28,176 research outputs found
Constraints on viewing geometries from radio observations of -ray-loud pulsars using a novel method
We present radio intensity and polarisation profiles of 28
-ray-detected pulsars with the aim of putting constraints on their
viewing geometries using data from the Parkes telescope. Constraints are formed
both from the goodness-of-fit of the position angles to the Rotating Vector
Model and from the beam opening angle considering aberration and retardation
effects. Uncertainties on the relevant parameters are systematically taken into
account in order to produce a more robust constraint, using a new approach.
Surprisingly, we find that the distribution of the magnetic inclination angle
() in this subset of pulsars peaks at low values, contrary to the
predictions of -ray models. We find a lack of correlation between these
and a set of values which were derived using -ray light
curves, suggesting a problem in the interpretation of the data in one or both
of these domains. Finally, we also show that the distribution of
pulsars with multiple radio components is no different to that of
single-component pulsars.Comment: 23 pages, 31 figures Submitted to MNRA
Magnetic, Transport, and Thermal Properties of Single Crystals of the Layered Arsenide BaMn2As2
Growth of BaMn2As2 crystals using both MnAs and Sn fluxes is reported. Room
temperature crystallography, anisotropic isothermal magnetization M versus
field H and magnetic susceptibility chi versus temperature T, electrical
resistivity in the ab plane rho(T), and heat capacity C(T) measurements on the
crystals were carried out. The tetragonal ThCr2Si2-type structure of BaMn2As2
is confirmed. After correction for traces of ferromagnetic MnAs impurity phase
using M(H) isotherms, the inferred intrinsic chi(T) data of the crystals are
anisotropic with chi_{ab}/chi_{c} \approx 7.5 at T = 2 K. The temperature
dependences of the anisotropic chi data suggest that BaMn2As2 is a collinear
antiferromagnet at room temperature with the easy axis along the c axis, and
with an extrapolated Neel temperature T_N \sim 500 K. The rho(T) decreases with
decreasing T below 310 K but then increases below \sim 50 K, suggesting that
BaMn2As2 is a small band-gap semiconductor with an activation energy of order
0.03 eV. The C(T) data from 2 to 5 K are consistent with this insulating ground
state, exhibiting a low temperature Sommerfeld coefficient gamma = 0.0(4)
mJ/mol K^2. The Debye temperature is determined from these data to be theta_D =
246(4) K. BaMn2As2 is a potential parent compound for ThCr2Si2-type
superconductors.Comment: 7 pages, 6 figures; v2: typos corrected, additional data and
discussion, accepted for publication in Phys. Rev.
Spontaneous Raman scattering for simultaneous measurements of in-cylinder species
A technique for multi-species mole fraction measurement in internal combustion engines is described. The technique is based on the spontaneous Raman scattering. It can simultaneously provide the mole fractions of several species of N-2, O-2, H2O, CO2 and fuel. Using the system, simultaneous measurement of air/fuel ratio and burnt residual gas are carried out during the mixture process in a Controlled Auto Ignition (CAI) combustion engine. The accuracy and consistency of the measured results were confirmed by the measured air fuel ratio using an exhaust gas analyzer and independently calculated mole fraction values. Measurement of species mole fractions during combustion process has also been demonstrated. It shows that the SRS can provide valuable data on this process in a CAI combustion engine
Explicit tracking of uncertainty increases the power of quantitative rule-of-thumb reasoning in cell biology
"Back-of-the-envelope" or "rule-of-thumb" calculations involving rough
estimates of quantities play a central scientific role in developing intuition
about the structure and behaviour of physical systems, for example in so-called
`Fermi problems' in the physical sciences. Such calculations can be used to
powerfully and quantitatively reason about biological systems, particularly at
the interface between physics and biology. However, substantial uncertainties
are often associated with values in cell biology, and performing calculations
without taking this uncertainty into account may limit the extent to which
results can be interpreted for a given problem. We present a means to
facilitate such calculations where uncertainties are explicitly tracked through
the line of reasoning, and introduce a `probabilistic calculator' called
Caladis, a web tool freely available at www.caladis.org, designed to perform
this tracking. This approach allows users to perform more statistically robust
calculations in cell biology despite having uncertain values, and to identify
which quantities need to be measured more precisely in order to make confident
statements, facilitating efficient experimental design. We illustrate the use
of our tool for tracking uncertainty in several example biological
calculations, showing that the results yield powerful and interpretable
statistics on the quantities of interest. We also demonstrate that the outcomes
of calculations may differ from point estimates when uncertainty is accurately
tracked. An integral link between Caladis and the Bionumbers repository of
biological quantities further facilitates the straightforward location,
selection, and use of a wealth of experimental data in cell biological
calculations.Comment: 8 pages, 3 figure
Absence of structural correlations of magnetic defects in heavy fermion LiV2O4
Magnetic defects have pronounced effects on the magnetic properties of the
face-centered cubic compound LiV2O4. The magnetic defects arise from crystal
defects present within the normal spinel structure. High-energy x-ray
diffraction studies were performed on LiV2O4 single crystals to search for
superstructure peaks or any other evidence of periodicity in the arrangement of
the crystal defects present in the lattice. Entire reciprocal lattice planes
are mapped out with help of synchrotron radiation. No noticeable differences in
the x-ray diffraction data between a crystal with high magnetic defect
concentration and a crystal with low magnetic defect concentration have been
found. This indicates the absence of any long-range periodicity or short-range
correlations in the arrangements of the crystal/magnetic defects.Comment: 6 pages, 4 figure
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