525 research outputs found
Extreme Covariant Quantum Observables in the Case of an Abelian Symmetry Group and a Transitive Value Space
We represent quantum observables as POVMs (normalized positive operator
valued measures) and consider convex sets of observables which are covariant
with respect to a unitary representation of a locally compact Abelian symmetry
group . The value space of such observables is a transitive -space. We
characterize the extreme points of covariant observables and also determine the
covariant extreme points of the larger set of all quantum observables. The
results are applied to position, position difference and time observables.Comment: 23 page
Broadband acoustic invisibility and illusions
Rendering objects invisible to impinging acoustic waves (cloaking) and creating acoustic illusions (holography) has been attempted using active and passive approaches. While most passive methods are inflexible and applicable only to narrow frequency bands, active approaches attempt to respond dynamically, interfering with broadband incident or scattered wavefields by emitting secondary waves. Without prior knowledge of the primary wavefield, the signals for the secondary sources need to be estimated and adapted in real time. This has thus far impeded active cloaking and holography for broadband wavefields. We present experimental results of active acoustic cloaking and holography without prior knowledge of the wavefield so that objects remain invisible and illusions intact even for broadband moving sources. This opens previously inaccessible research directions and facilitates practical applications including architectural acoustics, education, and stealth
Radiotherapy in langerhans cell histiocytosis - a rare indication in a rare disease
Introduction: Langerhans Cell Histiocytosis (LCH) represents a rare benign disorder, previously designated as âHistiocytosis Xâ, âType II Histiocytosisâ or âLangerhans Cell Granulomatosisâ. Clinical presentation includes osteolysis, ulcerations of skin and soft tissues but also involvement of the CNS is described. Because treatment concepts are not well defined the German Cooperative Group on Radiotherapy for Benign Diseases performed a retrospective analysis. Methods and material: Eight closely cooperating centres collected patientsâ data of the past 45 years. As study endpoints disease free survival, recurrent disease, death and therapy related side effects were defined. Results: A total of 80 patients with histologically proven LCH were irradiated within the past 45 years. According to the LCH classification of Greenberger et al. 37 patients had stage Ia, 21 patients stage Ib, 13 patients stage II and 9 patients stage IIIb and the median age was 29 years. The median Follow up was 54 months (range 9â134 months). A total of 39 patients had a surgical intervention and 23 patients a chemotherapy regimen. Radiation treatment was carried out with a median total dose of 15 Gy (range 3â50.4âGy). The median single fraction was 2 Gy (range 1.8-3 Gy). Overall, 77% patients achieved a complete remission and 12.5% achieved a partial remission. The long-term control rate reached 80%. Within an actuarial overall 5-year survival of 90% no radiogenic side and late effects â„EORTC/RTOG II° were observed. Conclusion: In the present study a large collective of irradiated patients was analysed. Radiotherapy (RT) is a very effective and safe treatment option and even low RT doses show sufficient local control.<br
Measuring the temporal coherence of an atom laser beam
We report on the measurement of the temporal coherence of an atom laser beam
extracted from a Rb Bose-Einstein condensate. Reflecting the beam from a
potential barrier creates a standing matter wave structure. From the contrast
of this interference pattern, observed by magnetic resonance imaging, we have
deduced an energy width of the atom laser beam which is Fourier limited by the
duration of output coupling. This gives an upper limit for temporal phase
fluctuations in the Bose-Einstein condensate.Comment: 4 pages, 3 figure
An Atom Laser with a cw Output Coupler
We demonstrate a continuous output coupler for magnetically trapped atoms.
Over a period of up to 100 ms a collimated and monoenergetic beam of atoms is
continuously extracted from a Bose- Einstein condensate. The intensity and
kinetic energy of the output beam of this atom laser are controlled by a weak
rf-field that induces spin flips between trapped and untrapped states.
Furthermore, the output coupler is used to perform a spectroscopic measurement
of the condensate, which reveals the spatial distribution of the magnetically
trapped condensate and allows manipulation of the condensate on a micrometer
scale.Comment: 4 pages, 4 figure
Optics with an Atom Laser Beam
We report on the atom optical manipulation of an atom laser beam. Reflection,
focusing and its storage in a resonator are demonstrated. Precise and versatile
mechanical control over an atom laser beam propagating in an inhomogeneous
magnetic field is achieved by optically inducing spin-flips between atomic
ground states with different magnetic moment. The magnetic force acting on the
atoms can thereby be effectively switched on and off. The surface of the atom
optical element is determined by the resonance condition for the spin-flip in
the inhomogeneous magnetic field. A mirror reflectivity of more than 98% is
measured
Lutzomyia naftalekatzi, a new Species of phlebotomine sand fly (Diptera: Psychodidae) from Zona da Mata region, Pernambuco, Brazil
Binary classification of spoken words with passive elastic metastructures
Many electronic devices spend most of their time waiting for a wake-up event:
pacemakers waiting for an anomalous heartbeat, security systems on alert to
detect an intruder, smartphones listening for the user to say a wake-up phrase.
These devices continuously convert physical signals into electrical currents
that are then analyzed on a digital computer -- leading to power consumption
even when no event is taking place. Solving this problem requires the ability
to passively distinguish relevant from irrelevant events (e.g. tell a wake-up
phrase from a regular conversation). Here, we experimentally demonstrate an
elastic metastructure, consisting of a network of coupled silicon resonators,
that passively discriminates between pairs of spoken words -- solving the
wake-up problem for scenarios where only two classes of events are possible.
This passive speech recognition is demonstrated on a dataset from speakers with
significant gender and accent diversity. The geometry of the metastructure is
determined during the design process, in which the network of resonators
('mechanical neurones') learns to selectively respond to spoken words. Training
is facilitated by a machine learning model that reduces the number of
computationally expensive three-dimensional elastic wave simulations. By
embedding event detection in the structural dynamics, mechanical neural
networks thus enable novel classes of always-on smart devices with no standby
power consumption.Comment: 13 pages, 9 figure
National Assessment of Human Health Effects of Climate Change in Portugal: Approach and Key Findings
In this study we investigated the potential impact of climate change in Portugal on heat-related mortality, air pollutionârelated health effects, and selected vectorborne diseases. The assessment used climate scenarios from two regional climate models for a range of future time periods. The annual heat-related death rates in Lisbon may increase from between 5.4 and 6 per 100,000 in 1980â1998 to between 8.5 and 12.1 by the 2020s and to a maximum of 29.5 by the 2050s, if no adaptations occur. The projected warmer and more variable weather may result in better dispersion of nitrogen dioxide levels in winter, whereas the higher temperatures may reduce air quality during the warmer months by increasing tropospheric ozone levels. We estimated the future risk of zoonoses using ecologic scenarios to describe future changes in vectors and parasites. Malaria and schistosomiasis, which are currently not endemic in Portugal, are more sensitive to the introduction of infected vectors than to temperature changes. Higher temperatures may increase the transmission risk of zoonoses that are currently endemic to Portugal, such as leishmaniasis, Lyme disease, and Mediterranean spotted fever
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