Swimming behaviour and calcium incorporation into inner ear otoliths of fish after vestibular nerve transection.

Previous investigations on neonate swordtail fish (Xiphophorus helleri) revealed that otolithic calcium incorporation (visualized using the calcium tracer alizarin complexone) and thus otolith growth had ceased after nerve transection, supporting a hypothesis according to which the gravity-dependent otolith growth is regulated neuronally. Subsequent investigations on larval cichlid fish (Oreochromis mossambicus) yielded contrasting results, repeatedly depending on the particular batch of cichlids investigated. Like most neonate swordtails, Type I cichlids revealed a stop of calcium incorporation after unilateral vestibular nerve transection. Their behaviour after transection was normal, and the otolithic calcium incorporation in controls of the same batch was symmetric. In Type II cichlids, however, vestibular nerve transection had no effect on otolithic calcium incorporation. They behaved kinetotically after transection (this kind of kinetosis was qualitatively similar to the swimming behaviour exhibited by larval cichlids during microgravity in the course of parabolic aircraft flights). The otolithic calcium incorporation in control animals was asymmetric. These results show that the effects of vestibular nerve transection as well as the efficacy of the mechanism, which regulates otolith growth/otolithic calcium incorporation, are--depending on the particular batch of animals--genetically predispositioned. In conclusion, the regulation of otolithic calcium incorporation is guided neuronally, in part via the vestibular nerve and, in part, via a further pathway, which remains to be addressed in the course of future investigations.     

Large light X-ray optics: basic ideas and concepts

One of the main guidelines for future X-ray astronomy projects like, e.g., XEUS (ESA) and Generation-X (NASA) is to utilize grazing-incidence focusing optics with extremely large telescopes (several tens of m² at 1 keV), with a dramatic increase in collecting area of about two order of magnitude compared to the current X-ray telescopes. In order to avoid the problem of the source's confusion limit at low fluxes, the angular resolution required for these optics should be superb (a few arcsec at most). The enormous mirror dimensions together with the high imaging performances give rise to a number of manufacturing problems. It is basically impossible to realize so large mirrors from closed Wolter I shells which benefit from high mechanical stiffness. Instead the mirrors need to be formed as rectangular segments and a series of them will be assembled in a petal. Taking into account the realistic load capabilities of space launchers, to be able to put in orbit so large mirror modules the mass/geometric-area ratio of the optics should be very small. Finally, with a so large optics mass it would be very difficult to provide the electric power for an optics thermal active control, able to maintain the mirrors at the usual temperature of 20 °C. Therefore, very likely, the optics will instead operate in extreme thermal conditions, with the mirror temperature oscillating between −30 and −40 °C, that tends to exclude the epoxy replication approach (the mismatch between the CTE of the substrate and that of the resin would cause prohibitively large deformations of the mirror surface profiles). From these considerations light weight materials with high thermal–mechanical properties such as glass or ceramics become attractive to realize the mirrors of future Xray telescopes. In this paper, we will discuss a segments manufacturing method based on Borofloat^TM glass. A series of finite element analysis concerning different aspects of the production, testing and integration of the optics are also presented as well.     

Effect of hypergravity on carboanhydrase reactivity in inner ear ionocytes of developing cichlid fish.

It has been shown earlier that hypergravity slows down inner ear otolith growth in developing fish. Otolith growth in terms of mineralization mainly depends on the enzyme carboanhydrase (CA), which is responsible for the provision of the pH-value necessary for calcium carbonate deposition. Larval siblings of cichlid fish (Oreochromis mossambicus) were subjected to hypergravity (3 g, hg; 6 h) during development and separated into normally and kinetotically swimming individuals following the transfer to 1 g (i.e., stopping the centrifuge; kinetotically behaving fish performed spinning movements). Subsequently, CA was histochemically demonstrated in inner ear ionocytes (cells involved in the endolymphatic ion exchange) and enzyme reactivity was determined densitometrically. It was found that both the total macular CA-reactivity as well as the difference in reactivities between the left and the right maculae (asymmetry) were significantly lower (1) in experimental animals as compared to the 1 g controls and (2) in normally swimming hg-animals as compared to the kinetotically behaving hg-fish. The results are in complete agreement with earlier studies, according to which hypergravity induces a decrease of otolith growth and the otolithic calcium incorporation (visualized using the calcium-tracer alizarin complexone) of kinetotically swimming hg-fish was higher as compared to normally behaving hyper-g animals. The present study thus strongly supports the concept that a regulatory mechanism, which adjusts otolith size and asymmetry as well as otolithic calcium carbonate incorporation towards the gravity vector, acts via activation/deactivation of macular CA.     

Cassini Radio Science

Cassini radio science investigations will be conducted both during the cruise (gravitational wave and conjunction experiments) and the Saturnian tour of the mission (atmospheric and ionospheric occultations, ring occultations, determinations of masses and gravity fields). New technologies in the construction of the instrument, which consists of a portion on-board the spacecraft and another portion on the ground, including the use of the Ka-band signal in addition to that of the S- and X-bands, open opportunities for important discoveries in each of the above scientific areas, due to increased accuracy, resolution, sensitivity, and dynamic range.This revised version was published online in July 2005 with a corrected cover date.     

Analog Computer Needed!

Science and technology advance neither steadily nor continuously. Concepts deemed obsolete and confined to oblivion find their niche in new developments. Discarded old methods revive as the key ingredients to new designs. Analog computing was the birthplace of two important technologies: Computer simulation, as applied to system design, was founded. The operational amplifier, to become the basis for modern linear circuitry, was perfected. Valuable as it was, analog simulation's quasi-hardware approach to analysis aggravated users as much as it aided them. When digital simulation languages arrived, simulation engineers readily adopted them. When the microprocessor transformed digital computers into inexpensive circuit components (more like gates, flip-flops, amplifiers, etc. than computers,) there arose unlimited prospects for digital control. But, the discrete digital and continuous analog worlds are not compatible. Timing discontinuities and variable resolution limitations create problems. Control system designs, especially microprocessor based ones, need laboratory development. For hands-on testing, the analog computer is as handy an instrument as a controls engineer could have. Its two unique and valuable functions are: Simulator of Systems to be Controlled... The electrical analogs or physical models, analog computer simulations offer predictable yet realistic representations of mechanisms and processes to be controlled. Programmable Linear Circuits Manifold... The terminal points for high quality, linear circuit devices, analog computer patch panels offer the only formal means of programing linear signal processing, interface and control circuits. This paper offers a discussion of these two analog computing uses.     

Minitact gyroscope-the low cost alternative

The allure of the solid state optical gyros is being challenged by the invention of a new spinning mass device, providing superior low noise drift performance, high reliability at a very low cost. The Minitact is a unique two axis gyroscope advancing the technology of spinning mass devices to set new low cost standards. Minitact provides all the low noise performance benefits of tuned rotor gyroscopes without the vagaries of fixture suspension systems. The Minitact design integrates together the advantages of a spherical hydrodynamic gas bearing and a three axis permanent magnet DC commutated, motor and torquer, into miniature two aids gyroscope with a dynamic range of greater than 10^-7. The design is described and performance data presented illustrating the capability of this low cost next generation rate gyroscope. The Minitact is the result of Integrated Product Development (IPD) and Design to Unit Production Cost (DTUPC) design processes and is expected to become the tactical performance benchmark     

On the Derivation and Numerical Evaluation of the Weibull-Rician Distribution

The Weibull-Rician distribution and density functions are derived by a method based on conditional probability. The derivation is much simpler than the usual Rician approach, giving both the distribution and density as single integrals that are easy to evaluate numerically.     

Comet West 1976 VI: Photopolarimetry by the Helios 2 Zodiacal Light Experiment

Shortly after it passed through perihelion on February 25, 1976 Comet West was observed by the Helios Zodiacal Light Experiment. Broadband photopolarimetric measurements of the head and of the tail were performed in three wavelength bands (U, B, V). The phase angles encountered range from 67° to 85°. The polarization measurements indicated wavelength independent linear polarization. The maximum degree of polarization in the visual channel was found to be .28 at a phase angle of 83°.     

A cost effective critical space systems design approach

NASA-ISC requires avionics platforms capable of serving a wide range of applications in a cost-effective manner. In part, making the avionics platform cost effective means adhering to open standards and supporting the integration of COTS products with custom products. Inherently, operation in space requires low power, mass, and volume while retaining high performance, reconfigurability, scalability, and upgradability. The Universal Mini-Controller (UMC) project is based on a modified PC/104-Plus architecture while maintaining full compatibility with standard COTS PC/104 products. The architecture consists of a library of stackable building block modules, which can be mixed and matched to meet a specific application. A set of NASA developed core building blocks, (e.g. processor card, analog input/output card, high level analog card, and a Mil-Std-1553 card) were constructed to meet critical functions and unique interfaces     

Assessment and improvement of the capabilities of a window correlator to model GPS multipath phase errors

The potential of output from a window correlator to mitigate GPS phase multipath is reviewed and assessed based on the analysis of data collected in controlled multipath environments under both static and kinematic conditions. Previous findings that the method is suboptimal for reflectors leading to additional path lengths of less than about 7m are confirmed, and methods for combining this output with two other multipath indicators: time series of signal-to-noise ratios (SNRs) and estimates of code multipath from dual frequency code and phase combinations, are investigated. A new method to combine all three indicators has been found and its application is shown to improve the quality of GPS static phase data by between 10% and 20% depending on the length of the additional path travelled by the reflected signal. The method can be applied completely automatically as it uses just the three multipath indicators; no knowledge of the surrounding environment is required. The paper concludes with some suggested practical applications.