Showing papers by "Technical University of Berlin published in 2009"

Cyanobacterial photosystem II at 2.9-Å resolution and the role of quinones, lipids, channels and chloride

Abstract: Photosystem II (PSII) is a large homodimeric protein-cofactor complex located in the photosynthetic thylakoid membrane that acts as light-driven water:plastoquinone oxidoreductase. The crystal structure of PSII from Thermosynechococcus elongatus at 2.9-A resolution allowed the unambiguous assignment of all 20 protein subunits and complete modeling of all 35 chlorophyll a molecules and 12 carotenoid molecules, 25 integral lipids and 1 chloride ion per monomer. The presence of a third plastoquinone Q(C) and a second plastoquinone-transfer channel, which were not observed before, suggests mechanisms for plastoquinol-plastoquinone exchange, and we calculated other possible water or dioxygen and proton channels. Putative oxygen positions obtained from a Xenon derivative indicate a role for lipids in oxygen diffusion to the cytoplasmic side of PSII. The chloride position suggests a role in proton-transfer reactions because it is bound through a putative water molecule to the Mn(4)Ca cluster at a distance of 6.5 A and is close to two possible proton channels.

Transiting exoplanets from the CoRoT space mission VIII. CoRoT-7b: the first Super-Earth with measured radius

Abstract: Aims. We report the discovery of very shallow (ΔF/F ≈ 3.4× 10 −4 ), periodic dips in the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion. Methods. We used CoRoT colours information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT light curve to derive parameters of the companion. Results. We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation >0.40 �� or triple systems are almost excluded with a 8 × 10 −4 risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 59 ± 3 × 10 −5 day and a radius of Rp = 1.68 ± 0.09 REarth .A nalysis of preliminary radial velocity data yields an upper limit of 21 MEarth for the companion mass, supporting the finding. Conclusions. CoRoT-7b is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, ≈1800–2600 K at the substellar point, and a very low one, ≈50 K, on its dark face assuming no atmosphere, have been derived.

Covariate Shift by Kernel Mean Matching

Abstract: This chapter contains sections titled: Introduction, Sample Reweighting, Distribution Matching, Risk Estimates, The Connection to Single Class Support Vector Machines, Experiments, Conclusion, Appendix: Proofs

Diamonds with a high density of nitrogen-vacancy centers for magnetometry applications

Abstract: Nitrogen-vacancy (NV) centers in millimeter-scale diamond samples were produced by irradiation and subsequent annealing under varied conditions. The optical and spin-relaxation properties of these samples were characterized using confocal microscopy, visible and infrared absorption, and optically detected magnetic resonance. The sample with the highest ${\text{NV}}^{\ensuremath{-}}$ concentration, approximately 16 ppm $(2.8\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3})$, was prepared with no observable traces of neutrally charged vacancy defects. The effective transverse spin-relaxation time for this sample was ${T}_{2}^{\ensuremath{\ast}}=118(48)\text{ }\text{ns}$, predominately limited by residual paramagnetic nitrogen which was determined to have a concentration of 49(7) ppm. Under ideal conditions, the shot-noise limited sensitivity is projected to be $\ensuremath{\sim}150\text{ }\text{fT}/\sqrt{\text{Hz}}$ for a $100\text{ }\ensuremath{\mu}\text{m}$-scale magnetometer based on this sample. Other samples with ${\text{NV}}^{\ensuremath{-}}$ concentrations from 0.007 to 12 ppm and effective relaxation times ranging from 27 to over 291 ns were prepared and characterized.

PeerSoN: P2P social networking: early experiences and insights

Abstract: To address privacy concerns over Online Social Networks (OSNs), we propose a distributed, peer-to-peer approach coupled with encryption. Moreover, extending this distributed approach by direct data exchange between user devices removes the strict Internet-connectivity requirements of web-based OSNs. In order to verify the feasibility of this approach, we designed a two-tiered architecture and protocols that recreate the core features of OSNs in a decentralized way. This paper focuses on the description of the prototype built for the P2P infrastructure for social networks, as a first step without the encryption part, and shares early experiences from the prototype and insights gained since first outlining the challenges and possibilities of decentralized alternatives to OSNs.

On dominant characteristics of residential broadband internet traffic

Abstract: While residential broadband Internet access is popular in many parts of the world, only a few studies have examined the characteristics of such traffic. In this paper we describe observations from monitoring the network activity for more than 20,000 residential DSL customers in an urban area. To ensure privacy, all data is immediately anonymized. We augment the anonymized packet traces with information about DSL-level sessions, IP (re-)assignments, and DSL link bandwidth.Our analysis reveals a number of surprises in terms of the mental models we developed from the measurement literature. For example, we find that HTTP - not peer-to-peer - traffic dominates by a significant margin; that more often than not the home user's immediate ISP connectivity contributes more to the round-trip times the user experiences than the WAN portion of the path; and that the DSL lines are frequently not the bottleneck in bulk-transfer performance.

Dirac strings and magnetic monopoles in the spin ice Dy2Ti2O7.

Abstract: Sources of magnetic fields-magnetic monopoles-have so far proven elusive as elementary particles. Condensed-matter physicists have recently proposed several scenarios of emergent quasiparticles resembling monopoles. A particularly simple proposition pertains to spin ice on the highly frustrated pyrochlore lattice. The spin-ice state is argued to be well described by networks of aligned dipoles resembling solenoidal tubes-classical, and observable, versions of a Dirac string. Where these tubes end, the resulting defects look like magnetic monopoles. We demonstrated, by diffuse neutron scattering, the presence of such strings in the spin ice dysprosium titanate (Dy2Ti2O7). This is achieved by applying a symmetry-breaking magnetic field with which we can manipulate the density and orientation of the strings. In turn, heat capacity is described by a gas of magnetic monopoles interacting via a magnetic Coulomb interaction.

The CoRoT-7 planetary system: two orbiting super-Earths

Abstract: We report on an intensive observational campaign carried out with HARPS at the 3.6 m telescope at La Silla on the star CoRoT-7. Additional simultaneous photometric measurements carried out with the Euler Swiss telescope have demonstrated that the observed radial velocity variations are dominated by rotational modulation from cool spots on the stellar surface. Several approaches were used to extract the radial velocity signal of the planet(s) from the stellar activity signal. First, a simple pre-whitening procedure was employed to find and subsequently remove periodic signals from the complex frequency structure of the radial velocity data. The dominant frequency in the power spectrum was found at 23 days, which corresponds to the rotation period of CoRoT-7. The 0.8535 day period of CoRoT-7b planetary candidate was detected with an amplitude of 3.3 m s −1 . Most other frequencies, some with amplitudes larger than the CoRoT-7b signal, are most likely associated with activity. A second approach used harmonic decomposition of the rotational period and up to the first three harmonics to filter out the activity signal from radial velocity variations caused by orbiting planets. After correcting the radial velocity data for activity, two periodic signals are detected: the CoRoT-7b transit period and a second one with a period of 3.69 days and an amplitude of 4 m s −1 . This second signal was also found in the pre-whitening analysis. We attribute the second signal to a second, more remote planet CoRoT-7c . The orbital solution of both planets is compatible with circular orbits. The mass of CoRoT-7b is 4.8 ± 0. 8( M⊕) and that of CoRoT-7c is 8.4 ± 0. 9( M⊕), assuming both planets are on coplanar orbits. We also investigated the false positive scenario of a blend by a faint stellar binary, and this may be rejected by the stability of the bisector on a nightly scale. According to their masses both planets belong to the super-Earth planet category. The average density of CoRoT-7b is ρ = 5.6 ± 1. 3gc m −3 , similar to the Earth. The CoRoT-7 planetary system provides us with the first insight into the physical nature of short period super-Earth planets recently detected by radial velocity surveys. These planets may be denser than Neptune and therefore likely made of rocks like the Earth, or a mix of water ice and rocks.

Designing long-term policy: rethinking transition management

Abstract: Long-term policy is enjoying something of a come-back in connection with sustainable development. The current revival tries to avoid the pitfalls of an earlier generation of positivistic long-range planning and control approaches. Instead, this new generation of policy design emphasises reflexive governance concepts. These aim at inducing and navigating complex processes of socio-technical change by means of deliberation, probing and learning. A practical expression of this move that is attracting growing international attention amongst researchers and practitioners is the policy of ‘Transition Management’ (TM) in the Netherlands. This article takes stock of TM implementation experience to date and discusses the critical issues it raises for long-term policy design. The article provides a framework and synthesis for this Special Issue, which comprises articles that address a range of those issues in more depth. We highlight three critical issues: the politics of societal learning, contextual embedding of policy design and dynamics of the design process itself. This leads us to propose a view on policy design as a contested process of social innovation. Our conclusion considers implications for continued work on designing transition management in practice as well as the reflexive capacities of democratic politics.

The slashdot zoo: mining a social network with negative edges

Abstract: We analyse the corpus of user relationships of the Slashdot technology news site. The data was collected from the Slashdot Zoo feature where users of the website can tag other users as friends and foes, providing positive and negative endorsements. We adapt social network analysis techniques to the problem of negative edge weights. In particular, we consider signed variants of global network characteristics such as the clustering coefficient, node-level characteristics such as centrality and popularity measures, and link-level characteristics such as distances and similarity measures. We evaluate these measures on the task of identifying unpopular users, as well as on the task of predicting the sign of links and show that the network exhibits multiplicative transitivity which allows algebraic methods based on matrix multiplication to be used. We compare our methods to traditional methods which are only suitable for positively weighted edges.

Opening up for competitive advantage – How Deutsche Telekom creates an open innovation ecosystem

Abstract: When, on 21st September 2006, ‘The Economist’ compared incumbent telecommunication operators with dinosaurs that could soon face extinction, most readers were ready to agree. The mixture of declining revenues and fierce competition was believed to shake the market and soon to dethrone former national champions. However, there are ways to fight that extinction and one way is to open up for competitive advantage. This paper reflects on a case study at Deutsche Telekom, the German national telecommunication operator. The aim of this study is to analyse to what extent the open innovation paradigm has been embraced inside this now multinational company. Using empirical evidence from 15 in-depth interviews, we identify 11 open innovation instruments and detail their value contribution. We can show that Deutsche Telekom has successfully enhanced its innovation capacity by opening up its traditional development process and embracing external creativity and knowledge resources.

What makes a planet habitable

Abstract: This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological time scales and for planets which evolve to one-plate planets. The discoveries of methane–ethane surface lakes on Saturn’s large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede, Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations of extraterrestrial life.

Robot trajectory optimization using approximate inference

Abstract: The general stochastic optimal control (SOC) problem in robotics scenarios is often too complex to be solved exactly and in near real time. A classical approximate solution is to first compute an optimal (deterministic) trajectory and then solve a local linear-quadratic-gaussian (LQG) perturbation model to handle the system stochasticity. We present a new algorithm for this approach which improves upon previous algorithms like iLQG. We consider a probabilistic model for which the maximum likelihood (ML) trajectory coincides with the optimal trajectory and which, in the LQG case, reproduces the classical SOC solution. The algorithm then utilizes approximate inference methods (similar to expectation propagation) that efficiently generalize to non-LQG systems. We demonstrate the algorithm on a simulated 39-DoF humanoid robot.

The variational gaussian approximation revisited

Abstract: The variational approximation of posterior distributions by multivariate gaussians has been much less popular in the machine learning community compared to the corresponding approximation by factorizing distributions. This is for a good reason: the gaussian approximation is in general plagued by an number of variational parameters to be optimized, being the number of random variables. In this letter, we discuss the relationship between the Laplace and the variational approximation, and we show that for models with gaussian priors and factorizing likelihoods, the number of variational parameters is actually . The approach is applied to gaussian process regression with nongaussian likelihoods.

Assessment of Precious Metal Flows During Preprocessing of Waste Electrical and Electronic Equipment

Abstract: Summary The manufacturing of electronic and electrical equipment (EEE) is a major demand sector for precious and special metals with a strong growth potential. Both precious and special metals are contained in complex components with only small concentrations per unit. After the use-phase, waste electronic and electrical equipment (WEEE) is an important source of these “trace elements.” Their recycling requires appropriate processes in order to cope with the hazardous substances contained in WEEE and to recover efficiently the valuable materials. Although state-of-the-art preprocessing facilities are optimized for recovering mass-relevant materials such as iron and copper, trace elements are often lost. The objective of this article is to show how a substance flow analysis (SFA) on a process level can be used for a holistic approach, covering technical improvement at process scale, optimization of product life cycles, and contributing to knowledge on economy-wide material cycles. An SFA in a full-scale preprocessing facility shows that only 11.5 wt.% of the silver and 25.6 wt.% of the gold and of the palladium reach output fractions from which they may potentially be recovered. For copper this percentage is 60. Considering the environmental rucksack of precious metals, an improvement of the recycling chain would significantly contribute to the optimization of the product life cycle impact of EEE and to ensuring the long-term supply of precious metals.

Carbon footprinting—opportunities and threats

Abstract: There are surprisingly many people out there that obviously think that carbon footprinting is a new thing. They obviously are not aware of the fact that it has been around for decades—just being called differently, i.e. the result of the life cycle impact category indicator global warming potential (GWP). However, carbon footprinting (CFP) is really fashionable these days. Like with all fashion, not all that glitters is gold. Taking carbon footprinting as the one and only yardstick, one has to face life-threatening trade-offs. If carbon footprint is the way to go, we need to shut down each waste-water treatment plant in the world, because it leads to an increased carbon footprint. You should also tear out the catalytic converter and diesel particulate filters from cars, because they lead to a higher CFP. Nuclear power would be obviously a most preferable energy generation option, because it has a lower carbon footprint than even most renewable energy sources—at least based on information provided by pertinent EPDs (Vattenfall 2005; 2007a, b). Recycling paper should be stopped, because compared to virgin paper with a carbon footprint close to ‘zero’, it comes with a higher burden—unless renewable energy is used for the processes necessary (Carbon Trust 2006). But, on the other hand, we have the market demand. Whether it is real or just perceived or just desired seems not so important. There is enough momentum for numerous international, national and sectoral initiatives underway to deal with CFP:

Advantages of Volunteer-Based Biodiversity Monitoring in Europe

Abstract: Without robust and unbiased systems for monitoring, changes in natural systems will remain enigmatic for policy makers, leaving them without a clear idea of the consequences of any environmental policies they might adopt. Generally, biodiversity-monitoring activities are not integrated or evaluated across any large geographic region. The EuMon project conducted the first large-scale evaluation of monitoring practices inEuropethroughanon-linequestionnaireandisreportingontheresultsofthissurvey.InSeptember 2007 the EuMon project had documented 395 monitoring schemes for species, which represents a total annual cost of about €4 million, involving more than 46,000 persons devoting over 148,000 person-days/year to biodiversity-monitoring activities. Here we focused on the analysis of variations of monitoring practices across a set of taxonomic groups (birds, amphibians and reptiles, mammals, butterflies, plants, and other insects) and across 5 European countries (France, Germany, Hungary, Lithuania, and Poland). Our results suggest that the overall sampling effort of a scheme is linked with the proportion of volunteers involved in that scheme. Because precision is a function of the number of monitored sites and the number of sites is maximized by volunteer involvement, our results do not support the common belief that volunteer-based schemes are too noisy to be informative. Just the opposite, we believe volunteer-based schemes provide relatively reliable data,

Understanding online social network usage from a network perspective

Abstract: Online Social Networks (OSNs) have already attracted more than half a billion users. However, our understanding of which OSN features attract and keep the attention of these users is poor. Studies thus far have relied on surveys or interviews of OSN users or focused on static properties, e. g., the friendship graph, gathered via sampled crawls. In this paper, we study how users actually interact with OSNs by extracting clickstreams from passively monitored network traffic. Our characterization of user interactions within the OSN for four different OSNs (Facebook, LinkedIn, Hi5, and StudiVZ) focuses on feature popularity, session characteristics, and the dynamics within OSN sessions. We find, for example, that users commonly spend more than half an hour interacting with the OSNs while the byte contributions per OSN session are relatively small.

Dynamics and functional relevance of ammonia-oxidizing archaea in two agricultural soils.

Abstract: Crucial steps in geochemical cycles are in many cases performed by more than one group of microorganisms, but the significance of this functional redundancy with respect to ecosystem functioning is poorly understood. Ammonia-oxidizing archaea (AOA) and their bacterial counterparts (AOB) are a perfect system to address this question: although performing the same transformation step, they belong to well-separated phylogenetic groups. Using pig manure amended with different concentrations of sulfadiazine (SDZ), an antibiotic that is frequently used in veterinary medicine, it was possible to affect AOB and AOA to different degrees. Addition of manure stimulated growth of AOB in both soils and, interestingly, also growth of AOA was considerably stimulated in one of the soils. The antibiotic treatments decreased the manure effect notably on AOB, whereas AOA were affected to a lower extent. Model calculations concerning the respective proportions of AOA and AOB in ammonia oxidation indicate a substantial contribution of AOA in one of the soils that further increased under the influence of SDZ, hence indicating functional redundancy between AOA and AOB.

The Concept of Recoverable Robustness, Linear Programming Recovery, and Railway Applications

Abstract: We present a new concept for optimization under uncertainty: recoverable robustness A solution is recovery robust if it can be recovered by limited means in all likely scenarios Specializing the general concept to linear programming we can show that recoverable robustness combines the flexibility of stochastic programming with the tractability and performances guarantee of the classical robust approach We exemplify recoverable robustness in delay resistant, periodic and aperiodic timetabling problems, and train platforming

Static Analysis of Executables for Collaborative Malware Detection on Android

Abstract: Smartphones are getting increasingly popular and several malwares appeared targeting these devices. General countermeasures to smartphone malwares are currently limited to signature-based antivirus scanners which efficiently detect known malwares, but they have serious shortcomings with new and unknown malwares creating a window of opportunity for attackers. As smartphones become host for sensitive data and applications, extended malware detection mechanisms are necessary complying with the corresponding resource constraints. The contribution of this paper is twofold. First, we perform static analysis on the executables to extract their function calls in Android environment using the command readelf. Function call lists are compared with malware executables for classifying them with PART, Prism and Nearest Neighbor Algorithms. Second, we present a collaborative malware detection approach to extend these results. Corresponding simulation results are presented.

Post-traumatic growth in people living with a serious medical condition and its relations to physical and mental health: A systematic review

Abstract: Purpose. The diagnosis of a life-threatening illness can be an extremely stressful, traumatic experience. However, many survivors report also various positive changes, referred in empirical literature as post-traumatic growth (PTG). Empirical studies that documented stress disorders and PTG in patients and survivors of life-threatening diseases are reviewed in three areas: Predictors of PTG, relationships between PTG and indicators of mental health and the impact of PTG on the process of convalescence.Method. The literature review was completed by making use of three major databases – PsycINFO, PILOTS and Medline.Results. The majority of the studies investigated PTG and its relationships to health indicators after the diagnosis of cancer, HIV/AIDS, cardiac disease, multiple sclerosis and rheumatoid arthritis. The review indicated that quality of social support, patients' coping strategies and several indicators of mental and physical health were consistently associated with post-traumatic growth. Associat...

Helical Nanofilament Phases

Abstract: Assembling achiral molecules typically generates achiral domains. However, odd things can happen when the molecules are banana-or boomerang-shaped—their cores can twist out of plain to form left- or right-handed helices, which can then pack into chiral domains that will polarize light (see the Perspective by Amabilino ). Hough et al. (p. [452][1]) show that if you make the situation even more complex by frustrating the packing of adjacent layers, you can create a material that appears to be macroscopically isotropic with only very local positional and orientational ordering of the molecules but still shows an overall chirality. In a second paper, Hough et al. (p. [456][2]) also show that if you change the chemistry of the molecules to allow for better overall packing, you can create a situation where helical filaments form that also tend to pack in layered structures. However, the frustration between the two types of packing leads to macroscopically chiral and mesoporous structures. [1]: /lookup/volpage/325/452 [2]: /lookup/volpage/325/456