31,436 research outputs found
From computation to black holes and space-time foam
We show that quantum mechanics and general relativity limit the speed
of a simple computer (such as a black hole) and its memory space
to \tilde{\nu}^2 I^{-1} \lsim t_P^{-2}, where is the Planck time.
We also show that the life-time of a simple clock and its precision are
similarly limited. These bounds and the holographic bound originate from the
same physics that governs the quantum fluctuations of space-time. We further
show that these physical bounds are realized for black holes, yielding the
correct Hawking black hole lifetime, and that space-time undergoes much larger
quantum fluctuations than conventional wisdom claims -- almost within range of
detection with modern gravitational-wave interferometers.Comment: A misidentification of computer speeds is corrected. Our results for
black hole computation now agree with those given by S. Lloyd. All other
conclusions remain unchange
A biological approach to metalworking based on chitinous colloids and composites
Biological systems evolve with minimum metabolic costs and use common
components, and they represent guideposts toward a paradigm of manufacturing
that is centered on minimum energy, local resources, and ecological
integration. Here, we demonstrate a new biological method of working metal that
exploits the unique ability of chitin to incorporate metals into the arthropod
cuticle in order to aggregate colloidal suspensions of different metals into
solid ultra-low-binder-content composites. These composites, which can contain
more than 99.5% metal, simultaneously show both biological affinity and the
electrical conductivity and durability of metals. This approach stands in
contrast with existing energy-demanding metalworking methods, taking place at
ambient temperature and pressure and being driven by water exchange.
Furthermore, all the nonmetallic components involved are metabolized in large
amounts in every ecosystem. Under these conditions, we demonstrate the ability
of the composites to be printed and cast into functional shapes with metallic
characteristics. The affinity of chitometallic composites for other biological
components also allows them to infuse metallic characteristics into other
biomaterials. Our findings and robust manufacturing examples go well beyond
basic demonstrations and offer a generalizable new approach to metalworking. We
highlight the potential for a paradigm shift toward structural biomaterials
based on their unique characteristics and native manufacturing methods.Comment: ^ pages, 3 main figures, 4 videos, supplementary materials and
methods, and 3 supplementary figure
Advanced flight control system study
A fly by wire flight control system architecture designed for high reliability includes spare sensor and computer elements to permit safe dispatch with failed elements, thereby reducing unscheduled maintenance. A methodology capable of demonstrating that the architecture does achieve the predicted performance characteristics consists of a hierarchy of activities ranging from analytical calculations of system reliability and formal methods of software verification to iron bird testing followed by flight evaluation. Interfacing this architecture to the Lockheed S-3A aircraft for flight test is discussed. This testbed vehicle can be expanded to support flight experiments in advanced aerodynamics, electromechanical actuators, secondary power systems, flight management, new displays, and air traffic control concepts
Chiral Correction to the Spin Fluctuation Feedback in two-dimensional p-wave Superconductors
We consider the stability of the superconducting phase for spin-triplet
p-wave pairing in a quasi-two-dimensional system. We show that in the absence
of spin-orbit coupling there is a chiral contribution to spin fluctuation
feedback which is related to spin quantum Hall effect in a chiral
superconducting phase. We show that this mechanism supports the stability of a
chiral p-wave state.Comment: 8 pages. The final version is accepted for publication in Europhys
Let
Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors
The flux-line lattice in the compound , which has a tendency to
ferromagnetic order in the a-b plane is studied with external magnetic field
direction close to the c-axis. We show the existence of an instability where
the direction of flux-lines spontaneously tilts away from that of the applied
field near the onset of ferromagnetic order. The enhanced fluctuations in the
flux lattice and the square flux lattice recently observed are explained and
further experiments suggested.Comment: 12 pages, Latex file, no figur
Spin-Orbit Coupling and Symmetry of the Order Parameter in Strontium Ruthenate
Determination of the orbital symmetry of a state in spin triplet
SrRuO superconductor is a challenge of considerable importance. Most of
the experiments show that the chiral state of the type
is realized and remains stable on lowering the temperature. Here we have
studied the stability of various superconducting states of SrRuO in the
presence of spin-orbit coupling.
Numerically we found that the chiral state is never the minimum energy. Alone
among the five states studied it has and is
therefore not affected to linear order in the coupling parameter . We
found that stability of the chiral state requires spin dependent pairing
interactions. This imposes strong constraint on the pairing mechanism.Comment: 4 pages, 4 figure
Neutrix Calculus and Finite Quantum Field Theory
In general, quantum field theories (QFT) require regularizations and infinite
renormalizations due to ultraviolet divergences in their loop calculations.
Furthermore, perturbation series in theories like QED are not convergent
series, but are asymptotic series. We apply neutrix calculus, developed in
connection with asymptotic series and divergent integrals, to QFT,obtaining
finite renormalizations. While none of the physically measurable results in
renormalizable QFT is changed, quantum gravity is rendered more manageable in
the neutrix framework.Comment: 10 pages; LaTeX; version to appear in J. Phys. A: Math. Gen. as a
Letter to the Edito
Neutrino Magnetic Moments and Minimal Supersymmetric SO(10) Model
We examine supersymmetric contributions to transition magnetic moments of
Majorana neutrinos. We first give the general formula for it. In concrete
evaluations, informations of neutrino mass matrix elements including CP phases
are necessary. Using unambiguously determined neutrino mass matrices in
recently proposed minimal supersymmetric SO(10) model, the transition magnetic
moments are calculated. The resultant neutrino magnetic moments are found to be
roughly an order of magnitude larger than those calculated in the standard
model extended to incorporate the see-saw mechanism.Comment: 8 pages, 4 figures, the version to be published in International
Journal of Modern Physics
Perspective on Quark Mass and Mixing Relations
Recent data indicate that , while
seems to be GeV. The relations and suggest that %a plausible clean separation of
the %origin of the quark mixing matrix: the down type sector is responsible for
and , while comes from the up
type sector. Five to six parameters might suffice to account for the ten quark
mass and mixing parameters, resulting in specific power series representations
for the mass matrices. In this picture, seems to be the more sensible
expansion parameter, while is
tied empirically to .Comment: 10 pages, ReVtex, no figure
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