Modeling diffusive movement of sterile insects released along aerial flight lines

The redistribution of insects that are released from an airplane is described using a diffusion equation to derive optimal spacing of flight lines and time interval between flights to achieve a reasonably uniform spatial distribution of released insects and to minimize costs. This optimization is done based on relative costs of sterile males and of flying time. An example is presented using data on the Mediterranean fruit fly, Ceratitis capitata (Weidmann), from the Moscamed program in Guatemala. For the parameter values used, the cost (sterile males plus flights) is minimized when insects are released at intervals of approximately every 2 days (for daily mortality μ = 0.24) to 10 days (for μ = 0.04) and flights are spaced at 300 m (for μ = 0.24) to 600 m (for μ = 0.04) apart, depending on daily medfly mortality estimates, which vary widely in the literature. A simpler approximate method of optimization is then presented based on a relationship observed in the optimization results between flight-line separations and the standard deviation of the distribution.     

Antibiotic resistance in Lactococcus species from bovine milk: presence of a mutated multidrug transporter mdt(A) gene in susceptible Lactococcus garvieae strains

A total of 72 Lactococcus strains (41 Lactococcus lactis and 31 Lactococcus garvieae) isolated from bovine milk were tested for susceptibility to 17 antibiotics and screened for the presence of antibiotic resistance genes using a microarray. Resistance to tetracycline, clindamycin, erythromycin, streptomycin, nitrofurantoin were found. The tetracycline-resistant L. garvieae and L. lactis harbored tet(M) and tet(S). L. lactis that were resistant to clindamycin were also resistant to erythromycin and possessed the erm(B) gene. The multidrug transporter mdt(A), originally described in L. lactis, was detected for the first time in L. garvieae and does not confer decreased susceptibility to erythromycin nor tetracycline in this species. Mdt(A) of L. garvieae contains one mutation in each antiporter motif C, which is known to play an essential role in drug efflux antiporters. This suggests that the mutations found in the C-motifs of Mdt(A) from L. garvieae may be responsible for susceptibility. The study revealed the presence of antibiotic resistance genes in non-pathogenic and pathogenic lactococci from bovine milk, including a mutated multidrug transporter in L. garvieae.     

Purification and physicochemical properties of deoxyribonuclease from pyloric caeca of Atlantic cod (Gadus morhuaL.)

A deoxyribonuclease (DNase) of pancreatic origin has been purified from extracts of the pyloric caeca from Atlantic cod (Gadus morhua L.). The crude extract was prepared by mincing frozen caeca tissue in equal volumes of buffer. The enzyme was isolated from the supernatant after streptomycin sulfate precipitation and centrifugation. The purification scheme further included chromatography on Q-Sepharose Fast Flow and hydroxyapatite columns. Affinity adsorption chromatography of the hydroxyapatite fraction on 8-(6-aminohexyl)-amino-5′-AMP-Sepharose, revealed an apparently homogeneous protein with molecular weight of 35,000 Da as judged by NaDodSO₄-PAGE. In sum a 644-fold enzymatic enrichment and 3.5% total enzyme recovery was achieved. The cod enzyme resembles DNase I-type enzymes with an alkaline pH activity optimum and shows dependency for Mg²⁺. The pI of the enzyme is 6.5 as determined by isoelectric focusing and DNase-zymography. Our findings suggest that the nuclease is a member of the cod's digestive enzymes secreted from the connective tissue surrounding the caeca.     

The use of Xe NMR spectroscopy for studying soils. A pilot study

Xenon nuclear magnetic resonance (¹²⁹Xe NMR) spectroscopy is a powerful technique to study microporous solids and semi-crystalline polymers. In this pilot study we investigate the use of ¹²⁹Xe NMR spectroscopy for studying soils by applying the technique to model systems of carbon black and kaolin powders and to humified sand. In contrast to e.g. zeolites no xenon is sorbed within the sand crystallites at room temperature and high pressure (10 atm). Xenon is only adsorbed at the crystallite surface. The exchange of xenon between the adsorbed and gas phase is so fast, that ¹²⁹Xe NMR spectroscopy cannot distinguish between the two. This results in a single peak in the ¹²⁹Xe NMR spectrum with a weighted-average chemical shift between the shift of xenon in the adsorbed and the gas state. A model is presented which relates the chemical shift to the local volume-to-area ratio of the intercrystallite pores at a submillimetre scale. If other heterogeneity types can be neglected, ¹²⁹Xe NMR spectroscopy potentially reveals information about pore size distributions in undisrupted soils.     

Extracting work from a single heat bath via vanishing quantum coherence

We present here a quantum Carnot engine in which the atoms in the heat bath are given a small bit of quantum coherence. The induced quantum coherence becomes vanishingly small in the high-temperature limit at which we operate and the heat bath is essentially thermal. However, the phase phi, associated with the atomic coherence, provides a new control parameter that can be varied to increase the temperature of the radiation field and to extract work from a single heat bath. The deep physics behind the second law of thermodynamics is not violated; nevertheless, the quantum Carnot engine has certain features that are not possible in a classical engine.     

Nanotubular highways for intercellular organelle transport

Cell-to-cell communication is a crucial prerequisite for the development and maintenance of multicellular organisms. To date, diverse mechanisms of intercellular exchange of information have been documented, including chemical synapses, gap junctions, and plasmodesmata. Here, we describe highly sensitive nanotubular structures formed de novo between cells that create complex networks. These structures facilitate the selective transfer of membrane vesicles and organelles but seem to impede the flow of small molecules. Accordingly, we propose a novel biological principle of cell-to-cell interaction based on membrane continuity and intercellular transfer of organelles.     

A new population of very high energy gamma-ray sources in the Milky Way

Very high energy gamma-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (HESS) reveals a population of eight previously unknown firmly detected sources of very high energy gamma-rays. At least two have no known radio or x-ray counterpart and may be representative of a new class of "dark" nucleonic cosmic ray sources.