6,617 research outputs found
Optical Coherence Tomography Angiography Features of Iris Racemose Hemangioma in 4 Cases.
Importance: Optical coherence tomography angiography (OCTA) allows visualization of iris racemose hemangioma course and its relation to the normal iris microvasculature.
Objective: To describe OCTA features of iris racemose hemangioma.
Design, Setting, and Participants: Descriptive, noncomparative case series at a tertiary referral center (Ocular Oncology Service of Wills Eye Hospital). Patients diagnosed with unilateral iris racemose hemangioma were included in the study.
Main Outcomes and Measures: Features of iris racemose hemangioma on OCTA.
Results: Four eyes of 4 patients with unilateral iris racemose hemangioma were included in the study. Mean patient age was 50 years, all patients were white, and Snellen visual acuity was 20/20 in each case. All eyes had sectoral iris racemose hemangioma without associated iris or ciliary body solid tumor on clinical examination and ultrasound biomicroscopy. By anterior segment OCT, the racemose hemangioma was partially visualized in all cases. By OCTA, the hemangioma was clearly visualized as a uniform large-caliber vascular tortuous loop with intense flow characteristics superimposed over small-caliber radial iris vessels against a background of low-signal iris stroma. The vascular course on OCTA resembled a light bulb filament (filament sign), arising from the peripheral iris (base of light bulb) and forming a tortuous loop on reaching its peak (midfilament) near the pupil (n = 3) or midzonal iris (n = 1), before returning to the peripheral iris (base of light bulb). Intravenous fluorescein angiography performed in 1 eye depicted the iris hemangioma; however, small-caliber radial iris vessels were more distinct on OCTA than intravenous fluorescein angiography.
Conclusions and Relevance: Optical coherence tomography angiography is a noninvasive vascular imaging modality that clearly depicts the looping course of iris racemose hemangioma. Optical coherence tomography angiography depicted fine details of radial iris vessels, not distinct on intravenous fluorescein angiography
Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy
While magnetoresistance (MR) has generally been found to be symmetric in
applied field in non-magnetic or magnetic metals, we have observed
antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and
transport measurements show that the antisymmetric MR is due to the appearance
of domain walls that run perpendicular to both the magnetization and the
current, a geometry existing only in materials with perpendicular magnetic
anisotropy. As a result, the extraordinary Hall effect (EHE) gives rise to
circulating currents in the vicinity of the domain walls that contributes to
the MR. The antisymmetric MR and EHE have been quantitatively accounted for by
a theoretical model.Comment: 17 pages, 4 figure
Anisotropic magnetoresistance of spin-orbit coupled carriers scattered from polarized magnetic impurities
Anisotropic magnetoresistance (AMR) is a relativistic magnetotransport
phenomenon arising from combined effects of spin-orbit coupling and broken
symmetry of a ferromagnetically ordered state of the system. In this work we
focus on one realization of the AMR in which spin-orbit coupling enters via
specific spin-textures on the carrier Fermi surfaces and ferromagnetism via
elastic scattering of carriers from polarized magnetic impurities. We report
detailed heuristic examination, using model spin-orbit coupled systems, of the
emergence of positive AMR (maximum resistivity for magnetization along
current), negative AMR (minimum resistivity for magnetization along current),
and of the crystalline AMR (resistivity depends on the absolute orientation of
the magnetization and current vectors with respect to the crystal axes)
components. We emphasize potential qualitative differences between pure
magnetic and combined electro-magnetic impurity potentials, between short-range
and long-range impurities, and between spin-1/2 and higher spin-state carriers.
Conclusions based on our heuristic analysis are supported by exact solutions to
the integral form of the Boltzmann transport equation in archetypical
two-dimensional electron systems with Rashba and Dresselhaus spin-orbit
interactions and in the three-dimensional spherical Kohn-Littinger model. We
include comments on the relation of our microscopic calculations to standard
phenomenology of the full angular dependence of the AMR, and on the relevance
of our study to realistic, two-dimensional conduction-band carrier systems and
to anisotropic transport in the valence band of diluted magnetic
semiconductors.Comment: 15 pages, Kohn-Littinger model adde
Proximity effects and triplet correlations in Ferromagnet/Ferromagnet/Superconductor nanostructures
We report the results of a study of superconducting proximity effects in
clean Ferromagnet/Ferromagnet/Superconductor ()
heterostructures, where the pairing state in S is a conventional singlet
s-wave. We numerically find the self-consistent solutions of the Bogoliubov-de
Gennes (BdG) equations and use these solutions to calculate the relevant
physical quantities. By linearizing the BdG equations, we obtain the
superconducting transition temperatures as a function of the angle
between the exchange fields in and . We find that
the results for in systems are clearly different
from those in systems, where monotonically increases
with and is highest for antiparallel magnetizations. Here,
is in general a non-monotonic function, and often has a minimum
near . For certain values of the exchange field and
layer thicknesses, the system exhibits reentrant superconductivity with
: it transitions from superconducting to normal, and then returns to a
superconducting state again with increasing . This phenomenon is
substantiated by a calculation of the condensation energy. We compute, in
addition to the ordinary singlet pair amplitude, the induced odd triplet
pairing amplitudes. The results indicate a connection between equal-spin
triplet pairing and the singlet pairing state that characterizes . We find
also that the induced triplet amplitudes can be very long-ranged in both the S
and F sides and characterize their range. We discuss the average density of
states for both the magnetic and the S regions, and its relation to the pairing
amplitudes and . The local magnetization vector, which exhibits reverse
proximity effects, is also investigated.Comment: 14 pages including 11 figure
Feynman Rules in the Type III Natural Flavour-Conserving Two-Higgs Doublet Model
We consider a two Higgs-doublet model with symmetry, which implies a
rather than 0 relative phase between the vacuum expectation
values . The corresponding Feynman rules are derived
accordingly and the transformation of the Higgs fields from the weak to the
mass eigenstates includes not only an angle rotation but also a phase
transformation. In this model, both doublets couple to the same type of
fermions and the flavour-changing neutral currents are naturally suppressed. We
also demonstrate that the Type III natural flavour-conserving model is valid at
tree-level even when an explicit symmetry breaking perturbation is
introduced to get a reasonable CKM matrix. In the special case , as the ratio runs from 0 to ,
the dominant Yukawa coupling will change from the first two generations to the
third generation. In the Feynman rules, we also find that the charged Higgs
currents are explicitly left-right asymmetric. The ratios between the left- and
right-handed currents for the quarks in the same generations are estimated.Comment: 16 pages (figures not included), NCKU-HEP/93-1
Multi-Lepton Collider Signatures of Heavy Dirac and Majorana Neutrinos
We discuss the possibility of observing multi-lepton signals at the Large
Hadron Collider (LHC) from the production and decay of heavy Standard Model
(SM) singlet neutrinos added in extensions of SM to explain the observed light
neutrino masses by seesaw mechanism. In particular, we analyze two `smoking
gun' signals depending on the Dirac or Majorana nature of the heavy neutrino:
(i) for Majorana case, the same-sign di-lepton signal which can be used as a
probe of lepton-number violation, and (ii) for Dirac case, the tri-lepton
signal which conserves lepton number but may violate lepton flavor. Within a
minimal Left-Right symmetric framework in which these additional neutrino
states arise naturally, we find that in both cases, the signals can be
identified with virtually no background beyond a TeV, and the heavy gauge boson
W_R can be discovered in this process. This analysis also provides a direct way
to probe the nature of seesaw physics involving the SM singlets at TeV scale,
and in particular, to distinguish type-I seesaw with purely Majorana heavy
neutrinos from inverse seesaw with pseudo-Dirac counterparts.Comment: 19 pages, 7 figures; typo in eq. 5 fixed; matches published versio
Massive Star Cluster Formation and Destruction in Luminous Infrared Galaxies in GOALS
We present the results of a {\it Hubble Space Telescope} ACS/HRC FUV, ACS/WFC
optical study into the cluster populations of a sample of 22 Luminous Infrared
Galaxies in the Great Observatories All-Sky LIRG Survey. Through integrated
broadband photometry we have derived ages and masses for a total of 484 star
clusters contained within these systems. This allows us to examine the
properties of star clusters found in the extreme environments of LIRGs relative
to lower luminosity star-forming galaxies in the local Universe. We find that
by adopting a Bruzual \& Charlot simple stellar population (SSP) model and
Salpeter initial mass function, the age distribution of clusters declines as
, consistent with the age distribution derived
for the Antennae Galaxies, and interpreted as evidence for rapid cluster
disruption occuring in the strong tidal fields of merging galaxies. The large
number of young clusters identified in the sample also
suggests that LIRGs are capable of producing more high-mass clusters than what
is observed to date in any lower luminosity star-forming galaxy in the local
Universe. The observed cluster mass distribution of is consistent with the canonical -2 power law used to describe the
underlying initial cluster mass function (ICMF) for a wide range of galactic
environments. We interpret this as evidence against mass-dependent cluster
disruption, which would flatten the observed CMF relative to the underlying
ICMF distribution.Comment: 63 pages, 58 Figures, 56 Tables, Accepted for publication in Ap
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Zero reverse recovery in SiC and GaN Schottky diodes: A comparison
Similarly to the unipolar SiC Schottky diodes, AlGaN/GaN Schottky devices have been suggested to have a negligible reverse recovery current during turn-off and can therefore be switched at very high frequencies with low power losses [1-2]. This study aims to investigate this claim by comparing the reverse recovery characteristic of an AlGaN/GaN diode with that of a SiC diode and a fast recovery Si P-N diode for the same current (4 A) and voltage rating (700 V). TCAD models of a SiC Schottky diode and an AlGaN/GaN diode have been developed and calibrated against fabricated devices for a better physical understanding of the experimentally observed results. The analysis is based on the trade-off between on-state and reverse recovery parameters at both room and high temperatures. Experimental and TCAD results show that while the AlGaN/GaN heterostructure Schottky diode is expected to provide a significant improvement in switching performance when compared to the conventional bipolar Si P-N diodes, the SiC diode offers a more favourable trade-off between on-state and reverse recovery
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