Metal-insulator crossover in high T c cuprates: A gauge field approach

A metal-insulator crossover appears in the experimental data for in-plane resistivity of underdoped cuprates and a range of superconducting cuprates in the presence of a strong magnetic field suppressing superconductivity. We propose an explanation for this phenomenon based on a gauge field theory approach to the t-J model. In this approach, based on a formal spin-charge separation, the low energy effective action describes gapful spinons (with a theoretically derived doping dependence of the gap m _s ² ∼ δ| ln δ|) and holons with finite Fermi surface (ɛF ∼ tδ) interacting via a gauge field whose basic effect on the spinons is to bind them into overdamped spin waves, shifting their gap by a damping term linear in T, which causes the metal-insulator crossover. The presence of a magnetic field perpendicular to the plane acts by increasing the damping, in turn producing a big positive transverse in-plane magnetoresistance at low T, as experimentally observed.     

Size limitations for the formation of ordered striped nanoparticles

A combination of immiscible molecules in the ligand shell of a gold nanoparticle (NP) has been shown to phase separate into a rippled structure; this phase separation can be used to direct the assembly of the NPs into chains. Here we demonstrate that only NPs within a certain size range can form chains, and we conclude that the rippled morphology of the ligand shell also exists only within that given size range. We corroborate this result with simulations of the ligand arrangement on NPs of various sizes.     

Rational design and assembly of synthetic trimodular polyketide synthases

Type I polyketide synthases (PKSs) consist of modules that add two-carbon units in polyketide backbones. Rearranging modules from different sources can yield novel enzymes that produce unnatural products, but the rules that govern module-module communication are still not well known. The construction and assay of hybrid bimodular units with synthetic PKS genes were recently reported. Here, we describe the rational design of trimodular PKSs by combining bimodular units. A cloning-expression system was developed to assemble and test 54 unnatural trimodular PKSs flanked by the loading module and the thioesterase from the erythromycin synthase. Remarkably, 96% of them produced the expected polyketide. The obtained results represent an important milestone toward the ultimate goal of making new bioactive polyketides by rational design. Additionally, these results show a path for the production of customized tetraketides by fermentation, which can be an important source of advanced intermediates to facilitate the synthesis of complex products.     

Speech enhancement using the modified phase-opponency model

In this paper we present a model called the Modified Phase-Opponency (MPO) model for single-channel speech enhancement when the speech is corrupted by additive noise. The MPO model is based on the auditory PO model, proposed for detection of tones in noise. The PO model includes a physiologically realistic mechanism for processing the information in neural discharge times and exploits the frequency-dependent phase properties of the tuned filters in the auditory periphery by using a cross-auditory-nerve-fiber coincidence detection for extracting temporal cues. The MPO model alters the components of the PO model such that the basic functionality of the PO model is maintained but the properties of the model can be analyzed and modified independently. The MPO-based speech enhancement scheme does not need to estimate the noise characteristics nor does it assume that the noise satisfies any statistical model. The MPO technique leads to the lowest value of the LPC-based objective measures and the highest value of the perceptual evaluation of speech quality measure compared to other methods when the speech signals are corrupted by fluctuating noise. Combining the MPO speech enhancement technique with our aperiodicity, periodicity, and pitch detector further improves its performance.     

Re(V) and Re(III) complexes with sal2phen and triphenylphosphine: rearrangement, oxidation and reduction

Reactions of Re(V), tetradentate Schiff base complexes with tertiary phosphines have previously yielded both rearranged Re(V) and reduced Re(III) complexes. To further understand this chemistry, the rigid diiminediphenol (N(2)O(2)) Schiff base ligand sal(2)phen (N,N'-o-phenylenebis(salicylaldimine)) was reacted with (n-Bu(4)N)[ReOCl(4)] to yield trans-[ReOCl(sal(2)phen)] (1). On reaction with triphenylphosphine (PPh(3)), a rearranged Re(V) product cis-[ReO(PPh(3))(sal(2)phen*)]PF(6) (2), in which one of the imines was reduced to an amine during the reaction, and the reduced Re(III) products trans-[ReCl(PPh(3))(sal(2)phen)] (4) and trans-[Re(PPh(3))(2)(sal(2)phen)](+) (5) were isolated. Reaction of sal(2)phen with [ReCl(3)(PPh(3))(2)(CH(3)CN)] resulted in the isolation of [ReCl(2)(PPh(3))(2)(salphen)] (3). The compounds were characterized using standard spectroscopic methods, elemental analyses and single crystal X-ray crystallography.     

Convergent Total Syntheses of (−)‐Rubriflordilactone B and (−)‐pseudo‐Rubriflordilactone B

A highly convergent strategy for the synthesis of the natural product (?)‐rubriflordilactone B, and the proposed structure of (?)‐pseudo‐rubriflordilactone B, is described. Late stage coupling of diynes containing the respective natural product FG rings with a common AB ring aldehyde precedes rhodium‐catalyzed [2+2+2] alkyne cyclotrimerization to form the natural product skeleton, with the syntheses completed in just one further operation. This work resolves the uncertainty surrounding the identity of pseudo‐rubriflordilactone B and provides a robust platform for further synthetic and biological investigations.     

泥沙输运模拟综述——现状及其发展趋势

随着流体力学中数值方法的飞速发展,计算模型已经成为研究流体运动,泥沙输运和不同环境(诸如河流,湖泊及沿海地区)中相应污染物归趋过程等方面非常有吸引力的工具,在过去的30多年里,发展了许多计算水动力学/泥沙输运模型.文章追溯当前具有代表性的(一维、二维、三维)模型的发展历程,描述他们各自的特点,优势及局限,力图作为对模型方面感兴趣读者的第一指南,同时也为大家讨论模型的局限性,未来的发展趋势和研究需求方面搭建一个平台.给出了模型的表达,时空特性,水动力学和沉积物的耦合方式,处理非恒定流,推移质和悬移质,泥沙交换过程,泥沙类型(粘性或非粘性)及非均匀泥沙输运的能力.总结了不同模型的应用实例,读者可以运用这些例子作为研究模型设置,模型率定及模型验证的参考.给出了选择泥沙输运模型应遵循的原则,模型输入及率定方面存在的问题及改进的途径.探讨了现有水动力学/泥沙输运模型在处理复杂湍流,泥沙携带,流动与输沙耦合,非均匀泥沙,离散和扩散系数,河岸来沙处理等方面的局限性及改进的方向.最后,对基于多相流思想的泥沙输运模型及其它一些交叉性问题作了评述与展望.     

A spin-parity analysis of the K+K+K− system produced in the reaction K+p → K+K+K−p

We present the first spin-parity analysis of the K⁺K⁺K^?) system produced in the reaction K⁺p → K⁺K⁺K^?p, and show that the general features of this system resemble those of the (ππ⁺π^?) and Kπ⁺π^?) systems produced in the reactions π(K)p → π(K)π⁺π^?p. There is a low mass enhancement, (47 ± 11)% of which corresponds to 1⁺ states decaying to Kø. At higher (K⁺K⁺K^?) masses 2^? → Kf′ becomes increasingly significant and at all masses there is a 0^? contribution of roughly 30%.     

An analysis of psychophysical tuning curves in normal and pathological ears

Simultaneous psychophysical tuning curves were obtained from normal-hearing and hearing-impaired listeners, using probe tones that were either at similar sound pressure levels or at similar sensation levels for the two types of listeners. Tuning curves from the hearing-impaired listeners were flat, erratic, broad, and/or inverted, depending upon the frequency region of the probe tone and the frequency characteristics of the hearing loss. Tuning curves from the normal-hearing listeners at low-SPL's were sharp as expected; tuning curves at high-SPL's were discontinuous. An analysis of high-SPL tuning curves suggests that tuning curves from normal-hearing listeners reflect low-pass filter characteristics instead of the sharp bandpass filter characteristics seen with low-SPL probe tones. Tuning curves from hearing-impaired listeners at high-SPL probe levels appear to reflect similar low-pass filter characteristics, but with much more gradual high-frequency slopes than in the normal ear. This appeared as abnormal downward spread of masking. Relatively good temporal resolution and broader tuning mechanisms were proposed to explain inverted tuning curves in the hearing-impaired listeners.