I soffi carotidei asintomatici scoperti in corso di bilancio preoperatorio. Condotta diagnostica e terapeutica.

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Promoted Thermal Reduction of Copper Oxide Surfaces by N-Heterocyclic Carbenes

The influence of metallic and oxide phases coexisting on surfaces is of fundamental importance in heterogeneous catalysis. Many reactions lead to the reduction of the oxidized areas, but the elucidation of the mechanisms driving these processes is often challenging. In addition, intermediate species or designed organic ligands increase the complexity of the surface. In the present study, we address the thermal reduction of a copper oxide overlayer grown on Cu(111) in the presence of N-heterocyclic carbene (NHC) ligands by means of scanning tunneling microscopy (STM) and density functional theory (DFT). We show that the NHC ligands actively participate in the copper oxide reduction, promoting its removal at temperatures as low as 470 K. The reduction of the oxide was tracked by employing scanning tunneling spectroscopy (STS), providing a chemical identification of metallic and oxide areas at the nanometric scale

Improving Matrix-vector Multiplication via Lossless Grammar-Compressed Matrices

As nowadays Machine Learning (ML) techniques are generating huge data collections, the problem of how to efficiently engineer their storage and operations is becoming of paramount importance. In this article we propose a new lossless compression scheme for real-valued matrices which achieves efficient performance in terms of compression ratio and time for linear-algebra operations. Ex- periments show that, as a compressor, our tool is clearly superior to gzip and it is usually within 20% of xz in terms of compression ratio. In addition, our compressed format supports matrix-vector multiplications in time and space proportional to the size of the compressed representation, unlike gzip and xz that require the full decompression of the compressed matrix. To our knowledge our lossless compressor is the first one achieving time and space com- plexities which match the theoretical limit expressed by the k-th order statistical entropy of the input. To achieve further time/space reductions, we propose column- reordering algorithms hinging on a novel column-similarity score. Our experiments on various data sets of ML matrices show that our column reordering can yield a further reduction of up to 16% in the peak memory usage during matrix-vector multiplication. Finally, we compare our proposal against the state-of-the-art Compressed Linear Algebra (CLA) approach showing that ours runs always at least twice faster (in a multi-thread setting), and achieves better compressed space occupancy and peak memory usage. This experimentally confirms the provably effective theoretical bounds we show for our compressed-matrix approach

Assessing the film-substrate interaction in germania films on reconstructed Au(111)

Purely amorphous germania bilayer films are grown on a reconstructed Au(111) surface. The presence of the film affects the native configuration of the Au soliton walls, as observed with scanning tunneling microscopy. They partly avoid the film islands, and partly penetrate under film patches. This behavior indicates a weaker film-substrate interaction than the one reported for other oxide films on reconstructed Au(111). Moreover, this new system highlights the impact of the metal support on the structure of ultrathin films of germania: With decreasing film-substrate interaction the amorphous phase is promoted. Density functional theory calculations confirm and rationalize the experimental observations. This work provides a useful generalization of the relationship between film structure and adhesion energy

Growth of N-Heterocyclic Carbene Assemblies on Cu(100) and Cu(111): from Single Molecules to Magic-Number Islands

N-Heterocyclic carbenes (NHCs) have superior properties as building blocks of self-assembled monolayers (SAMs). Understanding the influence of the substrate in the molecular arrangement is a fundamental step before employing these ligands in technological applications. Herein, we study the molecular arrangement of a model NHC on Cu(100) and Cu(111). While mostly disordered phases appear on Cu(100), on Cu(111) well-defined structures are formed, evolving from magic-number islands to molecular ribbons with coverage. This work presents the first example of magic-number islands formed by NHC assemblies on flat surfaces. Intermolecular interactions, diffusion and commensurability are key factors explaining the observed arrangements. These results shed light on the molecule-substrate interaction and open the possibility of tuning nanopatterned structures based on NHC assemblies

Covalent Adsorption of N-Heterocyclic Carbenes on a Copper Oxide Surface

Tuning the properties of oxide surfaces through the adsorption of designed ligands is highly desirable for several applications, such as catalysis. N-Heterocyclic carbenes (NHCs) have been successfully employed as ligands for the modification of metallic surfaces. On the other hand, their potential as modifiers of ubiquitous oxide surfaces still needs to be developed. Here we show that a model NHC binds covalently to a copper oxide surface under UHV conditions. In particular, we report the first example of a covalent bond between NHCs and oxygen atoms from the oxide layer. This study demonstrates that NHC can also act as a strong anchor on oxide surfaces

Growth of N-Heterocyclic Carbene Assemblies on Cu(100) and Cu(111): from Single Molecules to Magic-Number Islands

N-Heterocyclic carbenes (NHCs) have superior properties as building blocks of self-assembled monolayers (SAMs). Understanding the influence of the substrate in the molecular arrangement is a fundamental step before employing these ligands in technological applications. Herein, we study the molecular arrangement of a model NHC on Cu(100) and Cu(111). While mostly disordered phases appear on Cu(100), on Cu(111) well-defined structures are formed, evolving from magic-number islands to molecular ribbons with coverage. This work presents the first example of magic-number islands formed by NHC assemblies on flat surfaces. Intermolecular interactions, diffusion and commensurability are key factors explaining the observed arrangements. These results shed light on the molecule-substrate interaction and open the possibility of tuning nanopatterned structures based on NHC assemblies

Two-dimensional TiOx nanostructures on Au(111): a Scanning Tunneling Microscopy and Spectroscopy investigation

We investigated the growth of titanium oxide two-dimensional (2D) nanostructures on Au(111), produced by Ti evaporation and post-deposition oxidation. Scanning tunneling microscopy and spectroscopy (STM and STS) and low-energy electron diffraction (LEED) measurements characterized the morphological, structural and electronic properties of the observed structures. Five distinct TiOx phases were identified: the honeycomb and pinwheel phases appear as monolayer films wetting the gold surface, while nanocrystallites of the triangular, row and needle phases grow mainly over the honeycomb or pinwheel layers. Density Functional Theory (DFT) investigation of the honeycomb structure supports a (2 x 2) structural model based on a Ti-O bilayer having Ti2O3 stoichiometry. The pinwheel phase was observed to evolve, for increasing coverage, from single triangular crystallites to a well-ordered film forming a (4*sqrt(7) x 4*sqrt(7))R19.1° superstructure, which can be interpreted within a moire-like model. Structural characteristics of the other three phases were disclosed from the analysis of high-resolution STM measurements. STS measurements revealed a partial metallization of honeycomb and pinwheel and a semiconducting character of row and triangular phases

Conserved presence of G-quadruplex forming sequences in the Long Terminal Repeat Promoter of Lentiviruses

G-quadruplexes (G4s) are secondary structures of nucleic acids that epigenetically regulate cellular processes. In the human immunodeficiency lentivirus 1 (HIV-1), dynamic G4s are located in the unique viral LTR promoter. Folding of HIV-1 LTR G4s inhibits viral transcription; stabilization by G4 ligands intensifies this effect. Cellular proteins modulate viral transcription by inducing/unfolding LTR G4s. We here expanded our investigation on the presence of LTR G4s to all lentiviruses. G4s in the 5'-LTR U3 region were completely conserved in primate lentiviruses. A G4 was also present in a cattle-infecting lentivirus. All other non-primate lentiviruses displayed hints of less stable G4s. In primate lentiviruses, the possibility to fold into G4s was highly conserved among strains. LTR G4 sequences were very similar among phylogenetically related primate viruses, while they increasingly differed in viruses that diverged early from a common ancestor. A strong correlation between primate lentivirus LTR G4s and Sp1/NF\u3baB binding sites was found. All LTR G4s folded: their complexity was assessed by polymerase stop assay. Our data support a role of the lentiviruses 5'-LTR G4 region as control centre of viral transcription, where folding/unfolding of G4s and multiple recruitment of factors based on both sequence and structure may take place