555 research outputs found
Lightning-jumps in convective cells tracked by radar as a nowcasting tool in complex orography
Presentación realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019
Control of fine-structure splitting and excitonic binding energies in selected individual InAs/GaAs quantum dots
A systematic study of the impact of annealing on the electronic properties of
single InAs/GaAs quantum dots (QDs) is presented. Single QD cathodoluminescence
spectra are recorded to trace the evolution of one and the same QD over several
steps of annealing. A substantial reduction of the excitonic fine-structure
splitting upon annealing is observed. In addition, the binding energies of
different excitonic complexes change dramatically. The results are compared to
model calculations within eight-band k.p theory and the configuration
interaction method, suggesting a change of electron and hole wave function
shape and relative position.Comment: 4 pages, 4 figure
How observations from automatic hail sensors in Switzerland shed light on local hailfall duration and compare with hailpad measurements
Measuring the properties of hailstorms is a difficult task due to the rarity and mainly small spatial extent of the events. Especially, hail observations from ground-based time-recording instruments are scarce. We present the first study of extended field observations made by a network of 80 automatic hail sensors from Switzerland. The main benefits of the sensors are the live recording of the hailstone kinetic energy and the precise timing of the impacts. Its potential limitations include a diameter-dependent dead time, which results in less than 5 % of missed impacts, and the possible recording of impacts that are not due to hail, which can be filtered using a radar reflectivity filter. We assess the robustness of the sensors' measurements by doing a statistical comparison of the sensor observations with hailpad observations, and we show that, despite their different measurement approaches, both devices measure the same hail size distributions. We then use the timing information to measure the local duration of hail events, the cumulative time distribution of impacts, and the time of the largest hailstone during a hail event. We find that 75 % of local hailfalls last just a few minutes (from less than 4.4 min to less than 7.7 min, depending on a parameter to delineate the events) and that 75 % of the impacts occur in less than 3.3 min to less than 4.7 min. This time distribution suggests that most hailstones, including the largest, fall during a first phase of high hailstone density, while a few remaining and smaller hailstones fall in a second low-density phase.</p
Nowcasting of thunderstorm severity with Machine Learning in the Alpine Region
Presentación realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019
Characterisation of the melting layer variability in an Alpine valley based on polarimetric X-band radar scans
The melting layer designates the transition region from solid to liquid
precipitation, and is a typical feature of the vertical structure of
stratiform precipitation. As it is characterised by a well-known signature in
polarimetric radar variables, it can be identified by automatic detection
algorithms. Though often assumed to be uniform in space and time for
applications such as vertical profile correction, the spatial variability of
the melting layer remains poorly documented. This work aims to
characterise and quantify the spatial and temporal variability of the melting
layer using a method based on the Fourier transform, which is applied to
high-resolution X-band polarimetric radar data from two measurement campaigns in
Switzerland. It is first demonstrated that the proposed method can accurately
and concisely describe the spatial variability of the melting layer and may
therefore be used as a tool for comparison. The method is then used to
characterise the melting layer variability in summer precipitation on the
relatively flat Swiss Plateau and in winter precipitation in a large inner
Alpine valley (the Rhone valley in the Swiss Alps). Results indicate a higher
contribution of smaller spatial scales to the total melting layer variability
in the case of the Alpine environment. The same method is also applied to data from vertical scans in order to study the temporal variability of the
melting layer. The variability in space and time is then compared to
investigate the spatio-temporal coherence of the melting layer variability in
the two study areas, which was found to be more consistent with the
assumption of pure advection for the case of the plateau.</p
The social affordances of flashpacking: exploring the mobility nexus of travel and communication
The proliferation of digital devices and online social media and networking technologies has altered the backpacking landscape in recent years. Thanks to the ready availability of online communication, travelers are now able to stay in continuous touch with friends, family and other travelers while on the move. This article introduces the practice of ‘flashpacking’ to describe this emerging trend and interrogates the patterns of connection and disconnection that become possible as corporeal travel and social technologies converge. Drawing on the concepts of ‘assemblages’ and ‘affordances’, we outline several aspects of this new sociality: virtual mooring, following, collaborating, and (dis)connecting. The conclusion situates this discussion alongside broader questions about the shifting nature of social life in an increasingly mobile and mediated world and suggests directions for future research at the intersection of tourism and technology
Vertical-external-cavity surface-emitting lasers and quantum dot lasers
The use of cavity to manipulate photon emission of quantum dots (QDs) has
been opening unprecedented opportunities for realizing quantum functional
nanophotonic devices and also quantum information devices. In particular, in
the field of semiconductor lasers, QDs were introduced as a superior
alternative to quantum wells to suppress the temperature dependence of the
threshold current in vertical-external-cavity surface-emitting lasers
(VECSELs). In this work, a review of properties and development of
semiconductor VECSEL devices and QD laser devices is given. Based on the
features of VECSEL devices, the main emphasis is put on the recent development
of technological approach on semiconductor QD VECSELs. Then, from the viewpoint
of both single QD nanolaser and cavity quantum electrodynamics (QED), a
single-QD-cavity system resulting from the strong coupling of QD cavity is
presented. A difference of this review from the other existing works on
semiconductor VECSEL devices is that we will cover both the fundamental aspects
and technological approaches of QD VECSEL devices. And lastly, the presented
review here has provided a deep insight into useful guideline for the
development of QD VECSEL technology and future quantum functional nanophotonic
devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with
arXiv:0904.369
Specific Heat of a Three Dimensional Metal Near a T=0 Magnetic Transition with Dynamic Exponent z=2,3,4
We derive expressions for the universal contribution to the specific heat of
a three-dimensional metal near a zero-temperature phase transition with dynamic
exponent , or 4. The results allow a quantitative comparison of theory
to data. We illustrate the application of our results by analyzing data for
CeLuCuSi, which has been claimed to be near a quantum
critical point.Comment: 23 pages, revtex. For figures, send mail to [email protected]
Search for the rare decay
A search for the decay is performed, based on a data sample of 1.0 fb of collisions at collected by the LHCb experiment at the Large Hadron Collider. The observed number of candidates is consistent with the background-only hypothesis, yielding an upper limit of at 95 (90)% confidence level. This limit is a factor of thirty below the previous measurement
- …