1,552 research outputs found
Hexagonal Structure of Baby Skyrmion Lattices
We study the zero-temperature crystalline structure of baby Skyrmions by
applying a full-field numerical minimization algorithm to baby Skyrmions placed
inside different parallelogramic unit-cells and imposing periodic boundary
conditions. We find that within this setup, the minimal energy is obtained for
the hexagonal lattice, and that in the resulting configuration the Skyrmion
splits into quarter-Skyrmions. In particular, we find that the energy in the
hexagonal case is lower than the one obtained on the well-studied rectangular
lattice, in which splitting into half-Skyrmions is observed.Comment: RevTeX, 7 pages, 6 figure
3.3 Gigahertz Clocked Quantum Key Distribution System
A fibre-based quantum key distribution system operating up to a clock
frequency of 3.3GHz is presented. The system demonstrates significantly
increased key exchange rate potential and operates at a wavelength of 850nm.Comment: Presented at ECOC 05, Glasgow, UK, (September 2005
Moduli Spaces of Lumps on Real Projective Space
Harmonic maps that minimize the Dirichlet energy in their homotopy classes are known as lumps. Lump solutions on real projective space are explicitly given by rational maps subject to a certain symmetry requirement. This has consequences for the behaviour of lumps and their symmetries. An interesting feature is that the moduli space of charge three lumps is a D2-symmetric 7-dimensional manifold of cohomogeneity one. In this paper, we discuss the charge three moduli spaces of lumps from two perspectives: discrete symmetries of lumps and the Riemann-Hurwitz formula. We then calculate the metric and find explicit formula for various geometric quantities. We also discuss the implications for lump decay
An integral gated mode single photon detector at telecom wavelengths
We demonstrate an integral gated mode single photon detector at telecom
wavelengths. The charge number of an avalanche pulse rather than the peak
current is monitored for single-photon detection. The transient spikes in
conventional gated mode operation are canceled completely by integrating, which
enables one to improve the performance of single photon detector greatly with
the same avalanche photodiode. This method has achieved a detection efficiency
of 29.9% at the dark count probability per gate equal to 5.57E-6/gate
(1.11E-6/ns) at 1550nm.Comment: word to PDF, 3 pages with 4 figure
Correlation between OCVD carrier lifetime vs temperature measurements and reverse recovery behavior of the body diode of SiC power MOSFETs
The reverse recovery (RR) behavior of SiC MOSFET body diode is of great importance in power application, where these devices are used in a wide range of operating temperatures. The carrier lifetime in the drift region varies with temperature, and it heavily affects the tailoring of the RR current, opening reliability issues related to the RR voltage amplitude and to possible anomalous voltage oscillations during the recovery. From the users' point of view, it would be useful to have a simple technique able to give predictive information about the body diode RR behavior of commercial devices over the whole range of working temperatures. An experimental-simulation approach is presented in this paper to correlate the carrier lifetime measured by simple OCVD measurements versus temperature with the RR behavior of the body diode, that can be useful at the design stage of power converters. Simulations of the body diode reverse-recovery are performed for a wide range of carrier lifetimes. This allows to estimate the effect of changes of carrier lifetime with temperature on the body diode switching transients. Preliminary results obtained with a 1700 V/5A commercial MOSFET are shown
Diffusion-weighted MRI in the evaluation of renal lesions:preliminary results
The purpose of this study was to evaluate the capability and the reliability of diffusion-weighted MRI
in the evaluation of normal kidney and different renal lesions. 39 patients (10 normal volunteers and 29 patients
with known renal lesions) underwent MRI of the kidneys by using a 1.5 T superconducting magnet. Axial fat
suppressed turbo spin echo (TSE) T2 and coronal fast field echo (FFE) T1 or TSE T1 weighted images were
acquired for each patient. Diffusion-weighted (DW) images were obtained in the axial plane during breath-hold
(17 s) with a spin-echo echo planar imaging (SE EPI) single shot sequence (repetition time (TR)52883 ms, echo
time (TE)561 ms, flip angle590°), with b value of 500 s mm22. 16 slices were produced with slice thickness of
7 mm and interslice gap of 1 mm. An apparent diffusion coefficient (ADC) map was obtained at each slice
position. The ADC was measured in an approximately 1 cm region of interest (ROI) within the normal renal
parenchyma, the detected renal lesions and the collecting system if dilated. ADC values in normal renal
parenchyma ranged from 1.7261023 mm2 s21 to 2.6561023 mm2 s21, while ADC values in simple cysts
(n513) were higher (2.8761023 mm2 s21 to 4.0061023 mm2 s21). In hydronephrotic kidneys (n56) the ADC
values of renal pelvis ranged from 3.3961023 mm2 s21 to 4.0061023 mm2 s21. In cases of pyonephrosis (n53)
ADC values of the renal pelvis were found to be lower than those of renal pelvis of hydronephrotic kidneys
(0.7761023 mm2 s21 to 1.0761023 mm2 s21). Solid benign and malignant renal tumours (n57) showed ADC
values ranging between 1.2861023 mm2 s21 and 1.8361023 mm2 s21. In conclusion diffusion-weighted MR
imaging of the kidney seems to be a reliable way to differentiate normal renal parenchyma and different renal
diseases. Clinical experience with this method is still preliminary and further studies are required
GHz QKD at telecom wavelengths using up-conversion detectors
We have developed a hybrid single photon detection scheme for telecom
wavelengths based on nonlinear sum-frequency generation and silicon
single-photon avalanche diodes (SPADs). The SPAD devices employed have been
designed to have very narrow temporal response, i.e. low jitter, which we can
exploit for increasing the allowable bit rate for quantum key distribution. The
wavelength conversion is obtained using periodically poled Lithium niobate
waveguides (W/Gs). The inherently high efficiency of these W/Gs allows us to
use a continuous wave laser to seed the nonlinear conversion so as to have a
continuous detection scheme. We also present a 1.27GHz qubit repetition rate,
one-way phase encoding, quantum key distribution experiment operating at
telecom wavelengths that takes advantage of this detection scheme. The proof of
principle experiment shows a system capable of MHz raw count rates with a QBER
less than 2% and estimated secure key rates greater than 100 kbit/s over 25 km.Comment: 12 pages, 7 figure
Pliocene-Quaternary mass wasting along the Ionian Calabrian margin, offshore southern Italy
The Ionian Calabrian margin, offshore southern Italy, is a tectonically active area, located above a subduction zone dominated by the rollback of the African plate. A variety of mass wasting features are known to occur along the inner continental slope, based on seafloor mapping during the Italian project MaGIC (Marine Geohazards Along the Italian Coasts). New high-resolution geophysical data are available from a wider area following two surveys, in 2014 of the German RV Meteor, which acquired multibeam bathymetry (50 m DTM) and Parasound sub-bottom profiles, and in 2015 of the Italian RV OGS Explora, which acquired Chirp sub-bottom and multichannel seismic reflection profiles. Here we integrate these data with existing geophysical datasets and published exploration wells to map submarine slope failures and mass wasting deposits within the Pliocene-Quaternary succession.
The results show that features of mass failures are widespread along the steep (higher than 10\ub0) slopes of the Ionian margin south of Calabria and within the intra-slope basins of the margin east of Calabria. Seafloor features range from small-scale features (hundreds of meters in extent), mainly located on the canyon headwalls and sidewalls, to larger slides ( up to 10 km in extent) on open slopes. Subsurface profiles across open slopes and intra-slope basins provide evidence of repeated failures, particularly in the upper Quaternary. The stratigraphic distribution of failures suggests that widespread mass wasting features occur above an unconformity tentatively dated to the Middle Pleistocene (<1 Ma). This unconformity also provides a lower bound for the onset of canyon formation. We infer that the onset of both mass wasting and canyon formation could be a response to the rapid km-scale differential uplift of Calabria over last 1 Ma, which has driven a seaward tilting of the Ionian Calabrian margin
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