972 research outputs found
Theoretical spin-wave dispersions in the antiferromagnetic phase AF1 of MnWO based on the polar atomistic model in P2
The spin wave dispersions of the low temperature antiferromagnetic phase
(AF1) MnWO have been numerically calculated based on the recently reported
non-collinear spin configuration with two different canting angles. A
Heisenberg model with competing magnetic exchange couplings and single-ion
anisotropy terms could properly describe the spin wave excitations, including
the newly observed low-lying energy excitation mode =0.45 meV
appearing at the magnetic zone centre. The spin wave dispersion and intensities
are highly sensitive to two differently aligned spin-canting sublattices in the
AF1 model. Thus this study reinsures the otherwise hardly provable hidden polar
character in MnWO.Comment: 7 pages, 5 figure
Nature of the spin resonance mode in CeCoIn
Spin-fluctuation-mediated unconventional superconductivity can emerge at the
border of magnetism, featuring a superconducting order parameter that changes
sign in momentum space. Detection of such a sign-change is experimentally
challenging, since most probes are not phase-sensitive. The observation of a
spin resonance mode (SRM) from inelastic neutron scattering is often seen as
strong phase-sensitive evidence for a sign-changing superconducting order
parameter, by assuming the SRM is a spin-excitonic bound state. Here, we show
that for the heavy fermion superconductor CeCoIn, its SRM defies
expectations for a spin-excitonic bound state, and is not a manifestation of
sign-changing superconductivity. Instead, the SRM in CeCoIn likely arises
from a reduction of damping to a magnon-like mode in the superconducting state,
due to its proximity to magnetic quantum criticality. Our findings emphasize
the need for more stringent tests of whether SRMs are spin-excitonic, when
using their presence to evidence sign-changing superconductivity.Comment: accepted for publication in Communications Physic
Magnetic excitations of the charge stripe electrons below half doping in La2−xSrxNiO4 (x = 0.45, 0.4)
The low energy magnetic excitation spectrum of charge stripe ordered La2−xSrxNiO4, x = 0.4 and x = 0.45 were studied by neutron scattering. Two excitation modes are observed in both materials, one from the ordered magnetic moments, and a second mode consistent with pseudo-onedimensional antiferromagnetic excitations of the charge stripe electrons (q-1D). The dispersion of the q-1D excitation follows the same relation as in x = 1/3 composition, with even spectral weight in the two counter-propagating branches of the x = 0.4, however in the x = 0.45 only one dispersion branch has any measurable spectral weight. The evolution of the q-1D excitations on doping to the checkerboard charge ordered phase is discussed
The German Young Geoscientists Group – promoting exchange and information among the next generation of geoscientists
The group „Young geoscientists” of the Senate Commission for Joint Geoscientific Research (Geokommisson, www.geokommission.de) of the German Research Foundation (DFG), is dedicated towards the development of the working environment, workforce and scientific outcome of the next generation of geoscientists in Germany.Geoscientific research – basic as, well as applied – provides crucial contributions for mastering the economic, environmental and societal challenges of the near and medium-term future. Politics and society call for immediate answers, while geoscientific phenomena are complex and act on a large range of temporal and spatial scales.These demands, together with increases mobility requirements, lead to increasing pressure especially on young geoscientists. In this situation the main goals of the group “Young geoscientists” are:Promotion of networking among young geoscientistsInformation about science policy developments, funding opportunities and other relevant mattersRepresenting the interests of young scientists towards (science)-policy makersThe dynamic development of geoscientific research, particularly collaborations across traditional disciplines, as well as in increasing demands from public and policy, calls for a continuous integration of young scientists. We promote this process by organizing round-table discussions, e.g. on “Guaranteeing good scientific praxis” or on “Hot topics and research funding”, by communicating information via the internet and by identifying structural deficiencies that might hinder the advancement of the geosciences and reporting them to decision makers. In this context, we are looking for:European or international collaboratorsYoung geoscientists wishing to participate in / contribute to our activitiesSuggestions on how to improve working conditions of the young and advancing geoscientists</ul
From the zero-field metal-insulator transition in two dimensions to the quantum Hall transition: a percolation-effective-medium theory
Effective-medium theory is applied to the percolation description of the
metal-insulator transition in two dimensions with emphasis on the continuous
connection between the zero-magnetic-field transition and the quantum Hall
transition. In this model the system consists of puddles connected via saddle
points, and there is loss of quantum coherence inside the puddles. The
effective conductance of the network is calculated using appropriate
integration over the distribution of conductances, leading to a determination
of the magnetic field dependence of the critical density. Excellent
quantitative agreement is obtained with the experimental data, which allows an
estimate of the puddle physical parameters
The METCRAX II Field Experiment: A Study of Downslope Windstorm-Type Flows in Arizona\u2019s Meteor Crater
The second Meteor Crater Experiment (METCRAX II) was conducted in October 2013 at Arizona\u2019s Meteor Crater. The experiment was designed to investigate nighttime downslope windstorm 12type flows that form regularly above the inner southwest sidewall of the 1.2-km diameter crater as a southwesterly mesoscale katabatic flow cascades over the crater rim. The objective of METCRAX II is to determine the causes of these strong, intermittent, and turbulent inflows that bring warm-air intrusions into the southwest part of the crater. This article provides an overview of the scientific goals of the experiment; summarizes the measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results
Magnetic ordering in non-centrosymmetric CePdAl and CePtAl
Owing to the hybridization of cerium's localised 4 electron and conduction
band composed of -electrons, cerium based intermetallics exhibit various
kinds of magnetic interactions. In crystals, these can result in exotic types
of magnetic ordering. In this study, we report a detailed single-crystal
neutron diffraction study on CePdAl and CePtAl. We have synthesized a
large crystal of CePdAl, which crystallizes in a non-centrosymmetric,
orthorhombic structure with space group , a new, distorted variant of
the tetragonal BaNiSn structure observed in other CeAl compounds,
such as CePtAl. Low-temperature diffraction measurements showed that
CePdAl orders in a collinear antiferromagnetic structure below T=5.3
(1) K, with magnetic moments pointing along the -axis direction and an
ordered magnetic moment =1.64(3) /Ce. Tetragonal CePtAl
shows a modulated, cycloidal type of ordering with
, and a transition temperature T=3.2 K.
Symmetry analysis allows two types of ordering, which show modulation of both
amplitude and direction of magnetic moments. These results allow to conclude
that in CeAl system the orthorhombic distortion (=Pd, Ag) releases
some underlying magnetic frustration that results in modulated types of
magnetic ordering in tetragonal compounds (=Cu,Au,Pt)
Root functioning, tree water use and hydraulic redistribution in Quercus suber trees: a modeling approach based on root sap flow
Mediterranean evergreen oaks have to survive a long summer drought. Roots may play a relevant role
under these conditions. We studied their structure and function in a mature Quercus suber L. tree in central
Portugal. The root system was mapped till the lowest water table level (4.5 m depth). Xylem anatomy
was analyzed in a vertical profile belowground. Sap flow was continuously monitored for 1.5 yrs in the
stem and roots of this intensively studied tree (heat field deformation method) and in the stem of four
trees (Granier method), in relation to environmental variables and predawn leaf water potential. The
sources of water uptake were assessed by stable isotope analyses in summer. Results showed a dimorphic
root system with a network of superficial roots linked to sinker roots, and a taproot diverting into tangles
of deep fine roots submerged for long periods, with parenchyma aerenchyma. Transpiration was not
restricted in summer due to root access to groundwater. The isotopic d18O signature of twig xylem water
was similar to that of groundwater in the dry season. Two functional types of superficial roots were identified:
shallow connected and deep connected roots. A modeling approach was built considering that each
superficial root was linked to a sinker, with part of the root deep connected (between the stem and the
sinker) and part shallow connected (between the sinker and topsoil). This conceptual framework simulated
tree stem sap flow from root sap flow with a high efficiency (R2 = 0.85) in four plot trees.
On an annual basis, soil water and groundwater contributions were 69.5% and 30.5% of stem flow,
respectively. Annual hydraulic lift and hydraulic descent were 0.9% and 37.0% of stem flow, respectively.
The trees maximize the exploitation of the environmental resources by using the topsoil water during
most of the year, and groundwater together with hydraulic lift (nutrient supply) in the dry summer. This
study shows that a dimorphic root system, with roots reaching groundwater, is an efficient strategy of Q.
suber trees to cope with seasonal drought. Knowledge of the functional behavior of Q. suber trees under
shallow water table conditions may contribute to the definition of better adapted management practices
and to anticipate their responses to climate chang
What determines auditory similarity? The effect of stimulus group and methodology.
Two experiments on the internal representation of auditory stimuli compared the pairwise and grouping methodologies as means of deriving similarity judgements. A total of 45 undergraduate students participated in each experiment, judging the similarity of short auditory stimuli, using one of the methodologies. The experiments support and extend Bonebright's (1996) findings, using a further 60 stimuli. Results from both methodologies highlight the importance of category information and acoustic features, such as root mean square (RMS) power and pitch, in similarity judgements. Results showed that the grouping task is a viable alternative to the pairwise task with N > 20 sounds whilst highlighting subtle differences, such as cluster tightness, between the different task results. The grouping task is more likely to yield category information as underlying similarity judgements
Reminiscence bump in memory for public events
People tend to recall more personal events from adolescence and early adulthood than from other lifetime periods. Most evidence suggests that differential encoding causes this reminiscence bump. However, the question why personal events are encoded better in those periods is still unanswered. To shed more light on this discussion, we examined memory for public events. Since it is often impossible to ascertain that queried events are equally difficult, we circumvented the issue of equivalence by calculating deviation scores for each trial. We found that participants more frequently answered questions correctly about events that occurred in the period in which they were between 10 and 25 years old. Furthermore, we found that the reminiscence bump was more pronounced for cued recall than for recognition. We argue that these results support the biological account that events are stored better, because the memory system is working more efficiently during adolescence and early adulthood. These results do not falsify the other accounts for differential encoding, because they are not mutually exclusive. People speak of autobiographical memory when they are referring to the memories they have of their own life experiences (Robinson, 1986). Autobiographical memory does not only consist of personal memories that are remembered vividly, but also of autobiographical facts (Brewer, 1986). Some researchers have examined the contents of autobiographical memories (e.g., Fitzgerald, 1988; Niedźwieńska, 2003; Robinson, 1976), whereas other researchers have focused on the temporal distribution of memories of personal events across the lifespan (e.g., Janssen, Chessa, &
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