A comparative study of mid-infrared diffuse reflection (DR) and attenuated total reflection (ATR) spectroscopy for the detection of fungal infection on RWA2-corn

An investigation into the rapid detection of mycotoxin-producing fungi on corn by two mid-infrared spectroscopic techniques was undertaken. Corn samples from a single genotype (RWA2, blanks, and contaminated with Fusarium graminearum) were ground, sieved and, after appropriate sample preparation, subjected to mid-infrared spectroscopy using two different accessories (diffuse reflection and attenuated total reflection). The measured spectra were evaluated with principal component analysis (PCA) and the blank and contaminated samples were classified by cluster analysis. Reference data for fungal metabolites were obtained with conventional methods. After extraction and clean-up, each sample was analyzed for the toxin deoxynivalenol (DON) by gas chromatography with electron capture detection (GC-ECD) and ergosterol (a parameter for the total fungal biomass) by high-performance liquid chromatography with diode array detection (HPLC-DAD). The concentration ranges for contaminated samples were 880–3600 g/kg for ergosterol and 300–2600 g/kg for DON. Classification efficiency was 100% for ATR spectra. DR spectra did not show as obvious a clustering of contaminated and blank samples. Results and trends were also observed in single spectra plots. Quantification using a PLS1 regression algorithm showed good correlation with DON reference data, but a rather high standard error of prediction (SEP) with 600 g/kg (DR) and 490 g/kg (ATR), respectively, for ergosterol. Comparing measurement procedures and results showed advantages for the ATR technique, mainly owing to its ease of use and the easier interpretation of results that were better with respect to classification and quantification.     

Direct observation of tunneling and nonlinear self-trapping in a single bosonic Josephson junction

We report on the first realization of a single bosonic Josephson junction, implemented by two weakly linked Bose-Einstein condensates in a double-well potential. In order to fully investigate the nonlinear tunneling dynamics we measure the density distribution in situ and deduce the evolution of the relative phase between the two condensates from interference fringes. Our results verify the predicted nonlinear generalization of tunneling oscillations in superconducting and superfluid Josephson junctions. Additionally, we confirm a novel nonlinear effect known as macroscopic quantum self-trapping, which leads to the inhibition of large amplitude tunneling oscillations.     

Zur Theorie der Schwingungen

Ohne ZusammenfassungUnter diesem Titel soll eine Reihe von aufeinanderfolgenden Aufsätzen erscheinen, die hauptsächlich die Theorie der periodischen nichtlinearen erzwungenen Schwingungen mit Hilfe der Theorie der nichtlinearen Integralgleichungen aufbauen sollen. Die dabei zu verwendenden Methoden werden natürlich auch außerhalb dieses speziellen Anwendungsgebietes, insbesondere in der Variationsrechnung, von Nutzen sein. Auch für die Theorie der Randwertaufgaben allgemeiner nichtlinearer gewöhnlicher Differentialgleichungen zweiter Ordnung wird sich mancher Beitrag ergeben.     

Einige Maßzahlen für nichtkonvexe Mengen

Ohne Zusammenfassung     

Point-mutation effects on charge-transport properties of the tumor-suppressor gene p53

We report on a theoretical study of point mutations effects on charge transfer properties in the DNA sequence of the tumor-suppressor p53 gene. On the basis of effective tight-binding models which simulate hole propagation along the DNA, a statistical analysis of mutation-induced charge transfer modifications is performed. In contrast to noncancerous mutations, mutation hot spots tend to result in significantly weaker changes of transmission properties. This suggests that charge transport could play a significant role for DNA-repairing deficiency yielding carcinogenesis.     

Two-photon photoemission from Ni (1 1 0) and (1 1 1) surfaces

Photoemission was observed when the samples were irradiated with photons in the energy range from 2.5 to 3.3 eV from a tunable dye laser with an intensity of 10⁸Wcm^?2. The emission shows a quadratic intensity dependence. The variation with angle of incidence and polarization is different for the two surfaces. The result obtained from the (1 1 0) surface is discussed with help of the band structure as a two-photon surface photoelectric effect.     

The angular dependence of flux,mean energy and speed ratio for D2 molecules desorbing from a Ni(111) surface

Experimental data are presented for the angular dependence of the relative flux, the mean energy and the speed ratio of deuterium molecules desorbing from a Ni(111) crystal surface at a surface temperature of T_s = 1143 K and at sulphur coverages ranging between 30% and less than 2% of a monolayer.The angular flux distribution is sharply peaked in the forward direction (cos^dθwith 3 ? d ? 5) and the mean energy 〈E〉 of the desorbate depends strongly on the desorption angle θ. For normal desorption $\text{(θ = 0°)}\text{〈E〉}\text{2k}$ is about 700 K higher than T_s and for glancing angles (θ = 80°) it decreases to about 400 K below T_s The results obtained on sulphur free and sulphur covered Ni(111) surfaces are compared with our former data on polycrystalline nickel. The main differences in the kinetic features can be ascribed to the surface roughness. Accordingly, the angular distributions of flux, mean energy, and speed ratio, which deviate strongly from the Knudson and Maxwellian law, do not seem to depend considerably on sulphur coverage and surface structure. A qualitative explanation for these deviations is presented using the principle of detailed balancing.     

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Infrared (IR) spectroscopy of chemisorbed C₆₀ on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm^-1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C₆₀/Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest to be the frustrated translational mode of the adsorbed molecules. Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction coefficient of the C₆₀ molecules, which results in rather small values (∼2×10⁹ s^-1 for Ag and Au, and ∼1.6×10⁹ s^-1for Cu), consistent with a marked metallic character of the adsorbed molecules. Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C₆₀ deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due to strong electron–phonon coupling with induced surface states. Received: 6 June 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002