3,896 research outputs found
A Macromodeling-Based Hybrid Method for the Computation of Transient Electromagnetic Fields Scattered by Nonlinearly Loaded Metal Structures
In this article, we present a hybrid numerical scheme to compute the transient electromagnetic fields scattered by a metallic structure loaded with lumped nonlinear loads. The proposed scheme is based on three successive steps. First, the field coupling problem to the structure with the nonlinear loads removed is solved in the frequency domain using a method-of-moments (MoM) formulation. The unloaded structure is thus characterized as a generalized multiport Thevenin equivalent, whose components are represented as time-domain operators by performing a set of rational approximations followed by closed-form Laplace transform inversion. Transient port voltages and currents in the presence of nonlinear loads are then computed using a standard circuit solver. As a last step, the substitution theorem is used to solve the radiation problem again in the frequency domain using a MoM solver, the results of which are then translated into the time domain by means of rational approximations and recursive convolution operations. The proposed method enables an accurate and efficient evaluation of the transient nonlinearly scattered fields by the loaded structure, with a good potential for scalability to large-scale high-complexity nonlinear shields. Extensive validations are provided to demonstrate the accuracy of the proposed method, which is here applied to the characterization of energy-selective shielding for protection of sensitive devices from high-intensity radiated fields
ANOMALOUS GAUGE BOSON INTERACTIONS
We discuss the direct measurement of the trilinear vector boson couplings in
present and future collider experiments. The major goals of such experiments
will be the confirmation of the Standard Model (SM) predictions and the search
for signals of new physics. We review our current theoretical understanding of
anomalous trilinear gauge boson self-interactions. If the energy scale of the
new physics is TeV, these low energy anomalous couplings are expected
to be no larger than . Constraints from high precision
measurements at LEP and low energy charged and neutral current processes are
critically reviewed.Comment: 53 pages with 17 embedded figures, LaTeX, uses axodraw.sty, figures
available on request. The complete paper, is available at
ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z or
http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z Summary
of the DPF Working Subgroup on Anomalous Gauge Boson Interactions of the DPF
Long Range Planning Stud
Effects by Paramagnetic and Diamagnetic Materials in a 1.5-Tesla Highfield Magnetic Resonance Imaging System (MRI)
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugĂ€nglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Dieser Artikel zeigt die Ergebnisse einer experimentellen Untersuchung des Störeinflusses von paramagnetischen und diamagnetischen Materialien auf die Bildgebung in einem geschlossenen 1,5-Tesla-Hochfeld-Magnetresonanztomographen(MRT). Mit drei verschiedenen Sequenztypen (SE, GE, EPI) wurden unterschiedlich groĂe metallische und nichtmetallische WerkstĂŒckprofile hinsichtlich der entstehenden Artefakte untersucht. Zur Darstellung der Artefakte wurde ein mit Gd-Mn-Lösung gefĂŒllter KunststoffbehĂ€lter (Phantom) verwendet, zu dem die zu untersuchenden Materialien wĂ€hrend der VersuchsdurchfĂŒhrung in definierten AbstĂ€nden parallel verschoben wurden. Die Auswertung der Schnittbilder erfolgte in transversaler und sagittaler Untersuchungsebene und ergab, daĂ Aluminium- und Kunststoffprofile auch bei sehr geringem Abstand zum Phantom die kleinsten Bildstörungen verursachten. Besonders starke Artefakte wurden bei den untersuchten Stahl- und Kupferprofilen festgestellt. Bei einem Vergleich der angewendeten Sequenztypen konnte nachgewiesen werden, daĂ besonders die SE-Sequenz, trotz der teilweise stark variierenden Materialprofile, eine geringere ArtefaktanfĂ€lligkeit und somit eine höhere StabilitĂ€t in der Bildgebung im Gegensatz zur GE- und EPI-Sequenz aufwies. Diese Untersuchungen wurden im AnschluĂ an eine intensive Literaturstudie (Internet, Medline, Meditec) durchgefĂŒhrt. Relevante Publikationsquellen gibt es bisher nur sehr wenige.This article shows the results of an experimental investigation of the interference by paramagnetic and diamagnetic materials on imaging in a closed 1.5 Tesla high field magnetic resonance imaging System(MRI). For different types of sequences (SE, GE, EPI) the effects of metal and non-metal profiles in producing artefacts were investigated. A phantom (plastictrunk) filled with Gd-Mn-solution was used for representation of the artefacts. The materials analysed were placed parallel to the phantom at predetermined distances. The images were obtained in transverse and sagittal planes and analysed with respect to the resulting artefacts.The results show that aluminium and polymer profiles produce the weakest artefacts, even when the material is positioned close to the phantom. A comparison of the sequence types shows that the SE-sequence has a low sensitivity to artefacts, despite the great profile variation in size and shape. The SE-sequence accordingly showed a higher imaging stability scompared with the GE- and EPI-sequences. Steel and copper produced the strongest artefacts. The examination was begun after an intensive study of the literature(Internet, Medline, Meditec). So far have been few publications on this subject
Modus Vivendi Beyond the Social Contract: Peace, Justice, and Survival in Realist Political Theory
This essay examines the promise of the notion of modus vivendi for realist political theory. I interpret recent theories of modus vivendi as affirming the priority of peace over justice, and explore several ways of making sense of this idea. I proceed to identify two key problems for modus vivendi theory, so conceived. Normatively speaking, it remains unclear how this approach can sustain a realist critique of Rawlsian theorizing about justice while avoiding a Hobbesian endorsement of absolutism. And conceptually, the theory remains wedded to a key feature of social contract theory: political order is conceived as based on agreement. This construes the horizontal tensions among individual or group agents in society as prior to the vertical, authoritative relations between authorities and their subjects. Political authority thereby appears from the start as a solution to societal conflict, rather than a problem in itself. I argue that this way of framing the issue abstracts from political experience. Instead I attempt to rethink the notion of modus vivendi from within the lived experience of political conflict, as oriented not primarily toward peace, but political survival. With this shift of perspective, the idea of modus vivendi shows us, pace Bernard Williams, that the âfirst political questionâ is not how to achieve order and stability, but rather: what can I live with
The UVES Large Program for testing fundamental physics - III. Constraints on the fine-structure constant from 3 telescopes
Large statistical samples of quasar spectra have previously indicated
possible cosmological variations in the fine-structure constant, . A
smaller sample of higher signal-to-noise ratio spectra, with dedicated
calibration, would allow a detailed test of this evidence. Towards that end, we
observed equatorial quasar HS 15491919 with three telescopes: the Very Large
Telescope, Keck and, for the first time in such analyses, Subaru. By directly
comparing these spectra to each other, and by `supercalibrating' them using
asteroid and iodine-cell tests, we detected and removed long-range distortions
of the quasar spectra's wavelength scales which would have caused significant
systematic errors in our measurements. For each telescope we measure
the relative deviation in from the current laboratory value,
, in 3 absorption systems at redshifts
, 1.342, and 1.802. The nine measurements of
are all consistent with zero at the 2- level,
with 1- statistical (systematic) uncertainties 5.6--24 (1.8--7.0) parts
per million (ppm). They are also consistent with each other at the 1-
level, allowing us to form a combined value for each telescope and, finally, a
single value for this line of sight: ppm, consistent with both zero and
previous, large samples. We also average all Large Programme results measuring
ppm.
Our results demonstrate the robustness and reliability at the 3 ppm level
afforded by supercalibration techniques and direct comparison of spectra from
different telescopes.Comment: 24 pages, 11 figures, 9 table
Possible Signatures of a Cold-Flow Disk from MUSE using a z=1 galaxy--quasar pair towards SDSSJ1422-0001
We use a background quasar to detect the presence of circum-galactic gas
around a low-mass star forming galaxy. Data from the new Multi Unit
Spectroscopic Explorer (MUSE) on the VLT show that the host galaxy has a
dust-corrected star-formation rate (SFR) of 4.70.2 Msun/yr, with no
companion down to 0.22 Msun/yr (5 ) within 240 kpc (30"). Using a
high-resolution spectrum (UVES) of the background quasar, which is fortuitously
aligned with the galaxy major axis (with an azimuth angle of only
), we find, in the gas kinematics traced by low-ionization lines,
distinct signatures consistent with those expected for a "cold flow disk"
extending at least 12 kpc (). We estimate the mass accretion
rate to be at least two to three times larger than the SFR,
using the geometric constraints from the IFU data and the HI column density of
obtained from a {\it HST}/COS NUV spectrum. From
a detailed analysis of the low-ionization lines (e.g. ZnII, CrII, TiII, MnII,
SiII), the accreting material appears to be enriched to about 0.4
(albeit with large uncertainties: ), which is
comparable to the galaxy metallicity (), implying a
large recycling fraction from past outflows. Blue-shifted MgII and FeII
absorptions in the galaxy spectrum from the MUSE data reveal the presence of an
outflow. The MgII and FeII doublet ratios indicate emission infilling due to
scattering processes, but the MUSE data do not show any signs of fluorescent
FeII* emission.Comment: 17 pages, 11 figures, in press (ApJ), minor edits after the proofs.
Data available at http://muse-vlt.eu/science/j1422
The Cyborg Astrobiologist: Testing a Novelty-Detection Algorithm on Two Mobile Exploration Systems at Rivas Vaciamadrid in Spain and at the Mars Desert Research Station in Utah
(ABRIDGED) In previous work, two platforms have been developed for testing
computer-vision algorithms for robotic planetary exploration (McGuire et al.
2004b,2005; Bartolo et al. 2007). The wearable-computer platform has been
tested at geological and astrobiological field sites in Spain (Rivas
Vaciamadrid and Riba de Santiuste), and the phone-camera has been tested at a
geological field site in Malta. In this work, we (i) apply a Hopfield
neural-network algorithm for novelty detection based upon color, (ii) integrate
a field-capable digital microscope on the wearable computer platform, (iii)
test this novelty detection with the digital microscope at Rivas Vaciamadrid,
(iv) develop a Bluetooth communication mode for the phone-camera platform, in
order to allow access to a mobile processing computer at the field sites, and
(v) test the novelty detection on the Bluetooth-enabled phone-camera connected
to a netbook computer at the Mars Desert Research Station in Utah. This systems
engineering and field testing have together allowed us to develop a real-time
computer-vision system that is capable, for example, of identifying lichens as
novel within a series of images acquired in semi-arid desert environments. We
acquired sequences of images of geologic outcrops in Utah and Spain consisting
of various rock types and colors to test this algorithm. The algorithm robustly
recognized previously-observed units by their color, while requiring only a
single image or a few images to learn colors as familiar, demonstrating its
fast learning capability.Comment: 28 pages, 12 figures, accepted for publication in the International
Journal of Astrobiolog
Double quantum dot with tunable coupling in an enhancement-mode silicon metal-oxide semiconductor device with lateral geometry
We present transport measurements of a tunable silicon
metal-oxide-semiconductor double quantum dot device with lateral geometry.
Experimentally extracted gate-to-dot capacitances show that the device is
largely symmetric under the gate voltages applied. Intriguingly, these gate
voltages themselves are not symmetric. Comparison with numerical simulations
indicates that the applied gate voltages serve to offset an intrinsic asymmetry
in the physical device. We also show a transition from a large single dot to
two well isolated coupled dots, where the central gate of the device is used to
controllably tune the interdot coupling.Comment: 4 pages, 3 figures, to be published in Applied Physics Letter
Light-cone Gauge NSR Strings in Noncritical Dimensions II -- Ramond Sector
Light-cone gauge superstring theory in noncritical dimensions corresponds to
a worldsheet theory with nonstandard longitudinal part in the conformal gauge.
The longitudinal part of the worldsheet theory is a superconformal field theory
called X^{\pm} CFT. We show that the X^{\pm} CFT combined with the
super-reparametrization ghost system can be described by free variables. It is
possible to express the correlation functions in terms of these free variables.
Bosonizing the free variables, we construct the spin fields and BRST invariant
vertex operators for the Ramond sector in the conformal gauge formulation. By
using these vertex operators, we can rewrite the tree amplitudes of the
noncritical light-cone gauge string field theory, with external lines in the
(R,R) sector as well as those in the (NS,NS) sector, in a BRST invariant way.Comment: 33 pages; v2: minor modification
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