676 research outputs found
Simulations of Oscillation Modes of the Solar Convection Zone
We use the three-dimensional hydrodynamic code of Stein and Nordlund to
realistically simulate the upper layers of the solar convection zone in order
to study physical characteristics of solar oscillations. Our first result is
that the properties of oscillation modes in the simulation closely match the
observed properties. Recent observations from SOHO/MDI and GONG have confirmed
the asymmetry of solar oscillation line profiles, initially discovered by
Duvall et al. In this paper we compare the line profiles in the power spectra
of the Doppler velocity and continuum intensity oscillations from the SOHO/MDI
observations with the simulation. We also compare the phase differences between
the velocity and intensity data. We have found that the simulated line profiles
are asymmetric and have the same asymmetry reversal between velocity and
intensity as observed. The phase difference between the velocity and intensity
signals is negative at low frequencies and jumps in the vicinity of modes as is
also observed. Thus, our numerical model reproduces the basic observed
properties of solar oscillations, and allows us to study the physical
properties which are not observed.Comment: Accepted for publication in ApJ Letter
Using IR techniques to improve Automated Text Classification
This paper performs a study on the pre-processing phase of the automated text classification problem. We use the linear Support Vector Machine paradigm applied to datasets written in the English and the European Portuguese languages – the Reuters and the Portuguese Attorney General’s Office datasets, respectively.
The study can be seen as a search, for the best document representa- tion, in three different axes: the feature reduction (using linguistic in- formation), the feature selection (using word frequencies) and the term weighting (using information retrieval measures)
Extra Dirac Equations
This paper has rather a pedagogical meaning. Surprising symmetries in the
Lorentz group representation space are analyzed. The aim is
to draw reader's attention to the possibility of describing the particle world
on the ground of the Dirac "doubles". Several tune points of the variational
principle for this kind of equations are briefly discussed.Comment: REVTeX 3.0, 14p
Mathematical practice, crowdsourcing, and social machines
The highest level of mathematics has traditionally been seen as a solitary
endeavour, to produce a proof for review and acceptance by research peers.
Mathematics is now at a remarkable inflexion point, with new technology
radically extending the power and limits of individuals. Crowdsourcing pulls
together diverse experts to solve problems; symbolic computation tackles huge
routine calculations; and computers check proofs too long and complicated for
humans to comprehend.
Mathematical practice is an emerging interdisciplinary field which draws on
philosophy and social science to understand how mathematics is produced. Online
mathematical activity provides a novel and rich source of data for empirical
investigation of mathematical practice - for example the community question
answering system {\it mathoverflow} contains around 40,000 mathematical
conversations, and {\it polymath} collaborations provide transcripts of the
process of discovering proofs. Our preliminary investigations have demonstrated
the importance of "soft" aspects such as analogy and creativity, alongside
deduction and proof, in the production of mathematics, and have given us new
ways to think about the roles of people and machines in creating new
mathematical knowledge. We discuss further investigation of these resources and
what it might reveal.
Crowdsourced mathematical activity is an example of a "social machine", a new
paradigm, identified by Berners-Lee, for viewing a combination of people and
computers as a single problem-solving entity, and the subject of major
international research endeavours. We outline a future research agenda for
mathematics social machines, a combination of people, computers, and
mathematical archives to create and apply mathematics, with the potential to
change the way people do mathematics, and to transform the reach, pace, and
impact of mathematics research.Comment: To appear, Springer LNCS, Proceedings of Conferences on Intelligent
Computer Mathematics, CICM 2013, July 2013 Bath, U
A cAMP-binding ectoprotein in the yeast Saccharomyces cerevisiae
tides 10, 593-595
Influence of B - site Disorder in (B = Fe, Ru, Al and Ga) Manganites
We have investigated the influence of B - site doping on the crystal and
magnetic structure in (B= Fe, Ru, Al and
Ga) compounds using neutron diffraction, SANS, magnetization and resistivity
techniques. The B - site doped samples are isostructural and possess an
orthorhombic structure in \textit{Pnma} space group at 300K. A structural
transition from orthorhombic to monoclinic is found to precede the magnetic
transition to CE - type antiferromagnetic state in few of these samples. On
doping with Fe, charge and orbitally ordered CE - type antiferromagnetic state
is suppressed, followed by the growth in ferromagnetic insulating phase in
compounds. At higher Fe doping in , the
ferromagnetic state is also suppressed and no evidence of long range magnetic
ordering is observed. In Ru doped samples , the
ferromagnetic metallic state is favored at and
and no significant change in and as a
function of Ru doping is found. In contrast, with non magnetic Al substitution
for , the charge ordered CE - type antiferromagnetic state
coexists with the ferromagnetic metallic phase. With further increase in Al
doping , both CE - type antiferromagnetic and
ferromagnetic phases are gradually suppressed. This behavior is accompanied by
the evolution of A - type antiferromagnetic insulating state. Eventually, at
higher Al doping , this phase is also suppressed and
signature of spin glass like transition are evident in M(T). Likewise,
substitution with Ga is observed to induce similar effects as described for Al
doped samples. The presence of short ranged ferromagnetic ordering has been
further explored using SANS measurements in few of the selected samples.Comment: To appear in Journal of Physics: Condensed Matte
Rofecoxib for dysmenorrhoea: meta-analysis using individual patient data
BACKGROUND: Individual patient meta-analysis to determine the analgesic efficacy and adverse effects of single-dose rofecoxib in primary dysmenorrhoea. METHODS: Individual patient information was available from three randomised, double blind, placebo and active controlled trials of rofecoxib. Data were combined through meta-analysis. Number-needed-to-treat (NNT) for at least 50% pain relief and the proportion of patients who had taken rescue medication over 12 hours were calculated. Information was collected on adverse effects. RESULTS: For single-dose rofecoxib 50 mg compared with placebo, the NNTs (with 95% CI) for at least 50% pain relief were 3.2 (2.4 to 4.5) at six, 3.1 (2.4 to 9.0) at eight, and 3.7 (2.8 to 5.6) at 12 hours. For naproxen sodium 550 mg they were 3.1 (2.4 to 4.4) at six, 3.0 (2.3 to 4.2) at eight, and 3.8 (2.7 to 6.1) at 12 hours. The proportion of patients who needed rescue medication within 12 hours was 27% with rofecoxib 50 mg, 29% with naproxen sodium 550 mg, and 50% with placebo. In the single-dose trial, the proportion of patients reporting any adverse effect was 8% (4/49) with rofecoxib 50 mg, 12% (6/49) with ibuprofen 400 mg, and 6% (3/49) with placebo. In the other two multiple dose trials, the proportion of patients reporting any adverse effect was 23% (42/179) with rofecoxib 50 mg, 24% (45/181) with naproxen sodium 550 mg, and 18% (33/178) with placebo. CONCLUSIONS: Single dose rofecoxib 50 mg provided similar pain relief to naproxen sodium 550 mg over 12 hours. The duration of analgesia with rofecoxib 50 mg was similar to that of naproxen sodium 550 mg. Adverse effects were uncommon suggesting safety in short-term use of rofecoxib and naproxen sodium. Future research should include restriction on daily life and absence from work or school as outcomes
Low temperature synthesis, magnetic and magnetotransport properties of (La1-xLux)0.67Ca0.33MnO3 (0 < x < 0.12) system
We have been able to synthesize Lu+3 substituted La0.67Ca0.33MnO3 (LCMO) by
an auto-combustion method. Synthesis of this compound is not successful by
conventional ceramic or other chemical methods. Magnetic and electrical
transport properties of the Lu substituted LCMO [(La1-xLux)0.67Ca0.33MnO3 (0 <
x < 0.12)] system have been investigated and compared with those of the Y+3,
Pr+3, Dy+3 and Tb+3 substituted LCMO systems. All the compounds show a
ferromagnetic metal to paramagnetic insulator transition at TC. The tolerance
factor reduces from 0.917 for x = 0 to 0.909 for x = 0.12 and for this range
all are ferromagnetic metals indicating the dominance of the coupling between
spins due to double exchange over the antiferromagnetic superexchange
interaction. The transition temperatures and magnetization decrease as the Lu
concentration increases. This is satisfactorily accounted for on the basis of
transition from ferromagnetic at x = 0 to canted spin order for x > 0. All the
samples show higher magnitude of MR compared to that in pure LCMO at 80 kOe
field in the temperature range of 5 to 320K. A fairly high value of low field
magnetoresistance (LFMR) of about 30% is obtained in all the samples at a field
less than 5 kOe.Comment: Total 35 pages of text and figure
Spin half fermions with mass dimension one: theory, phenomenology, and dark matter
We provide the first details on the unexpected theoretical discovery of a
spin-one-half matter field with mass dimension one. It is based upon a complete
set of dual-helicity eigenspinors of the charge conjugation operator. Due to
its unusual properties with respect to charge conjugation and parity, it
belongs to a non-standard Wigner class. Consequently, the theory exhibits
non-locality with (CPT)^2 = - I. We briefly discuss its relevance to the
cosmological `horizon problem'. Because the introduced fermionic field is
endowed with mass dimension one, it can carry a quartic self-interaction. Its
dominant interaction with known forms of matter is via Higgs, and with gravity.
This aspect leads us to contemplate the new fermion as a prime dark matter
candidate. Taking this suggestion seriously we study a supernova-like explosion
of a galactic-mass dark matter cloud to set limits on the mass of the new
particle and present a calculation on relic abundance to constrain the relevant
cross-section. The analysis favours light mass (roughly 20 MeV) and relevant
cross-section of about 2 pb. Similarities and differences with the WIMP and
mirror matter proposals for dark matter are enumerated. In a critique of the
theory we bare a hint on non-commutative aspects of spacetime, and
energy-momentum space.Comment: 78 pages [Changes: referee-suggested improvements, additional
important references, and better readability
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