2,773 research outputs found
Simultaneous current-, force- and work function measurement with atomic resolution
The local work function of a surface determines the spatial decay of the
charge density at the Fermi level normal to the surface. Here, we present a
method that enables simultaneous measurements of local work function and
tip-sample forces. A combined dynamic scanning tunneling microscope and atomic
force microscope is used to measure the tunneling current between an
oscillating tip and the sample in real time as a function of the cantilever's
deflection. Atomically resolved work function measurements on a silicon
(111)-() surface are presented and related to concurrently recorded
tunneling current- and force- measurements.Comment: 8 pages, 4 figures, submitted to Applied Physics Letter
Statistical mechanics of temporal association in neural networks with transmission delays
We study the representation of static patterns and temporal sequences in neural networks with signal delays and a stochastic parallel dynamics. For a wide class of delay distributions, the asymptotic network behavior can be described by a generalized Gibbs distribution, generated by a novel Lyapunov functional for the determination dynamics. We extend techniques of equilibrium statistical mechanics so as to deal with time-dependent phenomena, derive analytic results for both retrieval quality and storage capacity, and compare them with numerical simulations
Carey Young’s 'Palais de Justice'
The symposium for this issue comprises six responses to the video artwork Palais de Justice (2017) by artist Carey Young. The video presents a study of the life of Brussels’ vast, late-nineteenth-century court building. In Palais de Justice, Young presents ‘a legal system seemingly centered on, and perhaps controlled by women’. The respondents are Jeanne Gaakeer, Ruth Herz, Joan Kee, Linda Mulcahy, Jeremy Pilcher and Gary Watt. Jeanne Gaakeer and Ruth Herz have the distinction of being, not only internationally respected scholars, but also experienced judges. Jeanne Gaakeer is a judge practicing in the Netherlands and Ruth Herz was formerly a judge in Germany. The six responses are followed by the artist’s own reflections on her artwork and her response to the commentators’ responses. Joan Kee writes that ‘Young highlights access as a key entry point for thinking about the law. Who can avail themselves of the law? Who may enter (or exit) the courts? Who is excluded and by whose authority? The surreptitious looking and peering that define the experience of watching the film suggests how these questions deny ready answers’
Collection of relevant results obtained with the Skylab images by the Institute for Space Research, INPE
There are no author-identified significant results in this report
Why, what, and how? case study on law, risk, and decision making as necessary themes in built environment teaching
The paper considers (and defends) the necessity of including legal studies as a core part of built environment undergraduate and postgraduate curricula. The writer reflects upon his own experience as a lawyer working alongside and advising built environment professionals in complex land remediation and site safety management situations in the United Kingdom and explains how themes of liability, risk, and decision making can be integrated into a practical simulation in order to underpin more traditional lecture-based law teaching. Through reflection upon the writer's experiments with simulation-based teaching, the paper suggests some innovations that may better orientate law teaching to engage these themes and, thereby, enhance the relevance of law studies to the future needs of built environment professionals in practice.</p
Exciton bimolecular annihilation dynamics in supramolecular nanostructures of conjugated oligomers
We present femtosecond transient absorption measurements on -conjugated
supramolecular assemblies in a high pump fluence regime.
Oligo(\emph{p}-phenylenevinylene) monofunctionalized with
ureido-\emph{s}-triazine (MOPV) self-assembles into chiral stacks in dodecane
solution below 75C at a concentration of M. We
observe exciton bimolecular annihilation in MOPV stacks at high excitation
fluence, indicated by the fluence-dependent decay of B-exciton
spectral signatures, and by the sub-linear fluence dependence of time- and
wavelength-integrated photoluminescence (PL) intensity. These two
characteristics are much less pronounced in MOPV solution where the phase
equilibrium is shifted significantly away from supramolecular assembly,
slightly below the transition temperature. A mesoscopic rate-equation model is
applied to extract the bimolecular annihilation rate constant from the
excitation fluence dependence of transient absorption and PL signals. The
results demonstrate that the bimolecular annihilation rate is very high with a
square-root dependence in time. The exciton annihilation results from a
combination of fast exciton diffusion and resonance energy transfer. The
supramolecular nanostructures studied here have electronic properties that are
intermediate between molecular aggregates and polymeric semiconductors
Distances sets that are a shift of the integers and Fourier basis for planar convex sets
The aim of this paper is to prove that if a planar set has a difference
set satisfying for suitable than
has at most 3 elements. This result is motivated by the conjecture that the
disk has not more than 3 orthogonal exponentials. Further, we prove that if
is a set of exponentials mutually orthogonal with respect to any symmetric
convex set in the plane with a smooth boundary and everywhere non-vanishing
curvature, then # (A \cap {[-q,q]}^2) \leq C(K) q where is a constant
depending only on . This extends and clarifies in the plane the result of
Iosevich and Rudnev. As a corollary, we obtain the result from \cite{IKP01} and
\cite{IKT01} that if is a centrally symmetric convex body with a smooth
boundary and non-vanishing curvature, then does not possess an
orthogonal basis of exponentials
Jacobi structures revisited
Jacobi algebroids, that is graded Lie brackets on the Grassmann algebra
associated with a vector bundle which satisfy a property similar to that of the
Jacobi brackets, are introduced. They turn out to be equivalent to generalized
Lie algebroids in the sense of Iglesias and Marrero and can be viewed also as
odd Jacobi brackets on the supermanifolds associated with the vector bundles.
Jacobi bialgebroids are defined in the same manner. A lifting procedure of
elements of this Grassmann algebra to multivector fields on the total space of
the vector bundle which preserves the corresponding brackets is developed. This
gives the possibility of associating canonically a Lie algebroid with any local
Lie algebra in the sense of Kirillov.Comment: 20 page
Phase Diagram for the Winfree Model of Coupled Nonlinear Oscillators
In 1967 Winfree proposed a mean-field model for the spontaneous
synchronization of chorusing crickets, flashing fireflies, circadian pacemaker
cells, or other large populations of biological oscillators. Here we give the
first bifurcation analysis of the model, for a tractable special case. The
system displays rich collective dynamics as a function of the coupling strength
and the spread of natural frequencies. Besides incoherence, frequency locking,
and oscillator death, there exist novel hybrid solutions that combine two or
more of these states. We present the phase diagram and derive several of the
stability boundaries analytically.Comment: 4 pages, 4 figure
Spatial representation of temporal information through spike timing dependent plasticity
We suggest a mechanism based on spike time dependent plasticity (STDP) of
synapses to store, retrieve and predict temporal sequences. The mechanism is
demonstrated in a model system of simplified integrate-and-fire type neurons
densely connected by STDP synapses. All synapses are modified according to the
so-called normal STDP rule observed in various real biological synapses. After
conditioning through repeated input of a limited number of of temporal
sequences the system is able to complete the temporal sequence upon receiving
the input of a fraction of them. This is an example of effective unsupervised
learning in an biologically realistic system. We investigate the dependence of
learning success on entrainment time, system size and presence of noise.
Possible applications include learning of motor sequences, recognition and
prediction of temporal sensory information in the visual as well as the
auditory system and late processing in the olfactory system of insects.Comment: 13 pages, 14 figures, completely revised and augmented versio
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