Contribution of low-level image statistics to EEG decoding of semantic content in multivariate and univariate models with feature optimization.

Spatio-temporal patterns of evoked brain activity contain information that can be used to decode and categorize the semantic content of visual stimuli. However, this procedure can be biased by low-level image features independently of the semantic content present in the stimuli, prompting the need to understand the robustness of different models regarding these confounding factors. In this study, we trained machine learning models to distinguish between concepts included in the publicly available THINGS-EEG dataset using electroencephalography (EEG) data acquired during a rapid serial visual presentation paradigm. We investigated the contribution of low-level image features to decoding accuracy in a multivariate model, utilizing broadband data from all EEG channels. Additionally, we explored a univariate model obtained through data-driven feature selection applied to the spatial and frequency domains. While the univariate models exhibited better decoding accuracy, their predictions were less robust to the confounding effect of low-level image statistics. Notably, some of the models maintained their accuracy even after random replacement of the training dataset with semantically unrelated samples that presented similar low-level content. In conclusion, our findings suggest that model optimization impacts sensitivity to confounding factors, regardless of the resulting classification performance. Therefore, the choice of EEG features for semantic decoding should ideally be informed by criteria beyond classifier performance, such as the neurobiological mechanisms under study.

The Effect of Social Distancing on the Early Spread of the Novel Coronavirus.

This article quantifies the effect of individual social distancing on the spread of the novel coronavirus. To do so, we use data on time spent by individuals on activities that would potentially expose them to crowds from the American Time Use Survey linked with state-level data on positive tests from the COVID Tracking Project. We estimate count data specifications of observed COVID-19 infections at the state level as a function of control demographic variables, and a measure of social distance that captures the amount of time individuals across the states spend in activities that potentially expose them to crowds. Parameter estimates reveal that the number of state-level novel coronavirus infections decrease with respect to our measure of individual social distance. From a practical perspective, our parameter estimates suggest that if the typical individual in a U.S. state were to spend eight hours away from crowds completely, this would translate into approximately 240,000 fewer COVID-19 infections across the states. Our results suggest that, at least in the United States, social distancing policies are effective in slowing the spread of the novel coronavirus.

Neighborhood conditions and the initial outbreak of COVID-19: the case of Louisiana.

The early outbreak of coronavirus disease-2019 (COVID)-19 became associated with various 'hot spots' in the USA, particularly in large cities. However, despite the widespread nature of the outbreak, much of what is known about the virus' impact and clusters is understood either for individuals, or at the state level. This paper assesses the predictors of outbreaks at the neighborhood level. Using data from the Louisiana Department of Health, we use spatial regression models to analyze the case count through 3 May 2020 and its relationship to individual and geographic neighborhood characteristics at the census tract level. We find a particularly strong and large correlation between race and COVID-19 cases, robust to model specification and spatial autocorrelation. In addition, neighborhoods with lower rates of poverty and those with fewer residents over 70 have fewer cases. Policy makers should adjust testing strategies to better service the hardest hit populations, particularly minorities and the elderly. In addition, the results are greater evidence of the impact of systemic issues on health, which require a long-term strategy for redress.

Multivariate analysis of attachment of biofouling organisms in response to material surface characteristics.

Multivariate analyses were used to investigate the influence of selected surface properties (Owens-Wendt surface energy and its dispersive and polar components, static water contact angle, conceptual sign of the surface charge, zeta potentials) on the attachment patterns of five biofouling organisms (Amphibalanus amphitrite, Amphibalanus improvisus, Bugula neritina, Ulva linza, and Navicula incerta) to better understand what surface properties drive attachment across multiple fouling organisms. A library of ten xerogel coatings and a glass standard provided a range of values for the selected surface properties to compare to biofouling attachment patterns. Results from the surface characterization and biological assays were analyzed separately and in combination using multivariate statistical methods. Principal coordinate analysis of the surface property characterization and the biological assays resulted in different groupings of the xerogel coatings. In particular, the biofouling organisms were able to distinguish four coatings that were not distinguishable by the surface properties of this study. The authors used canonical analysis of principal coordinates (CAP) to identify surface properties governing attachment across all five biofouling species. The CAP pointed to surface energy and surface charge as important drivers of patterns in biological attachment, but also suggested that differentiation of the surfaces was influenced to a comparable or greater extent by the dispersive component of surface energy.

Mini-review: Assessing the drivers of ship biofouling management--aligning industry and biosecurity goals.

Biofouling exerts a frictional and cost penalty on ships and is a direct cause of invasion by marine species. These negative consequences provide a unifying purpose for the maritime industry and biosecurity managers to prevent biofouling accumulation and transfer, but important gaps exist between these sectors. This mini-review examines the approach to assessments of ship biofouling among sectors (industry, biosecurity and marine science) and the implications for existing and emerging management of biofouling. The primary distinctions between industry and biosecurity in assessment of vessels biofouling revolve around the resolution of biological information collected and the specific wetted surface areas of primary concern to each sector. The morphological characteristics of biofouling and their effects on propulsion dynamics are of primary concern to industry, with an almost exclusive focus on the vertical sides and flat bottom of hulls and an emphasis on antifouling and operational performance. In contrast, the identity, biogeography, and ecology of translocated organisms is of highest concern to invasion researchers and biosecurity managers and policymakers, especially as it relates to species with known histories of invasion elsewhere. Current management practices often provide adequate, although not complete, provision for hull surfaces, but niche areas are well known to enhance biosecurity risk. As regulations to prevent invasions emerge in this arena, there is a growing opportunity for industry, biosecurity and academic stakeholders to collaborate and harmonize efforts to assess and manage biofouling of ships that should lead to more comprehensive biofouling solutions that promote industry goals while reducing biosecurity risk and greenhouse gas emissions.

Barnacles and biofouling.

Biofouling, the attachment and growth of organisms on submerged, man-made surfaces, has plagued ship operators for at least 2500 years. Accumulation of biofouling, including barnacles and other sessile marine invertebrates, increases the frictional resistance of ships' hulls, resulting in an increase in power and in fuel consumption required to make speed. Scientists and engineers recognized over 100 years ago that in order to solve the biofouling problem, a deeper understanding of the biology of the organisms involved, particularly with regard to larval settlement and metamorphosis and adhesives and adhesion, would be required. Barnacles have served as an important tool in pursuing this research. Over the past 20 years, the pace of these studies has accelerated, likely driven by the introduction of environmental regulations banning the most effective biofouling control products from the market. Research has largely focused on larval settlement and metamorphosis, the development of new biocides, and materials/surface science. Increased research has so far, however, failed to result in commercial applications. Two recent successes (medetomidine/Selektope(®), surface-bound noradrenaline) build on our improving understanding of the role of the larval nervous system in mediating settlement and metamorphosis. New findings with regard to the curing of barnacle adhesives may pave the way to additional successes. Although the development of most current biofouling control technologies remains largely uninfluenced by basic research on, for example, the ability of settling larvae to perceive surface cues, or the nature of the interaction between organismal adhesives and the substrate, newly-developed materials can serve as useful probes to further our understanding of these processes.

Variation in toxicity of copper pyrithione among populations and families of the barnacle, Balanus amphitrite.

Inter- and intra-population variation in the toxicity of the antifouling biocide copper pyrithione (CuPT) was examined for nauplius larvae of the barnacle Balanus amphitrite. Nauplii were collected from brooding adults from four sites within the Newport River estuary (NC), chosen based on an initial estimation of recent and historical human activities that affect local contamination levels. Each site was characterized for the presence of polycyclic aromatic hydrocarbons and for the frequency of gastropod imposex, an indicator of contamination by organotins. Sensitivity of nauplii to CuPT varied significantly across the sites/populations, with LC(50) values ranging from 4.0 microg l(-1) to 6.1 microg l(-1). Larvae from the most contaminated site were the most sensitive to CuPT. Intrapopulation variation in toxicity was investigated by exposing nauplius larvae from 15 maternal families to a fixed concentration of CuPT (6.1 microg l(-1)). Variation in larval mortality among the families was significant, ranging from 15.1% to 98.9%.

Sonication of bacteria, phytoplankton and zooplankton: Application to treatment of ballast water.

We investigated the effect of high power ultrasound, at a frequency of 19 kHz, on the survival of bacteria, phytoplankton and zooplankton, in order to obtain estimates of effective exposure times and energy densities that could be applied to design of ultrasonic treatment systems for ballast water. Efficacy of ultrasonic treatment varied with the size of the test organism. Zooplankton required only 3-9s of exposure time and 6-19 J/mL of ultrasonic energy to realize a 90% reduction in survival. In contrast, decimal reduction times for bacteria and phytoplankton ranged from 1 to 22 min, and decimal reduction energy densities from 31 to 1240 J/mL. Our results suggest that stand-alone ultrasonic treatment systems for ballast water, operating at 19-20 kHz, may be effective for planktonic organisms >100 microm in size, but smaller planktonic organisms such as phytoplankton and bacteria will require treatment by an additional or alternative system.

Contact angle anomalies indicate that surface-active eluates from silicone coatings inhibit the adhesive mechanisms of fouling organisms.

Silicone coatings with critical surface tensions (CST) between 20 and 30 mN m-1 more easily release diverse types of biofouling than do materials of higher and lower CST. Oils added to these coatings selectively further diminish the attachment strengths of different marine fouling organisms, without significantly modifying the initial CST. In a search for the mechanisms of this improved biofouling resistance, the interfacial instabilities of four silicone coatings were characterised by comprehensive contact angle analyses, using up to 12 different diagnostic fluids selected to mimic the side chain chemistries of the common amino acids of bioadhesive proteins. The surfaces of painted steel test panels were characterised both before and after exposure to freshwater, brackish water, and seawater over periods ranging from 9 months to nearly 4 years. Contact angle measurements demonstrated significant surface activity of the oil-amended coatings both before and after long-term underwater exposure. The surface activity of the control (coating without oil) increased as a result of underwater exposure, consistent with mild surface chain scission and hydrolysis imparting a self-surfactancy to the coating and providing a weak boundary layer promoting continuing easy release of attaching foulants. Coatings with additives that most effectively reduced biofouling showed both initial and persistent contact angle anomalies for the test liquid, thiodiglycol, suggesting lower-shear biofouling release mechanisms based upon diminished bioadhesive crosslinking by interfering with hydrogen- and sulfhydryl bonds. Swelling of the silicone elastomeric coatings by hydrocarbon fluids was observed for all four coatings, before and after immersion.

The effect of solid surface tension and exposure to elevated hydrodynamic shear on Pseudomonas fluorescens biofilms grown on modified titanium surfaces.

The solid surface tension of titanium was varied by using organosilane monolayers of various terminations, minimising differences in other material properties. Both the quantity of Pseudomonas fluorescens biofilms grown on the modified surfaces, and the percentage of biofilm remaining after exposure to hydrodynamic shear stress, varied significantly as a function of solid surface tension. The quantity of biofilm was less on chloropropyl-terminated surfaces than on an alkyl-terminated surfaces. However, the percentage of biofilm remaining after exposure to hydrodynamic shear stress (which depends on the adhesion and cohesion strengths of the biofilm) was less for the alkyl-terminated surface than for the chloropropyl-terminated surface, for one of the two sample sets analysed. These results demonstrate the importance of differentiating between the quantity of biofilm on a surface and the adhesion and cohesion strength of the biofilm, and may help explain discrepancies in the existing literature regarding the effect of solid surface tension on the propensity of a surface for microfouling.

Interspecific variation in patterns of adhesion of marine fouling to silicone surfaces.

The adhesion of six fouling organisms: the barnacle Balanus eburneus, the gastropod mollusc Crepidulafornicata, the bivalve molluscs Crassostrea virginica and Ostrea/Dendrostrea spp., and the serpulid tubeworms Hydroides dianthus and H. elegans, to 12 silicone fouling-release surfaces was examined. Removal stress (adhesion strength) varied among the fouling species and among the surfaces. Principal component analysis of the removal stress data revealed that the fouling species fell into two distinct groups, one comprising the bivalve molluscs and tubeworms, and the other the barnacle and the gastropod mollusc. None of the silicone materials generated a minimum in removal stress for all the organisms tested, although several surfaces produced low adhesion strengths for both groups of species. These results suggest that fouling-release materials do not rank (in terms of adhesion strength) identically for all fouling organisms, and thus development of a globally-effective hull coating will continue to require testing against a diversity of encrusting species.

Variation among families for characteristics of the adhesive plaque in the barnacle Balanus amphitrite.

A quantitative genetics approach was used to examine variation in the characteristics of the adhesive plaque of the barnacle Balanus amphitrite Darwin attached to two silicone substrata. Barnacles settled on silicone polymer films occasionally form thick, soft adhesive plaques, in contrast to the thin, hard plaques characteristic of attachment to other surfaces. The proportion of barnacles producing a thick adhesive plaque was 0.31 for Veridian, a commercially available silicone fouling-release coating, and 0.18 for Silastic T-2, a silicone rubber used for mold-making. For both materials, significant variation among maternal families in the proportion of barnacles producing a thick adhesive plaque was observed, which suggests the presence of genetic variation, or maternal environmental effects, for this plaque characteristic. For the Veridian coating, barnacles expressing the thick adhesive plaque also exhibited significantly reduced tenacity. This represents the first reported case for potential genetic control of intraspecific phenotypic variation in the physical characteristics and tenacity of the adhesive of a fouling invertebrate.

Evaluation of hydrodynamic drag on experimental fouling-release surfaces, using rotating disks.

Fouling by biofilms significantly increases frictional drag on ships' hulls. A device, the friction disk machine, designed to measure torque on rotating disks, was used to examine differences among experimental fouling-release coatings in the drag penalty due to accumulated biofilms. Penalties were measured as the percentage change in the frictional resistance coefficient Cf. Drag penalties due to microfouling ranged from 9% to 29%, comparable to previously reported values. An antifouling control coating showed a smaller drag penalty than the fouling-release coatings. There were also significant differences among the fouling-release coatings in drag due to biofilm formation. These results indicate that the friction disk machine may serve as a valuable tool for investigating the effects of experimental coatings, both antifouling and fouling-release, on microfouling and associated drag penalties.

Evaluation of brushes for removal of fouling from fouling-release surfaces, using a hydraulic cleaning device.

A portable hydraulic device has been developed for use in optimizing the design of brushes and cleaning units that may be employed to maintain fouling-release coatings. Laboratory tests showed that characteristics of experimental cleaning brushes, including bristle stiffness, density, and angle, significantly affected the shear and normal forces imparted to the surface and thus, to any encrusting organisms. The standoff distance between the cleaning unit and the surface also influenced the forces generated. The rate of rotation of the brush, however, had little effect on force. The hydraulic device, with its experimental brushes, can also be used to evaluate the cleanability of fouling-release surfaces in situ, or to assess wear of the coating system due to cleaning.

Structure-property relationships of silicone biofouling-release coatings: effect of silicone network architecture on pseudobarnacle attachment strengths.

Model silicone foul-release coatings with controlled molecular architecture were evaluated to determine the effect of compositional variables such as filler loading and crosslink density on pseudobarnacle attachment strength. Pseudobarnacle adhesion values correlated with filler loadings in both condensation and hydrosilylation-cured silicones. Variation of crosslink density of hydrosilylation-cured silicones had an insignificant effect on attachment strength. X-ray photoelectron spectroscopy (XPS) indicated that the mode of failure upon detachment of the pseudobarnacle was dependent upon the crosslink density; samples with high crosslink density failed cohesively within the silicone.

Silicone foul release coatings: effect of the interaction of oil and coating functionalities on the magnitude of macrofouling attachment strengths.

Silicone biofouling release coatings have been shown to be an effective method of combating fouling. Nearly all silicone foul release coatings are augmented with an oil additive to decrease macrofouling attachment strength. This paper addresses the effect of the type of oil that is incorporated into the silicone coating and the type of silicone coating itself (silica vs calcium carbonate filled) on macrofouling adhesion strengths to the coating. It was found that not only are the main effects of oil type and silicone coating type important in determining the magnitude of the attachment strength of the organism, but the interaction term (oil type crossed with coating type) is highly significant for all organisms studied, except oysters at the University of Hawaii test site (Oahu, Hawaii) which has a significance level of alpha = 0.1. Each of the organisms exhibited a unique response to the various silicone fouling release coatings. Thus, in order to predict the effectives of foul release coatings, the composition variables of the coatings and the type of target organisms must be considered.

The effects of silicone fluid additives and silicone elastomer matrices on barnacle adhesion strength.

Barnacle adhesion strength was used to screen seventy-seven polydimethylsiloxane elastomeric coatings for fouling-release properties. The test coatings were designed to investigate the effect on barnacle adhesion strength of silicone fluid additive type, additive location, additive molecular weight, additive loading level, mixtures of additives, coating matrix type and coating fillers. The type of silicone fluid additive was the primary controlling factor in barnacle fouling-release. The type of silicone matrix in which the fluid resided was found to alter the effect on fouling-release. Two PDMS fluids, DMSC15 and DBE224, significantly reduced the adhesion strength of barnacles compared to unmodified elastomers. Optimum fouling-release performance was dependent on the interaction of fluid type and elastomeric matrix.