1,263 research outputs found
Toward standardization of cardiac troponin I measurements part II: assessing commutability of candidate reference materials and harmonization of cardiac troponin I assays
No full textBACKGROUND: Cardiac tropoin I (cTnI) measurements show an approximately 20- to 40-fold difference between assays, and better standardization and harmonization are needed. Toward this goal, the AACC cTnI Standardization Committee collaborated with the National Institute of Standards and Technology (NIST) in an earlier study to select 2 candidate reference materials (cRMs). METHODS: Two troponin cRMs, a troponin C-troponin I-troponin T (CIT) complex from human heart tissue and a CIT complex from recombinant technology, were supplied to NIST for assessment of composition and purity, and cTnI value assignment. These cRMs and 6 cTnI-positive human serum pools were shipped to manufacturers of 15 cTnI assays. Commutability of the materials was examined by determining the numerical relationship for the cRM preparations between each manufacturer-specified field method and each of the other 14 field methods. These relationships were then compared with the corresponding numerical relationships for the human serum pools. Harmonization of methods was accomplished by determining regression parameters relative to the analytical system yielding values closest to the median for each serum pool. These regression parameters were used to recalculate pool values to harmonize the assays. Interassay CVs before and after harmonization were determined. RESULTS: Characterization of the CIT and CI cRMs showed that these materials were of specified composition. The proportion of cTnI methods that demonstrated commutability for the CIT cRM was 45%; for the CI cRM, 39% of methods demonstrated commutability. Interassay cTnI variability for the field methods ranged from 82% to 97%, median 88%. After harmonization, variability of the serum pools for the cTnI methods was decreased to between 9.0% and 23%, median 15.5%. CONCLUSIONS: The proportion of methods demonstrating commutability was too low for use as a common calibrator for the cTnI field methods. However a simple strategy using serum pools can improve harmonization of field cTnI methods by more than 5-fold. The CIT cRM was selected by the AACC cTnI standardization committee, and a new lot has been classified as the cTnI certified reference material Standard Reference Material 2921 by NIST
Evaluation of standardization capability of current cardiac troponin I assays by a correlation study: results of an IFCC pilot project
No full textBackground: As a part of an International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) project to prepare a commutable reference material for cardiac troponin I (cTnI), a pilot study evaluated current cTnI assays for measurement equivalence and their standardization capability.
Methods: cTnI-positive samples collected from 90 patients with suspected acute myocardial infarction were assessed for method comparison by 16 cTnI commercial assays according to predefined testing protocols. Seven serum pools prepared from these samples were also assessed.
Results: Each assay was assessed against median cTnI concentrations measured by 16 cTnI assays using Passing-Bablok regression analysis of 79 patient samples with values above each assay’s declared detection limit. We observed a 10-fold difference in cTnI concentrations for lowest to highest measurement results. After mathematical recalibration of assays, the between-assay variation
for patient samples reduced on average from 40% to 22% at low cTnI concentration, 37%–20% at medium concentration, and 29%–14% at high concentration. The average reduction for pools was larger at 16%, 13% and 7% for low, medium and high cTnI concentrations, respectively.
Overall, assays demonstrated negligible bias after recalibration (y-intercept: –1.4 to 0.3 ng/L); however, a few samples showed substantial positive and/or negative differences for individual cTnI assays.
Conclusions: All of the 16 commercial cTnI assays evaluated in the study demonstrated a significantly higher
degree of measurement equivalence after mathematical recalibration, indicating that measurement harmonization or standardization would be effective at reducing inter-assay bias. Pooled sera behaved similarly to individual samples in most assays
Maxillaria pyhalae D. E. Benn. & Christenson
No full textMaxillaria pyhalae D.E.Benn. & Christenson (Figs. 1–2) Type:— PERU. Huancavelica: Prov. of Tayacaja, Llactapata, 2600 m, 14 February 1999, León & Collantes 2975 (holotype MOL, photo!; isotype MOL, phtoto!). Plant up to 60 cm tall (including the inflorescence), terrestrial and occasionally epiphytic. Roots slender, born from the rhizome at the base of the pseudobulb. Rhizome stout, 8–10 × 0.8 cm, covered by scarious bracts. Pseudobulb 1.5–2.1 × 0.5–0.8 cm, covered by two scarious bracts, 1–2 articulated foliaceous bracts of 25–29 cm long. Leaf 20.5–39.5 × 3.2-3.8 cm, unifoliate; petiole 4.5–10 cm long; blade loriform, acute to acuminate apex. Inflorescence up to 60 cm long, basal, slender scape covered by 7–8 bracts; bracts 4.0– 6.5 cm long; floral bract 5.0 × 2.4 cm, ovate, cucullate and carinate on the back, acuminate, basally tubular and unguiculate along 0.8 mm. Flower non-resupinate, red and white, 4–5 cm long, facing downwards. Ovary dark purple, strongly recurved. Sepals with a longitudinal white stripe in the middle, flanked by two red stripes on the sides; dorsal sepal 4.2–4.8 × 1.1–1.2 cm, triangular oblong, apiculate apex, margin irregularly entire, 17-nerved; lateral sepals 3.6–4.3 × 1.8–2.0 cm, triangular falcate, acute and apiculate apex, 15–17-nerved. Petals 3.4–4.1 × 1.2–1.3 cm, triangular sub-falcate, with a longitudinal white stripe in the middle, flanked by two red stripes on the sides, 11–13-nerved. Labellum 2.0–2.1 × 1.5 cm, sub-pyriform, adaxial surface covered by abundant spherical and sub-spherical yellow pseudopollen granules forming plush clumps towards the disk base, a semi-circular callus at the middle on the adaxial surface, an arc of 6 mm long on the abaxial surface; basal half hemi-rounded with entire, dark red margins; distal half transversally extended in two dolabriform expansions, margins irregularly denticulate, dark cream, with irregular and enlarged dark garnet spots; apex dark mustard with dark brown spots or completely yellowish, margin revolute of 8–9 mm long; apex centre a semi-ellipsoidal to cupuliform protuberance of 2.5–3.0 mm long, covered by pseudopollen, revolute margins dorsally as closed or open lips. Column 12 × 5 cm, arcuate, semi-terete, slightly concave ventral surface, surface with minute dactylar papillae, cream and ventrally pale yellow with small and irregular dark red dots; clinandrium with minuscule dactylar appendices of variable size; column foot 16–18 × 5 mm, arcuate, dorsoventrally flattened and slightly concave with lateral ridges. Anther 5.8–6.4 × 5–5.5 mm, widely obovoid, slightly complanate dorsoventrally, thick dark cream with reddish brown spots at the centre or entirely cream, dorsal surface slightly concave, a thick carina extending rearward with a rounded superior margin from the middle to the apex, a conspicuous V-shaped promontory at the end of the carina. Pollinarium 5 × 3 mm, with four pollinia; viscidium saddle shaped; pollinium claviform, complanate, convex-concave, larger pair 5 × 2 mm, smaller pair 3.4 × 1.5 mm. Fruit, not recorded. Phenology: —Flowering between February and March (Collantes 2014). Distribution, habitat, and ecology: — Maxillaria pyhalae is only known from three localities (i.e. Regional Conservation Area Amaru-Chihuana, Velapaccha, and Roble) in the district of Huachocolpa, department of Huancavelica, Peru (Fig. 3; Collantes 2014). The species is locally abundant and can be found at elevations between 2300 and 2900 m. They grow in humid and shaded undergrowth on rocks, but may also be found as epiphytes. Additional specimens examined: — PERU. Huancavelica: Prov. of Tayacaja, Dist. of Huachocolpa, Llactapata, 2600 m, 14 February 1999, León & Collantes 2975[b] (MOL, photo; USM); Inquilpata, 2700 m, 22 March 2021, León 8651 (USM); Dist. of Robles, Bosque de Robles, 2630 m, 17 February 2014, Egoavil 152 (USM). Conservation status: — Maxillaria pyhalae is known only from three localities where it is locally abundant. However, the observed population is calculated as less than 1000 individuals given that most growth points are the result of vegetative growth from the rhizome. Therefore, following the IUCN Red List (IUCN 2019) criteria, the species would likely be categorized as Endangered (EN), criterion D, based on the number of mature individuals; the same categorization was previously assessed (Roque & León 2006) The species has been included in the Peruvian CITES list (Ministerio del Ambiente 2018) and the national plan for orchid conservation (SERNANP 2021). Comments: —Besides the new taxon proposed herein, we believe M. pyhalae is morphologically most similar to Maxillaria fucata Reichenbach (1886: 616), rather than Maxillaria fletcheriana R.H. Pearson (1913: 258) (a synonym of M. insignis Rolfe [1922: 25]) as suggested by Bennet & Christenson [2001] in the protologue. The line drawings of M. pyhalae published in the IOP misrepresents important details of the plant specimens, especially the labellum, which makes the identification of this taxon challenging at times. The labellum shape is also not described in detail in the protologue. This has caused confusion with regard to the identity and correct interpretation of this taxon. Additionally, it has been determined that the holotype and an isotype of M. phylae are gathered at MOL under the same collection number (i.e. León et al. 2975, MO; Trujillo 2014).Published as part of Martel, Carlos, Egoavil, Luis, Ocupa, Luis, Tello, Juan Andre, Patrón, Federico Rizo, Laura, César, León, Marco & Collantes, Benjamín, 2021, An homage to Peru's bicentenary: Maxillaria bicentenaria (Orchidaceae), a new species previously misidentified as M. pyhalae, pp. 87-99 in Phytotaxa 518 (2) on pages 89-91, DOI: 10.11646/phytotaxa.518.2.1, http://zenodo.org/record/545388
Quality specifications for B-type natriuretic peptide assays
No full textBackground: The objective of this report is to improve the quality of immunochemical measurements of B-type natriuretic peptide (BNP) and its N-terminal propeptide (NT-proBNP). The recommendations proposed are intended for use by manufacturers of commercial assays, by clinical laboratories using those assays, by clinical trial groups and research investigators, and by regulatory agencies, such as the United States Food and Drug Administration. Methods: A group of cardiac biomarker experts reviewed and abstracted the scientific literature to provide recommendations pertaining to the quality specifications for BNP/NT-proBNP assays. Results: The evidence-based recommendations encourage manufacturers to endorse and consistently follow the proposed recommendations; encourage that all package inserts for BNP/NT-proBNP immunoassays include uniform information on assay design, preanalytical performance characteristics, analytical performance characteristics, and clinical performance; and encourage regulatory agencies to adopt a minimal and uniform set of criteria for manufacturers to provide when seeking clearance for new and/or improved assays. Conclusions: These recommendations address the use of BNP and NT-proBNP as cardiac biomarkers and not their physiologic and/or pathophysiologic relevance
The SF-36: a simple, effective measure of mobility disability for epidemiological studies
No full textBackgroundMobility disability is a major problem in older people. Numerous scales exist for the measurement of disability but often these do not permit comparisons between study groups. The physical functioning (PF) domain of the established and widely used Short Form-36 (SF-36) questionnaire asks about limitations on ten mobility activities.ObjectivesTo describe prevalence of mobility disability in an elderly population, investigate the validity of the SF-36 PF score as a measure of mobility disability, and to establish age and sex specific norms for the PF score.MethodsWe explored relationships between the SF-36 PF score and objectively measured physical performance variables among 349 men and 280 women, 59-72 years of age, who participated in the Hertfordshire Cohort Study (HCS). Normative data were derived from the Health Survey for England (HSE) 1996.Results32% of men and 46% of women had at least some limitation in PF scale items. Poor SF-36 PF scores (lowest fifth of the gender-specific distribution) were related to: lower grip strength; longer timed-up-and-go, 3m walk, and chair rises test times in men and women; and lower quadriceps peak torque in women but not men. HSE normative data showed that median PF scores declined with increasing age in men and women.ConclusionOur results are consistent with the SF-36 PF score being a valid measure of mobility disability in epidemiological studies. This approach might be a first step towards enabling simple comparisons of prevalence of mobility disability between different studies of older people. The SF-36 PF score could usefully complement existing detailed schemes for classification of disability and it now requires validation against them
Complex calcium ferrites in the blast furnace process: Fluxed sinter formation and SFCA reduction under simulated conditions
No full textCivil Engineering and Geoscience
Softening in the blast furnace process: Local melt formation as the trigger for softening of ironbearing burden materials
No full textCivil Engineering and Geoscience
Micromilling of hardened tool steels
No full textMiniaturized parts are increasingly demanded in different fields like medical, transportation, environmental, and communication industries. In order to manufacture these parts in an economical way, mass replication methods, such as micro injection molding, have to be applied. Currently, Electro Discharge Machining (EDM) process is mainly used to manufacture the needed moulds for micro injection molding in industries. In order to achieve the final shape, several electrodes have to be made by milling with different levels of geometrical accuracy. Besides, the material removal rate of EDM is relatively low. This results in a long throughput-time and high manufacturing cost. Therefore, industries are looking for alternative technologies to overcome these drawbacks; micromilling is one of the promising technologies. The advantages of the micromilling technology include the applicability of a broad range of materials including hardened tool steels, the capability of manufacturing three dimensional geometries, accurate machining of complex features, and it is economical for small and medium lot sizes, etc. However, although micromilling in principle is a good alternative for the EDM process, it is found in research that some challenges have to be overcome before this technology is ready to be adopted in industrial applications. The literature survey shows that the fundamental micro cutting mechanism has been well investigated and understood through the study of micro orthogonal cutting and ultraprecision machining. Issues related to the application of micromilling have however not yet been well studied. Besides, inconsistent observations are commonly seen in literature. This is because observed results in micromilling are highly dependent on the experimental conditions. Based on the literature survey and initial micromilling tests, the general goal of this research has been defined as to develop and describe a reliable micromilling process for precision machining of hardened tool steels. It was decided to first improve lives of micro endmills to achieve a reliable cutting, and then to improve the performance of the process through process planning. In this research, experiments were mainly done with Ø 0.5 mm square endmills on hardened tool steels (AISI H11, H13, etc.). Experimental investigations were done to identify the main problems in micromilling. It was observed that the used commercial micro tools suffered severe wear, the tool life was too short to conduct a successful task, and the workpiece quality was not achieving the requirements. Investigations were conducted to understand tool wear types and mechanism. The factors which influence the tool performance were analyzed. It was found that the geometry of commercial tools is mainly derived from macro endmills, with which the cutting edge corners have the highest stress level. The machining parameters and tool paths are two factors that have significant effect on the tool performance; however, there was no good method available for the planning of the micromilling process. The geometry of micro endmills was studied theoretically by means of analytical modeling and FEA method. Having understood the relationship between geometrical features of the cutting tool and their influence on the tool performance (stiffness and strength of the cutting edge corners), the geometry of the micro endmill can be designed specifically for a given application to achieve the desired performance. This method was demonstrated by designing the micro square endmill especially for hard milling applications. The newly designed tools were manufactured and validated through experiments in comparison with the commercial tools. The experimental results have shown that the new designs have improved the tool performance as expected. The planning of the micromilling process has been divided into two parts. In the first part, design of experiments has been used to understand the relationship between input variables (machining parameters and tool paths) and process response (tool wear and surface finish). With this method, the significant variables can be identified by means of ANOVA analysis, and the cutting conditions can be planned accordingly to optimize the process output. For example, to have a long tool life is important for the roughing operation, and to achieve a good surface finish is of interest for the finishing operation. In the second part of the process planning, a knowledge-based method is used to plan cutting conditions for the machining of micro features with high aspect ratios. The selection of machining parameters was done by means of a force model, which describes the relation between machining parameters and average forces. The tool paths were tested by a FEM model. An improved tool path was proposed to overcome the disadvantage of the conventional tool path. Experiments were done with conditions chosen by the theoretical analysis, and the results proved the validity of the developed method. Micro ribs with aspect ratios higher than 50 could be machined successfully.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Design of a Micro Milling Setup with an Active Magnetic Bearing Spindle
No full textThis thesis describes the design of a micro milling setup with an active magnetic bearing spindle. Micro milling is the mechanical removal of material with sub millimeter tools. An active magnetic bearing typically consists of a set of magnetic actuators, a control loop and position sensors. Active Magnetic Bearings enable a very high rotational speed of 150.000 rpm and a high positioning accuracy. The use of bearing signals for process monitoring is a separate research topic in the same project. Special attention has been given to the design of magnetic actuators with low rotating losses. A design with an axial bias flux generated by permanent magnets has been applied. The rotordynamic modelling of the spindle is described as well as the controller design. The spindle has been realized and a rotational speed of 150.000 rpm has been achieved. The spindle has been integrated into a micro milling setup, where the work piece is positioned using an xy stage driven by Lorentz actuators. A novel tool clamping device had to be developed which matches the reduced dimensions of the spindle and which is able to withstand the very high rotational speed. A monolithic tool holder has been designed in which the clamping force increases with increasing rotational speed. The main improvements that can be made require the increase of the rotational speed and an increase of the flexural spindle resonance frequencies. A novel design has been presented to support a short, disk shaped rotor. This rotor shape has required the design of a controller which compensates the strong gyroscopic coupling in a rotating disk.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
- …
