Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption.

Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators.

Nonlocal effects in sand flows on an inclined plane.

The flow of sand on a rough inclined plane is investigated experimentally. We directly show that a jammed layer of grains spontaneously forms below the avalanche. Its properties and its relation with the rheology of the flowing layer of grains are presented and discussed.

Evidence for interacting two-level systems from the 1/f noise of a superconducting resonator.

The performance of a great variety of electronic devices--ranging from semiconductor transistors to superconducting qubits--is hampered by low-frequency noise with spectra proportional to 1/f. The ubiquity and negative impact of 1/f noise has motivated intensive research into its cause, and it is now believed to originate from a bath of fluctuating two-level defect states (TLSs) embedded in the material. This phenomenon is commonly described by the long-established standard tunnelling model (STM) of independent TLS.

Internal loss of superconducting resonators induced by interacting two-level systems.

In a number of recent experiments with microwave high quality superconducting coplanar waveguide resonators an anomalously weak power dependence of the quality factor has been observed. We argue that this observation implies that the monochromatic radiation does not saturate the two level systems (TLS) located at the interface oxide surfaces of the resonator and suggests the importance of their interactions. We estimate the microwave loss due to interacting TLS and show that the interactions between TLS lead to a drift of their energies that result in a much slower, logarithmic dependence of their absorption on the radiation power in agreement with the data.

Many-body green function of degenerate systems.

A rigorous nonperturbative adiabatic approximation of the evolution operator in the many-body physics of degenerate systems is derived. This approximation is used to solve the long-standing problem of the choice of the initial states of H(0) leading to eigenstates of H(0) + V for degenerate systems. These initial states are eigenstates of P(0)VP(0), where P(0) is the projection onto a degenerate eigenspace of H(0).

Clar's theory, pi-electron distribution, and geometry of graphene nanoribbons.

We show that Clar's theory of the aromatic sextet is a simple and powerful tool to predict the stability, the pi-electron distribution, the geometry, and the electronic/magnetic structure of graphene nanoribbons with different hydrogen edge terminations. We use density functional theory to obtain the equilibrium atomic positions, simulated scanning tunneling microscopy (STM) images, edge energies, band gaps, and edge-induced strains of graphene ribbons that we analyze in terms of Clar formulas. On the basis of their Clar representation, we propose a classification scheme for graphene ribbons that groups configurations with similar bond length alternations, STM patterns, and Raman spectra.

Boosting electronic transport in carbon nanotubes by isotopic disorder.

The current-voltage curve of metallic carbon nanotubes (CNTs) displays at high bias a sudden increase of the resistivity due to the scattering of electrons with phonons having an anomalously high population (hot phonons). Here, we show that it is possible to improve the electrical performances of metallic CNTs by 13C isotope enrichment. In fact, isotopic disorder creates additional channels for the hot-phonon deexcitation, reduces their population and, thus, the nanotube high-bias differential resistance.

Live-imaging of single stem cells within their niche reveals that a U3snoRNP component segregates asymmetrically and is required for self-renewal in Drosophila.

Stem cells generate self-renewing and differentiating progeny over many rounds of asymmetric divisions. How stem cell growth rate and size are maintained over time remains unknown. We isolated mutations in a Drosophila melanogaster gene, wicked (wcd), which induce premature differentiation of germline stem cells (GSCs).

Fibrillarin and Nop56 interact before being co-assembled in box C/D snoRNPs.

Small nucleolar RNAs play crucial roles in ribosome biogenesis. They guide folding, site-specific nucleotide modifications and participate in cleavage of precursor ribosomal RNAs. To better understand how the biogenesis of the box C/D small nucleolar RNPs (snoRNPs) occur in a cellular context, we used a new approach based on the possibility of relocalizing a given nuclear complex by adding an affinity tag for B23 to one component of this complex.

Involvement of SIRT7 in resumption of rDNA transcription at the exit from mitosis.

Sirtuins, also designated class III histone deacetylases, are implicated in the regulation of cell division, apoptosis, DNA damage repair, genomic silencing and longevity. The nucleolar Sirtuin7 (SIRT7) was reported to be involved in the regulation of ribosomal gene (rDNA) transcription, but there are no data concerning the regulation of SIRT7 during the cell cycle. Here we have analyzed the behavior of endogenous SIRT7 during mitosis, while rDNA transcription is repressed.

The loss of the snoRNP chaperone Nopp140 from Cajal bodies of patient fibroblasts correlates with the severity of spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a common autosomal recessive neurodegenerative disease caused by reduced survival motor neuron (SMN) levels. The assembly machinery containing SMN is implicated in the biogenesis of the spliceosomal small nuclear ribonucleoproteins (snRNPs). SMN is present in both the cytoplasm and nucleus, where it transiently accumulates in subnuclear domains named Cajal bodies (CBs) and functions in the maturation of snRNPs and small nucleolar (sno)RNPs.

Ubiquitin ligase adaptors: regulators of ubiquitylation and endocytosis of plasma membrane proteins.

The subcellular localization of plasma membrane proteins, such as receptors and transporters, must be finely tuned so that they can be readily downregulated in response to environmental cues. Some of these membrane proteins are post-translationally modified by conjugation to ubiquitin, which is used as a molecular tag to commit them to the endocytic pathway and promote their subsequent delivery to the lysosomes for degradation. This ubiquitylation step, which is performed by so-called ubiquitin ligases (or E3), appears therefore as a critical event for endocytosis and is subject to many levels of regulation.

Structure, stability, edge states, and aromaticity of graphene ribbons.

We determine the stability, the geometry, the electronic, and magnetic structure of hydrogen-terminated graphene-nanoribbon edges as a function of the hydrogen content of the environment by means of density functional theory. Antiferromagnetic zigzag ribbons are stable only at extremely low ultravacuum pressures. Under more standard conditions, the most stable structures are the mono- and dihydrogenated armchair edges and a zigzag edge reconstruction with one di- and two monohydrogenated sites.

Telomeric trans-silencing in Drosophila melanogaster: tissue specificity, development and functional interactions between non-homologous telomeres.

Background: The study of P element repression in Drosophila melanogaster led to the discovery of the telomeric Trans-Silencing Effect (TSE), a homology-dependent repression mechanism by which a P-transgene inserted in subtelomeric heterochromatin (Telomeric Associated Sequences, "TAS") has the capacity to repress in trans, in the female germline, a homologous P-lacZ transgene located in euchromatin. TSE can show variegation in ovaries, displays a maternal effect as well as an epigenetic transmission through meiosis and involves heterochromatin and RNA silencing pathways.

Principal Findings: Here, we analyze phenotypic and genetic properties of TSE.

Pattern formation during deformation of a confined viscoelastic layer: from a viscous liquid to a soft elastic solid.

We study pattern formation during tensile deformation of confined viscoelastic layers. The use of a model system [poly(dimethylsiloxane) with different degrees of cross-linking] allows us to go continuously from a viscous liquid to an elastic solid. We observe two distinct regimes of fingering instabilities: a regime called "elastic" with interfacial crack propagation, where the fingering wavelength scales only with the film thickness, and a bulk regime called "viscoelastic," where the fingering instability shows a Saffman-Taylor-like behavior.

Boroxol Rings in Liquid and Vitreous B2O3 from First Principles.

We investigate the structural and vibrational properties of glassy B2O3 using first-principles molecular dynamics simulations. In particular, we determine the boroxol rings fraction f for which there is still no consensus in the literature. Two numerical models containing either a low or a high level of boroxol rings are tested against a gamut of experimental probes (static structure factor, Raman, 11B and 17O NMR data).

Giant nonadiabatic effects in layer metals: raman spectra of intercalated graphite explained.

The occurrence of nonadiabatic effects in the vibrational properties of metals has been predicted since the 1960s, but hardly confirmed experimentally. We report the first fully ab initio calculations of nonadiabatic frequencies of a number of conventional (hcp Ti and Mg) and layered metals (MgB2, CaC6, and other intercalated graphites). Nonadiabatic effects can be spectacularly large (up to 30% of the phonon frequencies) in both cases, but they can only be experimentally observed in the Raman spectra of layered compounds.

Substrate- and ubiquitin-dependent trafficking of the yeast siderophore transporter Sit1.

Eukaryotic plasma membrane transporters are subjected to a tightly regulated intracellular trafficking. The yeast siderophore iron transporter1 (Sit1) displays substrate-regulated trafficking. It is targeted to the plasma membrane or to a vacuolar degradative pathway when synthesized in the presence or absence of external substrate, respectively.

Ear1p and Ssh4p are new adaptors of the ubiquitin ligase Rsp5p for cargo ubiquitylation and sorting at multivesicular bodies.

The ubiquitylation of membrane proteins destined for the vacuole/lysosome is essential for their recognition by the endosomal sorting machinery and their internalization into vesicles of multivesicular bodies (MVBs). In yeast, this process requires Rsp5p, an essential ubiquitin ligase of the Nedd4 family. We describe here two redundant proteins, Ear1p and Ssh4p, required for the vacuolar targeting of several cargoes originating from the Golgi or the plasma membrane.

Differentiation of C2C12 myoblasts expressing lamin A mutated at a site responsible for Emery-Dreifuss muscular dystrophy is improved by inhibition of the MEK-ERK pathway and stimulation of the PI3-kinase pathway.

Mutation R453W in A-type lamins, that are major nuclear envelope proteins, generates Emery-Dreifuss muscular dystrophy. We previously showed that mouse myoblasts expressing R453W-lamin A incompletely exit the cell cycle and differentiate into myocytes with a low level of multinucleation. Here we attempted to improve differentiation by treating these cells with a mixture of PD98059, an extracellular-regulated kinase (ERK) kinase (also known as mitogen-activated kinase, MEK) inhibitor, and insulin-like growth factor-II, an activator of phosphoinositide 3-kinase.

Destabilization of a Saffman-Taylor fingerlike pattern in a granular suspension.

We study the Saffman-Taylor instability in a granular suspension formed by micrometric beads immersed in a viscous liquid. When using an effective viscosity for the flow of the suspension in the Hele-Shaw cell to define the control parameter of the system, the results for the finger width of stable fingers are found to be close to the classical results of Saffman-Taylor. One observes, however, an early destabilization of the fingers that can be attributed to the discrete nature of the individual grains.

Trafficking of siderophore transporters in Saccharomyces cerevisiae and intracellular fate of ferrioxamine B conjugates.

We have studied the intracellular trafficking of Sit1 [ferrioxamine B (FOB) transporter] and Enb1 (enterobactin transporter) in Saccharomyces cerevisiae using green fluorescent protein (GFP) fusion proteins. Enb1 was constitutively targeted to the plasma membrane. Sit1 was essentially targeted to the vacuolar degradation pathway when synthesized in the absence of substrate.

von Hippel Lindau binding protein 1-mediated degradation of integrase affects HIV-1 gene expression at a postintegration step.

HIV-1 integrase, the viral enzyme responsible for provirus integration into the host genome, can be actively degraded by the ubiquitin-proteasome pathway. Here, we identify von Hippel-Lindau binding protein 1(VBP1), a subunit of the prefoldin chaperone, as an integrase cellular binding protein that bridges interaction between integrase and the cullin2 (Cul2)-based von Hippel-Lindau (VHL) ubiquitin ligase. We demonstrate that VBP1 and Cul2/VHL are required for proper HIV-1 expression at a step between integrase-dependent proviral integration into the host genome and transcription of viral genes.

Selective optical generation of coherent acoustic nanocavity modes.

Femtosecond pump-probe experiments on a Ga0.85In0.15As nanocavity enclosed by two Ga(0.

[Regulation of germline stem cells: the niche expands in Drosophila].

Our fascination for stem cells originates from their ability to divide asymmetrically in order to self-renew and produce daughter cells which can differentiate and replenish tissues. Stem cells could thus represent an unlimited source of differentiated cells that could be used to repair malformed, damaged or ageing tissues. Understanding how their behaviour is regulated is then of paramount medical interest.