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PubMed2000

Determination of analytical limits in solid sampling ETAAS: a new approach towards the characterization of analytical quality in rapid methods.

In the present study the lower analytical limits of solid sampling electrothermal atomization atomic absorption spectrometry (SS-ETAAS) were characterized by means of blank measurements and--for the first time--by means of the calibration curve method, where a calibration near the range of these limits (limit of decision, detection and quantification) was performed. The limit of decision as derived from blank measurements was calculated according to the 3sigma-criterion to be 0.003 and 0.019 ng for Cd and Pb, respectively. For Pb and Cd a roughly three-fold increase of these limits was observed when the calibration method according to DIN 32 645 was applied. When solid reference material was used, only a slight increase could be observed. The analytical limits were 2 to 20 times lower than reported for sample decomposition methods. The blank measurement and conventional calibration curve method, however, do not account for factors relating to solid sampling such as sample mass and matrix. Therefore, the calibration curve model was applied to data derived from comparisons between direct solid sampling ETAAS and a compound reference method (ETAAS following sample homogenization and digestion). The observed analytical limits were not found to be substantially increased if enough samples with low element contents were available for calibration. Coupling of the calibration curve model with the comparison of methods included real test samples and thus the relevant maximum sample mass and analyte content in the range of the lower analytical limits. As validation procedures frequently include comparisons of methods, the present approach might prove to be of some general interest for the characterization of analytical quality in rapid methods.

Animals↗
PubMed2005

Nutrient and temperature limitation of bacterioplankton growth in temperate lakes.

Limitation of bacterioplankton production by nutrients and temperature was investigated in eight temperate lakes in summer. Six of the lakes were resampled in autumn. The lakes differ in nutrient content, water color, and concentration of dissolved organic carbon. Nutrients (phosphorus, nitrogen, and organic carbon) were added alone and in all possible combinations to filtered lake water inoculated with bacteria from the lake. After incubation for 36-40 h at in situ temperatures (ranging from 7 to 20 degrees C), the response in bacterioplankton production was determined. The effect of increased temperature on bacterioplankton growth was also tested. Bacterioplankton production was often limited by phosphorus alone, organic carbon alone, or the two in combination. Phosphorus limitation of bacterioplankton production was more common in the summer, whereas limitation by organic carbon was more frequently observed in the autumn. There was a close balance between limitation by phosphorus and organic carbon in the epilimnion in the summer. In the hypolimnion in the summer, bacterioplankton growth was primarily phosphorus-limited. The effect of phosphorus additions decreased with increasing phosphorus concentrations in the lakes. However, there were no correlations between the effect of added organic carbon and water color, dissolved organic carbon concentration, or phosphorus concentration. When temperature was low (in the hypolimnion in the summer, and throughout the water column in the autumn) temperature also limited bacterioplankton production. Thus, temperature and inorganic nutrients or organic compounds can limit bacterioplankton growth both alone and simultaneously. However, at low temperatures, temperature is the most important factor influencing bacterioplankton growth.

Bacteria↗
PubMed2000

[Age limits from the legal perspective].

In this article age limits in law are discussed. Two things first: Legal commitments about old age are most commitments based on agreements which got manifest in legislation. Second, age limits hold for typifying certain facts of life, certain concerns of protection or other purposes. Therefore these age limits by law will be shown by the right of state (legal participation, citizenship and political participation, societal participation) and then according to various phases of life. Age limits generally exist in two phases during the life course: In the phase of childhood and youth, around the age of six to twenty-one (upbringing and education) and the phase of the transition from employment to retirement, around the age of sixty until seventy, at which age limits of monetary provisions for one's old age represent an important part. Furthermore, the legally achieved functions of age limits, like for example the limits of ability and protection, will be discussed. Finally, it will be shown, taking into account the comparison of legal aspects, if and how far age limits are of discriminate character.

Aged↗
PubMed2005

Are rates of functional limitations associated with access to care? A state-level analysis of the national survey of children with special health care needs.

OBJECTIVES: Health-related services and compensatory mechanisms have a potential role in minimizing functional limitations and increasing quality of life among children with special health care needs (CSHCN). We examined whether rates of functional limitations among CSHCN in the 50 states and District of Columbia were associated with state-level characteristics that reflect access to such services among CSHCN. METHODS: We aggregated child-level survey data from the National Survey of CSHCN to create 51 state-level estimates of the proportions who had functional limitations, had >/=1 unmet health needs, and lacked medical insurance coverage. State-level information about Medicaid spending per child enrollee in federal fiscal year 2000 was obtained from The Henry J. Kaiser Family Foundation website. We examined correlations between the percentages of CSHCN having functional limitations and each of the other state-level variables, and conducted multiple regression analyses that examined these associations while controlling for the statewide percentages of children living in poverty. RESULTS: The proportions of CSHCN with functional limitations were higher in states with higher rates of uninsured CSHCN (r = .49; p < .0001) and higher rates of CSHCN with unmet health needs (r = .62; p < .0001). Proportions of CSHCN with functional limitations were unrelated to per child Medicaid spending. These findings were robust when we controlled for percentages of children in poverty across states. CONCLUSIONS: Fewer unmet needs for health-related services are associated with lower statewide rates of functional limitations in CSHCN. As health care costs increase and state revenues decrease, CSHCN are at increasing risk of losing access to required services. Were this to happen we might expect an increase in the proportion of CSHCN who experience significant functional limitations. Thus, a key challenge is to provide CSHCN access to the amount and quality of health-related care they require to achieve their potential.

Child↗
PubMed1996

Exceeding the speed limit: an evaluation of the effectiveness of a police intervention.

Driving too fast is probably one of the main contributors to the occurrence and severity of road accidents, and intention to speed is an important predictor of exceeding speed limits. This study examined the effect of a police intervention on exceeding the posted speed limit (speed of vehicles on the target road) and on intentions to speed (attitude questionnaire). The intervention consisted of a week in which 'police speed check area' warning signs were put up on the target 40 mph limit road, followed by a week of active police presence, followed by a further week in which the signs remained. The speed of vehicles was measured using police data collection equipment for a total of 7 weeks. The effect on the intentions of drivers using the road to exceed speed limits was assessed across age, sex and pre-intervention speeding behaviour using questionnaire measures. Fewer people broke the speed limit during the intervention than before, this effect lasting to a limited extent up to 9 weeks after police activity ceased and 8 weeks after signs were removed. The effect on drivers breaking the speed limit by large amounts was more transient. The intervention reduced intention to speed for subject groupings with high pre-intervention intention. Traffic flow contributed significantly to the variance in vehicle speed, but was not responsible for differences between the weeks, which may therefore be attributed to the intervention. Traffic flow also did not account for differences in speed between the two directions of traffic, which may therefore be attributed to the fact that the road areas preceding the target area in each direction differed in their speed limits (70 vs 30 mph). Intentions to speed, as well as speed adaptation difficulties are though to contribute to these differences.

Adult↗
PubMed1986

Prevalence of activity limiting chronic conditions among children based on household interviews.

According to data from the National Health Interview Survey (NHIS) over two million children under 17 years (3.8%) are afflicted by chronic conditions that cause some limitation of activity. The limitations range from complete inability to attend school for school age children or inability to engage in play for preschoolers to limited ability to engage in athletics or other social activities. Analysis of micro data from the NHIS reveals that the leading causes of activity limitation include: respiratory diseases; speech, special sense and intelligence related impairments; and mental and nervous system disorders. Together these conditions account for 50% of all childhood activity limitations. Despite their small numbers, children with activity limitations are reported by the NHIS to consume a disproportionate share of health care resources, including over twice as many physician services and over seven times as many hospital services as other children. Household interviews appear to be a useful vehicle for assessing prevalence of activity limitations but researchers and others should be cautioned about the subjective nature of the activity limitation concept.

Activities of Daily Living↗
PubMed1995

Secondary nitrogen limitation in a subtropical lake impacted by non-point source agricultural pollution.

A 20-year history of nutrient limitation was quantified for Lake Okeechobee, a nutrient-impacted lake in Florida, USA. Limiting status (nitrogen versus phosphorus) was estimated from deviations between trophic state index (TSI) parameters, calculated from routine monitoring data. The lake is presently nitrogen-limited. However, historical trends in the TSI deviations indicate that contemporary nitrogen limitation is a secondary, unnatural condition that has arisen due to excessive phosphorus loading. Prior to 1980, there was evidence of lake-wide limitation by phosphorus, rather than nitrogen. The finding of secondary nitrogen limitation in Lake Okeechobee has important management implications. Phosphorus loads are presently being reduced in order to reduce in-lake concentrations and create phosphorus-limited conditions (nitrogen limitation is undersirable because it has favored bloom-forming cyanobacteria). The present results indicate that this long-term management goal is ecologically sound; it is consistent with the concept of restoration of the lake.

Journal Article↗
PubMed2005

Evaluation of variable speed limits for real-time freeway safety improvement.

Use of various variable speed limit (VSL) strategies as a tool for safety improvement on freeways was evaluated using simulation of a section of Interstate 4 in Orlando, FL. Real-time crash likelihood was calculated based on models developed in previous research by the first author [Abdel-Aty, M., Uddin, N., Pande, A., January 2005. Split models for predicting multi-vehicle crashes during high-speed and low-speed operating conditions on freeways. In: Presented at the 84th Annual Meeting of the Transportation Research Board, Washington, DC]. VSL implementation produced safety improvement by simultaneously implementing lower speed limits upstream and higher speed limits downstream of the location where crash likelihood is observed in real-time. This improvement was realized in the case of medium-to-high-speed regimes on the freeway, but no benefit was achieved in low-speed situations (no substantial safety benefit from implementing VSL in congested situation's simulation). The final recommendations for implementing VSL are: gradually introducing speed limit changes over time (5 mph every 10 min); abruptly changing speed limit in space ( no gap distance); reducing speed limits upstream and increasing speed limits downstream of location of interest; the speed limit changes up- and downstream should be large in magnitude (15 mph) and implemented within short distances (2 miles) of the location of interest. In addition to the safety benefit, this final strategy also produced travel time savings.

Accidents, Traffic↗
PubMed2006

Activity limitations in the lower extremities in patients with osteoarthritis: the modifying effects of illness perceptions and mental health.

OBJECTIVES: Using the International Classification of Functioning, Disability and Health as framework, we evaluated modifying effects of illness perceptions and mental health on the association between impairments in body structures and functions due to osteoarthritis (OA) and limitation in activities in the lower extremities. METHODS: Self-reported limitation in activities was assessed by the Western Ontario and McMaster Universities OA index (WOMAC) function subscale in 316 patients with knee or hip pain or evidence of OA on knee or hip radiographs. Body structures and functions were evaluated during clinical and radiological assessments. Illness perceptions and mental health were assessed with the revised Illness Perception Questionnaire (IPQ-R) and the mental component summary score of the RAND 36-item Health Survey, respectively. For each patient an expected WOMAC function score was calculated, using an equation based on a multivariate model of the association of body structures and functions with limitation in activities. RESULTS: The median (interquartile) self-reported WOMAC function score was 22.2 (9.6-43.5). Ninety-one patients reported more and 120 patients reported less limitation in activities than expected. Patients with lumbar spine degeneration, physical or exercise therapy and high IPQ-R identity, consequences and chronic timeline scores had an increased risk to report more limitation in activities than the expected range. Low IPQ-R identity, consequences and emotional representation scores and better mental health were associated with reporting less limitation in activities than the expected range. CONCLUSION: Illness perceptions and mental health modify the association between self-reported limitation in activities and calculated limitation in activities based on impairments in body structures and functions due to OA.

Adult↗
PubMed2005

A method to determine which nutrient is limiting for plant growth in estuarine waters--at any salinity.

A method, utilising overlaid graphs for nutrients vs salinity, was developed in order to determine which nutrient is limiting for plant growth in estuarine waters-at any salinity. Dissolved inorganic nitrogen (DIN=NO(3)(-)+NO(2)(-)+NH(4)(+)) and o-phosphate (PO(4)(-)) are the main forms of N and P that are readily bio-available for plant growth in waters and these have a Redfield atomic ratio of N:P=16:1 (i.e. aquatic plants absorb N and P in the average ratio of 16 atoms of N to 1 atom of P). Graphs are prepared for (i) DIN vs salinity and (ii) o-phosphate vs salinity with the vertical scales for DIN and o-phosphate set at a ratio of N:P=16:1; when these graphs are overlaid on each other then the lowermost trendline denotes the limiting nutrient for plant/algal growth-at any salinity. The graphs also indicate the extent by which one or other of the nutrients is limiting--at any salinity. Furthermore, if there is a transition from P to N limitation somewhere along the salinity gradient, then this occurs at the salinity where the trendlines intersect. The concept was applied to three estuaries in the southeast of Ireland and the results show that, in all of these circumstances, P is the limiting nutrient throughout--except for the higher salinities (i.e. salinities 30 per thousand), where either (i) N and P may become equally limiting at salinity approximately 35 per thousand or (ii) N may become limiting at salinity 30 per thousand. Overlaid nutrients vs salinity graphs were also used to demonstrate that, in the estuaries in southeast Ireland, carbon (as dissolved inorganic carbon, DIC=CO(2)+H(2)CO(3)+HCO(3)(-)+CO(3)(2-)) is not the limiting nutrient--at any salinity.

Carbon↗
PubMed2006

Deficient alpha-1-antitrypsin phenotypes and persistent airflow limitation in severe asthma.

BACKGROUND: Persistent airflow limitation is common among patients with severe asthma, but its pathogenesis has not been fully clarified. Severe alpha-1-antitrypsin (AAT) deficiency is a risk factor of chronic airflow limitation and emphysema, and partially deficient phenotypes have been associated with an accelerated decline in lung function. We hypothesized that partial deficiency of AAT (non-PiM AAT phenotype) is a risk factor of persistent airflow limitation in asthma. METHODS: In 122 patients with severe asthma (86 females; age (median (range)): 44.0 yr (18-75)) postbronchodilator FEV1 and FEV1/VC were measured and the AAT phenotype was determined. Persistent airflow limitation was defined as postbronchodilator FEV1 or FEV1/VC < 75% pred. with TLC > 75% pred. RESULTS: Six patients (4.9%) had a non-PiM phenotype (1 MF, 3 MS, 1 MZ and 1 SZ). Of the 58 patients with persistent airflow limitation only 1 patient (1.7%) had a non-PiM phenotype vs. 7.8% among the patients without persistent airflow limitation (P = 0.21). Postbronchodilator FEV1/VC (% pred.) was higher in the non-PiM patients than in the PiM patients (P = 0.02), the other lung function parameters were not different. Linear regression analysis showed no association between AAT phenotype and FEV1% predicted (P = 0.26). CONCLUSIONS: AAT heterozygoty does not seem to be an important risk factor of persistent airflow limitation in patients with asthma. Although confirmation by longitudinal follow-up studies with larger sample sizes is needed, these results suggest that routine assessment of the AAT phenotype is not indicated in asthmatic patients even if they exhibit fixed airflow limitation.

Adolescent↗
PubMed1992

The growth of mammals following a period of nutritional limitation.

A theory of predicting the growth of an animal following a period of nutritional limitation is proposed here. The theory consists of the following three propositions. Proposition 1: there is a scale of size, such that the growth rate following a period of nutritional limitation is that of normal animals at the same size. Proposition 2: any abnormalities in body composition at the end of the period of limitation will be corrected over time. Proposition 3: the rates at which abnormalities in body composition at the end of the period of limiting conditions are corrected, are always set by the conditions of rehabilitation. The propositions are connected with three other problems viz normal growth, growth under some limitation and the conditions needed by an animal to perform at its potential. These problems are dealt here by: (i) using a simple description of normal growth, (ii) considering the limitation by its effects rather by attempting to predict the effects of a given limitation, and (iii) using simple assumptions about protein and energy scales and requirements. The predictions of the theory are compared with experimental data, and a good qualitative agreement is found. Important conclusions from the theory are: (a) that it is essential to measure as fully as may be the state of the animal at the end of the period of limitation and to compare it with the state of normal animals and (b) that careful attention needs to be given to the choice and the description of the treatment, or preferably treatments, during the rehabilitation period.

Animals↗
PubMed1998

Extent of expiratory flow limitation influences the increase in maximal exercise ventilation in hypoxia.

Increasing ventilation (VE) during hypoxic exercise may help to defend arterial O2 saturation (SaO2) and VO2max however, many athletes experience limitations to ventilatory flow and are not able to increase VE at high workrates. Five of 19 highly trained endurance athletes screened had < 5% of their tidal flow volume loop during maximal exercise meet the boundary set by their maximal resting flow volume loop. These five athletes were grouped as non-flow limited and compared to the five athletes who demonstrated the greatest percent of tidal volume flow limitation (56 +/- 11%) during maximal exercise (flow limited). Each athlete completed two incremental treadmill tests to exhaustion: normoxia and hypoxia (FI(O2) = 0.187). Non-flow limited athletes increased VE at VO2max from normoxia to hypoxia (140.9 +/- 13.4 vs. 154.7 +/- 11.9 L/min, P < 0.05), while flow limited athletes did not (159.5 +/- 9.4 vs. 162.3 +/- 6.0 L/min). The decline in SaO2 at VO2max from normoxia to hypoxia was not significantly different between groups. We conclude that athletes with little or no expiratory flow limitation are able to increase VE during maximal exercise in mild hypoxia, compared to athletes with significantly higher degrees of mechanical limitation. However this 'mechanical ventilatory reserve' does not appear to influence the ability to defend SaO2 or VO2max during maximal exercise in mild hypoxia.

Adult↗
PubMed1997

Functional stability limits while holding loads in various positions.

Stability of the body during manual material handling is an important issue in the prevention of falls and over-exertion injuries. This research investigated stability limits while standing and holding loads in different positions relative to the body. Theoretically, the stability region is the full base of support defined by the perimeter of the foot contact area. However, the functional stability region may be smaller. The purpose of this study was to locate functional stability limits with respect to the base of support. Fifteen male subjects leaned as far as possible in four directions in the sagittal and frontal planes. Their center of gravity location at these extremes determined the stability limit. The results showed that functional stability limits reached only about 60% of the distance to the maximum base of support limits under the conditions of this study. The sway angles reached at the stability limits averaged 9.2 degrees anteroposteriorly and 15.3 degrees laterally. External load positions which lowered the center of gravity of the body-and-load system extended those stability limits. This study provides a postural stability perspective of load-holding which may be applied in establishing safe lifting and reach limits.

Accident Prevention↗
PubMed2003

Comparison of detectability limits for elemental mapping by EF-TEM and STEM-XEDS.

The analytical sensitivity in terms of the signal-to-noise ratio (SNR) was investigated for elemental mapping by a transmission electron microscope equipped with an energy filter (EF-TEM) and a scanning transmission electron microscope with an X-ray energy dispersive spectrometer (STEM-XEDS). To compare the detectability limits of the elemental maps by the two techniques, homogeneous Cu-0.98+/-0.34 wt% Mn and Cu-4.93+/-0.49 wt% Mn thin specimens were used. Elemental maps can be considered as either an image or a spectrum. Therefore, the detectability limits of the elemental maps were characterized by the spectral SNR. To evaluate the detectability limits of the elemental maps with statistical confidence limits such as 1 sigma, 2 sigma and 3 sigma, the SNR values were reviewed from the statistical point of view. In STEM-XEDS mapping, the spectral SNR values improve as the specimen thickness increases since the signal intensity increases. Conversely, the spectral SNR in EF-TEM mapping is maximized at a certain thickness and then reduces as the thickness increases. To compare the two mapping techniques with regard to the analytical sensitivity, a method to estimate the minimum mass fraction (MMF) from measured signal and background intensities was developed. In this experimental approach, the MMF value can be evaluated by selecting the appropriate SNR value corresponding to the statistical confidence limits. In comparing the estimated MMF values from the two mapping approaches, EF-TEM mapping can be more sensitive than STEM-XEDS mapping up to specimen thicknesses <20-30 nm in the 1 sigma confidence limit and < approximately 50 nm in the 3 sigma limits. However, as the specimen thickness increases, the XEDS maps provide better detectability limits in the Cu-Mn dilute alloy specimens.

Journal Article↗
PubMed2001

Effect of lipophilic ion-exchanger leaching on the detection limit of carrier-based ion-selective electrodes.

The equilibrium partitioning of lipophilic ion-exchanger salts from ion-selective polymeric membrane electrodes (ISEs) and its possible effect on the lower detection limit of these sensors is described. Predictions are made on the basis of various parameters, including the knowledge of tetraphenylborate potassium salt partitioning constants, the selectivity of ionophore-free ion-exchanger membranes, and ionophore stability constants in the membrane. Ion-exchanger lipophilicities are significantly increased if the membrane contains an ionophore that strongly binds the primary ion. Predicted detection limits are on the order of 10(-5)-10(-8) M for ionophore-free membranes, and may reach levels as low as 10(-18) M with adequate ionophores in the membrane. Experiments are performed for well-described lead-selective membranes containing different tetraphenylborate derivatives, and detection limits appear to be independent of the ion-exchanger used. However, they are much higher if a more hydrophilic carborane cation-exchanger is incorporated in the membrane. The first finding confirms recent theory, which states that transmembrane ion fluxes, given by a small level of ion-exchange at the sample side by interfering ions, normally dictate the detection limit of these sensing systems. Predicted detection limits on the basis of ion-exchanger leaching alone are here listed for a number of analytically relevant cases. For potassium-selective electrodes containing BME-44 and tetraphenylborate as ion-exchanger, the experimental detection limits are in agreement with predicted values. These results suggest that the detection limit of many current ISEs for ultratrace level analysis are, in optimal cases, dictated by transmembrane ion fluxes; however, because improved chemical solutions are being developed to reduce such effects, simple ion-exchanger partitioning may indeed become an important mechanism that can give higher detection limits than practically desired, and should not be ruled out.

Biosensing Techniques↗
PubMedDate not supplied

Salt accumulation resulting from base added for pH control, and not ethanol, limits growth of Thermoanaerobacteriumthermosaccharolyticum HG-8 at elevated feed xylose concentrations in continuous culture.

Thermoanaerobacter thermosaccharolyticum HG-8 was grown in continuous culture to characterize growth limitation at high feed substrate and product concentrations. Continuous fermentation of 50 and 73 g/L xylose at a dilution rate based on the feed flow, D(f), of 0.053 h(-)(1) and with the pH controlled at 7.0 by addition of KOH resulted in steady state utilization of >99% of the xylose fed and production of ethanol and acetic acid at a mass ratio of about 2:1. Continuous cultures of T. thermosaccharolyticum growing at D(f) = 0.053 h(-)(1) achieved complete utilization of 75 g/L xylose in the presence of 19.1 g/L K(+) (0.49 M) and an ethanol concentration of 22.4 g/L ethanol. When the feed to a culture initially at steady state with a 75 g/L xylose feed and D(f) = 0.053 h(-)(1) was increased to 87.5 g/L xylose, limitation of growth and xylose utilization was observed. This limitation was not relieved by repeating this feed upshift experiment in the presence of increased nutrient levels and was not reproduced by addition of ethanol to a steady-state culture fed with 75 g/L xylose. By contrast, addition of KCl to a steady-state culture fed with 75 g/L xylose reproduced the K(+) concentration, limitation of growth and xylose utilization, and product concentration profiles observed in the feed upshift experiment. The maximum concentration at which growth of batch cultures was observed was 0.43 M for KCl, NaCl, and equimolar mixtures of these salts, suggesting that the observed limitation is not ion-specific. These data support the interpretation that inhibition salt accumulation resulting from addition of KOH for pH control is the limiting factor manifested in the feed upshift experiment and that both nutrient limitation and ethanol inhibition played little or no role as limiting factors. More generally, salt inhibition would appear to be a possible explanation for the discrepancy between the tolerance to added ethanol and the maximum concentration of produced ethanol reported in the literature for fermentation studies involving thermophilic bacteria.

Bacteria, Anaerobic↗
PubMed2006

Optical limiting of gold nanoparticle aggregates induced by electrolytes.

The electronic absorption spectra and optical-limiting (OL) properties of gold nanoparticle (AuNP) aggregates induced by KCl and NaCl have been investigated using 4.1-ns laser pulses at 532 nm. Although the individual AuNP colloid shows no optical-limiting effect, the AuNP aggregates exhibit significant optical-limiting characteristics. With an increased concentration of KCl and NaCl, the surface plasmon resonance (SPR) band shifts to a longer wavelength, and the optical-limiting performance is enhanced. Both the electronic absorption and optical limiting are influenced by the particle size. The larger the individual nanoparticle, the further red-shifted the SPR band and the stronger the optical limiting. Optical limiting of aggregates induced by KCl is stronger than that of aggregates induced by NaCl. Mechanistic studies reveal that free-carrier absorption is the dominant contributor to the optical limiting, with negligible contribution from nonlinear scattering.

Journal Article↗