165,315 research outputs found
Research on the drag reduction performance induced by the counterflowing jet for waverider with variable blunt radii
Waverider will endure the huge aero-heating in the hypersonic flow, thus, it need be blunt for the leading edge. However, the aerodynamic performance will decrease for the blunt waverider because of the drag hoik. How to improve the aerodynamic performance and reduce the drag and aero-heating is very important. The variable blunt radii method will improve the aerodynamic performance, however, the huge aero-heating and bow shock wave at the head is still serious. In the current study, opposing jet is used in the waverider with variable blunt radii to improve its performance. The three-dimensional coupled implicit Reynolds-averaged Navier-Stokes(RANS) equation and the two equation SST kâÏ turbulence model have been utilized to obtain the flow field properties. The numerical method has been validated against the available experimental data in the open literature. The obtained results show that the L/D will drop 7â8% when R changes from 2 to 8. The lift coefficient will increase, and the drag coefficient almost keeps the same when the variable blunt radii method is adopted, and the L/D will increase. The variable blunt radii method is very useful to improve the whole characteristics of blunt waverider and the L/D can improve 3%. The combination of the variable blunt radii method and opposing jet is a novel way to improve the whole performance of blunt waverider, and L/D can improve 4â5%. The aperture as a novel way of opposing jet is suitable for blunt waverider and also useful to improve the aerodynamic and aerothermodynamic characteristics of waverider in the hypersonic flow. There is the optimal P0in/P0 that can make the detached shock wave reattach the lower surface again so that the blunt waverider can get the better aerodynamic performance
Field-induced quantum fluctuations in the heavy fermion superconductor CeCu2Ge2
Quantum-mechanical fluctuations in strongly correlated electron systems cause
unconventional phenomena such as non-Fermi liquid behavior, and arguably high
temperature superconductivity. Here we report the discovery of a field-tuned
quantum critical phenomenon in stoichiometric CeCu2Ge2, a spin density wave
ordered heavy fermion metal that exhibits unconventional superconductivity
under ~ 10 GPa of applied pressure. Our finding of the associated quantum
critical spin fluctuations of the antiferromagnetic spin density wave order,
dominating the local fluctuations due to single-site Kondo effect, provide new
information about the underlying mechanism that can be important in
understanding superconductivity in this novel compound.Comment: Heavy Fermion, Quantum Critical Phenomeno
Physics with Coherent Matter Waves
This review discusses progress in the new field of coherent matter waves, in
particular with respect to Bose-Einstein condensates. We give a short
introduction to Bose-Einstein condensation and the theoretical description of
the condensate wavefunction. We concentrate on the coherence properties of this
new type of matter wave as a basis for fundamental physics and applications.
The main part of this review treats various measurements and concepts in the
physics with coherent matter waves. In particular we present phase manipulation
methods, atom lasers, nonlinear atom optics, optical elements, interferometry
and physics in optical lattices. We give an overview of the state of the art in
the respective fields and discuss achievements and challenges for the future
Competing mechanisms of stress-assisted diffusivity and stretch-activated currents in cardiac electromechanics
We numerically investigate the role of mechanical stress in modifying the
conductivity properties of the cardiac tissue and its impact in computational
models for cardiac electromechanics. We follow a theoretical framework recently
proposed in [Cherubini, Filippi, Gizzi, Ruiz-Baier, JTB 2017], in the context
of general reaction-diffusion-mechanics systems using multiphysics continuum
mechanics and finite elasticity. In the present study, the adapted models are
compared against preliminary experimental data of pig right ventricle
fluorescence optical mapping. These data contribute to the characterization of
the observed inhomogeneity and anisotropy properties that result from
mechanical deformation. Our novel approach simultaneously incorporates two
mechanisms for mechano-electric feedback (MEF): stretch-activated currents
(SAC) and stress-assisted diffusion (SAD); and we also identify their influence
into the nonlinear spatiotemporal dynamics. It is found that i) only specific
combinations of the two MEF effects allow proper conduction velocity
measurement; ii) expected heterogeneities and anisotropies are obtained via the
novel stress-assisted diffusion mechanisms; iii) spiral wave meandering and
drifting is highly mediated by the applied mechanical loading. We provide an
analysis of the intrinsic structure of the nonlinear coupling using
computational tests, conducted using a finite element method. In particular, we
compare static and dynamic deformation regimes in the onset of cardiac
arrhythmias and address other potential biomedical applications
Numerical method to optimize the Polar-Azimuthal Orientation of Infrared Superconducting Nanowire Single-Photon Detectors
A novel finite-element method for calculating the illumination-dependence of
absorption in three-dimensional nanostructures is presented based on the RF
module of the COMSOL software package. This method is capable of numerically
determining the optical response and near-field distribution of sub-wavelength
periodic structures as a function of illumination orientations specified by
polar angle, fi, and azimuthal angle, gamma. The method was applied to
determine the illumination-angle-dependent absorptance in cavity-based
superconducting-nanowire single-photon detector (SNSPD) designs.
Niobium-nitride stripes based on dimensions of conventional SNSPDs and
integrated with ~ quarter-wavelength hydrogensilsesquioxane-filled nano-optical
cavities and covered by a thin gold film acting as a reflector were illuminated
from below by p-polarized light in this study. The numerical results were
compared to results from complementary transfer-matrix-method calculations on
composite layers made of analogous film-stacks. This comparison helped to
uncover the optical phenomena contributing to the appearance of extrema in the
optical response. This paper presents an approach to optimizing the absorptance
of different sensing and detecting devices via simultaneous numerical
optimization of the polar and azimuthal illumination angles.Comment: 15 pages, 4 figure
FĂ©nyhullĂĄmhosszon Ă©s rezgĂ©sidĆn belĂŒli skĂĄlĂĄkon szuperintenzĂv lĂ©zerterekben keltett legĂșjabb nemlineĂĄris ''attofizikai'' folyamatok elmĂ©leti Ă©s kĂsĂ©rleti vizsgĂĄlata. = Theoretical and experimental study of the newest nonlinear processes of ''attophysics'' generated by superintense laser fields within the light wavelength and oscillation period scale.
SzĂĄmos fĂ©ny-anyag kölcsönhatĂĄsra vonatkozĂł kĂsĂ©rleti vizsgĂĄlatot vĂ©geztĂŒnk el, femtoszekundumos, kevĂ©s ciklusĂș impulzusok ĂĄltal indukĂĄlt fotoemissziĂł Ă©s felĂŒleti plazmonok ĂĄltal erĆsĂtett elektrongyorsĂtĂĄs jelensĂ©gĂ©re vonatkozĂłan. Ezen kĂvĂŒl fejlesztĂ©seket hajtottunk vĂ©gre egy femtoszekundumos hosszĂș rezonĂĄtoros csörpölt impulzusĂș lĂ©zer oszcillĂĄtoron. Ez a fĂ©nyforrĂĄs nagyon hasznos eszköz a fent emlĂtett kĂsĂ©rletekben. A elmĂ©leti kutatĂĄsok sorĂĄn az attoszekundumos fizika, a nagy intenzitĂĄsĂș fĂ©ny-anyag kölcsönhatĂĄs Ă©s a kvantumoptika terĂŒletĂ©n vĂ©gezĂŒnk vizsgĂĄlatokat. A projekt sorĂĄn ezekbĆl az elmĂ©leti Ă©s kĂsĂ©rleti tĂ©mĂĄkbĂłl 19 referĂĄlt nemzetközi folyĂłiratbeli publikĂĄciĂł jelent meg. | We investigated several light-matter interaction phenomena experimentally, including few-cycle pulse-induced photoemission and surface plasmon enhanced electron acceleration. We have carried out femtosecond laser development based on long-cavity, chirped-pulse laser oscillators. These sources provide very useful tools for the above mentioned experiments. In terms of theoretical studies, we investigated various field in attosecond physics, high-intensity light-matter interaction and quantum optics. These experimental and theoretical studies yielded 19 peer-reviewed journal publications during the duration of the project
Complementarity and Scientific Rationality
Bohr's interpretation of quantum mechanics has been criticized as incoherent
and opportunistic, and based on doubtful philosophical premises. If so Bohr's
influence, in the pre-war period of 1927-1939, is the harder to explain, and
the acceptance of his approach to quantum mechanics over de Broglie's had no
reasonable foundation. But Bohr's interpretation changed little from the time
of its first appearance, and stood independent of any philosophical
presuppositions. The principle of complementarity is itself best read as a
conjecture of unusually wide scope, on the nature and future course of
explanations in the sciences (and not only the physical sciences). If it must
be judged a failure today, it is not because of any internal inconsistency.Comment: 29 page
Coupled magnetic plasmons in metamaterials
Magnetic metamaterials consist of magnetic resonators smaller in size than
their excitation wavelengths. Their unique electromagnetic properties were
characterized by the effective media theory at the early stage. However, the
effective media model does not take into account the interactions between
magnetic elements; thus, the effective properties of bulk metamaterials are the
result of the "averaged effect" of many uncoupled resonators. In recent years,
it has been shown that the interaction between magnetic resonators could lead
to some novel phenomena and interesting applications that do not exist in
conventional uncoupled metamaterials. In this paper, we will give a review of
recent developments in magnetic plasmonics arising from the coupling effect in
metamaterials. For the system composed of several identical magnetic
resonators, the coupling between these units produces multiple discrete
resonance modes due to hybridization. In the case of a system comprising an
infinite number of magnetic elements, these multiple discrete resonances can be
extended to form a continuous frequency band by strong coupling. This kind of
broadband and tunable magnetic metamaterial may have interesting applications.
Many novel metamaterials and nanophotonic devices could be developed from
coupled resonator systems in the future.Comment: 10 papges, 10 figures, It is a review paper about coupled magnetic
metamaterial
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