Significant Curvature Research Articles

On Application of EARSM Turbulence Model for Simulation of Flow Field behind Rack Station

This paper is interested in the mathematical modeling and approximation of the turbulent flow with strong anisotropy for the case of flow in a rack station. Turbulent models based on Boussinesq eddy viscosity assumption are traditionally employed for the solution of these types of flows. Linear eddy viscosity model and the assumption of isotropic Reynolds stress tensor are typically used in many cases. This leads to certain limitations in the cases of either separated flow or flow with significant curvature of the mean flow. The application of full Reynolds stress model is suitable for this case but it introduces at least seven additional equations and the model has much higher demand for computing time, grid parameters and discretization schemes. Therefore the Explicit Algebraic Reynolds Stress Model (EARSM) is used here. This model is based on two equations k – omega turbulence model with the nonlinear eddy viscosity model and explicit terms for anisotropic parts of the Reynolds stress tensor. The computational requirements are similar to the standard k – omega model. The numerical and experimental results from PIV measurement are compared.

Relationship between soldiers' body height-weight category and changes in their spinal column kyphotic curvature during a long-term military mission

Prolonged physical load can unfavourably influence the human vertebral column. Thirty-six well-trained male soldiers from the Estonian ESTCOY-8 infantry company were examined before and after a 6-month military mission to assess the effect of long-term physical load on soldiers’ spinal column kyphotic curvature in relation to their body build (height-weight category). Body height and weight of the men under study were measured before and after the 6-month-long military mission. BMI was calculated as the body weight (kg) divided by the square of the standing body height (m). Body height-weight category was assessed according to Kaarma et al. 2008. Spine kyphotic curvature in the sagittal plane was recorded using pantography. The results of the study showed that significant kyphotic curvature appeared in half of the well-trained soldiers. Changes in kyphotic curvature were related to the person’s body build (height-weight category). Subjects with a larger body seemed to have greater stability of kyphotic curvature.

Membrane-Dependent Conformation, Dynamics, and Lipid Interactions of the Fusion Peptide of the Paramyxovirus PIV5 from Solid-State NMR

The entry of enveloped viruses into cells requires protein-catalyzed fusion of the viral and cell membranes. The structure–function relation of a hydrophobic fusion peptide (FP) in viral fusion proteins is still poorly understood. We report magic-angle-spinning solid-state NMR results of the membrane-bound conformation, dynamics, and lipid interactions of the FP of the F protein of the paramyxovirus, parainfluenza virus 5 (PIV5). 13C chemical shifts indicate that the PIV5 FP structure depends on the composition of the phospholipid membrane: the peptide is α-helical in palmitoyloleoylphosphatidylglycerol-containing anionic membranes but mostly β-sheet in neutral phosphocholine membranes. Other environmental factors, including peptide concentration, cholesterol, membrane reconstitution protocol, and a Lys solubility tag, do not affect the secondary structure. The α-helical and β-sheet states exhibit distinct dynamics and lipid interactions. The β-sheet FP is immobilized, resides on the membrane surface, and causes significant membrane curvature. In contrast, the α-helical FP undergoes intermediate-timescale motion and maintains the lamellar order of the membrane. Two-dimensional 31P–1H correlation spectra show clear 31P–water cross peaks for anionic membranes containing the α-helical FP but weak or no 31P–water cross peak for neutral membranes containing the β-sheet FP. These results suggest that the β-sheet FP may be associated with high-curvature dehydrated fusion intermediates, while the α-helical state may be associated with the extended prehairpin state and the post-fusion state. Conformational plasticity is also a pronounced feature of the influenza and human immunodeficiency virus FPs, suggesting that these Gly-rich sequences encode structural plasticity to generate and sense different membrane morphologies.

Simultaneous Noninvasive Clinical Measurement of Lens Autofluorescence and Rayleigh Scattering Using a Fluorescence Biomicroscope

Lens autofluorescence increases with the age of the subject, and the fluorophores responsible are associated with cataract, retinopathy, and other complications of diabetes. We built a scanning confocal lens fluorescence biomicroscope suitable for routine clinical measurement of lens autofluorescence and light scattering and report data from 127 healthy subjects. The fluorescence biomicroscope focuses a beam of light from a blue light-emitting diode on the lens and measures fluorescent green light and blue scattered light using a sensitive silicon photomultiplier. The system includes a target fixation light and a video camera for alignment and automatic pupil tracking. Under software control, a volume of measurement is scanned from behind the posterior lens capsule, through the lens to the aqueous humor, and then back again. Software computes the average ratio of lens autofluorescence to scattered light in the central portion of the lens. Self-reported healthy nondiabetic subjects were examined by an optometrist; if their eyes were healthy and without significant cataract, they were entered into the study. Valid lens autofluorescence data were collected from 127 subjects between 21 and 70 years of age. A linear model for lens autofluorescence intensity with age was highly statistically significant, and the improvement in fit for higher-order polynomial models was not statistically significant. The ratio of lens autofluorescence to light scatter was also calculated; regression analysis showed significant curvature for the relationship of the fluorescence ratio to age, so a nonlinear model was used to estimate the mean ratio of autofluorescence to scatter and its prediction intervals as a function of age. Our observation of a strongly significant linear regression of fluorescence intensity with age of the subjects agrees with the results from previous studies, as does a nonlinear model for the fluorescence ratio. The fluorescence biomicroscope enables the clinician to identify patients with fluorescence ratio significantly higher than expected for their age.

Should screening for scoliosis be conducted?

This review provides an overview of the new evidence on the use of school screening for adolescent idiopathic scoliosis (AIS), in response to the concerns of the United States Preventive Services Task Force.School scoliosis screening, if carefully designed and planned, can effectively detect AIS patients with significant curvature. A tandem use of screening methods in addition to the conventional forward bending test may improve screening effectiveness. School scoliosis screening continues to be an effective platform for early conservative treatment of AIS.

Atom-by-Atom Observation of Grain Boundary Migration in Graphene

Grain boundary (GB) migration in polycrystalline solids is a materials science manifestation of survival of the fittest, with adjacent grains competing to add atoms to their outer surfaces at each other's expense. This process is thermodynamically favored when it lowers the total GB area in the sample, thereby reducing the excess free energy contributed by the boundaries. In this picture, a curved boundary is expected to migrate toward its center of curvature with a velocity proportional to the local radius of boundary curvature (R). Investigating the underlying mechanism of boundary migration in a 3D material, however, has been reserved for computer simulation or analytical theory, as capturing the dynamics of individual atoms in the core region of a GB is well beyond the spatial and temporal resolution limits of current characterization techniques. Here, we similarly overcome the conventional experimental limits by investigating a 2D material, polycrystalline graphene, in an aberration-corrected transmission electron microscope, exploiting the energy of the imaging electrons to stimulate individual bond rotations in the GB core region. The resulting morphological changes are followed in situ, atom-by-atom, revealing configurational fluctuations that take on a time-averaged preferential direction only in the presence of significant boundary curvature, as confirmed by Monte Carlo simulations. Remarkably, in the extreme case of a small graphene grain enclosed within a larger one, we follow its shrinkage to the point of complete disappearance.

THE DYNAMICAL MASS AND THREE-DIMENSIONAL ORBIT OF HR7672B: A BENCHMARK BROWN DWARF WITH HIGH ECCENTRICITY

The companion to the G0V star HR7672 directly imaged by Liu et al. (2002) has moved measurably along its orbit since the discovery epoch, making it possible to determine its dynamical properties. Originally targeted with adaptive optics because it showed a long-term radial velocity acceleration (trend), we have monitored this star with precise Doppler measurements and have now established a 24 year time baseline. The radial velocity variations show significant curvature (change in the acceleration) including an inflection point. We have also obtained a recent image of HR7672B with NIRC2 at Keck. The astrometry also shows curvature. In this paper, we use jointly-fitted Doppler and astrometric models to calculate the three-dimensional orbit and dynamical mass of the companion. The mass of the host star is determined using a direct radius measurement from CHARA interferometry in combination with high resolution spectroscopic modeling. We find that HR7672B has a highly eccentric, $e=0.50^{+0.01}_{-0.01}$, near edge-on, $i=97.3^{+0.4}_{-0.5}$ deg, orbit with semimajor axis, $a=18.3^{+0.4}_{-0.5}$ AU. The mass of the companion is $m=68.7^{+2.4}_{-3.1}M_J$ at the 68.2% confidence level. HR7672B thus resides near the substellar boundary, just below the hydrogen-fusing limit. These measurements of the companion mass are independent of its brightness and spectrum and establish HR7672B as a rare and precious "benchmark" brown dwarf with a well-determined mass, age, and metallicity essential for testing theoretical evolutionary models and synthetic spectral models. It is presently the only directly imaged L,T,Y-dwarf known to produce an RV trend around a solar-type star.

Can the Dean number Alone Characterize Flow Similarity in Differently Bent Tubes?

Although flows of fluids in curved channels belong to a classical problem of fluid dynamics, most publications are restricted to investigations of flows in tube coils, or in single bends. This paper presents experimental and numerical (CFD) results concerning Newtonian flows in a set of multiple S-type bends of various orientations. Investigations were conducted for a wide range of Re values (0–3500) and for a significant curvature ratio lying between 0.05 and 0.29, which corresponds to De value falling within the range 0.02–1200. A coiled tube was also examined and treated as the reference geometry. It was shown, that despite a completely different velocity pattern, the nonlinear dependence of normalized flow resistance of wavy tubes and coiled tube of the same curvature ratio overlap within a significant range of De. A novel, close phenomenological formula to estimate the nonlinear flow resistance of tortuous tube in a wide range of De was proposed and compared with those in the literature. The conditions were also determined in which the De might be the only dimensionless group that characterizes such flows.

Developmental Trajectories in Adolescents and Adults With Autism: The Case of Daily Living Skills

This study aimed to investigate the longitudinal course of daily living skills in a large, community-based sample of adolescents and adults with autism spectrum disorders (ASD) over a 10-year period. Adolescents and adults with ASD (n = 397) were drawn from an ongoing, longitudinal study of individuals with ASD and their families. A comparison group of 167 individuals with Down syndrome (DS) were drawn from a linked longitudinal study. The Waisman Activities of Daily Living Scale was administered four times over a 10-year period. We used latent growth curve modeling to examine change in daily living skills. Daily living skills improved for the individuals with ASD during adolescence and their early 20s, but plateaued during their late 20s. Having an intellectual disability was associated with lower initial levels of daily living skills and a slower change over time. Individuals with DS likewise gained daily living skills over time, but there was no significant curvature in the change. Future research should explore what environmental factors and interventions may be associated with continued gains in daily living skills for adults with ASD.

COLLISIONAL EXCITATION OF FAR-INFRARED LINE EMISSIONS FROM WARM INTERSTELLAR CARBON MONOXIDE (CO)

Motivated by recent observations with Herschel/PACS, and the availability of new rate coefficients for the collisional excitation of CO (Yang et al. 2010), the excitation of warm astrophysical CO is revisited with the use of numerical and analytic methods. For the case of an isothermal medium, results have been obtained for a wide range of gas temperatures (100 to 5000 K) and H2 densities (1E+3 to 1E+9 cm-3), and presented in the form of rotational diagrams, in which the logarithm of the column density per magnetic substate, log (N[J]/g[J]), is plotted for each state, as a function of its energy, E[J]. For rotational transitions in the wavelength range accessible to Herschel/PACS, such diagrams are nearly linear when n(H2) > 1E+8 cm-3. When log10(n[H2]) = 6.8 to 8, they exhibit significant negative curvature, whereas when log10(n[H2]) < 4.8 the curvature is uniformly positive throughout the PACS-accessible range. Thus, the observation of a positively-curved CO rotational diagram does not NECESSARILY require the presence of multiple temperature components. Indeed, for some sources observed with Herschel/PACS, the CO rotational diagrams show a modest positive curvature that can be explained by a single isothermal component. Typically, the required physical parameters are H2 densities in the 1E+4 to 1E+5 cm-3 range and temperatures, T, close to the maximum at which CO can survive. Other sources exhibit rotational diagrams with more curvature than can be accounted for by a single temperature component. For the case of a medium with a power-law distribution of gas temperatures, with dN/dT proportional to T to the power -b, results have been obtained for H2 densities 1E+3 to 1E+9 cm-3 and power-law indices, b, in the range 1 to 5; such a medium can account for a CO rotational diagram that is more positively curved than any resulting from an isothermal medium.

Interaction of Nucleobases with Wrinkled Graphene Surface: Dispersion Corrected DFT and AFM Studies

Graphene–nucleobase interaction is gaining importance due to its possible therapeutic applications. The dispersion interaction plays a major role in stacked aromatic compounds, such as graphene with amino acids or nucleobases. We have carried out detailed quantum chemical calculations of complexes of nanographene sheets and the nucleobases of DNA and RNA using dispersion corrected density functional theory. Binding energies show a trend as observed earlier by different theoretical and experimental measurements. However, in our present investigation, the optimized structures of the complex as well as isolated graphene show significant curvature, similar features are also observed by our Atomic Force Microscopic studies. Analysis of Natural Bond Orbital charges indicates the possibility of weak hydrogen bond-like interactions involving pyramidal amino groups of the nucleobases and π-center of the nanographene.

Quasi-static analysis of thrust-loaded angular contact ball bearings part I: theoretical formulation

Ball bearings play an important role in various rotating machineries, but the complicated kinematic and tribological features of ball bearings make many aspects of their operating behaviors still inconclusive. Most theoretical analyses of ball bearings up to date are based on either the hypothesis of race control or other empirical models to determine the ball motion of ball bearings, but none of these strategies can reveal and consequently employ the intrinsic coupling mechanism between the spin and the tangential traction of contacting bodies rolling upon one another. To remedy the deficiency of current analytical models for ball bearing analysis, the rolling contact theory is employed to establish an explicit link between motions and interactions within ball bearings. A differential slip model is established to precisely define the slip component due to the significant curvature of the common contact patches between the ball and inner/outer raceways. The creepage and the spin ratio are formulated to accurately define the relative rigid motion between the ball and the inner/outer raceway. Then a quasi-static analytical model is established that can accurately determine the motions of the balls and races of the ball bearing. It can also give a vivid description of the slip and traction distributions within the contact area. The analytical model can be effectively used to analyze the operational conditions and tribological features of solid-lubricated ball bearings. It can also be used optimize the construction of ball bearings for specific applications.

Notable formation of a cubic phase from small bent-angle molecules based on the 1,7-naphthalene central core and alkylthio tails

The mesomorphic properties of small angle, bent-shaped molecules [N(1,7)-S-n] consisting of a 1,7-naphthalene central core, typical Schiff-base side wings, and alkylthio tails with the carbon number n have been investigated, and a notable formation of a cubic (Cub) phase in addition to a distinct hexagonal columnar (Colh) phase was observed. The Cub phase can form when the terminal chain length is longer than 22 and is stable over a wider temperature range (25 °C) as the length increases up to 30. The space symmetry of the Cub phase was determined as Pmn with a lattice size of 160–170 A regardless of the terminal chain length. Assuming that the cubic unit cell is composed of a spherical assembly with a spatial electron density distribution, it can be described as containing eight spheres, each having a radius of 53 A and comprising 300 molecules. This formation of a novel Cub phase, like the micellar assembly phases, was understood as an enclosed layer formation caused by layer deformation with significant curvature resulting from the asymmetric packing of bent molecules in combination with the longer alkylthio tail groups of N(1,7)-S-n. It is noteworthy that the present observation of a Cub phase with unequivocal experimental evidence establishing both its lattice structure and size is the first example of a novel self-assembly mode in a bent-core liquid crystal (LC) molecular system.

Roper resonance in [formula omitted] flavor QCD

The low-lying even-parity states of the nucleon are explored in lattice QCD using the PACS-CS collaboration 2+1-flavor dynamical-QCD gauge-field configurations made available through the International Lattice Datagrid (ILDG). The established correlation-matrix approach is used, in which various fermion source and sink smearings are utilized to provide an effective basis of interpolating fields to span the space of low-lying energy eigenstates. Of particular interest is the nature of the first excited state of the nucleon, the N12+ Roper resonance of P11 pion–nucleon scattering. The Roper state of the present analysis approaches the physical mass, displaying significant chiral curvature at the lightest quark mass. These full QCD results, providing the worldʼs first insight into the nucleon mass spectrum in the light-quark regime, are significantly different from those of quenched QCD and provide interesting insights into the dynamics of QCD.

Ring formation mechanism of single-walled carbon nanotubes: Energy conservation between curvature elasticity and inter-tube adhesion

Rings of single-walled carbon nanotubes (SWNTs) exist widely during water evaporation from their dispersions at low concentration on such substrates as silica wafer. We examine the phenomenon in terms of energy conservation between the increased significant curvature energy and the inherent inter-tube van der Waals (vdW) attraction potentials. And thereby, the observed multi ring structures for coarse and long SWNT bundles have also gained detailed interpretation. We conclude that carbon nanotubes (CNTs) coil into rings by their own elastic mechanism. The formed rings with different width and diameters originate from appropriate sizes of SWNTs or the bundles. Specially, the associated elasticity may have prospective potentials to reveal other fascinating self-assembling phenomenon on CNTs, for instance, the known liquid crystallinity of them. Besides, we have also analyzed the external factors to the ring formation, both statistically and dynamically.

Wavelength Dependence of the Aerosol Angstrom Exponent and Its Implications Over Delhi, India

The aerosol optical depth (AOD), Angstrom coefficients (α and β), and the second-order Angstrom exponent (α′) obtained by Microtops-II sun photometer have been analyzed in the spectral range 0.34–0.87 μm over the urban polluted city of Delhi, India for the period 2007–2008, aiming at investigating the physical and optical properties of aerosols. The average values of AOD at 500 nm, α and β (in the range 340–870 nm) are found to be 0.78 ± 0.32, 0.78 ± 0.28, and 0.45 ± 0.21, respectively, for the entire period of observations. The AOD data show significant curvature in the lnτ versus lnλ relationship suggesting different dominant aerosol types depending on season. In order to analyze further the curvature effect and the relative dominance of aerosol size, α has been calculated in three wavelength bands, i.e., shorter (0.34–0.50 μm), longer (0.675–0.87 μm), and broad (0.34–0.87 μm) during four seasons, summer (April–June), monsoon (July–September), winter (October–January), and spring (February–March) accompanied with calculations of α′, which quantifies the deviation of logarithmic behavior of AOD with lnλ. The α′ values are found to be positive and higher in the months of October–December and mostly negative in February and March, while close to zero values of α′ are found in April–August. These results indicate that winter season exhibits dominance of fine-mode aerosols while summer relatively higher concentration of coarse-mode particles. On the other hand, monsoon and spring seasons revealed the presence of mixed type, both fine- and coarse-mode aerosols over Delhi.

Similarities and differences in O 2 chemisorption on graphene nanoribbon vs. carbon nanotube

A computational chemistry study was conducted to reveal similarities and differences in the adsorption of molecular oxygen on the edge sites of a carbon nanotube (CNT) and a graphene nanoribbon. Two prototypical CNT molecules with a carbene and a carbyne active site were selected, and this in turn defined two corresponding graphene molecules obtained by CNT unzipping. Their electronic and thermochemical properties before and after O 2 adsorption were compared using density functional theory at the B3LYP/3-21G ∗ level, as implemented in the Gaussian03 software. The sensitivity of the results to the basis set used and the selected CNT diameter was also assessed. Despite significant curvature in a subnanometer-diameter CNT, more similarities than differences were revealed with respect to graphene, both in their charge density distributions and thermochemical properties. Contrary to intuitive expectations, the intrinsic activity of an edge site (at least in the prototypical O 2 chemisorption process) is therefore not significantly modified when graphene is rolled up into a nanotube possessing a relatively large degree of pyramidalization. Greater differences exist between armchair and zigzag edges in both CNT and graphene. Both undergo a two-step mechanism of O 2 adsorption, but O 2 dissociates only on the armchair edge. Non-dissociative adsorption on an isolated zigzag site has both a lower affinity and a higher activation energy than the dissociative adsorption on the armchair site.

Oculo-motor patterns induced by reading in peripheral vision

There is clear evidence that slower reading in peripheral vision results from shrinkage of the visual span - the number of letters recognized with high accuracy without moving the eyes. Based on this evidence, an ideal-observer model, Mr. Chips (Legge et al., 2002), has been used to simulate saccade planning in reading. This model shows a strong relationship between the size of the visual span and saccade length. One prediction of this model is that reading speed in peripheral vision should be correlated with the saccade length (or more precisely with the horizontal component's length of saccades). This prediction is based on the implicit assumption that regression saccades do not occur too often. We have investigated this issue by measuring eye movements of 34 patients with central field loss (induced by age-related macular degeneration). Patients had to read aloud 14 French sentences displayed in succession (each sentence was displayed on one line). Character size was 3× the individual ETDRS acuity. Each patient had an absolute macular scotoma covering the fovea as assessed by MP1 microperimetry. Ocular data were collected with an Eyelink II eyetracker (500 Hz). The horizontal distribution of fixations was analyzed for each sentence with kernel density estimates. In addition, we assessed whether these distributions contained regions with statistically significant curvature – i.e., regions with a high density of fixations (called clusters hereafter). Results show a high variability of density estimates both within- and between patients: some sentences exhibit very homogeneous distributions while others show clear density peaks. The main finding is that reading speed is significantly slower for sentences that contain fixation clusters compared to sentences without clusters. This relationship between reading speed and the presence of fixation clusters has to our knowledge never been reported and should be taken into account to understand eccentric reading.

Investigating the interactions of amino acid components on a mannitol-based spray-dried powder formulation for pulmonary delivery: A design of experiment approach

Combining an amino acid and a sugar is a known strategy in the formulation of spray or freeze dried biomolecule powder formulations. The effect of the amino acid leucine in enhancing performance of spray-dried powders has been previously demonstrated, but interaction effects of several constituents which may provide multiple benefits, are less well-understood. A 3 factor 2 level (23) factorial design was used to study the effects of leucine, glycine and alanine in a mannitol-based dry powder formulation on particle size, aerosolisation, emitted dose and cohesion. Other qualitative tests including scanning electronic microscopy and X-ray powder diffraction were also conducted on the design of experiment (DoE) trials. The results show that the use of glycine and/or alanine, though structurally related to leucine, did not achieve similar aerosol performance enhancing effects, rather the particle formation was hindered. However, when used in appropriate concentrations with leucine, the combination of amino acids produced an enhanced performance regardless of the presence of glycine and/or alanine, yielding significantly modified particle properties. The results from the DoE analyses also revealed the lack of linearity of effects for certain responses with a significant curvature in the model which would otherwise not be discovered using a trial-and-error approach.

Characterization and Control of Residual Stress and Curvature in Anodically Bonded Devices and Substrates with Etched Features

While anodic bonding is commonly used in a variety of microelectromechanical systems (MEMS) applications, devices and substrates that incorporate this processing technique are often subjected to significant residual stress and curvature that create post-processing and reliability issues. Here, using an anisothermal anodic bonding procedure, residual stresses and the resulting wafer curvature in these structures are controlled by varying the initial bond temperatures of the silicon and Pyrex wafers independently. Residual stresses are quantified by measuring bulk wafer curvature and, locally, stress concentrations are measured using infrared photoelasticity accompanied by 3-D thermomechanical finite element analysis. Based on the good agreement between numerical predictions and experimental results, this process can be used to determine the bulk post-bond wafer curvature and to reduce the likelihood of structural failure at these sites, by changing the residual stresses from tensile in nature, which may drive initiation and growth of cracks, to compressive, which can suppress such failures.