299 research outputs found
Cat-qubit-inspired gate on cos() qubits
For qubits based on voltage-controlled semiconductor nanowire
Josephson junctions we introduce a single-qubit gate inspired by the
noise-bias preserving gate of the Kerr-cat qubit. This scheme relies on a
rotation in phase space via a beamsplitter-like transformation between a qubit
and ancilla qubit. The rotation is implemented by adiabatically changing the
potential energies of the two qubits such as to preserve a double-well
potential at all times. This gate constrains the dynamics in the subspace of a
qubit at all times, therefore yielding high-fidelity operation
while preserving the qubit's coherence. We introduce a circuit to realize this
gate and support our findings with numerical simulations.Comment: 12 pages, 9 figure
La genÚse des objets idéaux dans la phénoménologie tardive de Husserl
Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal
Méthode bayésienne de détection de rupture et/ou de tendance pour des données temporelles
Ce mémoire a pour but de déterminer des nouvelles méthodes de détection
de rupture et/ou de tendance. AprÚs une brÚve introduction théorique sur les
splines, plusieurs méthodes de détection de rupture existant déjà dans la littérature
seront présentées. Puis, de nouvelles méthodes de détection de rupture qui
utilisent les splines et la statistique bayésienne seront présentées. De plus, afin
de bien comprendre dâoĂč provient la mĂ©thode utilisant la statistique bayĂ©sienne,
une introduction sur la thĂ©orie bayĂ©sienne sera prĂ©sentĂ©e. Ă lâaide de simulations,
nous effectuerons une comparaison de la puissance de toutes ces méthodes. Toujours
en utilisant des simulations, une analyse plus en profondeur de la nouvelle
méthode la plus efficace sera effectuée. Ensuite, celle-ci sera appliquée sur des
données réelles. Une brÚve conclusion fera une récapitulation de ce mémoire.This thesis aims to identify new change-point detection methods and/or trend
in temporal data. After a brief theoretical introduction on splines, several existing
change-point detection already in the literature will be presented. Then, new
change-point detection methods using splines and Bayesian statistics will be presented.
Moreover, in order to understand the method using Bayesian statistics,
an introduction to Bayesian theory will be presented. Using simulations, we will
make a comparison of the power of all these methods. Still using simulations, an
analysis of the new most effective method will be performed. Then, this method
will be applied to real data. A brief conclusion will make a summary of this thesis
CaractĂ©risation de la sous-unitĂ© bĂȘta du translocon chez la levure Schizosaccharomyces pombe
La sĂ©crĂ©tion des protĂ©ines est un processus essentiel Ă la vie. Chez les eucaryotes, les protĂ©ines sĂ©crĂ©tĂ©es transitent dans le rĂ©ticulum endoplasmique par le pore de translocation. Le translocon est composĂ© de trois sous-unitĂ©s fondamentales nommĂ©es Sec61α, ÎČ et Îł chez les mammifĂšres, ou Sec61p, Sbh1p et Sss1p chez les levures. Tandis que le rĂŽle des sous-unitĂ©s α et Îł est bien connu, celui de la sous-unitĂ© ÎČ demeure Ă©nigmatique. Plusieurs phĂ©notypes distincts sont associĂ©s Ă cette protĂ©ine dans diffĂ©rents organismes, mais le haut niveau de conservation de sĂ©quence suggĂšre plutĂŽt une fonction universelle conservĂ©e. RĂ©cemment, Feng et al. (2007) ont montrĂ© que le domaine transmembranaire (TMD) de Sbh1p Ă©tait suffisant pour complĂ©menter plusieurs phĂ©notypes associĂ©s Ă la dĂ©lĂ©tion du gĂšne chez Saccharomyces cerevisiae, suggĂ©rant un rĂŽle important de cette rĂ©gion. Lâobjectif de mon projet de recherche consiste Ă Ă©tudier la fonction biologique de la sous-unitĂ© ÎČ du translocon et de son TMD chez Schizosaccharomyces pombe. Dans cette levure, jâai dĂ©couvert que le gĂšne sbh1+ nâĂ©tait pas essentiel Ă la viabilitĂ© Ă 30oC, mais quâil Ă©tait requis pour la croissance Ă basse tempĂ©rature. La dĂ©lĂ©tion de sbh1+ entraĂźne une sensibilitĂ© aux stress de la paroi cellulaire et une diminution de la sĂ©crĂ©tion des protĂ©ines Ă 23oC. La surexpression de Sbh1p diminue elle aussi la sĂ©crĂ©tion des protĂ©ines et altĂšre la morphologie cellulaire. Ces phĂ©notypes sont distincts de ceux observĂ©s chez S. cerevisiae, oĂč la dĂ©lĂ©tion des deux paralogues de Sec61ÎČ entraĂźne une sensibilitĂ© Ă haute tempĂ©rature plutĂŽt quâĂ basse tempĂ©rature. MalgrĂ© cela, les homologues de Sec61ÎČ de S. pombe et de S. cerevisiae sont tout deux capables de complĂ©menter la thermosensibilitĂ© respective de chaque levure. La complĂ©mentation est possible mĂȘme avec lâhomologue humain de Sec61ÎČ, indiquant la conservation dâune fonction de Sec61ÎČ de la levure Ă lâhomme. Remarquablement, le TMD de Sec61ÎČ de S. pombe, de S. cerevisiae et de lâhumain sont suffisants pour complĂ©menter la dĂ©lĂ©tion gĂ©nomique autant chez la levure Ă fission que chez la levure Ă bourgeons. Globalement, ces observations indiquent que le TMD de Sec61ÎČ exerce une fonction cellulaire conservĂ©e Ă travers les espĂšces.Protein secretion is an essential biological process. In eukaryotes, secreted proteins transit into the endoplasmic reticulum through the translocon pore. The core of the translocation channel is composed of three subunits called Sec61α, ÎČ and Îł in mammals, or Sec61p, Sbh1p and Sss1p in yeasts. While the role of the α and Îł subunit is well understood, the function of the ÎČ subunit remains ill-defined. Although numerous species-specific phenotypes have been reported for this protein, the striking sequence conservation among species argue in favour of a universal role. Recently, Feng et al. (2007) reported the surprising finding that the transmembrane domain (TMD) of Sbh1p was sufficient to complement different functions of the entire protein in Saccharomyces cerevisiae, suggesting an important role for this region. The aim of my project was to explore the biological function of the translocon ÎČ subunit and its TMD in Schizosaccharomyces pombe. In this yeast, we found that the sbh1+ gene is unessential for viability at 30oC, but is required for growth at low temperature. Knockout of sbh1+ results in sensitivity to cell-wall stress and reduced protein secretion at 23oC. Overexpression of Sbh1p also diminishes protein secretion and results in an elongated cell shape. These phenotypes contrast with those observed S. cerevisiae, as deletion of both Sec61ÎČ paralogs in this yeast results in heat sensitivity instead of cold sensitivity. Nevertheless, Sec61ÎČ homologs from both S. pombe and S. cerevisiae complement the respective temperature sensitivity of either yeast. This functional complementation can also be accomplished by the human homolog of the translocon ÎČ subunit, indicating that a fundamental function of Sec61ÎČ is conserved from yeast to human. Remarkably, the TMD of Sec61ÎČ homologs from S. pombe, S. cerevisiae and human are sufficient to complement the gene knockout in both fission and budding yeasts. Together, these observations indicate that the TMD of Sec61ÎČ exerts a cellular function that is conserved across species
Calnexin Regulates Apoptosis Induced by Inositol Starvation in Fission Yeast
Inositol is a precursor of numerous phospholipids and signalling molecules essential for the cell. Schizosaccharomyces pombe is naturally auxotroph for inositol as its genome does not have a homologue of the INO1 gene encoding inositol-1-phosphate synthase, the enzyme responsible for inositol biosynthesis. In this work, we demonstrate that inositol starvation in S. pombe causes cell death with apoptotic features. This apoptotic death is dependent on the metacaspase Pca1p and is affected by the UPR transducer Ire1p. Previously, we demonstrated that calnexin is involved in apoptosis induced by ER stress. Here, we show that cells expressing a lumenal version of calnexin exhibit a 2-fold increase in the levels of apoptosis provoked by inositol starvation. This increase is reversed by co-expression of a calnexin mutant spanning the transmembrane domain and C-terminal cytosolic tail. Coherently, calnexin is physiologically cleaved at the end of its lumenal domain, under normal growth conditions when cells approach stationary phase. This cleavage suggests that the two naturally produced calnexin fragments are needed to continue growth into stationary phase and to prevent cell death. Collectively, our observations indicate that calnexin takes part in at least two apoptotic pathways in S. pombe, and suggest that the cleavage of calnexin has regulatory roles in apoptotic processes involving calnexin
Abstract Fixpoint Computations with Numerical Acceleration Methods
Static analysis by abstract interpretation aims at automatically proving
properties of computer programs. To do this, an over-approximation of program
semantics, defined as the least fixpoint of a system of semantic equations,
must be computed. To enforce the convergence of this computation, widening
operator is used but it may lead to coarse results. We propose a new method to
accelerate the computation of this fixpoint by using standard techniques of
numerical analysis. Our goal is to automatically and dynamically adapt the
widening operator in order to maintain precision
Accurate methods for the analysis of strong-drive effects in parametric gates
The ability to perform fast, high-fidelity entangling gates is an important
requirement for a viable quantum processor. In practice, achieving fast gates
often comes with the penalty of strong-drive effects that are not captured by
the rotating-wave approximation. These effects can be analyzed in simulations
of the gate protocol, but those are computationally costly and often hide the
physics at play. Here, we show how to efficiently extract gate parameters by
directly solving a Floquet eigenproblem using exact numerics and a perturbative
analytical approach. As an example application of this toolkit, we study the
space of parametric gates generated between two fixed-frequency transmon qubits
connected by a parametrically driven coupler. Our analytical treatment, based
on time-dependent Schrieffer-Wolff perturbation theory, yields closed-form
expressions for gate frequencies and spurious interactions, and is valid for
strong drives. From these calculations, we identify optimal regimes of
operation for different types of gates including SWAP, controlled-Z, and
CNOT. These analytical results are supplemented by numerical Floquet
computations from which we directly extract drive-dependent gate parameters.
This approach has a considerable computational advantage over full simulations
of time evolutions. More generally, our combined analytical and numerical
strategy allows us to characterize two-qubit gates involving parametrically
driven interactions, and can be applied to gate optimization and cross-talk
mitigation such as the cancellation of unwanted ZZ interactions in multi-qubit
architectures.Comment: 20 pages, 9 figures, 62 reference
âDoggedâ Search of Fresh Nakhla Surfaces Reveals New Alteration Textures
Special Issue: 74th Annual Meeting of the Meteoritical Society, August 8-12, 2011, London, U.K.International audienceCarbonaceous chondrites are considered as amongst the most primitive Solar System samples available. One of their primitive characteristics is their enrichment in volatile elements.This includes hydrogen, which is present in hydrated and hydroxylated minerals. More precisely, the mineralogy is expected to be dominated by phyllosilicates in the case of CM chondrites, and by Montmorillonite type clays in the case of CI. Here, in order to characterize and quantify the abundance of lowtemperature minerals in carbonaceous chondrites, we performed thermogravimetric analysis of matrix fragments of Tagish Lake, Murchison and Orgueil
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