Helical Period Research Articles

Endocytosis behaviours of nanoparticles with helically decorated ligands

AbstractIn this work, the receptor‐mediated endocytosis of nanoparticles with helically decorated ligands was investigated by performing coarse‐grained molecular dynamics simulations. The results showed that a helical distribution of ligands can generate a unique spinning stage during endocytosis in which the nanoparticle is internalized with precession. This precession behaviour is primarily caused by a lateral torque acting on the nanoparticle. Compared with nanoparticles that present uniformly distributed ligands, nanoparticles with helically decorated ligands present an enhanced endocytosis capacity. Additionally, a longer spin duration and larger precessional angle were obtained by decreasing the helical period of the ligands. Increasing the aspect ratio of the nanoparticles strengthens their capacity to take the spinning endocytosis pathway. The present study not only reveals the mechanism underlying a new endocytosis pathway of nanoparticles with helically structured surfaces but also provides valuable theoretical information for the design of novel drug delivery systems that primarily occur via cellular uptake. © 2019 Society of Chemical Industry

Sensing Characterization of Helical Long Period Fiber Grating Fabricated by a Double-Side CO2 Laser in Single-Mode Fiber

A simple and efficient manufacture method of helical long period fiber grating (HLPFG) in a single-mode fiber (SMF) is designed and verified through experiment. Different from the previous fabricating methods, the SMF is heated by a double-side CO 2 laser beam after being twisted. There are multiple transmission depletions caused by model coupling which could be observed when the period length is 500 μm. The sensing characteristics of the HLPFG have been investigated. Experimental results demonstrate axial strain sensitivities of 3.3 and 6.4 pm/μe at the selected dips in the range of 0-450 μe or temperature sensitivities of 35.3 and 49.5 pm/°C at the selected dips in the range of 20-70 °C, respectively. Moreover, through theoretical analysis, it is found that the fabricated HLPFG can measure axial strain and temperature concurrently by monitoring the resonance wavelength shift. Therefore, the fabricated HLPFG has brilliant applications value in dual measurement.

A new ultra long-period fiber grating for measuring torsional characteristics

ABSTRACTIn this paper, we proposed a novel kind of periodic helical ultra-long period fiber grating (U-LPFG) for measuring the torsion rate and distinguishing the torsion direction. The sensor was fabricated by spirally deforming a common fiber by local heating for 4 periods. This method of fabrication was not only easy to implement, but also further increased the sensitivity of the grating to the torsion because of the spiral structure. This paper introduced the torsional characteristics of this sensor in detail and drew some relevant conclusions. Experimental results showed that the twist sensitivity of 0.085 nm/(rad/m). Meanwhile, the temperature sensing characteristic of the proposed U-LPFG was also tested as 68 pm/°C within the range of 30 °C ∼210 °C. Therefore, this proposed sensor could achieve good results in simultaneously measuring the torsion rate and distinguishing the torsion direction, and it may have great potential in some practical applications.

Fiber-optic sensor implanted with seven-core helical structure for measurement of tensile strain and extrusion bending

We proposed a fiber-optic sensor implanted with helical seven-core structure based on Mach–Zehnder interference, which can be used for the measurement of tensile strain and extrusion bending. The sensor consisted of a section of seven-core optical fiber with helical structure, which can be described as the SMF-Taper-HSCF-Taper-SMF (HSCF, helical seven-core fiber) sensor. When stretching or bending is applied, the sensor will undergo certain deformation, which will lead to the changes of interference modes in the optical fiber. The tensile strain and extrusion bending can be measured accurately according to the response of transmission spectrum to mode change. The helical seven-core structure can effectively stimulate higher order modes and induced deformation changes. In the experiment, three sensors with different helical periods were fabricated and their spectral characteristics were analyzed. Finally, we selected the sensor with a helical period of 190 μm to conduct a strain and bending test. The results show that the strain sensitivity of the sensor is −21.31 pm / μe in the range of 0 to 500 μe, and the curvature sensitivity of the sensor is −6.36 nm / m − 1 in the range of 0.16 to 1.6 m − 1. This sensor can detect strain and bending and has stable sensing performance and high sensitivity.

Residual-stress-induced helical long period fiber gratings for sensing applications.

We demonstrate a high-efficiency grating fabrication system, which can be used to inscribe a high-quality helical long period fiber grating (HLPFG) on single-mode fiber by means of hydrogen-oxygen flame. Such the HLPFG can be produced in enormous quantities with a uniform grating parameters and good reproducibility of grating inscription. Possible mechanisms for refractive index modulation in the HLPFG can be attributed to residual stress concentration by solidifying the periodic twisting stress under a fused status of optical fiber. Moreover, the HLPFG exhibits an excellence performance of high temperature sensing with a high sensitivity of ~132.8 pm/°C and a measuring range from room temperature to 900 °C. Comparing to the traditional LPFG fabricated by CO2 laser or arc discharge technique, the HLPFG has a low the bending and tensile strain sensitivity of 1.94 nm/(1/m) and 1.41 pm/με, respectively. So the proposed HLPFG could have a great potential in special applications as optical high-temperature sensors.

Engineering Dzyaloshinskii-Moriya interaction in B20 thin-film chiral magnets

Chiral magnetic Mn$_x$Fe$_{1-x}$Ge compounds have an antisymmetric exchange interaction that is tunable with the manganese stoichiometric fraction, $x$. Although millimeter-scale, polycrystalline bulk samples of this family of compounds have been produced, thin-film versions of these materials will be necessary for devices. In this study, we demonstrate the growth of epitaxial Mn$_x$Fe$_{1-x}$Ge thin films on Si (111) substrates with a pure B20 crystal structure in the stoichiometric fraction range x from 0 to 0.81. Following systematic physical and magnetic characterization including microwave absorption spectroscopy, we quantify the antisymmetric exchange interaction and helical period as a function of $x$, which ranges from 200 nm to 8 nm. Our results demonstrate an approach to engineering the size of magnetic skyrmions in epitaxial films that are grown using scalable techniques.

Orbital Angular Momentum Mode Converter Based on Helical Long Period Fiber Grating Inscribed by Hydrogen–Oxygen Flame

A high-efficiency grating fabrication method was, for the first time, demonstrated to inscribe helical long period fiber gratings (H-LPFGs) in small numbers by means of twisting a standard single-mode fiber (SMF) during hydrogen-oxygen flame heating and then cutting the helical fiber into in series of sections. Each section of the helical fiber was a desired LPFG whose resonant wavelength, i.e., grating pitch, can be changed by adjusting the twist rate of the helical fiber. The H-LPFG inscribed in a standard SMF could be used to generate orbital angular momentum (OAM) modes, i.e., OAM+1 mode, with a purity of 91% and a conversion efficiency of 87% within a large wavelength range from more than the cutoff wavelength of an SMF, which is highly advantageous to all-fiber optical communications based on the OAM mode-division multiplexing technique.

Fiber-Based Helical Channels Refractive Index Sensor Available for Microfluidic Chip

We propose and demonstrate a refractive index (RI) sensor based on a dual-hole elliptical core fiber (DHECF), which is available for microfluidic chips. By using the heating-twisting technology, we fabricate a helical long period grating (HLPG) structure in the DHECF. This sensor is convenient for microfluidic chips because of the dual-hole structure in the fiber, which is the natural microfluidic channels. The heating-twisting technology ensures that the fabrication of the gratings sensor is easy and low-cost. In addition, the dual-hole structure contributes to one internal sensing channel which contains two sensing routes (two holes), and one external sensing channel. Experimental results indicate that the testing sensitivity of the internal sensing channel can be 584 nm/RIU (RI range 1.385–1.405), and the sensitivity of the external sensing channel can be 1108.8 nm/RIU (RI range 1.385–1.405).

Automatic Arc Discharge-Induced Helical Long Period Fiber Gratings and Its Sensing Applications

We experimentally demonstrate an automatic arc discharge technology for inscribing high-quality helically twisted long period fiber gratings (H-LPFGs) with greatly improved inscription efficiency for single mode fibers. The proposed technology has been developed by implementing an embedded program in a commercial fusion splicer, which employs an ultraprecision motorized translation stage while the tensioning mass required by conventional inscribing technology is eliminated. More significantly, the arc-induced H-LPFGs have been reported to have potential usage as sensors in temperature, refractive index, twist stress, and strain.

Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by muon spin rotation

We have studied by muon spin resonance ({\mu}SR) the helical ground state and fluctuating chiral phase recently observed in the MnGe chiral magnet. At low temperature, the muon polarization shows double period oscillations at short time scales. Their analysis, akin to that recently developed for MnSi [A. Amato et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field distribution induced by the Mn helical order at the muon site. The refined muon position agrees nicely with ab initio calculations. With increasing temperature, an inhomogeneous fluctuating chiral phase sets in, characterized by two well separated frequency ranges which coexist in the sample. Rapid and slow fluctuations, respectively associated with short range and long range ordered helices, coexist in a large temperature range below T$_{N}$ = 170 K. We discuss the results with respect to MnSi, taking the short helical period, metastable quenched state and peculiar band structure of MnGe into account.

Multi-phase-shifted helical long period fiber grating based temperature-insensitive optical twist sensor.

A compact temperature-insensitive optical fiber twist sensor based on multi-phase-shifted helical long period fiber grating has been proposed and experimentally demonstrated in this paper. A multi-phase-shifted helical long period fiber grating is fabricated with a multi-period rotation technology. A π/2 and a 3π/2 phase shift is introduced in the helical long period fiber grating by changing the period. The helical pitch can be effectively changed with a different twist rate, which is measured by calculating the wavelength difference between two phase shift peaks. Although the wavelength of the phase shift peak also shifts with a change of the temperature, the wavelength difference between two phase shift peaks is constant due to two fixed phase shifts in the helical long period fiber grating, which is extremely insensitive to temperature change for the multi-phase-shifted helical long period fiber grating. The experimental results show that a sensitivity of up to 1.959 nm/(rad/m) is achieved.

Investigating the Interplay between Nucleoid-Associated Proteins, DNA Curvature, and CRISPR Elements Using Comparative Genomics

Many prokaryotic and eukaryotic genomes feature a characteristic periodic signal in distribution of short runs of A or T (A-tracts) phased with the DNA helical period of ∼10–11 bp. Such periodic spacing of A-tracts has been associated with intrinsic DNA curvature. In eukaryotes, this periodicity is a major component of the nucleosome positioning signal but its physiological role in prokaryotes is not clear. One hypothesis centers on possible role of intrinsic DNA bends in nucleoid compaction. We use comparative genomics to investigate possible relationship between the A-tract periodicity and nucleoid-associated proteins in prokaryotes. We found that genomes with DNA-bridging proteins tend to exhibit stronger A-tract periodicity, presumably indicative of more prevalent intrinsic DNA curvature. A weaker relationship was detected for nucleoid-associated proteins that do not form DNA bridges. We consider these results an indication that intrinsic DNA curvature acts collaboratively with DNA-bridging proteins in maintaining the compact structure of the nucleoid, and that previously observed differences among prokaryotic genomes in terms DNA curvature-related sequence periodicity may reflect differences in nucleoid organization. We subsequently investigated the relationship between A-tract periodicity and presence of CRISPR elements and we found that genomes with CRISPR tend to have stronger A-tract periodicity. This result is consistent with our earlier hypothesis that extensive A-tract periodicity could help protect the chromosome against integration of prophages, possibly due to its role in compaction of the nucleoid.

Segmented helical structures formed by ABC star copolymers in nanopores

Self-assembly of ABC star triblock copolymers confined in cylindrical nanopores is studied using self-consistent mean-field theory. With an ABC terpolymer forming hexagonally-arranged cylinders, segmented into alternative B and C domains, in the bulk, we observe the formation in the nanopore of a segmented single circular and non-circular cylinder, a segmented single-helix, and a segmented double-helix as stable phases, and a metastable stacked-disk phase with fourfold symmetry. The phase sequence from single-cylinder, to single-helix, and then to double-helix, is similar as that in the cylindrically-confined diblock copolymers except for the absence of an equilibrium stacked-disk phase. It is revealed that the arrangement of the three-arm junctions plays a critical role for the structure formation. One of the most interesting features in the helical structures is that there are two periods: the period of the B/C domains in the helix and the helical period. We demonstrate that the period numbers of the B/C domains contained in each helical period can be tuned by varying the pore diameter. In addition, it is predicted that the period number of B/C domains can be any rational in real helical structures whose helical period can be tuned freely.

Differences in DNA curvature-related sequence periodicity between prokaryotic chromosomes and phages, and relationship to chromosomal prophage content

BackgroundPeriodic spacing of A-tracts (short runs of A or T) with the DNA helical period of ~10–11 bp is characteristic of intrinsically bent DNA. In eukaryotes, the DNA bending is related to chromatin structure and nucleosome positioning. However, the physiological role of strong sequence periodicity detected in many prokaryotic genomes is not clear.ResultsWe developed measures of intensity and persistency of DNA curvature-related sequence periodicity and applied them to prokaryotic chromosomes and phages. The results indicate that strong periodic signals present in chromosomes are generally absent in phage genomes. Moreover, chromosomes containing prophages are less likely to possess a persistent periodic signal than chromosomes with no prophages.ConclusionsAbsence of DNA curvature-related sequence periodicity in phages could arise from constraints associated with DNA packaging in the viral capsid. Lack of prophages in chromosomes with persistent periodic signal suggests that the sequence periodicity and concomitant DNA curvature could play a role in protecting the chromosomes from integration of phage DNA.

Real-Space Observation of Skyrmion Lattice in Helimagnet MnSi Thin Samples

Observing and characterizing the spin distributions on a nanometer scale are of vital importance for understanding nanomagnetism and its application to spintronics. The magnetic structure in MnSi thin samples prepared from a bulk, which undergoes a transition from a helix to a skyrmion lattice, was investigated by in situ observation using Lorentz microscopy. Stripe domains were observed at zero applied field below 22.5 K. A skyrmion lattice with 6-fold symmetry in real space appeared when a field of 0.18 T was applied normal to the film plane. The lattice constant was estimated to be 18 nm, almost identical to the helical period. In comparison with the marginally stable skyrmion phase in a bulk sample, the skyrmion phase was stable over a wide range of temperatures and magnetic fields in the thin samples.

PerPlot & PerScan: tools for analysis of DNA curvature-related periodicity in genomic nucleotide sequences

BackgroundPeriodic spacing of short adenine or thymine runs phased with DNA helical period of ~10.5 bp is associated with intrinsic DNA curvature and deformability, which play important roles in DNA-protein interactions and in the organization of chromosomes in both eukaryotes and prokaryotes. Local differences in DNA sequence periodicity have been linked to differences in gene expression in some organisms. Despite the significance of these periodic patterns, there are virtually no publicly accessible tools for their analysis.ResultsWe present novel tools suitable for assessments of DNA curvature-related sequence periodicity in nucleotide sequences at the genome scale. Utility of the present software is demonstrated on a comparison of sequence periodicities in the genomes of Haemophilus influenzae, Methanocaldococcus jannaschii, Saccharomyces cerevisiae, and Arabidopsis thaliana. The software can be accessed through a web interface and the programs are also available for download.ConclusionsThe present software is suitable for comparing DNA curvature-related sequence periodicity among different genomes as well as for analysis of intrachromosomal heterogeneity of the sequence periodicity. It provides a quick and convenient way to detect anomalous regions of chromosomes that could have unusual structural and functional properties and/or distinct evolutionary history.

3D microlasers from self-assembled cholesteric liquid-crystal microdroplets

We demonstrate a tunable and omnidirectional microlaser in the form of a microdroplet of a dye-doped, cholesteric liquid crystal in a carrier fluid. The cholesteric forms a Bragg-onion optical microcavity and the omnidirectional 3D lasing is due to the stimulated emission of light from the dye molecules in the liquid crystal. The lasing wavelength depends solely on the natural helical period of the cholesteric and can be tuned by varying the temperature. Millions of microlasers can be formed simply by mixing a liquid crystal, a laser dye and a carrier fluid, thus providing microlasers for soft-matter photonic devices.

Comparative Analysis of Sequence Periodicity among Prokaryotic Genomes Points to Differences in Nucleoid Structure and a Relationship to Gene Expression

Regular spacing of short runs of A or T nucleotides in DNA sequences with a period close to the helical period of the DNA double helix has been associated with intrinsic DNA bending and nucleosome positioning in eukaryotes. Analogous periodic signals were also observed in prokaryotic genomes. While the exact role of this periodicity in prokaryotes is not known, it has been proposed to facilitate the DNA packaging in the prokaryotic nucleoid and/or to promote negative or positive supercoiling. We developed a methodology for assessments of intragenomic heterogeneity of these periodic patterns and applied it in analysis of 1,025 prokaryotic chromosomes. This technique allows more detailed analysis of sequence periodicity than previous methods where sequence periodicity was assessed in an integral form across the whole chromosome. We found that most genomes have the periodic signal confined to several chromosomal segments while most of the chromosome lacks a strong sequence periodicity. Moreover, there are significant differences among different prokaryotes in both the intensity and persistency of sequence periodicity related to DNA curvature. We proffer that the prokaryotic nucleoid consists of relatively rigid sections stabilized by short intrinsically bent DNA segments and characterized by locally strong periodic patterns alternating with regions featuring a weak periodic signal, which presumably permits higher structural flexibility. This model applies to most bacteria and archaea. In genomes with an exceptionally persistent periodic signal, highly expressed genes tend to concentrate in aperiodic sections, suggesting that structural heterogeneity of the nucleoid is related to local differences in transcriptional activity.

直線並びに螺旋上昇気泡運動に及ぼす混入微細粒子の影響

LDV, PIV and some methods using ultrasonic sound have been often employed to measure multiphase flows. Fine particles are usually added into flows as tracer or scattering particles. The effect of particles added in on the flow characteristics is, however, not examined in detail. In this study, the authors measured the movement of linearly and helically rising bubbles to investigate the effect of fine particles mixed into liquid phase. Polyethylene particles of 160μm medium diameter were used. The bubble size, terminal rising velocity, migration velocity of bubbles, diameter and wave length of helix, and helical period were measured. The reductions of bubble diameter, velocities of bubbles, and helical sizes were recognized by adding particles for some cases.

A coarse-grained model for the formation of α helix with a noninteger period on simple cubic lattices

Periodicity is an important parameter in the characterization of a helix in proteins. In this work, a coarse-grained model for a homopolypeptide in simple cubic lattices has been extended to build an alpha helix with a noninteger period. The lattice model is based on the bond fluctuation algorithm in which bond lengths and orientations are altered in a quasicontinuous way, and the simulation is performed via dynamic Monte Carlo simulation. Hydrogen bonds are assumed to be formed between a virtual-carbonyl group in a residue and a downstream virtual-imino group in another residue. Consequently, the period of the formed alpha helix is a noninteger. An improved spatial correlation function has been suggested to quantitatively describe the periodicity of the helical conformation, by which helical period and helical persistent length can be calculated by statistics. The resultant periods are very close to 3.6 residues; the persistent length based upon the improved definition can be larger or smaller than the chain length and reflect the inherent regularity of a chain including one or multiple helical blocks. The simulation outputs agree with the calculation of the Zimm-Bragg theory based upon the associated nucleation parameter and propagation parameter as well.