140 research outputs found
Sunspot waves and flare energy release
We address a possibility of the flare process initiation and further
maintenance of its energy release due to a transformation of sunspot
longitudinal waves into transverse magnetic loop oscillations with initiation
of reconnection. This leads to heating maintaining after the energy release
peak and formation of a flat stage on the X-ray profile. We applied the
time-distance plots and pixel wavelet filtration (PWF) methods to obtain
spatio-temporal distribution of wave power variations in SDO/AIA data. To find
magnetic waveguides, we used magnetic field extrapolation of SDO/HMI
magnetograms. The propagation velocity of wave fronts was measured from their
spatial locations at specific times. In correlation curves of the 17 GHz (NoRH)
radio emission we found a monotonous energy amplification of 3-min waves in the
sunspot umbra before the 2012 June 7 flare. This dynamics agrees with an
increase in the wave-train length in coronal loops (SDO/AIA, 171 {\AA})
reaching the maximum 30 minutes prior to the flare onset. A peculiarity of this
flare time profile in soft X-rays (RHESSI, 3-25 keV) is maintaining the
constant level of the flare emission for 10 minutes after the short impulse
phase, which indicates at the energy release continuation. Throughout this
time, we found 30-sec period transverse oscillations of the flare loop in the
radio-frequency range (NoRH, 17 GHz). This periodicity is apparently related to
the transformation of propagating longitudinal 3-min waves from the sunspot
into the loop transverse oscillations. The magnetic field extrapolation showed
the existence of the magnetic waveguide (loop) connecting the sunspot with the
energy release region. A flare loop heating can be caused by the interaction
(reconnections) of this transversally oscillating waveguide with the underlying
twisted loops.Comment: 7 pages, 9 figure
Informational completeness of continuous-variable measurements
We justify that homodyne tomography turns out to be informationally complete
when the number of independent quadrature measurements is equal to the
dimension of the density matrix in the Fock representation. Using this as our
thread, we examine the completeness of other schemes, when continuous-variable
observations are truncated to discrete finite-dimensional subspaces.Comment: To appear in Phys. Rev.
Feasibility of free space quantum key distribution with coherent polarization states
We demonstrate for the first time the feasibility of free space quantum key
distribution with continuous variables under real atmospheric conditions. More
specifically, we transmit coherent polarization states over a 100m free space
channel on the roof of our institute's building. In our scheme, signal and
local oscillator are combined in a single spatial mode which auto-compensates
atmospheric fluctuations and results in an excellent interference. Furthermore,
the local oscillator acts as spatial and spectral filter thus allowing
unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This
is an author-created, un-copyedited version of an article accepted for
publication in New Journal of Physics (Special Issue on Quantum Cryptography:
Theory and Practice). IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Triplet-like correlation symmetry of continuous variable entangled states
We report on a continuous variable analogue of the triplet two-qubit Bell
states. We theoretically and experimentally demonstrate a remarkable similarity
of two-mode continuous variable entangled states with triplet Bell states with
respect to their correlation patterns. Borrowing from the two qubit language,
we call these correlations triplet-like.Comment: 7 pages, 5 figures. Comments are welcom
Chromospheric seismology above sunspot umbrae
The acoustic resonator is an important model for explaining the three-minute
oscillations in the chromosphere above sunspot umbrae. The steep temperature
gradients at the photosphere and transition region provide the cavity for the
acoustic resonator, which allows waves to be both partially transmitted and
partially reflected. In this paper, a new method of estimating the size and
temperature profile of the chromospheric cavity above a sunspot umbra is
developed. The magnetic field above umbrae is modelled numerically in 1.5D with
slow magnetoacoustic wave trains travelling along magnetic fieldlines.
Resonances are driven by applying the random noise of three different
colours---white, pink and brown---as small velocity perturbations to the upper
convection zone. Energy escapes the resonating cavity and generates wave trains
moving into the corona. Line of sight (LOS) integration is also performed to
determine the observable spectra through SDO/AIA. The numerical results show
that the gradient of the coronal spectra is directly correlated with the
chromosperic temperature configuration. As the chromospheric cavity size
increases, the spectral gradient becomes shallower. When LOS integrations is
performed, the resulting spectra demonstrate a broadband of excited frequencies
that is correlated with the chromospheric cavity size. The broadband of excited
frequencies becomes narrower as the chromospheric cavity size increases. These
two results provide a potentially useful diagnostic for the chromospheric
temperature profile by considering coronal velocity oscillations
Squeezed-state quantum key distribution upon imperfect reconciliation
We address the security of continuous-variable quantum key distribution with
squeezed states upon realistic conditions of noisy and lossy environment and
limited reconciliation efficiency. Considering the generalized preparation
scheme and clearly distinguishing between classical and quantum resources, we
investigate the effect of finite squeezing on the tolerance of the protocol to
untrusted channel noise. For a long-distance strongly attenuating channel and
the consequent low reconciliation efficiency, we show that feasible limited
squeezing is surprisingly sufficient to provide the security of Gaussian
quantum key distribution in the presence of untrusted noise. We explain the
effect by behaviour of the Holevo quantity, which describes the information
leakage, and is effectively minimized by the squeezed states.Comment: 14 pages, 7 figure
Evolutionary Patterns in the Dentition of Duplicidentata (Mammalia) and a Novel Trend in the Molarization of Premolars
The cusp homology of Lagomorpha has long been problematic largely because their teeth are highly derived relative to their more typically tribosphenic ancestors. Within this context, the lagomorph central cusp has been particularly difficult to homologize with other tribosphenic cusps; authors have previously considered it the paracone, protocone, metacone, amphicone, or an entirely new cusp.Here we present newly described fossil duplicidentates (Lagomorpha and Mimotonidae) in the context of a well-constrained phylogeny to establish a nomenclatural system for cusps based on the tribosphenic pattern. We show that the central cusp of lagomorphs is homologous with the metaconule of other mammals. We also show that the buccal acquisition of a second cusp on the premolars (molarization) within duplicidentates is atypical with respect to other mammalian lineages; within the earliest lagomorphs, a second buccal cusp is added mesially to an isolated buccal cusp.The distal shift of the ‘ancestral’ paracone within early duplicidentates amounts to the changing of a paracone into a metacone in these lineages. For this reason, we support a strictly topological approach to cusp names, and suggest a discontinuity in nomenclature to capture the complexity of the interplay between evolutionary history and the developmental process that have produced cusp patterns in duplicidentates
Striatum-projecting prefrontal cortex neurons support working memory maintenance
Neurons in the medial prefrontal cortex (mPFC) are functionally linked to working memory (WM) but how distinct projection pathways contribute to WM remains unclear. Based on optical recordings, optogenetic perturbations, and pharmacological interventions in male mice, we report here that dorsomedial striatum (dmStr)-projecting mPFC neurons are essential for WM maintenance, but not encoding or retrieval, in a T-maze spatial memory task. Fiber photometry of GCaMP6m-labeled mPFC→dmStr neurons revealed strongest activity during the maintenance period, and optogenetic inhibition of these neurons impaired performance only when applied during this period. Conversely, enhancing mPFC→dmStr pathway activity—via pharmacological suppression of HCN1 or by optogenetic activation during the maintenance period—alleviated WM impairment induced by NMDA receptor blockade. Moreover, cellular-resolution miniscope imaging revealed that >50% of mPFC→dmStr neurons are active during WM maintenance and that this subpopulation is distinct from neurons active during encoding and retrieval. In all task periods, neuronal sequences were evident. Striatum-projecting mPFC neurons thus critically contribute to spatial WM maintenance
Atmospheric Channel Characteristics for Quantum Communication with Continuous Polarization Variables
We investigate the properties of an atmospheric channel for free space
quantum communication with continuous polarization variables. In our
prepare-and-measure setup, coherent polarization states are transmitted through
an atmospheric quantum channel of 100m length on the roof of our institute's
building. The signal states are measured by homodyne detection with the help of
a local oscillator (LO) which propagates in the same spatial mode as the
signal, orthogonally polarized to it. Thus the interference of signal and LO is
excellent and atmospheric fluctuations are autocompensated. The LO also acts as
spatial and spectral filter, which allows for unrestrained daylight operation.
Important characteristics for our system are atmospheric channel influences
that could cause polarization, intensity and position excess noise. Therefore
we study these influences in detail. Our results indicate that the channel is
suitable for our quantum communication system in most weather conditions.Comment: 6 pages, 4 figures, submitted to Applied Physics B following an
invitation for the special issue "Selected Papers Presented at the 2009
Spring Meeting of the Quantum Optics and Photonics Section of the German
Physical Society
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