202 research outputs found
Creation and counting of defects in a temperature quenched Bose-Einstein Condensate
We study the spontaneous formation of defects in the order parameter of a
trapped ultracold bosonic gas while crossing the critical temperature for
Bose-Einstein Condensation (BEC) at different rates. The system has the shape
of an elongated ellipsoid, whose transverse width can be varied to explore
dimensionality effects. For slow enough temperature quenches we find a
power-law scaling of the average defect number with the quench rate, as
predicted by the Kibble-Zurek mechanism. A breakdown of such a scaling is found
for fast quenches, leading to a saturation of the average defect number. We
suggest an explanation for this saturation in terms of the mutual interactions
among defects.Comment: 9 pages, 10 figure
Observation of Solitonic Vortices in Bose-Einstein Condensates
We observe solitonic vortices in an atomic Bose-Einstein condensate after
free expansion. Clear signatures of the nature of such defects are the twisted
planar density depletion around the vortex line, observed in absorption images,
and the double dislocation in the interference pattern obtained through
homodyne techniques. Both methods allow us to determine the sign of the
quantized circulation. Experimental observations agree with numerical
simulations. These solitonic vortices are the decay product of phase defects of
the BEC order parameter spontaneously created after a rapid quench across the
BEC transition in a cigar-shaped harmonic trap and are shown to have a very
long lifetime.Comment: 7 pages, 7 figure
Solitonic Vortices in Bose-Einstein Condensates
We analyse, theoretically and experimentally, the nature of solitonic
vortices (SV) in an elongated Bose-Einstein condensate. In the experiment, such
defects are created via the Kibble-Zurek mechanism, when the temperature of a
gas of sodium atoms is quenched across the BEC transition, and are imaged after
a free expansion of the condensate. By using the Gross-Pitaevskii equation, we
calculate the in-trap density and phase distributions characterizing a SV in
the crossover from an elongate quasi-1D to a bulk 3D regime. The simulations
show that the free expansion strongly amplifies the key features of a SV and
produces a remarkable twist of the solitonic plane due to the quantized
vorticity associated with the defect. Good agreement is found between
simulations and experiments.Comment: 6 pages, 4 figure
Dynamics and interaction of vortex lines in an elongated Bose-Einstein condensate
We study the real-time dynamics of vortex lines in a large elongated
Bose-Einstein condensate (BEC) of sodium atoms using a stroboscopic technique.
Vortices are spontaneously produced via the Kibble-Zurek mechanism in a quench
across the BEC transition and then they slowly precess keeping their
orientation perpendicular to the long axis of the trap as expected for
solitonic vortices in a highly anisotropic condensate. Good agreement with
theoretical predictions is found for the precession period as a function of the
orbit amplitude and the number of condensed atoms. In configurations with two
or more vortex lines, we see signatures of vortex-vortex interaction in the
shape and visibility of the orbits. In addition, when more than two vortices
are present, their decay is faster than the thermal decay observed for one or
two vortices. The possible role of vortex reconnection processes is discussed.Comment: 4 pages, 4 figure
Dynamics of Vortices and their Interactions in Bose-Einstein Condensates
Vortex reconnections and interactions play a fundamental role in the dynamics of fluids and turbulent flows, both in the classical and quantum regime. Studying vortices in a clean system like ultracold gases can therefore help, as a bottom-up approach, to understand the physics in a wider context, including superfluid helium, polariton condensates, fluid dynamics and turbulence, neutron stars and cosmological models. So far vortex-vortex interaction was studied in Bose-Einstein condensates either in rotating systems with the observation of regular Abrikosov lattices or in flat condensates across the Berezinskii-Kosterlitz-Thouless transition. In both cases the geometrical constraints allowed to study just a planar interaction among aligned or anti-aligned vortices. The present study instead is carried out in an axisymmetric cigar-shaped Bose-Einstein condensate. Vortices in prolate structures are also known as solitonic vortices. This geometry is especially suitable for investigating vortex interactions. Indeed vortices are oriented perpendicularly to the condensate axis to minimize their length, hence energy, and, because of the cylindrical symmetry, the orientation of a vortex in the radial plane has no constraints. These facts permit interactions to occur with different incoming relative angles between the vortex lines and with different relative velocities. The strong confinement, acting along the radial axis, enhances also interesting effects due to the boundaries
Collision of ductal adenocarcinoma and neuroendocrine tumor of the pancreas: a case report and review of the literature
Background: Simultaneous occurrence of exocrine and neuroendocrine tumors of the pancreas is very infrequent.
We report a patient with an endocrine tumor in the pancreatic-duodenal area and extensive exocrine carcinoma
involving the whole pancreas.
Case presentation: A 69-year-old woman was hospitalized in May 2016 for epigastric pain and weight loss. Her past
medical history revealed an undefined main pancreatic duct dilation that was subsequently confirmed at CT scan
(23 mm) and endoscopic ultrasound. There was no evidence of pancreatic masses, but the cephalic portion of the
main pancreatic duct presented hypoechoic nodules. A diagnosis of the main-duct intraductal papillary mucinous
neoplasm was made, and the patient underwent total pancreatectomy. Pathological examination showed a collision
tumor constituted by a ductal adenocarcinoma involving the whole pancreas and a neuroendocrine tumor located in
the duodenal peripancreatic wall and the head of the pancreas. There was one peripancreatic lymph node metastasis
from the ductal adenocarcinoma and eight node metastases from the neuroendocrine tumor. These findings
suggested a diagnosis of collision of neuroendocrine and ductal adenocarcinomas of the pancreas. The postoperative
course was uneventful.
Conclusions: The coexistence of pancreatic endocrine and exocrine tumors is very uncommon. When present,
problems in differential diagnosis may arise between mixed exocrine-endocrine carcinoma or the collision of separate
tumors
Sustainable urban freight transport adopting public transport-based crowdshipping for B2C deliveries
Abstract Cities crave innovative logistics solutions dealing with the requirements of the 'on demand economy'. The paper estimates the willingness to act as a crowdshipper (supply) and to buy a crowdshipping service (demand) to get goods delivered/picked-up in the last mile B2C e-commerce situation. Specifically, it innovates by considering an environmental-friendly crowdshipping based on the use of the mass transit network of the city where parcels customers/crowdshippers pick-up/drop-off goods in automated parcel lockers located either inside the transit stations or in the surroundings. This issue is very important since "standard" crowdshipping is usually not able to reduce congestion and polluting emissions due to the dedicated trips performed using private motorized vehicles. The paper rests on an extensive stated preference survey. The hypothetical scenarios used to acquire both demand (customers') and supply (crowdshippers') preferences make use of the most relevant attributes emerging from a preliminary investigation performed in the study context. The investigation is performed in the city of Rome and the metro is the transit system considered. The results are useful in understanding and quantifying the potential of this freight transport strategy for e-commerce in an urban context and in providing local policy makers with a good knowledge base for its future development
Plasma antioxidants from chocolate
There is some speculation that dietary flavonoids from chocolate, in particular (-)epicatechin, may promote cardiovascular health as a result of direct antioxidant effects or through antithrombotic mechanisms. Here we show that consumption of plain, dark chocolate results in an increase in both the total antioxidant capacity and the (-)epicatechin content of blood plasma, but that these effects are markedly reduced when the chocolate is consumed with milk or if milk is incorporated as milk chocolate. Our findings indicate that milk may interfere with the absorption of antioxidants from chocolate in vivo and may therefore negate the potential health benefits that can be derived from eating moderate amounts of dark chocolate
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