Apparatus for measuring strength in biaxial compression.

Most measurements of compressive strength of ductile materials have involved Hopkinson-Kolsky bars or Taylor anvils placing samples in uniaxial compression. In these geometries, strain is limited by the tendency of the sample to petal, in analogy to necking in uniaxial tension. Estimation of strength for any other form of the stress tensor requires assuming a shape of the yield surface; because data exist only for uniaxial compression, these assumptions are untested. In an imploding spherical shell, compression is biaxial, the plastic strain may not be small, and the material behavior may be nonlinear as a result of work hardening and heating by plastic work. We outline a method of measuring the strengths of materials in biaxial compression, both quasistatically and dynamically, using the compression of thin spherical shells. We suggest surrounding the shell with an annulus filled with a mixture of H2 and Cl2 gases whose homogeneous ignition is initiated by a flash of blue and near-ultraviolet light. Less promising approaches are described in Appendixes A-C.

Viscoelastic suppression of gravity-driven counterflow instability.

Attempts to achieve "top kill" of flowing oil wells by pumping dense drilling "muds," i.e., slurries of dense minerals, from above will fail if the Kelvin-Helmholtz instability in the gravity-driven counterflow produces turbulence that breaks up the denser fluid into small droplets. Here we estimate the droplet size to be submillimeter for fast flows and suggest the addition of a shear-thickening or viscoelastic polymer to suppress turbulence. We find in laboratory experiments a variety of new physical effects for a viscoelastic shear-thickening liquid in a gravity-driven counterstreaming flow. There is a progression from droplet formation to complete turbulence suppression at the relevant high velocities. Thick descending columns show a viscoelastic analogue of the viscous buckling instability. Thinner streams form structures resembling globules on a looping filament.

Pathology of the corneal endothelium.

Clinical specular microscopy has indicated that human cell healing occurs by spreading, there is a limited healing reserve, and premature cell loss is the equivalent of a "premature aging" that may lead to later decompensation. This instrument has been useful in studying healing and cell damage from surgery, drugs, and special procedures such as intraocular lens insertion. It pointed out extensive cell loss at the time of intraocular lens insertion, and subsequent studies have indicated that at least part of this cell loss may be due to the methacrylate surface of the lens. Laboratory studies suggest that coating that surface can prevent this component of cell loss. The magnitude of benefits to be found from such coating requires further clinical study.

Surgical management of necrotizing scleritis.

We successfully used autogenous periosteum to reinforce the weakened sclera of two patients with necrotizing scleritis. One of these patients previously had an onlay scleral graft made from homologous banked sclera, which had subsequently melted. Autogenous periosteum is suggested as an alternative to banked sclera for scleral reinforcement.

Herpes simplex retinitis and encephalitis in an adult.

A 17-year-old girl developed a viral encephalitis that was followed by massive exudative retinal detachments in both eyes. A diagnosis of herpes simplex encephalitis and retinitis was made as a result of finding rising herpes simplex viral titers. An examination of the patient's cell-mediated immune system showed it to be grossly intact.

Perforation of ileal conduit with pediatric gastroscope during endoscopy.

We report a case of perforation of ileal conduit during endoscopy, a rare complication of a procedure done infrequently in most institutions. We present one method of treatment.

Sclerocornea associated with the Smith-Lemli-Opitz syndrome.

A 2,000-g infant boy had many features of the Smith-Lemli-Opitz syndrome (prenatal growth deficiency and developmental retardation, microcephaly with unusual facies, hypospadias, and feeding difficulties) as well as sclerocornea. The association of this rare eye finding with this rare congenital syndrome is unique. Successful penetrating keratoplasty was performed in one eye at 8 months of age.

Mean-field model of layering instability in shearing suspensions.

Concentrated suspensions may shear thin when the suspended particles form planar sheets that slide over one another with less friction than if the particles are randomly distributed. In a naive model the suspension is described by a mean effective viscosity and particles that collide with each other redistribute the mean density in the shearing direction. This leads to a diffusion equation for the particle density. If the viscosity in the unthinned state is a steeply increasing function of particle density the effective diffusion coefficient is negative and the diffusion equation, meaningful only on scales larger than the particle separation, is ill posed. This singularity corresponds to the formation of planar sheets of particles and defines a critical particle density for the onset of shear thinning.

Effective-medium theory of elastic waves in random networks of rods.

We formulate an effective medium (mean field) theory of a material consisting of randomly distributed nodes connected by straight slender rods, hinged at the nodes. Defining wavelength-dependent effective elastic moduli, we calculate both the static moduli and the dispersion relations of ultrasonic longitudinal and transverse elastic waves. At finite wave vector k the waves are dispersive, with phase and group velocities decreasing with increasing wave vector. These results are directly applicable to networks with empty pore space. They also describe the solid matrix in two-component (Biot) theories of fluid-filled porous media. We suggest the possibility of low density materials with higher ratios of stiffness and strength to density than those of foams, aerogels, or trabecular bone.

Effect of intraocular lenses on the corneal endothelium.

Methacrylate surfaces adhere to corneal endothelial cell membranes and appear to tear off the cell membranes as they separate. This adhesion appears to cause much of the massive cell damage seen at the time of intraocular lens insertion even in the hands of several groups of very experienced implant surgeons. The damage appears correlated with the incidence of endothelial touch, and may be avoidable both by avoiding contact, even for a brief period, between the endothelium and the intraocular lens during insertion, and by increasing the safety of such lenses through a hydrophilic protective coating which would give a surface similar to human lens epithelium or soft contact lens material which does not damage the endothelium. It is possible that similar damage also plays a role in causing abdominal adhesions through contact with rubber gloves, as well as venous thromboses and urethral strictures.

Primary malignant melanoma of the female urethra.

We herein report a case of primary malignant melanoma of the female urethra, summarize the histopathology, review the available literature and discuss the treatment. Although a definitive regimen for the treatment of this virulent malignancy has not been established a 10-year-survival has been obtained by surgical extirpation preceded by preoperative radiotherapy.

Endothelial damage from intraocular lens insertion.

Previous studies have shown that approximately 40 per cent of the corneal endothelial cells can be lost at the time of intraocular lens insertion. Momentary contact between the methacrylate surface and the endothelial cells causes an adhesion between these surfaces and results in extensive cell damage upon separation of the surfaces. This type of damage appears to be due to a biophysical interaction between these surfaces and may be avoidable by altering the surface of the lens.

Slow-release artificial tears and the treatment of keratitis sicca.

The slow-release artificial tear (SRAT) is a biodegradable, cellulosic polymer without preservative which is inserted beneath the tarsus of the lower lid, and which provides continuous lubrication and tear film stability to the eye. The SR-AT has been shown to reduce both subjective symptoms and objective signs in patients with keratitis sicca, and is a valuable adjunct to therapy in patients with this disease.