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At least 253 records · Page 14Linked to original sources
PubMedDate not supplied

A simple algorithm for unique representation of chemical structures-cyclic/acyclic functionalized achiral molecules.

An algorithm, based on "vertex priority values" has been proposed to uniquely sequence and represent connectivity matrices of chemical structures of cyclic/acyclic functionalized achiral hydrocarbons and their derivatives. In this method, "vertex priority values" have been assigned in terms of atomic weights, subgraph lengths, loops, and heteroatom contents. Subsequently, the terminal vertices have been considered upon completing the sequencing of the core vertices. This approach provides a multilayered connectivity graph, which can be put to use in comparing two or more structures or parts thereof for any given purpose. Furthermore, the basic vertex connection tables generated here are useful in the computation of characteristic matrices/topological indices and automorphism groups and in storing, sorting, and retrieving chemical structures from databases.

Journal Article↗
PubMed1989

[The implant denture in the laboratory].

The authors analyzed the numerous devices and prosthetic kits currently available for implant prosthodontics. Existing systems can be classified into two fundamentally different categories: the gold ring cylinder (or its equivalent in resin for casting) and the prosthetic abutment core or post concept. The former is based on connection of two nearly flat, horizontal surfaces by means of a screw, which avoids problems of parallelism; the latter can be likened to insertion of one part into another, like a crown that slides along the vertical axis of an abutment, with connection being obtained by cementation and/or screwing. Prosthetic abutment core or post: Whether monoblock or multiblock, the implant core or post is very similar to a conventional metallic abutment. Construction of the implant prosthesis is generally no problem when parallelism has been respected during surgery; if problems are encountered with parallelism, options include: 1. Adjustment of the abutment core by grinding, 2. Use of a telescope to achieve parallelism, 3. Use of a bendable prosthetic abutment core, 4. Use of a prosthetic abutment core preangulated 10 degrees-20 degrees, 5. A combination of the above solutions. The implant prostheses may be screwed, cemented or clipped in position. Gold ring cylinder concept The gold ring cylinder (or its equivalent in resin for casting) theoretically eliminates problems of parallelism, but at the same time restricts the implant prosthesis to screw techniques. A special protocol is required for the impression and construction of the prosthesis. Impression with plaster is often the best method for total edentulism whereas "open" impression trays are advisable for partial prostheses. In the laboratory, use of a machined gold ring cylinder provides optimum precision, but intra-oral verification remains necessary. Implant prosthodontics unquestionably represent a new type of "know how": both the dentist and the dental lab technician must acquire the necessary training and adapt their work routines.

Dental Implantation↗
PubMedDate not supplied

Variable neighborhood search for extremal graphs. 6. Analyzing bounds for the connectivity index.

Recently, Araujo and De la Peña gave bounds for the connectivity index of chemical trees as a function of this index for general trees and the ramification index of trees. They also gave bounds for the connectivity index of chemical graphs as a function of this index for maximal subgraphs which are trees and the cyclomatic number of the graphs. The ramification index of a tree is first shown to be equal to the number of pending vertices minus 2. Then, in view of extremal graphs obtained with the system AutoGraphiX, all bounds of Araujo and De la Peña are improved, yielding tight bounds, and in one case corrected. Moreover, chemical trees of a given order and a number of pending vertices with minimum and with maximum connectivity index are characterized.

Journal Article↗
PubMed1994

[Surgical correction of anomalous venous connection of the left lung without extracorporeal circulation].

Surgical correction of anomalous pulmonary venous connection from the left lung to the innominate vein (through a vertical vein) without cardiopulmonary bypass, was performed in two patients, with excellent evolution. After median sternotomy, the ascending vertical vein was cut obliquely close to the vein, and connected to the left atrial appendage. In the postoperative period, the patients were in NYHA class I and the hemodynamic study showed normal venous drainage from the left lung to the left atrium.

Adolescent↗
PubMed2005

Heuristic search in constrained bipartite matching with applications to protein NMR backbone resonance assignment.

The constrained bipartite matching (CBM) problem is a variant of the classical bipartite matching problem that has been well studied in the Combinatorial Optimization community. The input to CBM is an edge-weighted complete bipartite graph in which there are a same number of vertices on both sides and vertices on one side are sequentially ordered while vertices on the other side are partitioned and connected into disjoint directed paths. In a feasible matching, a path must be mapped to consecutive vertices on the other side. The optimization goal is to find a maximum or a minimum weight perfect matching. Such an optimization problem has its applications to scheduling and protein Nuclear Magnetic Resonance peak assignment. It has been shown to be NP-hard and MAX SNP-hard if the perfectness requirement is dropped. In this paper, more results on the inapproximability are presented and IDA*, a memory efficient variant of the well known A* search algorithm, is utilized to solve the problem. Accordingly, search heuristics and a set of heuristic evaluation functions are developed to assist the search, whose effectiveness is demonstrated by a simulation study using real protein NMR backbone resonance assignment instances.

Algorithms↗
PubMed1993

Finite element stress analysis of tooth-to-implant fixed partial denture designs.

PURPOSE: The purpose of this study was to conduct a three-dimensional finite element stress analysis to compare models representing a natural tooth and an integrated implant connected with rigid and nonrigid prostheses. MATERIALS AND METHODS: The mathematical models described an integrated implant connected to a second premolar tooth with a three-unit metal-ceramic fixed partial denture. In one model, the tooth and implant were rigidly connected, and in the other, a nonrigid connection was assumed. From a simulated vertical load the computer generated resultant stress contours and values (compressive and tensile) in horizontal and vertical dimensions. RESULTS: A comparison of the magnitude and pattern of stresses generated in the models shows minimal differences. Although the maximum stress values were slightly higher in some areas of the rigid prosthesis model, the differences were negligible. CONCLUSIONS: Based on the similarities in both the patterns of stress contours and the stress values generated in the two models, advocating a nonrigid connection because of a biomechanical advantage may be erroneous.

Alveolar Process↗
PubMed1996

Electrophysiological elucidation of pathways of intrinsic horizontal connections in rat visual cortex.

Cortical neurons receive synaptic inputs through both vertical and horizontal pathways. We made a systematic survey of the synaptic strength and intracortical pathways of intrinsic horizontal connections in rat visual cortex using intracellular recordings from alice preparations. Excitatory postsynaptic potentials were recorded from pyramidal neurons of layers 2/3 and layers 5/6 in response to electrical shocks applied to these layers at a lateral distance of 1.0 mm from the impaled neuron or to the underlying white matter. When the threshold intensity of stimulation to activate monosynaptic excitatory postsynaptic potentials was compared, the vertical input had a lower threshold than the horizontal inputs. The threshold intensity of the horizontal inputs was lower, and the amplitude of the responses was larger in sagittally sectioned slices than in coronal slices, suggesting that the horizontal synaptic connection in the rat visual cortex was stronger in the rostrocaudal than in the mediolateral direction. Tetrodotoxin puffs focally applied to gray matter between the stimulation and the recording sites caused a transient depression of excitatory postsynaptic potentials, which was selective to the input conveyed through the puffed area. This pharmacological dissection revealed that routes parallel to the cortical Iaminae in the same layer as the stimulation site mediated the largest part of excitation conduction of intrinsic connections. Obliquely ascending routes mediated almost half of all the detected inputs originating from a deep layer to the neurons in either layers 5/6 or layers 2/3, whereas the contribution of obliquely descending routes from layers 2/3 to layers 5/6 was small (25%). Our results present semi-quantitative data on the connection diagram of the intrinsic neuronal circuits in the rat visual cortex, which will provide the basis for further investigations of the roles of the intrinsic connections in information processing in rodent cerebral cortex.

Action Potentials↗
PubMed2006

Eye-rotation-induced spatial reorganization of horizontal connections in field 17 of the cat cortex.

Six cats with rotation of one or both eyes (strabismus) produced surgically in the early postnatal period demonstrated torsional deviation of the eyes by 10-20 degrees in addition to the rotation. The spatial distribution of retrograde labeled neurons in field 17 was studied by microiontophoretic administration of horseradish peroxidase into individual cortical columns in fields 17 and 18. These studies showed that rotation of the eyes increased the extent of horizontal neuronal connections in field 17 along the projection of the vertical meridian of the field of vision. It is suggested that this reorganization of neuronal connections may support functional changes compensating for eye rotation, as described in the literature.

Animals↗
PubMed1996

Anisotropy of wave velocities in plants: gravitropism.

New measurements of W-wave velocities in plants suggest that the previously observed velocity of 96 cm/s in plants is not unique but that there are several higher velocities, which appear to be integral multiples of 96 cm/s. The velocities apparently depend on the species, environment, and type of pulse when changed artificially. Measured vertical velocities are larger than horizontal velocities. This may provide a basis for gravitropism and may suggest a cosmic connection. Mean ratios of reciprocals of horizontal and vertical internodal spacings, in simple structure cases, give ratios like 1.25, 1.33, 1.50, 1.66, 3.0, and likely others. These ratios appear to confirm the velocity measurements since ratios of integral multiples of 96 cm/s give the same ratios. The versatility of plant growth is enhanced by the velocity variability.

Anisotropy↗
PubMed2002

Robustness of the in-degree exponent for the World-Wide Web.

We consider a stochastic model for directed scale-free networks following power laws in the degree distributions in both incoming and outgoing directions. In our model, the number of vertices grow geometrically with time with a growth rate p. At each time step, (i) each newly introduced vertex is connected to a constant number of already existing vertices with the probability linearly proportional to in-degree distribution of a selected vertex, and (ii) each existing vertex updates its outgoing edges through a stochastic multiplicative process with mean growth rate of outgoing edges g and its variance sigma(2). Using both analytic treatment and numerical simulations, we show that while the out-degree exponent gamma(out) depends on the parameters, the in-degree exponent gamma(in) has two distinct values, gamma(in)=2 for p>g and 1 for p<g, independent of different parameters values. The latter case has logarithmic correction to the power law. Since the vertex growth rate p is larger than the degree growth rate g for the World-Wide Web (WWW) nowadays, the in-degree exponent appears robust as gamma(in)=2 for the WWW.

Journal Article↗
PubMed2006

Building k-connected neighborhood graphs for isometric data embedding.

Isometric data embedding using geodesic distance requires the construction of a connected neighborhood graph so that the geodesic distance between every pair of data points can be estimated. This paper proposes an approach for constructing k-connected neighborhood graphs. The approach works by applying a greedy algorithm to add each edge, in a nondecreasing order of edge length, to a neighborhood graph if end vertices of the edge are not yet k-connected on the graph. The k-connectedness between vertices is tested using a network flow technique by assigning every vertex a unit flow capacity. This approach is applicable to a wide range of data. Experiments show that it gives better estimation of geodesic distances than other approaches, especially when the data are undersampled or nonuniformly distributed.

Algorithms↗
PubMed2002

Esthetic correction of gingival recession using a modified tunnel technique and an acellular dermal connective tissue allograft.

UNLABELLED: Esthetic correction of gingival recession is an important goal of periodontal therapy. This article describes a surgical technique that combines a modified tunnel technique and an acellular dermal connective tissue allograft. With the aid of vertical incisions, a tunnel is created under the buccal mucosa of the affected tooth. These incisions enable easy access for graft placement and create mobility for gingival coronal positioning. The use of an acellular dermal connective tissue allograft eliminates the need for a surgical palatal donor site. This minimizes postsurgical complications. CLINICAL SIGNIFICANCE: The combination of a modified tunnel technique and an acellular dermal connective tissue allograft permits esthetic root coverage in a manner that reduces postsurgical complications.

Adult↗
PubMed2006

The immunity of polymer-microemulsion networks.

The concept of network immunity, i.e., the robustness of the network connectivity after a random deletion of edges or vertices, has been investigated in biological or communication networks. We apply this concept to a self-assembling, physical network of microemulsion droplets connected by telechelic polymers, where more than one polymer can connect a pair of droplets. The gel phase of this system has higher immunity if it is more likely to survive (i.e., maintain a macroscopic, connected component) when some of the polymers are randomly degraded. We consider the distribution p(sigma) of the number of polymers between a pair of droplets, and show that gel immunity decreases as the variance of p(sigma) increases. Repulsive interactions between the polymers decrease the variance, while attractive interactions increase the variance, and may result in a bimodal p(sigma).

Computer Simulation↗
PubMed1976

The organization and postnatal development of the commissural projection of the rat somatic sensory cortex.

Anterograde and retrograde tracing experiments have been used to demonstrate the origin and terminal distribution of commissural fibers in the first somatosensory cortex (SI) of the rat. The commissural fibers originate from pyramidal cells of all layers, but predominantly from layers III and V. The fibers terminate in a series of approximately vertical bands. In each of these there are concentrations of terminals extending from the inner portion of the molecular layer to the deep portion of layer III as well as in the superficial part of layer V, and in layer VI. Discrete vertical bands of cortex are reciprocally connected across the midline to give both the origin and terminal regions of the projection a patchy or "columnar" appearance. The commissural fibers arise from and terminate in areas of the cortex that lie between and alongside the aggregations of granule cells that distinguish SI of the rat. No commissural fibers terminate within the aggregations of layer IV cells themselves but the more superficial terminal ramifications may come to overlie these aggregations. A heterotopic projection to the contralateral second somatosensory cortex has been observed and is similar in form to the homotopic projection to SI. Many commissural fibers have crossed the midline in the corpus callosum by the day of birth but lie in the underlying white matter and do not enter the cortical plate until at least the third postnatal day. During the first postnatal week these fibers grow somewhat diffusely into the maturing cortex and their topographic and laminar pattern of distribution attains its adult characteristics by the end of the first week. Commissural axons, thus, arise from immature cells but the maturation of cell form seems to precede the ingrowth of these axons and the acquisition of commissural synapses.

Animals↗
PubMed1998

Helical perturbations of the flagellar filament: rhizobium lupini H13-3 at 13 A resolution

Flagellar filaments are highly conserved structures in terms of the underlying symmetry of the polymer, subunit domain organization of the flagellin monomer, amino acid composition and primary sequence at the N and C termini. Traditionally, filaments are classified as "plain" or "complex." In complex filaments, the helical lattice is perturbed in a pairwise manner such that the symmetry is reduced along the 6-start helical lines. Both plain (unperturbed) and complex (helically perturbed) components are helically symmetric and share a common lattice. The perturbation in Rhizobium lupini H13-3 results in a subunit composed of a dimer of flagellin. We have generated a approximately 13 A resolution three-dimensional density map of the complex filament of R. lupini H13-3 from low-dose images of negatively stained filaments. Compared to a previous map, which extended to only approximately 25 A resolution and which was generated from only five filaments containing six layer-lines each, the current map is a product of merging 139 data sets containing 66 layer-lines each. The higher resolution and improved signal-to-noise yield a detailed and interpretable density map. The density map is divided into four concentric rings. These amount to two dense cylinders interconnected by low density radial spokes and wrapped by a three-start external winding. The unperturbed component of the map is strikingly similar to the known plain filament maps and, in particular, to that of Caulobacter crescentus. The helically perturbed component contributes mainly to the filaments's exterior (domain D3) where it comprises the tips of the outer domains interconnecting, pairwise, along the 11-start protofilaments and, again, laterally along the 6-start lines forming vertical and horizontal loops. Strong intersubunit connectivity occurs in the D2 shell and in the inner shell which is dominated by 3-start densities. The contribution of the complex component to the radial spokes seems negligible. Copyright 1998 Academic Press.

Journal Article↗
PubMed1993

The spatial arrangement of Allium triquetrum chain quadrivalents at metaphase I as reviewed by confocal microscopy.

We examined the three-dimensional arrangement of bivalents and, in particular, a chain of four chromosomes (chain quadrivalent) in the metaphase I spindle of pollen mother cells of Allium triquetrum by confocal microscopy. Firstly, we show by optical sectioning and three-dimensional image reconstruction that the cooriented pairs of centromeres of all seven bivalents lie virtually parallel to each other in the metaphase I spindle, parallel to the long axis of the spindle. Secondly, we likewise show that the four centromeres of the chain quadrivalent are aligned in the metaphase I spindle in, essentially, a two-dimensional array, not in a three-dimensional array, as proposed by some other authors. This two-dimensionality has its basis, we argue, in the principle that poleward directed spindle forces minimise centromere-to-pole distances and therefore align pairs of centromeres connected to opposite poles most axially (vertically) in the spindle. These distances are minimised for the quadrivalent as a whole only when it lies in two dimensions, i.e. in a plane parallel to the spindle axis.

Allium↗
PubMed1980

New technical possibilities for simultaneous cystometry.

With the introduction of integrated semiconductor pressure pick-ups into the urodynamic methodology of analysis, the bladder and urethral manometry has been optimized, since the measuring transducer is positioned directly inside the lumen of the bladder. In this way, it is possible to eliminate the errors of conventional measuring methods with the liquid-filled or gas-filled catheter system, for example movements, vibrations, hydrostatic influences on the coupling medium by different vertical positions of the catheter or connecting tube, as well as cloggings due to haematuria or secretion of mucus. Owing to its dimensions and radiopaque properties, the IBW 78 tip manometer is suitable also for the pressure measurement in the upper urinary passages including the pyelon. The pressure signals obtained are further processed in a special plug-in unit for the biomonitor system, and thus they can be recorded on any multiple recorder.

Humans↗
PubMedDate not supplied

Total anomalous pulmonary venous connection to the portal vein.

Anomalous pulmonary venous return represents a rare congenital anomaly with wide anatomic and physiologic variability. We report a case of the newborn with a rare form of total infracardiac anomalous pulmonary venous connection (TAPVC). The pulmonary veins draining both lungs formed two vertical veins, which joined to a common pulmonary trunk below the diaphragm. This venous channel connected to the portal vein through the esophageal hiatus. The diagnosis was suggested by color Doppler sonography and confirmed by intravenous digital subtraction angiography, which allowed definition of the anatomy.

Angiography, Digital Subtraction↗