13,766 research outputs found
Strange pulsation modes in luminous red giants
We show that the spectrum of radial pulsation modes in luminous red giants
consists of both normal modes and a second set of modes with periods similar to
those of the normal modes. These additional modes are the red giant analogues
of the strange modes found in classical Cepheids and RR Lyrae variables. Here,
we describe the behaviour of strange and normal modes in luminous red giants
and discuss the dependence of both the strange and normal modes on the outer
boundary conditions. The strange modes always appear to be damped, much more so
than the normal modes. They should never be observed as self-excited modes in
real red giants but they may be detected in the spectrum of solar-like
oscillations. A strange mode with a period close to that of a normal mode can
influence both the period and growth rate of the normal mode.Comment: 6 pages, 5 figures, accepted by MNRA
Role of the medial part of the intraparietal sulcus in implementing movement direction
The contribution of the posterior parietal cortex (PPC) to visually guided movements has been originally inferred from observations made in patients suffering from optic ataxia. Subsequent electrophysiological studies in monkeys and functional imaging data in humans have corroborated the key role played by the PPC in sensorimotor transformations underlying goal-directed movements, although the exact contribution of this structure remains debated. Here, we used transcranial magnetic stimulation (TMS) to interfere transiently with the function of the left or right medial part of the intraparietal sulcus (mIPS) in healthy volunteers performing visually guided movements with the right hand. We found that a "virtual lesion" of either mIPS increased the scattering in initial movement direction (DIR), leading to longer trajectory and prolonged movement time, but only when TMS was delivered 100-160 ms before movement onset and for movements directed toward contralateral targets. Control experiments showed that deficits in DIR consequent to mIPS virtual lesions resulted from an inappropriate implementation of the motor command underlying the forthcoming movement and not from an inaccurate computation of the target localization. The present study indicates that mIPS plays a causal role in implementing specifically the direction vector of visually guided movements toward objects situated in the contralateral hemifield
Axion Cosmology Revisited
The misalignment mechanism for axion production depends on the
temperature-dependent axion mass. The latter has recently been determined
within the interacting instanton liquid model (IILM), and provides for the
first time a well-motivated axion mass for all temperatures. We reexamine the
constraints placed on the axion parameter space in the light of this new mass
function. We find an accurate and updated constraint f_a \le 2.8(\pm2)\times
10^{11}\units{GeV} or m_a \ge 21(\pm2) \units{\mu eV} from the misalignment
mechanism in the classic axion window (thermal scenario). However, this is
superseded by axion string radiation which leads to f_a \lesssim
3.2^{+4}_{-2} \times 10^{10} \units{GeV} or m_a \gtrsim 0.20 ^{+0.2}_{-0.1}
\units{meV}. In this analysis, we take care to precisely compute the effective
degrees of freedom and, to fill a gap in the literature, we present accurate
fitting formulas. We solve the evolution equations exactly, and find that
analytic results used to date generally underestimate the full numerical
solution by a factor 2-3. In the inflationary scenario, axions induce
isocurvature fluctuations and constrain the allowed inflationary scale .
Taking anharmonic effects into account, we show that these bounds are actually
weaker than previously computed. Considering the fine-tuning issue of the
misalignment angle in the whole of the anthropic window, we derive new bounds
which open up the inflationary window near . In particular,
we find that inflationary dark matter axions can have masses as high as
0.01--1\units{meV}, covering the whole thermal axion range, with values of
up to GeV. Quantum fluctuations during inflation exclude dominant
dark matter axions with masses above meV.Comment: 42 pages, 12 figures, version as accepted by Phys.Rev.
Symplectic integrators for index one constraints
We show that symplectic Runge-Kutta methods provide effective symplectic
integrators for Hamiltonian systems with index one constraints. These include
the Hamiltonian description of variational problems subject to position and
velocity constraints nondegenerate in the velocities, such as those arising in
sub-Riemannian geometry and control theory.Comment: 13 pages, accepted in SIAM J Sci Compu
Real-time assembly of ribonucleoprotein complexes on nascent RNA transcripts.
Cellular protein-RNA complexes assemble on nascent transcripts, but methods to observe transcription and protein binding in real time and at physiological concentrations are not available. Here, we report a single-molecule approach based on zero-mode waveguides that simultaneously tracks transcription progress and the binding of ribosomal protein S15 to nascent RNA transcripts during early ribosome biogenesis. We observe stable binding of S15 to single RNAs immediately after transcription for the majority of the transcripts at 35 °C but for less than half at 20 °C. The remaining transcripts exhibit either rapid and transient binding or are unable to bind S15, likely due to RNA misfolding. Our work establishes the foundation for studying transcription and its coupled co-transcriptional processes, including RNA folding, ligand binding, and enzymatic activity such as in coupling of transcription to splicing, ribosome assembly or translation
Quantifying Resonant Structure in NGC 6946 from Two-dimensional Kinematics
We study the two-dimensional kinematics of the H-alpha-emitting gas in the
nearby barred Scd galaxy, NGC 6946, in order to determine the pattern speed of
the primary m=2 perturbation mode. The pattern speed is a crucial parameter for
constraining the internal dynamics, estimating the impact velocities of the
gravitational perturbation at the resonance radii, and to set up an
evolutionary scenario for NGC 6946. Our data allows us to derive the best
fitting kinematic position angle and the geometry of the underlying gaseous
disk, which we use to derive the pattern speed using the Tremaine-Weinberg
method. We find a main pattern speed Omega_p=22 km/s/kpc, but our data clearly
reveal the presence of an additional pattern speed Omega_p=47 km/s/kpc in a
zone within 1.25 kpc of the nucleus. Using the epicyclic approximation, we
deduce the location of the resonance radii and confirm that inside the outer
Inner Lindblad Resonance radius of the main oval, a primary bar has formed
rotating at more than twice the outer pattern speed. We further confirm that a
nuclear bar has formed inside the Inner Lindblad Resonance radius of the
primary bar, coinciding with the inner Inner Lindblad Resonance radius of the
large-scale m=2 mode oval.Comment: Accepted for publication in ApJ Letter
UHE tau neutrino flux regeneration while skimming the Earth
The detection of Earth-skimming tau neutrinos has turned into a very
promising strategy for the observation of ultra-high energy cosmic neutrinos.
The sensitivity of this channel crucially depends on the parameters of the
propagation of the tau neutrinos through the terrestrial crust, which governs
the flux of emerging tau leptons that can be detected. One of the
characteristics of this propagation is the possibility of regeneration through
multiple conversions, which are often neglected
in the standard picture. In this paper, we solve the transport equations
governing the propagation and compare the flux of emerging tau
leptons obtained allowing regeneration or not. We discuss the validity of the
approximation of neglecting the regeneration using different
scenarios for the neutrino-nucleon cross-sections and the tau energy losses.Comment: 8 pages, 8 figure
Tau energy losses at ultra-high energy: continuous versus stochastic treatment
We study the energy losses of the tau lepton in matter through
electromagnetic processes at ultra-high energy (UHE). We use both a stochastic
and a continuous framework to treat these interactions and compare the flux of
tau leptons propagated after some amount of matter. We discuss the accuracy of
the approximation of continuous energy losses by studying the propagation in
standard rock of taus with both mono-energetic and power law injection spectra.Comment: 7 pages, 8 figure
Somatic mutations in benign breast disease tissue and risk of subsequent invasive breast cancer
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