Collective diffusion in two-dimensional systems: exact analysis based on the kinetic lattice gas model.

Using a gradient expansion of the local microscopic particle current, in the long-time and large-scale limit, we derive an exact analytical expression for the density and temperature dependence of the diffusivity in terms of the density dependence of correlation functions on a rectangular lattice. The latter are calculated by transfer matrix methods, generalized to an adsorbate with lateral interactions and subjected to an external field. This allows an examination of the effects of generalized hopping kinetics. Where both initial and final state interactions are involved, the Reed-Ehrlich factorization, commonly assumed, cannot apply.

Photo- and thermodesorption of helium on Pt(111).

In a detailed study of thermal desorption of monolayers of both 4He and 3He adsorbed on Pt(111) (binding energy about 9 meV), we have observed photodesorption induced by the blackbody radiation from a room temperature environment. This process proceeds independently of the thermal desorption. Theoretical treatments of both thermal and photodesorption are given and agree very well with the data in all important aspects. We conclude that the photodesorption is due to direct coupling of photons to the adsorbate.

Vascular anatomy of the brachioradialis rotational musculocutaneous flap.

The purpose of this 2-part vascular injection study was to (1) determine the sources of blood supply to the brachioradialis muscle and the distance around which the brachioradialis muscle flap may be rotated for local soft tissue reconstruction and (2) determine the fasciocutaneous vascular perfusion territory associated with the vascular pedicle of the brachioradialis muscle flap. Lead oxide injections were administered in 16 fresh frozen human upper extremity amputation specimens to determine the contribution of the isolated radial recurrent artery (RRA) and subsequent 3- and 6-cm segments of radial artery (RA) to a rotational brachioradialis muscle flap. The RRA perfused an average of 41% (range, 20% to 60%) of the brachioradialis muscle length. Selective injection of the RRA and the proximal 3-cm segment of the RA perfused 80% (range, 59% to 100%) of the muscle length, corresponding to more than 90% of muscle volume. Flap rotation consistently provided adequate tissue coverage to the antecubital fossa, the lateral elbow, and the proximal one-third volar forearm. Based on these findings, the fasciocutaneous perfusion territory of the isolated vascular pedicle was quantified by selective India ink injection studies in 10 fresh frozen cadaveric specimens. Consistent fasciocutaneous perfusion occurred directly over the muscle belly. No specimen, however, was perfused greater than approximately 1 cm distal to the musculocutaneous junction. This 2-part study defines the vascular anatomy and local utility of the brachioradialis rotational musculocutaneous flap.

Stretching a macromolecule in an atomic force microscope: statistical mechanical analysis.

We formulate the proper statistical mechanics to describe the stretching of a macromolecule under a force provided by the cantilever of an Atomic Force Microscope. In the limit of a soft cantilever, the generalized ensemble of the coupled molecule-cantilever system reduces to the Gibbs ensemble for an isolated molecule subject to a constant force in which the extension is fluctuating. For a stiff cantilever, one obtains the Helmholtz ensemble for an isolated molecule held at a fixed extension with the force fluctuating. Numerical examples and predictions for experiments with cantilevers of differing stiffness are given for short and long chains of poly (ethylene glycol), based on parameter-free ab initio calculations.

Stretching a macromolecule in an atomic force microscope: statistical mechanical analysis.

We formulate the proper statistical mechanics to describe the stretching of a macromolecule under a force provided by the cantilever of an atomic force microscope. In the limit of a soft cantilever the generalized ensemble of the coupled molecule/cantilever system reduces to the Gibbs ensemble for an isolated molecule subject to a constant force in which the extension is fluctuating. For a stiff cantilever we obtain the Helmholtz ensemble for an isolated molecule held at a fixed extension with the force fluctuating. Numerical examples are given for poly (ethylene glycol) chains.

Nerve repair and grafting in the upper extremity.

Knowledge of peripheral nerve anatomy, coupled with available clinical tools for examination, provides the foundation for initial evaluation. Use of this information may be related to the specific injury and a reconstructive plan formulated to maximize the potential for recovery. Realistic expectations can be presented to the patient based on information from summarized clinical experience. The field of nerve repair continues to change rapidly, and clinicians must utilize all resources available for planning, evaluation, and management. As the cellular behaviors of nerve regeneration are delineated, new avenues of research will open.

Neurotization of the rat soleus muscle: a quantitative analysis of reinnervation.

Neurotization--reinnervation of muscle by direct nerve implantation--has been the subject of several reports. The underlying neurobiology, however, has not been adequately studied. The use of a combined silver-acetylcholinesterase stain was used in this study to identify reinnervated motor endplates and to quantify motor endplates reinnervated by the neurotization process. This study examined the effect of distance between nerve implantation and native motor endplate zone on the formation of ectopic motor endplates and on the total number of motor endplates reinnervated. Experiments were performed on the rat soleus muscle. The transected tibial nerve was implanted directly into the motor endplate zone (near, n = 10) or distally, far from the motor endplate zone (far, n = 10). After a reinnervation interval, frozen sections were processed to demonstrate both axons and motor endplates. In the near group, a mean of 566 motor endplates were reinnervated in the native motor endplate zone and a mean of only 13 in distant locations. In the far group, a mean of 362 motor endplates were reinnervated in the native zone, while a mean of 477 were reinnervated in distant locations. Significantly more ectopic motor endplates were generated by far implantation, and native motor endplates were increased by near implantation. The total number of motor endplates was independent of implant location. These experiments demonstrate that the distance between implanted nerve and the native motor endplate zone influences the morphology of reinnervation.

Precise thickness and refractive index determination of polyimide films using attenuated total reflection.

Surface plasmons generated at a silver-polyimide interface and the guided modes coupled into planar films cause dips in the reflectivity curve of a transparent dielectric-silver-polyimide-air structure. These minima in the reflectivity curve were used to measure the polyimide thickness as well as the real and imaginary parts of the polymer refractive index (extinction). Precision within 1% of the polymer coat thickness was achieved through the use of this technique over the range 0.5-10 µm. In some cases, this technique is capable of yielding a precision of ~ 10% on the imaginary part of the polymer refractive index and provides a useful method for determining the performance of a low-loss polymer waveguide. Techniques in fitting the experimental reflectivity data to obtain the optical constants are also described.

The trial denture.

1. Many difficult situations can be avoided if the dentist keeps constantly aware of the physiologic, the psychologic, and the artistic factors involved in the construction of dentures, whether they be partial or complete. 2. No one would think of buying an automobile without getting adequate instruction in how to drive; neither should a patient expect to wear artifical restorations without training and practice. 3. The dentist at the try-in should check: a. The bases for fit and extension. b. Thin labial flange at frenum area. c. Posterior palatal seal and length of upper. d. Posterior tooth poisition for height of plane, relation of plane to alatragus line, tongue room, and ridge relation. e. Anterior tooth position for lip support, length, and relation to lower lip. f. Entire setup for vertical dimension of the face, test balance and simultaneous tooth contacts in all desired positions. If discrepancies exist between the articulator and the mouth, make new jaw relation records. g. Check palatal contour and incisor positions in speaking. "F" and "V" sounds to test the upper incisor, sibilant sounds for vertical dimension and lower-to-upper incisal relationships. h. Wax-up for support and proper external form. If tori exist on upper or lower, be sure there is sufficient thickness to allow relief later on. i. Be sure to repeat and continue instruction of the patient in his understanding and handling of the new dentures. Now, in addition to all these checks to dentist makes, he must constantly anticipate the thoughts and attitudes of the patient and interpret them for better rapport and ultimate patient understanding. No stage in complete dentures is anticipated with such mixed emotions as is the try-in. No stage is so significant to the future success or failure of the patient to take dentures in his stride. No stage has so much potential for making the person happy or sinking him into the depths of despair. The return of self-confidence, the pride in appearance, the sparkle and drive that return to a patient when the restorations are enthusiastically accepted are a wonderful reward for dentistry well done.

Adjustment of the lateral condylar guidances of Dentatus AR series of articulators.

A method of accurately adjusting the lateral condylar guidances of the Dentatus AR series of articulators is described which, hopefully, will serve to reinforce and improve the instructions provided by the manufacturer of this excellent instrument.