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We describe a stellar seismology photometric experiment which we have proposed to embark on-board the interplanetary vehicles belonging to the VESTA mission (France - USSR mission towards Mars and the asteroids belt, to be launched about 1994). The objective is to use the cruise time to obtain long, uninterrupted observations of the white light fluctuations in a few late-type stars, with a view to the detection of global non-radial modes at the level 10−5 to 10−6 mag. We have performed a design-study of the instrumentation, formed by a 5 cm spherical collector, working in two spectral bands 1500 A wide, with two photomultipliers as detectors. Advantages and difficulties of the system are briefly discussed.
Observations have been carried out using the oxygen VI multiplet ratio 1032/1038 Â from SUMER on SOHO. Analysis based on the Doppler dimming method shows that the outflow velocity in polar plumes is higher than that in the interplume region, contrary to many published suggestions. The addition of UVCS data for the interplume region, leads to a conclusion that the effective oxygen ion “temperature” in the radial direction has to rise to around 14 MK over the height range 1.5 to 1.8 R⊙.
Simultaneous XUV and microwave (μ – ѡ) observations of a solar filament, performed by several instruments onboard SOHO and by the Very Large Array (VLA), are analyzed. The filament appears as a dark structure, very similar in shape to the optical Hα filament, in all images taken in the transition region (TR) lines observed by CDS, in the Ne VIII lines observed by SUMER at λ = 770Å and 780Å and at all radio wavelengths with 1.7 cm ≤ λ ≤ 6 cm. Contrary to that, in six TR lines observed by SUMER at λ > 1300Å no trace of the filament, either in absorption or in emission, is visible. Finally, at λ = 21 cm, as well as in all images taken in coronal lines by CDS and EIT, a dark feature is present at the filament position, although with less defined contours than in the first-mentioned TR images. The constraints imposed by all these observations are discussed and interpreted.
Interstellar water ice is mainly amorphous, but the nature of its morphology still
remains poorly known. The experimental study described in this work focuses on how
relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent
recombination. We show that there is an exponential decrease in the porosity of the
amorphous water ice sample following hydrogen-atom irradiation. These and other laboratory
results lead us to suggest that water ice in space is almost certainly amorphous and
We explore experimentally the formation of water molecules from O2 and D atoms
on bare grains composed of amorphous silicates analogous to those in diffuse interstellar
clouds. We provide the fractions of D2O and D2O2
molecules formed on the silicate surface held at 10 K from the O2 + D pathway
using RAIRS and TPD techniques. For comparison, we also study the formation of water
molecules on surfaces covered with amorphous water ice representing the dense clouds.
We present a combined theoretical and experimental study of the adsorption of two pairs
of organic isomers, (i) acetic acid AA (CH3COOH) and methyl
formate MF (HCOOCH3), and (ii) ethanol EtOH
(CH3CH2OH) and dimethyl ether DME (CH3OCH3),
onto crystalline water ice surfaces at low temperatures. Both approaches show that, for
each pair, the most stable isomer from a thermodynamical point of view,
i.e. AA and EtOH, is
also the one which is the more tightly bound to the water ice surface compared to the less
stable isomers (MF and DME). This finding, which can be explained by the ability of AA or
EtOH to efficiently interact with the ice surface via hydrogen bondings, may have
important consequences in an astrophysical context, since it could explain why the most
stable isomer is not the most abundant observed in the interstellar gas phase.
The development of functional-structural plant models has opened interesting perspectives
for a better understanding of plant growth as well as for potential applications in
breeding or decision aid in farm management. Parameterization of such models is however a
difficult issue due to the complexity of the involved biological processes and the
interactions between these processes. The estimation of parameters from experimental data
by inverse methods is thus a crucial step. This paper presents some results and
discussions as first steps towards the construction of a general framework for the
parametric estimation of functional-structural plant models. A general family of models of
Carbon allocation formalized as dynamic systems serves as the basis for our study. An
adaptation of the 2-stage Aitken estimator to this family of model is introduced as well
as its numerical implementation, and applied in two different situations: first a
morphogenetic model of sugar beet growth with simple plant structure, multi-stage and
detailed observations, and second a tree growth model characterized by sparse observations
and strong interactions between functioning and organogenesis. The proposed estimation
method appears robust, easy to adapt to a wide variety of models, and generally provides a
satisfactory goodness-of-fit. However, it does not allow a proper evaluation of estimation
uncertainty. Finally some perspectives opened by the theory of hidden models are
Recent work has made it possible to deposit hermetic carbon coatings on optical fibers during the drawing process. These coatings are used to protect the silica portion of the fiber from undesirable loss increases and strength reductions caused by H2 and H2O, respectively. The hermetic properties of the carbon films have been evaluated using accelerated test conditions where the coated fibers are exposed to H2 at elevated temperatures and hydrogen pressures. In-situ spectral loss monitoring has made it possible to measure changes in the characteristic optical loss features associated with either molecular H2or with species such as OH which form when hydrogen reacts with defects in the silica. By using long lengths of fiber it is thus possible to optically measure the extremely small amounts of hydrogen that penetrate the carbon films during accelerated tests. At temperatures in the range of 100 to 145°C the diffusion of H2 is readily modeled using classical diffusion theories for a composite cylinder, allowing calculation of the diffusion coefficient and the solubility for H2 in the carbon. At higher temperatures the diffusing H2 is partially depleted by reaction with defects in the glass. For these conditions the inward diffusion of the H2 and its reaction at defect sites tend to balance each other, giving rise to a constant, but extremely low, concentration of H2 in the fiber.
For every mill the ideal roll can be considered as one that can be used in a mill stand indefinitely. Unfortunately for the roll user, such ideal rolls do not exist. One major reason for work roll changes (planned or unplanned) is “wear”. In the context of cold rolling and temper rolling, “wear” primarily refers to loss of roughness and/or surface texture. Another limitation to roll performance is the fact that mill incidents – minor as well as major incidents – inflict damage on the work rolls, requiring redressing in the roll shop. If a major defect is present in a forged roll, e.g. due to a mill incident, catastrophic roll failure may occur in a violent, explosive manner. Improvement of the value-in-use of a work roll implies a superior wear resistance, a superior damage resistance, and elimination of the safety risks associated with explosive roll failures. In order to deal with this in a concerted R&D approach, a consortium of two roll users in the steel industry, a leading roll manufacturer, a high-tech supplier of roll damage detection equipment, and specialised research institutes have joined forces. Cold rolling trials have been performed, using pilot mills as well as industrial mills, with both novel forged HSS work rolls and conventional forged 3–5%Cr steel work rolls. Separate trials have been designed to focus on either the aspect of roughness evolution or damage resistance. Complementary data from various laboratory tests and industrial mill and roll shop data have been collected. Models have been developed for damage evolution in a roll, and for roughness evolution of the roll surface. In addition, novel non-destructive detection systems and sensors have been designed and tested. This paper provides a concise overview of the results achieved.
This paper describes implementation and initial evaluation of
variable friction displays. We first analyse a device that comprises a stator of an ultrasonic motor supplied by only
one channel. In this way, the stator does not induce any rotative movement but
creates a slippery feeling on the stator's surface. Considering the range of frequency and amplitude needed to obtain this phenomenon, we
interpret it as the squeeze film effect, which may be the dominant factor causing an impression of lubrication. This effect is thus able to decrease
the friction coefficient between the fingertip and the stator as a function of the vibration amplitude. Moreover, if we add a position sensor, we can create a textured surface by generating alternatively sliding and braking sensations by tuning the vibration amplitude of the wave.
Then, based on the principle of the first device, another device is
proposed in order to enable a free exploration of the surface, according to ergonomic requirements.
Previous research has shown that a preoperative assessment clinic enhances hospital cost-efficiency. However, the differences in organization of the patient flow have not been analysed. In this descriptive study, we evaluated the consequences of the organization of the patient flow of a preoperative assessment clinic on its performance, by analysing two Dutch university hospitals, which are organized essentially differently.
In the final analysis, the study included 880 patients who visited either academic centre. The performance of the two preoperative assessment clinics was evaluated by measuring patient flow time, various procedure times and the total waiting time. Patients’ age, ASA physical status and any preoperative tests requested by the physician were also recorded.
There was a significant difference in patient flow time between the two preoperative assessment clinics. More time was needed for the preoperative assessment when patients’ ASA class was higher. The patient flow time was longer when electrocardiogram and venepuncture were performed at the general outpatient laboratory than when they were performed at the preoperative assessment clinic due to longer waiting times. More tests were requested when they were performed at the preoperative assessment clinic.
This study shows that the organization of patient flow is an important aspect of the logistic processes of the preoperative assessment clinic. It might influence patient flow times as well as the number of preoperative tests requested. Together with other aspects of logistic performance, patient satisfaction and quality of medical assessment, patient flow logistics can be used to assess the quality of a preoperative assessment clinic.
The aim of this paper is to define a linear model of a
planar standing wave ultrasonic motor (SWUM). First, the analytical
approach using the variational formulation is presented. An
identification method is deduced to find the parameters of a
vibrating rectangular plate. Non-linearities are also emphasized and
verified by the experimental measurements. Secondly, the mechanical
energy conversion of the actuator is identified, using an average
behavior modelling and a linear approach for the contact
interaction. Finally, a complete modelling of the actuator is
presented, using the Causal Ordering Graph formalism.
High power RF device performance
decreases as operation temperature increases (e.g. decreasing electron
mobility affects cut-off frequencies and degrades device reliability).
Therefore determination of device temperature is a key issue for device
topology optimisation. In this work the temperature variation of AlGaN/GaN
high-electron-mobility transistors grown either on silicon or sapphire
substrate under bias operation was measured by micro Raman scattering
spectroscopy. Temperature measurements up to power dissipation of 16 W for
4 mm development devices were carried out and a peak temperature of 650 K was
determined. The difference of thermal resistance for similar devices grown
on the two different substrates was assessed. The thermal resistances of
different device topologies were compared to optimise the component design.
The high power RF device performance decreases as the operation
temperature increases (e.g. fall of electron mobility impacting
the cut-off frequencies and degradation of device reliability).
Therefore the determination of device temperature is a key issue
for device topology optimisation. In this work the temperature
variation of AlGaN/GaN high-electron-mobility transistors grown
either on silicon or sapphire substrates under bias operation was
measured by micro Raman scattering spectroscopy. The differences
in thermal resistance for similar devices grown on the two
different substrates were assessed. The thermal resistances of
different device topologies were compared in order to optimise
the component design. The temperature measurement across the gate
and along the component fingers were made to quantify the thermal
gradient of the device. Temperature measurement up to a power
dissipation of 16 W for a 4 mm development device was carried out
and the peak temperature of 650 K was determined.
This paper deals with the causal modeling of a
Traveling Wave Ultrasonic Motor; the aim of the study is to build
an approach which may take into account the physical contact
responsible for the pull-out phenomenon, but straightforward
enough to be useful for control. As the parameters available for
the modeling can not be obtained following the well known
electromechanical equivalent scheme identification, a new
identification method is proposed. In this purpose, the model of
the motor is expressed in the traveling wave rotating frame.
D. Field, Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark and Observatoire de Paris-Meudon,
J. L. Lemaire, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France; Université de Cergy-Pontoise, F-95806 Cergy Cedex, France,
J. P. Maillard, Institut d'Astrophysique, 98bis, Boulevard Arago, F-75014 Paris, France,
S. Leach, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France,
G. Pineau des Forêts, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France,
E. Falgarone, Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France,
F. P. Pijpers, Theoretical Astrophysics Centre, University of Aarhus, DK-8000 Aarhus C, Denmark,
M. Gerin, Ecole Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France,
F. Rostas, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France,
D. Rouan, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France,
L. Vannier, Observatoire de Paris-Meudon, F-92195 Meudon Principal Cedex, France
High spatial and spectral resolution observations are reported of H2 infrared emission from the reflection nebulæ NGC2023 and NGC7023. The local molecular gas is strongly perturbed by the presence of the massive stars which power these nebulae. Data yield information on the small-scale structure, the temperature and density and the dynamics of the excited gas. Excited material is found to be hot (400-500K), dense (105-106 cm−3) and clumped containing substantial flows and velocity fields.
The two reflection nebulæ NGC2023 and NGC7023 are prototypes of regions in which recently formed massive stars are interacting strongly with their parent gas. The outcome of these interactions is important in understanding the cycle of star formation in which massive stars are created and, by perturbing their surroundings, influence the nature of the gas in which future stars may form. The goal of our work is to examine in detail the perturbed gas around massive young stars. Some of the observations of infrared (IR) emission of molecular hydrogen in NGC2023 and NGC7023, performed in recent years in our group, are described below.
Nebulosity in NGC2023 and NGC7023 is excited by B-stars of temperatures respectively 22,000K and 20,400K. The distance between the star and the illuminated surrounding gas is ∼ 0.1 pc in both nebulæ. NGC2023 shows a strong IR excess with emission from small dust particles plus extended red emission, and has an associated molecular cloud with OH, HCHO, HCN, CO, CH, CH+ and other detections (see Field et al. 1994).
The Faunal Reserve of the Lobéké area of south-eastern Cameroon is an important area for forest conservation. One day, it is hoped, it will be part of an international unit, in association with two protected areas in neighbouring countries (Dzanga-Ndoki National Park, Central African Republic and Nouabalé-Ndoki National Park, Congo). With a view to assessing the status of its avifauna in particular, 24 days were spent in three short surveys from 1997 to 1999. The main forest type is semi-evergreen, with an open canopy; the only natural savannas are small saline swamps. The total of 305 species of bird recorded includes a forest nightjar not yet identified (but more likely to be the rare Itombwe Nightjar Caprimulgus prigoginei than a new species) and the Dja River Warbler Bradypterus grandis. The latter is a species confined to Rhynchospora swamps and had not been re-located in Cameroon since it was first collected in 1914 west of the Dja river; the extent of suitable habitat in Lobéké makes this site the most important to date for its conservation. Other rare or little-known forest species recorded include Olive Ibis Bostrychia olivacea, Sandy Scops Owl Otus icterorhynchus, Zenker's Honeyguide Meligomon zenkeri, Tessmann's Flycatcher Muscicapa tessmanni and Yellow-capped Weaver Ploceus dorsomaculatus. Barred Owlet Glaucidium capense is locally common in open-canopy forest: this population was only recently discovered in central Africa and its taxonomic relationships have yet to be determined. We include a brief comparison with the avifauna of adjacent Dzangha-Ndoki National Park and Nouabalé-Ndoki National Park. A feature of the Lobéké avifauna is the presence of a few species normally associated with forest at higher altitudes (such as White-headed Wood Hoopoe Phoeniculus bollei, Uganda Woodland Warbler Phylloscopus budongoensis, Black-throated Apalis Apalis jacksoni), and perhaps absent from lower-lying Nouabalé-Ndoki.
In this paper, finite element method is used to compute inductance parameters of a
squirrel cage induction machine. To take into account saturation effect, saturated
equivalent parameters are introduced, which depend on the instantaneous value of the
magnetising current. For a balanced induction machine, the particular inductance
behaviors allow straightforward flux expressions without any cross saturation effect.
Moreover, these expressions are explained thanks to an extended analytical approach
considering a magnetic saliency phenomenon by a second order air-gap permeance. A
simple way of transformation ratio and leakage inductance computation is also deduced.
The numerical results show the compatibility between finite element approach and
extended analytical Park's method. Besides, two operating points (at no load and for nominal speed) studied by the both methods give very closed results.
The previous chapter contains contributions to the history of science in the field of space plasma physics. It explains how the plasmapause, this peculiar and unexpected magnetospheric frontier, was discovered independently in the late 1950s and early 1960s by two scientists from the two leading countries involved in space exploration. The discoveries were made by using two totally different technical methods of measurement: in situ spacecraft observations and electromagnetic sounding of the magnetosphere. These techniques were both in their infancy at the time.
The main results of electromagnetic sounding of the plasmasphere, from the ground and from satellites, will now be described. In situ satellite particle observations will be outlined in Chapter 3.
In both this chapter and the next the most relevant results will be presented without emphasis upon technical aspects of the experiments. Such aspects are well described in the specialized literature, examples in the case of the whistler method being works by Smith (1961a); Carpenter and Smith (1964); Helliwell (1965); Carpenter and Park (1973); Rycroft (1974a); Y. Corcuff (1975); Tarcsai (1975); P. Corcuff (1977); P. Corcuff, Y. Corcuff and Tarcsai (1977); Park and Carpenter (1978); Bernhardt (1979); Daniell (1986) and Rycroft (1987). An extensive review of the use of whistlers for magnetospheric diagnostics is given by Sazhin, Hayakawa and Bullough (1992).
As noted above, Storey (1953) used whistlers for the initial identification of the dense plasmasphere, and Carpenter (1962b) used evidence of unusually low whistler travel times to infer the occurrence of deep, factor-of-∼ 10 depressions in electron density during the severe magnetic storms of the IGY.
Besides whistler observations, direct particle measurements from spacecraft (especially from satellites with highly elliptical and geostationary orbits) have contributed significantly to our understanding of the plasmasphere and of its outer boundary, the plasmapause. In particular, such measurements permit us to investigate a number of topics that are not subject to direct observation by radio techniques, including low-energy ion composition, pitch angle distribution, and temperature.
Satellite instruments which have contributed to plasmaspheric studies involve both direct particle flux measurements as well as wave observations. We have already reported in Chapter 2 some results from wave experiments, and in the present chapter will discuss such observations only when they appear to be complementary to direct plasma measurements. Most of our attention will be focused on direct particle measurements, obtained with Langmuir probes, charged particle traps, retarding potential analyzers (RPA), and ion mass spectrometers of different types.
Several problems are inherent in measurements made with the above-mentioned devices. The most serious problems arise when the instruments operate in a very low-density plasma and/or when the energy of the measured particles is very low. Indeed, it is difficult in practice to eliminate all the factors distorting the direct measurements, in spite of the care taken by their developers, including extensive preflight tests and calibration.