Enriched workflow modelling and Stochastic Branch-and-Bound

Workflow systems provide means and techniques for modelling, designing, performing and controlling repetitive (business) processes. The quality of commercial workflow systems is usually determined to a large extent by their versatility and multi-purpose application. One of the current trends in improving workflow systems lies in enriching modelling methods and techniques in order to enlarge design alternatives.The need for such advanced methods is particularly apparent in those fields in which the process duration can be determined only vaguely, but whose completion schedules are at the same time strictly enforced by a highly competitive market by means of fines and penalties. The risk of an overrun has to be weighed against the expected costs and benefits of certain measures reducing turn-around time and their combinations. Because they can help to avoid such penalties—or, at least, keep any potential losses low by identifying critical subprocesses and evaluate appropriate measures—modelling and evaluation techniques are becoming essential features of workflow systems.Methodologically, we use Stochastic Branch-and-Bound as a technique for finding “optimal” bundles of measures. A numerical study shows the benefits of this meta-approach by means of five stepwise-developed decision scenarios requiring rich modelling. Petri nets as a modelling tool and Stochastic Branch-and-Bound as an optimization technique determine for multi-mode resource constrained workflows of varying complexity an optimal workforce strategy with respect to the number of workers and their qualification.     

Magnetotunneling spectroscopy of a biased triple-barrier semiconductor heterostructure

In this work we describe a magnetotunneling spectroscopy technique for probing the localization degree of two-dimensional states and mapping the subbands in the active region of a resonant-tunneling semiconductor heterostructure. The reported experimental data consist of the low-temperature tunneling current traces of an asymmetric triple-barrier structure measured by sweeping an in-plane magnetic field up to 10 T. According to our interpretation model, the main features observed in the tunnel current traces are due to the field-induced resonant transitions between two-dimensional states at the crossing region between dispersion curves. The data reveals the highly localized nature of the quantum states in an asymmetric double-quantum-well structure even for those with very narrow middle barriers.     

CO adsorption on clean and oxidized Al(110)

Electron-energy loss (EELS) spectra and thermal desorption (TDS) traces of carbon monoxide bound to the (100) surface of aluminum are presented. CO chemisorption on clean Al(100) is characterized by vibrational bands at 440 and 2060 cm⁻¹ and by desorption at 125 K. Oxide “islands”, formed by oxidation in O₂ at 575 K, have no observed electronic influence on open metallic areas of the adsorbent but merely block CO adsorption sites.     

Metal complexes of 1,4,10-trioxa-7,13 -diazacyclopentadecane-N,N'-diacetic acid

The cyclic diaza-crown ether complexone cTOPDA (1,4,10-trioxa-7,13-diaza- cyclopentadecane-N,N'-diacetic acid) has been synthesized and characterized by elemental analysis, titration and NMR spectroscopy. Its ionization constants and the stability constants of its ML and M₂L complexes formed with alkali, alkaline-earth and some transition and representative metals were determined at 25.0±0.1°C and ionic strength 0.10 M (Me₄NNO₃). This ligand forms considerably more stable complexes with the transition metals than the analogous tetraoxa-diaza crown ether complexone cTOODA (1,4,10,13- tetraoxa-7,16-diazacyclooctadecane-N,N'-diacetic acid), but this last ligand favours ions with larger size, particularly K⁺. The cobalt(II) complex of cTOPDA is more stable than the nickel(II) complex, hence the Irving-Williams' order of stability is not obeyed for its transition-metal complexes. These effects are discussed in terms of the size of the cavity of the ligand and of the stereochemical constraints that it may impose.     

π* ← n electronic absorption spectrum of 2,6-dichloropyrazine

The π* ← n electronic absorption system of 2,6-dichloropyrazine, corresponding to the ¹B_3u ← ¹A_1g transition of pyrazine, has been recorded in the vapour phase and in solution in cyclohexane. A vibrational analysis of this system has been proposed and it is shown that vibronic interaction between two excited states of 2,6-dichloropyrazine exists. Another system is observed in the solution spectrum of this molecule in cyclohexane and it is shown to be a π* ← π transition analogous to the ¹B_2u ← ¹A_1g transition in pyrazine.     

Compressed liquid densities of propane—normal butane mixtures between 10 and 60°C at pressures up to 9.6 MPa

Compressed liquid densities for propane—normal butane mixtures are reported at six temperatures between 10 and 60°C. For each isotherm, there are at least seven compositions ranging between 10 and 75 mol% propane at pressures from near saturation up to 9.65 MPa. The derived excess volumes are negative and represent a maximum of 0.5 percent of the mixture volume at 10°C. At 60°C, the excess volume can be up to 2.2% of the mixture volume. In addition to the binary data, limited density measurements were made on ternary mixtures containing up to 17 mol% ethane.     

Spin-resolved photoemission study of in situ grown epitaxial Fe layers on W(110)

Spin- and angle-resolved photoemission spectroscopy of in situ grown epitaxial Fe layers on W(110) shows bulk-like behavior for more than two atomic Fe layers. For about ten and more atomic layers of Fe we find a spin polarization to be about -100% near the Fermi energy and +80 % between 1 eV and 3 eV binding energy. For the bilayer of Fe drastic changes in the spin-resolved spectra and a 20 % enhancement of the spin polarization compared to the bulk value are observed. The monolayer of Fe is ferromagnetically ordered with a spin polarization reduced by about 50%. A switching of the easy magnetization axis from [001] to [11̄0] is observed in the spin polarization with decreasing Fe layer thickness near d = (65±5) Å.     

Molecular dynamics simulation and energy minimization of O2 adsorbed on a graphite surface

Simulation studies of O₂ on graphite show that the quadrupole interaction strongly affects the orientational correlation between neighbouring molecules in the adsorbed solid. The energy minimization study shows two non-equivalent competing structures with nearest neighbours arranged parallel and at an angle of 60°. The precise value of the quadrupole moment stabilises one structure with respect to the other. For Θ = 0 the simulated structure agrees with experiment. For values of the quadrupole close to the experimental value there is a significant discrepancy between experiment and theory. This discrepancy can be understood in terms of the neglect of the magnetic forces arising from the exchange interaction. The best effective σ₀₀ is 5% higher than the value recommended by bulk solid studies. The minimum energy structure is incommensurate and molecules are aligned preferentially parallel to the surface at the coverage in this study.     

Phase transition phenomena induced by the successive appearances of new types of aggregation states of water molecules in the “l-dipalmitoylphosphatidylcholine-water” system

Thermal analysis of the aggregation state of water molecules m the “L-di-palmitoylphosphatidylcholine (DPPC)-water system revealed that in the low-temperature crystal phase below the sub-transition temperature, there are three kinds of interlamellar water, i.e., tightly, loosely, and more loosely bound water, which are incorporated between the bilayers of l-DPCC molecules, while the Lβ' gel phase lacks the third bound water molecule. Furthermore, we found that both the sub- and pre-transitions below the main transition temperature appear, for the first time, at water contents of around 11 and 18 g%, respectively, just at which point the new types of water structure occur. These findings indicate that the condition necessary for the appearance of these two kinds of phase transition is the existence of the characterized aggregation state of water molecules, that is, more loosely bound water for the sub-transition and bulk free water coexisting with the Lβ' gel phase for the pre-transition.     

Damping in beams and plates due to slipping at the support boundaries

Dry friction damping due to axial sliding surfaces normal to the principal lateral direction of structural motion is studied. Primary emphasis is on sufficiently large motion that slipping occurs throughout a cycle. Beams with arbitrary support conditions and vibrating in an arbitrary mode are considered; also a pinned-pinned rectangular plate is studied. In all cases, a simple explicit formula is obtained for an equivalent, linear, viscous critical damping ratio.