Non-equilibrium effects in chaperone-assisted translocation of a stiff polymer

Chaperone-assisted biopolymer translocation is the main model proposed for translocation in vivo. A dynamical Monte Carlo method is used to simulate the translocation of a stiff homopolymer through a nanopore driven by chaperones. Chaperones are proteins that bind to the polymer near the wall and prevent its backsliding through Cis side. The important parameters include binding energy, size and the local concentration of the chaperones. The profile of these local concentrations, build up the chaperones distribution. Here we investigate the effects of binding energy, size and the exponential distribution of chaperones in their equilibration in each step of the polymer translocation needed for stable translocation time. The simulation results show that in case of chaperones with the size of a monomer ($\lambda =1$) and/or positive effective binding energy and/or uniform distribution, the chaperones binding equilibration rate/frequency is less than 5 times per monomer. However, in some special cases in the exponential distribution of chaperones with size $\lambda >1$ and negative effective binding energy the equilibration rate will diverge to more than 20 times per monomer. We show that this non-equilibrium effect results in supper diffusion, seen before. Moreover, we confirm the equilibration process theoretically.     

Quantitative and high mass ToF-SIMS studies of siloxane segregation in hydrogel polymers using cryogenic sample handling techniques

This paper examines the capabilities of cryogenic sample handling to examine composition and structure of hydrogel materials where siloxane components are central to the analysis. XPS analysis of multicomponent polymers with cryogenic sample handling following exposure to aqueous environments has revealed the composition and kinetics of near surface reorganization for siloxane and fluorocarbon containing polymers. In this study we report results from a ToF-SIMS protocol for cryogenic sample handling applied to the analysis of surface changes upon hydration/dehydration of hydrogel polymers. Comparison of results from angle dependent XPS and ToF-SIMS are discussed for a range of commercial soft contact lens materials. Both methods detected changes in surface chemistry between the hydrated (frozen) and dehydrated surfaces. Analysis of the hydrated surfaces detected polymer components indicative of the commercial formulation as well as ice clusters. Analysis of the dehydrated materials detected changes in surface chemistry relative to the hydrated surface in addition to loss of water due to sample dehydration. A quantitative standard additions method for ToF-SIMS data was used to determine submonolayer amounts of PDMS impurities at the surface of the hydrogels. ToF-SIMS analysis of a series of seven poly (allyl methacrylate-g-dimethylsiloxane), AMA-g-DMS, graft copolymers in the hydrated state revealed high mass oligomeric ion distributions for systems with bulk PDMS content greater than 25 wt.%. This marks the first time that detection of high mass oligomeric ion distributions from hydrated (frozen) surfaces has been reported. Analysis of the dehydrated surface detected formation of high mass oligomeric ion distributions for systems with PDMS bulk content greater than 15 wt.%, but only detected these ion distributions in wet (frozen) samples when the bulk concentration was greater than 25 wt.%.     

Influence of doping of mercury atom(s) on optoelectronic properties of binary cadmium chalcogenides - A density functional theory based investigation with different exchange-correlation functionals and including spin-orbit coupling

Influence of doping of mercury atom(s) on optoelectronic properties of binary cadmium chalcogenides have been investigated theoretically by designing the mercury doped cadmium chalcogenide ternary alloys in B3 phase at some specific Hg-concentrations and studying their optoelectronic properties using DFT based FP-LAPW methodology. The structural properties are computed using WC-GGA, while spin-orbit coupling included electronic and optical properties are computed using TB-mBJ, EV-GGA, B3LYP and WC-GGA exchange-correlation functionals. In addition, electronic properties of mercury chalcogenides are calculated precisely using the GGA+U functionals. The concentration dependence of lattice parameter and bulk modulus of each of the Hg_xCd_1−xS, Hg_xCd_1−xSe, Hg_xCd_1−xTe alloy systems show almost linearity. For each of the alloy systems, band gap decreases almost linearly with increase in Hg-concentration in the unit cell and contribution from charge exchange to the band gap bowing is larger than that from for each of the volume deformation and structural relaxation. Also, covalent bonding exists between different constituent atoms in each compound. Optical properties of each specimen are computed from their spectra of dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity, optical absorption coefficient and energy loss function. Several calculated results have been compared with available experimental and other theoretical data.     

新型高分子蓝色荧光材料的制备及性能

以吡唑啉为发光功能基团,设计并合成了4种新的聚酰胺类高分子化合物,采用核磁共振氢谱(H 1NMR)和凝胶色谱(GPC)对其结构进行了确证。进而测定了高分子化合物的液体及固体荧光激发、发射光谱,高分子J1,J2和J3具有良好的液体及固体荧光发光能力。所制备的高分子材料具有良好的成膜能力、成本低廉、热稳定性好,有望在电致发光器件中广泛应用。     

Formation Mechanism of Laser‐Synthesized Iron–Manganese Alloy Nanoparticles,Manganese Oxide Nanosheets and Nanofibers

Laser ablation in liquids (LAL) has emerged as a versatile approach for the synthesis of alloy particles and oxide nanomaterials. However, complex chemical reactions often take place during synthesis due to inevitable atomization and ionization of the target materials and decomposition/hydrolysis of solvent/solution molecules, making it difficult to understand the particle formation mechanisms. In this paper, a possible route for the formation of FeMn alloy nanoparticles as well as MnO_x nanoparticles, ‐sheets, and ‐fibers by LAL is presented. The observed structural, compositional, and morphological variations are clarified by transmission electron microscopy (TEM). The studies suggest that a reaction between Mn atoms and Fe ions followed by surface oxidation result in nonstoichiometric synthesis of Fe‐rich FeMn@FeMn₂O₄ core–shell alloy particles. Interestingly, a phase transformation from Mn₃O₄ to Mn₂O₃ and finally to Ramsdellite γ‐MnO₂ is accompanied by a morphology change from nanosheets to nanofibers in gradually increasing oxidizing environments. High‐resolution TEM images reveal that the particle‐attachment mechanism dominates the growth of different manganese oxides.     

Room‐temperature terahertz emission from ZnSe‐based quantum cascade structures: A simulation study

We identified conditions for room‐temperature operation of terahertz quantum cascade lasers (THz QCLs) where variable barrier heights are used on ZnSe/Zn_1–xMg_x Se material systems. The THz QCL devices are based on three‐level two‐well design schemes. The THz QCL lasers with alternating quantum barriers with different heights were compared with THz QCL laser structures with fixed quantum barrier heights. It is found that the THz QCL device with novel design employing variable barrier heights achieved the terahertz emission of about 1.45 THz at room‐temperature (300 K), and has improved laser performance due to the suppression of thermally activated carrier leakage via higher‐energy parasitic levels. Thus, THz QCL devices employing the design with variable barrier heights may lead to future improvements of the operating temperature and performance of THz QCL lasers. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Influence of charge distribution on the conformation of neutral polyampholytes

Summary Two polyampholyte copolymers based on sodium-2-acrylamido-2-methylsulfonate (NaAMPS) and methacryloyloxyethyltrimethylammonium chloride (MADQUAT) have been prepared either in homogeneous solution or by an inverse microemulsion polymerization technique. The copolymer microstructure was shown to depend on the method of preparation. The microemulsion polymerization yields copolymers with a monomer sequence distribution not far from random while those obtained by polymerization in solution have a strong tendency to alternation. The aqueous-solution properties of the two samples have been investigated by viscometry. The results show that the charge distribution along the copolymer chain affects considerably its conformation, in good agreement with recent theoretical studies. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994     

Quantum hall effect observations in commercial MOSFETs and effects of thermoelectric power

Summary We have performed quantum Hall effect measurements on commercial low-mobilityn-channel MOSFETs. The channel resistancevs. electron concentration has the expected oscillating behaviour and gives the quantized values for the Hall resistance, at least in the region of higher mobility. One class of the tested samples gave a surprising behaviour, both in QHE and in field effect mobility measurements: this is thought to be due to uncontrolled differences in the diffusion zones at the interface between the channel and the contacts. In particular, we attribute the deformation of the QHE curves to the onset of a thermoelectromotive force which is present in the electron gas even if the sample is isothermal. A clear evidence for thermoelectric effects is given by measurements made on a high-quality Hall geometry MOSFET.

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Riassunto Abbiamo eseguito misure di effetto Hall quantistico su MOSFET commerciali di bassa mobilità a canalen. Le curve di resistenza di canale in funzione della tensione di gate presentano l'atteso andamento oscillante e danno i valori quantizzati, almeno nelle regioni di maggiore mobilità. Una categoria di campioni ha mostrato andamenti sorprendenti, sia in misure di QHE che in misure di mobilità per effetto di campo: riteniamo che ciò sia dovuto a differenze incontrollabili nelle regioni di diffusione alle interfacce tra i contatti e il canale. In particolare, attribuiamo la deformazione delle curve di QHE all'instaurarsi di forze termoelettromotrici, che sono presenti nel gas elettronico nonostante i campioni siano isotermi. Misure eseguite su un MOSFET a geometria Hall di alta qualità forniscono una chiara evidenza dell'esistenza di effetti termoelettrici.

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Резюме Проводятся измерения квантового эффекта Холла на коммерческих MOSFET с малой подвижностью вn-канале. Зависмость сопротивления канала от концентрации электронов обнаруживает осцилляторное поведение и дает квантованные значения сопротивления Холла, по крайней мере, в области высокой подвижности. Один класс исследованных образцов обнаруживает удивительное поведение при измерении квантового эффекта Холла и при измерении зависимости подвижности от поля. Такое поведение, по-видимому, обусловлено неконтролируемыми различиями в зонах диффузии между каналом и контактами. В частности, мы приписываем деформацию кривых квантового эффекта Холла возникновению термоэлектродвижущей силы, которая присутствует в электронном газе, даже в изотермических образцах. Приводятся подтверждения для термоэлектрических эффектов, проводя измерения эффекта Холла в MOSFET с высокой подвижностью.

     

Self-consistent Monte Carlo simulations of the electron and ion distributions of inhomogeneous liquid alkali metals. II. Longitudinal and transverse density distributions in the liquid-vapor interface of binary metallic alloys

We present the results of Monte Carlo simulations of the liquid-vapor interface of sodium-cesium alloys. The longitudinal density profile of each alloy shows that the liquid-vapor interface consists of a well-defined monolayer of cesium sitting on top of a slab of the bulk alloy. Underneath the monolayer there is a slight excess of sodium. A comparison with a van der Waals analog of one of the alloys shows that the presence of the well-defined monolayer of cesium on the outside of the liquid-vapor interface is a feature peculiar to metallic mixtures. The transverse pair correlation functions of the cesium monolayer are insensitive to the composition of the bulk of the slab.     

Characterisation of precipitate phases in magnesium alloys using electron microdiffraction

Recent results of the characterisation of the structure, morphology and orientation of fine-scale, strengthening precipitate phases in selected magnesium alloys using transmission electron microscopy and microdiffraction are reviewed. The strengthening precipitate phases in Mg–Y–Nd alloys, aged to maximum hardness at 250°C, have been found to include two metastable precipitate phases β′ and β₁, and the equilibrium precipitate β. The β′ phase has a globular form, a base-centred orthorhombic structure (potential point group of mmm), and an orientation relationship such that (100)_β′//(1 10)_α, [001]_β′//[0001]_α. The β₁ phase has an f.c.c. structure (space group and an orientation relationship that may be described by (100)_β1//[0001]_α, and forms as plates parallel to The β phase has an f.c.c. structure (space group ) and also forms as plates on with an orientation relationship with the matrix phase that is identical to that observed for β₁ phase. Precipitates in Mg–Al alloys, aged isothermally at 200°C, invariably have the b.c.c. structure of the equilibrium precipitate phase β (Mg₁₇Al₁₂). Three orientation relationships have been observed between β and the matrix phase. Most precipitates have an irrational orientation relationship that approximates to the Burger's relationship, (001)_β//(0001)_α, and a faceted lath morphology with habit plane parallel to (0001)_α. A minor fraction of precipitates posses an orientation relationship that is of the form

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and have a prismatic rod morphology. The long axes of these rods are parallel to [0001]_α, and their faceted surfaces are parallel to A few precipitates are observed to have an orientation relationship such that

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and a rod shape, with their long axes apparently inclined with respect to [0001]_α.