. Black rabbit fur was valued for much of the Middle Ages, explaining why warreners of Lundy might have favoured them, but genes responsible for feral rabbit melanism remain unexplored. Further potential complicating factors occur in the form of recent (twentieth century) small-scale domestic rabbit introductions to the Lundy feral population. To gain insight into genetic mechanisms underlying melanism on Lundy, rabbit samples were collected and subjected to molecular analysis. The Lundy rabbit population is shown to harbour non-functional copies of the agouti signalling protein (Asip) gene, a main determinant of coat colour in mammals. The observed genetic mutation is not unique to Lundy, having been reported to underlie dark coat colour phenotypes in various domestic rabbit breeds. The mutation is recessive and only phenotypically expressed in homozygous individuals. Although presence of this particular allele does not preclude recent genetic augmentation or replacement, simple population genetics show that allele persistence from a medieval introduction is not impossible
What's on the menu: Drosera rotundifolia diet determination using DNA data
The round-leaved sundew, Drosera rotundifolia, is a carnivorous plant species. On Lundy it is found in the nutrient-poor bog environments of Pondsbury and the northernmost quarry, where it supplements its diet with invertebrate prey. To gain insight into the diet of these two sundew populations a metabarcoding approach was trialled. This is, to our knowledge, the first study to use DNA barcodes to identify Drosera prey. At each site, a 0.25m2 quadrat was placed in a representative Drosera patch and two daysâ worth of prey were collected. To identify prey items, Cytochrome c oxidase subunit I (COX1) sequences were obtained and compared to the Barcode of Life database. This revealed that Lundy sundews have a mixed diet. In total at least 20 different prey taxa were detected in the two 0.25m2 areas sampled. Sixteen taxa could be identified to species, indicating that metabarcoding permits accurate species level identification of sundew prey items. The majority of prey taxa were dipterans (two-winged flies), of which several have previously been reported on Lundy. Most prey taxa were detected in only one of the two quadrats examined (Jaccardâs index of Similarity=0.01; âdissimilarâ). This might indicate that the two Drosera populations feed on distinct prey communities, but more research is needed to confirm this
Sympathetic cooling route to Bose-Einstein condensate and Fermi-liquid mixtures
We discuss a sympathetic cooling strategy that can successfully mitigate
fermion-hole heating in a dilute atomic Fermi-Bose mixture and access the
temperature regime in which the fermions behave as a Fermi liquid. We introduce
an energy-based formalism to describe the temperature dynamics with which we
study a specific and promising mixture composed of 6Li and 87Rb. Analyzing the
harmonically trapped mixture, we find that the favourable features of this
mixture are further enhanced by using different trapping frequencies for the
two species.Comment: 4 pages, 2 figure
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