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At least 1,117 records · Page 62Linked to original sources

PubMed2001

Gravity-dependent perfusion of the lung demonstrated with the FAIRER arterial spin tagging method.

Magnetic resonance imaging of lung perfusion using an arterial spin tagging (AST) sequence called flow sensitive alternating inversion recovery with an extra RF pulse (FAIRER) was performed in the left and right lateral positions in five volunteers. Coronal slices were obtained and the average intensity of each lung was measured. In both positions, an increase in the intensity of the dependent lung was found (229% for left lateral, 40% for right lateral). No change was seen along an isogravitational plane. Lung volumes were measured in each position to account for the compression of the lungs by the heart. This effect was found to be symmetric and did not contribute to the perfusion gradient. This demonstrates that AST is sensitive to gravity-dependent perfusion gradients in the lung.

Adult↗

PubMed2000

Motion of the body centre of gravity as a summary indicator of the mechanics of human pathological gait.

Abnormal movements of the body segments due to lowest level gait disorders such as musculoskeletal disorders, peripheral neuropathies and radiculopathies or middle-level disorders such as hemiplegia, paraplegia and dystonia influence the motion of the centre of gravity (CG) during walking. The translation of the CG can be studied by the work done by muscles (WExt) with respect to the ground. The efficacy of gait's mechanism can be quantified by the energy transferred between gravitational potential and kinetic energies (recovery). WExt and recovery were investigated in lowest and middle-level gait disorders during level walking. No statistical significant difference was observed between patients with lowest-level gait disorders and normal subjects. However, WExt was increased for the patients with middle-level gait disorders and recovery decreased up to 20%. The measurement of changes in mechanical energy of the CG might be a summary indicator for the mechanics of pathological gait.

Adult↗

PubMed1998

Center of gravity dynamic stability in normal and vestibulopathic gait.

The purpose of this study was to examine the three-dimensional whole body center of gravity (CG) kinematics during free and paced gait in healthy subjects (n=16) and individuals with vestibulopathy (n=8). The cycle time, double and single stance phase durations, values and timing of CG forward velocity, and CG vertical displacement were recorded using an 11 segment, 66 degree of freedom whole body model. The free speed gait of the vestibulopathic individuals was remarkable for increased cycle time, increased percentage of time spent in the double stance phase, decreased forward velocity of the CG, and decreased vertical displacement of the CG. However, during paced gait, no statistically significant differences were found between the vestibulopathic and control groups in all measures. In all groups, CG horizontal velocity maxima and minima significantly lagged CG vertical minima and maxima respectively. We conclude that whole body CG control does not result purely from optimization of mechanical potential and kinetic energy exchanges: our temporal offsets in the maxima and minima of the CG horizontal velocity and vertical displacement make this mechanically impossible. Furthermore, individuals with vestibular impairment may self-select a slower walking speed to ease their biomechanic stability challenge despite being able to ambulate faster with 'normal' CG velocities and displacements. Copyright 1998 Elsevier Science B.V.

Journal Article↗

PubMed2002

Relationship between antagonistic leg muscles co-contractions and body centre of gravity mechanics in different level gait disorders.

Body centre of gravity (CG) mechanics and electromyographic activity of flexor-extensor antagonistic muscles of the lower limb were simultaneously recorded in lowest and middle-level gait disorders. Muscle co-contractions between tibialis anterior and triceps surae, and between rectus femoris and hamstrings were evaluated. CG mechanics was assessed by the external mechanical work (W(ext)) done to translate the CG with respect to the ground, and the recovery quantifying the efficacy of gait mechanism by the amount of energy transferred between gravitational potential and kinetic energies of the CG. The results showed a strong relationship between CG mechanics and the co-contractions of the main flexor-extensor ankle muscles. In middle-level gait disorders, our results suggest that the ankle antagonistic muscle co-contractions and the CG mechanics could provide information about gait mechanism and the integrity level of the locomotor program.

Adolescent↗

PubMed2005

Responses across the gravity continuum: hypergravity to microgravity.

In response to hypergravity, it appears that the larger the animal, the greater the response, if present. Therefore, the response of a rat exceeds that of a mouse in the same hypergravity environment. When investigated in the microgravity environment of space flight, this appears to hold true. The lack of definitive data obtained in space for either species makes the extrapolation of the continuum to levels below Earth-gravity problematic. However, in systems where responses are detected for both space flight and acceleration by centrifugation, a gravitational continuum is present supporting the "principle of continuity". For those and similar systems, it appears that the use of hypergravity could be used to predict responses to space flight.

Animals↗

PubMed2002

Vertical migration by the infective larvae of three species of parasitic nematodes: is the behaviour really a response to gravity?

Vertical migration by infective larvae (L3) of 3 species of nematodes was investigated. Upright truncated agarose cones were used to test upward migration, and comparable truncated cone-shaped agarose hollows were used to test downward migration. Flat agarose plates were control surfaces. When placed at the bases of upright cones, 74% of Ancylostoma caninum L3 migrated up, whereas only 16.5% migrated down the indented cones; this latter value was not significantly different from larval migration on flat plates. Strongyloides stercoralis L3 also migrated upward in significant numbers (80%). These larvae also failed to migrate downward under normal conditions. However, when the bottoms of the indented cones were 3-5 degrees C warmer than the tops, 75.5% of S. stercoralis L3 migrated down. In contrast, Haemonchus contortus L3 showed no tendency to crawl up or down cones, when compared with normal crawling behaviour on flat plates. Thus, L3 of A. caninum and S. stercoralis exhibited negative geotaxis, crawling against the pull of gravity, while H. contortus did not. The biology of these parasites may explain these behavioural differences.

Ancylostoma↗

PubMed2001

Particle characterization and separation by a coupled acoustic-gravity field.

A coupled acoustic-gravity field is proposed as a novel external field for particle separation and characterization. When a standing plane ultrasound wave is generated, particles move to the node of the wave along the ultrasound force gradient. If the particles also undergo a sedimentation force, they aggregate at the equilibrium position, where these two forces are balanced. The equilibrium position, which is determined by the density and compressibility of a medium and particles, characterizes the particles. The local ultrasound energy, which is necessary for quantitative discussions, is evaluated by using a standard particle, the physical parameters of which are unambiguously determined; aluminum particles are used in the present study. The local ultrasound energy makes possible the determination of the compressibility of unknown materials. Nonporous particles of inorganic and polymeric materials, the particle sizes of which range from 3 to 100 microm, follow a derived model, suggesting that the local ultrasound energy and a derived model be valid. The proposed external field can be used for separation of particles having different acoustic natures.

Journal Article↗

PubMed2006

Two-dimensional fluidics based on differential lyophobicity and gravity.

We have prepared planar fluidics devices using binary chemical patterns consisting of hydrophobic "roads" on which water droplets slide easily and more hydrophobic "curbs" that direct droplet motion. Contact angle and contact angle hysteresis both control the motion of liquid droplets on surfaces. The difference between the advancing contact angles of the two regions prevents the liquid from crossing the interface between them. The low hysteresis of the roads allows facile movement. Gravity (slight tilting of samples) forces droplets to move effortlessly in defined pathways even though the difference in contact angles is not large and both regions are hydrophobic.

Journal Article↗

PubMed2006

Proteomic analysis of Saccharomyces cerevisiae under high gravity fermentation conditions.

Saccharomyces cerevisiae KAY446 was utilized for ethanol production, with glucose concentrations ranging from 120 g/L (normal) to 300 g/L (high). Although grown in a high glucose environment, S. cerevisiae still retained the ability to produce ethanol with a high degree of glucose utilization. iTRAQ-mediated shotgun proteomics was applied to identify relative expression change of proteins under the different glucose conditions. A total of 413 proteins were identified from three replicate, independent LC-MS/MS runs. Unsurprisingly, many proteins in the glycolysis/gluconeogenesis pathway showed significant changes in expression level. Twenty five proteins involved in amino acid metabolism decreased their expression, while the expressions of 12 heat-shock related proteins were also identified. Under high glucose conditions, ethanol was produced as a major product. However, the assimilation of glucose as well as a number of byproducts was also enhanced. Therefore, to optimize the ethanol production under very high gravity conditions, a number of pathways will need to be deactivated, while still maintaining the correct cellular redox or osmotic state. Proteomics is demonstrated here as a tool to aid in this forward metabolic engineering.

Ethanol↗

PubMed2000

Differential accumulation of Aux/IAA mRNA during seedling development and gravity response in cucumber (Cucumis sativus L.).

The plant hormone auxin transcriptionally activates Aux/IAA genes. We have isolated three Aux/IAA cDNA from cucumber, two cDNAs (CS-IAA1 and CS-IAA2) containing the complete open reading frame (ORF), and one partial cDNA (CS-IAA3). Northern blotting analysis showed that Aux/IAA mRNAs were induced during the emergence of radicles from seed coats. After radicle emergence, their mRNAs accumulated in the basal part of the hypocotyl much more than in the apical part, and later in elongating region of hypocotyls. CS-IAAI and CS-IAA3 mRNA significantly accumulated in response to auxin, although the increment of the former mRNA accumulation by auxin application was much greater than that of the latter. CS-IAA2 did not show an apparent change by auxin treatment in our experiment. In horizontally germinating seedlings, the transition zone between hypocotyl and root curves was due to downward gravitropic growth. On the other hand, vertically germinating seedlings of cucumber do not curve in the early stage of seedling development. The CS-IAA1 mRNA accumulation in horizontally germinating seedlings was more than that in vertically germinating ones during radicle emergence. Furthermore, asymmetric distribution of CS-IAA1 mRNA was detected in the transition zone in in situ hybridization analysis. These results suggest that the CS-IAA1 gene product may be involved in the gravity response during early development of seedlings.

Amino Acid Sequence↗

PubMed2003

The center of gravity.

In "As far as possible': discovering our limits and finding ourselves" (Barish and Vida, 1998), we struggled with the constraints of being "two nice girls" in the context of our individual professional identities as traditionally trained psychoanalysts. We were surprised to discover, through sharing with one another some painful, confusing, and even terrifying clinical experiences, how wedded we were to certain psychoanalytic conventions. It was not a pleasant discovery. What we had to face was the extent of our submissiveness to psychoanalytic theory, and of the cost to our authentic selves of that submissiveness. This daughter-paper is about our learning not to do what we were supposed to do. Its gestation has taken a form that we could not have anticipated, for, as we pursued the writing of this sequel, we seemed to get lost along the way. After working with this over a very long time, we can see now that the paper that was ultimately born, this paper, has functioned as a vehicle for us to experience ourselves in relation in an uncertain, mingling way, conscious and unconscious, trying not to be self-conscious and not defensive. This, we can also see, is how we approach "the center of gravity," where our irreducible and irreconcilable tendencies are struggling to maintain a balance. And even more to the point, this paper is also a demonstration, a look at what developmental transformation is really like, the process to which we all give lip service, but hardly any of us ever pays attention to it in our "real" lives, and if we do, we never, never talk about it.

Adult↗

PubMed1995

Cognitive representation of motion: evidence for friction and gravity analogues.

Five experiments examined whether judgments of the locations of horizontally moving targets were influenced by implied friction between the targets and larger stationary surfaces. When targets crashed through a barrier, forward displacement decreased. When targets slid along the upper or lower edge of a single surface, forward displacement decreased. When targets slid along the upper or lower edge of a single surface, forward displacement decreased; when targets slid between the upper and lower edges of different surfaces, forward displacement decreased further. Targets not in contact with a surface exhibited larger forward displacement with greater target velocities, but contact with a surface attenuated or reversed this pattern. When targets slid along the upper edge of a surface, downward displacement increased; when targets slid along the lower edge of a surface, downward displacement reversed. Downward displacements were larger for larger targets, especially after contact with a surface. The data suggest that target representations contain analogues to friction and gravity that influence remembered position.

Adult↗

PubMedDate not supplied

Permanent distortion of positional system of Xenopus embryo by brief early perturbation in gravity.

The formation of a body plan from an initially radially symmetrical egg during animal development is presumed to involve a 'positional system'and a subsequent mechanism of local response to position values provided by this system. Early gene products intimately connected with the latter response mechanism have been identified in Drosophila, and because these share conserved sequences with possible counterparts in vertebrates , there is renewed interest in understanding the physiological nature of the positional system itself in a vertebrate embryo. In the frog Xenopus, body position value appears to be specified in outline across much of the egg material by stages comprising a few cells, after only approximately 2h of development. This is already suggestive of a structural or mechanical recording system rather than a diffusion-controlled gradient. I describe here an experiment aimed at perturbing the positional system by causing gravity-driven rearrangements within eggs which conflict with their own, self-organizing rearrangements near the time of the first cleavage. The system appears to retain its full regulatory properties during only a brief time interval, so that records of positional profiles disturbed at the close of that interval are permanent, and give rise to systematically abnormal body patterns in otherwise healthy larvae. The results are inconsistent with the notion that Xenopus primary pattern results from a set of determinant 'plasms' in the egg, or from a mechanism dominated by long-range diffusion of molecules.

Animals↗

PubMed2003

An extragalactic supernebula confined by gravity.

Little is known about the origins of globular clusters, which contain hundreds of thousands of stars in a volume only a few light years across. Radiation pressure and winds from luminous young stars should disperse the star-forming gas and disrupt the formation of the cluster. Globular clusters in our Galaxy cannot provide answers; they are billions of years old. Here we report the measurement of infrared hydrogen recombination lines from a young, forming super star cluster in the dwarf galaxy NGC5253. The lines arise in gas heated by a cluster of about one million stars, including 4,000-6,000 massive, hot 'O' stars. It is so young that it is still enshrouded in gas and dust, hidden from optical view. The gases within the cluster seem bound by gravity, which may explain why the windy and luminous O stars have not yet blown away those gases. Young clusters in 'starbursting' galaxies in the local and distant Universe may also be gravitationally confined and cloaked from view.

Journal Article↗

PubMed2001

Application of multistage continuous fermentation for production of fuel alcohol by very-high-gravity fermentation technology.

A fermentation system to test the merging of very-high-gravity (VHG) and multistage continuous culture fermentation (MCCF) technologies was constructed and evaluated for fuel ethanol production. Simulated mashes ranging from 15% to 32% w/v glucose were fermented by Saccharomyces cerevisiae and the dilution rates were adjusted for each glucose concentration to provide an effluent containing less than 0.3% w/v glucose (greater than 99% consumption of glucose). The MCCF can be operated with glucose concentrations up to 32% w/v, which indicates that the system can successfully operate under VHG conditions. With 32% w/v glucose in the medium reservoir, a maximum of 16.73% v/v ethanol was produced in the MCCF. The introduction of VHG fermentation into continuous culture technology allows an improvement in ethanol productivity while producing ethanol continuously. In comparing the viability of yeast by methylene blue and plate count procedures, the results in this work indicate that the methylene blue procedure may overestimate the proportion of dead cells in the population. Ethanol productivity (Yps) increased from the first to the last fermentor in the sequence at all glucose concentrations used. This indicated that ethanol is more effectively produced in later fermentors in the MCCF, and that the notion of a constant Yps is not a valid assumption for use in mathematical modeling of MCCFs.

Biomass↗

PubMed2005

Gravity-induced reorientation of the interface between two liquids of different densities flowing laminarly through a microchannel.

This paper experimentally quantifies the reorientation of the liquid-liquid interface between fluids of different densities flowing side-by-side in pressure-driven laminar flow in microchannels. A gravity-induced pressure mismatch at the interface will gradually drive the denser fluid to occupy the lower portion of the microchannel. The rate of this process is expected to depend on the interplay of viscous forces--which tend to dominate at the microscale-and inertial and gravitational forces. A correlation that relates the position of such a liquid-liquid interface to physical variables and channel dimensions was derived. The extent of reorientation of the streams was then related to two dimensionless numbers: Fr, the square root of the ratio of inertial to gravitational forces; and Re/Fr2, the ratio of gravitational to viscous forces. Further analysis showed that the reorientation of the streams depends only on the gravitational and viscous forces, but not inertia. The quantitative description of the position of the interface between liquids of different densities described in this paper aids in the rational design of the rapidly growing number of microchemical systems that utilize multistream laminar flow for performing spatially resolved chemistry and biology inside microfluidic channels.

Gravitation↗

PubMed1979

Impairment of flow in routine gravity-fed intravenous infusions to surgical patients.

1. Gravity-fed intravenous infusions were studied in patients by using continuous flow recording and a new resistance-measuring method. 2. A common, though preventable, cause of reduced flow was the gradual deformation of the plastic tubing under the regulator clamp. 3. In many cases there was some constriction of the cannulated vein and in a few this constriction was severe enough to seriously impair the infusion. The severity of the constriction varied periodically. 4. There was no evidence of troble due to a generally raised pressure in the arm veins nor was clotting in the cannula a serious problem. 5. A simple test is described which may be found useful clinically for assessing the difficult infusion.

Arm↗

PubMed2001

Determination of a gravity and shock score for prognosis in equine surgical colic.

A retrospective study evaluated 200 surgical colic cases. A gravity score (GS) based on four clinical parameters estimating intestinal obstruction (rectal palpation, borborygmi, abdominal distension, pain) and classified into three categories was established and tested to determine if it could evaluate prognosis. A shock score (SS) based on six parameters was also attributed to each case. The overall survival rate was 54%. The statistical analysis showed a significant (P < 0.01) difference in the survival rate in the different categories of the GS, as well as in the categories of the SS. A multivariate logistic regression model showed that horses with GS 3 are 10.6 times more likely to die than those with GS 1. A model combining the two scores showed an odds ratio of 7.1 for GS 3 versus GS 1, and for SS 3 versus SS 1, the odds ratio was 7.2.

Animals↗