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Search Results: 1 - 10 of 14078 matches for " Jan Lindemans "
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Periconceptional Maternal Folic Acid Use of 400 μg per Day Is Related to Increased Methylation of the IGF2 Gene in the Very Young Child
Régine P. Steegers-Theunissen,Sylvia A. Obermann-Borst,Dennis Kremer,Jan Lindemans,Cissy Siebel,Eric A. Steegers,P. Eline Slagboom,Bastiaan T. Heijmans
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0007845
Abstract: Countries worldwide recommend women planning pregnancy to use daily 400 μg of synthetic folic acid in the periconceptional period to prevent birth defects in children. The underlying mechanisms of this preventive effect are not clear, however, epigenetic modulation of growth processes by folic acid is hypothesized. Here, we investigated whether periconceptional maternal folic acid use and markers of global DNA methylation potential (S-adenosylmethionine and S-adenosylhomocysteine blood levels) in mothers and children affect methylation of the insulin-like growth factor 2 gene differentially methylation region (IGF2 DMR) in the child. Moreover, we tested whether the methylation of the IGF2 DMR was independently associated with birth weight.
Analytical Investigations of Toxic p-Phenylenediamine (PPD) Levels in Clinical Urine Samples with Special Focus on MALDI-MS/MS
Gero P. Hooff, Nick A. van Huizen, Roland J. W. Meesters, Eduard E. Zijlstra, Mohamed Abdelraheem, Waleed Abdelraheem, Mohamed Hamdouk, Jan Lindemans, Theo M. Luider
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0022191
Abstract: Para-phenylenediamine (PPD) is a common chromophoric ingredient in oxidative hair-dyes. In some African countries like Sudan, Egypt and Morocco but also in India this chemical is used alone or in combination with colouring extracts like Henna for dyeing of the hair or the skin. Excessive dermal exposure to PPD mainly leads to the N-mono- and N,N′-diacetylated products (MAPPD, DAPPD) by N-acetyltransferase 1 and 2 (NAT1 and 2) catalyzed reactions. Metabolites and PPD are mainly excreted via renal clearance. Despite a low risk of intoxication when used in due form, there are numerous cases of acute intoxication in those countries every year. At the ENT Hospital - Khartoum (Sudan) alone more than 300 cases are reported every year (~10% fatal), mostly caused by either an accidental or intended (suicidal) high systemic exposure to pure PPD. Intoxication leads to a severe clinical syndrome including laryngeal edema, rhabdomyolysis and subsequent renal failure, neurotoxicity and acute toxic hepatitis. To date, there is no defined clinical treatment or antidote available and treatment is largely supportive. Herein, we show the development of a quick on-site identification assay to facilitate differential diagnosis in the clinic and, more importantly, the implementation of an advanced analytical platform for future in-depth investigations of PPD intoxication and metabolism is described. The current work shows a sensitive (~25 μM) wet chemistry assay, a validated MALDI-MS/MS and HPLC-UV assay for the determination of PPD and its metabolites in human urine. We show the feasibility of the methods for measuring PPD over a range of 50–1000 μM. The validation criteria included linearity, lower limit of quantification (LLOQ), accuracy and precision, recovery and stability. Finally, PPD concentrations were determined in clinical urine samples of cases of acute intoxication and the applied technique was expanded to identify MAPPD and DAPPD in the identical samples.
Gonadotropin-Releasing Hormone and Adipokinetic Hormone Signaling Systems Share a Common Evolutionary Origin
Marleen Lindemans,Tom Janssen,Liliane Schoofs
Frontiers in Endocrinology , 2011, DOI: 10.3389/fendo.2011.00016
Abstract: Gonadotropin-releasing hormone (GnRH) is a critical and central hormone that regulates vertebrate reproduction. The high conservation of GnRH signaling within the chordates (deuterostomians) raises the important question as to whether its appearance might date back prior to the divergence of protostomian and deuterostomian lineages, about 700 million years ago. This leads to several important questions regarding the evolution of the GnRH family. Has GnRH been retained in most protostomian lineages? And was regulation of reproduction already a function of ancestral GnRH? The first question can undoubtedly be answered affirmatively since several GnRH-like sequences have been found in wide variety of protostomian and deuterostomian phyla. However, based on their different primary functions in different phyla – which implies a less unanimous answer on the second question – consistency in the nomenclature of this peptide family has been lost. A comparative and phylogenetic approach shows that the ecdysozoan adipokinetic hormones (AKHs), lophotrochozoan GnRHs and chordate GnRHs are structurally related and suggests that they all originate from a common ancestor. This review supports the view that the AKH–GnRH signaling system probably arose very early in metazoan evolution, prior to the divergence of protostomians and deuterostomians.
A Longitudinal Analysis of the Stability of Household Money Demand  [PDF]
Jan Tin
Modern Economy (ME) , 2011, DOI: 10.4236/me.2011.23046
Abstract: Past aggregate time-series studies, conducted under the assumption of a representative economic agent, frequently show that the demand for narrowly defined M1, especially non-interest-yielding demand deposit, is unstable during periods of financial innovations. Whether this is longitudinally the case among life-cycle savers is unclear. This study utilizes longitudinal data to take another look and find that volatility in the demand for non-interest-earning checking accounts in the mid and late 1990s is attributable solely to the portion held for the transactions motive. When the conventional Baumol-Tobin model is extended to include human capital and family formation variables representing the life-cycle motive, equilibrium money demand is a stable function of both economic and demographic variables.
A Spectral Method in Time for Initial-Value Problems  [PDF]
Jan Scheffel
American Journal of Computational Mathematics (AJCM) , 2012, DOI: 10.4236/ajcm.2012.23023
Abstract: A time-spectral method for solution of initial value partial differential equations is outlined. Multivariate Chebyshev series are used to represent all temporal, spatial and physical parameter domains in this generalized weighted residual method (GWRM). The approximate solutions obtained are thus analytical, finite order multivariate polynomials. The method avoids time step limitations. To determine the spectral coefficients, a system of algebraic equations is solved iteratively. A root solver, with excellent global convergence properties, has been developed. Accuracy and efficiency are controlled by the number of included Chebyshev modes and by use of temporal and spatial subdomains. As examples of advanced application, stability problems within ideal and resistive magnetohydrodynamics (MHD) are solved. To introduce the method, solutions to a stiff ordinary differential equation are demonstrated and discussed. Subsequently, the GWRM is applied to the Burger and forced wave equations. Comparisons with the explicit Lax-Wendroff and implicit Crank-Nicolson finite difference methods show that the method is accurate and efficient. Thus the method shows potential for advanced initial value problems in fluid mechanics and MHD.
Operationalizing Sustainability Principles in the Engineering Profession  [PDF]
Jan Adamowski
Natural Resources (NR) , 2012, DOI: 10.4236/nr.2012.34024
Abstract: The engineering profession has responded to the issue of sustainable development in two main ways. It has responded through public policy statements that acknowledge the magnitude of the problem in addition to pledging to steer engineering towards a more sustainable future, and it has also responded more directly through technological innovation. In this paper, these two responses will be explored with respect to the debate on how to operationalize sustainability principles in practical terms. This paper also attempts to provide the rationale for a philosophy of engineering ethics grounded in the notion of sustainable development. It is hoped that this would lead to a revised “social contract” that would enable engineers to engage more actively in political, technical, economic and social discussions and processes.
Chaos in Planar, Circular, Restricted Three-Body Problem  [PDF]
Jan Vrbik
Applied Mathematics (AM) , 2013, DOI: 10.4236/am.2013.41008

In this article we analyze the motion of a test particle of a planar, circular, restricted three-body problem in resonance, using the Kustaanheimo-Stiefel formalism. We show that a good qualitative description of the motion can be reduced to three simple equations for semi-major axis, eccentricity and resonance angle. Studying these equations reveals the onset of chaos, and sheds a new light on its weak nature. The 7:4 resonance is used as an example.

Compound Means and Fast Computation of Radicals  [PDF]
Jan ?ustek
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.516241
Abstract: In last decades, several algorithms were developed for fast evaluation of some elementary functions with very large arguments, for example for multiplication of million-digit integers. The present paper introduces a new fast iterative method for computing values \"\" with high accuracy, for fixed \"\" and \"\". The method is based on compound means and Padé approximations.
Short Report: A Sponge Phantom Provides a Homogeneous k-Space Pattern at MRI  [PDF]
Jan Menke
Open Journal of Radiology (OJRad) , 2014, DOI: 10.4236/ojrad.2014.42026
Abstract: Background: The spectral coverage of magnetic resonance (MR) sequences can be well assessed in k-space. However, many objects do not provide high signal intensities in the peripheral k-space. Purpose: To experimentally find a phantom that provides a homogeneous spectral pattern also at the high spatial frequencies of the k-space periphery. Material and Methods: Different phantoms were imaged on a 1.5 Tesla magnet, and the resulting MR images were viewed in k-space after fast Fourier transform. Results: Firstly, phantoms with a homogeneous physical structure were studied with a T2-weighted MR sequence, but they provided an inhomogeneous k-space pattern with dominant central low-frequency components. Secondly, phantoms with an inhomogeneous physical structure were studied. In this group, a water-soaked sponge showed a relatively homogeneous k-space pattern also at high spatial frequencies, owing to the fine porous structure. This sponge phantom can also be soaked with Gadolinium chelates for T1-weighted MR imaging. Conclusion: A simple sponge phantom provides a homogeneous k-space pattern, owing to its fine porous structure. This could be utilized in MR sequence development and for viewing the spectral coverage of MR sequences in k-space.

Fully Integrated High-Voltage Generators with Optimized Power Efficiency  [PDF]
Doutreloigne Jan
Journal of Computer and Communications (JCC) , 2014, DOI: 10.4236/jcc.2014.213001

This paper describes how the power efficiency of fully integrated Dickson charge pumps in high- voltage IC technologies can be improved considerably by implementing charge recycling techniques, by replacing the normal PN junction diodes by pulse-driven active diodes, and by choosing an appropriate advanced smart power IC technology. A detailed analysis reveals that the combination of these 3 methods more than doubles the power efficiency compared to traditional Dickson charge pump designs.

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