Covalently attached monolayers on crystalline hydrogen-terminated silicon: extremely mild attachment by visible light

A very mild method was developed for the attachment of high-quality organic monolayers on crystalline silicon surfaces. By using visible light sources, from 447 to 658 nm, a variety of 1-alkenes and 1-alkynes were attached to hydrogen-terminated Si(100) and Si(111) surfaces at room temperature. The presence and the quality of the monolayers were evaluated by static water contact angles, X-ray photoelectron spectroscopy, and IR spectroscopy. Monolayers prepared by thermal, UV light, or visible light initiation were compared. Additionally, the ability of infrared reflection-absorption spectroscopy to study organic monolayers on silicon was explored. A reaction mechanism is discussed on the basis of investigations of the reaction behavior of 1-alkenes with silicon wafers with varying types and levels of doping. Finally, a series of mixed monolayers derived from the mixed solutions of a 1-alkene and an omega-fluoro-1-alkene were investigated to reveal that the composition of the mixed monolayers was directly proportional to the molar ratio of the two compounds in the solutions.     

Lamé equations with algebraic solutions

In this paper we study Lamé equations L_n,By=0 in so-called algebraic form, having only algebraic functions as solution. In particular we provide a complete list of all finite groups that occur as the monodromy groups, together with a list of examples of such equations. We show that the set of such Lamé equations with is countable, up to scaling of the equation. This result follows from the general statement that the set of equivalent second-order equations, having algebraic solutions and all of whose integer local exponent differences are 1, is countable.     

IVUS flow measurements: line spread function and decorrelation pattern

A method to measure transverse blood flow, based on correlation between consecutive radio frequency (RF) signals, has been developed. Currently, we are implementing the method for an intravascular (IVUS) array catheter. In this paper, the acoustical beam (line-spread function, LSF) was experimentally measured and compared with the simulated one. Next, the experimental LSF(E) was convolved with a matrix of white noise to produce RF(E) signals. Decorrelation pattern from the RF(E) signals was compared with the correspondent autoconvolution of the LSF(E) and a good agreement was found. We conclude that the transverse decorrelation pattern of the IVUS array catheter can be assessed from the properties of the acoustical beam.     

Geodesic continued fractions and LLL

We discuss a proposal for a continued fraction-like algorithm to determine simultaneous rational approximations to d$d$ real numbers _α1,…,_αd${\alpha }_1,\dots ,{\alpha }_d$. It combines an algorithm of Hermite and Lagarias with ideas from LLL-reduction. We dynamically LLL-reduce a quadratic form with parameter t$t$ as t↓0$t\downarrow 0$. Suggestions in this direction have been made several times over in the literature, e.g. Chevallier (2013) [4] or Bosma and Smeets (2013) [2]. The new idea in this paper is that checking the LLL-conditions consists of solving linear equations in t$t$.     

Flow Injection Analysis of Hydrogen Peroxide,Sulfite, Formaldehyde and Hydroxymethanesulfonic Acid in Precipitation Samples

Abstract

Hydroxymethanesulfonic acid (HMSA), the reaction product of sulfite and formaldehyde plays an important part in the aqueous phase conversion of sulfite to sulfate. HMSA is fairly stable under acidic conditions and in presence of hydrogen peroxide. Sulfite is unstable under these conditions.

A flow injection set-up was developed, which allows the determination of H₂O₂, sulfite, formaldehyde and hydroxymethanesulfonic acid.

H₂O₂ analysis by amperometric detection offers the possibility of a simple, robust field instrument. The detection limit is 5μg/l and the method is linear up to 5mg/l.

Based on the 4,4-dithiodipyridine/sulfite reaction selective and sensitive spectrophotometric detections were developed for sulfite, formaldehyde and hydroxymethanesulfonic acid. The detection limit of these compounds is 50μg/l and the method is linear up to 5mg/l.

A large fraction of S(IV) is present as HMSA in fog, dew and precipitation samples in The Netherlands.     

Using wavelet methods to solve noisy Abel-type equations with discontinuous inputs

One way of estimating a function from indirect, noisy measurements is to regularise an inverse of its Fourier transformation, using properties of the adjoint of the transform that degraded the function in the first place. It is known that when the function is smooth, this approach can perform well and produce estimators that have optimal convergence rates. When the function is unsmooth, in particular when it suffers jump discontinuities, an analogue of this approach is to invert the wavelet transform and use thresholding to decide whether wavelet terms should be included or excluded in the final approximation. We evaluate the performance of this approach by applying it to a large class of Abel-type transforms, and show that the smoothness of the target function and the smoothness of the transform interact in a particularly subtle way to determine the overall convergence rate. The most serious difficulties arise when the target function has a jump discontinuity at the origin; this has a considerably greater, and deleterious, impact on performance than a discontinuity elsewhere. In the absence of a discontinuity at the origin, the rate of convergence is determined principally by an inequality between the smoothness of the function and the smoothness of the transform.     

Some congruences for the Apery numbers

In 1979 R. Apéry introduced the numbers a_n = Σ₀ⁿ(_kⁿ)²(_k^{n + k}) and u_n = Σ₀ⁿ(_kⁿ)²(_k^{n + k})² in his irrationality proof for ζ(2) and ζ(3). We prove some congruences for these numbers which generalize congruences previously published in this journal.     

One-step photochemical attachment of NHS-terminated monolayers onto silicon surfaces and subsequent functionalization

N-Hydroxysuccinimide (NHS)-ester-terminated monolayers were covalently attached in one step onto silicon using visible light. This mild photochemical attachment, starting from omega-NHS-functionalized 1-alkenes, yields a clean and flat monolayer-modified silicon surface and allows a mild and rapid functionalization of the surface by substitution of the NHS-ester moieties with amines at room temperature. Using a combination of analytical techniques (infrared reflection absorption spectroscopy (IRRAS), extensive X-ray photoelectron spectroscopy (XPS) in combination with density functional theory calculations of the XPS chemical shifts of the carbon atoms, atomic force microscopy (AFM), and static contact angle measurements), it was shown that the NHS-ester groups were attached fully intact onto the surface. The surface reactivity of the NHS-ester moieties toward amines was qualitatively and quantitatively evaluated via the reaction with para-trifluoromethyl benzylamine and biotin hydrazide.     

Validation of a new enzyme-linked immunosorbent assay to detect the triggering proteins and peptides for celiac disease: interlaboratory study

The performance of Gluten-Tec (EuroProxima, Arnhem, The Netherlands) was tested through an interlaboratory study in accordance with AOAC guidelines. Gluten-Tec is a competitive ELISA that detects an immunostimulatory epitope of a-gliadin in dietary food for celiacs. Fifteen laboratories, representing 14 different countries, announced their interest in taking part in this study. Of the 12 laboratories that sent the results within the established timeframe, two submitted inappropriate standard curves and were excluded from the statistical analysis. Four different food matrixes (rice-based baby food, maize bread, chocolate cake mix, and beer) were selected for preparing the test samples. Two gliadin extraction procedures were used: the conventional 60% ethanol, and a new method based on the reducing reagent dithiothreitol. The 38 samples (19 blind duplicates) tested in this study were prepared by diluting the different extracts in order to cover a wide range of gliadin levels. Both sample extraction and dilution were performed by EuroProxima; the present interlaboratory study was focused only on testing the ELISA part of the Gluten-Tec kit protocol. Repeatability values (within-laboratory variance), expressed as RSD(r) ranged from 6.2 to 25.7%, while reproducibility values (interlaboratory variance), expressed as RSD(R), ranged from 10.6 to 45.9%. Both statistical parameters were in the acceptable range of ELISAs under these conditions, and the method will be presented to the Codex Alimentarius as a preferred method for gluten analysis.