We discuss the instrumental and data reduction techniques used to suppress speckle noise with the Simultaneous Differential Imager (SDI) implemented at the VLT and the MMT. SDI uses a quad filter to ...take images simultaneously at 3 wavelengths surrounding the 1.62 $\mu$m methane bandhead found in the spectrum of cool brown dwarfs and gas giants. By performing a difference of images in these filters, speckle noise from the primary can be significantly attenuated, resulting in photon noise limited data. Non-trivial data reduction tools are necessary to pipeline the simultaneous differential imaging. Here we discuss a custom algorithm implemented in IDL to perform this reduction. The script performs basic data reduction tasks but also precisely aligns images taken in each of the filters using a custom shift and subtract routine. In our survey of nearby young stars at the VLT and MMT (see Biller et al., this conference), we achieved H band contrasts >25000 (5$\sigma \Delta$F1(1.575 $\mu$m) >10.0 mag, $\Delta$H$\,{>}\,$11.5 mag for a T6 spectral type object) at a separation of 0.5” from the primary star. We believe that our SDI images are among the highest contrast astronomical images ever made from ground or space for methane rich companions.
In order to stabilize Majorana excitations within vortices of proximity
induced topological superconductors, it is mandatory that the Dirac point
matches the Fermi level rather exactly, such that the ...conventionally confined
states within the vortex are well separated from the Majorana-type excitation.
Here, we show by angle resolved photoelectron spectroscopy that
(Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$ thin films with $x=0.94$ prepared by
molecular beam epitaxy and transferred in ultrahigh vacuum from the molecular
beam epitaxy system to the photoemission setup matches this condition. The
Dirac point is within 10 meV around the Fermi level and we do not observe any
bulk bands intersecting the Fermi level.
A combined theoretical and experimental study reveals evidence for the dual
topological insulating character of the stoichiometric natural superlattice
phase ...$\mathrm{Bi_{1}Te_{1}}=\mathrm{Bi_{2}_{1}Bi_{2}Te_{3}_{2}}$, being a
stack of alternating Bi bilayers and two quintuple layers of
$\mathrm{Bi_{2}Te_{3}}$. We identify $\mathrm{Bi_{1}Te_{1}}$ by density
functional theory to exhibit a non trivial time-reversal symmetry-driven
character of $\mathbb{Z}_{2}=(0;001)$ and additionally a mirror-symmetry
induced mirror Chern number of $n_{{\cal M}}=-2$, which indicates that
$\mathrm{Bi_{1}Te_{1}}$ is both a weak topological insulator and a topological
crystalline insulator. The coexistence of the two phenomena preordains distinct
crystal planes to host topological surface states that are protected by the
respective symmetries. The surface perpendicular to the stacking direction is
the 'dark' surface of the weak topological insulator, while hosting
mirror-symmetry protected surface states along the $\bar{\Gamma\mathrm{M}}$
direction at non-time-reversal invariant momenta points. We confirm the
stacking sequence of our MBE-grown $\mathrm{Bi_{1}Te_{1}}$ thin films by X-ray
diffraction and transmission electron microscopy, and find indications of the
topological crystalline and weak topological character in the surface
electronic spin structure by spin- and angle-resolved photoemission
spectroscopy, which nicely match the results from density functional theory.
To determine the clinical and functional findings in patients with late-onset cone dystrophy (LOCD) (after the age of 50 years), which is rare; and to compare them with those of patients with ...age-related macular degeneration (AMD).
Eleven LOCD patients underwent ophthalmologic and electroretinographic examinations. Full-field electroretinograms were recorded according to the International Society for Clinical Electrophysiology of Vision standard. The results were compared with those of a group of 20 AMD patients and a group of 23 age-related control subjects.
There was no difference between LOCD and AMD patients regarding the severity of visual acuity loss, color vision deficiencies, and central visual field defects. Alterations of the posterior pole were present in all LOCD and AMD patients. In contrast to the AMD group, all LOCD patients did not show drusen and 6 of the 11 LOCD patients displayed temporal optic disc pallor. The electroretinogram revealed the major functional difference, with severe reduction of cone-mediated responses and moderate reduction of rod-mediated responses in LOCD patients. Unexpectedly, the 30-Hz flicker amplitude was reduced in AMD patients compared with healthy controls.
Late-onset cone dystrophy and AMD have several features in common. In elderly patients with progressive visual loss and without drusen, LOCD should be considered. The electroretinographic results in a small group of AMD patients indicate a generalized cone dysfunction.
3D topological insulators are a new state of quantum matter which exhibits
both a bulk band structure with an insulating energy gap as well as metallic
spin-polarized Dirac fermion states when ...interfaced with a topologically
trivial material. There have been various attempts to tune the Dirac point to a
desired energetic position for exploring its unusual quantum properties. Here
we show a direct experimental proof by angle-resolved photoemission of the
realization of a vertical topological p-n junction made of a heterostructure of
two different binary 3D TI materials $\mathrm{Bi_2Te_3}$ and
$\mathrm{Sb_2Te_3}$ epitaxially grown on Si(111). We demonstrate that the
chemical potential is tunable by about 200 meV when decreasing the upper
$\mathrm{Sb_2Te_3}$ layer thickness from 25 to 6 quintuple layers without
applying any external bias. These results make it realistic to observe the
topological exciton condensate and pave the way of exploring other exotic
quantum phenomena in the near future.
Phase change alloys are used for non-volatile random access memories exploiting the conductivity contrast between amorphous and metastable, crystalline phase. However, this contrast has never been ...directly related to the electronic band structure. Here, we employ photoelectron spectroscopy to map the relevant bands for metastable, epitaxial GeSbTe films. The constant energy surfaces of the valence band close to the Fermi level are hexagonal tubes with little dispersion perpendicular to the (111) surface. The electron density responsible for transport belongs to the tails of this bulk valence band, which is broadened by disorder, i.e., the Fermi level is 100 meV above the valence band maximum. This result is consistent with transport data of such films in terms of charge carrier density and scattering time. In addition, we find a state in the bulk band gap with linear dispersion, which might be of topological origin.
Objective
Understanding of the molecular pathophysiology of spondylarthritis (SpA) remains largely elusive. This is related both to the complexity of the disease (axial versus peripheral disease, ...inflammation versus tissue remodeling) and to the difficulty in obtaining samples from primary disease sites. This study was undertaken to explore a gene expression approach for identifying novel candidate mediators of SpA.
Methods
Sacroiliac joint fluid aspirates from 3 SpA patients with active sacroiliitis were studied by microarray analysis. The expression of selected candidate molecules in peripheral synovitis was confirmed by reverse transcriptase–polymerase chain reaction and enzyme‐linked immunosorbent assay.
Results
Microarray analysis identified 4 sacroiliitis gene clusters, containing a total of 47 messenger RNA (mRNA) transcripts. Two clusters contained genes expressed in all sacroiliitis samples, corresponding to both known and unsuspected candidate mediators of SpA pathology. These included proinflammatory molecules as well as molecules involved in tissue remodeling, such as transforming growth factor β2. Of the novel candidate genes selected for confirmation, interleukin‐7 (IL‐7) mRNA expression was higher in SpA peripheral synovial fluid and synovial tissue samples than in osteoarthritis samples, and similar to expression in rheumatoid arthritis (RA) samples. At the protein level, synovial fluid IL‐7 levels were even higher in SpA than in RA, despite lower levels of tumor necrosis factor α and IL‐1β.
Conclusion
In the present study, both known and unsuspected candidate mediators of SpA pathogenesis were identified, including IL‐7. The specific overexpression of IL‐7 at sites of peripheral synovitis in SpA suggests that further functional investigations of the role of this cytokine in SpA pathogenesis are warranted.
Helical locking of spin and momentum and prohibited backscattering are the key properties of topologically protected states. They are expected to enable novel types of information processing such as ...spintronics by providing pure spin currents, or fault tolerant quantum computation by using the Majorana fermions at interfaces of topological states with superconductors. So far, the required helical conduction channels used to realize Majorana fermions are generated through application of an axial magnetic field to conventional semiconductor nanowires. Avoiding the magnetic field enhances the possibilities for circuit design significantly. Here, we show that sub-nanometer wide electron channels with natural helicity are present at surface step-edges of the recently discovered topological insulator Bi14Rh3I9. Scanning tunneling spectroscopy reveals the electron channels to be continuous in both energy and space within a large band gap of 200 meV, thereby, evidencing its non-trivial topology. The absence of these channels in the closely related, but topologically trivial insulator Bi13Pt3I7 corroborates the channels' topological nature. The backscatter-free electron channels are a direct consequence of Bi14Rh3I9's structure, a stack of 2D topologically insulating, graphene-like planes separated by trivial insulators. We demonstrate that the surface of Bi14Rh3I9 can be engraved using an atomic force microscope, allowing networks of protected channels to be patterned with nm precision.
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