Wavy Pattern Research Articles

Thermally-driven coalescence in thin liquid film flowing down a fibre

Abstract

Shape and Unification Pattern of Palatal Rugae as a Race Identification Tool- A Cross-Sectional Study

Background: One of the integral parts of forensic medicine is identification of individuals from biologicalsamples and from the anatomical signatures. Identification of individuals, races, species, gender from theanatomical signatures of teeth and oral cavity is one of such branches which existed in practice in crudeform even before origin of the Forensic odontology as a specialization. Individual variations in Palatal rugaepattern, and its biometric value as a potential tool for establishment of identity was reported centuries back. It’snot standardised or included in the regular standard protocols even today in the age of artificial intelligence.In this pilot study we are comparing two racial groups i.e., Indian and Malaysian with established parametersfor palate rugae with an objective of testing feasibility and validation for identification of individuals andracial groups and also to provide preliminary data for larger studies.Aims and Objectives: The aim of this pilot study is to explore the feasibility of palate rougoscopy as a toolfor race identification by studying the shape and unification Pattern of Palatal Rugae in Indian and Malaysianpopulation.Methodology: Study population was male Indian and Malaysian Medical and Dental students, aged 18-25years studying at Mangalore, India. Sample size 80 (40 in each group); were selected for studying PalatalRugae. The palate impressions were collected using maxillary alginate cast. The parameters assessed were:shape an unification based on classification of Thomas & Kotze. Comparison for two populations was doneusing non-parametric Mann-Whitney Test.Results : Predominant Shape: The Curvy patterns were more common in Malaysians compared to Indian.The Wavy patterns were more common in Malaysians than Indians.The Circular patterns were more commonin Indians than Malaysians.Predominant unification: Diverging patterns were more in Malaysians than Indians and Converging patternswere more in Indians than Malaysians and statistically significant.Conclusion : In the present study the Malaysians had predominantly curvy and wavy patterns and Indianshad circular shapes. Straight patterns were seen equally in both the populations. Although unification ofthe palate rugae was seen, the diverging patterns is more in Malaysians and Converging patterns more inIndians.

Wear patterns and dental functioning in an Early Cretaceous stegosaur from Yakutia, Eastern Russia.

Isolated stegosaurian teeth from the Early Cretaceous high-latitude (palaeolatitude estimate of N 62°- 66.5°) Teete locality in Yakutia (Eastern Siberia, Russia) are characterized by a labiolingually compressed, slightly asymmetrical and mesiodistally denticulated (9–14 denticles) crown, a pronounced ring-like cingulum, as well as a “complex network of secondary ridges”. The 63 teeth (found during on-site excavation in 2012, 2017–2019 and screen-washing in 2017–2019) most likely belong to one species of a derived (stegosaurine) stegosaur. Most of the teeth exhibit a high degree of wear and up to three wear facets has been observed on a single tooth. The prevalence of worn teeth with up to three wear facets and the presence of different types of facets (including steeply inclined and groove-like) indicate the tooth-tooth contact and precise dental occlusion in the Teete stegosaur. The microwear pattern (mesiodistally or slightly obliquely oriented scratches; differently oriented straight and curved scratches on some wear facets) suggest a complex jaw mechanism with palinal jaw motion. Histological analysis revealed that the Teete stegosaur is characterized by relatively short tooth formation time (95 days) and the presence of a “wavy enamel pattern”. Discoveries of a “wavy enamel pattern” in the Teete stegosaur, in a Middle Jurassic stegosaur from Western Siberia, and in the basal ceratopsian Psittacosaurus, suggest that this histological feature is common for different ornithischian clades, including ornithopods, marginocephalians, and thyreophorans. A juvenile tooth in the Teete sample indicates that stegosaurs were year-round residents and reproduced in high latitudes. The combination of high degree of tooth wear with formation of multiple wear facets, complex jaw motions, relatively short tooth formation time and possibly high tooth replacement rates is interpreted as a special adaptation for a life in high-latitude conditions or, alternatively, as a common stegosaurian adaptation making stegosaurs a successful group of herbivorous dinosaurs in the Middle Jurassic–Early Cretaceous and enabeling them to live in both low- and high-latitude ecosystems.

Numerical study of pattern formation in compliant surfaces scraped by a rigid tip.

The emergence of surface patterns on the surfaces of compliant materials subject to plowing wear is a complex problem which can be quantitatively characterized, e.g., on polymer surfaces scraped by an atomic force microscope (AFM) tip. Here we explore the applicability of a phenomenological model recently introduced to describe this phenomenon. Based on the competition between the viscoplastic indentation and the elastic shear stress caused by the tip, the model is able to reproduce the wavy features (ripples) observed when the tip is scanned along a series of parallel lines. For low values of the driving velocity v and the spacing b between scan lines, the existence of dotted areas formed by variously oriented pit alignments is observed. Moreover, coexistence of rippled with dotted domains is also observed at suitable parameter values. The formation process of the ripples is also described in detail. The amplitude, period, and orientation of these features are estimated numerically for different values of v and b parameters. We have also revisited the formation of the wavy patterns formed when a single line is scanned, and derived an equation which correctly describes their period and depth, and the static friction as well. This equation is not applicable when several lines are scanned one after the other and the ripples emerge as result of a cooperative process which involves the scanning of several lines.

Effects of high oil viscosity on oil‐gas downward flow in deviated pipes. Part 1: Experimental setup and flow pattern transitions

AbstractThis work provides new experimental data on high viscosity oil‐gas flow. A set of 170 downward flow experiments were carried out using a mixture of air and mineral oil (213 mPa · s, 50.8 mm internal diameter, 21.5 m long) for five different elevations: −45°, −60°, −70°, −80°, and −85°. Superficial liquid and gas velocities varied from 0.05 m/s to 0.7 m/s and 0.7 m/s to 7 m/s, respectively. Flow pattern transitions were identified and analyzed. The results helped to evaluate the effects of pipe inclination and liquid viscosity on the stratified‐annular transition, as well as the characterization of subclasses of annular flow pattern, named falling film, liquid slip, and wavy annular. Based on the experimental evidence, the study proposes a constant liquid‐fraction value as a transition between liquid slip and wavy annular flow patterns. A comparison of the present data with the flow pattern predictions of the available models were made. Results show disagreements, which justifies the need for a detailed study of the effects of viscosity and the inclination of the pipe in liquid‐gas downward flow mixtures.

A proposed wavy shield for suppression of supersonic jet noise utilizing reflections

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

Analysing effect of cement manufacturing industry on soils and agricultural plants

Today, the study of the effects of dust and gaseous pollutants in the soil as a result of the cement industry, the justification of changes in their properties, the creation of appropriate reclamation technologies is an urgent issue. In the study area, the main source of soil contamination under the influence of the cement industry is dust. The dust mainly spread around the cement plant to a radius of 5,000 meters, causing the soils to become mostly polluted. In the morphological observation of the cross-sections taken by the soil samples, it was mainly influenced by the change in soil colour in the soil surface layer. The chemical and physical properties of the soil change under the influence of pollution, including the tendency to increase the amount of humus as it moves away from the object of study in a wavy pattern. The pH of the soil changed alkalinity. Changes in the agrochemical and other properties of the soil as a result of the cement industry adversely affected the vegetative development of the agricultural plants grown on it, disrupting the growing season and photosynthesis processes and resulting in reduced yields.

The study of retinal structure in frugivorous bat (Rousettus aegyptiacus) by Light and Electron microscope

Vision is fundamentally important sense in animals for perceiving their environment, but in bat less well known. Due to the importance of vision in the bat as the only mammal that is able to fly, in present study, the retinal tissue of the frugivore bat (Rousettus aegyptiacus) was examined by light and electron microscope. So 5 male bats weighing of 123±0.8g were anesthetized, dissected, and their retina was removed. The sections (1×1mm) were isolated, fixed in 4% glutaradehyde and 2% paraformaldehyde (1hour) and rinsed with sodium cacodylate buffer (0.1). They were post fixed in osmium tetroxid 1%. The semithin sections (0.5μm) were stained with Toluidine blue, and the ultrathin sections (70 nm) were prepared. The retinal cells and layer thickness were measured by Grids-sterolite software. Obtained data were analyzed by ANOVA and t test (p < 0.05). Findings showed that the ratio of the eye’s diameter to the body length was 1:18.83. Retina layers conform to the general mammalian blueprint, but in wavy pattern with 106.61±16.19μm thickness. Inner nuclear layer was the thickest layer (18.52±1.55). Retina is duplex with dominant rod cells especially in centralis [≈25cell/(100μ)2], Cone/ Rod ratios: 1/ 7.95, and four other cell types with different density and distribution were seen. According to obtained electro-micrographs, retinal epithelial layer was thin with poor pigmentation and its surface was covered by microvilli. The arrangement of the photoreceptor parallel to the numerous choroidal papillae, and density of rod cells is higher than cone cells according to obtained results, this species of bat can be active in both dim light and daylight.

Design and test of a novel crawler-type multi-channel air-assisted orchard sprayer

In order to solve the problem of poor traveling stability and excessive pesticide application during plant protection operations in hilly orchards, a novel crawler-type multi-channel air-assisted sprayer that is particularly appropriate for hilly orchards was designed in this study. Considering anti-rolling requirements and the orchard environment in hilly areas, this study selected limits for uphill and downhill rolling angles as well as the transverse rolling angle as the evaluation indexes for determining both the layout and parameter settings of the sprayer. According to freely submerged jets and the requirements in plant protection operation, a multi-channel air-assisted system was developed. The test results showed that the anti-rolling performance and the designed air-assisted system were adequate. At 2 m from the longitudinal center plane of the sprayer, the airflow exhibited wavy distribution patterns under different parameter combinations since the four streams of the airflow were not thoroughly intersected and mixed. At 3 m from the longitudinal center plane of the sprayer, the jet was ejected at great velocity but underwent rapid attenuation; the airflow velocity in most areas barely satisfied the requirements for plant protection operation. In addition, different air outlet layout schemes led to significant differences in the spatial distribution of the airflow field. Compared with a traditional air-assisted sprayer, using the developed multi-channel air-assisted sprayer enhanced the droplet coverage uniformity by 19.4%, and the mean droplet deposition in the front, middle, and rear of the canopy was enhanced by 32.9%, 50.3%, and 78.1%, respectively, while reducing ground deposition and air drift by 26.8%. Keywords: fan, dual-flow-channel, plant protection, air-assisted, test DOI: 10.25165/j.ijabe.20201306.5362 Citation: Qiu W, Li X L, Li C C, Ding W M, Lv X L, Liu Y D. Design and test of a novel crawler-type multi-channel air-assisted orchard sprayer. Int J Agric & Biol Eng, 2020; 13(6): 60–67.

Extreme weather events related to climate change: widespread flooding in Iran, March–April 2019

This study investigates the extreme weather pattern accompanying the widespread flash flooding in unpredicted areas during mid-March to April of 2019 in Iran. During this time, the active weather frontal system with heavy and insistent rainfalls drenched Iran (mostly north, west and southern), Iraq and Turkey (eastern part). The climatological mean and anomalies of the meteorological datasets from the National Centers for Environmental Prediction (NCEP) reanalysis model are examined, and synoptic and dynamical patterns are compared. The anomaly weather maps are created for different parameters to show the abnormal features during the study period (months of March and April 2019) presenting significant differences from the thirty-year climate normals of the period 1981–2010. This research shows an intensified pressure gradient, strong vertical motion and strengthened 500 hPa mid-tropospheric westerly currents during the study period. The relative humidity at 850 hPa shows on average ~ 4–11% higher values than the climate normal. The surface wind vector analysis reveals the intensified south flows originated from Oman sea and the Indian Ocean providing rather warmer and wet air mass encounters with an abnormal regional colder surface air mass. Upper level wind vectors at 250 hPa and vertical profile of the meridional wind anomalies exhibit a wavy jet pattern compared to the climate normal structure along with the significant vertical meridional wind shear as the sign of climate change. These abnormal atmospheric changes can contribute to forming extreme weather development over the study area during the study period. Also, understanding the recent extreme atmospheric changes in the study area may contribute to a better future forecast when such floods may happen again.

Challenges in abrasive jet machining of fiber-reinforced polymeric composites – a review

PurposeThe purpose of this study is for solving many issues in production that includes processing of complex-shaped profile, machining of high-strength materials, good surface finish with high-level precision and minimization of waste. Among the various advanced machining processes, abrasive jet machining (AJM) is one of the non-traditional machining techniques used for various applications such as polishing, deburring and hole making. Hence, an overview of the investigations done on carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GRFP) composites becomes important.Design/methodology/approachDiscussion on various approaches to AJM, the effect of process parameters on the glass fiber and carbon fiber polymeric composites are presented. Kerf characteristics, surface roughness and various nozzle design were also discussed.FindingsIt was observed that abrasive jet pressure, stand-off distance, traverse rate, abrasive size, nozzle diameter, angle of attack are the significant process parameters which affect the machining time, material removal rate, top kerf, bottom kerf and kerf angle. When the particle size is maximum, the increased kinetic energy of the particle improves the penetration depth on the CFRP surface. As the abrasive jet pressure is increased, the cutting process is enabled without severe jet deflection which in turn minimizes the waviness pattern, resulting in a decrease of the surface roughness.Research limitations/implicationsThe review is limited to glass fiber and carbon fiber polymeric composites.Practical implicationsIn many applications, the use of composite has gained wide acceptance. Hence, machining of the composite need for the study also has gained wide acceptance.Social implicationsThe usage of composites reduces the usage of very costly materials of high density. The cost of the material also comes down.Originality/valueThis paper is a comprehensive review of machining composite with abrasive jet. The paper covers in detail about machining of only GFRP and CFRP composites with various nozzle designs, unlike many studies which has focused widely on general AJM of various materials.

Palatal rugae morphology is associated with variation in tooth number

This observational study compared palatal rugae morphology in adolescent subjects with normal tooth number and tooth agenesis. Maxillary dental study casts were used to compare rugae number, length and shape. Each study group contained 60 subjects (30 females and 30 males) mean age 13.4 (SD, 1.55) in control and 13.56 (SD, 1.54) years in tooth agenesis groups (p = 0.576). Mean number of missing tooth units in the tooth agenesis group was 2.1. Mean number of primary rugae in the whole sample was 4.35 (SD, 0.98) on the right and 4.33 (SD, 0.92) on the left with no significant differences (p = 0.236 and p = 0.404, respectively). However, the number of secondary rugae on the left (p = 0.006) and fragmentary rugae on the right (p = 0.004) was significantly increased in the tooth agenesis group. The shape of left primary rugae 2 and 3 also differed between groups, tending towards a wavy pattern in the control group and curved in the tooth agenesis group (p = 0.012 and p = 0.004, respectively). In addition, primary rugae 3 was more convergent (p = 0.008) whilst left primary rugae 3 and 5 were orientated in an antero-posterior direction (p = 0.04 for both rugae) in the tooth agenesis group. Subgroup analysis also identified significant associations between patterns of tooth agenesis and rugae number, in addition to shape of primary rugae. The identification of significant differences in rugae pattern between subjects with normal tooth number and agenesis suggests potential commonality in signal pathway disruption during establishment of these structures.

Buckling of bi-layers under in-plane compression

Surface, the front face of any materials or object. Surface properties define the physical appearance, chemical reactivity or stability, optical, friction, mechanical properties etc. To study and manipulate the surface properties is the dire need in present scenario. At present with modern instruments, better understanding of different biological phenomena particularly stability, pattern formation and small scale deformation of membranes have been gained. In the present article a two-dimensional film which is in a frictional contact with the substrate which developed between the film and the substrate using the contact interactions is studied. Surface morphology and stability evolution of a thin elastic film subjected to in-line axial force is investigated. The instability of the 2D thin film under different elastic conditions and boundary conditions is examined using finite element simulation. The response to perturbation in which surface of the film becomes unsteady and forms a wavy pattern without any simultaneous mass transport. A complete picture stability/bifurcation is obtained for different elastic modulus ratios of film and substrate. Result revealed that the wavelength is directly proportional to elastic modulus of the film. The growth rate of perturbations is also analysed. The pattern instability in the thin films which are fixed on a substrate by adhesive forces decreases with the decrease in elastic modulus of the film. Study revealed that the morphology of the film is independent of forces exerted however seems dependence on the nature of the film. The film shows stability in its pattern when its elastic modulus is same as substrate elastic modulus or the ratio of modulus is close to unity. This study will be helpful in in choosing the surface coating to coat over the base material, design material of required properties coating life and estimating the life of coating.

Evaluation of the Anterior Talofibular Ligament by Stress Ultrasound for Assessing Generalized Joint Hypermobility

Category:Ankle; Basic Sciences/BiologicsIntroduction/Purpose:Chronic ankle instability with generalized joint hypermobility (GJH) is considered a relative contraindication for the modified Bröstrom procedure. Most clinicians use the Beighton score to assess GJH. However, the Beighton score itself does not involve investigation of the ankle joint. In our experience, resting, longitudinal ultrasound images of the uninjured, intact ATFL frequently show a loose, wavy pattern in patients with high Beighton scores. We evaluated anterior talofibular ligament (ATFL) status according to Beighton score and the manual anterior drawer test (ADT). It was hypothesized that the value of ultrasound for ATFL would be significantly different between participants with GJH (Beighton score >= 5) and without GJH and show a correlation with participant’s Beighton scores and manual ADT grades.Methods:Forty-four healthy young patients (44 ankles) aged 20 to 40 years and without a history of ankle trauma or disease were included in the study. To assess GJH and ankle instability, Beighton scores and manual ADT grades were evaluated, respectively. For the investigation of ATFL, resting and stress ultrasonography were performed to assess its length, height, and thickness. Ultrasound images were taken in resting position and during maximal plantar-flexion and inversion (Figure: Ultrasound images of the ATFL in (a) the resting position and (b) stress position in a 21-year-old woman with Beighton score of 9. Dotted red line: Length, Yellow line: Height, Green double-headed arrow: Thickness). Beighton scores, manual ADT grades, and ultrasound parameters of participants with and without GJH were compared and the correlation coefficients among Beighton scores, manual ADT grades, and the length, height, and thickness of resting and stress ATFLs were analyzed.Results:The participants were divided into two groups, those without GJH (24 ankles) and with GJH (20 ankles). Mean Beighton scores and manual ADT grades were significantly different between the two groups (P < .05). The mean length, height of resting, stress ATFL and mean difference in height between resting and stress ATFL were significantly different between the two groups (P < .05). The resting and stress ATFL length, height, and difference in height between resting and stress ATFL showed a moderately positive linear relationship with Beighton scores and manual ADT grades (P < .05). Among the ATFL parameters, resting ATFL height showed the strongest relationship with the Beighton score (r = 0.763, P < .001) and ADT grade (r = 0.763, P < .001).Conclusion:The ATFL stress ultrasound parameters showed significant differences between participants with high and low Beighton scores and were correlated with Beighton scores and manual ADT grades. We believe that this ankle joint specific method might provide significant, quantitative parameters for assessing GJH in addition to the Beighton score.

Study on micromagnets induced local wavy mixing in a microfluidic channel

The phenomenon of ferrofluid-water mixing is investigated using a double-layer magnetic micromixer, in which a layer of micromagnet bars is placed immediately below the fluid layer. A wavy pattern of the ferrofluid–water interface is surprisingly observed at each micromagnet responsible for improved mixing. The mechanism causing the wavy mixing is discovered and analyzed through experimental measurements and numerical simulations, and the mixing efficiency under different flow conditions is discussed. For flows with Re ≪ 1, the resultant steep gradient of opposing magnetic forces by micromagnets in the ferrofluid region gives rise to a local pressure source that induces a transverse/spanwise pressure gradient and activates momentum transfer between fluids. The current finding enables effective localized mixing of ferrofluids with a small footprint and, thus, has great potential to achieve fast mixing for high-throughput flows with an integrated parallel system of multiple microfluidic channels and micromagnets.

Acoustic response of high-speed deep groove ball bearing by modifying the internal geometry

In this paper, a mathematical model to predict acoustic responses of high-speed bearing has been developed and demonstrated in an application of Induction motors. Effect on the acoustic behaviour of bearing has studied by modifying the internal geometry, such as the number of rotating elements, curvature ratio, rotating speed with the oval shape of the track raceway due to pre-operational damage. The mathematical model predicts the contact stress, elliptical contact area, noise level dB and Frequencies of waviness pattern. High-speed bearing is tested at four different speeds to monitor acoustic behaviour. This drive end bearing undergoes different rotational speeds; however, the author has simulated the results at a majorly driven constant speed. The author has incorporated application-level testing at the customized test rig. The mathematical model has simulated using coupled governing equations with the help of the Ranga-Kutta method. The simulation and experimental results presented in this paper in the form of a waterfall diagram, FFT spectrum and colour pressure plots. Acoustic characteristics during measurements of the rolling bearing have shown systematically to correlate the mathematical model with an experimental result. Results indicate the remarkable influence of raceway nonconformities of bearing on the noise level. The novelty of research study is to estimate the amplitude of noise level due to waviness generated on rings of bearing after pre-operation damage which is the realistic scenario that occurred after a complaint recorded by the motor manufacturer. The authors believe that this technique enables the bearing designer to choose the appropriate diametric ratio of the ball and track curvature for elliptical contact stress as well as acoustic level. This method is developed specifically for an application of drive-end position ball bearing. Practical use of this method is to determine the Noise level of an electric motor (up to 60 kW capacities) due to improper handling and inappropriate installation of bearing which cause inherent waviness on components.

A legend reborn: Additive manufacturing creates Wootz-Damascus steel

Artisans in ancient India melted iron with woodchips as sources of carbon in clay crucibles and produced a hypereutectoid steel (C content ∼1.5% by weight) called Wootz steel. Their technique, perfected over centuries, resulted in steels of high strength and ductility. These steels were traded in Damascus and spread to many countries, which turned them into swords of amazing performance with aesthetically pleasing wavy patterns on the surface. Combining the expertise of researchers at the Max Planck Institute for Iron Research in alloy design with that in laser processing by a team at the Fraunhofer Institute for Laser Technology, a new Damascus-like steel has now been created by additive manufacturing (AM), commonly known as three-dimensional (3D) printing. The key to the success of this work, as reported in a recent issue of Nature (doi:10.1038/s41586-020-2409-3), is the innovative use of the digital capabilities of AM to introduce a controlled hierarchical structure without the need for post-treatment.

Flow fields induced by longitudinal ventilation and water spray system in reduced-scale tunnel fires

Computational Fluid Dynamics (CFD) simulation results, obtained with FDS 6.0.1, are presented of reduced-scale tunnel fire tests with longitudinal mechanical ventilation and an activated water spray system. This is a sub-set of a more extensive data set, in the context of blocking fire-induced smoke tunnel tests conducted previously. As discussed in Sun et al. (2018), CFD can complement the experimental data, providing thermocouple tree temperature measurements, yielding insight into the turbulent flow field generated by the fire and the water spray. The CFD settings, decided upon on the basis of an extensive mesh sensitivity study in Sun et al. (2018), are applied here to illustrate the impact of longitudinal mechanical longitudinal ventilation in cases with and without the water spray system activated. Analysis of the mean flow and temperature fields provides significant additional insight into the impact of the combined longitudinal ventilation and the water spray system on the fire-induced smoke flow. The upward flow in between the water sprays in the absence of longitudinal ventilation is still observed, but it does not impinge onto the ceiling anymore: the horizontal momentum from the mechanical ventilation makes the ‘pushing’ force of the spray-induced downward flows impinging onto the floor less strong and moves them further downstream. Consequently, the smoke crosses the water spray system region. The smoke stratification is lost downstream of the spray region. Upstream of the water sprays, and throughout the tunnel in the absence of the water spray system, a wavy pattern is obtained in the smoke layer. This is related to the Froude or Richardson number for the flows with the settings at hand. The presence of the water spray system downstream of the fire affects the flow and temperature fields up to the fire source.

Snake Tracks in Polymer Land: Wavy Polymer Structures via Selective Solvent Vapor Annealing.

Wavy patterns are interesting geometric patterns and commonly seen in nature, such as serpentine streams or snake tracks in the sand. Although many efforts have been devoted to fabricating artificial wavy structures, it remains a great challenge to obtain wavy structures with controllable curvatures and desired functional properties. Here, we present an unprecedented approach to generate wavy polymer structures by annealing electrospun core-shell fibers on polymer films. Polystyrene (PS)/poly(methyl methacrylate) (PMMA) core-shell fibers, produced via the viscosity-induced phase separation in the electrospinning process, are annealed on PMMA films using vapors of acetic acid, a selective solvent for PMMA but not for PS. After the swollen PMMA chains of the PMMA shells are shed, the revealed PS cores start to buckle, driven by the elastic force from the strain release, forming the wavy structures. The degrees of the buckling, measured by the curvatures and the amplitudes of the wavy structures, are controlled by the annealing times. Furthermore, fluorescent properties are selectively introduced to the wavy structures using pyrene solutions or pyrene-containing vapors, demonstrating the potential application as fluorescent wavy materials.

Numerical analyses of crack path instabilities in quenched plates

Crack path instabilities are observed in rapidly quenched rectangular glass plates whereby wavy crack patterns form as a result of the induced temperature gradients. The peculiar characteristic of these instabilities is that the speed of propagation is several order of magnitudes lower that the Rayleigh wave speed. Experimental studies have shown the dependence of the instabilities on certain geometrical, material, and experimental parameters (e.g. plate width, material toughness, speed of quenching). By perturbing these parameters cracks are observed to propagate along a straight line, oscillate with a periodic sinusoidal or semi-circle like morphology, or propagate in a supercritical manner. Here we formulate the problem of a propagating crack in a brittle thermoelastic material while considering the possibility of the crack undergoing bursts of supercritical crack propagation, by extending the model in Negri and Ortner (2008). We also describe a novel higher order computational framework for its numerical solution centered around Universal Meshes, Mapped Finite Element Methods, and Interaction Integral Functionals. We verify the convergence of the results and compare them against experiments. We reveal crack behaviors not previously observed. Particularly we discuss periods of sudden crack propagation, followed by temporary arrest and crack kinking. We identify various crack morphologies: sinusoidal, asymmetric, semi-circle, kinked and flattened oscillations. We investigate the frequency content of the oscillatory crack paths and study their relation to the dominating problem parameters. Additionally, we identify two new thresholds in phase space corresponding to the transition from oscillatory propagation to rapid propagation and arrest, as well as from permanent crack arrest to temporary crack arrest followed by kinking and branching.