3,474 research outputs found
Heating-compensated constant-temperature tunneling measurements on stacks of BiSrCaCuO intrinsic junctions
In highly anisotropic layered cuprates such as BiSrCaCuO
tunneling measurements on a stack of intrinsic junctions in a high-bias range
are often susceptible to self-heating. In this study we monitored the
temperature variation of a stack ("sample stack") of intrinsic junctions by
measuring the resistance change of a nearby stack ("thermometer stack") of
intrinsic junctions, which was strongly thermal-coupled to the sample stack
through a common Au electrode. We then adopted a
proportional-integral-derivative scheme incorporated with a substrate-holder
heater to compensate the temperature variation. This in-situ temperature
monitoring and controlling technique allows one to get rid of spurious
tunneling effects arising from the self-heating in a high bias range.Comment: 3 pages, 3 figure
Collective Josephson vortex dynamics in a finite number of intrinsic Josephson junctions
We report the experimental confirmation of the collective transverse plasma
modes excited by the Josephson vortex lattice in stacks of intrinsic Josephson
junctions in BiSrCaCuO single crystals. The
excitation was confirmed by analyzing the temperature () and magnetic field
() dependencies of the multiple sub-branches in the Josephson-vortex-flow
region of the current-voltage characteristics of the system. In the near-static
Josephson vortex state for a low tunneling bias current, pronounced
magnetoresistance oscillations were observed, which represented a
triangular-lattice vortex configuration along the c axis. In the dynamic vortex
state in a sufficiently high magnetic field and for a high bias current,
splitting of a single Josephson vortex-flow branch into multiple sub-branches
was observed. Detailed examination of the sub-branches for varying field
reveals that sub-branches represent the different modes of the Josephson-vortex
lattice along the c axis, with varied configuration from a triangular to a
rectangular lattices. These multiple sub-branches merge to a single curve at a
characteristic temperature, above which no dynamical structural transitions of
the Josephson vortex lattice is expected
On-demand route discovery in a unicast manner
While having high bandwidth-efficiency, the ad-hoc on-demand distance vector (AODV) routing protocol suffers from high signaling overhead due to route request (RREQ) messages flooding, especially when the node density and the number of connections are increased. In order to resolve this broadcast storm problem of the AODV in a high node density mobile ad-hoc network, we propose a geographical on-demand route discovery scheme. Assuming a known location of the destination, the RREQ of the proposed routing protocol is propagated in a unicast manner by employing a novel parsing mechanism for possible duplicate RREQs. The routing overhead of the proposed routing protocol is greatly robust to the node density change. We derive the node density required for the proposed routing protocol to keep the same connectivity as the AODV under the circumstance where the nodes are uniformly distributed. In addition, we present an imaginary destination consideration method to incorporate the uncertainty of the destination???s location due to mobility. Computer simulations show that the proposed scheme enables the RREQ propagation to cover 95% of the one-hop communication area centered at the originally known location of the destination without sacrificing the unicast feature
Synthesis and Characterization of Nucleic Acid-functionalized Nanomaterials
Motor proteins such as kinesin move along microtubules in order to transport cellular cargos throughout the cell by obtaining energy from RNA hydrolysis which allows the cell to complete the tasks needed to stay alive. In this work, we developed synthetic molecular motors using DNA enzymes (DNAzyme) and fluorescent nanomaterials which mimic the functions and structures of motor proteins. A DNAzyme-capped CdS nanoparticle and a RNA-functionalized single-walled carbon nanotube (SWCNT) were used as a walker and a track in the motor platform, respectively. As a walking mechanism, the DNAzyme cleaved the RNA substrates in the presence of metal cations. The RNA molecules were functionalized with SWCNTs using pi-pi stacking. Due to their fluorescent properties under specific light excitations, they were visualized to track the position of our motor. In addition, we studied the kinetics of molecular motors in different environments. As a result, the fastest translocation velocity was found to be 1nm min-1 and the maximum displacement was 3µm. A turnover rate of 0.025s-1 was determined by making a kinetic model based on the density of the single motor reactions. We demonstrated that the cation concentration, type of metal cation, pH, and temperature all modify the kinetics of the molecular motor. In conclusion, we developed the bio-inspired synthetic motors using DNA nanotechnology and showed how to control their movements using design of structures and modification of chemical environments. In the future, we will develop the kinetic model to analyze their kinetics and design the optimized molecular motors on purpose
Islands in Proliferating de Sitter Spaces
We study two-dimensional de Sitter universe which evolves and proliferates
according to the Ginsparg-Perry-Bousso-Hawking mechanism, using
Jackiw-Teitelboim gravity coupled to conformal matter. Black holes are
generated by quantum gravity effects from pure de Sitter space and then
evaporate to yield multiple disjoint de Sitter spaces. The back-reaction from
the matter CFT is taken into account for the dilaton as a function of the
temperature of the CFT. We discuss the evaporation of black holes and calculate
the finite temperature entropy of an inflating region using the island formula.
We find that the island moves towards the apparent horizon of the black hole as
the temperature increases. The results are applied to the case of multiple
evaporating black holes, for which we suggest multiple islands.Comment: 26+1 pages, 6 figures, v2: clarified discussion, v3: published
versio
Functionalization and Length Fractionation of Single-Wall Carbon Nanotubes
Single-wall carbon nanotubes (SWCNTs) are a promising material for future biological applications such as imaging and targeted drug delivery. SWCNTs can be made soluble in water through surface functionalization, a priority for their use in biology. By studying the surface chemistry of SWCNTs, various functionalization methods can be accomplished without perturbing their electronic structure. This study probes the use of pyrene derivatives and phospholipids to non-covalently functionalize SWCNTs, maintaining useful surface properties. Phospholipids cross-linked to polyethylene glycol (PEG) or 1-pyrenebutyric acid conjugated to DNA is anchored onto the sidewalls of SWCNTs by hydrophobic interactions or π-stacking. The PEG/DNA portion is water soluble and biocompatible, thus solubilizing the SWCNTs. Biofunctional materials such as DNA or proteins can be attached to the functionalized nanotubes and used for biological applications. Functionalization is characterized by optical methods and atomic force microscopy (AFM). Length sorting of SWCNTs fit for use in bio-functionalization is also explored. By functionalizing SWCNTs with groups that are cytologically compatible, allowing for their dispersion in water, they show greater promise in future biological applications
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