We study the scattering of waves off a potential step in deformed honeycomb lattices. For deformations below a critical value, perfect Klein tunneling is obtained; i.e., a potential step transmits waves at normal incidence with nonresonant unit-transmission probability. Beyond the critical deformation a gap forms in the spectrum, and a potential step perpendicular to the deformation direction reflects all normally incident waves, exhibiting a dramatic transition form unit transmission to total reflection. These phenomena are generic to honeycomb lattices and apply to electromagnetic waves in photonic lattices, quasiparticles in graphene, and cold atoms in optical lattices.

The accuracy of ED measurement, Z determination, and iodine quantitation derived from DL-DECT was demonstrated with phantom measurements. The accuracies were not sensitive to scan and reconstruction parameters, namely tube potential, dose, rotation time, and spectral reconstruction level, especially in the case of electron density.

Purpose: Phantoms are a basic tool for assessing and verifying performance in CT research and clinical practice. Patient-based realistic lung phantoms accurately representing textures and densities are essential in developing and evaluating novel CT hardware and software. This study introduces PixelPrint, a 3D printing solution to create patient-based lung phantoms with accurate attenuation profiles and textures. Methods: PixelPrint, a software tool, was developed to convert patient digital imaging and communications in medicine (DICOM) images directly into FDM printer instructions (G-code). Density was modeled as the ratio of filament to voxel volume to emulate attenuation profiles for each voxel, with the filament ratio controlled through continuous modification of the printing speed. A calibration phantom was designed to determine the mapping between filament line width and Hounsfield units (HU) within the range of human lungs. For evaluation of PixelPrint, a phantom based on a single human lung slice was manufactured and scanned with the same CT scanner and protocol used for the patient scan. Density and geometrical accuracy between phantom and patient CT data were evaluated for various anatomical features in the lung. Results: For the calibration phantom, measured mean HU show a very high level of linear correlation with respect to the utilized filament line widths, (r > 0.999). Qualitatively, the CT image of the patient-based phantom closely resembles the original CT image both in texture and contrast levels (from −800 to 0 HU), with clearly visible vascular and parenchymal structures. Regions of interest comparing attenuation illustrated differences below 15 HU. Manual size measurements performed by an experienced thoracic radiologist reveal a high degree of geometrical correlation of details between identical patient and phantom features, with differences smaller than the intrinsic spatial resolution of the scans. Conclusion:The present study demonstrates the feasibility of 3D-printed patient-based lung phantoms with accurate organ geometry, image texture, and attenuation profiles.PixelPrint will enable applications in the research and development of CT technology, including further development in radiomics.

We use magnetic force microscopy (MFM) to characterize superconductivity across the superconducting dome in BaFe 2 (As 1-x P x ) 2 , a pnictide with a peak in the penetration depth ( ab λ )at optimal doping (x opt ), as shown in sample-wide measurements. Our local measurements show a peak at x opt and a C T vs.2 ab λ − dependence similar on both sides of x opt . Near the underdoped edge of the dome ab λ increases sharply suggesting that superconductivity competes with another phase. Indeed MFM vortex imaging shows correlated defects parallel to twin boundaries only in underdoped samples and not for x ≥ x opt .2The origin of superconductivity in the iron-based materials is still under debate although there is mounting evidence for the role of magnetic order and fluctuations [1][2][3][4]. For instance, it is well established that the parent compound for the pnictides is a metal with spin-density-wave (SDW) order and that doping by electrons, holes or isovalently gives rise to superconductivity and suppresses the magnetic order and an associated structural phase transition [5][6][7][8][9]. Moreover, the optimal doping for the superconducting transition temperature ( C T ) is only slightly higher than the maximum doping for which SDW order has been observed. Here we report magnetic force microscopy (MFM) measurements of the local absolute value of the in-plane penetration depth ( ab λ ) in BaFe 2 (As 1-x P x ) 2 . At the location where we measure ab λ we also measure the local C T in order to determine the relationship between these two fundamental superconducting properties. In addition we use MFM to map the location of superconducting vortices, which can become trapped by defects in the material. This allows us to learn about correlated defects that may arise as a result of structural and magnetic phase transitions.Our samples were high-quality single crystals grown by the self-flux method and annealed in affected by a region in the sample only up to a few micrometers in diameter and only a few hundred nanometers deep, on the order of ab λ , our results are less sensitive to inhomogeneity than measurements which average over the whole sample [28,29]. The locality also allows us to check homogeneity by comparing measurements from different areas in each sample.In our setup the magnetic MFM tip [30] is subjected to forces due to the Meissner response from the superconducting sample, the magnetic field from vortices and magnetic fields from other sources, if they are present. We minimize the electrostatic forces between the tip and the sample by compensating for the contact potential difference. We work with frequency modulated MFM in which the forces on the tip shift the resonant frequency of the cantilever holding it:is the cantilever's natural resonance frequency, 0 k is the spring constant, z is the direction normal to the sample surface and C is a constant offset) [31].For ab λ measurements we cool the sample in low magnetic field and find an area without vortices and visible defects. For this we scan...

No abstract