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At least 109 records · Page 6Linked to original sources
PubMed2005

External Quality Assessment in The Netherlands: time to introduce commutable survey specimens. Lessons from the Dutch "Calibration 2000" project.

The performance of suitable secondary reference material for the use of trueness control of six routinely measured clinical enzymes in the Dutch External Quality Assessment (EQA) scheme is described. The reference material of choice was selected using the split-patient-sample between-field method (twin study) design as described in an earlier study of the Calibration 2000 project in The Netherlands. This material, which was proven to be commutable for all wet chemistry systems, was implemented as the national enzyme calibrator. It consisted of a cryo-protected lyophilised serum with additions of recombinant human enzymes. Various batches of the frozen version of this material without cryo-protection additive, called native EQA samples, were used in the general EQA scheme for performance evaluation. The results of Calibration 2000 calibrated and non-Calibration 2000 calibrated laboratories were compared for both the regular (spiked with non-human enzymes) and native EQA samples in terms of precision and bias with established reference method values for the native samples. The regular samples showed mean between-laboratory CV ranges for all six enzymes involved (low-high) of 5.5-10.3% for the non-calibrated users vs. 4.6-10.8% for the calibrated users. For the native samples these respective ranges were 5.2-9.9% vs. 2.2-4.9%. Without exception, the group of Calibration 2000 calibrated users showed the lowest bias against the reference method values. Regular EQA samples (spiked with non-human enzymes) showed poorer performance than native samples and are not suitable for accuracy assessment purposes, the main aim of EQA schemes. Native samples that are commutable should be used for trueness control in current EQA schemes.

Calibration↗
PubMed2003

Seriousness of traffic accidents during work and commuting.

This study examined the seriousness of traffic accidents that happen-either on work errands or during commuting. The article was based on three independently gathered data sets, of which two were based on compensation claims to the insurance companies (N=2,050 and N=17,108) and one on the interviews of victims (N=328). The traffic accidents at work led to a major injury or death more often than the commuting accidents. On the other hand, the work-related traffic accidents were less serious than the leisure-time traffic accidents. One explanation could be that heavy vehicles used during the working hours protected the drivers of these vehicles.

Accidents, Traffic↗
PubMedDate not supplied

[Commutation systems of the roentgenodiagnostic apparatus operating with automatic exposure relays].

The automatic exposure relay (X-ray exposure meter) enables the exposure time in roentgenography of diverse human organs to be determined and fixed with a high degree of accuracy, but the subsequent protracted commutation of the main and control circuits of the roentgen-diagnostic apparatus tends to practically bring to naught this high precision. The paper deals with an analysis of commutation delays and lags in different control systems of the roentgen apparatus and with assessing the effect they have on the quality of the X-ray picture.

Methods↗
PubMed2002

The impact of commuter war on military personnel.

BACKGROUND: The U.S. armed forces recently experienced a reduction in forces along with an increase in operational tempo. The Air Force and other branches supporting its mission share this common military burden and also experience a unique stressor. The Air Force has developed a military force that can fight by night and return home by day. The relatively new phenomenon of "commuter war" was especially evident during Operation Allied Force over Kosovo. METHODS: Military personnel (N = 540) participating in Operation Allied Force were administered a survey measuring morale, wellness behaviors, and work-family conflict. RESULTS: The deployment had adverse effects on wellness behaviors of permanent party and temporary duty assignment populations. Additionally, levels of morale and motivation varied between the two groups. Permanent party personnel also reported increased rates of work-family conflict. CONCLUSIONS: Commuter war affects wellness behaviors, morale, and work-family conflicts of military personnel.

Adult↗
PubMed2002

Selection, preparation, and characterization of commutable frozen human serum pools as potential secondary reference materials for lipid and apolipoprotein measurements: study within the framework of the Dutch project "Calibration 2000".

BACKGROUND: The Dutch project "Calibration 2000" aims at harmonization of laboratory results via calibration by development of matrix-based secondary reference materials. We considered the selection, preparation, and characterization of 34 potential reference materials (PRMs). METHODS: Sixteen PRMs were prepared either strictly according to the NCCLS C37-A protocol or in a less stringent and more convenient way. In addition, 18 commercial, so-called human serum-based calibrators or controls were purchased and tested. Lipoprotein integrity was evaluated by examining the physicochemical characteristics of the materials. Commutability of the PRMs was assessed in 86 Dutch clinical laboratories, using a multicenter split-patient-sample between-field-method (twin-study) design. Normalized residuals of the PRMs with respect to the patient regression lines were calculated; in addition, the extra contribution of each PRM to the total measurement uncertainty (CV(Netto)) was calculated. On the basis of these results, the most native PRM was selected to investigate its potential to reduce interlaboratory variation and to improve lipid and apolipoprotein standardization. RESULTS: In general, only the NCCLS C37-A-type materials displayed normalized residuals below the decision limit for commutability and had small CV(Netto) values ranging between 0 and 3.8%. This contrasts with the findings in regularly pooled frozen sera and lyophilized cryoprotected PRMs. In two subsequent external quality assessment surveys, the NCCLS type C37-A materials contributed to reducing the intermethod lipid and (apo)lipoprotein variation to approximately 2-4%. CONCLUSIONS: NCCLS C37-A materials have a strong potential as secondary reference materials, not only for cholesterol but also for HDL-cholesterol, LDL-cholesterol, triglyceride, and apolipoprotein measurements.

Apolipoprotein A-I↗
PubMed2002

Geographic patterns of pilot fatality rates in commuter and air taxi crashes.

BACKGROUND: Geographic information systems are widely used in studies of diseases. However, their value for aviation safety research has not been adequately explored. PURPOSE: This study examined the geographic patterns of pilot fatality rates in commuter and air taxi operations. METHODS: Crash data recorded by the National Transportation Safety Board under FAR Part 135 were used to create a digital map of all crash sites in the continental United States between 1983 and 1998. Fatality rates in crashes were calculated and then interpolated to create a contoured map of rates. A test of significance was performed using Monte Carlo simulations. High-, medium-, and low-rate areas were then compared for pilot characteristics, airplane characteristics, and crash circumstance. RESULTS: Of the 1094 commuter and air taxi crashes studied, 25% resulted in a pilot fatality. A large geographic area with a pilot fatality rate of > or = 36% extended through portions of Michigan, Indiana, and Illinois. A relatively low fatality rate (< 15%) prevailed over an area extending from Texas to northwest Georgia. Crashes in high-rate areas were significantly more likely than crashes elsewhere to have occurred at night and during instrument meteorological conditions. CONCLUSION: The geographic analysis revealed a distinctive pattern of pilot fatality rates from Part 135 crashes. Factors underlying the geographic pattern should be investigated, with particular attention to the great geographic variability of terrain and weather phenomena between the north and south regions of the United States.

Accidents, Aviation↗
PubMed1995

Factors related to pilot survival in helicopter commuter and air taxi crashes.

We examined factors related to pilot survival in 167 consecutive helicopter commuter and air taxi crashes that occurred during 1983-88. Case fatality rates and adjusted odds ratios from multivariate logistic regression models were determined using data from the National Transportation Safety Board (NTSB). During this 6-year period, 29 pilots-in-command died in 167 helicopter commuter and air taxi crashes, a case fatality rate of 17.4%. Factors significantly associated with increased risk of pilot fatality were aircraft fire [odds ratio (OR) 20.0, 95% confidence interval (CI) 4.6-86.8], not using shoulder harnesses (OR 9.2, 95% CI 2.2-37.3), and aircraft with two engines (OR 4.8, 95% CI 1.3-17.4). In addition, we present data regarding success and failure of emergency flotation devices. The results suggest that the likelihood of pilot survival in helicopter crashes could be greatly improved by preventing crash associated fires and promoting the usage of shoulder restraints.

Accidents, Aviation↗
PubMed1995

Determination of alpha-amylase activity: methods comparison and commutability study of several control materials.

Six different methods for alpha-amylase determination were compared by assaying human serum samples covering a wide range of alpha-amylase values. All the methods studied use as substrate a maltooligosaccharide with a chromophore group at the reducing end; some are chemically blocked at the nonreducing end. Intermethod comparison by regression and correspondence analyses showed significant differences for two methods. The commutability of 12 commercial control materials containing alpha-amylase was also assessed by the different methods in comparison with human serum specimens containing the pancreatic and salivary isoenzymes. We also studied the behavior of pancreatic and salivary materials prepared in our laboratory. Control materials with alpha-amylase of non-human origin were not commutable with the enzyme in human sera and should not be used for intermethod calibration.

Animals↗
PubMed1993

Changing population structure and commuting situation in Tokyo Megalopolis: a municipality-based analysis.

Census data was analyzed for 20 municipalities along the Tohoku Line in Tokyo Megalopolis to elucidate the changes in the population structure and the commuting situation in the last two decades. The major findings were: (1) the changing pattern of population structure markedly varied among the municipalities, and (2) the long-distance commuting workers have increased particularly among those 50 km or more from central Tokyo.

Adolescent↗
PubMed1993

Accurate enzyme activity measurements. Two decades of development in the commutability of enzyme quality control materials.

Commercial serum preparations are integral components of both internal and external quality control programs for enzyme activity measurements. However, properties of these materials may differ significantly from those of clinical specimens. Differences from clinical specimens may include the following: species origin of the enzyme; isoenzyme form(s); integrity of the molecular species; matrix of the solution; processes such as lyophilization; and addition of preservatives. There are also significant differences among methods measuring the activity of a single enzyme including a diversity of compounds that may serve as substrate(s); variable cofactor or metal supplementation; and differences in the substrate concentration(s), buffer substances, pH, and temperature. The measured response to each of these variations in assay technique may differ among these types of specimens. To be acceptable, quality control materials must have properties similar to those of clinical specimens. Thus, the concept of commutability that we originated and first applied to enzyme activity measurements remains useful, and its further application to the problem of "matrix effects" is reviewed here. Multivariate display techniques are applied to the specific examples of aspartate aminotransferase, alpha-amylase, and alkaline phosphatase to judge the commutability of quality control materials for these enzymes.

Bias↗
PubMed1988

Interdistrict migration in Great Britain 1980-81: a multistream model with a commuting option.

"In this paper an existing three-stream model of migration is adopted and extended to provide a first representation of district-district flows within Great Britain in 1980-81. The extended model incorporates an option for prospective migrants to choose commuting rather than a residential move after finding a new workplace, and employs a logistic function of distance in the regional or environmental stream where migrational opportunities tend not to be independent. Results are presented for the distribution of flows between local, regional, and national streams and for the geographical pattern of pushes and pulls in each."

Behavior↗
PubMed1996

Commutator filter: a novel technique for the identification of structures producing significant susceptibility inhomogeneities and its application to functional MRI.

A robust postprocessing method to detect regions of magnetic field change is presented. High resolution gradient echo data is acquired to create a complex baseline image. From this image, two low resolution images are obtained by applying a low pass filter on the magnitude image and the complex image, respectively. Subtraction of the magnitude of the filtered complex image from the filtered magnitude image gives a new image called a commutator image in which regions of susceptibility-induced field variation are greatly enhanced. Results on phantoms and applications to visualize paramagnetic venous blood vessels in the human brain are presented. The use of this technique on a 3D gradient echo data set represents a new approach to obtain an MR venogram. The application of this method to blood oxygenation level dependent (BOLD) functional brain MR imaging is demonstrated and the important role susceptibility plays in this model is verified.

Algorithms↗
PubMed1999

The roles of estimation and the commutativity principle in the development of third graders' mental multiplication.

In this training experiment, pretesting identified 36 third graders (mean age = 8 years 5 months, SD = 4 months) with negligible mastery of multiplication combinations involving factors from 3 to 9. Participants were randomly assigned to 2 groups, which practiced different subsets of combinations, and were then retested. The results were inconsistent with R. S. Siegler's (1988) proposal that item-specific computational practice is necessary to promote changes in error patterns and combination mastery. The results were consistent with the hypotheses that children devise increasingly flexible and accurate estimation strategies and use relational knowledge such as the commutativity principle to master combinations. Because even fast mental-arithmetic errors and correct responses may be due to strategies other than retrieval, researchers need to craft ways of distinguishing between retrieval and nonretrieval strategies.

Association Learning↗
PubMed1982

A reliable multichannel commutator for making electrical contact with conscious, freely moving rats.

A counterbalanced mercury swivel arrangement is often used to make connections between electrodes implanted in the brain of conscious laboratory animals and electronic equipment so that movement is not restricted. There are certain disadvantages associated with this system and an alternative is described which is based on a rhodium plated slip ring. The device is reliable, robust, causes minimal hindrance to the movement of the animal and causes virtually no interference noise to low level electrical signals. The slip ring based commutator has been incorporated into an automated system for making in vivo voltammetric recordings from conscious rats where currents of less than 100 nA are measured. Some of the results are shown.

Animals↗
PubMedDate not supplied

Lightweight, multi-contact, slip-ring commutator for recording and stimulation with small animals.

A slip-ring commutator which can be used to electrically stimulate and/or record from the brains of small, unrestrained animals is described. In addition to providing 4 to 10 independent electrical contacts, featues of this model include its small size, low torque characteristics, low rate of contact oxidation, and minimal noise generated at the brush-ring surface. The compactness and light weight of this unit permit it to be suspended from a counterweighted boom assembly, thus providing additional freedom for vertical movement.

Animals↗
PubMed2005

Body mass index and cardiovascular disease in a birth cohort of commuter air carrier and air taxi pilots.

PURPOSE: Acute cardiovascular events such as heart attack and stroke in commercial pilots have been a concern to flight safety. The purpose of this study was to examine the association of body mass index (BMI) with cardiovascular disease in commercial pilots. METHODS: We followed from 1987 to 1997 a cohort of 3019 male commuter and air taxi pilots who were born between 1933 and 1942 and who were certified by the US Federal Aviation Administration. The relationship between BMI and the risk of cardiovascular disease was assessed using Poisson regression modeling based on generalized estimation equations. RESULTS: At baseline, 55% of the pilots were overweight (25 kg/m(2) BMI < 30 kg/m(2)) and 7% were obese (BMI >/= 30 kg/m(2)). The follow-up accumulated a total of 20,671 person-years and 1897 diagnoses of cardiovascular disease, yielding an incidence rate of 92 per 1000 person-years. The incidence rates of cardiovascular disease increased significantly with BMI. With adjustment for baseline history of cardiovascular disease and age, pilots who were overweight and obese had 6% and 22% higher risk of cardiovascular disease, respectively, than their counterparts with normal BMI. CONCLUSIONS: The prevalence of overweight/obesity and the relationship between BMI and cardiovascular disease among commercial pilots parallel findings from the general population. Incorporating BMI into the current medical standards for commercial pilots merits serious consideration.

Aviation↗
PubMed2006

Complexity and non-commutativity of learning operations on graphs.

We present results from numerical studies of supervised learning operations in small recurrent networks considered as graphs, leading from a given set of input conditions to predetermined outputs. Graphs that have optimized their output for particular inputs with respect to predetermined outputs are asymptotically stable and can be characterized by attractors, which form a representation space for an associative multiplicative structure of input operations. As the mapping from a series of inputs onto a series of such attractors generally depends on the sequence of inputs, this structure is generally non-commutative. Moreover, the size of the set of attractors, indicating the complexity of learning, is found to behave non-monotonically as learning proceeds. A tentative relation between this complexity and the notion of pragmatic information is indicated.

Artificial Intelligence↗