On swarm-level resource allocation in BitTorrent communities

BitTorrent is a peer-to-peer computer network protocol for sharing content in an efficient and scalable way. Modeling and analysis of the popular private BitTorrent communities has become an active area of research. In these communities users are strongly incentivized to contribute their resources, i.e., to share their files. In BitTorrent terminology, users who have finished downloading files and stay online to share these files with others in the network are called seeders. The combination of seeders and downloaders of a file is called a swarm. In this paper we examine and evaluate the efficiency of the resource allocation of seeders in multiple swarms. This is formulated as an integer linear fractional programming problem. The evaluation is done on traces representing two existing BitTorrent communities. We find that in communities, particularly with low users-to-files ratio (which is typically the case), there is room for improvement.     

Single-shot readout of electron spins in a semiconductor quantum dot

We report on a method for single-shot readout of spin states in a semiconductor quantum dot that is robust against charge noise and can be used even when the electron temperature exceeds the energy splitting between the states. The spin states are first correlated to different charge states using a spin dependence of the tunnel rates. A subsequent fast measurement of the charge on the dot then reveals the original spin state. The method is analyzed theoretically, and compared to a previously used method. We experimentally demonstrate the method by performing readout of the two-electron spin states, achieving a single-shot visibility of more than 80%. We find very long triplet-to-singlet relaxation times (up to several milliseconds), with a strong dependence on in-plane magnetic field.     

Attenuation of Biologically Effective UV Radiation in Tropical Atlantic Waters Measured with a Biochemical DNA Dosimeter

Abstract— A biochemical dosimeter was developed to study the attenuation of biologically effective UV radiation in marine tropical waters. Small quartz vials were used containing a solution of DNA molecules; the vials were incubated at discrete water depths. Subsequently, DNA damage was determined in these samples, using an antibody directed against thymine dimers followed by chemiluminescent detection. Measurements of DNA damage were compared with calculated biologically effective doses, as derived from spectroradiometer measurements. The biodosimeter was found to be a reliable and easy tool to determine levels of harmful UV radiation in marine waters. The highest attenuation coefficient (1.60 m^-l) measured with the biochemical dosimeter was found in eutrophic waters, at a coastal station off Curabcao, Netherlands Antilles. At the other stations attenuation coefficients ranged from 0.18 m^-1 in central Atlantic waters to 0.43 m^-1 close to the Curapcao coast line. Latter results indicate that biologically effective UV radiation may easily reach ecologically significant depths, e.g. coral reef communities.     

A comparison of complete global optimization solvers

Results are reported of testing a number of existing state of the art solvers for global constrained optimization and constraint satisfaction on a set of over 1000 test problems in up to 1000 variables, collected from the literature.The test problems are available online in AMPL and were translated into the input formats of the various solvers using routines from the COCONUT environment. These translators are available online, too.     

Capillary gas chromatographic determination of amitrole in water with alkali flame ionization detection

Summary A capillary gas-liquid chromatographic method with alkali flame ionization detection is described for the determination of amitrole in water samples. The method is based on the acetylation of amitrole with acetic anhydride. The limit of detection is ca. 0.1 μg per litre water. The average recovery in groundwater is 97%.     

The error in absorption measurements, caused by the use of non-monochromatic light-I Parabolic functions

The errors in absorption measurements in spectrophotometry, caused by the use of non-chromatic light, have been calculated. Parabolic functions have been assumed for the wavelength-dependence of the intensity of the incident light falling on the cell and of the absorbance of the compound measured. Results of the calculations may be used to predict non-linearity of absorbance-concentration curves or photometric titration curves.     

Pattern recognition. An application to the identification of some stereoisomeric N-acetylhexosamines by mass spectrometry

A method is reported for the identification of trimethylsilylated stereoisomeric N-acetyl-hexosamines by application of a pattern recognition procedure to mass spectral data. The selection of characteristic mass spectral data and the pattern recognition procedure are discussed.