Explicit Tests Research Articles

On stability of the second order neutral differential equation

There exist a well-developed stability theory for neutral differential equations of the first order and only a few results on functional differential equations of the second order. One of the aims of this paper is to fill this gap. Explicit tests for stability of linear neutral delay differential equations of the second order are obtained.

Comments on the entropic gravity proposal

Explicit tests are presented of the conjectured entropic origin of the gravitational force. The gravitational force on a test particle in the vicinity of the horizon of a large Schwarzschild black hole in arbitrary spacetime dimensions is obtained as entropic force. The same conclusion can be reached for the cases of a large electrically charged black hole and a large slowly rotating Kerr black hole. The generalization along the same lines to a test mass in the field of an arbitrary spherical star is also studied and found not to be possible. Our results thus reinforce the argument that the entropic gravity proposal cannot account for the gravitational force in generic situations.

Tests of size and growth effects on Arctic charr (Salvelinus alpinus) otolith δ18 O and δ13 C values.

Otolith δ18 O and δ13 C values have been used extensively to reconstruct thermal and diet histories. Researchers have suggested that individual growth rate and size may have an effect on otolith isotope ratios and subsequently confound otolith-based thermal and diet reconstructions. As few explicit tests of the effect on fish in freshwater environments exist, here we determine experimentally the potential for related growth rate and size effects on otolith δ18 O and δ13 C values. Fifty Arctic charr were raised in identical conditions for two years after which their otoliths were removed and analyzed for their δ18 O and δ13 C values. The potential effects of final length and the Thermal Growth Coefficient (TGC) on otolith isotope ratios were tested using correlation and regression analysis to determine if significant effects were present and to quantify effects when present. The analyses indicated that TGC and size had significant and similar positive non-linear relationships with δ13 C values and explained 35% and 42% of the variability, respectively. Conversely, both TGC and size were found to have no significant correlation with otolith δ18 O values. There was no significant correlation between δ18 O and δ13 C values. The investigation indicated the presence of linked growth rate and size effects on otolith δ13 C values, the nature of which requires further study. Otolith δ18 O values were unaffected by individual growth rate and size, confirming the applicability of these values to thermal reconstructions of fish habitat.

Discretized Keiper/Li Approach to the Riemann Hypothesis

ABSTRACTThe Keiper–Li sequence {λn} is most sensitive to the Riemann Hypothesis asymptotically (n → ∞), but highly elusive both analytically and numerically. We deform it to fully explicit sequences, simpler to analyze and to compute (up to n = 5 · 105 by G. Misguich). This also works on the Davenport–Heilbronn counterexamples, thus we can demonstrate explicit tests that selectively react to zeros off the critical line.

Evolution of floral traits and impact of reproductive mode on diversification in the phlox family (Polemoniaceae)

Pollinator-mediated selection is a major driver of evolution in flowering plants, contributing to the vast diversity of floral features. Despite long-standing interest in floral variation and the evolution of pollination syndromes in Polemoniaceae, the evolution of floral traits and known pollinators has not been investigated in an explicit phylogenetic context. Here we explore macroevolutionary patterns of both pollinator specificity and three floral traits long considered important determinants of pollinator attraction across the most comprehensive species-level phylogenetic tree yet produced for the family. The presence of floral chlorophyll is reconstructed as the ancestral character state of the family, even though the presence of floral anthocyanins is the most prevalent floral pigment in extant taxa. Mean corolla length and width of the opening of the floral tube are correlated, and both appear to vary with pollinator type. The evolution of pollination systems appears labile, with multiple gains and losses of selfing and conflicting implications for patterns of diversification. Explicit testing of diversification models rejects the hypothesis that selfing is an evolutionary dead-end. This study begins to disentangle the individual components that comprise pollination syndromes and lays the foundation for future work on the genetic mechanisms that control each trait.

Accounting comparability and relative performance evaluation in CEO compensation

We investigate whether accounting comparability is associated with the likelihood that CEO compensation is tied to relative accounting performance (e.g., return on assets). We predict that higher accounting comparability increases the risk-sharing benefit of accounting-based RPE because peer firm performance better controls for common risk in RPE firm performance. Thus, firms that have higher accounting comparability with potential performance peers will be more likely to include accounting-based RPE as a component of the total CEO compensation contract. We find support for this prediction using (1) an explicit test design that relies on the ex ante terms of CEO compensation contracts obtained from proxy disclosures, and (2) an implicit design that relies on the actual realizations of CEO compensation. To provide further evidence, we examine the association between accounting comparability and the selection of performance peers when the CEO compensation contract includes an accounting-based RPE component. We find that higher comparability between the RPE firm and a potential peer firm increases (decreases) the potential peer firm’s likelihood of being selected into (dropped from) the peer group. Cross-sectional analyses show that this association is less pronounced, or not present, when the relative performance measure is price-based (as opposed to accounting-based), indicating that these results do not merely reflect a more general role of comparability in all RPE contracts.

Positivity for non-Metzler systems and its applications to stability of time-varying delay systems

In 1950, Wazewski obtained the following necessary and sufficient condition for positivity of linear systems of ordinary differential equations: the matrix of coefficients is Metzler (i.e. off-diagonal elements in the matrix of coefficients are nonnegative). No results on the positivity of solutions to delay systems in the case where the matrix is non-Metzler were expected to be obtained. It was demonstrated that for delay systems the Wazewski condition is not a necessary one. We prove results on positivity of solutions for non-Metzler systems of delay differential equations. New explicit tests for exponential stability are obtained as applications of results on positivity for non-Metzler systems. Examples demonstrate possible applications of our theorems to stabilization. For instance, in view of our results, the implicit requirement on dominance of the main diagonal can be skipped. Our approach is based on nonoscillation of solutions and positivity of the Cauchy functions of scalar diagonal delay differential equations.

Shortfall risk through Fenchel duality

In this paper, we propose a Fenchel duality approach to study the minimization problem of the shortfall risk. We consider a general increasing and strictly convex loss function, which may be more general than the situation of convex risk measures usually assumed in the literature. We first translate the associated stochastic optimization problem to an equivalent static optimization problem, and then obtain the explicit structure of the optimal randomized test for both complete and incomplete markets. For the incomplete market case, to the best of our knowledge, we obtain for the first time the explicit randomized test, while previous literature only established the existence through the supermartingale optional decomposition approach. We also solve the shortfall risk minimization problem for an insider through the enlargement of filtrations approach.

Normal development of context processing using the AXCPT paradigm.

Context processing involves a flexible and continually updated representation of task relevant information and is a core aspect of cognitive control. The expectancy AX Continuous Performance Test (AXCPT) was designed to specifically measure context processing and has been widely applied to elucidate mechanisms of cognitive control and their impairments in conditions such as aging and schizophrenia. Here we present a large-sample, cross-sectional study of context processing aimed at characterizing its normal development from childhood to early adulthood (8 to 22 years old). We track the age-related changes in the standard AXCPT performance measures and also investigate their validity using detailed data-driven method. We show how critical maturational changes in context processing can be validly tracked from mid-adolescence onward with increasing reliance on preparatory, proactive strategies well into early adulthood. However, the early maturation from childhood into adolescence showed a sharp, two-fold discontinuity: while standard measures provide partially conflicting results suggesting an early worsening of proactive strategies, further analyses do not support their validity during this period. Our findings advocate the existence of multiple preparatory strategies that cannot be captured by indices that assume a simple dichotomy of proactive vs. reactive strategies. When evaluating context processing differences over development or in clinical populations, we advocate the explicit testing of the assumptions underlying standard AXCPT indices through complementary data-driven methods.

Testing a longitudinal compensation model in premanifest Huntington's disease.

The initial stages of neurodegeneration are commonly marked by normal levels of cognitive and motor performance despite the presence of structural brain pathology. Compensation is widely assumed to account for this preserved behaviour, but despite the apparent simplicity of such a concept, it has proven incredibly difficult to demonstrate such a phenomenon and distinguish it from disease-related pathology. Recently, we developed a model of compensation whereby brain activation, behaviour and pathology, components key to understanding compensation, have specific longitudinal trajectories over three phases of progression. Here, we empirically validate our explicit mathematical model by testing for the presence of compensation over time in neurodegeneration. Huntington's disease is an ideal model for examining longitudinal compensation in neurodegeneration as it is both monogenic and fully penetrant, so disease progression and potential compensation can be monitored many years prior to diagnosis. We defined our conditions for compensation as non-linear longitudinal trajectories of brain activity and performance in the presence of linear neuronal degeneration and applied our model of compensation to a large longitudinal cohort of premanifest and early-stage Huntington's disease patients from the multisite Track-On HD study. Focusing on cognitive and motor networks, we integrated progressive volume loss, task and resting state functional MRI and cognitive and motor behaviour across three sequential phases of neurodegenerative disease progression, adjusted for genetic disease load. Multivariate linear mixed models were fitted and trajectories for each variable tested. Our conceptualization of compensation was partially realized across certain motor and cognitive networks at differing levels. We found several significant network trends that were more complex than that hypothesized in our model. These trends suggest changes to our theoretical model where the network effects are delayed relative to performance effects. There was evidence of compensation primarily in the prefrontal component of the cognitive network, with increased effective connectivity between the left and right dorsolateral prefrontal cortex. Having developed an operational model for the explicit testing of longitudinal compensation in neurodegeneration, it appears that general patterns of our framework are consistent with the empirical data. With the proposed modifications, our operational model of compensation can be used to test for both cross-sectional and longitudinal compensation in neurodegenerative disease with similar patterns to Huntington's disease.

Spatial and environmental factors predict skull variation and genetic structure in the cosmopolitan bat Tadarida brasiliensis

AbstractAimTo assess if geographical and/or environmental factors are driving skull morphology and genetic structure in the cosmopolitan bat species, Tadarida brasiliensis.LocationNorth, Central and South America, Greater and Lesser Antilles.MethodsWe analysed morphometric, genetic and environmental data from the entire distribution of T. brasiliensis. Individuals were genotyped at nine nuclear loci, and clustering analyses were used to detect genetic groups and test correlations between genetic, geographical, and environmental distances. Museum specimens were photographed and 111 two‐dimensional landmarks were digitized per individual. Multivariate analyses were applied to explore whether factors such as sex, genetic group, subspecies, biogeographical regions, latitude, longitude and/or environment contribute to the morphometric variation of this species. We also applied a novel approach based on trend surface analyses and model selection to compare models of spatial and environmental dependence and to predict size, shape, and allometry‐free variation across the Americas.ResultsGenetic and morphometric differences among populations coincide with major biogeographical and climatic breaks in Nearctic, Neotropical and Antillean regions. Trend surface analyses showed that skull size variation can be explained by spatial factors (latitude and longitude), whereas skull shape can be explained by the interaction of spatial and environmental factors. However, allometry‐free shape variation might respond to complex interactions not captured by our models.Main conclusionOur explicit testing of spatial and environmental dependence using geostatistical model selection approaches allowed us to identify extrinsic factors that shape genetic and phenotypic responses in a cosmopolitan bat species. Our findings suggest that skull size is primarily driven by geographical factors (genetic drift), whereas shape variation is driven by adaptive responses to environmental conditions.

Learning for pitch and melody discrimination in congenital amusia

Congenital amusia is currently thought to be a life-long neurogenetic disorder in music perception, impervious to training in pitch or melody discrimination. This study provides an explicit test of whether amusic deficits can be reduced with training. Twenty amusics and 20 matched controls participated in four sessions of psychophysical training involving either pure-tone (500 Hz) pitch discrimination or a control task of lateralization (interaural level differences for bandpass white noise). Pure-tone pitch discrimination at low, medium, and high frequencies (500, 2000, and 8000 Hz) was measured before and after training (pretest and posttest) to determine the specificity of learning. Melody discrimination was also assessed before and after training using the full Montreal Battery of Evaluation of Amusia, the most widely used standardized test to diagnose amusia. Amusics performed more poorly than controls in pitch but not localization discrimination, but both groups improved with practice on the trained stimuli. Learning was broad, occurring across all three frequencies and melody discrimination for all groups, including those who trained on the non-pitch control task. Following training, 11 of 20 amusics no longer met the global diagnostic criteria for amusia. A separate group of untrained controls (n = 20), who also completed melody discrimination and pretest, improved by an equal amount as trained controls on all measures, suggesting that the bulk of learning for the control group occurred very rapidly from the pretest. Thirty-one trained participants (13 amusics) returned one year later to assess long-term maintenance of pitch and melody discrimination. On average, there was no change in performance between posttest and one-year follow-up, demonstrating that improvements on pitch- and melody-related tasks in amusics and controls can be maintained. The findings indicate that amusia is not always a life-long deficit when using the current standard diagnostic criteria.

Shortfall Risk Through Fenchel Duality

In this paper, we propose a Fenchel duality approach to study the minimization problem of the shortfall risk. We consider a general increasing and strictly convex loss function, which may be more general than the situation of convex risk measures usually assumed in the literature. We first translate the associated stochastic optimization problem to an equivalent static optimization problem, and then obtain the explicit structure of the optimal randomized test for both complete and incomplete markets. For the incomplete market case, to the best of our knowledge, we obtain for the first time the explicit randomized test, while previous literature only established the existence through the supermartingale optional decomposition approach. We also solve the shortfall risk minimization problem for an insider through the enlargement of filtrations approach.

Further evaluation of the use of preference categories to identify novel reinforcers: A systematic replication

Preference assessments are frequently used to identify reinforcers for individuals with autism spectrum disorder and intellectual and developmental disabilities. Although well‐established procedures have been shown to identify preferred stimuli for individual items that can be used in skill acquisition and behavior reduction programs, little research has been conducted on identifying categories of preferred items. In this study, paired‐stimulus preference assessments were conducted with 4 individuals with autism spectrum disorder. Researchers classified the edible stimuli as belonging to 1 of 4 categories: chocolate (e.g., chocolate chips and M&M's®), salty/crunchy (e.g., chips and crackers), gummy (e.g., Swedish Fish® and Starburst®), or fruit/vegetable (e.g., grape and apple). Preference hierarchies were identified for individual stimuli and for categories of stimuli. For all participants, at least 3 of the 4 most preferred items came from the same category. Novel items (i.e., items not included in the preference assessments) identified by the researchers as belonging to the high‐preference category functioned as effective reinforcers during subsequent reinforcer assessments for all participants. This finding suggests that clinicians could identify likely effective edible reinforcers based on an individual's categorical preference without explicit testing.

Can't Read my Broker Face: Learning About Trustworthiness With Age.

We assessed how age impacted learning who to trust, and the extent to which this type of learning relied on explicit memory. In contrast to prior studies, target faces were neutral without prior reputational information. Younger (YA) and older adults (OA) made investment decisions for 36 brokers, who yielded a good, neutral, or bad outcome. Brokers were encountered three times to measure adaptive learning. After the investment task, participants completed a surprise explicit source memory test for brokers. Although YA and OA learned to distinguish good and bad brokers from neutral ones, OA did not learn the brokers' behavior as well as younger adults. In addition, explicit source memory was highly correlated with investment decisions, although less so for good brokers for older than younger adults. Findings extend prior work by establishing that OA impairments in learning who to trust extend to neutral faces, and highlighting the role of explicit memory in investment performance. Future work should vary the task demands to explore the contribution of explicit and implicit processes.

Existing blood transcriptional classifiers accurately discriminate active tuberculosis from latent infection in individuals from south India

Several studies have identified blood transcriptomic signatures that can distinguish active from latent Tuberculosis (TB). The purpose of this study was to assess how well these existing gene profiles classify TB disease in a South Indian population. RNA sequencing was performed on whole blood PAXgene samples collected from 28 TB patients and 16 latently TB infected (LTBI) subjects enrolled as part of an ongoing household contact study. Differential gene expression and clustering analyses were performed and compared with explicit predictive testing of TB and LTBI individuals based on established gene signatures. We observed strong predictive performance of TB disease states based on expression of known gene sets (ROC AUC 0.9007–0.9879). Together, our findings indicate that previously reported classifiers generated from different ethnic populations can accurately discriminate active TB from LTBI in South Indian patients. Future work should focus on converting existing gene signatures into a universal TB gene signature for diagnosis, monitoring TB treatment, and evaluating new drug regimens.

Variable retention times and in-stream nutrient sinks

ABSTRACTLehman JT. 2018. Variable retention times and in-stream nutrient sinks. Lake Reserv Manage. 34:1–6.This note reports an explicit test of theory proposed by the author in a previous paper. A 1-season field campaign was conducted to test the proposition that point sources, nonpoint sources, and sinks can be distinguished from one another along stream segments where both are present. Both a conservative ion, chloride, and a non-conservative ion, nitrate, were measured. Predicted chloride fluxes matched measured fluxes almost perfectly, demonstrating point sources and nonpoint sources but no sinks. Nitrate fluxes proved problematic, however. Point sources, non-point sources, and sinks were evident and the data suggested that a 3-parameter plug flow reactor (PFR) model with variable retention times was superior at time scales of 1 week to the 2-parameter linear model that had been proposed earlier. Applied to historical data at the scale of 1 mo the 2 models were indistinguishable. By using the conservative tracer it was possible to verify the completeness of the water balance, which was essential for distinguishing between the 2 models at short time scales.

Permissible Collateral and Access to Finance: Evidence from a Quasi-Natural Experiment

By allowing large classes of movable assets to be used as collateral, the Property Law reform trans-formed the secured transactions in China. Difference-in-differences tests show firms operating with ex-ante more movable assets expand access to bank credit and prolong debt maturity. However, the reform does not seem to improve the efficiency of credit allocation, as debt capacity of ex-ante low quality firms expands the most following the reform. Credit expansion also does not lead to better firm performance. These findings are not driven by confounding factors such as improvements in creditor and property rights protection. Our results also cannot be explained by other important reforms which were introduced around the same time as the introduction of the Property Law. These include anti-tunneling and split-share reforms and amendments to the corporate tax structure in China. We conduct explicit robustness tests for these other reforms and amendments to the corporate tax structure in China. We conduct explicit robustness tests for these other reforms and hence contribute to the empirical literature on the reform process in China with new findings.

Model based insulin absorption into intravenous infusion sets in adult and neonatal intensive care unit’s

Abstract Introduction: While still a contentious topic, some studies suggest regulating blood glucose (BG) between 4.4 and 8.0 mmol/L improves clinical outcomes. Model based approaches have been successful at modulating BG in intensive care unit (ICU) setting using insulin. However, insulin absorption by infusion set materials may reduce the quality of control. Previous studies highlight the occurrence of significant absorption, but are highly variable in methodology and results. No study considers or accounts for all potential variables affecting insulin absorption by infusion tubing. This study will identify and model these variables to better understand and account for potential insulin losses. Modelling Methodology: The insulin absorption model developed is a compartment model based on conservation of mass. Literature data was collected and the model was validated based on fitting error. K1 and K2 are the absorption rates of insulin into the tubing and the rate of insulin release into free flow, respectively. K1 and K2 and were identified iteratively using Matlab to fit the model to literature data. Results and Discussion: The model fit the experimental data for PE and PVC tubes well, with a max percentage difference of 8.54% between the fitted and experimental data. The model was more inaccurate for PVC tubes than PE tubes. K1 values identified were similar magnitude for both materials, K2 was a similar magnitude for PVC, but not PE. Limited data from other studies meant they could not be used to test the model more completely. The assumption that the concentration of insulin in the syringe is what is specified could also be a source of variability. More experiments need to be carried out to make conclusions on K1 and K2, relative to specific materials, but this first model of this phenomenon is fundamentally sounds, justifying explicit validation testing.

Sheets impact simulation for safety guards design: experiments and correlation for FE Explicit models of non-alloy steel

In the last few years, some international standards for the safety of machine tools have been developed improving the ballistic protection of safety guards. The uncontrolled projection of parts of work piece or tools can often cause very dangerous perforations of the safety guards. In such a way specific experimental tests like the ones conducted in EU, have assured the possibility to write appendices of ISO standards for safety guards design of machine tools.These tests are based on impact between a particular standardized projectile, which exemplifies an impacting fragment of variable size and energy, and a flat plate placed in the trajectory of the projectile. The penetration or buckling of the target determines the non-suitability of a particular material of a given thickness, for the design and production of safety guards.However, these tests have following limitations: they are valid only for: a limited type of thickness and materials, a perpendicular impact with flat plates of about 500 mm x 500 mm and when the standardized penetrator is a cylinder with a prismatic head.Another limitation is based on design of real safety guards: difficulties in taking into account curved design of guards such as the ones typically used in the spindles of machine tools. Moreover, it is very difficult to take into account innovative materials different from the ones provided by the standards. It is also impossible to consider projected objects whose geometry is not regular, for example fragmented parts of tools, broken as a result of a wrong manoeuvre of the machine user.The focus of this paper is to give an overview of possible material models usable for FEM explicit virtual testing of safety guards. Correlation between experimental penetration of international standards and numerical tests will be presented as a proof of the possibility to implement reliable testing virtual procedures.It is possible to think of exploring the uncertainty of the standardized tests procedure due to, as an example, non-perpendicular impact of the projectile on the safety guard, using simulations.