3,271 research outputs found
Automatic Implementation of Neural Networks through Reaction Networks -- Part I: Circuit Design and Convergence Analysis
Information processing relying on biochemical interactions in the cellular
environment is essential for biological organisms. The implementation of
molecular computational systems holds significant interest and potential in the
fields of synthetic biology and molecular computation. This two-part article
aims to introduce a programmable biochemical reaction network (BCRN) system
endowed with mass action kinetics that realizes the fully connected neural
network (FCNN) and has the potential to act automatically in vivo. In part I,
the feedforward propagation computation, the backpropagation component, and all
bridging processes of FCNN are ingeniously designed as specific BCRN modules
based on their dynamics. This approach addresses a design gap in the
biochemical assignment module and judgment termination module and provides a
novel precise and robust realization of bi-molecular reactions for the learning
process. Through equilibrium approaching, we demonstrate that the designed BCRN
system achieves FCNN functionality with exponential convergence to target
computational results, thereby enhancing the theoretical support for such work.
Finally, the performance of this construction is further evaluated on two
typical logic classification problems
Coalescence modeling and experimental validation of sintering of thermoplastic polyamide fibers
In order to study the coalescence mechanisms of thermoplastic polymer powders, a 2D mathematical model has been established based on Frenkel, Eshelby and Pokluda’s model. Sintering experiments have been carried out by using two polyamide fibers that can be considered as infinite cylinders with its length much larger than the diameter. 2D mathematical model has been validated through comparison with results of sintering experiments as well as Constrained Natural Element Method (C-NEM) coalescence simulation. This consistence shows that the proposed coalescence model and experimental results can provide a reference for the numerical simulation of sintering process
Enabling urban-scale energy modelling: a new spatial approach
Urban-scale energy modelling provides an ideal tool for studying non-domestic energy consumption and emissions reduction at the community level. In principle, an approach based on the characteristics of individual commercial premises and buildings is attractive, but it poses a number of challenges, the most immediate of which is deciding precisely what to model. For a range of reasons connected with their self-contained nature, individual non-domestic buildings would ideally be selected. However, the main information sources available - digital mapping and business taxation data - are not based on 'buildings' and do not use the concept, thus making an automated approach problematic. At the same time, manual identification of the distinct buildings in a city is not a practical proposition because of the numbers involved. The digital mapping and business taxation data are brought together in the Local Land and Property Gazetteer (LLPG). An analysis of the relationships between the relevant elements, namely building polygons and premises attracting business taxation, allowed a unit to be defined that matches the definition of a 'building' in most circumstances and can be applied without the need for human intervention. This novel approach provides a firmer basis for modelling non-domestic building energy at the urban scale
Interference of Cooper quartet Andreev bound states in a multi-terminal graphene-based Josephson junction
In a Josephson junction (JJ), Cooper pairs are transported via Andreev bound
states (ABSs) between superconductors. The ABSs in the weak link of
multi-terminal (MT) JJs can coherently hybridize two Cooper pairs among
different superconducting electrodes, resulting in the Cooper quartet (CQ)
involving four fermions entanglement. The energy spectrum of these CQ-ABS can
be controlled by biasing MT-JJs due to the AC Josephson effect. Here, using
gate tunable four-terminal graphene JJs complemented with a flux loop, we
construct CQs with a tunable spectrum. The critical quartet supercurrent
exhibits magneto-oscillation associated with a charge of 4e; thereby presenting
the evidence for interference between entangled CQ-ABS. At a finite bias
voltage, we find the DC quartet supercurrent shows non-monotonic bias dependent
behavior, attributed to Landau-Zener transitions between different Floquet
bands. Our experimental demonstration of coherent non-equilibrium CQ-ABS sets a
path for design of artificial topological materials based on MT-JJs
On the Importance of Electroweak Corrections for Majorana Dark Matter Indirect Detection
Recent analyses have shown that the inclusion of electroweak corrections can
alter significantly the energy spectra of Standard Model particles originated
from dark matter annihilations. We investigate the important situation where
the radiation of electroweak gauge bosons has a substantial influence: a
Majorana dark matter particle annihilating into two light fermions. This
process is in p-wave and hence suppressed by the small value of the relative
velocity of the annihilating particles. The inclusion of electroweak radiation
eludes this suppression and opens up a potentially sizeable s-wave contribution
to the annihilation cross section. We study this effect in detail and explore
its impact on the fluxes of stable particles resulting from the dark matter
annihilations, which are relevant for dark matter indirect searches. We also
discuss the effective field theory approach, pointing out that the opening of
the s-wave is missed at the level of dimension-six operators and only encoded
by higher orders.Comment: 25 pages, 6 figures. Minor corrections to match version published in
JCA
The Pkn22 Ser/Thr kinase in Nostoc PCC 7120: role of FurA and NtcA regulators and transcript profiling under nitrogen starvation and oxidative stress
International audienceBackground: The filamentous cyanobacterium Nostoc sp. strain PCC 7120 can fix N2 when combined nitrogen is not available. Furthermore, it has to cope with reactive oxygen species generated as byproducts of photosynthesis and respiration. We have previously demonstrated the synthesis of Ser/Thr kinase Pkn22 as an important survival response of Nostoc to oxidative damage. In this study we wished to investigate the possible involvement of this kinase in signalling peroxide stress and nitrogen deprivation. Results: Quantitative RT-PCR experiments revealed that the pkn22 gene is induced in response to peroxide stress and to combined nitrogen starvation. Electrophoretic motility assays indicated that the pkn22 promoter is recognized by the global transcriptional regulators FurA and NtcA. Transcriptomic analysis comparing a pkn22-insertion mutant and the wild type strain indicated that this kinase regulates genes involved in important cellular functions such as photosynthesis, carbon metabolism and iron acquisition. Since metabolic changes may lead to oxidative stress, we investigated whether this is the case with nitrogen starvation. Our results rather invalidate this hypothesis thereby suggesting that the function of Pkn22 under nitrogen starvation is independent of its role in response to peroxide stress. Conclusions: Our analyses have permitted a more complete functional description of Ser/Thr kinase in Nostoc. We have decrypted the transcriptional regulation of the pkn22 gene, and analysed the whole set of genes under the control of this kinase in response to the two environmental changes often encountered by cyanobacteria in their natural habitat: oxidative stress and nitrogen deprivation
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