710 research outputs found
Majorana bound state of a Bogoliubov-de Gennes-Dirac Hamiltonian in arbitrary dimensions
We study a Majorana zero-energy state bound to a hedgehog-like point defect
in a topological superconductor described by a Bogoliubov-de Gennes (BdG)-Dirac
type effective Hamiltonian. We first give an explicit wave function of a
Majorana state by solving the BdG equation directly, from which an analytical
index can be obtained. Next, by calculating the corresponding topological
index, we show a precise equivalence between both indices to confirm the index
theorem. Finally, we apply this observation to reexamine the role of another
topological invariant, i.e., the Chern number associated with the Berry
curvature proposed in the study of protected zero modes along the lines of
topological classification of insulators and superconductors. We show that the
Chern number is equivalent to the topological index, implying that it indeed
reflects the number of zero-energy states. Our theoretical model belongs to the
BDI class from the viewpoint of symmetry, whereas the spatial dimension of the
system is left arbitrary throughout the paper.Comment: 12 page
Phospholipids undergo hop diffusion in compartmentalized cell membrane
The diffusion rate of lipids in the cell membrane is reduced by a factor of 5–100 from that in artificial bilayers. This slowing mechanism has puzzled cell biologists for the last 25 yr. Here we address this issue by studying the movement of unsaturated phospholipids in rat kidney fibroblasts at the single molecule level at the temporal resolution of 25 μs. The cell membrane was found to be compartmentalized: phospholipids are confined within 230-nm-diameter (φ) compartments for 11 ms on average before hopping to adjacent compartments. These 230-nm compartments exist within greater 750-nm-φ compartments where these phospholipids are confined for 0.33 s on average. The diffusion rate within 230-nm compartments is 5.4 μm2/s, which is nearly as fast as that in large unilamellar vesicles, indicating that the diffusion in the cell membrane is reduced not because diffusion per se is slow, but because the cell membrane is compartmentalized with regard to lateral diffusion of phospholipids. Such compartmentalization depends on the actin-based membrane skeleton, but not on the extracellular matrix, extracellular domains of membrane proteins, or cholesterol-enriched rafts. We propose that various transmembrane proteins anchored to the actin-based membrane skeleton meshwork act as rows of pickets that temporarily confine phospholipids
Gallbladder Cancer with Biliary Intraepithelial Neoplasia Complicated by Pancreaticobiliary Maljunction: A Case Report
We report herein a case of gallbladder cancer with biliary intraepithelial neoplasia (BilIN) complicated by pancreaticobiliary maljunction (PBM). A 60-year-old woman was referred to our hospital for thickening of the gallbladder wall diagnosed via ultrasonography at the referring clinic. The Radiographic images showed thickening of the gallbladder wall and a high confluence of pancreaticobiliary ducts outside the duodenal wall without dilatation of the bile duct. The amylase level in the bile duct was highly elevated. The patient was initially diagnosed with PBM without biliary dilatation, and laparoscopic cholecystectomy was performed. Histopathology of the resected specimen revealed gallbladder cancer localized in the mucosa propria with widespread BilIN. Immunohistochemical analyses showed positive results for S100P,IMP3 and p16ink4a in tumor cells, but a positive result for only IMP3 in adenocarcinoma. Expression of p53 was negative. Oncogenic KRAS mutations were not detected in tumor cells. The patient was diagnosed with gallbladder cancer with BilIN complicated by PBM. This case report may be useful in clarifying the carcinogenic process and genetic mutations for gallbladder cancer associated with PBM
Coexistence of Continuous Variable Quantum Key Distribution and 7 12.5 Gbit/s Classical Channels
We study coexistence of CV-QKD and 7 classical 12.5 Gbit/s on-off keying
channels in WDM transmission over the C-band. We demonstrate key generation
with a distilled secret key rate between 20 to 50 kbit/s in experiments running
continuously over 24 hours.Comment: 2018 IEEE Summer Topicals, paper MD4.
Quantum key distribution with an efficient countermeasure against correlated intensity fluctuations in optical pulses
Quantum key distribution (QKD) allows two distant parties to share secret
keys with the proven security even in the presence of an eavesdropper with
unbounded computational power. Recently, GHz-clock decoy QKD systems have been
realized by employing ultrafast optical communication devices. However,
security loopholes of high-speed systems have not been fully explored yet. Here
we point out a security loophole at the transmitter of the GHz-clock QKD, which
is a common problem in high-speed QKD systems using practical band-width
limited devices. We experimentally observe the inter-pulse intensity
correlation and modulation-pattern dependent intensity deviation in a practical
high-speed QKD system. Such correlation violates the assumption of most
security theories. We also provide its countermeasure which does not require
significant changes of hardware and can generate keys secure over 100 km fiber
transmission. Our countermeasure is simple, effective and applicable to wide
range of high-speed QKD systems, and thus paves the way to realize ultrafast
and security-certified commercial QKD systems
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