Ising model of polarity formation in molecular crystals: from the growth model to the asymptotic equilibrium state.

We analyze a layer-by-layer growth model of crystals consisting of dipolar molecules with two directional states. The model is characterized by the assumption of thermal equilibrium formation of new adlayers, whereas previous layers are treated as being "frozen" in the state in which they were formed. Longitudinal and transverse Ising-type nearest neighbor interactions are taken into account. Under such assumptions, bulk polarization is known to arise. We mainly consider asymptotic one- and two-layer statistics after many steps of growth; we have obtained a theorem relating this statistics to thermal equilibrium of an appropriate two-layer system. Local polarization patterns resembling those of ferromagnetism and antiferromagnetism emerge, depending on signs and magnitudes of the coupling constants. We have explored such effects by means of simulations, by a mean field approximation, and by a Bethe-Peierls analysis.

Temporal backward projection of optoacoustic pressure transients using fourier transform methods.

In medical imaging different techniques have been developed to gain information from inside a tissue. Optoacoustics is a method to generate tomography pictures of tissue using Q-switched laser pulses. Due to thermal and pressure confinement, a short light pulse generates a pressure distribution inside tissue, which mirrors absorbing structures and can be measured outside the tissue. Using a temporal back-projection method, the pressure distribution measured on the tissue surface allows us to gain a tomography picture of the absorbing structures inside tissue. This study presents a novel computational algorithm, which, at least in principle, yields an exact reconstruction of the absorbing structures in three-dimensional space inside the tissue. The reconstruction is based on 2D pressure distributions captured outside at different delay times. The algorithm is tested in a simulation and back-projection of pressure transients of a small absorber and a single point source.

Colloidal Particles at Solid-Liquid Interfaces: Mechanisms of Desorption Kinetics.

We study the sorption of colloids on equally charged surfaces. Our focus is on the time scale from hours to weeks, where adsorption is not an irreversible process but interplays with (spontaneous) desorption. Using model calculations, we show how the desorption kinetics is influenced by readsorption, a potential barrier, a secondary potential minimum, local variation of the potential, and bond aging. In the experimental part we present results of in situ observation of the sorption kinetics of polystyrene latex particles onto a glass surface. Combining the evanescent field method with video microscopy, we were able to identify the particle arrival and departure times individually and therefrom determine the adhesion time distribution function. The nonexponentiality of this function can be explained by a gamma distribution of the potential depth at the binding sites as well as by logarithmic bond aging. Copyright 1998 Academic Press.

Protrusive activity quantitatively determines the rate and direction of cell locomotion.

Locomoting blebbing cells have been used as a model to obtain novel insight into the mechanisms of cell locomotion. We tested the hypothesis that locomotion can be due to progressive one-sided protrusion of cellular volume into pseudopods. The hypothesis is supported by the finding that the rate and direction of locomotion of individual Walker carcinosarcoma cells can be predicted by sequential measurement of protrusive activity. Protrusive activity at the front is closely associated with forward movement of the rear part of the cell. During bleb formation the cell membrane of Walker carcinosarcoma cells is pushed forward faster (1.2-4.1 microns/sec) than known rates of actin elongation.

Computer-assisted evaluation of visual fields.

A computer program is described which provides statements in normal prose about the outcome of automated visual field examinations as well as hints concerning possible alternative interpretations and artifacts, if present. The program is intended as an aid to ophthalmologists being trained to evaluate critically visual fields. The limits of the applicability of this program are discussed.

The cumulative defect curve: separation of local and diffuse components of visual field damage.

We present a new display mode of the results of an Octopus visual field examination, which allows for an easy and reliable assessment of the local and diffuse components of the disturbances of a visual field. Essentially, this display consists of the cumulative distribution of the local defect values. Application to typical cases is discussed.

Plasmalactoferrin and the plasmalactoferrin/neutrophil ratio. A reassessment of normal values and of the clinical relevance.

In healthy subjects normal plasmalactoferrin (PLf) concentrations were found to be 0.206 +/- 0.06 mg/l in 49 men and 0.148 +/- 0.06 mg/l in 62 women. A highly significant correlation of PLf with the number of circulating neutrophils (PMN) and a PLf/PMN relationship suggesting proportionality was demonstrated. Among 73 patients absolute PLf concentrations were significantly increased in septicemia, cirrhosis of the liver and tumors with liver metastases, decreased in localized infection, tumors without liver involvement, iron deficiency and acute hepatitis B, and normal in acute myocardial infarction. The PLf/PMN ratio, on the other hand, was normal in liver cirrhosis, hepatitis B and in a part of the patients with septicemia and tumor disease with liver involvement. The ratio was increased in a part of the septicemic patients, and decreased in the remaining disease types. Positive PLf/PMN correlations were found in myocardial infarction, septicemia and liver cirrhosis, whereas a very close, negative correlation existed in acute hepatitis B. These findings are discussed on the basis of existing knowledge on lactoferrin physiology, the intravascular fate of PMN and the RES function.

Lens opacity meter: a new instrument to quantify lens opacity.

The lens opacity meter, a new instrument for quantifying the lens opacity, is described. The basic concept is the measurement of stray light produced by the lens. The measurement can be performed without dilating the pupil. A modulation of the light source renders the measurement insensitive to the surrounding light. The handling of the instrument is very simple. It is mounted on a slitlamp-like table. After adjusting the instrument to the eye, the measurement is initiated by depressing a console button.

The influence of mechanical forces and flow mechanisms on vessel occlusion.

The exact mechanism of irradiation-induced occlusion of normal or abnormal retinal vessels is still to a large extent obscure. Blood flow acts as a powerful heat dissipation mechanism. Therefore, a procedure which reduces flow velocity as rapidly as possible after the beginning of irradiation may work with higher efficiency. A theory based on a simplified assumption states that vessel narrowing techniques, which involve only a short length of the vessel to be occluded by a small focus diameter irradiation beam, are less efficient in bringing blood velocity down than a procedure which narrows the vessel over a greater length by a larger focus diameter irradiation beam. The thrombus building up over a greater length of the affected part of the vessel may also better resist the pressure head building up after thrombogenesis is complete because friction between thrombus and vessel wall is larger, and occlusion may, therefore, be more durable. One has to assess, therefore, whether a small-spot technique, which is presumed to be less efficient and may need repetitions, is in fact less innocuous for the surrounding retina--as is generally assumed--than a technique using a larger beam diameter, which, because it is more efficient, may need fewer or even no repetitions.

JO and STATJO: programs for investigating the visual field with the Octopus automatic perimeter.

In evaluating the effectiveness of glaucoma therapy the visual field is the most important consideration. Comparison of visual fields is difficult, however, and only large changes are detectable with the methods of manual perimetry currently used. Two programs created for use with the Octopus automatic perimeter are described in this paper. One of the programs, called JO, is sensitive to small changes in threshold; the other, called STATJO, calculates means and converts the results to a form suitable for statistical evaluation.

[A statistical program for determining fields of vision (author's transl)]. / Ein statistisches Programm zur Beurteilung von Gesichtsfeldern.

Statistical tests, oriented towards optimum distinction between normal and abnormal behavior, may be applied to the results of static perimetric examinations. Such tests are also important for establishing whether significant progression has occurred. A prototype version of an analytical program is presented here; it evaluates the data stored in the memory of the automated perimeter Octopus. Statistical decisions are printed out in verbal form. Reservations regarding conclusions are discussed. Correlated long-term fluctuations in thresholds complicate the separation of true progression from insignificant coincidence.

[The effects of a gigant-pulse-laser upon the iris of the pigmented rabbit eye (author's transl)]. / Die Wirkung eines Hochleistungslasers auf die Iris pigmentierter Kaninchenaugen.

The eyes of 10 pigmented rabbits were irradiated by a Q-switched Nd:YAG laser. The pulse energy delivered to the right eye was 187 mJ while the left eye was irradiated with 58 mJ. The pulse duration in both cases was 25 ns. The destructive effects were analysed for two different positions of the focus. In the upper half of the eye the focus was positioned at the anterior iris surface. In the lower half it was adjusted near the pigment epithelium. The eyes were analysed by electron microscopy at intervals of 15 minutes to 128 days after irradiation. The immediate effects were found to depend from the position of the focus but less from pulse energy. At later phases, tissue reaction depends from pulse energy. -- Scarification, at the lower energy level, is almost complete after 32 days. At the higher energy level, degenerative processi are setting in; 3 days after irradiation a progressing iris atrophy is observed which has not yet faded at the 128th day.

Morphological studies about the efficiency of laser beams upon the structures of the angle of the anterior chamber. Facts and concepts related to the treatment of the chronic simple glaucoma.

Working at a power density above optical breakdown threshold, irradiation effects upon the angle of the anterior chamber of the Macaca speciosa monkey by a Nd glass Q-switched laser, have been analysed with scanning electron microscopy. Two different damage effects can be identified: openings of Schlemm's canal and the creation of a cyclodialysis, that is opening the uveoscleral outflow routes; the latter may be a more effective one than the former. Also a third mechanism, namely a structural alteration of the trabecular meshwork, at the molecular level by laser action, has been inferred. The physical effects leading to optically induced mechanical damage are discussed. Applicability of such effects upon the morphological findings described here, is limited and to a greater part speculative. A better definition of the physical parameters, required for optimal therapeutical damage effects in the treatment of the wide angle glaucoma may be obtained by trial and error methods, which are guided by the results of electron microscopical analyses of samples obtained from in vivo and in vitro experiments.

On the effects of different laser energy sources upon the iris of the pigmented and the albino rabbit.

The irides of pigmented and albino rabbits have been irradiated by a) a CW argon laser beam (exposure duration up to 1 s), b) a 1 ms pulses Nd:YAG laser and c) a 30 ns pulses Q-switched ruby laser. The immediate and long-term pathologies were analysed by scanning and transmission electron microscopy over a period of 13 months. At both the gross and ultrastructural levels, damage configuration may differ considerably, depending on the three modes of irradiation. For each source there are both thermal and mechanical damage components and the significance of mechanical effects increases with decreasing pulse duration for a constant pulse energy. In the argon experiments, tissue destruction is predominantly a consequence of heat, resulting from conduction and convection. The subsequent regeneration of tissue after such heat-induced trauma is fast. The effects of the Nd:YAG laser, at the irradiance levels used in the present study, are again predominantly of a thermal nature and are caused by heating and local evaporation. The pigmented and the nonpigmented iris epithelium are destroyed and widespread decay of the stroma occurs over some months. Such damage never results in full repair. The most prominent feature of Q-switched ruby laser irradiations is their independence of the iris pigment content. In contrast, at the energy levels studied, the argon laser is entirely ineffective, whilst the effect of the Nd:YAG laser is much reduced in the absence of pigment. The consequences of these findings for the clinical applications of such lasers are discussed.

[Practical experiences with the Octopus automatic perimeter (author's transl)]. / Praktische Erfahrungen mit dem automatischen Perimeter Octopus.

A statistical analysis comparing the results of more than 1000 visual field examinations carried out with the automatic perimeter Octopus and with a conventional Goldman-perimeter, clearly demonstrates the superiority of the automatic instrument in many respects: Apart from a higher precision of the perimetric measurements (smaller fluctuations), a better reproducibility of the results (larger correlation coefficients) is noticed. Due to great ease of operation of the automatic perimeter, the ophthalmologist is discharged from the time-consuming task of perimetric examinations.