1,061 research outputs found
Definitive Evidence for Order-by-Quantum-Disorder in Er2Ti2O7
Here we establish the systematic existence of a U(1) degeneracy of all
symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice,
at the mean-field level. By extracting the Hamiltonian of Er2Ti2O7 from
inelastic neutron scattering measurements, we then show that the
U(1)-degenerate states of Er2Ti2O7 are its classical ground states, and
unambiguously show that quantum fluctuations break the degeneracy in a way
which is confirmed by experiment. This is the first definitive observation of
order-by-disorder in any material. We provide further verifiable consequences
of this phenomenon, and several additional comparisons between theory and
experiment.Comment: 4.5 pages, 3 figures, 7.5 pages of Supplemental Material, 8
supplemental figure
Networks and the epidemiology of infectious disease
The science of networks has revolutionised research into the dynamics of interacting elements. It could be argued that epidemiology in particular has embraced the potential of network theory more than any other discipline. Here we review the growing body of research concerning the spread of infectious diseases on networks, focusing on the interplay between network theory and epidemiology. The review is split into four main sections, which examine: the types of network relevant to epidemiology; the multitude of ways these networks can be characterised; the statistical methods that can be applied to infer the epidemiological parameters on a realised network; and finally simulation and analytical methods to determine epidemic dynamics on a given network. Given the breadth of areas covered and the ever-expanding number of publications, a comprehensive review of all work is impossible. Instead, we provide a personalised overview into the areas of network epidemiology that have seen the greatest progress in recent years or have the greatest potential to provide novel insights. As such, considerable importance is placed on analytical approaches and statistical methods which are both rapidly expanding fields. Throughout this review we restrict our attention to epidemiological issues
Improving Semiconductor Device Modeling for Electronic Design Automation by Machine Learning Techniques
The semiconductors industry benefits greatly from the integration of Machine
Learning (ML)-based techniques in Technology Computer-Aided Design (TCAD)
methods. The performance of ML models however relies heavily on the quality and
quantity of training datasets. They can be particularly difficult to obtain in
the semiconductor industry due to the complexity and expense of the device
fabrication. In this paper, we propose a self-augmentation strategy for
improving ML-based device modeling using variational autoencoder-based
techniques. These techniques require a small number of experimental data points
and does not rely on TCAD tools. To demonstrate the effectiveness of our
approach, we apply it to a deep neural network-based prediction task for the
Ohmic resistance value in Gallium Nitride devices. A 70% reduction in mean
absolute error when predicting experimental results is achieved. The inherent
flexibility of our approach allows easy adaptation to various tasks, thus
making it highly relevant to many applications of the semiconductor industry.Comment: Entirely rewrote and reorganized. Updated model
On the determination of redundancies in sociometric chains
The use of a matrix to represent a relationship between the members of a group is well known in sociometry. If this matrix is raised to a certain power, the elements appearing give the total number of connecting paths between each pair of members. In general, some of these paths will be redundant. Methods of finding the number of such redundant paths have been developed for three- and four-step chains by Luce and Perry (3) and Katz (2), respectively. We have derived formulas for the number of redundant paths of five and six steps; and in addition, an algorithm for determining the number of redundant paths of any given length.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45690/1/11336_2005_Article_BF02288782.pd
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PACAP neurons in the ventral premammillary nucleus regulate reproductive function in the female mouse
PACAP neurons in the ventral premammillary nucleus regulate reproductive function in the female mouse.
Pituitary adenylate cyclase activating polypeptide (PACAP, Adcyap1) is a neuromodulator implicated in anxiety, metabolism and reproductive behavior. PACAP global knockout mice have decreased fertility and PACAP modulates LH release. However, its source and role at the hypothalamic level remain unknown. We demonstrate that PACAP-expressing neurons of the ventral premamillary nucleus of the hypothalamus (PMVPACAP) project to, and make direct contact with, kisspeptin neurons in the arcuate and AVPV/PeN nuclei and a subset of these neurons respond to PACAP exposure. Targeted deletion of PACAP from the PMV through stereotaxic virally mediated cre- injection or genetic cross to LepR-i-cre mice with Adcyap1fl/fl mice led to delayed puberty onset and impaired reproductive function in female, but not male, mice. We propose a new role for PACAP-expressing neurons in the PMV in the relay of nutritional state information to regulate GnRH release by modulating the activity of kisspeptin neurons, thereby regulating reproduction in female mice
Control of dephasing in spin qubits during coherent transport in silicon
One of the key pathways towards scalability of spin-based quantum computing
systems lies in achieving long-range interactions between electrons and
increasing their inter-connectivity. Coherent spin transport is one of the most
promising strategies to achieve this architectural advantage. Experimental
results have previously demonstrated high fidelity transportation of spin
qubits between two quantum dots in silicon and identified possible sources of
error. In this theoretical study, we investigate these errors and analyze the
impact of tunnel coupling, magnetic field and spin-orbit effects on the spin
transfer process. The interplay between these effects gives rise to double dot
configurations that include regimes of enhanced decoherence that should be
avoided for quantum information processing. These conclusions permit us to
extrapolate previous experimental conclusions and rationalize the future design
of large scale quantum processors.Comment: 18 pages, 9 figure
Bounds to electron spin qubit variability for scalable CMOS architectures
Spins of electrons in CMOS quantum dots combine exquisite quantum properties
and scalable fabrication. In the age of quantum technology, however, the
metrics that crowned Si/SiO2 as the microelectronics standard need to be
reassessed with respect to their impact upon qubit performance. We chart the
spin qubit variability due to the unavoidable atomic-scale roughness of the
Si/SiO interface, compiling experiments in 12 devices, and developing
theoretical tools to analyse these results. Atomistic tight binding and path
integral Monte Carlo methods are adapted for describing fluctuations in devices
with millions of atoms by directly analysing their wavefunctions and electron
paths instead of their energy spectra. We correlate the effect of roughness
with the variability in qubit position, deformation, valley splitting, valley
phase, spin-orbit coupling and exchange coupling. These variabilities are found
to be bounded and lie within the tolerances for scalable architectures for
quantum computing as long as robust control methods are incorporated.Comment: 20 pages, 8 figure
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