Elliptical Tracks Research Articles

A Light-Powered Self-Circling Slider on an Elliptical Track with a Liquid Crystal Elastomer Fiber.

In this paper, we propose an innovative light-powered LCE-slider system that enables continuous self-circling on an elliptical track and is comprised of a light-powered LCE string, slider, and rigid elliptical track. By formulating and solving dimensionless dynamic equations, we explain static and self-circling states, emphasizing self-circling dynamics and energy balance. Quantitative analysis reveals that the self-circling frequency of LCE-slider systems is independent of the initial tangential velocity but sensitive to light intensity, contraction coefficients, elastic coefficients, the elliptical axis ratio, and damping coefficients. Notably, elliptical motion outperforms circular motion in angular velocity and frequency, indicating greater efficiency. Reliable self-circling under constant light suggests applications in periodic motion fields, especially celestial mechanics. Additionally, the system's remarkable adaptability to a wide range of curved trajectories exemplifies its flexibility and versatility, while its energy absorption and conversion capabilities position it as a highly potential candidate for applications in robotics, construction, and transportation.

LoRaWAN for Vehicular Networking: Field Tests for Vehicle-to-Roadside Communication.

Vehicular wireless networks are one of the most valuable tools for monitoring platforms in the automotive domain. At the same time, Internet of Things (IoT) solutions are playing a crucial role in the same framework, allowing users to connect to vehicles in order to gather data related to their working cycle. Such tasks can be accomplished by resorting to either cellular or non-cellular wireless technologies. While the former can ensure low latency but require high running costs, the latter can be employed in quasi-real-time applications but definitely reduce costs. To this end, this paper proposes the results of two measurement campaigns aimed at assessing the performance of the long-range wide-area network (LoRaWAN) protocol when it is exploited as an enabling technology to provide vehicles with connectivity. Performances are evaluated in terms of packet loss (PL) and received signal strength indicator (RSSI) in wireless links. The two testing scenarios consisted of a transmitter installed on a motorbike running on an elliptical track and a receiver placed in the centre of the track, and a transmitter installed on the roof of a car and a receiver placed next to a straight road. Several speeds were tested, and all the spreading factors (SFs) foreseen by the protocol were examined, showing that the Doppler effect has a marginal influence on the receiving performance of the technology, and that, on the whole, performance is not significantly affected by the speed. Such results prove the feasibility of LoRaWAN links for vehicular network purposes.

Comparison of distance covered, physiological cost, and perceived exertion in four six-minute walk test protocols.

Objective: There is evidence that indicates that the Walked Distance (WD) in the 6-Minute Walk Test (6MWT) would be sensitive to the type of track and encouragement. The aim of study was compared the impact of track type and verbal encouragement provided in the 6MWT on WD, physiological cost, perceived exertion, and gait efficiency in healthy young adults unfamiliar with the test. Method: WD, heart rate, subjective sensation of dyspnea (SSD), and fatigue (SSF) were measured in four 6MWT protocols: i) 30m linear track and protocolized encouragement (LT + PE), ii) 30m linear track and constant encouragement (LT + CE), iii) 81m elliptical track and protocolized encouragement (ET + PE), and iv) 81m elliptical track and constant encouragement (ET + CE). In addition, the Gait Efficiency Index (GIE) associated with physiological cost, dyspnea and fatigue was calculated and compared between the different protocols. Results: The WD was significantly higher in the ET + CE protocol. The percentage of the heart rate reserve used (%HRRu) at minute 6 was higher in the ET + CE protocol. The SSD and SSD had difference in startup time between the protocols. The GEI was higher in %HRRu, SSD, and SSF for the ET + CE protocol. Conclusion: The ET + CE protocol showed a significant increase in WD during the 6MWT in healthy young adults. Although it obtained the highest physiological cost, it did not present perceptual differences when entering cardiopulmonary assessment windows relevant to a more efficient test for the participant. It is advisable to discuss, based on the findings, the fundamental objective of the 6MWT and national and international recommendations to achieve a result as close as possible to the real maximal effort.

Music Tempo: A Tool for Regulating Walking Cadence and Physical Activity Intensity in Overweight Adults?

This study investigated if music tempo can prompt a desired walking cadence, and if music can provide a stimulus to regulate physical activity intensity in a longitudinal physical activity intervention with free-living adults. Overweight adults (n = 37; 94.26 ± 17.11 kg; 49.63 ± 12.37 years) were randomly assigned to an intervention (IG, n = 17) or usual care group (UC, n = 20) as part of a novel nine-month walking intervention. IG participants walked to self-selected music with a predetermined tempo and received a behavioural change support programme. At baseline, four-, six- and nine-months participants were asked to walk around an elliptical track at their habitual pace (0–2 min) and then in time to a predetermined tempo (2–8 min) designed to elicit moderate intensity. Cadence response (steps/min) was assessed and intensity (heart rate (bpm) recorded using wireless telemetry. A repeated measures general linear model (GLM) examined differences between groups over time (p < 0.05). All data is presented as means ± SD. At each assessment point both groups displayed an immediate cadence adjustment in response to music tempo (p < 0.01) i.e., habitual cadence vs. 3 METs target cadence (p < 0.05) and 3 METs target cadence vs. 5 METs target cadence (p < 0.05). Additionally, IG participants displayed an increased habitual cadence (0–2 min) at each assessment point (p < 0.05; 110 ± 9, 121.80 ± 7.5, 121.46 ± 10, 121.93 ± 7 steps/min respectively). UC participant’s habitual cadence was unchanged from 0–9 months (p > 0.05; 120 ± 10, 116 ± 13, 119 ± 12 and 119 ± 9 steps/min respectively). Music tempo may be a useful regulatory tool to prompt the free-living individual to reach an appropriate stride rate to achieve a walking pace that is at least moderate intensity. It also appears that results may be trainable as throughout the study an increased habitual walking cadence was observed, in the absence of music.

Improvement of Traction Indicators of a Track-Chain Tractor

The aim of this research was to conduct the comparative traction tests for T-170M1.03-55 tractor with a flat and elliptical rim. Structurally rational geometry of the crawler's support surface for tractors with semi-rigid suspension is realized by placing the support rollers at different heights relative to the cart. The results of traction tests showed that elliptical track rim has increased the maximum traction power by 10.4%, conditional traction propulsive efficiency coefficient to 7.43% and the specific traction effort by 8%. The increase in indicators is provided by a lower rolling resistance of a tractor with an elliptical rim. Reduction of the resistance power to rolling of the tractor with an ellipse track rim occurs due to alignment of support rollers vertical load and reduction of resistance to rollers movement on internal contours of tracks and in hinges of track chain links. The results of the research indicate a significant improvement in traction performance of T-170M1.03.55 tractors with elliptical track-chain rim.

A new insect trackway from the Upper Jurassic-Lower Cretaceous eolian sandstones of São Paulo State, Brazil: implications for reconstructing desert paleoecology.

The new ichnospecies Paleohelcura araraquarensis isp. nov. is described from the Upper Jurassic-Lower Cretaceous Botucatu Formation of Brazil. This formation records a gigantic eolian sand sea (erg), formed under an arid climate in the south-central part of Gondwana. This trackway is composed of two track rows, whose internal width is less than one-quarter of the external width, with alternating to staggered series, consisting of three elliptical tracks that can vary from slightly elongated to tapered or circular. The trackways were found in yellowish/reddish sandstone in a quarry in the Araraquara municipality, São Paulo State. Comparisons with neoichnological studies and morphological inferences indicate that the producer of Paleohelcura araraquarensis isp. nov. was most likely a pterygote insect, and so could have fulfilled one of the ecological roles that different species of this group are capable of performing in dune deserts. The producer could have had a herbivorous or carnivorous diet or been part of the fauna of omnivores, being able to adopt herbivorous, carnivorous, and saprophagous diets when necessary. In modern dune deserts, some species of pterygote insects are detritivores (like Tenebrionidae), relying on organic matter that accumulated among the sand grains of the dunes during dry periods with no plant growth. The presence of additional burrows suggests that the Botucatu paleodesert would have had a detritivorous fauna like this. Based on the interpretation of the ichnofossil producers, it was possible to reconstruct the food web of this paleodesert. All the omnivorous and herbivorous invertebrates and the herbivorous ornithopod dinosaurs made up the primary consumers. These animals were, in turn, the food source for bigger carnivorous or omnivorous animals unable to feed on detritus, like arachnids, possible predatory insects, mammaliaforms, and theropod dinosaurs. The highest trophic level was occupied by larger theropod dinosaurs and mammaliaforms, which, because of their size, could prey upon a wide range of animals. The producer of Paleohelcura araraquarensis isp. nov. could have been a primary consumer if it were an omnivorous detritivore or a herbivore, or a secondary consumer if it were produced by a predatory insect or an omnivore relying on animal biomass. The description of this new trackway expands the knowledge on the faunal composition of the Botucatu paleodesert and provides insights into the ecological relationships in ancient deserts. The presence of these arthropod trackways in Mesozoic eolian deposits helps to trace a continuity between Paleozoic and post-Paleozoic desert ichnofaunas, further reinforcing a single Octopodichnus—Entradichnus Ichnofacies for eolian deposits.

The expansion of TRIAC to TRIACII code for track measurements from SSNT detectors

The expansion of TRIAC to TRIACII code will be described. Both codes have been developed for recognition and parameters measurements of particles’ tracks from images of Solid State Nuclear Track Detectors. While the first program considers the tracks as circles, TRIACII code, using image analysis tools, counts the number of tracks and depending on the current working mode classifies them according to their radii (Mode I- circular tracks) or their axis (Mode II- elliptical tracks), their mean intensity value (brightness) and their orientation. Hough transform techniques are used for the estimation of tracks’ number and their parameters which are able to give results even for overlapping tracks. The new program has been used for radon’s progeny behavior and alpha particles’ energy discrimination.

An Immersed Boundary-Lattice Boltzmann Prediction for Particle Hydrodynamic Focusing in Annular Microchannels**Supported by the National Natural Science Foundation of China under Grant Nos 51728601 and 51771118, and the Natural Science Foundation of Jiangsu Province under Grant No BK20150600.

We numerically study the dynamics of particle crystals in annular microchannels by the immersed-boundary (IB) lattice Boltzmann (LB) coupled model, analyze the fluid-particle interactions during the migration of particles, and reveal the underlying mechanism of a particle focusing on the presence of fluid flows. The results show that the Reynolds and Dean numbers are key factors influencing the hydrodynamics of particles. The particles migrate onto their equilibrium tracks by adjusting the Reynolds and Dean numbers. Elliptical tracks of particles during hydrodynamic focusing can be predicted by the IB-LB model. Both the small Dean number and the small particle can lead to a small size of the focusing track. This work would possibly facilitate the utilization of annular microchannel flows to obtain microfluidic flowing crystals for advanced applications in biomedicine and materials synthesis.

Dynamic Behavior Analysis of a Rotor System Based on a Nonlinear Labyrinth-Seal Forces Model

Taking the flow field features of labyrinth seal into consideration, the fluid force generated from the seal cavity, which is spatially separated into two regions, is modeled with the perturbation method. The rotor orbit defined in the perturbation analysis is spatio-temporal varied, which is quite different from the usually preconditioned elliptical track. Meanwhile, the nonlinear fluid force originating from the seal clearance is delineated by the Muszynska's model. Based on the short bearings assumption, a nonlinear oil-film force model is employed. The rotating shaft is simulated by Timoshenko beam finite element with the consideration of geometric asymmetry. Applying the Lagrange's equations, the motion equations of the rotor-bearing-labyrinth seal system are derived. By means of spectrum cascades, bifurcation diagrams, Poincaré maps, etc., the numerical analysis of the system dynamic characteristics is conducted. The results show that abundant nonlinear behaviors can be triggered in the speed-up. The instability threshold and the vibration amplitude of the rotor system are, respectively, enhanced and reduced by the increasing inlet pressure. With shorter seal length, the sealing effect is decreased, whereas the system stability is improved. The fluid-whip phenomenon can be eliminated by increasing the mass unbalance eccentricity at a certain rotational speed.

Costo fisiológico de marcha confortable según el nivel socioeconómico en adultos mayores autovalentes de la comunidad en Talca, Chile

Introduction : Elderly functionality is conditioned by social, economic and cultural aspects. The Comfortable Gait Speed (cgs) is considered the most specific indicator of functional capacity, reflecting an associated Physiological Cost (fc). Under this scenario, the purpose of this research is to evaluate the Comfortable Gait Physiologic Cost (cgpc) according to Socioeconomic Status (ses) in self-reliant elderly. Materials and methods : 75 self-reliant elderly were classified into medium-low and medium-high SES levels. Each participant was asked to walk naturally for three minutes on an elliptical track. Traveled distance and heart rate were recorded every 15 seconds for the Physiological Cost Index (pci) calculation. Furthermore, the significant increase from baseline pci was established as the Critical Physiological Point (cpp). Results : There was no difference in the pci in relation to the sse (p = 0.885). However, it was higher in women (≈0,3 lat / m) when compared to men (≈ 0.2 beats/m; p < 0.001). The traveled distance was about 200 meters in both ses and gender, showing higher in the medium-low SES for the male versus the female group (p = 0.009). In women the cpp appears 15 seconds earlier in the medium-high ses, while in men the pci remains stable throughout the test. Conclusions : The ses does not influence the cgpc in self-reliant elderly; however gender is confirmed as the main factor in its translation. Methodological cpp inclusion is recommended given its relevance to the analysis of gait efficiency.

Imaging of Ultrasonic Guided Waves in Plate Based on Characteristic of Elliptical Cluster Tracks for Line-arc Kind of Array

There is an internal relationship among the line-arc kind of arrays(LAKA) including the regular lined arrays(LA),the arc arrays(AA) and the anomalous bessel arrays(BA),and the layout of the LAKA have much influence on imaging of ultrasonic guided waves.The LAKA and its foundation are discussed,the experimental system of imaging and testing of ultrasonic guided waves for LAKA are set up,and then both the LAKA and its characteristics of multichannel array signals are all analyzed.By expatiating the relationship between feature of LAKA and the characteristic of elliptical cluster tracks(CECT),the regulation of imaging resolution are proposed.The result of imaging experiment shows that synthesize aperture focusing based on CECT can be used into imaging and testing of ultrasonic guided waves for LAKA,which gray characteristics of image are in according with CECT.On condition of the same referenced LA for imaging of ultrasonic guided waves,the transverse imaging resolution of AA is higher than that of LA,the transverse imaging resolution of BA is higher than that of AA,and BA have the advantages like that of both LA and AA,which are in keep with the regulation of imaging resolution.The proposed research provides foundation for industrial imaging and testing of ultrasonic guided waves in plate with larger size.

Fast-neutron spectroscopy studies using induced-proton tracks in PADC track detectors

In this work, a simple and adequate method for fast-neutron spectroscopy is proposed. This method was performed by free-in-air fast-neutron irradiation of CR-39 Nuclear Track Detectors (NTD) using an Am-Be source. Detectors were then chemically etched to remove few layers up to a thickness of 6.25 μm. By using an automatic image analyzer system for studying the registration of the induced-proton tracks in the NTD, the obtained data were analyzed via two tracks shapes. In the first one, the elliptical tracks were eliminated from the calculation and only the circular ones were considered in developing the response function. In the second method all registered tracks were considered and the corresponding response function was obtained. The rate of energy loss of the protons as a function of V[(dE/dX) - V] was calculated using the Monte Carlo simulation. The induced-proton energy was extracted from the corresponding dE/dX in NTD using a computer program based on the Bethe-Bloch function. The energy of the incident particles was up to few hundred MeV/nucleon. The energy of the interacting neutrons was then estimated by means of the extracted induced-proton energies and the scattering angle. It was found that the present resulting energy distribution of the fast-neutron spectrum from the Am-Be source was similar to that given in the literature where an average neutron energy of 4.6MeV was obtained.

Knee Pain in a Young Wake Boarder

HISTORY: 19 year old healthy male, seen in Family Medicine Clinic for left knee pain and swelling after a wake boarding injury one week prior. The patient was initially evaluated at the ER 5 hours after the acute event and placed in a hinged knee brace and prescribed Vicodin 5/500 for severe pain and OTC Ibuprofen for inflammation. He complained of persistent left knee discomfort with minimal response to treatment of NSAID's and rest. He also continued to have restricted left knee extension and an inability to bear weight. He denied previous knee trauma or concomitant medical conditions. PHYSICAL EXAMINATION: Wt: 77.1 kg BP: 118/70 P: 68 General: Alert, pleasant male without distress Left knee: scant effusion and tenderness noted inferior to lateral patella, equivocal McMurray, negative anterior & posterior drawer, and negative Lachman's. He lacked full extension. Patient unable to bear weight without crutches. Neurological exam intact. DIFFERENTIAL DIAGNOSIS: Knee sprain Femoral condyle contusion Meniscal Tear ACL/PCL Tear Tibial Plateau Fracture TESTS AND RESULTS: 4 view Knee X-Ray: Negative for fracture dislocation or joint effusion (In ER) MR Left Knee: Minimal depression 3 mm impaction fracture along anterior articular surface of lateral tibial plateau with edema like signal at both femoral condyles. No meniscal tears. Ligaments intact. Small effusion. (Two weeks after injury) Knee X-Ray Patella+Flexion views: Negative for dislocation or fracture. No definite interval change. Minimal medial joint compartment narrowing. (6 weeks after injury) FINAL DIAGNOSIS: Impaction Tibial Plateau Fracture with Femoral Condyle Contusions TREATMENT: Sports Medicine Consultation: Non-weight bearing activities advised for initial 6 weeks post event. No surgical intervention warranted. Slow introduction of weight bearing exercises advised; i.e., bicycling, elliptical track, etc. No contact sports advised at this time. Patient recovering with minimal restrictions or pain.

Alpha spectroscopy in CR-39 SSNTDs using energy simulation and matrix of energy equations for open field studies

Encouraged with the success of the matrix of energy equations in resolving alpha spectra for narrow energy band [O.A. Bondarenko, P.L. Salmon, D.L. Henshaw, A.P. Fews, Radiat. Meas. 26 (1996) 59; O.A. Bondarenko, P.L. Salmon, D.L. Henshaw, A.P. Fews, A.N. Ross, Nucl. Instrum. Methods A 369 (1996) 582] and wide energy band [E.M. Awad, A.A. Soliman, Y.S. Rammah, Phys. Lett. A 369 (5–6) (2007) 359] as well, the present work extends the applicability of this method to work out for open field studies. 241Am alpha source was used for irradiating CR-39 samples in air at normal temperature and pressure and at three different distances to obtain three different energies. Alpha particles were sorted to ten different bins according to their dip angle and the energy inside each bin was determined using alpha particle range–energy relation. Then, the energy matrix inside each bin was constructed using some selected calibration tracks. This matrix was composed of two track axes, the track minor axis ( m ) and diameter of etched out track end ( d ) of some selected elliptical tracks. The energy E in ( m , d ) coordinates was given by E k = ∑ i , j = 0 2 a i j d k i m k j . The adjusting parameters a i j were obtained by solving an over-determined system of energy equations using the SVD method. The three energies in each bin were well resolved.

Alpha particle spectroscopy for CR-39 detector utilizing matrix of energy equations

Abstract A method for determining alpha-particle energy using CR-39 detector by utilizing matrix of energy equation was described. The matrix was composed from two axes; the track minor axis ( m ) and diameter of etched out track end ( d ) axis of some selected elliptical tracks. The energy E in ( m , d ) coordinate was approximated by matrix of energy equations given by: E k = ∑ i , j = 0 2 a i j d k i m k j , which was identified using two different approaches. First, i and j were treated as power exponents for d and m . The adjusting parameters values a i j were obtained and the energy of a given track was deduced directly from it. Second, i and j were treated as indices of some chosen tracks that were fitted to obtain iso-energy curves that were superimposed on m – d scatter plot as calibration curves. The energy between any two successive iso-energy curves in this case was assumed varied linearly with d for a given m . The energy matrix in both cases was solved numerically. Results of the two approaches were compared.

TRIAC II. A MatLab code for track measurements from SSNT detectors

A computer program named TRIAC II written in MATLAB and running with a friendly GUI has been developed for recognition and parameters measurements of particles' tracks from images of Solid State Nuclear Track Detectors. The program, using image analysis tools, counts the number of tracks and depending on the current working mode classifies them according to their radii (Mode I—circular tracks) or their axis (Mode II—elliptical tracks), their mean intensity value (brightness) and their orientation. Images of the detectors' surfaces are input to the code, which generates text files as output, including the number of counted tracks with the associated track parameters. Hough transform techniques are used for the estimation of the number of tracks and their parameters, providing results even in cases of overlapping tracks. Finally, it is possible for the user to obtain informative histograms as well as output files for each image and/or group of images. Program summary Title of program:TRIAC II Catalogue identifier:ADZC_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADZC_v1_0 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: Pentium III, 600 MHz Installations: MATLAB 7.0 Operating system under which the program has been tested: Windows XP Programming language used:MATLAB Memory required to execute with typical data:256 MB No. of bits in a word:32 No. of processors used:one Has the code been vectorized or parallelized?:no No. of lines in distributed program, including test data, etc.:25 964 No. of bytes in distributed program including test data, etc.: 4 354 510 Distribution format:tar.gz Additional comments: This program requires the MatLab Statistical toolbox and the Image Processing Toolbox to be installed. Nature of physical problem: Following the passage of a charged particle (protons and heavier) through a Solid State Nuclear Track Detector (SSNTD), a damage region is created, usually named latent track. After the chemical etching of the detectors in aqueous NaOH or KOH solutions, latent tracks can be sufficiently enlarged (with diameters of 1 μm or more) to become visible under an optical microscope. Using the appropriate apparatus, one can record images of the SSNTD's surface. The shapes of the particle's tracks are strongly dependent on their charge, energy and the angle of incidence. Generally, they have elliptical shapes and in the special case of vertical incidence, they are circular. The manual counting of tracks is a tedious and time-consuming task. An automatic system is needed to speed up the process and to increase the accuracy of the results. Method of solution: TRIAC II is based on a segmentation method that groups image pixels according to their intensity value (brightness) in a number of grey level groups. After the segmentation of pixels, the program recognizes and separates the track from the background, subsequently performing image morphology, where oversized objects or objects smaller than a threshold value are removed. Finally, using the appropriate Hough transform technique, the program counts the tracks, even those which overlap and classifies them according to their shape parameters and brightness. Typical running time: The analysis of an image with a PC (Intel Pentium III processor running at 600 MHz) requires 2 to 10 minutes, depending on the number of observed tracks and the digital resolution of the image. Unusual features of the program: This program has been tested with images of CR-39 detectors exposed to alpha particles. Also, in low contrast images with few or small tracks, background pixels can be recognized as track pixels. To avoid this problem the brightness of the background pixels should be sufficiently higher than that of the track pixels.

Novel image copy detection with rotating tolerance

In 2003, Kim applied the discrete cosine transform (DCT) technique to propose a content-based image copy detection method. He successfully detected the copies both with and without modifications, and his method is the first to detect the copies with water coloring and twirling modifications. However, Kim’s method can only detect copies having a 180° rotation. When copies have a 90° or 270° rotation, Kim’s method fails to discover them. Also, his method cannot deal with copies having only minor rotations of 1° or 5°, and so on. To conquer this weakness, we propose an elliptical track division strategy to extract two kinds of features in the design of our proposed methods. Furthermore, we propose a dynamic center point detection mechanism for the elliptical track of each image to deal with the shifting process. The experimental results confirm that both proposed methods can successfully capture the features of an image even if it is shifted, cropped or rotated to any degree. In addition, our hybrid method can further provide accurate detection performance for a variety of manipulations.

Cosmic rays tracks in the PICsIT instrument onboard the INTEGRAL satellite

The PICsIT (PIxelated CsI Telescope) instrument is the high energy plane of the IBIS imager onboard the INTEGRAL satellite, launched on October 2002 and currently fully operative. PICsIT consists of a 64 × 64 detectors array, each composed of a CsI(Tl) scintillating crystal with p-i-n photodiode readout. Since its first in-orbit activation, several count rate spikes have been detected. The tracks in the detector corresponding to those spikes clearly indicate that their origin is the interaction of cosmic rays with the detector or the satellite structure. Several extended elliptical tracks have been detected, indicating the presence of electromagnetic and hadronic showers initiated by primary cosmic rays interacting with the satellite structure. The tracks morphology and statistics is presented. There is strong evidence that tracks events are due to phosphorescence states excited in the CsI(Tl) crystals by a high energy deposit. Since events due to cosmic rays tracks account for a significant fraction of the instrument background, their rejection is important to improve the instrument sensitivity. Tracks rejection is especially important in those instruments, based on large quantities of alkali halide scintillators, designed to trigger on count rate increases, such as gamma-ray burst monitors. In the PICsIT detector operated in photon-by-photon mode, tracks events rejection can be easily accomplished thanks to the tracks peculiar geometrical and timing characteristics.

Muscles in microgravity: from fibres to human motion

In simulated or actual microgravity, human and animal postural muscles undergo substantial atrophy: after about 270 days, the muscle mass attains a constant value of about 70% of the initial one. Most animal studies reported preferential atrophy of slow twitch fibres whose mechanical properties change towards the fast type. However, in humans, at the end of a 42-days bed rest study, a similar atrophy of slow and fast fibres was observed. After microgravity, the maximal force of several muscle groups showed a substantial decrease (6–25% of pre-flight values). The maximal power during very short “explosive” efforts of 0.25–0.30 s showed an even greater fall, being reduced to 65% after 1 month and to 45% (of pre-flight values) after 6 months. The maximal power developed during 6–7 s “all-out” bouts on an isokinetic cycloergometer was reduced to a lesser extent, attaining about 75% of pre-flight values, regardless of the flight duration. In these same subjects, the muscle mass of the lower limbs declined by only 9–13%. Thus, a substantial fraction of the observed decreases of maximal power is probably due to a deterioration of the motor co-ordination brought about by the absence of gravity. To prevent this substantial decay of maximal absolute power, we propose that explosive exercise be added to the daily in-flight training schedule. We also describe a system aimed at reducing cardiovascular deconditioning wherein gravity is simulated by the centrifugal acceleration generated by the motion of two counter rotating bicycles ridden by the astronauts on the inner wall of a cylindrical space module. Finally, cycling on circular or elliptical tracks may be useful to reduce cardiovascular deconditioning in permanently manned lunar bases. Indeed, on the curved parts of the path, a cyclist generates an outward acceleration vector ( a c). To counterbalance ac, the cyclist must lean inwards, so that the vectorial sum of a c plus the lunar gravity tends to the acceleration of gravity prevailing on Earth.

The mechanics and origin of cometaria

The cometarium, literally a mechanical device for describing the orbit of a comet, had its genesis as a machine for illustrating the observable consequences of Kepler's second law of planetary motion. The device that became know as the cometarium was originally constructed by J T Desaguliers in 1732 to demonstrate, in a sensible fashion, the perihelion to aphelion change in velocity of the planet Mercury. It was only with the imminent, first predicted, return of Halley's comet in 1758 that the name cometarium was coined, and subsequent devices so named. Most early cometaria used a pair of elliptical formers joined via a figure-of-eight cord to translate uniform drive motion into the non-uniform motion of an object moving along an elliptical track. It is shown in a series of calculations, however, that two elliptical former cometaria do not actually provide a correct demonstration of Keplerian velocity variations and nor do they actually demonstrate Kepler's second law of planetary motion.