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PubMed2006

Modelled and measured dynamics of viruses in Arctic winter sea-ice brines.

We describe a model based on diffusion theory and the temperature-dependent mechanism of brine concentration in sea ice to argue that, if viruses partition with bacteria into sea-ice brine inclusions, contact rates between the two can be higher in winter sea ice than in seawater, increasing the probability of infection and possible virus production. To examine this hypothesis, we determined viral and bacterial concentrations in select winter sea-ice horizons using epifluorescence microscopy. Viral concentrations ranged from 1.6 to 82 x 10(6) ml(-1) of brine volume of the ice, with highest values in brines from coldest (-24 to -31 degrees C) ice horizons. Calculated virus-bacteria contact rates in underlying -1 degrees C seawater were similar to those in brines of -11 degrees C ice but up to 600 times lower than those in ice brines at or below -24 degrees C. We then incubated native bacterial and viral assemblages from winter sea ice for 8 days in brine at a temperature (-12 degrees C) and salinity ( approximately 160 psu) near expected in situ values, monitoring their concentrations microscopically. While different cores yielded different results, consistent with known spatial heterogeneity in sea ice, these experiments provided unambiguous evidence for viral persistence and production, as well as for bacterial growth, in -12 degrees C brine.

Arctic Regions↗
PubMed1995

Diffusion of innovation II: Formulary acceptance rates of new drugs in teaching and non-teaching British Columbia hospitals--a drug development perspective.

Diffusion theory was used to examine differences in adoption rates of new drugs by British Columbia teaching and non-teaching hospitals. Surveys were mailed in September 1990 to 41 hospital pharmacies (response rate = 88%), requesting hospital pharmacy directors to provide formulary inclusion dates of 29 study drugs marketed between July 1987 and March 1990. Of the 36 initial responses, 31 were suitable for further analysis and these were surveyed again in April 1993 (response rate = 100%) as to the formulary status of drugs not initially approved. The second survey ensured that all study drugs would have at least 36 months on the Canadian market when determining formulary acceptance times. Of the 29 study drugs, six were not approved for use in any of the 31 study hospitals. The six teaching hospitals had a median formulary approval time of 8.0 months compared to 12.8 months in the 25 non-teaching hospitals for the 23 study drugs. Although 21 of 23 study drugs were approved for use earlier in teaching hospitals than non-teaching hospitals, only alfentanil was found to be adopted significantly earlier (U = 11, n1 = 5, n2 = 19, alpha = 0.05). Variations in formulary approval times for new drugs have a bearing on patient care, Pharmacy and Therapeutics Committees, hospital budgets, and pharmaceutical firm revenues.

British Columbia↗
PubMed2006

Development and validation of a scale to assess attitudes of health care administrators toward the use of e-mail communication between patients and physicians.

BACKGROUND: The medical profession has been slow in embracing the e-mail as a means of improving patient communications. Today, most physicians work in group practices where administrators seek to develop standard procedures for care delivery. To understand the slow adoption of e-mail technology among physicians when communicating with their patients, it is important to understand these administrators' attitudes. OBJECTIVE: The purpose of this study was to develop and purify a scale to measure health care administrators' attitudes toward the use of e-mail communication and identify associations between e-mail communication attitudes and administrators' demographic and practice-related characteristics. METHODS: A preliminary list of features for e-mail communication was generated by reviewing the literature and Rogers' diffusion theory. The features were grouped initially into 5 hypothesized dimensions: relative advantage, norms (established rules of the social system), complexity, compatibility, and infrastructure. Following pilot testing, the main survey instrument was mailed to a total of 1500 health care administrators. Attitudes toward features of e-mail communication scale were analyzed using exploratory factor analysis with promax rotation. Internal consistency of the scale and its subscales was determined using Cronbach's alpha and item-total correlations. RESULTS: The overall response rate was 8.7%. Scale purification procedures reduced the preliminary scale of 22 items to a final scale of 20 items. The reliability of the scale measured by Cronbach's alpha was 0.81. Norms was considered the major barrier to e-mail communication, whereas infrastructure was considered a facilitator, and other features like relative advantage, complexity, and compatibility issues were perceived more as a barrier than a facilitator. The item related to and usage of e-mail by staff was statistically significant with the overall scale score (P=0.0095), complexity subscale score (P=0.0168), and infrastructure subscale score (P=0.0480). The relationship between number of years of experience of the administrator and infrastructure subscale score was statistically significant (P=0.0480). CONCLUSION: A scale developed to determine the attitudes of health care administrators regarding e-mail communication between patients and physicians demonstrated adequate content validity and reliability.

Adolescent↗
PubMed2006

Water absorption characteristics of novel Cu/LDPE nanocomposite for use in intrauterine devices.

Intrauterine devices (IUDs), especially the copper-containing IUDs (Cu-IUDs), are one of the worldwide used forms for birth control, owing to their advantages of long-lasting and high efficacy, economy, safety, and reversibility. However, it is not perfect for the existing Cu-IUDs; some shortcomings related to its side effects have not been overcome yet. For this reason, a new Cu-IUDs material, the copper/low-density polyethylene (Cu/LDPE) nanocomposite, has been developed in our research team. The structure and water uptake characteristics of this new Cu-IUDs material have been investigated by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and gravimetric analysis in this paper. The results of XRD, SEM, EDS, and FT-IR show three important outcomes associated with the structure of the nanocomposite. First, the nanocomposite is hybrid of the polymer and the copper nanoparticles (nano-Cu). Second, porosities, nano-Cu aggregates, and primary alcohol (R--CH(2)--OH) are existed in the nanocomposite. Third, the nano-Cu aggregates are distributed uniformly in the polymer matrix in general. The results of Gravimetric analysis, which associated with the water uptake characteristics of the nanocomposite, exhibit that the water absorption behavior of the nanocomposite obeys the classical diffusion theory very well, the water uptake of the nanocomposite increases with the increasing of the nano-Cu loading, and that the water uptake ability of the nanocomposite with 15.0 wt % nano-Cu (50 nm in diameter) is about 150 times larger than that of the base resin and about 45 times higher than that of the Cu/LDPE microcomposite with 15.0 wt % copper microparticles (5 microm in diameter). These water uptake characteristics are mainly attributed to the structure of the Cu/LDPE composites and the size effect of the nano-Cu.

Absorption↗
PubMed1995

Effect of static load on matrix synthesis rates in the intervertebral disc measured in vitro by a new perfusion technique.

The effect of static loading on matrix synthesis was measured in intact bovine coccygeal discs. The discs were maintained at 37 degrees C in a humid atmosphere and were perfused across their upper and lower surfaces for as long as 8 hours with media containing radioisotopes (3H-proline and 35S-sulphate) via porous filter disks embedded in Perspex (Plexiglas) holders. Static loads were applied to the disc with use of weights. The activity of free, nonincorporated isotope in the centre of the disc was monitored continuously with a microdialysis probe. Incorporated tracer in different regions of the disc was determined at the end of each experiment from the activity of the nondialysable tracer. Free tracer activity rose steeply over the first 3-4 hours of perfusion, as tracer diffused into the disc, and reached a steady value after 5-6 hours, as expected from diffusion theory. The rate of tracer incorporation estimated from the integrated value of free tracer concentration was constant for as long as 8 hours. Incorporation rates varied across the disc: the highest rates were in the inner layer of the annulus fibrosus, and the lowest rates were in the outer layer of the annulus. The rates for both 35S-sulphate and 3H-proline varied with load. The rates were lowest in the nucleus pulposus and the inner layer of the annulus fibrosus with a 0.5 kg load, and they almost doubled as the load was increased to 5-10 kg. Heavier loads (15 kg) led to a decrease in incorporation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Polystyrene latex adsorption at the gold/electrolyte interface.

Irreversible deposition of polystyrene latex particles (average diameter, 1.5 microm) on various solid/electrolyte interfaces was studied experimentally by using the direct microscope observation method. The substrate surfaces included bare mica (reference interface), gold covered mica (layer thickness of 50 nm), and solid gold plate. The morphology and thickness of the gold layer on mica was determined by atomic force microscopy. Well-defined transport conditions of particles were created by using the new impinging-jet cell. A characteristic feature of the cell was that the suspension stream was directed obliquely to the interface. This unique characteristic was advantageous allowing one for direct, in situ, observation of particle deposition at metals and other nontransparent interfaces. Experiments performed for various flow intensities indicated that the initial deposition kinetics at all interfaces was identical within the error bounds, in accordance with the model based on the convective-diffusion theory. It was concluded that the limiting flux was governed by the bulk transport rather than by the specific surface interactions.

Journal Article↗
PubMed1990

Absorption and metabolism of procaine by the rat small intestine.

The aim of this study was to obtain information about the absorption of procaine in the rat small intestine (Fisher-Parsons preparation). In the range from 0.25-10 mmol.l-1 procaine in the luminal perfusate, much more of the unchanged drug was absorbed in segments of the ileum than of the duodenum and jejunum. Besides procaine, two metabolites, p-aminobenzoic acid (PABA) and acetylated p-aminobenzoic acid (AABA), formed in the intestinal mucosa, appeared in the absorbate. With increasing substrate concentration in the perfusate the PABA in the absorbate increased considerably in all three segments; from 0.75 mmol.l-1 procaine upwards the PABA produced was highest in the jejunum. AABA formed in the mucosa and measured in the absorbate did not increase in the same manner with increasing substrate concentration; in the absorbate of jejunal segments the amount of AABA was significantly higher than in duodenal and ileal segments. Taking into account that in rats the microclimate of the ileum differs considerably from that of the upper part of the small intestine, the marked difference observed in the absorption of procaine between ileal segments on the one side, and duodenal and jejunal segments on the other, can be explained on the basis of the "non-ionic diffusion" theory.

4-Aminobenzoic Acid↗
PubMed2004

Enhanced cytotoxic effects of 5-aminolevulinic acid-mediated photodynamic therapy by concurrent hyperthermia in glioma spheroids.

During photodynamic therapy (PDT) both normal and pathological brain tissue, in close proximity to the light source, can experience significant temperature increases. The purpose of this study was to investigate the anti-tumor effects of concurrent 5-aminolevulinic acid (ALA)-mediated PDT and hyperthermia (HT) in human and rat glioma spheroids. Human or rat glioma spheroids were subjected to PDT, HT, or a combination of the two treatments. Therapies were given concurrently to simulate the conditions that will occur during patient PDT. Predictions of diffusion theory suggest that brain tissue immediately adjacent to a spherical light applicator may experience temperature increases approaching 8 degrees C for laser input powers of 2 W. In the in vitro model employed here, HT had no effect on spheroid survival at temperatures below 49 degrees C, while sub-threshold fluence PDT results in only modest decrease in survival. HT (40-46 degrees C) and PDT interact in a synergistic manner if the two treatments are given concurrently. The degree of synergism increases with increasing temperature and light fluence. Apoptosis is the primary mode of cell death following both low-fluence rate PDT and combined HT + PDT.

Aminolevulinic Acid↗
PubMed1993

Temperature rise in tumor tissue during high-dose-rate photoradiation.

The bioheat transfer equation and optical diffusion theory are used to develop a mathematical model for describing the thermal field in a spherical tumor and its surrounding normal tissue resulting from photoradiation. Analytical solutions to the model equations are presented for determining both the steady-state and transient temperature profiles. The effect of the optical and thermal properties of the surrounding normal tissue on the thermal field generated within the tumor is explored.

Body Temperature↗
PubMed1996

Spatially explicit models for the population dynamics of a species colonizing an island.

We construct reaction-diffusion models for the population dynamics of a species colonizing an island from a source population on a continent. We view the source population as inducing a density or flux of immigrants onto the island and interpret colonization as succeeding if the population on the island is predicted to persist even when immigration from the continent is stopped. To capture the observation that a sufficiently large population or density must be attained for colonization to succeed, we assume Allee (i.e., bistable) dynamics rather than logistic dynamics for the colonizing population. We consider the cases of colonization in both the absence and presence of a competitor. We use reaction-diffusion theory, especially comparison methods and sub- and supersolutions, to determine how parameters such as the distance from the continent to the island and the dispersal, birth and mortality rates, carrying capacity, and minimum viable population density of the colonizing species affect the outcome of the attempted colonization. In the case of colonization in the presence of a competitor we consider a number of scenarios involving different types and strengths of competition. Our analysis permits us to draw conclusions about the characteristics of a species that make it a good colonizer.

Animals↗
PubMed1983

Simulating allele frequencies in a population and the genetic differentiation of populations under mutation pressure.

A method is developed for simulating the allele frequencies in an equilibrium or transient population under the effects of neutral mutation and random drift. The method is based on diffusion theory and is fast so that it can be used to study in detail the distribution of heterozygosity or any quantity that can be expressed as a function of allele frequencies. It has been applied to study the distribution of heterozygosity and the distribution of the frequencies of the first three most frequent alleles in a population. It also has been applied to study the distribution of the number of alleles shared by two populations that were derived from a common stock.

Alleles↗
PubMed1990

Air quality in the vicinity of urban roads.

Motor vehicle emissions are a major source of CO, NOx and lead particulate concentrations to urban air quality. London urban Boroughs with high traffic densities are therefore a particular cause for concern. The air quality was monitored at an urban background site in the London Borough of Haringey for 2-years. The results of this study are assessed and their effect on human health is considered in the light of EC Directives and WHO guidelines. A desk top modelling technique based on Gaussian diffusion theory was used to predict the CO levels found at the background site. All predicted levels had a accuracy of better than 30%.

Air Pollution↗
PubMed1986

Photoplethysmographic evaluation of the relationship between skin reflectance and skin blood volume.

Although photoplethysmography can be used successfully to determine venous recovery time, it cannot be used in tests which rely on a determination of the blood volume change (e.g. maximum venous outflow). In seeking an explanation for this inadequacy it was shown that although the photoplethysmograph is able to indicate changes in reflectance, it is incapable of measuring reflectance, per se; information which is essential for an accurate calculation of venous volume decrease. A minor modification of the system enables relative reflectance measurements to be made. Measurements were performed under in vitro conditions to establish the skin-reflectance/skin-blood volume relationship; photon diffusion theory is then used to describe the skin-reflectance/skin-blood volume relationship and to determine the scattering and absorption coefficients of skin and whole blood.

Blood Volume↗
PubMed1988

Platelet deposition in a capillary perfusion model: quantitative and morphological aspects.

The capillary perfusion model according to Cazenave and co-workers was characterized by investigating the effects of protein precoating, perfusion time and shear rate on platelet deposition using 111Indium labelling of human platelets and scanning electron microscopy (SEM). Compared with uncoated polyethylene, platelet deposition was increased after precoating with purified human von Willebrand factor, fibrinogen or fibronectin, and decreased by preadsorbed immunoglobulin G, albumin or whole plasma. Platelet aggregates were observed on immunoglobulin G-coated polyethylene, whereas all other surfaces showed single adherent platelets. Complete platelet spreading was only observed after precoating with fibronectin. The quantitative data concerning platelet deposition were evaluated by using the convective-diffusion theory. Our results indicate the applicability of this perfusion model for the in vitro testing of biomaterials.

Adsorption↗
PubMed1993

The use of preventive health care services: carrier testing for the genetic disorder haemophilia.

A retrospective study was performed to explore carrier testing among women who were possible or obligate carriers of the haemophilia gene. Knowledge of the possibility of carrier testing and use of carrier testing were studied separately. In our exploration we were guided by the diffusion theory and the Health Belief Model. Logistic regression analysis showed that four factors were statistically significant related to knowledge of carrier testing: information via mass media, a haemophilic relative in the nuclear family rather than in the extended family, medical severity of haemophilia, and information from the patients' organization. For those women acquainted with carrier testing two of the four factors just mentioned were significantly related to the utilization of carrier testing i.e. having a haemophilic relative in the nuclear family and the medical severity of the haemophilia. In addition the following factors were associated: attitude towards abortion because of haemophilia, educational level, and marital status. Notwithstanding the prominent function of the mass media and the patients' organization, the respondents themselves stated that relatives, especially parents and sisters, were the most important source of information on genetic counselling and carrier testing.

Adolescent↗
PubMed1993

Fluorescence quenching by metal ions in lipid bilayers.

Fluorescence quenching of perylene by Co2+ and Ni2+ ions has been investigated both below and above the phase transition temperature in small unilamellar DPPC vesicles. Classic Förster type energy transfer was observed for perylene quenched by Co2+ ions below the phase transition when the effects of donor-donor energy transfer are taken into account. In the liquid crystalline phase a simple diffusion theory incorporating energy transfer was found to model the system well. For quenching by Ni2+ ions both above and below the phase transition temperature in lipid bilayers and in glycerol the data did not follow classic Förster type energy transfer but indicated that an additional quenching mechanism was present. A mechanism other than Förster behaviour was also observed for the quenching by Cr3+ ions in glycerol.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1996

On the relation between size of necrosis and diameter of tumor spheroids.

PURPOSE: In many previous experimental studies on multicellular tumor spheroids, the spheroid diameter at which central necrosis develops has been determined to be twice the thickness of the viable cell rim measured at a later stage of spheroid growth. This procedure tacitly assumes that there is a linear relation between the diameter of necrosis and that of the whole spheroid over the entire range of emergence and growth of necrosis. However, some experimental investigations have demonstrated that necroses do not grow gradually with spheroid diameter, but show a rapid initial increase, once a few cells have died. The present article offers an explanation for this phenomenon, which is derived from basic diffusion theory. METHODS AND MATERIALS: A theoretical relation between sizes of spheroids and of their central necroses is developed, which is based on the assumption that formation of necrosis is caused by depletion of substrates or accumulation of metabolic waste products. In a second part, the theoretical model is fitted to experimental data from the literature, and oxygen consumption rate as a function of spheroid size is determined. RESULTS: It turns out that the model closely mimics the experimentally observed behavior described above. These experimental results, therefore, do not furnish any evidence for assuming other hypotheses of necrosis formation. Resulting O2 consumption rates are well in the range of previously published data. In all cases, approximations to the measured data are better than the corresponding linear squares fits. CONCLUSION: At least in some tumor cell lines, depletion of substrates or accumulation of waste products can explain formation of necrosis without the assumption of any additional mechanisms. Moreover, the model presented in this article offers an alternative way of determining the turnover rate of a substrate or metabolic waste product provided that depletion/accumulation of this substance represents the cause for necrosis development.

Least-Squares Analysis↗
PubMed1996

In vivo absorption spectrum of disulphonated aluminium phthalocyanine in a murine tumour model.

The absorption spectrum of aluminum phthalocyanine with an average disulphonation of 2.1 (hereafter called disulphonated aluminum phthalocyanine, A1S2Pc) was measured in vivo in a murine tumour model by means of time-resolved reflectance. Mice bearing the L1210 leukaemia were administered 2.5 or 5 mg/kg body weight (b.w.) of A1S2Pc intraperitoneally. Reflectance measurements were performed in the 650-695 nm range before and 1, 4 and 7 h after the drug administration. Fitting of the data with the diffusion theory allowed us to assess the absorption coefficient in both conditions (i.e. before and after). As a difference between the latter and the former data, the in vivo absorption spectrum of A1S2Pc was evaluated. 1 h after the administration of 2.5 mg/kg b.w. A1S2Pc, the absorption peak was centred at 685 nm, red-shifted about 15 nm with respect to the spectrum in aqueous solution. For the lower dose, the absorption line shapes 4 and 7 h after the administration remained very similar. The red shift of the absorption spectrum is consistent with the therapeutic efficacy of the photodynamic therapy which was measured at 672, 685 and 695 nm, and proved to be maximum at 685 nm for both the L1210 leukaemia and the MS-2 fibrosarcoma. With the higher drug dose, the absorption spectra taken from different animals showed significant differences. In particular, in some mice the line shape was similar to that measured with 2.5 mg/kg b.w., while in other subjects it showed a broadening or a second peak at shorter wavelengths. Measurements on some animals were performed also 18 and 24 h after the injection of 5 mg/kg b.w., leading to no time evolution or to a progressive line shape narrowing.

Animals↗