ALBERT

Notes:   Clusters now form a central element in many regional economic development policies. Location within a cluster of related industries is thought to increase a firm's competitive advantage resulting in higher output and productivity growth rates than in similar firms located beyond the cluster. This study focuses on owner-managers operating small firms within a traditional cluster of metalworking industries and empirically examines the relationship between growth-orientation and the extent and nature of cluster embeddedness. The results indicate only a limited number of differences in growth-orientation given variations in levels of cluster embeddedness. Contrary to conventional wisdom, many of the most growth-oriented entrepreneurs focus their activities outside the cluster, especially in terms of market-based linkages. However, those firms with more advanced process technologies do tend to show above average within cluster linkages.

Notes: The allelopathic influence of four developmental stages of nodding thistle (small rosette, large rosette, bolting and dead plants) on eleven test species (six grasses, four legumes and itself) was investigated using aqueous extract bioassays, aqueous leachate bioassays, and bioassays based on addition of ground material to soil. The aqueous extract and leachate bioassays indicated that nodding thistle was most allelopathic at the rosette stages, while the bioassays involving amendment of soil with thistle tissue showed bolting live and dead plants to be the most allelopathic. It is proposed that nodding thistle is allelopathic at two phases of its development, i.e. at the early bolting stage when the larger rosette leaves are decomposing and releasing soluble inhibitors, and at the stage when bolting plants are dying and releasing insoluble inhibitors. Nodding thistle seedlings appear to be stimulated by addition of thistle tissues to soil, indicating that thistle plants may weaken pasture and simultaneously encourage recruitment of its own species. This is consistent with previous studies detecting high densities of thistle seedlings in the vicinity of deceased parent plants. The six grass species were generally more tolerant to thistle allelopathic effects than were the four legume species, but no consistent differences emerged between different grass or legume species. Influence de l'age de la plante sur le potentiel allélopathique du chardon penche (Carduus nutans L.) vis a vis des prairies de graminées et de légumineusesL'influence allélopathique de 4 stades de développement du chardon penché (petite rosette, grande rosette, montaison, plantes mortes) sur 11 espèces tests (6 graminées, 4 légumineuses et lui-même) a étéétudiée en utilisant des bioessais d'extraction acqueuse, des bioessais de lessivage acqueux et des bioessais fondés sur l'addition au sol d'amendement. Les bioessais d'extraction acqueuse et de lessivage ont montré que le chardon penchéétait plus allélopathique au stade rosette tandis que les bioessais impliquant l'amendement de sol avec des tissues de chardon ont montré que la montaison et les plantes mortes étaient les plus allélopathiques. Il est proposé que le chardon penché est allélopathique à 2 phases de son développement, par exemple au stade montaison précoce quand les plus grandes feuilles de la rosette se décomposent et relachent les inhibiteurs solubles, et au stade où les plantes montées meurent et relächent les inhibiteurs insolubles. Les plantules de chardon penché apparaissent être stimulées par l'addition de tissus de chardon au sol, montrant que les plantes de chardon peuvent affaiblir une prairie et simultanément favoriser sa propre réimplantation. Ceci est conforme avec des études précédentes montrant des fortes densités de plantules de chardon au voisinage de plantes parentes mortes. Les 6 espèces de graminées ont été de façon générale plus tolérantes aux effets allélopathiques que les 4 espèces de légumineuses, mais aucune différence importante ne s'est exprimée entre les différentes espèces de graminées ou de légumineuses. Einfluβ des Pflanzenalters der Nickenden Distel (Carduus nutans L.) auf die allelopathische Wirkung gegen Weidegräser und LeguminosenDie allelopathische Wirkung der Nickenden Distel wurde in 4 Entwicklungsstadien (in kleiner und in voller Rosette, blütentreibend und abgestorben) gegen 11 Pflanzenarten (6 Gräser, 5 Leguminosen und sich selbst) mit wäßrigen Auszügen, Perkolationswasser und Bodenmaterial zum Substrat geprüft. Mit den wäßrigen Auszügen und dem Perkolationswasser zeigte sich die Nickende Distel im Rosetten-Stadium am meisten allelopathisch, während Bodenmaterial mit Resten blütentreibender und abgestorbener Pflanzen wirksamer war. Es kann angenommen werden, daß die Nickende Distel in 2 Entwicklung sphasen allelopathisch wirkt, nämlich wenn die größeren Rosettenblätter oder wenn die blütentreibenden Pflanzen vergeben und 1ösliche Hemmstoffe entlassen. Keimpflanzen der Nickenden Distel werden offensichtlich durch Pflanzenmaterial der Distel im Wachstum angeregt; die Distel schwächt also Weide-Pflanzenarten und fördert zugleich ihre eigene Entwicklung. Dieser Befund deckt sich mit der Beobachtung hoher Keimpflanzen-Dichten um abgestorbenen Mutterpflanzen. Die 6 Gräser waren durchweg gegenüber der allelopathischen Wirkung der Distel unempfindlicher als die 4 Leguminosen, doch innerhalb dieser Gruppen zeigten sich keine klaren Unterschiede.

Notes: Swards of 10 pasture species (six grasses and four legumes) were established and planted with seeds of either of the thistle species Carduus nutans L. or Cirsium vulgare L., and emergence and growth of the thistle seedlings were subsequently monitored. Emergence of C. nutans seedlings was inhibited by ryegrass (Lolium perenne L.) and Yorkshire fog (Holcus lanatus L.) swards, while C, vulgare emergence was inhibited by Yorkshire fog relative to some of the other treatments. Speed of emergence of C. nutans and absolute emergence of C. vulgare seedlings were significantly negatively correlated with pasture cover density, presumably as a consequence of alteration of light quality by the pasture swards. All pasture species inhibited seedling shoot and root growth of both thistle species, although the grasses were the most effective inhibitors. The seedling emergence and growth data for C. nutans in the swards of the 10 species were significantly correlated with the results of a previous study on residual allelopathic effects of the same 10 species on nodding thistle root growth. It is concluded that inhibitory (including allelopathic) influences of pasture species on thistle seedlings have considerable potential as a mechanism for managing problematic thistle populations. Influence de converts de pature de graminees et de legumineuses sur la levée et la croissance de Carduus nutans L. et Cirsium vulgare L.Des couverts de 10 espèces fourrageres (6 graminées et 4 légumineuses) ont étéétablis et infestés avec des graines de 1'une ou 1'autre des espèces de chardon, Carduus nutans L. et Cirsium vulgare L.; la levée et la croissance des plantules de chardon ont été ensuite suivies. La levée des plantules de C. nutans a été inhibéee par les couverts de ray-grass (LoliumperenneL.) et de houlque laineuse (Holcus lanatus L.) tandis que la levée de C. vulgareétait inhibée par la houlque laineuse en comparaison de quelques-unes des autres modalites. La vitesse de levée de C. nutans et la levée globale de C. vulgare ont été corrélées négativement de façon significative avec la densité du couvert, probablement en conséquence de 1'altération de la qualité de la lumière par les tapis, fourragers. Toutes les espèces de fourrages ont inhibé la croissance des tiges et des racines des plantules des 2 espèces de chardon, bien que les graminèes aient été des inhibiteurs plus efficaces. La Ievée des plantules et les chiffres de la croissance de C. nutans dans les couverts des 10 espéces étaient correlées de façon significative avec les résultats d'une étude antérieure sur les effets allélopathiques résiduels de quelques-unes des 10 espèces sur la croissance racinaire du chardon. II est conclu que les effets inhibiteurs (y compris I'allélopathie) des espèces fourragères sur les plantules de chardon ont un potentiel considèrable pour gérer le problème des populations de chardon. Einfluβ von Weidegräser- und Leguminosen-Beständen auf Samenkeimung und Wachstum von Carduus nutans L. und Cirsium vulgare L.In Beständen von 10 Weide-Pflanzenarten (6 Gräser und 4 Leguminosen) wurden Samen der Disteln Carduus nutans L. und Cirsium vulgare L. ausgebracht und deren Keimung und Wachstum beobachtet. Die Keimung von Carduus nutans wurde in Beständen von Weidelgras (Lolium perenne L.) und Wolligem Honiggras (Holcus lanatus L.) gehemmt, während die Keimung von Cirsium vulgare in Wolligem Honiggras genauso wie in einigen anderen Beständen gehemmt war. Die Keimungsgeschwindigkeit von Carduus nutans und die gesamte Keimung von Cirsium vulgäre waren signifikant negativ mit der Dichte der Weide-Pflanzenbestände korreliert, vermutlich wegen Änderung der Lichtqualität durch die Pflanzendecke. Alle Weide-Pflanzenarten, besonders jedoch die Gräser, hemmten das Sproß- und Wurzelwachstum der Keimpflanzen der beiden Disteln. Keimung und Wachstum der Carduus-nutans-Keimpflanzen in den Beständen der 10 Arten entsprachen ganz den Befunden einer früheren Untersuchung über allelopathische Wirkungen derselben 10 Arten auf das Wurzelwachstum der Nickenden Distel. Den Hemmwirkungen (einschließlich allelopathischen) von Weide-Pflanzenarten auf Distel-Keim-pflanzen kommt offenbar eine erhebliche Bedeutung für die Unterdrückung problematischer Distelpopulationen zu.

Notes: Oxygen consumption rates were measured in a school of 56 horse mackerel Trachurus trachurus while at rest and while swimming at steady sustained speeds. Resting values of 38.76 and 42.10mg O2 kg−1 h−1 were measured in a sealed cylindrical tank (535 l) while observing that the fish school remained neutrally buoyant and inactive with only gentle pectoral fin movements and no swimming motion. The same school was trained to swim with projected light patterns within a 10-m diameter annular doughnut respirometer. The oxygen consumption increased from the resting level through 51 mg O2 kg−1 h−1 at the slowest swimming speeds of 0.29 m s−1 (0.95 L s−1) to around 259 mg O2 kg−1 h−1 at the higher measured swimming speed of 0.87 m s−1 (2.82 L s−1). The data fitted a curve where oxygen consumption rose in proportion to velocity to the power of 2.56 with the intercept at the resting level. The maximum sustained speed (80 min) of 1.12 m s−1 (3.63 Ls−1) was not achieved within the respirometer but corresponded to an estimated oxygen consumption of 458.33 mg O2 kg−1 h−1 giving a scope for aerobic activity of 419.02 mg O2 kg−1 h−1. At a speed of 0.87 m s−1, there was a lower bound on the aerobic efficiency of at least 38% and at 1.12 m s−1, the highest aerobic speed, of 40%. Sustained speeds swum in a curved path as here should be increased by 5% for a straight path giving a maximum sustained 80 min speed of 1.18 m s−1.

Notes: Electromyogram (EMG) signals from two points at about 40%L and 65%L(L= length) in the left latera1 muscle of mackerel (Scomber scombrus L.) L= 28–33 cm a nd saithe (Pollachius virens L.) L= 42–50 cm were recorded synchronously with films of steady straight swimming motions. In both species, the duration of EMG activity at both electrodes, remains a constant proportion of the tail cycle period Tat all the tail beat frequencies between 1–8 and 13 Hz. In mackerel and saithe respectively: onset of EMG activity at the front was 74%T and 77%T before the left-most tail blade position and fronl EMG-onset occurred 15%T and 18%T before rear onset. The duration of the EMG burst is longer at the front position (41%T and 47%T) than at the rear (25%T and 27%T), At all swimming speeds the wave of electrical activation of the muscle travelled between the two electrodes 25%L apart at a velocity between 1.5 and 1.6L T−1. Frequencies of spikes within the burst of EMG activity rose from 30–40 Hz at 2 T s−1 to 50–80 Hz at 8 T s−1. In muscle at 40%L EMG-onset happens at phase 30° just after muscle strain at this point reaches its resting length while lengthening (360°). At 65%L EMG-onset occurs earlier in the strain cycle-350° just before the muscle reaches it resting length while lengthening (360°). This could represent within the length of the fish, a phase shift of up to 90° in the EMG-onset in relation to the muscle strain cycle. These timings are discussed in relation to optimized work output and a single instant of maximum bending moment all along the left side of the body.

Notes: Sustained swimming of bluefin tuna was analysed from video recordings made of a captive patrolling fish school [lengths (L) 1.7–3.3 m, body mass (M) 54–433 kg]. Speeds ranged from 0.6 to 1.2 L s−1 (86–260 km day−1) while stride length during steady speed swimming varied between 0.54 and 0.93 L. Maximum swimming speed was estimated by measuring twitch contraction of the anaerobic swimming muscle in pithed fish 5 min after death. Muscle contraction time increased from the shortest just behind the head (30–50 ms at 20% L) to the longest at the tail peduncle (80–90 ms at 80% L) (all at 28°C). A fish (L = 2.26 m) with a muscle contraction time of 50 ms at 25% L can have a maximum tail beat frequency of 10 Hz and maximum swimming speed of 15m s−1 (54km h−1) with a stride length of 0.65L. With a stride length of 1 L a speed of 22.6 m s−1 (81.4 km h−1) is possible. Power used at maximum speed was estimated for this fish at between 10 and 40 kW, with corresponding values for the drag coefficient at a Reynolds number of 4.43 × 107 of 0.0007 and 0.0027.

Notes: Negatively-buoyant Atlantic mackerel, Scomber scombrus L., (fork length 30–39 cm) tilt their bodies with the head up while swimming at speeds below 0.8 body length per second (B.L. s−1). This behaviour is quantitatively described by the body attack angle and swimming speed measured from film records. The maximum recorded body attack angle was 27° in a 32 cm-long fish swimming at 0.45 B.L. s−1 while its nose followed a course close to the horizontal. In general, larger body attack angles were shown at lower swimming speeds and were associated with denser bodies at each speed. We consider that this behaviour pattern allows the fish to maintain a chosen swimming depth while its body creates lift by acting as a hydrofoil. Lift from the fins is insufficient at low swimming speeds.

Notes: Burst swimming speeds were measured in mackerel 0.275–0.380 m long by filming newly caught fish, first released into a large shore-sited tank, using a high-speed cine camera and real time TV camera. The highest speed was 5.50 m s−1 or 18 body length per second (b.l. s−1) in a 0.305 m long mackerel at 12° C. The recorded maximum tail beat frequency of 18 Hz agrees well with 19 Hz predicted from the measured contraction time of 0.026 s for the anterior lateral swimming muscle. The stride length was close to 1 B.L.; the power, calculated from the drag, was 4.53 W, and, calculated from the muscle used, was 5.07 W; all suggesting that the mackerel is swimming close to its physiological limit.

Notes: The schooling behaviour of Atlantic mackerel was studied in a large tank at different light intensities in the range 12.6–1.8 × 10−10μEs−1 m−2. Variable light intensity was produced by accurately controlling the current to a green light-emitting diode (LED) 3 m above the experimental tank. Under high light levels (1.8 × 10−6μEs−1 m−2) mackerel always formed a single school, whereas at lower levels (1.8 × 10−8μEs−1 m−2) they swam as individuals. At light levels down to 1.0 × 10−6μEs−1 m−2 the mean nearest neighbour distance in a school remained relatively constant (0.3–0.9 body lengths), and individual mackerel swam along a path which deviated from the position of their nearest neighbours by less than 14°. As light dropped below 1.8 × 10−7μEs−1 m−2, both nearest neighbour distance and heading angle between nearest neighbours increased, with mean values of 1–1.8 body lengths and 23–92°, respectively, at 1.8 × 10−9μEs−1 m−2. The results are discussed in terms of ambient light conditions in the sea.