1,732 research outputs found
Amine-Gold Linked Single-Molecule Junctions: Experiment and Theory
The measured conductance distribution for single molecule benzenediamine-gold
junctions, based on 59,000 individual conductance traces recorded while
breaking a gold point contact in solution, has a clear peak at 0.0064 G
with a width of 40%. Conductance calculations based on density functional
theory (DFT) for 15 distinct junction geometries show a similar spread.
Differences in local structure have a limited influence on conductance because
the amine-Au bonding motif is well-defined and flexible. The average calculated
conductance (0.046 G) is seven times larger than experiment, suggesting
the importance of many-electron corrections beyond DFT
A digital twin framework for predictive maintenance in industry 4.0
The rapid advancements in manufacturing technologies are transforming the current industrial landscape through Industry 4.0, which refers not only to the integration of information technology with industrial production, but also to the use of innovative technologies and novel data management approaches. The target is to enable the manufacturers and the entire supply chain to save time, boost productivity, reduce waste and costs, and respond flexibly and efficiently to consumers’ requirements.
Industry 4.0 moves the digitization of manufacturing components and processes a step further by creating smart factories. Within this context, one of the key enabling technologies for Industry 4.0 is the adoption and integration of the Digital Twin (DT). However, most of the DT solutions provided by the current leading vendors are in fact digital models or digital shadows, and not digital twins. This is due to the fact that there is no common understanding of the definition of the DT amongst the leading vendors, and its usage is slightly different but showcased under the same umbrella of DT. In this paper, a DT framework is proposed that replicates the processes of a real production line for product assembly using the Festo Cyber Physical Factory for Industry 4.0 located at Middlesex University. Moreover, the paper introduces a viable framework for interlinking the physical system with its digital instance in order to offer extended predictive maintenance services and form a fully integrated digital twin solution
Anomalous Chiral Symmetry Breaking above the QCD Phase Transition
We study the anomalous breaking of U_A(1) symmetry just above the QCD phase
transition for zero and two flavors of quarks, using a staggered fermion,
lattice discretization. The properties of the QCD phase transition are expected
to depend on the degree of U_A(1) symmetry breaking in the transition region.
For the physical case of two flavors, we carry out extensive simulations on a
16^3 x 4 lattice, measuring a difference in susceptibilities which is sensitive
to U_A(1) symmetry and which avoids many of the staggered fermion
discretization difficulties. The results suggest that anomalous effects are at
or below the 15% level.Comment: 10 pages including 2 figures and 1 tabl
Orbital Interaction Mechanisms of Conductance Enhancement and Rectification by Dithiocarboxylate Anchoring Group
We study computationally the electron transport properties of
dithiocarboxylate terminated molecular junctions. Transport properties are
computed self-consistently within density functional theory and nonequilibrium
Green's functions formalism. A microscopic origin of the experimentally
observed current amplification by dithiocarboxylate anchoring groups is
established. For the 4,4'-biphenyl bis(dithiocarboxylate) junction, we find
that the interaction of the lowest unoccupied molecular orbital (LUMO) of the
dithiocarboxylate anchoring group with LUMO and highest occupied molecular
orbital (HOMO) of the biphenyl part results in bonding and antibonding
resonances in the transmission spectrum in the vicinity of the electrode Fermi
energy. A new microscopic mechanism of rectification is predicted based on the
electronic structure of asymmetrical anchoring groups. We show that the peaks
in the transmission spectra of 4'-thiolato-biphenyl-4-dithiocarboxylate
junction respond differently to the applied voltage. Depending upon the origin
of a transmission resonance in the orbital interaction picture, its energy can
be shifted along with the chemical potential of the electrode to which the
molecule is more strongly or more weakly coupled
Stabilizing single atom contacts by molecular bridge formation
Gold-molecule-gold junctions can be formed by carefully breaking a gold wire
in a solution containing dithiolated molecules. Surprisingly, there is little
understanding on the mechanical details of the bridge formation process and
specifically on the role that the dithiol molecules play themselves. We propose
that alkanedithiol molecules have already formed bridges between the gold
electrodes before the atomic gold-gold junction is broken. This leads to
stabilization of the single atomic gold junction, as observed experimentally.
Our data can be understood within a simple spring model.Comment: 14 pages, 3 figures, 1 tabl
Shot noise suppression at room temperature in atomic-scale Au junctions
Shot noise encodes additional information not directly inferable from simple
electronic transport measurements. Previous measurements in atomic-scale metal
junctions at cryogenic temperatures have shown suppression of the shot noise at
particular conductance values. This suppression demonstrates that transport in
these structures proceeds via discrete quantum channels. Using a high frequency
technique, we simultaneously acquire noise data and conductance histograms in
Au junctions at room temperature and ambient conditions. We observe noise
suppression at up to three conductance quanta, with possible indications of
current-induced local heating and noise in the contact region at high
biases. These measurements demonstrate the quantum character of transport at
room temperature at the atomic scale. This technique provides an additional
tool for studying dissipation and correlations in nanodevices.Comment: 15 pages, 4 figures + supporting information (6 pages, 6 figures
Heat dissipation in atomic-scale junctions
Atomic and single-molecule junctions represent the ultimate limit to the
miniaturization of electrical circuits. They are also ideal platforms to test
quantum transport theories that are required to describe charge and energy
transfer in novel functional nanodevices. Recent work has successfully probed
electric and thermoelectric phenomena in atomic-scale junctions. However, heat
dissipation and transport in atomic-scale devices remain poorly characterized
due to experimental challenges. Here, using custom-fabricated scanning probes
with integrated nanoscale thermocouples, we show that heat dissipation in the
electrodes of molecular junctions, whose transmission characteristics are
strongly dependent on energy, is asymmetric, i.e. unequal and dependent on both
the bias polarity and the identity of majority charge carriers (electrons vs.
holes). In contrast, atomic junctions whose transmission characteristics show
weak energy dependence do not exhibit appreciable asymmetry. Our results
unambiguously relate the electronic transmission characteristics of
atomic-scale junctions to their heat dissipation properties establishing a
framework for understanding heat dissipation in a range of mesoscopic systems
where transport is elastic. We anticipate that the techniques established here
will enable the study of Peltier effects at the atomic scale, a field that has
been barely explored experimentally despite interesting theoretical
predictions. Furthermore, the experimental advances described here are also
expected to enable the study of heat transport in atomic and molecular
junctions, which is an important and challenging scientific and technological
goal that has remained elusive.Comment: supporting information available in the journal web site or upon
reques
Non-linear optical susceptibilities, Raman efficiencies and electrooptic tensors from first-principles density functional perturbation theory
The non-linear response of infinite periodic solids to homogenous electric
fields and collective atomic displacements is discussed in the framework of
density functional perturbation theory. The approach is based on the 2n + 1
theorem applied to an electric-field-dependent energy functional. We report the
expressions for the calculation of the non-linear optical susceptibilities,
Raman scattering efficiencies and electrooptic coefficients. Different
formulations of third-order energy derivatives are examined and their
convergence with respect to the k-point sampling is discussed. We apply our
method to a few simple cases and compare our results to those obtained with
distinct techniques. Finally, we discuss the effect of a scissors correction on
the EO coefficients and non-linear optical susceptibilities
Re-Focusing - Building a Future for Entrepreneurial Education & Learning
The field of entrepreneurship has struggled with fundamental
questions concerning the subject’s nature and purpose. To whom and to
what means are educational and training agendas ultimately directed?
Such questions have become of central importance to policy makers,
practitioners and academics alike. There are suggestions that university
business schools should engage more critically with the lived experiences
of practising entrepreneurs through alternative pedagogical approaches
and methods, seeking to account for and highlighting the social, political
and moral aspects of entrepreneurial practice. In the UK, where funding in
higher education has become increasingly dependent on student fees,
there are renewed pressures to educate students for entrepreneurial
practice as opposed to educating them about the nature and effects of
entrepreneurship. Government and EU policies are calling on business
schools to develop and enhance entrepreneurial growth and skill sets, to
make their education and training programmes more proactive in
providing innovative educational practices which help and facilitate life
experiences and experiential learning. This paper makes the case for
critical frameworks to be applied so that complex social processes
become a source of learning for educators and entrepreneurs and so that
innovative pedagogical approaches can be developed in terms both of
context (curriculum design) and process (delivery methods)
Digital twins: a survey on enabling technologies, challenges, trends and future prospects
Digital Twin (DT) is an emerging technology surrounded by many promises, and potentials to reshape the future of industries and society overall. A DT is a system-of-systems which goes far beyond the traditional computer-based simulations and analysis. It is a replication of all the elements, processes, dynamics, and firmware of a physical system into a digital counterpart. The two systems (physical and digital) exist side by side, sharing all the inputs and operations using real-time data communications and information transfer. With the incorporation of Internet of Things (IoT), Artificial Intelligence (AI), 3D models, next generation mobile communications (5G/6G), Augmented Reality (AR), Virtual Reality (VR), distributed computing, Transfer Learning (TL), and electronic sensors, the digital/virtual counterpart of the real-world system is able to provide seamless monitoring, analysis, evaluation and predictions. The DT offers a platform for the testing and analysing of complex systems, which would be impossible in traditional simulations and modular evaluations. However, the development of this technology faces many challenges including the complexities in effective communication and data accumulation, data unavailability to train Machine Learning (ML) models, lack of processing power to support high fidelity twins, the high need for interdisciplinary collaboration, and the absence of standardized development methodologies and validation measures. Being in the early stages of development, DTs lack sufficient documentation. In this context, this survey paper aims to cover the important aspects in realization of the technology. The key enabling technologies, challenges and prospects of DTs are highlighted. The paper provides a deep insight into the technology, lists design goals and objectives, highlights design challenges and limitations across industries, discusses research and commercial developments, provides its applications and use cases, offers case studies in industry, infrastructure and healthcare, lists main service providers and stakeholders, and covers developments to date, as well as viable research dimensions for future developments in DTs
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