28,131 research outputs found
Diffusing-wave spectroscopy of nonergodic media
We introduce an elegant method which allows the application of diffusing-wave
spectroscopy (DWS) to nonergodic, solid-like samples. The method is based on
the idea that light transmitted through a sandwich of two turbid cells can be
considered ergodic even though only the second cell is ergodic. If absorption
and/or leakage of light take place at the interface between the cells, we
establish a so-called "multiplication rule", which relates the intensity
autocorrelation function of light transmitted through the double-cell sandwich
to the autocorrelation functions of individual cells by a simple
multiplication. To test the proposed method, we perform a series of DWS
experiments using colloidal gels as model nonergodic media. Our experimental
data are consistent with the theoretical predictions, allowing quantitative
characterization of nonergodic media and demonstrating the validity of the
proposed technique.Comment: RevTeX, 12 pages, 6 figures. Accepted for publication in Phys. Rev.
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Fast, non-monte-carlo estimation of transient performance variation due to device mismatch
This paper describes an efficient way of simulating the effects of device random mismatch on circuit transient characteristics, such as variations in delay or in frequency. The proposed method models DC random offsets as equivalent AC pseudo-noises and leverages the fast, linear periodically time-varying (LPTV) noise analysis available from RF circuit simulators. Therefore, the method can be considered as an extension to DC match analysis and offers a large speed-up compared to the traditional Monte-Carlo analysis. Although the assumed linear perturbation model is valid only for small variations, it enables easy ways to estimate correlations among variations and identify the most sensitive design parameters to mismatch, all at no additional simulation cost. Three benchmarks measuring the variations in the input offset voltage of a clocked comparator, the delay of a logic path, and the frequency of an oscillator demonstrate the speed improvement of about 100-1000x compared to a 1000-point Monte-Carlo method
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Bandgap engineering in semiconductor alloy nanomaterials with widely tunable compositions
Over the past decade, tremendous progress has been achieved in the development of nanoscale semiconductor materials with a wide range of bandgaps by alloying different individual semiconductors. These materials include traditional II-VI and III-V semiconductors and their alloys, inorganic and hybrid perovskites, and the newly emerging 2D materials. One important common feature of these materials is that their nanoscale dimensions result in a large tolerance to lattice mismatches within a monolithic structure of varying composition or between the substrate and target material, which enables us to achieve almost arbitrary control of the variation of the alloy composition. As a result, the bandgaps of these alloys can be widely tuned without the detrimental defects that are often unavoidable in bulk materials, which have a much more limited tolerance to lattice mismatches. This class of nanomaterials could have a far-reaching impact on a wide range of photonic applications, including tunable lasers, solid-state lighting, artificial photosynthesis and new solar cells
Resource-Constrained Adaptive Search and Tracking for Sparse Dynamic Targets
This paper considers the problem of resource-constrained and noise-limited
localization and estimation of dynamic targets that are sparsely distributed
over a large area. We generalize an existing framework [Bashan et al, 2008] for
adaptive allocation of sensing resources to the dynamic case, accounting for
time-varying target behavior such as transitions to neighboring cells and
varying amplitudes over a potentially long time horizon. The proposed adaptive
sensing policy is driven by minimization of a modified version of the
previously introduced ARAP objective function, which is a surrogate function
for mean squared error within locations containing targets. We provide
theoretical upper bounds on the performance of adaptive sensing policies by
analyzing solutions with oracle knowledge of target locations, gaining insight
into the effect of target motion and amplitude variation as well as sparsity.
Exact minimization of the multi-stage objective function is infeasible, but
myopic optimization yields a closed-form solution. We propose a simple
non-myopic extension, the Dynamic Adaptive Resource Allocation Policy (D-ARAP),
that allocates a fraction of resources for exploring all locations rather than
solely exploiting the current belief state. Our numerical studies indicate that
D-ARAP has the following advantages: (a) it is more robust than the myopic
policy to noise, missing data, and model mismatch; (b) it performs comparably
to well-known approximate dynamic programming solutions but at significantly
lower computational complexity; and (c) it improves greatly upon non-adaptive
uniform resource allocation in terms of estimation error and probability of
detection.Comment: 49 pages, 1 table, 11 figure
Contributions on using embedded memory circuits as physically unclonable functions considering reliability issues
[eng] Moving towards Internet-of-Things (IoT) era, hardware security becomes a crucial
research topic, because of the growing demand of electronic products that are remotely
connected through networks. Novel hardware security primitives based on
manufacturing process variability are proposed to enhance the security of the IoT
systems. As a trusted root that provides physical randomness, a physically unclonable
function is an essential base for hardware security.
SRAM devices are becoming one of the most promising alternatives for the
implementation of embedded physical unclonable functions as the start-up value of
each bit-cell depends largely on the variability related with the manufacturing process.
Not all bit-cells experience the same degree of variability, so it is possible that some cells
randomly modify their logical starting value, while others will start-up always at the
same value. However, physically unclonable function applications, such as identification
and key generation, require more constant logical starting value to assure high reliability
in PUF response. For this reason, some kind of post-processing is needed to correct the
errors in the PUF response.
Unfortunately, those cells that have more constant logic output are difficult to be
detected in advance. This work characterizes by simulation the start-up value
reproducibility proposing several metrics suitable for reliability estimation during design
phases. The aim is to be able to predict by simulation the percentage of cells that will be
suitable to be used as PUF generators. We evaluate the metrics results and analyze the
start-up values reproducibility considering different external perturbation sources like several power supply ramp up times, previous internal values in the bit-cell, and
different temperature scenarios. The characterization metrics can be exploited to
estimate the number of suitable SRAM cells for use in PUF implementations that can be
expected from a specific SRAM design.[cat] En l’era de la Internet de les coses (IoT), garantir la seguretat del hardware ha
esdevingut un tema de recerca crucial, en especial a causa de la creixent demanda de
productes electrònics que es connecten remotament a través de xarxes. Per millorar la
seguretat dels sistemes IoT, s’han proposat noves solucions hardware basades en la
variabilitat dels processos de fabricació. Les funcions físicament inclonables (PUF)
constitueixen una font fiable d’aleatorietat física i són una base essencial per a la
seguretat hardware.
Les memòries SRAM s’estan convertint en una de les alternatives més prometedores per
a la implementació de funcions físicament inclonables encastades. Això és així ja que el
valor d’encesa de cada una de les cel·les que formen els bits de la memòria depèn en
gran mesura de la variabilitat pròpia del procés de fabricació. No tots els bits tenen el
mateix grau de variabilitat, així que algunes cel·les canvien el seu estat lògic d’encesa de
forma aleatòria entre enceses, mentre que d’altres sempre assoleixen el mateix valor
en totes les enceses. No obstant això, les funcions físicament inclonables, que s’utilitzen
per generar claus d’identificació, requereixen un valor lògic d’encesa constant per tal
d’assegurar una resposta fiable del PUF. Per aquest motiu, normalment es necessita
algun tipus de postprocessament per corregir els possibles errors presents en la resposta
del PUF. Malauradament, les cel·les que presenten una resposta més constant són
difícils de detectar a priori.
Aquest treball caracteritza per simulació la reproductibilitat del valor d’encesa de cel·les
SRAM, i proposa diverses mètriques per estimar la fiabilitat de les cel·les durant les fases de disseny de la memòria. L'objectiu és ser capaç de predir per simulació el percentatge
de cel·les que seran adequades per ser utilitzades com PUF. S’avaluen els resultats de
diverses mètriques i s’analitza la reproductibilitat dels valors d’encesa de les cel·les
considerant diverses fonts de pertorbacions externes, com diferents rampes de tensió
per a l’encesa, els valors interns emmagatzemats prèviament en les cel·les, i diferents
temperatures. Es proposa utilitzar aquestes mètriques per estimar el nombre de cel·les
SRAM adients per ser implementades com a PUF en un disseny d‘SRAM específic.[spa] En la era de la Internet de las cosas (IoT), garantizar la seguridad del hardware se ha
convertido en un tema de investigación crucial, en especial a causa de la creciente
demanda de productos electrónicos que se conectan remotamente a través de redes.
Para mejorar la seguridad de los sistemas IoT, se han propuesto nuevas soluciones
hardware basadas en la variabilidad de los procesos de fabricación. Las funciones
físicamente inclonables (PUF) constituyen una fuente fiable de aleatoriedad física y son
una base esencial para la seguridad hardware.
Las memorias SRAM se están convirtiendo en una de las alternativas más prometedoras
para la implementación de funciones físicamente inclonables empotradas. Esto es así,
puesto que el valor de encendido de cada una de las celdas que forman los bits de la
memoria depende en gran medida de la variabilidad propia del proceso de fabricación.
No todos los bits tienen el mismo grado de variabilidad. Así pues, algunas celdas cambian
su estado lógico de encendido de forma aleatoria entre encendidos, mientras que otras
siempre adquieren el mismo valor en todos los encendidos. Sin embargo, las funciones
físicamente inclonables, que se utilizan para generar claves de identificación, requieren
un valor lógico de encendido constante para asegurar una respuesta fiable del PUF. Por
este motivo, normalmente se necesita algún tipo de posprocesado para corregir los
posibles errores presentes en la respuesta del PUF. Desafortunadamente, las celdas que
presentan una respuesta más constante son difíciles de detectar a priori.
Este trabajo caracteriza por simulación la reproductibilidad del valor de encendido de
celdas SRAM, y propone varias métricas para estimar la fiabilidad de las celdas durante las fases de diseño de la memoria. El objetivo es ser capaz de predecir por simulación el
porcentaje de celdas que serán adecuadas para ser utilizadas como PUF. Se evalúan los
resultados de varias métricas y se analiza la reproductibilidad de los valores de
encendido de las celdas considerando varias fuentes de perturbaciones externas, como
diferentes rampas de tensión para el encendido, los valores internos almacenados
previamente en las celdas, y diferentes temperaturas. Se propone utilizar estas métricas
para estimar el número de celdas SRAM adecuadas para ser implementadas como PUF
en un diseño de SRAM específico
Adaptive Neural Coding Dependent on the Time-Varying Statistics of the Somatic Input Current
It is generally assumed that nerve cells optimize their performance to reflect the statistics of their input. Electronic circuit analogs of neurons require similar methods of self-optimization for stable and autonomous operation. We here describe and demonstrate a biologically plausible adaptive algorithm that enables a neuron to adapt the current threshold and the slope (or gain) of its current-frequency relationship to match the mean (or dc offset) and variance (or dynamic range or contrast) of the time-varying somatic input current. The adaptation algorithm estimates the somatic current signal from the spike train by way of the intracellular somatic calcium concentration, thereby continuously adjusting the neuronś firing dynamics. This principle is shown to work in an analog VLSI-designed silicon neuron
Parametrization of stochastic inputs using generative adversarial networks with application in geology
We investigate artificial neural networks as a parametrization tool for
stochastic inputs in numerical simulations. We address parametrization from the
point of view of emulating the data generating process, instead of explicitly
constructing a parametric form to preserve predefined statistics of the data.
This is done by training a neural network to generate samples from the data
distribution using a recent deep learning technique called generative
adversarial networks. By emulating the data generating process, the relevant
statistics of the data are replicated. The method is assessed in subsurface
flow problems, where effective parametrization of underground properties such
as permeability is important due to the high dimensionality and presence of
high spatial correlations. We experiment with realizations of binary
channelized subsurface permeability and perform uncertainty quantification and
parameter estimation. Results show that the parametrization using generative
adversarial networks is very effective in preserving visual realism as well as
high order statistics of the flow responses, while achieving a dimensionality
reduction of two orders of magnitude
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