5,021 research outputs found
Computational aspects of helicopter trim analysis and damping levels from Floquet theory
Helicopter trim settings of periodic initial state and control inputs are investigated for convergence of Newton iteration in computing the settings sequentially and in parallel. The trim analysis uses a shooting method and a weak version of two temporal finite element methods with displacement formulation and with mixed formulation of displacements and momenta. These three methods broadly represent two main approaches of trim analysis: adaptation of initial-value and finite element boundary-value codes to periodic boundary conditions, particularly for unstable and marginally stable systems. In each method, both the sequential and in-parallel schemes are used and the resulting nonlinear algebraic equations are solved by damped Newton iteration with an optimally selected damping parameter. The impact of damped Newton iteration, including earlier-observed divergence problems in trim analysis, is demonstrated by the maximum condition number of the Jacobian matrices of the iterative scheme and by virtual elimination of divergence. The advantages of the in-parallel scheme over the conventional sequential scheme are also demonstrated
Do the mildly superluminal VLBI knots exclude ultrarelativistic blazar jets?
We compute the effective values of apparent transverse velocity and flux
boosting factors for the VLBI radio knots of blazar jets, by integrating over
the angular distributions of these quantities across the widths of jets with
finite opening angles but constant velocities. For high bulk Lorentz factors
(Gamma > 10) variations across the jet can be quite large if the opening angle,
omega, is even a few degrees on sub-parsec scales. The resulting apparent
speeds are often much lower than those obtained from the usual analyses that
ignore the finite jet opening angles. We can thus reconcile the usually
observed subluminal or mildly superluminal speeds with the very high (>~ 20)
Gamma factors, required by the inverse Compton origin and rapid variability of
TeV fluxes, as well as by intraday radio variability. Thus it is possible to
associate the VLBI radio knots directly with shocks in the ultra-relativistic
main jet flow, without invoking very rapid jet deceleration on parsec scales,
or extremely unlikely viewing angles.Comment: 10 pages, 1 figure, to appear in ApJ Letters, Nov. 10 2004 issu
Multi-epoch intra-night optical monitoring of 8 radio-quiet BL Lac candidates
For a new sample of 8 weak-line-quasars (WLQs) we report a sensitive search
in 20 intranight monitoring sessions, for blazar-like optical flux variations
on hour-like and longer time scale (day/month/yearlike). The sample consists
exclusively of the WLQs that are not radioloud and have either been
classified as `radio-weak probable BL Lac candidates' and/or are known to have
exhibited at least one episode of large, blazarlike optical variability.
Whereas only a hint of intranight variability is seen for two of these WLQs,
J104833.5620305.0(z = 0.219) and J133219.6622715.9 (z = 3.15),
statistically significant internight variability at a few per cent level is
detected for three of the sources, including the radio-intermediate WLQ
J133219.6622715.9 (z = 3.15) and the well known bonafide radioquiet
WLQs J121221.5534128.0 (z = 3.10) and WLQ J153259.9003944.1 (z = 4.62).
In the restframe, this variability is intra-day and in the farUV band. On
the time scale of a decade, we find for three of the WLQs large brightness
changes, amounting to 1.6550.009, 0.1630.010 and 0.1440.018 mag,
for J104833.5620305.0, J123743.1630144.9 and J232428.4144324.4,
respectively. Whereas the latter two are confirmed radio-quiet WLQs, the
extragalactic nature of J104833.5620305.0 remains to be well established,
thanks to the absence of any feature(s) in its available optical spectra. The
present study forms a part of our ongoing campaign of intranight optical
monitoring of radio quiet weak-line quasars, in order to improve the
understanding of this enigmatic class of Active Galactic Nuclei and to look
among them for a possible tiny, elusive population of radio-quiet BL Lacs.Comment: Accepted to MNRAS. 12 pages, 1 figure, 4 Tabl
Stochastic Analysis of a Churn-Tolerant Structured Peer-to-Peer Scheme
We present and analyze a simple and general scheme to build a churn
(fault)-tolerant structured Peer-to-Peer (P2P) network. Our scheme shows how to
"convert" a static network into a dynamic distributed hash table(DHT)-based P2P
network such that all the good properties of the static network are guaranteed
with high probability (w.h.p). Applying our scheme to a cube-connected cycles
network, for example, yields a degree connected network, in which
every search succeeds in hops w.h.p., using messages,
where is the expected stable network size. Our scheme has an constant
storage overhead (the number of nodes responsible for servicing a data item)
and an overhead (messages and time) per insertion and essentially
no overhead for deletions. All these bounds are essentially optimal. While DHT
schemes with similar guarantees are already known in the literature, this work
is new in the following aspects:
(1) It presents a rigorous mathematical analysis of the scheme under a
general stochastic model of churn and shows the above guarantees;
(2) The theoretical analysis is complemented by a simulation-based analysis
that validates the asymptotic bounds even in moderately sized networks and also
studies performance under changing stable network size;
(3) The presented scheme seems especially suitable for maintaining dynamic
structures under churn efficiently. In particular, we show that a spanning tree
of low diameter can be efficiently maintained in constant time and logarithmic
number of messages per insertion or deletion w.h.p.
Keywords: P2P Network, DHT Scheme, Churn, Dynamic Spanning Tree, Stochastic
Analysis
Global Management Effectiveness Study: Integrated Social and Ecological Report for Non-node and Node Sites
The purpose of this study is to provide a critical assessment of the implementation, impact, and performance of Marine Managed Area (MMA) projects to serve as a basis for improved planning and implementation of new MMA projects worldwide. The specific objectives of the study are (1) to determine the socioeconomic, governance and ecological effects of MMAs; (2) to determine the critical factors influencing MMA effects, as well as the impact of the timing of those factors on the effects of the MMA; and (3) to provide tools for predicting MMA effects based on ecological, socioeconomic and governance variable
Seismic Behaviour of Water Front Structures with Tyre Chip Backfill
Water front structures have suffered significant damage in many of the recent earthquakes. One of the primary causes for the poor performance of these classes of structures is the liquefaction of the foundation soil and in some instances liquefaction of the backfill soil. The liquefaction of the soil in-front of the quay wall tends to cause large lateral displacements and rotation of the wall. Full or partial liquefaction of the backfill can result in the increase of lateral earth pressure exerted on the wall that can cause additional lateral displacement of the wall. In this paper numerical analyses of a gravity wall type water front structure will be considered. Often such gravity walls are placed on rubble mound that is deposited onto the sea bed. The problem will be based on a generic model although the simplifications in the generic model were derived based on observed failures of quay walls following the 1995 Kobe earthquake. The paper presents finite element analyses of such a problem in which strength degradation of the foundation soil and the backfill material will be modelled using PZ mark III constitutive relationship. At the Port and Airport Research Institute (PARI) in Japan the possibility of using tyre chips from used car tyres as the backfill material is being researched using 1G underwater shaking table and dynamic centrifuge modelling. The finite element analyses will be repeated by including a zone of backfill consisting of the tyre chips. The properties of this material will be derived from the element tests carried out at PARI. Finally the results from the analyses of the gravity wall founded rubble mound with liquefiable foundation soil and backfill will be compared to those with tyre chip backfill. The improvement in the performance of the wall in terms of decreased lateral displacements and/or reduction in the rotation suffered by the wall will be compared
Extragalactic radio sources with sharply inverted spectrum at metre wavelengths
We present the first results of a systematic search for the rare
extragalactic radio sources showing an inverted (integrated) spectrum, with
spectral index , a previously unexplored spectral domain. The
search is expected to yield strong candidates for , for which
the standard synchrotron self-absorption (characterized by a single power-law
energy distribution of relativistic electron population) would not be a
plausible explanation, even in an ideal case of a perfectly homogeneous source
of incoherent synchrotron radiation. Such sharply inverted spectra, if found,
would require alternative explanations, e.g., free-free absorption, or
non-standard energy distribution of relativistic electrons which differs from a
power-law (e.g., Maxwellian).
The search was carried out by comparing two sensitive low-frequency radio
surveys made with sub-arcminute resolution, namely, the WISH survey at 352 MHz
and TGSS/DR5 at 150 MHz. The overlap region between these two surveys contains
7056 WISH sources classified as `single' and brighter than 100 mJy at 352 MHz.
We focus here on the seven of these sources for which we find .
Two of these are undetected at 150 MHz and are particularly good candidates for
. Five of the seven sources exhibit a
`Gigahertz-Peaked-Spectrum' (GPS).Comment: 8 pages, 2 figures, accepted for publication in MNRA
Scattering of polarized laser light by an atomic gas in free space: a QSDE approach
We propose a model, based on a quantum stochastic differential equation
(QSDE), to describe the scattering of polarized laser light by an atomic gas.
The gauge terms in the QSDE account for the direct scattering of the laser
light into different field channels. Once the model has been set, we can
rigorously derive quantum filtering equations for balanced polarimetry and
homodyne detection experiments, study the statistics of output processes and
investigate a strong driving, weak coupling limit.Comment: 9 pages, 2 figure
UML Modeling for Tea / Coffee Machine
Unified Modeling language (UML) is one of the important modeling languages used for the visual representation of the research problem. In the present paper, UML model is designed for the Tea / Coffee Machine which is used for the purpose of the public in the hotels or restaurants2019;. The class and use case diagrams are designe
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