Gravitational Component Research Articles

Quantitative Evaluation of Effect of Gravity on Small-Scale Modeling

In many cases, small-scale modeling requires the scaling up of the gravitational acceleration. Yet this requirement sets a technical problem, and unless the use of a centrifuge is available, it is not fulfilled. Consequently there is a distortion in the extrapolated results of the small-scale model, which lacks scaling of gravity. So far, the extent of the effect of gravity scaling on the extrapolated results has been speculated. A quantitative way to evaluate this effect is suggested here. An expression for the distortion in the extrapolation of a measured model variable is developed, based on similitude requirements. This expression depends on the geometrical scaling factor, and on the ratio of a variable measured model value to the value of its gravitational component. It shows that for geometrical scaling factors of 10 and 50, the distortion is less than 10% when the gravitational component of the variable is less than 1% and ∼0.2%, respectively.

Spherical gravitational wave antennas and the truncated icosahedral arrangement.

A spherical gravitational wave detector can be equally sensitive to a wave from any direction, and also can be able to measure its direction and polarization. We derive a set of equations to describe the mechanics of a spherical antenna coupled to an arbitrary number of attached mechanical resonators. A special arrangement of six resonators is proposed, which we term a truncated icosahedral gravitational wave antenna. An analytic solution to the equations of motion is found for this case. We find that direct deconvolution of the gravitational tensor components can be accomplished with a specified set of linear combinations of the resonator outputs, which we call the mode channels. We develop one simple noise model for this system and calculate the resulting strain noise spectrum. We conclude that the angle-averaged energy sensitivity will be 56 times better than for the typical equivalent bar-type antenna with the same noise temperature.

Redshift and the Hubble constant in conformally flat spacetime

view Abstract Citations (18) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Redshift and the Hubble Constant in Conformally Flat Spacetime Endean, Geoffrey Abstract In conformally flat space-time (CFS), the cosmological redshift consists of a Doppler component, calculated using the radial recession velocity of the Friedmann-Robertson-Walker (FRW) coordinates, with respect to the CFS coordinates, and a gravitational component. It is shown that, for all forms of the FRW scaling factor R(t), where t is the FRW time coordinate, the fundamental formula for the total cosmological redshift z, namely, (1 + z) = R(t_0_)/R(t), is confirmed by calculations in CFS coordinates. Redshift-distance relations expressed in terms of the CFS absolute radial distance coordinate, instead of the more usual FRW elapsed time (t_0_ - t), are derived for the standard open three- dimensional space dust model. Attention is drawn to cataclysmic consequences resulting from any departure of the cosmological constant from zero. The product of the Hubble constant and the present age of the universe is substantially increased in the CFS description, its precise value depending only on the present age of the universe normalized to the characteristic scale length of the open three-dimensional space curvature. More precise observational determinations of the Hubble constant and the present age of the universe are needed to verify the correctness or otherwise of the CFS physical interpretation. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174741 Bibcode: 1994ApJ...434..397E Keywords: Coordinate Transformations; Cosmology; Doppler Effect; Gravitation; Hubble Constant; Red Shift; Relativity; Universe; Distance; Radial Velocity; Time; Astrophysics; COSMOLOGY: THEORY; GALAXIES: DISTANCES AND REDSHIFTS full text sources ADS |

The gravitational potential of a homogeneous polyhedron or don't cut corners

A polyhedron can model irregularly shaped objects such as asteroids, comet nuclei, and small planetary satellites. With minor effort, such a model can incorporate important surface features such as large craters. Here we develop closed-form expressions for the exterior gravitational potential and acceleration components due to a constant-density polyhedron. An equipotential surface of Phobos is illustrated.

DYNAMIC PUSH AND PULL FORCES WHILE USING A MANUAL MATERIAL HANDLING ASSIST DEVICE

Movement assist devices are quickly replacing traditional manual methods of material handling. By providing these devices, ergonomists assume they are substantially reducing the musculoskeletal strain associated with completing the task. Unfortunately, assist devices usually only minimize the gravitational force components of the task, and by their additional inertia, tend to increase dynamic manual requirements. The experiment reported here examines the dynamic force levels produced by inexperienced operators symmetrically pushing and pulling a small material handling assist device. Values are presented as a function of system and task parameters, such as load transported, movement distance, final placement accuracy and system friction. The results demonstrate that subjects performed the task using remarkably high push and pull forces. Experimental manipulations had only relatively small effects on the force levels observed. These results are discussed in terms of the ergonomic issues that may affect ind...

Gravity's rainbow

The temperature anisotropy of the cosmic microwave background may be partially the imprint left by gravitational waves. Measuring the gravitational wave component and spectral shape of the anisotropy is a critical test of inflationary cosmology and theories of large-scale structure formation.

Identification of passive knee joint and shank dynamics in paraplegics using quadriceps stimulation

The dynamics of the knee-joint-freely-swinging-lower-leg system of three sitting paraplegic patients was identified using a parameterized analytical model. Surface electrodes were used for stimulation. The output of the knee joint-lower leg system was the angular position, velocity and acceleration. A model structure was taken from the literature and its complexity minimized based on the experiments and offline identification. The resulting model structure facilitates possible recursive identification. Model parameters of the lower leg dynamics were estimated using a least-squares algorithm in combination with the Levenburg-Marquardt algorithm. The intersubject variability in parameter values for the knee joint damping and the gravitational component appeared to be small when normalized to the inertia of the lower leg. The identified model for the knee joint and shank dynamics accurately predicted passive lower leg movement and could be used to estimate the magnitude of active knee torque due to elicited quadriceps contraction.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Gravity as a monocular cue for perception of absolute distance and/or absolute size.

When the motion of an object is influenced by gravity (eg free fall, pendulum, wave motion), that influence may provide a cue to computing the absolute distance and/or size of the object. Formal analysis supports the claim that the distance and size of moving objects are generally computable with reference to the gravitational component of motion. Informal evidence from judgments of realism in films is consistent with this gravity-cue hypothesis.

The characteristics of arm movements executed in unusual force environments.

Human subjects pointed at stationary visual targets without sight of their arm while the force environment was varied by applying weight or spring loads to the hand. The path travelled by the finger, pointing accuracy, and the shape of the finger velocity profile remained invariant across all force environments after a single practice trial. However, the magnitude and duration of the velocity profile depended consistently on the presence and size of a weight load. In contrast, velocity was not affected by spring loads. An analysis of movement dynamics in our study indicated that inertial and gravitational load components were compensated by separate mechanisms, the former employing time- and the latter magnitude scaling of muscle force profiles. The presence of such separate mechanisms led us to predict little problems for movement dynamics in weightlessness, which was indeed confirmed in a study on pointing movements aboard the KC-135 aircraft.

The time delay in the twin QSO Q0957 + 561

view Abstract Citations (63) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Time Delay in the Twin QSO Q0957+561 Schild, Rudolph E. Abstract From 10 yr of brightness monitoring of the two gravitational mirage components of Q0957+561 A,B we show that the time delay is 1.11 yr. An intensive program of daily brightness monitoring suggests a further refinement of the time delay to 404 days. Careful superposition of the phased brightness records shows that small differences are seen. These differences are attributed to microlensing by a star or stars in the lens galaxy. Publication: The Astronomical Journal Pub Date: December 1990 DOI: 10.1086/115634 Bibcode: 1990AJ....100.1771S Keywords: Gravitational Lenses; Quasars; Astronomical Photometry; Brightness; Cross Correlation; Telescopes; Time Lag; Astrophysics; QUASARS full text sources ADS | data products NED (3) SIMBAD (2)

Overall efficiency of tubular inlets sampling at 0–90 degrees from horizontal aerosol flows

We have developed a unified and comprehensive model for the overall efficiency of tubular inlets sampling from horizontal aerosol flows at 0–90° relative to the wind direction. In our model, derived from experimental data obtained in our wind tunnel, the transmission efficiency is separated into two components: one due to gravitational settling in the boundary layer and the other due to impaction. The gravitational settling component is determined by extending our previously developed isoaxial sampling model to nonisoaxial sampling. The impaction component is determined by a new model that quantifies the particle losses caused by direct wall impaction. The model also quantifies the additional particle losses resulting from the turbulent motion in the vena contracta which is formed in the inlet when the inlet velocity is higher than the wind velocity. The equation for the gravitational settling component considers the inertial behaviour of the particles by including the Stokes number, the flow development in the boundary layer by including the Reynolds number and the gravitational settling in the boundary layer by including a modified gravitational settling parameter. The equation for the impaction component considers direct wall impaction and the losses due to vena contracta formation through the Stokes number, velocity ration and sampling angle. Direct wall impaction is further differentiated by the gravity effect on the impaction process which distinguishes upward from downward sampling. Our equations for transmission efficiency in combination with aspiration efficiency equations determine the overall efficiency of tubular, sharp-edged inlets at all orientations of the inlet relative to horizontal aerosol flows.

The pressure field in an unsteady‐state fluidized bed

AbstractAn assumption commonly, but by no means universally, made in the stability analysis of the homogeneously fluidized state is that the pressure field may be well approximated by its gravitational component alone. This assumption is critically examined: the results indicate that it is valid for most cases of practical interest but can lead to significant discrepancies for liquid fluidization of low‐density particles.

Backthrusting in accretionary wedges

Backthrusting of the rear of the accretionary wedge, arcward over the rocks of the forearc basin, is a common aspect of accretionary tectonics. An older assumption that backstops of accretionary wedges dip back toward the arc, and that accreted material is emplaced below such backstops, is contradicted by observations from many active forearcs that indicate (1) backthrusting is common, (2) forearc basins are nearly ubiquitous associates of accretionary wedges, and (3) forearc basement, where imaged, appears to diverge from the sedimentary package, dipping under the wedge while the overlying sediments are often lifted up against it. Backthrusting may be favored where relief is high between the crest of the wedge and the surface of the forearc basin because the relief must be supported by shear stress along the backthrust. We find ratios of Lt/Lb averaging 2.64±0.8, where Lt is the horizontal distance from the crest of the wedge to the front of the toe, and Lb is the distance from the crest of the wedge to the surface projection of the backthrust. This ratio is predicted to increase with total convergence and with sedimentation, because the toe undergoes higher deformation rates than the backthrust, and sedimentation in the trench favors outbuilding of the toe, whereas sedimentation in the forearc basin tends to cancel the gravitational component of the driving stress for the backthrust.

Methods and results of investigation of the stressed state of rock masses and the development of effective means of controlling mine pressure during underground excavation of ore

Experimental and theoretical work conducted in the Soviet Union in determining the stressed state of rock masses and developing underground strata control measures are reviewed. Methods of determining stresses in a rock mass were classified into two groups: mechanical and geophysical. A geodynamic model of the stressed state of the upper layers of the earth's crust was developed based on direct measurements in shafts using methods and apparatus developed in the USSR. Fundamental laws governing the initial stressed state of the earth's crust show that within the limits of a geologically homogeneous block, gravitational and tectonic components of the overall stress field are present with gradients of the stress field and its random components. A study was made of the stress-strain state of chamber roofs; the results made it possible to substantiate the limiting spans of fissured roofs in cleaned chambers.

Field water relations of a wet-tropical forest tree species, Pentaclethra macroloba (Mimosaceae).

The water relations of Pentaclethra macroloba (Willd.) Kuntze, a dominant, shade-tolerant, tree species in the Atlantic lowlands of Costa Rica, were examined within the forest canopy. Pressure-volume curves and diurnal courses of stomatal conductance and leaf water potential were measured in order to assess differences in water relations between understory, mid-canopy and canopy leaves. Leaves in the canopy had the smallest pinnules but the largest stomatal frequencies and stomatal conductances of the three forest levels. Osmotic potentials at full turgidity decreased with height in the forest; in the canopy and midcanopy they were reduced relative to those in the understory just enough to balance the gravitational component of water potential. Consequently, maximum turgor pressures were similar for leaves from all three canopy levels. Bulk tissue elastic modulus increased with height in the canopy. Leaf water potentials were lowest in the canopy and highest in the understory, even when the gravitational component was added to mid-canopy and canopy values. As a result, minimum turgor pressures were also lowest in the canopy compared to those at lesser heights, and approached zero in full sunlight on clear days.Osmotic potentials at each canopy level were similar for both wet and dry season samples dates suggesting that seasonal osmotic adjustment does not occur. Despite lowered predawn water potentials during the dry season, turgor was maintained in the understory by reduced stomatal conductances.

A new instrument for noninvasive measurement of intracranial pressure through the anterior fontanel. I. Preliminary report.

A pressure sensor has been developed with which intracranial pressure of infants with open anterior fontanell can be measured. The sensor consists of a light, small strain-gauge transducer (Statham P-50, Gould, USA), supported by a thin phosphorus bronze sheet having a strong spring quality characteristic. The light and small assembly, which weighs only 2.55 g, allows lengthy, continuous measurement with little drift. It eliminates almost any gravitational component in the recorded pressure. The thermal influence is also minimal and the thermal equilibrium is reached within 10 min. The sensor is precise and accurate in a range from 0 to 500 mm H2O, with excellent linear response. This newly developed fontanel pressure sensor has been successfully applied without the need for surgical procedures previously required to measure intracranial pressure.

Strain and deformation mechanisms in the Variscan nappes of Vendée, South Brittany, France

The Variscan nappes of Vendée (South Brittany, France) were displaced westward through a mechanism of regional subhorizontal ductile shear involving the entire body of the nappes. Ductile shear also affected the upper part of the Silurian footwall, including the rhyolite of Chapelle-Hermier, which was mylonitized and sheared with upward-increasing intensity, as well as the calcalkaline Vendée porphyroids of volcanic and volcanoclastic origin which form a mylonite sheet outlining the major basal thrust zone of the nappes. Nappe displacement was accompanied by a severe extensional strain, estimated at up to 300–400% in both the porphyroids and the rhyolite, and indicating that the deformational history may have involved a gravitational spreading component. Within the mylonitic rhyolite, accommodation of the bulk strain was mainly by solution-assisted mass-transfer, as shown by (1) growth of quartz fibres in low-pressure zones, (2) development of polycrystalline ribbons through continuous growth of quartz grains in pressure shadows and (3) crystallization of muscovite at the expense of the felsitic groundmass. A similar deformation process was probably active in the mylonitic porphyroids at the sole of the nappe, suggesting that pressure-solution flow was an important mechanism in nappe displacement.

Constant velocity dynamometer

Measurement characteristics of two constant velocity dynamometers (Cybex II, Lumex, Inc., NY) were evaluated at 11 selected speeds (0 to 5 rad X s-1) under various conditions of inert gravitational loading. A linear accelerometer was affixed to the lever arm. Speed settings were standardized percentages of each machine's maximum tachometer feedback voltage (0 to 100% Vfb max). Regression of Cybex transducer-observed voltages (V0) on true, i.e., expected, torques (Me) revealed that, for any static loading condition or angle, the measurement system was essentially linear and valid, although greater variance was evident for smaller torques. However, different calibrations, i.e., regression lines, were required for different speed settings. The error in predicting Me from V0 increased substantially with increased % Vfb max. Methodologies which assume constant velocity dynamic loading induce questionable, often invalid, results and inferences. Dynamic V0 represents both gravitational and inertial components. Considerable fluctuations in lever arm instantaneous velocity were ascribed to the combined influence of load and % Vfb max upon the servomotor. After computing inertia-corrected Me, calibration variability and prediction error were markedly reduced. Unexplained variability may be due to poor proximity of the Cybex transducer to the force application point. We concluded that: Cybex II should be calibrated only statically; use of an optimal filter will avoid false estimates of joint torque; inertial corrections must be applied in order to minimize potentially serious errors due to system angular acceleration; and reported muscle function relationships might be usefully re-assessed in view of these findings.

Separation of leaves from stems with a perforated rotating drum under suction

The aerodynamic drag force, at a perforated rotating drum under suction, was used to separate leaves from stems. This was achieved by continuous increase of the gravitational component perpendicular to the drum surface. The force due to the gravity and centrifugal accelerations, which act against the drag force, releases the stems before the leaves. Two versions of such a drum separator were developed: one processes the material on the outer surface of the drum and the other processes it on the inner surface. The separation efficiency of each of these separators was higher than that of conventional separators. A combination of the two separators gave the best results.

The inertial characteristics of dynamic robot models

Robot dynamics are embedded in the mathematical foundations of classical mechanics to introduce novel physical interpretations and structural characteristics of the Lagrangian dynamic robot model. Within this framework, the centrality of the inertial matrix emerges. The physical significance of the inertial coefficients is further illuminated by the introduction of the coefficient of coupling of robotic manipulators. The properties of the inertial matrix follow directly from the kinematic and dynamic parameters of the robot. These properties translate into the characteristics of the centrifugal, Coriolis and gravitational components of the dynamic robot model. The novel approach reinforces the need to integrate the mechanical and controller designs of robotic manipulators. The conceptual framework leads to design guidelines for simplifying and reducing the nonlinear kinematic and dynamic coupling of robot dynamics. The development of the paper is applied to illustrate the properties and structural characteristics of industrial robots.