A SSA-based CFFOPID drop deloaded tidal turbine controller using HVDC-link.

In contemporary scenario, electric power companies have observed upsurge in penetration level of tidal power plants (TPPs) in the traditional electric power system framework. However, the tidal turbines offer less frequency assistance due to their lesser rotor mass. Hence, TPPs may be collaborated with conventional units like diesel engine generator (DEG) to confirm system frequency stability in multi-area micro-grid system. The DEG comprises of primary and proportional integral derivative (PID) secondary frequency controls. However, in TPPs, to advance the system frequency regulation, deloading control approach is suggested and a cascade fuzzy fractional order PID-ID with derivative filter (CFFOPID-IDF) droop controller is suggested in place of the conventional non-cascade controller droop in the deloaded region. The suggested controller gains are fetched exploiting Salps swarm algorithm. For further enhancement of the dynamic responses, a precise high voltage direct current (AHVDC) link with the inertia emulation-based control (INEC) scheme is adopted, which allows the utilization of the gathered energy from the capacitance of the HVDC interface for frequency regulation. It provides better results compared to conventional AC tie line interface having less undershoot (34 %/20.63 %/43.75 %) and settling time (20.45 %/59.09 %/16.83 %) for variation in area-1 frequency/area-2 frequency/tie line power, respectively. The recommended control scheme is evidenced superior over numerous existing control techniques and provides least cost function in contrast to other control techniques. Additionally, it offers a highly stable performance under variable load conditions.

Ubiquitous filter feeders shape open ocean microbial community structure and function.

The mechanism of mortality plays a large role in how microorganisms in the open ocean contribute to global energy and nutrient cycling. Salps are ubiquitous pelagic tunicates that are a well-known mortality source for large phototrophic microorganisms in coastal and high-latitude systems, but their impact on the immense populations of smaller prokaryotes in the tropical and subtropical open ocean gyres is not well quantified. We used robustly quantitative techniques to measure salp clearance and enrichment of specific microbial functional groups in the North Pacific Subtropical Gyre, one of the largest ecosystems on Earth. We discovered that salps are a previously unknown predator of the globally abundant nitrogen fixer Crocosphaera; thus, salps restrain new nitrogen delivery to the marine ecosystem. We show that the ocean's two numerically dominant cells, Prochlorococcus and SAR11, are not consumed by salps, which offers a new explanation for the dominance of small cells in open ocean systems. We also identified a double bonus for Prochlorococcus, wherein it not only escapes salp predation but the salps also remove one of its major mixotrophic predators, the prymnesiophyte Chrysochromulina. When we modeled the interaction between salp mesh and particles, we found that cell size alone could not account for these prey selection patterns. Instead, the results suggest that alternative mechanisms, such as surface property, shape, nutritional quality, or even prey behavior, determine which microbial cells are consumed by salps. Together, these results identify salps as a major factor in shaping the structure, function, and ecology of open ocean microbial communities.

Gene expression patterns of Salpa thompsoni reveal remarkable differences in metabolism and reproduction near the Antarctic Polar Front.

Salpa thompsoni is an important grazer in the Southern Ocean and most abundant in the Antarctic Polar Front (APF) region. During recent decades, their distribution expanded southwards. However, it is unclear whether salps can maintain their populations in the high Antarctic regions throughout the year owing to a poor understanding of their physiological responses to changing environmental conditions. We examined gene expression signatures of salps collected in two geographically close regions south of the APF that differed in water mass composition and productivity. The observed differences in the expression of genes related to reproductive, cellular and metabolic processes reflect variations in water temperature and food supply between the two regions studied here. Our study contributes to a better understanding of the physiological responses of S. thompsoni to changing environmental conditions, and how the species may adapt to a changing environment through potential geographical population shifts under future climate change scenarios.

Bio-inspired soft pneumatic actuator based on a kresling-like pattern with a rigid skeleton.

INTRODUCTION: Biomimetic soft pneumatic actuators (SPA) with Kresling origami patterns have unique advantages over conventional rigid robots, owing to their adaptability and safety. OBJECTIVES: Inspired by cloning and moving behaviors observed from salps, we proposed an SPA based on a Kresling-like pattern with a rigid skeleton. The elongation and output force were tested, and the effectiveness of the applications with the SPA was evaluated. METHODS: The proposed SPA consists of rigid skeletons and a soft skin. The rigid skeletons are constructed using layers of Kresling-like patterns, while a novel extensible inserting structure is devised to replace the folds found in conventional Kresling patterns. This innovative approach ensures that the SPA exhibits axial contraction/expansion motion without any twisting movement. To mimic the bionic characteristics of swimming and ingesting progress of salps, the proposed SPA can perform an axial contraction motion without twisting and a controllable bending motion based on multi-layered Kresling-like patterns; to mimic the cloning and releasing life phenomena of salps, the number of layers of Kresling-like patterns is changeable by adding or reducing skeleton components according to the practical needs. RESULTS: The experimental elongation results on the SPA with multiple layers of Kresling-like patterns show that the elongation can increase to above 162% by adding layers; the experimental output force results show that the three-layer SPA can provide 6.36 N output force at an air flow rate of 10 L/min, and the output force will continue to increase as the number of layers of Kresling-like pattern increases or the air flow rate increases. Further, we demonstrate the applications of the SPA in soft grippers, scissor grippers, claw grippers and pipe crawlers. CONCLUSION: Our proposed SPA can avoid twisting in the radial contraction motion with high elongation and output force, and provide the practical guidance for bio-inspired soft robotic applications.

Assemblages of pelagic thaliaceans in oceanographic features at the tropical-temperate transition zone of a western boundary current.

Mesoscale oceanographic features influence the composition of zooplankton. Cyclonic eddies can promote upwelling and production of gelatinous zooplankton, which play critical roles in ocean biogeochemical cycling. We examined variation in assemblages of thaliaceans (salps, doliolids and pyrosomes) among mesoscale oceanographic features at the tropical-temperate boundary of the East Australian Current (EAC) in Spring 2019 and Autumn 2021. The influence of cyclonic eddies was examined in a large offshore cyclonic eddy in 2019 and a newly formed frontal eddy in 2021. Pyrosomes were most abundant in the offshore EAC jet, and salps and doliolids were most abundant in coastal features, including within eddies that were transported offshore. In 2019, Salpa fusiformis increased 4-fold over 8 days in the large cyclonic eddy, and in 2021, doliolids increased > 50-fold over 2 weeks in a chlorophyll-rich coastal eddy while abundances of other thaliaceans remained unchanged or decreased. Correlations between abundances of thaliaceans and chlorophyll-a concentrations across the 102 samples collected during both voyages revealed that doliolids occupy a wider range of chlorophyll-a concentrations than salps. Our observations indicate that doliolids thrive in productive shelf environments, salps occur in less productive shelf waters and pyrosomes are most abundant in oligotrophic waters of the south Coral Sea.

Cool your jets: biological jet propulsion in marine invertebrates.

Pulsatile jet propulsion is a common swimming mode used by a diverse array of aquatic taxa from chordates to cnidarians. This mode of locomotion has interested both biologists and engineers for over a century. A central issue to understanding the important features of jet-propelling animals is to determine how the animal interacts with the surrounding fluid. Much of our knowledge of aquatic jet propulsion has come from simple theoretical approximations of both propulsive and resistive forces. Although these models and basic kinematic measurements have contributed greatly, they alone cannot provide the detailed information needed for a comprehensive, mechanistic overview of how jet propulsion functions across multiple taxa, size scales and through development. However, more recently, novel experimental tools such as high-speed 2D and 3D particle image velocimetry have permitted detailed quantification of the fluid dynamics of aquatic jet propulsion. Here, we provide a comparative analysis of a variety of parameters such as efficiency, kinematics and jet parameters, and review how they can aid our understanding of the principles of aquatic jet propulsion. Research on disparate taxa allows comparison of the similarities and differences between them and contributes to a more robust understanding of aquatic jet propulsion.

Dense Dwarfs versus Gelatinous Giants: The Trade-Offs and Physiological Limits Determining the Body Plan of Planktonic Filter Feeders.

Most marine plankton have a high energy (carbon) density, but some are gelatinous with approximately 100 times more watery bodies. How do those distinctly different body plans emerge, and what are the trade-offs? We address this question by modeling the energy budget of planktonic filter feeders across life-forms, from micron-sized unicellular microbes such as choanoflagellates to centimeter-sized gelatinous tunicates such as salps. We find two equally successful strategies, one being small with high energy density (dense dwarf) and the other being large with low energy density (gelatinous giant). The constraint that forces large-but not small-filter feeders to be gelatinous is identified as a lower limit to the size-specific filter area, below which the energy costs lead to starvation. A further limit is found from the maximum size-specific motor force that restricts the access to optimum strategies. The quantified constraints are discussed in the context of other resource-acquisition strategies. We argue that interception feeding strategies can be accessed by large organisms only if they are gelatinous. On the other hand, organisms that use remote prey sensing do not need to be gelatinous, even if they are large.

Predatory zooplankton on the move: Themisto amphipods in high-latitude marine pelagic food webs.

Hyperiid amphipods are predatory pelagic crustaceans that are particularly prevalent in high-latitude oceans. Many species are likely to have co-evolved with soft-bodied zooplankton groups such as salps and medusae, using them as substrate, for food, shelter or reproduction. Compared to other pelagic groups, such as fish, euphausiids and soft-bodied zooplankton, hyperiid amphipods are poorly studied especially in terms of their distribution and ecology. Hyperiids of the genus Themisto, comprising seven distinct species, are key players in temperate and cold-water pelagic ecosystems where they reach enormous levels of biomass. In these areas, they are important components of marine food webs, and they are major prey for many commercially important fish and squid stocks. In northern parts of the Southern Ocean, Themisto are so prevalent that they are considered to take on the role that Antarctic krill play further south. Nevertheless, although they are around the same size as krill, and may also occur in swarms, their feeding behaviour and mode of reproduction are completely different, hence their respective impacts on ecosystem structure differ. Themisto are major predators of meso- and macrozooplankton in several major oceanic regions covering shelves to open ocean from the polar regions to the subtropics. Based on a combination of published and unpublished occurrence data, we plot out the distributions of the seven species of Themisto. Further, we consider the different predators that rely on Themisto for a large fraction of their diet, demonstrating their major importance for higher trophic levels such as fish, seabirds and mammals. For instance, T. gaudichaudii in the Southern Ocean comprises a major part of the diets of around 80 different species of squid, fish, seabirds and marine mammals, while T. libellula in the Bering Sea and Greenland waters is a main prey item for commercially exploited fish species. We also consider the ongoing and predicted range expansions of Themisto species in light of environmental changes. In northern high latitudes, sub-Arctic Themisto species are replacing truly Arctic, ice-bound, species. In the Southern Ocean, a range expansion of T. gaudichaudii is expected as water masses warm, impacting higher trophic levels and biogeochemical cycles. We identify the many knowlegde gaps that must be filled in order to evaluate, monitor and predict the ecological shifts that will result from the changing patterns of distribution and abundance of this important pelagic group.

Physical properties of the tunic in the pinkish-brown salp Pegea confoederata (Tunicata: Thaliacea).

BACKGROUND: Invisibility in the water column is a crucial strategy for gelatinous zooplanktons in avoiding detection by visual predators, especially for animals distributed in the euphotic zone during the daytime; i.e., surface dwellers that do not undergo diel vertical migration. Salps, a member of the subphylum Tunicata (Urochordata), usually have a transparent body that is entirely covered with a cellulosic matrix, called the tunic. Some non-migrator species are known to exhibit a nano-scale nipple array on the tunic surface. However, the physical properties of the salp tunic has been poorly investigated, except for Thetys vagina, in which the tunic was expected to show low reflectance based on the refractive index of the tunic. Pegea confoederata is a non-vertical migrant salp showing pinkish-brown body. We measured the hardness, water content, absorption spectra, and refractive index of its tunic to evaluate its fragility and visibility. RESULTS: There are nipple-like protuberances about 80 nm high on the surface of the tunic in P. confoederata. The tunic is very soft; the maximum force to pierce the tunic with a steel rod (1 mm diameter) was < 1 N. The water content of the tunic was > 95%. The absorption spectra of the tunic had no prominent peaks in the wavelength range of 280-800 nm, indicating the tunic is nearly transparent. The difference in refractive indices between tunic and seawater was estimated as 0.002-0.015 at 589 nm. Rigorous coupled wave analyses (RCWA) of light reflection based on 3-dimensional models supported an anti-reflective effect of the nipple array on the tunic surface, which was estimated to vary slightly depending on the forms and the arrangement patterns of nipple-like protuberances in an array. CONCLUSIONS: The tunic of P. confoederata is very soft and contains more water than those of sessile tunicates (ascidians). Based on the refractive index of the tunic, light reflection is expected to be very low, making this salp's tunic barely visible in water column. Our results suggest that the nipple array may produce an anti-reflective effect.

A new class of synthetic anti-lipopolysaccharide peptides inhibits influenza A virus replication by blocking cellular attachment.

Influenza A viruses are a continuous threat to human health as illustrated by the 2009 H1N1 pandemic. Since circulating influenza virus strains become increasingly resistant against currently available drugs, the development of novel antivirals is urgently needed. Here, we have evaluated a recently described new class of broad-spectrum antiviral peptides (synthetic anti-lipopolysaccharide peptides; SALPs) for their potential to inhibit influenza virus replication in vitro and in vivo. We found that particularly SALP PEP 19-2.5 shows high binding affinities for the influenza virus receptor molecule, N-Acetylneuraminic acid, leading to impaired viral attachment and cellular entry. As a result, replication of several influenza virus subtypes (H7N7, H3N2 and 2009 pandemic H1N1) was strongly reduced. Furthermore, mice co-treated with PEP 19-2.5 were protected against an otherwise 100% lethal H7N7 influenza virus infection. These findings show that SALPs exhibit antiviral activity against influenza viruses by blocking virus attachment and entry into host cells. Thus, SALPs present a new class of broad-spectrum antiviral peptides for further development for influenza virus therapy.

From gelatinous to muscle food chain: rock cod Patagonotothen ramsayi recycles coelenterate and tunicate resources on the Patagonian Shelf.

Stomach contents of 4808 fishes of 20 species caught in the eastern part of the Patagonian Shelf between 1999 and 2012 were analysed to assess dietary contributions of gelatinous plankton resources. Gelatinous plankton occurred in diets of seven species with two species, Patagonotothen ramsayi and Squalus acanthias, having >10% ctenophores in their diet. Consumption of gelatinous plankton was important in P. ramsayi and was strikingly seasonal, with maximum occurrence (up to 46% of non-empty stomachs) in late summer to autumn. Ctenophores were most abundant in P. ramsayi of 25-34 cm total length, L(T) whereas salps were more frequent in larger >35 cm L(T) individuals. In winter to spring, occurrence of gelatinous plankton in diets was minimal, reflecting their overall seasonal abundance in the ocean. The recent increase in abundance of P. ramsayi has enabled the species to recycle a significant proportion of the ecosystem production from gelatinous dead end to the main muscular food chain via seasonal reliance on ctenophores, jellyfish and tunicates. This additional influx of production that has been diverted from the gelatinous food chain favours the increase in abundance of several piscivorous top predators and affects the trophic web structure of the Patagonian Shelf ecosystem.

New record of Thalia cicar van Soest 1973 (Urochordata: Thaliacea) in the Equatorial Atlantic / Novo registro de Thalia cicar van Soest 1973 (Urochordata: Thaliacea) no Atlântico Equatorial

Thalia cicar van Soest 1973 (Urochordata, Thaliacea) is considered a tropical-subtropical species, registered in the Atlantic Ocean at latitudes between 7-34º S and 6-32º N. This work enlarges the occurrence of this species for Equatorial Atlantic waters. The specimens were found in a shelf break area of the Brazilian northeastern (07º 50'-07º 70' S and 34º 23' W) during the expedition JOPS-II (Joint Oceanographic Projects II) in March 1995; and, in São Pedro e São Paulo arquipelago (0º 55' N and 29º 20' W) in May and June, 2005. These two areas are characterized by the presence of local upwelling that induces the ascent of bottom waters rich in nutrients, generating areas of larger productivity than the typically oligotrophic Equatorial Atlantic waters. The new occurrence of Thalia cicar reported in this work can be related to these more productive waters of Equatorial Atlantic. The species that is most commonly found in the Atlantic Ocean is T. democratica, and the lack of past records of T. cicar might have been caused by the taxonomic difficulties determining of the solitary and aggregate zooids of these two species. This work suggests the potential use of the ratios among tunic lengths as an additional character to differentiate T. cicar and T. democratica oozooids.

Thalia cicar van Soest 1973 (Urochordata, Thaliacea) é considerada uma espécie tropical-subtropical, registrada no oceano Atlântico desde 7 a 34º S e 6 a 32ºN. Este trabalho amplia a ocorrência desta espécie para águas do Atlântico equatorial. Os espécimes foram encontrados na plataforma continental do Nordeste brasileiro (07º 50'-07º 70' S e 34º 23' W) durante a expedição JOPS-II (Joint Oceanographic Projects II) em março de 1995 e no arquipélago de São Pedro e São Paulo (0º 55' N e 29º 20' W) em maio e junho de 2005. Essas duas áreas se caracterizam pela presença de ressurgências locais que induzem a ascensão de nutrientes, gerando locais de alta produtividade, nas águas tipicamente oligotróficas do Atlântico equatorial. O registro de Thalia cicar nesses dois locais pode estar relacionado com essas águas de maior produtividade no Nordeste brasileiro. A espécie de Thalia comumente encontrada no oceano Atlântico é T. democratica e a ausência de registros passados de T. cicar pode decorrer das dificuldades taxonômicas em diferenciar os zoóides solitários e agregados dessas duas espécies. Este trabalho sugere a utilização da proporção entre os comprimentos das projeções da túnica como um caráter adicional para diferenciar os oozoóides destas duas espécies.