13,365 research outputs found
Pinned modes in two-dimensional lossy lattices with local gain and nonlinearity
We introduce a system with one or two amplified nonlinear sites ("hot spots",
HSs) embedded into a two-dimensional linear lossy lattice. The system describes
an array of evanescently coupled optical or plasmonic waveguides, with gain
applied at selected HS cores. The subject of the analysis is discrete solitons
pinned to the HSs. The shape of the localized modes is found in
quasi-analytical and numerical forms, using a truncated lattice for the
analytical consideration. Stability eigenvalues are computed numerically, and
the results are supplemented by direct numerical simulations. In the case of
self-focusing nonlinearity, the modes pinned to a single HS are stable or
unstable when the nonlinearity includes the cubic loss or gain, respectively.
If the nonlinearity is self-defocusing, the unsaturated cubic gain acting at
the HS supports stable modes in a small parametric area, while weak cubic loss
gives rise to a bistability of the discrete solitons. Symmetric and
antisymmetric modes pinned to a symmetric set of two HSs are considered too.Comment: Philosophical Transactions of the Royal Society A, in press (a
special issue on "Localized structures in dissipative media"
Redundancy relations and robust failure detection
All failure detection methods are based on the use of redundancy, that is on (possible dynamic) relations among the measured variables. Consequently the robustness of the failure detection process depends to a great degree on the reliability of the redundancy relations given the inevitable presence of model uncertainties. The problem of determining redundancy relations which are optimally robust in a sense which includes the major issues of importance in practical failure detection is addressed. A significant amount of intuition concerning the geometry of robust failure detection is provided
Anomalous kinetics of attractive reactions
We investigate the kinetics of reaction with the local attractive
interaction between opposite species in one spatial dimension. The attractive
interaction leads to isotropic diffusions inside segregated single species
domains, and accelerates the reactions of opposite species at the domain
boundaries. At equal initial densities of and , we analytically and
numerically show that the density of particles (), the size of domains
(), the distance between the closest neighbor of same species
(), and the distance between adjacent opposite species ()
scale in time as , , and respectively. These dynamical exponents form a new
universality class distinguished from the class of uniformly driven systems of
hard-core particles.Comment: 4 pages, 4 figure
Macroscopic objects in quantum mechanics: A combinatorial approach
Why we do not see large macroscopic objects in entangled states? There are
two ways to approach this question. The first is dynamic: the coupling of a
large object to its environment cause any entanglement to decrease
considerably. The second approach, which is discussed in this paper, puts the
stress on the difficulty to observe a large scale entanglement. As the number
of particles n grows we need an ever more precise knowledge of the state, and
an ever more carefully designed experiment, in order to recognize entanglement.
To develop this point we consider a family of observables, called witnesses,
which are designed to detect entanglement. A witness W distinguishes all the
separable (unentangled) states from some entangled states. If we normalize the
witness W to satisfy |tr(W\rho)| \leq 1 for all separable states \rho, then the
efficiency of W depends on the size of its maximal eigenvalue in absolute
value; that is, its operator norm ||W||. It is known that there are witnesses
on the space of n qbits for which ||W|| is exponential in n. However, we
conjecture that for a large majority of n-qbit witnesses ||W|| \leq O(\sqrt{n
logn}). Thus, in a non ideal measurement, which includes errors, the largest
eigenvalue of a typical witness lies below the threshold of detection. We prove
this conjecture for the family of extremal witnesses introduced by Werner and
Wolf (Phys. Rev. A 64, 032112 (2001)).Comment: RevTeX, 14 pages, some additions to the published version: A second
conjecture added, discussion expanded, and references adde
Variations in bilingual processing of positive and negative information
Past research suggests that the emotional content of words has greater impact when presented in a bilingual's first language (L1) compared to their second language (L2). This is predicted to be a consequence of automatic processing of emotional words in L1 compared to slower, semantic processing in L2. In the current study 58 Chinese-English bilinguals from Hong Kong rated the valence and arousal of positive, neutral, and negative words presented in Chinese (L1) and English (L2). In contrast to predictions, perceived emotionality of the words was higher in L2, with positive words rated more positively and negative words rated more negatively when presented in English compared to Chinese. The findings suggest that words presented in L2 did not have lower emotional impact than L1, the results indicate that emotional processing of words may be influenced by language proficiency and language complexity
Calculation of pure dephasing for excitons in quantum dots
Pure dephasing of an exciton in a small quantum dot by optical and acoustic
phonons is calculated using the ``independent boson model''. Considering the
case of zero temperature the dephasing is shown to be only partial which
manifests itself in the polarization decaying to a finite value. Typical
dephasing times can be assigned even though the spectra exhibits strongly
non-Lorentzian line shapes. We show that the dephasing from LO phonon
scattering, occurs on a much larger time scale than that of dephasing due to
acoustic phonons which for low temperatures are also a more efficient dephasing
mechanism. The typical dephasing time is shown to strongly depend on the
quantum dot size whereas the electron phonon ``coupling strength'' and external
electric fields tend mostly to effect the residual coherence. The relevance of
the dephasing times for current quantum information processing implementation
schemes in quantum dots is discussed
Charmed Strange Pentaquarks in the Large Limit
The properties of pentaquarks containing a heavy anti-quark and strange
quarks are studied in the bound state picture. In the flavor SU(3) limit, there
are many pentaquark states with the same binding energy. When the SU(3)
symmetry breaking effects are included, however, three states become
particularly stable due to a ``Gell-Mann--Okubo mechanism''. They are the and states discussed by Lipkin, and a a previously
unstudied state. These states will have and
their masses are estimated. These states, if exist, may be seen in experiments
in the near future.Comment: 12 pages in REVTeX, no figure
Robust effects of predictability across experimental contexts: Evidence from event-related potentials
Many experiments have shown that comprehenders can generate predictions about upcoming inputs on the fly, but relatively little is known about whether and how comprehenders' sensitivity to predictability may be modulated by the experimental context. The present study used event-related potentials (ERPs) in two experiments to ask whether changing the overall predictive validity of the stimuli will affect comprehenders' brain responses to predictable as well as unpredictable words by manipulating the filler sentences, which made up 50% of the stimuli in each experiment. Contrary to the prediction that predictable words should be processed more easily and elicit a smaller N400 response in a more prediction-encouraging experimental context, we found that participants' N400 response to predictable as well as unpredictable words was smaller when the overall predictive validity of the stimuli was low (that is, when the filler items were incongruous compared to when they were predictable). Further, even though the use of different filler sentences did modulate comprehenders' ERP and behavioural responses, it did not modulate the effect of target word predictability on participants' ERP responses at all. We take the present findings to suggest that healthy young adults’ brain responses are inherently sensitive to the predictability of the incoming linguistic stimuli, and that this robust sensitivity can be observed regardless of the make-up of the experimental stimuli
Comprehensive surface magnetotransport study of SmB6
After the theoretical prediction that SmB6 is a topological Kondo insulator, there has been an explosion of studies on the SmB6 surface. However, there is not yet an agreement on even the most basic quantities such as the surface carrier density and mobility. In this paper, we carefully revisit Corbino disk magnetotransport studies to find those surface transport parameters. We first show that subsurface cracks exist in the SmB6 crystals, arising both from surface preparation and during the crystal growth. We provide evidence that these hidden subsurface cracks are additional conduction channels, and the large disagreement between earlier surface SmB6 studies may originate from previous interpretations not taking this extra conduction path into account. We provide an update of more reliable magnetotransport data than the previous one (S. Wolgast et al., Phys. Rev. B 92, 115110) and find that the orders-of-magnitude large disagreements in carrier density and mobility come from the surface preparation and the transport geometry rather than the intrinsic sample quality. From this magnetotransport study, we find an updated estimate of the carrier density and mobility of 2.71×1013 (1/cm2) and 104.5 (cm2/Vsec), respectively. We compare our results with other studies of the SmB6 surface. By this comparison, we provide insight into the disagreements and agreements of the previously reported angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and magnetotorque quantum oscillations measurements
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