Helix Pitch Research Articles

Electrically induced transformations of defects in cholesteric layer with tangential-conical boundary conditions

Electric-field-induced changes of the orientational structures of cholesteric liquid crystal layer with the tangential-conical boundary conditions have been investigated. The samples with the ratio of the cholesteric layer thickness d to the helix pitch p equalled to 0.57 have been considered. The perpendicularly applied electric field causes a decrease of the azimuthal director angle at the substrate with the conical surface anchoring. In the cells with d = 22 μm, the defect loops having the under-twisted and over-twisted areas are formed. At the defect loop the pair of point peculiarities is observed where the 180° jump of azimuthal angle of the director occurs. Under the action of electric field the loops shrink and disappear. In the cells with d = 13 μm, the over-twisted and under-twisted defect lines are formed. Applied voltage results in the shortening of lines or/and their transformation into a defect of the third type. The director field distribution near defect lines of three types has been investigated by the polarising microscopy techniques. It has been revealed that the length ratio between the over-twisted and third-type defect lines can be controlled by the electric field.

Bend-induced long period grating in a helical core fiber.

We report on a new type of long-period-grating generated in a helical core fiber by bending. The grating arises from bend-induced modulation of an equivalent refractive index in the helical core with a period equal to the helix pitch. We experimentally demonstrate that such grating induces multiple resonant couplings between the fundamental modes guided in the central core and the helical side-core. We have also shown that by varying a direction of bending, one can generate the phase shifted grating. The experimental results are supported by numerical simulations based on the coupled mode equations.

Characterization of Tobacco Mosaic Virus Virions and Repolymerized Coat Protein Aggregates in Solution by Small-Angle X-Ray Scattering.

The structure of tobacco mosaic virus (TMV) virions and stacked disk aggregates of TMV coat protein (CP) in solution was analyzed by synchrotron-based small-angle X-ray scattering (SAXS) and negative contrast transmission electron microscopy (TEM). TMV CP aggregates had a unique stability but did not have helical symmetry. According to the TEM data, they were stacked disks associated into transversely striated rod-shaped structures 300 to 800 Å long. According to modeling based on the crystallographic model of the 4-layer TMV CP aggregate (PDB: 1EI7), the stacked disks represented hollow cylinders. The calculated SAXS pattern for the disks was compared to the experimental one over the entire measured range. The best correlation with the SAXS data was found for the model with the repeating central pair of discs; the SAXS curves for the stacked disks were virtually identical irrespectively of the protein isolation method. The positions of maxima on the scatter curves could be used as characteristic features of the studied samples; some of the peaks were assigned to the existing elements of the quaternary structure (periodicity of aggregate structure, virion helix pitch). Low-resolution structural data for the repolymerized TMV CP aggregates in solution under conditions similar to natural were produced for the first time. Analysis of such nano-size objects is essential for their application in biomedicine and biotechnology.

Improving light distribution and light/dark cycle of 900 L tangential spiral−flow column photobioreactors to promote CO2 fixation with Arthrospira sp. cells

The light distribution and light/dark cycle were improved in 900 L tangential spiral-flow column photobioreactors (TSCP) to promote CO2 fixation with Arthrospira sp. cells. Solar irradiation model was employed in CFD simulation to investigate light distribution and light/dark cycle in flow field composed of culture medium, CO2 bubbles and Arthrospira sp. cells under actual sunlight irradiation considering geolocation and time. An accurate way to divide light/dark zone based on saturate light intensity and light intensity field was adopted for the first time. When Arthrospira sp. cell concentration increased from 0.1 to 0.9 g/L, light/dark cycle frequency of cells firstly increased from 0.650 Hz to 0.868 Hz and then decreased to 0.117 Hz. Intracellular chlorophyll a content and carotenoids content of Arthrospira sp. cells in TSCP were 6% and 41% higher than those in conventional bubble column photobioreactor. This promoted cellular photosynthesis and stress resistance, which contributed to increase CO2 fixation rate of Arthrospira sp. cells by 59%. When CO2 aeration rate, CO2 volume concentration, and circulating pump power were 0.210 L/min, 15%, and 30 W, chlorophyll a content, helix pitch, and CO2 fixation rate of Arthrospira sp. cells all reached peak values of 8.769 mg/L, 78.26 μm and 0.358 g/L/d, respectively.

Observation of an anomalous SmA-SmC-SmA phase sequence in a bent-core liquid crystal derived from 4-cyanoresorcinol

The smectic phase with an anomalous dependence of the tilt angle on temperature for a bent-core liquid crystal is observed for the first time. In this phase, the tilt angle decreases on cooling and in the temperature range below the tilted phases, re-entrant orthogonal smectic phase (SmAPA) appears. At higher temperatures, a ferroelectric phase with a helix of short pitch is formed. As the tilt angle decreases on cooling, the helical phase transforms to a surface-stabilized (helixfree) flat anti-ferroelectric structure. This transition is explained by the out-of-plane biaxial anchoring energy

Effect of the selected machine variables on the structural characteristics of air-jet spun yarn

We investigate the manner in which the delivery speed and spinning air pressure of Rieter air-jet spinning machines affect the structural characteristics of viscose air-jet spun yarn (wrapper-fibre ribbon width, wrapper-fibre ribbon helix pitch, wrapper-fibre angle with respect to the yarn axis, yarn diameter, yarn packing density and number of wrapper fibres in the yarn cross section). The structural characteristics of the yarn were determined using an optical camera and by analysing the cross-sectional images and the longitudinal views of yarns. The results indicate that the frequency ratio of wrapper fibres varies from 0.21 to 0.26 and is independent of the delivery speed and spinning air pressure. However, these machine variables significantly influence the inner structure of the yarn, especially the wrapper-fibre angle with respect to the yarn axis and the yarn packing density. These characteristics are discussed with respect to the yarn tenacity and hairiness.

Effect of helical surface disc turbulator on thermal and friction characteristics of double pipe water to air heat exchanger

ABSTRACT The effect of helix angle and pitch ratio of helical surface disc turbulators on the thermal performance of double pipe heat exchanger are discussed in this study. Tests are performed with air as working fluid for different pitch ratios, numerous helix angles, and various Reynolds number. Water and air are allowed to flow along inner tube and through annulus, respectively. In each case, the thermal enhancement factor is observed to be higher than unit value. Smallest pitch ratio and highest helix angle yield highest thermo-hydraulic performance of 1.39 at Re = 3,500. Correlations are developed for various parameters.

A New Theory on Electron Wave-Particle Duality

A theory employing the vortex shape of the electron was presented to resolve the enigma of the wave-particle duality. Conventions such as “particle” and “wave” were used to describe the behavior of quantum objects such as electrons. A superfluid vacuum formed the base to describe the basic vortex structure and properties of the electron, whereas various formulations derived from hydrodynamic laws described the electron vortex circumference, radius, angular velocity and angular frequency, angular momentum (spin) and magnetic momentum. A vortex electron fully explained the associations between momentum and wave, and hydrodynamic laws were essential in deriving the energy and angular frequency of the electron. In general, an electron traveling in space possesses internal and external motions. To derive the angular frequency of its internal motion, the Compton wavelength was used to represent the length of one cycle of the internal motion that is equal to the circumference of the electron vortex. The angular frequency of the electron vortex was calculated to obtain the same value according to Planck’s theory. A traveling vortex electron has internal and external motions that create a three-dimensional helix trajectory. The magnitude of the instantaneous velocity of the electron is the resultant of its internal and external velocities, being equal to the internal velocity reduced by the Lorentz factor (whose essence is presented in a detailed formulation). The wavelength of the helix trajectory represents the distance traveled by a particle along its axis during one period of revolution around the axis, resulting in the same de Broglie wavelength that corresponds to the helix pitch of the helix. Mathematical formulations were presented to demonstrate the relation between the energy of the vortex and its angular frequency and de Broglie’s wavelength; furthermore, Compton’s and de Broglie’s wavelengths were also differentiated.

Performance Enhancement of Double Pipe Heat Exchanger with Helical Fin and Vortex Generator using CFD

Transferring heat from one fluid to another fluid without losing of major energy is a challenging task in the food processing and other industries. Double Pipe Heat Exchanger (DPHE) are light capacity Heat Exchangers (HE) used for air and other gas applications. In the present work an attempt is made to enhance the heat transfer of DPHE with helical fins and vortex generator. The working fluids are air and steam (water vapour) along outer and inner pipes. The parameters considered are helix angles, i.e. 350 , 400 , & 450 and pitch size i.e. 80 mm, 75 mm and 70 mm, and a vertex generator. CATIA V5 and Autodesk CFD are used for modelling and analysis. It is found that 400 angle helix fin 70 mm pitch along Delta Wing type (Triangular) vortex generator (VG) gives best performance.

Single-chain conformation of carboxylated schizophyllan, a triple helical polysaccharide, in dilute alkaline aqueous solution

Synchrotron-radiation small-angle X-ray scattering measurements were carried out for a schizophyllan (SPG) sample with the weight-average molar mass Mw of 340 kg mol−1 and five carboxylated SPG (sclerox) samples with different degrees of substitution (DS) ranging from 0.18 to 0.45 in 200 mM aqueous NaOH including 10 mM NaCl to determine Mw, the second virial coefficient A2, the particle scattering function P(q), and the radius of gyration ⟨S2⟩. Positive A2 values indicated that this alkaline solvent was a good solvent for all polysaccharide samples investigated. The resultant Mw values (~100 kg mol−1) were much smaller than that for the trimer in aqueous NaCl at neutral pH, indicating all SPG and sclerox samples dissolved as single chains in the alkaline solvent. Both P(q) and ⟨S2⟩ were consistently explained by the wormlike chain model. The obtained parameters were almost independent of DS. While the chain stiffness (12–18 nm) in terms of the Kuhn segment length or twice the persistence length was similar to those for the other single chain polysaccharides, the helix pitch per residue (0.1 nm) was quite smaller than the trimer state (0.3 nm). This shrunken main-chain helical structure is most likely due to hydrophobic interactions between helical main chain and side groups.

Conversion of NaHCO3 to Na2 CO3 with a growth of Arthrospira platensis cells in 660m2 raceway ponds with a CO2 bicarbonation absorber.

SummaryThe weight ratio of Na2 CO 3/NaHCO 3 was investigated in order to improve microalgal productivity in large‐scale industrial operations by converting NaHCO 3 to Na2 CO 3 with a growth of Arthrospira platensis cells in 660 m2 raceway ponds. Two microalgal cultivation systems with a NaHCO 3 by‐product (SPBP) and a CO 2 bicarbonation absorber (CBAP) were firstly thoroughly introduced. There was a 13.3% decrease in the initial weight ratio of Na2 CO 3/NaHCO 3 resulting in a 25.3% increase in the biomass growth rate with CBAP, compared to that of SPBP. Increased sunlight intensity, solution temperature and pH all resulted in both a higher HCO3- absorbance and CO32- release, thereby increasing the weight ratio of Na2 CO 3/NaHCO 3 during the growth of A. platensis. The biomass growth rate was peaked at 39.9 g m−2 day−1 when the weight ratio of Na2 CO 3/NaHCO 3 was 3.7. Correspondingly, the cell pigments (chlorophyll a and carotenoid) and trichome size (helix pitch and trichome length) reached to a maximum state of 8.47 mg l−1, 762 μg l−1, 57 and 613 μm under the CBAP system.

In-plane Switching Deformed Helix Ferroelectric Liquid Crystal Display Cells

In-plane electro-optical switching (IPS) is a natural feature of a conventional planar-aligned display cell based on the deformed helix ferroelectric liquid crystal effect (DHFLC-effect) with a sub-wavelength helix pitch, if the tilt angle is close to 40 degrees.

Effects of geometrical and operational parameters on heat transfer and fluid flow of three various water based nanofluids in a shell and coil tube heat exchanger

Heating and cooling of a system by heat exchanger Plays an important role in various industries. Improvement of heat transfer in heat exchangers resulted in reducing the size of heat exchanger, and utilizing more compressed heat exchangers with higher efficiency. Using helical/spiral tube is a passive method for improving the performance of heat exchangers due to its low geometry and high heat transfer coefficient. Also, in heat exchangers, one of the most important methods is additives such nanoparticles for liquids and classified as a passive method which does not need any external power like in active methods. The objective of this study is to investigate efficient operational and geometrical parameters. The considered geometrical parameters include helix pitch, coil diameter, and helix height. Also, the effect of using Al2O3, CuO, SiO2 nanofluids on thermal performance of the heat exchanger is investigated numerically. The results show that the geometric parameters of the coil have a significant effect on the heat exchangers of the shell and coil.

Cholesteric Flakes in Motion Driven by the Elastic Force from Nematic Liquid Crystals.

The paper presents a methodology to control the motion and orientation of suspended reflective cholesteric flakes in a nematic liquid crystal (LC) matrix. The flakes exhibit a dielectric anisotropy which controls their alignment with their in-plane axes parallel to an external electrical dc field. The elastic forces imposed by the LC host affect the switching behavior of the flakes and take care of the realignment to the planar state as soon as the dc field is switched off. When the LC host has a positive dielectric anisotropy, the switching voltage of the flakes is reduced by a factor of 2 in comparison with a LC host with negative dielectric anisotropy or in comparison with an isotropic host. We discovered that the LC host further regulates the back relaxation of cholesteric to return to the planar state upon retrieving the electric field. Whereas, in the isotropic fluid, flakes do not exhibit a preferred orientation when relaxed. Based on this newly proposed principle, we demonstrated its application as an optical switch for smart windows. Depending on the pitch of the cholesteric helix of the flakes, the light of a preset wavelength is reflected. Upon application of an electric field, the embedded flakes rotate their planes perpendicular to the substrate and consequently the incident light becomes fully transmitted without reflection or scattering of light.

The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix

Waveguide optical properties of a cholesteric liquid crystal (CLC) layer with a deformed lying helix (DLH) have been studied by numerical simulations using the finite difference time domain method. The DLH structure, when the helix’s axis is oriented in plane of a CLC layer, is induced by an electric field in a virtual CLC cell with periodic (planar/homeotropic) boundary conditions at one of the alignment surfaces. This in-plane helical structure is stable only in a permanently applied electric field providing the helix deformation. In this work the polarized light reflectance spectra have been studied at different electric fields and light impingement into a waveguide formed by the DLH layer. It is found that for light propagating along the helix axis the reflectance spectrum has multiple stop-bands centred at wavelengths , which is different from set of bands located at , and characteristic of CLC spectra for the Grandjean-plane textures subjected to distortion by an electric or magnetic field perpendicular to the helix axis, where j is a natural number, p is the helix pitch and is the average refractive index. Each of the higher order (j > 1) bands consists of three polarization-dependent sub-bands. In the case of an amplifying CLC DLH layer, depending on an extent of the helix deformation, the lasing modes can be excited at different edges of the sub-bands. While at the strongest deformation the lasing is preferable at the edges of the central sub-band; a lower extent of deformation makes favourable conditions for the lasing at edges of the two other sub-bands.

Deformed lying helix transition and lasing effect in cholesteric LC layers at spatially periodic boundary conditions

ABSTRACTThe field-induced orientational transition in layers of cholesteric liquid crystals with spatially periodic modulation of the surface anchoring is studied by numerical simulations and experimentally. The modulation of the surface anchoring is implemented using high-resolution focused ion-beam treatment of a polymer film providing planar alignment conditions. A specific feature of the orientational transition is that the thermodynamically stable initial planar structure with the helix axis along the normal to the layer transforms under an electric field into an equilibrium structure with a deformed lying helix (DLH) in the plane of the layer. For such a transition to occur the natural pitch of the cholesteric helix must be substantially less than the anchoring modulation period. The appearance of the DLH with a pitch corresponding to the anchoring modulation period results in strongly enhanced first-order diffraction efficiency. The orientational DLH transition is characterised by a rather narrow driving voltage range with a pronounced hysteresis. The waveguide lasing effect with characteristic of the deformed helix spectral modes is demonstrated in a range of the DLH transition.

Fluorescence and lasing in an electric-field-induced periodic structure of a cholesteric liquid crystal

Fluorescence and lasing in a structure with an electric-field-induced spatially periodic director modulation in the plane of a planar-oriented layer of a cholesteric liquid crystal (CLC) is experimentally investigated. The thickness of the CLC layer is chosen close to the natural pitch of the cholesteric helix, which corresponds to the second Grandjean zone. The electric-field-induced periodic field of the CLC director leads to spatial modulation of the refractive index and the appearance of optical properties typical of 1D photonic crystals, when light propagating in the plane of the CLC layer experiences Bragg reflection. In polarised light, the induced spatial modulation of the refractive index manifests itself in the form of banded domains oriented in the plane of the CLC layer perpendicular to the original (unperturbed electric field) direction of the director in the centre of the layer. For the electric field strengths that correspond to fundamentally different distributions of the field of a CLC director, the fluorescence spectra of the DCM laser dye are studied both for different geometries (including the waveguide regime) and for different levels of optical pumping. In the range of electrical voltages corresponding to the induction of a spatially periodic photonic structure, multimode lasing in the waveguide regime is detected. It is shown that the mode composition of lasing depends on the electric field, which affects the properties of the distributed feedback.

Normal Rack Grid Generation Method for Screw Machines with Large Helix Angles

Improving the efficiency of the screw machine is highly significant for industry. Numerical simulation is an important tool in developing these machines. The 3D computational fluid dynamic simulation can give a valuable insight into the flow parameters of screw machines. However, it is currently difficult to generate high quality computational grids required for screw rotors with large helix angle. This is mainly due to the excessively high cell skewness of the rotors with large helix angel, which would introduce errors in numerical simulation. This paper presents a novel grid generation algorithm used for the screw rotors with large helix angel. This method is based on the principles developed for the grid generation in transverse cross-section. Such mesh is generated by SCORGTM using normal rack grid generation method which means numerical meshes are generated in a plane normal to the pitch helix line. The mesh lines are then parallel to the helix line and thus an orthogonal mesh will be produced. The main flow and leakage flow directions are orthogonal to the mesh, potentially reducing numerical diffusion. This developed algorithm could also be employed for single screw machines.

Investigation of Planar and Helical Bend Losses in Single- and Few-Mode Optical Fibers

In this paper, we describe experimental, simulation, and analytical approaches to study bend losses in single and few-mode optical fibers bent into a circle (in-plane bend) and helix. For the in-plane bend case, we compute loss through simulations and experiments, over the bend diameter range of $9.5\text{--}19.5$ mm at 1550 nm wavelength. For in-plane bend simulations, we obtain the refractive index profile of an equivalent straight fiber by applying the geometrically exact beam theory (GEBT) and conformal mapping, against the conventional approach to use an elasto-optic factor to account for stresses experienced by the fiber. We apply GEBT to compute the strain tensor of a bent fiber. The strain tensor, in turn, is used in the stress-optic law to obtain the refractive index due to bending stress. To account for the geometric effect, we apply the conformal mapping technique. The refractive index profile obtained by applying GEBT followed by conformal mapping is used in full-vectorial FEM simulations carried out in COMSOL to compute bend loss at different diameters. The simulation and experimental results are in close agreement. We extend our approach to few-mode fibers by calculating the planar bend losses for higher order modes. The close agreement of the simulation results, generated without making any ad hoc assumptions about the elasto-optic factor to account for the stress effects, with literature validates our approach. Next, we describe the results of experiments to measure the bending losses of fibers wound helically around the mandrel for bend diameter range $9.5\text{--}19.5$ mm and different helix pitch values. We derive an analytical formula to compute helical bend losses based on the method outlined by Marcuse. Although the results from the formula are in close agreement with the experimental results and predict the exponential decrease of loss with increasing pitch, the formula does not account for the non-monotonous dependence of bend loss on helix pitch, observed experimentally. We present a simple empirical formula to account for the non-monotonic dependence. Finally, we study the influence of micro-bend loss, due to the surface roughness of the mandrels used in the experiments on the bending losses. While the effect of surface roughness can be neglected for the mandrels used in our experiments, its effect may become important in mandrels with higher surface roughness, especially at larger bend diameters.

Appearance of induced chiral nematic phase in solutions of 4-n-alkyloxy-4′-cyanobyphenyles with symmetric camphorsubstituted hemiporphyrazines

The synthesis of chiral symmetric camphorsubstituted hemiporphyrazine ((+)HPA) and its racemic mixture ((±)HPA) was carried out by crossover condensation of corresponding camphoradicyanopyrazines with 1,3-phenylenediamine under microwave radiation.By the method of polarizing microscopy, a chiral nematic phase formation of the 4-(n)alkoxy-4′-cyanobiphenyls (n = 3,4,5,6,7,8) nematic mixtures (CB6) was observed under the influence of the symmetric camphorsubstituted hemiporphyrazine, the clearing temperatures and helix pitch were measured, and the twisting power value β was calculated.The degree of destabilizing effect of the racemic mixture (±)HPA on the mesophase was shown to be higher than that of the chiral dopant. Under study the electric permittivity of the CB6 + (±)HPA and CB6 + (+)HPA binary systems the dielectric anisotropy of the achiral composition was found to weakly depend on the dopant concentration, whereas in the case of the spiral mesophase, there is a significant decrease in anisotropy with an increase in the (+)HPA content.At high concentrations of the chiral dopant, jumps in the temperature dependences of the electric permittivity components in the mesophase were detected. Such behavior has been interpreted in the framework of the notions of competition between the dopant and the magnetic field, which attempts to untwist the spiral mesophase.A non-monotonic change in the kinematic viscosity was found on the temperature dependences in the chiral nematic region. In this case, the twisting of the mesophase with a chiral dopant is counteracted by the orientation of the molecules by the flow of a liquid crystal. The equally weak effect of both the chiral dopant (+)HPA and its racemic mixture on the birefringence of LCs is shown, which is caused by the coincidence of the local orientational order in the nematic phase and in the quasinematic layers of the chiral nematic.