423 research outputs found
Uncovering Ramanujan's "Lost" Notebook: An Oral History
Here we weave together interviews conducted by the author with three
prominent figures in the world of Ramanujan's mathematics, George Andrews,
Bruce Berndt and Ken Ono. The article describes Andrews's discovery of the
"lost" notebook, Andrews and Berndt's effort of proving and editing Ramanujan's
notes, and recent breakthroughs by Ono and others carrying certain important
aspects of the Indian mathematician's work into the future. Also presented are
historical details related to Ramanujan and his mathematics, perspectives on
the impact of his work in contemporary mathematics, and a number of interesting
personal anecdotes from Andrews, Berndt and Ono
Mission Concept for the Single Aperture Far-Infrared (SAFIR) Observatory
The Single Aperture Far-InfraRed (SAFIR) Observatory's science goals are
driven by the fact that the earliest stages of almost all phenomena in the
universe are shrouded in absorption by and emission from cool dust and gas that
emits strongly in the far-infrared and submillimeter. Over the past several
years, there has been an increasing recognition of the critical importance of
this spectral region to addressing fundamental astrophysical problems, ranging
from cosmological questions to understanding how our own Solar System came into
being. The development of large, far-infrared telescopes in space has become
more feasible with the combination of developments for the James Webb Space
Telescope and of enabling breakthroughs in detector technology. We have
developed a preliminary but comprehensive mission concept for SAFIR, as a 10
m-class far-infrared and submillimeter observatory that would begin development
later in this decade to meet the needs outlined above. Its operating
temperature (<4K) and instrument complement would be optimized to reach the
natural sky confusion limit in the far-infrared with diffraction-limited
peformance down to at least 40 microns. This would provide a point source
sensitivity improvement of several orders of magnitude over that of Spitzer or
Herschel, with finer angular resolution, enabling imaging and spectroscopic
studies of individual galaxies in the early universe. We have considered many
aspects of the SAFIR mission, including the telescope technology, detector
needs and technologies, cooling method and required technology developments,
attitude and pointing, power systems, launch vehicle, and mission operations.
The most challenging requirements for this mission are operating temperature
and aperture size of the telescope, and the development of detector arrays.Comment: 36 page
A quadtree-polygon-based scaled boundary finite element method for image-based mesoscale fracture modelling in concrete
A quadtree-polygon scaled boundary finite element-based approach for image-based modelling of concrete fracture at the mesoscale is developed. Digital images representing the two-phase mesostructure of concrete, which comprises of coarse aggregates and mortar are either generated using a take-and-place algorithm with a user-defined aggregate volume ratio or obtained from X-ray computed tomography as an input. The digital images are automatically discretised for analysis by applying a balanced quadtree decomposition in combination with a smoothing operation. The scaled boundary finite element method is applied to model the constituents in the concrete mesostructure. A quadtree formulation within the framework of the scaled boundary finite element method is advantageous in that the displacement compatibility between the cells are automatically preserved even in the presence of hanging nodes. Moreover, the geometric flexibility of the scaled boundary finite element method facilitates the use of arbitrary sided polygons, allowing better representation of the aggregate boundaries. The computational burden is significantly reduced as there are only finite number of cell types in a balanced quadtree mesh. The cells in the mesh are connected to each other using cohesive interface elements with appropriate softening laws to model the fracture of the mesostructure. Parametric studies are carried out on concrete specimens subjected to uniaxial tension to investigate the effects of various parameters e.g. aggregate size distribution, porosity and aggregate volume ratio on the fracture of concrete at the meso-scale. Mesoscale fracture of concrete specimens obtained from X-ray computed tomography scans are carried out to demonstrate its feasibility
Scaling and self-averaging in the three-dimensional random-field Ising model
We investigate, by means of extensive Monte Carlo simulations, the magnetic
critical behavior of the three-dimensional bimodal random-field Ising model at
the strong disorder regime. We present results in favor of the two-exponent
scaling scenario, , where and are the
critical exponents describing the power-law decay of the connected and
disconnected correlation functions and we illustrate, using various finite-size
measures and properly defined noise to signal ratios, the strong violation of
self-averaging of the model in the ordered phase.Comment: 8 pages, 6 figures, to be published in Eur. Phys. J.
Stability of Cementite formed from Hematite and Titanomagnetite Ore
The stability of cementite formed during the reduction of hematite and preoxidized titanomagnetite ores in a methane-hydrogen gas mixture was examined in the temperature interval 500oC to 900oC for the hematite ore and 300oC to 1100oC for titanomagnetite. Cementite formed from hematite ore was most stable at temperatures between 750oC to 770oC. Its decomposition rate increased with decreasing temperature between 750oC and 600oC and with increasing temperature above 770oC. Cementite formed from preoxidized titanomagnetite was most stable in the temperature range 700oC to 900oC. The rate of cementite decomposition increased with decreasing temperature between 700oC and 400oC and with increasing temperature above 900oC. Cementite formed from titanomagnetite ore was more stable than cementite formed from hematite under all conditions examined
Projective dynamics and first integrals
We present the theory of tensors with Young tableau symmetry as an efficient
computational tool in dealing with the polynomial first integrals of a natural
system in classical mechanics. We relate a special kind of such first
integrals, already studied by Lundmark, to Beltrami's theorem about
projectively flat Riemannian manifolds. We set the ground for a new and simple
theory of the integrable systems having only quadratic first integrals. This
theory begins with two centered quadrics related by central projection, each
quadric being a model of a space of constant curvature. Finally, we present an
extension of these models to the case of degenerate quadratic forms.Comment: 39 pages, 2 figure
Revisiting the scaling of the specific heat of the three-dimensional random-field Ising model
We revisit the scaling behavior of the specific heat of the three-dimensional
random-field Ising model with a Gaussian distribution of the disorder. Exact ground states
of the model are obtained using graph-theoretical algorithms for different strengths
= 268 3Â spins. By numerically differentiating the bond energy
with respect to h, a specific-heat-like quantity is obtained whose
maximum is found to converge to a constant in the thermodynamic limit. Compared to a
previous study following the same approach, we have studied here much larger system sizes
with an increased statistical accuracy. We discuss the relevance of our results under the
prism of a modified Rushbrooke inequality for the case of a saturating specific heat.
Finally, as a byproduct of our analysis, we provide high-accuracy estimates of the
critical field hc =
2.279(7) and the critical exponent of the correlation exponent
Μ =
1.37(1), in excellent agreement to the most recent computations in the
literature
Magnetic Field Amplification in Galaxy Clusters and its Simulation
We review the present theoretical and numerical understanding of magnetic
field amplification in cosmic large-scale structure, on length scales of galaxy
clusters and beyond. Structure formation drives compression and turbulence,
which amplify tiny magnetic seed fields to the microGauss values that are
observed in the intracluster medium. This process is intimately connected to
the properties of turbulence and the microphysics of the intra-cluster medium.
Additional roles are played by merger induced shocks that sweep through the
intra-cluster medium and motions induced by sloshing cool cores. The accurate
simulation of magnetic field amplification in clusters still poses a serious
challenge for simulations of cosmological structure formation. We review the
current literature on cosmological simulations that include magnetic fields and
outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure
Dilepton mass spectra in p+p collisions at sqrt(s)= 200 GeV and the contribution from open charm
The PHENIX experiement has measured the electron-positron pair mass spectrum
from 0 to 8 GeV/c^2 in p+p collisions at sqrt(s)=200 GeV. The contributions
from light meson decays to e^+e^- pairs have been determined based on
measurements of hadron production cross sections by PHENIX. They account for
nearly all e^+e^- pairs in the mass region below 1 GeV/c^2. The e^+e^- pair
yield remaining after subtracting these contributions is dominated by
semileptonic decays of charmed hadrons correlated through flavor conservation.
Using the spectral shape predicted by PYTHIA, we estimate the charm production
cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) \mu b, which
is consistent with QCD calculations and measurements of single leptons by
PHENIX.Comment: 375 authors from 57 institutions, 18 pages, 4 figures, 2 tables.
Submitted to Physics Letters B. v2 fixes technical errors in matching authors
to institutions. Plain text data tables for the points plotted in figures for
this and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
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