1,515 research outputs found
Media-Based MIMO: A New Frontier in Wireless Communications
The idea of Media-based Modulation (MBM), is based on embedding information
in the variations of the transmission media (channel state). This is in
contrast to legacy wireless systems where data is embedded in a Radio Frequency
(RF) source prior to the transmit antenna. MBM offers several advantages vs.
legacy systems, including "additivity of information over multiple receive
antennas", and "inherent diversity over a static fading channel". MBM is
particularly suitable for transmitting high data rates using a single transmit
and multiple receive antennas (Single Input-Multiple Output Media-Based
Modulation, or SIMO-MBM). However, complexity issues limit the amount of data
that can be embedded in the channel state using a single transmit unit. To
address this shortcoming, the current article introduces the idea of Layered
Multiple Input-Multiple Output Media-Based Modulation (LMIMO-MBM). Relying on a
layered structure, LMIMO-MBM can significantly reduce both hardware and
algorithmic complexities, as well as the training overhead, vs. SIMO-MBM.
Simulation results show excellent performance in terms of Symbol Error Rate
(SER) vs. Signal-to-Noise Ratio (SNR). For example, a LMIMO-MBM is
capable of transmitting bits of information per (complex) channel-use,
with SER at dB (or SER
at dB). This performance is achieved using a single transmission
and without adding any redundancy for Forward-Error-Correction (FEC). This
means, in addition to its excellent SER vs. energy/rate performance, MBM
relaxes the need for complex FEC structures, and thereby minimizes the
transmission delay. Overall, LMIMO-MBM provides a promising alternative to MIMO
and Massive MIMO for the realization of 5G wireless networks.Comment: 26 pages, 11 figures, additional examples are given to further
explain the idea of Media-Based Modulation. Capacity figure adde
A single-phase synchronization technique for grid-connected energy storage system under faulty grid conditions
The control of a single-phase grid-connected energy storage system (ESS) requires a very fast and accurate estimation of grid voltage frequency and phase angle. A phase-locked loop (PLL) based synchronization algorithm usually extracts this information. The operation and control of the entire system are directly affected by the performance of PLL. In this article, a novel advanced single-phase PLL (ASÏ•PLL) technique with reduced complexity is proposed for the fast and accurate extraction of grid information in an ESS under distorted and abnormal grid conditions, including harmonics, interharmonics, dc offset, and grid faults. The proposed method provides a faster dynamic response, lower frequency overshoot, and accurate estimation under off-nominal grid frequencies with reduced computational complexity in comparison with the existing method. The advanced performance of the proposed ASÏ•PLL is verified through the simulation and experimental results
Identification of drug resistance mutations in HIV from constraints on natural evolution
Human immunodeficiency virus (HIV) evolves with extraordinary rapidity.
However, its evolution is constrained by interactions between mutations in its
fitness landscape. Here we show that an Ising model describing these
interactions, inferred from sequence data obtained prior to the use of
antiretroviral drugs, can be used to identify clinically significant sites of
resistance mutations. Successful predictions of the resistance sites indicate
progress in the development of successful models of real viral evolution at the
single residue level, and suggest that our approach may be applied to help
design new therapies that are less prone to failure even where resistance data
is not yet available.Comment: 5 pages, 3 figure
Melting of persistent double-stranded polymers
Motivated by recent DNA-pulling experiments, we revisit the Poland-Scheraga
model of melting a double-stranded polymer. We include distinct bending
rigidities for both the double-stranded segments, and the single-stranded
segments forming a bubble. There is also bending stiffness at the branch points
between the two segment types. The transfer matrix technique for single
persistent chains is generalized to describe the branching bubbles. Properties
of spherical harmonics are then exploited in truncating and numerically solving
the resulting transfer matrix. This allows efficient computation of phase
diagrams and force-extension curves (isotherms). While the main focus is on
exposition of the transfer matrix technique, we provide general arguments for a
reentrant melting transition in stiff double strands. Our theoretical approach
can also be extended to study polymers with bubbles of any number of strands,
with potential applications to molecules such as collagen.Comment: 9 pages, 7 figure
Positive Feedback Regulation Results in Spatial Clustering and Fast Spreading of Active Signaling Molecules on a Cell Membrane
Positive feedback regulation is ubiquitous in cell signaling networks, often
leading to binary outcomes in response to graded stimuli. However, the role of
such feedbacks in clustering, and in spatial spreading of activated molecules,
has come to be appreciated only recently. We focus on the latter, using a
simple model developed in the context of Ras activation with competing negative
and positive feedback mechanisms. We find that positive feedback, in the
presence of slow diffusion, results in clustering of activated molecules on the
plasma membrane, and rapid spatial spreading as the front of the cluster
propagates with a constant velocity (dependent on the feedback strength). The
advancing fronts of the clusters of the activated species are rough, with
scaling consistent with the Kardar-Parisi-Zhang (KPZ) equation in one
dimension. Our minimal model is general enough to describe signal transduction
in a wide variety of biological networks where activity in the
membrane-proximal region is subject to feedback regulation.Comment: 37 pages, 8 figures. Journal of Chemical Physics (in press
Apex Exponents for Polymer--Probe Interactions
We consider self-avoiding polymers attached to the tip of an impenetrable
probe. The scaling exponents and , characterizing the
number of configurations for the attachment of the polymer by one end, or at
its midpoint, vary continuously with the tip's angle. These apex exponents are
calculated analytically by -expansion, and numerically by simulations
in three dimensions. We find that when the polymer can move through the
attachment point, it typically slides to one end; the apex exponents quantify
the entropic barrier to threading the eye of the probe
Optimal Observer Synthesis for Microgrids With Adaptive Send-on-Delta Sampling Over IoT Communication Networks
State estimation is one of the main challenges in the microgrids, due to the complexity of the system dynamics and the limitations of the communication network. In this regard, a novel real-time event-based optimal state estimator is introduced in this paper, which uses the proposed adaptive send-on-delta (SoD) non-uniform sampling method over wireless sensors networks. The proposed estimator requires low communication bandwidth and incurs lower computational resource cost. The threshold for the SoD sampler is made adaptive based on the average communication link delay, which is computed in a distributed form using the event-based average consensus protocol. The SoD non-uniform signal sampling approach reduces the traffic over the wireless communication network due to the events transmitted only when there is a level crossing in the measurements. The state estimator structure is extended on top of the traditional Kalman filter with the additional stages for the fusion of the received events. The error correction stage is further improved by optimal reconstruction of the signals using projection onto convex sets (POCS) algorithm. Finally, an Internet of things (IoT) experimental platform based on LoRaWAN and IEEE 802.11 (WiFi) protocols is developed to analyse the performance of the state estimator for the IEEE 5 Bus case study microgrid
How nonuniform contact profiles of T cell receptors modulate thymic selection outcomes
T cell receptors (TCRs) bind foreign or self-peptides attached to major
histocompatibility complex (MHC) molecules, and the strength of this
interaction determines T cell activation. Optimizing the ability of T cells to
recognize a diversity of foreign peptides yet be tolerant of self-peptides is
crucial for the adaptive immune system to properly function. This is achieved
by selection of T cells in the thymus, where immature T cells expressing
unique, stochastically generated TCRs interact with a large number of
self-peptide-MHC; if a TCR does not bind strongly enough to any
self-peptide-MHC, or too strongly with at least one self-peptide-MHC, the T
cell dies. Past theoretical work cast thymic selection as an extreme value
problem, and characterized the statistical enrichment or depletion of amino
acids in the post-selection TCR repertoire, showing how T cells are selected to
be able to specifically recognize peptides derived from diverse pathogens, yet
have limited self-reactivity. Here, we investigate how the degree of enrichment
is modified by nonuniform contacts that a TCR makes with peptide-MHC.
Specifically, we were motivated by recent experiments showing that amino acids
at certain positions of a TCR sequence have large effects on thymic selection
outcomes, and crystal structure data that reveal a nonuniform contact profile
between a TCR and its peptide-MHC ligand. Using a representative TCR contact
profile as an illustration, we show via simulations that the degree of
enrichment now varies by position according to the contact profile, and,
importantly, it depends on the implementation of nonuniform contacts during
thymic selection. We explain these nontrivial results analytically. Our study
has implications for understanding the selection forces that shape the
functionality of the post-selection TCR repertoire.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
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