Forced versus Spontaneous Spreading of Liquids.

Two sets of experiments are performed, one for the free spreading of a liquid drop on a glass substrate and the other for the forced motion of a glass plate through a gas-liquid interface. The measured macroscopic advancing contact angle, θA, versus the contact line speed, U, differ markedly between the two configurations. The hydrodynamic theory (HDT) and the molecular kinetic theory (MKT) are shown to apply separately to the two systems. This distinction has not been previously noted. Rules of thumb are given that for an experimentalist involve a priori knowledge of the expected behavior.

Elastic membranes in confinement.

An elastic membrane stretched between two walls takes a shape defined by its length and the volume of fluid it encloses. Many biological structures, such as cells, mitochondria and coiled DNA, have fine internal structure in which a membrane (or elastic member) is geometrically 'confined' by another object. Here, the two-dimensional shape of an elastic membrane in a 'confining' box is studied by introducing a repulsive confinement pressure that prevents the membrane from intersecting the wall. The stage is set by contrasting confined and unconfined solutions. Continuation methods are then used to compute response diagrams, from which we identify the particular membrane mechanics that generate mitochondria-like shapes. Large confinement pressures yield complex response diagrams with secondary bifurcations and multiple turning points where modal identities may change. Regions in parameter space where such behaviour occurs are then mapped.

The effect of glass-forming sugars on vesicle morphology and water distribution during drying.

Cryopreservation requires that stored materials be kept at extremely low temperatures and uses cryoprotectants that are toxic to cells at high concentrations. Lyopreservation is a potential alternative where stored materials can remain at room temperatures. That storage process involves desiccating cells filled with special glass-forming sugars. However, current desiccation techniques fail to produce viable cells, and researchers suspect that incomplete vitrification of the cells is to blame. To explore this hypothesis, a cell is modelled as a lipid vesicle to monitor the water content and membrane deformation during desiccation. The vesicle is represented as a moving, bending-resistant, inextensible interface and is tracked by a level set method. The vesicle is placed in a fluid containing a spatially varying sugar concentration field. The glass-forming nature is modelled through a concentration-dependent diffusivity and viscosity. It is found that there are optimal regimes for the values of the osmotic flow parameter and of the concentration dependence of the diffusivity to limit water trapping in the vesicle. Furthermore, it is found that the concentration dependencies of the diffusivity and viscosity can have profound effects on membrane deformations, which may have significant implications for vesicle damage during the desiccation process.

Hydrodynamic theory of liquid slippage on a solid substrate near a moving contact line.

In this Letter a hydrodynamic theory of liquid slippage on a solid substrate near a moving contact line is proposed. A family of spatially varying slip lengths in the Navier slip law recovers the results of past formulations for slip in continuum theories and molecular dynamics simulations and is consistent with well-established experimental observations of complete wetting. This formulation gives a general approach for continuum hydrodynamic theories. New fluid flow behaviors are also predicted yet to be seen in experiment.

Self-organization of quantum dots in epitaxially strained solid films.

A nonlinear evolution equation for surface-diffusion-driven Asaro-Tiller-Grinfeld instability of an epitaxially strained thin solid film on a solid substrate is derived in the case where the film wets the substrate. It is found that the presence of a weak wetting interaction between the film and the substrate can substantially retard the instability and modify its spectrum in such a way that the formation of spatially regular arrays of islands or pits on the film surface becomes possible. It is shown that the self-organization dynamics is significantly affected by the presence of the Goldstone mode associated with the conservation of mass.

Faceting of a growing crystal surface by surface diffusion.

Consider faceting of a crystal surface caused by strongly anisotropic surface tension, driven by surface diffusion and accompanied by deposition (etching) due to fluxes normal to the surface. Nonlinear evolution equations describing the faceting of 1+1 and 2+1 crystal surfaces are studied analytically, by means of matched asymptotic expansions for small growth rates, and numerically otherwise. Stationary shapes and dynamics of faceted pyramidal structures are found as functions of the growth rate. In the 1+1 case it is shown that a solitary hill as well as periodic hill-and-valley solutions are unique, while solutions in the form of a solitary valley form a one-parameter family. It is found that with the increase of the growth rate, the faceting dynamics exhibits transitions from the power-law coarsening to the formation of pyramidal structures with a fixed average size and finally to spatiotemporally chaotic surfaces resembling the kinetic roughening.

Artificially low hemoglobin A1c caused by use of dapsone.

OBJECTIVE: To describe a case of artifactually decreased hemoglobin Alc (HbAlc) attributable to use of dapsone. METHODS: We present a detailed case report and results of a related literature search. In addition, potential causes of artifactually lowered HbAlc values are discussed. RESULTS: A 35-year-old patient with type I diabetes had high home-monitored blood glucose values, high clinic plasma glucose determinations, increased fructosamine levels, and low HbAlc values. The lowering of the HbAlc level was associated with use of dapsone, and the decrease in HbAlc value was proportional to the dose of dapsone. A literature search revealed one previous report of artifactual lowering of the HbAlc value, in which high methemoglobin levels were found and thought to be the cause of the artifactually decreased HbA1c. CONCLUSION: By increasing methemoglobin levels and decreasing erythrocyte survival, dapsone can artifactually lower HbA1c. Clinicians should be aware of this potential side effect of dapsone.

Convective Cahn-Hilliard models: from coarsening to roughening.

In this paper we demonstrate that convective Cahn-Hilliard models, describing phase separation of driven systems (e.g., faceting of growing thermodynamically unstable crystal surfaces), exhibit, with the increase of the driving force, a transition from the usual coarsening regime to a chaotic behavior without coarsening via a pattern-forming state characterized by the formation of various stationary and traveling periodic structures as well as structures with localized oscillations. Relation of this phenomenon to a kinetic roughening of thermodynamically unstable surfaces is discussed.

Lipoid pneumonia: a silent complication of mineral oil aspiration.

INTRODUCTION: Chronic constipation is a common symptom in pediatrics, and physicians often use mineral oil to treat chronic constipation in children. Mineral oil, a hydrocarbon, may not elicit a normal protective cough reflex and may impair mucociliary transport. These effects can increase the likelihood of its aspiration and subsequent impaired clearance from the respiratory tract. We report a case of a child with neurodevelopmental delay with chronic constipation and a history of chronic mineral oil ingestion presenting as asymptomatic exogenous lipoid pneumonia (ELP). CASE HISTORY: A 6-year-old white boy with a history of developmental delay was found to have an infiltrate in his right upper lobe on a chest radiograph obtained during evaluation for thoracic scoliosis. The patient had a long history of constipation with daily use of mineral oil. He was fed by mouth and had occasional episodes of coughing and choking during feeding. He was asymptomatic at presentation and physical examination was unremarkable. The patient was advised to stop administration of the mineral oil and was treated empirically with antibiotics during a 3-month period. At follow-up examination the patient continued to be asymptomatic, with the radiologic persistence of the infiltrate. Diagnosis of lipoid pneumonia was made by diagnostic bronchoscopy with bronchoalveolar lavage (BAL). The exogenous origin of the lipid in the BAL fluid was confirmed by gas chromatography/mass spectrometry. DISCUSSION: The clinical presentation of ELP is nonspecific and ranges from the totally asymptomatic patient with incidental radiologic finding, like our patient, to the patient with acute or chronic symptoms attributable to pneumonia, pulmonary fibrosis, or cor pulmonale. Bronchoscopy with BAL can be successful in establishing the diagnosis of ELP by demonstration of a high lipid-laden macrophage index. Treatment of ELP in children is generally supportive, with the symptoms and roentgenographic abnormalities resolving within months after stopping the use of mineral oil. CONCLUSION: Lipoid pneumonia as a result of mineral oil aspiration still occurs in the pediatric population. It can mimic other diseases because of its nonspecific clinical presentation and radiographic signs. In patients with swallowing dysfunction and pneumonia, a history of mineral oil use should be obtained and a diagnosis of ELP should be considered in the differential diagnoses if mineral oil use has occurred. Our case points to the need for increased awareness by the general pediatricians of the potential hazards of mineral oil use for chronic constipation.

Steps, kinetic anisotropy, and long-wavelength instabilities in directional solidification.

We consider the effect of anisotropic interface kinetics on long-wavelength instabilities during the directional solidification of a binary alloy having a vicinal interface. Linear theory predicts that a planar solidification front is stabilized under the effect of anisotropy as long as the segregation coefficient is small enough, whereas a novel instability appears at high rates of solidification. Furthermore, the neutral stability curve, indicating the values of the principal control parameter (here the morphological number) for which the growth rate of a sinusoidal perturbation of a given wavelength changes its sign, is shown to have up to three branches, two of them combining to form an isola for certain values of the control parameters. We identify conditions for which linear stability theory predicts the instability of the planar interface to long-wavelength traveling waves. A number of distinguished limits provide evolution equations that describe the resulting dynamical behavior of the crystal-melt interface and generalize previous work by Sivashinsky, Brattkus, and Davis and Riley and Davis. Bifurcation analysis and numerical computations for the derived evolution equations show that the anisotropy is able to promote the tendency to supercritical bifurcation, and also leads to the development of strongly preferred interface orientations for finite-amplitude deformations.

New therapies for cystic fibrosis.

In the decade since the gene responsible for cystic fibrosis (CF) was identified, our understanding of the pathophysiology of CF pulmonary disease has significantly improved. The current model for CF lung disease suggests several levels at which clinical interventions may be made in an attempt to alter the natural course of disease progression. The first part of this review highlights some of the progress made in novel forms of therapy directed at earlier portions of the pathophysiologic cascade such as gene therapy, protein therapy, and ion-transport regulatory therapy. New developments in well-established modes of therapy such as mucolytic therapy, airway clearance therapy, and antibiotic therapy are discussed next. The review concludes with a look at the use of two forms of therapy that have been adapted to CF care, anti-inflammatory therapy and lung transplantation.

Spontaneous subcutaneous emphysema.

Subcutaneous emphysema is an unusual complication of bronchiolitis. The investigators describe a patient with bronchiolitis who developed extensive subcutaneous emphysema. Despite an alarming appearance, the patient recovered with symptomatic care and observation. Review of the literature shows a multitude of causes of subcutaneous emphysema. The vast majority of cases resolve without intervention.

Intraarterial administration of lidocaine for analgesia in hepatic chemoembolization.

Hepatic chemoembolization (HCE) routinely results in severe pain requiring massive doses of intravenously administered narcotics. This study examines the efficacy and safety of lidocaine administered intraarterially for analgesia in HCE. In 45 HCE procedures, lidocaine was injected into hepatic arterial branches just prior to and during chemoembolization. Adjunctive analgesic doses given during the procedure and the need for a morphine sulfate drip infusion for postprocedural pain control were recorded and compared with those in 20 procedures performed previously without lidocaine. In procedures with lidocaine, an average of 0.13 mg of morphine sulfate and 1.3 mg of midazolam were required. This is significantly lower than the 11.7 mg of morphine sulfate and 3.7 mg of midazolam used during procedures without lidocaine. A postprocedural morphine drip infusion was required for control of severe pain in 16 of 20 (80%) procedures performed without lidocaine compared with nine of 45 (20%) of those performed with lidocaine. Peripheral blood levels of lidocaine were well below the toxic level, and no complications referable to lidocaine toxicity occurred. Marked reductions in the amount of narcotic analgesia in HCE procedures may be safely achieved with the administration of intraarterial lidocaine.

Use of an elastomeric material to improve the occlusal seat and marginal seal of cast restorations.

A method to improve the fit of castings by the use of a light-bodied condensation silicone impression material was tested. Eighteen-full coverage castings were made on individual resin dies and divided into two groups. The experimental group was adjusted internally to a uniform precementation space by using the silicone impression material as a disclosing agent for binding of the castings on the axial or occlusal walls. Measurements of marginal fit were made with a light microscope using a filar eyepiece both externally and internally by sectioning after cementation with a zinc phosphate cement. Results demonstrated a significant improvement in marginal seal and occlusal seating in the experimental group compared with the control group. The condensation silicone material proved to be an appropriate research tool for nondestructive, three-dimensional evaluation of the postcementation space and offers a new method of evaluation of cement thickness because seating was found to be not significantly different from that with zinc phosphate cement.

Nondestructive, three-dimensional internal fit mapping of fixed prostheses.

Crown fit may be three-dimensionally mapped by using a nondestructive optical technique. Reflected light transmission through thicknesses of a colored impression material was shown to follow the Beer-Lambert relationship over a range of approximately 10 to 300 microns, a useful range of interest for study of cement layer thickness. Control thicknesses of impression material were first formed between the measuring platens of a micrometer, and light transmission values (relative reflections) were measured through these control thicknesses of impression material held against air-abraded, noncast gold alloy. Relative reflection values were similarly measured from impression material formed inside cast gold crowns seated on their respective dies and these values were plotted against direct thickness measurements by using the Beer-Lambert relationship. It was established that the micrometer-produced control specimens yielded a valid standard curve for use with the cast gold crowns. Precementation space measurements determined photometrically were found to correlate significantly (r = 0.72, p less than 0.001) with zinc phosphate cement thickness measured on subsequently cemented and cross-sectioned crowns. A three-dimensional representation of the precementation space inside one crown was developed after mapping of 45 points in less than 5 minutes.

Haziness of the right hemithorax in a newborn.

We describe a neonate with an accessory diaphragm, a rare congenital anomaly. It almost always occurs in the right hemithorax, which appears diffusely hazy on the anterior chest roentgenogram. The lateral chest roentgenogram is essential in the diagnosis of this condition.