295 research outputs found
Local phase space control and interplay of classical and quantum effects in dissociation of a driven Morse oscillator
This work explores the possibility of controlling the dissociation of a
monochromatically driven one-dimensional Morse oscillator by recreating
barriers, in the form of invariant tori with irrational winding ratios, at
specific locations in the phase space. The control algorithm proposed by Huang
{\it et al.} (Phys. Rev. A {\bf 74}, 053408 (2006)) is used to obtain an
analytic expression for the control field. We show that the control term,
approximated as an additional weaker field, is efficient in recreating the
desired tori and suppresses the classical as well as the quantum dissociation.
However, in the case when the field frequency is tuned close to a two-photon
resonance the local barriers are not effective in suppressing the dissociation.
We establish that in the on-resonant case quantum dissociation primarily occurs
via resonance-assisted tunneling and controlling the quantum dynamics requires
a local perturbation of the specific nonlinear resonance in the underlying
phase space.Comment: 12 pages, 6 figures (reduced quality), submitted to Phys. Rev.
Curvilinearity provides additional information to lung clearance index only in a minority of children with early cystic fibrosis lung disease
Curvilinearity, as calculated from multiple-breath washout, is abnormal in a small number of children with cystic fibrosis when other tests are still normal https://bit.ly/3p9QAV4
Optical RKKY Interaction between Charged Semiconductor Quantum Dots
We show how a spin interaction between electrons localized in neighboring
quantum dots can be induced and controlled optically. The coupling is generated
via virtual excitation of delocalized excitons and provides an efficient
coherent control of the spins. This quantum manipulation can be realized in the
adiabatic limit and is robust against decoherence by spontaneous emission.
Applications to the realization of quantum gates, scalable quantum computers,
and to the control of magnetization in an array of charged dots are proposed.Comment: 4 pages, 2 figure
Cryo-EM structure in situ reveals a molecular switch that safeguards virus against genome loss
The portal protein is a key component of many double-stranded DNA viruses, governing capsid assembly and genome packaging. Twelve subunits of the portal protein define a tunnel, through which DNA is translocated into the capsid. It is unknown how the portal protein functions as a gatekeeper, preventing DNA slippage, whilst allowing its passage into the capsid, and how these processes are controlled. A cryo-EM structure of the portal protein of thermostable virus P23-45, determined in situ in its procapsid-bound state, indicates a mechanism that naturally safeguards the virus against genome loss. This occurs via an inversion of the conformation of the loops that define the constriction in the central tunnel, accompanied by a hydrophilic-hydrophobic switch. The structure also shows how translocation of DNA into the capsid could be modulated by a changing mode of protein-protein interactions between portal and capsid, across a symmetry-mismatched interface
Many-body theory for systems with particle conversion: Extending the multiconfigurational time-dependent Hartree method
We derive a multiconfigurational time-dependent Hartree theory for systems
with particle conversion. In such systems particles of one kind can convert to
another kind and the total number of particles varies in time. The theory thus
extends the scope of the available and successful multiconfigurational
time-dependent Hartree methods -- which were solely formulated for and applied
to systems with a fixed number of particles -- to new physical systems and
problems. As a guiding example we treat explicitly a system where bosonic atoms
can combine to form bosonic molecules and vise versa. In the theory for
particle conversion, the time-dependent many-particle wavefunction is written
as a sum of configurations made of a different number of particles, and
assembled from sets of atomic and molecular orbitals. Both the expansion
coefficients and the orbitals forming the configurations are time-dependent
quantities that are fully determined according to the Dirac-Frenkel
time-dependent variational principle. Particular attention is paid to the
reduced density matrices of the many-particle wavefunction that appear in the
theory and enter the equations of motion. There are two kinds of reduced
density matrices: particle-conserving reduced density matrices which directly
only couple configurations with the same number of atoms and molecules, and
particle non-conserving reduced density matrices which couple configurations
with a different number of atoms and molecules. Closed-form and compact
equations of motion are derived for contact as well as general two-body
interactions, and their properties are analyzed and discussed.Comment: 46 page
Diversity and Host Interactions Among Virulent and Temperate Baltic Sea Flavobacterium Phages
Viruses in aquatic environments play a key role in microbial population dynamics and nutrient cycling. In particular, bacteria of the phylum Bacteriodetes are known to participate in recycling algal blooms. Studies of phage-host interactions involving this phylum are hence important to understand the processes shaping bacterial and viral communities in the ocean as well as nutrient cycling. In this study, we isolated and sequenced three strains of flavobacteria-LMO6, LMO9, LMO8-and 38 virulent phages infecting them. These phages represent 15 species, occupying three novel genera. Additionally, one temperate phage was induced from LMO6 and was found to be competent at infecting LMO9. Functions could be predicted for a limited number of phage genes, mainly representing roles in DNA replication and virus particle formation. No metabolic genes were detected. While the phages isolated on LMO8 could infect all three bacterial strains, the LMO6 and LMO9 phages could not infect LMO8. Of the phages isolated on LMO9, several showed a host-derived reduced efficiency of plating on LMO6, potentially due to differences in DNA methyltransferase genes. Overall, these phage-host systems contribute novel genetic information to our sequence databases and present valuable tools for the study of both virulent and temperate phages
Unification of the conditional probability and semiclassical interpretations for the problem of time in quantum theory
We show that the time-dependent Schr\"odinger equation (TDSE) is the
phenomenological dynamical law of evolution unraveled in the classical limit
from a timeless formulation in terms of probability amplitudes conditioned by
the values of suitably chosen internal clock variables, thereby unifying the
conditional probability interpretation (CPI) and the semiclassical approach for
the problem of time in quantum theory. Our formalism stems from an exact
factorization of the Hamiltonian eigenfunction of the clock plus system
composite, where the clock and system factors play the role of marginal and
conditional probability amplitudes, respectively. Application of the Variation
Principle leads to a pair of exact coupled pseudoeigenvalue equations for these
amplitudes, whose solution requires an iterative self-consistent procedure. The
equation for the conditional amplitude constitutes an effective "equation of
motion" for the quantum state of the system with respect to the clock
variables. These coupled equations also provide a convenient framework for
treating the back-reaction of the system on the clock at various levels of
approximation. At the lowest level, when the WKB approximation for the marginal
amplitude is appropriate, in the classical limit of the clock variables the
TDSE for the system emerges as a matter of course from the conditional
equation. In this connection, we provide a discussion of the characteristics
required by physical systems to serve as good clocks. This development is seen
to be advantageous over the original CPI and semiclassical approach since it
maintains the essence of the conventional formalism of quantum mechanics,
admits a transparent interpretation, avoids the use of the Born-Oppenheimer
approximation, and resolves various objections raised about them.Comment: 10 pages. Typographical errors correcte
Dynamical Localization: Hydrogen Atoms in Magnetic and Microwave fields
We show that dynamical localization for excited hydrogen atoms in magnetic
and microwave fields takes place at quite low microwave frequency much lower
than the Kepler frequency. The estimates of localization length are given for
different parameter regimes, showing that the quantum delocalization border
drops significantly as compared to the case of zero magnetic field. This opens
up broad possibilities for laboratory investigations.Comment: revtex, 11 pages, 3 figures, to appear in Phys. Rev. A, Feb (1997
Kicked Bose-Hubbard systems and kicked tops -- destruction and stimulation of tunneling
In a two-mode approximation, Bose-Einstein condensates (BEC) in a double-well
potential can be described by a many particle Hamiltonian of Bose-Hubbard type.
We focus on such a BEC whose interatomic interaction strength is modulated
periodically by -kicks which represents a realization of a kicked top.
In the (classical) mean-field approximation it provides a rich mixed phase
space dynamics with regular and chaotic regions. By increasing the
kick-strength a bifurcation leads to the appearance of self-trapping states
localized on regular islands. This self-trapping is also found for the many
particle system, however in general suppressed by coherent many particle
tunneling oscillations. The tunneling time can be calculated from the
quasi-energy splitting of the corresponding Floquet states. By varying the
kick-strength these quasi-energy levels undergo both avoided and even actual
crossings. Therefore stimulation or complete destruction of tunneling can be
observed for this many particle system
“Nitrogen offset in N2 multiple washout method”. Katie J. Bayfield, Eric Alton, Samantha Irving, Andrew Bush, Jane C. Davies. ERJ Open Res 2019; 6: 00043-2020
This article was originally published with the sentence “Thank you for the opportunity to respond to the correspondence by J.G. Nielsen from Innovision about our recent paper”. The authors have since been made aware that J.G. Nielsen sold Innovision ApS (Glamsbjerg, Denmark) prior to the submission of his correspondence and, at the time of writing, has no financial interests in any business relating to lung clearance index technologies. This sentence has now been changed to “Thank you for the opportunity to respond to the correspondence by J.G. Nielsen about our recent paper” in the article itself
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