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PubMed2006

Optimisation of halogenase enzyme activity by application of a genetic algorithm.

A genetic algorithm (GA) was applied for the optimisation of an enzyme assay composition respectively the enzyme activity of a recombinantly produced FADH(2)-dependent halogenating enzyme. The examined enzyme belongs to the class of halogenases and is capable to halogenate tryptophan regioselective in position 5. Therefore, the expressed trp-5-halogenase can be an interesting tool in the manufacturing of serotonin precursors. The application of stochastic search strategies (e.g. GAs) is well suited for fast determination of the global optimum in multidimensional search spaces, where statistical approaches or even the popular classical one-factor-at-a-time method often failures by misleading to local optima. The concentrations of six different medium components were optimised and the maximum yield of the halogenated tryptophan could be increased from 3.5 up to 65%.

Algorithms↗
PubMed1993

Effect of restoration thickness on the sealing ability of TERM.

An in vitro study was done using a fluid filtration device to compare microleakage of Temporary Endodontic Restorative Material (TERM) at various thicknesses. Forty-four extracted mandibular molars had their roots removed at the cementoenamel junction, occlusal table flattened, and a standardized endodontic access made in the crown. The teeth were restored with TERM in thicknesses of 1, 2, 3, and 4 mm, and quantitatively measured for leakage (microliters/min) at intervals of 1 and 24 h and 1, 3, and 5 wk. Thermocycling was accomplished at the 5-wk interval. Positive controls received 4-mm-thick IRM or gutta-percha restorations and were measured at 24 h only. Repeated measures of analysis of variance found no significant difference (p < 0.05) in leakage values in any group over time or between any of the different thicknesses. Positive controls showed significantly more leakage than all other groups. TERM maintained as tight a seal at 1-, 2-, and 3-mm thicknesses as it did at 4 mm and may be suited for clinical situations where less than 4 mm of restorative space exists.

Analysis of Variance↗
PubMedDate not supplied

Finite group theory for large systems. 2. Generating relations and irreducible representations for the icosahedral point group, I(h).

Generating relations and irreducible representations are given for the icosahedral point group, I(h), that are suited to computerized projection of symmetry-adapted bases of arbitrary spaces invariant to the group. With 120 elements I(h ) is a good prototype for symmetry-adaptation to a large finite nonabelian group. The four- and five-dimensional irreducible representations are obtained by coupling direct products of the three-dimensional irreducible representations using the symmetry-adaptation algorithm. The method is applied to the Hückel treatment of icosahedral C(20) fullerene.

Journal Article↗
PubMed2002

Astrocyte modulation of neurotoxic injury.

Astrocytes produce trophic factors, regulate neurotransmitter and ion concentrations, and remove toxins and debris from the extracellular space of the CNS, maintaining an extracellular milieu that is optimally suited for neuronal function. Consequently, astrocytic functional impairments, as well as physiological reactions of astrocytes to injury have the potential to induce and/or exacerbate neuronal dysfunction. This mini-review showcases contemporary evidence provoking reformulation of concepts of the inter-dependence between astrocytes and neurons and advances several mechanisms used by astrocytes in potentiating or nullifying the final pathway of neuropathologic injury. Though clearly possessing an array of protective systems and upregulating a large number of protective molecules in response to xenobiotic exposure, recent evidence also invokes astrocytes in secondary amplification of cell injury in multiple neurodegenerative disorders.

Animals↗
PubMed1991

Perpetuation of misinterpretations due to lack of methodical insight. A critical re-evaluation of the determination of 45Ca release from intact guinea-pig atria.

1. The evaluation of still more pretentious and complicated methods is accompanied by a decline of methodical knowledge outside of the own technical field. Interpretations or extrapolations are taken as granted without critical examination of the methodical steps applied. An example is given by re-evaluating the 45Ca release from isolated cardiac tissue and the possible interpretations. 2. 45Ca release and tissue Ca content were measured in isolated guinea-pig left atria during Ca equilibrium and under conditions known to induce net Ca movements. 3. At equilibrium condition (1.8 mM Na2+0) 3 exponential phase of 45Ca release from the atria were observed. The compartments contained 61%, 29% and 10% of total 45Ca; the t1/2 were 2, 12 and 90 min, respectively. 4. The release of 45Ca from the slowly exchanging compartment (t1/2 90 min) decreased during incubation in nominal Ca-free solution, although a net loss of tissue Ca occurred. Addition of EGTA (5 x 10(-5) M) to the washout medium abolished this retardation of 45Ca release. 5. At external Na+ concentrations below 40 mM (substituted by sucrose), the 45Ca release from the slowly exchanging compartment decreased. Simultaneously, the tissue Ca content increased massively. The 45Ca release was further reduced in Na-poor, nominal Ca-free solution. Under both conditions, the presence of EGTA in the washout medium normalized the rate of 45Ca release. 6. The results suggest that the apparent decline of 45Ca release from intact atria upon reduction of the external Ca and Na concentration does not reflect a decrease of the cellular efflux rate, but is the consequence of an enhanced re-uptake of 45Ca from the extracellular space into the myocardial cells. The probability for the released 45Ca either to escape into the organ bath or to become reabsorbed depends on the specific radioactivity of 45Ca in the extracellular space during the washout phase. Thus, this experimental procedure is not suited to demonstrate a Na-Ca exchange at the cardiac sarcolemma.

Animals↗
PubMedDate not supplied

Robonaut: a robot designed to work with humans in space.

The Robotics Technology Branch at the NASA Johnson Space Center is developing robotic systems to assist astronauts in space. One such system, Robonaut, is a humanoid robot with the dexterity approaching that of a suited astronaut. Robonaut currently has two dexterous arms and hands, a three degree-of-freedom articulating waist, and a two degree-of-freedom neck used as a camera and sensor platform. In contrast to other space manipulator systems, Robonaut is designed to work within existing corridors and use the same tools as space walking astronauts. Robonaut is envisioned as working with astronauts, both autonomously and by teleoperation, performing a variety of tasks including, routine maintenance, setting up and breaking down worksites, assisting crew members while outside of spacecraft, and serving in a rapid response capacity.

Artificial Intelligence↗
PubMed2002

[New possibilities of the use of space technologies in the treatment of children with injuries of the central nervous system].

The computerized stabilography was used to study the role of the visual analyzer (VA) in vertical posture acquisition and specifics of posture implementation by patients with craniocerebral injury (CCI) wearing suit Adele for dynamic proprioception correction (SDPC). Results of the investigation revealed a decreased vertical stability (VS) of CCI patients and a greater reliance on VA, which may be a compensatory instrument. Following the SDPC course, vertical stability was improved and the VA role in posture acquisition normalized suggesting alteration of the interanalyzer interaction in CCI patients owing to the treatment of proprioception impulsation.

Accidental Falls↗
PubMed1995

The impact of culture on human and space development--new millennial challenge.

The Space Age is causing new applications to the concept of culture, a human coping tool. The exploration and exploitation of outer space resources are altering human culture both on Earth and in orbit. For the first time in history, our species need not merely react and adapt to environment, but plan for a space culture appropriate for extraterrestrial migration. The impact of culture can be analyzed in terms of how space developments alter human perceptions and behavior on this planet; the emergence of a new culture to suit the orbital environment; the organizations that build spacecraft and deploy people aloft; and the technological systems created for spacefaring. This article presents a paradigm for analyzing some of the non-technical human factors involved in space undertakings. It also offers a method for classifying a culture according to ten categories which may be applied both to a macroculture, such as a lunar base; or a microculture, such as a space agency or crew. Human enterprise in space is viewed as both altering the species, and providing a challenge for expanded behavioral and biological scientific research on living and working in space.

Adaptation, Psychological↗
PubMed2003

Sonification of range information for 3-D space perception.

We present a device that allows three-dimensional (3-D) space perception by sonification of range information obtained via a point laser range sensor. The laser range sensor is worn by a blindfolded user, who scans space by pointing the laser beam in different directions. The resulting stream of range measurements is then converted to an auditory signal whose frequency or amplitude varies with the range. Our device differs from existing navigation aids for the visually impaired. Such devices use sonar ranging whose primary purpose is to detect obstacles for navigation, a task to which sonar is well suited due to its wide beam width. In contrast, the purpose of our device is to allow users to perceive the details of 3-D space that surrounds them, a task to which sonar is ill suited, due to artifacts generated by multiple reflections and due to its limited range. Preliminary trials demonstrate that the user is able to easily and accurately detect corners and depth discontinuities and to perceive the size of the surrounding space.

Acoustics↗
PubMedDate not supplied

Development of an advanced rocket propellant handler's suit.

Most launch vehicles and satellites in the US inventory rely upon the use of hypergolic rocket propellants, many of which are toxic to humans. These fuels and oxidizers, such as hydrazine and nitrogen tetroxide have threshold limit values as low as 0.01 PPM. It is essential to provide space workers handling these agents whole body protection as they are universally hazardous not only to the respiratory system, but the skin as well. This paper describes a new method for powering a whole body protective garment to assure the safety of ground servicing crews. A new technology has been developed through the small business innovative research program at the Kennedy Space Center. Currently, liquid air is used in the environmental control unit (ECU) that powers the propellant handlers suit (PHE). However, liquid air exhibits problems with attitude dependence, oxygen enrichment, and difficulty with reliable quantity measurement. The new technology employs the storage of the supply air as a supercritical gas. This method of air storage overcomes all of three problems above while maintaining high density storage at relatively low vessel pressures (<7000 kPa or approximately 1000 psi). A one hour prototype ECU was developed and tested to prove the feasibility of this concept. This was upgraded by the design of a larger supercritical dewar capable of holding 7 Kg of air, a supply which provides a 2 hour duration to the PHE. A third version is being developed to test the feasibility of replacing existing air cooling methodology with a liquid cooled garment for relief of heat stress in this warm Florida environment. Testing of the first one hour prototype yielded data comparable to the liquid air powered predecessor, but enjoyed advantages of attitude independence and oxygen level stability. Thermal data revealed heat stress relief at least as good as liquid air supplied units. The application of supercritical air technology to this whole body protective ensemble marked an advancement in the state-of-the-art in personal protective equipment. Not only was long duration environmental control provided, but it was done without a high pressure vessel. The unit met human performance needs for attitude independence, oxygen stability and relief of heat stress. This supercritical air (and oxygen) technology is suggested for microgravity applications in life support such as the Extravehicular Mobility Unit.

Adult↗
PubMed1991

+Gx-tolerance in the final stage of space flights of various durations.

Study of acceleration tolerance at the final stage of orbital flights after exposure to weightlessness is an important element of medical support of space flights. The cosmonauts tolerance to accelerations has been analyzed during 38 space missions of 8- to 326-day duration. Tolerance to acceleration during descent in all cases was estimated as satisfactory. Acceleration tolerance during the final stage of orbital flights depended on flight duration, individual tolerance and use of countermeasures.

Acceleration↗
PubMed2005

Accelerating MR diffusion tensor imaging via filtered reduced-encoding projection-reconstruction.

MR diffusion tensor imaging (DTI) is a promising tool for characterizing the microstructure of ordered tissues. However, its practical applications are hampered by relatively low signal-to-noise-ratio and spatial and temporal resolution. Reduced-encoding imaging (REI) via k-space sharing with constrained reconstruction has previously been shown to be effective for accelerating DTI, although the implementation was based on rectilinear k-space sampling. Due to the intrinsic oversampling of central k-space and allowance for isotropic downsampling, projection-reconstruction (PR) imaging may be better suited for REI. In this study, regularization procedures, including radial filtering and baseline signal correction to adequately reconstruct reduced encoded PR imaging data, are investigated. The proposed filtered reduced-encoding projection-reconstruction (FREPR) technique is applied to DTI tissue fiber orientation and fractional anisotropy (FA) measurements. Results show that FREPR offers improved reconstructions of the reduced encoded images and on an equal total scan-time basis provides more accurate fiber orientation and FA measurements compared to rectilinear k-space sampling-based REI methods or a control experiment consisting of only fully encoded images. These findings suggest a potentially significant role of FREPR in accelerating repeated imaging and improving the data acquisition-time efficiency of DTI experiments.

Computer Simulation↗
PubMed1996

SRS-FT, a Fourier imaging method based on sparse radial scanning and Bayesian estimation.

A new 3D Fourier imaging method based on sparse radial scanning (SRS-FT) of k space is proposed. It allows acquisition of FIDs and is therefore well suited to imaging objects with very short T2. Use of a Bayesian procedure allows (1) an important reduction of scan time to below that of the projection-reconstruction (PR) method by reducing the number of "Cartesian radial" encoding directions, and (2) a good image quality by estimating missing and corrupted Cartesian samples. SRS-FT images reconstructed from FIDs are compared to conventional FT and PR images.

Bayes Theorem↗
PubMed2000

Combined space-variant maps for optical-flow-based navigation.

A robot navigating in an unstructured environment needs to avoid obstacles in its way and determine free spaces through which it can safely pass. We present here a set of optical-flow-based behaviors that allow a robot moving on a ground plane to perform these tasks. The behaviors operate on a purposive representation of the environment called the "virtual corridor" which is computed as follows: the images captured by a forward-facing camera rigidly attached to the robot are first remapped using a space-variant transformation. Then, optical flow is computed from the remapped image stream. Finally, the virtual corridor is extracted from the optical flow by applying simple but robust statistics. The introduction of a space-variant image preprocessing stage is inspired by biological sensory processing, where the projection and remapping of a sensory input field onto higher-level cortical areas represents a central processing mechanism. Such transformations lead to a significant data reduction, making real-time execution possible. Additionally, they serve to "re-present" the sensory data in terms of ecologically relevant features, thereby simplifying the interpretation by subsequent processing stages. In accordance with these biological principles we have designed a space-variant image transformation, called the polar sector map, which is ideally suited to the navigational task. We have validated our design with simulations in synthetic environments and in experiments with real robots.

Animals↗
PubMed2006

Residual solvent analysis by gas chromatography in radiopharmaceutical formulations containing up to 12% ethanol.

For the detection and quantification of residual solvents in solutions of radiopharmaceuticals for human applications, a new analysis method was set up. With a simple direct gas chromatography injection, no special sample treatments or special injection techniques (such as head-space or solid-phase microextraction) are necessary. This method is especially suited for the fast and quantitative analysis of residual solvents in radiopharmaceutical formulations where 5-12% ethanol is present. The method proved to be both accurate and linear. The quantification limit is in the lower parts-per-million range, which is sufficient given the need for a fast analysis and the maximally allowed concentration for these residual solvents.

Chemistry, Pharmaceutical↗
PubMed2000

Early treatment of vertical skeletal dysplasia: the hyperdivergent phenotype.

This cephalometric study evaluated an early nonextraction treatment approach for patients with severe vertical skeletal dysplasia and maxillary transverse constriction. Thirty-eight patients, 8.2 years (+/- 1.2 years) of age, were treated for 1.3 years (+/- 0.3 years) with lip seal exercises, a bonded palatal expander appliance, and a banded lower Crozat/lip bumper. The bonded palatal expander functioned as a posterior bite-block and was fixed in place throughout treatment. Patients with poor masticatory muscle force (79%) wore a high-pull chincup 12 to 14 hours per day. A control group was matched for age, sex, and mandibular plane angle. Treatment changes for chincup and other patients were not significantly different. Overall, treatment significantly enhanced condylar growth, altered it to a more anterosuperior direction, and produced "true" forward mandibular rotation 2.7 times greater than control values. Posterior facial height increased significantly more in patients than in controls, and the maxillary molars showed relative intrusion. In treated patients, articular angle increased, gonial angle decreased, and the chin moved anteriorly twice as much as in controls. Treatment also led to increased overbite and decreased overjet. Maxillary and mandibular expansion did not cause the mandibular plane angle to increase. The 16 patients with openbite malocclusions exhibited a 2.7 mm increase in overbite and inhibition of growth in anterior lower facial height. The aggregate of individual changes demonstrates a net improvement, indicating this treatment approach may be suited for hyperdivergent patients with skeletal discrepancies in all 3 planes of space.

Case-Control Studies↗
PubMed2004

Tonic inhibition in mouse hippocampal CA1 pyramidal neurons is mediated by alpha5 subunit-containing gamma-aminobutyric acid type A receptors.

The principal inhibitory neurotransmitter in the mammalian brain, gamma-aminobutyric acid (GABA), is thought to regulate memory processes by activating transient inhibitory postsynaptic currents. Here we describe a nonsynaptic, tonic form of inhibition in mouse CA1 pyramidal neurons that is generated by a distinct subpopulation of GABA type A receptors (GABA(A)Rs). This tonic inhibitory conductance is predominantly mediated by alpha5 subunit-containing GABA(A)Rs (alpha5GABA(A)Rs) that have different pharmacological and kinetic properties compared to postsynaptic receptors. GABA(A)Rs that mediate the tonic conductance are well suited to detect low, persistent, ambient concentrations of GABA in the extracellular space because they are highly sensitive to GABA and desensitize slowly. Moreover, the tonic current is highly sensitive to enhancement by amnestic drugs. Given the restricted expression of alpha5GABA(A)Rs to the hippocampus and the association between reduced alpha5GABA(A)R function and improved memory performance in behavioral studies, our results suggest that tonic inhibition mediated by alpha5GABA(A)Rs in hippocampal pyramidal neurons plays a key role in cognitive processes.

Animals↗