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Reference Level (reference + level)

Distribution by Scientific Domains

Medical Sciences	50%
Life Sciences	33%
Earth and Environmental Science	11%

Selected Abstracts

Using regional exposure criteria and upstream reference data to characterize spatial and temporal exposures to chemical contaminants,

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2000
Susan M. Cormier
Abstract Analyses of biomarkers in fish were used to evaluate exposures among locations and across time. Two types of references were used for comparison, an upstream reference sample remote from known point sources and regional exposure criteria derived from a baseline of fish from reference sites throughout Ohio, USA. Liver, bile, and blood were sampled from white suckers (Catostomus commersoni) and common carp (Cyprinus carpio) collected during 1993 and 1996 in the Ottawa River near Lima, Ohio. Levels of exposure were measured for petroleum by naphthalene-type metabolites, combustion by-products by benzo[a]pyrene-type metabolites, coplanar organic compounds by ethoxyresorufin- O -deethylase (EROD) activity, and urea by blood urea nitrogen (BUN) levels. The four biomarkers analyzed proved effective in determining differences between reference and polluted sampling sites, between geographically close (<0.5 km) sites, and between sampling years at sites common in both years. Calculated exposure criteria levels of the polycyclic aromatic hydrocarbon bile metabolites were found to be a conservative approximation of levels from a designated reference site and could thereby permit comparison of biomarker levels of fish from the Ottawa River to a regional reference level. Polycyclic aromatic hydrocarbon bile metabolite and EROD activity levels were more reflective of spatial patterns of contamination than BUN, although all biomarkers indicated differences overtime. Biomarkers from white suckers seemed to be more responsive in detecting changes in contaminant levels than the same biomarkers from common carp. Lower levels in 1996 of all biomarkers at many sites suggested lower exposures than in 1993 and could be indicative of some improvement over the period. [source]

Contribution of gravitational potential energy differences to the global stress field

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009
Attreyee Ghosh
SUMMARY Modelling the lithospheric stress field has proved to be an efficient means of determining the role of lithospheric versus sublithospheric buoyancies and also of constraining the driving forces behind plate tectonics. Both these sources of buoyancies are important in generating the lithospheric stress field. However, these sources and the contribution that they make are dependent on a number of variables, such as the role of lateral strength variation in the lithosphere, the reference level for computing the gravitational potential energy per unit area (GPE) of the lithosphere, and even the definition of deviatoric stress. For the mantle contribution, much depends on the mantle convection model, including the role of lateral and radial viscosity variations, the spatial distribution of density buoyancies, and the resolution of the convection model. GPE differences are influenced by both lithosphere density buoyancies and by radial basal tractions that produce dynamic topography. The global lithospheric stress field can thus be divided into (1) stresses associated with GPE differences (including the contribution from radial basal tractions) and (2) stresses associated with the contribution of horizontal basal tractions. In this paper, we investigate only the contribution of GPE differences, both with and without the inferred contribution of radial basal tractions. We use the Crust 2.0 model to compute GPE values and show that these GPE differences are not sufficient alone to match all the directions and relative magnitudes of principal strain rate axes, as inferred from the comparison of our depth integrated deviatoric stress tensor field with the velocity gradient tensor field within the Earth's plate boundary zones. We argue that GPE differences calibrate the absolute magnitudes of depth integrated deviatoric stresses within the lithosphere; shortcomings of this contribution in matching the stress indicators within the plate boundary zones can be corrected by considering the contribution from horizontal tractions associated with density buoyancy driven mantle convection. Deviatoric stress magnitudes arising from GPE differences are in the range of 1,4 TN m,1, a part of which is contributed by dynamic topography. The EGM96 geoid data set is also used as a rough proxy for GPE values in the lithosphere. However, GPE differences from the geoid fail to yield depth integrated deviatoric stresses that can provide a good match to the deformation indicators. GPE values inferred from the geoid have significant shortcomings when used on a global scale due to the role of dynamically support of topography. Another important factor in estimating the depth integrated deviatoric stresses is the use of the correct level of reference in calculating GPE. We also elucidate the importance of understanding the reference pressure for calculating deviatoric stress and show that overestimates of deviatoric stress may result from either simplified 2-D approximations of the thin sheet equations or the assumption that the mean stress is equal to the vertical stress. [source]

CRS-stack-based seismic imaging considering top-surface topography

GEOPHYSICAL PROSPECTING, Issue 6 2006
Z. Heilmann
ABSTRACT In this case study we consider the seismic processing of a challenging land data set from the Arabian Peninsula. It suffers from rough top-surface topography, a strongly varying weathering layer, and complex near-surface geology. We aim at establishing a new seismic imaging workflow, well-suited to these specific problems of land data processing. This workflow is based on the common-reflection-surface stack for topography, a generalized high-density velocity analysis and stacking process. It is applied in a non-interactive manner and provides an entire set of physically interpretable stacking parameters that include and complement the conventional stacking velocity. The implementation introduced combines two different approaches to topography handling to minimize the computational effort: after initial values of the stacking parameters are determined for a smoothly curved floating datum using conventional elevation statics, the final stack and also the related residual static correction are applied to the original prestack data, considering the true source and receiver elevations without the assumption of nearly vertical rays. Finally, we extrapolate all results to a chosen planar reference level using the stacking parameters. This redatuming procedure removes the influence of the rough measurement surface and provides standardized input for interpretation, tomographic velocity model determination, and post-stack depth migration. The methodology of the residual static correction employed and the details of its application to this data example are discussed in a separate paper in this issue. In view of the complex near-surface conditions, the imaging workflow that is conducted, i.e. stack , residual static correction , redatuming , tomographic inversion , prestack and post-stack depth migration, leads to a significant improvement in resolution, signal-to-noise ratio and reflector continuity. [source]

Influence of antibiotic therapy on serum levels of reactive oxygen species in ovariectomized bitches

JOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 1 2008
M. MUTINATI
This study was conducted on 60 ovariectomized bitches. The objectives were to measure the mean reactive oxygen species (ROS) concentrations before, during and after surgery, and to investigate the effect of the administration of five different antibiotic treatments: amoxicillin, benzylpenicillin/dihydrostreptomycin, sulfametazine/sulfamerazine/sulfathiazole, enrofloxacin, lincomycin/spectinomycin. The first value recorded represented the mean ROS concentration in anestral bitches and constitutes a reference level with which to compare the subsequent measurements. After premedication, induction of anesthesia and during maintenance and surgery, ROS serum concentrations showed constant values until the end of surgery. After surgery and during antibiotic administration, an increase in ROS concentration occurred, which differed among the five groups in relation to the antibiotics employed. The lowest increases occurred in the groups treated with the combination of lincomycin/spectinomycin, and with amoxicillin; whereas the highest increases were detected in the group treated with enrofloxacin. The three other antibiotics showed an intermediate level of influence on oxidative status. [source]

A case of generalized argyria after ingestion of colloidal silver solution

AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 3 2009
Yangho Kim
Abstract A 58-year-old woman was referred to our hospital due to progressive skin darkening, which began 5 months previously. The patient had strikingly diffuse blue-gray discoloration of the skin, most prominent in sun-exposed areas, especially her face and hands. The oral mucosa, tongue, gums, eye conjunctiva, ears, nail beds, and trunk were also involved. Bluish-gray discoloration of all nails was aggravated by cold weather. She had ingested 1 L of colloidal silver solution daily for approximately 16 months as a traditional remedy. Her serum silver concentration was 381 ng/ml which was a very high (reference level: <15 ng/ml). Light microscopic examination of a punch biopsy specimen from her nose revealed fine, minute, round, and brown-black granules deposited in the basement membrane of hair follicular epithelium. Scanning electron microscopic examination showed electron-dense granules deposited in the intercellular space of sweat glands. Energy disperse X-ray spectrometry analysis demonstrated peaks for silver and sulfur in the dense black deposits. The ingestion of colloidal silver appears to be an increasing practice among patients using alternative health practices. All silver-containing products including colloidal silver should be labeled with a clear warning to prevent argyria, especially in alternative health practices. Am. J. Ind. Med. 52:246,250, 2009. © 2008 Wiley-Liss, Inc. [source]

Development of an Algorithm to Regulate Pump Output for a Closed Air-Loop Type Pneumatic Biventricular Assist Device

ARTIFICIAL ORGANS, Issue 12 2009
Kyoung Won Nam
Abstract The closed air space-type of extracorporeal pneumatic ventricular assist device (VAD) developed by the Korea Artificial Organ Center utilizes a bellows-transforming mechanism to generate the air pressure required to pump blood. This operating mechanism can reduce the size and weight of the driving unit; however, the output of the blood pump can be affected by the pressure loading conditions of the blood sac. Therefore, to guarantee a proper pump output level, regardless of the pressure loading conditions that vary over time, automatic pump output regulation of the blood pump is required. We describe herein a pump output regulation algorithm that was developed to maintain pump output around a reference level against various afterload pressures, and verified the pump performance in vitro. Based on actual operating conditions in animal experiments, the pumping rate was limited to 40,84 beats per minute, and the afterload pressure was limited to 80,150 mm Hg. The tested reference pump output was 4.0 L/min. During experiments, the pump output was successfully and automatically regulated within the preset area regardless of the varying afterload conditions. The results of this preliminary experiment can be used as the basis for an automatic control algorithm that can enhance the stability and reliability of the applied VAD. [source]

Development of a higher power intermediate-frequency magnetic field exposure system for in vitro studies

BIOELECTROMAGNETICS, Issue 2 2010
Atsushi Fujita
Abstract In a previous article we developed an in vitro 23,kHz magnetic field (MF) exposure system that generated an MF of 532,µTrms. Using this system, the biological effects of 23,kHz MFs on cell functions have been reported. To further clarify the biological effect of intermediate-frequency (IF) MFs and investigate the dose,response relationship in cell lines, an exposure system that generates stronger MFs is required. To meet this requirement, we developed a 6.25,mTrms MF exposure system for in vitro study. This level is 1000 times the reference level for the general public in the ICNIRP guidelines. This system provides an MF of 6.25,mTrms at 23,kHz with a uniformity within ±5%. To verify that in vitro experimental conditions are maintained, we examined the temperature, environmental MF, and MF leakage for a sham exposure system. In addition, we examined the harmonics, coil shape, and heat generated in the medium by the high-strength MF. As a result, it was confirmed that this system can be used to evaluate the biological effects of IF MFs. This article presents the design and successful construction of the in vitro exposure system. Bioelectromagnetics 31:156,163, 2010. © 2009 Wiley-Liss, Inc. [source]

The association between socioeconomic status and exposure to mobile telecommunication networks in children and adolescents

BIOELECTROMAGNETICS, Issue 1 2010
Silke Thomas
Abstract A potential association between socioeconomic status (SES) and self-reported use of mobile phones has been investigated in a few studies. If measured exposure to mobile phone networks differs by SES in children, it has not yet been studied. Interview data of 1,481 children and 1,505 adolescents on participants' mobile phone use, socio-demographic characteristics and potential confounders were taken from the German MobilEe-study. Sociodemographic data was used to stratify participants into three "status groups" (low, middle, high). Using a personal dosimeter, we obtained an exposure profile over 24,h for each of the participants. Exposure levels during waking hours were expressed as mean percentage of the reference level. Children with a low SES were more likely to own a mobile phone (OR 2.1; 95% CI: 1.1,3.9) and also reported to use their mobile phone longer per day (OR 2.4; 95% CI: 1.1,5.4) than children with a high SES. For adolescents, self-reported duration of mobile phone use per day was also higher with a low SES (OR: 3.4; 95% CI: 1.4,8.4) compared with a high SES. No association between SES and measured exposure to mobile telecommunication networks was seen for children or adolescents. Mobile phone use may differ between status groups with higher use among disadvantaged groups. However, this does not result in higher overall exposure to mobile telecommunication networks. Whether short duration of own mobile phone use or the small numbers of participants with a low SES are causal, have to be investigated in further studies. Bioelectromagnetics 31:20,27, 2010. © 2009 Wiley-Liss, Inc. [source]

Proliferation and apoptosis in a neuroblastoma cell line exposed to 900 MHz modulated radiofrequency field

BIOELECTROMAGNETICS, Issue 3 2006
P. Merola
Abstract The aim of this study was to examine whether a modulated radiofrequency of the type used in cellular phone communications at a specific absorption rate (SAR) higher than International Commission on Non-ionizing Radiation Protection (ICNIRP) reference level for occupational exposure, could elicit alterations on proliferation, differentiation, and apoptosis processes in a neuroblastoma cell line. The cell line was exposed for 24, 48, and 72 h to 900 MHz radiofrequency and proliferation and differentiation were tested by WST-I assay and by a molecular analysis of specific markers, two oncogenes and a cytoskeleton protein, in exponential growth phase and in synchronized cell cultures. Apoptosis was evaluated by caspase activation analysis and by molecular detection of Poly (ADP-ribose) polimerase (PARP) cleavage. Combined exposures to radiofrequency and to the differentiative agent retinoic acid or to the apoptotic inducer camptothecin were carried out to test possible interference between electromagnetic field and chemical agents. Overall our data suggest that 900 MHz radiofrequency exposure up to 72 h does not induce significant alterations in the three principal cell activities in a neuroblastoma cell line. Bioelectromagnetics 27:164,171, 2006. © 2006 Wiley-Liss, Inc. [source]

Temporal trends and misclassification in residential 60 Hz magnetic field measurements

BIOELECTROMAGNETICS, Issue 3 2002
Robert S. Banks
Abstract This research addressed the question of how well measurement data collected during a single visit, made at an arbitrary hour of day, day of week, and season, estimate longer term residential 60 Hz magnetic field levels. We made repeat spot and 24 h measurements in 51 children's home, located in the Detroit, MI, and the Minneapolis-St. Paul, MN metropolitan areas, on a regular bimonthly schedule over a 1 year period, as well as a single 2 week measurement, for total of eight visits, producing 21 days of data for each residence. We defined the long term estimate (LTE) as the geometric mean of all available 24 h geometric means from the first six bimonthly visits. The LTE served as the reference level for assessing seasonal, day of week, and diurnal effects, as well as the potential for misclassification. We found a small, but statistically significant (P,<,.05), seasonal effect, with levels approximately 3% lower than the LTE in the spring and about 4% greater during the summer. No effect was found for day of week. However, we did find a systematic and appreciable diurnal effect, suggesting that, for example, an evening spot measurement may overestimate the LTE by 20% or more. We also assessed how well the 24 h measurement from the last visit, which was not used in calculation of the LTE, estimated the LTE. We found a high degree of correlation (r,=,.92) and fair to good agreement using four exposure categories (,,=,.53). Thus, the 24 h measurement appears to be a satisfactory LTE estimator. However, this finding must be interpreted with caution since considerable unexplained variability was present among the repeat 24 h measurements in about one-third of the homes. While the 2 week measurement does somewhat decrease exposure misclassification, its added intrusiveness and cost are likely to outweigh the improved precision. Bioelectromagnetics 23:196,205, 2002. © 2002 Wiley-Liss, Inc. [source]

Indoloquinolizidine Derivatives as Novel and Potent Apoptosis Inducers and Cell-Cycle Blockers

CHEMBIOCHEM, Issue 3 2008
Frank Wehner Prof.
Abstract A collection of approximately 11,000 natural-product derived and inspired compounds was screened for potential apoptosis inducers in the human tumour cell lines HepG2 (liver), HeLa (cervix) and MCF-7 (breast) by means of MTT and ATP-luminescence assays, automated cell counting, caspase 3/7 assay as well as by fluorescence activated cell sorting (FACS) analysis. A group of seven indoloquinolizidine derivatives was identified that exhibited IC50 values for cell proliferation as low as 2 ,mol,L,1, with no major necrosis of cells detectable. At the same time, an increase in the rate of apoptosis of up to 600,% relative to the reference level was observed. FACS analysis indicated that these effects are related to an arrest of cells in the G2M phase of the cell cycle. [source]

Optic disc biomorphometry with the Heidelberg Retina Tomograph at different reference levels

ACTA OPHTHALMOLOGICA, Issue 1 2002
Kyösti Vihanninjoki
ABSTRACT. Purpose: The Heidelberg Retina Tomograph (HRT) is a confocal scanning laser tomograph that produces high resolution optical section images of the optic disc and central retina. Measurement accuracy and reproducibility is good. Several of the stereometric variables depend on the definition of a reference plane level. The purpose of the present study was to evaluate the four different reference levels in terms of their advantages and disadvantages in clinical work. Methods: Sixty-seven randomly chosen eyes belonging to 67 subjects were included in this study. Forty of the eyes were healthy and 27 had glaucoma. The HRT with software versions 1.09 and 1.11 was used to acquire and evaluate topographic measurements of the optic disc. Image analysis was performed at four different reference levels: 320 µm fixed offset reference level (REFd) (version 1.09), an individually determined reference level (REFi), a papillo-macular reference level (REFm) and a flexible reference level (REFf) (version 1.11). ANOVA was used to determine differences in the topographic parameters between the reference levels. Results: In terms of the healthy eyes, all the variables using different reference levels give rather similar results. However, with advanced glaucoma the measurement values provided with REFd are clearly different to those of the other reference levels. The measurement values using REFm and REFf provide fairly similar results in all clinical groups. REFf indicates the lowest point in the segment between 350° and 356° along the contour line and thus provides the most stable and clinically useful reference level at present. Conclusion: At present, the flexible reference level REFf gives the most reliable and adequate HRT measurement values, both in normal and in glaucomatous eyes. [source]

Electromagnetic field exposure and health among RF plastic sealer operators

BIOELECTROMAGNETICS, Issue 1 2004
Jonna Wilén
Abstract Operators of RF plastic sealers (RF operators) are an occupational category highly exposed to radiofrequency electromagnetic fields. The aim of the present study was to make an appropriate exposure assessment of RF welding and examine the health status of the operators. In total, 35 RF operators and 37 controls were included. The leakage fields (electric and magnetic field strength) were measured, as well as induced and contact current. Information about welding time and productivity was used to calculate time integrated exposure. A neurophysiological examination and 24 h ECG were also carried out. The participants also had to answer a questionnaire about subjective symptoms. The measurements showed that RF operators were exposed to rather intense electric and magnetic fields. The mean values of the calculated 6 min, spatially averaged E and H field strengths, in line with ICNIRP reference levels, are 107 V/m and 0.24 A/m, respectively. The maximum measured field strengths were 2 kV/m and 1.5 A/m, respectively. The induced current in ankles and wrists varied, depending on the work situation, with a mean value of 101 mA and a maximum measured value of 1 A. In total, 11 out of 46 measured RF plastic sealers exceeded the ICNIRP reference levels. RF operators, especially the ready made clothing workers had a slightly disturbed two-point discrimination ability compared to a control group. A nonsignificant difference between RF operators and controls was found in the prevalence of subjective symptoms, but the time integrated exposure parameters seem to be of importance to the prevalence of some subjective symptoms: fatigue, headaches, and warmth sensations in the hands. Further, RF operators had a significantly lower heart rate (24 h registration) and more episodes of bradycardia compared to controls. Bioelectromagnetics 25:5,15, 2004. © 2003 Wiley-Liss, Inc. [source]

Age-specific reference levels of serum prostate-specific antigen and prostate volume in healthy Arab men

BJU INTERNATIONAL, Issue 3 2005
Elijah O. Kehinde
OBJECTIVE To determine age-specific reference ranges for serum prostate-specific antigen (PSA) concentration and prostate volumes in a population of healthy Arab men. SUBJECTS AND METHODS Blood samples were taken from 396 healthy Arab men (from Kuwait and Oman) aged 15,79 years and from across the social spectrum. Men aged >40 years had a digital rectal examination and transrectal ultrasonography of the prostate to determine prostate volume. The serum PSA level was measured using commercial kits, and age-specific ranges for PSA levels and prostate volume determined. RESULTS The serum PSA ranges (ng/mL) for each age range in Arab men were: 40,49 years, 0,0.9; 60,69, 0,2.7; 70,79, 0,5.5 ng/mL; the respective prostate volumes were 8,22, 9,30 and 10,33 mL. The serum PSA level and prostate volume correlated with age (P < 0.001). Arab men had lower serum PSA levels and prostate volumes than those reported for Caucasians, but similar to those reported for Asians (Japanese and Chinese). CONCLUSION These results indicate that Arab men have lower PSA levels and prostate volumes than Caucasians. The levels are slightly lower than those reported in the Japanese and, as in the Japanese, low PSA levels and small prostate volumes might be related to the low incidence of clinical prostate cancer in Arab men. [source]

Optic disc biomorphometry with the Heidelberg Retina Tomograph at different reference levels

Circadian systemic haemodynamics in borderline and mild hypertension

CLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 6 2000
R. Takalo
Circadian variations in blood pressure (BP), stroke volume (SV), heart rate (HR), cardiac output (CO) and total peripheral resistance (TPR) were determined by a pulse contour method from the intra-arterial pulse wave in 32 normotensive (NT), 32 borderline hypertensive (BHT) and 31 hypertensive (HT) middle-aged men. Daytime averages were used as the reference levels. The nocturnal decrease in BP and HR were similar in the three groups. In the night, SV did not change in the NT group, but was increased in the BHT and HT groups. The nocturnal increase in SV may reflect reduced venous capacity causing increased cardiac filling. As a consequence of the difference in SV, the nocturnal CO fall was diminished in the HT group as compared with the NT group. Moreover, TPR had a tendency to decrease in the HT group, which may be considered as a baroreflex response to buffer the expected rise in BP. Five years later, 25 NT, 24 BHT and 19 HT subjects were reassessed using casual BP measurements. In the NT and BHT groups, six and 17 subjects, respectively, had progressed to hypertension. In a logistic regression model for those who became HT, the nocturnal increase in SV was a significant predictor for future hypertension. In conclusion, the results suggest that circadian systemic haemodynamics may be altered before BP is markedly elevated, and that haemodynamic studies might be useful in predicting the development of sustained hypertension. [source]