Large Face Research Articles

Geometric displacement optimization of external helical gear pumps

An approach to geometric displacement optimization of external helical gear pumps is presented. In addition, relations of pump flow property and its influence factors are also investigated. During that, only the pumps with transverse contact ratios of not less than one are discussed. First, using the involute property, an analytic representation for flowrates is deduced, by which displacements and fluctuation coefficients of helical gear pumps can be calculated accurately and efficiently. Then, by incorporating several design considerations, optimization problems for maximum geometric displacement are formulated and solved integrally by an optimization code, Multifunctional Optimization System Tool, with which various types of design variables including real, integer, and discrete can be simultaneously dealt with. Finally, the desired pumps with optimal displacement can be obtained. The proposed approach facilitates the design optimization of helical gear pumps. Moreover, influences of design parameters on the displacement and flow characteristics of the optimal pumps by assigning individual parameters are investigated. The result also concludes that the pump with a larger module, larger face width, or smaller tooth number has bigger displacement but may cause more severe flowrate fluctuation.

Structures of Zinc Oxide Nanoclusters: As Found by Revolutionary Algorithm Techniques

We report the stable and low energy metastable structures of zinc oxide clusters, (ZnO)n, n = 1−32, found using an evolutionary algorithm with polarizable shell interatomic potentials. This study comprises the first systematic search for nanoparticulate structures for this compound above n = 18 and includes a comparison with other recent studies. As a function of n, global minimum and low energy metastable clusters evolve from rings (up to ca. 0.8 nm in diameter) to perfect closed bubbles (up to ca. 1.2 nm in diameter in the range reported), which are the structures that only contain tetragonal and hexagonal faces and all ions have a coordination number of three. The transition between the two structural families is blurred, with key structures that are also (i) open bubbles, which contain octagonal or larger faces, and (ii) bubbles that have handles, or two-dimensional ring fragments attached. A new nomenclature to describe these structures is defined. We find a greater stability of tetrahedral and trigonal coordinations compared to tetragonal for ZnO clusters in the range considered. Of the predicted global minimum clusters, spheroid cages n = 12, 16, and 28, with symmetry point groups Th, Td and T, and barrels, which are a common motif, exhibit a relatively high stability. Bulklike wurtzite, or multilayered clusters, as well as the simple cuboid and related rock salt configurations are not found to be thermodynamically stable in the size range considered.

Three-dimensional Facial Morphometry of Attractive Children and Normal Children in the Deciduous and Early Mixed Dentition

To identify possible esthetic canons in facial size and shape of Italian children. The three-dimensional coordinates of 50 facial landmarks (forehead, eyes, nose, cheeks, mouth, jaw, ears) were collected in 220 healthy reference children (4-9 years old) and in 89 "attractive" children of a similar age group selected by a commercial casting organization. Soft-tissue facial angles, distances, and volumes were computed. Comparisons were made with the Student's t-test. Attractive children had a larger face than the reference children, with a larger maxilla and forehead; overall, their faces were wider and deeper, but less vertically developed. Lips were more voluminous in attractive children, with a higher mouth. The nose was larger in attractive children than in reference children. The soft-tissue facial profile was more convex in attractive children, with a more prominent maxilla relative to the mandible. Overall, considering that in the analyzed ages body growth and dental changes are very fast and individually determined, all the measurements appeared sufficiently homogenous, and the quantitative characteristics of an "attractive" face well defined. Esthetic reference values can be used to determine optimal timing and goals in orthodontic treatment.

Facile Monolayer Assembly of Fluorophore‐Containing Zeolite Rods in Uniform Orientations for Anisotropic Photoluminescence

Which way to turn: The tendency of microcrystals to attach to surfaces through their largest faces has resulted in two orientations of zeolite L monolayers on glass. Fluorophore-containing cylindrical and hexagonal columnar zeolite L crystals assemble into vertically and horizontally oriented monolayers, respectively, on glass plates (see pictures). The photoluminescences of the monolayers are highly anisotropic.

Fluorescence losses from Yb:YAG slab lasers.

We report on the distribution of fluorescence that can be emitted through the surfaces of a ytterbium-doped yttrium aluminum garnet (Yb:YAG) slab-shaped high-power solid-state laser. Slab shapes considered include parallel or antiparallel Brewster endfaced slabs and rectangular parallelepiped slabs. We treat cases in which all the faces of these slabs are in air, or with water or another coating on the largest faces. The fraction of the fluorescence emitted through each face, its distribution over that face, and the directions in which it travels are shown to be important to the design of high-power slab lasers.

Maximum bite force, muscle efficiency and mechanical advantage in children with vertical growth patterns.

This study correlated maximum bite force and masticatory muscle electromyography (EMG) activity with craniofacial morphology and mechanical advantage of children with vertical growth patterns. From lateral cephalograms of 30 females and 17 males (9.3 +/- 3.6 years of age), 13 morphological and eight biomechanical measurements were recorded. Two maximum bite forces and 12 submaximal bite forces along with their associated EMG muscle activity were recorded at the right mandibular first molar. Muscle efficiency was evaluated using the relationship between bite forces and EMG activity levels. There were no significant sex differences (P > 0.05) for any of the morphological, functional or biomechanical variables. Factor analyses reduced: (1) the 13 morphological variables to four factors explaining 82.8 per cent of the morphological variance; (2) six functional variables to two factors explaining 68.8 per cent of the functional variance; and (3) 11 biomechanical variables to three factors explaining 90.9 per cent of the biomechanical variance. The vertical size factor was negatively correlated with the muscle efficiency factor (r = -0.39; P = 0.006) and positively correlated with the moment arm factor (r = 0.67; P < 0.001). The morphological divergence factor was negatively correlated with the bite force factor (r = -0.34; P = 0.019) and the mechanical advantage factor (r = -0.32; P = 0.028). The muscle efficiency factor (functional) was negatively correlated with the moment arm factor (r = -0.33; P = 0.023). It is concluded that: (1) independent of chronological age, children with larger faces have larger moment arms and require less muscle activity to attain any given force, and (2) greater hyperdivergence is related to poorer mechanical advantage and lower maximum bite force. These data support the relationships between bite force, muscle strength and morphology in children, similar to those reported for adults.

Surface Characterization of Cholesterol Monohydrate Single Crystals by Chemical Force Microscopy

Atomic force microscopy (AFM) and chemical force microscopy (CFM) techniques have been used to characterize the chemical functionality of cholesterol monohydrate single-crystal surfaces in different solution environments. Both synthetic and natural crystals adopt a platelike habit in which the largest face is (001). Under aqueous and organic solution conditions, in situ contact mode topographical images reveal that the plate face is primarily terminated by bilayer molecular structures and therefore largely homogeneous. Adhesion force measurements obtained with chemically modified tips demonstrate that the functionality of the crystal surface can be altered by changes in the solution composition. The 3-hydroxyl end of cholesterol molecules is presented on the plate face in aqueous media, while alkyl tail groups terminate the surface in organic solutions. Contact angle measurements on (001) surfaces exposed to solvents of different hydrophilicity also show similar trends, providing additional support to the...

Three-dimensional assessment of the effects of extraction and nonextraction orthodontic treatment on the face

The purpose of this prospective study was to compare the 3-dimensional (3-D) effects on the face of extraction and nonextraction orthodontic treatment in patients with skeletal Class I patterns. The sample of 24 patients included 12 whose treatment included extractions and 12 who were treated without extractions. Pretreatment study casts were assessed to evaluate dental differences between the 2 groups. Pretreatment and posttreatment lateral cephalograms and optical surface scans were also compared. In the lateral cephalometric assessment, the only significant (P <.05) pretreatment difference was lower lip length. Posttreatment, the nasolabial angle and lower lip thickness were significantly different (P <.05). Registration of the average 3-D optical surface scans indicated that, before treatment, the nonextraction group had longer and broader faces by 5 to 7 mm, and the upper lip and labiomental fold were 3 to 5 mm farther forward than in the extraction group. Posttreatment, the nonextraction group still had larger faces, but the difference was smaller. Faces in the extraction group became relatively more protrusive with treatment. The surface shape analysis technique showed that the cheeks were flatter in the nonextraction group at the start of treatment, but this reversed with time. In the extraction group, the concavity of the labiomental fold increased, while the nonextraction group showed no change in this area. The study demonstrates that 3-D optical surface scans offer more data for analysis compared with lateral cephalograms alone. It also highlights the changes that can be detected with surface shape analysis. (Am J Orthod Dentofacial Orthop 2002;121:244-56)

Relation between texture and critical current density of textured YBa/sub 2/Cu/sub 3/O/sub x/ plates

Textured YBa/sub 2/Cu/sub 3/O/sub x/ plates show a significant spread in the critical current density up to 12.000 A/cm/sup 2/ measured by direct transport current at 77 K. This spread is related to the crystalline texture of the material. Optical polarization microscopy is used for initial examination of crystal alignment and texture. We use synchrotron radiation at 100 keV to perform x-ray diffraction measurements to obtain quantitative information about the texture. The crystallographic [110]-direction is found to be preferentially along the slab and the c-axis is parallel to the largest face. DC-magnetization is used to measure the magnetization critical current density of pieces cut around each x-ray measurement point. The results from x-ray diffraction, optical microscopy and magnetization critical current density are compared to the transport critical current density. The magnetization critical current is found to decrease exponentially with the in-plane texture.

The local structure of various hydrogen bonded liquids: Voronoi polyhedra analysis of water, methanol, and HF

The local structure of three hydrogen bonded liquids comprising clusters of markedly different topology: water, methanol, and HF are investigated by analyzing the properties of the Voronoi polyhedra (VP) of the molecules in configurations obtained from Monte Carlo computer simulations. For comparisons, the properties of argon as a nonassociating reference liquid are also calculated. It is found that in liquid HF the fluctuation of the local density is much larger than in the other three liquids, and hence, besides the dense regions, this liquid contains numerous large voids as well. The size of the largest of these voids is found to be commensurate with a cluster of 11 HF molecules, whereas the number of voids as large as one molecule is in the order of the number of molecules. It is found that the number of the hydrogen-bonded neighbors of the HF molecules located at the boundary of such voids does not differ considerably from that of the other molecules, and thus they do not have any specific topological position (e.g., chain terminal) in the hydrogen bonded chains of the molecules. The shape of the VP is found to reflect the arrangement of the nearest neighbors of the molecules. Thus, the VP are considerably less spherical and their topological properties are distributed in a wider range in the associated liquids than in argon. Similarly, in the hydrogen bonded liquids considerably more geometric neighbors are found than the number of molecules belonging to the first coordination shell. On the other hand, in liquid argon, which is a closely packed system, the two values are found to be close to each other. The inhomogeneities of the local density of liquid HF are also reflected in the shape of the VP. The molecules located at the boundary of the large voids are found to have more spherical VP with more and larger faces than the other ones.

Failure of woven carbon–polyimide laminates under off-axis compression loading

This paper reports the failure mechanisms in a woven 0/90 carbon–polyimide laminate under 45° off-axis compression loading. The stress carried by the composite increased linearly with increasing levels of applied displacements and, at about 188 MPa, the load dropped suddenly to 172 MPa and remained constant thereafter till about 8.9% strain, at which point the load reduced drastically and resulted in the ultimate failure of the sample. The damage started with the nucleation of several in-plane cracks which split both the wrap and fill yarns completely, and ran diagonally across the sample’s entire width. Upon further loading, the cracking progressed in bundles towards the sample’s interior, and eventually, at a strain of about 5%, a saturation cracking state was reached with each bundle split by at least three-to-four longitudinal cracks. The sample was able to accommodate further strain via nucleation of additional cracks formed at the edges of the longitudinal cracks with their planes parallel to the loading axis and orthogonal to those occupied by the longitudinal cracks. Essentially, these new cracks separated the longitudinally-split bundles in the sample’s thickness direction and resulted in the creation of three-to-four independent bundles from the original well-bonded warp or fill bundle. At this stage, the compressive load carrying capacity of the original bundle was largely compromised and the sample failed through gross delaminations, resulting in the bulging of the sample normal to its largest faces. The above deformation was remarkably different from that observed under bundle-aligned compression loading where the samples failed at an average stress of 588 MPa [1][Grape, J. and Gupta, V. Composite Materials, 1995, 29, 1850] in more or less brittle catastrophic manner after undergoing only 1.5% strain.

Large faces in 4-critical planar graphs with minimum degree 4

We prove that the size of the largest face of a 4-critical planar graph with δ≥4 is at most one half the number of its vertices. Letf(n) denote the maximum of the sizes of largest faces of all such graphs withn vertices (n sufficiently large). We present an infinite family of graphs that shows $$\mathop {\lim }\limits_{n \to \infty } \frac{{f(n)}}{n} = \frac{1}{2}$$ .

Capillary phenomena. Part 10.—Behaviour of grooved rods at fluid/fluid interfaces

The force–displacement behaviour at a fluid/fluid interface is described for a vertically-positioned cylindrical solid, with recurring horizontal grooves, i.e., the solid consists of truncated cones alternately joined at pairs of smaller and larger faces. When the grooves are relatively large, the excess applied force needed to withdraw and immerse the rod shows loops with irreversible jumps as a function of displacement. These are explained in terms of stability and instability where the fluid/fluid interface meets the solid: at outer-edge, inner-waist and upper-and lower-sloping surfaces. When the grooves are small relative to the outer-solid radius the system provides a model for contactangle hysteresis due to surface roughness. An observed contact angle as a function of solid displacement gives a hysteresis loop for a chosen intrinsic contact angle.

Characterization and Sintering Behavior of Ba and Sr Ferrites

Barium oxide is essentially insoluble in BaO·6Fe2O3, and the nominal compositions BaO·5.5Fe2O3, and SrO·5.5Fe2O3 used commercially may consist of the 1:6 phase and, respectively, one and two minor phases. Compacts formed by mechanical pressure filtration in a magnetic field are characterized by oriented aggregates of platy particles with planar faces and planar and curved edges. The preferred growth of faces and especially larger faces with curved edges leads to fewer edge‐face‐edge contacts and to a greater degree of collective orientation.

Use of electromagnetic resonances in flat metal boxes for the measurement of D.C. size effects

It is shown that resonance experiments on flat thin-walled metal boxes, subjected to a static magnetic field, applied perpendicularly to their largest face, can yield d.c. size effect data.

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Nucleation and growth of twins in dislocation-free zinc crystals

Zinc whiskers and platelets with their largest faces in the basal plane and thin enough (~½ μ ) to be transparent to 100 kV electrons were strained in tension inside the electron microscope and the nucleation and growth of twins observed by the transmission technique. These observations were then related to the various stages of stress-strain curves obtained in a high-sensitivity tensile machine. All of the crystals were found to be initially completely free of dislocations. Twin nucleation occurred in a region where the applied stress was concentrated, namely at the specimen grips, at a corrosion pit or at a growth step. A critical resolved shear stress for twinning of ~ 50 Kg/mm 2 was found, which is a reasonable value for the theoretical twinning stress. Twins propagated at a rate controlled by the strain rate, at a stress of 2 to 20 Kg/mm 2 and by the nucleation and movement of twinning dislocations. Usually a single twin was formed and grew until it transformed the entire crystal. Basal glide often occurred in a twinned region, and fracture took place in the twin by the propagation of a crack along a basal plane on which a large amount of glide had occurred. The transformation of a matrix containing dislocations with various possible Burgers vectors is considered and the differences between twinning in bulk crystals and in whiskers and plates are discussed.

X-ray and electron microscope studies of the degradation of cellulose by sulphuric acid

Degradation of ramie and cotton fibres by sulphuric acid solutions of concentration near 950 g/l at temperatures up to 40°C leads to breakdown into elongated tabular of lateral dimensions about 30 A × 130 A and of widely varying lengths up to 2500 A. The particles are probably single crystallites of Cellulose I, and have their 101 crystallographic planes parallel to their largest faces. In the fibre the particles are arranged so that crystallographic orientation persists over relatively great distances. Similar results are obtained for the Cellulose II particles from mercerised fibres. Jute, containing a high proportion of lignin, tends to disintegrate in a fibrillar, as distinct from particulate, manner; but jute cellulose behaves more normally.