48,786 research outputs found
A Hierarchical Dirichlet Process Model with Multiple Levels of Clustering for Human EEG Seizure Modeling
Driven by the multi-level structure of human intracranial
electroencephalogram (iEEG) recordings of epileptic seizures, we introduce a
new variant of a hierarchical Dirichlet Process---the multi-level clustering
hierarchical Dirichlet Process (MLC-HDP)---that simultaneously clusters
datasets on multiple levels. Our seizure dataset contains brain activity
recorded in typically more than a hundred individual channels for each seizure
of each patient. The MLC-HDP model clusters over channels-types, seizure-types,
and patient-types simultaneously. We describe this model and its implementation
in detail. We also present the results of a simulation study comparing the
MLC-HDP to a similar model, the Nested Dirichlet Process and finally
demonstrate the MLC-HDP's use in modeling seizures across multiple patients. We
find the MLC-HDP's clustering to be comparable to independent human physician
clusterings. To our knowledge, the MLC-HDP model is the first in the epilepsy
literature capable of clustering seizures within and between patients.Comment: ICML201
Multi-user lattice coding for the multiple-access relay channel
This paper considers the multi-antenna multiple access relay channel (MARC),
in which multiple users transmit messages to a common destination with the
assistance of a relay. In a variety of MARC settings, the dynamic decode and
forward (DDF) protocol is very useful due to its outstanding rate performance.
However, the lack of good structured codebooks so far hinders practical
applications of DDF for MARC. In this work, two classes of structured MARC
codes are proposed: 1) one-to-one relay-mapper aided multiuser lattice coding
(O-MLC), and 2) modulo-sum relay-mapper aided multiuser lattice coding
(MS-MLC). The former enjoys better rate performance, while the latter provides
more flexibility to tradeoff between the complexity of the relay mapper and the
rate performance. It is shown that, in order to approach the rate performance
achievable by an unstructured codebook with maximum-likelihood decoding, it is
crucial to use a new K-stage coset decoder for structured O-MLC, instead of the
one-stage decoder proposed in previous works. However, if O-MLC is decoded with
the one-stage decoder only, it can still achieve the optimal DDF
diversity-multiplexing gain tradeoff in the high signal-to-noise ratio regime.
As for MS-MLC, its rate performance can approach that of the O-MLC by
increasing the complexity of the modulo-sum relay-mapper. Finally, for
practical implementations of both O-MLC and MS-MLC, practical short length
lattice codes with linear mappers are designed, which facilitate efficient
lattice decoding. Simulation results show that the proposed coding schemes
outperform existing schemes in terms of outage probabilities in a variety of
channel settings.Comment: 32 pages, 5 figure
A Study on Performance and Power Efficiency of Dense Non-Volatile Caches in Multi-Core Systems
In this paper, we present a novel cache design based on Multi-Level Cell
Spin-Transfer Torque RAM (MLC STTRAM) that can dynamically adapt the set
capacity and associativity to use efficiently the full potential of MLC STTRAM.
We exploit the asymmetric nature of the MLC storage scheme to build cache lines
featuring heterogeneous performances, that is, half of the cache lines are
read-friendly, while the other is write-friendly. Furthermore, we propose to
opportunistically deactivate ways in underutilized sets to convert MLC to
Single-Level Cell (SLC) mode, which features overall better performance and
lifetime. Our ultimate goal is to build a cache architecture that combines the
capacity advantages of MLC and performance/energy advantages of SLC. Our
experiments show an improvement of 43% in total numbers of conflict misses, 27%
in memory access latency, 12% in system performance, and 26% in LLC access
energy, with a slight degradation in cache lifetime (about 7%) compared to an
SLC cache
Equivalent-Capacity-Based Design of Space-Time Block-Coded Sphere-Packing-Aided Multilevel Coding
A multilevel coding (MLC) scheme invoking sphere packing (SP) modulation combined with space time block coding (STBC) is designed. The coding rates of each of the MLC component codes are determined using the so-called equivalent capacity based constituent-code rate-calculation procedure invoking a 4-dimensional (4D) sphere packing bit-to-symbol mapping scheme. Four different-rate Low-Density Parity Check (LDPC) constituent-codes are used by the MLC scheme. The performance of the resultant equivalent capacity based design is characterized using simulation results. Our results demonstrate an approximately 3.5dB gain over an identical scheme dispensing with SP modulation. Furthermore although a similar performance gain is attained by both the proposed MLC scheme and its benchmarker, which uses a single-class LDPC code, the MLC scheme is preferred, since it benefits from the new classic philosophy of using low-memory, low-complexity component codes as well as providing an unequal error protection capability
Dosimetric Performance and Planning/Delivery Efficiency of a Dual-Layer Stacked and Staggered MLC on Treating Multiple Small Targets: A Planning Study Based on Single-Isocenter Multi-Target Stereotactic Radiosurgery (SRS) to Brain Metastases.
Purpose: To evaluate the dosimetric performance and planning/delivery efficiency of a dual-layer MLC system for treating multiple brain metastases with a single isocenter.
Materials and Methods: 10 patients each with 6-10 targets with volumes from 0.11 to 8.57 cc, and prescription doses from 15 to 24 Gy, were retrospectively studied. Halcyon has only coplanar delivery mode. Halcyon V1 MLC modulates only with the lower layer at 1 cm resolution, whereas V2 MLC modulates with both layers at an effective resolution of 0.5 cm. For each patient five plans were compared varying MLC and beam arrangements: the clinical plan using multi-aperture dynamic conformal arc (DCA) and non-coplanar arcs, Halcyon-V1 using coplanar-VMAT, Halcyon-V2 using coplanar-VMAT, HDMLC-0.25 cm using coplanar-VMAT, and HDMLC-0.25 cm using non-coplanar-VMAT. All same-case plans were generated following the same planning protocol and normalization. Conformity index (CI), gradient index (GI), V12Gy, V6Gy, V3Gy, and brain mean dose were compared.
Results: All VMAT plans met clinical constraints for critical structures. For targets with diameter \u3c 1 cm, Halcyon plans showed inferior CI among all techniques. For targets with diameter \u3e1 cm, Halcyon VMAT plans had CI similar to non-coplanar VMAT plans, and better than non-coplanar clinical DCA plans. For GI, Halcyon MLC plans performed similarly to coplanar HDMLC plans and inferiorly compared to non-coplanar HDMLC plans. All coplanar VMAT plans (Halcyon MLC and HDMLC) and clinical DCA plans had similar V12Gy, but were inferior compared to non-coplanar VMAT plans. Halcyon plans had slightly reduced V3Gy and mean brain dose compared to HDMLC plans. The difference between Halcyon V1 and V2 is only significant in CI of tumors less than 1cm in diameter. Halcyon plans required longer optimization than Truebeam VMAT plans, but had similar delivery efficiency.
Conclusion: For targets with diameter \u3e1 cm, Halcyon\u27s dual-layer stacked and staggered MLC is capable of producing similar dose conformity compared to HDMLC while reducing low dose spill to normal brain tissue. GI and V12Gy of Halcyon MLC plans were, in general, inferior to non-coplanar DCA or VMAT plans using HDMLC, likely due to coplanar geometry and wider MLC leaves. HDMLC maintained its advantage in CI for smaller targets with diameter \u3c1 cm. © 2019 Li, Irmen, Liu, Shi, Alonso-Basanta, Zou, Teo, Metz and Dong
Birefringence analysis of multilayer leaky cladding optical fibre
We analyse a multilayer leaky cladding (MLC) fibre using the finite element
method and study the effect of the MLC on the bending loss and birefringence of
two types of structures: (i) a circular core large-mode-area structure and (ii)
an elliptical-small-core structure. In a large-mode-area structure, we verify
that the multilayer leaky cladding strongly discriminates against higher order
modes to achieve single-mode operation, the fibre shows negligible
birefringence, and the bending loss of the fibre is low for bending radii
larger than 10 cm. In the elliptical-small-core structure we show that the MLC
reduces the birefringence of the fibre. This prevents the structure from
becoming birefringent in case of any departures from circular geometry. The
study should be useful in the designs of MLC fibres for various applications
including high power amplifiers, gain flattening of fibre amplifiers and
dispersion compensation.Comment: 18 page
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