Estudio de la localización de radionucleidos en pastillas de combustible nuclear gastado y su liberación a las aguas subterráneas de un almacenamiento geológico profundo (AGP)

Actualment hi ha una gran demanda energètica, per això la quantitat de residus radioactius produïts augmenta considerablement cada vegada, principalment a causa de la utilització creixent de les centrals nuclears en la generació d'energia elèctrica. Per això és molt important una gestió correcta dels combustibles nuclears gastats (CNG). Avui dia, una de les solucions per a la correcta gestió dels CNG que més viabilitat presenta són els emmagatzematges en formacions geològiques profundes (AGP). Els AGP serien una solució definitiva per als residus nuclears, que consisteixen a isolar i confinar el CNG a formacions geològiques profundes basades en un sistema multibarrera que tenen com a objectiu assegurar que el temps de trànsit fins a l'arribada a la biosfera de qualsevol radionúclid emmagatzemat que pogués alliberar-se sigui prou llarg per a evitar un gran impacte en l'home i el medi ambient. Un dels problemes que més suscita és que la barrera pugui fallar i hi hagi filtracions d'aigües subterrànies i alhora alliberament de radionúclids continguts (RN) en aquest. Per això, per a poder garantir la seguretat cal desenvolupar models que puguin predir el comportament del CNG en contacte amb aigües subterrànies a llarg termini, així com la migració de RN al medi ambient. Aquest treball se concentra en l'estudi i la localització DE RADIONUCLEÏTS A PASTILLES DE COMBUSTIBLE NUCLEAR GASTAT I EL SEU ALLIBERAMENT A LES AIGÜES SUBTERRÀNIES D'UN EMMAGATZEMATGE GEOLÒGIC PROFUND. Es va fer l'estudi de l'alliberament de nou elements (U, Pu, Nd, Cs, Sr, Mo, Tc, Ru i Rh) en diferents tipus de combustibles i mostres. Els valors experimentals són obtinguts d'altres estudis i ens han permès de dur a terme els ajustaments mitjançant un model matemàtic de caràcter semi-empíric anomenat SERNIM que és obtingut a (1). S'han estudiat 6 mostres amb graus de cremat (GC): 42 GWd/tU, 54 GWd/tU i 60 GWd/tU), tipus de combustible (BWR i PWR), totes les mostres són pastilles, per a cada GQ hi ha dues mostres, MID i el FULL, aquestes mostres corresponen a diferents zones de la pastilla i Bicarbonat (BIC) com a lixiviant. Els resultats per al Cs i el Sr són els esperats per a tots els casos estudiats. Per al Ru i el Rh també s'obtenen els resultats esperats, perquè la seva solubilitat no és regida per la matriu del combustible. Amb el Pu s'esperava un millor ajustament i es va observar que en la major part de casos l'ajust era per sobre dels valors experimentals, però malgrat això la evolució del Pu és congruent amb el SERNIM. Finalment, tenim el Nd el Mo i el Tc. S'observa que els 3 RN són congruents amb l'urani per a valors alts de GQ sobretot per a les mostres d'un GQ 60GWd/tU.Actualmente existe una gran demanda energética, por eso cada vezla cantidad de residuos radiactivos producidos ha aumentado considerablemente debido, principalmente, a la utilización creciente de las centrales nucleares en la generación de energía eléctrica. Por eso, es muy importante una correcta gestión de los combustibles nucleares gastados (CNG). Hoy en día, una de las soluciones para la correcta gestión de los CNG que mayor viabilidad presenta son los almacenamientos en formaciones geológicas profundas (AGP). Los AGP serían una solución definitiva para los residuos nucleares, que consisten en aislar y confinar el CNG a formaciones geológicas profundas basadas en un sistema multibarrera cuyo objetivo es asegurar que el tiempo de tráfico hasta la llegada a la biosfera de cualquier radionucleido almacenado que pudiera liberarse sea lo suficientemente largo para evitar un gran impacto en el hombre y el medio ambiente. Uno de los problemas que más suscita es que la barrera pueda fallar y existan filtraciones de aguas subterráneas y al mismo tiempo la liberación de los radionucleidos contenidos (RN) en el mismo. Por eso, para poder garantizar la seguridad es necesario desarrollar modelos que puedan predecir el comportamiento del CNG en contacto con aguas subterráneas a largo plazo, así como la migración de RN al medio ambiente. Este trabajo se centra en el estudio y la localización DE RADIONUCLEIDOS EN PASTILLAS DE COMBUSTIBLE NUCLEAR GASTADO Y SU LIBERACIÓN EN LAS AGUAS SUBTERRÁNEAS DE UN ALMACENAMIENTO GEOLÓGICO PROFUNDO. Se realizó el estudio de la liberación de nueve elementos (U, Pu, Nd, Cs, Sr, Mo, Tc, Ru y Rh) en diferentes tipos de combustibles y muestras. Los valores experimentales se obtienen de otros estudios y nos han permitido llevar a cabo los ajustes mediante un modelo matemático de carácter semiempirico llamado SERNIM que se obtiene en (1). Se han estudiado 6 muestras con grados de quemado (GC): 42 GWd/tU, 54 GWd/tU y 60 GWd/tU), tipos de combustible (BWR y PWR), todas las muestran son pastillas, para cada GQ hay dos muestras, MID y FULL, estas muestras corresponden a diferentes zonas de la pastilla y Bicarbonato (BIC) como lixiviante. Los resultados para Cs y Sr son los esperados para todos los casos estudiados. Para Ru y Rh también se obtienen los resultados esperados, ya que su solubilidad no está regida por la matriz del combustible. Con el Pu se esperaba un mejor ajuste y se observó que en la mayoría de los casos el ajuste estaba por encima de los valores experimentales, pero aun así la evolución del Pu es congruente con el SERNIM. Por último, tenemos el Nd el Mo y el Tc. Se observa que los 3 RN son congruentes con el uranio para valores altos de GQ sobre todo para las muestras de un GQ 60GWd/tU.There is currently a great energy demand, which is why the amount of radioactive waste produced has increased considerably, mainly due to the growing use of nuclear power plants in the generation of electrical energy. That is why proper management of spent nuclear fuels (SNF) is very important. Today, one of the most viable solutions for the correctmanagement of SNF is storage in deep geological formations (DGF), DGF would be a definitive solution for nuclear waste, which consists of isolating and confining the SNF to deep geological formations based on a multi-barrier system whose objective is to ensure that the traffic time until the arrival in the biosphere of any stored radionuclide that could be released is long enough to avoid a major impact on man and the environment. One of the problems that most arises are the fact that the barrier can fail and that there could be leaks of groundwater and at the same time release of radionuclides (RN) contained in it. Therefore, to guarantee safety, it is necessary to develop models that can predict the long-term behavior of SNF in contact with groundwater, as well as the migration of NR into the environment. This work focuses on the study and location of RADIONUCLIDES IN SPENT NUCLEAR FUEL PILLS AND THEIR RELEASE IN GROUNDWATER FROM DEEP GEOLOGICAL STORAGE. The study of the release of nine elements (U, Pu, Nd, Cs, Sr, Mo, Tc, Ru and Rh) in different types of fuels and samples was carried out. The experimental values are obtained from other studies and have allowed us to carry out the adjustments using a semi-empirical mathematical model called SERNIM, which is obtained in (1). 6 samples have been studied with burnup degrees (GC): 42 GWd/tU, 54 GWd/tU and 60 GWd/tU), types of fuel (BWR and PWR), all samples being pellets, two samples for each GQ, MID and FULL, these samples corresponding to different areas of the tablet, and bicarbonate (BIC) as lixiviant. The results for Cs and Sr are as expected for all the cases studied. For Ru and Rh the expected results are also obtained since their solubility is not governed by the fuel matrix. A better fit was expected for Pu, and it was observed that in most cases the fit was above the experimental values, but even so, the evolution of Pu is consistent with SERNIM. Finally, with the Nd, the Mo, and the Tc, it is observed that the 3 RN are congruent with the uranium for high BU values, especially for the samples of a BU 60GWd/tU

Deep Lake: a Lakehouse for Deep Learning

Traditional data lakes provide critical data infrastructure for analytical workloads by enabling time travel, running SQL queries, ingesting data with ACID transactions, and visualizing petabyte-scale datasets on cloud storage. They allow organizations to break down data silos, unlock data-driven decision-making, improve operational efficiency, and reduce costs. However, as deep learning takes over common analytical workflows, traditional data lakes become less useful for applications such as natural language processing (NLP), audio processing, computer vision, and applications involving non-tabular datasets. This paper presents Deep Lake, an open-source lakehouse for deep learning applications developed at Activeloop. Deep Lake maintains the benefits of a vanilla data lake with one key difference: it stores complex data, such as images, videos, annotations, as well as tabular data, in the form of tensors and rapidly streams the data over the network to (a) Tensor Query Language, (b) in-browser visualization engine, or (c) deep learning frameworks without sacrificing GPU utilization. Datasets stored in Deep Lake can be accessed from PyTorch, TensorFlow, JAX, and integrate with numerous MLOps tools

Understanding Conformational Dynamics of Complex Lipid Mixtures Relevant to Biology

This is a perspective article entitled “Frontiers in computational biophysics: understanding conformational dynamics of complex lipid mixtures relevant to biology” which is following a CECAM meeting with the same name.Fil: Friedman, Ran. Linnæus University; ArgentinaFil: Khalid, Syma. University of Southampton; Reino UnidoFil: Aponte Santamaría, Camilo. Ruprecht-Karls-Universität Heidelberg; Alemania. Universidad de los Andes; ColombiaFil: Arutyunova, Elena. University of Alberta; CanadáFil: Becker, Marlon. Westfälische Wilhelms Universität; AlemaniaFil: Boyd, Kevin J.. University of Connecticut; Estados UnidosFil: Christensen, Mikkel. University Aarhus; DinamarcaFil: Coimbra, João T. S.. Universidad de Porto; PortugalFil: Concilio, Simona. Universita di Salerno; ItaliaFil: Daday, Csaba. Heidelberg Institute for Theoretical Studies; AlemaniaFil: Eerden, Floris J. van. University of Groningen; Países BajosFil: Fernandes, Pedro A.. Universidad de Porto; PortugalFil: Gräter, Frauke. Heidelberg University; Alemania. Heidelberg Institute for Theoretical Studies; AlemaniaFil: Hakobyan, Davit. Westfälische Wilhelms Universität; AlemaniaFil: Heuer, Andreas. Westfälische Wilhelms Universität; AlemaniaFil: Karathanou, Konstantina. Freie Universität Berlin; AlemaniaFil: Keller, Fabian. Westfälische Wilhelms Universität; AlemaniaFil: Lemieux, M. Joanne. University of Alberta; CanadáFil: Marrink, Siewert J.. University of Groningen; Países BajosFil: May, Eric R.. University of Connecticut; Estados UnidosFil: Mazumdar, Antara. University of Groningen; Países BajosFil: Naftalin, Richard. Colegio Universitario de Londres; Reino UnidoFil: Pickholz, Mónica Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Piotto, Stefano. Universita di Salerno; ItaliaFil: Pohl, Peter. Johannes Kepler University; AustriaFil: Quinn, Peter. Colegio Universitario de Londres; Reino UnidoFil: Ramos, Maria J.. Universidad de Porto; PortugalFil: Schiøtt, Birgit. University Aarhus; DinamarcaFil: Sengupta, Durba. National Chemical Laboratory India; IndiaFil: Sessa, Lucia. Universita di Salerno; ItaliaFil: Vanni, Stefano. University Of Fribourg;Fil: Zeppelin, Talia. University Aarhus; DinamarcaFil: Zoni, Valeria. University of Fribourg; SuizaFil: Bondar, Ana-Nicoleta. Freie Universität Berlin; AlemaniaFil: Domene, Carmen. University of Oxford; Reino Unido. University of Bath; Reino Unid

Spin-orbit optomechanics of space-variant birefringent media

Ce travail consiste en l'étude de phénomènes optomécaniques en d'interaction spin-orbite de la lumière, en utilisant des milieux inhomogènes et anisotropes comme systèmes modèles, différents types de systèmes matériels étant considérés en pratique. En particulier,nous avons utilisé des défauts de cristaux liquides nématiques pour lesquels nous avons identifié expérimentalement d'un couple optique de nature spin-orbite conduisant à des modifications de champ d'orientation moléculaire du cristal liquide. Aussi, grâce à l'utilisation de verres nanostructurés artificiellement permettant un contrôle de l'interaction spin-orbite à la demande,nous mettons en évidence un phénomène de couple optique inverse qui est l'analogue angulaire des forces optiques dites négatives. Cet effet optomécanique contre-intuitif est démontré expérimentalement, d'une manière indirecte, grâce à la mise en place de diverses expériences de décalage en fréquence Doppler associées aux degrés de liberté de rotation. Enfin, nous présentons nos tentatives en vue de réaliser expérimentalement l'observation directe d'un couple optique inverse. Plusieurs options sont envisagées, qui comprennent à la fois des approches à base de matériaux métalliques ou diélectriques. De manière générale, cela implique la miniaturisation des systèmes considérés, ce qui est effectué à la fois à l'échelle millimétrique et micrométrique.This work focuses on angular optomechanics driven by the spin-orbit interaction of light, using inhomogeneous and anisotropic media as model systems and different kinds of such material systems are considered in practice. In particular, we use nematic liquid crystal defects and report on the direct experimental observation of spin-orbit optical radiation torque that leads to distortion of molecular orientation pattern of the defects. Then, by using solid-state spin-orbit couplers of arbitrary order made of artificially nanostructured glasses, we unveil an optical torque reversal phenomenon that is the angular counterpart of so-called optical negative forces. This counterintuitive optomechanical effect is experimentally retrieved, in an indirect manner, via rotational Doppler frequency shift experiments. Finally, we report on our attempts to build up an experimental framework allowing the direct observation of optical torque reversal. Several options are considered, which include both metallic and dielectric approaches and involve sample miniaturization that has been explored at the millimeter and micrometer scale

Spin-orbit optomechanics of space-variant birefringent media

Ce travail consiste en l'étude de phénomènes optomécaniques en d'interaction spin-orbite de la lumière, en utilisant des milieux inhomogènes et anisotropes comme systèmes modèles, différents types de systèmes matériels étant considérés en pratique. En particulier,nous avons utilisé des défauts de cristaux liquides nématiques pour lesquels nous avons identifié expérimentalement d'un couple optique de nature spin-orbite conduisant à des modifications de champ d'orientation moléculaire du cristal liquide. Aussi, grâce à l'utilisation de verres nanostructurés artificiellement permettant un contrôle de l'interaction spin-orbite à la demande,nous mettons en évidence un phénomène de couple optique inverse qui est l'analogue angulaire des forces optiques dites négatives. Cet effet optomécanique contre-intuitif est démontré expérimentalement, d'une manière indirecte, grâce à la mise en place de diverses expériences de décalage en fréquence Doppler associées aux degrés de liberté de rotation. Enfin, nous présentons nos tentatives en vue de réaliser expérimentalement l'observation directe d'un couple optique inverse. Plusieurs options sont envisagées, qui comprennent à la fois des approches à base de matériaux métalliques ou diélectriques. De manière générale, cela implique la miniaturisation des systèmes considérés, ce qui est effectué à la fois à l'échelle millimétrique et micrométrique.This work focuses on angular optomechanics driven by the spin-orbit interaction of light, using inhomogeneous and anisotropic media as model systems and different kinds of such material systems are considered in practice. In particular, we use nematic liquid crystal defects and report on the direct experimental observation of spin-orbit optical radiation torque that leads to distortion of molecular orientation pattern of the defects. Then, by using solid-state spin-orbit couplers of arbitrary order made of artificially nanostructured glasses, we unveil an optical torque reversal phenomenon that is the angular counterpart of so-called optical negative forces. This counterintuitive optomechanical effect is experimentally retrieved, in an indirect manner, via rotational Doppler frequency shift experiments. Finally, we report on our attempts to build up an experimental framework allowing the direct observation of optical torque reversal. Several options are considered, which include both metallic and dielectric approaches and involve sample miniaturization that has been explored at the millimeter and micrometer scale

Authentication and Authorization Systems in Cloud Environments

The emergence of cloud computing paradigm offers attractive and innovative computing services through resource pooling and virtualization techniques. Cloud providers deliver various types of computing services to customers according to a pay-per-use economic model. However, this technology shift introduces a new concern for enterprises and businesses regarding their privacy and security. Security as a Service is a new cloud service model for the security enhancement of a cloud environment. This is a way of centralizing security solutions under the control of professional security specialists. Identity and access control services are one of the areas of cloud security services, and sometimes, are presented under the term Identity as a Service. This master thesis research is focused on identity-security solutions for cloud environments. More specifically, architecture of a cloud security system is designed and proposed for providing two identity services for cloud-based systems: authentication and authorization. The main contribution of this research is to design these services using service-oriented architectural approach, which will enable cloud-based application service providers to manage their online businesses in an open, flexible, interoperable and secure environment. First, the architecture of the proposed services is described. Through this architecture all system entities that are necessary for managing and providing those identity services are defined. Then, the design and specification of each service is described and explained. These services are based on existing and standardized security mechanisms and frameworks. As a demonstration, a prototype system of an authorization service is implemented and tested based on the designed authorization solution. The implementation is done using Web Service technology respective to the service-oriented design approach. It is shown that both services are at least computationally secure against potential security risks associated with replay attacks, message information disclosure, message tampering, repudiation and impersonation. The designed security system ensures a secure and reliable environment for cloud-based application services which is very easy to deploy and exploit on cloud-based platforms

Optomécanique des milieux biréfringents inhomogènes pilotée par l'interaction spinorbite de la lumière

This work focuses on angular optomechanics driven by the spin-orbit interaction of light, using inhomogeneous and anisotropic media as model systems and different kinds of such material systems are considered in practice. In particular, we use nematic liquid crystal defects and report on the direct experimental observation of spin-orbit optical radiation torque that leads to distortion of molecular orientation pattern of the defects. Then, by using solid-state spin-orbit couplers of arbitrary order made of artificially nanostructured glasses, we unveil an optical torque reversal phenomenon that is the angular counterpart of so-called optical negative forces. This counterintuitive optomechanical effect is experimentally retrieved, in an indirect manner, via rotational Doppler frequency shift experiments. Finally, we report on our attempts to build up an experimental framework allowing the direct observation of optical torque reversal. Several options are considered, which include both metallic and dielectric approaches and involve sample miniaturization that has been explored at the millimeter and micrometer scale.Ce travail consiste en l'étude de phénomènes optomécaniques en d'interaction spin-orbite de la lumière, en utilisant des milieux inhomogènes et anisotropes comme systèmes modèles, différents types de systèmes matériels étant considérés en pratique. En particulier,nous avons utilisé des défauts de cristaux liquides nématiques pour lesquels nous avons identifié expérimentalement d'un couple optique de nature spin-orbite conduisant à des modifications de champ d'orientation moléculaire du cristal liquide. Aussi, grâce à l'utilisation de verres nanostructurés artificiellement permettant un contrôle de l'interaction spin-orbite à la demande,nous mettons en évidence un phénomène de couple optique inverse qui est l'analogue angulaire des forces optiques dites négatives. Cet effet optomécanique contre-intuitif est démontré expérimentalement, d'une manière indirecte, grâce à la mise en place de diverses expériences de décalage en fréquence Doppler associées aux degrés de liberté de rotation. Enfin, nous présentons nos tentatives en vue de réaliser expérimentalement l'observation directe d'un couple optique inverse. Plusieurs options sont envisagées, qui comprennent à la fois des approches à base de matériaux métalliques ou diélectriques. De manière générale, cela implique la miniaturisation des systèmes considérés, ce qui est effectué à la fois à l'échelle millimétrique et micrométrique

Spin-orbit optomechanics of space-variant birefringent media

Ce travail consiste en l'étude de phénomènes optomécaniques en d'interaction spin-orbite de la lumière, en utilisant des milieux inhomogènes et anisotropes comme systèmes modèles, différents types de systèmes matériels étant considérés en pratique. En particulier,nous avons utilisé des défauts de cristaux liquides nématiques pour lesquels nous avons identifié expérimentalement d'un couple optique de nature spin-orbite conduisant à des modifications de champ d'orientation moléculaire du cristal liquide. Aussi, grâce à l'utilisation de verres nanostructurés artificiellement permettant un contrôle de l'interaction spin-orbite à la demande,nous mettons en évidence un phénomène de couple optique inverse qui est l'analogue angulaire des forces optiques dites négatives. Cet effet optomécanique contre-intuitif est démontré expérimentalement, d'une manière indirecte, grâce à la mise en place de diverses expériences de décalage en fréquence Doppler associées aux degrés de liberté de rotation. Enfin, nous présentons nos tentatives en vue de réaliser expérimentalement l'observation directe d'un couple optique inverse. Plusieurs options sont envisagées, qui comprennent à la fois des approches à base de matériaux métalliques ou diélectriques. De manière générale, cela implique la miniaturisation des systèmes considérés, ce qui est effectué à la fois à l'échelle millimétrique et micrométrique.This work focuses on angular optomechanics driven by the spin-orbit interaction of light, using inhomogeneous and anisotropic media as model systems and different kinds of such material systems are considered in practice. In particular, we use nematic liquid crystal defects and report on the direct experimental observation of spin-orbit optical radiation torque that leads to distortion of molecular orientation pattern of the defects. Then, by using solid-state spin-orbit couplers of arbitrary order made of artificially nanostructured glasses, we unveil an optical torque reversal phenomenon that is the angular counterpart of so-called optical negative forces. This counterintuitive optomechanical effect is experimentally retrieved, in an indirect manner, via rotational Doppler frequency shift experiments. Finally, we report on our attempts to build up an experimental framework allowing the direct observation of optical torque reversal. Several options are considered, which include both metallic and dielectric approaches and involve sample miniaturization that has been explored at the millimeter and micrometer scale

Spin-orbit optomechanics of space-variant birefringent media

Ce travail consiste en l'étude de phénomènes optomécaniques en d'interaction spin-orbite de la lumière, en utilisant des milieux inhomogènes et anisotropes comme systèmes modèles, différents types de systèmes matériels étant considérés en pratique. En particulier,nous avons utilisé des défauts de cristaux liquides nématiques pour lesquels nous avons identifié expérimentalement d'un couple optique de nature spin-orbite conduisant à des modifications de champ d'orientation moléculaire du cristal liquide. Aussi, grâce à l'utilisation de verres nanostructurés artificiellement permettant un contrôle de l'interaction spin-orbite à la demande,nous mettons en évidence un phénomène de couple optique inverse qui est l'analogue angulaire des forces optiques dites négatives. Cet effet optomécanique contre-intuitif est démontré expérimentalement, d'une manière indirecte, grâce à la mise en place de diverses expériences de décalage en fréquence Doppler associées aux degrés de liberté de rotation. Enfin, nous présentons nos tentatives en vue de réaliser expérimentalement l'observation directe d'un couple optique inverse. Plusieurs options sont envisagées, qui comprennent à la fois des approches à base de matériaux métalliques ou diélectriques. De manière générale, cela implique la miniaturisation des systèmes considérés, ce qui est effectué à la fois à l'échelle millimétrique et micrométrique.This work focuses on angular optomechanics driven by the spin-orbit interaction of light, using inhomogeneous and anisotropic media as model systems and different kinds of such material systems are considered in practice. In particular, we use nematic liquid crystal defects and report on the direct experimental observation of spin-orbit optical radiation torque that leads to distortion of molecular orientation pattern of the defects. Then, by using solid-state spin-orbit couplers of arbitrary order made of artificially nanostructured glasses, we unveil an optical torque reversal phenomenon that is the angular counterpart of so-called optical negative forces. This counterintuitive optomechanical effect is experimentally retrieved, in an indirect manner, via rotational Doppler frequency shift experiments. Finally, we report on our attempts to build up an experimental framework allowing the direct observation of optical torque reversal. Several options are considered, which include both metallic and dielectric approaches and involve sample miniaturization that has been explored at the millimeter and micrometer scale

Key molecular requirements for raft formation in lipid/cholesterol membranes.

The lipid mixture of DPPC (saturated lipid)/DUPC (unsaturated lipid)/CHOL (cholesterol) is studied with respect to its ability to form liquid-ordered and liquid-disordered phases. We employ coarse-grained simulations with MARTINI force field. All three components are systematically modified in order to explore the relevant molecular properties, leading to phase separation. Specifically, we show that the DPPC/DUPC/CHOL system unmixes due to enthalpic DPPC-DPPC and DPPC-CHOL interactions. The phase separation remains unchanged, except for the formation of a gel phase at long times after decreasing the conformational degrees of freedom of the unsaturated DUPC. In contrast, the phase separation can be suppressed by softening the DPPC chains. In an attempt to mimic the ordering and unmixing effect of CHOL the latter is replaced by a stiff and shortened DPPC-like lipid. One still observes phase separation, suggesting that it is mainly the rigid and planar structure of CHOL which is important for raft formation. Addition of an extra bead to the head of CHOL has no notable impact on the phase separation of the system, supporting the irrelevance of the Umbrella model for the phase separation. Reduction of the conformational entropy of CHOL by stiffening its last bead results in a significant increase of the order of the DPPC/CHOL domain. This suggests that the conformational entropy of CHOL is important to prohibit the gelation process. The interleaflet interactions as mediated by the terminal molecular groups seem to have a strong impact on the possibility of a subsequent gelation process after phase separation