1,812 research outputs found
The Aharonov-Bohm effect: the role of tunneling and associated forces
Through tunneling, or barrier penetration, small wavefunction tails can enter
a finitely shielded cylinder with a magnetic field inside. When the shielding
increases to infinity the Lorentz force goes to zero together with these tails.
However, it is shown, by considering the radial derivative of the wavefunction
on the cylinder surface, that a flux dependent force remains. This force
explains in a natural way the Aharonov-Bohm effect in the idealized case of
infinite shielding.Comment: 13 pages, 3 figures; minor changes, references added, typo corrected
in eq. (16). Accepted for publication in Journal of Physics
Experimental magnetic form factors in Co3V2O8: A combined study of ab initio calculations, magnetic Compton scattering and polarized neutron diffraction
We present a combination of ab initio calculations, magnetic Compton
scattering and polarized neutron experiments, which elucidate the density
distribution of unpaired electrons in the kagome staircase system Co3V2O8. Ab
initio wave functions were used to calculate the spin densities in real and
momentum space, which show good agreement with the respective experiments. It
has been found that the spin polarized orbitals are equally distributed between
the t2g and the eg levels for the spine (s) Co ions, while the eg orbitals of
the cross-tie (c) Co ions only represent 30% of the atomic spin density.
Furthermore, the results reveal that the magnetic moments of the cross-tie Co
ions, which are significantly smaller than those of the spine Co ions in the
zero-field ferromagnetic structure, do not saturate by applying an external
magnetic field of 2 T along the easy axis a, but that the increasing bulk
magnetization originates from induced magnetic moments on the O and V sites.
The refined individual magnetic moments are mu(Co_c)=1.54(4) mu_B,
mu(Co_s)=2.87(3) mu_B, mu(V)=0.41(4) mu_B, mu(O1)=0.05(5) mu_B, mu(O2)=0.35(5)
mu_B, and; mu(O3)=0.36(5) mu_B combining to the same macroscopic magnetization
value, which was previously only attributed to the Co ions
Privacy regulation and online advertising
Advertisers use online customer data to target their marketing appeals. This has heightened consumers' privacy concerns, leading governments to pass laws designed to protect consumer privacy by restricting the use of data and by restricting online tracking techniques used by websites. We use the responses of 3.3 million survey takers who had been randomly exposed to 9,596 online display (banner) advertising campaigns to explore how privacy regulation in the European Union (EU) has influenced advertising effectiveness. This privacy regulation restricted advertisers' ability to collect data on Web users in order to target ad campaigns. We find that, on average, display advertising became far less effective at changing stated purchase intent after the EU laws were enacted, relative to display advertising in other countries. The loss in effectiveness was more pronounced for websites that had general content (such as news sites), where non-data-driven targeting is particularly hard to do. The loss of effectiveness was also more pronounced for ads with a smaller presence on the webpage and for ads that did not have additional interactive, video, or audio features
The nature of iron-oxygen vacancy defect centers in PbTiO3
The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy
forms a charged defect associate, oriented along the crystallographic c-axis.
Its microscopic structure has been analyzed in detail comparing results from a
semi-empirical Newman superposition model analysis based on finestructure data
and from calculations using density functional theory.
Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor
center. The position of the iron ion in the ferroelectric phase is found to be
similar to the B-site in the paraelectric phase. Partial charge compensation is
locally provided by a directly coordinated oxygen vacancy.
Using high-resolution synchrotron powder diffraction, it was verified that
lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of
1.0721.Comment: 11 pages, 5 figures, accepted in Phys. Rev.
RNA:protein ratio of the unicellular organism as a characteristic of phosphorous and nitrogen stoichiometry and of the cellular requirement of ribosomes for protein synthesis
Background
Mean phosphorous:nitrogen (P:N) ratios and relationships of P:N ratios with the growth rate of organisms indicate a surprising similarity among and within microbial species, plants, and insect herbivores. To reveal the cellular mechanisms underling this similarity, the macromolecular composition of seven microorganisms and the effect of specific growth rate (SGR) on RNA:protein ratio, the number of ribosomes, and peptide elongation rate (PER) were analyzed under different conditions of exponential growth.
Results
It was found that P:N ratios calculated from RNA and protein contents in these particular organisms were in the same range as the mean ratios reported for diverse organisms and had similar positive relationships with growth rate, consistent with the growth-rate hypothesis. The efficiency of protein synthesis in microorganisms is estimated as the number of active ribosomes required for the incorporation of one amino acid into the synthesized protein. This parameter is calculated as the SGR:PER ratio. Experimental and theoretical evidence indicated that the requirement of ribosomes for protein synthesis is proportional to the RNA:protein ratio. The constant of proportionality had the same values for all organisms, and was derived mechanistically from the characteristics of the protein-synthesis machinery of the cell (the number of nucleotides per ribosome, the average masses of nucleotides and amino acids, the fraction of ribosomal RNA in the total RNA, and the fraction of active ribosomes). Impairment of the growth conditions decreased the RNA:protein ratio and increased the overall efficiency of protein synthesis in the microorganisms.
Conclusion
Our results suggest that the decrease in RNA:protein and estimated P:N ratios with decrease in the growth rate of the microorganism is a consequence of an increased overall efficiency of protein synthesis in the cell resulting from activation of the general stress response and increased transcription of cellular maintenance genes at the expense of growth related genes. The strong link between P:N stoichiometry, RNA:protein ratio, ribosomal requirement for protein synthesis, and growth rate of microorganisms indicated by the study could be used to characterize the N and P economy of complex ecosystems such as soils and the oceans
Holonomy in the Schwarzschild-Droste Geometry
Parallel transport of vectors in curved spacetimes generally results in a
deficit angle between the directions of the initial and final vectors. We
examine such holonomy in the Schwarzschild-Droste geometry and find a number of
interesting features that are not widely known. For example, parallel transport
around circular orbits results in a quantized band structure of holonomy
invariance. We also examine radial holonomy and extend the analysis to spinors
and to the Reissner-Nordstr\"om metric, where we find qualitatively different
behavior for the extremal () case. Our calculations provide a toolbox
that will hopefully be useful in the investigation of quantum parallel
transport in Hilbert-fibered spacetimes.Comment: 18 Latex pages, 3 figures. Second replacement. This version as
published in CQG with some misprints correcte
The Single-Particle density of States, Bound States, Phase-Shift Flip, and a Resonance in the Presence of an Aharonov-Bohm Potential
Both the nonrelativistic scattering and the spectrum in the presence of the
Aharonov-Bohm potential are analyzed. The single-particle density of states
(DOS) for different self-adjoint extensions is calculated. The DOS provides a
link between different physical quantities and is a natural starting point for
their calculation. The consequences of an asymmetry of the S matrix for the
generic self-adjoint extension are examined.
I. Introduction
II. Impenetrable flux tube and the density of states
III. Penetrable flux tube and self-adjoint extensions
IV. The S matrix and scattering cross sections
V. The Krein-Friedel formula and the resonance
VI. Regularization
VII. The R --> 0 limit and the interpretation of self-adjoint extensions
VIII. Energy calculations
IX. The Hall effect in the dilute vortex limit
X. Persistent current of free electrons in the plane pierced by a flux tube
XI. The 2nd virial coefficient of nonrelativistic interacting anyons
XII. Discussion of the results and open questionsComment: 68 pages, plain latex, 7 figures, 3 references and one figure added
plus a few minor text correction
Depression at Work, Authenticity in Question: Experiencing, Concealing and Revealing
Australia and the UK have both introduced policies to protect employees who experience mental illness, including depression. However, a better understanding of the issues workers face (e.g. sense of moral failure) is needed for the provision of appropriate and beneficial support. We analysed 73 interviews from the UK and Australia where narratives of depression and work intersected. Participants encountered difficulties in being (and performing as if) âauthenticâ at work, with depression contributing to confusions about the self. The diffuse post-1960s imperative to âbe yourselfâ is experienced in conflicting ways: While some participants sought support from managers and colleagues (e.g. sick leave, back to work plans), many others put on a façade in an attempt to perform the âwellâ and âauthenticâ employee. We outline the contradictory forces at play for participants when authenticity and visibility are expected, yet moral imperatives to be good (healthy) employees are normative
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