9,504 research outputs found
Splitting Sensitivity of the Ground and 7.6 eV Isomeric States of 229Th
The lowest-known excited state in nuclei is the 7.6 eV isomer of 229Th. This
energy is within the range of laser-based investigations that could allow
accurate measurements of possible temporal variation of this energy splitting.
This in turn could probe temporal variation of the fine-structure constant or
other parameters in the nuclear Hamiltonian. We investigate the sensitivity of
this transition energy to these quantities. We find that the two states are
predicted to have identical deformations and thus the same Coulomb energies
within the accuracy of the model (viz., within roughly 30 keV). We therefore
find no enhanced sensitivity to variation of the fine-structure constant. In
the case of the strong interaction the energy splitting is found to have a
complicated dependence on several parameters of the interaction, which makes an
accurate prediction of sensitivity to temporal changes of fundamental constants
problematical. Neither the strong- nor Coulomb-interaction contributions to the
energy splitting of this doublet can be constrained within an accuracy better
than a few tens of keV, so that only upper limits can be set on the possible
sensitivity to temporal variations of the fundamental constants.Comment: 4 pages, 2 figure
Effect of Age and Food Novelty on Food Memory
The influence of age of the consumer and food novelty on incidentally learned food memory was investigated by providing a meal containing novel and familiar target items under the pretense of a study on hunger feelings to 34 young and 36 older participants in France and to 24 young and 20 older participants in Denmark and testing them a day later on recognition of the targets among a set of distractors that were variations of the target made by adding or subtracting taste (sour or sweet) or aroma (orange or red berry flavor). Memory was also tested by asking participants to indicate whether the target and the distractors were equal to or less or more intense than the remembered target in sourness sweetness and aroma. The results showed that when novelty is defined as whether people know or not a given product, it has a strong influence on memory performance, but that age did not, the elderly performing just as well as the young. The change in the distractors was more readily detected with familiar than with novel targets where the participants were still confused by the target itself. Special attention is given to the influence of the incidental learning paradigm on the outcome and to the ways in which it differs from traditional recognition experiments
The relevance of a rules-based maize marketing policy : an experimental case study of Zambia
Strategic interaction between public and private actors is increasingly recognized as an important determinant of agricultural market performance in Africa and elsewhere. Trust and consultation tend to positively affect private activity while uncertainty of government behavior impedes it. This paper reports on a laboratory experiment based on a stylized model of the Zambian maize market. The experiment facilitates a comparison between discretionary interventionism and a rules-based policy in which the government pre-commits itself to a future course of action. A simple precommitment rule can, in theory, overcome the prevailing strategic dilemma by encouraging private sector participation. Although this result is also borne out in the economic experiment, the improvement in private sector activity is surprisingly small and not statistically significant due to irrationally cautious choices by experimental governments. Encouragingly, a rules-based policy promotes a much more stable market outcome, thereby substantially reducing the risk of severe food shortages. These results underscore the importance of predictable and transparent rules for the state's involvement in agricultural markets.Markets and Market Access,Food&Beverage Industry,Public Sector Corruption&Anticorruption Measures,Food Security,Access to Markets
The mass-metallicity relation for high-redshift damped Ly-alpha galaxies
We used our database of ESO VLT-UVES spectra of quasars to build up a sample
of 67 Damped Lyman-alpha (DLA) systems with redshifts 1.7<zabs<3.7. For each
system, we measured average metallicities relative to Solar, [X/H] (with either
X=Zn, S or Si), and the velocity widths of low-ionization line profiles, W1. We
find that there is a tight correlation between the two quantities, detected at
the 5sigma significance level. The existence of such a correlation, over more
than two orders of magnitude spread in metallicity, is likely to be the
consequence of an underlying mass-metallicity relation for the galaxies
responsible for DLA absorption lines. The best-fit linear relation is
[X/H]=1.35(\pm 0.11)\log W1 -3.69(\pm 0.18)$ with W1 expressed in km/s. While
the slope of this velocity-metallicity relation is the same within
uncertainties between the higher and the lower redshift bins of our sample,
there is a hint of an increase of the intercept point of the relation with
decreasing redshift. This suggests that galaxy halos of a given mass tend to
become more metal-rich with time. Moreover, the slope of this relation is
consistent with that of the luminosity-metallicity relation for local galaxies.
The DLA systems having the lowest metallicities among the DLA population would
therefore, on average, correspond to the galaxies having the lowest masses. In
turn, these galaxies should have the lowest luminosities among the DLA galaxy
population. This may explain the recent result that the few DLA systems with
detected Ly-alpha emission have higher than average metallicities.Comment: proceedings of IAU Colloquium No. 199, 2005, ``Probing Galaxies
through Quasar Absorption Lines'', P.R. Williams, C. Shu, B. Menard, ed
Mass-metallicity relation from z=5 to the present: Evidence for a transition in the mode of galaxy growth at z=2.6 due to the end of sustained primordial gas infall
We analyze the redshift evolution of the mass-metallicity relation in a
sample of 110 Damped Ly absorbers spanning the redshift range
and find that the zero-point of the correlation changes
significantly with redshift. The evolution is such that the zero-point is
constant at the early phases of galaxy growth (i.e. no evolution) but then
features a sharp break at with a rapid incline towards lower
redshifts such that damped absorbers of identical masses are more metal rich at
later times than earlier. The slope of this mass metallicity correlation
evolution is dex per unit redshift.
We compare this result to similar studies of the redshift evolution of
emission selected galaxy samples and find a remarkable agreement with the slope
of the evolution of galaxies of stellar mass log.
This allows us to form an observational tie between damped absorbers and
galaxies seen in emission.
We use results from simulations to infer the virial mass of the dark matter
halo of a typical DLA galaxy and find a ratio .
We compare our results to those of several other studies that have reported
strong transition-like events at redshifts around and argue that
all those observations can be understood as the consequence of a transition
from a situation where galaxies were fed more unprocessed infalling gas than
they could easily consume to one where they suddenly become infall starved and
turn to mainly processing, or re-processing, of previously acquired gas.Comment: 8 pages, 5 figures, accepted for publication in MNRA
Breakup of Air Bubbles in Water: Memory and Breakdown of Cylindrical Symmetry
Using high-speed video, we have studied air bubbles detaching from an
underwater nozzle. As a bubble distorts, it forms a thin neck which develops a
singular shape as it pinches off. As in other singularities, the minimum neck
radius scales with the time until breakup. However, because the air-water
interfacial tension does not drive breakup, even small initial cylindrical
asymmetries are preserved throughout the collapse. This novel, non-universal
singularity retains a memory of the nozzle shape, size and tilt angle. In the
last stages, the air appears to tear instead of pinch.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figures. Revised for
resubmissio
Modulation of L-lactate release by astrocytic GABA<sub>B</sub> receptors and cyclic AMP signalling in vitro
Antigen-induced strain-specific autoantiidiotypic antibodies modulate the immune response to dextran B 512.
Sera from CBA and C57BL mice immunized against dextran B 512 eight or more days earlier contain mainly IgG antibodies that specifically suppress the development of plaque-forming cells against dextran in vitro. Suppression was not caused by antibodies against the alpha 1-6 epitope of dextran to any major extent. Sera from CBA mice (IgCH allotype j) suppressed plaque-forming cells from CBA mice, whereas sera from C57BL mice (allotype b) inhibited plaques from C57BL and CBA/Ig-1b mice. Sera from dextran-tolerant mice or from mice that are genetic unresponders to dextran did not suppress plaque-forming cells. Both thymus-independent and thymus-dependent forms of dextran induced the appearance of these autoantiidiotypic antibodies that can distinguish between anti-alpha 1-6 antibodies produced in mouse strains having different IgCH-locus-determined allotypes
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