788 research outputs found
On the robustness of acoustic black hole spectra
We study the robustness of the spectrum emitted by an acoustic black hole by
considering series of stationary flows that become either subsonic or
supersonic, i.e. when the horizon disappears. We work with the superluminal
Bogoliubov dispersion of Bose--Einstein condensates. We find that the spectrum
remains remarkably Planckian until the horizon disappears. When the flow is
everywhere supersonic, new pair creation channels open. This will be the
subject of a forthcoming work.Comment: 4 pages, 2 figure, jpconf.cls; to appear in the proceedings of the
Spanish Relativity Meeting ERE201
Coherency in space of lake and river temperature and water quality records
Environmental time series observed over 100’s of monitoring locations usually possess some spatial structure in terms of common patterns throughout time, commonly described as temporal coherence. This paper will apply, develop and compare two methods for clustering time series on the basis of their patterns over time. The first approach treats the time series as functional data and applies hierarchical clustering while the second uses a state-space model based clustering approach. Both methods are developed to incorporate spatial correlation and stopping criteria are investigated to identify an appropriate number of clusters. The methods are applied to Total Organic Carbon data from river sites across Scotland
Hawking radiation in dispersive theories, the two regimes
We compute the black hole radiation spectrum in the presence of
high-frequency dispersion in a large set of situations. In all cases, the
spectrum diverges like the inverse of the Killing frequency. When studying the
low-frequency spectrum, we find only two regimes: an adiabatic one where the
corrections with respect to the standard temperature are small, and an abrupt
one regulated by dispersion, in which the near-horizon metric can be replaced
by step functions. The transition from one regime to the other is governed by a
single parameter which also governs the net redshift undergone by dispersive
modes. These results can be used to characterize the quasiparticles spectrum of
recent and future experiments aiming to detect the analogue Hawking radiation.
They also apply to theories of quantum gravity which violate Lorentz
invariance.Comment: 11 pages, 9 figure
Modification of magnetic and transport properties of manganite layers in Au/La_0.67Sr_0.33MnO_3/SrTiO_3 interfaces
The effect of gold capping on magnetic and transport properties of optimally
doped manganite thin films is studied. An extraordinary suppression of
conductivity and magnetic properties occurs in epitaxial (001)
La_0.67Sr_0.33MnO_3 (LSMO) films grown on SrTiO_3 upon deposition of 2 nm of
Au: in the case of ultrathin films of LSMO (4 nm thick) the resistivity
increases by four orders of magnitude while the Curie temperature decreases by
180 K. Zero-field 55Mn nuclear magnetic resonance reveals a significant
reduction of ferromagnetic double-exchange mechanism in manganite films upon
the gold capping. We find evidence for the formation of a 1.9-nm thick magnetic
"dead-layer" at the Au/LSMO interface, associated with the creation of
interfacial non double-exchange insulating phases.Comment: 4 figure
Black hole lasers in Bose-Einstein condensates
We consider elongated condensates that cross twice the speed of sound. In the
absence of periodic boundary conditions, the phonon spectrum possesses a
discrete and finite set of complex frequency modes that induce a laser effect.
This effect constitutes a dynamical instability and is due to the fact that the
supersonic region acts as a resonant cavity. We numerically compute the complex
frequencies and density-density correlation function. We obtain patterns with
very specific signatures. In terms of the gravitational analogy, the flows we
consider correspond to a pair of black hole and white hole horizons, and the
laser effect can be conceived as a self-amplified Hawking radiation. This is
verified by comparing the outgoing flux at early time with the standard black
hole radiation.Comment: iopams, 37 pages, 14 figures, 1 table; for associated gif animations,
see http://people.sissa.it/~finazzi/bec_bhlasers/movies/ or
http://iopscience.iop.org/1367-2630/12/9/095015/media. Published on New. J.
Phys. (http://iopscience.iop.org/1367-2630/12/9/095015/). V2: few new
comments, modified figure
The treatment of polycythaemia vera: an update in the JAK2 era
The clinical course of polycythaemia vera is marked by a high incidence of thrombotic complications, which represent the main cause of morbidity and mortality. Major predictors of vascular events are increasing age and previous thrombosis. Myelosuppressive drugs can reduce the rate of thrombosis, but there is concern that their use raises the risk of transformation into acute leukaemia. To tackle this dilemma, a risk-oriented management strategy is recommended. Low-risk patients should be treated with phlebotomy and low-dose aspirin. Cytotoxic therapy is indicated in high-risk patients, with the drug of choice being hydroxyurea because its leukaemogenicity is low. The recent discovery of JAK2 V617F mutation in the vast majority of polycythaemia vera patients opens new avenues for the treatment of this disease. Novel therapeutic options theoretically devoid of leukaemic risk, such as alpha-interferon and imatinib, affect JAK2 expression in some patients. Nevertheless, these drugs require further clinical experience and, for the time being, should be reserved for selected cases
Patient-specific cardiovascular superelastic NiTi stents produced by laser powder bed fusion
To date, there is a general lack of customizability within the selection of endovascular devices for catheter-based vascular interventions. Laser powder bed fusion (LPBF) has been flexibly exploited to produce customized implants using conventional biomedical alloys for orthopedic and dental applications. Applying LPBF for cardiovascular applications, patient-specific stents can be produced with small struts (approximately 100-300 µm), variable geometries, and clinically used metals capable of superelastic behaviour at body temperature (eg. equiatomic nickel-titanium alloys, NiTi). Additionally, the growing availability and use of patient-specific 3D models provides a unique opportunity to outline the necessary manufacturing process that would be required for customizable NiTi devices based on patient geometry. In order to fulfil the potential of the patient-specific superelastic stents, process and design know-how should be expanded to the novel material and fine details at the limits of conventional LPBF machines. In this work, a framework for developing a patient-specific superelastic NiTi stent produced by LPBF is demonstrated. At a proof-of-concept stage, the design procedures are shown in a geometry similar to the artery. The stents with 100 µm nominal strut diameter are later produced with a Ni50.8Ti49.2 powder and heat treated. The results confirm the possibility of producing stents with a design suitable for highly complex patient-specific anatomies and having superelastic behavior at body temperature
Black holes and Hawking radiation in spacetime and its analogues
These notes introduce the fundamentals of black hole geometry, the thermality
of the vacuum, and the Hawking effect, in spacetime and its analogues.
Stimulated emission of Hawking radiation, the trans-Planckian question, short
wavelength dispersion, and white hole radiation in the setting of analogue
models are also discussed. No prior knowledge of differential geometry, general
relativity, or quantum field theory in curved spacetime is assumed.Comment: 31 pages, 9 figures; to appear in the proceedings of the IX SIGRAV
School on 'Analogue Gravity', Como (Italy), May 2011, eds. D. Faccio et. al.
(Springer
A 20-year study of persistence of lower urinary tract symptoms and urinary incontinence in young women treated in childhood
OBJECTIVE: To determine whether urinary incontinence (UI) and lower urinary tract symptoms (LUTS) persist over years, patients treated for UI and LUTS in childhood were re-evaluated in adulthood.
MATERIALS AND METHODS:
Forty-seven women (cases) treated in childhood for daytime UI/LUTS (group A) and nocturnal enuresis (group B) self-completed (average age: 24.89 ± 3.5 years) the International Consultation on Incontinence Questionnaire for Female with LUTS (ICIQ-FLUTS). ICIQ-FLUTS was self-administered to 111 healthy women (average age: 23 ± 5.1 years) from a nursing school as a control group. Data obtained from ICIQ-FLUTS and quality of life (QoL) score (0-10) were compared (Fisher's exact test) between patients and controls, and between group A (n = 28) and group B (n = 19).
RESULTS:
Prevalence of LUTS was higher in patients than in controls. The difference between patients and controls was statistically significant (p = 0.0001) for UI (34% vs. 7%) and feeling of incomplete bladder emptying (49% vs. 28%). QoL score was >5 in 59% of patients and 1% of controls (p = 0.0001). No significant differences were found between groups A and B.
CONCLUSIONS:
UI and LUTS are confirmed in young women who suffered for the same condition in childhood. Longitudinal studies are needed to assess if these symptoms persist or are newly onset
- …