340 research outputs found
Capture of particles of dust by convective flow
Interaction of particles of dust with vortex convective flows is under
theoretical consideration. It is assumed that the volume fraction of solid
phase is small, variations of density due to nonuniform distribution of
particles and those caused by temperature nonisothermality of medium are
comparable. Equations for the description of thermal buoyancy convection of a
dusty medium are developed in the framework of the generalized Boussinesq
approximation taking into account finite velocity of particle sedimentation.
The capture of a cloud of dust particles by a vortex convective flow is
considered, general criterion for the formation of such a cloud is obtained.
The peculiarities of a steady state in the form of a dust cloud and backward
influence of the solid phase on the carrier flow are studied in detail for a
vertical layer heated from the sidewalls. It is shown that in the case, when
this backward influence is essential, a hysteresis behavior is possible. The
stability analysis of the steady state is performed. It turns out that there is
a narrow range of governing parameters, in which such a steady state is stable.Comment: 14 pages, 10 figures, published in Physics of Fluid
Analysis of vibration impact on stability of dewetting thin liquid film
Dynamics of a thin dewetting liquid film on a vertically oscillating
substrate is considered. We assume moderate vibration frequency and large
(compared to the mean film thickness) vibration amplitude. Using the
lubrication approximation and the averaging method, we formulate the coupled
sets of equations governing the pulsatile and the averaged fluid flows in the
film, and then derive the nonlinear amplitude equation for the averaged film
thickness. We show that there exists a window in the frequency-amplitude domain
where the parametric and shear-flow instabilities of the pulsatile flow do not
emerge. As a consequence, in this window the averaged description is reasonable
and the amplitude equation holds. The linear and nonlinear analyses of the
amplitude equation and the numerical computations show that such vibration
stabilizes the film against dewetting and rupture.Comment: 19 pages, 11 figure
A First Principle Approach to Rescale the Dynamics of Simulated Coarse-Grained Macromolecular Liquids
We present a detailed derivation and testing of our approach to rescale the
dynamics of mesoscale simulations of coarse-grained polymer melts (I. Y.
Lyubimov et al. J. Chem. Phys. \textbf{132}, 11876, 2010). Starting from the
first-principle Liouville equation and applying the Mori-Zwanzig projection
operator technique, we derive the Generalized Langevin Equations (GLE) for the
coarse-grained representations of the liquid. The chosen slow variables in the
projection operators define the length scale of coarse graining. Each polymer
is represented at two levels of coarse-graining: monomeric as a bead-and-spring
model and molecular as a soft-colloid. In the long-time regime where the
center-of-mass follows Brownian motion and the internal dynamics is completely
relaxed, the two descriptions must be equivalent. By enforcing this formal
relation we derive from the GLEs the analytical rescaling factors to be applied
to dynamical data in the coarse-grained representation to recover the monomeric
description. Change in entropy and change in friction are the two corrections
to be accounted for to compensate the effects of coarse-graining on the polymer
dynamics. The solution of the memory functions in the coarse-grained
representations provides the dynamical rescaling of the friction coefficient.
The calculation of the internal degrees of freedom provides the correction of
the change in entropy due to coarse-graining. The resulting rescaling formalism
is a function of the coarse-grained model and thermodynamic parameters of the
system simulated. The rescaled dynamics obtained from mesoscale simulations of
polyethylene, represented as soft colloidal particles, by applying our
rescaling approach shows a good agreement with data of translational diffusion
measured experimentally and from simulations. The proposed method is used to
predict self-diffusion coefficients of new polyethylene samples.Comment: 21 pages, 6 figures, 6 tables. Submitted to Phys. Rev.
Cryo-EM structure of a helicase loading intermediate containing ORC-Cdc6-Cdt1-MCM2-7 bound to DNA
In eukaryotes, the Cdt1-bound replicative helicase core MCM2-7 is loaded onto DNA by the ORC-Cdc6 ATPase to form a prereplicative complex (pre-RC) with an MCM2-7 double hexamer encircling DNA. Using purified components in the presence of ATP-ÎłS, we have captured in vitro an intermediate in pre-RC assembly that contains a complex between the ORC-Cdc6 and Cdt1-MCM2-7 heteroheptamers called the OCCM. Cryo-EM studies of this 14-subunit complex reveal that the two separate heptameric complexes are engaged extensively, with the ORC-Cdc6 N-terminal AAA+ domains latching onto the C-terminal AAA+ motor domains of the MCM2-7 hexamer. The conformation of ORC-Cdc6 undergoes a concerted change into a right-handed spiral with helical symmetry that is identical to that of the DNA double helix. The resulting ORC-Cdc6 helicase loader shows a notable structural similarity to the replication factor C clamp loader, suggesting a conserved mechanism of action
Neutral Particles in Light of the Majorana-Ahluwalia Ideas
The first part of this article (Sections I and II) presents oneself an
overview of theory and phenomenology of truly neutral particles based on the
papers of Majorana, Racah, Furry, McLennan and Case. The recent development of
the construct, undertaken by Ahluwalia [{\it Mod. Phys. Lett. A}{\bf 9} (1994)
439; {\it Acta Phys. Polon. B}{\bf 25} (1994) 1267; Preprints LANL
LA-UR-94-1252, LA-UR-94-3118], could be relevant for explanation of the present
experimental situation in neutrino physics and astrophysics.
In Section III the new fundamental wave equations for self/anti-self
conjugate type-II spinors, proposed by Ahluwalia, are re-casted to covariant
form. The connection with the Foldy-Nigam-Bargmann-Wightman- Wigner (FNBWW)
type quantum field theory is found. The possible applications to the problem of
neutrino oscillations are discussed.Comment: REVTEX file. 21pp. No figure
Dark matter and structure formation a review
This paper provides a review of the variants of dark matter which are thought
to be fundamental components of the universe and their role in origin and
evolution of structures and some new original results concerning improvements
to the spherical collapse model. In particular, I show how the spherical
collapse model is modified when we take into account dynamical friction and
tidal torques
Effective Functional Form of Regge Trajectories
We present theoretical arguments and strong phenomenological evidence that
hadronic Regge trajectories are essentially nonlinear and can be well
approximated, for phenomenological purposes, by a specific square-root form.Comment: 29 pages, LaTeX. Published versio
Mechanism and timing of Mcm2–7 ring closure during DNA replication origin licensing
The opening and closing of two ring-shaped Mcm2-7 DNA helicases is necessary to license eukaryotic origins of replication, although the mechanisms controlling these events are unclear. The origin-recognition complex (ORC), Cdc6 and Cdt1 facilitate this process by establishing a topological link between each Mcm2-7 hexamer and origin DNA. Using colocalization single-molecule spectroscopy and single-molecule Förster resonance energy transfer (FRET), we monitored ring opening and closing of Saccharomyces cerevisiae Mcm2-7 during origin licensing. The two Mcm2-7 rings were open during initial DNA association and closed sequentially, concomitant with the release of their associated Cdt1. We observed that ATP hydrolysis by Mcm2-7 was coupled to ring closure and Cdt1 release, and failure to load the first Mcm2-7 prevented recruitment of the second Mcm2-7. Our findings identify key mechanisms controlling the Mcm2-7 DNA-entry gate during origin licensing, and reveal that the two Mcm2-7 complexes are loaded via a coordinated series of events with implications for bidirectional replication initiation and quality control.National Institutes of Health (U.S.) (Grant R01 GM52339)National Institutes of Health (U.S.) (Pre-Doctoral Training Grant GM007287)National Cancer Institute (U.S.) (Koch Institute Support Grant P30-CA14051
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