2,109 research outputs found
When unlikely outcomes occur: the role of communication format in maintaining communicator credibility
The public expects science to reduce or eliminate uncertainty (Kinzig & Starrett, 2003), yet scientific forecasts are probabilistic (at best) and it is simply not possible to make predictions with certainty. Whilst an ‘unlikely’ outcome is not expected to occur, an ‘unlikely’ outcome will still occur one in five times (based on a translation of 20%, e.g. Theil, 2002), according to a frequentist perspective. When an ‘unlikely’ outcome does occur, the prediction may be deemed ‘erroneous’, reflecting a misunderstanding of the nature of uncertainty. Such misunderstandings could have ramifications for the subsequent (perceived) credibility of the communicator who made such a prediction. We examine whether the effect of ‘erroneous’ predictions on perceived credibility differs according to the communication format used. Specifically, we consider verbal, numerical (point and range [wide / narrow]) and mixed format probability expressions. We consistently find that subsequent perceptions are least affected by the ‘erroneous’ prediction when it is expressed numerically, regardless of whether it is a point or range estimate. Our findings suggest numbers should be used in consequential risk communications regarding ‘unlikely’ events, wherever possible
‘Because it’s our culture!’ (Re)negotiating the meaning of lobola in Southern African secondary schools
Payment of bridewealth or lobola is a significant element of marriage among the Basotho of Lesotho and the Shona of Zimbabwe. However, the functions and meanings attached to the practice are constantly changing. In order to gauge the interpretations attached to lobola by young people today, this paper analyses a series of focus group discussions conducted among senior students at two rural secondary schools. It compares the interpretations attached by the students to the practice of lobola with academic interpretations (both historical and contemporary). Among young people the meanings and functions of lobola are hotly contested, but differ markedly from those set out in the academic literature. While many students see lobola as a valued part of ‘African culture’, most also view it as a financial transaction which necessarily disadvantages women. The paper then seeks to explain the young people’s interpretations by reference to discourses of ‘equal rights’ and ‘culture’ prevalent in secondary schools. Young people make use of these discourses in (re)negotiating the meaning of lobola, but the limitations of the discourses restrict the interpretations of lobola available to them
Phenomenological constraints on Lemaitre-Tolman-Bondi cosmological inhomogeneities from solar system dynamics
We, first, analytically work out the long-term, i.e. averaged over one
orbital revolution, perturbations on the orbit of a test particle moving in a
local Fermi frame induced therein by the cosmological tidal effects of the
inhomogeneous Lemaitre-Tolman-Bondi (LTB) model. The LTB solution has recently
attracted attention, among other things, as a possible explanation of the
observed cosmic acceleration without resorting to dark energy. Then, we
phenomenologically constrain both the parameters K_1 = -\ddot R/R and K_2 =
-\ddot R^'/R^' of the LTB metric in the Fermi frame by using different kinds of
solar system data. The corrections to the standard
Newtonian/Einsteinian precessions of the perihelia of the inner planets
recently estimated with the EPM ephemerides, compared to our predictions for
them, yield K_1 = (4+8) 10^-26 s^-2, K_2 = (3+7) 10^-23 s^-2. The residuals of
the Cassini-based Earth-Saturn range, compared with the numerically integrated
LTB range signature, allow to obtain K_1/2 = 10^-27 s^-2. The LTB-induced
distortions of the orbit of a typical object of the Oort cloud with respect to
the commonly accepted Newtonian picture, based on the observations of the comet
showers from that remote region of the solar system, point towards K_1/2 <=
10^-30-10^-32 s^-2. Such figures have to be compared with those inferred from
cosmological data which are of the order of K1 \approx K2 = -4 10^-36 s^-2.Comment: LaTex2e, 18 pages, 3 tables, 3 figures. Minor changes. Reference
added. Accepted by Journal of Cosmology and Astroparticle Physics (JCAP
Optical Spectra of SNR Candidates in NGC 300
We present moderate-resolution (<5A) long-slit optical spectra of 51 nebular
objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter
Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting
the criterion of [SII]/Ha>=0.4 to confirm supernova remnants (SNRs) from
optical spectra, we find that of 28 objects previously proposed as SNRs from
optical observations, 22 meet this criterion with six showing [SII]/Ha of less
than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated
with the 28 previously proposed SNRs. Of these four, three (included in the 22
above) meet the criterion. In all, 22 of the 51 nebular objects meet the
[SII]/Ha criterion as SNRs while the nature of the remaining 29 objects remains
undetermined by these observations.Comment: Accepted for publication in Astrophysics & Space Scienc
Anisotropic Superparamagnetism of Monodispersive Cobalt-Platinum Nanocrystals
Based on the high-temperature organometallic route (Sun et al. Science 287,
1989 (2000)), we have synthesized powders containing CoPt_3 single crystals
with mean diameters of 3.3(2) nm and 6.0(2) nm and small log-normal widths
sigma=0.15(1). In the entire temperature range from 5 K to 400 K, the
zero-field cooled susceptibility chi(T) displays significant deviations from
ideal superparamagnetism. Approaching the Curie temperature of 450(10) K, the
deviations arise from the (mean-field) type reduction of the ferromagnetic
moments, while below the blocking temperature T_b, chi(T) is suppressed by the
presence of energy barriers, the distributions of which scale with the particle
volumes obtained from transmission electron microscopy (TEM). This indication
for volume anisotropy is supported by scaling analyses of the shape of the
magnetic absorption chi''(T,omega) which reveal distribution functions for the
barriers being also consistent with the volume distributions observed by TEM.
Above 200 K, the magnetization isotherms M(H,T) display Langevin behavior
providing 2.5(1) mu_B per CoPt_3 in agreement with reports on bulk and thin
film CoPt_3. The non-Langevin shape of the magnetization curves at lower
temperatures is for the first time interpreted as anisotropic
superparamagnetism by taking into account an anisotropy energy of the
nanoparticles E_A(T). Using the magnitude and temperature variation of E_A(T),
the mean energy barriers and 'unphysical' small switching times of the
particles obtained from the analyses of chi''(T,omega) are explained. Below T_b
hysteresis loops appear and are quantitatively described by a blocking model,
which also ignores particle interactions, but takes the size distributions from
TEM and the conventional field dependence of E_A into account.Comment: 12 pages with 10 figures and 1 table. Version accepted for
publication in Phys. Rev. B . Two-column layou
An Overview of the 13:8 Mean Motion Resonance between Venus and Earth
It is known since the seminal study of Laskar (1989) that the inner planetary
system is chaotic with respect to its orbits and even escapes are not
impossible, although in time scales of billions of years. The aim of this
investigation is to locate the orbits of Venus and Earth in phase space,
respectively to see how close their orbits are to chaotic motion which would
lead to unstable orbits for the inner planets on much shorter time scales.
Therefore we did numerical experiments in different dynamical models with
different initial conditions -- on one hand the couple Venus-Earth was set
close to different mean motion resonances (MMR), and on the other hand Venus'
orbital eccentricity (or inclination) was set to values as large as e = 0.36 (i
= 40deg). The couple Venus-Earth is almost exactly in the 13:8 mean motion
resonance. The stronger acting 8:5 MMR inside, and the 5:3 MMR outside the 13:8
resonance are within a small shift in the Earth's semimajor axis (only 1.5
percent). Especially Mercury is strongly affected by relatively small changes
in eccentricity and/or inclination of Venus in these resonances. Even escapes
for the innermost planet are possible which may happen quite rapidly.Comment: 14 pages, 11 figures, submitted to CMD
A novel nonsense CDK5RAP2 mutation in a Somali child with primary microcephaly and sensorineural hearing loss
Primary microcephaly is a genetically heterogeneous condition characterized by reduced head circumference (-3 SDS or more) and mild-to-moderate learning disability. Here, we describe clinical and molecular investigations of a microcephalic child with sensorineural hearing loss. Although consanguinity was unreported initially, detection of 13.7 Mb of copy neutral loss of heterozygosity (cnLOH) on chromosome 9 implicated the CDK5RAP2 gene. Targeted sequencing identified a homozygous E234X mutation, only the third mutation to be described in CDK5RAP2, the first in an individual of non-Pakistani descent. Sensorineural hearing loss is not generally considered to be consistent with autosomal recessive microcephaly and therefore it seems likely that the deafness in this individual is caused by the co-occurrence of a further gene mutation, independent of CDK5RAP2. Nevertheless, further detailed clinical descriptions of rare CDK5RAP2 patients, including hearing assessments will be needed to resolve fully the phenotypic range associated with mutations in this gene. This study also highlights the utility of SNP-array testing to guide disease gene identification where an autosomal recessive condition is plausible
Analysis of acoustic emission during the melting of embedded indium particles in an aluminum matrix: a study of plastic strain accommodation during phase transformation
Acoustic emission is used here to study melting and solidification of
embedded indium particles in the size range of 0.2 to 3 um in diameter and to
show that dislocation generation occurs in the aluminum matrix to accommodate a
2.5% volume change. The volume averaged acoustic energy produced by indium
particle melting is similar to that reported for bainite formation upon
continuous cooling. A mechanism of prismatic loop generation is proposed to
accommodate the volume change and an upper limit to the geometrically necessary
increase in dislocation density is calculated as 4.1 x 10^9 cm^-2 for the
Al-17In alloy. Thermomechanical processing is also used to change the size and
distribution of the indium particles within the aluminum matrix. Dislocation
generation with accompanied acoustic emission occurs when the melting indium
particles are associated with grain boundaries or upon solidification where the
solid-liquid interfaces act as free surfaces to facilitate dislocation
generation. Acoustic emission is not observed for indium particles that require
super heating and exhibit elevated melting temperatures. The acoustic emission
work corroborates previously proposed relaxation mechanisms from prior internal
friction studies and that the superheat observed for melting of these
micron-sized particles is a result of matrix constraint.Comment: Presented at "Atomistic Effects in Migrating Interphase Interfaces -
Recent Progress and Future Study" TMS 201
Self-optimization, community stability, and fluctuations in two individual-based models of biological coevolution
We compare and contrast the long-time dynamical properties of two
individual-based models of biological coevolution. Selection occurs via
multispecies, stochastic population dynamics with reproduction probabilities
that depend nonlinearly on the population densities of all species resident in
the community. New species are introduced through mutation. Both models are
amenable to exact linear stability analysis, and we compare the analytic
results with large-scale kinetic Monte Carlo simulations, obtaining the
population size as a function of an average interspecies interaction strength.
Over time, the models self-optimize through mutation and selection to
approximately maximize a community fitness function, subject only to
constraints internal to the particular model. If the interspecies interactions
are randomly distributed on an interval including positive values, the system
evolves toward self-sustaining, mutualistic communities. In contrast, for the
predator-prey case the matrix of interactions is antisymmetric, and a nonzero
population size must be sustained by an external resource. Time series of the
diversity and population size for both models show approximate 1/f noise and
power-law distributions for the lifetimes of communities and species. For the
mutualistic model, these two lifetime distributions have the same exponent,
while their exponents are different for the predator-prey model. The difference
is probably due to greater resilience toward mass extinctions in the food-web
like communities produced by the predator-prey model.Comment: 26 pages, 12 figures. Discussion of early-time dynamics added. J.
Math. Biol., in pres
Sequential Decay Distortion of Goldhaber Model Widths for Spectator Fragments
Momentum widths of the primary fragments and observed final fragments have
been investigated within the framework of an Antisymmetrized Molecular Dynamics
transport model code (AMD-V) with a sequential decay afterburner (GEMINI). It
is found that the secondary evaporation effects cause the values of a reduced
momentum width, , derived from momentum widths of the final fragments
to be significantly less than those appropriate to the primary fragment but
close to those observed in many experiments. Therefore, a new interpretation
for experiemental momentum widths of projectile-like fragments is presented.Comment: 4 pages, 3 figs. Accepted for publication in Phys. Rev. C as a Rapid
Communicatio
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