868 research outputs found
Relaxation of surface charge on rotating dielectric spheres: Implications on dynamic electrorheological effects
We have examined the effect of an oscillatory rotation of a polarized
dielectric particle. The rotational motion leads to a re-distribution of the
polarization charge on the surface of the particle. We show that the time
averaged steady-state dipole moment is along the field direction, but its
magnitude is reduced by a factor which depends on the angular velocity of
rotation. As a result, the rotational motion of the particle reduces the
electrorheological effect. We further assume that the relaxation of polarized
charge is arised from a finite conductivity of the particle or host medium. We
calculate the relaxation time based on the Maxwell-Wagner theory, suitably
generalized to include the rotational motion. Analytic expressions for the
reduction factor and the relaxation time are given and their dependence on the
angular velocity of rotation will be discussed.Comment: Accepted for publications by Phys. Rev.
Ground state of a polydisperse electrorheological solid: Beyond the dipole approximation
The ground state of an electrorheological (ER) fluid has been studied based
on our recently proposed dipole-induced dipole (DID) model. We obtained an
analytic expression of the interaction between chains of particles which are of
the same or different dielectric constants. The effects of dielectric constants
on the structure formation in monodisperse and polydisperse electrorheological
fluids are studied in a wide range of dielectric contrasts between the
particles and the base fluid. Our results showed that the established
body-centered tetragonal ground state in monodisperse ER fluids may become
unstable due to a polydispersity in the particle dielectric constants. While
our results agree with that of the fully multipole theory, the DID model is
much simpler, which offers a basis for computer simulations in polydisperse ER
fluids.Comment: Accepted for publications by Phys. Rev.
Discovery and Measurement of Sleptons, Binos, and Winos with a Z'
Extensions of the MSSM could significantly alter its phenomenology at the
LHC. We study the case in which the MSSM is extended by an additional U(1)
gauge symmetry, which is spontaneously broken at a few TeV. The production
cross-section of sleptons is enhanced over that of the MSSM by the process
, so the discovery potential for
sleptons is greatly increased. The flavor and charge information in the
resulting decay, , provides a useful handle on
the identity of the LSP. With the help of the additional kinematical constraint
of an on-shell Z', we implement a novel method to measure all of the
superpartner masses involved in this channel. For certain final states with two
invisible particles, one can construct kinematic observables bounded above by
parent particle masses. We demonstrate how output from one such observable,
m_T2, can become input to a second, increasing the number of measurements one
can make with a single decay chain. The method presented here represents a new
class of observables which could have a much wider range of applicability.Comment: 20 pages, 15 figures; v2 references added and minor change
Spin Measurements in Cascade Decays at the LHC
We systematically study the possibility of determining the spin of new
particles after their discovery at the LHC. We concentrate on angular
correlations in cascade decays. Motivated by constraints of electroweak
precision tests and the potential of providing a Cold Dark Matter candidate, we
focus on scenarios of new physics in which some discrete symmetry guarantees
the existence of stable neutral particles which escape the detector. More
specifically, we compare supersymmetry with another generic scenario in which
new physics particles have the same spin as their Standard Model partners. A
survey of possibilities of observing spin correlations in a broad range of
decay channels is carried out, with interesting ones identified. Rather than
confining ourselves to one "collider friendly" benchmark point (such as SPS1a),
we describe the parameter region in which any particular decay channel is
effective. We conduct a more detailed study of chargino's spin determination in
the decay channel . A scan
over the chargino and neutralino masses is performed. We find that as long as
the spectrum is not too degenerate the prospects for spin determination in this
channel are rather good.Comment: 36 pages, references added, 1 figure modifie
Radiocarbon evidence for the stability of polar ocean overturning during the Holocene
Funding: T.C. acknowledges support from the Strategic Priority Research Program of Chinese Academy of Sciences (XDB40010200), Fundamental Research Funds for the Central Universities (020614380116) and National Natural Science Foundation of China (41991325, 41822603 and 42021001). L.F.R. acknowledges support from the Natural Environment Research Council (NE/S001743/1, NE/R005117/1, NE/N003861/1 and NE/X00127X/1).Proxy-based studies have linked the pre-industrial atmospheric pCO2 rise of âŒ20âppmv in the mid- to late Holocene to an inferred increase in the Southern Ocean overturning and associated biogeochemical changes. However, the history of polar ocean overturning and ventilation through the Holocene remains poorly constrained, leaving important gaps in the assessment of the feedbacks between changes in ocean circulation and the carbon cycle in a warm climate state. The deep-ocean radiocarbon content, which provides a measure of ventilation, responds to circulation changes on centennial to millennial time scales. Here we present absolutely dated deep-sea coral radiocarbon records from the Drake Passage, between South America and Antarctica, and Reykjanes Ridge, south of Iceland, over the Holocene. Our data suggest that ventilation in the Antarctic circumpolar waters and North Atlantic Deep Water is surprisingly invariant within proxy uncertainties at our sampling resolution. Our findings indicate that long-term, large-scale polar ocean overturning has not been disturbed to a level resolvable by radiocarbon and is probably not responsible for the millennial atmosphere pCO2 evolution through the Holocene. Instead, continuous nutrient and carbon redistribution within the water column following deglaciation, as well as changes in land organic carbon stock, might have regulated atmospheric CO2 budget during this period.Publisher PDFPeer reviewe
D-Matter
We study the properties and phenomenology of particle-like states originating
from D-branes whose spatial dimensions are all compactified. They are
non-perturbative states in string theory and we refer to them as D-matter. In
contrast to other non-perturbative objects such as 't Hooft-Polyakov monopoles,
D-matter states could have perturbative couplings among themselves and with
ordinary matter. The lightest D-particle (LDP) could be stable because it is
the lightest state carrying certain (integer or discrete) quantum numbers.
Depending on the string scale, they could be cold dark matter candidates with
properties similar to that of wimps or wimpzillas. The spectrum of excited
states of D-matter exhibits an interesting pattern which could be distinguished
from that of Kaluza-Klein modes, winding states, and string resonances. We
speculate about possible signatures of D-matter from ultra-high energy cosmic
rays and colliders.Comment: 25 pages, 5 figures, references adde
Random Sierpinski network with scale-free small-world and modular structure
In this paper, we define a stochastic Sierpinski gasket, on the basis of
which we construct a network called random Sierpinski network (RSN). We
investigate analytically or numerically the statistical characteristics of RSN.
The obtained results reveal that the properties of RSN is particularly rich, it
is simultaneously scale-free, small-world, uncorrelated, modular, and maximal
planar. All obtained analytical predictions are successfully contrasted with
extensive numerical simulations. Our network representation method could be
applied to study the complexity of some real systems in biological and
information fields.Comment: 7 pages, 9 figures; final version accepted for publication in EPJ
Effects of genuine dimension-six Higgs operators
We systematically discuss the consequences of genuine dimension-six Higgs
operators. These operators are not subject to stringent constraints from
electroweak precision data. However, they can modify the couplings of the Higgs
boson to electroweak gauge bosons and, in particular, the Higgs
self-interactions. We study the sensitivity to which those couplings can be
probed at future \ee linear colliders in the sub-TeV and in the multi-TeV
range. We find that for GeV with a luminosity of 1 ab the
anomalous and couplings may be probed to about the 0.01 level, and
the anomalous coupling to about the 0.1 level.Comment: 21 pages, 17 figures; typos corrected and references adde
A 78 Day X-Ray Period Detected from NGC 5907 ULX1 by Swift
We report the detection of a 78.1 ± 0.5 day period in the X-ray light curve of the extreme ultraluminous X-ray source NGC 5907 ULX1 ( erg sâ1), discovered during an extensive monitoring program with Swift. These periodic variations are strong, with the observed flux changing by a factor of ~3â4 between the peaks and the troughs of the cycle; our simulations suggest that the observed periodicity is detected comfortably in excess of 3Ï significance. We discuss possible origins for this X-ray period, but conclude that at the current time we cannot robustly distinguish between orbital and super-orbital variations
Orbital stability: analysis meets geometry
We present an introduction to the orbital stability of relative equilibria of
Hamiltonian dynamical systems on (finite and infinite dimensional) Banach
spaces. A convenient formulation of the theory of Hamiltonian dynamics with
symmetry and the corresponding momentum maps is proposed that allows us to
highlight the interplay between (symplectic) geometry and (functional) analysis
in the proofs of orbital stability of relative equilibria via the so-called
energy-momentum method. The theory is illustrated with examples from finite
dimensional systems, as well as from Hamiltonian PDE's, such as solitons,
standing and plane waves for the nonlinear Schr{\"o}dinger equation, for the
wave equation, and for the Manakov system
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