Central Symmetry Axis Research Articles

I materiali di Villa Garzoni (Collodi)

Villa Garzoni and its garden are an extraordinary example of 18th-century Tuscan taste and culture. They are located on the slope of a hill at the mouth of the Pescia di Collodi stream in the Pescia plain (northern Tuscany). The garden presents scenographic and surprise effects that are part of a single decorative ensemble of great stylistic coherence. The steeply sloping terrain influenced the planimetric organisation, which develops along a central axis of symmetry, with an arrangement of terraces. In this paper the results of a diagnostic campaign performed on the materials of the villa and garden are reported. Stones, mortars and plasters were identified and analysed according to a well-established chemical and minero petrographic approach. Local and imported stones, raw materials and technologies used for the preparation of mortars and plasters, materials used for decoration were identified. To plan the best restoration approach their state of conservation was assess.

On the Topology of the Atmosphere Advected by a Periodic Array of Axisymmetric Thin-cored Vortex Rings

The fluid motion produced by a periodic array of identical, axisymmetric, thin-cored vortex rings is investigated. It is well known that such an array moves uniformly without change of shape or form in the direction of the central axis of symmetry, and is therefore an equilibrium solution of Euler's equations. In a frame of reference moving with the system of vortex rings, the motion of passive fluid particles is investigated as a function of the two non-dimensional parameters that define this system: $\varepsilon = a/R$, the ratio of minor radius to major radius of the torus-shaped vortex rings, and $\lambda = L/R$, the separation of the vortex rings normalized by their radii. Two bifurcations in the streamline topology are found that depend significantly on $\varepsilon$ and $\lambda$; these bifurcations delineate three distinct shapes of the 'atmosphere' of fluid particles that move together with the vortex ring for all time. Analogous to the case of an isolated vortex ring, the atmospheres can be 'thin-bodied' or 'thick-bodied'. Additionally, we find the occurrence of a 'connected' system, in which the atmospheres of neighboring rings touch at an invariant ring of fluid particles that is stationary in a frame of reference moving with the rings.

Структура рельсов после экстремально длительной эксплуатации

Using the methods of transmission electron diffraction microscopy the structure phase state and defect substructure in head of differentially quenched 100-meter rails at different depth after ultra long-term operation (passed gross tonnage 1770 mln. tons) are studied. The investigations are carried out along the rail head central axis of symmetry and working fillet rounding radius at the distances 0, 2, 10 mm from the tread surface. Dislocation ferrite substructure is presented by chaotically distributed dislocations and nets. The scalar and excess dislocation density increase as they approach the head rail surface. The values of these parameters on the surface are more than twice the corresponding value at a depth of 10 mm. The value of excess dislocation density is lower than scalar dislocation density which indicates elastic character of crystal lattice curvature-torsion. The quantitative evaluation of mechanisms dislocation strengthening is carried out.

Natural convection heat transfer from two horizontal cylinders using a large lateral shearing interferometer

AbstractNatural convection heat transfer from two horizontal cylinders in the air was investigated experimentally and numerically. Two cylinders were spaced at 1.3, 1.8, and 2.7 cylinder diameters horizontally. The experiments were carried out by large lateral shear interferometry (LSI) for various Rayleigh numbers in the range of 103 to 104. Large LSI is common path interferometry with the advantages of simple structure, strong antivibration, and fewer required optical components. It is not necessary for LSI to perform a complex algorithm to restore wavefront with a large shear amount. Simple and infinite fringe interferograms of the cylinders heated from ambient temperature 282.15 to 723.15 K were obtained. A numerical simulation was carried out with ANSYS‐Fluent 18.0. The influence of two factors, the distance between the cylinders, and the Rayleigh number, on the heat transfer of two horizontal cylinders was examined. The average Nusselt number and local Nusselt number were determined from the experimental results and numerical results, respectively, and the two results were in good agreement. The rising direction for the plume flow pattern of each horizontal cylinder was no longer simply vertically upward but was inclined toward the central symmetry axis of the two cylinders. In addition, the heat transfer from a cylinder increased with the cylinder spacing at any Rayleigh number.

Vesicular Polymer Hexosomes Exhibit Topological Defects.

Polymer hexosomes are block copolymer solution morphologies that adopt an internal structure composed of an inverse hexagonal (HII) phase. To date, most polymer hexosomes are reportedly rotationally symmetric solid structures that possess a common feature where hexagonally ordered inverted cylinders rotate along a central axis of symmetry to form circular hoops. Here, we report on the formation of polymer hexosomes whose inverted cylinders orient in an unusual manner, forming hoops that are noncircular. For topological reasons, this led to the generation of four defects in the resulting hexosome structure. We find that these defect-bearing hexosomes are hollow, thereby resembling polymer vesicles or polymersomes with an inverse hexagonal cylindrical morphology in the shell. The topological defects of these so-called "vesicular hexosomes" are enticing as they could serve as a platform to spatially anchor targeting ligands or biomolecules on the surface, while the hollow cylindrical shell and the vesicular lumen could spatially accommodate cargoes within the different domains. We propose that these vesicular hexosomes do not form via a conventional nucleation-growth self-assembly pathway, but rather via a two-step process involving first liquid-liquid phase separation followed by polymer microphase separation.

Stabilized narrow-beam emission from broad-area semiconductor lasers

We provide a feasible and compact scheme to control and stabilize the spatiotemporal dynamics of BAS lasers. The proposal is based on the ability of non-Hermitian potentials with given local symmetries to manage the flow of light. A local PT-symmetric configuration allows to control, enhance and localize the generated light. We impose a pump modulation, with a central symmetry axis which induces in-phase gain and refractive index modulations due to the Henry factor. Both modulations are, in turn, spatially dephased by an appropriate index profile to yield to a local PT-symmetry within the modified BAS laser. Such local PT-symmetry potential induces an inward mode coupling, accumulating the light generated from the entire active layer at the central symmetry axis, which ensures spatial regularization and temporal stability. By an exhaustive exploration of the modulation parameters, we show a significant improvement of the intensity concentration, stability and brightness of the emitted beam. This approach produces a two-fold benefit: light localization into a narrow beam emission and the control over the spatiotemporal dynamics, improving the laser performance.

RESEARCH OF WHEEL-RAIL WEAR DUE TO NON-SYMMETRICAL LOADING OF A FLAT CAR

Purpose. The paper is aimed at determining the influence of non-symmetrical loading of a flat car on the magnitude of the wear factor of a wheel-rail pair when changing the operation parameters that occur in operation. Methodology. The dynamic loading of the flat car, model 13-401 with typical three-piece bogies is studied using a model of spatial oscillations of a five-car coupling with the help of mathematical and computer simulation. Theoretical calculations are performed for the most dangerous sections of the railway track – small and medium radius curves in the range of permissible speeds. Findings. The indicators of wear of the rolling stock wheels and the rails are analysed on the example of flat cars in the presence of a longitudinal and transverse displacement of the load mass centre relative to the car symmetry centre. To obtain information on the effect of permissible deviations of the arrangement of cargo in the car on the magnitude of the dynamic loading of the wheel-rail contact, the authors performed theoretical studies of the spatial variations of the rail carriage and its interaction with the track. Originality. To determine the wear of the wheel-rail pair, the effect of displacement in two directions from the central axis of symmetry of the load gravity centre was studied, taking into account the value of the travel speed along the curved sections of the small and medium radius using a mathematical model of coupling of five freight cars. Practical value. As a result of the theoretical studies carried out, the authors assessed such factors as wear factor, directional force, and hunting of the wheel set of freight rolling stock in the event of load gravity centre displacement when moving along curved sections of the railway track. To establish the possible cause of intensive wear of the wheels and rails, the following parameters were analysed: lozenging of front bogie side frames; hunting of the left side frame of the front bogie; mutual longitudinal movement of the side frame and axle box of the front wheel set; mutual hunting of the left side frame of the bogie relative to the front wheel set.

STUDY OF DYNAMIC INDICATORS OF FLAT WAGON WITH LOAD CENTRE SHIFT

Purpose. The article deals with the determining the influence of the longitudinal and lateral shift of gravity centre of the heavy load on the flat wagons, taking into account the travel speed based on the main dynamic indicators – the maximum coefficients of the dynamic supplement of spring-suspended and unsprung parts, the maximum ratio of frame force to static axle load, the wheel derailment safety factor. Methodology. The study was carried out using the method of mathematical and computer simulation of the dynamic loading of flat wagons based on the model of spatial oscillations of five coupled wagons and the software complex developed in the branch research laboratory of the rolling stock dynamics and strength (BRL RSDS). Theoretical studies were carried out during the movement of the model 13-401 flat wagon on typical 18-100 bogies with speeds in the range from 50 to 90 km/h in curves with radii of 350 and 600 m, with 130 and 120 mm canting, respectively. Findings. The paper presents the analysis of theoretical studies of the rolling stock dynamics on the example of flat wagons. The calculations were carried out using an application software package. In the course of performing theoretical studies and after simulation, taking into account the processes of oscillation of the flat wagon and load in the presence of longitudinal and lateral shift of its gravity centre, the dependences of the main dynamic indicators were obtained with regard to the magnitude of the travel speed. Originality. Using the mathematical model of the five coupled wagons, the effect of shift in two directions from the central symmetry axis of the heavy load centre was studied with regard to the travel speed along the curved track of small and medium radius in order to determine the dynamic loading of the flat wagon. Practical value. As a result of the above theoretical studies, the recommendations on the maximum possible values of the centre shift of heavy loads during their transportation on flat wagons are substantiated and proposed.

Ion current density profiles in negative corona gaps versus EHD confinements

This paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode.

Role of Epithelium Sodium Channel in Bone Formation.

Objective:To review the recent developments in the mechanisms of epithelium sodium channels (ENaCs) induced bone formation and regulation.Data Sources:Studies written in English or Chinese were searched using Medline, PubMed and the index of Chinese-language literature with time restriction from 2005 to 2014. Keywords included ENaC, bone, bone formation, osteonecrosis, estrogen, and osteoporosis. Data from published articles about the structure of ENaC, mechanism of ENaC in bone formation in recent domestic and foreign literature were selected.Study Selection: and full text of all studies were required to obtain. Studies those were not accessible and those did not focus on the keywords were excluded.Results:ENaCs are tripolymer ion channels which are assembled from homologous α, β, and γ subunits. Crystal structure of ENaCs suggests that ENaC has a central ion-channel located in the central symmetry axis of the three subunits. ENaCs are protease sensitive channels whose iron-channel activity is regulated by the proteolytic reaction. Channel opening probability of ENaCs is regulated by proteinases, mechanical force, and shear stress. Several molecules are involved in regulation of ENaCs in bone formation, including nitride oxide synthases, voltage-sensitive calcium channels, and cyclooxygenase-2.Conclusion:The pathway of ENaC involved in shear stress has an effect on stimulating osteoblasts even bone formation by estrogen interference.

Dynamics of Conformational Transitions during KcsA Gating from EPR and Solution NMR Experiments

Despite its apparent simplicity, the potassium channel KcsA possesses a relatively complex gating cycle. Previous studies show conformational changes at the inner gate with an increase in distance from the central axis of symmetry when activated. These changes, coupled to rearrangements at the selectivity filter, are hypothesized to underlie activation, inactivation and modal gating. Defining the dynamic properties of the conformational wave linking the inner gate and selectivity filter is a critical step in understanding the mechanism of gating and permeation in K+ channels.Here, we have used CW and DEER Electron Paramagnetic Resonance to measure the opening of the inner gate and NMR to investigate the dynamics of the backbone of KcsA in a pH dependent manner. KcsA G116C was spin-labeled and reconstituted into liposomes or DDM micelles for EPR studies. NMR studies used wild type KcsA Δ125 in micelles (from pH7 to pH3 in 0.5 unit increments) with 2H/15N labeling and a TROSY pulse sequence. Pilot experiments investigating dynamics used a CPMG pulse sequence at pH7 and pH3.The extent of conformational dynamics from the inner gate ranged from 10.0 A (closed, pH7) to 23.7 A (open, pH3) with pH activation. Distance changes were abrupt near the pKa of activation (pH 3.9). Importantly, an observed increase in the width of the population distribution, and hence dynamics, was also observed at this point. Preliminary NMR experiments confirm that this region possesses distinct chemical shifts from a closed versus an open, inactivated state.Ongoing experiments target the process of backbone dynamics at different regions of KcsA. New pulse sequence schemes and kinetic gating mutants of KcsA are being studied to isolate the multiple dynamics components that define KcsA modal gating.

More precise positioning of the blank by means of implicit bases

Regardless of the geometry of the part being pro duced, three types of implicit bases may be distin guished: 1) a surface; 2) a line; 3) a point. The surface (symmetry plane) and line (symmetry axis) are most common. In contrast to the surface and line, the point may play various roles, such as the following: (1) the center of a part with a single surface (a sphere); (2) the vertex of a complete or truncated cone; (3) the point of intersection of two or more symmetry axes of cylindri cal surfaces inclined at some angle; (4) the point of intersection of the symmetry axes of two cylindrical surfaces with the central symmetry plane of a part (corresponding to various real surfaces); (5) the point of intersection of the central symmetry axis with explicit or implicit perpendicular planes. Example 1

Metal-driven Operation of the Human Large-conductance Voltage- and Ca2+-dependent Potassium Channel (BK) Gating Ring Apparatus

Large-conductance voltage- and Ca(2+)-dependent K(+) (BK, also known as MaxiK) channels are homo-tetrameric proteins with a broad expression pattern that potently regulate cellular excitability and Ca(2+) homeostasis. Their activation results from the complex synergy between the transmembrane voltage sensors and a large (>300 kDa) C-terminal, cytoplasmic complex (the "gating ring"), which confers sensitivity to intracellular Ca(2+) and other ligands. However, the molecular and biophysical operation of the gating ring remains unclear. We have used spectroscopic and particle-scale optical approaches to probe the metal-sensing properties of the human BK gating ring under physiologically relevant conditions. This functional molecular sensor undergoes Ca(2+)- and Mg(2+)-dependent conformational changes at physiologically relevant concentrations, detected by time-resolved and steady-state fluorescence spectroscopy. The lack of detectable Ba(2+)-evoked structural changes defined the metal selectivity of the gating ring. Neutralization of a high-affinity Ca(2+)-binding site (the "calcium bowl") reduced the Ca(2+) and abolished the Mg(2+) dependence of structural rearrangements. In congruence with electrophysiological investigations, these findings provide biochemical evidence that the gating ring possesses an additional high-affinity Ca(2+)-binding site and that Mg(2+) can bind to the calcium bowl with less affinity than Ca(2+). Dynamic light scattering analysis revealed a reversible Ca(2+)-dependent decrease of the hydrodynamic radius of the gating ring, consistent with a more compact overall shape. These structural changes, resolved under physiologically relevant conditions, likely represent the molecular transitions that initiate the ligand-induced activation of the human BK channel.

Early rebrightenings of X-ray afterglows from ring-shaped GRB jets

Early rebrightenings at a post-burst time of 10^2 - 10^4 s have been observed in the afterglows of some gamma-ray bursts (GRBs). Unlike X-ray flares, these rebrightenings usually last for a relatively long period. The continuous energy injection mechanism usually can only produce a plateau in the afterglow light curve, but not a rebrightening. Also, a sudden energy injection can give birth to a rebrightening, but the rebrightening is a bit too rapid. Here we argued that the early rebrightenings can be produced by the ring-shaped jet model. In this scenario, the GRB outflow is not a full cone, but a centrally hollowed ring. Assuming that the line of sight is on the central symmetry axis of the hollow cone, we calculate the overall dynamical evolution of the outflows and educe the multiband afterglow light curves. It is found that the early rebrightenings observed in the afterglows of a few GRBs, such as GRBs 051016B, 060109, 070103 and 070208 etc, can be well explained in this framework. It is suggested that these long-lasted early rebrightenings in GRB afterglows should be resulted from ring-shaped jets.

Comparing mixing performance of uniaxial and biaxial bin blenders

The dynamics involved in powder mixing remains a topic of interest for many researchers; however the theory still remains underdeveloped. Most of the mixers are still designed and scaled up on empirical basis. In many industries, including pharmaceutical, the majority of blending is performed using “tumbling mixers”. Tumbling mixers are hollow containers which are partially loaded with materials and rotated for some number of revolutions. Some common examples include horizontal drum mixers, v-blenders, double cone blenders and bin blenders. In all these mixers while homogenization in the direction of rotation is fast, mediated by a convective mixing process, mixing in the horizontal (axial) direction, driven by a dispersive process, is often much slower. In this paper, we experimentally investigate a new tumbling mixer that rotates with respect to two axes: a horizontal axis (tumbling motion), and a central symmetry axis (spinning motion). A detailed study is conducted on mixing performance of powders and the effect of critical fundamental parameters including blender geometry, speed, fill level, presence of baffles, loading pattern, and axis of rotation. In this work Acetaminophen is used as the active pharmaceutical ingredient and the formulation contains commonly used excipients such as Avicel and Lactose. The mixing efficiency is characterized by extracting samples after pre-determined number of revolutions, and analyzing them using Near Infrared Spectroscopy to determine compositional distribution. Results show the importance of process variables including the axis of rotation on homogeneity of powder blends.

Analysis of correlated mutations in HIV-1 protease using spectral clustering

Motivation: The ability of human immunodeficiency virus-1 (HIV-1) protease to develop mutations that confer multi-drug resistance (MDR) has been a major obstacle in designing rational therapies against HIV. Resistance is usually imparted by a cooperative mechanism that can be elucidated by a covariance analysis of sequence data. Identification of such correlated substitutions of amino acids may be obscured by evolutionary noise.Results: HIV-1 protease sequences from patients subjected to different specific treatments (set 1), and from untreated patients (set 2) were subjected to sequence covariance analysis by evaluating the mutual information (MI) between all residue pairs. Spectral clustering of the resulting covariance matrices disclosed two distinctive clusters of correlated residues: the first, observed in set 1 but absent in set 2, contained residues involved in MDR acquisition; and the second, included those residues differentiated in the various HIV-1 protease subtypes, shortly referred to as the phylogenetic cluster. The MDR cluster occupies sites close to the central symmetry axis of the enzyme, which overlap with the global hinge region identified from coarse-grained normal-mode analysis of the enzyme structure. The phylogenetic cluster, on the other hand, occupies solvent-exposed and highly mobile regions. This study demonstrates (i) the possibility of distinguishing between the correlated substitutions resulting from neutral mutations and those induced by MDR upon appropriate clustering analysis of sequence covariance data and (ii) a connection between global dynamics and functional substitution of amino acids.Contact: bahar@ccbb.pitt.eduSupplementary information: Supplementary data are available at Bioinformatics online.

Dipole and solenoidal magnetic moments of electronic surface currents on toroidal nanostructures

The time-dependent Schrodinger equation is developed for a spinless electron which is confined to move on a toroidal surface and curvature effects are taken into account. The electron motion is driven by linearly or circularly polarized microwaves including an interference field. To calculate the magnetic moments which are induced by the electronic surface currents on the torus an eight-state basis set is used. The system is driven at a resonance frequency to allow for transitions between states with opposite θ-parity. Optical transitions into modes of excitation can be observed that correspond to a magnetic dipole term parallel to the toroidal central symmetry axis as well as additional components in radial and azimuthal direction (solenoidal modes). Size and relative magnitude of the different components can be steered by adjusting magnitude, polarization, and phase information of the microwave field. Substantial enhancements of the solenoidal magnetic modes versus the dipole mode can be observed when adding a sufficiently strong static magnetic field parallel to the symmetry axis.

The leukocidin pore: Evidence for an octamer with four LukF subunits and four LukS subunits alternating around a central axis

The staphylococcal alpha-hemolysin (alphaHL) and leukocidin (Luk) polypeptides are members of a family of related beta-barrel pore-forming toxins. Upon binding to susceptible cells, alphaHL forms water-filled homoheptameric transmembrane pores. By contrast, Luk pores are formed by two classes of subunit, F and S, rendering a heptameric structure displeasing on symmetry grounds at least. Both the subunit stoichiometry and arrangement within the Luk pore have been contentious issues. Here we use chemical and genetic approaches to show that (1) the predominant, or perhaps the only, form of the Luk pore is an octamer; (2) the subunit stoichiometry is 1:1; and (3) the subunits are arranged in an alternating fashion about a central axis of symmetry, at least when a fused LukS-LukF construct is used. The experimental approaches we have used also open up new avenues for engineering the arrangement of the subunits of beta-barrel pore-forming toxins.

Nonlinear electron solutions and their characteristics at infinity

AbstractThe Maxwell-Dirac equations model an electron in an electromagnetic field. The two equations are coupled via the Dirac current which acts as a source in the Maxwell equation, resulting in a nonlinear system of partial differential equations (PDE's). Well-behaved solutions, within reasonable Sobolev spaces, have been shown to exist globally as recently as 1997 [12]. Exact solutions have not been found—except in some simple cases.We have shown analytically in [6, 18] that any spherical solution surrounds a Coulomb field and any cylindrical solution surrounds a central charged wire; and in [3] and [19] that in any stationary case, the surrounding electron field must be equal and opposite to the central (external) field. Here we extend the numerical solutions in [6] to a family of orbits all of which are well-behaved numerical solutions satisfying the analytic results in [6] and [11]. These solutions die off exponentially with increasing distance from the central axis of symmetry. The results in [18] can be extended in the same way. A third case is included, with dependence on z only yielding a related fourth-order ordinary differential equation (ODE) [3].

The deformation of a viscoelastic drop subjected to steady uniaxial extensional flow of a Newtonian fluid

In this paper, we investigate the fluid motion and shape of a non-Newtonian drop, modeled as a Chilcott–Rallison fluid, in the steady, uniaxial extensional flow of an unbounded Newtonian liquid. We consider two values of the capillary number, Ca = 0.05 and 0.10, below the critical value for continuous elongation of a Newtonian drop in the same flow. Solutions are then obtained for two values of the Chilcott–Rallison extensibility parameter, L 2 = 144 and 600, appropriate roughly for polymer solutions in the Boger fluid range of concentration, each for several values of the viscosity ratio λ, and the polymer concentration, c. It is shown that the main region of impact of the polymer on the flow inside the drop occurs on the central symmetry axis, and near the tips of the drop. The effect of polymer on the drop shape is complicated. In general, there is a balance between the influence of the viscoelastic tensile stress contribution in the direction of the symmetry axis, which tends to pull the interface inward and thus decrease the flow-induced deformation at the ends of the drop, and modifications of the viscous stress due to changes in the flow and the pressure due viscoelasticity, both of which tend to increase deformation. For L 2 = 600, the tensile stress effect is dominant and the viscoelastic drop is less deformed overall and has lower curvature at the tip than for a Newtonian drop at the same capillary number. For L 2 = 144, however, this trend is reversed and the effect of viscoelasticity is to increase deformation and increase the curvature at the end of the drop.