Academic literature on the topic 'Venus (Planet)'

Abstract A key item of interest for planetary scientists and astronomers is the habitable zone: the distance from a host star where a terrestrial planet can maintain necessary temperatures in order to retain liquid water on its surface. However, when observing a system’s habitable zone, it is possible that one may instead observe a Venus-like planet. We define “Venus-like” as greenhouse-gas-dominated atmosphere occurring when incoming solar radiation exceeds infrared radiation emitted from the planet at the top of the atmosphere, resulting in a runaway greenhouse. Our definition of Venus-like includes both incipient and post-runaway greenhouse states. Both the possibility of observing a Venus-like world and the possibility that Venus could represent an end state of evolution for habitable worlds require an improved understanding of the Venus-like planet, specifically the distances where these planets can exist. Understanding this helps us define a “Venus zone”—the region in which Venus-like planets could exist—and assess the overlap with the aforementioned “habitable zone.” In this study, we use a 1D radiative−convective climate model to determine the outer edge of the Venus zone for F0V, G2V, K5V, and M3V and M5V stellar spectral types. Our results show that the outer edge of the Venus zone resides at 3.01, 1.36, 0.68, 0.23, and 0.1 au, respectively. These correspond to incident stellar fluxes of 0.8, 0.55, 0.38, 0.32, and 0.3 S ⊙, respectively, where stellar flux is relative to Earth (1.0). These results indicate that there may be considerable overlap between the habitable zone and the Venus zone.

The purpose of this research is to find out how to determine the Qibla direction of aplace using the position of the planet Venus and how to prove the calculation of the position ofVenus in the sky. This research is motivated by the question of how to determine the Qibladirection at night if the conditions do not have sophisticated technological equipment. Thisresearch is a descriptive analysis research where all the data is collected through observationtechniques. The research results show that the position of the planet Venus can be used as analternative reference to determine the Qibla direction. Based on observations using astronomicalcalculations, it is known that Venus looks very luminous on the western horizon when the sky isclear and the sun has set perfectly. We can also see one of the planets Venus at dawn on theeastern horizon, so Venus is also often referred to as the morning star. Data on the position of theplanet Venus such as the altitude and azimuth of the planet Venus somewhere are then calculatedusing the horizon coordinate system. The data is used as a theodolite reference. Furthermore, toobtain the actual Qibla direction, the theodolite lens is directed to the position of the planet Venusand rotated clockwise (same as the difference in the azimuth angle with the Qibla azimuth ofVenus). Thus, the position of the planet Venus can be used as an alternative to determine the Qibladirection.

ABSTRACT A successful Solar system model must reproduce the four terrestrial planets. Here, we focus on (1) the likelihood of forming Mercury and the four terrestrial planets in the same system (a 4-P system); (2) the orbital properties and masses of each terrestrial planet; and (3) the timing of Earth’s last giant impact and the mass accreted by our planet thereafter. Addressing these constraints, we performed 450 N-body simulations of terrestrial planet formation based on narrow protoplanetary discs with mass confined to 0.7–1.0 au. We identified 164 analogue systems, but only 24 systems contained Mercury analogues, and eight systems were 4-P ones. We found that narrow discs containing a small number of embryos with individual masses comparable to that of Mars and the giant planets on their current orbits yielded the best prospects for satisfying those constraints. However, serious shortcomings remain. The formation of Mercury analogues and 4-P systems was too inefficient (5 per cent and 2 per cent, respectively), and most Venus-to-Earth analogue mass ratios were incorrect. Mercury and Venus analogues also formed too close to each other (∼0.15–0.21 au) compared to reality (0.34 au). Similarly, the mutual distances between the Venus and Earth analogues were greater than those observed (0.34 versus 0.28 au). Furthermore, the Venus–Earth pair was not reproduced in orbital-mass space statistically. Overall, our results suggest serious problems with using narrow discs to explain the inner Solar system. In particular, the formation of Mercury remains an outstanding problem for terrestrial planet formation models.

ABSTRACT Venus and Earth provide astonishingly different views of the evolution of a rocky planet, raising the question of why these two rocky worlds evolved so differently. The recently discovered transiting Super-Earth LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to the question. It circles a nearby M6V star in 8.46 d. LP890-9c receives similar flux as modern Earth, which puts it very close to the inner edge of the Habitable Zone (HZ), where models differ strongly in their prediction of how long rocky planets can hold onto their water. We model the atmosphere of a hot LP890-9c at the inner edge of the HZ, where the planet could sustain several very different environments. The resulting transmission spectra differ considerably between a hot, wet exo-Earth, a steamy planet caught in a runaway greenhouse, and an exo-Venus. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into the evolution of hot terrestrial planets into exo-Venus. Our model and spectra are available online as a tool to plan observations. They show that observing LP890-9c can provide key insights into the evolution of a rocky planet at the inner edge of the HZ as well as the long-term future of Earth.

Transit planet Venus di cakram matahari (jari-jari = 696000 km) merupakan peristiwa alam yang dapat dilihat secara berkala. Planet Venus merupakan planet kedua dalam sistem tata surya yang mempunyai orbit lebih dekat ke matahari (= 0,723 Astronomical Unit) dibanding jarak bumi-matahari (= 149.600.000 km = 1 AU). Sehingga pada suatu waktu tertentu ada peluang berada tepat di depan Bumi, saat menghadap matahari atau dikenal dengan transit Venus. Proses pengamatan fenomena transit Venus di cakram matahari tersebut dapat diimplimentasikan sebagai aplikasi dua segitiga sebangun, Dimana jari-jari planet Venus (jari-jari = 6051,8 km) dinyatakan sebagai tinggi benda dan jari-jari tinggi bayangan Venus sebesar 20880 km (= 3,65 mm pada cakram matahari). Dimana diameter matahari 1.392.000 km (= 240 mm pada lembar sket). Dengan pengukuran jarak tempuh Venus transit 72,4 mm (419 920 km di cakram matahari) terhadap waktu kontak pertama bayangan Venus pada jam 05.28 UT (12.28 WIB) di tepi timur hingga akhir transit pada 17.50 UT (14.50 WIB) diperoleh kecepatan bayangan Venus sebesar 49,286 km/detik

The competition between the torques induced by solid and thermal tides drives the rotational dynamics of Venus-like planets and super-Earths orbiting in the habitable zone of low-mass stars. The resulting torque determines the possible equilibrium states of the planet’s spin. Here we have computed an analytic expression for the total tidal torque exerted on a Venus-like planet. This expression is used to characterize the equilibrium rotation of the body. Close to the star, the solid tide dominates. Far from it, the thermal tide drives the rotational dynamics of the planet. The transition regime corresponds to the habitable zone, where prograde and retrograde equilibrium states appear. We demonstrate the strong impact of the atmospheric properties and of the rheology of the solid part on the rotational dynamics of Venus-like planets, highlighting the key role played by dissipative mechanisms in the stability of equilibrium configurations.

Abstract In spite of substantial advancements in simulating planet formation, the planet Mercury’s diminutive mass and isolated orbit and the absence of planets with shorter orbital periods in the solar system continue to befuddle numerical accretion models. Recent studies have shown that if massive embryos (or even giant planet cores) formed early in the innermost parts of the Sun’s gaseous disk, they would have migrated outward. This migration may have reshaped the surface density profile of terrestrial planet-forming material and generated conditions favorable to the formation of Mercury-like planets. Here we continue to develop this model with an updated suite of numerical simulations. We favor a scenario where Earth’s and Venus’s progenitor nuclei form closer to the Sun and subsequently sculpt the Mercury-forming region by migrating toward their modern orbits. This rapid formation of ∼0.5 M ⊕ cores at ∼0.1–0.5 au is consistent with modern high-resolution simulations of planetesimal accretion. In successful realizations, Earth and Venus accrete mostly dry, enstatite chondrite–like material as they migrate, thus providing a simple explanation for the masses of all four terrestrial planets, the inferred isotopic differences between Earth and Mars, and Mercury’s isolated orbit. Furthermore, our models predict that Venus’s composition should be similar to the Earth’s and possibly derived from a larger fraction of dry material. Conversely, Mercury analogs in our simulations attain a range of final compositions.

The Pioneer Venus Orbiter Infrared Radiometer and Venera 15 Fourier Transform Spectrometer observations of thermal emission from Venus' middle atmosphere between 10°S and 50°N were used to determine global maps of temperature, cloud optical depth and water vapour abundance. The spectral regions observed include the strong 15 μtm carbon dioxide band and the 45 μm fundamental rotational water band. The main aim of this thesis is to reconcile the water vapour abundance results from these two sets of observations reported in previous studies. New radiative transfer and retrieval models have been developed for this purpose based on new correlated-k absorption tables calculated with up-to-date spectral line data. The H₂SO₄ cloud opacity and scattering properties have been recalculated from new refractive index data using Mie theory. For the first time these two sets of observations have been analysed using the same retrieval tools. From the Pioneer Venus Orbiter Infrared Radiometer observations we report a high abundance of water vapour in the early afternoon at the equatorial cloud-top region and a strong day-night variability in the cloud-top pressure. From the Venera 15 Fourier Transform Spectrometer observations we report medium local variability in water vapour abundance, with highest values in the near-equatorial region and slight decrease towards the polar region. It is found that serious constraints are placed on the validation of the retrievals by the lack of adequately accurate H₂SO₄ optical properties data in the shorter wavelengths and by the poor vertical resolution when sensing the complex but interesting cloud region which prohibits its rigorous modelling. The proposed European Space Agency Venus Express mission will carry a number of high resolution infrared and UV instruments that will shed new light to the interesting question of water vapour abundance in Venus' middle atmosphere.

In questo lavoro di tesi è descritta parte della ricerca svolta presso l’Istituto di Fisica dello Spazio Interplanetario (IFSI) e presso l’Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF). Lo studio attuato riguarda l’analisi dei dati dello strumento Planetary Fourier Spectrometer (PFS) incluso nella missione ESA Mars Express (MEX) al pianeta Marte e del Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) incluso nella missione ESA Venus Express (VEX) orbitante attorno al pianeta Venere. Venere e Marte appartengono ai cosiddetti pianeti con atmosfere dominate dalla CO2 e, sperimentando condizioni atmosferiche fra loro diverse, forniscono una possibilità unica di ottenere informazioni complete su questi tipi di atmosfera ed a stadi evolutivi diversi, inoltre le informazioni ottenute dallo studio dei pianeti terrestri risultano fondamentali per una maggiore comprensione dell’evoluzione climatica passata e futura del nostro pianeta, rappresentando essi in qualche modo un possibile stadio o un cammino alternativo della storia della Terra. Utilizzando i dati acquisiti dai due satelliti dell’ESA abbiamo investigato la composizione atmosferica di Marte e Venere poiché essa, su scala globale e regionale, influenza il clima del pianeta e la sua evoluzione e le informazioni ricavate sui gas presenti possono perciò essere utilizzate come traccianti della circolazione atmosferica, permettendo di comprendere le proprietà principali dei due pianeti ed in particolare la stabilità atmosferica e l’evoluzione a lungo termine. Il lavoro è stato concentrato su argomenti ancora affetti da incertezze nella nostra comprensione dei costituenti atmosferici diversi dall’ anidride carbonica, al fine di fornire indicazioni per studi futuri riguardanti l’aeronomia e i fenomeni di interazione con la superficie quali il vulcanismo e la correlata emissione di gas. Su questo obbiettivo abbiamo avuto la prima possibilità di effettuare uno studio intensivo del vapor d’acqua su Venere (gli studi precedenti sono stati eseguiti su regioni del pianeta limitate nel tempo e nello spazio), avendo l’acqua il ruolo di tracciante fondamentale nella comprensione dell’attuale bilancio energetico atmosferico Venusiano, con particolare riferimento allo strato globale di nubi che avvolge permanentemente il pianeta. Su Marte ci siamo invece dedicati allo studio degli isotopi stabili contenuti nel carbonio e nell’ossigeno (isotopi del CO2), offrendo informazioni sull’origine del pianeta e le sue relazioni con la Terra. L’utilizzo degli isotopi dell’ossigeno è particolarmente utile su Marte essendo questo abbondantemente presente sia nell’atmosfera che nella litosfera Marziana sottoforma del maggior costituente, l’anidride carbonica. Abbiamo inoltre eseguito uno studio sul monossido di carbonio (CO) su Marte di particolare importanza essendo esso il principale prodotto della fotolisi del CO2 e quindi direttamente correlato al problema della stabilità dell’atmosfera Marziana. La spettroscopia infrarossa e gli attuali spettrometri ad alta risoluzione, i due strumenti più efficaci di telerilevamento nel contesto delle osservazioni planetarie, sono stati utilizzati per ottenere le informazioni trasportate dalla radiazione che ha direttamente interagito con il pianeta. Per analizzare I dati abbiamo sviluppato alcuni codici che modellano le atmosfere dei due pianeti descrivono appropriatamente ciò che lo strumento misura al fine di ricavare dagli spettri le quantità richieste, quale la composizione atmosferica delle specie considerate. Il contenuto di vapor d’acqua nella mesosfera di Venere era già stato misurato in esperimenti da terra e dallo spazio, che hanno dato risultati simili di qulache ppm fino a poco più di 10. Un’interessante eccezione è stata il forte incremento fino a valori maggiori di 100 ppm riscontratosi nelle regioni equatoriali intorno a mezzogiorno, osservato da Pioneer Venus OIR (Schoefield et al., 1982; Irwin et al., 1997; Koukouli et al., 2005). Di conseguenza il nostro studio ha avuto il duplice obiettivo di misurare il contenuto d’acqua alla sommità delle nubi e ricercare la presenza dei “wet spots” osservati da Pioneer Venus. Come prodotto di passaggio abbiamo misurato anche l’altezza delle nubi. Con una risoluzione spaziale di circa 10 km alla superficie delle nubi abbiamo ricavato un valore di abbondanza di vapor d’acqua a basse latitudini in regioni subsolari di circa 6 ± 2 ppm, fornendo, l’alta risoluzione spaziale, una prima occasione di misurare le variazioni locali, risultate essere attorno al 20%, non eccedendo l’errore casuale delle misure. Il livello riscontrato di massima sensitività alle variazioni di contenuto d’acqua è situato a circa 68 km. I risultati di abbondanza del monossido di carbonio nell’atmosfera Marziana ottenuti dai dati PFS indicano un valor medio di circa 800 ppm per un dataset di osservazioni acquisite in un intervallo di latitudini pari a (- 60) ÷ (+ 60) gradi e in un intervallo di longitudini solari che comprende l’estate e l’inizio dell’autunno nell’emisfero settentrionale. Valori più alti, circa 900 ppm, sono stati riscontrati in osservazioni acquisite alla fine dell’inverno e l’inizio della primavera dell’emisfero nord. In conclusione abbiamo osservato un incremento di CO nell’inverno sud ed a latitudini subsolari in cui il flusso solare è maggiore e di conseguenza la fotolisi del CO2 più efficiente. E’ stata rinvenuta una crescita anche a bassi angoli di incidenza solare, attorno a mezzogiorno. I risultati sull’abbondanze isotopiche del CO2 consistono principalmente nell’identificazione di tutti gli isotopi nei dati PFS con una risoluzione spettrale mai raggiunta prima da strumenti nello spazio. Le abbondanze trovate dei principali isotopi, fuori dal centro della banda di maggiore assorbimento del CO2 centrata attorno a 667 cm–1 (LWC) e confermate dai risultati ottenuti dal canale a frequenze corte (SWC), suggeriscono valori simili ai valori terrestri con una media pesata di circa 0.91 ± 0.18.
This work presents part of the efforts carried out in the Interplanetary Space Physics Institute (IFSI) and in the Cosmic Physics and Space Astrophysics Institute (IASF) of the Italian National Institute for Astrophysics (INAF) in the analysis of the data from the Planetary Fourier Spectrometer (PFS) experiment, included in the scientific payload of the ESA Mars Express (MEX) mission to Mars and the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) experiment, included in the ESA Venus Express (VEX) mission to Venus. Mars and Venus pertain to the planets with a “CO2 dominated” atmosphere and since they experiment different atmospheric conditions they provide an unique chance to obtain complete information on this atmospheric type at different evolutional stages; moreover, information obtained from the study of terrestrial planets are fundamental for the understanding of Earth past and future climate evolution, since other terrestrial planets represent in some sense a possible stage – or alternative path - of the Earth’s history. In particular, using the data acquired by the two ESA spacecraft we investigated the atmospheric composition of the two planets in order to give a contribute to the understanding of the main properties of Mars and Venus, since the composition of the atmosphere on global and regional scales influences the planetary climate and the evolution and the retrieved information can therefore be used to trace the atmospheric circulation, give constraints to the atmospheric stability and its long term evolution. For this task we had the first chance to perform an intensive study of water vapor on Venus, since the role of water as a trace constituent is key to illuminating the present-day Venus atmospheric energy balance, particularly with respect to the global cloud layers which permanently envelop the planet. On Mars we investigated the stable isotope record contained within carbon and oxygen (CO2 isotopes), to provide important constraints regarding the origin of the planet and its relationship to the Earth. Stable oxygen isotopes are particularly useful in the study of Mars because oxygen is abundantly present in both the Martian atmosphere and lithosphere, in particular in the main atmospheric constitute, carbon dioxide. We also investigated carbon monoxide (CO) on Mars, since it represents the main product of the CO2 photolysis and therefore is directly related to the problem of the stability of the Martian CO2 atmosphere. Infrared spectroscopy and present-day high resolution spectrometers, the most powerful remote sensing tools in the context of planetary observation, have been used to investigate the important information carried by the radiation which directly interacted with the planet. To analyze the data we developed some codes which model the two planets atmospheres and properly describe (simulate) what the instrument measures in order to retrieve from the spectra the required quantities, namely composition of the considered species. The water vapor abundance in the mesosphere of Venus has been already measured in a number of ground-based and spaceborn experiments. Various experiments gave approximately the same values from several ppm to a bit more than 10 ppm. An intriguing exception was the strong local enhancement up to 102 ppm soon after the subsolar point in the equatorial region observed by the Pioneer Venus OIR (Schoefield et al., 1982; Irwin et al., 1997; Koukouli et al., 2005). Thus our study had two main goals: to measure the water vapor abundance at the cloud tops with high spatial resolution, and to search for the wet spots observed by the Pioneer Venus. As a byproduct we measured the cloud top altitude. The Venus Express and VIRTIS observation strategy was particularly favorable for measurements at low latitudes around noon. Here the water vapor abundance near cloud top level at 2.5 μm was found to be 6 ± 2 ppm. Our best horizontal spatial resolution was about 10 km on the cloud “surface”, giving for the first time the chance with our high spatial resolution to measure local variations. Pixel-to pixel variations were within 20% and do not exceed random measurement error. Thus we did not observe any anomalously wet regions reported by the Pioneer Venus OIR experiment team. To be precise we have to note that the cloud top region in the far IR is located lower by several kilometers than that at 2.5 μm, and therefore we were sensitive to a higher level of atmosphere. The level of maximum sensitivity to the variations of water vapor is equal to 68 km, the corresponding cloud top altitude at 1.5 μm being equal to 75 ±1 km. Results show a CO mixing ratio with an average value of about 800 ppm from a first analyzed dataset observations acquired in a latitude range of approximately (- 60) ÷ (+ 60) degrees and in a solar longitude range which encompass the summer and the beginning of autumn in the northern hemisphere, therefore winter in the southern one (Ls range: 90° - 200°). Higher average values of about 900 ppm are found in the second dataset which comprises observations at the end of winter and beginning of spring in the north hemisphere (Ls range: 330° - 95°). In conclusion we find an increase in the Southern winter and at the latitudes of subsolar point where solar flux is higher and therefore CO2 photolysis is more efficient. In general seasonal features are more pronounced at equatorial latitudes and meridian profiles of the mixing ratio (for individual orbits) present seasonal shift of the maximum versus the sub solar point. We find an enhancement also at low incidence angles and at midday local time. Results on CO2 isotopes consisted primarily in the identification of all the CO2 isotopes in PFS data (LWC), with an instrumental spectral resolution never available before. The retrieved abundances of the main isotopes outside the center of the main CO2 absorption band at 667 cm–1 (LWC) performed from the analysis of the long wavelength channel of PFS spectrometer and confirmed by the short wavelength channel suggest results close to “terrestrial value” with a weighted-mean value which is equal to 0.91 ± 0.18.

Vénus, deuxième planète du système solaire, souvent appelée sœur de la Terre, car présentant des caractéristiques de taille et de masse similaires, est fort différente de notre planète. En effet, son atmosphère est beaucoup plus dense et dynamiquement active que celle de la Terre. Dans ce travail, nous nous concentrerons sur la région s'étendant de 70 km à 180~km d'altitude :la mésosphère et la basse thermosphère.

SOIR, acronyme de Solar Occultation in the InfraRed, est un instrument russo-franco-belge embarqué à bord de la mission Venus Express de l'Agence Spatiale Européenne. Il utilise un réseau à échelle comme élément diffractant. La plage de nombre d'onde mesurable par SOIR s'étend de 2200 cm-1 à 4400 cm-1, ou 4.3 µm à 2.2 µm en longueur d'onde. Les ordres de diffraction utiles varient de 101 à 194. Un filtre acousto-optique - AOTF - est utilisé comme passe-bande pour sélectionner les ordres de diffraction. La résolution de l'instrument varie de 0.13 à 0.24 cm-1.

Du fait d'un temps de développement raccourci, presque toutes les calibrations de l'instrument ont dû être réalisées en vol. Elles comprennent les calibrations relatives au réseau à échelle (angle exact de Blaze et fonction de Blaze), au détecteur (non-uniformité pixel à pixel, courbe de sensibilité spectrale, relation entre les pixels et les nombres d'onde, résolution de l'instrument, intervalle d'échantillonnage spectral, rapport signal sur bruit, background thermique) et à l'AOTF (relation entre la radio-fréquence d'excitation de l'AOTF et les nombres d'onde, fonction de transfert de l'AOTF). L'approche et la réalisation de ces différentes calibrations sont présentées dans le présent travail. Les caractéristiques de l'instrument y sont également décrites.

Un algorithme d'inversion spectrale a été développé pour le cas spécifique de SOIR. Tenant compte du mode de mesure, l'occultation solaire, la méthode de la pelure d'oignons a été implémentée dans un algorithme dit de l'Estimation Optimale. Cette méthode permet d'inverser l'ensemble des mesures spectrales en une fois, et également d'en tirer d'autres informations, comme l'amélioration de certaines caractéristiques instrumentales. Les paramètres qui sont ajustés au sein de l'algorithme sont la densité de la ou des espèces absorbant dans la région spectrale concernée, la température, les paramètres de la ligne de base, qui permettent de déterminer les caractéristiques des aérosols, le déplacement Doppler des raies qui trouve principalement son origine dans la vitesse de déplacement du satellite, et l'amélioration de certaines calibrations. Une étude de sensibilité des différents paramètres de l'algorithme est également présentée, ainsi qu'une évaluation des erreurs instrumentales systématiques.

Dans l'ensemble des spectres enregistrés durant les 4 premières années de la mission, des profils verticaux de CO2, CO, H2O, HDO, SO2, H2SO4, HCl et HF ont été obtenus. Des valeurs limites de densité de OCS, H2CO, O3 et CH4 ont également été calculées.

Les résultats concernant le dioxyde de carbone sont développés dans le texte. Des profils verticaux de CO2 s'étendant de 70 km à 180 km d'altitude sont analysés en profondeur. Ils sont comparés aux profils dits hydrostatiques, et des hypothèses quant à la dynamique agissant au niveau des deux terminateurs de Vénus sont formulées.

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Venus, second planet of the solar system, is often seen as the sister planet of the Earth. In terms of size and mass, they are indeed very similar, but the Venus atmosphere is much thicker and active. The altitude region extending from 70 km to 180~km is studied in this thesis, namely the mesosphere and the lower thermosphere.

SOIR, which stands for Solar Occultation in the InfraRed, is a Russian / French / Belgian instrument flying on board of the Venus Express (VEX) spacecraft of the European Space Agency. The diffracting device of SOIR is an echelle grating. The wavenumber region studied ranges from 2200 cm-1 to 4400 cm-1, or 4.3 µm to 2.2 µm in wavelength. The diffraction orders used with SOIR vary from 101 to 194. To select the required echelle grating diffraction order, an Acousto-Optical Tunable Filter - AOTF - is located after the entrance slit of the instrument. The instrument resolution varies from 0.13 to 0.24 cm-1.

SOIR was developed in a very short time. Thus, virtually all the calibrations had to be made in-flight. These concern the echelle grating (exact Blaze angle computation, Blaze function), the detector (pixel-to-pixel non-uniformity, spectral sensitivity curve, pixel-to-wavenumber relationship, instrument resolution, spectral sampling interval, signal-to-noise ratio, thermal background) and the AOTF (wavenumber to AOTF frequency relation, AOTF transfer function). The procedure for and the computation of these calibrations are described in this work, as well as the instrument characteristics.

A spectral inversion algorithm was developed specifically for the SOIR measurement technique: the solar occultation. The onion peeling method is implemented using the Optimal Estimation Method. It allows the inversion of the spectral data in one go, and also the enhancement of some instrumental characteristics. The algorithm variables are the densities of the species absorbing in the diffraction order, the temperature of the atmosphere under study, the spectral background parameters, that allow the determination of the Venus aerosols characteristics, the Doppler shift (mainly linked to the shift induced by the satellite displacement), and the improvement of some instrumental calibrations. A sensitivity study on the algorithm parameters is also presented, and the instrumental systematic errors are investigated.

Vertical profiles of CO2, CO, H2O, HDO, SO2, H2SO4, HCl and HF are derived from the spectra measured during the first 4 mission years. Upper limits on OCS, H2CO, O3 and CH4 have also been calculated.

We focus on the carbon dioxide results in the present study. A selection of vertical profiles extending from 70 km to 180 km are analyzed in details. They are compared to the hydrostatic profiles, and propositions concerning the terminators' dynamics are formulated.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

Solar chimney power plant (SCPP) is a solar thermal energy conversion system which converts solar energy into thermal energy and indirectly to mechanical/electrical energy using air as the working fluid to drive a turbine-generator. The main challenge of SCPP is the plant’s low efficiency. This research focus on improving the SCPP collector’s efficiency through the use of underneath air-vents. The study revealed that the power output of the SCPP with air-vents improved by 60%.

As can easily be seen with a polarizer, halo scattering by birefringent crystals gives rise to a strong peak in the polarization, concentrated in a narrow scattering angular range. This peak can easily be observed in ice crystal halos by the naked eye, equipped with a polarizer. It becomes immediately evident that the inner edge of a parhelion is completely polarized. This narrow polarization peak provides a sensitive diagnostic for detecting birefringent crystals in their often complicated atmosphere and it may be worthwhile to scan their polarization with high angular resolution to look for their halos. However, as the halo angles for bright halos are considerably less than 90°, one has to be at the far side of the planet. For Earth-bound observers, this is only possible for the inner planets, of which only Venus has an atmosphere.

The amounts of material from different parts of the zone from 0.7 to 1.5 AU from the Sun, which entered into almostformed the Earth and Venus, differed for these planets by no more than 3 times. For the TRAPPIST exoplanetary system,the ratio of the fraction of planetesimals collided with the planet, around which orbit initial orbits of planetesimals werelocated, to the fraction of planetesimals collided with the neighbouring planet was typically less than 4. Embryos of theEarth and the Moon with a total mass equaled to about 0.01-0.1 Earth mass could be formed as a result of compressionof a rarefied condensation. The fraction of material ejected from the Earth’s embryo and acquired by the Moon’s embryocould exceed by an order of magnitude the sum of the total mass of the planetesimals acquired by the Moon’s embryo andof the initial mass of the Moon’s embryo.

Abstract This paper reports a numerical study of buoyancy-induced flow and heat transfer in an enclosure with vents. The geometry closely resembles a “set-top-box” application frequently encountered in electronics cooling applications. The heat generating module is modeled as a planar heat source placed on a conducting printed circuit board (PCB). Full 3D and simplified 2D conjugate heat transfer models accounting for conduction and radiation in the solids and conduction and convection in the fluid were used Experiments performed to validate the 3D model have shown excellent comparisons with numerical results. A parametric study involving vent size, power dissipation, number of high conductivity power planes in the PCB has been performed with both the 3D and the 2D models. Although the quantitative results obtained from both types of analyses are similar only under certain conditions, qualitatively, the 2D analysis can be used to obtain useful insights into the complex overall transport mechanisms.

Unique cooling systems have to be designed to cool the electronic components of space exploration rover, especially in places like Venus, which has harsh surface conditions. The atmospheric pressure and temperature at the surface of Venus are 92 bars and 450°C respectively which make operation of electronic devices and sensors very difficult. Conventional cooling methods are currently deemed unfeasible due to the short life span of moving parts of the refrigerator systems at high temperatures. Furthermore, alternate energy sources such as solar power is not an option on Venus, since the cloud layer consisting of concentrated sulfuric acid droplets is thick and the surface reduces the solar intensity at the surface to about 2% of the intensity above the atmosphere. Therefore developing alternate method of power and cooling system is essential for Venus operation of any robotic rover. The advantages of using thermoacoustic systems are that there are no moving parts and they have efficiency comparable to conventional systems. Additionally there is a dearth in literature at using thermoacoustic refrigeration at high temperatures. This work discusses the development and optimization of a standing wave thermoacoustic engine refrigerator system to be used as a cooling device for the electronic components. The effects of various parameters such as gas mixture ratio, pressure, stack material etc. are discussed. The system designed provides cooling from 443K to 323K providing 150W of cooling.

The design of a dual shell or a dual pressure condenser employed in a coal fired plant is different from that in a combined cycle plant. The coal fired plant dual pressure condenser is equipped with feedwater heaters in the condenser neck, extraction piping, an external flash tank and a large number of vents and drains. Dual shell or dual pressure condenser in a combined cycle plant does not include feedwater heaters in the condenser neck and the related extraction piping. There is no external flash tank and the number of vents and drains are minimal. Combined cycle plants have a higher steam flowrate, are required to operate in bypass mode and in certain instances have high make up water flowrate. Apart from the above major differences there are a number of minor differences that must be accounted and addressed when converting a coal fired plant dual shell or dual pressure condenser into a combined cycle plant condenser. This paper highlights the major and minor differences in the design, construction and operation of dual shell or dual pressure condenser operating in a coal fired plants and combined cycle plant. The modifications required to convert the condenser from coal fired application to combined cycle application are discussed. Precautions to be followed in operating the condenser in the new role are addressed.

This paper offers a graphical exposition of the GTAP model of global trade. Particular emphasis is placed on the accounting, or equilibrium, relationships in the model. It begins with a treatment of the a one region version of GTAP, thereafter adding a rest of world region to highlight the treatment of trade flows in the model. The implementation of policy instruments in GTAP is also explored, using simple supply-demand graphics. The material provided in this paper was first developed as an introduction to GTAP for participants taking the annual short course. Based on its success in that venue, this paper has been placed on the "highly recommended" reading list for individuals seeking an introduction and overview of the GTAP framework. This paper offers a graphical exposition of the GTAP model of global trade. Particular emphasis is placed on the accounting, or equilibrium, relationships in the model. It begins with a treatment of the a one region version of GTAP, thereafter adding a rest of world region to highlight the treatment of trade flows in the model. The implementation of policy instruments in GTAP is also explored, using simple supply-demand graphics. The material provided in this paper was first developed as an introduction to GTAP for participants taking the annual short course. Based on its success in that venue, this paper has been placed on the highly recommended reading list for individuals seeking an introduction and overview of the GTAP framework.

A model of the energy balance of a transpiring crop in a greenhouse was developed in a format suitable for use in climate control algorithms aimed at dissipating excess heat during the warm periods. The model's parameters use external climatic variables as input. It incorporates radiation and convective transfer functions related to the operation of control devices like shading screens, vents, fans and enhanced evaporative cooling devices. The model identified the leaf boundary-layer resistance and the leaf stomatal and cuticular resistance as critical parameters regulating the temperature of the foliage. Special experiments evaluated these variables and established their relation to environmental factors. The research established that for heat load conditions in Mediterranean and arid climates transpiring crops maintained their foliage temperature within the range allowing high productivity. Results specify that a water supply ensuring minimum leaf resistance to remain below 100 s m-1, and a ventilation rate of 30 air exchanges per hour, are the conditions needed to achieve self cooling. Two vegetable crops, tomato and sweet pepper fulfilled maintained their leaf resistance within the prescribed range at maturity, i.e., during the critical warm season. The research evaluates the effects of additional cooling obtained from wet pad systems and spray wetting of foliage.

The size and shape of plant leaves are extremely diverse within and among species, and are also sensitive to growth conditions. Compound leaves, such as those of tomato, maintain morphogenetic activity during early stages of their development, enabling them to elaborate lateral appendages such as leaflets. The aim of the research project was to understand the interaction between the plant hormone auxin, the putative auxin response inhibitor ENTIRE (E, SlIAA9) and the NAM/CUC transcription factor GOBLET (GOB) in compound-leaf development in tomato (Solanum lycopersicum). The specific aims of the project were: 1. Investigation of the role of GOB in compound-leaf development. 2. Characterization of E function in auxin signaling. 3. Characterization of the role of auxin in compound-leaf development. 4. Investigation of the genetic and molecular interaction between E and GOB. 5. Investigate the role of these factors in fruit development. There were no major changes in these objectives. GOB was shown to mark and promote the boundaries between the leaf and initiating leaflets. Its accurate distribution was found to be required for proper leaflet initiation and separation. E was found to interact with the TIR1 and AFB6 proteins in an auxin-dependant manner, indicating that these are functional auxin receptors that mediate E degradation in the presence of auxin. This was further supported by the stabilization of E by a mutation in domain II of the protein, which is thought to mediate its auxin-dependant degradation. Over expression of this stabilized form in tomato leaves and characterization of the e mutant phenotype and the E expression domain indicated that E acts between initiating leaflets to inhibit auxin response and lamina growth. Generation and analysis of tomato plants expressing the auxin response reporter DR5::VENUS, and analysis of the effect of auxin microapplication or overexpression of an auxin biosynthesis gene, indicated that auxin marks the sites of leaflet initiation and promotes lamina growth. Investigation of the molecular and genetic interaction between auxin, GOB and E revealed a complex network of mutual regulation that is utilized to precisely pattern the leaf margin in a manner that enables the combination of tight control and flexibility. E, auxin and GOB were shown to affect fruit development and fruit set, and in an extension of the project are currently utilized to identify new players that affect these processes. The research project yielded enhanced understanding of the mechanisms of compound leaf patterning and provided tools that will enable the manipulation of leaf shape and fruit set.

The objectives of this project were to predict the performance of naturally and fan-ventilated greenhouses as a function of climate, type of crop, evaporative cooling and greenhouse size, and to estimate the effects of the two cooling systems on yield, quality and disease development in the different crops under study. Background In the competitive field of greenhouse cultivation, growers and designers in both the US and Israel are repeatedly forced to choose between naturally ventilated (NV) and fan ventilated (FV) cooling systems as they expand their ranges in an effort to remain profitable. The known advantages and disadvantages of each system do not presently allow a clear decision. Whether essentially zero operating costs can offset the less dependable cooling of natural ventilation systems is question this report hopes to answer. Major Conclusions US It was concluded very early on that FV greenhouses without evaporative pad cooling are not competitive with NV greenhouses during hot weather. During the first year, the US team found that average air temperatures were always higher in the FV houses, compared to the NV houses, when evaporative pad cooling was not used, regardless of ventilation rate in the FV houses or the vent configuration in the NV houses. Canopy temperatures were also higher in the FV ventilated houses when three vents were used in the NV houses. A second major conclusion was that the US team found that low pressure fogging (4 atm) in NV houses does not completely offset the advantage of evaporative pad cooling in FV houses. High pressure fog (65 atm) is more effective, but considerably more expensive. Israel Experiments were done with roses in the years 2003-2005 and with tomatoes in 2005. Three modes of natural ventilation (roof, side and side + roof openings) were compared with a fan-ventilated (with evaporative cooling) house. It was shown that under common practice of fan ventilation, during summer, the ventilation rate is usually lower with NV than with FV. The microclimate under both NV and FV was not homogeneous. In both treatments there were strong gradients in temperature and humidity in the vertical direction. In addition, there were gradients that developed in horizontal planes in a direction parallel to the direction of the prevailing air velocity within the greenhouse. The gradients in the horizontal direction appear to be larger with FV than with NV. The ratio between sensible and latent heat fluxes (Bowen ratio) was found to be dependent considerably on whether NV or FV is applied. This ratio was generally negative in the naturally ventilated house (about -0.14) and positive in the fan ventilated one (about 0.19). Theoretical models based on Penman-Monteith equation were used to predict the interior air and crop temperatures and the transpiration rate with NV. Good agreement between the model and experimental results was obtained with regard to the air temperature and transpiration with side and side + roof ventilation. However, the agreement was poor with only roof ventilation. The yield (number of rose stems longer than 40 cm) was higher with FV

Introduction u cours des deux derniers millénaires, il y a eu plusieurs façons de conserver, transmettre et même créer la connaissance ; la tradition orale, l’écrit manuscrit, l’écrit imprimé et l’écrit numérisé. La tradition orale et le manuscrit ont dominé pendant plus de 1400 ans, et ce, jusqu’à l’apparition du livre imprimé en 1451, résultant de l’invention mécanique de Gutenberg. Il faudra attendre un peu plus de 550 ans, avant que l’invention du support électronique déloge à son tour le livre imprimé, prenant une ampleur sans précédent grâce à la révolution numérique contemporaine, résultat du maillage des technologies de l’informatique, de la robotique et de la science des données. Les premières universités qui sont nées en Occident, au Moyen Âge, ont développé cette tradition orale de la connaissance tout en multipliant l’usage du manuscrit créant ainsi de véritables communautés de maîtres et d’étudiants ; la venue de l’imprimerie permettra la multiplication des universités où l’oral et l’écrit continueront de jouer un rôle déterminant dans la création et la transmission des connaissances même si le « support » a évolué du manuscrit à l’imprimé puis vers le numérique. Au cours de toutes ces années, le modèle de l’université s’est raffiné et perfectionné sur une trajectoire somme toute assez linéaire en élargissant son rôle dans l’éducation à celui-ci de la recherche et de l’innovation, en multipliant les disciplines offertes et les clientèles desservies. L’université de chaque ville universitaire est devenue une institution florissante et indispensable à son rayonnement international, à un point tel que l’on mesure souvent sa contribution par la taille de sa clientèle étudiante, l’empreinte de ses campus, la grandeur de ses bibliothèques spécialisées ; c’est toutefois la renommée de ses chercheurs qui consacre la réputation de chaque université au cours de cette longue trajectoire pendant laquelle a pu s’établir la liberté universitaire. « Les libertés universitaires empruntèrent beaucoup aux libertés ecclésiastiques » : Étudiants et maîtres, qu'ils furent, ou non, hommes d'Église, furent assimilés à des clercs relevant de la seule justice ecclésiastique, réputée plus équitable. Mais ils échappèrent aussi largement à la justice ecclésiastique locale, n'étant justiciables que devant leur propre institution les professeurs et le recteur, chef élu de l’université - ou devant le pape ou ses délégués. Les libertés académiques marquèrent donc l’émergence d'un droit propre, qui ménageait aux maîtres et aux étudiants une place à part dans la société. Ce droit était le même, à travers l'Occident, pour tous ceux qui appartenaient à ces institutions supranationales que furent, par essence, les premières universités. À la fin du Moyen Âge, l'affirmation des États nationaux obligea les libertés académiques à s'inscrire dans ce nouveau cadre politique, comme de simples pratiques dérogatoires au droit commun et toujours sujettes à révision. Vestige vénérable de l’antique indépendance et privilège octroyé par le prince, elles eurent donc désormais un statut ambigu » . La révolution numérique viendra fragiliser ce statut. En effet, la révolution numérique vient bouleverser cette longue trajectoire linéaire de l’université en lui enlevant son quasi monopole dans la conservation et le partage du savoir parce qu’elle rend plus facile et somme toute, moins coûteux l’accès à l’information, au savoir et aux données. Le numérique est révolutionnaire comme l’était l’imprimé et son influence sur l’université, sera tout aussi considérable, car cette révolution impacte radicalement tous les secteurs de l’économie en accélérant la robotisation et la numérisation des processus de création, de fabrication et de distribution des biens et des services. Ces innovations utilisent la radio-identification (RFID) qui permet de mémoriser et de récupérer à distance des données sur les objets et l’Internet des objets qui permet aux objets d’être reliés automatiquement à des réseaux de communications .Ces innovations s’entrecroisent aux technologies de la réalité virtuelle, à celles des algorithmiques intelligentes et de l’intelligence artificielle et viennent littéralement inonder de données les institutions et les organisations qui doivent alors les analyser, les gérer et les protéger. Le monde numérique est né et avec lui, a surgi toute une série de compétences radicalement nouvelles que les étudiants, les enseignants et les chercheurs de nos universités doivent rapidement maîtriser pour évoluer dans ce Nouveau Monde, y travailler et contribuer à la rendre plus humain et plus équitable. En effet, tous les secteurs de l’activité commerciale, économique, culturelle ou sociale exigent déjà clairement des connaissances et des compétences numériques et technologiques de tous les participants au marché du travail. Dans cette nouvelle logique industrielle du monde numérique, les gagnants sont déjà bien identifiés. Ce sont les fameux GAFAM (Google, Apple, Facebook, Amazon et Microsoft) suivis de près par les NATU (Netflix, Airbnb, Tesla et Uber) et par les géants chinois du numérique, les BATX (Baidu, Alibaba, Tenant et Xiaomi). Ces géants sont alimentés par les recherches, les innovations et les applications mobiles (APPs) créées par les partenaires de leurs écosystèmes regroupant, sur différents campus d’entreprises, plusieurs des cerveaux qui sont au cœur de cette révolution numérique. L’université voit donc remise en question sa capacité traditionnelle d’attirer, de retenir et de promouvoir les artisans du monde de demain. Son aptitude à former des esprits critiques et à contribuer à la transmission des valeurs universelles est également ébranlée par ce tsunami de changements. Il faut cependant reconnaître que les facultés de médecine, d’ingénierie et de sciences naturelles aux États-Unis qui ont développé des contacts étroits, abondants et suivis avec les hôpitaux, les grandes entreprises et l’administration publique et cela dès la fin du 19e siècle ont été plus en mesure que bien d’autres, de recruter et retenir les gens de talent. Elle ont énormément contribué à faire avancer les connaissances scientifiques et la scolarisation en sciences appliquées ..La concentration inouïe des Prix Nobel scientifiques aux États-Unis est à cet égard très convaincante . La révolution numérique contemporaine survient également au moment même où de grands bouleversements frappent la planète : l’urgence climatique, le vieillissement des populations, la « déglobalisation », les déplacements des populations, les guerres, les pandémies, la crise des inégalités, de l’éthique et des démocraties. Ces bouleversements interpellent les universitaires et c’est pourquoi leur communauté doit adopter une raison d’être et ainsi renouveler leur mission afin des mieux répondre à ces enjeux de la civilisation. Cette communauté doit non seulement se doter d’une vision et des modes de fonctionnement adaptés aux nouvelles réalités liées aux technologies numériques, mais elle doit aussi tenir compte de ces grands bouleversements. Tout ceci l’oblige à s’intégrer à des écosystèmes où les connaissances sont partagées et où de nouvelles compétences doivent être rapidement acquises. Le but de ce texte est de mieux cerner l’ampleur du défi que pose le monde numérique au milieu universitaire et de proposer quelques idées pouvant alimenter la réflexion des universitaires dans cette démarche d’adaptation au monde numérique. Or, ma conviction la plus profonde c’est que la révolution numérique aura des impacts sur nos sociétés et notre civilisation aussi grands que ceux provoqués par la découverte de l’imprimerie et son industrialisation au 15e siècle. C’est pourquoi la première section de ce document est consacrée à un rappel historique de la révolution de l’imprimerie par Gutenberg alors que la deuxième section illustrera comment les caractéristiques de la révolution numérique viennent soutenir cette conviction si profonde. Une troisième section fournira plus de détails sur le défi d’adaptation que le monde numérique pose aux universités alors que la quatrième section évoquera les contours du changement de paradigme que cette adaptation va imposer. La cinquième section servira à illustrer un scénario de rêves qui permettra de mieux illustrer l’ampleur de la gestion du changement qui guette les universitaires. La conclusion permettra de revenir sur quelques concepts et principes clefs pour guider la démarche vers l’action. L’université ne peut plus « être en haut et seule », elle doit être « au centre et avec » des écosystèmes de partenariats multiples, dans un modèle hybride physique/virtuel. C’est ainsi qu’elle pourra conserver son leadership historique de vigie du savoir et des connaissances d’un monde complexe, continuer d’établir l’authenticité des faits et imposer la nécessaire rigueur de la science et de l’objectivité.