Increased Capture Efficiency Research Articles

Factors affecting post-capture survivability of lobster Homarus americanus

Technological advances in gear and fishing practices have driven the global expansion of the American lobster live seafood market. These changes have had a positive effect on the lobster industry by increasing capture efficiency. However, it is unknown what effect these improved methods will have on the post-capture fitness and survival of lobsters. This project utilized a repeated measures design to compare the physiological changes that occur in lobsters over time as the result of differences in depth, hauling rate, and storage methodology. The results indicate that lobsters destined for long distance transport or temporary storage in pounds undergo physiological disturbance as part of the capture process. These changes are significant over time for total hemocyte counts, crustacean hyperglycemic hormone, L-lactate, ammonia, and glucose. Repeated measures multivariate analysis of variance (MANOVA) for glucose indicates a significant interaction between depth and storage methodology over time for non-survivors. A Gram-negative bacterium, Photobacterium indicum, was identified in pure culture from hemolymph samples of 100% of weak lobsters. Histopathology revealed the presence of Gram-negative bacteria throughout the tissues with evidence of antemortem edema and necrosis suggestive of septicemia. On the basis of these findings, we recommend to the lobster industry that if a reduction in depth and hauling rate is not economically feasible, fishermen should take particular care in handling lobsters and provide them with a recovery period in recirculating seawater prior to land transport. The ecological role of P. indicum is not fully defined at this time. However, it may be an emerging opportunistic pathogen of stressed lobsters. Judicious preemptive antibiotic therapy may be necessary to reduce mortality in susceptible lobsters destined for high-density holding facilities.

Efficient Biosensor Interfaces Based on Space-Controlled Self-Assembled Monolayers

In this paper we demonstrate control over the spacing of surface-modifying probe molecules through the use of labile dendron spacers. During this process, anchor molecules are first adsorbed to a surface, with dendron modifiers attached. Steric interactions of the bulky dendrons control the density of anchor molecules bound to the surface. The dendron branches are subsequently detached from the anchor molecules, and the anchors are chemically modified with probe molecules, resulting in a surface with controlled spacing between probe molecules. Control over this spacing is important when the probe size is small in comparison with the target molecule. This importance is demonstrated for the binding of protein (streptavidin) targets to the probe (biotin) surface. The effect of probe space control on the efficiency of target capture is evaluated by examining the binding of streptavidin to thiolated biotin for a series of mixed monolayers. Surface modification is monitored by Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS). The relative concentration of probe molecules at the surface is measured using X-ray photoelectron spectroscopy (XPS) measurements. Thiolated-biotin surfaces with optimized spacing show an increased capture efficiency for streptavidin relative to surfaces with nonoptimal or no control over probe spacing, as measured by surface plasmon resonance (SPR) spectroscopy. These results are of potential significance for the optimization and fabrication of micro- and nanoarrays used in chemical and biochemical measurements.

Regulation of Cell Adhesion by Affinity and Conformational Unbending of α4β1 Integrin

Rapid activation of integrins in response to chemokine-induced signaling serves as a basis for leukocyte arrest on inflamed endothelium. Current models of integrin activation include increased affinity for ligand, molecular extension, and others. In this study, using real-time fluorescence resonance energy transfer to assess alpha(4)beta(1) integrin conformational unbending and fluorescent ligand binding to assess affinity, we report at least four receptor states with independent regulation of affinity and unbending. Moreover, kinetic analysis of chemokine-induced integrin conformational unbending and ligand-binding affinity revealed conditions under which the affinity change was transient whereas the unbending was sustained. In a VLA-4/VCAM-1-specific myeloid cell adhesion model system, changes in the affinity of the VLA-4-binding pocket were reflected in rapid cell aggregation and disaggregation. However, the initial rate of cell aggregation increased 9-fold upon activation, of which only 2.5-fold was attributable to the increased affinity of the binding pocket. These data show that independent regulation of affinity and conformational unbending represents a novel and fundamental mechanism for regulation of integrin-dependent adhesion in which the increased affinity appears to account primarily for the increasing lifetime of the alpha(4)beta(1) integrin/VCAM-1 bond, whereas the unbending accounts for the increased capture efficiency.

Capture of DNA in microfluidic channel using magnetic beads: Increasing capture efficiency with integrated microfluidic mixer

We have studied the hybridization of target DNA in solution with probe DNA on magnetic beads immobilized on the channel sidewalls in a magnetic bead separator. The hybridization is carried out under a liquid flow and is diffusion limited. Two systems are compared: one with a straight microfluidic channel and one with an integrated staggered herringbone mixer. Fluorescence microscopy studies show that the hybridization is much more efficient in the system with the integrated mixer. The results, which are discussed in terms of a simple model, are relevant for any diffusion-limited reaction taking place on the surface in a microfluidic system.

Concentration of Bacillus Spores by Using Silica Magnetic Particles

Silica particles are mainly used for the concentration of nucleic acid for diagnostic purposes. This is usually done under acidic or chaotropic conditions that will demolish most of the living organisms and prevent the application of other diagnostic tests. Here we describe the development of a method for the capturing and concentration of Bacillus spores using silica magnetic particles to enable fast and sensitive detection. We have shown that capturing various Bacilli spores via silica magnetic particles is limited, with large differences between spore batches (42 +/- 25%). The hydrophobic exosporium layer of spore limits the capture by the hydrophilic silica beads. Partial removal of Bacillus exosporium increases capture efficiency. To increase capturing efficiency without harming the spores' viability, a cationic lipid, didecyldimethylammonium bromide (DDAB), was used as a coat for the negatively charged silica particles. DDAB treatment increased capture efficiency from 42% to more than 90%. Using this method, we were able to capture as few as 100 Bacillus anthracis spores/mL with 90% efficacy. Release of captured spores was achieved by the addition of albumin. The capture and release processes were verified by plating and by flow cytometry using light scatter analysis. The method is simple, efficient, easy to operate, and fast.

Nocturnal and diurnal foraging behaviour of brown bears (Ursus arctos) on a salmon stream in coastal British Columbia

Brown bears (Ursus arctos) have been reported to be primarily diurnal throughout their range in North America. Recent studies of black bears during salmon migration indicate high levels of nocturnal foraging with high capture efficiencies during darkness. We investigated the extent of nocturnal foraging by brown bears during a salmon spawning migration at Knight Inlet in coastal British Columbia, using night-vision goggles. Adult brown bears were observed foraging equally during daylight and darkness, while adult females with cubs, as well as subadults, were most prevalent during daylight and twilight but uncommon during darkness. We observed a marginal trend of increased capture efficiency with reduced light levels (day, 20%; night, 36%) that was probably due to the reduced evasive behaviour of the salmon. Capture rates averaged 3.9 fish/h and differed among photic regimes (daylight, 2.1 fish/h; twilight, 4.3 fish/h; darkness, 8.3 fish/h). These results indicate that brown bears are highly successful during nocturnal foraging and exploit this period during spawning migration to maximize their consumption rates of an ephemeral resource.

Size-based Prey Selectivity and Dietary Shifts in the Jellyfish, Aurelia aurita

Gut content analyses on field-caught Aurelia aurita showed both quantitative and qualitative change in diet as a function of medusa size. Larger medusae tended towards greater numbers and diversity of prey (up to 1550 individual prey representing as many as 13 different prey groups). We also found that medusa size was a good predictor of prey diversity recovered from the medusa gut. While a shift toward greater prey diversity in larger medusae might be explained by increased contact rates with rare' prey taxa, we also found size-based prey selectivity changes in A. aurita. We used in situ gut content data to describe selectivity by A. aurita for three prey types representing varying degrees of swimming or escape velocity. Fish eggs were used as a non-swimming prey, and small ( 1 mm) copepods were used as slow and fast swimming/escaping prey, respectively. Size-dependent increases in selectivity of small copepods can be explained by increased capture efficiency by larger medusae. Selectivity indices of fish eggs and large copepods did not vary with medusa size. Based on these data, we argue that growth to a large size by scyphomedusae can provide a means to enhance diet which, in turn, may positively influence growth and reproduction.

Light Emitting Diode with Charge Asymmetric Resonance Tunneling

We suggest a system of two wells connected with Charge Asymmetric Resonance Tunneling (CART) as a basic element of light emitting diode (LED) structure for semiconductors with different masses of electrons and holes. The system consists of an emitter of electrons, an emitter of holes and an active layer. The hole emitter is coupled with the active in such a way that holes can be freely supplied into the active layer without a barrier. The electron emitter is coupled to the active layer via a barrier. The barrier design uses the charge asymmetric resonance tunneling phenomenon which allows to make the barrier transparent for electrons and blocking for holes. Advantages of this design are: the increased capture efficiency of the electrons into the active layer due to direct resonance tunneling of the electrons from the electron emitter on bound electron level in the active quantum well, the suppression of electron leakage into the hole emitter, the elimination of the parasitic light generated outside the active layer, and the electron emitter acts also as a good current spreading layer. First results of experimental investigation and theoretical modeling of the CART LED devices are reported.

Effect of diatomic islands on step morphological stability of a terrace edge in molecular beam epitaxy

The effect of two-dimensional diatomic-island nucleation on the linear stability of the step morphology during molecular beam epitaxy is investigated numerically via shooting methods. It is found that the effect of diatomic islands on the step morphological stability is significant. The greater the effects of diatomic islands, the more stable the step morphology. Increasing capture efficiency can decrease the critical surface capillary length and shift the critical wave number toward short-wavelength regimes. The unstable region is shrunk with increasing capture efficiency. Further, increasing flux coverage and/or surface coverage can decrease the critical surface capillary length and shift the critical wave number toward short-wavelength regimes.

Influence of prey detection on capture success for the ctenophore Mnemiopsis leidyi feeding upon adult Acartia tonsa and Oithona colcarva copepods

Although the lobate ctenophore Mnemiopsis leidyi is known to be an important copepod predator, the mechanistic basis for its predatory success is not well understood. We directly observed and recorded predation by free-swimming M. leidyi ctenophores on Acartia tonsa and Oithona colcarva copepods (n = 349 encounters, 25 different ctenophores) in the laboratory using videographic methods. Overall capture success was relatively high (74 %) following copepod contact with M. leidyi. However, average retention of copepods initially contacting the interior surfaces of the oral lobes (the major capture sites) was considerably lower (34 %). Average retention was low because copepods most frequently collided head-first with the oral lobes and bounced away without being captured. Escape success for copepods declined rapidly during ensuing contacts, and most captures (57 %) involved multiple contacts within an encounter. Our most novel finding was that almost half (49 % ) of the encounters involved alterations of oral lobe positions which preceded, or anticipated, actual contact with a copepod. Anticipatory responses were cued to fluid disturbances created by swimming copepods. Anticipation of prey contact allowed ctenophores to shift oral lobe positions and reduce copepod escape avenues, thereby increasing the number of contacts per encounter and significantly increasing capture efficiency.

The use of snowmobiles in the drug immobilization of muskoxen

During the early winter in 1983 and 1985 on Victoria and Banks islands, respectively, we used snowmobiles to approach and hold muskoxen (Ovibos moschatus) in tight groups, while individual animals were darted with a mixture of M99 and Rompun. We immobilized 47 muskoxen with one capture-related mortality from an accidental overdose. The effective dosage that resulted in acceptable induction and recovery times for most adult muskoxen was 7–8 mg M99 and 25–30 mg Rompun. Considerably cheaper to use than helicopters, snowmobiles also were more effective in holding muskoxen together and in reducing stress prior to immobilization. Darts could be fired at close range allowing for easier selection of individual muskoxen and for proper dart placement. Simultaneous darting and recovery of several animals in a group further reduced animal stress and increased capture efficiency.

Selective Predation with Respect to Body Size in a Population of the Fish Xenomelaniris Venezuelae (Atherinidae)

The food habits of the planktivorous fish Xeonomelaniris venezuelae (Atherinidae) in Lake Valencia, Venezuela, were studied in relation to fish size. Mean selection for major prey types and mean breadth of diet were determined for each size class of fish. The smallest fish select the rotifer Brachionus calyciflorus while successively larger fish select successively larger prey. Mean length and mean dry mass of the items eaten by the fish are directly related to fish length. Diet breadth, however, is inversely related to fish length, indicating that large fish feed more selectively than small fish. Evidence is presented which suggests that the relationship between Xenomerlaniris body size and prey selection is due to increased capture efficiency with size, and that the relationship of body size to diet breadth results from growth—related improvements in vision.

Electron-electron effects in the writing and erasing of dual-dielectric charge-storage cells

We have found an abrupt drop in the capture efficiency of dopant-induced interfacial states in DDC’s when the stored-charge density exceeds 7×1012/cm2. The constancy of this number with electric field strength and with increasing capture efficiency from increased induced-state density suggests Coulombic repulsion ultimately limits writing efficiency. Erasing characteristics are also explained by barrier lowering due to electron-electron repulsion.

Progress in the Efficiency of Free-Space Microwave Power Transmission*

ABSTRACTRecent developments in rectenna design and microwave beam launching have increased the ratio of the dc power output from the rectifier at the receiving point to the rf power input to the transmitting antenna from 0.41 to 0.60. The efficiency of microwave beam launching has been improved through the use of the dual-mode horn which has exceptionally low power loss in its side lobes. Improvement in the efficiency at the receiving point has resulted from increased capture efficiency of the rectenna.