2,024 research outputs found
Entanglement and Superdense Coding with Linear Optics
We discuss a scheme for a full superdense coding of entangled photon states
employing only linear-optics elements. By using the mixed basis consisting of
four states that are unambiguously distinguishable by a standard and polarizing
beam splitters we can deterministically transfer four messages by manipulating
just one of the two entangled photons. The sender achieves the determinism of
the transfer either by giving up the control over 50% of sent messages
(although known to her) or by discarding 33% of incoming photons.Comment: 8 pages, 1 figur
Nonequilibrium Green's functions and atom-surface dynamics: Simple views from a simple model system
We employ Non-equilibrium Green's functions (NEGF) to describe the real-time
dynamics of an adsorbate-surface model system exposed to ultrafast laser
pulses. For a finite number of electronic orbitals, the system is solved
exactly and within different levels of approximation. Specifically i) the full
exact quantum mechanical solution for electron and nuclear degrees of freedom
is used to benchmark ii) the Ehrenfest approximation (EA) for the nuclei, with
the electron dynamics still treated exactly. Then, using the EA, electronic
correlations are treated with NEGF within iii) 2nd Born and with iv) a recently
introduced hybrid scheme, which mixes 2nd Born self-energies with
non-perturbative, local exchange-correlation potentials of Density Functional
Theory (DFT). Finally, the effect of a semi-infinite substrate is considered:
we observe that a macroscopic number of de-excitation channels can hinder
desorption. While very preliminary in character and based on a simple and
rather specific model system, our results clearly illustrate the large
potential of NEGF to investigate atomic desorption, and more generally, the non
equilibrium dynamics of material surfaces subject to ultrafast laser fields.Comment: 10 pages, 5 figure
Casimir attractive-repulsive transition in MEMS
Unwanted stiction in micro- and nanomechanical (NEMS/MEMS) systems due to
dispersion (van der Waals, or Casimir) forces is a significant hurdle in the
fabrication of systems with moving parts on these length scales. Introducing a
suitably dielectric liquid in the interspace between bodies has previously been
demonstrated to render dispersion forces repulsive, or even to switch sign as a
function of separation. Making use of recently available permittivity data
calculated by us we show that such a remarkable non-monotonic Casimir force,
changing from attractive to repulsive as separation increases, can in fact be
observed in systems where constituent materials are in standard NEMS/MEMS use
requiring no special or exotic materials. No such nonmonotonic behaviour has
been measured to date. We calculate the force between a silica sphere and a
flat surface of either zinc oxide or hafnia, two materials which are among the
most prominent for practical microelectrical and microoptical devices. Our
results explicate the need for highly accurate permittivity functions of the
materials involved for frequencies from optical to far-infrared frequencies. A
careful analysis of the Casimir interaction is presented, and we show how the
change in the sign of the interaction can be understood as a result of multiple
crossings of the dielectric functions of the three media involved in a given
set-up.Comment: 6 pages, 4 figure
Interface damage modeled by spring boundary conditions for in-plane elastic waves
In-plane elastic wave propagation in the presence of a damaged interface is investigated. The damage is modeled as a distribution of small cracks and this is transformed into a spring boundary condition. First the scattering by a single interface crack is determined explicitly in the low frequency limit for the case of a plane wave normally incident to the interface. The transmission at an interface with a random distribution of small cracks is then determined and is compared to periodically distributed cracks. The cracked interface is then described by a distributed spring boundary condition. As an illustration the dispersion relation of the first modes in a thick plate with a damaged interface in the middle is given
Comment on "Thermal Effects on the Casimir Force in the 0.1-5 micrometer Range"
In a recent paper (M. Bostrom and Bo E. Sernelius, Phys. Rev. Lett. 84, 4757
(2000)) the combined effect of finite conductivity and finite temperature on
the Casimir force is analyzed, and significant deviations from other
theoretical results and a recent experiment are obtained.
In this Comment, I show that the extrapolation to zero frequency is incorrect
because the authors have neglected that the wavenumber and frequency of the
electromagentic mode must simultaneously appraoch zeroComment: Final version (two previous versions, first was partly incorrect)
Rejected by PRL
Compositional nanodomain formation in hybrid formate perovskites
We report the synthesis and structural characterisation of three mixed-metal
formate perovskite families [C(NH)]MCu(HCOO) (M = Mn,
Zn, Mg). Using a combination of infrared spectroscopy, non-negative matrix
factorization, and reverse Monte Carlo refinement, we show that the Mn- and
Zn-containing compounds support compositional nanodomains resembling the polar
nanoregions of conventional relaxor ferroelectrics. The M = Mg family exhibits
a miscibility gap that we suggest reflects the limiting behaviour of nanodomain
formation.Comment: 4 pages, 3 figure
Non-Perturbative Theory of Dispersion Interactions
Some open questions exist with fluctuation-induced forces between extended
dipoles. Conventional intuition derives from large-separation perturbative
approximations to dispersion force theory. Here we present a full
non-perturbative theory. In addition we discuss how one can take into account
finite dipole size corrections. It is of fundamental value to investigate the
limits of validity of the perturbative dispersion force theory.Comment: 9 pages, no figure
VACCINATION AGAINST SWINE FLU CAUSED NARCOLEPSY IN SEVERAL EUROPEAN COUNTRIES
Publisher Copyright: © 2020 Boström I., Lindberger O., Partinen M., Landtblom A.M. All Rights Reserved.Narcolepsy is a rare sleeping disorder that gives sleep onset rapid eye movement periods and excessive daytime sleepiness. It is divided into two subgroups, narcolepsy type 1 where there also is orexin deficiency and cataplexy and narcolepsy type 2 that lack these features. Narcolepsy type 1 is assumed to be an autoimmune disease with destruction of orexin-producing cells. The pathology behind is unclear. There is a strong association to a class II HLA allele, HLADQB1*06:02 and the H1N1-virus and streptococcal infections has also been associated with narcolepsy. The severity of narcolepsy differs between patients from those who can manage their disease without medication to those who has a severe impact on their everyday life. There is a diagnostic delay between the onset of symptoms and time for diagnosis that in some cases can be more than a decade. The global mean prevalence is 30 per 100 000 inhabitants. The incidence in children in northern Europe has risen since 2010. An early study of the 2009 H1N1 influenza A pandemic indicated a high mortality and prompted efforts to rapidly come up with a vaccine. One of these was Pandemrix that was the most widely used in Europe and 61 % of the inhabitants in Sweden was vaccinated. Studies have shown an increased incidence of narcolepsy type 1 in European countries that had used Pandemrix, but no increased risk was seen in countries that had used other vaccines than Pandemrix.Peer reviewe
Controlling the magnetic state of the proximate quantum spin liquid α-RuCl<sub>3</sub> with an optical cavity
Harnessing the enhanced light-matter coupling and quantum vacuum fluctuations resulting from mode volume compression in optical cavities is a promising route towards functionalizing quantum materials and realizing exotic states of matter. Here, we extend cavity quantum electrodynamical materials engineering to correlated magnetic systems, by demonstrating that a Fabry-Pérot cavity can be used to control the magnetic state of the proximate quantum spin liquid α-RuCl3. Depending on specific cavity properties such as the mode frequency, photon occupation, and strength of the light-matter coupling, any of the magnetic phases supported by the extended Kitaev model can be stabilized. In particular, in the THz regime, we show that the cavity vacuum fluctuations alone are sufficient to bring α-RuCl3 from a zigzag antiferromagnetic to a ferromagnetic state. By external pumping of the cavity in the few photon limit, it is further possible to push the system into the antiferromagnetic Kitaev quantum spin liquid state
Vascular endothelium plays a key role in directing pulmonary epithelial cell differentiation.
The vascular endothelium is critical for induction of appropriate lineage differentiation in organogenesis. In this study, we report that dysfunctional pulmonary endothelium, resulting from the loss of matrix Gla protein (MGP), causes ectopic hepatic differentiation in the pulmonary epithelium. We demonstrate uncontrolled induction of the hepatic growth factor (HGF) caused by dysregulated cross talk between pulmonary endothelium and epithelium in Mgp-null lungs. Elevated HGF induced hepatocyte nuclear factor 4 α (Hnf4a), which competed with NK2 homeobox 1 (Nkx2.1) for binding to forkhead box A2 (Foxa2) to drive hepatic differentiation in Mgp-null airway progenitor cells. Limiting endothelial HGF reduced Hnf4a, abolished interference of Hnf4a with Foxa2, and reduced hepatic differentiation in Mgp-null lungs. Together, our results suggest that endothelial-epithelial interactions, maintained by MGP, are essential in pulmonary cell differentiation
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