21,274 research outputs found
Properties of tug-of-war model for cargo transport by molecular motors
Molecular motors are essential components for the biophysical functions of
the cell. Our current quantitative understanding of how multiple motors move
along a single track is not complete; even though models and theories for
single motor chemomechanics abound. Recently, M.J.I. Mller {\em
et al.} have developed a tug-of-war model to describe the bidirectional
movement of the cargo (PNAS(2008) 105(12) P4609-4614). Through Monte Carlo
simulations, they discovered that the tug-of-war model exhibits several
qualitative different motility regimes, which depend on the precise value of
single motor parameters, and they suggested the sensitivity can be used by a
cell to regulate its cargo traffic. In the present paper, we carry out a
thorough analysis of the tug-of-war model. All the stable, i.e., biophysically
observable, steady states are obtained. Depending on several parameters, the
system exhibits either uni-, bi- or tristability. Based on the separating
boundary of the different stable states and the initial numbers of the
different motor species that are bound to the track, the steady state of the
cargo movement can be predicted, and consequently the steady state velocity can
be obtained. It is found that, the velocity, even the direction, of the cargo
movement change with the initial numbers of the motors which are bound to the
track and several other parameters
Controlling for heterogeneity in gravity models of trade and integration
This paper compares various specifications of the gravity model of trade as nested versions of a general specification that uses bilateral country-pair fixed effects to control for heterogeneity. For each specification, we show that the atheoretical restrictions used to obtain them from the general model are not supported statistically. Because the gravity model has become the "workhorse" baseline model for estimating the effects of international integration, this has important empirical implications. In particular, we show that, unless heterogeneity is accounted for correctly, gravity models can greatly overestimate the effects of integration on the volume of trade.International trade
Differential equation based method for accurate approximations in optimization
A method to efficiently and accurately approximate the effect of design changes on structural response is described. The key to this method is to interpret sensitivity equations as differential equations that may be solved explicitly for closed form approximations, hence, the method is denoted the Differential Equation Based (DEB) method. Approximations were developed for vibration frequencies, mode shapes and static displacements. The DEB approximation method was applied to a cantilever beam and results compared with the commonly-used linear Taylor series approximations and exact solutions. The test calculations involved perturbing the height, width, cross-sectional area, tip mass, and bending inertia of the beam. The DEB method proved to be very accurate, and in most cases, was more accurate than the linear Taylor series approximation. The method is applicable to simultaneous perturbation of several design variables. Also, the approximations may be used to calculate other system response quantities. For example, the approximations for displacements are used to approximate bending stresses
Controlling for heterogeneity in gravity models of trade and integration
This paper compares various specifications of the gravity model of trade as nested versions of a general specification that uses bilateral country-pair fixed effects to control for heterogeneity. For each specification, we show that the a theoretical restrictions to obtain them from the general model are not supported statistically. Because the gravity model has become the ‘workhorse’ baseline model for estimating the effects of international integration, this has important empirical implications. In particular, we show that, unless heterogeneity is accounted for correctly, gravity models can greatly overestimate the effects of integration on the volume of trade.International trade
Lunar analogs of fluvial landscapes - Possible implications, 1 March 1968 - 1 February 1970
Geomorphic approach to possibility of fluid erosion on moo
The Therapeutic Bond Scales: Psychometric Characteristics and Relationship to Treatment Effectiveness
The Therapeutic Bond Scales assess the quality of the therapeutic relationship from the patient\u27s perspective. The therapeutic bond is composed of 3 aspects: working alliance, empathic resonance, and mutual affirmation. Scales were developed to measure these aspects and the therapeutic bond as a whole. The correlations between these scales and 2 measures of outcome (session quality assessed by the patient and termination outcome evaluated by nonparticipant raters) were examined. All scales were significantly correlated with session quality. Therapeutic bond was significantly correlated with termination outcome in both a linear and a curvilinear fashion, suggesting that, at least in the initial phase of therapy, the therapeutic bond can be too high as well as too low
A vocabulary list based on word frequency in fifth and sixth grade textbooks
Thesis (Ed.M.)--Boston Universit
Relaxation time of the topological T1 process in a two-dimensional foam
The elementary topological T1 process in a two-dimensional foam corresponds
to the "flip" of one soap film with respect to the geometrical constraints.
From a mechanical point of view, this T1 process is an elementary relaxation
process through which the entire structure of an out-of-equilibrium foam
evolves. The dynamics of this elementary relaxation process has been poorly
investigated and is generally neglected during simulations of foams. We study
both experimentally and theoretically the T1 dynamics in a dry two-dimensional
foam. We show that the dynamics is controlled by the surface viscoelastic
properties of the soap films (surface shear plus dilatational viscosity, ms+k,
and Gibbs elasticity e), and is independent of the shear viscosity of the bulk
liquid. Moreover, our approach illustrates that the dynamics of T1 relaxation
process provides a convenient tool for measuring the surface rheological
properties: we obtained e = 32+/-8 mN/m and ms+k = 1.3+/-0.7 mPa.m.s for SDS,
and e = 65+/-12 mN/m and ms+k = 31+/-12 mPa.m.s for BSA, in good agreement with
values reported in the literature
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