Gate-tuned normal and superconducting transport at the surface of a topological insulator

Three-dimensional topological insulators are characterized by the presence of a bandgap in their bulk and gapless Dirac fermions at their surfaces. New physical phenomena originating from the presence of the Dirac fermions are predicted to occur, and to be experimentally accessible via transport measurements in suitably designed electronic devices. Here we study transport through superconducting junctions fabricated on thin Bi2Se3 single crystals, equipped with a gate electrode. In the presence of perpendicular magnetic field B, sweeping the gate voltage enables us to observe the filling of the Dirac fermion Landau levels, whose character evolves continuously from electron- to hole-like. When B=0, a supercurrent appears, whose magnitude can be gate tuned, and is minimum at the charge neutrality point determined from the Landau level filling. Our results demonstrate how gated nano-electronic devices give control over normal and superconducting transport of Dirac fermions at an individual surface of a three-dimensional topological insulator.Comment: 28 pages, 5 figure

Spin-related tunneling through a nanostructured electric-magnetic barrier on the surface of a topological insulator

We investigate quantum tunneling through a single electric and/or magnetic barrier on the surface of a three-dimensional topological insulator. We found that (1) the propagating behavior of electrons in such system exhibits a strong dependence on the direction of the incident electron wavevector and incident energy, giving the possibility to construct a wave vector and/or energy filter; (2) the spin orientation can be tuned by changing the magnetic barrier structure as well as the incident angles and energies

Josephson supercurrent through a topological insulator surface state

Topological insulators are characterized by an insulating bulk with a finite band gap and conducting edge or surface states, where charge carriers are protected against backscattering. These states give rise to the quantum spin Hall effect without an external magnetic field, where electrons with opposite spins have opposite momentum at a given edge. The surface energy spectrum of a threedimensional topological insulator is made up by an odd number of Dirac cones with the spin locked to the momentum. The long-sought yet elusive Majorana fermion is predicted to arise from a combination of a superconductor and a topological insulator. An essential step in the hunt for this emergent particle is the unequivocal observation of supercurrent in a topological phase. Here, we present the first measurement of a Josephson supercurrent through a topological insulator. Direct evidence for Josephson supercurrents in superconductor (Nb) - topological insulator (Bi2Te3) - superconductor e-beam fabricated junctions is provided by the observation of clear Shapiro steps under microwave irradiation, and a Fraunhofer-type dependence of the critical current on magnetic field. The dependence of the critical current on temperature and length shows that the junctions are in the ballistic limit. Shubnikov-de Haas oscillations in magnetic fields up to 30 T reveal a topologically non-trivial two-dimensional surface state. We argue that the ballistic Josephson current is hosted by this surface state despite the fact that the normal state transport is dominated by diffusive bulk conductivity. The lateral Nb-Bi2Te3-Nb junctions hence provide prospects for the realization of devices supporting Majorana fermions

How a Diverse Research Ecosystem Has Generated New Rehabilitation Technologies: Review of NIDILRR’s Rehabilitation Engineering Research Centers

Over 50 million United States citizens (1 in 6 people in the US) have a developmental, acquired, or degenerative disability. The average US citizen can expect to live 20% of his or her life with a disability. Rehabilitation technologies play a major role in improving the quality of life for people with a disability, yet widespread and highly challenging needs remain. Within the US, a major effort aimed at the creation and evaluation of rehabilitation technology has been the Rehabilitation Engineering Research Centers (RERCs) sponsored by the National Institute on Disability, Independent Living, and Rehabilitation Research. As envisioned at their conception by a panel of the National Academy of Science in 1970, these centers were intended to take a “total approach to rehabilitation”, combining medicine, engineering, and related science, to improve the quality of life of individuals with a disability. Here, we review the scope, achievements, and ongoing projects of an unbiased sample of 19 currently active or recently terminated RERCs. Specifically, for each center, we briefly explain the needs it targets, summarize key historical advances, identify emerging innovations, and consider future directions. Our assessment from this review is that the RERC program indeed involves a multidisciplinary approach, with 36 professional fields involved, although 70% of research and development staff are in engineering fields, 23% in clinical fields, and only 7% in basic science fields; significantly, 11% of the professional staff have a disability related to their research. We observe that the RERC program has substantially diversified the scope of its work since the 1970’s, addressing more types of disabilities using more technologies, and, in particular, often now focusing on information technologies. RERC work also now often views users as integrated into an interdependent society through technologies that both people with and without disabilities co-use (such as the internet, wireless communication, and architecture). In addition, RERC research has evolved to view users as able at improving outcomes through learning, exercise, and plasticity (rather than being static), which can be optimally timed. We provide examples of rehabilitation technology innovation produced by the RERCs that illustrate this increasingly diversifying scope and evolving perspective. We conclude by discussing growth opportunities and possible future directions of the RERC program

Plasma glycosaminoglycan scores in early stage renal cell carcinoma

Introduction & Objectives No diagnostic blood biomarker for RCC is currently used in the clinical routine. Using a systems biology approach, we previously developed a score based on circulating glycosaminoglycans (GAGs) that detected metastatic clear cell renal cell carcinoma (RCC) with 92.6%, 93.7%, and 100% accuracy vs. healthy subjects using either plasma, urine, or combined measurements in a validation cohort (Gatto et al., 2016, Cell Reports). It is still unknown if this test is accurate in early stage RCC or other RCC histologies. The primary endpoint of this study was the area-under-thecurve (AUC) in the use of plasma GAG scores to detect pre-operative RCC, any stage and any histology, versus healthy individuals

Domain-dependent surface adhesion in twisted few-layer graphene: Platform for moir\'e-assisted chemistry

Twisted van der Waals multilayers are widely regarded as a rich platform to access novel electronic phases, thanks to the multiple degrees of freedom such as layer thickness and twist angle that allow control of their electronic and chemical properties. Here, we propose that the stacking domains that form naturally due to the relative twist between successive layers act as an additional "knob" for controlling the behavior of these systems, and report the emergence and engineering of stacking domain-dependent surface chemistry in twisted few-layer graphene. Using mid-infrared near-field optical microscopy and atomic force microscopy, we observe a selective adhesion of metallic nanoparticles and liquid water at the domains with rhombohedral stacking configurations of minimally twisted double bi- and tri-layer graphene. Furthermore, we demonstrate that the manipulation of nanoparticles located at certain stacking domains can locally reconfigure the moir\'e superlattice in their vicinity at the {\mu}m-scale. In addition, we report first-principles simulations of the energetics of adhesion of metal atoms and water molecules on the stacking domains in an attempt to elucidate the origin of the observed selective adhesion. Our findings establish a new approach to controlling moir\'e-assisted chemistry and nanoengineering.Comment: 11 pages, 3 figure

Emergent Phenomena Induced by Spin-Orbit Coupling at Surfaces and Interfaces

Spin-orbit coupling (SOC) describes the relativistic interaction between the spin and momentum degrees of freedom of electrons, and is central to the rich phenomena observed in condensed matter systems. In recent years, new phases of matter have emerged from the interplay between SOC and low dimensionality, such as chiral spin textures and spin-polarized surface and interface states. These low-dimensional SOC-based realizations are typically robust and can be exploited at room temperature. Here we discuss SOC as a means of producing such fundamentally new physical phenomena in thin films and heterostructures. We put into context the technological promise of these material classes for developing spin-based device applications at room temperature

The Image Quality and Radiation Dose of 100-kVp versus 120-kVp ECG-Gated 16-Slice CT Coronary Angiography

Objective: This study was conducted to assess the feasibility of performing 100-kVp electrocardiogram (ECG)-gated coronary CT angiography, as compared to 120-kVp ECG-gated coronary CT angiography. Materials and Methods: We retrospectively evaluated one hundred eighty five gencler- and body mass index-matched 16-slice coronary CT sets of data, which were obtained using either 100 kVp and 620 effective mAs or 120 kVp and 500 effective mAs. The density measurements (image noise, vessel density, signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) and the estimated radiation dose were calculated. As a preference test, two image readers were independently asked to choose one image from each pair of images. The results of both protocols were compared using the paired t-test or the Wilcoxon signed rank test. Results: The 100-kVp images showed significantly more noise and a significantly higher vessel density than did the 120-kVp images. There were no significant differences in the SNR and CNR. The estimated reduction of the radiation dose for the 100-kVp protocol was 24%; 7.8 +/- 0.4 mSV for 1 00-kVp and 10.1 +/- 1.0 mSV for 120-kVp (p < 0.001). The readers preferred the 1 00-kVp images for reading (reader 1, p = 0.01; reader 2, p = 0.06), with their preferences being stronger when the subject`s body mass index was less than 25. Conclusion: Reducing the tube kilovoltage from 120 to 100 kVp allows a significant reduction of the radiation dose without a significant change in the SNR and the CNR.Stolzmann P, 2008, RADIOLOGY, V249, P71, DOI 10.1148/radiol.2483072032Earls JP, 2008, RADIOLOGY, V246, P742, DOI 10.1148/radiol.2463070989Stolzmann P, 2008, EUR RADIOL, V18, P592, DOI 10.1007/s00330-007-0786-8Schoenhagen P, 2008, EUR HEART J, V29, P153, DOI 10.1093/eurheartj/ehm614Heyer CM, 2007, RADIOLOGY, V245, P577, DOI 10.1148/radiol.2452061919Paul JF, 2007, EUR RADIOL, V17, P2028, DOI 10.1007/s00330-007-0584-3McCollough CH, 2007, RADIOLOGY, V243, P775, DOI 10.1148/radiol.2433061165Schueller-Weidekamm C, 2006, RADIOLOGY, V241, P899, DOI 10.1148/radiol.2413040128Hsieh J, 2006, MED PHYS, V33, P4236, DOI 10.1118/1.2361078d`Agostino AG, 2006, EUR RADIOL, V16, P2137, DOI 10.1007/s00330-006-0218-1Hohl C, 2006, EUR RADIOL, V16, P1841, DOI 10.1007/s00330-005-0124-yJohnson TRC, 2006, EUR RADIOL, V16, P1409, DOI 10.1007/s00330-006-0298-yAbada HT, 2006, AM J ROENTGENOL, V186, pS387, DOI 10.2214/AJR.05.0216Hausleiter J, 2006, CIRCULATION, V113, P1305, DOI 10.1161/CIRCULATIONAHA.105.602490NAKAYAMA Y, 2006, AM J ROENTGENOL, V187, pW490Ghersin E, 2006, AM J ROENTGENOL, V186, P177, DOI 10.2214/AJR.04.1232Haberl R, 2005, AM HEART J, V149, P1112, DOI 10.1016/j.ahj.2005.02.048Wintersperger B, 2005, EUR RADIOL, V15, P334, DOI 10.1007/s00330-004-2575-ySigal-Cinqualbre AB, 2004, RADIOLOGY, V231, P169, DOI 10.1148/radiol.2311030191Kalra MK, 2004, RADIOLOGY, V230, P619, DOI 10.1148/radiol.2303021726Jung B, 2003, EUR RADIOL, V13, P2560, DOI 10.1007/s00330-003-2111-5Jakobs TF, 2002, EUR RADIOL, V12, P1081, DOI 10.1007/s00330-001-1278-xHuda W, 2000, RADIOLOGY, V217, P430Kalender WA, 1999, EUR RADIOL, V9, P3231

Entrapment neuropathy results in different microRNA expression patterns from denervation injury in rats

<p>Abstract</p> <p>Background</p> <p>To compare the microRNA (miRNA) expression profiles in neurons and innervated muscles after sciatic nerve entrapment using a non-constrictive silastic tube, subsequent surgical decompression, and denervation injury.</p> <p>Methods</p> <p>The experimental L4-L6 spinal segments, dorsal root ganglia (DRGs), and soleus muscles from each experimental group (sham control, denervation, entrapment, and decompression) were analyzed using an Agilent rat miRNA array to detect dysregulated miRNAs. In addition, muscle-specific miRNAs (miR-1, -133a, and -206) and selectively upregulated miRNAs were subsequently quantified using real-time reverse transcription-polymerase chain reaction (real-time RT-PCR).</p> <p>Results</p> <p>In the soleus muscles, 37 of the 47 miRNAs (13.4% of the 350 unique miRNAs tested) that were significantly downregulated after 6 months of entrapment neuropathy were also among the 40 miRNAs (11.4% of the 350 unique miRNAs tested) that were downregulated after 3 months of decompression. No miRNA was upregulated in both groups. In contrast, only 3 miRNAs were upregulated and 3 miRNAs were downregulated in the denervated muscle after 6 months. In the DRGs, 6 miRNAs in the entrapment group (miR-9, miR-320, miR-324-3p, miR-672, miR-466b, and miR-144) and 3 miRNAs in the decompression group (miR-9, miR-320, and miR-324-3p) were significantly downregulated. No miRNA was upregulated in both groups. We detected 1 downregulated miRNA (miR-144) and 1 upregulated miRNA (miR-21) after sciatic nerve denervation. We were able to separate the muscle or DRG samples into denervation or entrapment neuropathy by performing unsupervised hierarchal clustering analysis. Regarding the muscle-specific miRNAs, real-time RT-PCR analysis revealed an ~50% decrease in miR-1 and miR-133a expression levels at 3 and 6 months after entrapment, whereas miR-1 and miR-133a levels were unchanged and were decreased after decompression at 1 and 3 months. In contrast, there were no statistical differences in the expression of miR-206 during nerve entrapment and after decompression. The expression of muscle-specific miRNAs in entrapment neuropathy is different from our previous observations in sciatic nerve denervation injury.</p> <p>Conclusions</p> <p>This study revealed the different involvement of miRNAs in neurons and innervated muscles after entrapment neuropathy and denervation injury, and implied that epigenetic regulation is different in these two conditions.</p