Transparent Spheres Research Articles

Structure of Cinaciguat (BAY 58–2667) Bound to Nostoc H-NOX Domain Reveals Insights into Heme-mimetic Activation of the Soluble Guanylyl Cyclase

Heme is a vital molecule for all life forms with heme being capable of assisting in catalysis, binding ligands, and undergoing redox changes. Heme-related dysfunction can lead to cardiovascular diseases with the oxidation of the heme of soluble guanylyl cyclase (sGC) critically implicated in some of these cardiovascular diseases. sGC, the main nitric oxide (NO) receptor, stimulates second messenger cGMP production, whereas reactive oxygen species are known to scavenge NO and oxidize/inactivate the heme leading to sGC degradation. This vulnerability of NO-heme signaling to oxidative stress led to the discovery of an NO-independent activator of sGC, cinaciguat (BAY 58-2667), which is a candidate drug in clinical trials to treat acute decompensated heart failure. Here, we present crystallographic and mutagenesis data that reveal the mode of action of BAY 58-2667. The 2.3-A resolution structure of BAY 58-2667 bound to a heme NO and oxygen binding domain (H-NOX) from Nostoc homologous to that of sGC reveals that the trifurcated BAY 58-2667 molecule has displaced the heme and acts as a heme mimetic. Carboxylate groups of BAY 58-2667 make interactions similar to the heme-propionate groups, whereas its hydrophobic phenyl ring linker folds up within the heme cavity in a planar-like fashion. BAY 58-2667 binding causes a rotation of the alphaF helix away from the heme pocket, as this helix is normally held in place via the inhibitory His(105)-heme covalent bond. The structure provides insights into how BAY 58-2667 binds and activates sGC to rescue heme-NO dysfunction in cardiovascular diseases.

Generalized radiative transfer equation for porous medium upscaling: Application to the radiative Fourier law

Many porous media cannot be homogenized as Beerian semi-transparent media. Effective extinction, absorption and scattering coefficients can indeed have no physical meaning for small or intermediate optical thicknesses. A generalized radiative transfer equation (GRTE), directly based on the extinction cumulative distribution function, the absorption and scattering cumulative probabilities and the scattering phase function is established for this optical thickness range. It can be solved by a statistical Monte Carlo approach. For a phase of a porous medium that is optically thick at local scale, the GRTE degenerates into a classical Beerian RTE. In these conditions, a radiative conductivity tensor is directly obtained, by a perturbation method, and expressed with the radiative coefficients of this RTE and temperature. As illustrations, exhaustive radiative conductivity results are given for a set of overlapping transparent spheres within an opaque phase and for opaque rod bundles.

Preparation and characterization of calcium hydroxyapatite and balloon-like calcium phosphate particles from forced hydrolysis of Ca(OH) 2–triphosphate solution

Calcium phosphate particles were prepared by aging a solution of dissolved Ca(OH) 2 and sodium triphosphate (sodium tripolyphosphate, Natpp: Na 5P 3O 10) at 100–150 °C for 18 h in a Teflon-lined screw-capped Pyrex test tube. Large spherical and/or small aggregated spherical particles were precipitated with an extremely fast rate of reaction under 100 °C. The large spherical particles were amorphous and the small aggregated ones were α-CaNa 2P 2O 7 .4H 2O. The former amorphous ones crystallized to β-Ca 2P 2O 7 after being calcined above 600 °C. Calcium hydroxyapatite (Ca 10(PO 4) 6(OH) 2, Hap), with rod-like and ellipsoidal or spherical aggregated shapes, was successfully produced using polyphosphates as a source of orthophosphate ions. Time resolved TEM measurement revealed that the crystallization of Hap particles takes place on the surface of tiny amorphous particles precipitated before aging. The tiny particles played the role of nuclei for Hap crystallization. The aging temperature drastically varied the particle shape under conditions for producing uniform amorphous spherical particles; solid spherical particles were produced with an aging temperature of up to 120 °C, whilst transparent balloon-like hollow spheres were precipitated at 125 °C. Finally, fully transparent balloon-like hollow spheres were produced with mere trace amounts of small rod-like particles after aging the solution above 127 °C. The time resolved TEM observation and ICP-AES measurements revealed that the balloon-like hollow spheres were produced by dissolving the interior of solid spherical particles after reinforcing their shell by the adsorption of unhydrolyzed tpp and/or pyrophosphate (pp) ions, which are the hydrolysis product of tpp. The balloon-like hollow spheres of calcium phosphate may have the potential use as drug delivery vehicles and have biocompatibility advantages.

Experimental and computational study of constrained melting of phase change materials (PCM) inside a spherical capsule

An experimental and computational investigation directed at understanding the role of buoyancy-driven convection during constrained melting of phase change materials (PCM) inside a spherical capsule is reported. The computations are based on an iterative, finite-volume numerical procedure that incorporates a single-domain enthalpy formulation for simulation of the phase change phenomenon. A Darcy’s Law-type porous media treatment links the effect of phase change on convection. Paraffin wax n-octadecane was constrained during melting inside a transparent glass sphere through the use of thermocouples installed inside the sphere. The melting phase front and melting fraction of the PCM are analyzed and compared with numerical solution obtained from the CFD code Fluent. Following a short period of symmetric melting due to prominence of diffusion, expedited phase change in the top region of the sphere and a wavy surface at the bottom of the PCM are observed. The computational predictions point to the strong thermal stratification in the upper half of the sphere that results from rising of the molten liquid along the inner surface of the sphere thus displacing the colder fluid. The waviness and excessive melting of the bottom of the PCM is shown to be underestimated by the experimental observation. This discrepancy is linked to the use of a support structure to hold the sphere. Measured temperature data and computational results near the bottom indicate the establishment of an unstable fluid layer that promotes chaotic fluctuations and is responsible for waviness of the bottom of the PCM. On the other hand, the comparison between the measured and computed temperatures in the top half of the sphere show the stable nature of the molten liquid layer. The computational results start to deviate from the thermocouple readings as one moves lower from the top of the sphere. This delay in predicting the melting instant is linked to the thermal stratification within the “constant temperature bath” that encloses the capsule.

Transantarctic Mountain microtektites: Geochemical affinity with Australasian microtektites

We extended the petrographic and geochemical dataset for the recently discovered Transantarctic Mountain microtektites in order to check our previous claim that they are related to the Australasian strewn field. Based on color and composition, the 465 microtektites so far identified include two groups of transparent glass spheres less than ca. 800 μm in diameter: the most abundant pale-yellow, or normal, microtektites, and the rare pale-green, or high-Mg, microtektites. The major element composition of normal microtektites determined through electron microprobe analysis is characterized by high contents of silica (SiO 2 = 71.5 ± 3.6 (1σ) wt%) and alumina (Al 2O 3 = 15.5 ± 2.2 (1σ) wt%), low total alkali element contents (0.50–1.85 wt%), and MgO abundances <6 wt%. The high-Mg microtektites have a distinctly higher MgO content >10 wt%. Transantarctic Mountain microtektites contain rare silica-rich (up to 93 wt% SiO 2) glassy inclusions similar to those found in two Australasian microtektites analyzed here for comparison. These inclusions are interpreted as partially digested, lechatelierite-like inclusions typically found in tektites and microtektites. The major and trace element (by laser ablation – inductively coupled plasma – mass spectrometry) abundance pattern of the Transantarctic Mountain microtektites matches the average upper continental crust composition for most elements. Major deviations include a strong to moderate depletion in volatile elements including Pb, Zn, Na, K, Rb, Sr and Cs, as a likely result of severe volatile loss during the high temperature melting and vaporization of crustal target rocks. The normal and high-Mg Transantarctic Mountain microtektites have compositions similar to the most volatile-poor normal and high-Mg Australasian microtektites reported in the literature. Their very low H 2O and B contents (by secondary ion mass spectrometry) of 85 ± 58 (1σ) μg/g and 0.53 ± 0.21 μg/g, respectively, evidence the extreme volatile loss characteristically observed in tektites. The Sr and Nd isotopic compositions of multigrain samples of Transantarctic Mountain microtektites are 87Sr/ 86Sr ≈ 0.71629 and 143Nd/ 144Nd ≈ 0.51209, and fall into the Australasian tektite compositional field. The Nd model age calculated with respect to the chondritic uniform reservoir (CHUR) is T Nd CHUR ≈ 1.1 Ga, indicating a Meso-Proterozoic crustal source rock, as was derived for Australasian tektites as well. Coupled with the Quaternary age from the literature, the extended dataset presented in this work strengthens our previous conclusion that Transantarctic Mountain microtektites represent a major southward extension of the Australasian tektite/microtektite strewn field. Furthermore, the significant depletion in volatile elements (i.e., Pb, B, Na, K, Zn, Rb, Sr and Cs) of both normal and high-Mg Transantarctic Mountain microtektites relative to the Australasian ones provide us with further confirmation of a possible relationship between high temperature–time regimes in the microtektite-forming process and ejection distance.

Organic nanostructures on silicon, created with semitransparent polystyrene spheres and248 nm laser pulses

Arrays of nanostructures are made starting with a template of close-packed,polystyrene spheres on a silicon surface. The spheres are either 1.091 or2.99 µm indiameter (d) and are of polystyrene (PS). They are irradiated with a pulse of either 308 or 248 nm lightto which they are transparent and semitransparent, respectively. A transparent sphere withd = 1.091 µm diameter concentrates incident light onto a small substrate area. As has been previouslyreported, that creates silicon nanobumps that rise from circular craters. At 248 nm andd = 2.99 µm, the light energy is mainly absorbed, destroys the sphere, and leaves a shrunkenmass (typically about 500 nm wide and 100 nm high) of organic material thatis probably polystyrene and its thermal degradation products. At 248 nm andd = 1.091 µm, the residual organic structures are on the order of 300 nm wide and 100 nm high. A distinctivefeature is that these organic structures are connected by filaments that are on the order of50 nm wide and 10 nm high. Filaments form because the close-packed PS spheres expandinto each other during the early part of the laser pulse, and then, as the main structuresshrink, their viscoelasticity leads to threads between them. Our results with 248 nm andd = 1.091 µm differ from those described by Huang et al with 248 nm andd = 1.0 µm. Future studies might include the further effect of wavelength and fluence upon the processas well the use of other materials and the replacement of nanospheres by other focusingshapes, such as ellipsoids or rods.

Rainbows from inhomogeneous transparent spheres: a ray-theoretic approach

A ray-theoretic account of the passage of light through a radially inhomogeneous transparent sphere has been used to establish the existence of multiple primary rainbows for some refractive index profiles. The existence of such additional bows is a consequence of a sufficiently attractive potential in the interior of the drop, i.e., the refractive index gradient should be sufficiently negative there. The profiles for which this gradient is monotonically increasing do not result in this phenomenon, but nonmonotone profiles can do so, depending on the form of n. Sufficiently oscillatory profiles can lead to apparently singular behavior in the deviation angle (within the geometrical optics approximation) as well as multiple rainbows. These results also apply to systems with circular cylindrical cross sections, and may be of value in the field of rainbow refractometry.

Theory of resonance shifts in TE and TM whispering gallery modes by nonradial perturbations for sensing applications

A perturbation theory is presented for the frequency shift of highly resonant photonic whispering gallery modes in a transparent sphere. Using a vector wave equation, we derive a general formula for the shifts in TE and TM polarization by adsorption of another dielectric medium. The adsorbed medium can have an arbitrary shape and refractive-index profile. The formula is applied to adsorption of a thin layer and deposition of a small spherical particle, many such particles, and thin cylindrical particles on the resonator surface. We found that the ratio of the TM mode shift to the TE mode shift is sensitive to the shape of the adsorbates and their orientation. Calculation results are discussed in terms of a dipolar field.

A transparent macroscopic sphere is cross-sectionally equivalent to a superposition of two quantum-like radial potentials

We consider two frameworks (i) the electromagnetic generalized Lorenz–Mie theory describing the interaction between an electromagnetic arbitrary shaped beam and a homogeneous, non-magnetic sphere, with an isotropic, linear, material and (ii) a quantum generalized Lorenz–Mie theory describing the interaction between a quantum eigen-arbitrary shaped beam and a quantum radial potential. For the time being, we restrict ourselves in this paper to elastic scattering cross-sections. We then demonstrate that a transparent macroscopic sphere in the first framework is equivalent to a superposition of two quantum-like radial potentials in the second framework. The restrictive meaning of “quantum-like” will be discussed when appropriate.

Axially symmetric focusing as a cuspoid diffraction catastrophe: Scalar and vector cases and comparison with the theory of Mie

An analytical description of arbitrary strongly aberrated axially symmetric focusing is developed. This is done by matching the solution of geometrical optics with a wave pattern which is universal for the underlying ray structure. The corresponding canonical integral is the Bessoid integral, which is a three-dimensional generalization of the Pearcey integral that approximates the field near an arbitrary two-dimensional cusp. We first develop the description for scalar fields and then generalize it to the vector case. As a practical example the formalism is applied to the focusing of light by transparent dielectric spheres with a few wavelengths in diameter. The results demonstrate good agreement with the Mie theory down to Mie parameters of about 30. Compact analytical expressions are derived for the intensity on the axis and the position of the diffraction focus both for the general case and for the focusing by microspheres. The high intensity region is narrower than for an ideal lens of the same aperture at the expense of longitudinal localization and has a polarization dependent fine structure, which can be explained quantitatively. The results are relevant for aerosol and colloid science where natural light focusing occurs and can be used in laser micro- and nano-processing of materials.

A Model to Characterize the D-T Layer of ICF Targets by Backlit Optical Shadowgraphy

A numerical model is presented in order to modelize the bright ring that appears in backlit optical shadowgraphy on a transparent hollow sphere with a solid deuterium-tritium layer inside. This novel model is based on computational calculations applied to the problem of the targets used in inertial confinement fusion.The model takes into account the influences of the optical imaging system (numerical aperture, source divergence, camera resolution, etc.) and the effect of the capsule itself, diameter, thickness, and refractive index, and allows one to analyze the inner surface of a capsule in terms of thickness and roughness.

Four-wave mixing in a liquid suspension of transparent dielectric microspheres

The process of four-wave mixing in an artificial heterogeneous nonlinear medium—a liquid suspension of transparent dielectric microspheres—is considered. The dynamics of the concentration response to gradient forces that act on microspheres in the interference field of interacting waves are investigated on the basis of the Smolukhovskii equation. Kinetic equations for the amplitudes of light-induced concentration gratings that take part in the four-wave mixing are obtained with the use of the Fourier series expansion of the distribution function of microspheres. The ratios of the microsphere radius to the grating periods are obtained under which the resultant gradient force vanishes and, hence, a suspension of dielectric microspheres does not exhibit nonlinear properties irrespective of the intensities of the interacting waves. The kinetics of the process of four-wave mixing is investigated under efficient energy exchange between reference, signal, and reversed waves. It is shown that a liquid suspension of transparent dielectric spheres is a highly effective wideband nonlinear medium for reversing the wave front of low-intensity radiation of continuous-wave lasers.

Observation of the skin-depth effect on the Casimir force between metallic surfaces.

We have performed measurements of the Casimir force between a metallic plate and a transparent sphere coated with metallic films of different thicknesses. We have observed that, if the thickness of the coating is less than the skin-depth of the electromagnetic modes that mostly contribute to the interaction, the force is significantly smaller than that measured with a thick bulk-like film. Our results provide direct evidence of the skin-depth effect on the Casimir force between metallic surfaces.

Reconstituting the Public-Private Divide under Global Conditions

How is the line to be drawn in the public-private divide when those who would bridge it also assert that globalization restricts the state’s ability to deliver public policy objectives? Critics of modernity have seen the distinction between two public-private discourses, state and market, the open and the hidden, as a modern flawed version of classic notions of the democratic citizen community. The projection of the divide on to a global stage appears to take us even further from that ideal. We report the results of a narrative analysis of the way practitioners in the Netherlands and England and Wales now deliver global public goods in the management of water as compared with their predecessors delivering public health and progress in the 19th century. In their adherence to the water systems concept we find them actively supporting a transparent public sphere beyond the state where multiple forms of agency assert global responsibilities.

Three-dimensional Structure-from-motion Selectivity in the Anterior Superior Temporal Polysensory Area, STPa, of the Behaving Monkey

Human and non-human primates are able to perceive three-dimensional structure from motion displays. Three-dimensional structure-from-motion (object-motion) displays were used to test the hypothesis that neurons in the anterior division of the superior temporal polysensory area (STPa) of monkeys can selectively respond to three-dimensional structure-from-motion. Monkeys performed a reaction time task that required the detection of a change in the fraction of structure in three-dimensional transparent sphere displays. Neurons were able to distinguish structured and unstructured three-dimensional optic flow. These cells could differentiate the change in structure-from-motion at stimulus presentation and when the animal was detecting the amount of structure in the display. Some of these neurons were also tuned for characteristics of the sphere stimuli. Cells were also tested with navigational motion and many were found to respond both to three-dimensional structure-from-motion and navigational motion. These results suggest that STPa neurons represent specific aspects of three-dimensional surface structure and that neurons within STPa contribute to the perception of three-dimensional structure-from-motion.

Three-dimensional optical trapping of partially silvered silica microparticles

We demonstrate three-dimensional trapping of micrometer-diameter silica particles, partially coated with silver, within conventional optical tweezers. Although metallic particles are usually repelled from the beam focus by the scattering force, we show that transparent spheres partially coated with silver can be trapped with efficiencies comparable with dielectric particles. The trapping characteristics of these particles are examined as a function of metallic coverage, and the application of these particles to surface-enhanced resonance Raman scattering is investigated.

Elliptical instability in a rotating spheroid

This paper concerns the elliptical instability of a flow in a rotating deformed sphere. The aim of our work is to analyse the characteristics of this instability experimentally and to provide a theoretical model which accounts for the observations. For this purpose, an elastic and transparent hollow sphere has been moulded in a silicone gel block. The flow is visualized using Kalliroscope flakes illuminated with a laser sheet as the sphere is set into rotation and compressed by two rollers. The elliptical instability occurs by the appearance of the so-called ‘spin-over’ mode whose growth rate and saturation amplitude are measured by video image analysis at different Ekman numbers. Growth rates are predicted well by the linear stability analysis. A nonlinear model is developed and is shown to describe correctly the saturated regimes observed in the experiments. At low Ekman numbers, a secondary instability leading to an intermittent regime is also discovered.

AS FRONTEIRAS MAL DEMARCADAS DO PÚBLICO E DO PRIVADO NO BRASIL: a prática do nepotismo na administração pública brasileira.

Análise sobre a problemática que envolve as relações entre as esferas pública e privada tanto no campo teórico, quanto nos seus desdobramentos para a evolução histórica do Brasil. Analisa-se, mais especificamente, a prática do nepotismo ”“ contratação de parentes sem concurso ”“ na administração pública, como um traço constitutivo da permanência do clientelismo e do patrimonialismo na condução do Estado brasileiro. Apesar de alguns avanços legais, o nepotismo apresenta suas conseqá¼ências, em termos estruturais, numa certa privatização do aparelho estatal. O nepotismo se perpetua e se amplia em todas as dimensões, apesar das tentativas da sociedade civil em barrar tal prática. Conclui-se na perspectiva de superação do nepotismo na administração pública; na definição clara dos limites e funções das esferas pública e privada no contexto nacional e na direção da republicanização do Estado, no sentido da constituição de uma esfera pública democrática e transparente no Brasil.

Factors influencing the ability to detect motion reversals in rotation simulations.

Five experiments probed the conditions under which observers fail to report instantaneous reversals in the direction of motion of pixels that define the rotation of a transparent sphere or plane. Our results showed that the extent to which rotation reversals were not reported depended upon whether observers used strict or lax criteria to make their judgments, the degree of perspective present in the rotation simulations, and the percentage of pixels that actually reversed direction. Furthermore, we found failures to report rotation reversals both with stimuli whose pixels were confined to smooth surfaces and scattered within volumes. Reversal detection with planar stimuli, unlike sphere stimuli, depended upon the orientation of the stimulus at the moment of reversal. Treue et al. (1995) postulated a surface-interpolation process as the explanation for the apparent insensitivity of observers to such reversals. However, we suggest that other stages of processing (e.g. a structure-from-motion process) are required to account for these results.

Direct identification of absorption and scattering coefficients and phase function of a porous medium by a Monte Carlo technique

A general method of direct identification of absorption and scattering coefficients and phase function of porous media, assumed statistically homogeneous and isotropic, has been developed for wavelengths small in regard of the typical structure length (i.e. by neglecting diffraction). This method is here limited to a transparent fluid phase and an opaque solid phase. Diffuse and specular reflection laws and combination of these laws are considered. First results have been obtained for sets of Dispersed radius Overlapping Opaque Spheres (DOOS) in a transparent fluid phase, or sets of Dispersed radius Overlapping Transparent Spheres (DOTS) in an opaque solid phase. In the case of DOOS models, the absorption and scattering coefficients have the same analytical expressions as those characterizing the optically thin limit for any porous medium. For DOTS models, these coefficients have been, for porosity higher than 0.65, identified from Monte Carlo calculations versus the porosity or the specific area per unit volume of the fluid phase. For DOOS models, the phase functions have been expressed by a simple analytical expression in the case of a specular reflection law, and derived from Monte Carlo calculations in the case of the diffuse reflection law. For DOTS models, phase function have been numerically calculated from Monte Carlo calculations. The case of the combination of the two reflection laws is finally discussed.