371 research outputs found
Shaken and stirred: conduction and turbulence in clusters of galaxies
(abridged) Uninhibited radiative cooling in clusters of galaxies would lead
to excessive mass accretion rates contrary to observations. One of the key
proposals to offset radiative energy losses is thermal conduction from outer,
hotter layers of cool core clusters to their centers. However, conduction is
sensitive to magnetic field topology. In cool-core clusters the heat buoyancy
instability (HBI) leads to B-fields ordered preferentially in the direction
perpendicular to that of gravity, which significantly reduces the level of
conduction below the classical Spitzer-Braginskii value. However, the cluster
cool cores are rarely in perfect hydrostatic equilibrium. Sloshing motions due
to minor mergers, galaxy motions or AGN can significantly perturb the gas and
affect the level of thermal conduction. We perform 3D AMR MHD simulations of
the effect of turbulence on the properties of the anisotropic thermal
conduction in cool core clusters. We show that very weak subsonic motions, well
within observational constraints, can randomize the magnetic field and
significantly boost effective thermal conduction beyond the saturated values
expected in the pure unperturbed HBI case. We find that the turbulent motions
can essentially restore the conductive heat flow to the cool core to level
comparable to the theoretical maximum of 1/3 Spitzer for a highly tangled
field. Runs with radiative cooling show that the cooling catastrophe can be
averted and the cluster core stabilized. Above a critical Froude number, these
same turbulent motions also eliminate the tangential bias in the velocity and
magnetic field that is otherwise induced by the trapped g-modes. Our results
can be tested with future radio polarization measurements, and have
implications for efficient metal dispersal in clusters.Comment: submitted to ApJ, references added, expanded Section
HB 2108, HD 1, Relating to Fishing Regulations - Statement for Senate Committee on Economic Development Public Hearing - March 20, 1984
HB 1749, Relating to Waimea Bay - Statement for House Committee on Ocean and Marine Resources Public Hearing - February 3, 1986
SB 2025, Fishing in Certain Waters – House Committee on Ocean and Marine Resources Public Hearing – March 13, 1986
HR 97, Supporting a Tri-Fly Control Program Without the Use of Aerial Sprays - Statement for House Committees on Agriculture; Planning, Energy, and Environmental Protection; Health Public Hearing - February 13, 1985
Parker/buoyancy instabilities with anisotropic thermal conduction, cosmic rays, and arbitrary magnetic field strength
We report the results of a local stability analysis for a magnetized,
gravitationally stratified plasma containing cosmic rays. We account for
cosmic-ray diffusion and thermal conduction parallel to the magnetic field and
allow beta to take any value, where p is the plasma pressure and B is the
magnetic field strength. We take the gravitational acceleration to be in the
-z-direction and the equilibrium magnetic field to be in the y-direction, and
we derive the dispersion relation for small-amplitude instabilities and waves
in the large-|k_x| limit. We use the Routh-Hurwitz criterion to show
analytically that the necessary and sufficient criterion for stability in this
limit is n k_B dT/dz + dp_cr/dz + (1/8pi)dB^2/dz > 0, where T is the
temperature, n is the number density of thermal particles, and p_cr is the
cosmic-ray pressure. We present approximate analytical solutions for the normal
modes in the low- and high-diffusivity limits, show that they are consistent
with the derived stability criterion, and compare them to numerical results
obtained from the full, unapproximated, dispersion relation. Our results extend
earlier analyses of buoyancy instabilities in galaxy-cluster plasmas to the
beta <= 1 regime. Our results also extend earlier analyses of the Parker
instability to account for anisotropic thermal conduction, and show that the
interstellar medium is more unstable to the Parker instability than was
predicted by previous studies in which the thermal plasma was treated as
adiabatic.Comment: 36 pages, 2 figures, Accepted for publication in Ap
The structure of the ternary Eg5–ADP–ispinesib complex
The human kinesin Eg5 is responsible for bipolar spindle formation during early mitosis. Inhibition of Eg5 triggers the formation of monoastral spindles, leading to mitotic arrest that eventually causes apoptosis. There is increasing evidence that Eg5 constitutes a potential drug target for the development of cancer chemotherapeutics. The most advanced Eg5-targeting agent is ispinesib, which exhibits potent antitumour activity and is currently in multiple phase II clinical trials. In this study, the crystal structure of the Eg5 motor domain in complex with ispinesib, supported by kinetic and thermodynamic binding data, is reported. Ispinesib occupies the same induced-fit pocket in Eg5 as other allosteric inhibitors, making extensive hydrophobic interactions with the protein. The data for the Eg5-ADP-ispinesib complex suffered from pseudo-merohedral twinning and revealed translational noncrystallographic symmetry, leading to challenges in data processing, space-group assignment and structure solution as well as in refinement. These complications may explain the lack of available structural information for this important agent and its analogues. The present structure represents the best interpretation of these data based on extensive data-reduction, structure-solution and refinement trials
TEF, Vol. 2 No. 1
The second annual literary anthology of students writing from Stephen F Austin State College.https://scholarworks.sfasu.edu/tef/1001/thumbnail.jp
Identification and validation of the mode of action of the chalcone anti-mycobacterial compounds
Objectives The search for new TB drugs has become one of the great challenges for modern medicinal chemistry. An improvement in the outcomes of TB chemotherapy can be achieved by the development of new, shorter, cheap, safe and effective anti-TB regimens. Methods Chalcones (1a-1o) were synthesized and evaluated for their antimycobacterial activity against Mycobacterium bovis BCG using growth inhibition assays. Compound 1a was selected as a ‘hit’ compound. The mode of action of compound 1a, was identified by mycolic acid methyl esters (MAMEs) and fatty acid methyl esters (FAMEs) analysis using thin layer chromatography. Dose dependent experiments were conducted by over-expressing components of FAS-II in M. bovis BCG to confirm the target. Ligand binding using intrinsic tryptophan assay and molecular docking were used to further validate the target. Results MAMEs and FAMEs analysis showed dose-dependent reduction of MAMEs with the overall abundance of FAMEs suggesting that compound 1a targets mycolic acid biosynthesis. Direct binding of 1a to InhA was observed using an intrinsic tryptophan fluorescence binding assay, and a 2-fold IC50 shift was observed with an InhA overexpressing strain confirming InhA as the cellular target. Conclusion The chalcone 1a exhibits potent antimycobacterial activity, displays a good safety profile and is a direct inhibitor of InhA, a key component in mycolic acid synthesis, validating this series for further anti-TB drug development
Deriving mesoscopic models of collective behaviour for finite populations
Animal groups exhibit emergent properties that are a consequence of local
interactions. Linking individual-level behaviour to coarse-grained descriptions
of animal groups has been a question of fundamental interest. Here, we present
two complementary approaches to deriving coarse-grained descriptions of
collective behaviour at so-called mesoscopic scales, which account for the
stochasticity arising from the finite sizes of animal groups. We construct
stochastic differential equations (SDEs) for a coarse-grained variable that
describes the order/consensus within a group. The first method of construction
is based on van Kampen's system-size expansion of transition rates. The second
method employs Gillespie's chemical Langevin equations. We apply these two
methods to two microscopic models from the literature, in which organisms
stochastically interact and choose between two directions/choices of foraging.
These `binary-choice' models differ only in the types of interactions between
individuals, with one assuming simple pair-wise interactions, and the other
incorporating higher-order effects. In both cases, the derived mesoscopic SDEs
have multiplicative, or state-dependent, noise. However, the different models
demonstrate the contrasting effects of noise: increasing order in the pair-wise
interaction model, whilst reducing order in the higher-order interaction model.
Although both methods yield identical SDEs for such binary-choice, or
one-dimensional, systems, the relative tractability of the chemical Langevin
approach is beneficial in generalizations to higher-dimensions. In summary,
this book chapter provides a pedagogical review of two complementary methods to
construct mesoscopic descriptions from microscopic rules and demonstrates how
resultant multiplicative noise can have counter-intuitive effects on shaping
collective behaviour.Comment: Second version, 4 figures, 2 appendice
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