Artificial Impedance Surfaces for Reduced Dispersion in Antenna Feeding Systems

An impedance surface is presented that reduces the dispersion experienced upon propagation of broadband pulses within rectangular waveguides. The surface impedance is selected so that, within a frequency range, the transverse resonance condition is satisfied for longitudinal wavenumber that varies linearly with frequency. A synthesis procedure for practical surface topologies consisting of periodic dipole arrays is described. An example involving a finite structure is employed to illustrate the reduced dispersion. Numerical simulation results obtained from in-house mode-matching method as well as HFSS are presented. A prototype is fabricated and tested experimentally validating the theoretical predictions.

Feeding and digestive strategies in deposit-feeding holothurians

Deposit-feeding holothurians employ a range of feeding and digestive strategies depending on the Particular environment to which they are adapted. Habitat and feeding specialisation is reflected in the tentacles, which show high diversity.

Tentacular diversity in deep-sea deposit-feeding holothurians: implications for biodiversity in the deep sea

The tentacles of deep-sea holothurians show a wide range of morphological diversity. The present paper examines gross tentacle morphology in surface deposit feeding holothurians from a range of bathymetric depths. Species studied included the elasipods: Oneirophanta mutabilis, Psychropotes longicauda and Benthogone rosea and the aspidochirotids: Paroriza prouhoi, Pseudostichopus sp., Bathyplotes natans and Paroriza pallens. The sympatric abyssal species Oneirophanta mutabilis, Psychropotes longicauda and Pseudostichopus sp. show subtle differences in diet and the structure and filling patterns of the gut that suggest differences in feeding strategies which may represent one mechanism to overcome competition for food resources in an environment where nutrient resources are considered to be, at least periodically, limiting. Interspecific differences in tentacle functional morphology and digestive strategies, which reflects taxonomic diversity could be explained in terms of Sanders'; Stability–Time Hypothesis. Since different tentacle types will turn over sediments to different extents, their impact on sedimentary communities will be enormous so that high diversity in meiofaunal communities may be explained most simply by Dayton and Hessler's Biological Disturbance Hypothesis.

Further observations on tentacular feeding mechanisms in holothurians

Resource partitioning by aspidochirote holothurians from Beacon Island, Western Australia is largely on the basis of distinct macro- and micro-habitat preferences. Where two or more species occur together or overlap, food partitioning may be by using distinct feeding techniques (Holothuria cinerascens (Brandt), H. impatiens (Forskal) and H. difficilis Semper) or by particle selectivity (H. cf. pervicax Selenka and H. hartmeyeri Erwe). Methods of particle handling by the majority of species studied are similar, involving the use of tentacular nodules on sediment deposits but H. cinerascens collects particles from suspension in a dendrochirote-like tentacle. The nature and rôle of surface secretions are considered for both types of tentacles and the taxonomic value of tentacle form in the Holothurioidea questioned.

Deposit-feeding mechanisms and resource partitioning in tropical holothurians

Aspidochirote holothurians found on tropical reef flats feed on particulate deposits which form a variety of substrata. The synaptid holothurian Opheodesoma grisea (Semper) feeds in a similar manner by scraping deposits from the surfaces of sea grasses. Distributional and gut content analyses showed that species partitioning is on the basis of substratum and particle size preference. Scanning electron microscopy revealed that the tentacles of aspidochirotes have a nodular surface while those of O. grisea have a tessellated surface structure. The twelve different species examined were shown to have different tentacular surface textures which bore an apparent relationship with the mean particle sizes selected by the different species. Light microscope studies of tentacle sections confirmed earlier observations on the extent of the water vascular system in aspidochirote and pinnate tentacles. From these observations a functional interpretation is proposed for tentacular operation and the means of particle selection in such holothurians.

Relationships between lameness and feeding behaviour in cubicle-housed Holstein-Friesian dairy cows

The relationship between lameness and feeding behaviour in dairy cows is not yet fully understood. This study examined the effect of lameness on feeding behaviour at two points during lactation. Forty-five Holstein–Friesian dairy cows (average parity 3.3) were housed in cubicle accommodation after calving and fed a total mixed ration (TMR). At approximately 60 and 120 days post partum, 48 h of information on feeding behaviour (including number of meals eaten, meal duration, meal size and feeding rate) was collected for each animal using feed boxes fitted to a data recording system. At the same time points, locomotion scores were recorded for each cow as a measure of lameness (1.0-sound to 4.5-severely lame). Relationships between feeding behaviour and locomotion score were analysed using Residual Maximum Likelihood (REML) analysis. At both time points, cows with higher locomotion scores ate fewer (P < 0.001), larger meals (P < 0.001) and had a shorter total feeding time (P < 0.001). At day 60 post partum, an increase in locomotion score was associated with a decrease in dry matter intake (P < 0.05), but at day 120 post partum no relationship was found between locomotion score and DMI. No relationship was found at either time point between locomotion score and mean meal duration or rate of feeding. The results of this study suggest that the effect of lameness on feeding behaviour in dairy cows does not remain constant across lactation.