4,245 research outputs found
On the Linearity of Semantic Change: Investigating Meaning Variation via Dynamic Graph Models
We consider two graph models of semantic change. The first is a time-series
model that relates embedding vectors from one time period to embedding vectors
of previous time periods. In the second, we construct one graph for each word:
nodes in this graph correspond to time points and edge weights to the
similarity of the word's meaning across two time points. We apply our two
models to corpora across three different languages. We find that semantic
change is linear in two senses. Firstly, today's embedding vectors (= meaning)
of words can be derived as linear combinations of embedding vectors of their
neighbors in previous time periods. Secondly, self-similarity of words decays
linearly in time. We consider both findings as new laws/hypotheses of semantic
change.Comment: Published at ACL 2016, Berlin (short papers
Language classification from bilingual word embedding graphs
We study the role of the second language in bilingual word embeddings in
monolingual semantic evaluation tasks. We find strongly and weakly positive
correlations between down-stream task performance and second language
similarity to the target language. Additionally, we show how bilingual word
embeddings can be employed for the task of semantic language classification and
that joint semantic spaces vary in meaningful ways across second languages. Our
results support the hypothesis that semantic language similarity is influenced
by both structural similarity as well as geography/contact.Comment: To be published at Coling 201
Dynamics of vortices with magnetic impurities
We investigate the dynamics of BPS vortices in the presence of magnetic impurities taking the form of axially-symmetric localised lumps and delta-functions. We present numerical results for vortices on flat space, as well as exact results for vortices on hyperbolic space in the presence of delta-function impurities. In fact, delta-function impurities of appropriate strength can be captured within the moduli space approximation by keeping one or more of the vortices fixed. We also show that previous work on vortices on the 2-sphere extends naturally to the inclusion of delta-function impurities
Dynamic optimization of metabolic networks coupled with gene expression
The regulation of metabolic activity by tuning enzyme expression levels is
crucial to sustain cellular growth in changing environments. Metabolic networks
are often studied at steady state using constraint-based models and
optimization techniques. However, metabolic adaptations driven by changes in
gene expression cannot be analyzed by steady state models, as these do not
account for temporal changes in biomass composition. Here we present a dynamic
optimization framework that integrates the metabolic network with the dynamics
of biomass production and composition, explicitly taking into account enzyme
production costs and enzymatic capacity. In contrast to the established dynamic
flux balance analysis, our approach allows predicting dynamic changes in both
the metabolic fluxes and the biomass composition during metabolic adaptations.
We applied our algorithm in two case studies: a minimal nutrient uptake
network, and an abstraction of core metabolic processes in bacteria. In the
minimal model, we show that the optimized uptake rates reproduce the empirical
Monod growth for bacterial cultures. For the network of core metabolic
processes, the dynamic optimization algorithm predicted commonly observed
metabolic adaptations, such as a diauxic switch with a preference ranking for
different nutrients, re-utilization of waste products after depletion of the
original substrate, and metabolic adaptation to an impending nutrient
depletion. These examples illustrate how dynamic adaptations of enzyme
expression can be predicted solely from an optimization principle
End-to-End Algebraic Network Coding for Wireless TCP/IP Networks
The Transmission Control Protocol (TCP) was designed to provide reliable
transport services in wired networks. In such networks, packet losses mainly
occur due to congestion. Hence, TCP was designed to apply congestion avoidance
techniques to cope with packet losses. Nowadays, TCP is also utilized in
wireless networks where, besides congestion, numerous other reasons for packet
losses exist. This results in reduced throughput and increased transmission
round-trip time when the state of the wireless channel is bad. We propose a new
network layer, that transparently sits below the transport layer and hides non
congestion-imposed packet losses from TCP. The network coding in this new layer
is based on the well-known class of Maximum Distance Separable (MDS) codes.Comment: Accepted for the 17th International Conference on Telecommunications
2010 (ICT2010), Doha, Qatar, April 4 - 7, 2010. 6 pages, 7 figure
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