Constriction in the flow passage of the physiological circulatory system is central to the occurrence of several diseased conditions such as thrombosis and is also pivotal towards the understanding of several regulatory processes in the human microvasculature. It is, therefore, imperative to advance a mechanistic insight into the dynamics of lipid vesicles, cell mimicking, fluid-filled compartments, through a physiologically relevant microconfinement, with particular focus on deciphering the role of its mechanophysical properties. Here we bring out the role of membrane bending rigidity and the initial deflation (deviation in shape from sphericity) on the transient shape evolution of a lipid vesicle as it migrates through a microfluidic constriction, a paradigm that is unexplored thus far. Based on our experimental observations as well as theoretical insights, we construct a regime map to elucidate the range of the key dimensionless parameters orchestrating this dynamical transition. Furthermore, our observations on the vesicle's stretching dynamics emerging from selective mapping with viscosity contrast between the encapsulated and the suspending fluid medium offer potential physiologically relevant cues on the impact of cell aging on its deformability across a constricted path. Such mechanistic insights may help in establishing quantitative correlations between the dynamical transition of a lipid vesicle and its membrane mechanics, which may in turn have decisive implications in health and disease while circulating across microvascular fluidic pathways.

A model is presented to explain why tubular halloysite rolls in preference to tetrahedral rotation to correct misfit of the octahedral and tetrahedral sheets. It is shown that the rolling mechanism operates as it encounters significantly less resistance from Si-Si repulsion in comparison to tetrahedral rotation to correct the same amount of misfit. The model explains the observed and experimental rolling of planar kaolinites to form tubular halloysite upon hydration and exfoliation.

A well-characterized kaolinite has been hydrated in order to test the hypothesis that platey kaolinite will roll upon hydration. Kaolinite hydrates are prepared by repeated intercalation of kaolinite with potassium acetate and subsequent washing with water. On hydration, kaolinite plates roll along the major crystallographic directions to form tubes identical to proper tubular halloysite. Most tubes are elongated along the b crystallographic axis, while some are elongated along the a axis. Overall, the tubes exhibit a range of crystallinity. Well-ordered examples show a 2-layer structure, while poorly ordered tubes show little or no 3-dimensional order. Cross-sectional views of the formed tubes show both smoothly curved layers and planar faces. These characteristics of the experimentally formed tubes are shared by natural halloysites. Therefore, it is proposed that planar kaolinite can transform to tubular halloysite.

Kaolin-group clay minerals can be modified to form nanotubular and mesoporous structures with interesting catalytic properties, but knowledge of the best methods for preparing these structures is still incomplete. The objective of this study was to investigate intercalation/deintercalation as a method for the delamination and rolling of kaolinite layers in relation to structural order. To prepare nanotubular material, kaolinites of different crystallinities and halloysite (all from Polish deposits) were chosen. The experimental procedure consisted of four stages: (1) preparation of a dimethyl sulfoxide precursor intercalate; (2) interlayer grafting with 1,3-butanediol; (3) hexylamine intercalation; and (4) deintercalation of amine-intercalated minerals using toluene as the solvent. Structural perturbations and changes in the morphology of the minerals were examined by X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and transmission electron microscopy (TEM). The number of rolled kaolinite layers depended heavily on the efficiency of the intercalation steps. An increase in the structural disorder and extensive delamination of the minerals subjected to chemical treatment were recorded. Kaolinite particles which exhibited tubular morphology or showed rolling effects were observed using TEM. The nanotubes formed were ∼30 nm in diameter, with their length depending on the particle sizes of the minerals.

Flat products of carbon nanotubes (CNTs) reinforced Al matrix composites were fabricated using flake powder metallurgy via shift-speed ball milling and hot-rolling. The evolution of CNTs during preparation and the final distribution in the Al matrix were investigated, and the effect of CNT content on mechanical properties were discussed. Due to the combined effect of uniform dispersion of CNTs, structural integrity, interfacial bonding and directional alignment, the balance between high strength and ductility was successfully achieved in the annealed rolled composites with 1.5 wt% CNT addition, with the value of 382.6 MPa in tensile strength and 9.8% in fracture ductility. The load transfer strengthening was the main mechanism of the strength enhancement with CNTs addition. In addition, a strong rotated cube {001}〈110〉 texture was found in the final flat product of rolled composites. This study provides an effective route to produce and improve the mechanical properties of CNT/Al flat products.

Robotic hands use rolling contact to manipulate a grasped object to a desired location, even when the finger and the palm linkage mechanisms lack degrees of freedom. This paper presents a systematic approach to the forward and inverse kinematics of in-hand manipulation. The moving frame method in differential geometry is integrated into the product of exponential formula to establish a pure geometric framework of the kinematics of a robot hand. The forward and inverse kinematics of a multifingered hand are obtained in terms of the joint rates and contact trajectories. A two-fingered planar robot hand and a three-fingered spatial robot hand are used to demonstrate the proposed approach. The proposed formulation amounts to solving a univariate polynomial, providing an alternative to the existing ones that require numerical integration.

Various routes (unidirectional, cross, and three directions) normal and different speed rolling (DSR) are conducted on pure titanium sheet at 673 K and sequent 933 K annealing is followed. The results show that transverse direction (TD)-split double peak texture is kept during unidirectional rolling and a fiber basal texture is formed after cross and three-direction rolling. However, TD-split texture is preserved and rotates about 45° while the fiber basal texture is generated after cross and three direction rolling combining (DSTDR) DSR, respectively. This may be related to the changed strain path and induced shear deformation as well as thermal activation. Due to rotation of grains, the anisotropy of mechanical properties of Ti sheets decreases, especially in various DSR routes. Erichsen value is improved greatly in DSTDR specimens.

Between 1995 and 2011 a global positioning system survey of 13 boulders and three ablation stakes (long stakes frozen in the ice) on the frozen surface of Lake Hoare was undertaken. Data interpretation illustrates complexities of post-depositional transport dynamics of boulders. Earlier studies on comparable datasets have suggested linear ‘conveyor’ type transport mechanisms for lake surface boulders. Yet explanations for non-linear boulder displacements or ‘walks’ and the mechanisms responsible for movements are inadequate. Two modes of boulder specific movement were observed. First, localized changes in the ice surface promote individual boulder movement (rolling). Second, ice rafting, which indicates the displacement of ‘plates’ of lake ice on which the boulder is located. Ablation stakes used as fixed survey control points support the hypothesis that ice cover moves as discrete plates rather than as a single homogenous mass. Factors that create the conditions to generate either of the two modes of movement may be related to location specific energy budgets. A relationship between average orientations and prevailing wind direction was also observed. The investigation describes the local-scale behaviour of surveyed boulders, and offers methodologies and interpretive frameworks for additional studies of modern and ancient sediment transportation dynamics in Antarctic lacustrine environments.

Cast AZ31B-H24 magnesium alloy, comprising Mg with 3.27 wt% Al and 0.96 wt% Zn, was cold rolled and subsequently annealed. Global texture evolutions in the specimens were observed by X-ray diffractometry after the thermomechanical processing. Image-based microstructure and texture for the deformed, recrystallized, and grown grains were observed by electron backscattered diffractometry. Recrystallized grains could be distinguished from deformed ones by analyzing grain orientation spread. Split basal texture of ca. ±10–15° in the rolling direction was observed in the cold-rolled sample. Recrystallized grains had widely spread basal poles at nucleation stage; strong {0001} basal texture developed with grain growth during annealing.

Following the Upper Bound Method (UBM), the velocity field in a rolling process is theone that minimises the power function [W. Prager, P.G. Hodge, Theory of PerfectlyPlasticity Solids, Wiley, New York, 1951]. Generally, a family of velocity fields with fewparameters is studied and the velocity field which minimises the power function is thebest approximation of the real one. The lower the power, the better the approximation is.This paper presents a new family of velocity fields for the UBM approach of a rollingprocess in plane-strain conditions (2D). That family is based on the addition by an“oscillating perturbation” to a classic velocity field whose longitudinal component isconstant in the strip thickness. We show that the best field of that family gives a betterapproximation than the classic one. This study proves there is an oscillating part in thevelocity field during the rolling process. A careful observation of the fields obtained bya finite-element method, Lam3-Tec3 (1), shows that the oscillation phenomenon is in factreally present. And the oscillations predicted by the analytical model (UBM) match the FEMresults very well.

Experimental rolling trials were performed at different temperatures on EN 1.4462 duplexsteel imposing also different reduction ratios and a possible solution quenching. A clearand significant relation between the applied thermo-mechanical process and themicrostructural evolution was shown, and it is useful for designing the steelmicrostructure. The mechanical properties, the micro-structural features and the texturecharacteristics were defined for each condition in order to point out the operativeparameters (i.e. thermal level, imposed strains and application of solution quenching)that permit to maximize the formability of the final hot-rolled products.

Dans certains procédés de mise en forme, tel que le laminage, l'apparition des contraintes résiduelles est inévitable et peut engendrer le flambage qui se traduit en défauts géométriques. Ceci exige la modélisation de ce phénomène d'instabilité mécanique afin de bien définir la forme et l'amplitude de ces défauts. Cela nécessite un modèle complet ayant des capacités pour le calcul du post-flambage. Dans le présent article, on présente un modèle de flambage possédant la faculté de détecter la charge critique de flambage et la forme post-flambée d'une plaque sous contraintes résiduelles. Des applications à des cas académiques et un cas de laminage seront aussi traités.

Le travail présenté ici porte sur l'application au laminage des modèles de comportement récemment développés en plasticité grandes déformations en vue de la simulation numérique des procédés de mise en forme et notamment de l'emboutissage : modèle rigide plastique avec écrouissage isotrope, critère de Hill quadratique ou non-quadratique, plasticité associée ou non, viscoplasticité. Après avoir brièvement présenté ces modèles nous les intégrons dans le modèle classique de laminage (méthode des tranches, équation de Karman). La solution est obtenue en déterminant le point neutre par une méthode de tir.Ces modélisations sont ensuite illustrées par une analyse paramétrique de l'influence des divers paramètres constitutifs sur la réponse et une comparaison sur un matériau donné de différents modèlesen exploitant les modèles identifiéspar A. Khalfallah, A. Znaidi et A. Darsouni finalise ce travail.

Cover-crop residues left on the soil surface as a mulch in no-till crop production systems protect the soil from erosion, increase water infiltration and suppress weeds. Because many growers using cover crops want to reduce chemical inputs, non-chemical methods of killing or suppressing cover crops are needed. In the first part of this paper we review the current literature and discuss advantages and disadvantages of five mechanical methods for killing cover crops, i.e., mowing, rolling, roll-chopping, undercutting and partial rototilling. We also report on three new studies that broaden the current literature, including planting into freshly killed residue. In the first study, the use of planter attachments to remove surface residues from the planter row improved stands when cotton was no-till planted 2–7 days after mowing cover crops in Mississippi. In the second study, 100% of a rye/vetch cover crop in Missouri was killed by mowing, and greater than 90% was killed by roll-chopping. Cotton stands were reduced by the use of row cleaners that clogged when the cover crop was roll-chopped or mowed on the same day that the crop was planted. The third study evaluated three methods of mechanically killing summer cover crops in North Carolina. Undercutting provided greater than 95% kill for five of six broadleaf species, and two of five grass species. Mowing effectively killed all six broadleaf cover crops, but re-growth occurred with three of five grasses, with the exception of nearly mature German foxtail millet and mature Japanese millet. In general, rolling did not effectively kill broadleaf or grass cover crops, with the exception of nearly mature German foxtail millet, mature Japanese millet and mature buckwheat.

In many cases in experimental science, the instrument interface becomes a limiting factor in the efficacy of carrying out unusual experiments or prevents the complete understanding of the acquired data. We have developed an advanced interface for scanning probe microscopy (SPM) that allows intuitive rendering of data sets and natural instrument control, all in real time. The interface, called the nanoManipulator, combines a high-performance graphics engine for real-time data rendering with a haptic interface that places the human operator directly into the feedback loop that controls surface manipulations. Using a hand-held stylus, the operator moves the stylus laterally, directing the movement of the SPM tip across the sample. The haptic interface enables the user to “feel” the surface by forcing the stylus to move up and down in response to the surface topography. In this way the user understands the immediate location of the tip on the sample and can quickly and precisely maneuver nanometer-scale objects. We have applied this interface to studies of the mechanical properties of nanotubes and to substrate-nanotube interactions. The mechanical properties of carbon nanotubes have been demonstrated to be extraordinary. They have an elastic modulus rivaling that of the stiffest material known, diamond, while maintaining a remarkable resistance to fracture. We have used atomic-force microscopy (AFM) to manipulate the nanotubes through a series of configuration that reveal buckling behavior and high-strain resilience. Nanotubes also serve as test objects for nanometer-scale contact mechanics. We have found that nanotubes will roll under certain conditions. This has been determined through changes in the images and through the acquisition of lateral force during manipulation. The lateral force data show periodic stick-slip behavior with a periodicity matching the perimeter of the nanotube.