5,988 research outputs found
Pregnancy-associated breast cancer - Special features in diagnosis and treatment
For obvious psychological reasons it is difficult to associate pregnancy - a life-giving period of our existence with life-threatening malignancies. Symptoms pointing to malignancy are often ignored by both patients and physicians, and this, together with the greater difficulty of diagnostic imaging, probably results in the proven delay in the detection of breast cancers during pregnancy. The diagnosis and treatment of breast cancer are becoming more and more important, as the fulfillment of the desire to have children is increasingly postponed until a later age associated with a higher risk of carcinoma, and improved cure rates of solid tumors no longer exclude subsequent pregnancies. The following article summarizes the special features of the diagnosis and primary therapy of pregnancy-associated breast cancer with particular consideration of cytostatic therapy
Анализ поляризационных состояний умеренно релятивистских позитронов при регистрации аннигиляционных фотонов
Предложен и обоснован новый метод анализа поляризационных состояний умеренно релятивистских позитронных пучков. В отличие от известных методов предлагается измерить продольную поляризацию позитронов по выходу аннигиляционных квантов из намагниченной железной мишени, через которую проходит позитронный пучок. На базе библиотек GEANT4 построена математическая модель эксперимента. Проведены сравнения с существующей моделью
Direct evidence for efficient ultrafast charge separation in epitaxial WS/graphene heterostructure
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to
investigate ultrafast charge transfer in an epitaxial heterostructure made of
monolayer WS and graphene. This heterostructure combines the benefits of a
direct gap semiconductor with strong spin-orbit coupling and strong
light-matter interaction with those of a semimetal hosting massless carriers
with extremely high mobility and long spin lifetimes. We find that, after
photoexcitation at resonance to the A-exciton in WS, the photoexcited holes
rapidly transfer into the graphene layer while the photoexcited electrons
remain in the WS layer. The resulting charge transfer state is found to
have a lifetime of \,ps. We attribute our findings to differences in
scattering phase space caused by the relative alignment of WS and graphene
bands as revealed by high resolution ARPES. In combination with spin-selective
excitation using circularly polarized light the investigated WS/graphene
heterostructure might provide a new platform for efficient optical spin
injection into graphene.Comment: 28 pages, 14 figure
Direct evidence for efficient ultrafast charge separation in epitaxial WS<sub>2</sub>/graphene heterostructures
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS2 and graphene. This heterostructure combines the benefits of a direct-gap semiconductor with strong spin-orbit coupling and strong light-matter interaction with those of a semimetal hosting massless carriers with extremely high mobility and long spin lifetimes. We find that, after photoexcitation at resonance to the A-exciton in WS2, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS2 layer. The resulting charge-separated transient state is found to have a lifetime of ∼1 ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS2 and graphene bands as revealed by high-resolution ARPES. In combination with spin-selective optical excitation, the investigated WS2/graphene heterostructure might provide a platform for efficient optical spin injection into graphene
Measurement of the Permanent Electric Dipole Moment of the Xe Atom
We report on a new measurement of the CP-violating permanent Electric Dipole
Moment (EDM) of the neutral Xe atom. Our experimental approach is based
on the detection of the free precession of co-located nuclear spin-polarized
He and Xe samples. The EDM measurement sensitivity benefits
strongly from long spin coherence times of several hours achieved in diluted
gases and homogeneous weak magnetic fields of about 400~nT. A finite EDM is
indicated by a change in the precession frequency, as an electric field is
periodically reversed with respect to the magnetic guiding field. Our result,
ecm, is consistent with zero and is
used to place a new upper limit on the Xe EDM: ecm (95% C.L.). We also discuss the implications of this result for
various CP-violating observables as they relate to theories of physics beyond
the standard model
A model of driven and decaying magnetic turbulence in a cylinder
Using mean-field theory, we compute the evolution of the magnetic field in a
cylinder with outer perfectly conducting boundaries, an imposed axial magnetic
and electric field. The thus injected magnetic helicity in the system can be
redistributed by magnetic helicity fluxes down the gradient of the local
current helicity of the small-scale magnetic field. A weak reversal of the
axial magnetic field is found to be a consequence of the magnetic helicity flux
in the system. Such fluxes are known to alleviate so-called catastrophic
quenching of the {\alpha}-effect in astrophysical applications. Application to
the reversed field pinch in plasma confinement devices is discussed.Comment: 7 pages, 4 figures, submitted to Phys. Rev.
Comment on "On the temperature dependence of the Casimir effect"
Recently, Brevik et al. [Phys. Rev. E 71, 056101 (2005)] adduced arguments
against the traditional approach to the thermal Casimir force between real
metals and in favor of one of the alternative approaches. The latter assumes
zero contribution from the transverse electric mode at zero frequency in
qualitative disagreement with unity as given by the thermal quantum field
theory for ideal metals. Those authors claim that their approach is consistent
with experiments as well as with thermodynamics. We demonstrate that these
conclusions are incorrect. We show specifically that their results are
contradicted by four recent experiments and also violate the third law of
thermodynamics (the Nernst heat theorem).Comment: 11 pages, 3 figures, changed in accordance with the final published
versio
Effects of Vacuum Polarization in Strong Magnetic Fields with an Allowance Made for the Anomalous Magnetic Moments of Particles
Given the anomalous magnetic moments of electrons and positrons in the
one-loop approximation, we calculate the exact Lagrangian of an intense
constant magnetic field that replaces the Heisenberg-Euler Lagrangian in
traditional quantum electrodynamics (QED). We have established that the derived
generalization of the Lagrangian is real for arbitrary magnetic fields. In a
weak field, the calculated Lagrangian matches the standard Heisenberg-Euler
formula. In extremely strong fields, the field dependence of the Lagrangian
completely disappears, and the Lagrangian tends to a constant determined by the
anomalous magnetic moments of the particles.Comment: 19 pages, 3 figure
Theory of dressed states in quantum optics
The dual Dyson series [M.Frasca, Phys. Rev. A {\bf 58}, 3439 (1998)], is used
to develop a general perturbative method for the study of atom-field
interaction in quantum optics. In fact, both Dyson series and its dual, through
renormalization group methods to remove secular terms from the perturbation
series, give the opportunity of a full study of the solution of the
Schr\"{o}dinger equation in different ranges of the parameters of the given
hamiltonian. In view of recent experiments with strong laser fields, this
approach seems well-suited to give a clarification and an improvement of the
applications of the dressed states as currently done through the eigenstates of
the atom-field interaction, showing that these are just the leading order of
the dual Dyson series when the Hamiltonian is expressed in the interaction
picture. In order to exploit the method at the best, a study is accomplished of
the well-known Jaynes-Cummings model in the rotating wave approximation, whose
exact solution is known, comparing the perturbative solutions obtained by the
Dyson series and its dual with the same approximations obtained by Taylor
expanding the exact solution. Finally, a full perturbative study of high-order
harmonic generation is given obtaining, through analytical expressions, a clear
account of the power spectrum using a two-level model, even if the method can
be successfully applied to a more general model that can account for ionization
too. The analysis shows that to account for the power spectrum it is needed to
go to first order in the perturbative analysis. The spectrum obtained gives a
way to measure experimentally the shift of the energy levels of the atom
interacting with the laser field by looking at the shifting of hyper-Raman
lines.Comment: Revtex, 17 page
Isotopic Dependence of the Casimir Force
We calculate the dependence of the Casimir force on the isotopic composition
of the interacting objects. This dependence arises from the subtle influence of
the nuclear masses on the electronic properties of the bodies. We discuss the
relevance of these results to current experiments utilizing the iso-electronic
effect to search at very short separations for new weak forces suggested by
various unification theories.Comment: 12 pages, Revtex (to appear in Physical Review Letters
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