950 research outputs found
Study of the threshold line between macroscopic and bulk behaviors for homogeneous type II superconductors
In this work we solved the time dependent Ginzburg-Landau equations to
simulate homogeneous superconducting samples with square geometry for several
lateral sizes. As a result of such simulations we notice that in the Meissner
state, when the vortices do not penetrate the superconductor, the response of
small samples are not coincident with that expected for the bulk ones, i.e.,
. Thus, we focused our analyzes on the way which the curves
approximate from the characteristic curve of bulk superconductors. With such
study, we built a diagram of the size of the sample as a function of the
temperature which indicates a threshold line between macroscopic and bulk
behaviors.Comment: 6 pages, 5 figure
Vortex-chain phases in layered superconductors
Layered superconductors in tilted magnetic field have a very rich spectrum of
vortex lattice configurations. In the presence of in-plane magnetic field, a
small c-axis field penetrates in the form of isolated vortex chains. The
structure of a single chain is mainly determined by the ratio of the London
[] and Josephson [] lengths, . At large the chain is composed of tilted
vortices [tilted chains] and at small it consists of a crossing array
of Josephson vortices and pancake stacks [crossing chains]. We studied the
chain structures at intermediate 's and found two types of behavior.
(I) In the range a c-axis field first penetrates in the
form of pancake-stack chains located on Josephson vortices. Due to attractive
coupling between deformed stacks, their density jumps from zero to a finite
value. With further increase of the c-axis field the chain structure smoothly
evolves into modulated tilted vortices and then transforms via a second-order
phase transition, into the tilted straight vortices. (II) In the range a c-axis field first penetrates in the form of kinks creating
kinked tilted vortices. With increasing the c-axis field this structure is
replaced via a first-order phase transition by the strongly deformed crossing
chain. This transition is accompanied by a large jump of pancake density.
Further evolution of the chain structure is similar to the higher anisotropy
scenario: it smoothly transforms back into the tilted straight vortices.Comment: Accepted to Phys. Rev. B, 20 pages 12 figures, animation of chain
structure is available in http://mti.msd.anl.gov/movies/Chains/Nl8al06Im.gif
(gif, 441 KB
What does the âElephant-Equusâ event mean today? Reflections on mammal dispersal events around the Pliocene-Pleistocene boundary and the flexible ambiguity of biochronology
The dispersal of primitive elephantines and monodactyl equids in Eurasia has long been regarded as representative of a substantial turnover in mammal faunas, denoting the spread of open environments linked to the onset of cold and dry conditions in the Northern Hemisphere. During the 1980s, this event was named the âElephant-Equus eventâ and it was correlated with the Gauss-Matuyama reversal, today corresponding to the Pliocene-Pleistocene transition and the beginning of the Quaternary, dated at ~2.6 Ma. Therefore, the Elephant-Equus event became a concept of prominent biochronological and paleoecological significance, especially in western Europe. Yet, uncertainties surrounding the taxonomy and chronology of early âelephantâ and âEquusâ, as well as conceptual differences in adopting (or understanding) the Elephant-Equus event as an intercontinental dispersal event or as a stratigraphic datum, engendered ambiguity and debate. Here, we provide a succinct review of the Elephant-Equus event, considering separately the available evidence on the âelephantâ and the âEquusâ. Elephantines dispersed out of Africa during the Pliocene (Piacenzian). Their earliest calibrated occurrences from eastern Europe date at ~3.2 Ma and they are usually referred to Mammuthus rumanus, although the allocation of several samples to this species is tentative. Available dating constraints for other localities do not resolve whether the dispersal of Mammuthus was synchronous across Eurasia, but this possibility cannot be ruled out. The spread of Mammuthus was part of an intercontinental faunal exchange between Africa and Eurasia that occurred during the Piacenzian, but in this scenario, Mammuthus is quite unique in being the only genus of African origin dispersing to western Eurasia. The arrival of monodactyl equids from North America coincides with the Pliocene-Pleistocene transition, with several occurrences dated or calibrated at ~2.6 Ma and no compelling evidence prior to this age. In Europe, early monodactyl equids are often aligned to Equus livenzovensis, but the material from the type locality of this species is chronologically time-averaged and taxonomically heterogeneous, and western European samples are seldom abundant or informative. Regardless, this does not diminish the biochronological significance of the âEquus eventâ. Indeed, while the term âElephant-Equus eventâ should no longer be used, as the appearance of elephantines in the European fossil record markedly precedes that of monodactyl equids, we endorse the use of the âEquus eventâ as a valid alternative to refer to the intercontinental dispersal event that characterizes the middle Villafranchian faunal turnover, epitomized by but not limited to monodactyl equids
Vortex-antivortex annihilation in mesoscopic superconductors with a central pinning center
In this work we solved the time-dependent Ginzburg-Landau equations, TDGL, to
simulate two superconducting systems with different lateral sizes and with an
antidot inserted in the center. Then, by cycling the external magnetic field,
the creation and annihilation dynamics of a vortex-antivortex pair was studied
as well as the range of temperatures for which such processes could occur. We
verified that in the annihilation process both vortex and antivortex acquire an
elongated format while an accelerated motion takes place.Comment: 4 pages, 5 figures, work presented in Vortex VII
Braincase With Natural Endocast of a Juvenile Rhinocerotinae From the Late Middle Pleistocene Site of Melpignano (Apulia, Southern Italy)
Cranial remains of juvenile fossil rhinoceroses are rarely described in literature and very few is known about the ontogenetic development of their inner anatomy. In this study, we report the first CT based description of a juvenile braincase and its natural brain endocast of a late Middle Pleistocene Rhinocerotinae from Melpignano (Apulia, Italy). The specimen belongs to an individual about 12â18 months old, representing to date the youngest Pleistocene rhinoceros of Mediterranean Europe documented by neurocranial material. Through digital visualization methods the neurocranium has been restored and the anatomy of both the brain and the paranasal sinuses has been obtained and compared with those of juvenile and adult Pleistocene rhinoceroses. We evidence a different morphological development of the inner cranial anatomy in fossil and extant African species
Instabilities in the Flux Line Lattice of Anisotropic Superconductors
The stability of the flux line lattice has been investigated within
anisotropic London theory. This is the first full-scale investigation of
instabilities in the `chain' state. It has been found that the lattice is
stable at large fields, but that instabilities occur as the field is reduced.
The field at which these instabilities first arise, ,
depends on the anisotropy and the angle at which the
lattice is tilted away from the -axis. These instabilities initially occur
at wavevector , and the component of along the
average direction of the flux lines, , is always finite. As the
instability occurs at finite the dependence of the cutoff on is
important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The
instabilities only occur for values of the anisotropy appropriate to
a material like BSCCO, and not for anisotropies more appropriate to YBCO. The
lower critical field is calculated as a function of the angle
at which the applied field is tilted away from the crystal axis. The
presence of kinks in is seen to be related to instabilities in
the equilibrium flux line structure.Comment: Extensively revised paper, with modified analysis of elastic
instabilities. Calculation of the lower critical field is included, and the
presence of kinks in is seen to be related to the elastic
instabilities. 29 pages including 16 figures, LaTeX with epsf styl
The lost hyena from Paciano (Umbria, Italy) reconsidered
We redescribe and revise the taxonomic attribution of a lost hyena hemimandible recovered from Paciano (Umbria, Italy), originally reported in the early 1900s, by comparing it with relevant samples of Pliocene, Pleistocene, and extant species. The mandible of the Paciano hyena was initially attributed to Hyaena striata (= Hyaena hyaena) and subsequently listed as a record of the giant hyena Pachycrocuta brevirostris, but is here assigned to another âbone-crackingâ hyena, the Pliocene-Early Pleistocene Pliocrocuta perrieri. The Paciano hyena contributes to the discussion on the relationships and turnover between Pl. perrieri and P. brevirostris. On the one hand, the two species are very similar in craniodental morphology; their isolated remains are often separated by size; and P. brevirostris is thought to derive from a large-sized population of Pl. perrieri. On the other, a larger size is not an aspect to disregard in hyenas as it usually correlates with the acquisition or better development of âbone-crackingâ features; remains attesting the co-occurrence of Pl. perrieri and P. brevirostris are known from some sites dated at around 2.0â1.8 Ma; and the observed size differences between the two species exceed those recorded between extant and (at times) sympatric species. Therefore, taken alone the competition with P. brevirostris does not explain the extinction of Pl. perrieri, but considering it together with the concurrent spread and resulting peak of carnivoran diversity in Late Villafranchian faunas might. Pliocrocuta perrieri was outcompeted by its larger descendent in scavenging carcasses, while other carnivorans limited its options to deviate to other resources or adopt a different feeding behavior (e.g., active hunting). The case of Paciano is also significant in that it offers an example of the importance and feasibility of reconsidering historical collections, even when the original material is lost entirely. In general, the seek for ânoveltyâ that permeates current scientific literature ensues in few descriptions or reconsiderations of historical samples, especially if the new examinations confirm old results, but we emphasize the significance of such efforts in making old data truly available for the scientific community. In addition, the hyena from Paciano has a biochronological and stratigraphic value, confirming the occurrence in western Umbria of a depositional cycle older than the late Early Pleistocene one (well represented by the rich assemblages from Pietrafitta and Selvella; Farneta Faunal Unit)
Synchrotron radiation reveals the identity of the large felid from Monte Argentario (Early Pleistocene, Italy)
We describe here a partial skull with associated mandible of a large felid from Monte Argentario, Italy (Early Pleistocene; ~1.5 million years). Propagation x-ray phase-contrast synchrotron microtomography of the specimen, still partially embedded in the rock matrix, allows ascribing it reliably to Acinonyx pardinensis, one of the most intriguing extinct carnivorans of the Old World Plio-Pleistocene. The analysis of images and 3D models obtained through synchrotron microtomography â here applied for the first time on a Plio-Pleistocene carnivoran â reveals a mosaic of cheetah-like and Panthera-like features, with the latter justifying previous attributions of the fossil to the extinct Eurasian jaguar Panthera gombaszoegensis. Similarly, we reassign to A. pardinensis some other Italian materials previously referred to P. gombaszoegensis (sites of Pietrafitta and Ellera di Corciano). The recognition of Panthera-like characters in A. pardinensis leads to reconsidering the ecological role of this species, whose hunting strategy was likely to be different from those of the living cheetah. Furthermore, we hypothesise that the high intraspecific variation in body size in A. pardinensis can be the result of sexual dimorphism, as observed today in all large-sized felids
Meta-analysis of Quality of Life Data in Subjects at High Risk for Psychosis.
The nosology of the psychosis high-risk (HR) state is highly controversial. Traditionally conceived as an 'at-risk" state for the development of psychotic disorders, it is also conceptualized as a clinical syndrome associated with functional impairment and disability. In this meta-analysis quality of life (QoL) in HR were compared to healthy controls (HC) and psychotic patients (PS). We performed a systematic search of studies published until 2013 selecting cross-sectional studies addressing QoL in HR. Raw scores, demographic data were extracted by two independent authors. We performed the meta-analyses comparing QoL data between HR, HC and PS 945 subjects : mean age 23, 40% female). The analysis found HR subjects experience a significantly worse QoL than healthy controls (Hedges' g=-1.824, 95% CI from â2.853 to â0.795, p=0.001, 4 studies included), while no difference with psychotic subjects was found (Hedges' g=0.017, 95% CI from â0.636 to 0.671, p=0.958, 3 studies included). Despite the high heterogeneity (l2=95,18%) the effect size of each study comparing HR and healthy controls was significant and coherent in the direction of the effect. Our results indicate that the HR state is characterised by consistent and large reduction in QoL, a clinical indicator for functional disruption: these impairments would call not only for prevention of a future transition to psychosis, but also for treatment of the current disorder. Acknowledging the limitation of our study, due to the reduced number of studies included and the high heterogeneity, these preliminary results urge for further research on this domain
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