A Non‐Gaussian Spatio‐Temporal Model for Daily Wind Speeds Based on a Multi‐Variate Skew‐t Distribution

Facing increasing domestic energy consumption from population growth and industrialization, Saudi Arabia is aiming to reduce its reliance on fossil fuels and to broaden its energy mix by expanding investment in renewable energy sources, including wind energy. A preliminary task in the development of wind energy infrastructure is the assessment of wind energy potential, a key aspect of which is the characterization of its spatio‐temporal behavior. In this study we examine the impact of internal climate variability on seasonal wind power density fluctuations over Saudi Arabia using 30 simulations from the Large Ensemble Project (LENS) developed at the National Center for Atmospheric Research. Furthermore, a spatio‐temporal model for daily wind speed is proposed with neighbor‐based cross‐temporal dependence, and a multi‐variate skew‐t distribution to capture the spatial patterns of higher‐order moments. The model can be used to generate synthetic time series over the entire spatial domain that adequately reproduce the internal variability of the LENS dataset.     

一个基于双流体理论预测三维流化床内流动特性的数学模型(Ⅱ)液固体系流体动力学特性

将考虑拟平衡状态下颗粒与流体相互作用的附加力添加在基于双流体理论的动量方程中的数学模型,用于预报三维液固流化床内流体动力学特性。该模型主要特点是将表征颗粒离散属性的特征长度视为颗粒直径的同一数量级且只需曳力系数一个关联式来封闭控制方程。在商业软件CFX4.4平台上,通过增加用户自定义子程序考察了液体速度突变后水-颗粒（密度3000 kg·m^-3,粒径为2.5×10^-3 m）体系在长0.1 m、宽0.1 m和高0.5 m流化床内时空分布特性。三维、X和Y方向中间截面上固含率的模拟结果表明：当液体入口速度增大时,床层表面和分隔界面均随时间呈上升趋势,且分隔界面呈现波浪状;当液体入口速度减小时,下降的床层表面和上升的分隔界面与时间呈较好的线性关系。对床层膨胀和收缩过程的动态响应时间进行了定量化模拟,其结果与Didwanla和Homsy的二维实验研究以及Gibilaro的一维理论分析相吻合。     

Demonstration by burst-phase analysis of a robust folding intermediate in the FF domain

The role of intermediates in the folding reaction of single-domainproteins is a controversial issue. It was previously shown bydifferent methods that an on-pathway intermediate is populatedin the presence of sodium sulphate during the folding of theFF domain from HYPA/FBP11. Here we demonstrate using analysisof the amplitudes of kinetic traces that this burst-phase foldingintermediate is present at different salt concentration andat various pH, and is also found in roughly 30 site-directedmutants. The intermediate appears robust to changing conditionsand thus fulfils an important criterion for a productive molecularspecies on the folding reaction pathway.     

Oxygen dissociation by concerted action of di-iron centers in metal-organic coordination networks at surfaces: modeling non-heme iron enzymes

The high chemical reactivity of unsaturated metal sites is a key factor for the development of novel devices with applications in sensor engineering and catalysis. It is also central in the research for sustainable energy concepts, e.g., the efficient production and conversion of chemical fuels. Here, we study the process of oxygen dissociation by a surface-supported metal-organic network that displays close structural and functional analogies with the cofactors of non-heme enzymes. We synthesize a two-dimensional array of chemically active di-iron sites on a Cu(001) surface where molecular oxygen readily dissociates at room temperature. We provide an atomic-level structural and electronic characterization before and after reaction by combining scanning tunneling microscopy, X-ray absorption spectroscopy, and density functional theory. The latter identifies a novel mechanism for O2 dissociation controlled by the cooperative catalytic action of two Fe2+ ions. The high structural flexibility of the organic ligands, the mobility of the metal centers, and the hydrogen bonding formation are shown to be essential for the functionality of these active centers allowing to mimick biologically relevant reactions in a confined environment.     

Designer magnetoplasmonics with nickel nanoferromagnets

We introduce a new perspective on magnetoplasmonics in nickel nanoferromagnets by exploiting the phase tunability of the optical polarizability due to localized surface plasmons and simultaneous magneto-optical activity. We demonstrate how the concerted action of nanoplasmonics and magnetization can manipulate the sign of rotation of the reflected light's polarization (i.e., to produce Kerr rotation reversal) in ferromagnetic nanomaterials and, further, how this effect can be dynamically controlled and employed to devise conceptually new schemes for biochemosensing.     

Theta-shaped plasmonic nanostructures: bringing "dark" multipole plasmon resonances into action via conductive coupling

Quadrupole plasmon and (octupolar) Fano resonances are induced in lithographically fabricated theta-shaped ring-rod gold nanostructures. The optical response is characterized by measuring the light scattered by individual nanostructures. When the nanorod is brought within 3 nm of the ring wall, a weak quadrupolar resonance is observed due to capacitive coupling, and when a necklike conductive bridge links the nanorod to the nanoring the optical response changes dramatically bringing the quadrupolar resonance into prominence and creating an octupolar Fano resonance. The Fano resonance is observed due to the destructive interference of the octupolar resonance with the overlapping and broadened dipolar resonance. The quadrupolar and Fano resonances are further enhanced by capacitive coupling (near-field interaction) that is favored by the theta-shaped arrangement. The interpretation of the data is supported by FDTD simulation.     

Label-free probing of G-quadruplex formation by surface-enhanced Raman scattering

In this work, we establish the use of surface-enhanced Raman scattering (SERS) as a label-free analytical technique for the direct detection of G-quadruplex formation. In particular, we demonstrate that SERS analysis allows the evaluation of the relative stability of G quadruplexes that differ for the number of G tetrads and investigate several structural features of quadruplexes, such as the orientation of glycosidic bonds, the identification of distortions in the sugar-phosphate backbone, and the degree of hydrogen-bond solvation. Herein, the fluctuation of the SERS spectra, due to the specific interaction of vibrational modes with the SERS-active substrate, is quantitatively analyzed before and after quadruplex formation. The results of this study suggest a perpendicular orientation of the quadruplexes (with or without the 3'-tetra end linker) with respect to the silver colloidal surface, which opens new perspectives for the use of SERS as a label-free analytical tool for the study of the binding mode between quadruplexes and their ligands.     

Peptides with regular enantiomeric sequences: a wide class of modular self-assembling architectures

Organic trans-annular assemblies constitute an expanding class of structures with promising applications for the design of nanotechnological devices. Among the strategies developed for the engineering of organic nanotubes, those characterized by regular alternating enantiomeric amino acid sequences have been proven particularly useful. In fact, cyclic peptides with an even number of regularly alternating D- and L-amino acids have the tendency to adopt local beta-conformation that are capable of forming trans-annular self-assembling architectures, hydrogen bond directed. The formation of such structures is the result of the conformational equivalence of the monomer units, a general principle that associates stereo-chemical to chemical equivalence in a polymer chain. For configurationally alternating sequences the conformational equivalence produces cyclic structures, where a monomer unit is related to the adjacent along the chain by a roto-reflection axis, Sn. A slight relaxation of the conformational equivalence can formally transform a cyclic structure into a conformationally quasi-equivalent helical structures characterized by the presence of polar inner channels, which allow the transient binding for an activated flow of specific ions. To prove our early predictions, we synthesized different alternating polypeptide and the corresponding linear and cyclic oligopeptides and investigated their conformations by NMR and CD spectroscopy as well as the formation of self-assembling structures by increasing the concentration in solution. Moreover, their predicted ability to behave as an ion-channel across bilayer membranes are investigated and experimental evidence of single molecule conducting events are reported. Finally, the possibility is suggested to obtain self-assembled trans-annular structures by chemically bridging the amino acid side chains stabilized using different strategies. A complex construct with good perspective for nano-technological applications is proposed in which cyclic DL-lysine side chains are bridged by the formation of salycilaldimmine metal chelates.