4,070 research outputs found
ABC implies primitive prime divisors in arithmetic dynamic
Let K be a number field, let f(x) in K(x) be a rational function of degree d>
1, and let z in K be a wandering point such that f^n(z) is nonzero for all n >
0. We prove that if the abc-conjecture holds for K, then for all but finitely
many positive integers n, there is a prime p of K such that p | f^n(z) and p
does not divide f^m(z) for all positive integers m < n. We prove the same
result unconditionally for function fields of characteristic 0 when f is not
isotrivial.Comment: 15 page
Cosmic Perturbations Through the Cyclic Ages
We analyze the evolution of cosmological perturbations in the cyclic model,
paying particular attention to their behavior and interplay over multiple
cycles. Our key results are: (1) galaxies and large scale structure present in
one cycle are generated by the quantum fluctuations in the preceding cycle
without interference from perturbations or structure generated in earlier
cycles and without interfering with structure generated in later cycles; (2)
the ekpyrotic phase, an epoch of gentle contraction with equation of state
preceding the hot big bang, makes the universe homogeneous, isotropic
and flat within any given observer's horizon; and, (3) although the universe is
uniform within each observer's horizon, the global structure of the cyclic
universe is more complex, owing to the effects of superhorizon length
perturbations, and cannot be described in a uniform Friedmann-Robertson-Walker
picture. In particular, we show that the ekpyrotic phase is so effective in
smoothing, flattening and isotropizing the universe within the horizon that
this phase alone suffices to solve the horizon and flatness problems even
without an extended period of dark energy domination (a kind of low energy
inflation). Instead, the cyclic model rests on a genuinely novel,
non-inflationary mechanism (ekpyrotic contraction) for resolving the classic
cosmological conundrums.Comment: 28 pages, 5 figures, 1 tabl
Quantitative image mean squared displacement (iMSD) analysis of the dynamics of profilin 1 at the membrane of live cells.
Image mean square displacement analysis (iMSD) is a method allowing the mapping of diffusion dynamics of molecules in living cells. However, it can also be used to obtain quantitative information on the diffusion processes of fluorescently labelled molecules and how their diffusion dynamics change when the cell environment is modified. In this paper, we describe the use of iMSD to obtain quantitative data of the diffusion dynamics of a small cytoskeletal protein, profilin 1 (pfn1), at the membrane of live cells and how its diffusion is perturbed when the cells are treated with Cytochalasin D and/or the interactions of pfn1 are modified when its actin and polyphosphoinositide binding sites are mutated (pfn1-R88A). Using total internal reflection fluorescence microscopy images, we obtained data on isotropic and confined diffusion coefficients, the proportion of cell areas where isotropic diffusion is the major diffusion mode compared to the confined diffusion mode, the size of the confinement zones and the size of the domains of dynamic partitioning of pfn1. Using these quantitative data, we could demonstrate a decreased isotropic diffusion coefficient for the cells treated with Cytochalasin D and for the pfn1-R88A mutant. We could also see changes in the modes of diffusion between the different conditions and changes in the size of the zones of pfn1 confinements for the pfn1 treated with Cytochalasin D. All of this information was acquired in only a few minutes of imaging per cell and without the need to record thousands of single molecule trajectories
Abundances and Kinematics of Field Halo and Disk Stars I: Observational Data and Abundance Analysis
We describe observations and abundance analysis of a high-resolution,
high-S/N survey of 168 stars, most of which are metal-poor dwarfs. We follow a
self-consistent LTE analysis technique to determine the stellar parameters and
abundances, and estimate the effects of random and systematic uncertainties on
the resulting abundances. Element-to-iron ratios are derived for key alpha,
odd, Fe-peak, r- and s-process elements. Effects of Non-LTE on the analysis of
Fe I lines are shown to be very small on the average. Spectroscopically
determined surface gravities are derived that are generally close to those
obtained from Hipparcos parallaxes.Comment: 41 pages, 7 Postscript figures. Accepted for publication in the A
The composition of HB stars : RR Lyrae variables
We used moderately high-resolution, high S/N spectra to study the chemical
composition of 10 field ab-type RR Lyrae stars. A new temperature scale was
determined from literature Infrared Flux Method measures of subdwarfs and the
Kurucz (1992) model atmospheres, and used to calibrate colors for both dwarfs
and RR Lyraes. The applicability of Kurucz (1992) model atmospheres in the
analysis of RR Lyraes at minimum light was analyzed: we found that they are
able to reproduce colors, excitation and ionization equilibria as well as the
wings of Halpha. We derived abundances for 21 species. The metal abundances of
the program stars span the range -2.50<[Fe/H]<+0.17$. Lines of most elements
are found to form in LTE conditions. Fe lines satisfy very well the excitation
and ionization equilibria. RR Lyraes share the typical abundance pattern of
other stars of similar [Fe/H]: alpha-elements are overabundant by about 0.4dex
and Mn is underabundant by about 0.6dex in stars with [Fe/H]<-1. Significant
departures from LTE are found only for a few species. We used our new [Fe/H]
abundances, as well as values from Butler and coworkers (corrected to our
system), and from high resolution spectroscopy of globular clusters giants, to
obtain a new calibration of the DeltaS index: [Fe/H]= -0.194(\pm 0.011)DeltaS
-0.08(\pm 0.18) and to update the metallicity calibration of the Ca II K line
index: [Fe/H]= 0.65(\pm 0.17)W'(K) -3.49(\pm 0.39). Finally, our new
metallicity scale was used to revise the [Fe/H] dependence of the absolute
magnitude of RR Lyrae stars, Mv: Mv = 0.20(\pm 0.03)[Fe/H] + 1.06(\pm 0.04).Comment: 59 pages, Latex using aaspp.sty, ps-files of text, tables (21) and
figures (23) available from ftp://boas3.bo.astro.it/pub/gisella To appear in
October 1995 Astronomical Journa
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Gender-role beliefs and the self-perception of women with learning disabilities: meanings of motherhood and attributions for childlessness
Aims of Present study
In contrast to mainstream literature gender as a frame of reference has not been applied to people with learning disabilities. The present study emerged from the need to redress this imbalance. Specifically, the study aimed to investigate both gender-attitudes and gender typing of the self in women with learning disabilities. A further aim was to focus on one traditional female role in some detail: women's perceptions about motherhood and beliefs/experiences of childlessness.
Design and measures
The study is cross-sectional and employs a within and between groups design. Both quantitative and qualitative research paradigms were used. Part one of the study consisted of the administration of a gender inventory (OAT-PM/AM) to eighteen women with learning disabilities. A control group of eighteen non-disabled women also completed the inventory. Part two involved semi-structured interviews with six women with learning disabilities on issues relating to motherhood and childlessness.
Results
Results demonstrated some significant differences between the groups of women using the gender measure (OAT-PM/AM). Qualitative data obtained from the interviews were analysed using Interpretative Phenomenological Analysis (Smith, 1995).
Conclusions
Women with learning disabilities were found to hold less flexible gender attitudes than the non-disabled women. Furthermore, they were found to aspire to traditional female roles more than masculine roles. Interestingly, women with learning disabilities were found to engage in less traditional female activities than the non-disabled group. Data from the interviews served to highlight the distress which may be experienced by the loss of the motherhood role. Both clinical and service implications which emerged from the research are discussed
Participatory evaluation for large-scale arts programmes: challenges, adaptations and unexpected shifts in culture
Researchers at Staffordshire University have a long history of undertaking community-based research in and with communities in Stoke-on-Trent. Commitment to the principles and practice of participatory research by the university’s Creative Communities Unit (CCU) team led to an approach to participatory action research called Get Talking. This article highlights the use of Get Talking to evaluate Appetite, an Arts Council England Creative People and Places project in Stoke-on-Trent. Staffordshire University conducted a participatory evaluation using Get Talking for the three years of the programme’s first phase. As well as reflecting on the strengths of the approach, we also discuss the ways in which the approach was adapted in order to address some of the key challenges that were encountered, and the impact of taking a participatory approach to the evaluation on the programme’s culture in relation to community engagement and co-production
A Model for Abundances in Metal-Poor Stars
It is argued that the abundances of r-process related elements in stars with
-3<[Fe/H]<-1 can be explained by the contributions of three sources. The
sources are: the first generations of very massive (>100 solar masses) stars
that are formed from Big Bang debris and are distinct from SNII, and two types
of SNII, the H and L events, which can occur only at [Fe/H]>-3. The H events
are of high frequency and produce dominantly heavy (A>130) r-elements but no Fe
(presumably leaving behind black holes). The L events are of low frequency and
produce Fe and dominantly light (A<130) r-elements (essentially none above Ba).
By using the observed abundances in two ultra-metal-poor stars and the solar
r-abundances, the initial or prompt inventory of elements produced by the first
generations of very massive stars and the yields of H and L events can be
determined. The abundances of a large number of elements in a star can then be
calculated from the model by using only the observed Eu and Fe abundances. To
match the model results and the observational data for stars with -3<[Fe/H]<-1
requires that the solar r-abundances for Sr, Y, Zr, and Ba must be
significantly increased from the standard values. Whether the solar
r-components of these elements used here to obtain a fit to the stellar data
can be reconciled with those obtained from solar abundances by subtracting the
s-components calculated from models is not clear.Comment: 47 pages, 19 figures, to appear in Ap
Evolution of O Abundance Relative to Fe
We present a three-component mixing model for the evolution of O abundance
relative to Fe, taking into account the contributions of the first very massive
(> 100 solar masses) stars formed from Big Bang debris. We show that the
observations of O and Fe abundances in metal-poor stars in the Galaxy by
Israelian et al. and Boesgaard et al. can be well represented both
qualitatively and quantitatively by this model. Under the assumption of an
initial Fe ([Fe/H] = -3) and O inventory due to the prompt production by the
first very massive stars, the data at -3 < [Fe/H] < -1 are interpreted to
result from the addition of O and Fe only from type II supernovae (SNII) to the
prompt inventory. At [Fe/H] = -1, SNII still contribute O while both SNII and
type Ia supernovae contribute Fe. During this later stage, (O/Fe) sharply drops
off to an asymptotic value of 0.8(O/Fe)_sun. The value of (O/Fe) for the prompt
inventory at [Fe/H] = -3 is found to be (O/Fe) = 20(O/Fe)_sun. This result
suggests that protogalaxies with low ``metallicities'' should exhibit high
values of (O/Fe). The C/O ratio produced by the first very massive stars is
expected to be much less than 1 so that all the C should be tied up as CO and
that C dust and hydrocarbon compounds should be quite rare at epochs
corresponding to [Fe/H] < -3.Comment: 25 pages, 8 postscript figures, to appear in Ap
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