2,521 research outputs found
Three-dimensional simulations of the orientation and structure of reconnection X-lines
This work employs Hall magnetohydrodynamic (MHD) simulations to study the
X-lines formed during the reconnection of magnetic fields with differing
strengths and orientations embedded in plasmas of differing densities. Although
random initial perturbations trigger the growth of X-lines with many
orientations, at late time a few robust X-lines sharing an orientation
reasonably consistent with the direction that maximizes the outflow speed, as
predicted by Swisdak and Drake [Geophys. Res. Lett., 34, L11106, (2007)],
dominate the system. The existence of reconnection in the geometry examined
here contradicts the suggestion of Sonnerup [J. Geophys. Res., 79, 1546 (1974)]
that reconnection occurs in a plane normal to the equilibrium current. At late
time the growth of the X-lines stagnates, leaving them shorter than the
simulation domain.Comment: Accepted by Physics of Plasma
Municipality Size and Efficiency of Local Public Services: Does Size Matter?
Similarly to western Germany in the 1960s and 1970s, the eastern part of Germany has experienced a still ongoing process of numerous amalgamations among counties, towns and municipalities since the mid-1990s. The evidence in the economic literature is mixed with regard to the claimed expenditure reductions and efficiency gains from municipal mergers. We therefore analyze the global efficiency of the municipalities in Saxony-Anhalt, for the first time in this context, using a double-bootstrap procedure combining DEA and truncated regression. This allows including environmental variables to control for exogenous determinants of municipal efficiency. Our focus thereby is on institutional and fiscal variables. Moreover, the scale efficiency is estimated to find out whether large units are necessary to benefit from scale economies. In contrast to previous studies, we chose the aggregate budget of municipal associations (“Verwaltungsgemeinschaften”) as the object of our analysis since important competences of the member municipalities are settled on a joint administrative level. Furthermore, we use a data set that has been carefully adjusted for bookkeeping items and transfers within the communal level. On the “eve” of a mayor municipal reform the majority of the municipalities were found to have an approximately scale-efficient size and centralized organizational forms (“Einheitsgemeinden”) showed no efficiency advantage over municipal associations.efficiency, local government, DEA, bootstrap, demographic change, local institutions
Prevalence of X-ray variability in the Chandra Deep Field South
We studied the X-ray variability of sources detected in the Chandra Deep
Field South (Giacconi et al. 2002), nearly all of which are low to moderate z
AGN (Tozzi et al. 2001). We find that 45% of the sources with >100 counts
exhibit significant variability on timescales ranging from a day up to a year.
The fraction of sources found to be variable increases with observed flux,
suggesting that >90% of all AGNs possess intrinsic variability. We also find
that the fraction of variable sources appears to decrease with increasing
intrinsic absorption; a lack of variability in hard, absorbed AGNs could be due
to an increased contribution of reflected X-rays to the total flux. We do not
detect significant spectral variability in the majority (~70%) of our sources.
In half of the remaining 30%, the hardness ratio is anti-correlated with flux,
mimicking the high/soft-low/hard states of galactic sources. The X-ray
variability appears anti-correlated with the luminosity of the sources, in
agreement with previous studies. High redshift sources, however, have larger
variability amplitudes than expected from extrapolations of their low-z
counterparts, suggesting a possible evolution in the accretion rate and/or size
of the X-ray emitting region. Finally, we discuss some effects that may produce
the observed decrease in the fraction of variable sources from z=0.5 out to
z=2.Comment: 24 pages, including 15 figures and 1 table. In press on Ap
Parameter estimation and accuracy matching strategies for 2-D reactor models
AbstractThe mathematical modelling of a special modular catalytic reactor kit leads to a system of partial differential equation in two space dimensions. As customary, this model contains uncertain physical parameters, which may be adapted to fit experimental data. To solve this nonlinear least-squares problem we apply a damped Gauss–Newton method. A method of lines approach is used to evaluate the associated model equations. By an a priori spatial discretization, a large DAE system is derived and integrated with an adaptive, linearly implicit extrapolation method. For sensitivity evaluation we apply an internal numerical differentiation technique, which reuses linear algebra information from the model integration. In order not to interfere with the control of the Gauss–Newton iteration these computations are done usually very accurately and, therefore, with substantial cost. To overcome this difficulty, we discuss several accuracy adaptation strategies, e.g., a master–slave mode. Finally, we present some numerical experiments
The Elusive Active Nucleus of NGC 4945
We present new HST NICMOS observations of NGC 4945, a starburst galaxy
hosting a highly obscured active nucleus that is one of the brightest
extragalactic sources at 100 keV. The HST data are complemented with ground
based [FeII] line and mid--IR observations. A 100pc-scale starburst ring is
detected in Pa alpha, while H_2 traces the walls of a super bubble opened by
supernova-driven winds. The conically shaped cavity is particularly prominent
in Pa alpha equivalent width and in the Pa alpha/H_2 ratio. Continuum images
are heavily affected by dust extinction and the nucleus of the galaxy is
located in a highly reddened region with an elongated, disk-like morphology. No
manifestation of the active nucleus is found, neither a strong point source nor
dilution in CO stellar features, which are expected tracers of AGN activity.
Even if no AGN traces are detected in the near-IR, with the currently available
data it is still not possible to establish whether the bolometric luminosity of
the object is powered by the AGN or by the starburst: we demonstrate that the
two scenarios constitute equally viable alternatives. However, the absence of
any signature other than in the hard X-rays implies that, in both scenarios,
the AGN is non-standard: if it dominates, it must be obscured in all
directions, conversely, if the starburst dominates, the AGN must lack UV
photons with respect to X-rays. An important conclusion is that powerful AGNs
can be hidden even at mid-infrared wavelengths and, therefore, the nature of
luminous dusty galaxies cannot be always characterized by long-wavelength data
alone but must be complemented with sensitive hard X-ray observations.Comment: Accepted for publication in A&A, high quality color pictures
available at http://www.arcetri.astro.it/~marconi/colpic.htm
Instantaneous frequency and amplitude of complex signals based on quaternion Fourier transform
The ideas of instantaneous amplitude and phase are well understood for
signals with real-valued samples, based on the analytic signal which is a
complex signal with one-sided Fourier transform. We extend these ideas to
signals with complex-valued samples, using a quaternion-valued equivalent of
the analytic signal obtained from a one-sided quaternion Fourier transform
which we refer to as the hypercomplex representation of the complex signal. We
present the necessary properties of the quaternion Fourier transform,
particularly its symmetries in the frequency domain and formulae for
convolution and the quaternion Fourier transform of the Hilbert transform. The
hypercomplex representation may be interpreted as an ordered pair of complex
signals or as a quaternion signal. We discuss its derivation and properties and
show that its quaternion Fourier transform is one-sided. It is shown how to
derive from the hypercomplex representation a complex envelope and a phase.
A classical result in the case of real signals is that an amplitude modulated
signal may be analysed into its envelope and carrier using the analytic signal
provided that the modulating signal has frequency content not overlapping with
that of the carrier. We show that this idea extends to the complex case,
provided that the complex signal modulates an orthonormal complex exponential.
Orthonormal complex modulation can be represented mathematically by a polar
representation of quaternions previously derived by the authors. As in the
classical case, there is a restriction of non-overlapping frequency content
between the modulating complex signal and the orthonormal complex exponential.
We show that, under these conditions, modulation in the time domain is
equivalent to a frequency shift in the quaternion Fourier domain. Examples are
presented to demonstrate these concepts
Finding commercially attractive user innovations: A test of lead user theory
Firms and governments are increasingly interested in learning to exploit the value of lead user innovations for commercial advantage. Improvements to lead user theory are needed to inform and guide these efforts. In this paper we empirically test and confirm the basic tenants of lead user theory. We also discover some new refinements and related practical applications.
Using a sample of users and user-innovators drawn from the extreme sport of kite surfing, we analyze the relationship between the commercial attractiveness of innovations developed by users and the intensity of the lead user characteristics those users display. We provide a first empirical analysis of the independent effects of its two key component variables. In our empirical study of user modifications to kite surfing equipment, we find that both components independently contribute to identifying commercially attractive user innovations. Component 1 (the "high expected benefits" dimension) predicts innovation likelihood, and component 2 (the "ahead of the trend" dimension) predicts both the commercial attractiveness of a given set of user-developed innovations and innovation likelihood due to a newly-proposed innovation supply side effect. We conclude that the component variables in the lead user definition are indeed independent dimensions and so neither can be dropped without loss of information - an important matter for lead user theory. We also find that adding measures of users' local resources can improve the ability of the lead user construct to identify commercially-attractive innovations under some conditions.
The findings we report have practical as well as theoretical import. Product modification and development has been found to be a relatively common user behavior in many fields. Thus, from 10% to nearly 40% of users report having modified or developed a product for in-house use in the case of industrial products, or for personal use in the case of consumer products, in fields sampled to date. As a practical matter, therefore, it is important to find ways to selectively identify the user innovations that manufacturers will find to be the basis for commercially attractive products in the collectivity of user-developed innovations. We discuss the implications of these findings for theory and also for practical applications of the lead user construct, i.e. how variables used in lead user studies can profitably be adapted to fit specific study contexts and purposes
Sideband Transitions and Two-Tone Spectroscopy of a Superconducting Qubit Strongly Coupled to an On-Chip Cavity
Sideband transitions are spectroscopically probed in a system consisting of a
Cooper pair box strongly but non-resonantly coupled to a superconducting
transmission line resonator. When the Cooper pair box is operated at the
optimal charge bias point the symmetry of the hamiltonian requires a two photon
process to access sidebands. The observed large dispersive ac-Stark shifts in
the sideband transitions induced by the strong non-resonant drives agree well
with our theoretical predictions. Sideband transitions are important in
realizing qubit-photon and qubit-qubit entanglement in the circuit quantum
electrodynamics architecture for quantum information processing.Comment: 4 pages, 5 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
An Investigation of the Character Traits of Decision-Makers Open to Intuition as a Tool
The increasing complexity of business environments has resulted in decision-making also becoming more complicated. While classical decision-making theories purport strategic decision-making to be a result of rational contemplation, more recent research findings have put forward a more holistic view, which includes intuition as a tool for decision-making processes. Studies illustrate, that the implementation of intuition as a part of decision-making in companies can lead to improved company performance. Dealing with decisions and the way decisions are made is very individual and according to Musso and Francioni (2012) is mostly influenced by the decision maker’s personality. Traditionally, there has been a differentiation made between decision-makers that employ a rational method of decision-making and those that use intuition. Successful decision-makers appear to be able to commingle both of these decision-making methods and it is the character traits of precisely these decision-makers which will be scrutinized. The aim of this paper is to discuss the personality of the decision-maker who is open to intuition
Hubble Space Telescope Imaging in the Chandra Deep Field South: III. Quantitative Morphology of the 1Ms Chandra Counterparts and Comparison with the Field Population
We present quantitative morphological analyses of 37 HST/WFPC2 counterparts
of X-ray sources in the 1 Ms Chandra Deep Field-South (CDFS). We investigate:
1) 1-D surface brightness profiles via isophotal ellipse fitting; 2) 2-D, PSF-
convolved, bulge+disk+nucleus profile-fitting; 3) asymmetry and concentration
indices compared with all ~3000 sources in our three WFPC2 fields; and 4) near-
neighbor analyses comparing local environments of X-ray sources versus the
field control sample. Significant nuclear point-source optical components
appear in roughly half of the resolved HST/WFPC2 counterparts, showing a narrow
range of F_X/F_{opt,nuc} consistent with the several HST-unresolved X-ray
sources (putative type-1 AGN) in our fields. We infer roughly half of the
HST/WFPC2 counterparts host unobscured AGN, which suggests no steep decline in
the type-1/type-2 ratio out to the redshifts z~0.5-1 typical of our sources.
The concentration indices of the CDFS counterparts are clearly larger on
average than those of the field distribution, at 5-sigma, suggesting that the
strong correlation between central black hole mass and host galaxy properties
(including concentration index) observed in nearby galaxies is already evident
by z~0.5-1. By contrast, the asymmetry index distribution of the 21 resolved
CDFS sources at I<23 is indistinguishable from the I<23 field. Moreover, the
frequency of I<23 near neighbors around the CDFS counterparts is not
significantly different from the field sample. These results, combined with
previous similar findings for local samples, suggest that recent merger/
interaction history is not a good indicator of AGN activity over a substantial
range of look-back time.Comment: 30 pages, incl. 8 figures; accepted for publication in the
Astrophysical Journa
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