Jet Off Research Articles

Spatial Nonuniformity of Excitation–Contraction Coupling Causes Arrhythmogenic Ca 2+ Waves in Rat Cardiac Muscle

Ca2+ waves underlying triggered propagated contractions (TPCs) are initiated in damaged regions in cardiac muscle and cause arrhythmias. We studied Ca2+ waves underlying TPCs in rat cardiac trabeculae under experimental conditions that simulate the functional nonuniformity caused by local mechanical or ischemic local damage of myocardium. A mechanical discontinuity along the trabeculae was created by exposing the preparation to a small jet of solution with a composition that reduces excitation-contraction coupling (ECC) in myocytes within that segment. The jet solution contained either caffeine (5 mmol/L), 2,3-butanedione monoxime (BDM; 20 mmol/L), or low Ca2+ concentration ([Ca2+]; 0.2 mmol/L). Force was measured with a silicon strain gauge and sarcomere length with laser diffraction techniques in 15 trabeculae. Simultaneously, [Ca2+]i was measured locally using epifluorescence of Fura-2. The jet of solution was applied perpendicularly to a small muscle region (200 to 300 microm) at constant flow. When the jet contained caffeine, BDM, or low [Ca2+], during the stimulated twitch, muscle-twitch force decreased and the sarcomeres in the exposed segment were stretched by shortening normal regions outside the jet. Typical protocols for TPC induction (7.5 s-2.5 Hz stimulus trains at 23 degrees C; [Ca2+]o=2.0 mmol/L) reproducibly generated Ca2+ waves that arose from the border between shortening and stretched regions. Such Ca2+ waves started during force-relaxation of the last stimulated twitch of the train and propagated (0.2 to 2.8 mm/sec) into segments both inside and outside of the jet. Arrhythmias, in the form of nondriven rhythmic activity, were induced when the amplitude of the Ca2+-wave was increased by raising [Ca2+]o. Arrhythmias disappeared rapidly when uniformity of ECC throughout the muscle was restored by turning the jet off. These results show, for the first time, that nonuniform ECC can cause Ca2+ waves underlying TPCs and suggest that Ca2+ dissociated from myofilaments plays an important role in the initiation of Ca2+ waves.

Spatial Nonuniformity of Contraction Causes Arrhythmogenic Ca2+ Waves in Rat Cardiac Muscle

Landesberg and Sideman's four state model of the cardiac cross-bridge (XB) hypothesizes a feedback of force development to Ca(2+) binding by troponin C (TnC). We have further modeled this behavior and observed that the force (F)-Ca(2+) relationship as well as the F-sarcomere length (SL) relationship and the time course of F and Ca(2+) transients in cardiac muscle can be reproduced faithfully by a single effect of F on deformation of the TnC-Ca complex and, thereby, on the dissociation rate of Ca(2+). Furthermore, this feedback predicts that rapid decline of F in the activated sarcomere causes release of Ca(2+) from TnC-Ca(2+), which is sufficient to initiate arrhythmogenic Ca(2+) release from the sarcoplasmic reticulum (SR). This work investigated the initiation of Ca(2+) waves underlying triggered propagated contractions (TPCs) in rat cardiac trabeculae under conditions that simulate functional nonuniformity caused by mechanical or ischemic local damage of the myocardium. A mechanical discontinuity along the trabeculae was created by exposing the preparation to a small constant flow jet of solution that reduces excitation-contraction coupling in myocytes within that segment. Force was measured, and SL as well as [Ca(2+)](i) were measured regionally. When the jet contained caffeine, 2,3-butanedione monoxime or low-[Ca(2+)], muscle-twitch F decreased and the sarcomeres in the exposed segment were stretched by shortening the normal regions outside the jet. During relaxation, the sarcomeres in the exposed segment shortened rapidly. Short trains of stimulation at 2.5 Hz reproducibly caused Ca(2+) waves to rise from the borders exposed to the jet. Ca(2+) waves started during F relaxation of the last stimulated twitch and propagated into segments both inside and outside of the jet. Arrhythmias, in the form of nondriven rhythmic activity, were triggered when the amplitude of the Ca(2+) wave increased by raising [Ca(2+)](o). The arrhythmias disappeared when the muscle uniformity was restored by turning the jet off. These results show that nonuniform contraction can cause Ca(2+) waves underlying TPCs, and suggest that Ca(2+) dissociated from myofilaments plays an important role in the initiation of arrhythmogenic Ca(2+) waves.

Culture, Apology, and International Negotiation: The Case of the Sino-U.S. "Spy Plane" Crisis

AbstractThis article traces the course of the Sino-U.S. negotiation in April 2001, to resolve the crisis following the collision of a U.S. surveillance aircraft with a Chinese fighter jet off of China's coast and the subsequent unauthorized emergency landing of the U.S. plane at a Chinese airfield on Hainan Island. The negotiation focused on the Chinese demand for a full apology from the United States and the U.S. resistance to this demand. The article examines the role that culture, particularly linguistic differences, played in the course of the negotiation and its eventual resolution.

Dynamic Stall Control Using a Model-Based Observer

Dynamic stall control is of interest for its potential to enhance the performance of rotorcraft. The experiments described used pulsed vortex generator jets, shown previously to prevent separation on steady wings and airfoils, to delay dynamic stall on a rapidly pitching airfoil. In tests performed on a NACA-0012 airfoil at low Reynolds numbers, the jets yielded a 25‐ 35% increase in the lift coefe cient achievable without moment stall. Next, a differential equation model of the dynamic stall process was derived and experimentally validated. Models of this form enable the application of well-known control theory to the design of e ow control systems. In the e nal round of experiments, a state observer based on the mathematical model detected incipient dynamic stall. A controller used the stall prediction to operate the pulsed jets only when needed to prevent stall. The controller turned the jets off for the remainder of the oscillation cycle. The controller only operated the jets for about 25% of the pitch cycle, so that the best lift increases of the early experiments could be achieved with only 25% of the air mass e ow.

The Shear, Convergence, and Thermohaline Structure of a Front*

With the objective of measuring convergence directly to confirm previous observations of frontal subduction, a seaward upwelling jet off central California was studied using satellite infrared images, hydrographic sections, ship drift, and clusters of surface drifters. The cyclonic front of the jet was sharper than 1 km, resulting in a shear several times larger than f. A cross-frontal convergence of 7 cm s−1 over the width of the front (equivalent to 0.8f) was visible as a 20-m-wide accumulation of debris. The sharpness of the front lasted at least for a day. Away from the cyclonic front, the divergence of the flow was small and the shear was less than 0.6f. Thermohaline layers, originating at the front, were interleaving along isopycnals, suggesting water subduction. It is proposed that the asymetry between anticyclonic and cyclonic sides of the jet, and the strong convergence at the cyclonicfront, resulted from a frictionally driven ageostrophic secondary circulation superimposed on the geostrophic flow.

Assimilating altimetric data into a South China Sea model

Sea surface heights from the TOPEX/Poseidon altimeter are assimilated into a three‐dimensional primitive equation model to derive the circulation in the South China Sea. With data assimilation the model resolves not only the basin‐wide circulation but also a dipole off Vietnam and a low/high feature near the Luzon Strait. Mesoscale features are missing in the simulation without data assimilation because of poor resolution in the wind field and inadequate knowledge of the transport through the Luzon Strait. Compared to the case without data assimilation, data assimilation reduces the root mean square error between the simulated and observed sea surface heights by a factor of 2–3. Circulation derived from data assimilation under climatological conditions is contrasted with that during El Niño. In the normal winter of 1993–1994, flow at 50 m depth is strong and cyclonic. Flow at 900 m depth is cyclonic as well. The deep cyclone persists into the following summer. During the 1994–1995 El Niño winter, features in the flow field at 50 m depth either weaken or disappear, and circulation at 900 m depth is anticyclonic. In the summer of 1995 the dipole and the eastward jet off Vietnam at 50 m depth are missing, and the anticyclonic circulation at 900 m depth persists. Temperature at 65 m shows significant warming from fall 1994 to summer 1995. A weakened flow field and warming in the upper ocean are consistent with findings from earlier El Niño events.

Transport of anchovy and sardine eggs and larvae from the western Agulhas Bank to the West Coast during the 1993/94 and 1994/95 spawning seasons

The transport of eggs and larvae of anchovy Engraulus capensis and sardine Sardinops sagax from the western Agulhas Bank to the nursery grounds on the Cape west coast was investigated. Samples were taken monthly between August 1993 and March 1994 and September 1994 and March 1995. A comparison of eggs and larval distributions with current features from selected months supports previous studies, indicating that the frontal jet plays an important role in the transport of the early life history stages of anchovy and sardine, but that the position of such transport can vary between the 200 and 500-m isobaths. During October 1994, November 1994 and February 1995, the greatest concentrations of eggs corresponded with areas of strong north-north-westerly flow just beyond the 200 m isobath off the Cape Peninsula, whereas in November 1993 and January 1994 eggs were concentrated farther offshore, increasing the vulnerability of developing larvae to further dispersion offshore. Offshore concentrations, intensified by strong south-easterly winds, occurred during January 1994. Areas of probable egg loss include the western Agulhas Bank, where currents flowing south-south-west can remove eggs before they are transported to the West Coast. Offshore currents also can develop west of the Cape Peninsula, but onshore currents are able to return eggs to the region of the jet, from where they are transported northwards. Other losses may result from offshore transport in the outer branch of the frontal jet off Cape Columbine. Variations in the ability of the jet current flowing north-north-west to transport eggs and larvae to areas favourable for growth and survival may influence recruitment success.

Wind‐forced modeling studies of currents, meanders, and eddies in the California Current system

This process‐oriented study of the California Current system (CCS) uses a high‐resolution, multilevel, primitive equation ocean model on a β plane to isolate the response of that eastern boundary oceanic regime to temporal and spatially varying wind forcing. To study the generation, evolution, and maintenance of many of the observed features such as currents, meanders, and eddies in the CCS, the model is forced from rest with seasonal climatological winds. In response to the prevailing wind direction, surface equatorward currents develop, along with upwelling of cooler water along the coast and a poleward undercurrent. Baroclinic/barotropic instabilities in the equatorward surface current and poleward undercurrent result in the generation of meanders near the coast. As the meanders intensify, cold upwelling filaments develop along the coast and subsequently extend farther offshore. In time, the meanders form both cyclonic and anticyclonic eddies, which subsequently propagate farther offshore. Longer simulation times (∼3–4 years), in which a quasi‐equilibrium state for the CCS is reached, show a seasonal cycle in response to the wind forcing for the coastal currents, upwelling, and filaments. The meanders and eddies, however, can be quasi‐permanent as well as seasonal features. The quasi‐permanent features play a significant role in modifying coastal currents, upwelling, and filaments, which leads to large temporal and spatial variability in the CCS. In a sensitivity study, the results from several numerical experiments are used to examine the dependence of the generation of the currents, meanders, and eddies on the type of Coriolis parameterization, wind forcing, and coastline geometry. Both the meridional variability of ƒ(β plane) and the alongshore component of the wind stress are shown to be key ingredients for generating realistic vertical and horizontal structures for the cores of the surface equatorward and the subsurface poleward currents. With such structures the currents are baroclinically and barotropically unstable, resulting in the generation of meanders, filaments, and eddies. Irregularities in the coastline geometry are shown to be important for “anchoring” upwelling and filaments as well as for enhancing the growth of meanders and eddies. Cyclonic eddies tend to form in the vicinity of capes, while anticyclonic eddies tend to form in the coastal indentations between capes. The region off Cape Blanco is identified as the location where the coastal, equatorward flow off Oregon leaves the coast to develop a meandering jet off California. The results from these experiments support the hypothesis that wind forcing and coastline irregularities on a beta plane are important mechanisms for the generation of many of the observed features of the CCS.

WFPC2 Observations of the Cooling Flow Elliptical in Abell 1795

We present WFPC2 images of the core of the cooling flow cD galaxy in Abell 1795. An irregular, asymmetric dust lane extends 7 h^(-1)/75 kpc in projection to the north-northwest. The dust shares the morphology observed in the Ha and excess UV emission. We see both diffuse and knotty blue emission around the dust lane, especially at the ends. The dust and emission features lie on the edge of the radio lobes, suggesting star formation induced by the radio source or the deflection of the radio jets off of preexisting dust and gas. We measure an apparent R(V) significantly less than 3.1, implying that the extinction law is not Galactic in the dust lane, or the presence of line emission that is proportional to the extinction. The dust mass is at least 2 x 10^5 h^(-2)/75 M_☉ and is more likely to be 6.5 x 10^5 h^(-2)/75 M_☉.

The large‐scale summer circulation of the California Current

Satellite data from the Geosat altimeter and the Advanced Very High Resolution Radiometer (AVHRR) are used to show the large‐scale structure of the surface circulation of the California Current System in summer. These data show the connection between an equatorward jet and temperature front off Oregon that lies within 100 km of the coast, similar to that first observed in the 1960's and 1970's, and a jet that meanders along the convoluted offshore edge of a temperature front off California, as repeatedly observed in the 1980's.

The jet off Point Arena, California: Its role in aspects of secondary production in the copepod Eucalanus californicus Johnson

The most abundant large herbivorous copepod in the jet off Point Arena, California, was Eucalanus californicus. In July 1988, females were actively laying eggs and also had a sac of stored lipid. If egg production is a function of present food supply, food concentrations within the jet become the primary factor governing egg laying. However, if stored lipid is the nutritive source for egg production, the critical food supply governing egg laying can be quite distant in space and time from the actual egg laying. In this jet, present food concentration was the factor governing egg production. The size of the lipid sac was also positively correlated with egg production, suggesting that lipid was not being used for oogenesis. Such a life history strategy, in which egg laying and lipid storage are proceeding concurrently in females, has not been described before. Reproductive females were found primarily nearshore and along the southern edge of the jet; highest rates of egg laying and largest lipid reserves were also in these areas. We speculate that temperature affinities of Eucalanus californicus result in maximized abundance, egg production, and lipid sequestration at temperatures below approximately 13°C. In the Point Arena region, this results in a nearshore portion of the population inhabiting surface layers and showing potential for very high rates of secondary production. The jet acts to transport E. californicus from the nearshore zone into its offshore habitat on a regular basis. Eddies in the region may be the mechanism by which E. californicus is returned to the nearshore zone.

The structure of the transition zone between coastal waters and the open ocean off northern California, winter and spring 1987

Physical and biological fields in the coastal transition zone off northern California were measured during February, March, May and June 1987 in an extended alongshore region between 60 km and 150 km offshore. The spring transition, as seen in coastal sea level and winds, occurred in mid‐March. Surface variability during the two spring cruises was stronger and of larger scale than that seen during the two winter cruises. An equatorward‐tending current, flowing along the boundary between low steric sea level inshore and high steric sea level offshore, dominated both the directly‐measured (acoustic Doppler current profiler) and geostrophic current fields during spring. Current jets of comparable strength directed both offshore and onshore were seen off Cape Mendocino and Point Arena; these evolved significantly in the 3 weeks between cruises. Inshore of the current, properties associated with upwelled water were found near the surface, including low temperature and high salinity, nutrients and chlorophyll; offshore of the current, waters were warmer, less saline, lower in nutrients and more oligotrophic. Geostrophic and directly measured volume transports in the current were about 2–3 Sv. Isopycnals inshore of the spring upwelling front were displaced vertically by O(40–80 m) from their depths during the winter survey; these displacements extended deep into the water column and were largely independent of depth between 100 and 400 m. Surface mixed layers tended to be deep in winter and shallower inshore of the upwelling front in spring. A connection between the equatorward‐tending frontal jet off northern California and the more well‐studied California Current further south is suggested by the similarity of their transports and of their dynamic height values.

A clamshell for Blandford-Rees jets

A number of possible causes for one-sided radio jets are examined. I show that, although one-sided breakthrough of a shock in a confining cloud can produce a single jet, the characteristic time scales of such a mechanism are almost certainly those associated with orbital motions in the galactic nucleus, and these: except in contrived cases: do not fit sources like NGC 6251 or 4C 32.69. Instead, I propose that the one-sidedness of jets is due to the following ''thrust reverser,'' or clamshell, mechanism. Because the fluid in the central cavity of a Blandford-Rees jet must be forced from a spherically symmetric into a twin-exhaust pattern, the flow has a saddle point near the equatorial plane. The position of this point is determined by the balance of the momentum density in the jet cavity and in the gas ouside the jets. This external gas is set in motion by stress between the jets and their surroundings. The stress is mediated by turbulent viscosity, brought about by instabilities on the interface between the jet and its confining cloud. The resulting external flow, upon reaching the equatorial plane of the jets, shapes the central cavity and makes the jets asymmetric, in some casesmore » switching one jet off altogether. Thus the clamshell mechanism contains as essential ingredients all the components that are known to exist in jet outflow: the flow in the cavity, through the nozzle, in the external medium, and in the shear layer between that medium and the jet fluid. The length and time scales implied by this mechanism agree tolerably well with the observations.« less

The spray volume shed by an uncambered planing hull in steady planing

Earlier papers (Payne, 1981 a,b,c) have developed what might be called a virtual mass theory which in principle permits the forces on any planing hull form to be calculated. In the present paper, this methodology is extended to calculate the thickness and momentum of the jet or spray sheet thrown off by the planing surface. For a two-dimensional flat planing plate—the only case where comparison is possible—the theory gives essentially the same result as that of Pierson and Leshnover (1948). For a three-dimensional flat plate and prismatic hulls, the results seem physically reasonable. For the small trim angles associated with efficient planing, on a weightless inviscid fluid the total pressure drag of any hull can be reduced to close to zero by deflecting the jet rearwards and parallel to the undisturbed surface, the residual resistance being due to the cross-flow force which varies as (trim angle) 2.

Effect of Over-the-Wing Nacelles on Wing-Body Aerodynamics

An investigation was conducted in the Langley 16-ft transonic tunnel to further study benefits in climb and cruise performance due to blowing the jet over the wing for a transport-type wing-body configuration. In this investigation, a wing-body model powered-nacelle test rig combination was tested at Mach numbers of 0.5 and 0.8 at angles of attack from — 2-4 deg and jet total-pressure ratios from jet off to 3 or 4 (depending on Mach number) for a variety of nacelle locations relative to the wing. Results from this investigation show that positioning of the nacelles can have very large effects on the wing-body drag (nacelles were nonmetric). Some positions yielded much higher drag than the baseline wing-body, while others yielded drag somewhat lower than the baseline. Nomenclature CD = drag coefficient CL = lift coefficient Cm = pitching moment coefficient D — jet-exit diameter JO - jet off LE = leading edge M = Mach number NPR = nozzle pressure ratio—ratio of jet total-pressure to freestream static pressure x — position of nacelle exit with respect to wing leading edge-positive aft W-B = wing-body wrt = with respect to z = height of centerline of nacelle exit above wing chord plane a = angle of attack

Spotting glueballs in collinear gluon jets

We suggest looking for pure gluon hadronic states (glueballs) in ϒ→ 3g → low spherically final state (collinear gluon jets). In these events one gluon has the maximum energy, Mϒ 2 , favouring fragmentation into a glueball. The signature for a true C = G + glueball is its prominence at the ϒ resonance in e +e − →ϒ → (glueball → four charged pions) + … and its absence in q q jets off (we do not expect significant quark fragmentation into glueballs).

Zonal winds associated with the dry period 1975–76 in England and Wales

THE low rainfall in England and Wales during the period May 1975 to August 1976 was discussed by Morris and Ratcliffe1 and was shown to be associated with a progressive shift northwards in the position of the mean jetstream over the north-east Atlantic during the three successive years 1974–76. We report here that marked circulation changes in the 500-mbar (5.5 km) flow during the dry period occurred both in the vicinity of the British Isles and over the central Pacific. The flow is compared with an analysis of 5-d mean charts exhibiting blocking of the 500-mbar flow in the vicinity of the British Isles and it is suggested that the anomalous displacement of the jetstream during the dry period may have been associated with an eastward surge in the subtropical jet off south-east Asia.

“Basic” jet noise patterns after deletion of convection and refraction effects: Experiments vs. Theory

In earlier work of Grande experimental jet-noise polar plots were corrected for refraction (by experiment) and for convection (by theory) to yield the relatively small experimental basic directivity in narrow frequency bands. The experimental correction for refraction at each frequency was obtained from the difference in the directional patterns of a point source placed in the air jet with jet off and jet on. In the present work, with new measurements, the procedure has been updated and extended. There is a minor change in the convection correction dictated by theory, and a substantial change in the refraction correction, owing to a shortcoming of the injected point source technique, (i) The results have been presented in the equivalent forms of spectra and narrow-band directivities at jet Mach numbers of 0'5 and 0'9. (ii) Theory has been fitted in two-parameter form at each frequency to generate spectral curves of basic self-noise a(CfDJU) and shear-noise b(CfD/U). The peaks occur at the theoretical 2/1 in frequency, and the Doppler-corrected Strouhal numbers CfD/U are invariant with Mach number, (iii) The semi-empirical theory, with convection and refraction re-introduced, has been used to predict the overall directivity in narrow frequency bands. The agreement with the direct measurements is quite good for what is essentially a two-point fit. (iv) The broadband convection factor C−5, with α = 0·55 and Mc = 0·5 Uj/C0 (supported by theoretical arguments), is found to correlate well with experimental results—these and others—for Uj up to turbojet speeds (e.g., 1·64 C0). (The factor C−3 with α = 0 and Mc = 0·63 Uj/C0 that has been proposed for shear noise fails badly at these high speeds ; but if Mc is reduced to correct this, the factor fails at low speeds.) (v) A critique is given of analytical factors for Doppler shift and convective amplification, including the effect of the general flow enveloping the moving eddies.

Basic Directivity of Jet Noise with Improved Correction for Refraction

In earlier work of Grande, experimental jet-noise polar plots were corrected for refraction (by experiment) and for convection (by theory) to yield the experimental basic directivity in narrow frequency bands. The experimental correction for refraction at each frequency was obtained from the difference in the directional patterns of a point source placed in the air jet with jet off and jet on. Before refraction, this point source will produce a spherical directional pattern, but the narrow-band jet noise will have an elongated pattern owing to convection. It has been realized belatedly that the refractive change in intensity at corresponding angles cannot be taken as the same for the two different initial polar patterns: there is some violation of energy conservation. To avoid this error, later unpublished measurements by MacGregor have been reworked by Lain, incorporating a correction to the refraction effect measured with the point source. The correction was specified by an assumed functional form as a polar plot; the amplitude was then dictated by the requirement of conservation of energy. The measured jet noise data, processed along the lines of Grande, then leads to much improved agreement of experiment and theory. [Research supported by Air Force Office of Scientific Research.]

Chip Removal by a Hydraulic Jet

Abstract Although adequate removal of cuttings from beneath a drill bit is important for efficient drilling operations, very little basic data are available relative to the fundamentals of chip removal by hydraulic jets. A discussion is presented in this paper of an experimental investigation of the jetting action of hydraulic jets in removing loose particles from the bottom of a cylindrical hole. Conditions for which the jet is no longer capable of removing chips from the bottom of the hole are determined. This situation represents equilibrium between the chip removal force and chip holddown forces such as gravity and pressure. In most of the tests loose particles were jetted with water or a water-glycerine mixture to determine the dependence of chip removal on hole size, jet size, height of jet off bottom of hole, flow rate, particle density and fluid viscosity. A test with a pressurized mud system indicated that relatively low pressures can completely overcome the removal action of a hydraulic jet. Although the system studied herein is not directly applicable to a rotary drill bit, the work with such simplified systems can provide a better understanding of the chip removal action of jets, and with logical extensions it may provide a reasonable basis for the best use of fluid jets in drilling. Introduction The primary deterrent to maximum drilling rates is the inability of the drilling system to remove rock cuttings efficiently enough to prevent interference with the drilling action. The objective of chip removal studies is to permit predicting and controlling removal forces under downhole drilling conditions. Conditions at the bottom of a hole during rotary drilling are exceedingly complex and are not likely to be described in a quantitative way by investigations in terms of the total drilling action until a better understanding is developed of the simplified components of the problem. The present study is concerned with the elementary condition of removal of chips by a single central jet. Even this relatively simple model provides mathematical difficulties because of the turbulent nature of the flow from the jet and because of the shape of the bottom of the hole beneath the jet. Theoretical and experimental studies have been made of turbulent jets impinging normally on an infinite body and deductions based on analytical solutions to simplified problems can give some insight into the problem of cutting removal by a jet. However, because of the present lack of understanding of the behavior of the interaction between the fluid jet and the chips being removed, an experimental approach was chosen for the present study. Methods have been developed for maximizing hydraulic horsepower, impact force and jet velocity; but whether maximizing these parameters maximizes chip removal with present drilling bits has not been demonstrated. Simplifying the problem of chip removal may make it possible to develop some understanding of the manner in which the jet velocity is dissipated. Better understanding of a simple case should materially assist in extending analysis to more complicated cases. Thus, we are not concerned in the present study with the rock fracturing process itself but only with the removal of the debris from the bottom of the hole. A problem which is quite similar to the chip removal problem is the suspension of solids in stirred vessels. This problem has been studied by the chemical industry and correlations have been obtained by dimensional analysis which permit the design of mixing vats. An approach similar to that used in the mixing vat problem is used in the analysis of the jetting data in the present paper. EXPERIMENTAL PROCEDURE The test equipment arrangement shown schematically in Fig. 1 allows the jetting action to remove particles until an equilibrium height is attained for each combination of hole size, jet size and flow rate.*** Equilibrium conditions require that the removal force is unable to remove additional particles. This balance between holddown and removal forces implies a relationship between the two forces which is constant for the particular system. When the holddown forces are constant, SPEJ P. 21ˆ