Rod Density Research Articles

Characterization of Retinal Structure in ATF6-Associated Achromatopsia.

PurposeMutations in six genes have been associated with achromatopsia (ACHM): CNGA3, CNGB3, PDE6H, PDE6C, GNAT2, and ATF6. ATF6 is the most recent gene to be identified, though thorough phenotyping of this genetic subtype is lacking. Here, we sought to test the hypothesis that ATF6-associated ACHM is a structurally distinct form of congenital ACHM.MethodsSeven genetically confirmed subjects from five nonconsanguineous families were recruited. Foveal hypoplasia and the integrity of the ellipsoid zone (EZ) band (a.k.a., IS/OS) were graded from optical coherence tomography (OCT) images. Images of the photoreceptor mosaic were acquired using confocal and nonconfocal split-detection adaptive optics scanning light ophthalmoscopy (AOSLO). Parafoveal cone and rod density values were calculated and compared to published normative data as well as data from two subjects harboring CNGA3 or CNGB3 mutations who were recruited for comparative purposes. Additionally, nonconfocal dark-field AOSLO images of the retinal pigment epithelium were obtained, with quantitative analysis performed in one subject with ATF6-ACHM.ResultsFoveal hypoplasia was observed in all subjects with ATF6 mutations. Absence of the EZ band within the foveal region (grade 3) or appearance of a hyporeflective zone (grade 4) was seen in all subjects with ATF6 using OCT. There was no evidence of remnant foveal cone structure using confocal AOSLO, although sporadic cone-like structures were seen in nonconfocal split-detection AOSLO. There was a lack of cone structure in the parafovea, in direct contrast to previous reports.ConclusionsOur data demonstrate a near absence of cone structure in subjects harboring ATF6 mutations. This implicates ATF6 as having a major role in cone development and suggests that at least a subset of subjects with ATF6-ACHM have markedly fewer cellular targets for cone-directed gene therapies than do subjects with CNGA3- or CNGB3-ACHM.

Equation of state of colloidal membranes.

In the presence of a non-adsorbing polymer, monodisperse rod-like colloids assemble into one-rod-length thick liquid-like monolayers, called colloidal membranes. The density of the rods within a colloidal membrane is determined by a balance between the osmotic pressure exerted by the enveloping polymer suspension and the repulsion between the colloidal rods. We developed a microfluidic device for continuously observing an isolated membrane while dynamically controlling the osmotic pressure of the polymer suspension. Using this technology we measured the membrane rod density over a range of osmotic pressures than is wider that what is accessible in equilibrium samples. With increasing density we observed a first-order phase transition, in which the in-plane membrane order transforms from a 2D fluid into a 2D solid. In the limit of low osmotic pressures, we measured the rate at which individual rods evaporate from the membrane. The developed microfluidic technique could have wide applicability for in situ investigation of various soft materials and how their properties depend on the solvent composition.

Evolution of the visual sensory system in the deep-sea fishes from the Sargasso Sea

Evolution of the visual sensory system in the deep-sea fishes from the Sargasso Sea

Diffusion of Rodlike Polymers: Pulsed Gradient Spin Echo NMR of Poly(γ-stearyl-α,l-glutamate) Solutions and the Importance of Helix Stability.

Many natural and synthetic polymers and particles have a rodlike shape, leading to important and intriguing solution behavior, such as high intrinsic viscosities and liquid crystalline phases. Much of what is known about suspensions of rods has been learned by studying helical polypeptides, even though such molecules are not perfectly rigid, smooth cylinders. Previous optical tracer self-diffusion studies of poly(γ-benzyl-α,l-glutamate) (PBLG) revealed that the molecule initially resists topological constraints imposed by neighboring molecules, but diffusion strongly decreases as concentration rises beyond a certain number density. In contrast, the tracer self-diffusion coefficient of truly rigid tobacco mosaic virus begins decreasing immediately with concentration. We used pulsed gradient spin echo NMR to measure another polypeptide, poly(γ-stearyl-α,l-glutamate) (PSLG), to gain physical insight into the question of polypeptide diffusion in crowded isotropic solutions. The PSLG molecule, with long alkyl sidechains, is semiflexible like PBLG but does not exhibit the same ability to evade topological constraints. Instead, PSLG follows a simple exponential decay, D/ DKR = A e(-κν/ν*) + B, where DKR is the Kirkwood-Riseman expectation for rod diffusion, ν is the number density of rods, ν* is the Onsager expectation for the number density at the onset of liquid crystal formation, A = 1 ± 0.1, B = 0.1 ± 0.01, and κ = 4.5 ± 0.5. The results emphasize the importance of helix stability when choosing rodlike polypeptides as model systems, particularly with regard to the chain ends.

Systematic analysis for electrical conductivity of network of conducting rods by Kirchhoff's laws and block matrices

In recent years, high-aspect-ratio materials, such as metallic nanowires and carbon nanotubes, have become attractive alternatives for the next generation of transparent conductive films. The functionality of the films is represented by their opto-electric performance, which is primarily affected by the nano- or micro-structures inside the films. In this study, we focus on the analysis of the electrical conductivity of two-dimensional networks of conducting rods by treating parts of the networks as a linear circuit system. For the analysis, multi-nodal representation is used to assign the nodes and edges of the circuit. Based on Kirchhoff's laws, the relation between the current and electrical potential is formulated using a block matrix equation. After a series of block-matrix manipulations, the equation can be reduced to yield several simple equations expressed in terms of the incidence matrices and the weighted graph Laplacians. Among these, the equation representing the Ohm's-law-like relation between the total current and the bias voltage can be used to derive the explicit expression for the normalized conductivity, which can quantify the effect of the network. During the analysis, we also deduce the normalized number of edges, that is, the combination of variables used in the system. The normalized number of edges can be related to the reduced number density of rods by using a proper statistical model. Moreover, we found the direct relation between the normalized number of edges and the backbone fraction, which is a representative quantity related with the electrical conductivity.

Effects of pH, extrusion tip size and storage protocol on the structural properties of Ca(II)-alginate beads

The Ca(II)-alginate beads were formulated changing some synthesis variables: pH (3.8–6.8), extrusion tip size (0.25–0.50 mm) and washing/storage protocol, to evaluate possible implications in the structural properties of beads, which are critical to scale and standardize their production at industrial level. Regardless of the macro- (diameter, area, perimeter and roundness, studied by image analysis) and micro-structural (size, density and interconnectivity of rods assessed by SAXS) parameters analyzed, there are no effects related to the washing and storage protocol employed for any synthesis conditions. Structural parameters are only influenced by the synthesis pH. Both washing protocol and extrusion tip size effects on the consolidation of the alginate network are negligible at each pH value. Besides, none of the synthesis variables affected the availability of water within the beads as assessed by diffusion coefficient and water activity measurements. A model, relating chain-chain interactions and polymer chain packing, is proposed.

Flexural properties of sandwich composite laminates reinforced with glass and carbon Z-pins

This study aims to enhance the flexural properties of sandwich composites made from glass or carbon face and glass and carbon fibre Z-pin inserted extruted-polystyrene (XPS) foam cores. Carbon and glass pins were placed through XPS foams with two different column and row densities (15 and 30 mm). Results indicated that flexural loads, strength and modulus of glass/XPS and carbon/XPS sandwich composites significantly increased after inserting of glass and carbon rods. Core shear strengths and facing stresses of glass/XPS and carbon/XPS increased by increasing of carbon or glass rod densities. The rod type, rod density and face type of the sandwich composites are considered as significant parameters which affect the flexural behaviour of sandwich composites while using carbon rods enhanced flexural properties more than that of using glass rods due to better interfacial bonding.

Collective behavior of self-propelled rods with quorum sensing

Active agents-like phoretic particles, bacteria, sperm, and cytoskeletal filaments in motility assays-show a large variety of motility-induced collective behaviors, such as aggregation, clustering, and phase separation. The behavior of dense suspensions of engineered phoretic particles and of bacteria during biofilm formation is determined by two qualitatively different physical mechanisms: (i) volume exclusion (short-range steric repulsion) and (ii) quorum sensing (longer-range reduced propulsion due to alteration of the local chemical environment). To systematically characterize such systems, we study semi-penetrable self-propelled rods in two dimensions, with a propulsion force that decreases with increasing local rod density, by employing Brownian dynamics simulations. Volume exclusion and quorum sensing both lead to phase separation; however, the structure of the systems and the rod dynamics vastly differ. Quorum sensing enhances the polarity of the clusters, induces perpendicularity of rods at the cluster borders, and enhances cluster formation. For systems where the rods essentially become passive at high densities, formation of asters and stripes is observed. Systems of rods with larger aspect ratios show more ordered structures compared to those with smaller aspect ratios, due to their stronger alignment, with almost circular asters for strongly density-dependent propulsion force. With increasing range of the quorum-sensing interaction, the local density decreases, asters become less stable, and polar hedgehog clusters and clusters with domains appear.

The topography of rods, cones and intrinsically photosensitive retinal ganglion cells in the retinas of a nocturnal (Micaelamys namaquensis) and a diurnal (Rhabdomys pumilio) rodent.

We used immunocytochemistry to determine the presence and topographical density distributions of rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs) in the four-striped field mouse (Rhabdomys pumilio) and the Namaqua rock mouse (Micaelamys namaquensis). Both species possessed duplex retinas that were rod dominated. In R. pumilio, the density of both cones and rods were high (cone to rod ratio: 1:1.23) and reflected the species’ fundamentally diurnal, but largely crepuscular lifestyle. Similarly, the ratio of cones to rods in M. namaquensis (1:12.4) reflected its nocturnal lifestyle. Similar rod density peaks were observed (R. pumilio: ~84467/mm2; M. namaquensis: ~81088/mm2), but a density gradient yielded higher values in the central (~56618/mm2) rather than in the peripheral retinal region (~32689/mm2) in R. pumilio. Two separate cone types (S-cones and M/L-cones) were identified implying dichromatic color vision in the study species. In M. namaquensis, both cone populations showed a centro-peripheral density gradient and a consistent S- to M/L-cone ratio (~1:7.8). In R. pumilio, S cones showed a centro-peripheral gradient (S- to M/L-cone ratio; central: 1:7.8; peripheral: 1:6.8) which appeared to form a visual streak, and a specialized area of M/L-cones (S- to M/L-cone ratio: 1:15) was observed inferior to the optic nerve. The number of photoreceptors per linear degree of visual angle, estimated from peak photoreceptor densities and eye size, were four cones and 15 rods per degree in M. namaquensis and 11 cones and 12 rods per degree in R. pumilio. Thus, in nocturnal M. namaquensis rods provide much finer image sampling than cones, whereas in diurnal/crepuscular R. pumilio both photoreceptor types provide fine image sampling. IpRGCs were comparably sparse in R. pumilio (total = 1012) and M. namaquensis (total = 862), but were homogeneously distributed in M. namaquensis and densest in the dorso-nasal quadrant in R. pumilio. The adaptive significance of the latter needs further investigation.

Mineral–Water Interface Structure of Xenotime (YPO4) {100}

Crystal truncation rod (CTR) measurements and density functional theory (DFT) calculations were performed to determine the atomic structure of the mineral–water interface of the {100} surface of xenotime (nominally YPO4). This mineral is important, because it incorporates a variety of rare earth elements (REEs) in its crystal structure. REEs are critical materials necessary for a variety of renewable and energy efficient technologies. Current beneficiation techniques are not highly selective for REE ore minerals, and large amounts go to waste; this is a first step toward designing more efficient beneficiation. Evidence is found for minor relaxation of the surface within the topmost monolayer with little or no relaxation in subsurface layers. Justification for ordered water at the interface is found, where water binds to surface cations and donates hydrogen bonds to surface phosphates. The average bond lengths between cations and oxygens on water are 228 pm in the best fit to the CTR data, versus 243 and 2...

Spontaneous distortion via the appearance of ferromagnetism in Pd ultrathin films: Observation of an inverse mechanism for the Stoner criterion

We study the crystal structure of Pd(100) ultrathin films, which show ferromagnetism induced by the quantum confinement effect, using in-situ X-ray crystal truncation rod measurement and density functional calculation. The energy gain due to the appearance of ferromagnetism in Pd results in flatter and uniform film growth of ferromagnetic Pd films compared with paramagnetic Pd. In addition, ferromagnetic Pd films expand the lattice constant in order to suppress the increase in kinetic energy of electrons accompanied by the occurrence of exchange splitting. Although the traditional theory of magnetism in metals indicates that the increase in density of states that induces ferromagnetism (Stoner criterion), our present finding reveals a mechanism of modulation in the density of states via the appearance of ferromagnetism, i.e., the inverse mechanism of Stoner's theory.

Synthesis of zinc oxide microrod arrays and their performance as piezo-generators

ABSTRACTZinc oxide microrods were synthesized by aqueous chemical growth using zinc nitrate and zinc acetate solutions without seed layer. Rod length of around 10 µm was obtained after 5 hr at 95°C. Solution replenishment led to a better alignment normal to the substrate; however, only zinc acetate solution resulted in bigger rods, reaching about 12 µm in length and 5 µm in diameter. X-ray diffraction revealed a pure hexagonal wurtzite structure with high crystallographic texture. Raman spectroscopy showed no evidence of lattice stress. The ZnO microrod arrays were used to fabricate piezoelectric generators, and the largest output was obtained from the generator with the higher density of rods. The use of a piezoelectric polymer in the generators led to an improved performance of at least 200% compared to reports that used a dielectric polymer.

The feasibility study of an in situ marine polysaccharide-based hydrogel as the vitreous substitute.

Although various biopolymers and synthetic compounds have been proposed and tested as the vitreous substitutes, no ideal material has been identified yet. In the present study, we developed an in situ-formed hydrogel by crosslinking hydroxypropyl chitosan with alginate dialdehyde. Physical properties of the hydrogel were studied and the cytotoxicity was evaluated using L929 fibroblasts, rabbit corneal endothelial cells and retinal pigment epithelial cells. In a preliminary in vivo study, the hydrogel was employed as vitreous substitute after vitrectomy surgery on rabbits and multiple parameters indicating biosafety and biocompatibility were measured and analyzed postoperatively. Our results showed that the refractive index, transmittance, pH value and density of the hydrogel were similar to those of human vitreous. Cytotoxicity tests demonstrated the hydrogel to be nontoxic to all of the three cell lines selected. Using the rabbit model, we showed that the hydrogel could form in situ and postoperative analysis of slit-lamp observation, intraocular pressure, corneal endothelium examination, B-scan ultrasound and fundus photography showed no significant adverse reactions in the operated eyes during the 90-day follow-up. However, electroretinogram and histopathological examinations indicated minor vision decline and decrease of the densities of cones and rods in the operated rabbit eyes. Collectively, our study suggested that the in situ-formed hydrogel could potentially be used as a vitreous substitute, with its long-term safety and efficacy to be further assessed. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1997-2006, 2018.

Optimization of Supporting Structures and Parameters of Tunnels in Soft Phyllite

The study investigated the extra-long Shuangxiling tunnel in soft phyllite within Nanchang–Ningdu highway in Jiangxi province, China. The supporting scheme of reducing the size and density of anchor rods while strengthening the stiffness and strength of preliminary support was put forward aiming at the repeated occurrence of great deformation of surrounding rocks during tunneling. Moreover, two groups of comparative supporting schemes were introduced for comparison. Based on the numerical simulation, the study calculated the amount of displacement deformation, stress on anchor rods, development of plastic zones, stress on shotcrete, and stress on secondary lining structure under different supporting schemes. By conducting field monitoring test, the surrounding rock deformations and pressures under different supporting schemes were monitored and measured in real time. The research results showed that after strengthening the stiffness and strength of preliminary support, the surrounding rock pressure on the supporting structure increased. It limited the preliminary stress release rate of surrounding rocks, protected the integrity of surrounding rocks and controlled the sustained deformation of surrounding rocks. However, weakening the size and density of anchor rods had an insignificant effect on the whole supporting effect. The result of field test was basically consistent with that obtained through numerical simulation, which theoretically and practically verified the scientificity and feasibility of the supporting scheme of weakening the size and density of anchor rod while strengthening the stiffness and strength of preliminary support. The research result provides references for the support optimization of similar tunnels along the highway.

Elastic moduli of a smectic membrane: a rod-level scaling analysis

Chiral rodlike colloids exposed to strong depletion attraction may self-assemble into chiral membranes whose twisted director field differs from that of a 3D bulk chiral nematic. We formulate a simple microscopic variational theory to determine the elastic moduli of rods assembled into a bidimensional smectic membrane. The approach is based on a simple Onsager–Straley theory for a non-uniform director field that we apply to describe rod twist within the membrane. A microscopic approach enables a detailed estimate of the individual Frank elastic moduli (splay, twist and bend) as well as the twist penetration depth of the smectic membrane in relation to the rod density and shape. We find that the elastic moduli are distinctly different from those of a bulk nematic fluid, with the splay elasticity being much stronger and the curvature elasticity much weaker than for rods assembled in a three-dimensional nematic fluid. We argue that the use of the simplistic one-constant approximation in which all moduli are assumed to be of equal magnitude is not appropriate for modelling the structure-property relation of smectic membranes.

Thermal-electric modeling of graphite: Analysis of charge carrier densities and Joule heating of intrinsic graphite rods

Graphite is a versatile material with many applications. Its intrinsic density has been extensively studied and quantified experimentally and theoretically. Experimental data suggest that the electron and hole densities are roughly equal, but the degree of inequality or the magnitude of the difference has not been quantified before for intrinsic graphite under biased (applied voltage) conditions. In this paper, a steady-state one-dimensional drift-diffusion thermal-electric model is developed to explore and analyze the nature of the electron, hole and intrinsic carrier densities of graphite rods under an externally applied voltage. The maximum difference between hole and electron densities as a function of length and applied voltage are numerically determined, showing that the maximum absolute difference between hole and electron densities decreases as the ratio of length over electric field increases. Moreover, it is observed that the difference between hole and electron densities varies with position. The model is further utilized for the analysis of the dependency of charge carrier transport, heat transport and temperature under a variety of operating conditions. The results show that higher applied voltages lead to higher current densities and higher current densities result in higher power generation by Joule heating, leading to higher lattice temperatures and voltage gradients along the length of the graphite rod. Dimensionless and scaling analysis showed that in the range of operating conditions, convective and radiation losses were negligible, with the lattice temperature increasing significantly when Joule heating was high.

Mechanistic constitutive model for wormlike micelle solutions with flow-induced structure formation

We present a tensor constitutive model for predicting stress and flow-induced structure formation in dilute wormlike micellar solutions. The micellar solution is treated as a dilute suspension of rigid Brownian rods whose length varies dynamically. Consistent with the mechanism presented by Turner and Cates [J. Phys.: Condens. Matter 4, 3719 (1992)], flow-induced alignment of the rods is assumed to promote increase of rod length that corresponds to the formation of flow-induced structures observed in experiments. At very high deformation rate, hydrodynamic stresses causes the rod length to decrease. These mechanisms are implemented in a phenomenological equation governing the evolution of rod length, with the number density of rods appropriately modified to ensure conservation of surfactant mass. The model leads first to an increase in both shear and extensional viscosity as deformation rate increases and then to a decrease at higher rates. If the rate constant for flow-induced rod growth is sufficiently large, the model predicts a multivalued relation between stress and deformation rate in both shear and uniaxial extension. Predictions for shear and extensional flow at steady state are in reasonable agreement with experimental results. By design, the model is simple enough to serve as a tractable constitutive relation for computational fluid dynamics studies.

Different phases of a system of hard rods on three dimensional cubic lattice

We study the different phases of a system of monodispersed hard rods of length k on a cubic lattice, using an efficient cluster algorithm able to simulate densities close to the fully-packed limit. For , the system is disordered at all densities. For , we find a single density-driven transition, from a disordered phase to high density layered-disordered phase, in which the density of rods of one orientation is strongly suppressed, breaking the system into weakly coupled layers. Within a layer, the system is disordered. For , three density-driven transitions are observed numerically: isotropic to nematic to layered-nematic to layered-disordered. In the layered-nematic phase, the system breaks up into layers, with nematic order in each layer, but very weak correlation between the ordering directions of different layers. We argue that the layered-nematic phase is a finite-size effect, and in the thermodynamic limit, the nematic phase will have higher entropy per site. We expect the systems of rods in four and higher dimensions will have a qualitatively similar phase diagram.

Use of the “dual construct” for the management of complex spinal reconstructions

Background ContextSurgical management of complex spinal reconstructions remains a clinical challenge, as pseudoarthrosis with subsequent rod breakage can occur. Increased rod density in the form of “satellite” or “outrigger” rods have been described; however, rod-fracture above or below satellite rods persist and can result in dissociation of the construct, loss of correction, and recurrence of deformity. The use of four distinct and mechanically independent rods (dual construct) reduces this concern. Since the original case description in 2006, there have been no other studies that use the dual construct for the surgical management of complex spinal reconstructions. PurposeThe purpose of this study is to review the long-term experience and surgical technique using the dual construct, and to present our complications, rod fracture rates, and outcomes for the surgical management of complex spinal reconstructions. Study DesignThis study used a surgical technique with case series outcomes. Patient SamplePatients were from a single-institute who underwent dual construct between 2010 and 2014 and who were available for 2-year follow-up. Outcome MeasuresRadiographic and functional outcomes, complications, rod fracture rates, and revision surgery rates were the outcome measures. MethodsA retrospective review was conducted from a single institution between 2010 and 2014, with a subsequent 2-year follow-up period. Extensive review of patients' medical record, radiographs, and advanced imaging where available was performed. Medical record was evaluated for patient demographics, surgical procedure, and complications. Radiographic measurements included presence or absence of implant failure and proximal junctional kyphosis or distal junctional kyphosis. ResultsA total of 36 patients underwent surgical reconstruction. The average estimated blood loss was 1,856 cc (range, 400–4,000 cc). The average length of stay was 7.3 days (range, 4–22 days). Clinical follow-up reported 21 patients (58.3%) with no or minimal pain. There were six deaths during the follow-up unrelated to the index procedure. Radiographic follow-up revealed three patients (8.3%) with rod fracture; one patient with one rod fracture, and two patients with two rod fractures. No patient had three or all four rod fractures. There were no screw fractures. None of the patients with rod fractures required revision surgery. ConclusionsThe biggest advantage of the dual construct is that rod breakage, although uncommon, is typically minimal, or asymptomatic, and more importantly does not result in loss of alignment, and therefore has not required revision surgery. The dual construct approach is a safe alternative to traditional two-rod constructs, with encouraging outcomes at follow-up.

Drag coefficient estimation using flume experiments in shallow non-uniform water flow within emergent vegetation during rainfall

Vegetation persistence on low-gradient slopes in dryland regions is presumed to be supported by lateral flow of water originating from bare sites with low permeability soil. The hydrodynamics of these flows, which occur during and immediately following intense rainfall events, are challenging to describe with classical approximations to the Saint-Venant equations (SVE). Flume experiments with varying rod density and applied water along the vegetated section are conducted to explore common approximations used to close the SVE when predicting water depth. Guided by these experiments, expressions are then derived that describe the simultaneous effects of spatially uniform vegetation density and rainfall intensity on the drag coefficient (Cd) linking the friction slope to the local kinetic energy head for steady non-uniform flow on a flat surfaces. Spatial variations in Cd through the vegetated patch either exhibit monotonic declines during rain or a non-monotonic ‘hump’ shape without rain with increasing longitudinal distance into the vegetated section. These spatial variations arise due to the indirect effect of rainfall on the dynamic component of the mean pressure gradient driving flow.