219 research outputs found
Exciton dissociation at donor-acceptor polymer heterojunctions: quantum nonadiabatic dynamics and effective-mode analysis
The quantum-dynamical mechanism of photoinduced subpicosecond exciton
dissociation and the concomitant formation of a charge-separated state at a
TFB:F8BT polymer heterojunction is elucidated. The analysis is based upon a
two-state vibronic coupling Hamiltonian including an explicit 24-mode
representation of a phonon bath comprising high-frequency (CC stretch) and
low-frequency (torsional) modes. The initial relaxation behavior is
characterized by coherent oscillations, along with the decay through an
extended nonadiabatic coupling region. This region is located in the vicinity
of a conical intersection hypersurface. A central ingredient of the analysis is
a novel effective mode representation, which highlights the role of the
low-frequency modes in the nonadiabatic dynamics. Quantum dynamical simulations
were carried out using the multiconfiguration time-dependent Hartree (MCTDH)
method
The mystery of relationship of mechanics and field in the many-body quantum world
We have revealed three fatal errors incurred from a blind transferring of
quantum field methods into the quantum mechanics. This had tragic consequences
because it produced crippled model Hamiltonians, unfortunately considered
sufficient for a description of solids including superconductors. From there,
of course, Fr\"ohlich derived wrong effective Hamiltonian, from which incorrect
BCS theory arose.
1) Mechanical and field patterns cannot be mixed. Instead of field methods
applied to the mechanical Born-Oppenheimer approximation we have entirely to
avoid it and construct an independent and standalone field pattern. This leads
to a new form of the Bohr's complementarity on the level of composite systems.
2) We have correctly to deal with the center of gravity, which is under the
field pattern "materialized" in the form of new quasipartiles - rotons and
translons. This leads to a new type of relativity of internal and external
degrees of freedom and one-particle way of bypassing degeneracies (gap
formation).
3) The possible symmetry cannot be apriori loaded but has to be aposteriori
obtained as a solution of field equations, formulated in a general form without
translational or any other symmetry. This leads to an utterly revised view of
symmetry breaking in non-adiabatic systems, namely Jahn-Teller effect and
superconductivity. These two phenomena are synonyms and share a unique symmetry
breaking.Comment: 24 pages, 9 sections; remake of abstract, introduction and
conclusion; more physics, less philosoph
ExaHyPE: An engine for parallel dynamically adaptive simulations of wave problems
ExaHyPE (“An Exascale Hyperbolic PDE Engine”) is a software engine for solving systems of first-order hyperbolic partial differential equations (PDEs). Hyperbolic PDEs are typically derived from the conservation laws of physics and are useful in a wide range of application areas. Applications powered by ExaHyPE can be run on a student’s laptop, but are also able to exploit thousands of processor cores on state-of-the-art supercomputers. The engine is able to dynamically increase the accuracy of the simulation using adaptive mesh refinement where required. Due to the robustness and shock capturing abilities of ExaHyPE’s numerical methods, users of the engine can simulate linear and non-linear hyperbolic PDEs with very high accuracy. Users can tailor the engine to their particular PDE by specifying evolved quantities, fluxes, and source terms. A complete simulation code for a new hyperbolic PDE can often be realised within a few hours — a task that, traditionally, can take weeks, months, often years for researchers starting from scratch. In this paper, we showcase ExaHyPE’s workflow and capabilities through real-world scenarios from our two main application areas: seismology and astrophysics
Low-energy unphysical saddle in polynomial molecular potentials
Vibrational spectra of polyatomic molecules are often obtained from a
polynomial expansion of the adiabatic potential around a minimum. For several
molecules, we show that such an approximation displays an unphysical saddle
point of comparatively small energy, leading to a region where the potential is
negative and unbounded. This poses an upper limit for a reliable evaluation of
vibrational levels. We argue that the presence of such saddle points is
general.Comment: The preprint version of the published Mol. Phys. paper, 19 pages, 3
figure
Megascopic Quantum Phenomena. A Critical Study of Physical Interpretations
A megascopic revalidation is offered providing responses and resolutions of
current inconsistencies and existing contradictions in present-day quantum
theory. As the core of this study we present an independent proof of the
Goldstone theorem for a quantum field formulation of molecules and solids.
Along with phonons two types of new quasiparticles appear: rotons and
translons. In full analogy with Lorentz covariance, combining space and time
coordinates, a new covariance is necessary, binding together the internal and
external degrees of freedom, without explicitly separating the centre-of-mass,
which normally applies in both classical and quantum formulations. The
generally accepted view regarding the lack of a simple correspondence between
the Goldstone modes and broken symmetries, has significant consequences: an
ambiguous BCS theory as well as a subsequent Higgs mechanism. The application
of the archetype of the classical spontaneous symmetry breaking, i.e. the
Mexican hat, as compared to standard quantum relations, i.e. the Jahn-Teller
effect, superconductivity or the Higgs mechanism, becomes a disparity. In
short, symmetry broken states have a microscopic causal origin, but transitions
between them have a teleological component. The different treatments of the
problem of the centre of gravity in quantum mechanics and in field theories
imply a second type of Bohr complementarity on the many-body level opening the
door for megascopic representations of all basic microscopic quantum axioms
with further readings for teleonomic megascopic quantum phenomena, which have
no microscopic rationale: isomeric transitions, Jahn-Teller effect, chemical
reactions, Einstein-de Haas effect, superconductivity-superfluidity, and
brittle fracture.Comment: 117 pages, 17 sections, final revised version from 20 May 2019 but
uploaded after the DOI was know
Technical design of the phase I Mu3e experiment
The Mu3e experiment aims to find or exclude the lepton flavour violating decay μ→eee at branching fractions above 10−16. A first phase of the experiment using an existing beamline at the Paul Scherrer Institute (PSI) is designed to reach a single event sensitivity of 2⋅10−15. We present an overview of all aspects of the technical design and expected performance of the phase I Mu3e detector. The high rate of up to 108 muon decays per second and the low momenta of the decay electrons and positrons pose a unique set of challenges, which we tackle using an ultra thin tracking detector based on high-voltage monolithic active pixel sensors combined with scintillating fibres and tiles for precise timing measurements
Technical design of the phase I Mu3e experiment
The Mu3e experiment aims to find or exclude the lepton flavour violating
decay at branching fractions above . A first
phase of the experiment using an existing beamline at the Paul Scherrer
Institute (PSI) is designed to reach a single event sensitivity of . We present an overview of all aspects of the technical design and
expected performance of the phase~I Mu3e detector. The high rate of up to
muon decays per second and the low momenta of the decay electrons and
positrons pose a unique set of challenges, which we tackle using an ultra thin
tracking detector based on high-voltage monolithic active pixel sensors
combined with scintillating fibres and tiles for precise timing measurements.Comment: 114 pages, 185 figures. Submitted to Nuclear Instruments and Methods
A. Edited by Frank Meier Aeschbacher This version has many enhancements for
better readability and more detail
Permian high-temperature metamorphism in the Western Alps (NW Italy)
During the late Palaeozoic, lithospheric thinning in part of the Alpine realm caused high-temperature low-to-medium pressure metamorphism and partial melting in the lower crust. Permian metamorphism and magmatism has extensively been recorded and dated in the Central, Eastern, and Southern Alps. However, Permian metamorphic ages in the Western Alps so far are constrained by very few and sparsely distributed data. The present study fills this gap. We present U/Pb ages of metamorphic zircon from several Adria-derived continental units now situated in the Western Alps, defining a range between 286 and 266 Ma. Trace element thermometry yields temperatures of 580-890°C from Ti-in-zircon and 630-850°C from Zr-in-rutile for Permian metamorphic rims. These temperature estimates, together with preserved mineral assemblages (garnet-prismatic sillimanite-biotite-plagioclase-quartz-K-feldspar-rutile), define pervasive upper-amphibolite to granulite facies conditions for Permian metamorphism. U/Pb ages from this study are similar to Permian ages reported for the Ivrea Zone in the Southern Alps and Austroalpine units in the Central and Eastern Alps. Regional comparison across the former Adriatic and European margin reveals a complex pattern of ages reported from late Palaeozoic magmatic and metamorphic rocks (and relics thereof): two late Variscan age groups (~330 and ~300 Ma) are followed seamlessly by a broad range of Permian ages (300-250 Ma). The former are associated with late-orogenic collapse; in samples from this study these are weakly represented. Clearly, dominant is the Permian group, which is related to crustal thinning, hinting to a possible initiation of continental rifting along a passive margin
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