4,510 research outputs found
Entropic Stabilization of Tunable Planar Modulated Superstructures
Self-assembling novel ordered structures with nanoparticles has recently
received much attention. Here we use computer simulations to study a
two-dimensional model system characterized by a simple isotropic interaction
that could be realized with building blocks on the nanoscale. We find that the
particles arrange themselves into hexagonal superstructures of twin boundaries
whose superlattice vector can be tuned reversibly by changing the temperature.
Thermodynamic stability is confirmed by calculating the free energy with a
combination of thermodynamic integration and the Frenkel-Ladd method. Different
contributions to the free energy difference are discussed.Comment: 4 pages, 5 figures plus 7 pages of supplementary figure
Compatible orders and fermion-induced emergent symmetry in Dirac systems
We study the quantum multicritical point in a (2+1)-dimensional Dirac system
between the semimetallic phase and two ordered phases that are characterized by
anticommuting mass terms with and symmetry, respectively.
Using expansion around the upper critical space-time dimension of
four, we demonstrate the existence of a stable renormalization-group fixed
point, enabling a direct and continuous transition between the two ordered
phases directly at the multicritical point. This point is found to be
characterized by an emergent symmetry for arbitrary values of
and and fermion flavor numbers , as long as the corresponding
representation of the Clifford algebra exists. Small -breaking
perturbations near the chiral fixed point are therefore irrelevant. This
result can be traced back to the presence of gapless Dirac degrees of freedom
at criticality, and it is in clear contrast to the purely bosonic fixed
point, which is stable only when . As a by-product, we obtain
predictions for the critical behavior of the chiral universality classes
for arbitrary and fermion flavor number . Implications for critical
Weyl and Dirac systems in 3+1 dimensions are also briefly discussed.Comment: 5+2 pages, 1 figure, 1 tabl
Miniature modular microwave end-to-end receiver
An end-to-end microwave receiver system contained in a single miniature hybrid package mounted on a single heatsink is presented. It includes an input end connected to a microwave receiver antenna and an output end which produces a digital count proportional to the amplitude of a signal of a selected microwave frequency band received at the antenna and corresponding to one of the water vapor absorption lines near frequencies of 20 GHz or 30 GHz. The hybrid package is on the order of several centimeters in length and a few centimeters in height and width. The package includes an L-shaped carrier having a base surface, a vertical wall extending up from the base surface and forming a corner therewith, and connection pins extending through the vertical wall. Modular blocks rest on the base surface against the vertical wall and support microwave monolithic integrated circuits on top surfaces thereof connected to the external connection pins. The modular blocks lie end-to-end on the base surface so as to be modularly removable by sliding along the base surface beneath the external connection pins away from the vertical wall
Characterization and Verification Environment for the RD53A Pixel Readout Chip in 65 nm CMOS
The RD53 collaboration is currently designing a large scale prototype pixel
readout chip in 65 nm CMOS technology for the phase 2 upgrades at the HL-LHC.
The RD53A chip will be available by the end of the year 2017 and will be
extensively tested to confirm if the circuit and the architecture make a solid
foundation for the final pixel readout chips for the experiments at the HL-LHC.
A test and data acquisition system for the RD53A chip is currently under
development to perform single-chip and multi-chip module measurements. In
addition, the verification of the RD53A design is performed in a dedicated
simulation environment. The concept and the implementation of the test and data
acquisition system and the simulation environment, which are based on a modular
data acquisition and system testing framework, are presented in this work
Putting probabilities first. How Hilbert space generates and constrains them
We use correlation arrays, the workhorse of Bub's (2016) Bananaworld, to analyze the correlations found in an experimental setup due to Mermin (1981) for measurements on the singlet state of a pair of spin-1/2 particles. Adopting an approach pioneered by Pitowsky (1989b) and promoted in Bananaworld, we geometrically represent the class of correlations allowed by quantum mechanics in this setup as an elliptope in a non-signaling cube. To determine which of these quantum correlations are allowed by local hidden-variable theories, we investigate which ones we can simulate using raffles with baskets of tickets that have the outcomes for all combinations of measurement settings printed on them. The class of correlations found this way can be represented geometrically by a tetrahedron contained within the elliptope. We use the same Bub-Pitowsky framework to analyze a generalization of the Mermin setup for measurements on the singlet state of two particles with higher spin. The class of correlations allowed by quantum mechanics in this case is still represented by the elliptope; the subclass of those whose main features can be simulated with our raffles can be represented by polyhedra that, with increasing spin, have more and more vertices and facets and get closer and closer to the elliptope. We use these results to advocate for Bubism (not to be confused with QBism), an interpretation of quantum mechanics along the lines of Bananaworld. Probabilities and expectation values are primary in this interpretation. They are determined by inner products of vectors in Hilbert space. Such vectors do not themselves represent what is real in the quantum world. They encode families of probability distributions over values of different sets of observables. As in classical theory, these values ultimately represent what is real in the quantum world. Hilbert space puts constraints on possible combinations of such values, just as Minkowski space-time puts constraints on possible spatio-temporal constellations of events. Illustrating how generic such constraints are, the constraint derived in this paper, the equation for the elliptope, is a general constraint on correlation coefficients that can be found in older literature on statistics and probability theory. Yule (1896) already stated the constraint. De Finetti (1937) already gave it a geometrical interpretation sharing important features with its interpretation in Hilbert space
- …