357 research outputs found
Growth, Injury, and Population Dynamics in the Extant Cyrtocrinid Holopus mikihe (Crinoidea, Echinodermata) near Roatan, Honduras
The crinoid order Cyrtocrinida is known mainly from Mesozoic fossils; its few surviving members, all from bathyal environments, are among the most peculiar living crinoids. Cyrtocrinids attributed to Holopus mikihe Donovan and Pawson, 2008, have been observed in large numbers via submersible off the western coast of RoatĂĄn, Honduras, on vertical and overhanging walls at depths between 430 and 640 m. Observations in 2012, 2013, and 2014 have permitted the first estimates of population structure, growth, and regeneration. Two size modes were observed; the flat barnacle-like âjuvenileâ stage resembles confamilial and co-occurring Cyathidium pourtalesiAmĂ©ziane, 1999, whereas the larger âadultsâ elevate the crown on a stumplike calyx. The 99th percentile growth rate was 0.19 cm yrâ1, giving a minimum predicted age of 16 yrs for the largest specimen and 8.7 yrs for the median specimen; the median growth rate was 0.04 cm yrâ1, corresponding to 72 and 39 yrs. However, the slower rate of growth in juvenile compared to adult specimens means that these ages are underestimates; actual median age may be closer to 50 yrs. Arm regeneration rate is estimated at 0.6 cm yrâ1, and 9.8% of adult individuals were visibly injured, giving an interval of about 1.4 yrs between arm loss events. No recruitment or mortality was observed, and aggregations of evenly-sized individuals were prevalent, consistent with sporadic local recruitment and mortality
A Model of Vertical Oligopolistic Competition
This paper develops a model of successive oligopolies with endogenous market entry, allowing for varying degrees of product differentiation and entry costs in both markets. Our analysis shows that the downstream conditions dominate the overall profitability of the two-tier structure while
the upstream conditions mainly affect the distribution of profits. We compare the welfare effects of upstream versus downstream deregulation policies and show that the impact of deregulation may be overvalued when ignoring feedback effects from the other market. Furthermore, we analyze how different forms of vertical restraints influence the endogenous market structure and show when they are welfare enhancing
Towards Logical Specification of Statistical Machine Learning
We introduce a logical approach to formalizing statistical properties of
machine learning. Specifically, we propose a formal model for statistical
classification based on a Kripke model, and formalize various notions of
classification performance, robustness, and fairness of classifiers by using
epistemic logic. Then we show some relationships among properties of
classifiers and those between classification performance and robustness, which
suggests robustness-related properties that have not been formalized in the
literature as far as we know. To formalize fairness properties, we define a
notion of counterfactual knowledge and show techniques to formalize conditional
indistinguishability by using counterfactual epistemic operators. As far as we
know, this is the first work that uses logical formulas to express statistical
properties of machine learning, and that provides epistemic (resp.
counterfactually epistemic) views on robustness (resp. fairness) of
classifiers.Comment: SEFM'19 conference paper (full version with errors corrected
Statistical Epistemic Logic
We introduce a modal logic for describing statistical knowledge, which we
call statistical epistemic logic. We propose a Kripke model dealing with
probability distributions and stochastic assignments, and show a stochastic
semantics for the logic. To our knowledge, this is the first semantics for
modal logic that can express the statistical knowledge dependent on
non-deterministic inputs and the statistical significance of observed results.
By using statistical epistemic logic, we express a notion of statistical
secrecy with a confidence level. We also show that this logic is useful to
formalize statistical hypothesis testing and differential privacy in a simple
and abstract manner
An empirical analysis of countervailing power in business-to-business bargaining
Pricing schemes in business-to-business (B2B) relationships reflect price discrimination and bargaining over rents. Bargaining outcomes are determined by upstream market power and countervailing buyer power downstream. This paper uses an exceptional panel of B2B transactions in the UK brick market to study B2B transaction prices. The empirical analysis identifies three effects on prices: nonlinear volume and freight absorption effects; countervailing power effects arising from buyers' local commercial significance; and competition effects due to the buyers' local potential suppliers. And it shows that small buyers benefit more from competition than large buyers because they are not constrained by the suppliers' capacity
Predicting new venture survival and growth: does the fog lift?
This paper investigates whether new venture performance becomes easier to predict as the venture ages: does the fog lift? To address this question we primarily draw upon a theoretical framework, initially formulated in a managerial context by Levinthal (Adm Sci Q 36(3):397â420, 1991) that sees new venture sales as a random walk but survival being determined by the stock of available resources (proxied by size). We derive theoretical predictions that are tested with a 10-year cohort of 6579 UK new ventures in the UK. We observe that our ability to predict firm growth deteriorates in the years after entryâin terms of the selection environment, the âfogâ seems to thicken. However, our survival predictions improve with timeâimplying that the âfogâ does lift
- âŠ