45,825 research outputs found
A covariant gauge-invariant three-dimensional description of relativistic bound-states
A formalism is presented which allows covariant three-dimensional bound-state
equations to be derived systematically from four-dimensional ones without the
use of delta-functions. The amplitude for the interaction of a bound state
described by these equations with an electromagnetic probe is constructed. This
amplitude is shown to be gauge invariant if the formalism is truncated at the
same coupling-constant order in both the interaction kernel of the integral
equation and the electromagnetic current operator.Comment: 17 pages, RevTeX, uses BoxedEPS.te
Morphological Phase Diagram for Lipid Membrane Domains with Entropic Tension
Circular domains in phase-separated lipid vesicles with symmetric leaflet composition commonly exhibit three stable morphologies: flat, dimpled, and budded. However, stable dimples (i.e., partially budded domains) present a puzzle since simple elastic theories of domain shape predict that only flat and spherical budded domains are mechanically stable in the absence of spontaneous curvature. We argue that this inconsistency arises from the failure of the constant surface tension ensemble to properly account for the effect of entropic bending fluctuations. Formulating membrane elasticity within an entropic tension ensemble, wherein tension represents the free energy cost of extracting membrane area from thermal bending of the membrane, we calculate a morphological phase diagram that contains regions of mechanical stability for each of the flat, dimpled, and budded domain morphologies
Chiral effective theory predictions for deuteron form factor ratios at low Q^2
We use chiral effective theory to predict the deuteron form factor ratio
G_C/G_Q as well as ratios of deuteron to nucleon form factors. These ratios are
calculated to next-to-next-to-leading order. At this order the chiral expansion
for the NN isoscalar charge operator (including consistently calculated 1/M
corrections) is a parameter-free prediction of the effective theory. Use of
this operator in conjunction with NLO and NNLO chiral effective theory wave
functions produces results that are consistent with extant experimental data
for Q^2 < 0.35 GeV^2. These wave functions predict a deuteron quadrupole moment
G_Q(Q^2=0)=0.278-0.282 fm^2-with the variation arising from short-distance
contributions to this quantity. The variation is of the same size as the
discrepancy between the theoretical result and the experimental value. This
motivates the renormalization of G_Q via a two-nucleon operator that couples to
quadrupole photons. After that renormalization we obtain a robust prediction
for the shape of G_C/G_Q at Q^2 < 0.3 GeV^2. This allows us to make precise,
model-independent predictions for the values of this ratio that will be
measured at the lower end of the kinematic range explored at BLAST. We also
present results for the ratio G_C/G_M.Comment: 31 pages, 7 figure
Structural domain and spin ordering induced glassy magnetic phase in single layered manganite PrSrMnO
The single layered manganite PrSrMnO undergoes
structural transition from high temperature tetragonal phase to low temperature
orthorhombic phase below room temperature. The orthorhombic phase was reported
to have two structural variants with slightly different lattice parameters and
Mn-3 levels show orbital ordering within both the variants, albeit having
mutually perpendicular ordering axis. In addition to orbital ordering, the
orthorhombic variants also order antiferromagnetically with different N\'eel
temperatures. Our magnetic investigation on the polycrystalline sample of
PrSrMnO shows large thermal hysteresis indicating the
first order nature of the tetragonal to orthorhombic transition. We observe
magnetic memory, large relaxation, frequency dependent ac susceptbility and
aging effects at low temperature, which indicate spin glass like magnetic
ground state in the sample. The glassy magnetic state presumably arises from
the interfacial frustration of orthorhombic domains with orbital and spin
orderings playing crucial role toward the competing magnetic interactions.Comment: 6 pages, 4 figures, Accepted in Europhysics Letter
Instabilities in Josephson Ladders with Current Induced Magnetic Fields
We report on a theoretical analysis, consisting of both numerical and
analytic work, of the stability of synchronization of a ladder array of
Josephson junctions under the influence of current induced magnetic fields.
Surprisingly, we find that as the ratio of the mutual to self inductance of the
cells of the array is increased a region of unstable behavior occurs followed
by reentrant stable synchronization. Analytic work tells us that in order to
understand fully the cause of the observed instabilities the behavior of the
vertical junctions, sometimes ignored in analytic analyses of ladder arrays,
must be taken into account.Comment: RevTeX, 4 pages, 3 figure
ICT as learning media and research instrument: What eResearch can offer for those who research eLearning?
Students‘ interactions in digital learning environments are distributed over time and space, and many aspects of eLearning phenomenon cannot be investigated using traditional research approaches. At the same time, the possibility to collect digital data about students‘ online interactions and learning opens a range of new opportunities to use ICT as research tool and apply new research approaches. This symposium brings together some of the recent advancements in the area of ICT-enhanced research and aims to discuss future directions for methodological innovation in this area. The session will include four presentations that will explore different directions of ICT use for eLearning research
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