Coherent range-gated laser displacement metrology with compact optical head.

We describe a new architecture for laser displacement metrology with a drastic reduction in the size and complexity of the optical head. Connected by a single optical fiber, the compact heads are easy to integrate and readily multiplexed to support applications requiring large numbers of sensors. The approach is made possible by modulating the outgoing laser light with a binary random noise code, allowing the detected signals to be discriminated based on their propagation delay. We demonstrate a displacement resolution of 1.1 nm rms.

Widow and widower remarriage: an analysis in a rural 19th century Costa Rican population and a cross-cultural discussion.

Although the topic of remarriage features saliently in the cultural anthropological literature, it is virtually absent in the biological anthropology journals. This is perplexing, given that remarriage affects the differential reproductive success of males and females in a community, and could well impact a community's population structure. In this paper, we research remarriage practices in a rural 19th century community in Costa Rica. Although we find support for the proposition that males are more likely to remarry than females, we find that widows who remarry are not all young and able to reproduce. Our findings support the cross-culturally-generated suggestion that a female's ability not to remarry is tied to her to ability to own property. Remarriage is a topic of interest to biological anthropologists from a cross-cultural and biocultural perspective.

Ethnicity, gene flow, and population subdivision in Limón, Costa Rica.

In this paper we examine the effects of ethnicity on the gene flow between two groups living in Limón, Costa Rica. Our main interest is to determine if ethnicity has acted as a barrier to the exchange of genes, and if the groups have remained distinct genetically. We report the admixture estimates, F(st) values, and inbreeding coefficients of the two samples. The data consist of blood samples and surnames obtained from 375 individuals. The subjects' two surnames were analyzed to determine the ethnicity of their parents (individuals carry their father's and mother's first surnames). We used the formula of Crow and Mange ([1965] Eugen Q 12:199-203) to compute F(t), F(n), and F(r) with the surnames. Admixture estimates were computed for both groups using the computer program ADMIX.PAS kindly provided by Jeffrey Long. The estimates for the Hispanic-Limonense group are M1 = 0.5866 European, M2 = 0.3383 Amerindian, and M3 = 0.0751 African ancestry. For the Afro-Limonense group, the admixture estimates indicate M1 = 0.1047 European, M2 = 0.1357 Amerindian, and M3 = 0.7595 African ancestry. The F(st) values are F(st) = 0.00558 for the Hispanic group and F(st) = 0.05137 for the Afro-Limonense group. These F(st) values indicate that the Afro-Limonense group has experienced more genetic drift than has the other group, possibly as a result of its long history of isolation in Costa Rica. Indeed, when plotted along a scaled eigenvector R matrix of Caribbean gene frequencies, the two Limonense groups did not cluster with each other. Thus we conclude that the two ethnic groups have remained distinct breeding populations.

Mating pattern and population structure in Escazú, Costa Rica: a study using marriage records.

A primary focus of historical demographic research is to understand how a population's mating pattern can affect its genetic structure. By using surnames, researchers can reconstruct gene flow into a population as well as within it: the population structure. Indeed, Lasker (1988a) noted that the distribution of surnames reflects the effect of mate choice on a population's genetic structure. Here, we study the mating pattern of a small, clearly established breeding population in Costa Rica (Escazú) during 1800-1839 and 1850-1899. We found that a large proportion of marriages involved individuals who were members of long-standing or core families. Indeed, 27 families provided 56% of all consorts throughout the period under study. When new surnames appeared in the records (presumably as a result of immigration), they were introduced more frequently by males, indicating that more males than females migrated into the community. The core families did not mate preferentially among themselves but appear to have readily accepted the migrants. Indeed,the greatest preponderance of repeated-surname marriages was that expected by chance. However, nonrandom surname repetition is evident when marriages between nonillegitimate consorts are analyzed. That is, the frequency of repeated-pair surname marriages is statistically significant in marriages involving brides and grooms who carried 2 surnames. Interestingly, significant departures from random repetition of surnames occurred during the decade in which the great cholera epidemic affected Costa Rica and during the decade following it. This departure from panmixia supports the notion that mating patterns were altered as a result of the epidemic, a suggestion we made previously when we reported that inbreeding increased in these same decades (Madrigal and Ware 1997).

Inbreeding in Escazú, Costa Rica (1800-1840, 1850-1899): isonymy and ecclesiastical dispensations.

We investigate the inbreeding levels in Escazú, Costa Rica, during 1800-1840 and 1850-1899. Inbreeding was researched through analysis of ecclesiastical dispensations and by two isonymy methods (Crow and Mange 1965; Pinto-Cisternas et al. 1985). As expected, the dispensation inbreeding coefficients were lower than those obtained through isonymy. However, the three methods indicate that consanguinity increased in the community during the second part of the nineteenth century.

How acute and community nurses are sharing skills.

The shift in emphasis from secondary to primary care has considerable implications for nurses and patients. Initiatives in Avon are seeking to smooth the transition from acute to community-based care. Skill-sharing between nurses working in acute and community settings is highlighted as a way of promoting seamless care.

Selection bias from differential residential mobility as an explanation for associations of wire codes with childhood cancer.

Several studies of childhood cancer, especially leukemia, in residential areas have reported an association with wire configuration codes. These codes were suggested to be surrogates of electromagnetic field exposure. However, the selection criteria used in several of the studies caused the case and control populations to be non-comparable, especially with respect to residential mobility. Specifically, controls were required to be residentially stable but cases were not. Thus, an artificial association between residential mobility and cancer was created by the subject selection procedure. The present study of 5721 residences in Columbus, Ohio was conducted to learn if bias due to differences in residential mobility, rather than electromagnetic fields, could explain the reported association between wire configuration codes and childhood cancer. It was found that the proportion of homes classified as "high" wire code in the non-stable population was 31% greater than the corresponding proportion in the stable population. This finding shows that high wire codes are associated with homes in which the residents are mobile and low wire codes are associated with homes occupied by stable residents. Thus, as a consequence of this association between residential mobility and high wire codes, studies that created an artificial association between residential mobility and childhood cancer will also produce a false association between high wire codes and cancer.

A national study of required family medicine clinical rotations.

The authors collected information from each family medicine department with a required clinical rotation. Timing of such rotations are predominantly during the third year (56%), using a combination of family practice centers and community preceptor sites. Formal didactic instructions are offered for a mean of 28 hours. This instruction is offered in combinations of introductory, weekly, and terminal didactic blocks. Most programs (68%) assign reading from an article file, and 51% develop their own examinations. Clinical evaluations represent the largest portion (61%) of final grades, with 30% coming from examinations and lesser amounts from home visits, student presentations, etc. The implications of these findings are discussed.

The office diagnosis of common intestinal parasitic diseases.

The diagnosis of parasitic infections is becoming more frequent in the ambulatory setting. This article explains collection of specimens, testing, and considerations.

Actin critical concentration optimizes at intermediate [cytochalasin B]/[actin] ratios.

Effect of cytochalasin B on actin critical concentration has been assayed using the fluorescence enhancement of pyrene-labeled actin. A peak effect of cytochalasin B on the critical concentration is observed in the presence of either 100 mM K+, or 100 mM K+ plus 2 mM Mg2+. This may result from two competing activities of cytochalasin B, one associated with its capping activity to the barbed end of actin filaments, and the other associated with its lateral binding site(s) along the filaments resulting in a severing activity of cytochalasin B.

pH dependence of actin self-assembly.

Fluorescence enhancement and fluorescence photobleaching recovery have been utilized to examine actin self-assembly over the pH range 6.6-8.0. The kinetics of assembly are faster and the critical concentrations are lower at lower pH. Filament diffusion coefficients are not a function of pH, indicating that average filament lengths are not pH dependent. Although critical actin concentrations are a sensitive function of the concentrations of various cations in the medium, the relative pH dependences of critical concentrations are similar for all combinations of cations employed. The pH dependence of actin self-assembly is sufficiently great that it should be taken into account when comparing data from different reports and when relating in vitro measurements to cytoplasmic mechanisms.

Actin filament capping and cleaving activity of cytochalasins B, D, E, and H.

The concentration dependences of the activities of cytochalasin B, D, E, and H in capping and cleaving actin filaments have been assayed using fluorescence photobleaching recovery. Filament capping was detected by the increase in mobile G-actin. Cytochalasin D (CD) showed the strongest filament capping activity, with an apparent dissociation constant from filament ends of 50 nM. The order of capping activity was CD greater than CH greater than CE much greater than CB. Filament cleavage was detected by the increase in the diffusion coefficients of actin filaments. By this criterion the order of filament cleavage activity was CD, CE greater than CH much greater than CB. Cytochalasin B shows some activity in cleavage of filaments over a concentration range (0-100 microM) at which it shows no appreciable capping activity. This activity, together with results from other groups, is interpreted to mean that CB binds to protomers within the filament, but not to the barbed end. The reversal of activities for CH and CE, combined with the activity profile of CB, constitute the strongest evidence to date that there is more than one cytochalasin binding site on the actin molecule.

Analysis of rhodamine and fluorescein-labeled F-actin diffusion in vitro by fluorescence photobleaching recovery.

Properties of filamentous acetamidofluorescein-labeled actin and acetamidotetramethylrhodamine-labeled actin (AF and ATR-actin, respectively) were examined to resolve discrepancies in the reported translational diffusion coefficients of F-actin measured in vitro by FPR and other techniques. Using falling-ball viscometry and two independent versions of fluorescence photobleaching recovery (FPR), the present data indicate that several factors are responsible for these discrepancies. Gel filtration chromatography profoundly affects the viscosity of actin solutions and filament diffusion coefficients. ATR-actin and, to a lesser degree, AF-actin show a reduction in viscosity in proportion to the fraction labeled, presumably due to filament shortening. Actin filaments containing AF-actin or ATR-actin are susceptible to photoinduced damage, including a covalent cross-linking of actin protomers within filaments and an apparent cleavage of filaments detected by a decrease of the measured viscosity and an increase in the measured filament diffusion coefficients. Quantum yields of the two photoinduced effects are quite different. Multiple cross-links are produced relative to each photobleaching event, whereas less than 1% filament cleavage occurs. Substantial differences in the filament diffusion coefficients measured by FPR are also the result of differences in illumination geometry and sampling time. However, under controlled conditions, FPR can be used as a quantitative tool for measuring the hydrodynamic properties of actin filaments. Incremented filament shortening caused by photoinduced cleavage or incremental addition of filament capping proteins produces a continuous and approximately linear increase of filament diffusion coefficients, indicating that filaments are not associated in solution. Our results indicate that actin filaments exhibit low mobilities and it is inferred that actin filaments formed in vitro by column-purified actin, under standard conditions, are much longer than has conventionally been presumed.

Actin assembly activity of cytochalasins and cytochalasin analogs assayed using fluorescence photobleaching recovery.

The effects on actin self-assembly of 9 common cytochalasins and 9 synthetic analogs have been assayed using fluorescence photobleaching recovery (FPR). The specific assembly activities of cytochalasins determined by this assay are (i) reduction of the fraction of actin molecules incorporated into filaments; (ii) increase of the steady-state diffusion coefficients of filaments, from which filaments shortening may be inferred; and (iii) acceleration of the initial rate of assembly. Of the compounds studied, only cytochalasin D shows strong activity of all three types. The range of activities shown by other compounds indicates clearly that these three activity types are distinct and independent. Inspection of the molecular structures of these 18 compounds for correlation of structure and activity reveals that the three different activities depend on distinct structural features. The Mg2+ dependence of filament-shortening activity by certain cytochalasins may be explained by the Mg2+ chelating ability of two suitably positioned oxygen atoms on the convex face of the bicyclic isoindolone system. Inhibition of filament elongation may involve very specific, high-affinity cytochalasin interactions at a binding site on terminal actin molecules, while accelerating activity may occur by weaker, less specific binding interactions of cytochalasins with monomeric actin.

Rheology of G-actin solutions.

Recent reports that dilute solutions of G-actin form viscoelastic gels have been investigated using several experimental variations of three distinct physical techniques in independent laboratories. Direct measurement of storage and loss moduli were made using two rheometers of different design. Measurements of the diffusion of G-actin and of tracer particles added to G-actin solutions were carried out using dynamic light scattering and fluorescence photobleaching recovery techniques. Measurements were performed over a period of many hours, on actin solutions prepared under conditions for which anomalous gelation had been reported. All data from this investigation are consistent with the conclusion that dilute G-actin solutions behave as newtonian liquids.

Actin assembly by lithium ions.

The ability of Li+ to promote the assembly of actin has been compared with the more common cations used in actin assembly assays, K+, Mg2+, and Ca2+. The principal assay of actin assembly utilized was fluorescence photobleaching recovery (FPR), from which it is possible to determine the fraction of actin protomers incorporated into filaments and the average diffusion coefficients of the filaments. In addition, critical concentrations of actin over a range of concentrations of all of these cations have been determined using an assay that involves sonication and dilution of assembled actin filaments containing trace amounts of pyrene-labeled actin. The results demonstrate that Li+ is a more potent promoter of actin assembly than is K+. The more rapid assembly of actin in the presence of Li+ is attributable to an increased rate of filament elongation. Filaments assembled in equivalent concentrations of Li+ or K+ have the same diffusion coefficients, and thus presumably the same average lengths. The critical concentration of actin is about three times less in the presence of Li+ than in the presence of an equal concentration of K+. Cytochalasin D accelerates the rate of Li+-promoted actin assembly and reduces slightly the total fraction of actin assembly. However, cytochalasin D causes less shortening of filaments in the presence of Li+ than in the presence of K+ or Mg2+. By the criteria of assembly kinetics and critical concentration, Li+ is much less potent as a promoter of actin assembly than either Mg2+ or Ca2+. These results are discussed in terms of the role of electrostatic forces in the actin assembly mechanism and in terms of possible relationships to therapeutic and toxicity mechanisms for Li+.