Gravitational Orientation Research Articles

Chaotic dynamics of a swirling flame front instability generated by a change in gravitational orientation.

We have intensively examined the dynamic behavior of flame front instability in a lean swirling premixed flame generated by a change in gravitational orientation [H. Gotoda, T. Miyano, and I. G. Shepherd, Phys. Rev. E 81, 026211 (2010)PLEEE81539-375510.1103/PhysRevE.81.026211] from the viewpoints of complex networks, symbolic dynamics, and statistical complexity. Here, we considered the permutation entropy in combination with the surrogate data method, the permutation spectrum test, and the multiscale complexity-entropy causality plane incorporating a scale-dependent approach, none of which have been considered in the study of flame front instabilities. Our results clearly show the possible presence of chaos in flame front dynamics induced by the coupling of swirl-buoyancy interaction in inverted gravity. The flame front dynamics also possesses a scale-free structure, which is reasonably shown by the probability distribution of the degree in ε-recurrence networks.

Features of reducing the turbulent friction of a liquid on the channel wall by gas-saturation

The report presents the results of an experimental study of the efficiency of reducing the local friction at gas saturation of the turbulent boundary layer (TBL) in the input section of the channel at different gravitational orientation of the wall, and its dependence on the structure of gas-liquid flow. Profiles of gas concentration have a peak near the wall, which increases with the gas flow increase. The growth of concentration in the near-wall zone leads to rapid coalescence of bubbles, as a result of which the flow in TBL transits to the film-bubble regime with increasing the buoyancy effect of the gas phase, especially at low flow rates. It is shown that the key parameter of friction reduction by gas saturation is the gas phase concentration in the inner region of the boundary layer, whose magnitude is determined by the gas flow rate, the flow velocity, the distance downstream behind the gas generator, and the gravitational orientation of the wall.

Hybrid gravitational orientation system of small spacecraft

In this article is considered the problem of small satellite's angular position control. This problem is solved by some improvement. The authors offer to use active control element, in the form of gyrodyne, which to fix on the end of gravitational rod. This improvement transforms the gravitational system of orientation into a control system along three axes of orientation: yaw, roll and pitch.

Solid-state thermal diode with shape memory alloys

Analogous to the electronic diode, a thermal diode transports heat mainly in one preferential direction rather than in the opposite direction. Phase change thermal diodes usually rectify heat transport much more effectively than solid state thermal diodes due to the latent heat phase change effect. However, they are limited by either the gravitational orientation or one dimensional configuration. On the other hand, solid state thermal diodes come in many shapes and sizes, durable, relatively easy to construct, and are simple to operate, but their diodicity (rectification coefficient) is always in the order of η∼1 or lower. Thus, it is difficult to find any potential applications. In order to be practically useful for most engineering systems, a thermal diode should exhibit a diodicity in the order of η∼10 or greater. In this study, a passive solid state thermal diode with shape memory alloy is built and investigated experimentally. The diodicity is recorded at about 90. This promising result could have important applications in the development of future thermal circuits or for thermal management.

Near-field behavior of variable property jet with swirling flow generated by a change in gravitational orientation

This paper presents the near-field behavior of a variable property jet with swirling flow generated by a change in gravitational orientation, focusing on the onset of vortex formation at the jet interface and the subsequent vortex breakdown (VB). Two types of gases are used to create a significant difference in the physical properties between the inner and outer fluids: CO2 with high-density and low-viscosity, and helium with low-density and high-viscosity. We propose a nondimensional instability parameter M∗ as a useful index for predicting the onset of vortex formation at a swirling jet interface. Inverted gravity (+1g) enlarges the region of unstable VB of the CO2 jet compared with that in normal gravity (−1g), which clearly shows that the buoyancy force has a significant impact on unstable VB. The trends of the changes in the jet half-angle and stagnation point height are investigated in detail for the preceding stable VB. Our physical model derived by considering the momentum balance in a swirling flow is adopted to understand the mechanism of the notable change in the stagnation point height in +1g with increasing swirl number of the inner jet and Reynolds number of the outer jet.

Contribution of Bodily and Gravitational Orientation Cues to Face and Letter Recognition.

Sensory information provided by the vestibular system is crucial in cognitive processes such as the ability to recognize objects. The orientation at which objects are most easily recognized--the perceptual upright (PU)--is influenced by body orientation with respect to gravity as detected from the somatosensory and vestibular systems. To date, the influence of these sensory cues on the PU has been measured using a letter recognition task. Here we assessed whether gravitational influences on letter recognition also extend to human face recognition. 13 right-handed observers were positioned in four body orientations (upright, left-side-down, right-side-down, supine) and visually discriminated ambiguous characters ('p'-from-'d'; 'i'-from-'!') and ambiguous faces used in popular visual illusions ('young woman'-from-'old woman'; 'grinning man'-from-'frowning man') in a forced-choice paradigm. The two transition points (e.g., 'p-to-d' and 'd-to-p'; 'young woman-to-old woman' and 'old woman-to-young woman') were fit with a sigmoidal psychometric function and the average of these transitions was taken as the PU for each stimulus category. The results show that both faces and letters are more influenced by body orientation than gravity. However, faces are more optimally recognized when closer in alignment with body orientation than letters--which are more influenced by gravity. Our results indicate that the brain does not utilize a common representation of upright that governs recognition of all object categories. Distinct areas of ventro-temporal cortex that represent faces and letters may weight bodily and gravitational cues differently--possibly to facilitate the specific demands of face and letter recognition.

Time-strip visualization and thermo-hydrodynamics in a Closed Loop Pulsating Heat Pipe

New trends in the microprocessor industry are leading not only to miniaturization and integration but also to increases in power dissipation rates which now require advanced cooling solutions to prevent thermal damage to the devices. Pulsating heat pipes (PHPs) represent a promising solution for passive on-chip, two-phase cooling of such electronics, providing advantages such as a simple construction and operation in any gravitational orientation. Unfortunately, the unique coupling of thermodynamics, hydrodynamics and heat transfer responsible for their operation has so far eluded comprehensive description or accurate prediction. This paper reports on flow visualization experiments in a Closed Loop Pulsating Heat Pipe (CLPHP)-charged with R245fa-operating over a range of test conditions. A novel time-strip image processing technique has been applied to the flow videos to extract qualitative details of flow regimes and quantitative flow data concerning the liquid/vapor interface dynamics. The latter can be coupled with thermal data to reveal new details regarding flow characteristics, such as two-phase flow pattern and its oscillation. Four distinct flow regimes and their steady thermal oscillation characteristics have been identified and discussed.

Comparative toxicity of physiological and biochemical parameters in Euglena gracilis to short-term exposure to potassium sorbate.

Potassium sorbate is the potassium salt of sorbic acid, is a widespread and efficient antioxidant that has multiple functions in plants, traditionally associated with the reactions of photosynthesis; however, it has moderate toxicity to various species including rat, fish, bacteria and human health. The effects of potassium sorbate on the movement and photosynthetic parameters of Euglena gracilis were studied during short-term exposure. Potassium sorbate showed acute toxicity to the green flagellate E. gracilis affecting different physiological parameters used as endpoints in an automatic bioassay such as motility, precision of gravitational orientation (r-value), upward movement and alignment, with mean EC50 values of 2867.2mgL(-1). The concentrations above 625mgL(-1) of potassium sorbate induce an inhibition of the photosynthetic efficiency and electron transport rate and, in concentrations more than 2500.0mgL(-1), the Euglena cells undergo a complete inhibition of photosynthesis even at low light irradiation.

Potential environmental toxicity from hemodialysis effluent

Understanding the toxicity of certain potentially toxic compounds on various aquatic organisms allows to assess the impact that these pollutants on the aquatic biota. One source of pollution is the wastewater from hemodialysis. The process of sewage treatment is inefficient in inhibition and removal of pathogenic bacteria resistant to antibiotics in this wastewater. In many countries, such as Brazil, during emergencies, sewage and effluents from hospitals are often dumped directly into waterways without any previous treatment. The objective of this study was to characterize the effluents generated by hemodialysis and to assess the degree of acute and chronic environmental toxicity. The effluents of hemodialysis showed high concentrations of nitrites, phosphates, sulfates, ammonia, and total nitrogen, as well as elevated conductivity, turbidity, salinity, biochemical and chemical oxygen demand, exceeding the thresholds defined in the CONAMA Resolution 430. The samples showed acute toxicity to the green flagellate Euglena gracilis affecting different physiological parameters used as endpoints in an automatic bioassay such as motility, precision of gravitational orientation (r-value), compactness, upward movement, and alignment, with mean EC50 values of recalculate as 76.90 percent (±4.68 percent) of the undiluted effluents. In tests with Daphnia magna, the acute toxicity EC50 was 86.91 percent (±0.39 percent) and a NOEC value of 72.97 percent and a LEOC value 94.66 percent.

Spatial and temporal film thickness measurement of a soap bubble based on large lateral shearing displacement interferometry

The film thickness of a hanging soap bubble has been studied along its gravitational orientation after its birth and before its bursting using large lateral shearing displacement interferometry, with a theoretical error of less than 0.325λ. The results show that the spatial distribution of the film thickness could be approximated with an exponential model in all captured frames, especially in the lower half of the soap bubble. Before its bursting, a special zone, where the water layer has drained out while the surfactant solution layer remains, will occur at the top of the soap bubble and gradually expand toward the bottom. Moreover, the simulated fringe patterns based on the computed values match well with the experimentally observed ones.

Realization of modes of satellite attitude motion with a small level of microaccelerations using electromechanical executive devices

Quasi-static microaccelerations are estimated for a satellite specially designed to perform space experiments in the field of microgravity. Three modes of attitude motion of the spacecraft are considered: passive gravitational orientation, orbital orientation, and semi-passive gravitational orientation. In these modes the lengthwise axis of the satellite is directed along the local vertical, while solar arrays lie in the orbit plane. The second and third modes are maintained using electromechanical executive devices: flywheel engines or gyrodynes. Estimations of residual microaccelerations are performed with the help of mathematical modeling of satellite’s attitude motion under the action of gravitational and aerodynamic moments, as well as the moment produced by the gyro system. It is demonstrated that all modes ensure rather low level of quasi-static microaccelerations on the satellite and provide for a fairly narrow region of variation for the vector of residual microacceleration. The semi-passive gravitational orientation ensures also a limited proper angular momentum of the gyro system.

Planar jumping-drop thermal diodes

Phase-change thermal diodes rectify heat transport much more effectively than solid-state ones, but are limited by either the gravitational orientation or one-dimensional configuration. Here, we report a planar phase-change diode scalable to large areas with an orientation-independent diodicity of over 100, in which water/vapor is enclosed by parallel superhydrophobic and superhydrophilic plates. The thermal rectification is enabled by spontaneously jumping dropwise condensate which only occurs when the superhydrophobic surface is colder than the superhydrophilic surface.

Time course of the recovery of three-dimensional eye position in patients with acute cerebellitis

Listing's plane is a construction derived from eye position and reflects gravitational orientation. The cerebellum plays a key role in orienting and integrating sensory input concerning gravity from visual, vestibular and proprioceptive apparatuses. This suggests that the thickness of Listing's plane could serve as a novel parameter for evaluating the accuracy of the constructed gravity-oriented internal model. We report a case with acute cerebellitis along with data on Listing's plane, calculated from consecutive infrared video-oculogram recordings. We found thickening of Listing's plane at the early stage of the disease, and a gradual reduction of the thickness into normal range in parallel with the recovery of the patient's posture and gate. Notably, clinical improvement of the patient's posture was delayed relative to the normalization of the thickness of Listing's plane. The thickness of Listing's plane reflects the stability of the cerebellar-mediated cognitive gravitational reference frame. This thickness value could serve as a parameter to quantitatively evaluate the function of the constructed internal model. Recovery from cerebellar ataxia (manifested as normalization of the thickness of Listing's plane) was followed by recovery of muscular strength lost during the period the patient was by his disease forced to assume a lying position.

Rotational dynamics and internal structure of Titan

Estimates of the moments of inertia of Titan, as separately deduced from its gravitational field and spin pole orientation, are quite different. This discrepancy can be resolved if Titan is either not precessing as a rigid body (e.g. if the shell is decoupled from the interior by an ocean), or if the spin pole is not fully damped (e.g. due to atmospheric excitation). By the end of the Cassini mission, continued monitoring of the changing spin pole orientation, by Cassini radar observations, will determine which effect dominates.

Modeling of the aerodynamic moment acting upon a satellite

We consider the issues of modeling the moments of aerodynamic forces acting upon a satellite with gravitational system of stabilization. It is assumed that satellite orbits are almost circular with heights in the range 550–750 km. Simplified analytical expressions are suggested for the aerodynamic moment in the case when a satellite moves in the regime of gravitational orientation. Accuracy of the obtained expressions is estimated to be compared with that of expressions derived under the assumption of constant coefficient of frontal resistance. An analysis is made of short-periodic variations of the atmosphere density occurring due to orbital motion of a satellite. It is demonstrated that these variations can result in a substantial change of the aerodynamic moment, and their approximation by a truncated Fourier series is suggested. Estimates of the accuracy of the suggested approximation are given.

Effects of electrotactile vestibular substitution on rehabilitation of patients with bilateral vestibular loss

The present study evaluated the effectiveness of electrotactile tongue biofeedback (BrainPort ®) as a sensory substitute for the vestibular apparatus in patients with bilateral vestibular loss (BVL) who did not have a good response to conventional vestibular rehabilitation (VR). Seven patients with BVL were trained to use the device. Stimulation on the surface of the tongue was created by a dynamic pattern of electrical pulses and the patient was able to adjust the intensity of stimulation and spatially centralize the stimulus on the electrode array. Patients were directed to continuously adjust head orientation and to maintain the stimulus pattern at the center of the array. Postural tasks that present progressive difficulties were given during the use of the device. Pre- and post-treatment distribution of the sensory organization test (SOT) composite score showed an average value of 38.3 ± 8.7 and 59.9 ± 11.3, respectively, indicating a statistically significant improvement ( p = 0.01). Electrotactile tongue biofeedback significantly improved the postural control of the study group, even if they had not improved with conventional VR. The electrotactile tongue biofeedback system was able to supply additional information about head position with respect to gravitational vertical orientation in the absence of vestibular input, improving postural control. Patients with BVL can integrate electrotactile information in their postural control in order to improve stability after conventional VR. These results were obtained and verified not only by the subjective questionnaire but also by the SOT composite score. The limitations of the study are the small sample size and short duration of the follow-up. The current findings show that the sensory substitution mediated by electrotactile tongue biofeedback may contribute to the improved balance experienced by these patients compared to VR.

Flow and Particle Dispersion in a Pulmonary Alveolus—Part II: Effect of Gravity on Particle Transport

The acinar region of the human lung comprises about 300x10(6) alveoli, which are responsible for gas exchange between the lung and the blood. As discussed in Part I (Chhabra and Prasad, "Flow and Particle Dispersion in a Pulmonary Alveolus-Part I: Velocity Measurements and Convective Particle Transport," ASME J. Biomech. Eng., 132, p. 051009), the deposition of aerosols in the acinar region can either be detrimental to gas exchange (as in the case of harmful particulate matter) or beneficial (as in the case of inhalable pharmaceuticals). We measured the flow field inside an in-vitro model of a single alveolus mounted on a bronchiole and calculated the transport and deposition of massless particles in Part I. This paper focuses on the transport and deposition of finite-sized particles ranging from 0.25 microm to 4 microm under the combined influence of flow-induced advection (computed from velocity maps obtained by particle image velocimetry) and gravitational settling. Particles were introduced during the first inhalation cycle and their trajectories and deposition statistics were calculated for subsequent cycles for three different particle sizes (0.25 microm, 1 microm, and 4 microm) and three alveolar orientations. The key outcome of the study is that particles <or=0.25 microm follow the fluid streamlines quite closely, whereas midsize particles (d(p)=1 microm) deviate to some extent from streamlines and exhibit complex trajectories. The motion of large particles >or=4 microm is dominated by gravitational settling and shows little effect of fluid advection. Additionally, small and midsize particles deposit at about two-thirds height in the alveolus irrespective of the gravitational orientation whereas the deposition of large particles is governed primarily by the orientation of the gravity vector.

Dynamic properties of unstable motion of swirling premixed flames generated by a change in gravitational orientation

The dynamic behavior of swirling premixed flames generated by the effect of the gravitational orientation has been experimentally and numerically investigated. When the gravitational direction relative to the flame front is changed, i.e., in inverted gravity (-1G), an unstable flame is formed in a limited domain of equivalence ratio and swirl number. The time history of flame front fluctuation shows that high-energy chaotic motion is superimposed on a periodic oscillation generated by unstable vortex motion in the combustion products. This results in the dynamic motion of the unstable flame becoming deterministically chaotic. This is clearly demonstrated by sophisticated nonlinear time series analysis, which has not been widely applied to the investigation of combustion phenomena.

Liquid and surfactant delivery into pulmonary airways

We describe the mechanisms by which liquids and surfactants can be delivered into the pulmonary airways. These are instilled and transported throughout the lung in clinical therapies such as surfactant replacement therapy, partial liquid ventilation and drug delivery. The success of these treatments is contingent on the liquid distribution and the delivery to targeted regions of the lung. The targeting of a liquid plug can be influenced by a variety of factors such as the physical properties of the liquid, the interfacial activity, the gravitational orientation, instillation method and propagation speed. We provide a review of experimental and theoretical studies that examine these effects in single tubes or channels, in tubes with single bifurcations and in the whole lung.

Spot-GTA 용접자세에 따른 304 스테인리스강 용융지 표면 및 용접부 형상 거동

Effects of gravitational orientation on gas tungsten arc welding (GTAW) for 304 stainless steel were studied to determine the critical factors for weld pool formation, such as weld surface deformation and weld pool shape. This study was accomplished through an analytical study of weld pool stability as a function of primary welding parameters (arc current and arc holding time), material properties (surface tension and density), and melting efficiency (cross-sectional area). The stability of weld pool shape and weld surface deformation was confirmed experimentally by changing the welding position. The arc current and translational velocity were the major factors in determining the weld pool stability as a function of the gravitational orientation. A 200A spot GTAW showed a significant variation of the weld pool formation as the arc held longer than 3 seconds, however the weld pool shape and surface morphology for a 165A spot GTAW were 'stable', i.e., constant regardless of the gravitational orientation. The cross-sectional area of the weld (CSA) was one of the critical factors in determining the weld pool stability. The measured CSA (<TEX>$13.5mm^2$</TEX>) for the 200A spot GTAW showed a good agreement with the calculated CSA (<TEX>$14.9mm^2$</TEX>).