54 research outputs found
Maximal Acceleration Corrections to the Lamb Shift of Muonic Hydrogen
The maximal acceleration corrections to the Lamb shift of muonic hydrogen are
calculated by using the relativistic Dirac wave functions. The correction for
the transition is meV and is higher than the accuracy of
present QED calculations and of the expected accuracy of experiments in
preparation.Comment: LaTex file, 9 pages, to be published in Il Nuovo Cimento
Machine learning provides predictive analysis into silver nanoparticle protein corona formation from physicochemical properties
Proteins encountered in biological and environmental systems bind to engineered nanomaterials (ENMs) to form a protein corona (PC) that alters the surface chemistry, reactivity, and fate of the ENMs. Complexities such as the diversity of the PC and variation with ENM properties and reaction conditions make the PC population difficult to predict. Here, we support the development of predictive models for PC populations by relating biophysicochemical characteristics of proteins, ENMs, and solution conditions to PC formation using random forest classification. The resulting model offers a predictive analysis into the population of PC proteins in Ag ENM systems of various ENM size and surface coatings. With an area under the receiver operating characteristic curve of 0.83 and F1-score of 0.81, a model with strong performance has been constructed based upon experimental data. The weighted contribution of each variable provides recommendations for mechanistic models based upon protein enrichment classification results. Protein biophysical properties such as pI and weight are weighted heavily. Yet, ENM size, surface charge, and solution ionic strength also proved essential to an accurate model. The model can be readily modified and applied to other ENM PC populations. The model presented here represents the first step toward robust predictions of PC fingerprints
Aero-acoustics of Drag Generating Swirling Exhaust Flows
Aircraft on approach in high-drag and high-lift configuration create unsteady flow structures which inherently generate noise. For devices such as flaps, spoilers and the undercarriage there is a strong correlation between overall noise and drag such that, in the quest for quieter aircraft, one challenge is to generate drag at low noise levels. This paper presents a rigorous aero-acoustic assessment of a novel drag concept. The idea is that a swirling exhaust flow can yield a steady, and thus relatively quiet, streamwise vortex which is supported by a radial pressure gradient responsible for pressure drag. Flows with swirl are naturally limited by instabilities such as vortex breakdown. The paper presents a first aero-acoustic assessment of ram pressure driven swirling exhaust flows and their associated instabilities. The technical approach combines an in-depth aerodynamic analysis, plausibility arguments to qualitatively describe the nature of acoustic sources, and detailed, quantitative acoustic measurements using a medium aperture directional microphone array in combination with a previously established Deconvolution Approach for Mapping of Acoustic Sources (DAMAS). A model scale engine nacelle with stationary swirl vanes was designed and tested in the NASA Langley Quiet Flow Facility at a full-scale approach Mach number of 0.17. The analysis shows that the acoustic signature is comprised of quadrupole-type turbulent mixing noise of the swirling core flow and scattering noise from vane boundary layers and turbulent eddies of the burst vortex structure near sharp edges. The exposed edges are the nacelle and pylon trailing edge and the centerbody supporting the vanes. For the highest stable swirl angle setting a nacelle area based drag coefficient of 0.8 was achieved with a full-scale Overall Sound Pressure Level (OASPL) of about 40dBA at the ICAO approach certification point
Can Gravity Distinguish Between Dirac and Majorana Neutrinos?
We show that spin-gravity interaction can distinguish between Dirac and
Majorana neutrino wave packets propagating in a Lense-Thirring background.
Using time-independent perturbation theory and gravitational phase to generate
a perturbation Hamiltonian with spin-gravity coupling, we show that the
associated matrix element for the Majorana neutrino differs significantly from
its Dirac counterpart. This difference can be demonstrated through significant
gravitational corrections to the neutrino oscillation length for a two-flavour
system, as shown explicitly for SN1987A.Comment: 4 pages, 2 figures; minor changes of text; typo corrected; accepted
in Physical Review Letter
Isospin violation and the proton's neutral weak magnetic form factor
The effects of isospin violation on the neutral weak magnetic form factor of
the proton are studied using two-flavour chiral perturbation theory. The first
nonzero contributions appear at O(p^4) in the small-momentum expansion, and the
O(p^5) corrections are also calculated. The leading contributions from an
explicit Delta(1232) isomultiplet are included as well. At such a high order in
the chiral expansion, one might have expected a large number of unknown
parameters to contribute. However, it is found that no unknown parameters can
appear within loop diagrams, and a single tree-level counterterm at O(p^4) is
sufficient to absorb all divergences. The momentum dependence of the neutral
weak magnetic form factor is not affected by this counterterm.Comment: 26 pages including 9 figure
Tidal Dynamics in Cosmological Spacetimes
We study the relative motion of nearby free test particles in cosmological
spacetimes, such as the FLRW and LTB models. In particular, the influence of
spatial inhomogeneities on local tidal accelerations is investigated. The
implications of our results for the dynamics of the solar system are briefly
discussed. That is, on the basis of the models studied in this paper, we
estimate the tidal influence of the cosmic gravitational field on the orbit of
the Earth around the Sun and show that the corresponding temporal rate of
variation of the astronomical unit is negligibly small.Comment: 12 pages, no figures, REVTeX 4.0; appendix added, new references, and
minor changes throughout; to appear in Classical and Quantum Gravity; v4:
error in (A24) of Appendix A corrected, results and conclusions unchanged. We
thank L. Iorio for pointing out the erro
The implications of noninertial motion on covariant quantum spin
It is shown that the Pauli-Lubanski spin vector defined in terms of
curvilinear co-ordinates does not satisfy Lorentz invariance for spin-1/2
particles in noninertial motion along a curved trajectory. The possibility of
detecting this violation in muon decay experiments is explored, where the
noninertial contribution to the decay rate becomes large for muon beams with
large momenta and trajectories with radius of curvature approaching the muon's
Compton wavelength scale. A new spacelike spin vector is derived from the
Pauli-Lubanski vector that satisfies Lorentz invariance for both inertial and
noninertial motion. In addition, this spin vector suggests a generalization for
the classification of spin-1/2 particles, and has interesting properties that
are applicable for both massive and massless particles.Comment: REVTeX file; 7 pages; 2 figures; slightly revised with new abstract;
accepted for publication in Classical and Quantum Gravit
Effects of Space-Time Curvature on Spin-1/2 Particle Zitterbewegung
This paper investigates the properties of spin-1/2 particle Zitterbewegung in
the presence of a general curved space-time background described in terms of
Fermi normal co-ordinates, where the spatial part is expressed using general
curvilinear co-ordinates. Adopting the approach first introduced by Barut and
Bracken for Zitterbewegung in the local rest frame of the particle, it is shown
that non-trivial gravitational contributions to the relative position and
momentum operators appear due to the coupling of Zitterbewegung frequency terms
with the Ricci curvature tensor in the Fermi frame, indicating a formal
violation of the weak equivalence principle. Explicit expressions for these
contributions are shown for the case of quasi-circular orbital motion of a
spin-1/2 particle in a Vaidya background. Formal expressions also appear for
the time-derivative of the Pauli-Lubanski vector due to space-time curvature
effects coupled to the Zitterbewegung frequency. As well, the choice of
curvilinear co-ordinates results in non-inertial contributions in the time
evolution of the canonical momentum for the spin-1/2 particle, where
Zitterbewegung effects lead to stability considerations for its propagation,
based on the Floquet theory of differential equations.Comment: 22 pages, no figures; slight revisions; accepted for publication in
Classical and Quantum Gravit
Chiral perturbation theory calculation for pn -> dpipi at threshold
We investigate the reaction pn -> dpipi in the framework of Chiral
Perturbation Theory. For the first time a complete calculation of the leading
order contributions is presented. We identify various diagrams that are of
equal importance as compared to those recognized in earlier works. The diagrams
at leading order behave as expected by the power counting. Also for the first
time the nucleon-nucleon interaction in the initial, intermediate and final
state is included consistently and found to be very important. This study
provides a theoretical basis for a controlled evaluation of the non-resonant
contributions in two-pion production reactions in nucleon-nucleon collisions.Comment: 24 pages, 3 figures, 3 table
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