Crystal Channels Research Articles

Thermally excited fluid flow in a microsized liquid crystal channel with a free surface

The temperature-induced reorientation dynamics in microsized liquid crystal (LC) channel with a free LC/vacuum interface has been investigated theoretically based on the hydrodynamic theory including the director motion, the thermally excited fluid flow v, and the temperature T redistribution, produced by induced heating in the interior of the LC sample. Analysis of the numerical results shows that due to interaction between ∇T and the gradient of the director field ∇nˆ in the LC channel bounded by the free LC/vacuum interface, a thermally excited vortical fluid flow is maintained in the vicinity of the heat source. Calculations also show that in the case of the fast heating, the LC sample settles down to three-vortical flow regime, whereas in the case of the slow heating, the LC material settles down to bi-vortical flow regime. As for nematogenic material, we have considered the LC channel to be occupied by 4-n-pentyl-4′-cyanobiphenyl and investigated the effect of both ∇nˆ and ∇T on the magnitude and direction of v, as well as on the height of the LC film on the solid surface, for a number of heating and hydrodynamic regimes.

Purification of proteins from solutions containing residual host cell proteins via preparative crystallization.

To investigate quantitatively and reproducibly a scalable, preparative crystallization method in novel stirred tanks using three different protein solutions containing residual microbial host cell proteins (HCP). Lysozyme from solutions being spiked with up to 15% host cell proteins (HCP) (corresponding to 176,500 ppm) was crystallized within a 2.4-4.6 h at 93.7% yield using NaCl and glycerol. Lipase was crystallized under comparable conditions using NaCl and a mixture of two polyethylene glycols (PEG). Enhanced green fluorescent protein (eGFP) was overexpressed in E. coli yielding a solution containing 23% target protein. Residual HCP content after pre-treatment was 7-16%. eGFP was crystallized from these solutions within 1.75-4 h at 88.7% step yield using ethanol and the same mixture of two PEG as in the case of lipase. HCP contained in the solvent channels of the protein crystals could be removed by diffusive washing yielding final purities at or above 99%. Preparative crystallization can be carried out with fast kinetics and high yields from solutions containing residual impurities and may represent an attractive alternative purification method compared to preparative chromatography, especially at large production scales.

Synthesis and confinement of carbon dots in lysozyme single crystals produces ordered hybrid materials with tuneable luminescence.

The synthesis and confinement of graphitic nanoparticles (carbon dots) in the nanoscale solvent channels of cross-linked lysozyme single crystals is used to prepare novel biohybrid luminescent materials. Co-sequestration of acridine orange within the biohybrid crystals from acidic or neutral solutions yields FRET-mediated phosphors emitting white or green light, respectively. The results offer a route to new types of tuneable multicolour luminescent materials based on microcrystalline host-guest energy-transfer systems.

Benchmark of the FLUKA model of crystal channeling against the UA9-H8 experiment

Channeling in bent crystals is increasingly considered as an option for the collimation of high-energy particle beams. The installation of crystals in the LHC has taken place during this past year and aims at demonstrating the feasibility of crystal collimation and a possible cleaning efficiency improvement. The performance of CERN collimation insertions is evaluated with the Monte Carlo code FLUKA, which is capable to simulate energy deposition in collimators as well as beam loss monitor signals. A new model of crystal channeling was developed specifically so that similar simulations can be conducted in the case of crystal-assisted collimation. In this paper, most recent results of this model are brought forward in the framework of a joint activity inside the UA9 collaboration to benchmark the different simulation tools available. The performance of crystal STF 45, produced at INFN Ferrara, was measured at the H8 beamline at CERN in 2010 and serves as the basis to the comparison. Distributions of deflected particles are shown to be in very good agreement with experimental data. Calculated dechanneling lengths and crystal performance in the transition region between amorphous regime and volume reflection are also close to the measured ones.

TeV/m nano-accelerator: Investigation on feasibility of CNT-channeling acceleration at Fermilab

The development of high gradient acceleration and tight phase-space control of high power beams is a key element for future lepton and hadron colliders since the increasing demands for higher energy and luminosity significantly raise costs of modern HEP facilities. Atomic channels in crystals are known to consist of 10–100V/Å potential barriers capable of guiding and collimating a high energy beam providing continuously focused acceleration with exceptionally high gradients (TeV/m). However, channels in natural crystals are only angstrom-size and physically vulnerable to high energy interactions, which has prevented crystals from being applied to high power accelerators. Carbon-based nano-crystals such as carbon-nanotubes (CNTs) and graphenes have a large degree of dimensional flexibility and thermo-mechanical strength, which could be suitable for channeling acceleration of MW beams. Nano-channels of the synthetic crystals can accept a few orders of magnitude larger phase-space volume of channeled particles with much higher thermal tolerance than natural crystals. This paper presents the current status of CNT-channeling acceleration research at the Advanced Superconducting Test Accelerator (ASTA) in Fermilab.

Angular distributions of relativistic electrons under channeling in half-wavelength crystal and corresponding radiation

New experiments on channeling of 255MeV electrons in a half-wavelength crystals (HWC) were performed at SAGA Light Source facilities. The simulations of trajectories for (220) and (111) planar channeling in Si were performed using the computer code BCM-1.0. Comparison of experimental and theoretical results shows a good agreement. The results of calculations of spectral distribution of radiation in forward direction (θ=0°) from 255MeV electrons at (220) channeling in HWC silicon are presented. Qualitative comparison with radiation spectrum from an electron moving in an arc is performed.

Raman spectroscopy of bromine chains inside the one-dimensional channels of AlPO4-5 single crystals

Raman spectroscopy of the one-dimensional atomic or molecular chains, which are the attractive building blocks of advanced nanoscale materials, is crucial in understanding the physical properties of the one-dimensional atomic or molecular chains. Here, we introduce the bromine into the one-dimensional channels of AlPO4-5 single crystals through a physical vapor diffusion method. Raman spectroscopy indicates that the confined bromine structures mainly exist as (Br2)n chains, individual Br2 molecules, and a small amount of Br3− chains inside the channels of AlPO4-5 single crystals. Polarized Raman spectra demonstrate that the bromine molecular chains are approximately parallel to the channel direction of AlPO4-5 single crystals. Copyright © 2015 John Wiley & Sons, Ltd.

光子晶体信道分路滤波器特性的研究

光子晶体信道分路滤波器特性的研究

Analysis of trap distribution in polysilicon channel transistors using the variable amplitude charge pumping method

The trap distribution of a polysilicon (poly-Si) channel in a metal–oxide–semiconductor field effect transistor (MOSFET) was extracted successfully using a variable amplitude charge pumping method (VACP) and an energy band bending model. Compared to single crystal Si channels, the poly-Si channels exhibited a high density of bulk channel traps due to the presence of grain boundaries. The densities of the trap states existing in the poly-silicon channel with various grain sizes and channel thicknesses were extracted and compared. The grain size of poly-Si was found to have a stronger impact on the trap distribution than the channel thickness. After hot carrier stress, the trap density in the poly-silicon channel increases and the generated traps are located both at mid gap energy level and near the conduction band energy level.

MAP_CHANNELS: a computation tool to aid in the visualization and characterization of solvent channels in macromolecular crystals.

A computation tool is described that facilitates visualization and characterization of solvent channels or pores within macromolecular crystals. A scalar field mapping the shortest distance to protein surfaces is calculated on a grid covering the unit cell and is written as a map file. The map provides a multiscale representation of the solvent channels, which when viewed in standard macromolecular crystallographic software packages gives an intuitive sense of the solvent channel architecture. The map is analysed to yield descriptors of the topology and the morphology of the solvent channels, including bottleneck radii, tortuosity, width variation and anisotropy.

Single-channel Q-switching in a system of coherently combined fiber lasers

We experimentally investigate passive interferometric coherent combining of two photonic crystal fiber laser channels within a common cavity, wherein only one channel is Q-switched. We demonstrate an average power of more than 20 W and the peak power of 97 kW with more than 98 % combining efficiency. The measured spectral bandwidth is 0.13 nm, and it does not change at different operation conditions. Our results show efficient imposing of temporal and spectral characteristics of the Q-switched channel on the free-running channel.

Strong anisotropic dynamics of ultra-confined water.

Dynamics of water confined in ∼5 Å diameter channels of beryl and cordierite single crystals were studied by using inelastic (INS) and quasielastic (QENS) neutron scattering. The INS spectra for both samples were similar and showed that there are no hydrogen bonds acting on water molecule, which experiences strong anisotropic potential, steep along the channels and very soft perpendicular to it. The high-resolution (3.4 μeV) QENS data revealed gradual freezing out of the water molecule dynamics for both minerals at temperatures below about 80 K when the scattering momentum transfer was parallel to the channels, but not when it was perpendicular to the channels. The QENS study with medium energy resolution (0.25 meV) of the beryl with the scattering momentum transfer along the channels showed gradual freezing out of water molecule dynamics at temperatures below about 200 K, whereas at higher temperatures the data could be described as 2-fold rotational jumps about the axis coinciding with the direction of the dipole moment (that is, perpendicular to the channels), with a residence time of 5.5 ps at 225 K. The energy resolution dependence of the apparent dynamics freezing temperature suggests gradual slowing down of the rotational jumps as the temperature is decreased, until the associated QENS broadening can no longer be detected, rather than actual freezing.

Photonic crystal channel drop filters based on fractal structures

In this paper we introduce new configurations of channel drop filters based on two-dimensional photonic crystals. Structures consist of two photonic crystal waveguides and a fractal-shaped resonator between them. The effect of structural parameters on resonance frequency and drop efficiency is investigated. Calculations of band structure and propagation of electromagnetic field through devices are done by plane wave expansion (PWE) and finite difference time domain (FDTD) methods, respectively. In our designs more than 95% drop efficiency with quality factor of ~1150 is achievable at wavelength near 1540nm, which in comparison with other photonic crystal resonator structures is a very satisfactory and acceptable result.

Crystal devices for beam steering in the IHEP accelerator

Different crystal devices are described, which provide an extraction and splitting of beams for a long period of time at the U-70 accelerator of IHEP. The modes of channeling and volume reflections in the bent crystals are used for these tasks. In regular accelerator runs crystals produce the particle beams in a wide range of intensity, from 106 up to 1012 particles in a cycle. Novel crystal techniques suitable for charged particle beams deflection and focus as well as photon generation are presented also.

DNA crystals as vehicles for biocatalysis.

Here we demonstrate that protein enzymes captured in the solvent channels of three-dimensional DNA crystals are catalytically active. Using RNase A as a model enzyme system, we show that crystals infused with enzyme can cleave a dinucleotide substrate with similar kinetic restrictions as other immobilized enzyme systems. This new vehicle for immobilized enzymes, created entirely from biomolecules, opens possibilities for developing modular solid-state catalysts that could be both biocompatible and biodegradable.

Simulation of radiation energy losses by channeled relativistic electrons in a crystal

A computer code is developed to calculate the radiation energy losses (RELs) of electrons during both 〈100〉 axis and (100) plane channeling in a thin Si crystal. A computer simulation of these losses is carried out by taking the initial angular divergence of the beam into account, and the REL dependences on the angle of electron entry into the crystal are obtained for both axial and planar channeling (orientational dependences). The calculations are carried out in connection with experiments on the interaction of 20–255 MeV electrons with crystals conducted at the SAGA Light Source linear accelerator (Tosu, Saga, Japan). The simulation results show the possibility of using the orientational dependence of the RELs of channeled electrons in thin crystals to diagnose the initial angular divergence of the electron beam and to orient crystals.

Multiterawatt femtosecond laser system with kilohertz pulse repetition rate

The basic principles, layout and components are presented for a multiterawatt femtosecond laser system with a kilohertz pulse repetition rate , based on their parametric amplification and laser amplification of picosecond radiation that pumps the stages of the parametric amplifier. The results of calculations for a step-by-step increase in the output power from the LBO crystal parametric amplifier channel up to the multiterawatt level are presented. By using the developed components in the pump channel of the laser system, the parameters of the regenerative amplifier with the output energy at the wavelength and with are experimentally studied. The optical scheme of the diode-pumped multipass cryogenic laser ceramic amplifier is developed and its characteristics are determined that provide the output energy within the range .

Steering of a sub-GeV electron beam through planar channeling enhanced by rechanneling.

We report the observation of efficient steering of a 855MeV electron beam at MAMI (MAinzer MIkrotron) facilities by means of planar channeling and volume reflection in a bent silicon crystal. A 30.5 μm thick plate of (211) oriented Si was bent to cause quasimosaic deformation of the (111) crystallographic planes, which were used for coherent interaction with the electron beam. The experimental results are analogous to those recorded some years ago at energy higher than 100GeV, which is the only comparable study to date. MonteCarlo simulations demonstrated that rechanneling plays a considerable role in a particle's dynamics and hinders the spoiling of channeled particles. These results allow a better understanding of the dynamics of electrons subject to coherent interactions in a bent silicon crystal in the sub-GeV energy range, which is relevant for realization of innovative x-ray sources based on channeling in periodically bent crystals.

Comparison of the efficiency of the deflection of proton beams with various energies by a bent crystal with the use of planar channeling and the stochastic deflection mechanism

The efficiency of the deflection of 50-, 15-, and 1.3-GeV proton beams by means of planar channeling in a bent silicon crystal has been compared to that by means of the stochastic mechanism of the deflection of charged particles by the bent crystal. The deflection of protons at single passage through the crystal has been simulated. The results of the experiment on the deflection of a circulating beam at the U-70 accelerator (Institute for High Energy Physics, Protvino, Moscow region) are presented. It has been shown that the efficiency of the stochastic deflection mechanism increases with a decrease in the energy, whereas the efficiency of the planar channeling for deflection decreases.

Studies of relativistic electron scattering at planar alignment in a thin Si crystal

Abstract Experiments on 255-MeV electron scattering under (220) planar channeling conditions in a Si crystal were carried out at the linac of the SAGA Light Source. The spatial and angular distributions of electrons penetrating through a 20-μm thick Si crystal at different incident angles with respect to the (220) plane were measured, and features characteristic of the planar alignment were identified. The experimental results were compared with computer simulations, and showed a reasonable agreement. A comparison with doughnut scattering at axial channeling in the same crystal was also performed. It was confirmed that the planar alignment effect is weaker than the axial alignment effect. These studies are important for understanding the basic mechanism of electron scattering and radiation processes in a crystal.