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1.
H. Suchowski B. D. Bruner A. Ganany-Padowicz I. Juwiler A. Arie Y. Silberberg 《Applied physics. B, Lasers and optics》2011,105(4):697-702
A new method for efficient, broadband sum and difference frequency generation of ultrafast pulses is demonstrated. The principles
of the method follow from an analogy between frequency conversion and coherent optical excitation of a two-level system. For
conversion of ultrafast pulses, the concepts of adiabatic conversion are developed further in order to account for dispersion
and group velocity mismatch. The scheme was implemented using aperiodically poled nonlinear crystals and a single step nonlinear
mixing process, leading to conversion of near-IR (∼790 nm) ultrafast pulses into the blue (∼450 nm) and mid-IR (∼3.15 μm)
spectral regions. Conversion bandwidths up to 15 THz FWHM and efficiencies up to 50% are reported. 相似文献
2.
Irit Peled Einav Keisar 《International Journal of Mathematical Education in Science & Technology》2013,44(4):570-583
In this action research, first-graders were challenged to cope with a sequence of modelling tasks involving an analysis of given situations and choices of mathematical tools. In the course of the sequence, they underwent a change in the nature of their problem-solving processes and developed modelling competencies. Moreover, during the task sequence, the first-graders spontaneously discovered the power of organizing problem data in a table. They did not merely use their existing mathematical knowledge, but also ‘reinvented’ tables as a new mathematical tool. This paper describes the gradual development of this tool as the children moved along the task sequence. Notably, the first-graders exhibited this progress in spite of having relatively little mathematical knowledge. 相似文献
3.
Rosenblum G Meroueh S Toth M Fisher JF Fridman R Mobashery S Sagi I 《Journal of the American Chemical Society》2007,129(44):13566-13574
Activation of matrix metalloproteinase zymogen (pro-MMP) is a vital homeostatic process, yet its molecular basis remains unresolved. Using stopped-flow X-ray spectroscopy of the active site zinc ion, we determined the temporal sequence of pro-MMP-9 activation catalyzed by tissue kallikrein protease in milliseconds to several minutes. The identity of three intermediates seen by X-ray spectroscopy was corroborated by molecular dynamics simulations and quantum mechanics/molecular mechanics calculations. The cysteine-zinc interaction that maintains enzyme latency is disrupted via active-site proton transfers that mediate transient metal-protein coordination events and eventual binding of water. Unexpectedly, these events ensue as a direct result of complexation of pro-MMP-9 and kallikrein and occur before proteolysis and eventual dissociation of the pro-peptide from the catalytic site. Here we demonstrate the synergism among long-range protein conformational transitions, local structural rearrangements, and fine atomic events in the process of zymogen activation. 相似文献
4.
Anat Frydman‐Marom Meirav Rechter Irit Shefler Yaron Bram Deborah E. Shalev Dr. Ehud Gazit Prof. 《Angewandte Chemie (International ed. in English)》2009,48(11):1981-1986
A rationally designed oligomerization inhibitor interacts with early intermediate assemblies of amyloid‐β polypeptide (Aβ) through the aromatic elements and inhibits their assembly into the toxic oligomers that cause Alzheimer's disease by a unique Cα‐methylation β‐breakage strategy. The electrostatic potential of the low‐energy conformation of the dipeptide inhibitor bound to Aβ is shown.
5.
We consider an infinitely repeated two-person zero-sum game with incomplete information on one side, in which the maximizer
is the (more) informed player. Such games have value v
∞ (p) for all 0≤p≤1. The informed player can guarantee that all along the game the average payoff per stage will be greater than or equal to
v
∞ (p) (and will converge from above to v
∞ (p) if the minimizer plays optimally). Thus there is a conflict of interest between the two players as to the speed of convergence
of the average payoffs-to the value v
∞ (p). In the context of such repeated games, we define a game for the speed of convergence, denoted SG
∞ (p), and a value for this game. We prove that the value exists for games with the highest error term, i.e., games in which v
n (p)− v
∞ (p) is of the order of magnitude of . In that case the value of SG
∞ (p) is of the order of magnitude of . We then show a class of games for which the value does not exist. Given any infinite martingale 𝔛∞={X
k }∞
k=1, one defines for each n : V
n (𝔛∞) ≔E∑n
k=1 |X
k+1 − X
k|. For our first result we prove that for a uniformly bounded, infinite martingale 𝔛∞, V
n (𝔛∞) can be of the order of magnitude of n
1/2−ε, for arbitrarily small ε>0.
Received January 1999/Final version April 2002 相似文献
6.
Abhaya K. Mishra Galit Parvari Irit Cohen Natalia Fridman Yoav Eichen 《Journal of Coordination Chemistry》2018,71(11-13):2082-2089
AbstractAmine-tetrachloromethane charge-transfer complexes have recently been shown to be useful intermediates in transition-metal free solar light-assisted organic synthetic chemistry. Of particular promise is the complex of 1,4-diazabicyclo[2.2.2]octane (DABCO) which may serve as a starting point for several potential reactions involving oxidation of organic compounds. Here we disclose the crystal structure of the [DABCO???CCl4] complex, and computational studies of two possible complex structures in their ground state, as well as in their first singlet and first triplet excited states. 相似文献
7.
8.
In standing-wave enhancement cavities for frequency doubling, second-harmonic fields are generated in both directions of propagation. To add the fields coherently, one should compensate for the phase shifts introduced by dispersive elements in the cavity. We experimentally demonstrate phase compensation in a compact standing-wave frequency-doubling cavity by use of a wedged periodically poled KTP crystal. The highest conversion efficiency and second-harmonic power obtained by pumping with a 1064-nm cw Nd:YAG laser were 69.4% and 268 mW, respectively. 相似文献
9.
Martin Kutz Gerth Stølting Brodal Kanela Kaligosi Irit Katriel 《Journal of Discrete Algorithms》2011,9(4):314-325
We present algorithms for finding a longest common increasing subsequence of two or more input sequences. For two sequences of lengths n and m, where m?n, we present an algorithm with an output-dependent expected running time of and O(m) space, where ? is the length of an LCIS, σ is the size of the alphabet, and Sort is the time to sort each input sequence. For k?3 length-n sequences we present an algorithm which improves the previous best bound by more than a factor k for many inputs. In both cases, our algorithms are conceptually quite simple but rely on existing sophisticated data structures. Finally, we introduce the problem of longest common weakly-increasing (or non-decreasing) subsequences (LCWIS), for which we present an -time algorithm for the 3-letter alphabet case. For the extensively studied longest common subsequence problem, comparable speedups have not been achieved for small alphabets. 相似文献
10.
Ira Raveh Boris Koichu Irit Peled Orit Zaslavsky 《Research in Mathematics Education》2016,18(1):43-60
In this article we present an integrative framework of knowledge for teaching the standard algorithms of the four basic arithmetic operations. The framework is based on a mathematical analysis of the algorithms, a connectionist perspective on teaching mathematics and an analogy with previous frameworks of knowledge for teaching arithmetic operations with rational numbers. In order to evaluate the potential applicability of the framework to task design, it was used for the design of mathematical learning tasks for teachers. The article includes examples of the tasks, their theoretical analysis, and empirical evidence of the sensitivity of the tasks to variations in teachers’ knowledge of the subject. This evidence is based on a study of 46 primary school teachers. The article concludes with remarks on the applicability of the framework to research and practice, highlighting its potential to encourage teaching the four algorithms with an emphasis on conceptual understanding. 相似文献