Periodic Reorientation Research Articles

Generalized micromechanical formulation of fiber orientation tensor evolution equations

Fiber orientation tensors are widely used to efficiently describe the fiber orientation evolution of anisotropic fiber suspensions during mold-filling. Real viscous fiber suspensions show fiber-induced anisotropic behavior. It is an open question how to correctly account for the anisotropic microstructure of fiber suspensions in general in the evolution equation of the fiber orientation tensors. In this study, a generalized evolution equation for the fiber orientation tensor of arbitrary even order is formulated, which takes into account the microstructural anisotropy of the fiber suspension. This formulation is based on a linear homogenization approach which allows the application of arbitrary mean-field models. The derived interaction term, representing the anisotropic environment of a single fiber, is discussed as a micromechanical convergence criterion of the underlying integral operator. It is shown and discussed in detail how the special cases of the Jeffery equation and the Folgar–Tucker equation follow from this general formulation. In addition, the generalized evolution equation is specified for selected mean-field models. In this context, an equation is presented to describe the evolution of the fiber orientation tensor depending on the spatial distribution of the fibers. For simple shear flow, all models describing the orientation dynamics are numerically investigated and compared. The results for the second-order orientation tensor as well as for a single fiber show that the well-known periodic behavior is present and strongly depends on the volume fraction and the chosen mean-field model. Considering the spatial distribution of the fibers has a significant effect on the orientation evolution and strongly affects the periodic reorientation.

Periodic liquid crystalline waveguiding microstructures

Different methods allowing for creating optical waveguides with liquid–crystal (LC) cores, in which molecules form periodic patterns with precisely controlled periods, are reported. The first one is based on reversible photoalignment with high-resolution selective illumination and allows to control the period of LC molecules inside silica microcapillaries. The second method employs microstructures formed in PDMS, allowing to obtain both: LC-core waveguides and a set of specially designed periodic microelectrodes used for the periodic reorientation of molecules. Using both methods, we successfully controlled the period of the patterned alignment in the range from about 500 µm and scaled it down to as small as 20 µm. We performed experimental studies on waveguiding phenomenon in such structures, in view to obtain transmission spectra typical to optical fiber gratings. Since the results achieved in experimental conditions differed from those expected, the additional numerical simulations were performed to explain the observed effects. Finally, we obtained the waveguiding in a blue phase LC, characterized by naturally created three-dimensional periodicity with periods smaller than one micrometer. In such a structure, we were able to observe first-order bandgap, and moreover, we were able to tune it thermally in nearly the whole visible spectral range.

Somebody Expects You Home Tonight: Exploring Safety Practices in Technical School Shops

The study explored safety practices in technical school shops. The area of the study was North-Eastern Nigeria. The study adopted descriptive survey research design and the population of the study comprises of 134 carpentry and joinery Teachers/Instructors, 97 workshop attendants and 783 Carpentry and Joinery Students from the 29 Technical Colleges thereby making a population size of 1014. The instrument used for data collection was a structured questionnaire on a five-point scale adapted from a previous study. The reliability coefficient of the instrument was 0.78. Mean was used to analyze the research questions. Findings from the study indicated that safety practices around Technical School shop environment, and the observation of safety practices by workshop personnel were to a moderately extents. It was recommended among others that School administrators should organize periodic reorientation programmes for carpentry and joinery workshop personnel to reeducate them on the need to strictly comply with all the safety standards guiding carpentry and joinery workshop operations.

Effectiveness of combined non-pharmacological interventions in the prevention of delirium in critically ill patients: A randomized clinical trial.

Delirium is a common dysfunction in the intensive care unit (ICU) and it is associated with negative short- and long-term outcomes. This study evaluated the effectiveness of combined non-pharmacological interventions in preventing delirium in critically ill patients. This is a single-center randomized controlled trial conducted in three Brazilian ICUs from February to September 2019. Patients assigned to the control group received standard care (n=72) and those assigned to the experimental group (n=72) received a bundle of non-pharmacological interventions (periodic reorientation, cognitive stimulation, correction of sensory deficits [visual or hearing impairment], environmental management and sleep promotion) throughout the ICU stay. Delirium was monitored twice a day with the Confusion Assessment Method for the Intensive Care Unit Flowsheet. The primary outcome was the incidence density of delirium. The incidence density of delirium was lower in the intervention group (1.3×10-2 person-days) than in the control group (2.3×10-2 person-days), with a hazard ratio of 0.40 (95% confidence intervals, 0.17-0.95; p = 0.04) after adjustment for Simplified Acute Physiology Score III, surgical admission and alcoholism. Combined non-pharmacological interventions reduced delirium in critically ill patients, compared to standard care. Brazilian Registry of Clinical Trials (ReBEC), Identifier RBR-6xq95s, October 03, 2018.

KNOWLEDGE, ATTITUDE AND PRACTICES AMONG HEALTH CARE WORKERS TOWARDS BIO MEDICAL WASTE MANAGEMENT IN MEDICALAND SURGICAL SETTINGS AT A GOVERNMENT MEDICAL COLLEGE, GOA

Background: Correct knowledge and attitude are critical towards bringing about a favourable change in practice. Medical professionals in India have always turned a blind eye to scientific management of BMW. Objective: To assess knowledge, attitude and practices of health care workers regarding specific aspects of Bio Medical Waste Rules, 2016 and its amendments. Material & Methods: In this cross-sectional survey data was collected among 250 randomly selected doctors and nurses from an apex Government medical college hospital in Goa during the period September 2019 to December 2019 using a self-administered questionnaire. The results are expressed as percentages, and the significance of difference in percentages is expressed using chi-square test at 95% confidence level. Results: Overall, the knowledge regarding BMW Rules was poor, especially with regards to the segregation practices and the colour coded bins, with their practices being non-concurrent with the prevailing rules. An assessment of attitudes, however, revealed their positive inclination towards proper BMWM. Conclusion: The study emphasizes the need for periodic reorientation of these health care workers in elements of Bio Medical Waste Management, especially the segregation.

Knowledge and skills of accredited social health activists in home based new-born care in a rural community of Northern India: an evaluative survey

Background: Home based new-born care (HBNC) is a strategy implemented by the Government of India to overcome the problem of new-born deaths and reach the unreached new-borns in the community. Aim was to assess the knowledge and skills of ASHA workers and factors influencing the skills.Methods: In an observational study, a total of 48 accredited social health activists (ASHA) working under a primary health centre (PHC) were enrolled using a total enumeration sampling technique. A self-developed, pre-tested and validated tool based on home based new-born care was used for data collection.Results: Mean knowledge and skill scores of ASHA workers were 16.4±4.2 and 27.7±4.3 respectively. Nearly half of the ASHA workers had average knowledge, while two-thirds had good skills towards HBNC. Most of ASHA workers had shown good skills in measuring the temperature of new-borns, handwashing and count the respiration correctly, while less than 40% of ASHA workers performed weight recording correctly. Knowledge and overall skill scores of ASHA workers were positively correlated (r=0.58, p<0.001). Statistically significant associations were observed between the overall skills scores of ASHA workers and educational status, working experience and the last training attended on HBNC (p=0.001).Conclusions: Most of the ASHA workers had exhibited good skills, but were lacking scientific knowledge related to HBNC. There is need for having periodic re-orientation training for facilitating application of scientific knowledge to HBNC.

Experimental study of micromixing in curved tube reactors by the reactive tracer method

The effect of basic process conditions and the initial distribution of mixed liquids on mixing on the molecular scale was studied experimentally for helical and twisted bends reactors. The selectivity of two competitive-parallel reactions, acid-base neutralization and alkaline ester hydrolysis, carried out in aqueous solutions between initially unmixed reactants, was used to quantify micromixing in steady-state, isothermal and laminar flow. Faster micromixing is achieved in the twisted bends mixer than in the helical mixer due to the periodic reorientation of Dean vortices, present in curved conduits. The difference in micromixing performance of the two reactors decreases for high Reynolds numbers (Re>1000) when ester hydrolysis is no longer controlled by mixing. Micromixing for lower Reynolds numbers can be improved by changing the ratio of volumetric flows of the reactant solutions and by using a distribution head, which at the reactor entrance creates the contact surface between mixed liquids perpendicular to the curvature plane of the first pipe bend. When micromixing in the reactor becomes so slow that the final selectivity approaches its maximum value, changing the ester to a slower reacting one helps to adjust the sensitivity of the test reaction system to the deteriorating mixing conditions.

Anelastic Phenomena Preceding the Melting of Pure Metals and Alloys

Precursor phenomena of melting in pure metals (In, Pb, Bi and Sn) and alloys of the systems Pb-Bi and In-Sn with different compositions have been investigated by means of Mechanical Spectroscopy (MS), i.e. dynamic modulus and damping measurements. MS tests evidenced that a sharp drop of dynamic modulus E takes place in a temperature range ΔT before the formation of the first liquid: the modulus variation ΔE and the corresponding temperature range ΔT depend on the specific metal or alloy. The modulus drop is consistent with a relevant increase of interstitial concentration (self-interstitials assuming the dumbbell configuration), as predicted by the Granato’s theory of melting. The increase of damping in the same temperature range of modulus drop supports this explanation. Owing to their dumbbell configuration self-interstitials interact with the flexural vibration of samples and the periodic re-orientation under the external applied stress leads to energy loss and damping increase. The increase of self-interstitials has the effect to weaken interatomic bonds (modulus drop) and favours the collapse of crystal lattice (melting).

Three-dimensional vector holograms formed in twisted-nematic azo-dye-doped polymer liquid-crystal composite

Three-dimensional (3D) vector holograms have been formed in twisted-nematic (TN) azo-dye-doped polymer liquid crystal (LC) composites whose director is gradually rotated around the thickness direction in the initial state. Polarization states of diffracted beams were rotated in accordance with the twist angle, and the diffraction efficiency depended markedly on the incident angle. We confirmed that the 3D director distributions corresponded to the polarization modulation caused not only by light interference and the propagation in the LCs but also by the initial orientation of the LCs. In order to explain the observed properties a theoretical model of the periodic reorientation distribution in TN LCs was presented. The Jones matrix method is used to describe the interference of two polarized light beams in the anisotropic media. Then the finite-difference time-domain method was applied to analyze the diffraction properties of the 3D vector holograms recorded in the model medium.

On an objective experimental method for the determination of the electrohydrodynamic instability thresholds in a nematic liquid crystal

The case of an electrohydrodynamically excited and homogeneously aligned nematic liquid crystal layer, which exhibits a spatially periodic reorientation of its director field, is considered. A previously reported work proposed an optical method to measure the director relaxation time by diffraction, through monitoring the intensities of low-order fringes. This light diffraction technique was applied at a single frequency, while the excitation voltage was temporarily zero. The current article is a continuation of the aforementioned experimental technique. Here, we present a completely objective method for the experimental determination of the instability threshold at any given frequency in the conductive regime, based on the dependence of the decay time of the director field on the value of the AC voltage applied across the nematic layer when the excitation field is temporarily zero or lower than its corresponding threshold value.

Near-wall streak modification by spanwise oscillatory wall motion and drag-reduction mechanisms

AbstractDirect numerical simulations for fully developed channel flow, subjected to oscillatory spanwise wall motion, have been performed and analysed in an effort to illuminate the fundamental mechanisms responsible for the reduction in turbulent friction drag, observed to result from the spanwise wall motion. A range of statistical data are discussed, including second-moment budgets, joint-probability-density functions, enstrophy and energy-spectra maps. Structural features are also investigated by reference to the response of streak properties to the oscillatory forcing. The unsteady cross-flow straining is shown to cause major spanwise distortions in the streak near-wall structures, leading to a pronounced reduction in the wall-normal momentum exchange in the viscous sublayer, hence disrupting the turbulence contribution to the wall shear stress. The response of the streaks, in terms of their periodic reorientation in wall-parallel planes, the decline and recovery of their intensity during the cyclic actuation, and their wall-normal coherence, is shown to be closely correlated with the temporal variation of the shear-strain vector. Furthermore, a modulating ‘top-to-bottom’ effect, associated with large-scale outer-layer structures, is highlighted and deemed responsible for the observed reduction in the actuation efficiency as the Reynolds number is increased.

Chaotic mixing in electromagnetically controlled thermal convection of glass melt

A numerical investigation has been carried out to study the mixing behavior of electromagnetically controlled thermal convection of glass melt in a cylindrical crucible. Thermal convection caused by the internal heating of the glass melt is controlled by an external magnetic field applied along the axis of the crucible. Unlike in thermal convection without and with steady external magnetic fields, Lagrangian particle motion exhibits chaotic behavior in an oscillating magnetic field. The present study shows that the asymmetric thermal field caused by the gravitational body force is rotated in the clockwise and anticlockwise directions alternatively by the Lorentz force imposed by the oscillating magnetic field. As the magnetic field varies sinusoidally with time, the flow field undergoes periodic reorientation causing repeated stretching and folding of the material lines resulting in better mixing in the glass melt. The degree of mixing increases with the period of oscillation till it reaches a maximum and subsequently decreases with further increase in the period. A decline in the mixing performance is observed with increase in the magnetic field strength for a given period of oscillation. This is on account of the fact that the Lorentz forces try to nullify the asymmetry created by the gravitational body forces. The computational results presented here will be useful for developing better glass homogenization systems.

An experimental and theoretical study of the mixing characteristics of a periodically reoriented irrotational flow

The minimum-energy method to generate chaotic advection should be to use an irrotational flow. However, irrotational flows have no saddle connections to perturb in order to generate chaotic orbits. To the early work of Jones & Aref (Jones & Aref 1988 Phys. Fluids 31, 469-485 (doi:10.1063/1.866828)) on potential flow chaos, we add periodic reorientation to generate chaotic advection with irrotational experimental flows. Our experimental irrotational flow is a dipole potential flow in a disc-shaped Hele-Shaw cell called the rotated potential mixing flow; it leads to chaotic advection and transport in the disc. We derive an analytical map for the flow. This is a partially open flow, in which parts of the flow remain in the cell forever, and parts of it pass through with residence-time and exit-time distributions that have self-similar features in the control parameter space of the stirring. The theory compares well with the experiment.

Light-field-induced spatially periodic freedericksz transition in a planar nematic cell

It is shown that a threshold spatially periodic reorientation of the director by a light field is possible in a planar nematic liquid crystal cell if the ratio of the Frank elastic constants, K2/K1, exceeds a critical value. The periodic director structure arising in the cell leads to a self-diffraction of the incident light wave. The dependences obtained for this phenomenon make it possible to determine the values of the elastic constants K1 and K2, the director reorientation threshold, and the period of the director structure from the experimental values of the self-diffraction angle.

Influence of anchoring at a nematic cell surface on threshold spatially periodic reorientation of a director

We have analysed the influence of surface director anchoring in a planar flexoelectric nematic cell on the threshold spatially periodic reorientation of the director in an external dc electric field. By minimizing the free energy of the nematic cell we obtained the equations for a director and numerically solved them in the one elastic constant approximation. The dependences of the threshold electric field and the spatial period of director structure on the azimuthal and polar anchoring energy, as well as the flexoelectric parameters, are determined. It is shown that the domain of the flexoelectric parameter values, at which the spatially periodic reorientation of a director takes place, increases with decreasing azimuthal anchoring energy and increasing polar anchoring energy.

Designing forested landscapes to provide multiple services.

Abstract Forest services are benefits generated for society by the existence of certain forest types and their attributes. The particular mix of services, and their amount and quality, depend on the condition of the forest resource. Water and nitrogen processes are determined to a great extent by forest management. Streamwater runoff in areas where water is a scarce resource is significantly affected by tree cover and tree age. Old forests may provide better vistas and more suitable habitat than young forests. Such examples illustrate the overriding importance of the particular forest condition which is created by forest management. Most of the world's forests are utilized by humans and this implies that the dynamics of a forest ecosystem is not so much an ecological, but predominantly a cultural problem. The requirements for forest services are manifold and they are not constant over time. Traditional forest planning is based on principles of constancy and long-term stability. Silvicultural programmes were assumed to remain constant for at least one rotation. In reality, however, periodic reorientation and frequent changes of forest policy are quite common. The history of silviculture is not characterized by constancy, but rather by continuous change in policy. Concrete examples of this vicissitude are changes in the preferred silvicultural systems (clearfelling vs selective harvesting; planting vs natural regeneration), the preferred tree species (beech, spruce, 'exotic' species) and the preferred forest structures (even-aged monocultures; uneven-aged multispecies forest). In view of the difficulty in predicting the direction and rate of change, some of the assumptions that have guided forest planning in the past are re-examined. We first define some of the terminology and show that the dynamic development of a managed forest ecosystem is not only an ecological but predominantly an economic and a cultural problem. We then show that the common practice of standardizing silviculture complicates decision-making and is ineffective in providing multiple services, because it assumes that social, economic and environmental conditions remain constant over time. Nyberg (1998) thus proposed greater emphasis on adaptive management, which involves systematic learning on the basis of the results of past silvicultural activities. Such learning may be slow, however. For this reason, it is advisable to use new paradigms of managing forest ecosystems, together with improved modelling tools, which permit accurate forecasting and systematic evaluation of different management options, based on current information about the forest resource. The 'Multiple Path' theory, which may be considered as a particular form of adaptive forest management, provides a suitable basis for designing forested landscapes. The basic idea is not entirely new and has been implemented in various simplified forms, in North America and Northern Europe. Extensions to cover a desired mix of services have been developed for smaller applications, but the concept has never been recognized as a general basis for designing forests with the aim of delivering multiple services in societies which are committed to the standard of Public Choice. Some principles of forest design are presented and outlined in some detail: how to initialize the landscape and link the levels of the spatial hierarchy; how to balance the mix of services and design their spatial arrangement; and how to integrate varied forms of expertise into forest design. Several of the required modelling tools are briefly explained.

Spatially periodic reorientation of liquid crystal director at planar Freedericksz transition

Conditions for the formation of a spatially periodic structure in a liquid crystal cell at the threshold planar-planar director reorientation in a dc electric field are considered. The dependences of the threshold and the wave number of the arising structure on (i) the polar and azimuthal anchoring energy at the surface of the cell substrates, (ii) the ratio r of the elastic constants of the liquid crystal, and (iii) the value of the flexoelectric parameter v are calculated. It is shown that the range of the parameters r and v corresponding to the spatially periodic director reorientation depends strongly on the anchoring energy. The range of allowable values of the parameter r narrows with a decrease in the azimuthal anchoring energy and expands with a decrease in the polar anchoring energy, while the range of allowable values of the parameter v widens with decreasing azimuthal anchoring energy and depends nonmonotonically on the polar anchoring energy.

Threshold spatially periodic structure of the director in a nematic flexoelectric cell with finite anchoring energy

The influence of the finiteness of the anchoring energy of a director and the value of flexoelectric polarization on the threshold of a spatially periodic reorientation of the director and the period of the arising structure is considered for a planar nematic cell. The threshold and the period are calculated numerically and the corresponding analytical expressions are obtained for the case of a strong anchoring of the director. It is shown that for a finite azimuthal anchoring energy the range of admissible values of the flexoelectric parameter ν widens, while for a finite polar anchoring energy this range narrows as compared to the case of an absolutely rigid orientation of the director at the cell surface.

Inhomogeneous Threshold Director Reorientation in a Planar Nematic Flexoelectric Cell with Finite Anchoring Energy

The dependence of the threshold parameters and the period of the electric-field-induced spatially periodic reorientation of the director in a flexoelectric nematic liquid crystal (NLC) on the anchoring conditions at the surface of a planar NLC cell has been studied. The threshold electric field and the corresponding wave-number of the periodic structure of the director field have been numerically calculated for arbitrary values of the anchoring energy. In the case of strong anchoring, the corresponding analytical expressions are obtained in a single-constant approximation. A decrease in the azimuthal anchoring energy leads to an increase in the intervals of possible values of the flexoelectric parameter ν and the ratio K2/K1 of the Frank elastic constants. A decrease in the polar anchoring energy leads to narrowing of these intervals as compared to the case of infinitely strong anchoring at the NLC cell surface.

High Sensitive and Efficient Holographic Grating Generation in Functionalized Polymer-Dissolved Liquid Crystal Composites

High sensitive and efficient holographic gratings were generated in functionalized polymer-dissolved liquid crystal composites. The gratings originate in the photorefractive-like space charge filed and resultant periodic reorientation of liquid crystal molecules. The demonstration for edge-enhancement of two-dimensional optical images was performed by using the developed materials.