Sm-Nd isotope systematics in deep-sea sediments: clay-size versus coarser fractions

in Marine Geology (2000), 168(1-4), 79-87

Sm-Nd studies were carried out on Last Glacial and Holocene sediments from the Labrador Sea. Three grain-size fractions were analyzed for each sediment: the clay-size fraction (<2 mu m), the fine cohesive ... [more ▼]

Sm-Nd studies were carried out on Last Glacial and Holocene sediments from the Labrador Sea. Three grain-size fractions were analyzed for each sediment: the clay-size fraction (<2 mu m), the fine cohesive silts (2-10 mu m) and the coarse silts (10-63 mu m) In most cases, Sm-Nd signatures are different from one grain-size to another. In addition, different Sm-Nd signatures are derived from the clay-size fractions compared to the cohesive silt fraction, indicating that the cohesive fraction is heterogeneous and that distinct origins in terms of source-areas are implied. Silt fractions record the influence of supplies from the North American Precambrian Shield, whereas clay-size fractions (<2 mu m) are more sensitive to sedimentary input from the Eastern Basins, in relation with deep currents. Coupling Sm-Nd studies on silt and clay fractions may be a powerful tool to unravel the evolution of deep circulations versus detrital supplies. (C) 2000 Elsevier Science B.V. All rights reserved. [less ▲]

SM98-146/413 Effective Modal Parameters to Evaluate Structural Stresses

in Spacecraft Structures, Materials and Mechanical Testing (1999)

Small animal imaging with human PET

Poster (2012, September)

PET studies provide valuable information in the assessment of animal models for human diseases. MicroPET systems provide the high resolution needed to explore small organs but suffer from a reduced axial ... [more ▼]

PET studies provide valuable information in the assessment of animal models for human diseases. MicroPET systems provide the high resolution needed to explore small organs but suffer from a reduced axial FOV. Multiple bed positions are then used to obtain whole body scans resulting in increased scan time and incomplete dynamic data. In contrast, human PET systems have larger axial FOV but a lower resolution. In this study, an image-based model of the scanner spatial response function combined with a 3D-OSEM reconstruction algorithm were used to improve spatial resolution of the Siemens ECAT EXACT HR+ PET scanner. A stationary double Gaussian model [1] of the ECAT EXACT HR+ point spread function was derived from 18F point source measurements performed at different radial and axial locations in the scanner FOV. This model was used in a 3D-OSEM reconstruction (3D-OSEM-RM). Sinograms were normalized and attenuation and scatter corrected using the Siemens ECAT tools before reconstruction. Both NEMA NU 2-1994 performance phantoms and NEMA NU4-2008 image quality phantom mimicking small animals were used to evaluate the accuracy of corrections for physical effects and the overall image quality. A 50 min dynamic FDG rat study was conducted on the ECAT HR+ and reconstructed with 3D-OSEM-RM. The images were used to compute the metabolic rate of glucose (MRglu) in multiple brain structures. These images were also visually compared to the static image obtained with a FOCUS 120 microPET immediately after the HR+ dynamic scan. The standard deviations of the two Gaussians used to model the transaxial (axial) resolution in a central FOV of 5 cm radius were σ1 = 1.6 (2.75) mm and σ2 = 3.66 (4.16) mm, and the ratio of the weights between the first and second Gaussians was ρ = 0.2 (0.7). Image uniformity and accuracy of scatter and attenuation corrections, evaluated following NEMA NU 2-1994, were found to be very similar between 3D-OSEM, 3D-OSEM-RM, 2D- and 3D-FBP reconstructed images. When using the NEMA NU4-2008 image quality phantom a significant increase of the hot rod recovery coefficient was observed. This effect was rod size dependent and amounted to 17-35% for the 3D-OSEM-RM compared to the 3D-OSEM and to 35-62% compared to the FBP reconstructions. Nevertheless the values obtained with 3D-OSEM-RM were around 20-35% lower than those obtained with the FOCUS 120 microPET scanner. Most of the small brain structures observed on microPET images were also visible on the images obtained with the HR+ scanner and 3D-OSEM-RM. Rat cerebral MRglu values calculated on 3D-OSEM-RM images were in the range of published values [2] (e.g. whole brain = 25.34 μmol/min/100g). Using an approximate model of the ECAT EXACT HR+ spatial response in 3D-OSEM resulted in sufficient image quality for dynamic whole body scans of small rodents, despite the large FOV, and resulted in improved contrast compared to images generated using the built-in software. This methodology will be applied for future small animal dosimetry and modeling studies in our laboratory. [1] Comtat et al. IEEE Nucl Sci Symp Conf Record. pp. 4120-4123 (2008) [2] Schiffer et al. J Nucl Med 48:277-287 (2007) [less ▲]

Small Bowel Enema and Diagnosis of Chronic Nonischemic Disturbance of Superior Mesenteric Venous Blood Flow

in Abdominal Imaging (1993), 18(3), 265-70

Chronic nonischemic disturbance of mesenteric venous blood flow is reported in 11 patients with a mean age of 19 years. This entity, rarely discussed in the literature, is different from acute thrombosis ... [more ▼]

Chronic nonischemic disturbance of mesenteric venous blood flow is reported in 11 patients with a mean age of 19 years. This entity, rarely discussed in the literature, is different from acute thrombosis and chronic thrombotic forms with portal hypertension or hypercoagulopathy. In eight patients this syndrome was secondary to organic lesions of different origin: mesenteric vein squeezed by fibrous bands or an abnormal jejunal artery (four cases), lymphoma involving the distal superior mesenteric veins (three cases), hemangioma causing microthrombi (one case). In three patients no etiology or predisposing factor was found. All patients presented with rectal hemorrhage. Small bowel enema showed a constant pattern in 11 patients: small nodules, modified by compression or peristalsis, involving the mesenteric border of the jejunoileal segment, and associated with thick, straight but regular folds. Mesenteric varices were suspected and led to angiographic studies which were normal in three cases, confirmed varices in eight cases, and thrombosis in four cases. Laparotomy was normal in three cases and established the etiological diagnosis in eight cases. Varices were shown in six cases. Arteriography and laparotomy were unable to reach a complete diagnosis. [less ▲]

Small effect of the androgen receptor gene GGN repeat polymorphism on serum testosterone levels in healthy men

in European Journal of Endocrinology (2009), 161(1), 171-7

OBJECTIVE: The human androgen receptor (AR) contains a polyglutamine and a polyglycine stretch which are highly polymorphic and are coded respectively by a CAG and GGN repeat in exon 1 of the AR gene ... [more ▼]

OBJECTIVE: The human androgen receptor (AR) contains a polyglutamine and a polyglycine stretch which are highly polymorphic and are coded respectively by a CAG and GGN repeat in exon 1 of the AR gene. Although the in vitro studies indicated a possible effect of the GGN repeat polymorphism on the AR gene transcription and clinical observations suggest that it might modulate the androgen action, its functional significance remains unclear. We wanted to assess whether the GGN repeat affects the serum testosterone levels in healthy men, which is the expected outcome through feedback regulation if it influences androgen action as has been shown to be the case for the CAG repeat. DESIGN AND PATIENTS: A population based cross-sectional cohort study including 1476 healthy young, middle-aged, and elderly men. MEASUREMENT: Testosterone and LH levels were determined by immunoassay; free testosterone (FT) levels were calculated. Genotyping of the GGN repeat was performed using the sequencing technique. RESULTS: The GGN repeat number was significantly associated with circulating testosterone and FT levels (P=0.017 and P=0.013 respectively). However, taking into account that age, body mass index, and CAG are already in the regression model, the GGN repeat could explain only a small part of the variation of both testosterone and FT. CONCLUSION: To our knowledge, this study is the first to demonstrate a significant positive association between the GGN repeat and androgen levels in a large cohort of healthy men. Although the present study thus adds credence to the view that the polyglycine tract in the AR can modulate AR action, this effect appears to be only small so that its clinical relevance remains questionable. [less ▲]

Small Integrin-Binding Ligand N-Linked Glycoproteins (Siblings): Multifunctional Proteins in Cancer

in Nature Reviews. Cancer (2008), 8(3), 212-26

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin ... [more ▼]

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets. [less ▲]

Small mafic intrusions as indicators of downslope draining of dense residual liquids in anorthositic diapirs

in Geophysical Research Abstracts (2003), 5

The small nu(cleo)lar RNA cap trimethyltransferase is required for ribosome synthesis and intact nucleolar morphology

Conference (2004)

A small overview of available computer software to support computerized adaptive testing

Conference (2013, August 27)

Computerized adaptive testing (CAT) is becoming a central tool for testing and assessment. It offers many advantages over fixed (“paper-and-pencil”) methods, such as individualized assessment, reduction ... [more ▼]

Computerized adaptive testing (CAT) is becoming a central tool for testing and assessment. It offers many advantages over fixed (“paper-and-pencil”) methods, such as individualized assessment, reduction of fraud, and straightforward estimation of proficiency levels. CAT has been studied for decades and remains an up-to-date research field in psychometrics and educational science. Practical CAT administration, however, is less frequently considered in such studies. Assigning CAT to respondents requires both the sufficient availability of computer machines, and the use of a powerful and easy-to-use CAT software. With the fast increase of computer resources at moderate cost, the availability of computer machines is becoming a less central, yet important, issue in the practical assessment of CAT tests. The choice of an accurate CAT software, on the other hand, should be guided by its flexibility, its underlying statistical modeling, and its user-friendly potential. According to the type of research or data analysis, some CAT software might be preferred to another. It is therefore important for the researcher or the clinician to know about the current availability of such software, in line with current research and practice in the CAT framework. Moreover, these software should allow enough flexibility to incorporate updates and new theoretical developments, such as e.g., new rules for next item selection. This talk proposes a simple and user-oriented presentation of several CAT software that are currently available. The software to be presented are: the Firestar software (Choi, 2009), the R package catR (Magis & Raîche, 2012), the R package catIrt (Nydick, 2012) and the CAT web-platform Concerto (Kosinski & Rust, 2011). The first three are non-commercial software, while Concerto is a web interface between end users (willing to develop computerized assessment tests) and catR (as underlying routine software). Both R packages are written to be most useful for researchers, without end-user interface, and are therefore less appealing for applied researchers who are not familiar with R. Yet, they offer flexible solutions by means of many options to optimize the design of the test and generate many response patterns for further analyses. Also, they can be easily integrated as sub-routines for more sophisticated CAT software. Firestar provides a user interface and makes all necessary computations with underlying R code. This talk aims at focusing on freely available CAT software. For this reason, only the four aforementioned programs will be presented, although it exists other, commercial CAT software such as e.g., the CATSim software (Assessment Systems Corporation, 2012). The different CAT software are briefly presented and their advantages and drawbacks, flexibility and usefulness are compared, mostly from the point of view of the applied researcher and clinician. The following criteria were retained for objective comparison: (a) their main goal of application; (b) the type of data and IRT modeling they can deal with; (c) the type of users they are focusing on; (d) their operating options; (e) their availability and flexibility for further improvements. A small demonstration of the R package catR will be proposed optionally, depending on time limitation. References Assessment Systems Corporation (2012). CATSim: Comprehensive simulation of computerized adaptive testing. St. Paul, MN. URL: http://www.assess.com/. Choi , S. W. (2009). Firestar: Computerized adaptive testing simulation program for polytomous item response theory models. Applied Psychological Measurement, 33, 644-645. Kosinski, M., & Rust, J. (2011). The development of Concerto: An open source online adaptive testing platform. Paper presented at the International Association for Computerized and Adaptive Testing (IACAT), Pacific Grove, CA. Magis, D., & Raîche, G. (2012). Random generation of response patterns under computerized adaptive testing with the R package catR. Journal of Statistical Software, 48, 1-31. Nydick, S. W. (2012). catIrt: An R package for simulating IRT-based computerized adaptive tests. R package version 0.3-0. [less ▲]

SMALL SAMPLE SIZE CAPABILITY INDEX FOR ASSESSING VALIDITY OF ANALYTICAL METHODS

Poster (2012, March)

Analytical method’s capability evaluation can be a useful methodology to assess the fitness of purpose of these methods for their future routine application. However, care on how to compute the capability ... [more ▼]

Analytical method’s capability evaluation can be a useful methodology to assess the fitness of purpose of these methods for their future routine application. However, care on how to compute the capability indices has to be made. Indeed, the commonly used formulas to compute capability indices such as Cpk, will highly overestimate the true capability of the methods. Especially during methods validation or transfer, there are only few experiments performed and, using in these situations the commonly applied capability indices to declare a method as valid or as transferable to a receiving laboratory will conduct to inadequate decisions. In this work, an improved capability index, namely Cpk-tol and the corresponding estimator of proportion of non conforming results (tolCpk−π) is proposed. Through Monte-Carlo simulations, they have been shown to greatly increase the estimation of analytical methods capability in particular in low sample size situations as encountered during methods validation or transfer. Additionally, the usefulness of this capability index is illustrated through several case studies. [less ▲]