Use of Dye Containing Polymeric Microcapsules for Determining Shear Stresses

This paper evaluates a method of measuring shear stress, in-situ, in polymer flows. The rupture response of two different dye containing polymeric microcapsules, CM511 and CM567, is examined in both an internal batch mixer and a lab scale single screw extruder (SSE), using ultraviolet/visible spectrophotometry (UV/VIS), colorimetric analysis (CA) and optical microscopy (OM). It is observed that both particles rupture over a wide range of shear stresses and times. In particular, both CM511 and CM567 begin to rupture at ∼ 100 kPa, while complete rupture is only detected for the CM567 at average stress levels greater than or equal to ∼ 230 kPa. Complete rupture for the CM511 is not observed over the average shear stress range investigated. The microcapsules further indicate the change in the melting mechanism in a SSE when the processing conditions are changed.

Laser heating of solid matter by light-pressure-driven shocks at ultrarelativistic intensities

The heating of solid targets irradiated by 5 x 10(20) W cm(-2), 0.8 ps, 1.05 microm wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo, and V. A surface layer is heated to approximately 5 keV with an axial temperature gradient of 0.6 microm scale length. Images of Ni Ly(alpha) show the hot region has <or=25 microm diameter. These data are consistent with collisional particle-in-cell simulations using preformed plasma density profiles from hydrodynamic modeling which show that the >100 G bar light pressure compresses the preformed plasma and drives a shock into the solid, heating a thin layer.

Socio-demographic features and fluoride technologies contributing to higher fluorosis scores in permanent teeth of Canadian children

OBJECTIVE

To examine levels of fluorosis among children in two Canadian communities exposed to fluoride.

BACKGROUND

One community had discontinued fluoride, the other had maintained it. Water supplies, however, were fluoridated for all the children when their esthetically important teeth were mineralized.

METHODS

We examined 8,277 children to assess Thystrup-Fejerskov Index (TFI) scores. Multivariate Poisson regression models were used to identify the relationship between TFI and water fluoride status, age, gender, SES, and dietary and fluoride exposure histories (supplements, rinses, toothpaste amount, tooth brushing frequency, and tooth brushing starting age). Parent(s) completed questionnaires.

RESULTS

Overall, levels of fluorosis were low to mild, with residents of the fluoridation-ended communities having marginally higher TFI scores than those of the still-fluoridated community. Females had higher TFI scores than males. Children aged 10 years or more had higher TFI scores than younger children. Consuming bottled water between birth and 6 months of age was protective. Exposure to fluoridation technologies was consistently associated with fluorosis experience. Children who began brushing with fluoride toothpaste between their first and second birthdays had higher TFI scores than those who began between their second and third birthdays, regardless of daily brushing frequency. Children who regularly used supplements had higher TFI scores than those who did not. Children with a college-educated father had higher TFI scores than those whose fathers had less education.

CONCLUSIONS

Higher fluoride exposure slightly increased the likelihood that a child had a higher TFI score, especially when more fluoridation technologies were used at home.

Detection of eubacterial 3-hydroxy-3-methylglutaryl coenzyme a reductases from natural populations of actinomycetes

Three natural populations of actinomycetes were investigated by PCR for the presence of type I 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA), a gene associated with isoprenoid biosynthesis. The populations were obtained from an agricultural site (69 isolates), a coastal salt marsh (220 isolates), and a desert soil (96 isolates). A set (34) of standard actinomycete reference strains were also investigated. The target gene was only detected in 5 of the 419 actinomycetes screened, which represented 4 from the coastal salt marsh and one reference strain. The isolates that contained the gene were taxonomically diverse (4 Streptomyces spp. and 1 Nocardia sp.). These results suggest that type I HMG CoA containing pathways are rare in actinomycetes and their distribution within actinomycetes populations is not random.

Detection of Borrelia lonestari in Amblyomma americanum (Acari: Ixodidae) from Tennessee

Genetic sequences characteristic of Borrelia lonestari (Barbour et al. 1996) were detected in two pools of adult Amblyomma americanum (L.) from Tennessee, corresponding to an estimated minimum field infection rate of 8.4 infected ticks/1000 adults. DNA amplification was conducted using primers derived from the B. lonestari flagellin gene that would also amplify Borrelia burgdorferi (Johnson, Schmid, Hyde, Steigerwalt, and Brenner). Species-specific, internal probes were then used to differentiate between genetic sequences of the spirochetes. Subsequent nucleotide sequencing confirmed the presence of B. lonestari in A. americanum; B. burgdorferi was not detected. This represents the first report of B. lonestari from Tennessee, and suggests that Lyme-like illness may occur in Tennessee.

Tooth-surface progression and reversal changes in fluoridated and no-longer-fluoridated communities over a 3-year period

OBJECTIVE

To compare permanent tooth surface-specific progression/reversal changes between fluoridation-ended (F-E) and still-fluoridated (S-F) communities in British Columbia, Canada, over a 3-year period.

METHODS

D1D2MFS examinations were contrasted for 2,964 schoolchildren in 1993/94 (grades 2, 3, 8 and 9) and 1996/97 (grades 5, 6, 11 and 12). Generalized Estimating Equation (GEE) models explored the relation between progression/reversal changes and fluoridation status, age, gender, socioeconomic status, and dietary/fluoride histories.

RESULTS

Within a scenario of low levels of caries overall, few children had multiple surfaces progressing. At least one smooth surface progressed in 31.4% of subjects; at least one pit-and-fissure (PF) surface progressed in 43.1% of subjects. At least one smooth surface reverted in 89% of subjects who had reversible stages; at least one PF surface reverted in 23.8% of subjects who had reversible stages. GEE (smooth) indicated that odds ratios of progression were twice as large in the F-E site compared to the S-F site, and slightly increased in older participants and in participants exposed to more fluoride technologies. GEE (PF) also indicated that progression was slightly more common in the F-E site; more frequent snacking and lower parental educational attainment had modest associations with increased progression in PF surfaces. For the two types of surfaces, GEE models demonstrated that unerupted surfaces were less likely to progress than sound surfaces. No associations were found between reversals and independent variables.

CONCLUSION

Progressions were found to be weakly linked to socio-demographic factors; baseline surface statuses were better predictors of progression. Using the current definitions for disease transitions, F-E communities had more frequent progressions than a S-F community.

Patterns of dental caries following the cessation of water fluoridation

OBJECTIVES

To compare prevalence and incidence of caries between fluoridation-ended and still-fluoridated communities in British Columbia, Canada, from a baseline survey and after three years.

METHODS

At the baseline (1993/4 academic year) and follow-up (1996/7) surveys, children were examined at their schools. Data were collected on snacking, oral hygiene, exposure to fluoride technologies, and socio-economic level. These variables were used together with D1D2MFS indices in multiple regression models.

RESULTS

The prevalence of caries (assessed in 5,927 children, grades 2, 3, 8, 9) decreased over time in the fluoridation-ended community while remaining unchanged in the fluoridated community. While numbers of filled surfaces did not vary between surveys, sealed surfaces increased at both study sites. Caries incidence (assessed in 2,994 life-long residents, grades 5, 6, 11, 12) expressed in terms of D1D2MFS was not different between the still-fluoridating and fluoridation-ended communities. There were, however, differences in caries experienced when D1D2MFS components and surfaces at risk were investigated in detail. Regression models did not identify specific variables markedly affecting changes in the incidence of dental decay.

CONCLUSIONS

Our results suggest a complicated pattern of disease following cessation of fluoridation. Multiple sources of fluoride besides water fluoridation have made it more difficult to detect changes in the epidemiological profile of a population with generally low caries experience, and living in an affluent setting with widely accessible dental services. There are, however, subtle differences in caries and caries treatment experience between children living in fluoridated and fluoridation-ended areas.

The effectiveness of 10% chlorhexidine varnish treatment on dental caries incidence in adults with dry mouth

OBJECTIVES

This study compared a 10% chlorhexidine varnish treatment with placebo and sham treatments for preventing dental caries in adult patients with xerostomia (dry mouth).

DESIGN

The study was a multicentred, randomized, parallel group, double blind, placebo-controlled clinical trial.

SETTING

All examinations and procedures were performed at Tuft's University, Boston, MA, the University of British Columbia, Vancouver, BC or the University of Western Ontario, London, ON.

SUBJECTS

Subjects were adults with recent or current dental caries experience, high salivary levels of cariogenic microorganisms and low salivary flow rates.

RESULTS

236 subjects completed at least one post-treatment examination. There were 697 new carious lesions diagnosed, 446 (64%) located on coronal surfaces and 251 (36%) located on root surfaces. The mean attack rate was 0.23 surfaces/100 surfaces at risk. A treatment difference observed between the Active and Placebo groups was statistically significant for root caries increment (p = .02) and total caries increment (p = .03). A treatment difference observed between the Active and Sham groups was not statistically significant for coronal, root or total caries increment. Analysis of variance of treatment group differences was performed using mutans streptococci counts, salivary flow rates, age, sex, caries prevalence, medications, time to first event and early withdrawal as co-variables. These factors did not meaningfully alter the findings.

CONCLUSIONS

The difference between the 10% chlorhexidine varnish and placebo treatments is considered to be highly clinically significant for root caries increment (41% reduction) and for total caries increment (25% reduction) but only for coronal caries increment (14%).

Social constructs of curricular change

The adoption of problem-based approaches to teaching and learning in dental and medical education requires educators to consider a significantly different role and responsibilities as teacher from what they have experienced previously. This qualitative study explored how some educators experienced and interpreted changes in the newly merged dental and medical curriculum at the University of British Columbia. Our findings present how educators explained and dealt with change. In-depth interviews provided considerable insight into factors influencing the resistance or acceptance to change. The educators' beliefs about teaching and learning and their understanding of the development and implementation process of change mediated these factors. Findings from this study should help administrators, faculty developers, and educators themselves to understand better how curricular change is experienced and to plan effective and appropriate faculty development.

Effects of dietary fish oil supplementation on the phospholipid composition and fluidity of cell membranes from human volunteers

BACKGROUND

Membrane fluidity is an important aspect of cellular physiology which may be manipulated by diet.

METHODS

We studied the effect of dietary fish oil on the membrane composition of erythrocytes and cheek cells, and on membrane fluidity of erythrocytes as assessed by fluorescence recovery after photobleaching (FRAP). Healthy volunteers received a daily supplement of fish oil (930 mg EPA, 630 mg DHA) for 42 days.

RESULTS

The intervention reduced the ratio of n-6 to total fatty acid in the phospholipid fraction of erythrocyte membranes but the n-3 fraction remained stable and the ratio of cholesterol to phospholipid increased. The level of EPA and DHA in cheek cells increased significantly during the intervention period. The mean diffusion coefficient of the fluorescent probe in erythrocyte membranes increased from 7.2 +/- 0.7 x 10-9 cm2/s at the start to 9.8 +/- 0.5 x 10-9 cm2/s after 21 days. Membrane fluidity remained higher than the initial value 42 days after withdrawal of the supplement. Fish oil also reduced platelet aggregation in response to ADP but there was no effect on plasma lipid profiles.

CONCLUSION

We conclude that n-3 fatty acids influence erythrocyte membrane composition at relatively low levels of supplementation by a mechanism which does not necessarily involve an increase in the level of EPA or DHA present in the membrane.

Studies of suicide in later life: methodologic considerations and research directions

Later-life suicide is a tragedy that occurs worldwide. Often it is preventable. Here, the authors summarize an international workshop where they review four research approaches to studying putative risk factors: epidemiologic studies of suicidal behaviors, clinic-based follow-up studies, studies of suicide attempters, and psychological autopsy studies. They provide brief descriptions of the approaches, examples of questions best addressed by each approach, and their weaknesses and limitations; they also recommend promising areas for future research and propose opportunities for research that could be conducted cross-nationally.

Esophageal atresia and tracheoesophageal fistula

Esophageal atresia, with or without tracheoesophageal fistula, is a fairly common congenital disorder that family physicians should consider in the differential diagnosis of a neonate who develops feeding difficulties and respiratory distress in the first few days of life. Esophageal atresia is often associated with other congenital anomalies, most commonly cardiac abnormalities such as ventricular septal defect, patent ductus arteriosus or tetralogy of Fallot. Prompt recognition, appropriate clinical management to prevent aspiration, and swift referral to an appropriate tertiary care center have resulted in a significant improvement in the rates of morbidity and mortality in these infants over the past 50 years.

The effect of entering drug treatment on involvement in HIV-related risk behaviors

The research described here is based on a sample of 8,241 out-of-drug-treatment users of injected drugs and/or crack, aged 18 or older, recruited from 22 sites across the United States and Puerto Rico. The study divided respondents into three groups-(a) cocaine or crack users who did not also use heroin or speedball (cocaine-only users), (b) heroin injectors who did not also use cocaine or crack or speedball (heroin injectors), and (c) users of cocaine or crack and injected heroin or speedball (dual users)--and compared the efficacy of entering drug treatment for these groups' involvement in HIV-related risk behaviors. The study found that entry into treatment corresponded to greater reductions in substance abusers' frequency of drug use and involvement in risky injection practices compared to those observed in people who did not enter treatment between their baseline and 6-month follow-up interviews. Entry into drug treatment was also associated with reductions in the practice of risky sexual behaviors, but these reductions were less substantial and less consistent than those noted for drug use and injection risk behaviors.

Adolescent suicide

This article reviews the origin of youth suicide. Theoretic suicide risk factors and empirically observed suicide risk factors are discussed along with proposed resiliency factors that prevent suicide. Finally, suicide prevention and intervention strategies are covered, and a call for better studies on suicide prevention is heralded.

The influence of various fluoride exposures on the prevalence of esthetic problems resulting from dental fluorosis

OBJECTIVES

This study sought to determine the prevalence of esthetic problems due to dental fluorosis, and determine the relationship of different fluoride exposure histories to the occurrence of these problems.

METHODS

In 1993-94 2,715 children in grades 2 and 3 and 3,297 adolescents in grades 8 and 9 were examined by four dentists. Questionnaires detailing exposures to various fluoride technologies were collected from 3,022 of these study participants. Esthetic ratings of the participants' maxillary anterior teeth were made by the examiners, the participants themselves, and their parents using questionnaires designed for this purpose.

RESULTS

Data indicate that 46 percent of the participants had dental fluorosis. Only 40 percent had fluorosis on anterior maxillary teeth. The prevalence of esthetic problems ranged from about 1 percent to 4 percent, depending on how an esthetic problem was defined. Esthetic problems as defined by the participant were more prevalent for the "over 11" age group. Logistic regression results demonstrated significant associations between several of the classifications of esthetic problems and the use of fluoride supplements and dentifrices, and exposure to fluoridated water during the third year of life.

CONCLUSIONS

Results suggest that the prevalence of esthetic problems is low in the communities surveyed, and that exposure to any number of fluoride technologies in the third year of life can increase a child's risk for this problem.

The relationship between the number of sound, decayed, and filled permanent tooth surfaces and the number of sealed surfaces in children and adolescents

OBJECTIVES

The purpose of this investigation was to determine the prevalence of sound, decayed, filled, and sealed permanent tooth surfaces for children and adolescents from three fluoridated communities in British Columbia and to develop a predictive model of sealant use that included the dental caries status of tooth surfaces.

METHODS

Children in grades 2 and 3 (n = 2,715) and adolescents in grades 8 and 9 (3,317) were surveyed to determine the prevalence of sound, decayed, filled, and sealed permanent tooth surfaces. The DMFS index, modified to include incipient (D1) and cavitated (D2) lesions, was used to measure the status of all tooth surfaces. The prevalence of D1D2MF and sealed tooth surfaces was estimated by age group and tooth type. Logistic regression models were developed to analyze the association between a number of independent variables and sealant use.

RESULTS

About 60 percent of surveyed students had one or more sealants present, with a mean of 3.2 sealants per subject. Of all pit and fissure surfaces on permanent first molars, 23.4 percent and 20.1 percent were sealed for the 11 years and younger and 12 years and older age groups, respectively. For these same two age groups, the percentages of pit and fissure surfaces that were decayed and filled were 6.7 percent and 19.7 percent, respectively. For both age groups combined, 10.8 percent and 23.7 percent of all pit and fissure surfaces on second molars and premolars, respectively, were sealed. The prevalence of decayed and filled pit and fissure surfaces was 5.6 percent and 1.8 percent, respectively, for second molars and premolars. Premolars were being sealed at a rate of 13 to 1 compared to the number of decayed and filled surfaces. Logistic regression failed to identify meaningful predictors of sealant use.

CONCLUSIONS

Results from this study found an increase in the prevalence of sealants in the three communities surveyed, yet failed to identify criteria used by dentists or auxiliaries when making decisions about sealant placement. Professional education in the appropriate use of sealants may be necessary.

Effect of Lipid Phase State and Foam Film Type on the Properties of DMPG Stabilized Foams

The drainage and stability of DMPG (l -alpha-phosphatidyl-dl -glycerol dimyristoyl) foams were studied by a microconductivity method under conditions where three different foam film types could be formed-thin foam films (TFF), common black foam films (CBF), and Newton black foam films (NBF). Foaming properties were investigated at 20 and 28&deg;C where DMPG is in the gel and liquid-crystalline states. Higher conductivity signals were observed at the higher temperature where DMPG was in the liquid-crystalline state, which is indicative of wetter or more stable foams under these conditions. This effect was observed independent of foam film type. However, for a given phase state, the type of foam films formed significantly influenced the stability and rate of drainage of the foam. Indeed, the water content of the foams, obtained under conditions for formation of different foam films, is ranked in the order TFF > CBF > NBF. When the temperature was increased to 28&deg;C (i.e., in the liquid-crystalline state), CBF and NBF showed a slight decrease in film thickness and an increase in film lifetime and surface molecular diffusion coefficient in the adsorbed layer. It is likely that the fluidity of the interfacial layer is an important factor contributing to DMPG foam stabilization.

Lateral mobility of plasma membrane lipids in bull spermatozoa: heterogeneity between surface domains and rigidification following cell death

Compartmentalization of surface membrane antigens into discrete regions or domains is a characteristic feature of differentiated cells. In mammalian spermatozoa at least 5 surface domains are known, implying the presence of barriers or boundaries within the plasma membrane. Using the technique of fluorescence recovery after photobleaching (FRAP) to measure diffusibility of fluorescent lipid analogues 1,1′-dihexadecyl-3,3,3′3′-tetramethylindocarbocyanine (DiIC[16]) and 5-(N-octa-decanoyl) aminofluorescein (ODAF), we have investigated lipid topology and dynamics in the plasma membrane of ejaculated bull spermatozoa. Contrary to reports in the literature, we have found that DiIC(16) stains only dead or damaged spermatozoa whereas ODAF intercalates into the plasma membrane of both live and dead cells, each type showing a distinctive staining pattern. FRAP analysis with ODAF revealed that diffusion coefficients on live spermatozoa are significantly faster on the acrosome and postacrosome (29.3x10(−9) cm2/second) than on the midpiece and principal piece (11.8x10(−9) cm2/second). Recovery (R) is &gt;90% in all domains. ODAF diffusion also shows regionalized temperature-sensitivity with a 4-fold increase over the sperm head and a 1.8-fold increase on the tail between 20 degrees C and 37 degrees C. Remarkably, dead or permeabilized spermatozoa rapidly develop a large immobile phase (R&lt;25%) over the whole plasma membrane. This rigidification is temperature insensitive and irreversible suggesting major changes in the physical state of membrane lipids. It is concluded that lipid diffusion in the plasma membrane of live bull spermatozoa is rapid and varies significantly between surface domains. Following permeabilization or cell death, however, a large immobile phase develops indicating substantial changes in membrane lipid disposition.

An outcomes assessment of a hybrid-PBL course in treatment planning

As part of an ongoing process of curriculum development, a new course was developed at the University of British Columbia (UBC) to address problems such as lack of student enjoyment of the learning process, poor student preparedness for clinical treatment planning, and underdeveloped critical thinking skills in students beginning their clinical experience. The new course utilized a hybrid problem-based learning (PBL) format that provided students with an overview in lecture format while encouraging active learning in small group tutorials and seminars. Half the second-year class was randomly selected to participate in the new course, while the other half received the standard lectures on the subject. An outcomes assessment examined whether the aforementioned problems had been addressed in the new course. Course participants completed a post-course evaluation, and all students completed a self-assessment of their preparedness and progress in treatment planning and diagnostic. Clinical instructors, who were blind to the identity of the new course participants, were asked to independently assess each student using the same criteria. Results indicate that students who participated in the hybrid-PBL course enjoyed the learning process and later rated themselves as being better prepared and improving more in the areas of treatment planning and diagnostic records than their counterparts, although the latter results were not routinely statistically significant (p < 0.1). Instructor evaluations supported these differences between the two groups.

The influence of dietary lipids on the composition and membrane fluidity of rat hepatocyte plasma membrane

Weanling male Wistar rats were fed for five weeks on standard rat chow (23 g fat/kg diet) or one of four synthetic diets with butterfat, coconut oil, corn oil, or fish oil as the main lipid source (100 g fat/kg diet). In all diets, 10% of the fat was provided as corn oil to prevent essential fatty acid deficiency. Significant differences were observed in the saturated, monounsaturated, and polyunsaturated fatty acid composition, and in the ratio of cholesterol to phospholipid, in the hepatocyte membranes. The fluidity of hepatocyte plasma membranes was assessed using the fluorescence recovery after photobleaching technique and steady-state fluorescence anisotropy of diphenylhexatriene. No significant differences were found in the fluidity of plasma membranes between animals on the different fat diets, despite diet-induced changes in their fatty acid composition. However, the proportion of lipid free to diffuse in the plasma membrane varied with diet, being significantly greater (P < 0.05) in animals fed chow (63.7%), coconut oil (61.5%), and butterfat (57.6%) diets than in those fed the corn oil (47.3%) diet. Animals fed fish oil showed an intermediate (50.0%) proportion of lipid free to diffuse. The data support the hypothesis that dietary lipids can change both the chemical composition and lateral organization (lipid domain structure) of rat hepatocyte plasma membranes.

The influence of membrane fluidity, TNF receptor binding, cAMP production and GTPase activity on macrophage cytokine production in rats fed a variety of fat diets

The effects of different dietary fats on peritoneal macrophage plasma membrane fluidity, intracellular cyclic AMP (cAMP) production, GTP hydrolysis and TNF binding and TNF-induced IL1 and IL6 production was investigated. After a four week period, fluidity, as determined by both fluorescence recovery after photobleaching (FRAP) and anisotropy was lowest and highest in animals fed corn and fish oil respectively. After eight weeks feeding, lateral membrane movements were decreased substantially in fish, olive and coconut oil fed dietary groups, whereas an increase in the corn oil fed group was observed, no effect was observed in macrophages from the butter fed group. However, an increase in the packing was observed in macrophages from all dietary groups except in the olive oil fed group. GTPase values for the coconut oil and butter groups were higher than in any other dietary group. After receiving the diet for 8 weeks these differences between the groups were no longer apparent. Exposure of macrophages to TNF had no effect on the rate of GTP hydrolysis. A major enhancement of cAMP production became apparent between weeks 4 and 8 of dietary treatment. After 4 weeks on the diet, values were significantly higher from cells of animals fed corn and olive oils than from animals fed fish oil. After 8 weeks, while there was a general enhancement of production, further differences became apparent. Feeding corn and coconut oils resulted in the highest values and olive oil and chow in the lowest. It is proposed that fats rich in n-3 fatty acids (fish oils) alter membrane fluidity, decrease TNF binding affinity, GTPase activity and cAMP production which appears not to modify cytokine production after short term dietary supplementation. However, after long term feeding it appears that increases in the sensitivity of the TNF receptors plays a major role in modifying cytokine production.

Atomic Force Microscopy of Interfacial Protein Films

Atomic force microscopy (AFM) has been used to image interfacial films of bovine serum albumen and beta-casein produced at hexadecane/water and air/water interfaces, respectively. Planar oil/water and air/water interfaces have been used to model protein films such as may form in emulsions and foams. The protein films were picked up onto mica sheets and imaged under butanol. Both systems studied yielded homogeneous flat networks which could be imaged at molecular resolution and which demonstrate the potential for using AFM to probe interfacial networks.

Molecular mobility in the monolayers of foam films stabilized by porcine lung surfactant

Certain physical properties of a range of foam film types that are believed to exist in vivo in the lung have been investigated. The contribution of different lung surfactant components found in porcine lung surfactant to molecular surface diffusion in the plane of foam films has been investigated for the first time. The influence of the type and thickness of black foam films, temperature, electrolyte concentration, and extract composition on surface diffusion has been studied using the fluorescence recovery after photobleaching technique. Fluorescent phospholipid probe molecules in foam films stabilized by porcine lung surfactant samples or their hydrophobic extracts consisting of surfactant lipids and hydrophobic lung surfactant proteins, SP-B and SP-C, exhibited more rapid diffusion than observed in films of its principal lipid component alone, L-alpha-phosphatidylcholine dipalmitoyl. This effect appears to be due to contributions from minor lipid components present in the total surfactant lipid extracts. The minor lipid components influence the surface diffusion in foam films both by their negative charge and by lowering the phase transition temperature of lung surfactant samples. In contrast, the presence of high concentrations of the hydrophillic surfactant protein A (SP-A) and non-lung-surfactant proteins in the sample reduced the diffusion coefficient (D) of the lipid analog in the adsorbed layer of the films. Hysteresis behavior of D was observed during temperature cycling, with the cooling curve lying above the heating curve. However, in cases where some surface molecular aggregation and surface heterogeneity were observed during cooling, the films became more rigid and molecules at the interfaces became immobilized. The thickness, size, capillary pressure, configuration, and composition of foam films of lung surfactant prepared in vitro support their investigation as realistic structural analogs of the surface films that exist in vivo in the lung. Compared to other models currently in use, foam films provide new opportunities for studying the properties and function of physiologically important alveolar surface films.

Lateral diffusion in planar lipid bilayers: a fluorescence recovery after photobleaching investigation of its modulation by lipid composition, cholesterol, or alamethicin content and divalent cations

In spite of the fact that planar lipid bilayers are still the best-suited artificial membrane system for the study of reconstituted ion channels and receptors, data dealing with their physical characterization, especially as regards dynamics, are scanty. A combined electrical and optical chamber was designed and allowed fluorescence recovery after photobleaching recovery curves to be recorded from stable virtually solvent-free bilayers. D, the lateral diffusion coefficient of N-(7-nitrobenzoyl-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn- glycero-3-phosphoethanolamine, was found to be relatively insensitive to the phospholipid composition (headgroup, chain unsaturation, etc.), whereas inclusion of 33-50% cholesterol in the membrane reduced D by a factor of 2. Divalent cations significantly reduced D of negatively charged bilayers. These results compare well with data gathered on other model and natural systems. In addition, the incorporation of the voltage-dependent pore-former alamethicin did slightly reduce lipid lateral mobility. This study demonstrates the feasibility of such experiments with planar bilayers, which are amenable to physical constraints, and thus offers new opportunities for systematic studies of structure-function relationships in membrane-associating molecules.

Interaction of nisin with planar lipid bilayers monitored by fluorescence recovery after photobleaching

Nisin, a prominent member of the lantibiotic family of antimicrobial agents, has wide application as a food preservative despite poor understanding of its mode of action. Fluorescence recovery after photobleaching has been used with planar lipid bilayers as a model membrane system to examine how nisin might interact with the surface of bacterial cells. Nisin associates with planar lipid bilayers in the absence of an applied membrane potential causing an array of effects consistent with adsorption of nisin onto the membrane surface which involves inhibition of the lateral diffusion and fluorescence of the lipid probe N-(7--1,2,3-benzoxadiazol-4-yl) phosphatidylethanolamine (NBD-PE) and a reduction of the capacitance of the bilayer. Nisin adsorption is dependent on phospholipid composition. In the presence of dioleoylphosphatidylcholine (PC): cardiolipin (CL) 4:1, the rate of lateral mobility of phospholipid is reduced to 61% of the control level which decreases to a value of 46% when CL is replaced by 1-palmitoyl-2-oleoylphosphatidylserine (PS). These effects on bilayer parameters are transient, and with time the values return to near original levels. High electrical conductivity is observed on application of a voltage ramp suggesting that insertion into the membrane follows surface association. Results have been interpreted in terms of a model in which nisin initially binds to the surface of the membrane causing a modulation of bilayer properties.

DQE(f) of four generations of computed radiography acquisition devices

Measurements were made of the MTF(f), NPS(f), and DQE(f) of four generations of computed radiography (CR) imaging plates and three generations of CR image readers. The MTF generally showed only a minor change between generations of plates and readers, but the DQE(f) has improved substantially from a very early plate/reader combination to a more recent one. The DQE in the more recent plate/reader combination is 1.3X greater at low frequencies and about 3X greater at high frequencies than the much earlier versions. Thus there has been substantial improvement in the imaging performance obtainable with CR since some of the early observer studies which indicated poorer performance with CR than with screen-film.

Genetic aspects of communication during male-male competition in the Madagascar hissing cockroach: honest signalling of size

Male Madagascar hissing cockroaches, Gromphadorhina portentosa, engage in agonistic contests with other males and produce audible sounds or 'hisses' during these interactions. Hisses are used to maintain, rather than to establish, social relationships among males. The agonistic hisses of males are variable and could be used as signals to communicate size or competitive ability of an individual. In this study we examined how size influences male-male competition, as well as the genetic variation and covariation of male body size and components of the agonistic hiss. We found that male size affected the outcome of agonistic interactions between pairs of males: a male that dominated in a pair was significantly larger than the male that was subordinate. However, we found no differences in the hisses produced by dominant and subordinate males after controlling for male weight. We estimated heritabilities, evolvability and genetic correlations for male size and characteristics of the hiss from a full-sib analysis of brothers. The patterns of heritabilities and evolvabilities were very similar. The heritabilities of both male weight and duration of the hiss were significantly greater than zero. There was a significant positive genetic correlation between duration of the agonistic hiss and male weight, and a significant negative genetic correlation between hiss duration and the beginning dominant frequency. There was also a positive phenotypic correlation and a negative environmental correlation between male weight and hiss duration. Thus, hiss duration can signal the present influence of the environment on male size, whereas information from hiss duration and beginning dominant frequency can signal the male's ability to transmit genetic influence for size.(ABSTRACT TRUNCATED AT 250 WORDS)

Child bereavement after paternal suicide

BACKGROUND

Studies of child suicide survivors are rare and often these studies have not included direct interviews with children.

OBJECTIVES

To describe the bereavement process in a sample of prepubertal children whose fathers died by suicide within the previous three years.

METHODS

Sixteen prepubertal children, their mothers, and a relative or caretaker were interviewed to examine grief, trauma, and behavior within 25 months of paternal suicide.

RESULTS

Reminiscing was the most frequently endorsed grief behavior. Males were more likely than females to score above the standard means for CBCL scores. PTSD scores were significantly related to parental threats of divorce and exposure to death by discovery of the body.

CONCLUSIONS

The concept of grief and trauma as separate and overlapping phenomena is supported by the study findings.