A physical explanation for the origin of self-similar magnetoconductance fluctuations in semiconductor billiards

We report quantum-mechanical calculations which replicate the self-similar magnetoconductance fluctuations observed in recent experiments on semiconductor Sinai billiards. We interpret these fluctuations by considering the mixed stable-chaotic classical dynamics of electrons in the billiard. In particular, we show that the fluctuation patterns are dominated by individual stable orbits. The scaling characteristics of the self-similar fluctuations depend on the geometry of the associated stable orbit. We find that our analysis is insensitive to the details of the potential landscape, and is applicable to real devices with a wide range of soft-wall profiles. We show that our analysis also provides a possible explanation for the distinct series of magnetoconductance fluctuations observed in recent experiments on carbon nanotubes.     

使用色散可调啁啾光纤光栅在常规单模光纤中实现超过100km,10Gb/s的转输 *

报道了用简单的应力方法使均匀光栅成为线性啁啾光纤光栅的技术 ,并推导出了相应理论 ,发现最大色散补偿带宽与色散的乘积近似为常数 .在常规单模光纤G652,10Gb/s系统中实现超过100km的色散补偿 .     

Permanent holographic recording in indium oxide thin films using 193 nm excimer laser radiation

Permanent holographic recording in sputtered indium oxide (InO_x) thin films is demonstrated, using ultraviolet radiation at 193 nm emitted by an ArF excimer laser. Steady-state refractive index changes of up to 5×10^-3 are calculated from the measured diffraction efficiency of a HeNe laser probe beam. The recorded gratings exhibit a dynamic behaviour that relaxes to a steady-state value that depends on the oxygen partial pressure used during growth and on the recording beam intensity. The observed behaviour is explained in terms of laser-induced structural changes. Received: 12 October 1998 / Accepted: 8 March 1999 / Published online: 4 August 1999     

Photosensitized Generation of Singlet Oxygen from (Substituted Bipyridine)ruthenium(II) Complexes

Photophysical properties in dilute MeCN solution are reported for seven Ru^II complexes containing two 2,2′‐bipyridine (bpy) ligands and different third ligands, six of which contain a variety of 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridines, for one complex containing no 2,2′‐bipyridine, but 2 of these different ligands, for three multinuclear Ru^II complexes containing 2 or 4 [Ru(bpy)₂] moieties and also coordinated via 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridine ligands, and for the complex [(Ru(bpy)₂(L)]²⁺ where L is N,N′‐([2,2′‐bipyridine]‐4,4′‐diyl)bis[3‐methoxypropanamide]. Absorption maxima are red‐shifted with respect to [Ru(bpy)₃]²⁺, as are phosphorescence maxima which vary from 622 to 656 nm. The lifetimes of the lowest excited triplet metal‐to‐ligand charge transfer states ³MLCT in de‐aerated MeCN are equal to or longer than for [Ru(bpy)₃]²⁺ and vary considerably, i.e., from 0.86 to 1.71 μs. Rate constants k_q for quenching by O₂ of the ³MLCT states were measured and found to be well below diffusion‐controlled, ranging from 1.2 to 2.0⋅10⁹ dm³ mol⁻¹ s⁻¹. The efficiencies f of singlet‐oxygen formation during oxygen quenching of these ³MLCT states are relatively high, namely 0.53 – 0.89. The product of k_q and f gives the net rate constant k for quenching due to energy transfer to produce singlet oxygen, and k_q−k equals k, the net rate constant for quenching due to energy dissipation of the excited ³MLCT states without energy transfer. The quenching rate constants were both found to correlate with ΔG^CT, the free‐energy change for charge transfer from the excited Ru complex to oxygen, and the relative and absolute values of these rate constants are discussed.     

Mapping strains at the nanoscale using electron back scatter diffraction

In this paper, we describe the use of electron back scatter diffraction (EBSD) to study strain variations in crystalline samples at the nanoscale. The analysis relies on cross correlation measurements of small shifts in the EBSD pattern measured at many points dispersed across the pattern. The method allows the full strain tensor, and lattice rotations to be obtained at a sensitivity of ～10^?4. The method is applied to study variations of strains and rotations near the surface of 200 nm thick epitaxial layers of Si_0.85Ge_0.15 grown on a Si substrate patterned with rectangular and square mesa. Linescans across rectangular mesas show that strain relaxation and accompanying lattice rotations are restricted to the edges of wide mesas but that the relaxation extends across the entirety of mesas narrower than ～6 μm. Two dimensional maps of the strain variation in a ～3 μm wide square mesa are also presented.     

The <Emphasis Type="Italic">C</Emphasis><Superscript>1</Superscript> generic diffeomorphism has trivial centralizer

Answering a question of Smale, we prove that the space of C ¹ diffeomorphisms of a compact manifold contains a residual subset of diffeomorphisms whose centralizers are trivial.     

An ultrasonic transducer transient compensator design based on a simplified Variable Structure Control algorithm

A non-linear control method, known as Variable Structure Control (VSC), is employed to reduce the duration of ultrasonic (US) transducer transients. A physically realizable system using a simplified form of the VSC algorithm is proposed for standard piezoelectric transducers and simulated. Results indicate a VSC-controlled transmitter reduces the transient duration to less than a carrier wave cycle. Applications include high capacity ultrasound communication and localization systems.     

三维光存储中折射率失配引起的球差补偿

为实现三维光存储中折射率失配引起的球差补偿,建立了光学存储系统模型,获得了折射率失配引起的波前偏差函数与存储深度的表达式.采用泽尔尼克循环多项式对波前偏差函数进行补偿展开.在双光子荧光和单光子共焦荧光读出方式下,均可获得读出荧光强度与存储深度的关系:在折射率失配引起的球差未得到补偿矫正的情况下,存储深度在200 μm左右读出荧光强度基本上下降为零;当折射率失配引起的初级球差被补偿矫正后,读出荧光强度随存储深度的下降得到较好改善;当折射率失配引起的二级球差被补偿矫正后,存储深度在1 mm内存储点强度随深度基本上没有明显地变化.并且对像差补偿方法进行了具体地分析.     

Structure,biosynthetic origin,and engineered biosynthesis of calcium-dependent antibiotics from Streptomyces coelicolor

The calcium-dependent antibiotic (CDA), from Streptomyces coelicolor, is an acidic lipopeptide comprising an N-terminal 2,3-epoxyhexanoyl fatty acid side chain and several nonproteinogenic amino acid residues. S. coelicolor grown on solid media was shown to produce several previously uncharacterized peptides with C-terminal Z-dehydrotryptophan residues. The CDA biosynthetic gene cluster contains open reading frames encoding nonribosomal peptide synthetases, fatty acid synthases, and enzymes involved in precursor supply and tailoring of the nascent peptide. On the basis of protein sequence similarity and chemical reasoning, the biosynthesis of CDA is rationalized. Deletion of SCO3229 (hmaS), a putative 4-hydroxymandelic acid synthase-encoding gene, abolishes CDA production. The exogenous supply of 4-hydroxymandelate, 4-hydroxyphenylglyoxylate, or 4-hydroxyphenylglycine re-establishes CDA production by the DeltahmaS mutant. Feeding analogs of these precursors to the mutant resulted in the directed biosynthesis of novel lipopeptides with modified arylglycine residues.     

Nano-architecture and material designs for water splitting photoelectrodes

This review concerns the efficient conversion of sunlight into chemical fuels through the photoelectrochemical splitting of water, which has the potential to generate sustainable hydrogen fuel. In this review, we discuss various photoelectrode materials and relative design strategies with their associated fabrication for solar water splitting. Factors affecting photoelectrochemical performance of these materials and designs are also described. The most recent progress in the research and development of new materials as well as their corresponding photoelectrodes is also summarized in this review. Finally, the research strategies and future directions for water splitting are discussed with recommendations to facilitate the further exploration of new photoelectrode materials and their associated technologies.