Beautiful Structure Research Articles

Hyperbolic Planforms in Relation to Visual Edges and Textures Perception

We propose to use bifurcation theory and pattern formation as theoretical probes for various hypotheses about the neural organization of the brain. This allows us to make predictions about the kinds of patterns that should be observed in the activity of real brains through, e.g., optical imaging, and opens the door to the design of experiments to test these hypotheses. We study the specific problem of visual edges and textures perception and suggest that these features may be represented at the population level in the visual cortex as a specific second-order tensor, the structure tensor, perhaps within a hypercolumn. We then extend the classical ring model to this case and show that its natural framework is the non-Euclidean hyperbolic geometry. This brings in the beautiful structure of its group of isometries and certain of its subgroups which have a direct interpretation in terms of the organization of the neural populations that are assumed to encode the structure tensor. By studying the bifurcations of the solutions of the structure tensor equations, the analog of the classical Wilson and Cowan equations, under the assumption of invariance with respect to the action of these subgroups, we predict the appearance of characteristic patterns. These patterns can be described by what we call hyperbolic or H-planforms that are reminiscent of Euclidean planar waves and of the planforms that were used in previous work to account for some visual hallucinations. If these patterns could be observed through brain imaging techniques they would reveal the built-in or acquired invariance of the neural organization to the action of the corresponding subgroups.

Measurement of the charm and beauty structure functions using the H1 vertex detector at HERA

Inclusive charm and beauty cross sections are measured in e-p and e+p neutral current collisions at HERA in the kinematic region of photon virtuality 5<Q^2<2000 GeV^2 and Bjorken scaling variable 0.0002<x<0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189 pb^-1. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.

The Chiani Suspension Bridge: A Complete Overhaul

The paper presents the rehabilitation works carried out on the Chiani suspension bridge in Algeria. The bridge, designed by the French engineer Arnodin at the beginning of the last century, has a main span of 105 m and a mixed cable supporting system with a stayed deck portion near the towers. The bridge was designed and built before the similar Sidi M'Cid one in Constantine, Algeria. The strengthening works carried out on this bridge by the same authors during the 1990s was reported in Structural Engineering International (4/2000).4 Following the successful experience of the Sidi M'Cid bridge, the authors have been asked to engineer a complete overhaul of the Chiani bridge, a beautiful structure completely abandoned and closed to traffic because of its severe state of degradation. The works included the complete substitution of the suspension system, the widening of the superstructure with new pedestrian sidewalks moved out of the parapet girders and a new concrete deck to allow for unrestricted vehicular traffic to transit on it. Works have been carried out without supports from below, with the deck weight transferred from one suspension system to the other while the bridge remained open to pedestrian, motorbikes and herds. An innovative suspension system with resin-encased strands has been used for main cables, stays and hangers in lieu of ropes and steel bars. New saddles, made of welded plates following a concept originally developed for the third generation suspension bridges, have been placed over the existing ones with the two systems working in parallel during the load transfer.

Geometrical approach to hydrodynamics and low-energy excitations of spinor condensates

In this work, we derive the equations of motion governing the dynamics of spin-$F$ spinor condensates. We pursue a description based on standard physical variables (total density and superfluid velocity), alongside $2F$ ``spin nodes:'' unit vectors that describe the spin-$F$ state and also exhibit the point-group symmetry of a spinor condensate's mean-field ground state. In the first part of our analysis, we derive the hydrodynamic equations of motion, which consist of a mass continuity equation, $2F$ Landau-Lifshitz equations for the spin nodes, and a modified Euler equation. In particular, we provide a generalization of the Mermin-Ho relation to spin one and find an analytic solution for the skyrmion texture in the incompressible regime of a spin-half condensate. In the second part, we study the linearized dynamics of spinor condensates. We provide a general method to linearize the equations of motion based on the symmetry of the mean-field ground state using the local stereographic projection of the spin nodes. We also provide a simple construction to extract the collective modes from symmetry considerations alone akin to the analysis of vibrational excitations of polyatomic molecules. Finally, we present a mapping between the spin-wave modes, and the wave functions of electrons in atoms, where the spherical symmetry is degraded by a crystal field. These results demonstrate the beautiful geometrical structure that underlies the dynamics of spinor condensates.

Let's twist again

A dislocation running through the trunk of a nanowire offers a new twist to the growth of chiral branched nanostructures, producing beautiful tree-like structures in the process.

A facile synthesis of ordered ultralong silver nanobelts

Large-scale ordered ultralong silver nanobelts, which built a beautiful chrysanthemum-like structure, are prepared on the interface between dibutyl sebacate (DBS) and silver nitrate solution by a chemical electro-deposition technique. The influences of chemical circumvent of interface, concentration of silver nitrate solution and applied voltage on the formation of silver nanobelts are investigated. It is shown that the silver nanobelts possess a perfect single crystal structure and well-defined nanobelt-like morphology with a length of 5 mm, width 80–150 nm, and thickness 20 nm, respectively. The growth mechanism of the nanobelts is discussed. Furthermore, UV–vis spectra of the silver nanobelts show similar surface plasmon resonance properties to silver nanowires.

Parabolic section and distance excess of space curves applied to protein structure classification

Proteins are long chain molecules that fold up into beautiful and complicated three-dimensional structures before fulfilling their biological functions in the living organisms. With the aim of providing an efficient tool for describing the proteins’ native folds, we present a global geometric measure of a space curve. This geometric measure allows us to define descriptors of protein structures that quantify how parallel the secondary structure elements of a protein are. These descriptors are C 2 in deformations of the protein structure, are evaluated very fast and reliably, and are demonstrated to capture essential parts of the protein native fold universe.

The enigmatic snowflake

Sometimes the simple things in nature can be the most puzzling. Take the humble snowflake, that familiar winter icon immediately recognizable by its beautiful structure and distinctive symmetry. One might think that the process whereby water vapour condenses into crystalline ice would be well understood. A closer look, however, reveals that even some very basic questions about how snow crystals form remain unanswered.

Generation of Protein Structures for the 21st Century

I am personally not excited about solving structures with novel folds so I am not a participant in a PSI-2 production center. My interests are in structural neurobiology and in developing critically needed technologies that help myself and others accomplish their research goals. However, I do appreciate the passion the PSI-2 production centers have for their work and understand and appreciate the big picture that will result from their dedicated effort, as I also appreciate the enormous efforts of those working on viruses, ribosomes, and other very challenging structural biology projects. Once PSI-2 is completed in the summer of 2010, the issue of how we will generate the structural data that the scientific community needs will not go away. Protein structures will continue to be critical for the understanding of chemistry and biology. Key considerations for a Protein Initiative-3 (or 1) include:•Careful re-evaluation of the targets/approaches for biomedical research.•Continuation of technology development. This is critical for studying the larger complexes and challenging proteins like those that exist in the membrane. We also need increased production of these very challenging protein structures so that we improve our fundamental understanding of these key biological macromolecules.•Function is as important as the structures being generated and this should become a more central focus of any future program. Already, movement is evident in this area with chemical profiling of protein families in a structural genomics setting (Allali-Hassani et al., 2007xStructural and chemical profiling of the human cytosolic sulfotransferases. Allali-Hassani, A., Pan, P.W., Dombrovski, L., Najmanovich, R., Tempel, W., Dong, A., Loppnau, P., Martin, F., Thornton, J., Edwards, A.M. et al. PLoS Biol. 2007; 5: e97CrossRef | PubMed | Scopus (32)See all ReferencesAllali-Hassani et al., 2007).•Better coordination with other proteomics approaches (e.g., activity-based profiling, metabolite profiling of enzyme families, and mass spectrometry differentiation among various cellular species).•Although we have seen X-ray and NMR complement one another better through PSI, electron microscopy has not been integrated as well, in part due to the proteins being studied. As we start to investigate larger complexes, the membrane, and entire cells, electron microscopy and single molecule analysis advances will be extremely important techniques to integrate and further our understanding of biological structures and their functions.There is no question that certain things could be done better in PSI, as is often the case when change occurs. What is important is that we have made tremendous strides in improving our approaches to collect and understand protein structures in the past several years, and we are now in a better position to keep up with the demand for more structural data. I applaud NIGMS staff for talking to scientific leaders about current limitations and potential new directions in the field, and for taking the initiative to change the way we do science based on prior investments and new discoveries.

Following the Chromosome Path to the Garden of the Genome

I have been fascinated by chromosomes for longer than I care to mention; their beautiful structure, cell-type-specific changes in morphology, and elegant movements delight me. Shortly before I began graduate study, the development of nucleic acid hybridization made it possible to compare two nucleic acids whether or not their sequences were known. From this stemmed a progression of development in tools and techniques that continues to enhance our understanding of how chromosomes function. As my PhD project I contributed to this progression by developing in situ hybridization, a technique for hybridization to nucleic acids within their cellular context. Early studies with this technique initiated several lines of research, two of which I describe here, that I have pursued to this day. First, analysis of RNA populations by hybridization to polytene chromosomes (a proto-microarray-type experiment) led us to characterize levels of regulation during heat shock beyond those recognizable by puffing studies. We found also that one still-undeciphered major heat shock puff encodes a novel set of RNAs for which we propose a regulatory role. Second, localization of various multicopy DNA sequences has suggested roles for them in chromosome structure: Most recently we have found that Drosophila telomeres consist of and are maintained by special non-LTR (long terminal repeat) retrotransposons.

RECURRENCE QUANTIFICATIONS: FEATURE EXTRACTIONS FROM RECURRENCE PLOTS

Recurrence plots are two-dimensional representations of multidimensional dynamics captured by applying time delays to a single series (vector) of ordinal data in time or space. Recurrence plots may be presented with beautiful lace-like structures, but most important is the inference these patterns make about the underlying dynamics. Complex patterns in recurrence plots can be reduced to primary diagonal, vertical and horizontal dot patterns aligned on a grid. It is the mixing and matching of these primary structures that give rise to all derivative graphical complexities. Once strict definitions are in place, features are easily quantified from recurrence plots of any form including cross recurrence plots.

Cyclic Nucleotide-Regulated Ion Channels: Spotlight on Symmetry

In this issue of Structure, Chiu et al. (2007) report the 16 A EM structure of the prokaryotic cyclic nucleotide-regulated K(+) channel MloK1. This structure reveals that the channel is arranged as a four-fold symmetric tetramer.

THE CEREBRUM

The cerebrum is the crown jewel of creation and evolution. It is a remarkably delicate, intricate, and beautiful structure. The goal of this chapter is to provide the information needed to permit the neurosurgeon to navigate accurately, gently, and safely around and through the cerebrum and intracranial space. The location of deep structures is frequently described in relation to cranial and superficial cerebral landmarks in order to develop the concept of see-through, x-ray type knowledge of the cerebrum. In numerous illustrations, stepwise dissections are used to clarify the relationship between structures in different layers. Important clinical and surgical concepts are intermixed with the description of the cerebrum and its arteries, veins, and ventricles.

Synaptic signalling in cerebellar plasticity

A major goal of learning and memory research is to correlate the function of molecules with the behaviour of organisms. The beautiful laminar structure of the cerebellar cortex lends itself to the study of synaptic plasticity, because its clearly defined patterns of neurons and their synapses form circuits that have been implicated in simple motor behaviour paradigms. The best understood in terms of molecular mechanism is the parallel fibre-Purkinje cell synapse, where presynaptic long-term potentiation and postsynaptic long-term depression and potentiation finely tune cerebellar output. Our understanding of these forms of plasticity has mostly come from the electrophysiological and behavioural analysis of knockout mutant mice, but more recently the knock-in of synaptic molecules with mutated phosphorylation sites and binding domains has provided more detailed insights into the signalling events. The present review details the major forms of plasticity in the cerebellar cortex, with particular attention to the membrane trafficking and intracellular signalling responsible. This overview of the current literature suggests it will not be long before the involvement of the cerebellum in certain motor behaviours is fully explained in molecular terms.

Aesthetics and Economy in Pedestrian Bridge Design

Two common pitfalls of pedestrian bridge design are explored: the idea that a structure that is efficient will automatically be elegant versus the notion that a lot of money must be spent to get a beautiful structure. The drive for landmark bridges has led some engineers to disregard the engineering ethic of economy with some recent footbridges. The Töss Footbridge by structural artist Robert Maillart is shown as a model structure, with Maillart's calculations and a description of the bridge's structural behavior presented. Then an extremity on the other side of the spectrum is analyzed: the Turtle Bay Sundial Bridge in Redding, California. The cost escalation and a scientific explanation of the irrationality of the bridge form are presented for this $23.5 million footbridge. In order to explore both pitfalls in the United States an informal national study of all 50 states was performed. Results from the national study (including costs) are described and interpreted. Three unique structures from this study are presented which are reasonably economical and prove that a so-called signature bridge does not require extreme cost.

Structure functions at HERA

HERA provides the key facility for the measurement of proton structure functions. Formalism and methods are outlined for the measurement and interpretation of inclusive structure functions, including the use of polarised e ± beams. The measurement of charm, beauty and photon structure functions is discussed, together with special runs at low proton energy for measurement of the longitudinal structure function. Finally, the functions accessed using polarised beams on polarised targets are indicated.

Volume of truncated fundamental domains

For T > 0, by applying Arthur's analytic truncation AT to the constant function 1 on G(F)\G(A)1, we obtain a characteristic function of a compact subset i(T) of G(F)\G(A)1. The aim of this paper is to give a general formula for the volume of a(T), which is an exponential polynomial function of T. Consequently, by letting T -* oo, we obtain a new way to evaluate the volume of fundamental domain for G(F)\G(A)1. While a(T) seems to be quite arbitrary, its volume admits beautiful structures: (i) Surprisingly enough, the coefficients of T are special values of zeta functions. (ii) The volume is an alternating sum associated to standard parabolic subgroups. ((ii) is suggested by geometry after all, a(T) is obtained from G(F)\G(A)1 by truncating off cuspidal regions which are known to be parametrized by standard parabolic subgroups.) Besides all basic properties of Arthur's analytic truncation, our method is based on a fundamental formula of Jacquet-Lapid-Rogawski on an integration of truncated Eisenstein series associated to cusp forms. Their formula, an advanced version of the Rankin-Selberg method, is obtained using the so-called Bernstein principle via regularized integration over cones.

Flux vacua and supermanifolds

As been recently pointed out, physically relevant models derived from string theory require the presence of non-vanishing form fluxes besides the usual geometrical constraints. In the case of NS-NS fluxes, the Generalized Complex Geometry encodes these informations in a beautiful geometrical structure. On the other hand, the R-R fluxes call for supergeometry as the underlying mathematical framework. In this context, we analyze the possibility of constructing interesting supermanifolds recasting the geometrical data and RR fluxes. To characterize these supermanifolds we have been guided by the fact topological strings on supermanifolds require the super-Ricci flatness of the target space. This can be achieved by adding to a given bosonic manifold enough anticommuting coordinates and new constraints on the bosonic sub-manifold. We study these constraints at the linear and non-linear level for a pure geometrical setting and in the presence of p-form field strengths. We find that certain spaces admit several super-extensions and we give a parameterization in a simple case of d bosonic coordinates and two fermionic coordinates. In addition, we comment on the role of the RR field in the construction of the super-metric. We give several examples based on supergroup manifolds and coset supermanifolds.

打放しコンクリートの色彩に及ぼすセメントおよび細骨材の色彩の影響

Color coordinate of architectural concrete is a very important factor of structure's beauty. However in the present circumstances, there were extremely few reports on quantitative analysis of the influence of the color of cement and fine aggregate on the color of concrete. Then, the influence on the color of architectural concrete was experimentally examined using cement and fine aggregate with different color. According to the result, the correlation between the color of architectural concrete, and the color of cement, fine aggregate, the mixture of cement and fine aggregate, mortar was clarified. And through analyzing the influence of the color of cement and fine aggregate, the color of the mixture of cement and fine aggregate was quantified.

New good quasi-cyclic codes over GF(3)

In this paper some good quasi-cyclic codes over GF(3) are presented. These quasi-cyclic codes improve the already known lower bounds on the minimum distance of the previously known quasi-cyclic codes. Even though these codes do not improve the minimum distance of the best unstructured code known, their beautiful structure and simplicity provide several advantages in comparison to other random codes. Also, three of the ternary quasi-cyclic codes presented have parameters [66,11,33;3], [65,13,30;3], [56,14,24;3] and so their minimum distances beat the minimum distances of the previously known quasi-cyclic codes and meet the minimum distances of the best unstructured linear codes with these parameters. Mathematics Subject Classification: 94B05, 94B25