Ultra-thin Topological Insulator Bi2Se3 Nanoribbons Exfoliated by Atomic Force Microscopy

Ultra-thin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak Van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi2Se3), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi2Se3 nanoribbons (> 50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultra-thin nanoribbons, showing drastic difference in sheet resistance between 1~2 QLs and 4~5 QLs. Transport measurement carried out on an exfoliated (\leq 5 QLs) Bi2Se3 device shows non-metallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (> 50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states

Unsteady Unidirectional MHD Flow of Voigt Fluids Moving between Two Parallel Surfaces for Variable Volume Flow Rates

The velocity profile and pressure gradient of an unsteady state unidirectional MHD flow of Voigt fluids moving between two parallel surfaces under magnetic field effects are solved by the Laplace transform method. The flow motion between parallel surfaces is induced by a prescribed inlet volume flow rate that varies with time. Four cases of different inlet volume flow rates are considered in this study including 1 constant acceleration piston motion, 2 suddenly started flow, 3 linear acceleration piston motion, and 4 oscillatory piston motion. The solution for each case is elaborately derived, and the results of associated velocity profile and pressure gradients are presented in analytical forms

Impact of Enhancer of Zeste Homolog 2 on T Helper Cell-Mediated Allergic Rhinitis

Enhancer of zeste homolog 2 (Ezh2) has been shown to play a role in the differentiation of T helper (Th) 1 and 2 cells in mice studies using Ezh2-deficient T cells. However, the results have been inconsistent, and the function of Ezh2 in human Th1 and Th2 cell differentiation and its association with disease remains controversial. We measured the expression of Ezh2 in Th1 and Th2 cells in peripheral blood mononuclear cells after acute challenge with house dust mite using flow cytometry in patients with allergic rhinitis (AR) and controls. The role of Ezh2 was further explored by adding the p38 inhibitor to see if this affected allergen-induced Th1 and Th2 differentiation. The expression of Ezh2 in the Th1 and Th2 cells was significantly lower in the patients than in the controls and was negatively correlated with serum IL-17A levels in the patients. Ex vivo allergen challenge resulted in rapid Th2 cell differentiation, which was negatively associated with the Ezh2 expression in Th2 cells. Inhibiting p38 activity increased the expression of Ezh2 in Th2 cells and reduced the number of differentiated Th2 cells. Our findings suggest that Ezh2 expression is potentially associated with AR development

Magnetic Doping and Kondo Effect in Bi2Se3 Nanoribbons

A simple surface band structure and a large bulk band gap have allowed Bi2Se3 to become a reference material for the newly discovered three-dimensional topological insulators, which exhibit topologically-protected conducting surface states that reside inside the bulk band gap. Studying topological insulators such as Bi2Se3 in nanostructures is advantageous because of the high surface-to-volume ratio, which enhances effects from the surface states; recently reported Aharonov-Bohm oscillation in topological insulator nanoribbons by some of us is a good example. Theoretically, introducing magnetic impurities in topological insulators is predicted to open a small gap in the surface states by breaking time-reversal symmetry. Here, we present synthesis of magnetically-doped Bi2Se3 nanoribbons by vapor-liquid-solid growth using magnetic metal thin films as catalysts. Although the doping concentration is less than ~ 2%, low-temperature transport measurements of the Fe-doped Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K, confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The capability to dope topological insulator nanostructures magnetically opens up exciting opportunities for spintronics.Comment: 16 pages, 4 figure

Floating Hem-o-Lok Clips in the Bladder without Stone Formation after Robot-Assisted Laparoscopic Radical Prostatectomy

Hem-o-Lok clips (Weck Surgical Instruments, Teleflex Medical, Durham, NC, USA) are widely used in robot-assisted laparoscopic radical prostatectomy because of their easy application and secure clamping. To date, there have been some reports of intravesical migration of these clips causing urethral erosion, bladder neck contractures, and subsequent calculus formation. We report the first case of bladder migration of Hem-o-Lok clips without stone formation after robot-assisted laparoscopic radical prostatectomy. The Hem-o-Lok clips were found during urethral dilation with a guide wire for bladder neck contracture under cystourethroscopy. The Hem-o-Lok clips were floating in the bladder without stone formation and were removed by a cystoscopic procedure