1,085 research outputs found
Effects of friction and surface tide angle of incidence on the coastal generation of internal tides
For the generation of internal waves by long surface waves, the normal-mode equations and solutions that satisfy the boundary conditions in a two-layer system are found analytically. Frictional effects decrease the amplitude of an internal wave over the shelf, changing it from a standing wave to a wave that progresses coastward and decreases the interference on the amplitude of the offshore progressive wave traveling seaward. Model studies, using a two-layer system of fresh water and saline water in a 9.9-m-long channel, gave favorable results relative to the theoretical results
Investigation of the Dzyaloshinskii-Moriya interaction and room temperature skyrmions in W/CoFeB/MgO thin films and microwires
Recent studies have shown that material structures, which lack structural
inversion symmetry and have high spin-orbit coupling can exhibit chiral
magnetic textures and skyrmions which could be a key component for next
generation storage devices. The Dzyaloshinskii-Moriya Interaction (DMI) that
stabilizes skyrmions is an anti-symmetric exchange interaction favoring
non-collinear orientation of neighboring spins. It has been shown that material
systems with high DMI can lead to very efficient domain wall and skyrmion
motion by spin-orbit torques. To engineer such devices, it is important to
quantify the DMI for a given material system. Here we extract the DMI at the
Heavy Metal (HM) /Ferromagnet (FM) interface using two complementary
measurement schemes namely asymmetric domain wall motion and the magnetic
stripe annihilation. By using the two different measurement schemes, we find
for W(5 nm)/Co20Fe60B20(0.6 nm)/MgO(2 nm) the DMI to be 0.68 +/- 0.05 mJ/m2 and
0.73 +/- 0.5 mJ/m2, respectively. Furthermore, we show that this DMI stabilizes
skyrmions at room temperature and that there is a strong dependence of the DMI
on the relative composition of the CoFeB alloy. Finally we optimize the layers
and the interfaces using different growth conditions and demonstrate that a
higher deposition rate leads to a more uniform film with reduced pinning and
skyrmions that can be manipulated by Spin-Orbit Torques
Настройка моделей при создании систем поддержки принятия стратегических решений
Показана актуальность разработки платформы (программной среды), позволяющей на её основе создавать системы стратегического управления организациями, используя сквозные технологии поддержки принятия решений и универсальные инструментальные средства. Статья посвящена решению одной из задач, возникающей при разработке такой платформы - настройке универсальных моделей поддержки принятия решений под условия принятия решений и особенности предметной области стратегического управления. Разработан механизм настройки моделей, выявлены и представлены параметры настройки
Introduction to the papers of TWG16: Learning Mathematics with Technology and Other Resources
The use of technology and other resources for mathematical learning is a current issue in the field of
mathematics education and lags behind the rapid advances in Information and Communication Technology. Technological developments offer opportunities, which are not straightforward to exploit in regular teaching. In CERME10 TWG16, the recent research findings, issues and future questions have been explored and discussed in detail. In this introductory chapter, we will outline the
scope and focus of the work, describe the results with respect to existing questions, and identify upcoming topics as well as missing topics that might set the agenda for future work in this domain
Individual grain boundary properties and overall performance of metal-organic deposition coated conductors
have investigated single grain boundaries (GBs) isolated in coated
conductors produced by metal-organic deposition. When a magnetic field is swept in the film plane, an angle-dependent crossover from boundary to grain limited critical current density J(c) is found. In the
force-free orientation, even at fields as high as 8 T, the GBs still limit Jc. We deduce that this effect is a direct consequence of GB meandering. We have employed these single GB results to explain the dependence of Jc of polycrystalline tracks on their width: in-plane measurements become flatter as the tracks are narrowed down. This result is consistent with the stronger GB limitation at field configurations close to force-free found from the isolated boundaries. Our study shows that for certain geometries even at high fields the effect of GBs cannot be neglected.This work was supported by the Engineering and Physical Sciences Research Council [grant numbers EP/C011546/1 and EP/C011554/1
Unification, KK-thresholds and the top Yukawa coupling in F-theory GUTs
In a class of F-theory SU(5) GUTs the low energy chiral mass spectrum is
obtained from rank one fermion mass textures with a hierarchical structure
organised by U(1) symmetries embedded in the exceptional E_8 group. In these
theories chiral fields reside on matter `curves' and the tree level masses are
computed from integrals of overlapping wavefuctions of the particles at the
triple intersection points. This calculation requires knowledge of the exact
form of the wavefuctions. In this work we propose a way to obtain a reliable
estimate of the various quantities which determine the strength of the Yukawa
couplings. We use previous analysis of KK threshold effects to determine the
(ratios of) heavy mass scales of the theory which are involved in the
normalization of the wave functions. We consider similar effects from the
chiral spectrum of these models and discuss possible constraints on the
emerging matter content. In this approach, we find that the Yukawa couplings
can be determined solely from the U(1) charges of the states in the
`intersection' and the torsion which is a topological invariant quantity. We
apply the results to a viable SU(5) model with minimal spectrum which satisfies
all the constraints imposed by our analysis. We use renormalization group
analysis to estimate the top and bottom masses and find that they are in
agreement with the experimental values.Comment: 28 pages, 2 figure
Chiral symmetry breaking of magnetic vortices by sample roughness
Finite-element micromagnetic simulations are employed to study the chiral
symmetry breaking of magnetic vortices, caused by the surface roughness of
thin-film magnetic structures. An asymmetry between vortices with different
core polarizations has been experimentally observed for square-shaped
platelets. E.g., the threshold fields for vortex core switching were found to
differ for core up and down. This asymmetry was however not expected for these
symmetrically-shaped structures, where both core polarizations should behave
symmetrically. Three-dimensional finite element simulations are employed to
show that a small surface roughness can break the symmetry between vortex cores
pointing up and down. A relatively small sample roughness is found sufficient
to reproduce the experimentally observed asymmetries. It arises from the lack
of mirror-symmetry of the rough thin-film structures, which causes vortices
with different handedness to exhibit asymmetric dynamics
Gauge Fluxes in F-theory and Type IIB Orientifolds
We provide a detailed correspondence between G_4 gauge fluxes in F-theory
compactifications with SU(n) and SU(n)x(1) gauge symmetry and their Type IIB
orientifold limit. Based on the resolution of the relevant F-theory Tate models
we classify the factorisable G_4-fluxes and match them with the set of
universal D5-tadpole free U(1)-fluxes in Type IIB. Where available, the global
version of the universal spectral cover flux corresponds to Type IIB gauge flux
associated with a massive diagonal U(1). In U(1)-restricted Tate models extra
massless abelian fluxes exist which are associated with specific linear
combinations of Type IIB fluxes. Key to a quantitative match between F-theory
and Type IIB is a proper treatment of the conifold singularity encountered in
the Sen limit of generic F-theory models. We also shed further light on the
brane recombination process relating generic and U(1)-restricted Tate models.Comment: 53 pages, 3 figures; v2: Refs added; v3: minor corrections to match
version published in JHE
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