1,720,969 research outputs found
DC behaviour of a non-volatile memristor: part I
No full textThis paper presents graphical tools from nonlinear
system theory so as to unveil the properties of the switching
kinetics of a tantalum oxide memristor. These theoretic concepts
lie at the basis of the analysis of the device DC behaviour provided
in part II
Fading memory effects in a memristor for Cellular Nanoscale Network applications
No full textCNN based analogic cellular computing is a unified
paradigm for universal spatio-temporal computation with
several applications in a large number of different fields of
research. By endowing CNN with local memory, control, and
communication circuitry, many different hardware architectures
with stored programmability, showing an enormous computing
power - trillion of operations per second may be executed on a
single chip -, have been realized. The complex spatio-temporal
dynamics emerging in certain CNN may lead to the development
of more efficient information processing methods as compared
to conventional strategies. Memristors exhibit a rich variety of
nonlinear behaviours, occupy a negligible amount of integrated
circuit area, consume very little power, are suited to a massivelyparallel
data flow, and may combine data storage with signal
processing. As a result, the use of memristors in future CNNbased
computing structures may improve and/or extend the
functionalities of state-of-the art hardware architectures. This
contribution provides a detailed analysis of the system-theoretic
model of a tantalum oxide memristor, in view of its potential
adoption for the implementation of synaptic operators in CNN
architectures
History Erase Effect in a Non-Volatile Memristor
No full textThis work presents a detailed study of the nonlinear
dynamics of a tantalum oxide memristor recently fabricated at
Hewlett Packard Labs. Our investigations uncover direct current,
quasi-static, and alternating current behavior of the nanodevice.
A thorough study of the dynamics emerging in the nanoscale element
under various input/initial condition combinations reveals a
fundamental property of the tantalum oxide device, which was unnoticed
so far. The initial condition has no effect on the steady-state
operation of the memristor under non-zero input. This property,
known as fading memory in system theory, implies the uniqueness
of asymptotic behavior of the memristor. The progressive
input-induced memory erase phenomenon is solely determined
by the switching dynamics of the nanodevice, mathematically
described by the state evolution function, which governs the rate
of evolution of the memristor state. A constant-sign DC input
will activate on or off switching dynamics only. Consequently,
due to the limited on/off memductance ratio, the memristor will
asymptotically attain a fully-conducting or highly-resistive state,
irrespective of the initial condition. Most interestingly, under AC
periodic excitations, it is the pronounced asymmetry in the state
dependence of on and off switching processes which is at the basis
of the reported history erase effect. It is important to point out
that this novel fading memory phenomenon does not compromise
the nonvolatile behavior of the nanostructure. In fact, despite the
device may be stimulated so as to forget its past history, it still has
a continuum of analog nonvolatile memory states
DC behaviour of a non-volatile memristor: part II
No full textAdopting the system theoretic tools introduced in
part I, this paper gains a deep insight into the fading memory
effects emerging in a non-volatile memristor under DC inputs.
Experimental evidence for the history erase phenomenon is also
provided here
Memory loss in a tantalum oxide memristor
No full textThe tantalum oxide memristor may have a promising future as key element in innovative
very-high speed ultra-low power extra-large density nonvolatile memories. It is therefore timely and relevant to investigate the nonlinear dynamics of this device in view of the interesting opportunities it may open up in the world of electronics in the years to come. In numerical simulations of an accurate model of the tantalum oxide memristor manufactured at Hewlett Packard Labs we observed a surprising phenomenon which was never reported earlier. Under AC periodic excitation the memristor exhibits unique asymptotic behaviour, irrespective of the initial condition. Thus the device may be stimulated in such a way to forget its past history. This memory erase effect, unexpected in a memristor device, is closely related to the concept of fading memory from nonlinear system theory, and was recently confirmed through experiments conducted on a sample device
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
