Influence of low concentration silver nanoparticles on the electrical and electro-optical parameters of nematic liquid crystals

Thermodynamical, optical, dielectric and electro-optical characterisation of nematic liquid crystals (LCs) and silver nanoparticle (NP) composites have been carried out. Transition temperatures of pure and composites systems have been measured. Thermodynamical studies suggest increase of clearing temperature of the composite material as compared to the pure material. Threshold voltage for switching from bright to dark state and splay elastic constant of the pure and composite materials have been determined. From frequency dependence of dielectric measurements, permittivity, loss, relaxation frequency and dielectric strength of flip-flop mechanism of LC molecules in the nematic phase have been calculated. Dielectric properties of composites have been explained in reference of Maier and Meier theory. The effects of doping of NPs on dielectric and electro-optic properties of LC-NP composites have been discussed.     

The growth of giant pumpkins: How extreme weight influences shape

Great morphological differences exist among fruits and vegetables. In this combined experimental and theoretical study, we predict pumpkin shape evolution and maximum size based on their material properties. Using time-lapse photography and measurements collected by volunteer farmers, we show that as pumpkins grow, they morph from spherical to pancake shapes, flattening up to 50% in height-to-width aspect ratio. By compressing whole pumpkins in material-testing machines, we find that the elastic response of the pumpkin is insufficient to account for the large deformations characteristic of large pumpkins. We hypothesize that pumpkin flattening is caused by the weight of the pumpkin retarding its normal growth processes. We test this hypothesis using a mathematical model that assumes plant growth is stimulated in response to a tensile yield stress. We are able to predict pumpkin shapes consistent with those observed. The observed growth plasticity allows the fruit to redistribute internal stresses, thereby growing to extreme sizes without breaking.     

Tailoring and patterning of dielectric interfaces for the development of advanced organic field-effect transistors

The progress of organic field-effect transistors (OFETs) has led to the advent of a new area of printed and/or flexible electronics. In organic transistors and circuits, the interface between a gate insulator (GI) and an organic semiconductor (OS) plays a critical role on the electrical performance together with the functionality, the reliability and the long-term stability. In this review, we describe the basic principles of engineering a variety of the GI/OS interfaces for the development of advanced OFETs from the framework of the surface morphology and the physico-chemical surface interactions. We also discuss the dielectric interface modification and the resultant device performance of the OFETs.     

The influence of dielectric layer on the thermal boundary resistance of GaN-on-diamond substrate

The cooling behavior of GaN-on-diamond substrate can be enhanced by reducing the thermal boundary resistance (TBR), which is mainly determined by the nature of interlayer. Although SiN film is considered as the primary candidate of dielectric layer, it is still needed to be optimized. In order to facilitate the understanding of the influence of dielectric layer on the TBR of GaN-on-Diamond substrate, aluminum nitride (AlN), and silicon nitride (SiN) film were compared systematically, both of which are 100 nm. The time-domain thermoreflectance (TDTR) measurements, adhesion evaluation, and microstructural analysis methods were adopted to analyse these two interlayers. The results show the TBR of SiN interlayer is as low as 38.5 ± 2.4 m²K GW⁻¹, comparing with the value of 56.4 ± 5.5 m²K GW⁻¹ for AlN interlayer. The difference of TBR between these two interlayers is elucidated by the diamond nucleation density, and the adhesion between the diamond film and GaN substrate, both of which are affected by the surface charge and chemical groups of the dielectric layer.     

An Introduction to the Solid State Polymerization of Transition-metal Complexes: A Comparative Study

Preliminary studies in this laboratory^' of topochemical and topotactic polyreactions of NiBr₂[P(CH₂CH₂CN)₃]₂ have shown that the reactions are in many cases characterized by a) product specificity, b) stereospecificity, c) “crystallographic specificity” and d) highly anisotropic “front motion” through individual single crystals. The polymerization reaction under investigation here is     

The influence of defects in the pb and o sub-lattices on dielectric properties and phase transitions in PbZrO3

From studies of the influence of controlled introduction of defects into the Pb and O sub-lattices of PbZrO₃ it was ascertained that marked changes are caused in the dielectric parameters and the transitions between the antiferroelectric and ferroelectric states and the ferroelectric and paraeiectric states. With increasing amount of defects the temperature range in which the ferroelectric state occurs is narrowed during the heating process and widened during the cooling process. An attempt has been made to explain the observed effects within the context of existing theoretical models.     

Influence of damping on the excitation of the double giant resonance

We study the effect of the spreading widths on the excitation probabilities of the double giant dipole resonance. We solve the coupled-channels equations for the excitation of the giant dipole resonance and the double giant dipole resonance. Taking Pb+Pb collisions as example, we study the resulting effect on the excitation amplitudes, and cross sections as a function of the width of the states and of the bombarding energy. Received: 13 July 1999     

Electromagnetic interactions at RHIC and LHC

At LHC energies, the Lorentz factor will be 3400 for Pb+Pb collisions, and the electromagnetic interactions will play important roles. The cross sections for the electromagnetic particle productions are very large and cannot be ignored for the lifetimes of the beams and background. In this article, we are going to study some of the electromagnetic processes at the RHIC and the LHC and show the cross section calculations of the electron-positron pair production with the giant dipole resonance of the ions.     

Optical spectra and electron structure of cubic boron nitride

On the basis of the known reflection spectrum, we calculate a complete set of fundamental optical functions for cubic boron nitride (c-BN) in the region of 2–23 eV. The integral spectrum of dielectric permeability is decomposed into 16 elementary components. Three main parameters (maximum energy, half-width, and oscillator force) for each of the components are determined. Using the well-known theoretical calculations for bands of boron nitride as the base we suggest a scheme of the nature of these dielectric permeability components. To whom correspondence should be addressed. Udmurtiya State University, 1, Universitetskaya Str., Izhevsk, 426034, Russia:e-mail: sobolev@matsim.udmurtia.su. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 579–583, July–August, 1999.     

Preparation of ureido group bearing polymers and their upper critical solution temperature in water

Poly(2‐ureidoethylmethacrylate) (PUEM_n) was synthesized via reversible addition‐fragmentation chain transfer (RAFT) radical polymerization and following polymer reaction. We prepared two PUEM_n samples with different degrees of polymerization (n = 100 and 49). The polymers exhibited upper critical solution temperature (UCST) in phosphate‐buffered saline (PBS) solution. The phase separation temperature (T_p) in PBS can be controlled ranging from 17 to 55 °C by changing molecular weight of the polymer, polymer concentration, and adding NaCl concentration. The polymers in PBS formed coacervate drops by liquid–liquid phase separations below T_p. Results of the dielectric relaxation measurement, the hydration number per monomeric unit was 5 above T_p. Based on a fluorescence study, the polymer formed slightly hydrophobic environments below T_p. The liquid–liquid phase separation was occurred presumably because of weak hydrophobic interactions and intermolecularly hydrogen bonding interactions between the pendant ureido groups. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2845–2854