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971.
972.
973.
Nitride-based light-emitting diodes suffer from a reduction (droop) of the internal quantum efficiency (IQE) with increasing
injection current. Using advanced device simulation, we investigate the impact of electron leakage on the IQE droop for different
properties of the electron blocker layer (EBL). The simulations show a strong influence of the EBL acceptor density on the
droop. We also find that the electron leakage decreases with increasing temperature, which contradicts common assumptions. 相似文献
974.
Kevin M. Wright Joshua Warner Luca Venturi Robert B. Piggott Simon Donell Brian P. Hills 《Magnetic resonance imaging》2010
Image contrast is calculated by inputting experimental 2D T1–T2 relaxation spectra into the ODIN software interface. The method involves characterising a magnetic resonance imaging pulse sequence with a “relaxation signature” which describes the sensitivity of the sequence to relaxation and is independent of sample parameters. Maximising (or minimising) the overlap between the experimental 2D T1–T2 relaxation spectra and the relaxation signature can then be used to maximise image contrast. The concept is illustrated using relaxation signatures for the echo planar imaging and Turbo spin-echo imaging sequences, together with in-vitro 2D T1–T2 spectra for liver and cartilage. 相似文献
975.
J. Bekesi J. J. J. Kaakkunen W. Michaeli F. Klaiber M. Schoengart J. Ihlemann P. Simon 《Applied Physics A: Materials Science & Processing》2010,99(4):691-695
A new two-step method, facilitating the rapid generation of super-hydrophobic surface structures via parallel laser processing
followed by a replica generation by injection molding is reported. A self-made fused silica-based diffractive optical element
(DOE) is applied to distribute the laser energy into a 25×25 dot matrix. This DOE is used as a transmission mask for surface
ablation of metal molds, applying short-pulse UV laser pulses. In a subsequent process step, replicas of the processed stamp
are produced by variothermal injection molding, enabling the mass production of the surface pattern on plastics parts. The
resulting topography facilitates a super-hydrophobic behavior of the fabricated components. 相似文献
976.
Simon Dagois-Bohy Sandrine Ngo Sylvain Courrech du Pont Stéphane Douady 《Ultrasonics》2010,50(2):127-132
Some desert sand dunes have the peculiar ability to emit a loud sound up to 110 dB, with a well-defined frequency: this phenomenon, known since early travelers (Darwin, Marco Polo, etc.), has been called the song of dunes. But only in late 19th century scientific observations were made, showing three important characteristics of singing dunes: first, not all dunes sing, but all the singing dunes are composed of dry and well-sorted sand; second, this sound occurs spontaneously during avalanches on a slip face; third this is not the only way to produce sound with this sand.More recent field observations have shown that during avalanches, the sound frequency does not depend on the dune size or shape, but on the grain diameter only, and scales as the square root of g/d - with g the gravity and d the diameter of the grains - explaining why all the singing dunes in the same vicinity sing at the same frequency.We have been able to reproduce these singing avalanches in laboratory on a hard plate, which made possible to study them more accurately than on the field. Signals of accelerometers at the flowing surface of the avalanche are compared to signals of microphones placed above, and it evidences a very strong vibration of the flowing layer at the same frequency as on the field, responsible for the emission of sound.Moreover, other characteristics of the booming dunes are reproduced and analyzed, such as a threshold under which no sound is produced, or beats in the sound that appears when the flow is too large. Finally, the size of the coherence zones emitting sound has been measured and discussed. 相似文献
977.
We study the behavior of Airy beams propagating from a nonlinear medium to a linear medium. We show that an Airy beam initially driven by a self-defocusing nonlinearity experiences anomalous diffraction and can maintain its shape in subsequent propagation, but its intensity pattern and acceleration cannot persist when driven by a self-focusing nonlinearity. The unusual behavior of Airy beams is examined from their energy flow as well as the Brillouin zone spectrum of self-induced chirped photonic lattices. 相似文献
978.
Simon Thomas 《Israel Journal of Mathematics》2018,225(1):321-342
It is shown that for the conjugation action of the symmetric group Sn, when n = 6 or n ≥ 8, all S n -irreducibles appear as constituents of a single conjugacy class, namely, one indexed by a partition λ of n with at least two parts, whose parts are all distinct and taken from the set of odd primes and 1. A simple characterisation of conjugacy classes containing all irreducibles is proved. 相似文献
979.
A careful look at rough path topology applied to Brownian motion reveals new possible properties of the well-known Lévy area, in particular the presence of an intrinsic drift of this area. Using renormalization limit of Markov chains on periodic graphs, we present a construction of such a non-trivial drift and give an explicit formula for it. Several examples with explicit computations are included. 相似文献
980.
Simon Müller 《代数通讯》2018,46(11):4978-4984
A quasi-order on a set S is a binary, reflexive and transitive relation on S. In [3], Fakhruddin introduced the notion of (totally) quasi-ordered fields and showed that each such field is either an ordered field or else a valued field. Hence, quasi-ordered fields are very well suited to treat ordered and valued fields simultaneously. The aim of the present paper is to prove that an analogous dichotomy holds for commutative rings with 1 as well. 相似文献