Exact methods for the resource levelling problem

We present a project scheduling problem subject to general temporal constraints where the utilization of a set of renewable resources has to be smoothed over time. For solving the NP-hard optimization problem, we point out some important structural properties and introduce a new enumeration scheme. Combining this enumeration scheme with some branch-and-bound techniques, we propose an appropriate solution procedure for the project scheduling problem at hand. To outline the practical importance of resource levelling, we sketch exemplary the optimization of mid-term planning schedules with regard to the resource requirements of IT projects. Finally, we present results from a comprehensive computational study on problem instances of the well-known rlp_j10 and rlp_j20 test sets devised by Kolisch et al. (Benchmark Instances for Project Scheduling Problems, Kluwer, Boston, 1999).     

A kinetic study of Am(III)/humic colloid interactions

The interaction kinetics of the Am(III) ion with aquatic humic colloids is investigated under near-natural conditions by column experiments with a sandy aquifer sample rich in humic substancesforthe appraisal of the migration behavior of Am. The association and dissociation kinetics of the Am ion onto and from humic colloids control the migration of colloid-borne Am. As the contact time between Am and humic colloids prior to introduction into a column is increased, the mobility of colloid-borne Am is enhanced and hence the recovery of Am in the effluent increases. On the other hand, an increase of the migration time and residence time in column, respectively, reduces the Am recovery. Considering these experimental results a refined version of the kinetic model KICAM (Kinetically Controlled Availability Model), which suggests different Am binding modes with humic colloids, was developed. Applying KICAM it is possible to predict static and dynamic experiments affected by the kinetically controlled Am/humic colloid interactions over the range of 1 h up to several months. However, to apply these experimental results to long-term conditions, the Am binding scheme as proposed in KICAM needs to be verified. This paper provides, therefore, a basis for a better understanding of the colloid-borne Am migration in porous aquifer systems.     

Microwave treatment of dietary gelatin does not generate cis-4-hydroxy-l-proline, an inhibitor of collagen biosynthesis

Aqueous solutions (5?g/100?ml) of commercial preparations of (a) an enzymatic partial hydrolysate of gelatin and (b) type A gelatin were subjected to threefold heating to boiling in a domestic microwave oven at 750?W and to conventional heating. Then samples were totally hydrolyzed (6?M hydrochloric acid, 110??°C, 24?h) and investigated for the presence of eight possible stereoisomers of 3- and 4-hydroxyproline (Hyp) using capillary gas chromatography. Amino acids were analyzed as N(O)-trifluoroacetyl 2-propyl esters on Chirasil-l-Val and detected by selected ion monitoring mass spectrometry. Blanks of (a) and (b) were analyzed in parallel. Relative amounts of 5.0±0.2% cis-4-d-Hyp were generated from native trans-4-l-Hyp as a result of total hydrolysis in all samples and independent of previous treatment. Notably, neither cis-3-l-Hyp nor cis-4-l-Hyp could be detected in either of the gelatin samples. Thus a report on the generation of antifibrotic and therefore potentially hazardous cis-3-l-Hyp and cis-4-l-Hyp from protein-bonded native trans-3-l-Hyp and trans-4-l-Hyp on microwave heating of infant formulae could not be confirmed.     

On-road measurement of particle emission in the exhaust plume of a diesel passenger car

Particle size distributions were measured under real world dilution conditions in the exhaust plume of a diesel passenger car closely followed by a mobile laboratory on a high speed test track. Under carefully controlled conditions the exhaust plume was continuously sampled and analyzed inside the mobile laboratory. Exhaust particle size distribution data were recorded together with exhaust gas concentrations, i.e., CO, CO2, and NO(x), and compared to data obtained from the same vehicle tested on a chassis dynamometer. Good agreement was found for the soot mode particles which occurred at a geometric mean diameter of approximately 50 nm and a total particle emission rate of 10(14) particles km(-1). Using 350 ppm high sulfur fuel and the standard oxidation catalyst a bimodal size distribution with a nucleation mode at 10 nm was observed at car velocities of 100 km h(-1) and 120 km h(-1), respectively. Nucleation mode particles were only present if high sulfur fuel was used with the oxidation catalyst installed. This is in agreement with prior work that these particles are of semivolatile nature and originate from the nucleation of sulfates formed inside the catalyst. Temporal effects of the occurrence of nucleation mode particles during steady-state cruising and the dynamical behavior during acceleration and deceleration were investigated.     

Estimating the Optimal Margins of Embeddings in Euclidean Half Spaces

Concept classes can canonically be represented by matrices with entries 1 and –1. We use the singular value decomposition of this matrix to determine the optimal margins of embeddings of the concept classes of singletons and of half intervals in homogeneous Euclidean half spaces. For these concept classes the singular value decomposition can be used to construct optimal embeddings and also to prove the corresponding best possible upper bounds on the margin. We show that the optimal margin for embedding n singletons is and that the optimal margin for half intervals over {1,...,n} is . For the upper bounds on the margins we generalize a bound by Forster (2001). We also determine the optimal margin of some concept classes defined by circulant matrices up to a small constant factor, and we discuss the concept classes of monomials to point out limitations of our approach.     

On-line coupling of size exclusion chromatography with electrospray ionization-tandem mass spectrometry for the analysis of aquatic fulvic and humic acids

A method was developed for the analysis of humic and fulvic acids by size-exclusion chromatography-electrospray ionization-tandem mass spectrometry using a completely volatile eluent. Humic and fulvic acids were separated into three peaks. These fractions occupied different mass ranges and showed differences in the fine structure of their mass spectra. The low-molecular-weight (LMW) fraction of fulvic acids is most sensitively determined by ESI-MS, and it appears that previous results obtained by infusion-ESI-MS were primarily determined by this fulvic acid fraction. The average molecular weight of this fractions turned out to be lower than that reported from infusion-ESI-MS measurements. Its scan spectra and the product ion spectra of some of its molecular anions perfectly match those previously obtained from whole fulvic acid mixtures. Obviously, a class of well-defined polycarboxylated molecules exist that occurs in all fulvic acid fractions thus far investigated. With decreasing elution time and increasing molecular weight, detection by ESI-MS loses sensitivity as compared to the parallel UV recording, and the fine structure of the scan spectra becomes increasingly uniform for both fulvic and humic acids. The average molecular weight of the HMW fraction exceeds those values calculated from infusion experiments. Scan spectra and product ion spectra of the high-molecular-weight (HMW) fraction of both the humic and the fulvic acids suggest that the HMW fraction consists of several subunits that originate from the LMW fraction.     

Induction of apoptosis in human microvascular endothelial cells by divalent cobalt ions. Evidence for integrin-mediated signaling via the cytoskeleton

Wound healing following implantation is characterized by an acute inflammatory reaction and a subsequent reorganizing phase in which angiogenesis is involved. Endothelial cells (EC) participate in both inflammation and angiogenesis. Thus, the effects on functions of EC exerted by implanted materials could affect the progression of wound healing. The corrosion of metallic implants can cause high concentrations of heavy metal ions in the peri-implant tissues. The purpose of the present study was to test the effects of possible corrosion products on the function and viability of human EC in vitro. Long-term exposure of EC to CoCl2 and NiCl2 (3 days, 0.7 mM) leads to a decrease of cell number and changes in cellular morphology. However, the morphological changes between CoCl2- and NiCl2-treated cells differ significantly. The changed morphology of CoCl2-treated EC and the fragmented DNA pattern indicates apoptosis. Nickel-treated cells demonstrated necrosis. The activity of integrins was tested by an assay of cellular adhesion on collagen-coated surfaces. It was shown that the number of adherent cells significantly decreased upon exposure to CoCl2. Our studies suggest that induction of cell death in EC upon exposure to CoCl2 could be attributed to impaired integrin signaling, which leads to a damaged cytoskeleton and culminates in apoptosis.     

Computational aspects of prospect theory with asset pricing applications

We develop an algorithm to compute asset allocations for Kahneman and Tversky’s (Econometrica, 47(2), 263–291, 1979) prospect theory. An application to benchmark data as in Fama and French (Journal of Financial Economics, 47(2), 427–465, 1992) shows that the equity premium puzzle is resolved for parameter values similar to those found in the laboratory experiments of Kahneman and Tversky (Econometrica, 47(2), 263–291, 1979). While previous studies like Benartzi and Thaler (The Quarterly Journal of Economics, 110(1), 73–92, 1995), Barberis, Huang and Santos (The Quarterly Journal of Economics, 116(1), 1–53, 2001), and Grüne and Semmler (Asset prices and loss aversion, Germany, Mimeo Bielefeld University, 2005) focussed on dynamic aspects of asset pricing but only used loss aversion to explain the equity premium puzzle our paper explains the unconditional moments of asset pricing by a static two-period optimization problem. However, we incorporate asymmetric risk aversion. Our approach allows reducing the degree of loss aversion from 2.353 to 2.25, which is the value found by Tversky and Kahneman (Journal of Risk and Uncertainty, 5, 297–323, 1992) while increasing the risk aversion from 1 to 0.894, which is a slightly higher value than the 0.88 found by Tversky and Kahneman (Journal of Risk and Uncertainty, 5, 297–323, 1992). The equivalence of these parameter settings is robust to incorporating the size and the value portfolios of Fama and French (Journal of Finance, 47(2), 427–465, 1992). However, the optimal prospect theory portfolios found on this larger set of assets differ drastically from the optimal mean-variance portfolio.     

Fractal substructure of a nanopowder generated by repeated fragmentation and sedimentation: the rôle of the dust

Packings of cohesive nanoparticles, that is nanopowders, may be obtained as the result of repeated fragmentation–reagglomeration cycles (Schwager et al. in Phys Rev Lett 100:218002, 2008) such that the resulting sediment reveals a fractal structure. The size distribution of the fragments after a fragmentation step is a superposition of a narrow distribution of large particles (chunks) whose size is determined by the cutting length and a power-law distribution for small particles, representing scale invariant dust. It was shown that the exponent of the power-law, \(\tau \), is in non-trivial relation to the fractal dimension, \(d_f\), via \(d_f(2-\tau )=1\). This poses the question for the structure of the sediment created by repeated fragmentation–reagglomeration cycles when the dust particles are excluded from the reagglomeration step. We found that even in this case, repeated fragmentation–reagglomeration cycles yield a sediment of fractal structure with slightly reduced fractal dimension while the dust exponent, \(\tau \), remains unchanged.