163 research outputs found
A computer program for model verification of dynamic systems
Dynamic model verification is the process whereby an analytical model of a dynamic system is compared with experimental data, and then qualified for future use in predicting system response in a different dynamic environment. There are various ways to conduct model verification. The approach adopted in MOVER II employs Bayesian statistical parameter estimation. Unlike curve fitting whose objective is to minimize the difference between some analytical function and a given quantity of test data (or curve), Bayesian estimation attempts also to minimize the difference between the parameter values of that function (the model) and their initial estimates, in a least squares sense. The objectives of dynamic model verification, therefore, are to produce a model which: (1) is in agreement with test data, (2) will assist in the interpretation of test data, (3) can be used to help verify a design, (4) will reliably predict performance, and (5) in the case of space structures, facilitate dynamic control
O desenvolvimento de um sistema computacional de sumarização multidocumento com base em um método linguisticamente motivado
This paper presents the studies conducted in the area of Natural Language Processing, more specifically, in Automatic Multi-document Summarization. We describe the steps for the production of a computational prototype, based on a linguistically motivated method, for summarizing news texts in Portuguese.Este trabalho apresenta os estudos realizados na área de Processamento de Linguagem Natural, mais especificamente, em Sumarização Automática Multidocumento. São descritos os passos para a produção de um protótipo computacional, baseado em um método linguisticamente motivado, para a produção de sumários de notícias jornalísticas escritas em português.FAPESPICMCPró-reitoria de Pesquis
Nonlinear dynamics induced by parallel and orthogonal optical injection in 1550 nm Vertical-Cavity Surface-Emitting Lasers (VCSELs)
We report a first experimental study of the nonlinear dynamics appearing in a 1550 nm single-mode VCSEL subject to parallel and to orthogonal optical injection. For the first time to our knowledge we report experimentally measured stability maps identifying the boundaries between regions of different nonlinear dynamics for both cases of polarized injection. A rich variety of nonlinear behaviours, including periodic (limit cycle, period doubling) and chaotic dynamics have been experimentally observed. ©2010 Optical Society of America
Roadmapping the Next Generation of Silicon Photonics
Silicon photonics has developed into a mainstream technology driven by
advances in optical communications. The current generation has led to a
proliferation of integrated photonic devices from thousands to millions -
mainly in the form of communication transceivers for data centers. Products in
many exciting applications, such as sensing and computing, are around the
corner. What will it take to increase the proliferation of silicon photonics
from millions to billions of units shipped? What will the next generation of
silicon photonics look like? What are the common threads in the integration and
fabrication bottlenecks that silicon photonic applications face, and which
emerging technologies can solve them? This perspective article is an attempt to
answer such questions. We chart the generational trends in silicon photonics
technology, drawing parallels from the generational definitions of CMOS
technology. We identify the crucial challenges that must be solved to make
giant strides in CMOS-foundry-compatible devices, circuits, integration, and
packaging. We identify challenges critical to the next generation of systems
and applications - in communication, signal processing, and sensing. By
identifying and summarizing such challenges and opportunities, we aim to
stimulate further research on devices, circuits, and systems for the silicon
photonics ecosystem
Stability of the nonlinear dynamics of an optically injected VCSEL
Automated protocols have been developed to characterize time series data in terms of stability. These techniques are applied to the output power time series of an optically injected vertical cavity surface emitting laser (VCSEL) subject to varying injection strength and optical frequency detuning between master and slave lasers. Dynamic maps, generated from high resolution, computer controlled experiments, identify regions of dynamic instability in the parameter space. © 2012 Optical Society of America
Design and modeling of a transistor vertical-cavity surface-emitting laser
A multiple quantum well (MQW) transistor vertical-cavity surface-emitting
laser (T-VCSEL) is designed and numerically modeled. The important physical
models and parameters are discussed and validated by modeling a conventional
VCSEL and comparing the results with the experiment. The quantum capture/escape
process is simulated using the quantum-trap model and shows a significant
effect on the electrical output of the T-VCSEL. The parameters extracted from
the numerical simulation are imported into the analytic modeling to predict the
frequency response and simulate the large-signal modulation up to 40 Gbps
Reversible Induction of Phantom Auditory Sensations through Simulated Unilateral Hearing Loss
Tinnitus, a phantom auditory sensation, is associated with hearing loss in most cases, but it is unclear if hearing loss causes tinnitus. Phantom auditory sensations can be induced in normal hearing listeners when they experience severe auditory deprivation such as confinement in an anechoic chamber, which can be regarded as somewhat analogous to a profound bilateral hearing loss. As this condition is relatively uncommon among tinnitus patients, induction of phantom sounds by a lesser degree of auditory deprivation could advance our understanding of the mechanisms of tinnitus. In this study, we therefore investigated the reporting of phantom sounds after continuous use of an earplug. 18 healthy volunteers with normal hearing wore a silicone earplug continuously in one ear for 7 days. The attenuation provided by the earplugs simulated a mild high-frequency hearing loss, mean attenuation increased from <10 dB at 0.25 kHz to >30 dB at 3 and 4 kHz. 14 out of 18 participants reported phantom sounds during earplug use. 11 participants presented with stable phantom sounds on day 7 and underwent tinnitus spectrum characterization with the earplug still in place. The spectra showed that the phantom sounds were perceived predominantly as high-pitched, corresponding to the frequency range most affected by the earplug. In all cases, the auditory phantom disappeared when the earplug was removed, indicating a causal relation between auditory deprivation and phantom sounds. This relation matches the predictions of our computational model of tinnitus development, which proposes a possible mechanism by which a stabilization of neuronal activity through homeostatic plasticity in the central auditory system could lead to the development of a neuronal correlate of tinnitus when auditory nerve activity is reduced due to the earplug
65 GOPS/neuron Photonic Tensor Core with Thin-film Lithium Niobate Photonics
Photonics offers a transformative approach to artificial intelligence (AI)
and neuromorphic computing by providing low latency, high bandwidth, and
energy-efficient computations. Here, we introduce a photonic tensor core
processor enabled by time-multiplexed inputs and charge-integrated outputs.
This fully integrated processor, comprising only two thin-film lithium niobate
(TFLN) modulators, a III-V laser, and a charge-integration photoreceiver, can
implement an entire layer of a neural network. It can execute 65 billion
operations per second (GOPS) per neuron, including simultaneous weight
updates-a hitherto unachieved speed. Our processor stands out from conventional
photonic processors, which have static weights set during training, as it
supports fast "hardware-in-the-loop" training, and can dynamically adjust the
inputs (fan-in) and outputs (fan-out) within a layer, thereby enhancing its
versatility. Our processor can perform large-scale dot-product operations with
vector dimensions up to 131,072. Furthermore, it successfully classifies
(supervised learning) and clusters (unsupervised learning) 112*112-pixel images
after "hardware-in-the-loop" training. To handle "hardware-in-the-loop"
training for clustering AI tasks, we provide a solution for multiplications
involving two negative numbers based on our processor.Comment: 19 pages, 6 figure
CD98 Increases Renal Epithelial Cell Proliferation by Activating MAPKs
CD98 heavy chain (CD98hc) is a multifunctional transmembrane spanning scaffolding protein whose extracellular domain binds with light chain amino acid transporters (Lats) to form the heterodimeric amino acid transporters (HATs). It also interacts with β1 and β3 integrins by its transmembrane and cytoplasmic domains. This interaction is proposed to be the mechanism whereby CD98 mediates cell survival and growth via currently undefined signaling pathways. In this study, we determined whether the critical function of CD98-dependent amino acid transport also plays a role in cell proliferation and defined the signaling pathways that mediate CD98-dependent proliferation of murine renal inner medullary collecting duct (IMCD) cells. We demonstrate that downregulating CD98hc expression resulted in IMCD cell death. Utilizing overexpression studies of CD98hc mutants that either lacked a cytoplasmic tail or were unable to bind to Lats we showed that CD98 increases serum-dependent cell proliferation by a mechanism that requires the CD98hc cytoplasmic tail. We further demonstrated that CD98-dependent amino acid transport increased renal tubular epithelial cell proliferation by a mechanism that does not require the CD98hc cytoplasmic tail. Both these mechanisms of increased renal tubular epithelial cell proliferation are mediated by Erk and p38 MAPK signaling. Although increased amino transport markedly activated mTor signaling, this pathway did not alter cell proliferation. Thus, these studies demonstrate that in IMCD cells, the cytoplasmic and extracellular domains of CD98hc regulate cell proliferation by distinct mechanisms that are mediated by common MAPK signaling pathways
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