758 research outputs found
Effect of Distributed Particle Magnetic Moments on the Magnetization of NiO Nanoparticles
Magnetization of nanoparticles of NiO are measured and analyzed taking into
account a distribution in particle magnetic moment. We find that disregarding
this distribution in the analysis is the reason for the many anomalous
observations reported on this system in the literature.Comment: 4 pages, 2 figure
Exact Study of the Effect of Level Statistics in Ultrasmall Superconducting Grains
The reduced BCS model that is commonly used for ultrasmall superconducting
grains has an exact solution worked out long ago by Richardson in the context
of nuclear physics. We use it to check the quality of previous treatments of
this model, and to investigate the effect of level statistics on pairing
correlations. We find that the ground state energies are on average somewhat
lower for systems with non-uniform than uniform level spacings, but both have
an equally smooth crossover from the bulk to the few-electron regime. In the
latter, statistical fluctuations in ground state energies strongly depend on
the grain's electron number parity.Comment: 4 pages, 3 eps figs, RevTe
Superconducting correlations in metallic nanoparticles: exact solution of the BCS model by the algebraic Bethe ansatz
Superconducting pairing of electrons in nanoscale metallic particles with
discrete energy levels and a fixed number of electrons is described by the
reduced BCS model Hamiltonian. We show that this model is integrable by the
algebraic Bethe ansatz. The eigenstates, spectrum, conserved operators,
integrals of motion, and norms of wave functions are obtained. Furthermore, the
quantum inverse problem is solved, meaning that form factors and correlation
functions can be explicitly evaluated. Closed form expressions are given for
the form factors that describe superconducting pairing.Comment: revised version, 5 pages, revtex, no figure
Multivariate analysis of biologging data reveals the environmental determinants of diving behaviour in a marine reptile
Diving behaviour of ‘surfacers' such as sea snakes, cetaceans and turtles is complex and multi-dimensional, thus may be better captured by multi-sensor biologging data. However, analysing these large multi-faceted datasets remains challenging, though a high priority. We used high-resolution multi-sensor biologging data to provide the first detailed description of the environmental influences on flatback turtle (Natator depressus) diving behaviour, during its foraging life-history stage. We developed an analytical method to investigate seasonal, diel and tidal effects on diving behaviour for 24 adult flatback turtles tagged with biologgers. We extracted 16 dive variables associated with three-dimensional and kinematic characteristics for 4128 dives. K-means and hierarchical cluster analyses failed to identify distinct dive types. Instead, principal component analysis objectively condensed the dive variables, removing collinearity and highlighting the main features of diving behaviour. Generalized additive mixed models of the main principal components identified significant seasonal, diel and tidal effects on flatback turtle diving behaviour. Flatback turtles altered their diving behaviour in response to extreme tidal and water temperature ranges, displaying thermoregulation and predator avoidance strategies while likely optimizing foraging in this challenging environment. This study demonstrates an alternative statistical technique for objectively interpreting diving behaviour from multivariate collinear data derived from biologgers
Lean-Burn Stationary Natural Gas Reciprocating Engine Operation with a Prototype Miniature Diode Side Pumped Passively Q-switched Laser Spark Plug
To meet the ignition system needs of large bore lean burn stationary natural gas engines a laser diode side pumped passively Q-switched laser igniter was developed and used to ignite lean mixtures in a single cylinder research engine. The laser design was produced from previous work. The in-cylinder conditions and exhaust emissions produced by the miniaturized laser were compared to that produced by a laboratory scale commercial laser system used in prior engine testing. The miniaturized laser design as well as the combustion and emissions data for both laser systems was compared and discussed. It was determined that the two laser systems produced virtually identical combustion and emissions data
Modified differentials and basic cohomology for Riemannian foliations
We define a new version of the exterior derivative on the basic forms of a
Riemannian foliation to obtain a new form of basic cohomology that satisfies
Poincar\'e duality in the transversally orientable case. We use this twisted
basic cohomology to show relationships between curvature, tautness, and
vanishing of the basic Euler characteristic and basic signature.Comment: 20 pages, references added, minor corrections mad
Interplay between pairing and exchange in small metallic dots
We study the effects of the mesoscopic fluctuations on the competition
between exchange and pairing interactions in ultrasmall metallic dots when the
mean level spacing is comparable or larger than the BCS pairing energy. Due to
mesoscopic fluctuations, the probability to have a non-zero spin ground state
may be non-vanishing and shows universal features related to both level
statistics and interaction. Sample to sample fluctuations of the renormalized
pairing are enlightened.Comment: 10 pages, 5 figure
Conformal mapping methods for interfacial dynamics
The article provides a pedagogical review aimed at graduate students in
materials science, physics, and applied mathematics, focusing on recent
developments in the subject. Following a brief summary of concepts from complex
analysis, the article begins with an overview of continuous conformal-map
dynamics. This includes problems of interfacial motion driven by harmonic
fields (such as viscous fingering and void electromigration), bi-harmonic
fields (such as viscous sintering and elastic pore evolution), and
non-harmonic, conformally invariant fields (such as growth by
advection-diffusion and electro-deposition). The second part of the article is
devoted to iterated conformal maps for analogous problems in stochastic
interfacial dynamics (such as diffusion-limited aggregation, dielectric
breakdown, brittle fracture, and advection-diffusion-limited aggregation). The
third part notes that all of these models can be extended to curved surfaces by
an auxilliary conformal mapping from the complex plane, such as stereographic
projection to a sphere. The article concludes with an outlook for further
research.Comment: 37 pages, 12 (mostly color) figure
(47171) 1999 TC36, A Transneptunian Triple
We present new analysis of HST images of (47171) 1999 TC36 that confirm it as
a triple system. Fits to the point-spread function consistently show that the
apparent primary is itself composed of two similar-sized components. The two
central components, A1 and A2, can be consistently identified in each of nine
epochs spread over seven years of time. In each instance the component
separation, ranging from 0.023+/-0.002 to 0.031+/-0.003 arcsec, is roughly one
half of the Hubble Space Telescope's diffraction limit at 606 nm. The orbit of
the central pair has a semi-major axis of a~867 km with a period of P~1.9 days.
These orbital parameters yield a system mass that is consistent with Msys =
12.75+/-0.06 10^18 kg derived from the orbit of the more distant secondary,
component B. The diameters of the three components are dA1= 286(+45,-38) km,
dA2= 265(+41,-35 km and dB= 139(+22,-18) km. The relative sizes of these
components are more similar than in any other known multiple in the solar
system. Taken together, the diameters and system mass yield a bulk density of
p=542(+317,-211) kg m^-3. HST Photometry shows that component B is variable
with an amplitude of >=0.17+/-0.05 magnitudes. Components A1 and A2 do not show
variability larger than 0.08+/-0.03 magnitudes approximately consistent with
the orientation of the mutual orbit plane and tidally-distorted equilibrium
shapes. The system has high specific angular momentum of J/J'=0.93, comparable
to most of the known Transneptunian binaries.Comment: 16 pages, 8 figures, 6 tables. Accepted to Icaru
Report on the collision between a spinner dolphin and a boat in the Fernando de Noronha Archipelago, Western Equatorial Atlantic, Brazil
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