770 research outputs found
Adaptive multibeam phased array design for a Spacelab experiment
The parametric tradeoff analyses and design for an Adaptive Multibeam Phased Array (AMPA) for a Spacelab experiment are described. This AMPA Experiment System was designed with particular emphasis to maximize channel capacity and minimize implementation and cost impacts for future austere maritime and aeronautical users, operating with a low gain hemispherical coverage antenna element, low effective radiated power, and low antenna gain-to-system noise temperature ratio
Study on successive superconducting transitions in TaSC from electrical resistivity and nonlinear AC magnetic susceptibility
TaSC compound undergoes superconducting transitions at K and K. The nature of successive
superconducting transitions has been studied from electrical resistivity,
linear and nonlinear AC magnetic susceptibilities. The resistivity at
= 0 shows a local maximum near , a kink-like behavior around
, and reduces to zero at below = 2.1 K. The dependence
of is observed at = 50 kOe at low temperatures, which is due to
two-dimensional weak-localization effect. Below a two-dimensional
superconducting phase occurs in each TaC layer. The linear and nonlinear
susceptibilities , ,
, and as well as the difference
() between the FC and ZFC
susceptibilities, start to appear below 6.0 K, the onset temperature of
irreversibility. A drastic growth of the in-plane superconducting coherence
length below 6.0 K gives rise to a three-dimensional superconducting phase
below , through interplanar Josephson couplings between adjacent TaC
layers. The oscillatory behavior of ,
, and below is
related to the nonlinear behavior arising from the thermally activated flux
flow.Comment: 11 pages, 10 figures, Physical Review B (accepted for publication
Biological Nanomotors with a Revolution, Linear, or Rotation Motion Mechanism
The ubiquitous biological nanomotors were classified into two categories in the past: linear and rotation motors. In 2013, a third type of biomotor, revolution without rotation (http://rnanano.osu.edu/movie.html), was discovered and found to be widespread among bacteria, eukaryotic viruses, and double-stranded DNA (dsDNA) bacteriophages. This review focuses on recent findings about various aspects of motors, including chirality, stoichiometry, channel size, entropy, conformational change, and energy usage rate, in a variety of well-studied motors, including FoF1 ATPase, helicases, viral dsDNA-packaging motors, bacterial chromosome translocases, myosin, kinesin, and dynein. In particular, dsDNA translocases are used to illustrate how these features relate to the motion mechanism and how nature elegantly evolved a revolution mechanism to avoid coiling and tangling during lengthy dsDNA genome transportation in cell division. Motor chirality and channel size are two factors that distinguish rotation motors from revolution motors. Rotation motors use right-handed channels to drive the right-handed dsDNA, similar to the way a nut drives the bolt with threads in same orientation; revolution motors use left-handed motor channels to revolve the right-handed dsDNA. Rotation motors use small channels (\u3c 2 nm in diameter) for the close contact of the channel wall with single-stranded DNA (ssDNA) or the 2-nm dsDNA bolt; revolution motors use larger channels (\u3e 3 nm) with room for the bolt to revolve. Binding and hydrolysis of ATP are linked to different conformational entropy changes in the motor that lead to altered affinity for the substrate and allow work to be done, for example, helicase unwinding of DNA or translocase directional movement of DNA
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