5,147 research outputs found
Controlled biomineralization of magnetite (Fe<sub>3</sub>O<sub>4</sub>) by <i>Magnetospirillum gryphiswaldense</i>
Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (∼14-67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range
Deciphering nonfemtoscopic two-pion correlations in collisions with simple analytical models
A simple model of nonfemtoscopic particle correlations in proton-proton
collisions is proposed. The model takes into account correlations induced by
the conservation laws as well as correlations induced by minijets. It
reproduces well the two-pion nonfemtoscopic correlations of like-sign and
unlike-sign pions in proton-proton collision events at GeV
analyzed by the ALICE Collaboration. We also argue that similar nonfemtoscopic
correlations can appear in the hydrodynamic picture with event-by-event
fluctuating nonsymmetric initial conditions that are typically associated with
nonzero higher-order flow harmonics.Comment: 21 pages, 10 figures, misprints correcte
Particle Size Determination: An undergraduate lab in Mie scattering
A technique for determining the size of microscopic spherical particles using light scattering is presented as an undergraduate physics lab. Scatterer size is determined from angular scattering distribution measurements of laser light scattered from a dilute suspension of latex spheres with diameters of 4.99±0.05 and 6.038±0.045 μm. Previous experiments of this type used approximate theoretical corrections and required the construction of specialized sample cells to minimize complicating effects. As a significant improvement to these, we generate angular scattering distributions from Mie theory and, using an accurate numerical procedure, correct these distributions for Snell’s law and foreshortening effects. Scatterer size is then determined using a fast, robust fitting algorithm to compare these corrected angular scattering distributions to measured angular scattering distributions. We fit the scatter from a solution of 6.04-μm-diam spheres to spheres of 5.95±0.11 μm diameter, and that from a solution of 4.99-μm spheres to 4.85±0.15 μm. Additionally, scattering data for a 2:1 mixture of spheres of diameters 4.99 and 6.04 μm are taken, and after numerical adjustment for Snell’s law and foreshortening effects, good agreement with theory is obtained
Flavor in Supersymmetry with an Extended R-symmetry
We propose a new solution to the supersymmetric flavor problem without
flavor-blind mediation. Our proposal is to enforce a continuous or a suitably
large discrete R-symmetry on weak scale supersymmetry, so that Majorana gaugino
masses, trilinear A-terms, and the mu-term are forbidden. We find that
replacing the MSSM with an R-symmetric supersymmetric model allows order one
flavor-violating soft masses, even for squarks of order a few hundred GeV. The
minimal R-symmetric supersymmetric model contains Dirac gaugino masses and
R-symmetric Higgsino masses with no left-right mixing in the squark or slepton
sector. Dirac gaugino masses of order a few TeV with vanishing A-terms solve
most flavor problems, while the R-symmetric Higgs sector becomes important at
large tan(beta). epsilon_K can be accommodated if CP is preserved in the SUSY
breaking sector, or if there is a moderate flavor degeneracy, which can arise
naturally. epsilon'/epsilon, as well as neutron and electron EDMs are easily
within experimental bounds. The most striking phenomenological distinction of
this model is the order one flavor violation in the squark and slepton sector,
while the Dirac gaugino masses tend to be significantly heavier than the
corresponding squark and slepton masses.Comment: 15 pages, REVTEX4, 9 figure files, typos fixed, refs added, published
versio
Solving the Hierarchy Problem with Exponentially Large Dimensions
In theories with (sets of) two large extra dimensions and supersymmetry in
the bulk, the presence of non-supersymmetric brane defects naturally induces a
logarithmic potential for the volume of the transverse dimensions. Since the
logarithm of the volume rather than the volume itself is the natural variable,
parameters of O(10) in the potential can generate an exponentially large size
for the extra dimensions. This provides a true solution to the hierarchy
problem, on the same footing as technicolor or dynamical supersymmetry
breaking. The area moduli have a Compton wavelength of about a millimeter and
mediate Yukawa interactions with gravitational strength. We present a simple
explicit example of this idea which generates two exponentially large
dimensions. In this model, the area modulus mass is in the millimeter range
even for six dimensional Planck scales as high as 100 TeV.Comment: 13 pages, 7 figures, corrected typo
Obstacles Faced by Latina Mothers of Children with Autism
Abstract The CDC's most recent autism prevalence estimates document the continued trend of higher prevalence among non-Hispanic white children compared to Hispanic children. The disproportionate underrepresentation of Latino children in the health, education and service systems is measurable, disadvantaging the child and family. This quantitative study identifies support needs and obstacles experienced by 96 Latina mothers of children with autism, active in Spanish-language parent groups in California. Study measures included the Family Needs Survey and the Caring for My Child Survey. To determine the significance of the results on the Family Needs Survey, an item-by-item chi-square analysis compared results to those of to a similar population from a different study that used the same measure. A high proportion of mothers reported substantial levels of unmet needs in their role as primary caregiver using the Family Needs Survey: all 35 survey items were unmet for at least 50% of mothers; 28 items were common needs. The level and number of unmet needs of mothers in the present study in areas such as social support and care services were significantly greater than the comparison group. On the Caring for My Child Survey, mothers identified multiple barriers personally encountered in obtaining assistance for their children including psychosocial, economic, political, and healthcare factors. Findings are relevant to improve access for Latinos in the health, education and service systems, and to establish a baseline for comparison
Superrevivals in the quantum dynamics of a particle confined in a finite square well potential
We examine the revival features in wave packet dynamics of a particle
confined in a finite square well potential. The possibility of tunneling
modifies the revival pattern as compared to an infinite square well potential.
We study the dependence of the revival times on the depth of the square well
and predict the existence of superrevivals. The nature of these superrevivals
is compared with similar features seen in the dynamics of wavepackets in an
anharmonic oscillator potential.Comment: 8 pages in Latex two-column format with 5 figures (eps). To appear in
Physical Review
Defining forgiveness: Christian clergy and general population perspectives.
The lack of any consensual definition of forgiveness is a serious weakness in the research literature (McCullough, Pargament & Thoresen, 2000). As forgiveness is at the core of Christianity, this study returns to the Christian source of the concept to explore the meaning of forgiveness for practicing Christian clergy. Comparisons are made with a general population sample and social science definitions of forgiveness to ensure that a shared meaning of forgiveness is articulated. Anglican and Roman Catholic clergy (N = 209) and a general population sample (N = 159) completed a postal questionnaire about forgiveness. There is agreement on the existence of individual differences in forgiveness. Clergy and the general population perceive reconciliation as necessary for forgiveness while there is no consensus within psychology. The clergy suggests that forgiveness is limitless and that repentance is unnecessary while the general population suggests that there are limits and that repentance is necessary. Psychological definitions do not conceptualize repentance as necessary for forgiveness and the question of limits has not been addressed although within therapy the implicit assumption is that forgiveness is limitless.</p
Excitation-assisted inelastic processes in trapped Bose-Einstein condensates
We find that inelastic collisional processes in Bose-Einstein condensates
induce local variations of the mean-field interparticle interaction and are
accompanied by the creation/annihilation of elementary excitation. The physical
picture is demonstrated for the case of three body recombination in a trapped
condensate. For a high trap barrier the production of high energy trapped
single particle excitations results in a strong increase of the loss rate of
atoms from the condensate.Comment: 4 pages, no figure
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