20,846 research outputs found
Electric field induced charge noise in doped silicon: ionization of phosphorus donors
We report low frequency charge noise measurement on silicon substrates with
different phosphorus doping densities. The measurements are performed with
aluminum single electron transistors (SETs) at millikelvin temperatures where
the substrates are in the insulating regime. By measuring the SET Coulomb
oscillations, we find a gate voltage dependent charge noise on the more heavily
doped substrate. This charge noise, which is seen to have a 1/f spectrum, is
attributed to the electric field induced tunneling of electrons from their
phosphorus donor potentials.Comment: 4 page, 3 figure
Generalized Tomonaga-Schwinger equation from the Hadamard formula
A generalized Tomonaga--Schwinger equation, holding on the entire boundary of
a {\em finite} spacetime region, has recently been considered as a tool for
studying particle scattering amplitudes in background-independent quantum field
theory. The equation has been derived using lattice techniques under
assumptions on the existence of the continuum limit. Here I show that in the
context of continuous euclidean field theory the equation can be directly
derived from the functional integral formalism, using a technique based on
Hadamard's formula for the variation of the propagator.Comment: 11 pages, no figure
Globalization and the Marginalization of Educational Purpose: Preparation of Workers and Citizens for the 21st Century and the Vision of Sustainable Futures
Human capital development remains a primary goal of modern schooling. This paper raises questions concerning the link between global economic needs and school-based human capital development. The primary mission of preparing students for the workplace may weaken other educational missions vital in achieving a more sustainable future for humanity
More maximal arcs in Desarguesian projective planes and their geometric structure
In a previous paper R. Mathon gave a new construction method for maximal arcs in finite Desarguesian projective planes via closed sets of conics, as well as giving many new examples of maximal arcs. In the current paper, new classes of maximal arcs are constructed, and it is shown that every maximal arc so constructed gives rise to an infinite class of maximal arcs. Apart from when they are of Denniston type or dual hyperovals, closed sets of conics are shown to give maximal arcs that are not isomorphic to the known constructions. An easy characterisation of when a closed set of conics is of Denniston type is given. Results on the geometric structure of the maximal arcs and their duals are proved, as well as on elements of their collineation stabilisers
Metamaterials for light rays: ray optics without wave-optical analog in the ray-optics limit
Volumes of sub-wavelength electromagnetic elements can act like homogeneous
materials: metamaterials. In analogy, sheets of optical elements such as prisms
can act ray-optically like homogeneous sheet materials. In this sense, such
sheets can be considered to be metamaterials for light rays (METATOYs).
METATOYs realize new and unusual transformations of the directions of
transmitted light rays. We study here, in the ray-optics and scalar-wave
limits, the wave-optical analog of such transformations, and we show that such
an analog does not always exist. Perhaps, this is the reason why many of the
ray-optical possibilities offered by METATOYs have never before been
considered.Comment: 10 pages, 3 figures, references update
The 2nd order renormalization group flow for non-linear sigma models in 2 dimensions
We show that for two dimensional manifolds M with negative Euler
characteristic there exists subsets of the space of smooth Riemannian metrics
which are invariant and either parabolic or backwards-parabolic for the 2nd
order RG flow. We also show that solutions exists globally on these sets.
Finally, we establish the existence of an eternal solution that has both a UV
and IR limit, and passes through regions where the flow is parabolic and
backwards-parabolic
Observing sub-microsecond telegraph noise with the radio frequency single electron transistor
Telegraph noise, which originates from the switching of charge between
meta-stable trapping sites, becomes increasingly important as device sizes
approach the nano-scale. For charge-based quantum computing, this noise may
lead to decoherence and loss of read out fidelity. Here we use a radio
frequency single electron transistor (rf-SET) to probe the telegraph noise
present in a typical semiconductor-based quantum computer architecture. We
frequently observe micro-second telegraph noise, which is a strong function of
the local electrostatic potential defined by surface gate biases. We present a
method for studying telegraph noise using the rf-SET and show results for a
charge trap in which the capture and emission of a single electron is
controlled by the bias applied to a surface gate.Comment: Accepted for publication in Journal of Applied Physics. Comments
always welcome, email [email protected], [email protected]
Nonholonomic Ricci Flows: II. Evolution Equations and Dynamics
This is the second paper in a series of works devoted to nonholonomic Ricci
flows. By imposing non-integrable (nonholonomic) constraints on the Ricci flows
of Riemannian metrics we can model mutual transforms of generalized
Finsler-Lagrange and Riemann geometries. We verify some assertions made in the
first partner paper and develop a formal scheme in which the geometric
constructions with Ricci flow evolution are elaborated for canonical nonlinear
and linear connection structures. This scheme is applied to a study of
Hamilton's Ricci flows on nonholonomic manifolds and related Einstein spaces
and Ricci solitons. The nonholonomic evolution equations are derived from
Perelman's functionals which are redefined in such a form that can be adapted
to the nonlinear connection structure. Next, the statistical analogy for
nonholonomic Ricci flows is formulated and the corresponding thermodynamical
expressions are found for compact configurations. Finally, we analyze two
physical applications: the nonholonomic Ricci flows associated to evolution
models for solitonic pp-wave solutions of Einstein equations, and compute the
Perelman's entropy for regular Lagrange and analogous gravitational systems.Comment: v2 41 pages, latex2e, 11pt, the variant accepted by J. Math. Phys.
with former section 2 eliminated, a new section 5 with applications in
gravity and geometric mechanics, and modified introduction, conclusion and
new reference
Resolving Gas Dynamics in the Circumnuclear Region of a Disk Galaxy in a Cosmological Simulation
Using a hydrodynamic adaptive mesh refinement code, we simulate the growth
and evolution of a galaxy, which could potentially host a supermassive black
hole, within a cosmological volume. Reaching a dynamical range in excess of 10
million, the simulation follows the evolution of the gas structure from
super-galactic scales all the way down to the outer edge of the accretion disk.
Here, we focus on global instabilities in the self-gravitating, cold,
turbulence-supported, molecular gas disk at the center of the model galaxy,
which provide a natural mechanism for angular momentum transport down to sub-pc
scales. The gas density profile follows a power-law scaling as r^-8/3,
consistent with an analytic description of turbulence in a quasi-stationary
circumnuclear disk. We analyze the properties of the disk which contribute to
the instabilities, and investigate the significance of instability for the
galaxy's evolution and the growth of a supermassive black hole at the center.Comment: 16 pages (includes appendix), submitted to ApJ. Figures here are at
low resolution; for higher resolution version, download
http://casa.colorado.edu/~levinerd/ms.pd
A super-analogue of Kontsevich's theorem on graph homology
In this paper we will prove a super-analogue of a well-known result by
Kontsevich which states that the homology of a certain complex which is
generated by isomorphism classes of oriented graphs can be calculated as the
Lie algebra homology of an infinite-dimensional Lie algebra of symplectic
vector fields.Comment: 15 page
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