Background: Carpenter ants (genus Camponotus) are considered to be omnivores. Nonetheless, the genome sequence of Blochmannia floridanus, the obligate intracellular endosymbiont of Camponotus floridanus, suggests a function in nutritional upgrading of host resources by the bacterium. Thus, the strongly reduced genome of the endosymbiont retains genes for all subunits of a functional urease, as well as those for biosynthetic pathways for all but one (arginine) of the amino acids essential to the host.

A chemically defined diet is a useful tool for the study of nutritional physiology of organisms. We have developed such a diet for Camponotus carpenter ants to facilitate experiments on nutritional requirements of these ants. Worker colonies of Camponotus floridanus were fed with a chemically defined diet, containing all essential minerals, amino acids, vitamins, growth factors and sucrose in an agar matrix. After 13 weeks, neither the number of raised pupae, their dry weight, nor the mortality of workers in subcolonies fed with this diet differed significantly from control colonies fed with Bhatkar-Whitcomb-agar, in addition to cockroaches and diluted honey. Therefore, this diet is adequate for a normal brood production and a maximal growth rate of C. floridanus larvae, at least for a period of three months. This diet should be suitable for ants that are able to feed on agar-based food resources in general.

The new development of the bioconcentration factor (BCF) base-line model of Dimitrov et al. [SAR QSAR Environ. Res. 6 (2005), pp. 531-554] is presented. The model applicability domain was expanded by enlarging the training set of the model up to 705 chemicals. The list of chemical-dependent mitigating factors was expanded by including water solubility of chemicals. The original empirical term for estimating ionization of chemicals was mechanistically analysed using two different approaches. In the first one, the ionization potential of chemicals was estimated based on the acid dissociation constant (pK(a) ). This term was found to be less adequate for inclusion in the ultimate BCF model, due to overestimating ionization of chemicals. The second approach, estimating the ionization as a ratio between distribution and partition coefficients (log P and log D), was found to be more successful. The new ionization term allows modelling of chemicals with both acidic and basic functionalities and chemicals undergoing different degrees of ionization. The significance of the different mitigating factors which can reduce the maximum bioconcentration potential of the chemicals was re-formulated and model parameters re-evaluated.

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Time-resolved investigations on the photoluminescence of GaAs/Al"Ga& "As quantum wires as a function of the wire width and the potential well depth indicate a reduction of the energy relaxation in quasi-one-dimensional (1D) systems. The systematic change of the wire width and potential well depth of the quantum wires with mask widths down to 40 nm were realized by ion-implantation-induced intermixing of quantum wells. Lifetime measurements on the high-energy side of the quantum wire emission yield increased decay times for the smallest wires. This is consistent with our observation of increased carrier temperatures and slowed cooling in the quantum wires with increasing carrier confinement. We explain the reduction of the relaxation with the decreased possibility for the scattering particles to fulfill both energy and momentum relaxation in wires with gradually increasing 1D behavior.The investigation of oneand zero-dimensional semiconductor systems has attracted great interest in the past few years both theoretically and experimentally. From the change of the density of states enhancements of the optical nonlinearities are expected. A series of theoretical investigations also deals with the scattering of carriers and predicts a suppression of all elastic scattering processes' and therefore extremely high mobilities at least at low temperatures. Inelastic scattering via optical or acoustic phonons is also believed to be slower at least in zero dimensions. ' On the other hand, there are now various ways to fabricate such structures. Among these the intermixing of quantum wells induced by ion implantation seems to be very promising, because the problems of free-standing surfaces as in etched systems are avoided and high lateral barriers for confining the carriers can be achieved. These systems are now available in a quality to permit optical studies concerning the carrier relaxation.In this paper we report on measurements of the photoluminescence (PL) lifetimes and carrier temperatures in intermixed quantum wires (QWR) as a function of the wire width. We find that the lifetimes on the high-energy side of the QWR emission are increased for the smallest wires. We attribute this to a reduction of the energy relaxation in one-dimensional (1D) systems. A comparison of samples with different height of the lateral barrier shows that this effect is more pronounced in the sample with the deeper lateral potential. Consistent with the increased high-energy lifetime of the thin wires the carrier temperature exceeds the value of the wide wires by a factor of 2. We think that the observed reduction of the relaxation is due to the decreasing possibility for the scattering particles to fulfill both energy and momentum conservation in one-dimensional systems and the reduced density of states. For the realization of QWR systems with width and potential depth variation we started from GaAs/Alo 3sGa0 6&As single quantum well (QWL) samples grown by molecular-beam epitaxy with well widths 3.1 (sample 1) and 3.6 nm (sample 2). The defini...