Features of magnetic resonance in nanoporous carbon with pores filled with transition-metal atoms

Properties of nanoporous carbon (NPC) free of metal atoms and NPC containing atoms of Ni, Co and Pd in their pores are studied by electron spin resonance (ESR). The asymmetrical ESR line with the so-called Dyson line shape points out that charge carriers are responsible for the resonance spectrum in metal-free NPC. Although the amount of Ni, Co, and Pd introduced into nanopores is small, the NPC properties change significantly. A bulk ferromagnetism is observed in the case of NPC with Co and Pd, but not in NPC:Ni. Co atoms in pores of NPC cause the formation of a new material, namely, a disordered ferromagnetic medium with some features in the Co atom distribution. Magnetic properties are strongly temperature-dependent. The temperature dependences of the conductivity and ESR integral intensity in NPC:Ni reveal an exponential growth with the same activation energy. The magnetic resonance spectrum of NPC:Pd consists of four signals for NPC which is produced from SiC. There are one ferromagnetic and three paramagnetic signals belonging to the carbon dangle sp³- and sp²-bonds kind and to the paramagnetic clusters of Pd atoms.     

Mining combinatorial data in protein sequences and structures

Combinatorial searches of structural and physical chemical properties involving the components of libraries of dipeptide, tripeptide and tetra peptide fragments were carried out in the Protein Data Bank and the SwissProt databases. The properties investigated are structural propensities, co localization of peptide fragments in protein sequences, interactions between peptide fragments in close structural proximity and the participation of physical chemical profiles in the distribution of structural motifs among peptide fragments. The results obtained for each combinatorial search in the study are classified according to the structural motifs alpha-helix, beta-sheet, reverse turn I and reverse turn II. The application of combinatorial data mined in protein databases to the design of new peptide libraries is discussed. The present findings have implications for the study of protein structure which are also discussed.     

非线性光子晶体的单向透射性

利用非线性时域有限差分方法(FDTD)对光从某些一维缺陷层掺杂克尔非线性介质的四分之一波长光子晶体的正反两个不同方向入射时对应的一般透射特性进行了数值分析.计算表明：一定频率范围及一定光强范围的光从非线性光子晶体的正向入射时,透射率是其从非线性光子晶体相反方向入射时的数倍,具有单向透射性,表现为全光二极管的行为.进一步对交替介质层由空气和金红石(TiO2)组成而非线性缺陷层由聚合物(polydiacetykene 9-BCMU)组成的光子晶体模型的透射特性进行了数值分析.在某一频率和强度附近,该模型的正向透射率是反向的6倍左右,表明其可作为一种全光二极管使用.     

“Small and beautiful” – The novel structures and phases of nano-oxides

Low-dimensional oxide nanostructures supported on well-defined metal surfaces raise scientific interest both on a fundamental level and for potential technological applications. These systems may be regarded as artificially created hybrid materials with novel emergent properties, supporting new concepts of geometrical structure, electronics and magnetism, complex phase diagrams and particular chemical reactivity. The coupling of the oxide nano-phase to the metal support surface by electronic and elastic interactions together with the low dimensionality aspects are at the origin of the particular behaviour of these hybrid structures. By way of prototypical examples, this Prospective article highlights some of the novel properties of nano-oxides and, as a side aspect, comments on the aesthetics of their structural motifs.     

GeS2-In2S3硫系玻璃的物化性质与晶化行为研究

认识玻璃组成-性能-结构之间关系是玻璃科学中经久不衰的研究课题之一. 在制得(100-x) GeS₂-xIn₂S₃ (x=10, 15, 20, 25或30 mol%) 系列玻璃和玻璃陶瓷样品的基础上, 利用可见-近红外透过光谱, DSC, XRD和Raman光谱等测试技术表征了随组份变化的光学带隙, 玻璃转变温度以及晶化行为等, 并结合GeS₂-Ga₂S₃玻璃研究结果探讨了Ga, In 元素及其形成的网络结构对玻璃性质的影响.研究发现, 在硫系玻璃中In比Ga对光学带隙和玻璃转变温度等性质的影响要大. 它们所形成玻璃的晶化行为也截然不同, 但与其各自的材料相图有着密切的联系. 利用偏振拉曼光谱获得玻璃网络中的基本结构单元信息.最后, 结合材料相图, 玻璃随组成变化的物化性质和晶化行为以及基本网络结构单元的认识, 探讨了玻璃的化学拓扑与网络拓扑之间的联系, 为今后研究提供一种新的研究思路.     

The motifs of crystals and their nano-aggregates

Metal-organic-hybrid bulk chain-like, block, tubular, and plate crystals have been synthesized by a wet chemical method. Single crystal X-ray diffraction and TEM reveal that all the nano-structures are associated with their crystal motifs, which provide a successful and effective access to assemble controlled specific nano-structures from bulk crystal of which the motifs are much desired.     

Ordering effects in disordered systems: the Au-Si system

We have characterized the short-range order in the liquid and undercooled states of Au-Si alloy at the eutectic composition using molecular dynamics simulations. The interactions are described via a modified embedded-atom model refined to take into account the liquid properties. For the eutectic liquid, the local structure is characterized by a strong Au-Si affinity, namely a well-pronounced chemical short-range order which leads to the slowing down of the formation of icosahedral local motifs in the undercooled regime. Moreover we discuss the influence of this peculiar local structure on the dynamic and thermodynamic properties of the liquid phase and compare our results with available experimental data.     

Electrophysical studies of nanoporous carbon materials prepared of silicon carbide powders

Measurements of the electrophysical properties of nanoporous carbon (NPC) samples (conductivity and Hall effect), as well as studies of the same samples using electron spin resonance (ESR), are summarized. Free holes are shown to play the major part in charge transport in such materials, thus permitting identification of the ESR signal with free holes. An analysis of the shape of the resonance lines, as well as of their dependence on temperature and the technology employed in sample preparation, established the ESR signals to consist of two superimposed resonance lines associated with carriers, free or localized to various extents, whose magnetic susceptibility obeys Pauli and Curie-Weiss laws, respectively. The temperature dependences of the ESR signal parameters were studied, and the experimental relations were compared with theory to determine the model-parameters. An analysis of the temperature behavior of these parameters suggests the conclusion that NPC samples are heterophase porous systems whose properties are dominated by structural characteristics.     

Study of both fingerprint and high wavenumber Raman spectroscopy of pathological nasopharyngeal tissues

High wavenumber (HW) Raman spectroscopy has weaker fluorescence background compared with fingerprint (FP) region. This study aims to evaluate the discrimination feasibility of nasopharyngeal non‐cancerous and nasopharyngeal cancer (NPC) tissue with both FP and HW Raman spectroscopy. HW Raman spectra of nasopharyngeal tissue were obtained for the first time. Raman spectra were collected to differentiate nasopharyngeal non‐cancerous (n = 37) from NPC (n = 41) tissues in FP (800–1800cm⁻¹), HW (2700–3100cm⁻¹), and integrated FP/HW region. First, to assess the utility of this method, the averaged Raman spectral intensities and intensity ratios of corresponding Raman bands were analyzed in HW and FP regions, respectively. The results show that intensities as well as the ratios of specific Raman peaks might be helpful in distinguishing nasopharyngeal non‐cancerous from NPC tissue with the HW Raman spectroscopy, as with FP Raman reported before. The multivariate statistical method based on the combination of principal component analysis–liner discriminant analysis (PCA‐LDA), together with leave‐one‐patient‐out, cross‐validation diagnostic algorithm, was used for discriminating nasopharyngeal non‐cancerous from NPC tissue, generating sensitivities of 87.8%, 85.4%, and 95.1% and specificities of 86.5%, 91.9%, and 89.2%, respectively, with Raman spectroscopy in the FP, HW, and integrated FP/HW regions. The posterior probability of classification results and receiver operating characteristic curves were utilized to evaluate the discrimination of PCA‐LDA algorithm, verifying that HW Raman spectroscopy has a positive effect on the differentiation for the diagnosis of NPC tissue by integrated FP/HW Raman spectroscopy. What's more, the potential of Raman spectroscopy used for differentiating different pathology NPC tissues was also discussed. The results demonstrate that both FP and HW Raman spectroscopy have the potential for diagnosis and detection in early nasopharyngeal carcinoma, and HW Raman spectroscopy may improve the discrimination of NPC tissue compared with FP region alone, providing a promising diagnostic tool for the diagnosis of NPC tissue. Copyright © 2015 John Wiley & Sons, Ltd.     

A Photostable, pH-Invariant Fluorescein Derivative for Single-Molecule Microscopy

We herein report the comprehensive characterization of the spectral and single-photon fluorescence properties of a recently synthesized fluorescein derivative and its biotinylated analog. The fluorophore displays significant increases in photostability compared to the known fluorescein label fluorescein isothiocyanate (FITC), as well as superb pH independence. This fluorescein variant has two readily accessible functional groups (aniline NH₂ and phenol OH) that can be activated or blocked independently and can serve, for instance, as a fluorescent bridge between two different recognition motifs. Excellent single-photon counting fluorescence data demonstrates that it is also a particularly appropriate probe for single-molecule studies of biological interactions.     

中等尺寸硫化锌团簇结构和稳定性

通过第一性原理方法研究中等尺寸硫化锌团簇(ZnS)_n(n=24,28,36,和48)的结构和稳定性.团簇初始结构主要通过手工搭建和从体材料中切割得来.研究表明:对于中等尺寸的团簇,空心的笼状和管状结构能量最低;随着团簇尺寸的增大,洋葱结构能量越来越低.此外,对中等尺寸硫化锌团簇,纤锌矿结构比闪锌矿结构更稳定.说明在小尺寸下,纤锌矿硫化锌结构更稳定.     

Relationship between local structure and relaxor behavior in perovskite oxides

Despite intensive investigations over the past five decades, the microscopic origins of the fascinating dielectric properties of ABO3 relaxor ferroelectrics are currently poorly understood. Here, we show that the frequency dispersion that is the hallmark of relaxor behavior is quantitatively related to the crystal chemical characteristics of the solid solution. Density functional theory is used in conjunction with experimental determination of cation arrangement to identify the 0 K structural motifs. These are then used to parametrize a simple phenomenological Landau theory that predicts the universal dependence of frequency dispersion on the solid solution cation arrangement and off-center cation displacements.     

Dynamics of network motifs in genetic regulatory networks

Network motifs hold a very important status in genetic regulatory networks. This paper aims to analyse the dynamical property of the network motifs in genetic regulatory networks. The main result we obtained is that the dynamical property of a single motif is very simple with only an asymptotically stable equilibrium point, but the combination of several motifs can make more complicated dynamical properties emerge such as limit cycles. The above-mentioned result shows that network motif is a stable substructure in genetic regulatory networks while their combinations make the genetic regulatory network more complicated.     

Deep level states and negative photoconductivity in n-ZnO/p-Si hetero-junction diodes

Negative photoconductivity (NPC) was observed in n-ZnO/p-Si heterojunction diode grown by ultra-high vacuum sputtering method under nitrogen ambient. Under the illumination of ultra-violet light, positive photoconductivity was observed at low bias voltages, whereas NPC was observed at high bias voltages. The defect states in the ZnO layers grown on Si were analyzed by photoluminescence and deep level transient spectroscopy measurements. Two deep levels were measured at E_c-0.51 eV and E_c-0.54 eV, which might be originated from oxygen vacancy and nitrogen atom related defects, respectively. Based on the simulation of band diagram, the defect states were located below Fermi level at zero bias voltage. However, as increasing the bias voltages, NPC was observed due to the increase of empty defect states. This analysis allowed us to consider the possibility that the NPC phenomenon in n-ZnO/p-Si heterojunction diode is originated dominantly from the defect states as a carrier recombination center in ZnO layer.     

Dynamic pattern formation in a vesicle-generating microfluidic device

Spatiotemporal pattern formation occurs in a variety of nonequilibrium physical and chemical systems. Here we show that a microfluidic device designed to produce reverse micelles can generate complex, ordered patterns as it is continuously operated far from thermodynamic equilibrium. Flow in a microfluidic system is usually simple-viscous effects dominate and the low Reynolds number leads to laminar flow. Self-assembly of the vesicles into patterns depends on channel geometry and relative fluid pressures, enabling the production of motifs ranging from monodisperse droplets to helices and ribbons.     

Bridge and brick motifs in complex networks

Acknowledging the expanding role of complex networks in numerous scientific contexts, we examine significant functional and topological differences between bridge and brick motifs for predicting network behaviors and functions. After observing similarities between social networks and their genetic, ecological, and engineering counterparts, we identify a larger number of brick motifs in social networks and bridge motifs in the other three types. We conclude that bridge and brick motif content analysis can assist researchers in understanding the small-world and clustering properties of network structures when investigating network functions and behaviors.     

Structures,microstructures, physical and chemical properties of different rice grains

Herein, we demonstrated a well-rounded exploration of the universal structures, microstructures and physical properties of different rice grains. We show that these rice grains are nanocrystalline in nature, have the standard pattern of type A rice crystalline, and can be attributed to the hexagonal crystal structure with space group of P6. These rice grains have uneven surfaces, clusters of the granules, or schistose structure. Carbon, nitrogen and oxygen elements are presented in the rice grains. No significant difference is observed in FTIR spectra in these rice grains, indicating the fundamental chemical structures of these rice grains are analogical. Their microstructural and physical properties were investigated in detail. Moreover, chemical properties (e.g. thermal stability) of the rice grains were explored. This research provides an in-depth understanding on the physical and structural properties on the atomic and molecular level, as well as guidance for food and industry applications.     

Thermal Analysis for Velocity,Kinetics, and Enthalpy Reaction Measurements in Microfluidic Devices

Abstract

The aim of this work is to present new devices for the measurement of velocity, kinetics, and enthalpy of chemical reactions occurring in a microfluidic chip, co-flow, or droplets flow. The thermal analysis goes from the macroscopic approach by microcalorimetry to microscopic analysis inside the microchannel by IR thermography. Concerning microcalorimetry, the enthalpy is deduced from the measurement of the global heat flux dissipated by the chemical reaction as a function of the molar flow rate. A validation is presented on a well-known acid-base reaction. This device can be combined with an IR camera for local characterization. The processing of the measured temperature fields allows the estimation of properties of great importance for chemical engineers, such as heating source distribution (i.e., the kinetics) of the chemical reaction along the channel. A validation experiment of a temperature field processing method is proposed with the Joule effect. From such a previous experiment, a Peclet field is estimated and used in a further step in order to study an acid-base co-flow configuration. Finally, a first tentative of thermal characterization inside droplets flow during an acid-base chemical reaction is also presented.     

Synthesis,Morphological Control,and Properties of Silver Nanoparticles in Potential Applications

Nanostructured materials, especially nanoparticles (NPs), of noble metal NPs such as silver (Ag) have been the focus of research in recent decades because of their distinct physical, chemical, and biological properties. These materials have attracted considerable attention because of their potential applications, such as catalysis, biosensing, drug delivery, and nanodevice fabrication. Previous studies on Ag NPs have clearly demonstrated that their electromagnetic, optical, and catalytic properties are strongly influenced by their shape, size, and size distribution, which can be varied by using different synthetic methods, reducing agents, and stabilizers. The valuable optical properties of Ag NPs have allowed for new approaches in sensing and imaging applications, offering a wide range of detection modes, such as colorimetric, scattering, and surface‐enhanced Raman scattering techniques, at extremely low detection limits. Here, an overview of the various chemical, physical, and biological properties of Ag NP fabrication approaches to obtain the various shapes and sizes is presented.     

Structural,electronic,vibrational,and thermodynamic properties of Zr_(1-x)Hf_xCo:A first-principles-based study

The physical properties including structural,electronic,vibrational and thermodynamic properties of Zr1-xHfx Co(x is the concentration of constituent element Hf,and changes from 0 to 1) are investigated in terms of the ABINIT program.The results reveal that all of Zr_(1-x)Hf_x Co have similar physical properties.When Hf concentration x gradually increases from 0.0 to 1.0,the lattice constant decreases from 3.217 ?A to 3.195 ?A very slowly.The calculated density of states(DOS)indicates that the metallic nature is enhanced and the electrical conductivity turns better with the increase of Hf.Moreover,as Hf concentration increases from 0 to 1,the Fermi energy gradually increases from-6.96 e V to-6.21 e V,and the electronic density of states at the Fermi level(N(E_f)) decreases from 2.795 electrons/e V f.u.down to 2.594 electrons/e V f.u.,both of which imply the decrease of chemical stability.The calculated vibrational properties show that the increase of Hf concentration from 0 to 1 causes the maximum vibrational frequency to decrease gradually from about 223 cm~(-1) to 186 cm~(-1),which suggests a lower dispersion gradient and lower phonon group velocities for these modes.Finally,the phonon related thermodynamic properties are obtained and discussed.