A Conceptual Framework for B2B Electronic Contracting

Electronic contracting aims at improving existing business relationship paradigms and at enabling new forms of contractual relationships. To successfully realize these objectives, an integral understanding of the contracting field must be established. In this paper, we propose a conceptual framework for business-to-business contracting support. The framework provides a complete view over the contracting field. It allows positioning research efforts in the domain, analysing them, placing their goals into perspective, and overseeing future research topics and issues. It is the basis for drawing conclusions about basic requirements to contracting systems

Synthetic Spectra for Type Ia Supernovae at Early Epochs

We present the current status of our construction of synthetic spectra for type Ia supernovae. These properly take into account the effects of NLTE and an adequate representation of line blocking and blanketing. The models are based on a sophisticated atomic database. We show that the synthetic spectrum reproduces the observed spectrum of 'normal' SN-Ia near maximum light from the UV to the near-IR. However, further improvements are necessary before truly quantitative analyses of observed SN-Ia spectra can be performed. In particular, the inner boundary condition has to be fundamentally modified. This is due to the dominance of electron scattering over true absorption processes coupled with the flat density structure in these objectsComment: To appear in "Proceedings of the IAU Colloquium 192 - Supernovae (10 Years of SN1993J)", eds. J.M. Marcaide and K.W. Weile

Surface detonation in type Ia supernova explosions?

We explore the evolution of thermonuclear supernova explosions when the progenitor white dwarf star ignites asymmetrically off-center. Several numerical simulations are carried out in two and three dimensions to test the consequences of different initial flame configurations such as spherical bubbles displaced from the center, more complex deformed configurations, and teardrop-shaped ignitions. The burning bubbles float towards the surface while releasing energy due to the nuclear reactions. If the energy release is too small to gravitationally unbind the star, the ash sweeps around it, once the burning bubble approaches the surface. Collisions in the fuel on the opposite side increase its temperature and density and may -- in some cases -- initiate a detonation wave which will then propagate inward burning the core of the star and leading to a strong explosion. However, for initial setups in two dimensions that seem realistic from pre-ignition evolution, as well as for all three-dimensional simulations the collimation of the surface material is found to be too weak to trigger a detonation.Comment: 5 pages, 3 figures, in: Proceedings of the SciDAC 2006 Meeting, Denver June 25-26 2006, also available at http://herald.iop.org/jpcs46/m51/gbr//link/40

Can Deflagration-Detonation-Transitions occur in Type Ia Supernovae?

The mechanism for deflagration-detonation-transition (DDT) by turbulent preconditioning, suggested to explain the possible occurrence of delayed detonations in Type Ia supernova explosions, is argued to be conceptually inconsistent. It relies crucially on diffusive heat losses of the burned material on macroscopic scales. Regardless of the amplitude of turbulent velocity fluctuations, the typical gradient scale for temperature fluctuations is shown to be the laminar flame width or smaller, rather than the factor of thousand more required for a DDT. Furthermore, thermonuclear flames cannot be fully quenched in regions much larger than the laminar flame width as a consequence of their simple ``chemistry''. Possible alternative explosion scenarios are briefly discussed.Comment: 8 pages, uses aastex; added references. Accepted by ApJ Letter

Quasilinear Drift Of Cosmic Rays In Weak Turbulent Electromagnetic Fields

A general quasilinear transport parameter for particle drift in arbitrary turbulence geometry is presented. The new drift coefficient is solely characterized by a nonresonant term and is evaluated for slab and two-dimensional turbulence geometry. The calculations presented here demonstrate that fluctuating electric fields are a key quantity for understanding quasilinear particle drift in slab geometry. It is shown that particle drift does not exist in unpolarized and purely magnetic slab fluctuations. This is in stark contrast to previous models, which are restricted to slab geometry and the field line random walk limit. The evaluation of the general transport parameter for two-dimensional turbulence geometry, presented here for the first time for dynamical magnetic turbulence, results in a drift coefficient valid for a magnetic power spectrum and turbulence decay rate varying arbitrarily in wavenumber. For a two-component, slab/two-dimensional turbulence model, numerical calculations are presented. The new quasilinear drift, induced by the magnetic perturbations, is compared with a standard drift expression related to the curvature and gradient of an unperturbed heliospheric background magnetic field. The considerations presented here offer a solid ground and natural explanation for the hitherto puzzling observation that drift models often describe observations much better when drift effects are reduced.Comment: 23 pages, 6 figures, accepted for publication in Ap

Shell structure and electron-electron interaction in self-assembled InAs quantum dots

Using far-infrared spectroscopy, we investigate the excitations of self-organized InAs quantum dots as a function of the electron number per dot, 1<n<6, which is monitored in situ by capacitance spectroscopy. Whereas the well-known two-mode spectrum is observed when the lowest s - states are filled, we find a rich excitation spectrum for n=3, which reflects the importance of electron-electron interaction in the present, strongly non-parabolic confining potential. From capacitance spectroscopy we find that the electronic shell structure in our dots gives rise to a distinct pattern in the charging energies which strongly deviates from the monotonic behavior of the Coulomb blockade found in mesoscopic or metallic structures.Comment: 4 pages, 3 PostScript figure

Explosion models for thermonuclear supernovae resulting from different ignition conditions

We have explored in three dimensions the fate of a massive white dwarf as a function of different initial locations of carbon ignition, with the aid of a SPH code. The calculated models cover a variety of possibilities ranging from the simultaneous ignition of the central volume of the star to the off-center ignition in multiple scattered spots. In the former case, there are discussed the possibility of a transition to a detonation when the mean density of the nuclear flame decreases below 2x10**7 g cm**-3, and its consequences. In the last case, the dependence of the results on the number of initial igniting spots and the chance of some of these models to evolve to the pulsating delayed detonation scenario are also outlined.Comment: 5 pages, 1 figure, proceedings of IAU Colloquium 192, 'Supernovae (10 years of SN1993J)', 22-26 April 2003, Valencia, Spai

Low-cost Sensor System for Non-invasive Monitoring of Cell Growth in Disposable Bioreactors

AbstractTo ensure productivity and product quality, the parameters of biotechnological processes need to be monitored. Along temperature or pH, one important parameter is the cell density in the culture medium. In this work, we present a low-cost sensor system for online cell growth monitoring in bioreactors via permittivity measurements based on coplanar transmission lines. To evaluate the sensor, E. coli cultivations are performed. We found a good correlation between optical density of the culture medium and the effective permittivity at a frequency of 1kHz when the sensor is submerged into the culture medium. Measurements at higher frequencies additionally allow monitoring the osmolarity. Furthermore, an improved sensor was successfully used for first non-invasive measurements through the polymer wall of a disposable bioreactor

Near Infrared Spectra of Type Ia Supernovae

We report near infrared (NIR) spectroscopic observations of twelve ``Branch-normal'' Type Ia supernovae (SNe Ia) which cover the wavelength region from 0.8-2.5 microns. Our sample more than doubles the number of SNe Ia with published NIR spectra within three weeks of maximum light. The epochs of observation range from thirteen days before maximum light to eighteen days after maximum light. A detailed model for a Type Ia supernovae is used to identify spectral features. The Doppler shifts of lines are measured to obtain the velocity and, thus, the radial distribution of elements. The NIR is an extremely useful tool to probe the chemical structure in the layers of SNe Ia ejecta. This wavelength region is optimal for examining certain products of the SNe Ia explosion that may be blended or obscured in other spectral regions. We identify spectral features from MgII, CaII, SiII, FeII, CoII, NiII and possibly MnII. We find no indications for hydrogen, helium or carbon in the spectra. The spectral features reveal important clues about the physical characteristics of SNe Ia. We use the features to derive upper limits for the amount of unburned matter, to identify the transition regions from explosive carbon to oxygen burning and from partial to complete silicon burning, and to estimate the level of mixing during and after the explosion.Comment: 44 pages, 7 figures, 3 tables, accepted by Ap

Electrically tunable g-factors in quantum dot molecular spin states

We present a magneto-photoluminescence study of individual vertically stacked InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied electric field tunes the relative energies of the two dots, we observe a strong resonant increase or decrease in the g-factors of different spin states that have molecular wavefunctions distributed over both quantum dots. We propose a phenomenological model for the change in g-factor based on resonant changes in the amplitude of the wavefunction in the barrier due to the formation of bonding and antibonding orbitals.Comment: 5 pages, 5 figures, Accepted by Phys. Rev. Lett. New version reflects response to referee comment