47,369 research outputs found
Clerocidin selectively modifies the gyrase-DNA gate to induce irreversible and reversible DNA damage
Clerocidin (CL), a microbial diterpenoid, reacts with DNA via its epoxide group and stimulates DNA cleavage by type II DNA topoisomerases. The molecular basis of CL action is poorly understood. We establish by genetic means that CL targets DNA gyrase in the gram-positive bacterium Streptococcus pneumoniae, and promotes gyrase-dependent single- and double-stranded DNA cleavage in vitro. CL-stimulated DNA breakage exhibited a strong preference for guanine preceding the scission site (-1 position). Mutagenesis of -1 guanines to A, C or T abrogated CL cleavage at a strong pBR322 site. Surprisingly, for double-strand breaks, scission on one strand consistently involved a modified (piperidine-labile) guanine and was not reversed by heat, salt or EDTA, whereas complementary strand scission occurred at a piperidine-stable -1 nt and was reversed by EDTA. CL did not induce cleavage by a mutant gyrase (GyrA G79A) identified here in CL-resistant pneumococci. Indeed, mutations at G79 and at the neighbouring S81 residue in the GyrA breakage-reunion domain discriminated poisoning by CL from that of antibacterial quinolones. The results suggest a novel mechanism of enzyme inhibition in which the -1 nt at the gyrase-DNA gate exhibit different CL reactivities to produce both irreversible and reversible DNA damage
Constructing the cultural repertoire in a natural disaster: The role of social media in the Thailand flood of 2011
In 2011, Thailand witnessed its worst flooding catastrophe in half a century. In this study, we explored social media as a new and promising weapon to address the physical and morale challenges caused by the natural disaster. A case study was conducted in the context of crisis response, whichinvestigated the use of social media to contribute to the collective cultural repertoire during the natural disaster. By investigating two paths toward the cultural repertoire construction considering different social groups, this study also identified the roles of social media as an information market and an information threshold in the crisis response
Rheology of human blood plasma: Viscoelastic versus Newtonian behavior
We investigate the rheological characteristics of human blood plasma in shear
and elongational flows. While we can confirm a Newtonian behavior in shear flow
within experimental resolution, we find a viscoelastic behavior of blood plasma
in the pure extensional flow of a capillary break-up rheometer. The influence
of the viscoelasticity of blood plasma on capillary blood flow is tested in a
microfluidic device with a contraction-expansion geometry. Differential
pressure measurements revealed that the plasma has a pronounced flow resistance
compared to that of pure water. Supplementary measurements indicate that the
viscoelasticity of the plasma might even lead to viscoelastic instabilities
under certain conditions. Our findings show that the viscoelastic properties of
plasma should not be ignored in future studies on blood flow.Comment: 4 figures, 1 supplementary material Highlighted in
http://physics.aps.org/articles/v6/1
The induced representations of Brauer algebra and the Clebsch-Gordan coefficients of SO(n)
Induced representations of Brauer algebra from with are discussed. The induction coefficients
(IDCs) or the outer-product reduction coefficients (ORCs) of with up to a normalization factor are
derived by using the linear equation method. Weyl tableaus for the
corresponding Gel'fand basis of SO(n) are defined. The assimilation method for
obtaining CG coefficients of SO(n) in the Gel'fand basis for no modification
rule involved couplings from IDCs of Brauer algebra are proposed. Some
isoscalar factors of for the resulting irrep
with
$\sum\limits_{i=1}^{4}\lambda_{i}\leq .Comment: 48 pages latex, submitted to Journal of Phys.
Post-Newtonian factorized multipolar waveforms for spinning, non-precessing black-hole binaries
We generalize the factorized resummation of multipolar waveforms introduced
by Damour, Iyer and Nagar to spinning black holes. For a nonspinning
test-particle spiraling a Kerr black hole in the equatorial plane, we find that
factorized multipolar amplitudes which replace the residual relativistic
amplitude f_{l m} with its l-th root, \rho_{l m} = f_{l m}^{1/l}, agree quite
well with the numerical amplitudes up to the Kerr-spin value q \leq 0.95 for
orbital velocities v \leq 0.4. The numerical amplitudes are computed solving
the Teukolsky equation with a spectral code. The agreement for prograde orbits
and large spin values of the Kerr black hole can be further improved at high
velocities by properly factoring out the lower-order post-Newtonian
contributions in \rho_{l m}. The resummation procedure results in a better and
systematic agreement between numerical and analytical amplitudes (and energy
fluxes) than standard Taylor-expanded post-Newtonian approximants. This is
particularly true for higher-order modes, such as (2,1), (3,3), (3,2), and
(4,4) for which less spin post-Newtonian terms are known. We also extend the
factorized resummation of multipolar amplitudes to generic mass-ratio,
non-precessing, spinning black holes. Lastly, in our study we employ new,
recently computed, higher-order post-Newtonian terms in several subdominant
modes, and compute explicit expressions for the half and one-and-half
post-Newtonian contributions to the odd-parity (current) and even-parity (odd)
multipoles, respectively. Those results can be used to build more accurate
templates for ground-based and space-based gravitational-wave detectors.Comment: 37 pages, 11 figures; Typos in Sec.IV Eqs.(38-42) fixe
Various Correlations in Anisotropic Heisenberg XYZ Model with Dzyaloshinski-Moriya Interaction
Various thermal correlations as well as the effect of intrinsic decoherence
on the correlations are studied in a two-qubit Heisenberg XYZ spin chain with
the Dzyaloshinski--Moriya (DM) interaction along the z direction, i.e. Dz. It
is found that tunable parameter Dz may play a constructive role on the
concurrence (C), classical correlation (CC) and quantum discord (QD) in thermal
equilibrium while it plays a destructive role on the correlations in the
intrinsic decoherence case. The entanglement and quantum discord exhibit
collapse and revival under the phase decoherence. With a proper combination of
the system parameters, the correlations can effectively be kept at high steady
state values despite the intrinsic decoherence.Comment: 4 pages, 4 figure
Nanoladder cantilevers made from diamond and silicon
We present a "nanoladder" geometry that minimizes the mechanical dissipation
of ultrasensitive cantilevers. A nanoladder cantilever consists of a
lithographically patterned scaffold of rails and rungs with feature size
100 nm. Compared to a rectangular beam of the same dimensions, the mass and
spring constant of a nanoladder are each reduced by roughly two orders of
magnitude. We demonstrate a low force noise of zN and zN in a one-Hz bandwidth for devices made from silicon and
diamond, respectively, measured at temperatures between 100--150 mK. As opposed
to bottom-up mechanical resonators like nanowires or nanotubes, nanoladder
cantilevers can be batch-fabricated using standard lithography, which is a
critical factor for applications in scanning force microscopy
Current Path Properties of the Transport Anisotropy at Filling Factor 9/2
To establish the presence and orientation of the proposed striped phase in
ultra-high mobility 2D electron systems at filling factor 9/2, current path
transport properties are determined by varying the separation and allignment of
current and voltage contacts. Contacts alligned orthogonal to the proposed
intrinsic striped phase produce voltages consistent with current spreading
along the stripes; current driven along the proposed stripe direction results
in voltages consistent with channeling along the stripes. Direct comparison is
made to current spreading/channeling properties of artificially induced 1D
charge modulated systems, which indicates the 9/2 direction.Comment: 10 pages, 4 figure
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