Planck pre-launch status: Expected LFI polarisation capability

We present a system-level description of the Low Frequency Instrument (LFI) considered as a differencing polarimeter, and evaluate its expected performance. The LFI is one of the two instruments on board the ESA Planck mission to study the cosmic microwave background. It consists of a set of 22 radiometers sensitive to linear polarisation, arranged in orthogonally-oriented pairs connected to 11 feed horns operating at 30, 44 and 70 GHz. In our analysis, the generic Jones and Mueller-matrix formulations for polarimetry are adapted to the special case of the LFI. Laboratory measurements of flight components are combined with optical simulations of the telescope to investigate the values and uncertainties in the system parameters affecting polarisation response. Methods of correcting residual systematic errors are also briefly discussed. The LFI has beam-integrated polarisation efficiency >99% for all detectors, with uncertainties below 0.1%. Indirect assessment of polarisation position angles suggests that uncertainties are generally less than 0°.5, and this will be checked in flight using observations of the Crab nebula. Leakage of total intensity into the polarisation signal is generally well below the thermal noise level except for bright Galactic emission, where the dominant effect is likely to be spectral-dependent terms due to bandpass mismatch between the two detectors behind each feed, contributing typically 1–3% leakage of foreground total intensity. Comparable leakage from compact features occurs due to beam mismatch, but this averages to < 5 × 10^(-4) for large-scale emission. An inevitable feature of the LFI design is that the two components of the linear polarisation are recovered from elliptical beams which differ substantially in orientation. This distorts the recovered polarisation and its angular power spectrum, and several methods are being developed to correct the effect, both in the power spectrum and in the sky maps. The LFI will return a high-quality measurement of the CMB polarisation, limited mainly by thermal noise. To meet our aspiration of measuring polarisation at the 1% level, further analysis of flight and ground data is required. We are still researching the most effective techniques for correcting subtle artefacts in polarisation; in particular the correction of bandpass mismatch effects is a formidable challenge, as it requires multi-band analysis to estimate the spectral indices that control the leakage

The N N -> NN pi+ Reaction near Threshold in a Chiral Power Counting Approach

Power-counting arguments are used to organize the interactions contributing to the N N -> d pi, p n pi reactions near threshold. We estimate the contributions from the three formally leading mechanisms: the Weinberg-Tomozawa (WT) term, the impulse term, and the $\Delta$-excitation mechanism. Sub-leading but potentially large mechanisms, including $S$-wave pion-rescattering, the Galilean correction to the WT term, and short-ranged contributions are also examined. The WT term is shown to be numerically the largest, and the other contributions are found to approximately cancel. Similarly to the reaction p p -> p p pi0, the computed cross sections are considerably smaller than the data. We discuss possible origins of this discrepancy.Comment: 31 pages, 17 figure

Quantum Hall Effect in Graphene with Interface-Induced Spin-Orbit Coupling

We consider an effective model for graphene with interface-induced spin-orbit coupling and calculate the quantum Hall effect in the low-energy limit. We perform a systematic analysis of the contribution of the different terms of the effective Hamiltonian to the quantum Hall effect (QHE). By analysing the spin-splitting of the quantum Hall states as a function of magnetic field and gate-voltage, we obtain different scaling laws that can be used to characterise the spin-orbit coupling in experiments. Furthermore, we employ a real-space quantum transport approach to calculate the quantum Hall conductivity and investigate the robustness of the QHE to disorder introduced by hydrogen impurities. For that purpose, we combine first-principles calculations and a genetic algorithm strategy to obtain a graphene-only Hamiltonian that models the impurity

Mechanically-Induced Transport Switching Effect in Graphene-based Nanojunctions

We report a theoretical study suggesting a novel type of electronic switching effect, driven by the geometrical reconstruction of nanoscale graphene-based junctions. We considered junction struc- tures which have alternative metastable configurations transformed by rotations of local carbon dimers. The use of external mechanical strain allows a control of the energy barrier heights of the potential profiles and also changes the reaction character from endothermic to exothermic or vice-versa. The reshaping of the atomic details of the junction encode binary electronic ON or OFF states, with ON/OFF transmission ratio that can reach up to 10^4-10^5. Our results suggest the possibility to design modern logical switching devices or mechanophore sensors, monitored by mechanical strain and structural rearrangements.Comment: 10 pages, 4 figure

Modular termination verification for non-blocking concurrency

© Springer-Verlag Berlin Heidelberg 2016.We present Total-TaDA, a program logic for verifying the total correctness of concurrent programs: that such programs both terminate and produce the correct result. With Total-TaDA, we can specify constraints on a thread’s concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for nonblocking algorithms, e.g. a counter and a stack. Our specifications can express lock- and wait-freedom. More generally, they can express that one operation cannot impede the progress of another, a new non-blocking property we call non-impedance. Moreover, our approach is modular. We can verify the operations of a module independently, and build up modules on top of each other

Effect of supplementary food on age ratios of European turtle doves (Streptopelia turtur L.)

Efecto de la alimentación complementaria en la razón de edad de la tórtola europea (Streptopelia turtur L.) Son numerosas las aves de los hábitats agrícolas que tienen dificultades para encontrar suficiente alimento en los ecosistemas agrícolas intensivos y que, en los hábitats explotados de forma más extensiva, suelen ser atraídas por las fuentes antrópicas de alimento. La tórtola europea, Streptopelia turtur, se alimenta de semillas que se hallan en el suelo y es atraída inmediatamente por los cereales que se aportan como complemento a los comederos. El aporte complementario de alimento es una práctica habitual en la gestión de los cotos de caza de todo el mundo. Este estudio se realizó en 40 cotos de caza ubicados en el centro y el oeste de España: 20 zonas en las que se aportó alimentación complementaria para atraer a las tórtolas y 20 zonas de control sin comederos. En las zonas con alimentación complementaria, las razones de edad en el campo y en las aves cazadas fueron, respectivamente, un 20% y un 33% más elevadas que en las zonas de control, lo que indica que la alimentación complementaria tiene un efecto positivo en el éxito reproductivo en torno a las zonas con aporte de alimento complementario. Tanto la cantidad de alimento suministrado por día como el período en el que se aportó (20-120 días) se correlacionaron positivamente con la razón de edad en el campo y, con menos intensidad, con la razón de edad en las aves cazadas. Estos datos sugieren que el suministro de alimento extra puede aumentar el éxito reproductivo de esta especie si la cantidad aportada es suficientemente abundante y si se empieza a proporcionar a principios de la temporada de cría. No obstante, la presión cinegética también fue mayor en las zonas con aporte de alimento complementario, por lo que sería necesario analizar minuciosamente los efectos positivos y negativos de dicho aporte con vistas a determinar qué prácticas de gestión garantizarán la viabilidad de estas importantes poblaciones de tórtola europea.Many farmland birds have difficulties finding sufficient food in intensely managed agricultural ecosystems, and in more extensively worked landscapes they are often attracted to human–induced dietary sources. European turtle doves Streptopelia turtur feed on seeds collected on the ground, and are readily attracted to supplementary provided grain at feeding stations. Supplementary feeding is a common management practice on hunting estates around the world. This study was conducted in 40 hunting estates located in central west Spain: 20 sites where supplementary food was provided to attract turtle doves and 20 control sites without feeding stations. At sites with supplemental feeding, the field age ratio was 20% higher and the hunted age ratio was 33% higher than at control sites, indicating a positive effect of the food supplementation of the breeding success around supplemented sites. Both the amount of food provided per day and the amount of time where supplemental food was given (20–120 days) were positively correlated with the field age ratio and, less strongly, with the hunted age ratio. These data suggest that providing extra food can increase the breeding success of this species when the amount provided is sufficiently large and when supplementary food is provided early in the breeding season. However, hunting pressure was also higher at supplemented sites. Future studies should therefore closely monitor the positive and negative effects in order to ascertain which management practices will ensure the viability of these important European turtle dove populations.Efecto de la alimentación complementaria en la razón de edad de la tórtola europea (Streptopelia turtur L.) Son numerosas las aves de los hábitats agrícolas que tienen dificultades para encontrar suficiente alimento en los ecosistemas agrícolas intensivos y que, en los hábitats explotados de forma más extensiva, suelen ser atraídas por las fuentes antrópicas de alimento. La tórtola europea, Streptopelia turtur, se alimenta de semillas que se hallan en el suelo y es atraída inmediatamente por los cereales que se aportan como complemento a los comederos. El aporte complementario de alimento es una práctica habitual en la gestión de los cotos de caza de todo el mundo. Este estudio se realizó en 40 cotos de caza ubicados en el centro y el oeste de España: 20 zonas en las que se aportó alimentación complementaria para atraer a las tórtolas y 20 zonas de control sin comederos. En las zonas con alimentación complementaria, las razones de edad en el campo y en las aves cazadas fueron, respectivamente, un 20% y un 33% más elevadas que en las zonas de control, lo que indica que la alimentación complementaria tiene un efecto positivo en el éxito reproductivo en torno a las zonas con aporte de alimento complementario. Tanto la cantidad de alimento suministrado por día como el período en el que se aportó (20-120 días) se correlacionaron positivamente con la razón de edad en el campo y, con menos intensidad, con la razón de edad en las aves cazadas. Estos datos sugieren que el suministro de alimento extra puede aumentar el éxito reproductivo de esta especie si la cantidad aportada es suficientemente abundante y si se empieza a proporcionar a principios de la temporada de cría. No obstante, la presión cinegética también fue mayor en las zonas con aporte de alimento complementario, por lo que sería necesario analizar minuciosamente los efectos positivos y negativos de dicho aporte con vistas a determinar qué prácticas de gestión garantizarán la viabilidad de estas importantes poblaciones de tórtola europea