Observation of unintentionally incorporated nitrogen-related complexes in ZnO and GaN nanowires.

We report the observation of unintentionally incorporated nitrogen-related complexes in ZnO and GaN nanowires grown by the catalytic vapor-phase transport method. In particular, our experimental findings from Raman scattering spectroscopy and mass-selected time-of-flight particle emission measurements suggest the presence of interstitial nitrogen molecules that are formed during the nanowire growth. These results may be relevant for many nanowire systems, emphasizing the necessity of more studies on unintentional impurity incorporations in these nanomaterials.

Photoinduced formation of zinc nanoparticles by UV laser irradiation of ZnO.

Simple exposure of single-crystal ZnO to 193 nm excimer laser radiation at room temperature results in unexpected coloration. The gray to nearly black colored material, seen principally in the irradiated laser spot, is superficial. We present unambiguous evidence that this coloration is due to high densities of metallic Zn nanoparticles growing on the exposed surface of the crystal. Higher fluence laser exposure generates accumulated surface metal just outside of the irradiated spot. We suggest that the near surface bulk is photodecomposing; thermally driven diffusion leads to surface Zn metal aggregation.

Motion and dissolution of drops of sparingly soluble alcohols on water.

The dissolution of liquids with low mutual solubility is typically slow. However, drops of sparingly soluble, low-density, low-surface-tension liquids often dissolve rapidly on water due to surface tension instabilities and gradients. We report observations of the motion and dissolution of drops of aliphatic alcohols of a wide range of alkyl chain lengths as they dissolve in water. The alcohol drops are rendered visible by adding small amounts of iodine or other dyes. These drops display dewetting instabilities, fragmentation, fingering, and oscillation. As the length of the alcohol carbon chain increases from n = 4 to n = 9, dissolution slows dramatically. The roles of alcohol solubility and water surface area in promoting rapid dissolution are discussed.

Dropwise condensation: experiments and simulations of nucleation and growth of water drops in a cooling system.

Dropwise condensation of water vapor from a naturally cooling, hot water reservoir onto a hydrophobic polymer film and a silanized glass slide was studied by direct observation and simulations. The observed drop growth kinetics suggests that smallest drops grow principally by the diffusion of water adsorbed on the substrate to the drop perimeter, while drops larger than about 50 microm in diameter grow principally by direct deposition from the vapor onto the drop surface. Drop coalescence plays a critical role in determining the drop-size distribution and stimulates the nucleation of new, small drops on the substrates. Simulations of drop growth incorporating these growth mechanisms provide a good description of the observed drop-size distribution. Because of the large role played by coalescence, details of individual drop growth make little difference to the final drop-size distribution. The rate of condensation per unit substrate area is especially high for the smallest drops and may help account for the high heat transfer rates associated with dropwise condensation relative to filmwise condensation in heat exchange applications.

Scanning-induced growth on single crystal calcite with an atomic force microscope.

We report observations of localized growth on the (1014) surface of single-crystal CaCO3 in supersaturated solutions while scanning with the tip of an atomic force microscope (AFM). At low contact forces, AFM scanning strongly enhances deposition along preexisting steps. This enhancement increases rapidly with increasing solution supersaturation, and is capable of filling in multilayer etch pits to produce defect-free surfaces at the resolution of the AFM. Attempts to achieve similar deposition rates in the absence of scanning require high supersaturations that produce three-dimensional crystal nuclei, which are important defects. Localized deposition produced by drawing the AFM tip back and forth across step edges can produce monolayer deposits extending well over a micron from the scanned area. These tip-induced deposits provide convincing evidence for the importance of ledge diffusion in calcite crystal growth.

Influence of molecular weight on nanoscale modification of poly(methyl methacrylate) due to simultaneous mechanical and chemical stimulation.

We report observations of poly(methyl methacrylate) films modified by the synergistic effect of solvent exposure and mechanical stress applied by the tip of an atomic force microscope (AFM). We show that these modifications are sensitive to polymer molecular weight as well as solvent strength and the force applied by the tip. Small-area scanning often produces localized patches of raised material as well as depressed areas. The volume change associated with the depressed areas generally increases with increasing solvent strength, increasing applied normal force, and decreasing polymer molecular weight. In contrast, the volume change associated with the raised patches is greatest for 25-145K Mw films in 60 and 100% ethanol solutions. In each case, the normal force applied by the AFM tip must exceed a threshold to significantly modify the surface; this threshold is associated with an increase in lateral force applied by the AFM tip during small-area scanning. We attribute the raised patches to mechanically enhanced swelling due to diffusion of solvent into near-surface material. Permanent net volume loss, when observed, is attributed to localized polymer dissolution.

The emission of atoms and molecules accompanying fracture of single-crystal MgO.

We have been investigating the emission of particles due to deformation and fracture of materials. We observe the emission of electrons (exoelectron emission), ions, neutral species, photons (triboluminescence), as well as long wavelength electromagnetic radiation; collectively we refer to these emissions as fractoemission. In this paper we describe measurements of the neutral emission accompanying the fracture of single-crystal MgO. Masses detected are tentatively assigned to the emission of H2, CH4, H2O, CO, O2, CO2, and atomic Mg. Other hydrocarbons are also observed. The time dependencies of some of these emissions relative to fracture are presented for two different loading conditions.

"Practical suggestions on facial plastic surgery--how i do it". Z-plasty repositioning of an anatomical unit.

The Z-Plasty was originally described in the writings of Hippocrates and since that time has developed into one of the most useful techniques in facial plastic surgery. Familiarity with its myriad of uses is invaluable to the practicing otolaryngologist. The basic technique of Z-Plasty consists in the design and transposition of adjacent triangular soft tissue flaps. Most common applications capitalize on the changes which occur during transposition to the common limb between the flaps. The resultant lengthening is used to provide needed tissue in areas of contracted scars and the change in direction is useful in camouflage of scars which cross skin tension lines. Additionally, displaced anatomical units such as the auricle, angle of the mouth or eyelid can be included in the flaps of the Z-Plasty to transpose them into a new anatomical position. Many congenital and acquired deformities can be corrected by this technique without loss of valuable tissue. The purpose of this paper is to illustrate the above principle utilizing two patients with congenitally displaced auricles.

Presternal bronchogenic cysts.

A presternal subcutaneous cyst was removed from a 21-month-old male infant. This is a rare congenital lesion that typically appears as a pinpoint opening over the sternum that periodically drains small amounts of mucinous material. Histologically, these lesions have the features of their intrathoracic and mediastinal counterparts. Surgical excision is advocated because of the potential for infection.

Soft tissue trauma.

Prior to surgical repair of maxillofacial injuries, a surgeon should formulate an operative plan based upon a careful and complete pre-operative analysis. Obviously this may effect the timing of repair. However, it is more efficacious to delay surgery for up to 24 hours than to close lacerations over a lacerated facial nerve, a severed parotid duct, or other undiagnosed lesions. Repair should include meticulous cleansing and removal of all embedded foreign material if hypertrophy, scars, or tattooing is to be avoided; repair of underlying soft tissue damage, including mucosa, muscle, nerve, cartilage, and subcutaneous tissue; and meticulous closure of the lacerations in accordance with their anatomical location. In wounds involving tissue loss the judicious application of skin grafts, as well as local or regional flaps, is of infinite value. With the careful adherence to the basic principles of plastic reconstructive surgery, the majority of patients with maxillofacial injuries should obtain a good functional and esthetic restoration. In patients in whom this cannot be accomplished because of extensive tissue damage, the primary repair should enhance the feasibility and results of secondary reconstruction.

Medial conchal excision in otoplasty.

The most common cartilaginous deformities in protruding ears include an inadequate antihelical fold and an enlarged concha. We have employed medial conchal excision to correct deep conchas in 25 patients, all of whom were pleased with the postoperative result. Obvious wrinkling of the anterior skin occurred in four patients, and several patients displayed slight distortion of the helical crus. Medial conchal excision does not impede management of the antihelical fold with mattress sutures or by other means. We consider the risk of minor alterations of the concha justified if even slight distortion of the more conspicuous lateral auricle can be avoided.