1,351 research outputs found
Is innovation always beneficial? A meta-analysis of the relationship between innovation and performance in SMEs
The performance implications of innovation in small and medium-sized enterprises (SMEs) have attracted considerable interest among academics and practitioners. However, empirical research on the innovation–performance relationship in SMEs shows controversial results. This meta-analysis synthesizes empirical findings in order to obtain evidence whether and especially under which circumstances smaller, resource-scarce firms benefit from innovation. We find that innovation–performance relationship is context dependent. Factors such as the age of the firm, the type of innovation, and the cultural context affect the impact of innovation on firm performance to a large extent
Mechanics of bundled semiflexible polymer networks
While actin bundles are used by living cells for structural fortification,
the microscopic origin of the elasticity of bundled networks is not understood.
Here, we show that above a critical concentration of the actin binding protein
fascin, a solution of actin filaments organizes into a pure network of bundles.
While the elasticity of weakly crosslinked networks is dominated by the affine
deformation of tubes, the network of bundles can be fully understood in terms
of non-affine bending undulations.Comment: 5 pages, 3 figures, final version as publishe
Microrheology, stress fluctuations and active behavior of living cells
We report the first measurements of the intrinsic strain fluctuations of
living cells using a recently-developed tracer correlation technique along with
a theoretical framework for interpreting such data in heterogeneous media with
non-thermal driving. The fluctuations' spatial and temporal correlations
indicate that the cytoskeleton can be treated as a course-grained continuum
with power-law rheology, driven by a spatially random stress tensor field.
Combined with recent cell rheology results, our data imply that intracellular
stress fluctuations have a nearly power spectrum, as expected for
a continuum with a slowly evolving internal prestress.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let
Nucleation-induced transition to collective motion in active systems
While the existence of polar ordered states in active systems is well
established, the dynamics of the self-assembly processes are still elusive. We
study a lattice gas model of self-propelled elongated particles interacting
through excluded volume and alignment interactions, which shows a phase
transition from an isotropic to a polar ordered state. By analyzing the
ordering process we find that the transition is driven by the formation of a
critical nucleation cluster and a subsequent coarsening process. Moreover, the
time to establish a polar ordered state shows a power-law divergence
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Steric regulation of tandem calponin homology domain actin-binding affinity.
Tandem calponin homology (CH1-CH2) domains are common actin-binding domains in proteins that interact with and organize the actin cytoskeleton. Despite regions of high sequence similarity, CH1-CH2 domains can have remarkably different actin-binding properties, with disease-associated point mutants known to increase as well as decrease affinity for F-actin. To investigate features that affect CH1-CH2 affinity for F-actin in cells and in vitro, we perturbed the utrophin actin-binding domain by making point mutations at the CH1-CH2 interface, replacing the linker domain, and adding a polyethylene glycol (PEG) polymer to CH2. Consistent with a previous model describing CH2 as a steric negative regulator of actin binding, we find that utrophin CH1-CH2 affinity is both increased and decreased by modifications that change the effective "openness" of CH1 and CH2 in solution. We also identified interface mutations that caused a large increase in affinity without changing solution "openness," suggesting additional influences on affinity. Interestingly, we also observe nonuniform subcellular localization of utrophin CH1-CH2 that depends on the N-terminal flanking region but not on bulk affinity. These observations provide new insights into how small sequence changes, such as those found in diseases, can affect CH1-CH2 binding properties
On the Efficient Calculation of a Linear Combination of Chi-Square Random Variables with an Application in Counting String Vacua
Linear combinations of chi square random variables occur in a wide range of
fields. Unfortunately, a closed, analytic expression for the pdf is not yet
known. As a first result of this work, an explicit analytic expression for the
density of the sum of two gamma random variables is derived. Then a
computationally efficient algorithm to numerically calculate the linear
combination of chi square random variables is developed. An explicit expression
for the error bound is obtained. The proposed technique is shown to be
computationally efficient, i.e. only polynomial in growth in the number of
terms compared to the exponential growth of most other methods. It provides a
vast improvement in accuracy and shows only logarithmic growth in the required
precision. In addition, it is applicable to a much greater number of terms and
currently the only way of computing the distribution for hundreds of terms. As
an application, the exponential dependence of the eigenvalue fluctuation
probability of a random matrix model for 4d supergravity with N scalar fields
is found to be of the asymptotic form exp(-0.35N).Comment: 21 pages, 19 figures. 3rd versio
Grain Boundary Scars and Spherical Crystallography
We describe experimental investigations of the structure of two-dimensional
spherical crystals. The crystals, formed by beads self-assembled on water
droplets in oil, serve as model systems for exploring very general theories
about the minimum energy configurations of particles with arbitrary repulsive
interactions on curved surfaces. Above a critical system size we find that
crystals develop distinctive high-angle grain boundaries, or scars, not found
in planar crystals. The number of excess defects in a scar is shown to grow
linearly with the dimensionless system size. The observed slope is expected to
be universal, independent of the microscopic potential.Comment: 4 pages, 3 eps figs (high quality images available from Mark Bowick
Mechanical tension and spontaneous muscle twitching precede the formation of cross-striated muscle in vivo
Muscle forces are produced by repeated stereotypical actomyosin units called sarcomeres. Sarcomeres are chained into linear myofibrils spanning the entire muscle fiber. In mammalian body muscles, myofibrils are aligned laterally, resulting in their typical cross-striated morphology. Despite this detailed textbook knowledge about the adult muscle structure, it is still unclear how cross-striated myofibrils are built in vivo. Here, we investigate the morphogenesis of Drosophila abdominal muscles and establish them as an in vivo model for cross-striated muscle development. By performing live imaging, we find that long immature myofibrils lacking a periodic actomyosin pattern are built simultaneously in the entire muscle fiber and then align laterally to give mature cross-striated myofibrils. Interestingly, laser micro-lesion experiments demonstrate that mechanical tension precedes the formation of the immature myofibrils. Moreover, these immature myofibrils do generate spontaneous Ca2+-dependent contractions in vivo, which, when chemically blocked, result in cross-striation defects. Taken together, these results suggest a myofibrillogenesis model in which mechanical tension and spontaneous muscle twitching synchronize the simultaneous self-organization of different sarcomeric protein complexes to build highly regular cross-striated myofibrils spanning the length of large muscle fibers
Evidence-based entrepreneurship: Cumulative science, action principles, and bridging the gap between science and practice
10.1561/0300000044Foundations and Trends in Entrepreneurship811-6
Ein Status Quo: Haben Milchkühe Zahnprobleme?
Dental abnormalities in cows have seldomly been examined in research and veterinary check-up. This study estimated the prevalence of dental problems in cows. The skulls of 151 adult (> 4 years) dairy cows (Brown Swiss cattle n=81, Swiss
Fleckvieh n=70) were categorized into three age groups (AK1: 4-6 / AK2: 7-9 / AK3: 10-16 years old) and examined for the existence of 11 dental cheek teeth abnormalities, based on well-known dental pathologies in horses. The four most
prevalent dental abnormalities found were presence of abnormal spaces between 2 adjacent cheek teeth (Diastema), parodontosis, wavemouth, and food packing between cheek teeth. In 85% of all recorded skulls, 1 or more abnormalities were recorded. There were no differences in the occurrence of dental abnormalities in the
two breeds. Older animals of AK3 showed more abnormalities than younger animals, but also in the lower age categories, in average 2 abnormalities per skull were recorded. 36% of all skulls showed the presence of Diastema, which has been
described as one of the most painful oral abnormalities in horse. Dental abnormalities are prevalent in cows and probably a not recognized cause of health disorders
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