528 research outputs found
Dirac electron behavior and NMR evidence for topological band inversion in ZrTe5
We report Te NMR measurements of the topological quantum material
ZrTe. Spin-lattice relaxation results, well-explained by a theoretical
model of Dirac electron systems, reveal that the topological characteristic of
ZrTe is -dependent, changing from weak topological insulator to strong
topological insulator as temperature increases. Electronic structure
calculations confirm this ordering, the reverse of what has been proposed. NMR
results demonstrate a gapless Dirac semimetal state occurring at a Lifshitz
transition temperature, K in our crystals. We demonstrate that the
changes in NMR shift at also provide direct evidence of band inversion
when the topological phase transition occurs.Comment: 5 pages, 4 figure
Topological nodal line in ZrTe demonstrated by nuclear magnetic resonance
In this work, we report nuclear magnetic resonance (NMR) combined with
density functional theory (DFT) studies of the transition metal dichalcogenide
ZrTe. The measured NMR shift anisotropy reveals a quasi-2D behavior
connected to a topological nodal line close to the Fermi level. With the
magnetic field perpendicular to the ZrTe layers, the measured shift can be
well-fitted by a combination of enhanced diamagnetism and spin shift due to
high mobility Dirac electrons. The spin-lattice relaxation rates with external
field both parallel and perpendicular to the layers at low temperatures match
the expected behavior associated with extended orbital hyperfine interaction
due to quasi-2D Dirac carriers. In addition, calculated band structures also
show clear evidence for the existence of nodal line in ZrTe between
and A. For intermediate temperatures, there is a sharp reduction in
spin-lattice relaxation rate which can be explained as due to a reduced
lifetime for these carriers, which matches the reported large change in
mobility in the same temperature range. Above 200 K, the local orbital
contribution starts to dominate in an orbital relaxation mechanism revealing
the mixture of atomic functions.Comment: 9 pages, 5 figure
Gap-opening transition in Dirac semimetal ZrTe
We apply Te nuclear magnetic resonance (NMR) spectroscopy to
investigate the Dirac semimetal ZrTe. With the NMR magnetic field parallel
to the -axis, we observe significant quantum magnetic effects. These include
an abrupt drop at 150 K in spin-lattice relaxation rate. This corresponds to a
gap-opening transition in the Dirac carriers, likely indicating the onset of
excitonic pairing. Below 50 K, we see a more negative shift for the Te
bridging site indicating the repopulation of Dirac levels with spin polarized
carriers at these temperatures. This is the previously reported 3D quantum Hall
regime; however, we see no sign of a charge density wave as has been proposed.Comment: 5 pages, 4 figure
Separation and contrast enhancement of overlapping cast shadow components using polarization
Shadow is an inseparable aspect of all natural scenes. When there are multiple light sources or multiple reflections several different shadows may overlap at the same location and create complicated patterns. Shadows are a potentially good source of information about a scene if the shadow regions can be properly identified and segmented. However, shadow region identification and segmentation is a difficult task and improperly identified shadows often interfere with machine vision tasks like object recognition and tracking. We propose here a new shadow separation and contrast enhancement method based on the polarization of light. Polarization information of the scene captured by our polarization-sensitive camera is shown to separate shadows from different light sources effectively. Such shadow separation is almost impossible to realize with conventional, polarization-insensitive imaging
Display of polarization information by coherently moving dots
It is known that human eyes are effectively polarization-blind. Therefore, in order to display the polarization information in an image, one may require exhibiting such information using other visual cues that are compatible with the human visual system and can be easily detectable by a human observer. Here, we present a technique for displaying polarization information in an image using coherently moving dots that are superimposed on the image. Our examples show that this technique would allow the image segments with polarization signals to pop out easily, which will lead to better target feature detection and visibility enhancement
Polarization- and Specular-Reflection-Based, Non-contact Latent Fingerprint Imaging and Lifting
In forensic science the finger marks left unintentionally by people at a crime scene are referred to as latent fingerprints . Most existing techniques to detect and lift latent fingerprints require application of certain material directly onto the exhibit. The chemical and physical processing applied onto the fingerprint potentially degrades or prevents further forensic testing on the same evidence sample. Many existing methods also come with deleterious side effects. We introduce a method to detect and extract latent fingerprint images without applying any powder or chemicals on the object. Our method is based on the optical phenomena of polarization and specular reflection together with the physiology of fingerprint formation. The recovered image quality is comparable to existing methods. In some cases like the sticky side of a tape our method shows unique advantages
Adaptive Algorithms for 2–Channel Polarization Sensing under Various Polarization Statistics with Non-Uniform Distributions
The polarization of light carries much useful information about the environment. Biological studies have shown that some animal species use polarization information for navigation and other purposes. It has been previously shown that a bio-inspired Polarization Difference Imaging technique can facilitate detection and feature extraction of targets in scattering media. It has also been established by S. Tyo1 that Polarization Sum and Polarization Difference are the optimum pair of linear combinations of images taken through two orthogonally oriented linear polarizers of a scene having a uniform distribution of polarization directions. However, in many real environments the scene has a non-uniform distribution of polarization directions. Using principal component analysis of the polarization statistics of the scene, here we develop a method to determine the two optimum information channels with unequal weighting coefficients that can be formed as linear combinations of the images of a scene taken through a pair of linear polarizers not constrained to the horizontal and vertical directions of the scene We determine the optimal orientations of linear polarization filters that enhance separation of a target from the background, where the target is defined as an area with distinct polarization characteristics as compared to the background. Experimental results confirm that in most situations adaptive polarization difference imaging outperforms conventional polarization difference imaging with fixed channels
Oxidative Stress and Heme Oxygenase-1 Regulated Human Mesenchymal Stem Cells Differentiation
This paper describes the effect of increased expression of HO-1 protein and increased levels of HO activity on differentiation of bone-marrow-derived human MSCs. MSCs are multipotent cells that proliferate and differentiate into many different cell types including adipocytes and osteoblasts. HO, the rate-limiting enzyme in heme catabolism, plays an important role during MSCs differentiation. HO catalyzes the stereospecific degradation of heme to biliverdin, with the concurrent release of iron and carbon monoxide. Upregulation of HO-1 expression and increased HO activity are essential for MSC growth and differentiation to the osteoblast lineage consistent with the role of HO-1 in hematopoietic stem cell differentiation. HO-1 participates in the MSC differentiation process shifting the balance of MSC differentiation in favor of the osteoblast lineage by decreasing PPARγ and increasing osteogenic markers such as alkaline phosphatase and BMP-2. In this paper, we define HO-1 as a target molecule in the modulation of adipogenesis and osteogenesis from MSCs and examine the role of the HO system in diabetes, inflammation, osteoporosis, hypertension, and other pathologies, a burgeoning area of research
Analytical Study of Sub-Wavelength Imaging by Uniaxial Epsilon-Near-Zero Metamaterial Slabs
We discuss the imaging properties of uniaxial epsilon-near-zero metamaterial
slabs with possibly tilted optical axis, analyzing their sub-wavelength
focusing properties as a function of the design parameters. We derive in closed
analytical form the associated two-dimensional Green's function in terms of
special cylindrical functions. For the near-field parameter ranges of interest,
we are also able to derive a small-argument approximation in terms of simpler
analytical functions. Our results, validated and calibrated against a full-wave
reference solution, expand the analytical tools available for
computationally-efficient and physically-incisive modeling and design of
metamaterial-based sub-wavelength imaging systems.Comment: 25 pages, 9 figures (modifications in the text; two figures and
several references added
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