10,078 research outputs found
Statistical properties of chaotic microcavities in small and large opening cases
We study the crossover behavior of statistical properties of eigenvalues in a
chaotic microcavity with different refractive indices. The level spacing
distributions change from Wigner to Poisson distributions as the refractive
index of a microcavity decreases. We propose a non-hermitian matrix model with
random elements describing the spectral properties of the chaotic microcavity,
which exhibits the crossover behaviors as the opening strength increases.Comment: 22 pages, 6 figure
Congestion Control and Routing over Challenged Networks
This dissertation is a study on the design and analysis of novel, optimal
routing and rate control algorithms in wireless, mobile communication networks.
Congestion control and routing algorithms upto now have been designed and
optimized for wired or wireless mesh networks. In those networks, optimal
algorithms (optimal in the sense that either the throughput is maximized or
delay is minimized, or the network operation cost is minimized) can be
engineered based on the classic time scale decomposition assumption that the
dynamics of the network are either fast enough so that these algorithms
essentially see the average or slow enough that any changes can be tracked to
allow the algorithms to adapt over time. However, as technological advancements
enable integration of ever more mobile nodes into communication networks, any
rate control or routing algorithms based, for example, on averaging out the
capacity of the wireless mobile link or tracking the instantaneous capacity
will perform poorly. The common element in our solution to engineering
efficient routing and rate control algorithms for mobile wireless networks is
to make the wireless mobile links seem as if they are wired or wireless links
to all but few nodes that directly see the mobile links (either the mobiles or
nodes that can transmit to or receive from the mobiles) through an appropriate
use of queuing structures at these selected nodes. This approach allows us to
design end-to-end rate control or routing algorithms for wireless mobile
networks so that neither averaging nor instantaneous tracking is necessary
Quasiattractors in coupled maps and coupled dielectric cavities
We study the origin of attracting phenomena in the ray dynamics of coupled
optical microcavities. To this end we investigate a combined map that is
composed of standard and linear map, and a selection rule that defines when
which map has to be used. We find that this system shows attracting dynamics,
leading exactly to a quasiattractor, due to collapse of phase space. For
coupled dielectric disks, we derive the corresponding mapping based on a ray
model with deterministic selection rule and study the quasiattractor obtained
from it. We also discuss a generalized Poincar\'e surface of section at
dielectric interfaces.Comment: 7 pages, 7 figure
Antiresonance induced by symmetry-broken contacts in quasi-one-dimensional lattices
We report the effect of symmetry-broken contacts on quantum transport in
quasi-one-dimensional lattices. In contrast to 1D chains, transport in
quasi-one-dimensional lattices, which are made up of a finite number of 1D
chain layers, is strongly influenced by contacts. Contact symmetry depends on
whether the contacts maintain or break the parity symmetry between the layers.
With balanced on-site potential, a flat band can be detected by asymmetric
contacts, but not by symmetric contacts. In the case of asymmetric contacts
with imbalanced on-site potential, transmission is suppressed at certain
energies. We elucidate these energies of transmission suppression related to
antiresonance using reduced lattice models and Feynman paths. These results
provide a nondestructive measurement of flat band energy which it is difficult
to detect.Comment: 8 pages, 5 figure
Reconfiguration of quantum states in -symmetric quasi-one dimensional lattices
We demonstrate mesoscopic transport through quantum states in quasi-1D
lattices maintaining the combination of parity and time-reversal symmetries by
controlling energy gain and loss. We investigate the phase diagram of the
non-Hermitian system where transitions take place between unbroken and broken
-symmetric phases via exceptional points. Quantum transport in
the lattice is measured only in the unbroken phases in the energy band-but not
in the broken phases. The broken phase allows for spontaneous symmetry-broken
states where the cross-stitch lattice is separated into two identical single
lattices corresponding to conditionally degenerate eigenstates. These
degeneracies show a lift-up in the complex energy plane, caused by the
non-Hermiticity with -symmetry.Comment: 12 pages, 7 figure
Quasiscarred modes and their branching behavior at an exceptional point
We study quasiscarring phenomenon and mode branching at an exceptional point
(EP) in typically deformed microcavities. It is shown that quasiscarred (QS)
modes are dominant in some mode group and their pattern can be understood by
short-time ray dynamics near the critical line. As cavity deformation
increases, high-Q and low-Q QS modes are branching in an opposite way, at an
EP, into two robust mode types showing QS and diamond patterns, respectively.
Similar branching behavior can be also found at another EP appearing at a
higher deformation. This branching behavior of QS modes has its origin on the
fact that an EP is a square-root branch point.Comment: 5 pages, 5 figure
Oscillation death in coupled counter-rotating identical nonlinear oscillators
We study oscillatory and oscillation suppressed phases in coupled
counter-rotating nonlinear oscillators. We demonstrate the existence of limit
cycle, amplitude death, and oscillation death, and also clarify the Hopf,
pitchfork, and infinite period bifurcations between them. Especially, the
oscillation death is a new type of oscillation suppressions of which the
inhomogeneous steady states are neutrally stable. We discuss the robust neutral
stability of the oscillation death in non-conservative systems via the
anti-PT-symmetric phase transitions at exceptional points in terms of
non-Hermitian systems.Comment: 7 pages, 4 figure
Building World-Class Universities in Developing Systems: The Success Case of the Indian Institutes of Technology
With a global shift towards knowledge-based economy,universities are required to produce knowledge and cutting-edge technologies to support their respective country’s economy. In response, many countries around the world seek to build their own world-class universities. Altbach (2010, p.1) argues that world-class universities‘demonstrate world class thinking and policy development in the sense that they employ state of the art solutions to pressing challenges of the twenty first century’.However, world-class universities are found only in a few wealthy Western countries. For instance, if one takes a quick glance at Global University Rankings (GUR), nearly every top university is situated in a high-income country. There are exceptions, such as the Indian Institutes of Technology (IIT), which are known to produce the world’s most creative engineers. The GUR of IIT steadily rose over the past few years, drawing much attention from the industry for its unprecedented success. This research aims to trace the successful path of IIT to identify its success factors which may serve as reference points for other developing systems that aim to build world-class universities of their own. The study takes the two most prominent IIT, namely IIT Delhi and IIT Bombay.It also hypothesises and investigates whether the considerable amount of international co-operation activities IIT engaged in at the establishments have played a significant role in its success. The findings of the study showed that IIT’s limited financial resources were complemented by a highly concentrated pool of talented and motivated students,as well as professors who have abundant experiences in top-tier research and technical firms aboard. Another major factor was the government’s dedication. The government focused on creating a favourable environment for the institution and also prioritised IIT in its allocation of financial resources. Meanwhile, the study was unsuccessful in illustrating the role of international cooperation as the two sets of the collected data were contradictive
- …