4,428 research outputs found
The oscillatory distribution of distances in random tries
We investigate \Delta_n, the distance between randomly selected pairs of
nodes among n keys in a random trie, which is a kind of digital tree.
Analytical techniques, such as the Mellin transform and an excursion between
poissonization and depoissonization, capture small fluctuations in the mean and
variance of these random distances. The mean increases logarithmically in the
number of keys, but curiously enough the variance remains O(1), as n\to\infty.
It is demonstrated that the centered random variable
\Delta_n^*=\Delta_n-\lfloor2\log_2n\rfloor does not have a limit distribution,
but rather oscillates between two distributions.Comment: Published at http://dx.doi.org/10.1214/105051605000000106 in the
Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute
of Mathematical Statistics (http://www.imstat.org
Lasing in metamaterial nanostructures
A self-consistent computational scheme is presented for one dimensional (1D)
and two dimensional (2D) metamaterial systems with gain incorporated into the
nanostructures. The gain is described by a generic four-level system. The loss
compensation and the lasing behavior of the metamaterial system with gain are
studied. A critical pumping rate exists for compensating the losses of the
metamaterial. There exists a wide range of input signals where the composite
system behaves linearly. Nonlinearities arise for stronger signals due to gain
depletion. The retrieved effective parameters are presented for one layer of
gain embedded in two layers of Lorentz dielectric rods and split ring
resonators with two different gain inclusions: (1) gain is embedded in the gaps
only and (2) gain is surrounding the SRR. When the pumping rate increases,
there is a critical pumping rate that the metamaterial system starts lasing.Comment: 18 pages, 19 figures, submitted to Journal of Optics A: Pure and
Applied Optic
The Swap Matching Problem Revisited
In this paper, we revisit the much studied problem of Pattern Matching with
Swaps (Swap Matching problem, for short). We first present a graph-theoretic
model, which opens a new and so far unexplored avenue to solve the problem.
Then, using the model, we devise two efficient algorithms to solve the swap
matching problem. The resulting algorithms are adaptations of the classic
shift-and algorithm. For patterns having length similar to the word-size of the
target machine, both the algorithms run in linear time considering a fixed
alphabet.Comment: 23 pages, 3 Figures and 17 Table
Nonplanar Chiral Metamaterials with Negative Index
We demonstrate experimentally and numerically that nonplanar chiral
metamaterials give giant optical activity, circular dichroism, and negative
refractive index. The transmission, reflection, and the retrieval results of
the experiments agree pretty well with the simulations. This is an important
step toward the design and fabrication of three-dimensional isotropic chiral
metamaterials.Comment: 3 pages 4 figure
Optical anisotropic metamaterials: Negative refraction and focusing
We design three-dimensional (3D) metallic nanowire media with different
structures and numerically demonstrate that they can be homogeneous effective
indefinite anisotropic media by showing that their dispersion relations are
hyperbolic. For a finite slab, a nice fitting procedure is exploited to obtain
the dispersion relations from which we retrieve the effective permittivities.
The pseudo focusing for the real 3D wire medium agrees very well with the
homogeneous medium having the effective permittivity tensor of the wire medium.
Studies also show that in the long-wavelength limit, the hyperbolic dispersion
relation of the 3D wire medium can be valid even for evanescent modes.Comment: 7 pages, 9 figure
Non-Perturbative Gravitational Corrections in a Class of N=2 String Duals
We investigate the non-perturbative equivalence of some heterotic/type II dual pairs with N=2 supersymmetry. The perturbative heterotic scalar manifolds are respectively SU(1, 1)/U(1) x SO(2, 2+NV)/ SO(2) x SO(2+NV) and SO(4, 4+NH)/ SO(4) x SO(4+NH) for moduli in the vector multiplets and hypermultiplets. The models under consideration correspond, on the type II side, to self-mirror Calabi-Yau threefolds with Hodge numbers h(1,1)= NV +3= h(2,1)= NH +3, which are K3 fibrations. We consider three classes of dual pairs, with NV=NH=8, 4 and 2. The models with h(1,1)=7 and 5 provide new constructions, while the h(1,1)=11, already studied in the literature, is reconsidered here. Perturbative R2-like corrections are computed on the heterotic side by using a universal operator whose amplitude has no singularities in the (T,U) space, and can therefore be compared with the type II side result. We point out several properties connecting K3 fibrations and spontaneous breaking of the N=4 supersymmetry to N=2. As a consequence of the reduced S- and T- duality symmetries, the instanton numbers in these three classes are restricted to integers, which are multiples of 2, 2 and 4, for NV=8, 4 and 2, respectively
Dielectric Metamaterials with Toroidal Dipolar Response
Toroidal multipoles are the terms missing in the standard multipole
expansion; they are usually overlooked due to their relatively weak coupling to
the electromagnetic fields. Here we propose and theoretically study
all-dielectric metamaterials of a special class that represent a simple
electromagnetic system supporting toroidal dipolar excitations in the THz part
of the spectrum. We show that resonant transmission and reflection of such
metamaterials is dominated by toroidal dipole scattering, the neglect of which
would result in a misunderstanding interpretation of the metamaterials
macroscopic response. Due to the unique field configuration of the toroidal
mode the proposed metamaterials could serve as a platform for sensing, or
enhancement of light absorption and optical nonlinearities
Tempo and intensity of pre-task music modulate neural activity during reactive task performance
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2013 The Authors.Research has shown that not only do young athletes purposively use music to manage their emotional state (Bishop, Karageorghis, & Loizou, 2007), but also that brief periods of music listening may facilitate their subsequent reactive performance (Bishop, Karageorghis, & Kinrade, 2009). We report an fMRI study in which young athletes lay in an MRI scanner and listened to a popular music track immediately prior to performance of a three-choice reaction time task; intensity and tempo were modified such that six excerpts (2 intensities Ă— 3 tempi) were created. Neural activity was measured throughout. Faster tempi and higher intensity collectively yielded activation in structures integral to visual perception (inferior temporal gyrus), allocation of attention (cuneus, inferior parietal lobule, supramarginal gyrus), and motor control (putamen), during reactive performance. The implications for music listening as a pre-competition strategy in sport are discussed
Negative refractive index due to chirality
We demonstrate experimentally and numerically that metamaterials based on
bilayer cross wires give giant optical activity, circular dichroism, and
negative refractive index. The presented chiral design offers a much simpler
geometry and more efficient way to realize negative refractive index at any
frequency. We also developed a retrieval procedure for chiral materials which
works successfully for circularly polarized waves
The X-ray Properties of the Nearby Star-Forming Galaxy IC 342: The XMM-Newton View
We present the X-ray properties of IC342 using XMM-Newton. Thirty-five
sources are detected coincident with the disk of IC342 (more than tripling the
number known), of which ~31 are likely to be intrinsic to IC342. This
population shows a range of spectral properties and has an X-ray luminosity
function slope and infrared luminosity comparable to that of starburst galaxies
such as M82 and the Antennae, while its relative lack of extended X-ray
emission is similar to the properties of quiescent spirals. We do detect
long-term variability between this observation and the 1991 ROSAT and 1993/2000
ASCA observations for five sources. Notably, the second most luminous source
IC342 X-2 is is found to be in its the lowest luminosity state observed for X-2
to date, although the slope of the spectrum is intermediate between the
previously observed low/hard and high/soft states. IC342 X-1, on the other
hand, is found to be in an identical state to that observed in 2000 with ASCA.
Assuming X-1 is in an anomalous very high (VH) state, then either (1) X-1 has
remained in this state between 2000 and 2002, and is therefore the longest
duration VH-state binary ever observed, or (2) it was simply caught in a VH
state by chance in both the 2000 ASCA and 2002 XMM-Newton observations. We have
also confirmed the ROSAT HRI result that the nucleus of IC342 is made up of
both point-like and extended emission. The relative fluxes of the two spectral
components suggest that the nucleus is complex, with a soft extended component
contributing approximately half of the total luminosity. (Abridged)Comment: AJ in press (December 2003), 9 pages, 7 figures, 2 tables,
emulateapj.cls use
- …