Swimming in the electric eels and knifefishes

1983 ◽  
Vol 61 (6) ◽  
pp. 1432-1441 ◽  
Author(s):  
R. W. Blake
Keyword(s):  
Rigid Body ◽  
Body Wave ◽  
The Body ◽  
Viscous Drag ◽  
Entire Body ◽  
Number Range ◽  
Large Amplitude Motions ◽  
Burst Swimming ◽  
Experimental Values ◽  
Notopterus Notopterus

The kinematics of steady forward swimming in six species of Gymnotidae and three species of Notopteridae are described. All the gymnotids and one notopterid (Xenomystis nigri) are propelled by the action of an undulatory anal fin (gymnotiform mode). Notopterus notopterus and Notopterus chilata employ the body and anal fin as a single propulsive unit and generate a body wave. Rapid bouts of burst swimming activity (e.g., escape responses) are generated by large amplitude motions of the entire body in all species studied. Experimentally determined drag coefficients exceed the theoretical rigid body predicted minimum values for the case of a laminar boundary layer and reasons for this are suggested. Values of the drag coefficient inferred from hydromechanical theory are within 20% of the experimental values. It is concluded that fish swimming in the gymnotiform mode may be subject to significantly less viscous drag than fish of equivalent size swimming at the same speed in the subcarangiform mode. Hydromechanical theory indicates a significant enhancement of fin added mass (due to the presence of a rigid body) over that of an isolated fin. The hydromechanical efficiency of the undulating fin system ranged from about 0.6 to 0.9 over a speed range of 0.2–5.0 lengths∙s−1 (corresponding to a Reynolds number range of about 103–105). It is suggested that undulatory median fin propulsion in the electric eels and knifefishes is an adaptation to swimming with high hydromechanical efficiency at low absolute forward speeds. Similarities and differences in body form between the species and the evolution of gymnotiform swimming are discussed.

scholarly journals The disappearance of laminar and turbulent wakes in complex flows

2002 ◽  
Vol 457 ◽  
pp. 111-132 ◽  
Author(s):  
J. C. R. HUNT ◽  
I. EAMES
Keyword(s):  
Flow Field ◽  
Rigid Body ◽  
The Body ◽  
Viscous Drag ◽  
Total Force ◽  
Far Field ◽  
Volume Flux ◽  
Wake Region ◽  
Complex Flows ◽  
Turbulent Wakes

The singular effects of steady large-scale external strain on the viscous wake generated by a rigid body and the overall flow field are analysed. In an accelerating flow strained at a positive rate, the vorticity field is annihilated owing to positive and negative vorticity either side of the wake centreline diffusing into one another and the volume flux in the wake decreases with downwind distance. Since the wake disappears, the far-field flow changes from monopolar to dipolar. In this case, the force on the body is no longer proportional to the strength of the monopole, but is proportional to the strength of the far field dipole. These results are extended to the case of strained turbulent wakes and this is verified against experimental wind tunnel measurements of Keffer (1965) and Elliott & Townsend (1981) for positive and negative strains. The analysis demonstrates why the total force acting on a body may be estimated by adding the viscous drag and inviscid force due to the irrotational straining field.Applying the analysis to the wake region of a rigid body or a bubble shows that the wake volume flux decreases even in uniform flows owing to the local straining flow in the near-wake region. While the wake volume flux decreases by a small amount for the flow over streamline and bluff bodies, for the case of a clean bubble the decrease is so large as to render Betz's (1925) drag formula invalid.To show how these results may be applied to complex flows, the effects of a sequence of positive and negative strains on the wake are considered. The average wake width is much larger than in the absence of a strain field and this leads to diffusion of vorticity between wakes and the cancellation of vorticity. The latter mechanism leads to a net reduction in the volume flux deficit downstream which explains why in calculations of the flow through groups of moving or stationary bodies the wakes of upstream bodies may be ignored even though their drag and lift forces have a significant effect on the overall flow field.

Surface ultrastructure of juvenile and adult stages of Centrocestus armatus

1998 ◽  
Vol 72 (3) ◽  
pp. 215-219 ◽  
Author(s):  
Ho-Choon Woo ◽  
Myung-Deuk Seo ◽  
Sung-Jong Hong
Keyword(s):  
Oral Sucker ◽  
Body Surface ◽  
Dorsal Surface ◽  
High Density ◽  
The Body ◽  
Albino Rats ◽  
Entire Body ◽  
Type Ii ◽  
Posterior Half ◽  
Surface Ultrastructure

AbstractCentrocestus armatus (Trematoda: Heterophyidae) develops rapidly and produces eggs at 3 days postinfection in albino rats. Excysted metacercariae are pear-shaped and concave ventrally, with 42–44 peg-like circumoral spines. The entire body surface is densely covered with scale-like serrated spines. On juveniles, serration of the tegumental spines is greatest in the middle of the ventral and dorsal surfaces, and decreases anteriorly and posteriorly. Ciliated sensory papillae are concentrated around the oral sucker. Several nonciliated sensory papillae (type II papillae) occur equidistantly on the acetabulum and are arranged in a linear symmetry on the dorsal surface. On adults, the serration of the tegumental spines decreases to 14–17 tips on the ventrolateral surface. The high density of tegumental spines on posterior half of the body and the distribution of type II papillae on dorsal surface are considered to be characteristic of C. armatus.

A Benchmark Control Problem for Supercavitating Vehicles and an Initial Investigation of Solutions

2003 ◽  
Vol 9 (7) ◽  
pp. 791-804 ◽  
Author(s):  
John Dzielski ◽  
Andrew Kurdila
Keyword(s):  
High Speed ◽  
Linear Models ◽  
The Body ◽  
Control Surface ◽  
Force Model ◽  
Entire Body ◽  
Benchmark Problem ◽  
Supercavitating Vehicles ◽  
Forcing Function ◽  
Natural Cavitation

At very high speeds, underwater bodies develop cavitation bubbles at the trailing edges of sharp corners or from contours where adverse pressure gradients are sufficient to induce flow separation. Coupled with a properly designed cavitator at the nose of a vehicle, this natural cavitation can be augmented with gas to induce a cavity to cover nearly the entire body of the vehicle. The formation of the cavity results in a significant reduction in drag on the vehicle and these so-called high-speed supercavitating vehicles (HSSVs) naturally operate at speeds in excess of 75 m s-1. The first part of this paper presents a derivation of a benchmark problem for control of HSSVs. The benchmark problem focuses exclusively on the pitch-plane dynamics of the body which currently appear to present the most severe challenges. A vehicle model is parametrized in terms of generic parameters of body radius, body length, and body density relative to the surrounding fluid. The forebody shape is assumed to be a right cylindrical cone and the aft two-thirds is assumed to be cylindrical. This effectively parametrizes the inertia characteristics of the body. Assuming the cavitator is a flat plate, control surface lift curves are specified relative to the cavitator effectiveness. A force model for a planing afterbody is also presented. The resulting model is generally unstable whenever in contact with the cavity and stable otherwise, provided the fin effectiveness is large enough. If it is assumed that a cavity separation sensor is not available or that the entire weight of the body is not to be carried on control surfaces, limit cycle oscillations generally result. The weight of the body inevitably forces the vehicle into contact with the cavity and the unstable mode; the body effectively skips on the cavity wall. The general motion can be characterized by switching between two nominally linear models and an external constant forcing function. Because of the extremely short duration of the cavity contact, direct suppression of the oscillations and stable planing appear to present severe challenges to the actuator designer. These challenges are investigated in the second half of the paper, along with several approaches to the design of active control systems.

Fractures in the northern plains, stream patterns, and the midcontinent stress field

1987 ◽  
Vol 24 (6) ◽  
pp. 1086-1097 ◽  
Author(s):  
Mel R. Stauffer ◽  
Don J. Gendzwill
Keyword(s):  
Stress Field ◽  
Horizontal Stress ◽  
The Body ◽  
North American Plate ◽  
Plate Motion ◽  
Viscous Drag ◽  
Near Surface ◽  
The North ◽  
Elastic Rebound ◽  
Western North Dakota

Fractures in Late Cretaceous to Late Pleistocene sediments in Saskatchewan, eastern Montana, and western North Dakota form two vertical, orthogonal sets trending northeast–southwest and northwest–southeast. The pattern is consistent, regardless of rock type or age (except for concretionary sandstone). Both sets appear to be extensional in origin and are similar in character to joints in Alberta. Modem stream valleys also trend in the same two dominant directions and may be controlled by the underlying fractures.Elevation variations on the sub-Mannville (Early Cretaceous) unconformity form a rectilinear pattern also parallel to the fracture sets, suggesting that fracturing was initiated at least as early as Late Jurassic. It may have begun earlier, but there are insufficient data at present to extend the time of initiation.We interpret the fractures as the result of vertical uplift together with plate motion: the westward drift of North America. The northeast–southwest-directed maximum principal horizontal stress of the midcontinent stress field is generated by viscous drag effects between the North American plate and the mantle. Vertical uplift, erosion, or both together produce a horizontal tensile state in near-surface materials, and with the addition of a directed horizontal stress through plate motion, vertical tension cracks are generated parallel to that horizontal stress (northeast–southwest). Nearly instantaneous elastic rebound results in the production of second-order joints (northwest–southeast) perpendicular to the first. In this manner, the body of rock is being subjected with time to complex alternation of northeast–southwest and northwest–southeast horizontal stresses, resulting in the continuous and contemporaneous production of two perpendicular extensional joint sets.

The philometrid nematodePhilometroides acreanensis n. sp. from the stomach wall of the catfishPimelodus blochiiin north-western Brazil

2017 ◽  
Vol 92 (1) ◽  
pp. 109-115 ◽  
Author(s):  
P.H.O. Cavalcante ◽  
F. Moravec ◽  
C.P. Santos
Keyword(s):  
Body Length ◽  
Gravid Female ◽  
Drainage System ◽  
Nematode Species ◽  
Fish Host ◽  
The Body ◽  
Stomach Wall ◽  
Amazon River ◽  
Entire Body ◽  
South American

AbstractA new nematode species,Philometroides acreanensisn. sp. (Philometridae), is described from female specimens recovered from the stomach wall of the freshwater catfishPimelodus blochiiValenciennes (Pimelodidae) collected in the Acre River (Amazon River basin), Acre State, Brazil. Based on examination by light and scanning electron microscopy, the new species differs from the two other South American congeneric species mainly in the body length of the gravid female (240–280 mm), the length of the oesophagus (1.25 mm in holotype) representing 0.5% of the entire body length, the range of cuticular embossment, as well as the location in the host (stomach), order of the fish host (Siluriformes) and the geographical distribution (Amazon River drainage system). This is the third known species ofPhilometroidesYamaguti, 1935 reported from South America. A key to species ofPhilometroidesoccurring in the fish of America is provided.

Effect of shodhana and shamana chikitsa in mandala kustha (psoriasis): A case study

2019 ◽  
Vol 7 (03) ◽  
Author(s):  
Jyoti Bala Sahu
Keyword(s):  
Body Temperature ◽  
The Body ◽  
Entire Body ◽  
Men And Women ◽  
Remarkable Improvement ◽  
Males And Females ◽  
Regulate Body Temperature ◽  
Old Men

Skin is the largest organ of the body both by surface area and weight. This covers the entire body. The thickness of skin varies considerably over all parts of the body and between young and old, men and women. It helps to regulate body temperature, stores water fat and permit sensation of touch. Psoriasis is a chronic dermatosis characterized by covered by silvery loose scales. Treatment available on contemporary system is not curative but suppressive only. The prevalence of psoriasis is 8%. Prevalence equal in males and females. A case of Mandala Kustha discussed here. Patient successfully treated with Shodhana (Virechana karma) & Shamana Chikitsa. After course of 2 months treatment provides significant relief in Sign and Symptoms. In our classics mentioned Shodhana Chikitsa for Kustha Roga. Considering the sign and symptoms of patient was treated with classical Virechana karma (therapeutic purgation) and Shamana Chikitsa according to line of treatment of Kustha (Psoriasis). Assessment was done on before treatment, after treatment and after follow up of 2 months; pictures were taken before treatment and after treatment. Remarkable improvement was noticed, induration and itching after Virechana treatment.

Focal mechanism and source depth of earthquakes from body- and surface-wave data

1971 ◽  
Vol 61 (5) ◽  
pp. 1369-1379 ◽  
Author(s):  
Nezihi Canitez ◽  
M. Nafi Toksöz
Keyword(s):  
Surface Wave ◽  
Body Wave ◽  
Source Parameters ◽  
Focal Depth ◽  
Spectral Ratio ◽  
The Body ◽  
Spectral Ratios ◽  
Motion Data ◽  
Wave Data ◽  
Surface Wave Data

abstract The determination of focal depth and other source parameters by the use of first-motion data and surface-wave spectra is investigated. It is shown that the spectral ratio of Love to Rayleigh waves (L/R) is sensitive to all source parameters. The azimuthal variation of the L/R spectral ratios can be used to check the fault-plane solution as well as for focal depth determinations. Medium response, attenuation, and source finiteness seriously affect the absolute spectra and introduce uncertainty into the focal depth determinations. These effects are nearly canceled out when L/R amplitude ratios are used. Thus, the preferred procedure for source mechanism studies of shallow earthquakes is to use jointly the body-wave data, absolute spectra of surface waves, and the Love/Rayleigh spectral ratios. With this procedure, focal depths can be determined to an accuracy of a few kilometers.

The Global Motion of a Rigid Body Subject to Periodic Body-Fixed Torques

1995 ◽  
Author(s):  
X. Tong ◽  
B. Tabarrok
Keyword(s):  
Rigid Body ◽  
Equations Of Motion ◽  
Melnikov Method ◽  
The Body ◽  
Body Motion ◽  
Heteroclinic Orbits ◽  
Coordinate Frame ◽  
Global Motion ◽  
Stable And Unstable Manifolds ◽  
Body Subject

Abstract In this paper the global motion of a rigid body subject to small periodic torques, which has a fixed direction in the body-fixed coordinate frame, is investigated by means of Melnikov’s method. Deprit’s variables are introduced to transform the equations of motion into a form describing a slowly varying oscillator. Then the Melnikov method developed for the slowly varying oscillator is used to predict the transversal intersections of stable and unstable manifolds for the perturbed rigid body motion. It is shown that there exist transversal intersections of heteroclinic orbits for certain ranges of parameter values.

Preliminary body-wave analysis of the St. Elias, Alaska earthquake of February 28, 1979

1980 ◽  
Vol 70 (2) ◽  
pp. 419-436
Author(s):  
John Boatwright
Keyword(s):  
New York ◽  
Body Wave ◽  
The Body ◽  
Rupture Velocity ◽  
Wave Analysis ◽  
S Waves ◽  
Initial Event ◽  
Whole Space ◽  
A New Technique ◽  
Alaska Earthquake

abstract Employing a new technique for the body-wave analysis of shallow-focus earthquakes, we have made a preliminary analysis of the St. Elias, Alaska earthquake of February 28, 1979, using five long-period P and S waves recorded at three WWSSN stations and at Palisades, New York. Using a well determined focal mechanism and an average source depth of ≈ 11 km, the interference of the depth phases (i.e., pP and sP, or sS) has been deconvolved from the recorded pulse shapes to obtain velocity and displacement pulse shapes as they would appear if the earthquake had occurred within an infinite medium. These “approximate whole space” pulse shapes indicate that the rupture contained three distinct subevents as well as a small initial event which preceded this subevent sequence by about 7 sec. From the pulse rise times of the subevents, their rupture lengths are estimated as 12, 27, and 17 km, assuming that the subevent rupture velocity was 3 km/sec. Overall, the earthquake ruptured ≈ 60 km to the southeast with an average rupture velocity of 2.2 km/sec. The cumulative body-wave moment for the whole event, 1.2 × 1027 dyne-cm, is substantially smaller than the surface-wave moments reported by Lahr et al. (1979) of 5 × 1027 dyne-cm. The moments of the subevents are estimated to be 0.6, 3.2, and 7.5 × 1026 dyne-cm, respectively.

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