Factors associated with growth changes in ‘gazelles’

The goal of this paper is to identify the factors that precede and may cause sudden changes in the pace of growth of high-growth SMEs or gazelles. A retrospective longitudinal case study of seven high growth SMEs that had undergone a total of 14 sudden shifts in growth reveals that a number of events caused the changes of pace. Some were triggered by the entrepreneur's decisions while others resulted from events beyond his/her control. Management's motivation for growth was an important element and this motivation changed over time, being influenced by both success and problems associated with actual growth. The success of growth strategies also appears to depend on the firm's proximity to its client base and its ability to obtain the information required for sound decision-making. Lastly, the availability of tangible and intangible resources was found essential in allowing the company to seize growth opportunities and proximity to the business milieu may help accessing these resources

Quantum dynamics in high codimension tilings: from quasiperiodicity to disorder

We analyze the spreading of wavepackets in two-dimensional quasiperiodic and random tilings as a function of their codimension, i.e. of their topological complexity. In the quasiperiodic case, we show that the diffusion exponent that characterizes the propagation decreases when the codimension increases and goes to 1/2 in the high codimension limit. By constrast, the exponent for the random tilings is independent of their codimension and also equals 1/2. This shows that, in high codimension, the quasiperiodicity is irrelevant and that the topological disorder leads in every case, to a diffusive regime, at least in the time scale investigated here.Comment: 4 pages, 5 EPS figure

Critical properties of the Fermi-Bose Kondo and pseudogap Kondo models: Renormalized perturbation theory

Magnetic impurities coupled to both fermionic and bosonic baths or to a fermionic bath with pseudogap density of states, described by the Fermi-Bose Kondo and pseudogap Kondo models, display non-trivial intermediate coupling fixed points associated with critical local-moment fluctuations and local non-Fermi liquid behavior. Based on renormalization group together with a renormalized perturbation expansion around the free-impurity limit, we calculate various impurity properties in the vicinity of those intermediate-coupling fixed points. In particular, we compute the conduction electron T matrix, the impurity susceptibility, and the residual impurity entropy, and relate our findings to certain scenarios of local quantum criticality in strongly correlated lattice models.Comment: 16 pages, 5 figs; (v2) large-N results for entropy of Bose-Kondo model added; (v3) final version as publishe

Dispersion of Ordered Stripe Phases in the Cuprates

A phase separation model is presented for the stripe phase of the cuprates, which allows the doping dependence of the photoemission spectra to be calculated. The idealized limit of a well-ordered array of magnetic and charged stripes is analyzed, including effects of long-range Coulomb repulsion. Remarkably, down to the limit of two-cell wide stripes, the dispersion can be interpreted as essentially a superposition of the two end-phase dispersions, with superposed minigaps associated with the lattice periodicity. The largest minigap falls near the Fermi level; it can be enhanced by proximity to a (bulk) Van Hove singularity. The calculated spectra are dominated by two features -- this charge stripe minigap plus the magnetic stripe Hubbard gap. There is a strong correlation between these two features and the experimental photoemission results of a two-peak dispersion in La$_{2-x}$Sr$_x$CuO$_4$, and the peak-dip-hump spectra in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The differences are suggestive of the role of increasing stripe fluctuations. The 1/8 anomaly is associated with a quantum critical point, here expressed as a percolation-like crossover. A model is proposed for the limiting minority magnetic phase as an isolated two-leg ladder.Comment: 24 pages, 26 PS figure

Aqueous dune-like bedforms in Athabasca Valles and neighbouring locations utilized in palaeoflood reconstruction

Putative fluvial dunes have been identified within the Athabasca Valles and associated network of channels on Mars. Previous published work identified and measured bedforms in Athabasca Valles using photoclinometry methods on 2–3 m/pixel resolution Mars Orbiter Camera Narrow Angle images, and argued that these were created by an aqueous megaflood that occurred between 2 and 8 million years ago. This event is likely to have occurred due to geological activity associated with the Cerberus Fossae fracture system at the source of Athabasca Vallis. The present study has used higher resolution, 25 cm/pixel images from the Mars Reconnaissance Orbiter HiRISE camera, as well as stereo-derived digital terrain models and GIS software, to re-measure and evaluate these bedforms together with data from newly discovered neighbouring fields of bedforms. The analysis indicates that the bedforms are aqueous dunes, in that they occur in channel locations where dunes would be expected to be preserved and moreover they have geometries very similar to megaflood dunes on Earth. Dune geometries are used to estimate megaflood discharge rates, including uncertainty, which results support previous flood estimates that indicate that a flood with a discharge of ∼2 × 106m3s−1 created these bedforms

Patterns of ash (Fraxinus excelsior L.) colonization in mountain grasslands: the importance of management practices

International audienceWoody colonization of grasslands is often associated with changes in abiotic or biotic conditions or a combination of both. Widely used as fodder and litter in the past traditional agro-pastoral system, ash (Fraxinus excelsior L.) has now become a colonizing species of mountain grasslands in the French Pyrenees. Its present distribution is dependent on past human activities and it is locally controlled by propagule pressure and abiotic conditions. However, even when all favourable conditions are met, all the potentially colonizable grasslands are not invaded. We hypothesize that management practices should play a crucial role in the control of ash colonization. From empirical field surveys we have compared the botanical composition of a set of grasslands (present and former) differing in management practices and level of ash colonization. We have displayed a kind of successional gradient positively linked to both ash cover and height but not to the age of trees. We have tested the relationships between ash presence in grassland and management types i.e. cutting and/or grazing, management intensity and some grassland communities' features i.e. total and local specific richness and species heterogeneity. Mixed use (cutting and grazing) is negatively linked to ash presence in grassland whereas grazing alone positively. Mixed use and high grazing intensity are directly preventing ash seedlings establishment, when low grazing intensity is allowing ash seedlings establishment indirectly through herbaceous vegetation neglected by livestock. Our results show the existence of a limit between grasslands with and without established ashes corresponding to a threshold in the intensity of use. Under this threshold, when ash is established, the colonization process seems to become irreversible. Ash possesses the ability of compensatory growth and therefore under a high grazing intensity develops a subterranean vegetative reproduction. However the question remains at which stage of seedling development and grazing intensity these strategies could occur

Integrated analysis of environmental and genetic influences on cord blood DNA methylation in new-borns

Epigenetic processes, including DNA methylation (DNAm), are among the mechanisms allowing integration of genetic and environmental factors to shape cellular function. While many studies have investigated either environmental or genetic contributions to DNAm, few have assessed their integrated effects. Here we examine the relative contributions of prenatal environmental factors and genotype on DNA methylation in neonatal blood at variably methylated regions (VMRs) in 4 independent cohorts (overall n = 2365). We use Akaike’s information criterion to test which factors best explain variability of methylation in the cohort-specific VMRs: several prenatal environmental factors (E), genotypes in cis (G), or their additive (G + E) or interaction (GxE) effects. Genetic and environmental factors in combination best explain DNAm at the majority of VMRs. The CpGs best explained by either G, G + E or GxE are functionally distinct. The enrichment of genetic variants from GxE models in GWAS for complex disorders supports their importance for disease risk

Modelling the germination of Buddleia Davidii under constant conditions with the hydrothermal time concept

Buddleia davidii is a weed naturalized in New Zealand. It invades radiata pine plantations and causes major growth reduction and economic losses. Modelling its germination for predicting its occurrence will help foresters minimise its influence in forest plantations. Germination experiments have been carried out in laboratory to assess the influence of seed origin, defoliation, temperature and water stress on germination. Defoliation treatments did not significantly affect germination. The pattern of germination for seeds from four different places within New Zealand revealed so little difference that there is no need to define different models according to the site considered. However this similarity in germination pattern is limited to New Zealand and cannot be generalised to other countries where germination appears to be significantly different. The germination of Buddleia davidii seed appeared to be a function of hydrothermal time. The base, optimum and ceiling temperatures for Buddleia are respectively 9, 25 and from 30 to 35?, and Buddleia seed germinate between 0 and approximately -6 bars. In constant conditions, the predicted germination for Buddleia davidii with the thermal time model was limited to sub-optimal temperatures and the hydrotime and hydrothermal time models described well the germination pattern at any temperature and water potential. The modified hydrothermal time model proposed by Alvarado and Bradford (2002) most accurately predicted germination although it tended to overestimate the asymptotes. Overall the hydrothermal time model allowed prediction of actual timing of germination with much accuracy. This threshold model can therefore be used for modelling the germination of Buddleia davidii subjected to constant temperature and water potential conditions