Chemical Synthesis and Enzymatic Testing of CMP‐Sialic Acid Derivatives

The cycloSal approach has been used in the past for the synthesis of a range of phosphorylated bioconjugates. In those reports, cycloSal nucleotides were allowed to react with different phosphate nucleophiles. With glycopyranosyl phosphates as nucleophiles, diphosphate‐linked sugar nucleotides were formed. Here, cycloSal‐nucleotides were used to prepare monophosphate‐linked sugar nucleotides successfully in high anomeric purity and high chemical yield. The method was successfully used for the synthesis of three nucleotide glycopyranoses as model compounds. The method was then applied to the syntheses of CMP‐N‐acetyl‐neuraminic acids (CMP‐Neu5NAc) and of four derivatives with different modifications at their amino functions (N‐propanoyl, N‐butanoyl, N‐pentanoyl and N‐cyclopropylcarbonyl). The compounds were used for initial enzymatic studies with a bacterial polysialyltransferase (polyST). Surprisingly, the enzyme showed marked differences in terms of utilisation of the four derivatives. The N‐propanoyl, N‐butanoyl, and N‐pentanoyl derivatives were efficiently used in a first transfer with a fluorescently labelled trisialo‐acceptor. However, elongation of the resulting tetrasialo‐acceptors worsened progressively with the size of the N‐acyl chain. The N‐pentanoyl derivative allowed a single transfer, leading to a capped tetramer. The N‐cyclopropylcarbonyl derivative was not transferred.     

On-machine wire electrical discharge dressing (WEDD) of metal-bonded grinding wheels

Traditional multivariate control charts such as Hotelling’s χ ² and T ² control charts are designed to monitor vectors of variable quality characteristics. However, in certain situations, data are expressed in linguistic terms and, under these circumstances, variable or attribute multivariate control charts are not suitable choices for monitoring purposes. Fuzzy multivariate control charts such as fuzzy Hotelling’s T ² could be considered as efficient tools to overcome the problems of linguistic observations. The purpose of this paper is to develop a fuzzy multivariate exponentially weighted moving average (F-MEWMA) control chart. In this paper, multivariate statistical quality control and fuzzy set theory are combined to develop the proposed method. Fuzzy sets and fuzzy logic are powerful mathematical tools for modeling uncertain systems in industry, nature, and humanity. Through a numerical example, the performance of the proposed control chart was compared to the fuzzy Hotelling’s T ² control chart. Results indicate uniformly superior performance of the F-MEWMA control chart over Hotelling’s T ² control chart.     

Intrinsic Seebeck Coefficient of Quantum Dots

The Seebeck coefficient S is an important performance characteristic of thermoelectric materials. In this paper we establish the fact that quantum dots and single-electron tunneling devices with narrow, well-spaced energy levels and sharp transmission resonances have a Seebeck coefficient independent of material parameters. By employing a delta function for the transmission resonances we arrive at an intrinsic expression for S in terms of the fundamental electronic charge e. We further confirm the validity of our result in the case of a transmission resonance with finite width.     

The effective hydrodynamic radius of single DNA-grafted colloids as measured by fast Brownian motion analysis

Optical tweezers accomplished with fast position detection enable one to carry out Brownian motion analysis of single DNA-grafted (grafting density: ∼1000 molecules per particle, molecular weight: 4000 bp) colloids in media of varying NaCl concentration. By that the effective hydrodynamic radius of the colloid under study is determined and found to be strongly dependent on the conformation of the grafted DNA chains. Our results compare well both with recent measurements of the pair interaction potential between DNA-grafted colloids (Kegler et al. Phys Rev Lett 2008; 100:118302) and with microfluidic studies (Gutsche et al. Microfluid Nanofluid 2006; 2:381-386). The observed scaling of the brush height with the ion concentration is in full accord with the theoretical predictions by Pincus, Zhulina, Birshtein and Borisov.     

Bolus ingestion of white and green tea increases the concentration of several flavan‐3‐ols in plasma,but does not affect markers of oxidative stress in healthy non‐smokers

White tea (WT) is rich in flavan‐3‐ols as green tea (GT) and might provide health protective effects due to the strong antioxidant properties of flavan‐3‐ols. Since intervention studies with WT are lacking, we evaluated the effects of WT consumption on antioxidant status, antioxidant capacity and biomarkers of oxidative stress compared to water and GT. After an overnight fast, 70 healthy non‐smokers were randomized to consume 600 mL of WT, GT or water (control). Plasma (epi‐)catechin and epi(gallo)catechingallate, antioxidant capacity (Folin assay, trolox equivalent antioxidant capacity test), 8‐iso‐prostaglandin F_2α, ascorbic acid and uric acid were determined before and several times within 8 h after consumption. DNA strand breaks were measured in vivo and ex vivo (H₂O₂ stimulation) in leukocytes. Plasma flavan‐3‐ols significantly increased after WT and GT ingestion. Trolox equivalent antioxidant capacity was lower after 5 h in controls versus WT (p=0.031) and GT (p=0.005). Folin‐Ciocalteu reducing capacity, ascorbic and uric acid as well as markers of oxidative stress (8‐iso‐prostaglandin‐F_2α, DNA strand breaks) were not affected by the beverages. A short‐term increase of catechins does not change plasma antioxidant capacity in healthy subjects. Conclusions with respect to health protective effects of WT and GT on the basis of these biomarkers can, thus, not be drawn.     

Complexing agent assisted synthesis of high aspect ratio Fe3 +/Mg2 + layered double hydroxides

A new, facile synthesis for Fe^3 +/Mg^2 + LDHs is developed and investigated. The crucial feature of the synthesis is the usage of a complexing agent (diethylenetriamine, DETA) to increase the solubility of iron phases precipitated intermediately. The influences of different synthesis parameter like DETA concentration, pH value, and temperature are investigated. The optimized synthesis route yields high aspect ratio Fe^3 +/Mg^2 + LDHs which are expected to be interesting filler materials for flame retardant nanocomposites.     

Spiral-CT-based assessment of tracheal stenoses using 3-D-skeletonization

PURPOSE: Demonstration of a technique for three-dimensional (3-D) assessment of tracheal-stenoses, regarding site, length and degree, based on spiral computed tomography (S-CT). PATIENTS AND METHODS: S-CT scanning and automated segmentation of the laryngo-tracheal tract (LTT) was followed by the extraction of the LTT medial axis using a skeletonization algorithm. Orthogonal to the medial axis the LTT 3-D cross-sectional profile was computed and presented as line charts, where degree and length was obtained. Values for both parameters were compared between 36 patients and 18 normal controls separately. Accuracy and precision was derived from 17 phantom studies. RESULTS: Average degree and length of tracheal stenoses was found to be 60.5% and 4.32 cm in patients compared with minor caliber changes of 8.8% and 2.31 cm in normal controls (p < 0.0001). For the phantoms an excellent correlation between the true and computed 3-D cross-sectional profile was found (p < 0.005) and an accuracy for length and degree measurements of 2.14 mm and 2.53% respectively could be determined. The corresponding figures for the precision were found to be 0.92 mm and 2.56%. CONCLUSION: LTT 3-D cross-sectional profiles permit objective, accurate and precise assessment of LTT caliber changes. Minor LTT caliber changes can be observed even in normals and, in case of an otherwise normal S-CT study, can be regarded as artifacts.     

Finite element analysis of a polymer composite subjected to a sliding steel asperity Part I Normal fibre orientation

FE micro-models have been developed in order to determine contact, stress and strain conditions produced by a steel asperity sliding on the surface of a normally oriented fibre-reinforced polymer composite. A displacement coupling technique was introduced to model a micro-environment as part of a macro-environment and to get more realistic simulation results about the failure conditions in the composite structure, in comparison to the so far widely applied anisotropic analytical or numerical macro-models. On the basis of the results, conclusions may be drawn for the possible wear mechanisms of the fibre-reinforced polymer composite. Stress results in the vicinity of the fibers in the contact area show high shear loading of the matrix leading to the formation of stretched-out matrix wear debris. In addition, high repeated compression-tension stresses at the fibre/matrix interface near the surface can lead to fibre debonding phenomena. Considering the fibre ends in the contact region, high compression stresses at their rear edges can produce fibre cracking features. To study the wear mechanisms experimentally, a single asperity scratch test was also performed showing shear failure events of the polymer matrix, fibre/matrix debonding and fibre cracking effects, as expected from the modelling studies.