Structure of nanoscale-pitch helical phases: blue phase and twist-bend nematic phase resolved by resonant soft X-ray scattering

Periodic structures of phases with orientational order of molecules, but homogenous electron density distribution: a short pitch cholesteric, blue phase and twist-bend nematic phase, were probed by a resonant soft x-ray scattering (RSoXS) at the carbon K-edge. The theoretical model shows that in case of a simple heliconical nematic structure two resonant signals corresponding to the full and half pitch band should be present, while only the full pitch band is observed in experiment. This suggests that the twist-bend nematic phase has complex structure with a double-helix, built of two interlocked, shifted helices. We confirm that the helical pitch in the twist-bend nematic phase is in a 10 nm range, for both, the chiral and achiral materials. We also show that the symmetry of a blue phase can unambiguously be determined through a resonant enhancement of x-ray diffraction signals, by including polarization effects, which are found to be an important indicator in phase structure determination

Backbone-free duplex-stacked monomer nucleic acids exhibiting Watson-Crick selectivity.

We demonstrate that nucleic acid (NA) mononucleotide triphosphates (dNTPs and rNTPs), at sufficiently high concentration and low temperature in aqueous solution, can exhibit a phase transition in which chromonic columnar liquid crystal ordering spontaneously appears. Remarkably, this polymer-free state exhibits, in a self-assembly of NA monomers, the key structural elements of biological nucleic acids, including: long-ranged duplex stacking of base pairs, complementarity-dependent partitioning of molecules, and Watson-Crick selectivity, such that, among all solutions of adenosine, cytosine, guanine, and thymine NTPs and their binary mixtures, duplex columnar ordering is most stable in the A-T and C-G combinations

Design of the full hydraulic driving high frame field operation vehicle

In China, field management mechanization of corn, tobacco and sugarcane with high stalks is an important technical problem in agricultural mechanization development.  According to the characteristics of high stalk crops planted in different row spacing in the plain area of Henan province, this paper designed a full hydraulic driving field high frame operation vehicle, included power system, engine placement and M type three-wheeled high frame structure.  It also adopted a closed hydraulic system fully driven by three hydraulic motors, hydraulic power steering system and hydraulic track adjustment system.  Its maximum clearance height is 1,800 mm. Speed ranges from 0-17 km/h with the hydraulic control.  The back wheel track adjustment ranges from 2,000-2,400 mm.  It can solve the problems of the high cost price in complex transmission system of the most domestic off highroad vehicles that the track cannot be changed.  In this paper, a field high frame operation vehicle for the high stalk crop in field management operation has been provided.Keywords: high stalk crop, full hydraulic driving, three-wheeled, high traffic ability, field operation vehicl

Effect of crystallization of the polyhedral oligomeric silsesquioxane block on self-assembly in hybrid organic-inorganic block copolymers with salt

[EN] We present a DSC and X-ray scattering study investigating the effect of polyhedral oligomeric silsesquioxane (POSS) block crystallinity on the self-assembly of a poly(acryloisobutyl polyhedral oligomeric silsesquioxane)- b -poly(ethylene oxide)- b -poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (POSS-PEO-POSS) triblock copolymer and poly(ethylene oxide)- b - poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (PEO-POSS) diblock copolymers mixed with lithium bis(trifluoromethanesulfonyl)imide salt. The POSS block in all copolymer/salt mixture organizes into a rhombohedral crystal, similar to that of the POSS homopolymer. Semicrystalline polymer/salt mixtures favor morphologies with flat interfaces ( i.e ., lamellae) despite the asymmetric nature of the copolymers; PEO/salt volume fractions range from 0 to 0.85. Coexisting lamellae and hexagonally packed cylinders as well as coexisting lamellae with different domain spacings are seen in many copolymer/salt mixtures wherein the POSS block is amorphous. Morphological phase transitions in these systems are seen in the vicinity of the POSS crystallization temperature.This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract DE-AC02- 05CH11231 under the Battery Materials Research Program. X-ray work performed at Advanced Light Source, which is a DOE Office of Science User Facility, was supported by Contract No. DE-AC02- 05CH11231 . X-ray work performed at the Stanford Synchrotron Radiation Light Source, a user facility at SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy , Office of Science, Office of Basic Energy Sciences under Contract No. DE- AC02-76SF00515 . Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE- AC02-05CH11231 . G.K.S. acknowledges funding from a National Science Foundation Graduate Student Research Fellowship

Reversible Interlayer Sliding and Conductivity Changes in Adaptive Tetrathiafulvalene-Based Covalent Organic Frameworks.

Ordered interlayer stacking is intrinsic in two-dimensional covalent organic frameworks (2D COFs) and has strong implications on COF's optoelectronic properties. Reversible interlayer sliding, corresponding to shearing of 2D layers along their basal plane, is an appealing dynamic control of both structures and properties, yet it remains unexplored in the 2D COF field. Herein, we demonstrate that the reversible interlayer sliding can be realized in an imine-linked tetrathiafulvalene (TTF)-based COF TTF-DMTA. The solvent treatment induces crystalline phase changes between the proposed staircase-like sql net structure and a slightly slipped eclipsed sql net structure. The solvation-induced crystallinity changes correlate well with reversible spectroscopic and electrical conductivity changes as demonstrated in oriented COF thin films. In contrast, no reversible switching is observed in a related TTF-TA COF, which differs from TTF-DMTA in terms of the absence of methoxy groups on the phenylene linkers. This work represents the first 2D COF example of which eclipsed and staircase-like aggregated states are interchangeably accessed via interlayer sliding, an uncharted structural feature that may enable applications such as chemiresistive sensors

Dietary phytochemicals: As a potential natural source for treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a common neurodegenerative disease, which seriously impairs human health and life. At present, scientists have proposed more than a dozen hypotheses about the pathogenesis of AD, including the tau propagation hypothesis. However, the exact ultimate pathogenic factor of AD remains unknown. Based on the current hypotheses, some anti-AD drugs (e.g., donepezil and Ketamine) have been developed and used in clinical treatment, which fall into two main categories, acetylcholinesterase inhibitors (AChEIs) and N-methyl-D-aspartate (NMDA) receptor antagonists, the former representative drug is donepezil, and the latter representative drug is memantine. Since these drugs have undesirable side effects, it is necessary to find safer alternatives for AD treatment. Interestingly, dietary phytochemicals have the advantages of wide source, safety, and high biological activity, which is the natural route for screening anti-AD drugs. In this study, several representatives’ dietary phytochemicals with anti-AD effect, including resveratrol, lycopene, gallic acid, berberine, ginsenoside Rg1, pseudoginsenoside-F11, ginsenoside Rh2, artemisinin, and torularhodin were selected from the published data over the last 10 years and their potential molecular mechanisms and clinical applications reviewed in the treatment of AD

The interplay between spatial and heliconical orientational order in twist-bend nematic materials

The helical pitch formed by organic molecules, such as the α-helix of proteins, usually requires hydrogen bonding between chiral units and long-range positional order. It was recently found that certain liquid crystal oligomers can have a twist-bend nematic (NTB) phase with nanoscale heliconical structure without hydrogen bonding, molecular chirality or positional order. To understand the nature of this unique structure, here we present hard and resonant tender X-ray scattering studies of two novel sulfur containing dimer materials. We simultaneously measure the temperature dependences of the helical pitch and the correlation length of both the helical and positional order. In addition to an unexpected strong variation of the pitch with the length of the spacer connecting the monomer units, we find that at the transition to the NTBphase the positional correlation length drops. The helical structure was found not only in the NTBphase but observed even in the upper range of a smectic phase that forms just below the NTBstate. The coexistence of smectic layering and the heliconical order indicates a layered (SmATB) phase wherein the rigid units of the dimers are tilted with respect to the smectic layer normal in order to accommodate the bent conformation of the dimers and the tilt direction rotates along the heliconical axis