333 research outputs found
Magnetic ordering in GdNi2B2C revisited by resonant x-ray scattering: evidence for the double-q model
Recent theoretical efforts aimed at understanding the nature of
antiferromagnetic ordering in GdNi2B2C predicted double-q ordering. Here we
employ resonant elastic x-ray scattering to test this theory against the
formerly proposed, single-q ordering scenario. Our study reveals a satellite
reflection associated with a mixed-order component propagation wave vector,
viz., (q_a,2q_b,0) with q_b = q_a approx= 0.55 reciprocal lattice units, the
presence of which is incompatible with single-q ordering but is expected from
the double-q model. A (3q_a,0,0) wave vector (i.e., third-order) satellite is
also observed, again in line with the double-q model. The temperature
dependencies of these along with that of a first-order satellite are compared
with calculations based on the double-q model and reasonable qualitative
agreement is found. By examining the azimuthal dependence of first-order
satellite scattering, we show the magnetic order to be, as predicted,
elliptically polarized at base temperature and find the temperature dependence
of the "out of a-b plane" moment component to be in fairly good agreement with
calculation. Our results provide qualitative support for the double-q model and
thus in turn corroborate the explanation for the "magnetoelastic paradox"
offered by this model.Comment: 8 pages, 5 figures. Submitted to Phys. Rev.
The malleability of uranium: manipulating the charge-density wave in epitaxial films
We report x-ray synchrotron experiments on epitaxial films of uranium,
deposited on niobium and tungsten seed layers. Despite similar lattice
parameters for these refractory metals, the uranium epitaxial arrangements are
different and the strains propagated along the a-axis of the uranium layers are
of opposite sign. At low temperatures these changes in epitaxy result in
dramatic modifications to the behavior of the charge-density wave in uranium.
The differences are explained with the current theory for the electron-phonon
coupling in the uranium lattice. Our results emphasize the intriguing
possibilities of producing epitaxial films of elements that have complex
structures like the light actinides uranium to plutonium.Comment: 6 pages, 6 figure
Emergence of a Dynamic Super-Structural Order Integrating Antiferroelectric and Antiferrodistortive Competing Instabilities in EuTiO3
Microscopic structural instabilities of EuTiO3 single crystal were
investigated by synchrotron x-ray diffraction. Antiferrodistortive (AFD) oxygen
octahedral rotational order was observed alongside Ti derived antiferroelectric
(AFE) distortions. The competition between the two instabilities is reconciled
through a cooperatively modulated structure allowing both to coexist. The
electric and magnetic field effect on the modulated AFD order shows that the
origin of large magnetoelectric coupling is based upon the dynamic equilibrium
between the AFD - antiferromagnetic interactions versus the electric
polarization - ferromagnetic interactions
A TRADE LIBERALIZATION IN INTERNATIONAL DAIRY MARKETS
International dairy industries remain among the most distorted agricultural sectors. Dairy average bound tariffs remain among the highest of all agricultural commodities, and dairy trade is characterized by a large number of megatariffs and tariff-rate quotas (TRQs). The objective of our study is to examine how the international dairy markets might respond to policy changes under various assumptions, using a partial equilibrium, multiple-commodity, multiple-region model of agricultural policy and trade. Our results indicate that liberalization will reduce supplies, increase dairy trade, and raise world prices.Dairy Markets, Trade Liberalization, Model, Policy, International Relations/Trade,
Comment on "Correlation between Compact Radio Lout Quasars and Ultrahigh Energy Cosmic Rays"
In a recent paper, Farrar and Biermann argue that there is a strong
correlation between the direction of the five highest-energy cosmic-ray events
and compact, radio-loud quasars. This Comment shows that this analysis contains
several inconsistencies and errors so that the significance of any such
correlation is certainly greatly overestimated and perhaps nonexistent.Comment: 2 pages, REVTE
The effect of a 24-hour photoperiod on the survival, growth and swim bladder inflation of pre-flexion yellowfin tuna (Thunnus albacares) larvae
The effects of two different continuous photoperiod regimes on survival, growth and swim bladder inflation of pre-flexion yellowfin tuna (Thunnus albacares) larvae were investigated. Each photoperiod regime was tested twice with a different larval cohort to confirm the observed results. Trials 1 and 2 tested the effect of a reduced night-time light intensity (10-molesm-2s-1=30% of the daytime intensity) and found that those larvae reared for 8days under the 24h lighting (24-L) photoperiod exhibited a slight improvement in survival compared to those reared under the control photoperiod of 12h light (12-L), however these improvements were not significant. In addition, those larvae reared under this photoperiod regime were equal in length to those in the control. Trials 3 and 4 compared the same variables in larvae reared under a continuous photoperiod (24-L) with a constant light intensity of 30-molesm-2s-1, against those reared under the aforementioned 12-L photoperiod. Survival of larvae under the continuous photoperiods were 9±1% (n=2) and 10±2% (n=3) for Trials 3 and 4, respectively, compared to less than 1% in both control treatments; differences that in both cases were highly significant. In addition, in both trials larvae cultured under the 24-L photoperiod were significantly larger and exhibited more advanced development than those reared under the 12-L photoperiod, however swim bladder inflation was significantly lower. We suggest that the improved survival and growth achieved under a continuous photoperiod is due to the extended foraging time combined with the prevention of mortality caused by night-time sinking
AGRICULTURAL POLICY REFORM IN THE WTO: THE ROAD AHEAD
Agricultural trade barriers and producer subsidies inflict real costs, both on the countries that use these policies and on their trade partners. Trade barriers lower demand for trade partners' products, domestic subsidies can induce an oversupply of agricultural products which depresses world prices, and export subsidies create increased competition for producers in other countries. Eliminating global agricultural policy distortions would result in an annual world welfare gain of $56 billion. High protection for agricultural commodities in the form of tariffs continues to be the major factor restricting world trade. In 2000, World Trade Organization (WTO) members continued global negotiations on agricultural policy reform. To help policymakers and others realize what is at stake in the global agricultural negotiations, this report quantifies the costs of global agricultural distortions and the potential benefits of their full elimination. It also analyzes the effects on U.S. and world agriculture if only partial reform is achieved in liberalizing tariffs, tariff-rate quotas (limits on imported goods), domestic support, and export subsidies.Agricultural and Food Policy, International Relations/Trade,
A Large Scale Double Beta and Dark Matter Experiment: GENIUS
The recent results from the HEIDELBERG-MOSCOW experiment have demonstrated
the large potential of double beta decay to search for new physics beyond the
Standard Model. To increase by a major step the present sensitivity for double
beta decay and dark matter search much bigger source strengths and much lower
backgrounds are needed than used in experiments under operation at present or
under construction. We present here a study of a project proposed recently,
which would operate one ton of 'naked' enriched GErmanium-detectors in liquid
NItrogen as shielding in an Underground Setup (GENIUS). It improves the
sensitivity to neutrino masses to 0.01 eV. A ten ton version would probe
neutrino masses even down to 10^-3 eV. The first version would allow to test
the atmospheric neutrino problem, the second at least part of the solar
neutrino problem. Both versions would allow in addition significant
contributions to testing several classes of GUT models. These are especially
tests of R-parity breaking supersymmetry models, leptoquark masses and
mechanism and right-handed W-boson masses comparable to LHC. The second issue
of the experiment is the search for dark matter in the universe. The entire
MSSM parameter space for prediction of neutralinos as dark matter particles
could be covered already in a first step of the full experiment - with the same
purity requirements but using only 100 kg of 76Ge or even of natural Ge -
making the experiment competitive to LHC in the search for supersymmetry.
The layout of the proposed experiment is discussed and the shielding and
purity requirements are studied using GEANT Monte Carlo simulations. As a
demonstration of the feasibility of the experiment first results of operating a
'naked' Ge detector in liquid nitrogen are presented.Comment: 22 pages, 12 figures, see also
http://pluto.mpi-hd.mpg.de/~betalit/genius.htm
Highly Pathogenic H5N1 Avian Influenza: Entry Pathways into North America via Bird Migration
Given the possibility of highly pathogenic H5N1 avian influenza arriving in North America and monitoring programs that have been established to detect and track it, we review intercontinental movements of birds. We divided 157 bird species showing regular intercontinental movements into four groups based on patterns of movement—one of these groups (breed Holarctic, winter Eurasia) fits well with the design of the monitoring programs (i.e., western Alaska), but the other groups have quite different movement patterns, which would suggest the importance of H5N1 monitoring along the Pacific, Atlantic, and Gulf coasts of North America
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