Forward Thrust Research Articles

Body Form and Locomotion in Sharks

A revised interpretation of the mode of action of the heterocercal tail in sharks shows that the upturned tail axis tends to produce a thrust directed downwards behind the centre of balance of the fish and thus gives a moment turning the head upwards. This is countered in two ways—by the rotation of the tail along its longitudinal axis during each lateral beat, and through the action of the ventral hypochordal lobe. The shape of the tail and the mode of action of the tail in all sharks so far considered reflects a balance between these three factors, in all of them the net effect being the production of a forward thrust from the tail that passes directly through the centre of balance of the fiish. There is normally therefore no tendency for the fish to turn around the centre of balance in a sagittal plane but there is a net sinking effect that is countered by the planning effect of the pectoral fins and the ventral surface of the head. A study of 56 species of sharks shows that the tail is constructed according to a remarkably consistent common plan, the extremes being the high angled rather symmetrical tail of pelagic sharks such as hums, Lamna and Rhincodon and the straight tails of benthic sharks such as Ginglymostoma in which a ventral hypochordal lobe is absent. When the general body shape of sharks, including the position of insertion of the median and paired fins and the pattern of growth of fin surface areas is considered, the uniformity of the shark body plan and locomolor function is further emphasised. Four patterns of body form in sharks are recognised: 1) The fast swimming pelagic sharks and the whale sharks have a tail with a high aspect ratio, a conical head, a lateral fluke on the caudal peduncle. 2) The generalised sharks typified by the Carcharhinidae, have lower heterocercal angles, a flattened ventral surface on the head and lack the caudal fluke. 3) The demersal sharks typified by the catsharks (Scyliorhinidae) have a very low, almost straight tail. The ventral hypochordal lobe is absent and the first dorsal fin is posterior in position. 4) The squalomorph sharks are distinct in the absence of the anal fin, presence of a marked epicaudal lobe in the tail and often an elevated insertion of the pectorals. The anal and second dorsal fins are always the smallest fins and the pectorals grow at the fastest rate. In general there is an inverse relationship between size and rale of growth of all fins and the ventral surface of the head. In hammerheads the growth data confirms that the head has a significant planing action in swimming. The pectoral, second dorsal and anal fins show an extreme constancy of position of insertion in all sharks studied. The locomotor mechanism of sharks is adapted for an efficient cruising swimming but at the same time, the potential instability in the sagittal plan allows for the production of turning moments that are used in attack and feeding.

Structural correlates of forelimb function in fur seals and sea lions.

Dissections, manipulation of ligamentary preparations, analysis of limb proportions, and quantitative aspects of forelimb myology are used to correlate forelimb morphology in fur seals and sea lions (sub-family Otariinae) with previously published data as to their locomotor function (English, '76a). Comparisons to structure and function in generalized fissiped carnivores are then used to elucidate locomotor adaptations in fur seals and sea lions. Unique features of forelimb function during swimming in these pinnipeds include the amounts of abduction-adduction and rotary movements used. Modifications of the size, attachments and fasicle architecture of the muscles and the structure and range of possible movement of the joints suggest that in fur seals and sea lions these movements (1) take place about the glenohumeral (shoulder) joints, (2) that the movements are probably finely controlled, and (3) that they contribute to the generation of massive forward thrust via the cooperative activity of muscles capable of generating large amounts of force throughout the range of movement. Recovery movements occur through a similarly large range, and modifications of forelimb anatomy either to minimize or overcome water resistance are noted. The adaptive significance of these modifications is interpreted as allowing fur seals and sea lions to swim at speeds necessary to feed on the fast swimming prey presumably abundant in their adaptive zone.

Hydromechanics of lunate-tail swimming propulsion. Part 2

This paper investigates the propulsive performance of the lunate tails of aquatic animals achieving high propulsive efficiency (the hydromechanical efficiency being defined as the ratio of the work done by the mean forward thrust to the mean rate at which work is done by the tail movements on the surrounding fluid). Small amplitude heaving and pitching motions of a finite flat-plate wing of general planform with a rounded leading edge and a sharp trailing edge are considered. This is a generalization of Chopra's (1974) work on model rectangular tails. This motion characterizes vertical oscillations of the horizontal tail flukes of some cetacean mammals. The same oscillations, turned through a right angle to become horizontal motions of side-slip and yaw, characterize the caudal fins of certain fast-swimming fishes; viz. wahoo, tunny, wavyback skipjack, etc., from the Percomorphi and whale shark, porbeagle, etc., from the Selachii. Davies’ (1963, 1976) method of finding the loading distribution on the wing and generalized force coefficients, through approximate solution of an integral equation relating the loading and the upwash (lifting-surface theory), is used to find the total thrust and the rate of working of the tail, which in turn specify the hydromechanical swimming performance of the animals. The physical parameters concerned are the tail aspect ratio ((span)2/planform area), the reduced frequency (angular frequency x typical length/forward speed), the feathering parameter (the ratio of the tail slope to the slope of the path of the pitching axis), the position of the pitching axis, and the curved shapes of the leading and trailing edges. The variation of the thrust and the propulsive efficiency with these parameters has been discussed to indicate the optimum shape of the tail. It is found that, compared with a rectangular tail, a curved leading edge as in lunate tails gives a reduced thrust contribution from the leading-edge suction for the same total thrust; however, a sweep angle of the leading edge exceeding about 30° leads to a marked reduction of efficiency. Another implication of the present analysis is that no negative work is involved in the actual oscillation of the tail.The present results are used to obtain an estimate of the drag coefficient for the motion of the animals, based on observed data and the computed thrust. The results show some evidence of differences between the CD's for cetacean mammals and scombroid fish respectively. Some discussion of this difference is also given.

Atlatl Function: a Reply to Butler

which is still in contact with the dart. thrower's hand continues to move forward and downward during the last part of dart/atlatl contact; this is the downward curving thrust mentioned in my article. It is merely that portion of the path of the thrower's hand between the point that the hand releases the dart and the point that the dart leaves the atlatl. As I stated in the article: The portion of the curved thrust which is converted to forward thrust is very small; therefore, a rather short atlatl will obtain all the additional thrust available from this source.

The relative application of endoscopy and other diagnostic methods in achalasia

Clinical, radiologic, manometric, and endoscopic data were applied to distinguish achalasia in a group of 52 patients complaining of dysphagia or chest pain or both. Endoscopically, achalasia was characterized by a non-relaxing lower esophageal sphincter that would yield to gentle but firm forward thrust of the instrument. The finding of hiatal hernia or esophagitis was against a diagnosis of achalasia. Manometry was particularly helpful in achalasia patients with little or no esophageal dilation by radiography. Peroral endoscopy was found to add essential information leading to the correct diagnosis of patients with dysphagia or esophageal chest pain.

Citizens' agenda: Action consensus

National Civic ReviewVolume 64, Issue 4 p. 188-191 Article Citizens' agenda: Action consensus James R. Ellis, James R. Ellis James R. Ellis, Seattle attorney, was formerly president of the Municipal League of Seattle and King County, and Forward Thrust, Inc. He is a regent of the University of Washington and a trustee of the Ford Foundation. He also is a vice president of the National Municipal League.Search for more papers by this author James R. Ellis, James R. Ellis James R. Ellis, Seattle attorney, was formerly president of the Municipal League of Seattle and King County, and Forward Thrust, Inc. He is a regent of the University of Washington and a trustee of the Ford Foundation. He also is a vice president of the National Municipal League.Search for more papers by this author First published: April 1975 https://doi.org/10.1002/ncr.4100640406 AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume64, Issue4April 1975Pages 188-191 RelatedInformation

Jet-propulsion in anisopteran dragonfly larvae

Jet-propulsion in dragonfly larvae is achieved by the rapid ejection of water from a specialised rectal chamber via the anus, at a frequency of up to 2.2 cycles/s. Movement, forward thrust and muscular activity have been recorded in restrained and free-swimming larvae. Forward thrusts of up to 1.5 g wt result from the expiratory phases of cycles lasting 0.1 to 0.4 s. Swimming velocities are in the order of 10 cm/s. The following muscles are shown to be active during expiratory phases of jetting: anterior, posterior and respiratory dorso-ventrals; primary and secondary longitudinal tergals; lateral primary longitudinal sternopleural; dorso-ventral oblique; ventral adductors of the anal appendages. The sub-intestinal muscle is active during the inspiratory phases of jetting. Activity recorded is compared with that found during normal ventilation. The larval jet-propulsive mechanism is compared with that of certain cephalopods and found to be very effective for the larva's relatively small size.

Neural Control of Swimming in the Leech

Leeches swim by undulating; they alternately form crests then troughs at their anterior end and move Them backward, thereby producing forward thrust. These movements are accomplished by alternating contractions of dorsal and ventral longitudinal muscles in each of the 21 body segments. These contractions are caused by bursts of impulses in groups of excitatory and inhibitory motor neurons. Connections among motor neurons help to coordinate these bursts: synergistic muscle excitors are electrotonically coupled, which aids in keeping their bursts nearly synchronous; muscle inhibitors also inhibit the excitors to the same muscles, and it is this inhibition which keeps the excitors from being tonically active during swimming. Neurons sensitive to either dorsal or ventral body wall stretch produce reciprocal stretch reflexes to the muscle excitors, probably via the inhibitors. That these stretch reflexes may be involved in generating the periodic bursts is supported by the results of both behavioral and electrophysiological experiments.

Problems of Social Stratification and the Demarcation of National and Local Elites in British Ceylon

Political developments in Ceylon during the 1950's drew attention to the forward thrust of a social formation in the Sinhala districts which has been described variously as “the rural middle classes,” “the lower middle-class traditionalists,” a “new village leadership” and so on. The political antecedents of this “group” were not traced beyond the 1930's, though several writers recognized that it was part of a social category which existed in British times. In recent articles it has been argued that the political activities of individuals drawn from this social category date back to the late nineteenth century. Be that as it may, it is obviously of value to clarify the lines of differentiation between this middle-level social category and the indigenous elite placed hierarchically above them. The former can be described as a “sub-elite,” a “subordinate elite,” an “intermediate elite,” or a “local elite.” The latter can be described as a “macro-elite,” a “central elite” or a “national elite.” Though convenience dictates the choice of one of these combinations, a reference to the alternatives is necessary because each captures a facet which the other labels do not convey.

Developmental Disabilities: An Overview

Since the establishment of university affiliated facilities (UAF), a forward thrust has been given to the interdisciplinary training of professionals and supportive personnel for the care and management of the developmentally disabled child and family. Not only has medical and dental care significantly improved, but the interdisciplinary habilitation methods have also been refined and new ones innovated to significantly benefit the handicapped and his family. If the return to the community movement is to be enhanced, training must be continued in a realistic fashion coupled with pilot study projects and other research endeavors to closely monitor new methods of treatment prior to their being instituted. It is hoped that this article has assisted in giving an overall view as to the breadth and scope of the developmental disabilities and a sampling of the roles of the various professionals.

Hydromechanics of lunate-tail swimming propulsion

This paper investigates the non-uniform motion of a thin plate of finite aspect ratio, with a rounded leading edge and sharp trailing edge, executing heaving and pitching oscillations at zero mean lift. Such vertical motions characterize the horizontal lunate tails with which cetacean mammals propel themselves, and the same motions, turned through 90° to become horizontal motions of sideslip and yaw, characterize the vertical lunate tails of certain fast-swimming fishes. An oscillating vortex sheet consisting of streamwise and spanwise components is shed to trail behind the body and it is this additional feature of the streamwise component resulting from the finiteness of the plate that makes this study a generalization of the two-dimensional treatment of lunate-tail propulsion by Lighthill (1970). The forward thrust, the power required, the energy imparted to the wake and the hydromechanical propulsive efficiency are determined for this general motion as functions of the physical parameters defining the problem: namely the aspect ratio, the reduced frequency, the feathering parameter and the position of the pitching axis. The dependence of the thrust coefficient and propulsive efficiency on these physical parameters, for the complete range of variation consistent with the assumptions of the problem, has been depicted graphically.

The bacterial flagella and the flagellar protein flagellin.

AbstractIn comparison with the relatively complicated flagella of all nucleated organisms, most of the actively motile bacteria have very much simpler locomotion organelles. These flagella are long thin filaments with a helical superstructure, anchored at one end in the cell membrane. Helical waves pass along the flagella in the distal direction during locomotion. In the flagella, identical structural units of a single protein species, flagellin, are linked to one another by non‐covalent bonds. The flagellin subunits can be separated from one another by mild methods, and their biochemistry as well as their structure and morphology can be investigated in the isolated state. Under certain conditions they can reaggregate in vitro to form polymorphous helical filaments, which are practically indistinguishable from intact flagella. In the flagellum, the elongated flagellin molecules have a layered arrangement in about ten parallel strands, which in turn form a hollow cylinder. Since this cylinder is deformed into a large helix, the individual chemically identical flagellin protomers and the protomer strands in the helical flagella are only quasi‐equivalent. The conformation and bonding pattern of the individual longitudinal flagellin lines can presumably be controlled in vitro by the basal structures, so that movement within the flagellum could conceivably occur as follows. A cyclically induced change in the length of the individual strands could result in an apparent rotation of the helical flagellum. According to hydrodynamic calculations, the resulting forward thrust is sufficient to propel the bacteria at the observed speeds of up to 50 μm/s.

Variations in the mode of stolon growth among different genera of colonial hydroids, and their evolutionary implications.

Stolonic growth has been compared among several genera of calyptoblastic (Campanularia flexuosa, C. calceolifera, Gonothyraea and Sertularia) and gymnoblastic (Pennaria, Bougainvillia, Eudendrium and Cordylophora) hydroids with respect to such features as the (1) complexity and uniformity of the tip movements, (2) constancy of growth cycle duration, (3) variability in growth among cycles, (4) growth rate, and (5) variability of retractions among cycles. The "growth cycle," previously described in C. flexuosa, is the basis for elongation in all species observed. Its pattern is indistinguishable between the Campanularia species; however, at the generic level the tip movements show peculiarities which delineate each genus from all others. In addition, the movements in all calyptoblasts are uniform from cycle to cycle and comparatively simple, whereas those of the gymnoblasts are complicated by the variable appearance of one or more secondary forward thrusts between crests. A dichotomy is seen between the calyptoblasts and most gymnoblasts in other respects as well. Cycle time is very predictable and cycle-to-cycle variability in growth is relatively narrow in all calyptoblasts. However, in most gymnoblasts both features are much more loosely regulated: only Pennaria shows some degree of control to its timing mechanism, and only in Bougainvillia and Eudendrium does the uniformity of growth per cycle reach the calyptoblast level. On the premise that calyptoblasts are evolutionarily the more advanced group, simplicity and regularity of growth movements are concluded to be the evolved, and complexity and variability the primitive, conditions. On this basis the evolutionary relations among the four gymnoblasts, as deduced from their stolonic growth behavior alone, are consistent in many but not all respects with those interpreted from morphological considerations.

The parapodial and segmental musculature of Harmothoë imbricata (L.).

The segmental anatomy of Harmothoë imbricata deviates from the plan of a typical errant polychaete only slightly. The body is partitioned into 37 nonmetameric segments and is covered by 15 pairs of elytra. The segmental musculature consists of paired dorsal and ventral longitudinal muscles, pairs of dorso-ventral muscles, and in places the external surface of the worm is covered by a sheet of circularly coursing muscle fibers subjacent to the cuticle. The dorsal tubercles, elytrophores, cirratophores and ventral cirri are moved by muscles derived from segmental and intrinsic parapodial muscles. From the anatomy it is surmised that the lateral bending of the worm during swimming is due to cycles of activity involving the longitudinal muscles (S-waves). During a cycle of parapodial stepping, parapodial levators and promotors raise a parapodium from the substrate and direct it forward (the recovery stroke), at which time the muscles of the aciculum and setal sacs withdraw the neuropodial setae. During the power stroke parapodial depressors and remotors bring the tip of the parapodium against the substrate, applying a forward thrust and the neuropodial setae are extended. At the conclusion of the power stroke, the recovery stroke begins anew.

A radiographic analysis of the tongue-thrust swallowing habit: A preliminary report

T he tongue-thrust swallowing habit has been recognized and studied.lMQ Although many authors have attempted to analyze the causes of the tongue-thrust swallowing habit on a developmental and clinical basis, a review of the literature disclosed no information relating to radiographic changes occurring in thr periodontium attributable to the tongue-thrust movement. During normal swallowing, the maxillary and mandibular incisors arc momentarily in contact as the tip of the tongue touches the lingual interdental papillae of the maxillary arch. The dorsum of the tongue closely approximates the palate, the lips are tightly closed together, and the act of swallowing occurs. In the abnormal swallowing sequence being investigated, the teeth are separa.ted. the tongue thrusts forward into the excessive overjet, and the dorsum of the tongue drops away from the palatal vault. Instead of the lips creating a firm seal with each other, the upper lip remains relatively functionless while the mentalis muscle exerts a strong forward and upward thrust of the lower lip against the lingual surfaces of the maxillary incisors.1o Force and frequency of swallowing have been reported.ll-I3 The force exerted by the tongue varies from 5 to 10 psi. The exact force is dependent upon the circumstances under which swallowing is performed, that is, standing, lying down, or with or without the presence of food.

Relation between forward thrust on a perforator and its characteristics, the bit shape, and the rock-breaking process

1. The forward thrust depends on the parameters of the perforator and bit and on the characteristics of the rock being drilled. 2. The optimal forward thrust should ensure that the perforator operates so that in each cycle the body drops on to the shoulder before the bit emerges to the level of the preceding impact, and the withdrawal of the body should be equal to the depth of penetration per impact. 3. The equations found above can be used to determine the forward thrust in the design of feed mechanisms, as well as to elucidate the laws of change of this thrust in drilling with a given perforator and various bits, or in various rocks: this may prove useful in the design of drilling machines with automated setting to optimal drilling conditions.

Preliminary investigations into the performance of different shaped blades for the rotary tillage of wet rice soil

This work considers two aspects of rotary tillage of wet (supersaturated) soils by power-driven soil-engaging blades, viz. power requirement of blades; forward thrust due to blades. The shape of the blades was found to be an important factor greatly affecting both these aspects.

Senescence: The enemy of progress

Consideration should be given to a problem that may be more significant than any other single factor in retarding progress in chemistry and chemical education. This is the overwhelming influence of old people in the rendering of decisions for the support of science. The fact of the matter is that the mean age of this particular Conference is at least 15 years greater than it should be. I am impressed with some of the comments made about the progress of technical men in industry. There is an obvious attractiveness to a system in which people move from one kind of work to another, since this may preserve both the man and the institution. By way of contrast the style of the international academic community is to decree that a man is either a professor for life or a failure. I believe that a large number of the senior professors in all fields of learning are thoroughly bored with their work and that they should be given easy opportunity to retire from academic work and find other fields in which they can experience renewal of their creative faculties at a relatively early age, such as 50 years. Not all should take this course, but it should be an easy and normally acceptable procedure. One result would be that planning by groups such as this Conference would be done by people who view the future as almost infinite in duration. Another advantage would be a trend toward teaching of students by faculty members who are more nearly a peer group and share with students the view that intellectual horizons are still expanding. Finally, we could avoid the situation in which research, money and facilities are monopolized to a dangerous extent by established men who continue to do the same kind of work that made them eminent 20 years ago. The work usually continues to be good, but often does not really have the novelty and forward thrust offered by the programmes of some of their struggling young colleagues.

The dynamics of stolon elongation in the hydroid, Campanularia flexuosa

AbstractStolon elongation in Campanularia has been shown to occur in cycles, each consisting of the following phases: (a) extended and resting, (b) retraction, (c) retracted and resting, (d) re‐extension to the length in phase (a), (e) resting, and (f) extension. Three features of this cycle — cycle duration, magnitude of extension and magnitude of retraction — have been evaluated to determine their inherent constancy and their modification by environmental and other factors.In the strain studied, cycle duration was a highly reproducible 6.15 ± 0.05 minutes at 20° C, consistent both from cycle to cycle in a given stolon, and among different stolons. This time is most markedly affected by temperature but is also genetically regulated within moderate limits and is affected to a small degree by the organic content of the sea water.Extension per cycle averages 20 μ (about 5.0 mm daily) in most older stolons, though individual cycles vary randomly from this mean by ± 20%. This average varies considerably among different genetic stocks, is less in newly‐initiated than in older, establised, stolons and is markedly reduced at temperatures exceeding 22° C. It is remarkably resistent in established stolons to all but severe starvation.The magnitude of retraction is highly variable (1 to 28 μ) from cycle to cycle, though this variation occurs in a predictable fashion. Evidence is presented that the extent of retraction is determined by the degree of internal hydroplasmic pressure behind the tip.Isolated stolon tips 300–500 μ long (diameter about 200 μ) display all essential features of the normal growth cycle. Such rhythmic activity is therefore intrinsic to the cells at or within 0.3 mm of the tip. Effects exerted by more distant regions may modify but do not basically change this pattern.Synchronized with this elongation cycle is a cycle of thinning and thickening of the epidermal layer at the stolon tip. Thinning is interpreted as a passive response to the forward thrust of the gastrodermis.

Taiwan: Looking to the Mainland

As President Chiang Kai-shek celebrates his eightieth birthday (by the Western calendar), the Republic of China (ROC) has considerable cause for optimism. Official Taipei, viewing the mainland's great cultural revolution with remarkable restraint, apparently sees the possibility of a dramatic change in leadership in Peking that could evolve into a breakup of centralized power and provide appropriate conditions for the long-awaited return of the Nationalists. New government structures have been set up to deal with that potentiality. At the same time, Taiwan, as the base for any recovery operation, continues its forward economic thrust characterized by impressive achievements in national growth, external trade and other areas. President Chiang set the tone of caution in a 1967 New Year's message in which he placed an armed counterattack second to measures evidently intended to smooth the transition from Communist to Nationalist rule. question of the recovery of the mainland today is how to tidy up the calamitous situation which Mao has left behind; when to counterattack the mainland and how to bury Mao have become secondary questions, the generalissimo said. Political means, he explained, are even more important than military preparations, although the latter should not for a moment be relaxed.' Chiang gave the strong impression that it is no longer necessary for the ROC to launch a lightning strike against the mainland inasmuch as Mao's extremist measures to save his regime are bound to produce similar effects, and at less cost. The meaning of Chiang's reference to political means became clear in February with the announcement of the establishment of a National Security Council under Vice-Premier Huang Shao-ku. Besides enhancing the President's personal powers in this, the so-called period of rebellion, the NSC itself has been given broad functions embracing national reconstruction planning, strategy and defense, post-recovery administration, and mobilization.2 Thus, the Council, dominated by members of the Kuomintang Central Committee and the military, could be used as easily to promote internal change as to engineer the military and logistics of supplanting the Communist mainland regime.