294 research outputs found
Continuum Limit of from 2+1 Flavor Domain Wall QCD
We determine the neutral kaon mixing matrix element in the continuum
limit with 2+1 flavors of domain wall fermions, using the Iwasaki gauge action
at two different lattice spacings. These lattice fermions have near exact
chiral symmetry and therefore avoid artificial lattice operator mixing.
We introduce a significant improvement to the conventional NPR method in
which the bare matrix elements are renormalized non-perturbatively in the
RI-MOM scheme and are then converted into the MSbar scheme using continuum
perturbation theory. In addition to RI-MOM, we introduce and implement four
non-exceptional intermediate momentum schemes that suppress infrared
non-perturbative uncertainties in the renormalization procedure. We compute the
conversion factors relating the matrix elements in this family of RI-SMOM
schemes and MSbar at one-loop order. Comparison of the results obtained using
these different intermediate schemes allows for a more reliable estimate of the
unknown higher-order contributions and hence for a correspondingly more robust
estimate of the systematic error. We also apply a recently proposed approach in
which twisted boundary conditions are used to control the Symanzik expansion
for off-shell vertex functions leading to a better control of the
renormalization in the continuum limit.
We control chiral extrapolation errors by considering both the NLO SU(2)
chiral effective theory, and an analytic mass expansion. We obtain
B_K^{\msbar}(3 GeV) = 0.529(5)_{stat}(15)_\chi(2)_{FV}(11)_{NPR}. This
corresponds to . Adding
all sources of error in quadrature we obtain , with an overall combined error of 3.6%.Comment: 65 page
Infrared Properties of QCD from Dyson-Schwinger equations
I review recent results on the infrared properties of QCD from
Dyson-Schwinger equations. The topics include infrared exponents of
one-particle irreducible Green's functions, the fixed point behaviour of the
running coupling at zero momentum, the pattern of dynamical quark mass
generation and properties of light mesons.Comment: 47 pages, 19 figures, Topical Review to be published in J.Phys.G, v2:
typos corrected and some references adde
Performance-based vs socially supportive culture:a cross-national study of descriptive norms and entrepreneurship
This paper is a cross-national study testing a framework relating cultural descriptive norms to entrepreneurship in a sample of 40 nations. Based on data from the Global Leadership and Organizational Behavior Effectiveness project, we identify two higher-order dimensions of culture – socially supportive culture (SSC) and performance-based culture (PBC) – and relate them to entrepreneurship rates and associated supply-side and demand-side variables available from the Global Entrepreneurship Monitor. Findings provide strong support for a social capital/SSC and supply-side variable explanation of entrepreneurship rate. PBC predicts demand-side variables, such as opportunity existence and the quality of formal institutions to support entrepreneurship
A Cortical Attractor Network with Martinotti Cells Driven by Facilitating Synapses
The population of pyramidal cells significantly outnumbers the inhibitory interneurons in the neocortex, while at the same time the diversity of interneuron types is much more pronounced. One acknowledged key role of inhibition is to control the rate and patterning of pyramidal cell firing via negative feedback, but most likely the diversity of inhibitory pathways is matched by a corresponding diversity of functional roles. An important distinguishing feature of cortical interneurons is the variability of the short-term plasticity properties of synapses received from pyramidal cells. The Martinotti cell type has recently come under scrutiny due to the distinctly facilitating nature of the synapses they receive from pyramidal cells. This distinguishes these neurons from basket cells and other inhibitory interneurons typically targeted by depressing synapses. A key aspect of the work reported here has been to pinpoint the role of this variability. We first set out to reproduce quantitatively based on in vitro data the di-synaptic inhibitory microcircuit connecting two pyramidal cells via one or a few Martinotti cells. In a second step, we embedded this microcircuit in a previously developed attractor memory network model of neocortical layers 2/3. This model network demonstrated that basket cells with their characteristic depressing synapses are the first to discharge when the network enters an attractor state and that Martinotti cells respond with a delay, thereby shifting the excitation-inhibition balance and acting to terminate the attractor state. A parameter sensitivity analysis suggested that Martinotti cells might, in fact, play a dominant role in setting the attractor dwell time and thus cortical speed of processing, with cellular adaptation and synaptic depression having a less prominent role than previously thought
Varieties of export-oriented entrepreneurship in Asia
This paper explores differences in the proportion of export-oriented early-stage entrepreneurial activity in 12 Asian countries. Drawing on varieties of capitalism theory, we find that Asian countries with high quality institutions are more likely to have higher proportions of young export-oriented firms. However, analysis on a 51 country data set indicates that Asian countries have significantly fewer young export-oriented firms than do non-Asian countries. Furthermore, the multi-country study reveals that countries with higher proportions of export-oriented entrepreneurial activity tend to have flexible industrial relations, high quality vocational training, and confrontational labor-employer relations, however the proportion of export-oriented new ventures is not related to the quality of corporate governance and inter-firm relations
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Greasing the wheels? The impact of regulations and corruption on firm entry
This paper investigates the question of whether corruption might ‘grease the
wheels’ of an economy. We investigate whether and to what extent the impact of regulations
on entrepreneurship is dependent on corruption. We first test whether regulations robustly
deter firm entry into markets. Our results show that the existence of a larger number
of procedures required to start a business, as well as larger minimum capital requirements
are detrimental to entrepreneurship. Second, we test whether corruption reduces the negative
impact of regulations on entrepreneurship in highly regulated economies. Our empirical
analysis, covering a maximum of 43 countries over the 2003–2005 period, shows that corruption
facilitates firm entry in highly regulated economies. For example, the ‘greasing’
effect of corruption kicks in at around 50 days required to start a new business. Our results
thus provide support for the ‘grease the wheels’ hypothesis
A Neurocomputational Model of Stimulus-Specific Adaptation to Oddball and Markov Sequences
Stimulus-specific adaptation (SSA) occurs when the spike rate of a neuron decreases with repetitions of the same stimulus, but recovers when a different stimulus is presented. It has been suggested that SSA in single auditory neurons may provide information to change detection mechanisms evident at other scales (e.g., mismatch negativity in the event related potential), and participate in the control of attention and the formation of auditory streams. This article presents a spiking-neuron model that accounts for SSA in terms of the convergence of depressing synapses that convey feature-specific inputs. The model is anatomically plausible, comprising just a few homogeneously connected populations, and does not require organised feature maps. The model is calibrated to match the SSA measured in the cortex of the awake rat, as reported in one study. The effect of frequency separation, deviant probability, repetition rate and duration upon SSA are investigated. With the same parameter set, the model generates responses consistent with a wide range of published data obtained in other auditory regions using other stimulus configurations, such as block, sequential and random stimuli. A new stimulus paradigm is introduced, which generalises the oddball concept to Markov chains, allowing the experimenter to vary the tone probabilities and the rate of switching independently. The model predicts greater SSA for higher rates of switching. Finally, the issue of whether rarity or novelty elicits SSA is addressed by comparing the responses of the model to deviants in the context of a sequence of a single standard or many standards. The results support the view that synaptic adaptation alone can explain almost all aspects of SSA reported to date, including its purported novelty component, and that non-trivial networks of depressing synapses can intensify this novelty response
Measures and Limits of Models of Fixation Selection
Models of fixation selection are a central tool in the quest to understand how the human mind selects relevant information. Using this tool in the evaluation of competing claims often requires comparing different models' relative performance in predicting eye movements. However, studies use a wide variety of performance measures with markedly different properties, which makes a comparison difficult. We make three main contributions to this line of research: First we argue for a set of desirable properties, review commonly used measures, and conclude that no single measure unites all desirable properties. However the area under the ROC curve (a classification measure) and the KL-divergence (a distance measure of probability distributions) combine many desirable properties and allow a meaningful comparison of critical model performance. We give an analytical proof of the linearity of the ROC measure with respect to averaging over subjects and demonstrate an appropriate correction of entropy-based measures like KL-divergence for small sample sizes in the context of eye-tracking data. Second, we provide a lower bound and an upper bound of these measures, based on image-independent properties of fixation data and between subject consistency respectively. Based on these bounds it is possible to give a reference frame to judge the predictive power of a model of fixation selection . We provide open-source python code to compute the reference frame. Third, we show that the upper, between subject consistency bound holds only for models that predict averages of subject populations. Departing from this we show that incorporating subject-specific viewing behavior can generate predictions which surpass that upper bound. Taken together, these findings lay out the required information that allow a well-founded judgment of the quality of any model of fixation selection and should therefore be reported when a new model is introduced
SMEs and regional economic growth in Brazil
This is a working paper. It is also available at: http://ideas.repec.org/p/lbo/lbowps/2010_01.htmlThis paper examines the relationship between the Small and Medium Enterprise
(SME) sector and economic growth for an annual panel of Brazilian states for the
period 1985-2004. We investigate the importance of the relative size of the SME
sector measured by the share of the SME employment in total formal employment
and the level of human capital in SMEs measured by the average years of schooling
of SME employees. The empirical results indicate that the relative importance of
SMEs is negatively correlated with economic growth, a result that is consistent with
previous studies examining developing countries. In addition, our results also show
that human capital embodied in SMEs may be more important for economic growth
than the relative size of the SME sector
Prospect theory and the effects of bankruptcy laws on entrepreneurial aspirations
We apply prospect theory to explain how personal and corporate bankruptcy laws affect risk perceptions of entrepreneurs at time of entry and therefore their growth ambitions. Previous theories have reached ambiguous conclusions as to whether countries with more debtor-friendly bankruptcy laws (i.e. laws that are more forgiving towards debtors in bankruptcy proceedings) are likely to have more entrepreneurs, or whether, creditorfriendly regimes have positive effects on new ventures via enhanced incentives for the supply of credit to entrepreneurs. Responding to this ambiguity, we apply prospect theory to propose that entrepreneurs do not attach the same significance to different elements of bankruptcy codes—and to explain which aspects of debtor-friendly bankruptcy laws matter more to entrepreneurs. Based on this, we derive and confirm hypotheses about the impact of aspects of bankruptcy codes on entrepreneurial activity using the Global Entrepreneurship Monitor combined with data on both personal and corporate bankruptcyregulations for 15 developed OECD countries. We use multilevel random coefficient logistic regressions to take account of the hierarchical nature of the data (country and individual levels). Because entrepreneurs and creditors are sensitive to different elements of the codes, there is scope for optimisation of the legal design of bankruptcy law to achieve both an adequate supply of credit and to encourage high-ambition entrepreneurship
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