13,660 research outputs found
Melting of Discrete Vortices via Quantum Fluctuations
We consider nonlinear boson states with a nontrivial phase structure in the
three-site Bose-Hubbard ring, {\em quantum discrete vortices} (or {\em
q-vortices}), and study their "melting" under the action of quantum
fluctuations. We calculate the spatial correlations in the ground states to
show the superfluid-insulator crossover and analyze the fidelity between the
exact and variational ground states to explore the validity of the classical
analysis. We examine the phase coherence and the effect of quantum fluctuations
on q-vortices and reveal that the breakdown of these coherent structures
through quantum fluctuations accompanies the superfluid-insulator crossover.Comment: Revised version, 4 pages, 5 figures, Accepted for publication in
Physical Review Letter
Spin injection across magnetic/non-magnetic interfaces with finite magnetic layers
We have reconsidered the problem of spin injection across
ferromagnet/non-magnetic-semiconductor (FM/NMS) and
dilute-magnetic-semiconductor/non-magnetic-semiconductor interfaces, for
structures with \textit{finite} magnetic layers (FM or DMS). By using
appropriate physical boundary conditions, we find expressions for the
resistances of these structures which are in general different from previous
results in the literature. When the magnetoresistance of the contacts is
negligible, we find that the spin-accumulation effect alone cannot account for
the dependence observed in recent magnetoresistance data. In a limited
parameter range, our formulas predict a strong dependence arising from the
magnetic contacts in systems where their magnetoresistances are sizable.Comment: 6 pages, 3 eps figs. (extended version- new title + two new figures
added
Four-dimensional light shaping: manipulating ultrafast spatio-temporal foci in space and time
Spectral dispersion of ultrashort pulses allows simultaneous focusing of
light in both space and time creating so-called spatio-temporal foci. Such
space-time coupling may be combined with existing holographic techniques to
give a further dimension of control when generating focal light fields. It is
shown that a phase-only hologram placed in the pupil plane of an objective and
illuminated by a spatially chirped ultrashort pulse can be used to generate
three dimensional arrays of spatio-temporally focused spots. Exploiting the
pulse front tilt generated at focus when applying simultaneous spatial and
temporal focusing (SSTF), it is possible to overlap neighbouring foci in time
to create a smooth intensity distribution. The resulting light field displays a
high level of axial confinement, with experimental demonstrations given through
two-photon microscopy and non-linear laser fabrication of glass
Gross karyotypic and phenotypic alterations among different progenies of the candida glabrata cbs138/atcc2001 reference strain
Peer reviewedPublisher PD
q-Deformed Superalgebras
The article deals with q-analogs of the three- and four-dimensional Euclidean
superalgebra and the Poincare superalgebra.Comment: 38 pages, LateX, no figures, corrected typo
RNA secondary structure design
We consider the inverse-folding problem for RNA secondary structures: for a
given (pseudo-knot-free) secondary structure find a sequence that has that
structure as its ground state. If such a sequence exists, the structure is
called designable. We implemented a branch-and-bound algorithm that is able to
do an exhaustive search within the sequence space, i.e., gives an exact answer
whether such a sequence exists. The bound required by the branch-and-bound
algorithm are calculated by a dynamic programming algorithm. We consider
different alphabet sizes and an ensemble of random structures, which we want to
design. We find that for two letters almost none of these structures are
designable. The designability improves for the three-letter case, but still a
significant fraction of structures is undesignable. This changes when we look
at the natural four-letter case with two pairs of complementary bases:
undesignable structures are the exception, although they still exist. Finally,
we also study the relation between designability and the algorithmic complexity
of the branch-and-bound algorithm. Within the ensemble of structures, a high
average degree of undesignability is correlated to a long time to prove that a
given structure is (un-)designable. In the four-letter case, where the
designability is high everywhere, the algorithmic complexity is highest in the
region of naturally occurring RNA.Comment: 11 pages, 10 figure
Uncovering the natural variability of araucariacean exudates from ex situ and in situ tree populations in New Caledonia using FTIR spectroscopy
Background Understanding the natural variability of plant resins is crucial for evaluating the chemical information stored in ambers that may support inferring palaeoenvironmental conditions. However, even among extant resin-producing plants, the variation of resinous exudates within and between tree genera and species is still poorly understood. Methods We analysed plant exudates from across the Araucariaceae in New Caledonia using Fourier-transform infrared spectroscopy in attenuated total reflection mode (FTIR-ATR). Both, wild (in situ) and arboretum grown (ex situ) populations were used to uncover the effects of intergeneric, inter- and intraspecific variation of the araucariacean plants on the resin chemistry. Results We show that even resins from the same species in the same habitat do have natural (intraspecific) chemical variation. Some of the variation can result from the degree of resin polymerisation, but this is not the only source of variation. Wild sourced resins have greater natural intraspecific chemical variation than the arboretum sourced ones. Interspecific and intergeneric differences were not easy to distinguish in the resins sampled. This has strong implications for the evaluation of the chemical information from worldwide ambers: multiple samples should be analysed to give a more accurate picture of the natural chemical variation present and how this may or may not overlap with the chemistries of other resin types. Additionally we discovered that the Araucariacean species can produce up to three distinct types of exudate (gum, resin, and gum resin). This is the first time that gum resins have been identified and characterized with FTIR-ATR. We also provide a guide on how to distinguish the exudate types when using FTIR-ATR.Peer reviewe
Development of atopic sensitization in Finnish and Estonian children : A latent class analysis in a multicenter cohort
Background: The prevalence of atopy is associated with a Western lifestyle, as shown by studies comparing neighboring regions with different socioeconomic backgrounds. Atopy might reflect various conditions differing in their susceptibility to environmental factors. Objective: We sought to define phenotypes of atopic sensitization in early childhood and examine their association with allergic diseases and hereditary background in Finland and Estonia. Methods: The analysis included 1603 Finnish and 1657 Estonian children from the DIABIMMUNE multicenter young children cohort. Specific IgE levels were measured at age 3, 4, and 5 years, respectively, and categorized into 3 CAP classes. Latent class analysis was performed with the statistical software package poLCA in R software. Results: Both populations differed in terms of socioeconomic status and environmental determinants, such as pet ownership, farm-related exposure, time spent playing outdoors, and prevalence of allergic diseases (all P Conclusion: Despite profound differences in environmental exposures, there might exist genuine patterns of atopic sensitization. The distribution of these patterns might determine the contribution of atopic sensitization to disease onset.Peer reviewe
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