Greater Feeding Rates Research Articles

Experimental study on machining properties of a high-strength composite material with Ti-555 titanium alloy matrix

Targeted at a composite material with a novel Ti-555 high-strength titanium alloy matrix developed using the method of "reinforcement wet grinding-spark plasma sintering-heat treatment", a study is conducted on the machining performance during the machining process. Orthogonal experiment method, single factor experiment comparison method and empirical model analysis method are adopted to explore the pattern of changes in cutting force, surface roughness and the wearing of cutting tools under different parameters. There are a number of points revealed by the experimental results as follows. In the machining process, due to the high-strength and hardness of the composite material with Ti-555 high-strength titanium alloy matrix, the selection of machining parameters is limited, and the highest machining speed reaches up to merely 45 m/min. Most affected by the depth of machining, the cutting force increases as machining depth and feed rate are on the rise. The empirical model of cutting force is constructed using the least square regression method, the level of significance is high as indicated by the F test method. and feed rate will make difference to surface roughness. Not only will a greater feed rate increase roughness value, it will also aggravate the wearing of the tool.

Influence of Tool Nose Radius and Cutting Performance during Face Milling of Magnesium Alloy for Output Responses by Taguchi based Grey Relation Analysis

In order to take advantage of the machining characteristics of magnesium, it is useful to consider recommended tool design and angles. The geometry of the tool can have a large influence on the machining process. Tool geometry can be used to aid with chip flow and clearance, reduce excessive heat generation, reduce tool build up, enable greater feed rates to be employed and improved tool life. This paper presents a new approach for the optimization of machining parameters on face milling of ZE41 with multiple responses based on orthogonal array with grey relational analysis. Machining tests are carried out by inserting 12 mm diameter of insert having 1 flute under dry condition. In this study, machining parameters namely cutting speed, feed and depth of cut and tool node radius are optimized with the considerations of multi responses such as surface roughness, material removal rate, tool wear and thrust force. A grey relational grade is obtained from the grey analysis. Based on the grey relational grade, optimum levels of parameters have been identified and significant contribution of parameters is determined by ANOVA. Confirmation test is conducted to validate the test result. Experimental results have shown that the responses in Machining process can be improved effectively through the new approach.

Dairy calf growth performance when fed a modified accelerated milk replacer program

ABSTRACT Objective Our previous studies demonstrated that a modified accelerated milk replacer (MR) having a 24:20 CP:fat concentration fed at higher feeding rates (FR) resulted in improved growth performance and G:F, but the result was not linear. The objective of the current study was to evaluate preweaning (d 1 to 42) and postweaning (d 43 to 56) calf performance when a modified accelerated MR was fed at greater FR compared with a MR having similar or greater CP and lower fat concentrations. Materials and Methods A total of 126 (2 to 5 d old) Holstein heifer calves (40.1 ± 0.76 kg) were blocked by birthdate and randomly assigned to 1 of 5 treatments. Treatments of MR fed at 14.7% solids were (1) control (C−): all milk 24:20 MR fed at 0.26 kg at 2×/d from d 1 to 35; (2) C+: C− MR fed at 0.32 kg 2×/d from d 1 to 35; (3) LF: CP and low fat (24:16) MR fed at 0.32 kg 2×/d from d 1 to 35; (4) LF+: LF MR fed at 0.32 kg 2×/d from d 1 to 7 and at 0.39 kg from d 8 to 35; and (5) HP+: high CP:LF MR (26:16) using the same FR as LF+. All MR were fed 1×/d from d 36 to weaning at d 42 with water and 18% CP texturized calf starter offered free choice at all times. Results and Discussion Calves fed C+ had greater (P Implications and Applications This study demonstrates that feeding a modified accelerated MR (24:20) at a moderate FR improves ADG and frame measurements for calves fed MR having similar or different CP and fat concentrations. The development of a modified accelerated feeding program optimized the protein-to-energy ratio for producing a dairy heifer with a frame that is taller and wider, without having a postweaning BW gain slump.

Growth performance of newborn dairy calves fed a milk replacer containing 24% crude protein and 20% fat fed at different feeding rates

ABSTRACT Objective The objective was to evaluate the preweaning (d 1 to 42) and postweaning (d 43 to 56) performance and health of calves fed a 24% CP:20% fat milk replacer (MR) at different feeding rates based on our previous work that calves fed greater feeding rates of MR demonstrated improved growth. Materials and Methods A total of 108 (2- to 5-d-old) Holstein heifer calves (40 ± 0.69 kg) were randomly assigned to 1 of 4 treatments. The same all-milk-protein MR was fed at 14.7% solids, with treatments of (1) control (MR57): MR fed at 0.57 kg daily from d 1 to 35; (2) MR71: MR fed at 0.71 kg daily from d 1 to 35; (3) MR85: MR fed at 0.68 kg daily from d 1 to 7 and at 0.85 kg daily from d 8 to 35; and (4) MR99: MR fed at 0.68 kg daily from d 1 to 7 and at 0.99 kg daily from d 8 to 35. All treatments were fed MR one time per day from d 36 to weaning, after d 42 with water, and an 18% CP texturized calf starter offered free choice. Results and Discussion Preweaning and overall ADG (0.78, 0.82, 0.83, and 0.85 kg/d for MR57, MR71, MR85, and MR99, respectively) were greater (P 0.10) and intermediate. Overall d 1 to 56 calf starter intakes were greater (P 0.10). Preweaning G:F was lowest for calves fed MR57, whereas d 1 to 56 G:F (0.49, 0.52, 0.52, and 0.54 kg/kg of DM) was greater (P Implications and Applications This study demonstrated that higher feeding rate of a 24:20 MR resulted in increased ADG and feed conversion (G:F).

Social housing influences the behavior and feed intake of dairy calves during weaning

We investigated the effect of social housing on the behavioral, intake, and physiological changes that occur at weaning for dairy calves fed milk ad libitum. These changes were evaluated during the weaning (d 40 to 48 of age) and postweaning (d 49 to 56 of age) stages. Twenty male Holstein calves were fed milk replacer ad libitum and weaned gradually by dilution over 9 d starting at d 40 of age. Calves were housed in pairs (10 calves) or individually (10 calves) from birth until the beginning of the postweaning phase, when all calves were paired. Feed and water intake were monitored daily. Feeding time was video-recorded, and blood β-hydroxybutyrate concentration was measured on alternate days beginning on d 40 and ending on d 56 of age. Electronic accelerometers continuously recorded standing and lying behavior for the 17-d study. Solid feed consumption increased by more than 5-fold over the weaning phase in all calves; during this phase pair-housed calves consumed more than twice (0.96 vs. 0.50 kg/d on d 48) that of the individually housed calves. Postweaning all calves rapidly increased their solid feed intake, and to a greater extent for previously individually housed calves, such that intake was similar between treatments by d 56. Free water intake was stable during weaning; however, a decrease (of 6.6 L) occurred in the constituent milk replacer water intake across this phase. As result, total water intake (free water + milk replacer water content) decreased (by 6.0 L) over the weaning phase between d 40 (14.9 L/d) and d 48 (8.9 L/d). On the first day postweaning (d 49), total water intake for all calves increased sharply (to 19.0 L/d) and then returned to a lower baseline (13.2 L/d) the next day (d 50), and slowly increased over the following week. During the weaning phase, feeding time and feeding rate increased with time for all calves, whereas pair-housed calves had greater feeding rates than individually housed calves (13.4 vs. 6.6 g of DM/min). After weaning, calves previously housed individually spent more time feeding in the early hours of the day than calves housed in pairs. Lying time and lying bout frequency decreased with calf age during the weaning period across treatments, and pair-housed calves tended to spend less time lying than individually housed calves (1,015 vs. 1,039 min/d) during this time period. Blood β-hydroxybutyrate increased across treatments over the weaning period, with the largest increase occurring between d 48 (0.05 mmol/L) and d 50 (0.2 mmol/L). These results show that calves alter their behavioral patterns during weaning and that housing calves in pairs may ease the transition from milk to solid feed.

Experiments of Drilling Titanium Alloy with Varying Operation Parameters

Drilling experiments of titanium alloy Ti6Al4V were conducted. Taking the speed and feed as the process variables, a set of experimental cutting forces are obtained and compared. From the experimental results it is concluded that within the experimental extent the thrust force and torque of drilling process rises with the feed rate. The lower spindle speed resulted in the greater amount of thrust. Feed rates have greater influence on the thrust force than the spindle speed. The combination of greater feed rate and lower spindle speed results in the maximum amount of thrust. However, combination of greater feed rate and spindle speed resulted in maximum amount of torque.

THE EFFECT OF CUTTING PARAMETERS ON SURFACE INTEGRITY IN MILLING TI6AL4V

The objective of machining performance is to reduce operational costs and to increase the production rate while maintaining or improving the required surface integrity of the machined component. Together with industrial partners, several benchmark titanium components were selected and machined to achieve this. Titanium alloys are used extensively in several industries due to its unique strength-to-weight ratio and corrosion resistance. Its properties, however, also make it susceptible to surface integrity damage during machining operations. The research objectives of this study were to understand the effect of cutting parameters on surface integrity to ensure that machined components are within the required surface quality tolerances. The effect of cutting speed and feed rate on surface roughness, micro-hardness, and the microstructure of the work piece were studied for milling Ti6Al4V. The surface roughness increased with a greater feed rate and a decrease in cutting speed. The maximum micro-hardness was 23 per cent harder than the bulk material. Plastic deformation and grain rotation below the machined surface were found with the rotation of the grain lines in the direction of feed. There was no evidence of subsurface defects for any of the cutting conditions tested.

OPTIMASI PARAMETER PERMESINAN TERHADAP WAKTU PROSES PADA PEMROGRAMAN CNC MILLING DENGAN BERBASIS CAD/CAM

Milling process is one of many machining processes for manufacturing component. The length of time in the process of milling machining is influenced by selection and design of machining parameters including cutting speed, feedrate and depth of cut. The purpose of this study to know the influence of cutting speed, feedrate and depth of cut as independent variables versus operation time at CNC milling process as dependent variables. Each independent variable consists of three level of factors; low, medium and high.Time machining process is measured from operation time simulation program, feed cut length and rapid traverse length. The results of statistically from software simulation MasterCam X Milling, then do comparison to CNC Milling machine. The data from experiments was statistical analyzed by Anova and Regression methods by software minitab 16.Results show that the greater feedrate and depth of cut shorten the operation time of machinery, whereas cutting speed is not significant influence. Depth of cut has the most highly contribution with the value of 49.56%, followed by feedrate 43% and cutting speed 0.92%. Optimal time of machining process total is 71.92 minutes, with machining parameter on the condition cutting speed is 75360 mm/minutes, feedrate is 800 mm/minutes and depth of cut = 1 mm. Results of comparison time machining process in software Mastercam X milling with CNC Milling machine indicates there is difference not significant with the value of 0,35%.

Mathematical Modelling of Surface Roughness on Tropical Wood Machining Using Response Surface Methodology

Surface roughness is an important indicator to assess the surface processing quality and has a decisive impact on the furniture finishing effects. In this research, the application of response surface methodology (RSM) has been carried out for modelling and analysing of influences in the sanding process on wood materials. Surface roughness parameterRashowed surface characteristics of Tembesu, Jati and Petanang. This study is aimed to observe the effect of feed rate and grit size onRa. The central composite design (CCD) was used as a design of experiment (DOE). There were 8 runs at factorial points and additional 5 replicated runs at the centre point. The sanding process was done using a modified horizontal milling machine. The results are statistically analysed by using Design Expert software. It was found that increasing of feed rate had a positive effect on the roughness value ofRaand greater feed rates increased the surface roughness. On the other hand, grit size influenced negative effect. Larger grit size affected the smoother surface roughness. At the end of this study, it was also revealed that the optimum machining conditions in terms of feed rate and grit size were 17 mm/min and 240 for Tembesu and Jati, while Petanang was 18.63 mm/min and 226.52.

Elevational clines in the temperature dependence of insect performance and implications for ecological responses to climate change.

To what extent is insect hopping and feeding performance, which constrains the ability to obtain and assimilate resources, thermally adapted along an elevation gradient? Does temperature dependence vary between populations and species and can differences account for individualistic responses to past climate change? We investigate these questions for three species of grasshoppers along a Rocky Mountain elevation gradient. All species and populations exhibit warm adaptation for consumption and digestion, with only modest inter- and intra-specific differences. Species differ substantially in the temperature of peak hopping performance. Low-elevation populations of the warm-adapted species exhibit the highest performance at high temperatures and the lowest performance at low temperatures. Developmental plasticity influences the temperature dependence of performance; grasshoppers reared at higher temperatures perform better at higher temperatures and possess broader thermal tolerance. We fitted thermal performance curves to examine whether performance shifts can account for changes in abundance between initial surveys in 1958-1960 and recent surveys since 2006. All species and populations are able to achieve greater feeding rates now. Estimated shifts in hopping performance vary between species and along the elevation gradient. The cool-adapted species has experienced declines in hopping performance, particularly at the lower elevation sites, while the warm-adapted species has experienced increases in performance concentrated at higher elevations. These estimated performance shifts broadly concur with observed abundance shifts. Performance metrics may have a greater potential to elucidate differential responses to climate change between populations and species than coarser and oft-used proxies, such as thermal tolerance. Assessing performance directly when temperature dependence varies between processes such as the acquisition and assimilation of energy may be essential to understanding population- and species-level impacts.

Effects of food origin and availability on sea urchin condition and feeding behaviour

The origin of food is recognised to be an important trait for sedentary consumers that have little control over the source of their food. Elevated herbivory in sea urchins is often linked to poor gonad condition as provoked by reduced food availability, but there is little recognition of the possibility that the origin of food may contribute to their poor condition and elevated feeding. This study assesses the possibility that variation in food availability and origin may together affect urchin condition and feeding rates such that they account for more intensive grazing (by Heliocidaris erythrogramma) on sheltered than exposed coasts (South Australia). We experimentally tested the hypothesis that reduced food availability from sheltered coasts would result in poor gonad condition and greater feeding rate; whilst enhanced food availability from exposed coasts would result in better condition and reduced feeding rates. We found that reduced food had negative effects on condition and positive effects on feeding rates independently of coastal source. Greater food availability did not equate to better condition, rather it was the delivery of more food from exposed than sheltered coasts that translated into the better gonad condition and lower feeding rates. These results suggest that plant origin and availability could help explain the greater impacts of these urchins on sheltered coasts. Whilst other factors such as water energy and sea urchin density may contribute to variation in herbivory our results suggest that origin of food may also play a role in sea urchin condition and behaviour. Understanding how such traits link to large scale features of the environment may improve models that account for variation in strength of consumer effects across landscapes.

Temporal feed restriction and overstocking increase competition for feed by dairy cattle

Dairy cows are often overstocked. Some managers are now using “slick bunk” (i.e., feeding for 0% orts) management to save on feed costs, but this reduces the time that cows have access to feed. Both practices may increase competition and affect feeding behavior in dairy cows. The aim was to determine the effects of temporal and spatial restrictions on the feeding and competitive behavior of group-housed cows. Treatments were 2 levels of stocking (2:1 versus 1:1 cows:feed bin) and 2 levels of feed access time (14 versus 24h/d access). Eight groups (each of 6 cows) were tested on each of the 4 treatment combinations for 1 wk, with treatment order assigned using a replicated 4×4 Latin square design. Dry matter intake (DMI), feeding time, and feeding rate were measured for the last 4d of each week, and data were summarized daily and for the 2-h period immediately after the morning feeding. Displacements were recorded for 2h after the delivery of morning feed (peak feeding period) and 2h following the afternoon milking. The DMI did not decline when temporal access was restricted (27.0 vs. 25.7±0.5kg/d), and was not affected by overstocking (26.4±1.9, mean ± SD). Cows with restricted temporal access spent less time feeding (190.9 vs. 207.9±6.1min). Overstocked cows that were temporally restricted had greater feeding rates during the day (156 vs. 137±4g/min) and especially during the peak feeding period (175 vs. 146±4g/min) compared with cows that were not restricted. In the peak feeding period, overstocked cows had reduced DMI (3.0 vs. 3.4±0.1kg/h) and feeding times (20.8 vs. 25.8±1.0min/h) and increased feeding rates (161 vs. 138±4g/min). Cows with restricted temporal access had greater DMI (3.9 vs. 2.6±0.2kg/h) and time spent feeding (27.3 vs. 19.2±1.3min/h) during the peak feeding period compared with cows that had continuous access to feed. Restricting temporal access in conjunction with overstocking resulted in the greatest increase in daily displacements (15.0 vs. 3.8±1.4 displacements/d); the majority of these occurred during the peak feeding period. Adequate space and time to access feed is essential to minimize feed bunk competition in indoor group housing systems.

Phenotypic and genetic relationships among feeding behavior traits, feed intake, and residual feed intake in steers fed grower and finisher diets1

Data from a 3-yr feeding trial of crossbred steers (n = 331) were used to examine the relationship between feeding behavior traits and feed efficiency in steers fed grower and finisher diets, successively. There were 2 feeding periods each year whereby the steers were fed a grower diet in the first feeding period (P1) and a finisher diet in the second feeding period (P2). Each feeding period lasted for a minimum of 10 wk, ad libitum. In addition to feed intake, records on 3 measures of feeding behavior [feeding duration (FD), head-down time (HDT), and feeding frequency (FF)] were collected using the GrowSafe feeding system. Residual feed intake (RFI) was calculated by regression, after which the steers were classified as low (<0.5 SD), medium (±0.5 SD), or high (>0.5 SD) from the mean. The steers had greater (P < 0.001) FD, HDT, and FF when the grower diet was fed but greater feeding rate (FR) when the finisher diet was fed. Including the measures of feeding behavior as covariates to the feed intake prediction model containing ADG, metabolic midweight, and ultrasound backfat accounted for more variation in DMI than models that did not contain these additional parameters. The FD and HDT were significantly different (P < 0.05) among the RFI classes regardless of the feeding period, whereas no differences (P > 0.90) were found for FR among the RFI classes. For the growing period and finishing period, respectively, FD had phenotypic correlations with HDT (0.79, 0.83), FF (0.14, 0.55), DMI (0.38, 0.34), and FR (-0.34, -0.21). Heritability estimates in P1 and P2 for FD, HDT, and FF were 0.25 ± 0.16, 0.14 ± 0.11; 0.14 ± 0.15, 0.09 ± 0.10; and 0.56 ± 0.19, 0.59 ± 0.18, respectively. Genetic correlations between P1 and P2 were 0.91 ± 0.26, 0.93 ± 0.37, and 0.94 ± 0.11 for FD, HDT, and FF, respectively. The results suggest that it may be appropriate to include feeding behavior traits as covariates to indicate measure(s) of animal activity in the calculation of RFI. Feeding behavior phenotypes were greater during the grower-fed period than the finisher-fed period. During these feeding periods, efficient steers exhibited fewer FF, shorter FD, and shorter HDT than inefficient steers.

Effect of selection for residual feed intake on feeding behavior and daily feed intake patterns in Yorkshire swine1

Residual feed intake (RFI) is a measure of feed efficiency defined as the difference between observed and predicted feed intake based on average requirements for growth and maintenance. The objective of this study was to evaluate the effect of selection for decreased RFI on feeding behavior traits and to estimate their relationships with RFI. Three data sets from the 4th and 5th generations of a selection experiment with a line selected for reduced RFI (LRFI) and a randomly selected control line (CTRL) were analyzed. Lines were mixed in pens of 16 and evaluated for feeding behavior traits obtained from a single-space electronic feeder over a growing period of ~3 mo before ~115 kg. The following traits were evaluated as averages over the entire test period and over the first and second half of the test period: number of visits per day and hour; occupation time per day, visit, and hour; feed intake (FI) per day, visit, and hour; and FI rate per visit. Models used included fixed effects of line and feeder, covariates of on-test age and FI per day, and random effects of pen, on-test group, sire, and litter. Repeated measures models were used to analyze feeding patterns during the day. The LRFI pigs had significantly less FI per day than CTRL pigs for all 3 data sets. With adjustment for FI per day, line differences of all traits were in the same direction for all 3 data sets but differed in significance and size. Feed intake per visit and hour and visits per day and hour did not differ between lines, but the trend was for LRFI pigs to have fewer visits, in particular during peak eating times. The LRFI pigs had a greater feeding rate and less occupation time per day, visit, and hour than CTRL pigs, but this was not significant for all data sets. Correlations of RFI with FI per day and visit and visits per day were positive. Average daily gain was positively correlated with FI per day and visit and occupation time per visit but negatively correlated with visits per day. Feed intake per day was positively correlated with backfat. In conclusion, feed efficiency may be affected by FI behavior because selection for decreased RFI has resulted in pigs that spend less time eating and eat faster.

Adição de complexo enzimático e da granulometria da soja integral desativada melhora desempenho de frangos de corte

O experimento foi conduzido com objetivo de avaliar o efeito da adição de complexo enzimático e da granulometria da soja integral desativada sobre o desempenho de frangos no período de um a 42 dias de idade. Foram utilizados 480 pintos machos da linhagem Ross, distribuídos em um delineamento inteiramente casualizado, em esquema fatorial 2x2 (enzima x granulometria). As rações experimentais foram formuladas à base de milho, farelo de soja e soja integral desativada (±1,5mm), soja integral desativada (±1,5mm) + enzima, soja integral desativada (±4,0mm) e soja integral desativada (±4,0mm) + enzima. O complexo enzimático (xilanase, β-glucanase, mannase, pectinase e protease) foi adicionado na dosagem de 50g t-1 de ração. A adição do complexo enzimático aumentou (P=0,053) em 4% o consumo de ração e 2,8% o ganho de peso no período final de criação. O consumo de ração foi aumentado em 3% no período final e (P=0,048) 2% no período total em aves que ingeriram ração com granulometria 1,5mm. No período inicial, as aves que ingeriram ração com granulometria 4,0mm tiveram aumento de 5% no ganho de peso e obtiveram os melhores índices de conversão alimentar. A adição do complexo enzimático em dietas à base de soja integral melhora o desempenho de frangos. Não é recomendada a utilização da soja com granulometria 1,5mm nas fases iniciais para frangos.

Growth-dependent and species-specific accumulation of polychlorinated biphenyls (PCBs) in tidal flat organisms collected from the Ariake Sea, Japan.

The growth-related as well as species-specific accumulation of polychlorinated biphenyls (PCBs) was studied for tidal flat organisms collected from the Ariake Sea, western Japan. Elevated concentrations of PCBs were found in omnivore fishes, followed in decreasing order by crabs, herbivore fishes, and mussels. This revealed that trophic levels play an important role in PCB accumulation in these organisms. Age- and body length-dependent accumulations of PCBs were observed in herbivorous mudskippers, although a large range of concentrations was found in similar growth stage of fishes. High correlations have been found between concentrations and body length rather than age, which may indicate that the growth rate, which is strongly influenced by the feeding rate of diets, seems to be the predominant factor in determining PCB accumulation. Besides, based on PCB levels in eggs and the whole body in herbivore fishes, the transfer rate of PCBs was estimated to be approximately 10% of female body burdens. Comparison of PCB compositions between eggs and whole body suggests the selective transfer of lower-chlorinated congeners to eggs, which may be due to their instantaneous periods to achieve steady state between egg and whole body lipids. The relationship between BSAFs (biota-sediment accumulation factors) in organisms and log Kow revealed that omnivore mudskipper significantly accumulated PCBs in their body, which might be due to their greater feeding rate and/or higher trophic status in the tidal flat environment.

Use of prey resources by the seastars Leptasterias polaris and Asterias vulgaris: a comparison between field observations and laboratory experiments

The subtidal predators Leptasterias polaris and Asterias vulgaris strongly overlap in their size, distribution and use of prey resources. We evaluate the factors determining their use of prey (feeding rate and prey selection) by comparing prey use in the laboratory and in the field. Both seastars have the same preferred prey, the mussel Mytilus edulis, select medium-sized mussels (1.5–3.0 cm), and show similar responses to increasing mussel density (functional response). Differences between the two seastars in their feeding abilities appear to affect both their size selection of mussels and use of alternative prey when mussels become rare or absent. A. vulgaris selects larger mussels than L. polaris when mussel abundance is low, and this may optimize its energetic intake. L. polaris is be better able to prey on the crevice-dwelling clam Hiatella arctica and A. vulgaris on the ophiuroid Ophiopholis aculeata. These differences in prey selection may reduce potential competitive interactions between the two seastars, as they cause prey partitioning when the preferred prey is rare or absent. The greater feeding rate of A. vulgaris on larger mussels likely provides it with a competitive advantage when the abundance of preferred prey is limited.

The foraging ecology of the Gulf of Mexico stone crab Menippe adina (Williams et Felder)

Laboratory experiments were used to study prey species and size selection by the Gulf of Mexico stone crab Menippe adina (Williams et Felder) on oysters, i.e., Crassostrea virginica Gmelin and southern oyster drills Stramonita ( Thais) haemastoma Grey. Stone crabs select smaller rather than larger oyster drills, and smaller rather than larger oysters. Two results support the idea that size selection in this crab is more the result of mechanical limitations to feeding on large prey than active choice for smaller prey. First, differences in size selection disappear when feeding rates are weighted by differences in handling times, which increase with prey size. Second, an estimate of prey value (tissue dry mass divided by handling time) does not differ dramatically with prey type or size, suggesting large variations in handling time obscure differences in prey energy content. Stone crabs select small oysters over small oyster drills. Stone crabs attack larger oyster drills more frequently than small oyster drills, and persist longer before rejecting them as prey. Neither attack frequency nor persistence increase significantly with increasing oyster size. We also studied aggressive interactions between stone crabs provided with oysters as prey and found that larger stone crabs had greater feeding rates than smaller crabs, and exhibited higher frequencies of dominant behaviors. Our results suggest that the relative importance of active choice vs. mechanical limitations in determining prey selection varies with the specific crab predator-prey system. Gulf of Mexico stone crabs may also affect oyster and oyster drill populations by selectively removing smaller individuals. Finally, smaller stone crabs may be forced to forage in suboptimal habitats, or at suboptimal times, by larger, more aggressive conspecifics.

Oscillatory cross‐flow electrophoresis

AbstractElectrophoresis is a useful analytic technique for the separation of proteins and other large molecules, but has proven resistant to scale‐up to production levels. In this article we describe a new technique that permits the use of much greater feed rates than possible in a conventional electrophoresis unit. The technique, in its simplest form similar to the cyclical field‐flow fractionation technique developed by Giddings (1986) and extended by Shmidt and Cheh (1990), relies on the application of an oscillatory electric field across the narrow gap of the electrophoretic cell. The motion of the solute species induced by this field interacts with an oscillatory cross‐flow to cause a separation based on the electrophoretic mobility of the species. This horizontal separation is combined further with a gradient in the strength of the oscillating electric field and oscillations in the vertical downflow to lead to different steady streamlines for species with different mobilities.

Effects of depth on the feeding capabilities of two octocorals

Feeding abilities of Plexaura homomalla and P. nina were measured during a saturation dive in the underwater habitat Hydrolab at Salt River Canyon, St. Croix, US Virgin Islands. Feeding rates were measured as the number of Sephadex beads ingested by polyps exposed to a known density of beads for 15 min. At Salt River, P. homomalla is found above 20 m and P. nina below 20 m. Feeding abilities were measured in each species' own habitat. At both 17 and 29 m P. nina had greater feeding rates than P. homomalla. These differences can be attributed to P. nina's larger polyps. Feeding rates of both species tend to be lower at 29 m than at 17 m, but feeding rates of P. homomalla at 17 m are equal to those of P. nina at 29 m. Habitat related differences in feeding rates correlate with light availability, but the distribution pattern of P. nina and P. homomalla at Salt River cannot be explained by their heterotrophic and photoautotrophic abilities.