36,640 research outputs found
Standard 1D solar atmosphere as initial condition for MHD simulations and switch-on effects
Many applications in Solar physics need a 1D atmospheric model as initial
condition or as reference for inversions of observational data. The VAL
atmospheric models are based on observations and are widely used since decades.
Complementary to that, the FAL models implement radiative hydrodynamics and
showed the shortcomings of the VAL models since almost equally long time. In
this work, we present a new 1D layered atmosphere that spans not only from the
photosphere to the transition region, but from the solar interior up to far in
the corona. We also discuss typical mistakes that are done when switching on
simulations based on such an initial condition and show how the initial
condition can be equilibrated so that a simulation can start smoothly. The 1D
atmosphere we present here served well as initial condition for HD and MHD
simulations and should also be considered as reference data for solving inverse
problems.Comment: 10 pages, 3 figures, published versio
Lifetimes of impurity states in crossed magnetic and electric fields
We study the quantum dynamics of localized impurity states created by a point
interaction for an electron moving in two dimensions under the influence of a
perpendicular magnetic field and an in-plane weak electric field. All impurity
states are unstable in presence of the electric field. Their lifetimes are
computed and shown to grow in a Gaussian way as the electric field tends to
zero.Comment: 13 pages, no figures, submitted to J. Math. Phy
Application of the electromotive force as a shock front indicator in the inner heliosphere
The electromotive force (EMF) describes how the evolution and generation of a
large-scale magnetic field is influenced by small-scale turbulence. Recent
studies of in-situ measurements have shown a significant peak in the EMF while
a coronal mass ejection (CME) shock front passes by the spacecraft. The goal of
this study is to use the EMF as an indicator for the arrival of CME shock
fronts. With Helios spacecraft measurements we carry out a statistical study on
the EMF during CMEs in the inner heliosphere. We develop an automated shock
front detection algorithm using the EMF as the main detection criterion and
compare the results to an existing CME database. The properties of the EMF
during the recorded events are discussed as a function of the heliocentric
distance. Our algorithm reproduces most of the the events from Kilpua et al.
(2015) and finds many additional CME-like events which proves the EMF as a good
shock front indicator. The largest peaks in the EMF are found from 0 to 50
minutes after the initial shock. We find a power law of -1.54 and -2.18 for two
different formulations of the EMF with the heliocentric distance.Comment: 6 pages, 5 figures, publishe
A new species of Anadia (Reptilia, Squamata) from the Venezuelan 'Lost World', northern South America
A new gymnophthalmid lizard of the genus Anadia Gray, 1845 is described from the summit of Abakapá-tepui, Bolívar State, Venezuela, between 2200-2242 m elevation. The new species, Anadia mcdiarmidi sp. nov., is endemic to the Chimantá Massif and seemingly also occurs on Amurí-tepui and Murei-tepui. The new taxon is mainly distinguished from all known congeners by the following combination of characters: body fairly robust, dorsal scales small and quadrangular, middorsal scales 53-57, suboculars large, subequal in size, with sometimes one scale slightly protruding downward between 4th and 5th supralabial, nasal entire, without sub-nostril groove, body uniform beige or greyish to bluish brown in life, devoid of any conspicuous pattern in males, venter immaculate golden grey in life, femoral pores 9-10 on each side in males, preanal pores absent, hemipenis globose, weakly bilobed, bordered by numerous fl ounces (>20) bearing comblike rows of minute weakly mineralized spinules. The presence of a species of Anadia, a primarily Andean genus, on the top of tepuis is of considerable interest to the understanding of the Pantepui biogeography
Uncertainty Relation for the Discrete Fourier Transform
We derive an uncertainty relation for two unitary operators which obey a
commutation relation of the form UV=exp[i phi] VU. Its most important
application is to constrain how much a quantum state can be localised
simultaneously in two mutually unbiased bases related by a Discrete Fourier
Transform. It provides an uncertainty relation which smoothly interpolates
between the well known cases of the Pauli operators in 2 dimensions and the
continuous variables position and momentum. This work also provides an
uncertainty relation for modular variables, and could find applications in
signal processing. In the finite dimensional case the minimum uncertainty
states, discrete analogues of coherent and squeezed states, are minimum energy
solutions of Harper's equation, a discrete version of the Harmonic oscillator
equation.Comment: Extended Version; 13 pages; In press in Phys. Rev. Let
- …