Dynamic assembly of Hda and the sliding clamp in the regulation of replication licensing

Regulatory inactivation of DnaA (RIDA) is one of the major regulatory mechanisms of prokaryotic replication licensing. In RIDA, the Hda-sliding clamp complex loaded onto DNA directly interacts with adenosine triphosphate (ATP)-bound DnaA and stimulates the hydrolysis of ATP to inactivate DnaA. A prediction is that the activity of Hda is tightly controlled to ensure that replication initiation occurs only once per cell cycle. Here, we determined the crystal structure of the Hda-�� clamp complex. This complex contains two pairs of Hda dimers sandwiched between two �� clamp rings to form an octamer that is stabilized by three discrete interfaces. Two separate surfaces of Hda make contact with the �� clamp, which is essential for Hda function in RIDA. The third interface between Hda monomers occludes the active site arginine finger, blocking its access to DnaA. Taken together, our structural and mutational analyses of the Hda-�� clamp complex indicate that the interaction of the �� clamp with Hda controls the ability of Hda to interact with DnaA. In the octameric Hda-�� clamp complex, the inability of Hda to interact with DnaA is a novel mechanism that may regulate Hda function. ? The Author(s) 2017.113Ysciescopu

Dyson-Schwinger Equations - aspects of the pion

The contemporary use of Dyson-Schwinger equations in hadronic physics is exemplified via applications to the calculation of pseudoscalar meson masses, and inclusive deep inelastic scattering with a determination of the pion's valence-quark distribution function.Comment: 4 pages. Contribution to the Proceedings of ``DPF 2000,'' the Meeting of the Division of Particles and Fields of the American Physical Society, August 9-12, 2000, Department of Physics, the Ohio State University, Columbus, Ohi

Motion Robust Magnetic Susceptibility and Field Inhomogeneity Estimation Using Regularized Image Restoration Techniques for fMRI

In functional MRI, head motion may cause dynamic nonlinear field-inhomogeneity changes, especially with large out-of-plane rotations. This may lead to dynamic geometric distortion or blurring in the time series, which may reduce activation detection accuracy. The use of image registration to estimate dynamic field inhomogeneity maps from a static field map is not sufficient in the presence of such rotations. This paper introduces a retrospective approach to estimate magnetic susceptibility induced field maps of an object in motion, given a static susceptibility induced field map and the associated object motion parameters. It estimates a susceptibility map from a static field map using regularized image restoration techniques, and applies rigid body motion to the former. The dynamic field map is then computed using susceptibility voxel convolution. The method addresses field map changes due to out-of-plane rotations during time series acquisition and does not involve real time field map acquisitions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85944/1/Fessler233.pd

Adhesive latching and legless leaping in small, worm-like insect larvae

Jumping is often achieved using propulsive legs, yet legless leaping has evolved multiple times. We examined the kinematics, energetics, and morphology of long-distance jumps produced by the legless larvae of gall midges (Asphondylia sp.). They store elastic energy by forming their body into a loop and pressurizing part of their body to form a transient “leg”. They prevent movement during elastic loading by placing two regions covered with microstructures against each other, which likely serve as a newly-described adhesive latch. Once the latch releases, the transient “leg” launches the body into the air. Their average takeoff speeds (mean: 0.88 m s-1; range: 0.38-1.33 m s-1) and horizontal travel distances (up to 36 times body length or 121 mm) rival those of legged insect jumpers and their mass specific power density (mean: 1390 W kg-1; range: 240-2950 W kg-1) indicates the use of elastic energy storage to launch the jump. Based on the forces reported for other microscale adhesive structures, the adhesive latching surfaces are sufficient to oppose the loading forces prior to jumping. Energetic comparisons of insect larval crawling versus jumping indicate that these jumps are orders of magnitude more efficient than would be possible if the animals had crawled an equivalent distance. These discoveries integrate three vibrant areas in engineering and biology - soft robotics, small, high acceleration systems, and adhesive systems - and point toward a rich, and as-yet untapped area of biological diversity of worm-like, small, legless jumpers

Meson Structure Functions in Valon Model

Parton distributions in a {\it{valon}} in the next-to-leading order is used to determine the patron distributions in pion and kaon. The validity of the valon model is tested and shown that the partonic content of the valon is universal and independent of the valon type. We have evaluated the valon distribution in pion and kaon, and in particular it is shown that the results are in good agreement with the experimental data on pion structure in a wide range of $x=[10^{-4},1]$Comment: 13 pages with 7 figures included, The manuscript is revised, figures are added and some errors are corrected. Accepted for publication in Physical Review

Higher twists in the pion structure function

We calculate the QCD moments of the pion structure function using Drell-Yan data on the quark distributions in the pion and a phenomenological model for the resonance region. The extracted higher twist corrections are found to be larger than those for the nucleon, contributing around 50% of the lowest moment at Q^2=1 GeV^2.Comment: 8 pages, 3 figures, to appear in Phys. Rev.

Quantum oscillation of magnetoresistance in tunneling junctions with a nonmagnetic spacer

We make a theoretical study of the quantum oscillations of the tunneling magnetoresistance (TMR) as a function of the spacer layer thickness. Such oscillations were recently observed in tunneling junctions with a nonmagnetic metallic spacer at the barrier-electrode interface. It is shown that momentum selection due to the insulating barrier and conduction via quantum well states in the spacer, mediated by diffusive scattering caused by disorder, are essential features required to explain the observed period of oscillation in the TMR ratio and its asymptotic value for thick nonmagnetic spacer.Comment: 4 pages, 5 figures, two column, REVTex4 styl

Valence-quark distributions in the pion

We calculate the pion's valence-quark momentum-fraction probability distribution using a Dyson-Schwinger equation model. Valence-quarks with an active mass of 0.30 GeV carry 71% of the pion's momentum at a resolving scale q_0=0.54 GeV = 1/(0.37 fm). The shape of the calculated distribution is characteristic of a strongly bound system and, evolved from q_0 to q=2 GeV, it yields first, second and third moments in agreement with lattice and phenomenological estimates, and valence-quarks carrying 49% of the pion's momentum. However, pointwise there is a discrepancy between our calculated distribution and that hitherto inferred from parametrisations of extant pion-nucleon Drell-Yan data.Comment: 8 pages, 3 figures, REVTEX, aps.sty, epsfig.sty, minor corrections, version to appear in PR

X-Ray Scattering Measurements of the Transient Structure of a Driven Charge-Density-Wave

We report time-resolved x-ray scattering measurements of the transient structural response of the sliding {\bf Q}$_{1}$ charge-density-wave (CDW) in NbSe$_{3}$ to a reversal of the driving electric field. The observed time scale characterizing this response at 70K varies from $\sim$ 15 msec for driving fields near threshold to $\sim$ 2 msec for fields well above threshold. The position and time-dependent strain of the CDW is analyzed in terms of a phenomenological equation of motion for the phase of the CDW order parameter. The value of the damping constant, $\gamma = (3.2 \pm 0.7) \times 10^{-19}$ eV $\cdot$ seconds $\cdot$ \AA$^{-3}$, is in excellent agreement with the value determined from transport measurements. As the driving field approaches threshold from above, the line shape becomes bimodal, suggesting that the CDW does not depin throughout the entire sample at one well-defined voltage.Comment: revtex 3.0, 7 figure