12,607 research outputs found
Giant phonon anomalies in the pseudo-gap phase of TiOCl
We report infrared and Raman spectroscopy results of the spin-1/2 quantum
magnet TiOCl. Giant anomalies are found in the temperature dependence of the
phonon spectrum, which hint to unusual coupling of the electronic degrees of
freedom to the lattice. These anomalies develop over a broad temperature
interval, suggesting the presence of an extended fluctuation regime. This
defines a pseudo-gap phase, characterized by a local spin-gap. Below 100 K a
dimensionality cross-over leads to a dimerized ground state with a global
spin-gap of about 2~430 K.Comment: 4 pages, 3 figures, for further information see
http://www.peter-lemmens.d
Quantum coherent transport in a three-arm beam splitter and a Braess paradox
The Braess paradox encountered in classical networks is a counterintuitive
phenomenon when the flow in a road network can be impeded by adding a new road
or, more generally, the overall net performance can degrade after addition of
an extra available choice. In this work, we discuss the possibility of a
similar effect in a phase-coherent quantum transport and demonstrate it by
example of a simple Y-shaped metallic fork. To reveal the Braess-like partial
suppression of the charge flow in such device, it is proposed to transfer two
outgoing arms into a superconducting state. We show that the differential
conductance-vs-voltage spectrum of the hybrid fork structure varies
considerably when the extra link between the two superconducting leads is added
and it can serve as an indicator of quantum correlations which manifest
themselves in the quantum Braess paradox.Comment: 9 pages, 3 figures, the author version presented at the Quantum 2017
Workshop (Torino, Italy, 7-13 May 2017) and submitted to the International
Journal of Quantum Information; v2: reference 9 added and the introduction
extende
Improved Implementation of Point Location in General Two-Dimensional Subdivisions
We present a major revamp of the point-location data structure for general
two-dimensional subdivisions via randomized incremental construction,
implemented in CGAL, the Computational Geometry Algorithms Library. We can now
guarantee that the constructed directed acyclic graph G is of linear size and
provides logarithmic query time. Via the construction of the Voronoi diagram
for a given point set S of size n, this also enables nearest-neighbor queries
in guaranteed O(log n) time. Another major innovation is the support of general
unbounded subdivisions as well as subdivisions of two-dimensional parametric
surfaces such as spheres, tori, cylinders. The implementation is exact,
complete, and general, i.e., it can also handle non-linear subdivisions. Like
the previous version, the data structure supports modifications of the
subdivision, such as insertions and deletions of edges, after the initial
preprocessing. A major challenge is to retain the expected O(n log n)
preprocessing time while providing the above (deterministic) space and
query-time guarantees. We describe an efficient preprocessing algorithm, which
explicitly verifies the length L of the longest query path in O(n log n) time.
However, instead of using L, our implementation is based on the depth D of G.
Although we prove that the worst case ratio of D and L is Theta(n/log n), we
conjecture, based on our experimental results, that this solution achieves
expected O(n log n) preprocessing time.Comment: 21 page
Isolation of triterpenes from propolis (bee glue)
Propolis (bee glue) is a natural substance produced by bees upon collection of mainly plant resins. Bees use it as antiseptic sealing agent between honeycombs and to preserve the hive from external contamination. Numerous scientific studies have been published on the biological properties of propolis including its anti-inflammatory, anti-oxidant, immunostimulant, antitumour and antimicrobial activity. Different propolis chemotypes have been characterised based on the nature of the plant-derived substances present and the geographical origin of collection. Here, we describe the isolation of nine triterpenes from a sample of propolis originating from North-Western Cameroon. All compounds were identified following analysis of their spectroscopic data and comparison with previously published reports
Mixed Integer Neural Inverse Design
In computational design and fabrication, neural networks are becoming important surrogates for bulky forward simulations. A long-standing, intertwined question is that of inverse design: how to compute a design that satisfies a desired target performance? Here, we show that the piecewise linear property, very common in everyday neural networks, allows for an inverse design formulation based on mixed-integer linear programming. Our mixed-integer inverse design uncovers globally optimal or near optimal solutions in a principled manner. Furthermore, our method significantly facilitates emerging, but challenging, combinatorial inverse design tasks, such as material selection. For problems where finding the optimal solution is not desirable or tractable, we develop an efficient yet near-optimal hybrid optimization. Eventually, our method is able to find solutions provably robust to possible fabrication perturbations among multiple designs with similar performances
Mixed Integer Neural Inverse Design
In computational design and fabrication, neural networks are becoming
important surrogates for bulky forward simulations. A long-standing,
intertwined question is that of inverse design: how to compute a design that
satisfies a desired target performance? Here, we show that the piecewise linear
property, very common in everyday neural networks, allows for an inverse design
formulation based on mixed-integer linear programming. Our mixed-integer
inverse design uncovers globally optimal or near optimal solutions in a
principled manner. Furthermore, our method significantly facilitates emerging,
but challenging, combinatorial inverse design tasks, such as material
selection. For problems where finding the optimal solution is not desirable or
tractable, we develop an efficient yet near-optimal hybrid optimization.
Eventually, our method is able to find solutions provably robust to possible
fabrication perturbations among multiple designs with similar performances
United States benefits of improved worldwide wheat crop information from a LANDSAT system
The value of worldwide information improvements on wheat crops, promised by LANDSAT, is measured in the context of world wheat markets. These benefits are based on current LANDSAT technical goals and assume that information is made available to all (United States and other countries) at the same time. A detailed empirical sample demonstration of the effect of improved information is given; the history of wheat commodity prices for 1971-72 is reconstructed and the price changes from improved vs. historical information are compared. The improved crop forecasting from a LANDSAT system assumed include wheat crop estimates of 90 percent accuracy for each major wheat producing region. Accurate, objective worldwide wheat crop information using space systems may have a very stabilizing influence on world commodity markets, in part making possible the establishment of long-term, stable trade relationships
Quantum many-body scars with chiral topological order in two dimensions and critical properties in one dimension
We construct few-body, interacting, nonlocal Hamiltonians with a quantum scar state in an otherwise thermalizing many-body spectrum. In one dimension, the embedded state is a critical state, and in two dimensions, the embedded state is a chiral topologically ordered state. The models are defined on slightly disordered lattices, and the scar state appears to be independent of the precise realization of the disorder. A parameter allows the scar state to be placed at any position in the spectrum. We show that the level spacing distributions are Wigner-Dyson and that the entanglement entropies of the states in the middle of the spectrum are close to the Page value. Finally, we confirm the topological order in the scar state by showing that one can insert anyons into the state
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