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31.
Yuval Berg Sharone Goldring Shaul Pearl Ady Arie 《Applied physics. B, Lasers and optics》2013,111(3):425-428
A new method for Q-switching an all-fiber laser is presented. It is based on induced acoustic long period grating operating on a null coupler, which acts as acoustically controlled tunable output coupler. Q-switching is achieved by switching on and off the acoustic wave in a burst mode, thereby generating laser pulses that are ~400 times shorter than the acoustically controlled coupler’s rise time. Output pulse energy of 22 μJ and temporal width of ~100 ns were measured at a wavelength of 1.54 μm. 相似文献
32.
Or Dishi Yuval Rahav Dr. Raanan Carmieli Prof. Ori Gidron 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202202082
Macrocyclic furans are predicted to switch between global aromaticity and antiaromaticity, depending on their oxidation states. However, the macrocyclic furans reported to date are stabilized by electron withdrawing groups, which result in inaccessible oxidation states. To circumvent this problem, a post-macrocyclization approach was applied to introduce methylene-substituted macrocyclic furans, which display an extremely low oxidation potential of −0.23 vs. Fc/Fc+, and are partially oxidized in ambient conditions. Additional oxidation to the dication results in aromaticity switching to a global 30πe− aromatic state, as indicated by the formation of a strong diatropic current observed in the 1H NMR spectrum. NICS and ACID calculations support this trend and provide evidence for a different pathway for the global current in the neutral and dicationic states. According to these findings, macrocyclic furans can be rendered as promising p-type materials with stable oxidation states. 相似文献
33.
Various statistics on wreath products are defined via canonical words, “colored” right to left minima and “colored” descents.
It is shown that refined counts with respect to these statistics have nice recurrence formulas of binomial-Stirling type.
These extended Stirling numbers determine (via matrix inversion) dual systems, which are also shown to have combinatorial
realizations within the wreath product. The above setting also gives rise to a MacMahon-type equi-distribution theorem over
subsets with prescribed statistics.
Partially supported by Minerva Grant No. 8441 and by EC's IHRP Programme, within the Research Training Network “Algebraic
Combinatorics in Europe”, grant HPRN-CT-2001-00272.
Partially supported by EC's IHRP Programme, within the Research Training Network “Algebraic Combinatorics in Europe”, grant
HPRN-CT-2001-00272. 相似文献
34.
We consider the fractal percolation process on the unit square with fixed decimation parameterN and level-dependent retention parameters {p
k}; that is, for allk ⩾ 1, at thek th stage every retained square of side lengthN
1−
k is partitioned intoN
2 congruent subsquares, and each of these is retained with probabilityp
k. independent of all others. We show that if Πk
p
k =0 (i.e., if the area of the limiting set vanishes a.s.), then a.s. the limiting set contains no directed crossings of the
unit square (a directed crossing is a path that crosses the unit square from left to right, and moves only up, down, and to
the right). 相似文献
35.
The expressions for the fractional number ofK
0's and¯K
0's in a neutral kaon beam are discussed with reference to time-reversal asymmetry. The suggested relation between the sign of Re ( is the Lee-WuT-violation parameter) and the cosmological arrow of time ifCPT is broken is further clarified.Research sponsored by the Air Force Office of Scientific Research, Office of Aerospace Research, U.S. Air Force, under AFOSR grant number EOOAR-68-0010, through the European Office of Aerospace Research. 相似文献
36.
37.
In this paper we analyse a two-stage game involving the government and n agents who engage in a single activity (driving). The government establishes the legal policy setting and the agents proceed to play a non-cooperative game of incomplete information with a risk of accident in which their behavioral strategy is their level of care. We examine the Nash-equilibrium conditions for single-activity accidents between heterogeneous agents, ‘good’ drivers or ‘bad’ drivers allowing a variable damage function and a liability rule defined on the cube. The relative desirability for society of alternative equilibria and the conditions under which they can obtain are discussed. The constraints which circumscribe the ability of the government to induce an equilibrium involving careful driving are demonstrated. It transpires that when the proportion of good drivers increases, it becomes more difficult to sustain a careful equilibrium whereas an equilibrium of reckless behavior becomes easier to sustain. Various extensions of the models are also presented. 相似文献
38.
It is shown that the edges of any n-point vertex expander can be replaced by new edges so that the resulting graph is an edge expander, and such that any two vertices that are joined by a new edge are at distance in the original graph. This result is optimal, and is shown to have various geometric consequences. In particular, it is used to obtain an alternative perspective on the recent algorithm of Arora et al. [Proceedings of the 36th Annual ACM Symposium on the Theory of Computing, 2004, pp. 222-231.] for approximating the edge expansion of a graph, and to give a nearly optimal lower bound on the ratio between the observable diameter and the diameter of doubling metric measure spaces which are quasisymmetrically embeddable in Hilbert space. 相似文献
39.
Suppose that we are given a function f : (0, 1)→(0,1) and, for some unknown p∈(0, 1), a sequence of independent tosses of a p-coin (i.e., a coin with probability p of “heads”). For which functions f is it possible to simulate an f(p)-coin? This question was raised by S. Asmussen and J. Propp. A simple simulation scheme for the constant function f(p)≡1/2 was described by von Neumann (1951); this scheme can be easily implemented using a finite automaton. We prove that in
general, an f(p)-coin can be simulated by a finite automaton for all p ∈ (0, 1), if and only if f is a rational function over ℚ. We also show that if an f(p)-coin can be simulated by a pushdown automaton, then f is an algebraic function over ℚ; however, pushdown automata can simulate f(p)-coins for certain nonrational functions such as
. These results complement the work of Keane and O’Brien (1994), who determined the functions f for which an f(p)-coin can be simulated when there are no computational restrictions on the simulation scheme.
* Supported by a Miller Fellowship.
† Supported in part by NSF Grant DMS-0104073 and by a Miller Professorship.
‡ This work is supported under a National Science Foundation Graduate Research Fellowship. 相似文献
40.
Transport through quantum dots in the Kondo regime obeys an effective low-temperature theory in terms of weakly interacting quasiparticles. Despite the weakness of the interaction, we find that the backscattering current and hence the shot noise are dominated by two-quasiparticle scattering. We show that the simultaneous presence of one- and two-quasiparticle scattering results in a universal average charge 5/3e as measured by shot-noise experiments. An experimental verification of our prediction would constitute a most stringent test of the low-energy theory of the Kondo effect. 相似文献