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Online Learning of Network Bottlenecks via Minimax Paths
Get PDFIn this paper, we study bottleneck identification in networks via extracting minimax paths. Many real-world networks have stochastic weights for which full knowledge is not available in advance. Therefore, we model this task as a combinatorial semi-bandit problem to which we apply a combinatorial version of Thompson Sampling and establish an upper bound on the corresponding Bayesian regret. Due to the computational intractability of the problem, we then devise an alternative problem formulation which approximates the original objective. Finally, we experimentally evaluate the performance of Thompson Sampling with the approximate formulation on real-world directed and undirected networks
Engineering yeast for high-level production of diterpenoid sclareol
Get PDFThe diterpenoid sclareol is an industrially important precursor for alternative sustainable supply of ambergris. However, its current production from plant extraction is neither economical nor environmental-friendly, since it requires laborious and cost-intensive purification procedures and plants cultivation is susceptible to environmental factors. Engineering cell factories for bio-manufacturing can enable sustainable production of natural products. However, stringent metabolic regulation poses challenges to rewire cellular metabolism for overproduction of compounds of interest. Here we used a modular approach to globally rewire the cellular metabolism for improving sclareol production to 11.4 g/L in budding yeast Saccharomyces cerevisiae, the highest reported diterpenoid titer in microbes. Metabolic flux analysis showed that modular balanced metabolism drove the metabolic flux toward the biosynthesis of targeted molecules, and transcriptomic analysis revealed that the expression of central metabolism genes was shaped for a new balanced metabolism, which laid a foundation in extensive metabolic engineering of other microbial species for sustainable bio-production
Effects of Nb on borosiliciding of CoCrFeNiNbx high-entropy alloy
No full textThe effect of Nb addition (2, 5, 10 at. %) on the borosiliciding behavior of CoCrFeNiNbx high-entropy alloy was studied. Vacuum arc melted CoCrFeNiNbx alloys consisted of FCC and Laves-C14 phases. The increase of Nb in the alloys resulted in a decrease of the amount of FCC phase and an increase of the amount of Laves phase. A multiphase boride layer (BL) and a silicon-rich layer (SL) were evident with the formation of Ni2Si, FeB, Fe2B, Co2B, Cr5B3, Nb5Si3 and NbB2 phases after the thermochemical treatment. The Nb5Si3 and NbB2 phase formation was caused by the Nb addition into the CoCrFeNi alloy. The thickness of the SL + BL dramatically decreased, and the thickness of the transition zone/diffusion zone (DZ) decreased with increasing Nb content. The Nb content in the alloys hinders the inward diffusion of Si/B atoms and decreases the Si/B penetration depth. The total layer thicknesses were 45 μm, 27 μm and 12 μm for the alloys containing 2, 5 and 10 at. % Nb, respectively. The surface hardness values of alloys increased after surface treatment
A micromechanics based model for rate dependent compression loaded unidirectional composites
Get PDFStrain-rate effects in a unidirectional non-crimp fabric carbon/epoxy composite are addressed.\ua0To allow for kink-band formation including strain-rate\ua0 effects and damage in such composites, the paper advances a recent model focused on compression loading at small off-axis angles.\ua0The model is based on computational \textit{homogenization} with a subscale represented by matrix and fibre constituents at finite deformation.\ua0The fibre constituent is assumed to be elastic transversely isotropic and the matrix is viscoelastic--viscoplastic with damage degradation.\ua0Novel model improvements of special importance to small off-axis loading relate to the \textit{isostress} formulation of the homogenized response in transverse shear.\ua0In this context, an enhanced homogenized elastic response is proposed based on Halpin--Tsai corrections to account for the nonuniform stress distribution on the microscale.\ua0The model captures the strongly rate sensitive kink-band formation due to localized matrix shearing and fibre rotation, confirming the experimentally observed increase in compressive strength for high strain rates
On the simulation of neutron noise induced by vibrations of fuel pins in a fuel assembly
Get PDFVibrations of fuel assemblies are an important issue in the safe operation of nuclear reactors, because they can challenge the integrity of the fuel with potential for radioactive releases. Reactor neutron noise-based techniques for monitoring vibrations are valuable for core diagnostic since they are not intrusive and make use of ordinary neutron flux measurements from ex-core and in-core detectors. The application of these techniques involves the solution of inverse problems that require numerical simulations capable of estimating the reactor neutron noise, given a model of the vibrations. For this purpose, several novel reactor neutron noise solvers have been developed in the CORTEX project using either Monte Carlo or deterministic methods, such as the discrete ordinates method, the method of characteristics, and the diffusion approximation. In the current work, these solvers have been scrutinized by computing the neutron noise induced by vibrations of one or multiple fuel pins in a simplified UOX fuel assembly benchmark, via proper variations of macroscopic neutron cross sections. The comparison of these neutron noise solutions obtained from the different methods shows novel insights into the simulation of neutron noise induced by mechanical vibrations, such as the challenges posed by the Monte Carlo method, the impact of the angular discretization on the application of the discrete ordinates method, and the accuracy of the diffusion approximation assessed via the higher-order neutron transport methods
Power sum polynomials and the ghosts behind them
Get PDFThe power sum polynomial associated to a multi-subset of the projective plane PG (2 , q) is the sum of the (q- 1) -th powers of the R\ue9dei factors of the points in the multi-subset. The classification of multi-subsets having the same power sum polynomial passes through the determination of those multi-subsets associated to the zero polynomial, called ghosts. In this paper we provide new classes of ghosts and compute the dimension of the ghost subspace by exploiting the linear code generated by the lines of PG (2 , q) and its dual. Moreover, we explicitly enumerate and classify ghosts for planes of order 2,\ua03,\ua04
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No full text18.73% efficient and stable inverted organic photovoltaics featuring a hybrid hole-extraction layer
No full textDeveloping efficient and stable organic photovoltaics (OPVs) is crucial for the technology\u27s commercial success. However, combining these key attributes remains challenging. Herein, we incorporate the small molecule 2-((3,6-dibromo-9H-carbazol-9-yl)ethyl)phosphonic acid (Br-2PACz) between the bulk-heterojunction (BHJ) and a 7 nm-thin layer of MoO3 in inverted OPVs, and study its effects on the cell performance. We find that the Br-2PACz/MoO3 hole-extraction layer (HEL) boosts the cell\u27s power conversion efficiency (PCE) from 17.36% to 18.73% (uncertified), making them the most efficient inverted OPVs to date. The factors responsible for this improvement include enhanced charge transport, reduced carrier recombination, and favourable vertical phase separation of donor and acceptor components in the BHJ. The Br-2PACz/MoO3-based OPVs exhibit higher operational stability under continuous illumination and thermal annealing (80 degrees C). The T-80 lifetime of OPVs featuring Br-2PACz/MoO3 - taken as the time over which the cell\u27s PCE reduces to 80% of its initial value - increases compared to MoO3-only cells from 297 to 615 h upon illumination and from 731 to 1064 h upon continuous heating. Elemental analysis of the BHJs reveals the enhanced stability to originate from the partially suppressed diffusion of Mo ions into the BHJ and the favourable distribution of the donor and acceptor components induced by the Br-2PACz
Discussion on the Relationship between Computation, Information, Cognition, and Their Embodiment
Get PDFThree special issues of Entropy journal have been dedicated to the topics of “Information-Processing and Embodied, Embedded, Enactive Cognition”. They addressed morphological computing, cognitive agency, and the evolution of cognition. The contributions show the diversity of views present in the research community on the topic of computation and its relation to cognition. This paper is an attempt to elucidate current debates on computation that are central to cognitive science. It is written in the form of a dialog between two authors representing two opposed positions regarding the issue of what computation is and could be, and how it can be related to cognition. Given the different backgrounds of the two researchers, which span physics, philosophy of computing and information, cognitive science, and philosophy, we found the discussions in the form of Socratic dialogue appropriate for this multidisciplinary/cross-disciplinary conceptual analysis. We proceed as follows. First, the proponent (GDC) introduces the info-computational framework as a naturalistic model of embodied, embedded, and enacted cognition. Next, objections are raised by the critic (MM) from the point of view of the new mechanistic approach to explanation. Subsequently, the proponent and the critic provide their replies. The conclusion is that there is a fundamental role for computation, understood as information processing, in the understanding of embodied cognition
Power Extraction in Military Aircraft
Get PDFMilitary aircraft require more and more power. Pneumatic and hydraulic systems are being replaced by electrical equipment and new, power consuming equipmentis introduced in the aircraft. Increased power extraction brings new challenges for the aircraft jet engine, both in terms of operability and with regards to engine performance.This thesis describes how the engine performance of a conventional low bypass ratio mixed flow turbofan engine is affected by power extraction from the highpressure shaft, the low-pressure shaft or a combination of the two. A twin-spool low bypass ratio mixed flow turbofan engine has been developed ina Chalmers in-house tool to evaluate engine performance in different parts of the flight envelope. In order to evaluate the impact of aircraft/engine interaction on flight performance, an aircraft performance tool has been developed as well. A turbine inlet gas temperature increase is required when power is extracted\ua0from the HP or LP shaft. This temperature increase is more considerable if power is\ua0extracted from the high-pressure shaft, increasing specific thrust and specific fuel\ua0consumption. When the engine is running close to, or at the maximum turbine\ua0inlet temperature limit, power extraction will have a detrimental impact on the\ua0engine performance, whether power is extracted from the high-pressure shaft or the\ua0low-pressure shaft, but the thrust reduction will be more substantial if power is extracted from the high-pressure shaft. When the engine is running close to or at the maximum overall pressure ratio limit, the thrust reduction due to high-pressure\ua0shaft power extraction is more moderate compared to the low-pressure shaft powerextraction case, provided that the required temperature increase is acceptable from an engine operability perspective