13 research outputs found
Applications of Stochastic Ordering to Wireless Communications
Stochastic orders are binary relations defined on probability distributions
which capture intuitive notions like being larger or being more variable. This
paper introduces stochastic ordering of instantaneous SNRs of fading channels
as a tool to compare the performance of communication systems over different
channels. Stochastic orders unify existing performance metrics such as ergodic
capacity, and metrics based on error rate functions for commonly used
modulation schemes through their relation with convex, and completely monotonic
(c.m.) functions. Toward this goal, performance metrics such as instantaneous
error rates of M-QAM and M-PSK modulations are shown to be c.m. functions of
the instantaneous SNR, while metrics such as the instantaneous capacity are
seen to have a completely monotonic derivative (c.m.d.). It is shown that the
commonly used parametric fading distributions for modeling line of sight (LoS),
exhibit a monotonicity in the LoS parameter with respect to the stochastic
Laplace transform order. Using stochastic orders, average performance of
systems involving multiple random variables are compared over different
channels, even when closed form expressions for such averages are not
tractable. These include diversity combining schemes, relay networks, and
signal detection over fading channels with non-Gaussian additive noise, which
are investigated herein. Simulations are also provided to corroborate our
results.Comment: 25 pages, 10 figures, Submitted to the IEEE transactions on wireless
communication
Finite Element Study on the Effect of Geometrical Parameters on the Mechanical Behavior of 3D Reentrant Auxetic Honeycombs.
Abstract
Auxetic materials are a special case of cellular materials, which exhibit a negative Poissonâs ratio. This in fact is the reason behind their peculiar behavior i.e. lateral shrinkage under longitudinal compression and vice versa. Since these materials do not obey the laws of ânormalâ materials and go beyond common sense, they are still an emerging class which can be put to use for various purposes like self-locking reinforcing fibers in composites, controlled release media, self-healing films, piezoelectric sensors, and also be used in biomedical engineering. Their stress-strain behavior, Poissonâs ratio and impact energy absorption are controlled by bulk material as well as the unit cell geometry. Among many forms of auxetic structures available, we have chosen a three-dimensional reentrant auxetic honeycomb unit cell. The unit cell geometrical parameters were taken from literature. In this study, we try to understand the effects of strut angle through finite element simulations while keeping the bulk material, unit cell size, strut thickness and number of repetitions constant. A total of three different angles were tested, based on which we conclude that as angle increases, the Poissonâs ratio increases and Energy absorption is maximum at 30 deg
Revealing the higher-order spin nature of the Hall effect in non-collinear antiferromagnet
Ferromagnets generate an anomalous Hall effect even without the presence of a
magnetic field, something that conventional antiferromagnets cannot replicate
but noncollinear antiferromagnets can. The anomalous Hall effect governed by
the resistivity tensor plays a crucial role in determining the presence of time
reversal symmetry and the topology present in the system. In this work we
reveal the complex origin of the anomalous Hall effect arising in noncollinear
antiferromagnets by performing Hall measurements with fields applied in
selected directions in space with respect to the crystalline axes. Our coplanar
magnetic field geometry goes beyond the conventional perpendicular field
geometry used for ferromagnets and allows us to suppress any magnetic dipole
contribution. It allows us to map the in-plane anomalous Hall contribution and
we demonstrate a 120 symmetry which we find to be governed by the
octupole moment at high fields. At low fields we subsequently discover a
surprising topological Hall-like signature and, from a combination of
theoretical techniques, we show that the spins can be recast into dipole,
emergent octupole and noncoplanar effective magnetic moments. These co-existing
orders enable magnetization dynamics unachievable in either ferromagnetic or
conventional collinear antiferromagnetic materials
Summer program Report : Quality control and Aging study for the GE1/1 detectors in CMS Muon endcap upgrade
In this report, I summarize the work I did during my tenure in the Summer program. The project started with conducting three quality controls -- gas leak test, High Voltage test and Gas gain test. These are necessary to check if the GE1/1 detectors pass the requirements necessary for its deployment in the CMS. Then, I explain how aging study of the detectors was conducted and how the data was analyzed to ascertain if the detector has undergone aging. Lastly, the ongoing process of setting up a further accelerated aging study within the GEM lab is explained, with some potential difficulties associated with it