63 research outputs found
Electrical resistance of individual defects at a topological insulator surface
Three-dimensional topological insulators host surface states with linear
dispersion, which manifest as a Dirac cone. Nanoscale transport measurements
provide direct access to the transport properties of the Dirac cone in real
space and allow the detailed investigation of charge carrier scattering. Here,
we use scanning tunnelling potentiometry to analyse the resistance of different
kinds of defects at the surface of a (Bi0.53Sb0.47)2Te3 topological insulator
thin film. The largest localized voltage drop we find to be located at domain
boundaries in the topological insulator film, with a resistivity about four
times higher than that of a step edge. Furthermore, we resolve resistivity
dipoles located around nanoscale voids in the sample surface. The influence of
such defects on the resistance of the topological surface state is analysed by
means of a resistor network model. The effect resulting from the voids is found
to be small compared to the other defects
Quantum transport in topological surface states of BiTe nanoribbons
Quasi-1D nanowires of topological insulators are emerging candidate
structures in superconductor hybrid architectures for the realization of
Majorana fermion based quantum computation schemes. It is however technically
difficult to both fabricate as well as identify the 1D limit of topological
insulator nanowires. Here, we investigated selectively-grown BiTe
topological insulator nanoribbons and nano Hall bars at cryogenic temperatures
for their topological properties. The Hall bars are defined in deep-etched
SiN/SiO nano-trenches on a silicon (111) substrate followed by a
selective area growth process via molecular beam epitaxy. The selective area
growth is beneficial to the device quality, as no subsequent fabrication needs
to be performed to shape the nanoribbons. Transmission line measurements are
performed to evaluate contact resistances of Ti/Au contacts applied as well as
the specific resistance of the BiTe binary topological insulator. In
the diffusive transport regime of these unintentionally -doped BiTe
topological insulator nano Hall bars, we identify distinguishable electron
trajectories by analyzing angle-dependent universal conductance fluctuation
spectra. When the sample is tilted from a perpendicular to a parallel magnetic
field orientation, these high frequent universal conductance fluctuations merge
with low frequent Aharonov-Bohm type oscillations originating from the
topologically protected surface states encircling the nanoribbon cross section.
For 500 nm wide Hall bars we also identify low frequent Shubnikov-de Haas
oscillations in the perpendicular field orientation, that reveal a topological
high-mobility 2D transport channel, partially decoupled from the bulk of the
material.Comment: 13 pages, 5 figures, 6 pages supplementary information, 5
supplementary figure
Gate-induced decoupling of surface and bulk state properties in selectively-deposited BiTe nanoribbons
Three-dimensional topological insulators (TIs) host helical Dirac surface
states at the interface with a trivial insulator. In quasi-one-dimensional TI
nanoribbon structures the wave function of surface charges extends
phase-coherently along the perimeter of the nanoribbon, resulting in a
quantization of transverse surface modes. Furthermore, as the inherent
spin-momentum locking results in a Berry phase offset of of
self-interfering charge carriers an energy gap within the surface state
dispersion appears and all states become spin-degenerate. We investigate and
compare the magnetic field dependent surface state dispersion in selectively
deposited BiTe TI micro- and nanoribbon structures by analysing the
gate voltage dependent magnetoconductance at cryogenic temperatures. While in
wide microribbon devices the field effect mainly changes the amount of bulk
charges close to the top surface we identify coherent transverse surface states
along the perimeter of the nanoribbon devices responding to a change in top
gate potential. We quantify the energetic spacing in between these quantized
transverse subbands by using an electrostatic model that treats an initial
difference in charge carrier densities on the top and bottom surface as well as
remaining bulk charges. In the gate voltage dependent transconductance we find
oscillations that change their relative phase by at half-integer values
of the magnetic flux quantum applied coaxial to the nanoribbon, which is a
signature for a magnetic flux dependent topological phase transition in narrow,
selectively deposited TI nanoribbon devices.Comment: 11 pages, 5 figure
In-plane magnetic field-driven symmetry breaking in topological insulator-based three-terminal junctions
Topological surface states of three-dimensional topological insulator
nanoribbons and their distinct magnetoconductance properties are promising for
topoelectronic applications and topological quantum computation. A crucial
building block for nanoribbon-based circuits are three-terminal junctions.
While the transport of topological surface states on a planar boundary is not
directly affected by an in-plane magnetic field, the orbital effect cannot be
neglected when the surface states are confined to the boundary of a nanoribbon
geometry. Here, we report on the magnetotransport properties of such
three-terminal junctions. We observe a dependence of the current on the
in-plane magnetic field, with a distinct steering pattern of the surface state
current towards a preferred output terminal for different magnetic field
orientations. We demonstrate that this steering effect originates from the
orbital effect, trapping the phase-coherent surface states in the different
legs of the junction on opposite sides of the nanoribbon and breaking the
left-right symmetry of the transmission across the junction. The reported
magnetotransport properties demonstrate that an in-plane magnetic field is not
only relevant but also very useful for the characterization and manipulation of
transport in three-dimensional topological insulator nanoribbon-based junctions
and circuits, acting as a topoelectric current switch.Comment: Main Text (8 pages, 5 figures) + Supplemental Material (13 pages, 10
figures
Reliability and validity of cutaneous sarcoidosis outcome instruments among dermatologists, pulmonologists, and rheumatologists
IMPORTANCE: Dermatologists, pulmonologists, and rheumatologists study and treat patients with sarcoidosis with cutaneous manifestations. The validity of cutaneous sarcoidosis outcome instruments for use across medical specialties remains unknown.
OBJECTIVE: To assess the reliability and validity of cutaneous sarcoidosis outcome instruments for use by dermatologists and nondermatologists treating sarcoidosis.
DESIGN, SETTING, AND PARTICIPANTS: We performed a cross-sectional study evaluating the use of the Cutaneous Sarcoidosis Activity and Morphology Instrument (CSAMI) and Sarcoidosis Activity and Severity Index (SASI) to assess cutaneous sarcoidosis disease severity and the Physician's Global Assessment (PGA) as a reference instrument. Four dermatologists, 3 pulmonologists, and 4 rheumatologists evaluated facial cutaneous sarcoidosis in 13 patients treated at a cutaneous sarcoidosis clinic in a 1-day study on October 24, 2014; data analysis was performed from November through December 2014.
MAIN OUTCOMES AND MEASURES: Interrater and intrarater reliability and convergent validity, with correlation with quality-of-life measures as the secondary outcome.
RESULTS: All instruments demonstrated excellent intrarater reliability. Interrater reliability (reported as intraclass correlation coefficient [95% CI]) was good for the CSAMI Activity scale (0.69 [0.51-0.87]) and PGA (0.66 [0.47-0.85]), weak for the CSAMI Damage scale (0.26 [0.11-0.52]), and excellent for the modified Facial SASI (0.78 [0.63-0.91]). The CSAMI Activity scale and modified Facial SASI showed moderate correlations (95% CI) with the PGA (0.67 [0.57-0.75] and 0.57 [0.45-0.66], respectively). The CSAMI Activity scale but not the modified Facial SASI showed significant correlations (95% CI) with quality-of-life instruments, such as the Dermatology Life Quality Index (Spearman rank correlation, 0.70 [0.25-0.90]) and the Skin Stigma raw score of the Sarcoidosis Assessment Tool (Pearson product moment correlation, 0.56 [0.01-0.85]).
CONCLUSIONS AND RELEVANCE: The CSAMI and SASI were reliable and valid in assessing cutaneous sarcoidosis among our diverse group of specialists. The CSAMI Activity score also correlated with quality-of-life measures and suggested construct validity. These results lend credibility to expand the use of the CSAMI and SASI by dermatologists and nondermatologists in assessing cutaneous sarcoidosis disease activity
Stencil lithography of superconducting contacts on MBE-grown topological insulator thin films
Topological insulator (Bi0.06Sb0.94)2Te3 thin films grown by molecular beam epitaxy have been capped in-situ with a 2 nm Al film to conserve the pristine topological surface states. Subsequently, a shadow mask - structured by means of focus ion beam - was in-situ placed underneath the sample to deposit a thick layer of Al on well-defined microscopically small areas. The 2 nm thin Al layer fully oxidizes after exposure to air and in this way protects the TI surface from degradation. The thick Al layer remains metallic underneath a 3–4 nm thick native oxide layer and therefore serves as (super-) conducting contacts. Superconductor-Topological Insulator-Superconductor junctions with lateral dimensions in the nm range have then been fabricated via an alternative stencil lithography technique. Despite the in-situ deposition, transport measurements and transmission electron microscope analysis indicate a low transparency, due to an intermixed region at the interface between topological insulator thin film and metallic Al
Níveis de lisina digestível em rações, em que se manteve ou não a relação aminoacídica, para frangos de corte de 1 a 21 dias de idade, mantidos em estresse por calor
Dois ensaios foram conduzidos para avaliar os efeitos de níveis de lisina digestível em rações em que se manteve ou não a relação aminoacídica sobre o desempenho de frangos de corte machos de 1 a 21 dias de idade, criados em alta temperatura. O delineamento experimental utilizado em ambos os ensaios foi o inteiramente casualizado. As aves, no ensaio 1, foram distribuídas em cinco tratamentos (0,92; 0,98; 1,04; 1,10 e 1,16% de lisina digestível em ração convencional), oito repetições e dez aves por repetição. No ensaio 2, os frangos foram distribuídos em quatro tratamentos (1,04; 1,10; 1,16 e 1,22% de lisina digestível em rações mantendo a relação aminoacídica), oito repetições e dez aves por repetição. No ensaio 1, os tratamentos influenciaram quadraticamente o ganho de peso e o consumo de ração, que aumentaram até os níveis de 1,14 e 1,09% de lisina, respectivamente. Embora a conversão alimentar tenha melhorado de forma linear, o modelo LRP foi o que melhor se ajustou aos dados, estimando em 1,097% o nível de lisina a partir do qual ocorreu um platô. Não houve efeito dos tratamentos sobre os pesos absolutos do coração, fígado e intestinos, enquanto o peso absoluto da moela aumentou linearmente. O peso absoluto da carcaça aumentou, enquanto os pesos relativos do coração e do fígado reduziram quadraticamente com os tratamentos. No ensaio 2, os tratamentos influenciaram de forma linear crescente o ganho de peso e a conversão alimentar, enquanto o consumo de ração não variou. Os tratamentos influenciaram linearmente o peso absoluto da carcaça, enquanto os pesos absoluto e relativo das vísceras não variaram. Concluiu-se que frangos de corte machos, de 1 a 21 dias de idade, mantidos em estresse por calor, exigem, no mínimo, 1,14 e 1,22% de lisina digestível em ração convencional e em ração em que se manteve a relação aminoacídica, respectivamente.Two trials were conducted to evaluate the effects of digestible lysine levels in diets maintaining or not the relationship of amino acids, on performance of broilers from 1 to 21 days, kept under heat stress. A completely randomized experimental design was used in both trials. In the trial 1, the broilers were allotted in five treatments (0.92; 0.98; 1.04; 1.10 and 1.16% of lysine in conventional diets), eight replicates and ten broilers per replicate. In the trial 2, the broilers were allotted in four treatments (1.04; 1.10; 1.16 and 1.22% of lysine in diet maintaining the relationship of amino acids), eight replicates and ten broilers per replicate. In the trial 1, the digestible lysine levels influenced quadraticly the weight gain and the feed intake that increased up to 1.14 and 1.09%, respectively. Although feed:gain ratio had changed by linear way, the LRP model adjusted better to the data, estimating in 1.097% the lysine level where occurred a "plateau". There was no effect of treatments on absolute weights of heart, liver and intestines, while the absolute weight of gizzard increased linearly. The absolute weight of carcass increased while the relative weights of heart and liver reduced quadraticly. In the trial 2, the treatments influenced in a crescent linear way the weight gain and the feed:gain ratio while the feed intake was not influenced. The treatments influenced linearly the absolute weight of carcass while the absolute and relative weights of the organs were not influenced. It was concluded that male broilers, in the period from 1 to 21 days of age, kept under heat stress, require at least 1.14 and 1.22% of digestible lysine in conventional diet and in diet maintaining the relationship of amino acid, respectively
Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers
https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd
[Stammbuch Daniel Philipp Rosenbach] / D. P. Rosenbach
[STAMMBUCH DANIEL PHILIPP ROSENBACH] / D. P. ROSENBACH
[Stammbuch Daniel Philipp Rosenbach] / D. P. Rosenbach (1)
Einband (1)
Widmung des Eigners (7)
Register (8)
Einträge S. 1 - 139 (12)
Einträge S. 140 - 200 (33)
Einträge S. 201 - 256 (60
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