3,987 research outputs found
Atom laser dynamics in a tight-waveguide
We study the transient dynamics that arise during the formation of an atom
laser beam in a tight waveguide. During the time evolution the density profile
develops a series of wiggles which are related to the diffraction in time
phenomenon. The apodization of matter waves, which relies on the use of smooth
aperture functions, allows to suppress such oscillations in a time interval,
after which there is a revival of the diffraction in time. The revival time
scale is directly related to the inverse of the harmonic trap frequency for the
atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th
WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ",
organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007
Diffraction in time of a confined particle and its Bohmian paths
Diffraction in time of a particle confined in a box which its walls are
removed suddenly at is studied. The solution of the time-dependent
Schr\"{o}dinger equation is discussed analytically and numerically for various
initial wavefunctions. In each case Bohmian trajectories of the particles are
computed and also the mean arrival time at a given location is studied as a
function of the initial state.Comment: 8 pages, 6 figure
Confronting the trans-Planckian question of inflationary cosmology with dissipative effects
We provide a class of QFTs which exhibit dissipation above a threshold
energy, thereby breaking Lorentz invariance. Unitarity is preserved by coupling
the fields to additional degrees of freedom (heavy fields) which introduce the
rest frame. Using the Equivalence Principle, we define these theories in
arbitrary curved spacetime. We then confront the trans-Planckian question of
inflationary cosmology. When dissipation increases with the energy, the quantum
field describing adiabatic perturbations is completely damped at the onset of
inflation. However it still exists as a composite operator made with the
additional fields. And when these are in their ground state, the standard power
spectrum obtains if the threshold energy is much larger that the Hubble
parameter. In fact, as the energy redshifts below the threshold, the composite
operator behaves as if it were a free field endowed with standard vacuum
fluctuations. The relationship between our models and the Brane World scenarios
studied by Libanov and Rubakov displaying similar effects is discussed. The
signatures of dissipation will be studied in a forthcoming paper.Comment: 30 pages, 1 Figure, to appear in CQ
Emerging Universe from Scale Invariance
We consider a scale invariant model which includes a term in action
and show that a stable "emerging universe" scenario is possible. The model
belongs to the general class of theories, where an integration measure
independent of the metric is introduced. To implement scale invariance (S.I.),
a dilaton field is introduced. The integration of the equations of motion
associated with the new measure gives rise to the spontaneous symmetry breaking
(S.S.B) of S.I. After S.S.B. of S.I. in the model with the term (and
first order formalism applied), it is found that a non trivial potential for
the dilaton is generated. The dynamics of the scalar field becomes non linear
and these non linearities are instrumental in the stability of some of the
emerging universe solutions, which exists for a parameter range of the theory.Comment: 21 pages, 4 figures. Accepted for publication in JCA
What is the best method for preserving the genuine black truffle (Tuber melanosporum) aroma? An olfactometric and sensory approach
The aim of this work was to evaluate the effects of different preservation methods (freeze-drying, hot-air drying, freezing and canning) on the aroma profile of T. melanosporum truffles. Volatile organic compounds (VOCs) were extracted by solid-phase microextraction (SPME) and analysed by gas-chromatography olfactometry to monitor changes occurring in key-aroma compounds. Samples were also submitted to descriptive sensory analysis by a panel of trained judges, with the aim of correlating both sets of data. Freeze-drying - and to a lesser extent hot-air drying - were the only treatments able to retain key-compounds such as dimethylsulphide (DMS) and dimethyldisulphide (DMDS), evoking the aroma typically associated with fresh truffle. Principal component analysis (PCA) performed on the descriptive data showed the sensorial proximity between fresh and freeze-dried truffle, and also the differences between them and those frozen and canned. Despite some differences in the odour volatile profile of fresh and freezed-dried truffles (mainly the lack of 2, 3-butanedione and branched ethyl esters), freeze-drying is the most suitable technique for preserving the overall original aroma of fresh truffle. Several key-odour compounds - mainly unsaturated linear chain carbonyl compounds, sulphur and pyrrole derivates - emerge as biomarkers of the studied technologies
Heatmaps in soccer: event vs tracking datasets
We investigate how similar heatmaps of soccer players are when constructed
from (i) event datasets and (ii) tracking datasets. When using event datasets,
we show that the scale at which the events are grouped strongly influences the
correlation with the tracking heatmaps. Furthermore, there is an optimal scale
at which the correlation between event and tracking heatmaps is the highest.
However, even at the optimal scale, correlations between both approaches are
moderate. Furthermore, there is high heterogeneity in the players' correlation,
ranging from negative values to correlations close to the unity. We show that
the number of events performed by a player does not crucially determine the
level of correlation between both heatmaps. Finally, we analyzed the influence
of the player position, showing that defenders are the players with the highest
correlations while forwards have the lowest.Comment: 6 pages, 5 figure
Shortcuts to adiabaticity in a time-dependent box
A method is proposed to drive an ultrafast non-adiabatic dynamics of an
ultracold gas trapped in a box potential. The resulting state is free from
spurious excitations associated with the breakdown of adiabaticity, and
preserves the quantum correlations of the initial state up to a scaling factor.
The process relies on the existence of an adiabatic invariant and the inversion
of the dynamical self-similar scaling law dictated by it. Its physical
implementation generally requires the use of an auxiliary expulsive potential
analogous to those used in soliton control. The method is extended to a broad
family of many-body systems. As illustrative examples we consider the ultrafast
expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in
different dimensions, where the method exhibits an excellent robustness against
different regimes of interactions and the features of an experimentally
realizable box potential.Comment: 6 pp, 4 figures, typo in Eq. (6) fixe
A randomized, phase II study of afatinib versus cetuximab in metastatic or recurrent squamous cell carcinoma of the head and neck.
BackgroundAfatinib is an oral, irreversible ErbB family blocker that has shown activity in epidermal growth factor receptor (EGFR)-mutated lung cancer. We hypothesized that the agent would have greater antitumor activity compared with cetuximab in recurrent or metastatic (R/M) head and neck squamous cell carcinoma (HNSCC) patients, whose disease has progressed after platinum-containing therapy.Patients and methodsAn open-label, randomized, phase II trial was conducted in 43 centers; 124 patients were randomized (1 : 1) to either afatinib (50 mg/day) or cetuximab (250 mg/m(2)/week) until disease progression or intolerable adverse events (AEs) (stage I), with optional crossover (stage II). The primary end point was tumor shrinkage before crossover assessed by investigator (IR) and independent central review (ICR).ResultsA total of 121 patients were treated (61 afatinib, 60 cetuximab) and 68 crossed over to stage II (32 and 36 respectively). In stage I, mean tumor shrinkage by IR/ICR was 10.4%/16.6% with afatinib and 5.4%/10.1% with cetuximab (P = 0.46/0.30). Objective response rate was 16.1%/8.1% with afatinib and 6.5%/9.7% with cetuximab (IR/ICR). Comparable disease control rates were observed with afatinib (50%) and cetuximab (56.5%) by IR; similar results were seen by ICR. Most common grade ≥3 drug-related AEs (DRAEs) were rash/acne (18% versus 8.3%), diarrhea (14.8% versus 0%), and stomatitis/mucositis (11.5% versus 0%) with afatinib and cetuximab, respectively. Patients with DRAEs leading to treatment discontinuation were 23% with afatinib and 5% with cetuximab. In stage II, disease control rate (IR/ICR) was 38.9%/33.3% with afatinib and 18.8%/18.8% with cetuximab.ConclusionAfatinib showed antitumor activity comparable to cetuximab in R/M HNSCC in this exploratory phase II trial, although more patients on afatinib discontinued treatment due to AEs. Sequential EGFR/ErbB treatment with afatinib and cetuximab provided sustained clinical benefit in patients after crossover, suggesting a lack of cross-resistance
A single atom detector integrated on an atom chip: fabrication, characterization and application
We describe a robust and reliable fluorescence detector for single atoms that
is fully integrated into an atom chip. The detector allows spectrally and
spatially selective detection of atoms, reaching a single atom detection
efficiency of 66%. It consists of a tapered lensed single-mode fiber for
precise delivery of excitation light and a multi-mode fiber to collect the
fluorescence. The fibers are mounted in lithographically defined holding
structures on the atom chip. Neutral 87Rb atoms propagating freely in a
magnetic guide are detected and the noise of their fluorescence emission is
analyzed. The variance of the photon distribution allows to determine the
number of detected photons / atom and from there the atom detection efficiency.
The second order intensity correlation function of the fluorescence shows
near-perfect photon anti-bunching and signs of damped Rabi-oscillations. With
simple improvements one can boost the detection efficiency to > 95%.Comment: 24 pages, 11 figure
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