La zone de déformation compressive des Brooks Range et des British-Barn située entre l’Alaska (Etats-Unis) et la région du Nord Yukon (Canada), en position arrière-arc, se développe dans un contexte cinématique et géodynamique depuis longtemps débattu. L’histoire tectonique du bloc continental Arctique d’Alaska, situé dans l’avant-pays de Brooks Range, est diversement interprétée dans les reconstructions de l’ouverture du bassin canadien. La chaîne de Brooks se développe à partir du Crétacé inférieur et sa mise en place se poursuit au Cénozoïque. Mieux contraindre son histoire d’exhumation, en relation avec le raccourcissement est essentiel dans cette région arctique où la cinématique des plaques, associée à l’ouverture du bassin canadien au Nord, fait l'objet de nombreux modèles géodynamiques controversés. La relation avec la subduction active Pacifique au Sud et les grands décrochements en arrière de la subduction fait de cette chaîne, en position arrière arc, une zone-clef pour affiner les reconstructions géodynamiques régionales et notre compréhension des processus orogéniques. Si le lien n'est pas établi entre la déformation mise en jeu dans cette subduction au Mésozoïque et la déformation dans la chaîne de Books, ce lien est en revanche assez bien documenté à l'heure actuelle. Il est donc légitime d'appréhender les événements sud-alaskans dans l'étude de cette chaîne de Brooks. La croissance de la chaîne au Cénozoïque est également mal comprise. Or, il s’agit d’un exemple quasi-unique de chaîne en milieu arctique active durant le Cénozoïque et qui a donc potentiellement enregistré des bouleversements climatiques majeurs, en l'occurrence depuis l‘optimum climatique à la transition Paléocène-Eocène, le refroidissement Oligocène jusqu’à la mise en place de glaciers et de la calotte nord-américaine au Quaternaire. Cet orogène est donc clef pour étudier voire quantifier l'impact du climat sur la construction topographique nord-alaskane. Ce travail a combiné une étude thermochronométrique basse-température multidatation (FT, (U-Th)/He) dans les massifs granitiques et dans les sédiments, qui ont fait l'objet de modélisation thermo-cinématiques via Pecube, dans le but de contraindre la construction orogénique depuis 100 Ma jusqu’à l’actuel. En parallèle, une approche structurale de terrain (Nord Yukon et Brooks Range) et l'analyse de données de subsurface ont été menées. Les données thermochronologiques, couplées à des analyses thermométriques RSCM et de la modélisation thermique soulignent la mise en place de reliefs au Crétacé supérieur avec une exhumation modérée (0.2 km/Ma) qui se poursuit jusqu'à la fin de l'Eocène, où les taux d'exhumation dans les chaînes de Brooks et British-Barn sont clairemement orogéniques (1.25-1.29km/Ma), et associés à la migration de la déformation vers les bassins adjacents. Ce travail souligne une migration de la déformation du SO vers le NE. Dans les deux segments de la chaîne un événement d'exhumation distinct est identifié à l'Oligocène : celui-ci est clairement associé dans la partie interne de la chaîne de Brooks à la mise en place hors-séquence d'un duplex crustal ; et associé à la migration de la déformation compressive en mer au large de la chaîne de British-Barn. Si le calendrier tectonique est semblable dans ces deux zones d'étude, il existe une différence majeure dans le style de déformation entre ces deux régions. Le front de déformation semble beaucoup plus éloigné de la chaîne et les failles beaucoup plus espacées dans la partie canadienne, éloignement et espacement probablement liés à l’épaisseur de sédiments syn-sédimentaires présents dans le bassin... / The kinematics and geodynamics associated with the compressional deformation in the Brooks Range and British-Barn Mountains, respectively in Alaska (USA) and North Yukon (Canada), in a back-arc setting has long been debated. In particular, the tectonic history of the Arctic Alaska continental block located in the foreland of the Brooks Range has been diversely interpreted in the plate reconstructions proposed for the Canadian basin. The Brooks Range mountain chain develops from the Lower Cretaceous to the Cenozoic. Constraining its exhumational history and its link with shortening evolution is essential in this arctic area where plate tectonics, associated to the Canadian basin opening in the North, has led to controversial geodynamic models. Tectonic coupling with the active Pacific subduction in the south as well as major seismogenic strike-slip faulting make this orogen a key area where to refine the regional plate reconstructions and understanding of orogenic processes. The Cenozoic evolution of the Brooks Mountains is poorly understood although it is a nearly unique example of arctic orogen, which have potentially recorded major climate changes like Paleocene-Eocene Thermal Maximum, the Oligocene cooling and Quaternary glaciations. This orogen is a key to study and quantify the climate impact on the north-alaskan topographic growth. This study combined low-temperature thermochronometry (FT, U-Th/He) on granitic and sedimentary rocks, which were thermo-kinematically modeled using Pecube in order to define the orogenic evolution of this arctic region since 100 Ma. In parallel, a field-based structural study (North Yukon and Brooks Range) was combined with the analysis of subsurface data. Thermochronological data, coupled to thermometric RSCM analyses and thermal modeling first define a slow exhumation period (0.2 km/Ma) from Upper Cretaceous up to the Eocene. With the Eocene, exhumation rates drastically increased to reach 1.25-1.29km/Ma as the deformation also migrates from SW toward NE. In both alaskan and canadian parts of mountains ranges a clear Oligocene exhumational event is identified. This event is linked to out-of-sequence crustal duplexing in the internal part of the range in the Brooks Range, contemporaneous with the propagation of deformation offshore, along British and Barn Mountains...

Präzise neutroneninduzierte Spaltquerschnitte von Actinoiden wie den Plutoniumisotopen haben für die Entwicklung zukünftiger Transmutationstechnologien eine große Bedeutung. Die Unsicherheiten des Pu(242)-Spaltquerschnitts im schnellen Bereich des Spektrums betragen derzeit etwa 21 %. Aktuelle Sensitivitätsstudien haben gezeigt, dass nur eine Reduzierung dieser Unsicherheiten auf unter 5% verlässliche neutronenphysikalische Simulationen zulässt. Diese anspruchsvolle Aufgabe konnte im Rahmen der vorliegenden Arbeit an der Neutronenfugzeitanlage nELBE durchgeführt werden. Dünne, homogene und großfächige Actinoiden-Proben wurden dem Helmholtz-Zentrum Dresden-Rossendorf innerhalb des TRAKULA-Verbundprojektes zur Verfügung gestellt. Eingesetzt in eine neu entwickelte Spaltionisationskammer ermöglichten sie eine akkurate Bestimmung des Pu(242)- Spaltquerschnitts relativ zu U(235). Die Flächendichten der Plutoniumschichten wurden anhand der spontanen Spaltrate von Pu(242) bestimmt. Aufwändige Teilchentransportsimulationen (durchgeführt mit Geant 4, MCNP 6 und FLUKA) wurden genutzt, um die auftretende Neutronenstreuung zu korrigieren. Die gewonnenen Ergebnisse sind im Rahmen ihrer Unsicherheiten in guter Übereinstimmung mit aktuellen Kerndatenevaluierungen. / Neutron induced fssion cross sections of actinides like the Pu-isotopes are of relevance for the development of nuclear transmutation technologies. For Pu(242), current uncertainties are of around 21%. Sensitivity studies show that the total uncertainty has to be reduced to below 5% to allow for reliable neutron physics simulations. This challenging task was performed at the neutron time-of-fight facility of the new German National Center for High Power Radiation Sources at HZDR, Dresden. Within the TRAKULA project, thin, large and homogeneous deposits of U(235) and Pu(242) have been produced successfully. Using two consecutively placed fssion chambers allowed the determination of the neutron induced fssion cross section of Pu(242) relative to U(235). The areal density of the Plutonium targets was calculated using the measured spontaneous fssion rate. Experimental results of the fast neutron induced fssion of Pu(242) acquired at nELBE will be presented and compared to recent experiments and evaluated data. Corrections addressing the neutron scattering are discussed by using results of different neutron transport simulations (Geant 4, MCNP 6 and FLUKA).

Comment les cellules établissent leurs formes et organisations internes est un problème biologique fondamental. Au cours de cette thèse, j’ai étudié le développement de la forme cellulaire et de la polarité chez la cellule de levure fissipare. Ces études sont fondées sur l’exploration de la façon dont les petites spores symétriques de levures se développent et s’organisent pour briser la symétrie pour la définition de leur tout premier axe de polarité. Dans une première partie, j’ai étudié les couplages entre la mécanique de surface de la paroi cellulaire des spores et la stabilité de domaines de polarité de Cdc42 qui contrôlent les aspects spatio-temporelles de la brisure de symétrie de ces spores. Dans une seconde partie, j’ai étudié les mécanismes par lesquels ces domaines de polarité contrôlent leur taille et l'adapte à la géométrie de la cellule, un processus vraisemblablement pertinents pour comprendre comment des domaines fonctionnels corticaux s’adaptent à la taille des cellules. Globalement, ces nouvelles recherches focalisant sur la façon dont les cellules développent dynamiquement leur forme et polarité de novo, permettent de mettre en évidence des couplages complexes dans la morphogenèse qui ne peuvent pas être testés en regardant les cellules à « l’état stationnaire» ou avec des outils génétiques. / How cells establish their proper shapes and organization is a fundamental biological problem. In this thesis, I investigated the dynamic development of cellular form and polarity in the rod-shape fission yeast cell. These studies are based on monitoring how small symmetric fission yeast spores grow and self-organize to break symmetry for the definition of their very first polarity axis. In a first part, I studied interplays between surface mechanics of the spore cell wall and the stability of Cdc42-based polarity domains which control spatio-temporal aspects of spore symmetry breaking. In a second part, I studied mechanisms by which these polarity domains control their width and adapt it to cell surface geometry, a process likely relevant to understand how functional cortical domains scale to cell size. Overall these novel investigations focusing on how cells dynamically develop their form and polarity de novo highlight complex feedbacks in morphogenesis that cannot be evidenced by looking at cells at “steady state” or with genetics.

Präzise neutroneninduzierte Spaltquerschnitte von Actinoiden wie den Plutoniumisotopen haben für die Entwicklung zukünftiger Transmutationstechnologien eine große Bedeutung. Die Unsicherheiten des Pu(242)-Spaltquerschnitts im schnellen Bereich des Spektrums betragen derzeit etwa 21 %. Aktuelle Sensitivitätsstudien haben gezeigt, dass nur eine Reduzierung dieser Unsicherheiten auf unter 5% verlässliche neutronenphysikalische Simulationen zulässt. Diese anspruchsvolle Aufgabe konnte im Rahmen der vorliegenden Arbeit an der Neutronenfugzeitanlage nELBE durchgeführt werden. Dünne, homogene und großfächige Actinoiden-Proben wurden dem Helmholtz-Zentrum Dresden-Rossendorf innerhalb des TRAKULA-Verbundprojektes zur Verfügung gestellt. Eingesetzt in eine neu entwickelte Spaltionisationskammer ermöglichten sie eine akkurate Bestimmung des Pu(242)- Spaltquerschnitts relativ zu U(235). Die Flächendichten der Plutoniumschichten wurden anhand der spontanen Spaltrate von Pu(242) bestimmt. Aufwändige Teilchentransportsimulationen (durchgeführt mit Geant 4, MCNP 6 und FLUKA) wurden genutzt, um die auftretende Neutronenstreuung zu korrigieren. Die gewonnenen Ergebnisse sind im Rahmen ihrer Unsicherheiten in guter Übereinstimmung mit aktuellen Kerndatenevaluierungen.:1 Einleitung 1.1 Partitionierung und Transmutation 1.2 Die Bedeutung von Pu(242) für P&T 1.3 Bisherige Experimente 1.4 Evaluierungen 1.5 Gliederung dieser Arbeit 2 Spaltwahrscheinlichkeit 2.1 Statistisches Modell und Compoundkern 2.2 Kernreaktionsrechnungen 3 Die Neutronenfugzeitanlage nELBE 4 Spaltionisationskammern 4.1 Die nELBE Spaltkammern 4.1.1 Actinoidenschichten 4.1.2 Aufbau 4.1.3 Gasversorgung 4.1.4 Optimierung des elektrischen Feldes 4.1.5 Simulationen von Impulshöhenverteilungen 4.2 Die PTB U(235) Spaltkammer H19 5 Experimente zur Spaltung von Pu(242) 5.1 Experimentelle Bestimmung neutroneninduzierter Spaltquerschnitte 5.2 Messaufbau 5.3 Datenaufnahme und -verarbeitung 5.4 Datenanalyse 5.4.1 Bestimmung der Spontanspaltrate 5.4.2 Bestimmung des neutroneninduzierten Spaltquerschnitts von Pu(242) 5.5 Ergebnisse und Diskussion 5.5.1 Diskussion 5.5.2 Unsicherheiten 5.5.3 Vergleich mit Kernreaktionsrechnungen 6 Zusammenfassung und Ausblick Anhang A.1 Depositionszelle A.2 Neutronenfugzeitanlagen A.3 Spaltfragmentverteilungen mit GEF A.4 Experimenteller Aufbau A.5 Aufbau der Datenaufnahme/-verarbeitung A.5.1 Verwendete Elektronik A.6 Stabilität der Datenaufnahme A.7 Konsistenzbetrachtung der Querschnittsbestimmung Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Liste der verwendeten Akronyme Publikationen / Neutron induced fssion cross sections of actinides like the Pu-isotopes are of relevance for the development of nuclear transmutation technologies. For Pu(242), current uncertainties are of around 21%. Sensitivity studies show that the total uncertainty has to be reduced to below 5% to allow for reliable neutron physics simulations. This challenging task was performed at the neutron time-of-fight facility of the new German National Center for High Power Radiation Sources at HZDR, Dresden. Within the TRAKULA project, thin, large and homogeneous deposits of U(235) and Pu(242) have been produced successfully. Using two consecutively placed fssion chambers allowed the determination of the neutron induced fssion cross section of Pu(242) relative to U(235). The areal density of the Plutonium targets was calculated using the measured spontaneous fssion rate. Experimental results of the fast neutron induced fssion of Pu(242) acquired at nELBE will be presented and compared to recent experiments and evaluated data. Corrections addressing the neutron scattering are discussed by using results of different neutron transport simulations (Geant 4, MCNP 6 and FLUKA).:1 Einleitung 1.1 Partitionierung und Transmutation 1.2 Die Bedeutung von Pu(242) für P&T 1.3 Bisherige Experimente 1.4 Evaluierungen 1.5 Gliederung dieser Arbeit 2 Spaltwahrscheinlichkeit 2.1 Statistisches Modell und Compoundkern 2.2 Kernreaktionsrechnungen 3 Die Neutronenfugzeitanlage nELBE 4 Spaltionisationskammern 4.1 Die nELBE Spaltkammern 4.1.1 Actinoidenschichten 4.1.2 Aufbau 4.1.3 Gasversorgung 4.1.4 Optimierung des elektrischen Feldes 4.1.5 Simulationen von Impulshöhenverteilungen 4.2 Die PTB U(235) Spaltkammer H19 5 Experimente zur Spaltung von Pu(242) 5.1 Experimentelle Bestimmung neutroneninduzierter Spaltquerschnitte 5.2 Messaufbau 5.3 Datenaufnahme und -verarbeitung 5.4 Datenanalyse 5.4.1 Bestimmung der Spontanspaltrate 5.4.2 Bestimmung des neutroneninduzierten Spaltquerschnitts von Pu(242) 5.5 Ergebnisse und Diskussion 5.5.1 Diskussion 5.5.2 Unsicherheiten 5.5.3 Vergleich mit Kernreaktionsrechnungen 6 Zusammenfassung und Ausblick Anhang A.1 Depositionszelle A.2 Neutronenfugzeitanlagen A.3 Spaltfragmentverteilungen mit GEF A.4 Experimenteller Aufbau A.5 Aufbau der Datenaufnahme/-verarbeitung A.5.1 Verwendete Elektronik A.6 Stabilität der Datenaufnahme A.7 Konsistenzbetrachtung der Querschnittsbestimmung Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Liste der verwendeten Akronyme Publikationen

In mammalian cells, homeostasis and fate during development relies on the proper transport of membrane-bound cargoes to their designated cellular locations. The hetero-tetrameric adaptor protein complexes (APs) are required for sorting and concentration of cargo at donor membranes, a crucial step during targeted transport. AP2, which functions at the plasma membrane during clathrin-mediated endocytosis, is well characterized. In contrast, AP1 a clathrin adaptor mediating the delivery of lysosomal hydrolases via mannose 6-phosphate receptors (MPRs) and AP3 an adaptor ensuring the proper targeting of lysosomal membrane protein are difficult to study by classic cell biology tools. To gain new insights on these APs, our lab has previously designed an in vitro system. Reconstituted liposomes were modified with small peptides mimicking the cytosolic domains of bona fide cargoes for AP1 and AP3 respectively and thereby enabling the selective recruitment of these APs and the identification of the interacting protein network. In the study at hand we utilize above-described liposomes to generate supported lipid bilayers and Giant Unilamellar Vesicles (GUVs), large-scale membrane systems suited for analysis by fluorescence microscopy. By using cytosol containing fluorescently-tagged subunits, we visualized clathrin coats on artificial membranes under near physiological conditions for the first time. Moreover, we demonstrated clathrin-independent recruitment of AP3 coats on respective GUVs. Presence of active ARF1 was sufficient for the selective assembly of AP1-dependent clathrin coats and AP3 coats on GUVs. By using dye-conjugated ARF1, we show that ARF1 colocalized with AP3 coats on GUVs and that increased association of ARF1 with GUVs coincided with AP1-dependent clathrin coats. Our previous study identified members of the septin family together with AP3 coats on liposomes. Here we show on GUVs, that active ARF1 stimulated the assembly of septin7 filaments, which may constrain the size and mobility of AP3 coats on the surface. Subsequent cell biology studies in HeLa cells linked septins to actin fibers on which they may control mobility of AP3-coated endosomes and thus their maturation. An actin nucleation complex, based on CYFIP1 was identified together with AP1 on liposomes before. Here we show on GUVs, that CYFIP1 is recruited on the surface surrounding clathrin coats. Upon supply of ATP, sustained actin polymerization generated a thick shell of actin on the GUV surface. The force generated by actin assembly lead to formation of long tubular protrusions, which projected from the GUV surface and were decorated with clathrin coats. Thereby the GUV model illustrated a possible mechanism for tubular carriers formation. The importance of CYFIP1-reliant actin polymerization for the generation of MPR-positive tubules at the trans-Golgi network (TGN) of HeLa cells was subsequently demonstrated in our lab. The notion that tubulation of artificial membranes could be triggered by actin polymerization allowed us to perform a comparative mass spectrometry screen. By comparing the abundance of proteins on liposomes under conditions promoting or inhibiting actin polymerization, candidates possibly involved in stabilization, elongation or fission of membrane tubules could be identified. Among the proteins enriched under conditions promoting tubulation, we identified type I phosphatidylinositol-4-phosphate 5-kinases. Their presence suggested an involvement of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in tubule formation. By cell biology studies in HeLa we show, that down regulation of these enzymes altered the dynamics of fluorescently-tagged MPRs, illustrating the importance of locally confined PI(4,5)P2 synthesis during formation of coated carriers at the TGN. Bin–Amphiphysin–Rvs (BAR) domains are known to sense membrane curvature and induce membrane tubulation. Among various BAR domain proteins, Arfaptin2 was enriched under conditions allowing tubulation of liposomes. By microscopy studies on HeLa cells we show, that Arfaptin2 as well as its close paralog Arfaptin1 were present on AP1-coated MPR tubules emerging from the TGN. We further show, that tubule fission occurred at regions were Arfaptin1 is concentrated and that simultaneous down regulation of both Arfaptins lead to increased number and length of MPR tubules. Since fission of coated transport intermediates at the TGN is poorly understood, our findings contribute a valuable component towards a model describing the entire biogenesis of coated post-Golgi carriers. In conclusion, combining artificial membrane systems and cell biology studies allowed us to propose new models for formation as wall as for fission of AP1-coated transport intermediates at the TGN. Further we gained new insights on AP3 coats and the possible involvement of septin filaments in AP3-dependent endosomal maturation.

In response to DNA damage during S phase, cells slow DNA replication. This slowing is orchestrated by the intra-S checkpoint and involves inhibition of origin firing and reduction of replication fork speed. Slowing of replication allows for tolerance of DNA damage and suppresses genomic instability. Although the mechanisms of origin inhibition by the intra-S checkpoint are understood, major questions remain about how the checkpoint regulates replication forks: Does the checkpoint regulate the rate of fork progression? Does the checkpoint affect all forks, or only those encountering damage? Does the checkpoint facilitate the replication of polymerase-blocking lesions? To address these questions, we have analyzed the checkpoint in the fission yeast Schizosaccharomyces pombe using a single-molecule DNA combing assay, which allows us to unambiguously separate the contribution of origin and fork regulation towards replication slowing, and allows us to investigate the behavior of individual forks. Moreover, we have interrogated the role of forks interacting with individual sites of damage by using three damaging agents—MMS, 4NQO and bleomycin—that cause similar levels of replication slowing with very different frequency of DNA lesions. We find that the checkpoint slows replication by inhibiting origin firing, but not by decreasing fork rates. However, the checkpoint appears to facilitate replication of damaged templates, allowing forks to more quickly pass lesions. Finally, using a novel analytic approach, we rigorously identify fork stalling events in our combing data and show that they play a previously unappreciated role in shaping replication kinetics in response to DNA damage.

Les cellules dans la nature se développent dans un large éventail de formes, suivant divers modèles de croissance. Malgré l'importance de ces processus fondamentaux, la façon dont les cellules régulent leur croissance et leur morphogenèse est encore mal comprise. Dans cette thèse, j'ai exploré ces aspects, avec une approche principalement biomécanique, en concentrant mes investigations sur des cellules à paroi à croissance de pointe et en exploitant en particulier la levure fissipare Schyzosaccharomyces pombe. J'ai d'abord développé de nouvelles méthodes pour mesurer les paramètres mécaniques clés de la paroi cellulaire in vivo et à grande échelle, ce qui a permis les premières observations de la dynamique des parois cellulaires. Ceci a révélé que la paroi cellulaire est plus souple et très variable au niveau des pôles de croissance, et presque stable et plus rigide dans les sites non cultivés. Au cours de l'allongement, il existe une interaction entre la mécanique des parois et la croissance cellulaire, dont le contrôle actif permet l'expansion cellulaire tout en préservant l'intégrité des cellules. De plus, j'ai observé qu'il existe une forte corrélation entre la mécanique des parois cellulaires et la morphologie cellulaire, et des perturbations des propriétés de la paroi affectent directement l'établissement et la maintenance de la forme. Ensemble, mes résultats montrent que la régulation de la paroi est fondamentale dans la détermination de la dynamique cellulaire dans les cellules à parois épaissies. Globalement, cela suggère que l'observation dynamique de la mécanique de surface cellulaire est essentielle pour une compréhension complète des processus multifactoriels et complexes comme la croissance et la morphogenèse. / Cells in nature develop in a wide range of forms, following diverse growth patterns. Despite the importance of these fundamental processes, how cells regulate their growth and morphogenesis is still poorly understood. In this thesis, I explored these processes, focusing my investigations on tip growing walled cells and in particular, by exploiting the fission yeast Schyzosaccharomyces pombe, adopting a mainly biomechanical approach. To this aim, I first developed novel methods to measure key cell wall mechanical parameters in vivo and in large scale, which allowed the very first observations of cell wall dynamics. This revealed that the cell wall is softer and highly variable at growing poles, and almost stable and stiffer at non-growing sites. During elongation, there is an interplay between wall mechanics and cell growth, whose active control allows cell expansion while preserving cell integrity. In addition, I observed that there is a strong correlation between cell wall mechanics and cell morphology, and ectopic perturbations of wall properties directly affect shape establishment and maintenance. Together my results show that the regulation of wall mechanics is fundamental in the determination of cell dynamics in tip growing walled cells. Moreover, this suggests that dynamic observation of cell surface mechanics is crucial for a complete understanding of multifactorial and complex processes as growth and morphogenesis.

No description available.

No description available.

[pt] Um espectrômetro de massa PDMS-252Cf-TOF (Time-of-Flight Plasma Dessorption Mass Spectrometry) foi usado para analisar amostras condensadas de água pura e misturas de H2O:C2H2, H2O:C2H6 e H2O:N2O, em temperaturas entre 10 e 100 K. Os íons dessorvidos devido ao impacto foram identificados e seus rendimentos de dessorção determinados. Observa-se que a distribuição desses rendimentos em função da massa dos íons pode ser descrita pela soma de duas exponenciais. Este resultado sugere fortemente que ocorrem dois processos de formação de agregados: um, via emissão direta de fragmentos do sólido e outro, via recombinação de fragmentos na fase gasosa. Para H2O puro, os principais agregados dessorvidos são: ((H2O)nH2O+, (H2O)nH3O+, On +, (H2O)nO−, (H2O)nOH− e On −. Para misturas de gelos H2O:C2H2 e H2O:C2H6, são observadas as séries (C2H2)n + e (C2H6)n +. Para H2O:N2O, as séries Nn +, (O)nN2 +, (O)nN2−, (O)nN4−, e (N2)nNO+ são as mais abundantes. A Teoria do Funcional da Densidade (DFT), no nível B3LYP/6-31G, foi usada para calcular a estabilidade molecular dos íons moleculares secundários emitidos. Cálculos para as estruturas C2Hm + (com m = 1 a 6) geraram 26 estruturas estáveis. As curvas de estabilidade por massa/carga obtidas são comparadas com aquelas obtidas experimentalmente para os rendimentos de dessorção por massa/carga para os mesmos íons. Tal metodologia é utilizada para prever as conformações mais prováveis dos íons dessorvidos. / [en] A PDMS-252Cf-TOF (Time-of-Flight Plasma Desorption Mass Spectrometry) mass spectrometer was used to analyze condensed samples of pure water and mixtures of H2O:C2H2, H2O:C2H6 and H2O:N2O, at temperatures between 10 and 100 K. The ions desorbed due to the projectile impact were identified and their desorption yields determined. It is observed that the yield distributions as a function of the mass of the ions can be described by the sum of two exponentials. This result strongly suggests that two processes of aggregate formation occur: one, via direct emission of fragments from the solid and the other, via recombination of fragments in the gas phase. For pure H2O, the main desorbed aggregates are: ((H2O)nH2O+, (H2O)nH3O+, On +, (H2O)nO−, (H2O)nOH− and On −. For mixtures of ices H2O:C2H2 and H2O:C2H6, the series (C2H2)n + and (C2H6)n + are observed. For H2O:N2O, the series Nn +, (O)nN2 +, (O)nN2−, (O)nN4−, and (N2)nNO+ are the most abundant. Density Functional Theory (DFT), at the B3LYP/6-31G level, was used to calculate the molecular stability of emitted secondary molecular ions. Calculations for the C2Hm + structures (with m = 1 to 6) generated 26 stable structures. The stability curves per mass/charge obtained are compared with those obtained experimentally for the desorption yields per mass/charge for the same ions. Such methodology is used to predict the most likely conformations of the desorbed ions.