The composition of primycin

The macrolide antibiotic primycin is shown to consist of more than twenty compounds. Nine components, representing about 90 % of the total, have been isolated and their structures elucidated by spectroscopic methods. Molecular weights were determined by FAB mass spectrometry. The components studied belong to three groups (see Fig.), depending on substituent R₂ and each set represents homologous series, differing in substituent R₁. The structure proposed previously for primycin was unambiguously proved and assigned as that of the A₁ component.     

The phonon-assisted photon-drag effect in a two-dimensional semiconductor quantum-well structure

The phonon-assisted photon-drag effect in a two-dimensional semiconductor quantum well structure is investigated. By making use of second-order perturbation theory and the classical Boltzmann equation we found, by considering both intrasubband and the intersubband electronic transitions, that the electric field generated by the photon-drag effect in a typical GaAs–AlGaAs two-dimensional system is enhanced by almost one order of magnitude as compared with that of a bulk system. Moreover, the results can qualitatively account for the observed absorption spectra due to intersubband electronic transitions occurring in GaAs quantum wells.     

A smooth nonparametric quantile estimator from right-censored data

Based on randomly right-censored data, a smooth nonparametric estimator of the quantile function of the lifetime distribution is studied. The estimator is defined to be the solution x_n(p) of F_n(x_n(p)) = p, where F_n is the distribution function corresponding to a kernel estimator of the lifetime density. The strong consistency and asymptotic normality of x_n(p) are shown. Data-based selection of the bandwidth required for computing F_n is investigated using bootstrap methods. Illustrative examples are given.     

Modelling resource availability in general hospitals design and implementation of a decision support model

Admission planning in general hospitals means selecting elective patients from a waiting list in order to obtain optimal utilisation of the available beds, nursing staff and operating theatre facilities while taking into account emergency admissions. Also, a wide variety of other factors, often situational and not explicitly stated, play a part in this decision process. As such, it is a complex problem which is difficult to handle for any decision maker. In this paper a statistical model for the prediction of resource availability is presented. The model is first tested on empirical data. On the basis of the model a DSS was designed which is now in daily use in several hospitals. Problems encountered in that implementation process will be stated. The results obtained with the model show that such an approach based on statistical data provides sufficiently accurate results to be useful.     

H3PO4 activated biochars derived from different agricultural biomasses for the removal of ciprofloxacin from aqueous solution

Biochars were prepared by the pyrolysis of various H₃PO₄ activated agricultural biomasses at 600 °C and subsequently used as adsorbents for the removal of ciprofloxacin (CIP) from aqueous solution. Peanut shell-based biochar (PSBC), corncob-based biochar (CCBC) and cotton-based biochar (CTBC) had high surface areas (571.0–1006.3 m²/g), well-developed pore structures (mesopores with large pore volumes) and available adsorption functional groups (C=C, C–N and C–O–C). The CIP adsorption onto the biochars was investigated by batch experiments (kinetics, isotherms, thermodynamics, pH, etc.). Thermodynamics calculations showed the spontaneous (ΔG^θ<0) and endothermic (ΔH^θ>0) nature of the mechanism. In particular, CCBC exhibited high adsorption capacity (120.6 mg/g) of CIP in real lake water and it also had significant removal efficiency of other common pharmaceutical contaminants from real lake environment, and even in a coexisting quintuple system. Finally, multiple interaction mechanisms of CIP adsorption onto aromatized biochar were explored combining characterization analysis and theoretical calculations. Elucidation of the mechanism of CIP adsorption onto biochar provides new insights into the assessment of the removal of pharmaceuticals from the aqueous environment.     

Messenger sneutrinos as cold dark matter

In models where supersymmetry breaking is communicated into the visible sector via gauge interactions the lightest supersymmetric particle is typically the gravitino which is too light to account for cold dark matter. We point out that the lightest messenger sneutrinos with mass in the range of one to three TeV may serve as cold dark matter over most of the parameter space due to one-loop electroweak radiative corrections. However, in the minimal model this mass range has been excluded by the direct dark matter searches. We propose a solution to this problem by introducing terms that explicitly violate the messenger number. This results in low detection rate for both direct and indirect searches and allows messenger sneutrinos to be a valid dark matter candidate in a wide region of SUSY parameter space.     

Atmospheric peroxy radicals: ROXMAS,a new mass-spectrometric methodology for speciated measurements of HO2 and ∑RO2 and first results

ROXMAS (ROx Chemical Conversion/CIMS), a novel method for atmospheric speciated measurements of HO₂ and the sum of organic peroxy radicals (∑RO₂) developed by MPI-K, has been successfully deployed in a field campaign on Monte Cimone, Italy, June-July 2000. The method relies on amplifying chemical conversion of peroxy radicals to gaseous sulfuric acid via the chain reaction with NO and SO₂ and detection of the sulfuric acid by CIMS. Speciated measurements have been realized by diluting atmospheric air in either N₂ or O₂ buffer, thus exploiting the dependence of the conversion efficiency of RO₂ to HO₂ on [O₂], [NO], and [SO₂]. Speciated measurements of HO₂ and RO₂ are required to provide further insight into radical partitioning and thus to elucidate further the mechanisms of the oxidation of volatile organic compounds in the troposphere. This methodology yields useful speciated results for atmospheric conditions where CH₃O₂ makes a major contribution to total RO₂. Under other conditions it gives an upper limit for [HO₂] and a lower limit for [∑RO₂].     

The ESR observation of 14NH+3 and 15NH+3 trapped in an argon matrix at 14 K

The molecular ion NH⁺₃ has been trapped in an argon matrix at 14 K by photoionisation of an NH₃/Ar mixture during deposition. The NH⁺₃ cation has been found to be rigidly trapped in the argon matrix and exhibits a powder ESR spectrum. The derived magnetic parameters agree well with those obtained by other workers in different matrices. A strong reversible temperature dependence of the linewidth of the NH⁺₃ spectrum has been observed.