Following adsorption kinetics at electrolyte/metal interfaces through crystal truncation scattering: sulfur on Au(111).

Combining electrochemical methods, in situ scanning tunneling microscopy, and surface x-ray diffraction allowed study of the structure and kinetics of S/Au(111) electrodes in aqueous electrolytes under potential control. Integrated intensities of a particular crystal truncation rod at anti-Bragg conditions were used to trace the sulfur adsorption and desorption as a function of electrode potential in real time. The S desorption is a first order process and the adsorption follows a Langmuir isotherm. A weakly bound S layer is found on the surface before charge transfer, and then specific adsorption occurs.

Relations between drawing cubes and copying line diagrams of cubes in 7- to 10-year-old children.

Previous research has suggested both links and differences between children's copying of line diagrams and their drawings of solid objects. If the diagram represents a familiar object, children make more errors than when copying a diagram of a nonobject or unfamiliar object, as if they are drawing from their representation of the object rather than copying the surface features of the diagram. However, copying a diagram yields fewer and different types of errors than drawing the equivalent solid, which suggests a different process. In Experiment 1 (n = 72), possible relations between copying and drawing are investigated by asking children to draw a solid cube, then to copy or trace a line diagram of the cube in oblique projection, and finally to draw the solid again. Copying was better than drawing, and there was positive transfer to a subsequent drawing. Tracing was very accurate, but transfer to drawing did not occur, possibly because of the automatic nature of tracing. In Experiment 2 (n = 120) different groups received versions of the copying task that differed in the extent to which temporal order of line copying was structured. Asking children to copy the lines in a systematic order led to improved copies, but this performance did not carry over to a subsequent drawing of the solid. In contrast, when temporal ordering of line copying was not manipulated, there was positive transfer from copying to the subsequent drawing. In Experiment 3 (n = 80), provision of structure that emphasized faces by color-groupings of lines or coloring faces led to improved copies and did not hinder transfer to drawing the solid. Experiment 4 (n = 90) showed that in a solid drawing task emphasis on faces but not edges produced a positive effect, both on the immediate drawing and on a subsequent drawing of a plain cube. We conclude that emphasis on order of line copying improves performance in a copying task because in that case line-to-line matching is an important element of the skill, whereas this does not aid drawing of the solid object, in which the focus is primarily on representation of faces and their interrelations.

A change in viewpoint promotes use of height-in-picture as a depth cue in 5- to 7-year-olds' drawings of a simple depth relationship.

Height-in-picture emerges between 6 and 7 years of age in children's drawings as the first indication of portrayal of depth relationships, but can be promoted earlier by the use of a number of experimental manipulations. The present studies investigate whether changing, and hence drawing attention to, the child's viewpoint promotes use of height-in-picture. In the first study, 5/6- and 6/7-year-old children were asked to draw two blocks, arranged in depth. Following this, the child-array relationship was altered, either by moving the child through 90 degrees or by rotating the array through 90 degrees. Children then drew again what was now a left-right arrangement, whereupon the transformation was reversed and they made a final drawing. Only when children moved to a new standpoint was there a significant increase in vertical portrayal between first and third drawings. It was not simply the movement of the child that prompted use of height-in-picture because there was no such effect in conditions in which the child was moved but made an unrelated drawing from the new position. These results indicate that making viewpoint salient by asking for a drawing from a new position prompts young children to portray a simple depth relationship.

Processes underlying young children's spatial orientation during movement.

Children between 1.5 and 4 years old were tested for their ability to relocate a hidden object after a 180 degrees self-produced movement around an array of four locations. In one task the object's location relative to the other locations could be uniquely defined within one dimension, while in another two dimensions were needed to do this. No differences emerged between conditions, and by 3 years few errors occurred, despite the fact that children were unable to view the array during movement. This indicates either that young children encounter no specific difficulty in coordinating dimensions or that they solved the task without recourse to such a system. An error analysis supports the second possibility. Children apparently tackled the task by a system directly related to body movement, since errors were frequently the result of incomplete compensation for movement around the array. In a second study in which the four containers were placed in contact, children's performance declined and the relation between direction of movement and error was replaced by some evidence for updating on the near-far dimension accompanied by failure to update the left-right dimension. Thus children appear to change strategy when the problem requires more precise specification of target location.

Protraction of the maxillofacial complex.

The purpose of this study was to evaluate the orthopedic effects of reverse headgear therapy in children with skeletal Class III malocclusions. Data based on pretreatment and posttreatment lateral cephalometric radiographs of seven boys and five girls, ages 4 through 14 years, were used. Comparison of the pretreatment and posttreatment cephalograms revealed a significant (p less than 0.05) increase in the SNA angle that indicated the maxilla was positioned farther forward after reverse headgear therapy. Both the maxillary and the mandibular effective lengths increased significantly from pretreatment to posttreatment, as did anterior and posterior total face height. These linear increases are most likely a reflection of growth rather than a direct result of the therapy. There was no significant change in the anteroposterior position of the mandible, although there was a tendency for the mandibular plane angle and the gonial angle to decrease. The results of this study indicate that maxillary protraction with a reverse headgear should be considered an alternative to orthognathic surgery in the treatment of children and adolescents with skeletal Class III malocclusion characterized by maxillary retrognathism.

Bond strength comparison: a simplified indirect technique versus direct placement of brackets.

Two methods for orthodontic bonding were used to attach brackets to 48 incisor and 48 premolar extracted human teeth. Half of the sample teeth were bonded by means of a highly filled bis-GMA adhesive by a direct placement method. The remaining teeth were bonded with the same adhesive by an indirect method suggested by Thomas. Actual chairside bonding procedures were simulated with regard to the timing and manipulation of adhesives and attachments. Tensile and shear bond strengths are reported for each of the two methods of bracket attachment.

Aligning, leveling, and torque control--a pilot study.

Aligning, leveling, and anterior torque control of teeth from the onset of treatment is suggested with thermal ni-ti rectangular low stiffness wires. Before and after superimpositions show the degree that torque control was achieved on four clinical patients.

Thermomechanical study of Ni-Ti alloys.

A preliminary study was conducted to demonstrate the usefulness of the combined technique of differential scanning calorimetry (DSC) and mechanical testing for the shape memory metals of 54NiTi and 53NiTiCo(3%) alloys. The DSC technique was used to measure precise transformation temperatures and the amount of thermal energy required for the corresponding phase transformation. The degree of plastic deformation by bending and the effect of alloying (such as Co) were studied with combined DSC and mechanical property measurements.

Bonding and debonding brackets to porcelain and gold.

Today's orthodontic practice includes a larger proportion of adults. Because many of these adults have crown and bridge restorations fabricated from porcelain or gold, the orthodontist must use methods that permit the attachment of orthodontic brackets to porcelain and nonprecious metal or gold. A bracket may be placed on single-unit crowns of porcelain or gold, but banding becomes difficult. Thus bonding the orthodontic bracket to the restoration provides a satisfactory alternative. This clinical report describes several techniques for bonding orthodontic brackets to porcelain or gold surfaces, and some suggestions for removal of bonded brackets.

Decidium. A novel fluorescent probe of the agonist/antagonist and noncompetitive inhibitor sites on the nicotinic acetylcholine receptor.

We have examined the interaction of the nicotinic acetylcholine receptor with decidium diiodide, a bisquaternary analogue of ethidium containing 10 methylene groups between the endocyclic and trimethylamino quaternary nitrogens. Decidium inhibits mono-[125I]iodo-alpha-toxin binding, inhibits agonist-elicited 22Na+ influx in intact cells, augments agonist competition with mono-[125I]iodo-alpha-toxin binding, and enhances [3H]phencyclidine (PCP) binding to a noncompetitive inhibitor site. These effects occur over similar concentration ranges (half-maximum effects between 0.1 and 0.4 microM). Thus, decidium binds to the agonist site and converts the receptor to a desensitized state exhibiting increased affinity for agonist and heterotropic inhibitors. These properties are similar to metaphilic antagonists characterized in classical pharmacology. At higher concentrations decidium associates directly with the noncompetitive inhibitor site identified by [3H]phencyclidine binding. Dissociation constants of decidium at this site in the resting and desensitized states are determined to be 29 and 1.2 microM, respectively. Analysis of fluorescence excitation and emission maxima reveal that binding to both the agonist and noncompetitive inhibitor sites is associated with approximately 2-fold enhancement of fluorescence. The excitation maximum for decidium bound at the agonist site appears at 490 nm while that for decidium bound at the noncompetitive inhibitor site appears at 530 compared to 480 nm in buffer. These results suggest that decidium experiences a more hydrophobic environment upon binding to the nicotinic acetylcholine receptor sites, particularly to the noncompetitive inhibitor site. Fluorescence energy transfer between N'-fluorescein isothiocyanate-lysine-23 alpha-toxin (FITC-toxin), and decidium is not detected when each is bound to one of the two agonist sites on the receptor. This allows a minimal distance to be estimated between fluorophores. In contrast, energy transfer is observed between decidium nonspecifically associated with the membrane or with nonspecific sites and the FITC-toxin at the agonist sites.

Stiffness changes in thermodynamic Nitinol with increasing temperature.

The purpose of this study was to measure and describe the physical properties of a recently-developed thermodynamic Nitinol alloy, type A-138, at intervals of temperature between room and body temperatures. The properties of stiffness, flexure yield strength and permanent deformation were measured, demonstrating that the working range of Nitinol A-138 is directly related to increases in temperature between 75 degrees F and 100 degrees F. As stiffness of the .017'' round A-138 Nitinol wire increases, the yield point decreases. In the loading cycle, yield points dropped from 36 degrees angular deflection at 75 degrees F to 25 degrees at 100 degrees F. In the unloading cycle, the yield point at 75 degrees F was 41 degrees of deflection, with force dropping to zero at 35 degrees; at 100 degrees F, yield point was only 12 degrees and force did not drop to zero until unloaded to 3 degrees angular deflection.