Theory of the helical spin crystal: a candidate for the partially ordered state of MnSi

MnSi is an itinerant magnet which at low temperatures develops a helical spin-density wave. Under pressure it undergoes a transition into an unusual partially ordered state whose nature is debated. Here we propose that the helical spin crystal (the magnetic analog of a solid) is a useful starting point to understand partial order in MnSi. We consider different helical spin crystals and determine conditions under which they may be energetically favored. The most promising candidate has bcc structure and is reminiscent of the blue phase of liquid crystals in that it has line nodes of magnetization protected by symmetry. We introduce a Landau theory to study the properties of these states, in particular, the effect of crystal anisotropy, magnetic field, and disorder. These results compare favorably with existing data on MnSi from neutron scattering and magnetic field studies. Future experiments to test this scenario are also proposed.     

Spin-charge separated solitons in a topological band insulator

In this Letter we construct a simple, controllable, two-dimensional model based on a topological band insulator. It has many attractive properties. (1) We obtain spin-charge separated solitons that are associated with dynamic pi fluxes. (2) These solitons obey Bose statistics and their condensation triggers a phase transition from a spin Hall insulator to an easy-plane ferromagnet. (3) It suggests an alternative way to classify the Z2 topological band insulator without resorting to the sample boundary.     

Ultrasound assisted synthesis of isopropyl esters from palm fatty acid distillate

Esterification is one of the most preferred synthesis routes for organic esters which are most frequently used as plasticizers, solvents and perfumery and flavour chemicals. The present work deals with acid catalyzed synthesis of isopropyl esters from palm fatty acid distillate (PFAD) in the presence of ultrasonic irradiations operating at 25kHz frequency and 1kW of supplied power. Effect of different operating parameters such as molar ratio of reactants, catalyst quantity and operating temperature has been studied with an aim of optimization. It has been observed that ultrasound enhances the rate of reaction and the extent of equilibrium conversion. The optimum parameters for this process have been found to be 1:5 molar ratio of PFAD to isopropanol, catalyst concentration of 5% of PFAD and 60 degrees C reaction temperature. Maximum conversion levels of about 80% have been obtained in 6h of reaction time under these optimized conditions. Analysis of the kinetic data indicates that the reaction follows first order reversible path.     

Inertia effects in circular squeeze film bearing using Herschel–Bulkley lubricants

Recent engineering trends in lubrication emphasize that in order to analyze the performance of bearings adequately, it is necessary to take into account the combined effects of fluid inertia forces and non-Newtonian characteristics of lubricants. In the present work, the effects of fluid inertia forces in the circular squeeze film bearing lubricated with Herschel–Bulkley fluids with constant squeeze motion have been investigated. Herschel–Bulkley fluids are characterized by an yield value which leads to the formation of a rigid core in the flow region. The shape and extent of the core formation along the radial direction is determined numerically for various values of Herschel–Bulkley number and power-law index. The bearing performances such as pressure distribution and load capacity for different values of Herschel–Bulkley number, Reynolds number, power-law index have been computed. The effects of fluid inertia and non-Newtonian characteristics on the bearing performances have been discussed.     

Dibutyltin oxide catalyzed aminolysis of oxalate to carbamate,oxamate and derivatives of imidazolidine trione

Catalytic aminolysis of oxalates by simple and substituted ureas has been shown to give carbamates, oxamates and derivatives of imidazolidine trione. Various substituted ureas and oxalates were screened to verify the applicability of the protocol. The role of dibutyltin oxide as catalyst, effect of solvent and reaction conditions on product distribution pattern has been discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Cosmic ray results on the A dependence of multiplicity and angular distributions in proton nuclear interactions above 100 GeV

A calorimeter-spark chamber system was used to collect data on several hundred proton-nucleus interactions above 100 GeV using targets of C, Al, Fe, Sn and Pb. The average charged prong multiplicity is found to depend on atomic mass number as 〈n_c〉 = 〈n_c〉(p-p)A^x where x = 0.129 ± 0.004, with the dominant increase in multiplicity occuring in the backward (p-p c.m.) hemisphere. The value of x shows no significant energy dependence.     

Electrochemical preparation of crystalline γ-CuI thin films through potential-controlled anodization of copper and its photoelectrochemical investigations

Journal of Solid State Electrochemistry - Copper iodide (CuI) thin film has been fabricated by controlled potential anodization of copper (Cu) in the potassium iodide (KI) electrolyte. Thin film...     

Nematic order by disorder in spin-2 Bose-Einstein condensates

We show that quantum and thermal fluctuations in spin-2 Bose-Einstein condensates lift the accidental degeneracy of the mean-field phase diagram. Fluctuations select the uniaxial (square biaxial) nematic state for scattering lengths a4>a2 (a4相似文献   

Effect of electron beam irradiation on physico-chemical properties of pullulan

Many widely used polymers undergo main chain scission or crosslinking when exposed to radiation. Effects of electron beam irradiation at different doses up to 500?kGy on the biodegradable pullulan polymer films have been investigated by ultraviolet?Cvisible (UV?CVIS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) techniques. UV?CVisible study shows increase of optical absorbance with increase of doses, attributing to the formation some groups or radicals. FTIR and TGA results reveal the processes of both crosslinking and degradation of polymer taking place depending upon the dose of e-beam radiation. The surface morphology of the film is found to be altered by the e-beam radiation as indicated by SEM micrographs.