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PubMed2000

Detection of groundwater conduits in limestones with gravity surveys: data from the area of the Chicxulub Impact crater, Yucatan Peninsula, Mexico.

Small negative gravity anomalies are found in gravity data from along the northwestern shoreline of the Yucatan Peninsula. These anomalies are shown to be due to elongate, shallow anomalous porosity zones in the Tertiary carbonates. These zones are caused primarily by groundwater solution and are presently active conduits for groundwater flow. The association of these small gravity anomalies with known topographic and structural features of the area, which partially overlies the Chicxulub Impact crater, indicates their development was influenced by structures, faults and/or fractures, within the Tertiary and pre-Tertiary carbonates.

Calcium Carbonate↗
PubMed1982

A comparison of counterflow centrifugation and unit gravity sedimentation in the separation of mouse bone marrow progenitor cells.

Both Unit Gravity Sedimentation and Counterflow Centrifugation separate cells primarily on the basis of size. However, when performed concurrently on the same normal mouse bone marrow cell suspensions, Unit Gravity Sedimentation was found to be far superior in terms of the recovery of total nucleated cell load and the recovery and enrichment of two classes of functional progenitors: (1) those responsive to the combined stimulus of pregnant mouse uterus extract (PMUE) plus human spleen conditioned medium (HUSPCM), and (2), those responsive to PMUE alone. Neither technique was able to resolve PMUE from PMUE + HUSPCM progenitors. The major limitation of Counterflow Centrifugation for the separation of sub-populations of marrow cells is related to the complexity and range of cell sizes in marrow cell suspensions which lead to significant pellet formation within the elutriator chamber. Furthermore, cells undergoing Counterflow Centrifugation are subjected to forces not encountered in Unit Gravity Sedimentation. Therefore, the basis of the separations is not identical and this is reflected in cell volume distributions of comparable fractions separated by each method.

Animals↗
PubMed1991

Upward displacement of the centre of gravity in paraplegic patients.

The centres of gravity of 44 complete chronic spinal cord injured patients and 24 normal subjects were measured using a gamma ray scanner (Barycentremetre). The results are expressed as a percentage of body length and as anatomical level. The mean weight of paraplegic patients was 12kg less than the controls. The centre of gravity was 5% of body length higher in the paraplegic patients than in the controls, equivalent to 3 to 4 vertebrae level. The importance of such changes in the centre of gravity for the design of stable wheelchairs is discussed.

Adolescent↗
PubMed2004

A microfluidic device based on gravity and electric force driving for flow cytometry and fluorescence activated cell sorting.

A novel method based on gravity and electric force driving of cells was developed for flow cytometry and fluorescence activated cell sorting in a microfluidic chip system. In the experiments cells flowed spontaneously under their own gravity in a upright microchip, passed through the detection region and then entered into the sorting electric field one by one at an average velocity of 0.55 mm s(-1) and were fluorescence activated cell sorted (FACS) by a switch-off activation program. In order to study the dynamical and kinematic characteristics of single cells in gravity and electric field of microchannels a physical and numerical module based on Newton's Law of motion was established and optimized. Hydroxylpropylmethyl cellulose (HPMC) was used to minimize cell assembling, sedimentation and adsorption to microchannels. This system was applied to estimate the necrotic and apoptotic effects of ultraviolet (UV) light on HeLa cells by exposing them to UV radiation for 10, 20 or 40 min and the results showed that UV radiation induced membrane damage contributed to the apoptosis and necrosis of HeLa cells.

Apoptosis↗
PubMed2003

Gravity-regulated differential auxin transport from columella to lateral root cap cells.

Gravity-induced root curvature has long been considered to be regulated by differential distribution of the plant hormone auxin. However, the cells establishing these gradients, and the transport mechanisms involved, remain to be identified. Here, we describe a GFP-based auxin biosensor to monitor auxin during Arabidopsis root gravitropism at cellular resolution. We identify elevated auxin levels at the root apex in columella cells, the site of gravity perception, and an asymmetric auxin flux from these cells to the lateral root cap (LRC) and toward the elongation zone after gravistimulation. We differentiate between an efflux-dependent lateral auxin transport from columella to LRC cells, and an efflux- and influx-dependent basipetal transport from the LRC to the elongation zone. We further demonstrate that endogenous gravitropic auxin gradients develop even in the presence of an exogenous source of auxin. Live-cell auxin imaging provides unprecedented insights into gravity-regulated auxin flux at cellular resolution, and strongly suggests that this flux is a prerequisite for root gravitropism.

Arabidopsis↗
PubMed2000

Microtubule self-organization is gravity-dependent.

Although weightlessness is known to affect living cells, the manner by which this occurs is unknown. Some reaction-diffusion processes have been theoretically predicted as being gravity-dependent. Microtubules, a major constituent of the cellular cytoskeleton, self-organize in vitro by way of reaction-diffusion processes. To investigate how self-organization depends on gravity, microtubules were assembled under low gravity conditions produced during space flight. Contrary to the samples formed on an in-flight 1 x g centrifuge, the samples prepared in microgravity showed almost no self-organization and were locally disordered.

Animals↗
PubMed1985

Analysis of vertical displacements of the center of gravity in the cat during limb flexion induced by cortical stimulation.

A limb movement and the associated postural adjustment result in a displacement of the center of gravity of the body. The vertical component of this displacement has been calculated from the variations in the sum of vertical forces at each limb. Through these variations, it is possible to measure the vertical acceleration of the center of gravity. Velocity and displacement are then obtained by two successive integrations of acceleration values. The magnitude of displacement of the center of gravity depends on the magnitude of limb displacement, and hindlimb flexion induces larger displacement than forelimb flexion. It is also directly linked to the time course of the vertical force variations recorded at each limb. The feed-forward character of the postural adjustment appears to minimize this amplitude, which leads us to discuss the functional significance of this postural adjustment.

Journal Article↗
PubMed2002

Evaluation of rapid readout biological indicators for 132 degrees C gravity and 132 degrees C vacuum-assisted steam sterilization cycles using a new automated fluorescent reader.

OBJECTIVE: The primary objective of this study was to evaluate fluorescent readout results of Attest 1291 Biological Indicators (BIs) (3M Health Care, St. Paul, MN) and Attest 1296 BI test packs (containing Attest 1292 BIs) using full and fractional cycles compared with the growth data when prolonged incubation (7 days) was included. Gravity displacement and vacuum-assisted steam sterilization cycles were evaluated. A secondary objective of this study was to evaluate the new automated rapid fluorescent reader (Attest 290 Auto Reader). DESIGN: The rapid readout BIs for gravity displacement and vacuum-assisted steam autoclave cycles at 132 degrees C were processed using full (4 minutes) and four fractional cycles that provided 30% to 80% positive results for growth after 24 hours of incubation (48 hours of incubation for Attest 1292 BIs from the Attest 1296 test packs). Sixty of each type of BI were tested for each cycle (300 of each BI type in total). RESULTS: For all full steam sterilization cycles, results of the rapid fluorescent readout and the 24-hour, 48-hour, and 7-day growth tests were negative for all Attest 1291 and 1292 BIs tested. For all fractional cycles, the 24- and 48-hour growth results for the Attest 1291 and 1292 BIs, respectively, were the same as the 7-day growth results. The fractional cycle data indicated that fluorescent rapid readout was a more sensitive indicator than growth. There were rare (0.9%) false-negative results for BIs under fractional cycle conditions and these all correlated with short fractional cycle exposure times. CONCLUSIONS: The fluorescent rapid readout results of the 1291 BIs and 1296 BI test packs reliably predict both 24- and 48-hour and 7-day growth. These data support the value of rapid readout BIs for sterilizer monitoring for both the vacuum-assisted and the gravity displacement steam sterilization cycles. The new automated reader requires less manipulation of the BI and makes monitoring user friendly and less prone to user errors.

Biomarkers↗
PubMed1995

Evaluation of a rapid readout biological indicator for 121 degrees C gravity and 132 degrees C vacuum-assisted steam sterilization cycles.

OBJECTIVE: A biological indicator (BI), based on fluorescent detection of a spore-associated enzyme, has been developed. We evaluated the new BI against five conventional self-contained BIs in a 121 degrees C gravity-displacement sterilizer and, packaged in towel packs and disposable steam test packs, in a 132 degrees C vacuum-assisted sterilizer. DESIGN: In the 121 degrees C gravity-displacement sterilizer, rapid readout BIs and conventional BIs were tested together in an otherwise empty chamber. Exposure times were 5, 10, and 15 minutes. In the 132 degrees C vacuum-assisted steam sterilizer, BIs were contained in towel packs or disposable steam test packs. Surgical packs were added to represent a full load. Exposure times were 0, 1, and 2 minutes. RESULTS: In gravity-displacement 5-minute cycles, the rapid readout BIs yielded 100% positive results within 30 minutes. The conventional BIs ranged from 72% to 100% positive in 48 hours. At 10 minutes, the rapid readout BIs were 83% positive after 3 hours, whereas the conventional BIs ranged from 0% to 37% positive after 48 hours. All indicators were negative after 15-minute exposures. In vacuum-assisted cycles, all indicators were negative after 3 minutes. After 1-minute exposures, the rapid readout BIs were 40% to 60% positive, whereas the conventional BIs were 15% to 20% positive. CONCLUSION: The rapid readout BIs are a more sensitive indicator of marginal steam sterilization cycles than conventional self-contained BIs. They yield results within 3 hours, as compared to 24 to 48 hours for the conventional BIs.

Evaluation Studies as Topic↗
PubMed1991

Isolation of hybridoma forming cells from immune spleens by unit gravity sedimentation.

In 1975 a method for the production of hybridomas that secrete monoclonal antibodies was first described (1). Since that time, surprisingly little information has emerged on the identity of the fusible spleen cell. In this report we describe the isolation of hybridoma forming cells from immune spleens and the enrichment of B cell populations in different states of activation. The B cells that reside in immune spleens are comprised of heterogeneous populations that differ in their states of activation. These populations have been difficult to separate and, therefore, difficult to characterize. Two factors that discriminate B cells in different states of activation are cell size and density. Unit gravity sedimentation is a simple, reliable and reproducible method for separating cells based on their size and density. Immune B cells were fractionated on a 10 to 25% serum gradient at unit gravity. Cells were collected and pooled, when necessary, to perform functional assays. Fractionated B cells were assayed for hybridoma formation, PFC response, Ig secretion and proliferation. The cells that exhibited hybridoma formation, PFC activity and Ig secretion were all found in the large cell fractions that comprised less than 10% of the cells recovered from the gradient. Proliferating B cells were found primarily in smaller cell fractions compared to antibody forming cells. Resting B cells were located in the smallest cell fractions recovered from the gradient. Data show that separation of immune B cells by unit gravity sedimentation is an effective means to isolate hybridoma forming cells and enrich for B cell subpopulations in different states of activation.

Animals↗
PubMed2002

Tonic gravity changes alter gene expression in the efferent vestibular nucleus.

To assess effects of tonic gravity changes on efferent vestibular neurons, immediate early gene (IEG) protein expression was compared in the efferent vestibular nucleus (EVe) of adult rats exposed to microgravity during the NASA Neurolab Mission (STS-90), and matching control animals on the ground. Rats sacrificed 1 day and 12 days after launch (experiencing approximately 0g) showed significantly fewer IEG protein-expressing cells than corresponding ground control animals (at 1 g). Normal IEG protein-expressing cell numbers reappeared within I day after flight animals returned to earth, and were maintained at 14 days after landing. EVe neurons appear to play a role in gravity-induced modifications of vestibular hair cell synapses; a contribution to gravity-induced plasticity of the vestibulo-ocular reflex (VOR) is also suggested.

Animals↗
PubMed1995

Extravasation rates and complications of intraosseous needles during gravity and pressure infusion.

OBJECTIVE: To compare the extravasation rates and insertion complications under gravity and 300 mm Hg (40 kPa) pressure infusion of threaded (SurFast and Sussmane-Raszynski intraosseous needles, Cook Critical Care, Bloomington, IN); and nonthreaded needles (16-gauge disposable intraosseous needle with 45 degrees trocar Cook Critical Care, Bloomington, IN; Jamshidi bone marrow needle; Baxter Health Care Corp, Valencia, CA). DESIGN: A prospective, randomized study. SETTING: An animal laboratory at a university center. SUBJECTS: Five healthy mix breed piglets, weighing 15 to 15.5 kg. INTERVENTIONS: Piglets were anesthetized and ventilated. Tibial, femoral, and humeral osseous sites were exposed by dissection of overlying tissue. All bleeding points were cauterized and oozing was prevented by sealing with cyanoacrylate. Intraosseous access devices then were inserted one at a time in random order and rated for difficulty of insertion. Normal saline solution was infused under gravity or 300 mm Hg (40 kPa) pressure. Extravasation rates then were calculated from the increase in weight of a gauze sponge wrapped tightly at the base of the needle during infusion. MEASUREMENTS AND MAIN RESULTS: No significant (p > .05) differences in extravasation rates were noted among the different types of needles, either under gravity or pressure infusions. The Sussmane-Raszynski needle was significantly more difficult to insert than the others (rated difficult to insert and control in 16 of 34 attempts). Inadvertent penetration of both cortices occurred with nonthreaded needles only (three of 66 attempts). The SurFast needle provided greatest penetration control and was most resistant to accidental dislodgement. CONCLUSIONS: Under ideal conditions, needle type does not influence extravasation rates. However, difficulty with insertion and penetration of both cortices occur commonly and may lead to extravasation during stressful emergency situations or when performed by unskilled personnel.

Animals↗
PubMed1997

The evaluation of arterial inflow by gravity cavernosometry.

PURPOSE: We determined whether the comparison between equilibrium pressure after intracavernous injection of vasodilators and maximal corporeal pressure at gravity cavernosometry could provide information about the relative contribution of arterial inflow and cavernous wall resistance to the erection process. MATERIALS AND METHODS: The results of gravity cavernosometry performed in 68 impotent patients were compared to those of duplex scanning in 53 and penile angiography in 10. RESULTS: A highly statistically significant (p < 0.01) but nonlinear correlation was observed between the equilibrium pressure after injection and maximal corporeal pressure, which indicates a paramount role of the corporeal veno-occlusive mechanism in the development of penile rigidity. However, in most patients with a pressure increase of more than 30 mm. Hg from the equilibrium pressure after injection to the maximal corporeal pressure, arterial insufficiency was diagnosed by duplex scanning and/or arteriography, and seemed to be the main limiting factor in the development of penile rigidity. CONCLUSIONS: Gravity cavernosometry provides functional information about the corporeal veno-occlusive mechanism and arterial inflow and, therefore, about the relative roles of these mechanisms in the development of penile rigidity.

Adult↗
PubMed1984

Lumbar curve, trunk muscles, and line of gravity with different heel heights.

The influence of different heel heights on the lumbar curve, pelvic inclination, trunk muscle activity, and the position of the line of gravity was examined in 18 healthy women. They were examined while standing on heel-supports, being 4.5 cm elevated, at the level of and 2.5 cm lower than the support of the forefoot, respectively (Figure 1). Each examination was preceeded by one-hour adaptation to a corresponding shoe type. With increasing heel height, the lumbar lordosis and the pelvis inclination were decreased. The back and abdominal muscles did not alter their activities. The position of the line of gravity kept the distance from the forefoot almost constant, but the ankle joint was shifted towards the line of gravity with increasing heel height.

Adult↗
PubMed2004

Effects of changing the direction of gravity on sector pupil dilations.

PURPOSE: To study anterior segment aqueous humor kinetics by using sector pupil dilations with different directions of gravity to change the direction of convectional flow in the anterior chamber. METHODS: Sector pupil dilations were elicited using focal applications of phenylephrine at the limbus. To vary the direction of gravity (and hence the direction of convectional flow) relative to the eye, subjects' heads were tilted left side down or right side down with gaze horizontal. Pupil elongation and pupil center displacement were measured as functions of time. RESULTS: Early stages of pupil dilation were dominated by pupil elongation toward the site of drug application. Amplitude of elongation was about the same for all the application points, but center displacement depended on the application point. Later stages of pupil dilation showed an interaction between the site of drug application and the direction of gravity. CONCLUSIONS: The results are interpreted in terms of anterior chamber convectional flow and its interaction with transpupillary aqueous flow and diffusion. Early distribution in the anterior segment of a substance applied to the limbus appears to be determined primarily by local diffusion, whereas later distribution is affected by movement of the drug in convectional and transpupillary flow.

Adult↗
PubMed2002

The effect of gravity on coral morphology.

Coral morphological variability reflects either genetic differences or environmentally induced phenotypic plasticity. We present two coral species that sense gravity and accordingly alter their morphology, as characterized by their slenderness (height to diameter) ratio (SR). We experimentally altered the direction (and intensity) of the gravitational resultant force acting along or perpendicular to the main body axis of coral polyps. We also manipulated light direction, in order to uncouple gravity and light effects on coral development. In the experiments, vertically growing polyps had significantly higher SR than their horizontal siblings even when grown in a centrifuge (experiencing different resultant gravitational forces in proximal and distal positions). Lowest SR was in horizontal side-illuminated polyps, and highest in vertical top-illuminated polyps. Adult colonies in situ showed the same pattern. Gravitational intensity also affected polyp growth form. However, polyp volume, dry skeleton weight and density in the various centrifuge positions, and in aquaria experiments, did not differ significantly. This reflects the coral's ability to sense altered gravity direction and intensity, and to react by changing the development pattern of their body morphology, but not the amount of skeleton deposited.

Animals↗
PubMed2006

New 'phase' of quantum gravity.

The emergence of loop quantum gravity over the past two decades has stimulated a great resurgence of interest in unifying general relativity and quantum mechanics. Among a number of appealing features of this approach is the intuitive picture of quantum geometry using spin networks and powerful mathematical tools from gauge field theory. However, the present form of loop quantum gravity suffers from a quantum ambiguity, owing to the presence of a free (Barbero-Immirzi) parameter. Following the recent progress on conformal decomposition of gravitational fields, we present a new phase space for general relativity. In addition to spin-gauge symmetry, the new phase space also incorporates conformal symmetry making the description parameter free. The Barbero-Immirzi ambiguity is shown to occur only if the conformal symmetry is gauge fixed prior to quantization. By withholding its full symmetries, the new phase space offers a promising platform for the future development of loop quantum gravity. This paper aims to provide an exposition, at a reduced technical level, of the above theoretical advances and their background developments. Further details are referred to cited references.

Journal Article↗
PubMed1999

Experimental measurements of sidebranching in thermal dendrites under terrestrial-gravity and microgravity conditions.

We perform sidebranch measurements on pure succinonitrile dendrites grown in both microgravity and terrestrial-gravity conditions for a set of supercoolings within the range 0.1-1.0 K. Two distinct types of sidebranch regions, uniform and coarsening, exist, and are characterized by the distance from the tip at which the region began, D(i), and the average spacing of sidebranches within that region, lambda(i). There does not appear to be any significant dependence on either gravity level or supercooling when D(i) or lambda(i) are normalized with respect to the radius of curvature of the tip, R. The apparently constant normalized proportionality factor between D(i), lambda(i), and R, regardless of the relative importance of diffusion and convective heat transport, demonstrates self-similarity between dendrites of different length scales propagating under various heat transfer conditions. However, when the form of the sidebranch envelope is defined by a power law relating the amplitude and relative positions of the sidebranches normalized to the radius of the tip, the form is seen to have significant variations with supercooling between the terrestrial gravity and microgravity growth dendrites. Furthermore, both the amplitude coefficient and exponent from the power-law regressions of the microgravity data are statistically different (95% confidence level) than their terrestrial counterparts.

Journal Article↗