1,488 research outputs found
Changes in the polar vortex: Effects on Antarctic total ozone observations at various stations
October mean total column ozone data from four Antarctic stations form the basis for understanding the evolution of the ozone hole since 1960. While these stations show similar emergence of the ozone hole from 1960 to 1980, the records are divergent in the last two decades. The effects of long-term changes in vortex shape and location are considered by gridding the measurements by equivalent latitude. A clear eastward shift of the mean position of the vortex in October with time is revealed, which changes the fraction of ozone measurements taken inside/outside the vortex for stations in the vortex collar region. After including only those measurements made inside the vortex, ozone behavior in the last two decades at the four stations is very similar. This suggests that dynamical influence must be considered when interpreting and intercomparing ozone measurements from Antarctic stations for detecting ozone recovery and ozone-related changes in Antarctic climate
Influence of a random telegraph process on the transport through a point contact
We describe the transport properties of a point contact under the influence of a classical two-level fluctuator. We employ a transfer matrix formalism allowing us to calculate arbitrary correlation functions of the stochastic process by mapping them on matrix products. The result is used to obtain the generating function of the full counting statistics of a classical point contact subject to a classical fluctuator, including extensions to a pair of two-level fluctuators as well as to a quantum point contact. We show that the noise in the quantum point contact is a sum of the (quantum) partitioning noise and the (classical) noise due to the two-level fluctuator. As a side result, we obtain the full counting statistics of a quantum point contact with time-dependent transmission probabilitie
Signatures of Alfven waves in the polar coronal holes as seen by EIS/Hinode
Context. We diagnose the properties of the plume and interplume regions in a
polar coronal hole and the role of waves in the acceleration of the solar wind.
Aims. We attempt to detect whether Alfven waves are present in the polar
coronal holes through variations in EUV line widths. Methods. Using spectral
observations performed over a polar coronal hole region with the EIS
spectrometer on Hinode, we study the variation in the line width and electron
density as a function of height. We use the density sensitive line pairs of Fe
xii 186.88 A & 195.119 A and Fe xiii 203.82 A & 202.04 A . Results. For the
polar region, the line width data show that the nonthermal line-of-sight
velocity increases from 26 km/s at 1000 above the limb to 42 km/s some 15000
(i.e. 110,000 km) above the limb. The electron density shows a decrease from
3:3 10^9 cm^-3 to 1:9 10^8 cm^-3 over the same distance. Conclusions. These
results imply that the nonthermal velocity is inversely proportional to the
quadratic root of the electron density, in excellent agreement with what is
predicted for undamped radially propagating linear Alfven waves. Our data
provide signatures of Alfven waves in the polar coronal hole regions, which
could be important for the acceleration of the solar wind.Comment: 5 pages, 11 figures. Astronomy and Astrophysics Letters (accepted)
http://www.aanda.org/articles/aa/pdf/forth/aa12242-09.pd
Dessins, their delta-matroids and partial duals
Given a map on a connected and closed orientable surface, the
delta-matroid of is a combinatorial object associated to which captures some topological information of the embedding. We explore how
delta-matroids associated to dessins d'enfants behave under the action of the
absolute Galois group. Twists of delta-matroids are considered as well; they
correspond to the recently introduced operation of partial duality of maps.
Furthermore, we prove that every map has a partial dual defined over its field
of moduli. A relationship between dessins, partial duals and tropical curves
arising from the cartography groups of dessins is observed as well.Comment: 34 pages, 20 figures. Accepted for publication in the SIGMAP14
Conference Proceeding
Using Qubits to Measure Fidelity in Mesoscopic Systems
We point out the similarities in the definition of the `fidelity' of a
quantum system and the generating function determining the full counting
statistics of charge transport through a quantum wire and suggest to use flux-
or charge qubits for their measurement. As an application we use the notion of
fidelity within a first-quantized formalism in order to derive new results and
insights on the generating function of the full counting statistics.Comment: 5 pages, 1 figur
Technical Note: A new global database of trace gases and aerosols from multiple sources of high vertical resolution measurements
A new database of trace gases and aerosols with global coverage, derived from high vertical resolution profile measurements, has been assembled as a collection of binary data files; hereafter referred to as the "Binary DataBase of Profiles" (BDBP). Version 1.0 of the BDBP, described here, includes measurements from different satellite- (HALOE, POAM II and III, SAGE I and II) and ground-based measurement systems (ozonesondes). In addition to the primary product of ozone, secondary measurements of other trace gases, aerosol extinction, and temperature are included. All data are subjected to very strict quality control and for every measurement a percentage error on the measurement is included. To facilitate analyses, each measurement is added to 3 different instances (3 different grids) of the database where measurements are indexed by: (1) geographic latitude, longitude, altitude (in 1 km steps) and time, (2) geographic latitude, longitude, pressure (at levels ~1 km apart) and time, (3) equivalent latitude, potential temperature (8 levels from 300 K to 650 K) and time. <br><br> In contrast to existing zonal mean databases, by including a wider range of measurement sources (both satellite and ozonesondes), the BDBP is sufficiently dense to permit calculation of changes in ozone by latitude, longitude and altitude. In addition, by including other trace gases such as water vapour, this database can be used for comprehensive radiative transfer calculations. By providing the original measurements rather than derived monthly means, the BDBP is applicable to a wider range of applications than databases containing only monthly mean data. Monthly mean zonal mean ozone concentrations calculated from the BDBP are compared with the database of Randel and Wu, which has been used in many earlier analyses. As opposed to that database which is generated from regression model fits, the BDBP uses the original (quality controlled) measurements with no smoothing applied in any way and as a result displays higher natural variability
Coulomb-assisted braiding of Majorana fermions in a Josephson junction array
We show how to exchange (braid) Majorana fermions in a network of
superconducting nanowires by control over Coulomb interactions rather than
tunneling. Even though Majorana fermions are charge-neutral quasiparticles
(equal to their own antiparticle), they have an effective long-range
interaction through the even-odd electron number dependence of the
superconducting ground state. The flux through a split Josephson junction
controls this interaction via the ratio of Josephson and charging energies,
with exponential sensitivity. By switching the interaction on and off in
neighboring segments of a Josephson junction array, the non-Abelian braiding
statistics can be realized without the need to control tunnel couplings by gate
electrodes. This is a solution to the problem how to operate on topological
qubits when gate voltages are screened by the superconductor
PARG: A Macrodomain in Disguise
Our understanding of poly-ADP-ribosylation as a posttranslational modification was limited by the lack of structural information on poly-ADP-ribose (PAR) hydrolysing enzymes. A recent study in Nature (Slade et al., 2011) reports the structure of PAR glycohydrolase (PARG), revealing unexpected similarity to the ubiquitous ADP-ribose-binding macrodomains
Wave-packet Formalism of Full Counting Statistics
We make use of the first-quantized wave-packet formulation of the full
counting statistics to describe charge transport of noninteracting electrons in
a mesoscopic device. We derive various expressions for the characteristic
function generating the full counting statistics, accounting for both energy
and time dependence in the scattering process and including exchange effects
due to finite overlap of the incoming wave packets. We apply our results to
describe the generic statistical properties of a two-fermion scattering event
and find, among other features, sub-binomial statistics for nonentangled
incoming states (Slater rank 1), while entangled states (Slater rank 2) may
generate super-binomial (and even super-Poissonian) noise, a feature that can
be used as a spin singlet-triplet detector. Another application is concerned
with the constant-voltage case, where we generalize the original result of
Levitov-Lesovik to account for energy-dependent scattering and finite
measurement time, including short time measurements, where Pauli blocking
becomes important.Comment: 20 pages, 5 figures; major update, new figures and explanations
included as well as a discussion about finite temperatures and subleading
logarithmic term
Full counting statistics for noninteracting fermions: Joint probability distributions
The joint probability distribution in the full counting statistics (FCS) for
noninteracting electrons is discussed for an arbitrary number of initially
separate subsystems which are connected at t=0 and separated at a later time. A
simple method to obtain the leading order long time contribution to the
logarithm of the characteristic function is presented which simplifies earlier
approaches. New explicit results for the determinant involving the scattering
matrices are found. The joint probability distribution for two leads is
discussed for Y-junctions and dots connected to four leads.Comment: 17 pages, 3 figure
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