The moderating role of learning on competitive advantage : longitudinal evidence from young firms

The question of how young firms reconcile the absence of well-established learning routines arising from the “liabilities of newness” with the “learning advantages of newness” has received scant attention in entrepreneurship. While older firms follow established learning routines and sometimes face problems in overcoming inertia, young firms with lower levels of inertia are better poised to explore, search and test unique avenues for their products and services. The process of learning and capability development as well as establishing uniqueness in their product offerings is an important part not only in the early stages of firm growth, but also in firm survival. Given their inexperience, for young firms, these learning processes are iterative and include contrasting learning loops that sometimes progress and at other times digress from initially perceived unique ideas. Such processes are embedded within capabilities that the firm develops and nurtures. Based on this premise and adopting a capabilities-based view, we examine how strategic networks and environmental knowledge affects uniqueness- mediated performance in young firms. We identify firms with digressive learning strategies based on their self-assessment of learning and compare them with other firms to demonstrate a differential effect on performance.

Recombination, decreased host specificity and increased mobility may have driven the emergence of maize streak virus as an agricultural pathogen

Maize streak virus (MSV; family Geminiviridae, genus Mastrevirus), the causal agent of maize streak disease, ranks amongst the most serious biological threats to food security in subSaharan Africa. Although five distinct MSV strains have been currently described, only one of these - MSV-A - causes severe disease in maize. Due primarily to their not being an obvious threat to agriculture, very little is known about the 'grass-adapted' MSV strains, MSV-B, -C, -D and -E. Since comparing the genetic diversities, geographical distributions and natural host ranges of MSV-A with the other MSV strains could provide valuable information on the epidemiology, evolution and emergence of MSV-A, we carried out a phylogeographical analysis of MSVs found in uncultivated indigenous African grasses. Amongst the 83 new MSV genomes presented here, we report the discovery of six new MSV strains (MSV-F to -K). The non-random recombination breakpoint distributions detectable with these and other available mastrevirus sequences partially mirror those seen in begomoviruses, implying that the forces shaping these breakpoint patterns have been largely conserved since the earliest geminivirus ancestors. We present evidence that the ancestor of all MSV-A variants was the recombinant progeny of ancestral MSV-B and MSV-G/-F variants. While it remains unknown whether recombination influenced the emergence of MSV-A in maize, our discovery that MSV-A variants may both move between and become established in different regions of Africa with greater ease, and infect more grass species than other MSV strains, goes some way towards explaining why MSV-A is such a successful maize pathogen. © 2008 SGM.

Dating the origins of the maize-adapted strain of maize streak virus, MSV-A

Maize streak virus (MSV), which causes maize streak disease (MSD), is one of the most serious biotic threats to African food security. Here, we use whole MSV genomes sampled over 30 years to estimate the dates of key evolutionary events in the 500 year association of MSV and maize. The substitution rates implied by our analyses agree closely with those estimated previously in controlled MSV evolution experiments, and we use them to infer the date when the maize-adapted strain, MSV-A, was generated by recombination between two grass-adapted MSV strains. Our results indicate that this recombination event occurred in the mid-1800s, ∼20 years before the first credible reports of MSD in South Africa and centuries after the introduction of maize to the continent in the early 1500s. This suggests a causal link between MSV recombination and the emergence of MSV-A as a serious pathogen of maize. © 2009 SGM.

Inhibition of maize streak virus (MSV) replication by transient and transgenic expression of MSV replication-associated protein mutants

Maize streak disease is a severe agricultural problem in Africa and the development of maize genotypes resistant to the causal agent, Maize streak virus (MSV), is a priority. A transgenic approach to engineering MSV-resistant maize was developed and tested in this study. A pathogen-derived resistance strategy was adopted by using targeted deletions and nucleotide-substitution mutants of the multifunctional MSV replication-associated protein gene (rep). Various rep gene constructs were tested for their efficacy in limiting replication of wild-type MSV by co-bombardment of maize suspension cells together with an infectious genomic clone of MSV and assaying replicative forms of DNA by quantitative PCR. Digitaria sanguinalis, an MSV-sensitive grass species used as a model monocot, was then transformed with constructs that had inhibited virus replication in the transient-expression system. Challenge experiments using leafhopper-transmitted MSV indicated significant MSV resistance - from highly resistant to immune - in regenerated transgenic D. sanguinalis lines. Whereas regenerated lines containing a mutated full-length rep gene displayed developmental and growth defects, those containing a truncated rep gene both were fertile and displayed no growth defects, making the truncated gene a suitable candidate for the development of transgenic MSV-resistant maize. © 2007 SGM.

Reconstructing the history of maize streak virus strain a dispersal to reveal diversification hot spots and its origin in southern Africa

Maize streak virus strain A (MSV-A), the causal agent of maize streak disease, is today one of the most serious biotic threats to African food security. Determining where MSV-A originated and how it spread transcontinentally could yield valuable insights into its historical emergence as a crop pathogen. Similarly, determining where the major extant MSV-A lineages arose could identify geographical hot spots of MSV evolution. Here, we use model-based phylogeographic analyses of 353 fully sequenced MSV-A isolates to reconstruct a plausible history of MSV-A movements over the past 150 years. We show that since the probable emergence of MSV-A in southern Africa around 1863, the virus spread transcontinentally at an average rate of 32.5 km/year (95% highest probability density interval, 15.6 to 51.6 km/year). Using distinctive patterns of nucleotide variation caused by 20 unique intra-MSV-A recombination events, we tentatively classified the MSV-A isolates into 24 easily discernible lineages. Despite many of these lineages displaying distinct geographical distributions, it is apparent that almost all have emerged within the past 4 decades from either southern or east-central Africa. Collectively, our results suggest that regular analysis of MSV-A genomes within these diversification hot spots could be used to monitor the emergence of future MSV-A lineages that could affect maize cultivation in Africa. © 2011, American Society for Microbiology.

Near work-induced contrast adaptation in emmetropic and myopic children

Purpose. Contrast adaptation may induce an error signal for emmetropization. This research aims to determine whether reading causes contrast adaptation in children and, if so, to determine whether myopes exhibit greater contrast adaptation than emmetropes. Methods. Baseline contrast sensitivity was determined in 34 emmetropic and 34 spectacle-corrected myopic children for 0.5, 1.2, 2.7, 4.4, and 6.2 cycles per degree (cpd) horizontal sine-wave gratings. Effects of near tasks on contrast sensitivity were determined during periods spent looking at a 6.2 cpd horizontal grating and during periods spent reading lines of English text, with 1.2 cpd row frequency and 6 cpd stroke frequency. Results. Both emmetropic and myopic groups (mean ± SD; age, 10.3 ± 1.4 years) showed reduced contrast sensitivity during both near tasks, with greatest overall adaptation at 6.2 cpd. Adaptation induced by viewing the grating (0.15 ± 0.17 log unit [40%]; range, 0.07-0.27 log unit) was significantly greater than adaptation induced by reading text (0.11 ± 0.18 log unit [29%], 0.08-0.16 log unit) (F(1,594) = 10.7; P = 0.001). Myopic children showed significantly greater adaptation across the tasks (0.15 ± 0.18 log unit [42%]) than emmetropic children (0.10 ± 0.16 log unit [26%]) (F(1,66) = 7.30; P = 0.009), with the greatest difference occurring at 4.4 cpd (mean, 0.11 log unit [30%]). Conclusions. Grating and reading tasks induced contrast adaptation; viewing horizontal gratings induced greater adaptation than reading, and myopes exhibited greater adaptation than emmetropes. Contrast adaptation effects may underlie findings of prolonged near work being associated with myopia. However, our research does not show whether this is consequential or causal.

Change-induced stressors and effective coping strategies in nursing

This study seeks to examine the causality of non-nursing and nursing stressors on the job satisfaction of nurses and how coping strategies have a mediating influence on this relationship in the context of sector-wide reform. To conceptualize the relationships, a mediation path model was developed. Data were collected at two time points using a self-completed online survey over a six monthly interval. During time 1, 306 Australian nurses completed the online survey. In the first wave (time 1), 306 Australian nurses completed the survey. In the second wave (time 2), matched survey data were collected from 119 nurses. The analysis showed a significant causal relationship between time 1 administrative and role stressors and an increase in nursing stress in time 2. A significant relationship was also identified between job specific context stressors and the adoption of effective coping strategies to deal with increased level of change-induced stress and strain and the likelihood of reporting higher level of job satisfaction in time 2. This study contributes by providing an integrated theoretical perspective on how stress affects retention that has so far been elusive. This is useful to researchers wanting to examine this phenomenon further and practitioners responsible for implementing change programs.

Variation in risk seeking behavior in a natural experiment following a large negative wealth shock induced by a natural disaster

An ongoing challenge in behavioral economics is to understand the variations observed in risk attitudes as a function of their environmental context. Of particular interest is the effect of wealth on risk attitudes. The research in this area has however faced two constraints: the difficulty to study the causal effects of large changes in wealth, and the causal effects of losses on risk behavior. The present paper address this double limitation by providing evidence of the variation of risk attitude after large losses using a natural disaster (Brisbane floods) as the setting for a natural experiment.

The effect of alcohol and drug consumption on academic performance : a treatment effect evaluation

It is often argued that consumption of alcohol, tobacco and drugs is detrimental to the cognitive abilities of teenagers. In order to disentangle a possible causal effect of these substances use from a self-selection bias, we control for pupils previous performance and for their previous rate of progression applying a DiDiD strategy. Using the NELS 1988 panel dataset, we find that the effects of alcohol and tobacco on test scores disappear once the selection bias is controlled for (this does not preclude long term detrimental effects). However, we find reliable evidence that heavy use of drugs (marijuana and cocaine) has direct detrimental effects on educational achievements. Hence, our results may have significant policy implications.

Candidate radial-inflow turbines and high-density working fluids for geothermal power systems

Optimisation of Organic Rankine Cycles (ORCs) for binary-cycle geothermal applications could play a major role in the competitiveness of low to moderate temperature geothermal resources. Part of this optimisation process is matching cycles to a given resource such that power output can be maximised. Two major and largely interrelated components of the cycle are the working fluid and the turbine. Both components need careful consideration. Due to the temperature differences in geothermal resources a one-size-fits-all approach to surface power infrastructure is not appropriate. Furthermore, the traditional use of steam as a working fluid does not seem practical due to the low temperatures of many resources. A variety of organic fluids with low boiling points may be utilised as ORC working fluids in binary power cycle loops. Due to differences in thermodynamic properties, certain fluids are able to extract more heat from a given resource than others over certain temperature and pressure ranges. This enables the tailoring of power cycle infrastructure to best match the geothermal resource through careful selection of the working fluid and turbine design optimisation to yield the optimum overall cycle performance. This paper presents the rationale for the use of radial-inflow turbines for ORC applications and the preliminary design of several radial-inflow turbines based on a selection of promising ORC cycles using five different high-density working fluids: R134a, R143a, R236fa, R245fa and n-Pentane at sub- or trans-critical conditions. Numerous studies published compare a variety of working fluids for various ORC configurations. However, there is little information specifically pertaining to the design and implementation of ORCs using realistic radial turbine designs in terms of pressure ratios, inlet pressure, rotor size and rotational speed. Preliminary 1D analysis leads to the generation of turbine designs for the various cycles with similar efficiencies (77%) but large differences in dimensions (139289 mm rotor diameter). The highest performing cycle (R134a) was found to produce 33% more net power from a 150°C resource flowing at 10 kg/s than the lowest performing cycle (n-Pentane).

Anomalous event detection using a semi-two dimensional hidden Markov model

The rapid increase in the deployment of CCTV systems has led to a greater demand for algorithms that are able to process incoming video feeds. These algorithms are designed to extract information of interest for human operators. During the past several years, there has been a large effort to detect abnormal activities through computer vision techniques. Typically, the problem is formulated as a novelty detection task where the system is trained on normal data and is required to detect events which do not fit the learned `normal' model. Many researchers have tried various sets of features to train different learning models to detect abnormal behaviour in video footage. In this work we propose using a Semi-2D Hidden Markov Model (HMM) to model the normal activities of people. The outliers of the model with insufficient likelihood are identified as abnormal activities. Our Semi-2D HMM is designed to model both the temporal and spatial causalities of the crowd behaviour by assuming the current state of the Hidden Markov Model depends not only on the previous state in the temporal direction, but also on the previous states of the adjacent spatial locations. Two different HMMs are trained to model both the vertical and horizontal spatial causal information. Location features, flow features and optical flow textures are used as the features for the model. The proposed approach is evaluated using the publicly available UCSD datasets and we demonstrate improved performance compared to other state of the art methods.

Governance of learning mechanisms : evidence from construction firms

The focus of knowledge management (KM) in the construction industry is moving towards capability building for value creation. The study reported by this paper is motivated by recent assertions about the genesis and evolution of knowledge management capability (KMC) in the strategic management field. It attempts to shed light on the governance of learning mechanisms that develop KMC within the context of construction firms. A questionnaire survey was administered to a sample of construction contractors operating in the very dynamic Hong Kong market to elicit opinions on the learning mechanisms and business outcomes of targeted firms. On the basis of a total of 149 usable responses, structural equation modeling (SEM) analysis identified relationships among knowledge-governance mechanisms, knowledge processes, and business performance, thereby supporting the existence of strategic learning loops. The study findings provide evidence from the construction context for capability assertions that knowledge-governance mechanisms and processes form learning mechanisms that carry out strategic learning to create value, effect performance outcomes, and ultimately drive the evolution of KMC. The findings imply that it is feasible for managing construction firms to govern learning mechanisms through managing the capability-based holistic KM system, thereby reconfiguring KMC to match needs in the dynamic market environment over time.

Modeling as a means for making powerful ideas accessible to children at an early age

The SimCalc Vision and Contributions Advances in Mathematics Education 2013, pp 419-436 Modeling as a Means for Making Powerful Ideas Accessible to Children at an Early Age Richard Lesh, Lyn English, Serife Sevis, Chanda Riggs … show all 4 hide » Look Inside » Get Access Abstract In modern societies in the 21st century, significant changes have been occurring in the kinds of “mathematical thinking” that are needed outside of school. Even in the case of primary school children (grades K-2), children not only encounter situations where numbers refer to sets of discrete objects that can be counted. Numbers also are used to describe situations that involve continuous quantities (inches, feet, pounds, etc.), signed quantities, quantities that have both magnitude and direction, locations (coordinates, or ordinal quantities), transformations (actions), accumulating quantities, continually changing quantities, and other kinds of mathematical objects. Furthermore, if we ask, what kind of situations can children use numbers to describe? rather than restricting attention to situations where children should be able to calculate correctly, then this study shows that average ability children in grades K-2 are (and need to be) able to productively mathematize situations that involve far more than simple counts. Similarly, whereas nearly the entire K-16 mathematics curriculum is restricted to situations that can be mathematized using a single input-output rule going in one direction, even the lives of primary school children are filled with situations that involve several interacting actions—and which involve feedback loops, second-order effects, and issues such as maximization, minimization, or stabilizations (which, many years ago, needed to be postponed until students had been introduced to calculus). …This brief paper demonstrates that, if children’s stories are used to introduce simulations of “real life” problem solving situations, then average ability primary school children are quite capable of dealing productively with 60-minute problems that involve (a) many kinds of quantities in addition to “counts,” (b) integrated collections of concepts associated with a variety of textbook topic areas, (c) interactions among several different actors, and (d) issues such as maximization, minimization, and stabilization.

Effects of schedule pressure on construction performance

Accelerating a project can be rewarding. The consequences, however, can be troublesome if productivity and quality are sacrificed for the sake of remaining ahead of schedule, such that the actual schedule benefits are often barely worth the effort. The tradeoffs and paths of schedule pressure and its causes and effects are often overlooked when schedule decisions are being made. This paper analyses the effects that schedule pressure has on construction performance, and focuses on tradeoffs in scheduling. A research framework has been developed using a causal diagram to illustrate the cause-and-effect analysis of schedule pressure. An empirical investigation has been performed by using survey data collected from 102 construction practitioners working in 38 construction sites in Singapore. The results of this survey data analysis indicate that advantages of increasing the pace of work—by working under schedule pressure—can be offset by losses in productivity and quality. The negative effects of schedule pressure arise mainly by working out of sequence, generating work defects, cutting corners, and losing the motivation to work. The adverse effects of schedule pressure can be minimized by scheduling construction activities realistically and planning them proactively, motivating workers, and by establishing an effective project coordination and communication mechanism.

Candidate gene analysis for quantitative traits using the transmission disequilibrium test : the example of the melanocortin 4-receptor in pigs

Population-wide associations between loci due to linkage disequilibrium can be used to map quantitative trait loci (QTL) with high resolution. However, spurious associations between markers and QTL can also arise as a consequence of population stratification. Statistical methods that cannot differentiate between loci associations due to linkage disequilibria from those caused in other ways can render false-positive results. The transmission-disequilibrium test (TDT) is a robust test for detecting QTL. The TDT exploits within-family associations that are not affected by population stratification. However, some TDTs are formulated in a rigid-form, with reduced potential applications. In this study we generalize TDT using mixed linear models to allow greater statistical flexibility. Allelic effects are estimated with two independent parameters: one exploiting the robust within-family information and the other the potentially biased between-family information. A significant difference between these two parameters can be used as evidence for spurious association. This methodology was then used to test the effects of the fourth melanocortin receptor (MC4R) on production traits in the pig. The new analyses supported the previously reported results; i.e., the studied polymorphism is either causal of in very strong linkage disequilibrium with the causal mutation, and provided no evidence for spurious association.