Rat muscle plasticity in response to simulated or real microgravity.
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Animals↗
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Body volume changes during simulated microgravity: auditory changes, segmental fluid redistribution, and regional hemodynamics.
Space adaptation syndrome (SAS), manifested by cephalad fluid shifts, spacial disorientation, nausea, and vomiting, is of varied expression and uncertain etiology. One theory is that fluid shift to the upper body alters the function of the vestibular apparatus to create an entity similar to Meniere's disease. Since clinical vestibular dysfunction syndromes are mirrored by altered cochlear function, this experiment was undertaken to study the relation between fluid redistribution and the auditory effects of initial antiorthostatic bed rest. Manual and bone audiometry, impedance tympanometry, and brain-stem evoked potentials were used to monitor auditory changes prior to, during, and following short term exposure to -6 degrees head down tilt. Impedance plethysmography was performed to assess the segmental and intracranial fluid redistribution and hemodynamic changes during short-term head down tilt simulated microgravity. Even though significant cephalad fluid shift produced marked intracranial congestion and the subjects exhibited SAS symptoms, no clinically significant changes in the auditory system could be detected.
Acoustic Impedance Tests↗
Improving the temporal resolution of functional MR imaging using keyhole techniques.
Using a keyhole technique, it is shown that the data acquisition rate of gradient-echo imaging for functional MRI (fMRI) studies can be increased substantially. The resulting enhancement of the temporal resolution of fMRIs was accomplished without modifying the hardware of a conventional MRI system. High spatial resolution fMRI images were first collected with conventional full k-space acquisition and image reconstruction. Using the same data set, simulation reconstruction using the keyhole principle and zero-padding were performed for comparison with the full k-space reconstruction. No significant changes were found for fMRI images generated from the keyhole technique with a data sharing profile of 50% of the k-space. As k-space data sharing profiles increased to 75 and 87.5%, the keyhole fMRI images began to show only modest changes in activation intensity and area compared with the standard images. In contrast, zero-padding fMRI images produced a significant disparity both in activation intensity and area relative to the truly high-resolution fMRI images. The keyhole technique's ability to retain the intensity and area of fMRI information, while substantially reducing acquisition time, makes it a promising method for fMRI studies.
Adult↗
A simulation study comparing different experimental designs for estimating uptake and elimination rates.
The design of ecotoxicological studies requires decisions about the number and spacing of exposure groups tested, the number of replications, the spacing of sampling times, the duration of the study, and other considerations. For example, geometric spacing of sampling times or toxicant concentrations is often used as a default design. Optimal design methods in statistics can suggest alternative spacing of sampling times that yield more precise estimates of regression coefficients. In this study, we use a computer simulation to explore the impact of the spacing of sampling times and other factors on the estimation of uptake and elimination rate constants in an experiment addressing the bioaccumulation of a contaminant. Careful selection of sampling times can result in smaller standard errors for the parameter estimates, thereby allowing the construction of smaller, more precise confidence intervals. Thus, the effort invested in constructing an optimal experimental design may result in more precise inference or in a reduction of replications in an experimental design.
Animals↗
Designing generalized statistical ensembles for numerical simulations of biopolymers.
Conformational properties of polymers, such as average dihedral angles or molecular alpha-helicity, display a rather weak dependence on the detailed arrangement of the elementary constituents (atoms). We propose a computer simulation method to explore the polymer phase space using a variant of the standard multicanonical method, in which the density of states associated to suitably chosen configurational variables is considered in place of the standard energy density of states. This configurational density of states is used in the Metropolis acceptance/rejection test when configurations are generated with the help of a hybrid Monte Carlo algorithm. The resulting configurational probability distribution is then modulated by exponential factors derived from the general principle of the maximal constrained entropy by requiring that certain average configurational quantities take preassigned (possibly temperature dependent) values. Thermal averages of other configurational quantities can be computed by using the probability distributions obtained in this way. Moments of the energy distribution require an extra canonical sampling of the system phase space at the desired temperature, in order to locally thermalize the configurational degrees of freedom. As an application of these ideas we present the study of the structural properties of two simple models: a bead-and-spring model of polyethylene with independent hindered torsions and an all-atom model of alanine and glycine oligomers with 12 amino acids in vacuum.
Biopolymers↗
Nanofabrication of a space-variant optical transmission filter.
A space-variant optical transmission filter is demonstrated for which a simplified process is used to tailor the spatial response of the filter across the surface of a single wafer. A multilayer stack, of alternating high or low refractive index dielectric materials, was used to produce a narrow transmission notch in the center of a wide stop band. Subsequent patterning and etching of arrays of holes through the volume of the dielectric stack was performed to control the fill factor of the dielectric in the layers. The position of the transmission notch within the reflection spectrum was varied across the device surface by adjusting the hole diameter of the hole arrays. Experimental and numerical simulation were used to confirm the space-variant transmission characteristics of a single-wafer sample with two zones of different hole diameter arrays in the 1550 nm wavelength regime.
Journal Article↗
Computational modelling of effect of tonsillectomy on voice production.
The aim of this study is to develop mathematical 3D finite element (FE) models for numerical simulations of vibroacoustic properties of the human vocal tract after a tonsillectomy. Similar experimental studies are not easily realizable on living subjects. The FE models of the acoustic spaces corresponding to the human vocal tract for the Czech vowels /a:/ and /i:/ and the acoustic space around the human head were used in numerical simulations of phonation. The acoustic resonant characteristics of the FE models were studied using modal and transient analyses (excitation by a short pulse). Calculated results show that a tonsillectomy causes a frequency shift of the 3rd (down by approximately 180 Hz) and 4th (down by approximately 120 Hz) formants down to the lower frequencies for the vowel /a:/ and similarly for the 2nd, 4th and 5th formants for the vowel /i:/ (all down by approximately 100 Hz). Similar effects and results can be found in experimental studies in literature. The formant changes are dependent on the size of additional acoustic spaces that occur after a tonsillectomy. The verification of the model was performed on the recordings of patients before and after the tonsillectomy operation. Multi-Dimensional Voice Program (MDVP Advanced, KAY Elemetrics Corp.) was used for the comparing of the formant centre frequencies. Very small differences in the results of subjective evaluation of the voice before and after tonsillectomy were found.
Adolescent↗
Formation of bioorganic compounds in simulated planetary atmospheres by high energy particles or photons.
Various types of organic compounds have been detected in Jupiter, Titan, and cometary coma. It is probable that organic compounds were formed in primitive Earth and Mars atmospheres. Cosmic rays and solar UV are believed to be two major energy sources for organic formation in space. We examined energetics of organic formation in simulated planetary atmospheres. Gas mixtures including a C-source (carbon monoxide or methane) and a N-source (nitrogen or ammonia) was irradiated with the followings: High energy protons or electrons from accelerators, gamma-rays from 60Co, UV light from a deuterium lamp, and soft X-rays or UV light from an electron synchrotron. Amino acids were detected in the products of particles, gamma-rays and soft X-rays irradiation from each gas mixture examined. UV light gave, however, no amino acid precursors in the gas mixture of carbon monoxide, nitrogen and nitrogen. It gave only a trace of them in the gas mixture of carbon monoxide, ammonia and water or that of methane, nitrogen and water. Yield of amino acid precursors by photons greatly depended on their wavelength. These results suggest that nitrogen-containing organic compounds like amino acid precursors were formed chiefly with high energy particles, not UV photons, in Titan or primitive Earth/Mars atmospheres where ammonia is not available as a predominant N-source.
Alanine↗
Modelling inorganic solids and their interfaces: a combined approach of atomistic and electronic structure simulation techniques.
We are seeking to combine the reliability of the structures and energies obtained from quantum mechanical methods with the insights given by larger scale simulations, which are better able to search configurational space. We will discuss our recent work using quantum mechanical methods, based on DFT, which have been applied to the study of a number of solids. Al2O3, CeO2, MnO2 and CaCO3, and compare these with results using atomistic simulation where the forces between atoms are modelled using interatomic potentials. The results show that such quantum methods can be used successfully to screen the different potential models and where necessary, provide sufficient data to allow us to re-consider the potential models. In addition, we show examples where the quantum based methods can give further insights into the reactivity, particularly of surfaces. However, it still remains computationally expensive to search all possible configurations and by using the atomistic simulations to search through different configurations we can identify new structures which can be verified with the quantum based simulations.
Journal Article↗
Accuracy and resolution power of aerosol-derived airway morphometry in a simple lung model.
Aerosol-derived airway morphometry (ADAM) uses sedimentational deposition of monodisperse aerosol particles during breathhold to estimate intrapulmonary air-space dimensions. To determine the accuracy and resolution power of this technique a simple physical lung model comprised of uniform glass beads was investigated. Using the chordlength model, aerosol recovery from this porous medium was calculated by computer simulation of the geometrical structure of air-spaces between glass beads. The results of this calculation were then compared with experimental data: Calculated and measured air-space dimensions differ less than 2% for particles with diameters above about 1 micron. The measured air-space dimension can be described geometrically by the mean chordlength of the porous medium. To estimate the resolution power of ADAM, a defined change in air-space dimensions represented by a horizontal air slit was introduced into the porous medium. This air slit induces a marked increase of measured air-space dimensions. The volumetric width of this increase is the higher the deeper the slit is situated within the medium. Intercomparison of these data with the results of aerosol bolus dispersion measurements suggests that the resolution power of ADAM is decreased by the same mechanisms that increase dispersion of aerosol boluses, demonstrating the close relationship between both methods.
Aerosols↗
Review of spaceflight and hindlimb suspension unloading induced sarcomere damage and repair.
Hindlimb suspension unloading (HSU) and spaceflight microgravity induce atrophy of the slow adductor longus muscle fibers which, following reloading, exhibit eccentric contraction (EC)-like lesions (abnormal widening of sarcomeres with A band disruption and excessively wavy, extracted Z lines). These lesions are similar morphologically to those produced in normal muscles after strenuous eccentric exercise. It appears that atrophic muscles exhibit increased susceptibility to eccentric damage because lesions are produced during nonstressful voluntary movements upon return to weightbearing. The EC-like lesions are absent in the unweighted conditions, but appear in HSU rats 15-60 minutes after reloading and in space-flown rates about 4 hrs after landing. By 12 hours, many EC-like lesioned sarcomeres are fully covered by longitudinal patches of Z line-like material which increases in density by 48 hours, producing the so-called "Z line streaming" morphology. In this case, Z line streaming is indicative of rapid repair of damaged sarcomeres rather than the onset of sarcomere breakdown. Immunoelectron microscopy is necessary to determine the composition of this dense material. By 9 days of reloading at 1 gravity, sarcomeres have regained normal structure, except for very rare persistence of faint Z patches. The morphological data indicate that Z patches serve at least two functions: 1) to permit contractile force to be transmitted across the damaged sarcomeres and 2) to provide a scaffold upon which sarcomeres are reconstructed in an active functional muscle.
Animals↗
Simulating and testing visual exploration in spatial neglect based on a new model for cortical coordinate transformation.
Most studies of object and space perception have focused on neural representations of either object-centered or egocentric coordinate systems. But daily life requires interactions of both kinds of coordinates. We have recently proposed an 'integrated space-object (ISO-) map' combining both coordinate systems in one representation. Based on a lesioned version of this model, here we present results from visual search simulations demonstrating that the model accounts for contralesional neglect during space-centered and object-centered exploration tasks. Interestingly, the model simulations also predicted an amelioration of neglect symptoms during exploration with more ipsilesional object positions. By measuring the eye movements of neglect patients during different exploratory tasks, we confirmed all model predictions. These results corroborate the view that the brain might combine coordinates for object and space perception in an integrated coordinate system as suggested by the ISO-map model.
Aged↗
Effect of simulated microgravity on the production of IL-12 by PBMCs.
During space flight immunity is altered. This phenomenon is partly due to the microgravity condition itself. Our earlier space experiments (INTERFERON) indicated that microgravity has a significant effect at the cellular level. In our subsequent terrestrial studies we applied the Rotating Cell Culture System (RCCS) developed by NASA to mimick microgravity on ground. Previously we reported that human peripheral blood mononuclear cells (PBMCS) respond to simulated microgravity conditions with elevated tumor necrosis factor-alpha (TNF-alpha) production. We extended our investigations to the production of interleukin (IL)-12 under modelled microgravity conditions by separated PBMCs. In simulated microgravity we found significantly elevated level of secreted IL-12 compared to static, standard tissue culture conditions. Following a maximum of TNF-alpha production at 24 hours, the peak of IL-12 production was observed at 48 hours after the start of the experiment. Our results suggest that simulated microgravity favors the establishment of a Th1 type cytokine response.
Journal Article↗
Mass-weighted molecular dynamics simulation of cyclic polypeptides.
A modified molecular dynamics (MD) method in which atomic masses are weighted was developed previously for studying the conformational flexibility of neuroregulating tetrapeptide Phe-Met-Arg-Phe-amide (FMRF-amide). The method has now been applied to longer and constrained molecules, namely a disulfide-linked cyclic hexapeptide, c[CYFQNC], and its linear and "pseudo-cyclic" analogues. The sampling of dehedral conformational space of teh linear hexapeptide in mass-weighted MD simulations was found to be improved significantly over conventional MD simulations, as in the case of the shorter FMRF-amide molecule studied previously. In the cyclic hexapeptide, the internal constraint of the molecule due to the intramolecular disulfide bond (hence the absence of free terminals in the molecule) does not adversely affect the significant improvement of conformational sampling in mass-weighted MD simulations over normal MD simulations. The pseudo-cyclic polypeptide is identical to the linear CYFQNC molecule in amino acid sequence (i.e., side chains of the cysteine residues are reduced), but the positions of its two terminal heavy atoms were held fixed in space such that the molecule has a nearly cyclic conformation. For this molecule, the mass-weighted MD simulation generated a wide range of polypeptide backbone conformations covering the internal dihedral degrees of freedom; moreover, the physical space of the pseudo-cyclic structure was also sampled in a complete revolution of the entire molecular fragment about the two fixed termini during the simulation. These characteristics suggest that mass-weighted MD can also be an extremely useful method for conformational analyses of constrained molecules and, in particular, for modeling loops on protein surfaces.
Amino Acid Sequence↗
Chaos control by using Motor Maps.
In this paper a new method for chaos control is proposed, consisting of an unsupervised neural network, namely a Motor Map. In particular a feedback entrainment scheme is adopted: a chaotic system with a given parameter set generates the reference trajectory for another chaotic system with different parameters to be controlled: the Motor Map is required to provide the appropriate time-varying gain value for the feedback signal. The state of the controlled system is considered as input to the Motor Map. Particular efforts have been paid to the feasibility of the implementation. Indeed, the simulations performed have been oriented to design a Motor Map suitable for an hardware realization, thus some restrictive hypotheses, such as for example a low number of neurons, have been assumed. A huge number of simulations has been carried out by considering as system to be controlled a Double Scroll Chua Attractor as well as other chaotic attractors. Several reference trajectories have also been considered: a limit cycle generated by a Chua's circuit with different parameters values, a double scroll Chua attractor, a chaotic attractor of the family of the Chua's circuit attractors. In all the simulations instead of controlling the whole state space, only two state variables have been fed back. Good results in terms of settling time (namely, the period in which the map learns the control task) and steady state errors have been obtained with a few neurons. The Motor Map based adaptive controller offers high performances, specially in the case when the reference trajectory is switched into another one. In this case, a specialization of the neurons constituting the Motor Map is observed: while a group of neurons learns the appropriate control law for a reference trajectory, another group specializes itself to control the system when the other trajectory is used as a reference. A discrete components electronic realization of the Motor Map is presented and experimental results confirming the simulation results are shown. (c) 2002 American Institute of Physics.
Journal Article↗
Experimental studies on effects of simulated weightlessness on myocardial function and structure.
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Adrenergic beta-Agonists↗
[Expression of PIN and AUX1 genes encoding carrier proteins for auxin polar transport in higher plants under simulated microgravity conditions on a three-dimensional clinostat].
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Arabidopsis↗
Johnson Space Center's Regenerative Life Support Systems Test Bed.
The Regenerative Life Support Systems (RLSS) Test Bed at NASA's Johnson Space Center is an atmospherically closed, controlled environment facility for human testing of regenerative life support systems using higher plants in conjunction with physicochemical life support systems. The facility supports NASA's Advanced Life Support (ALS) Program. The facility is comprised of two large scale plant growth chambers, each with approximately 11 m2 growing area. The root zone in each chamber is configurable for hydroponic or solid media plant culture systems. One of the two chambers, the Variable Pressure Growth Chamber (VPGC), is capable of operating at lower atmospheric pressures to evaluate a range of environments that may be used in a planetary surface habitat; the other chamber, the Ambient Pressure Growth Chamber (APGC) operates at ambient atmospheric pressure. The air lock of the VPGC is currently being outfitted for short duration (1 to 15 day) human habitation at ambient pressures. Testing with and without human subjects will focus on 1) integration of biological and physicochemical air and water revitalization systems; 2) effect of atmospheric pressure on system performance; 3) planetary resource utilization for ALS systems, in which solid substrates (simulated planetary soils or manufactured soils) are used in selected crop growth studies; 4) environmental microbiology and toxicology; 5) monitoring and control strategies; and 6) plant growth systems design. Included are descriptions of the overall design of the test facility, including discussions of the atmospheric conditioning, thermal control, lighting, and nutrient delivery systems.
Atmospheric Pressure↗