Thermal desorption of cryopumped gases from laser treated copper

Recently, laser processing of copper samples has been demonstrated to produce rough surfaces whose nanostructuring ensures unquestionable advantages for electron cloud mitigation in future particle accelerators. The actual application of laser treated surfaces in accelerators implies that this new material is compliant with many issues, going from impedance vacuum properties to many others. A significant experimental effort is therefore ongoing to study and optimize their various properties of interest. Here we analyze their vacuum behavior versus temperature. To this end, we studied thermal programmed desorption from CO, ${\mathrm{CH}}_{4}$ and ${\mathrm{H}}_{2}$ once cryosorbed on laser treated copper substrate and on its flat counterpart. These molecules are typically present in the residual vacuum of any accelerator. The results show that the desorption of such gases from the laser treated substrates occurs in a much broader and higher temperature range with respect to what is observed from the flat substrate. We also show that, at equal doses, treated samples adsorb/desorb significantly more gas than their flat counterpart. These findings can be ascribed to their nanostructured porous morphology. A quantitative analysis is given, allowing to properly estimate fluctuations of the number of molecules during unavoidable temperature variations of the cryogenic vacuum system

Some exact results for the multicomponent t-J model

We present a generalization of the Sutherland's multicomponent model. Our extension includes both the ferromagnetic and the antiferromagnetic t-J model for any value of the exchange coupling J and the hopping parameter t. We prove rigorously that for one dimensional chains the ground-state of the generalized model is non-degenerate. As a consequence, the ordering of energy levels of the antiferromagnetic t-J model is determined. Our result rigorously proves and extends the analysis carried out by Sutherland in establishing the phase diagram of the model as a function of the number of components.Comment: 11 pages, RevTeX 3.0, no figure

On the compatibility of porous surfaces with cryogenic vacuum in future high-energy particle accelerators

Recently, pulsed laser processing of Cu samples has been demonstrated to produce rough surfaces whose structuring at the nanoscale ensures an impressive reduction of the secondary electron yield. This feature has an undoubted appealing for applications in future high energy particle accelerators. However, the effective application of such laser treated surfaces in this context requires a rigorous evaluation of their vacuum behavior, especially when used at cryogenic temperatures. To this aim, here, we compare thermal programmed desorption between 20 and 70 K by dosing Ar multilayers of different thicknesses on a laser treated copper substrate and on its flat counterpart. Our results highlight that the spongelike structural features confer to the laser treated sample's non-negligible effects due to the gas-substrate interaction. This results in a much vaster and higher desorption temperature range with respect to what is observed from the flat substrates. This evidence could render it very difficult to find temperature intervals for which detrimental vacuum transients could be avoided in the cryogenic beam pipes. On these bases, although the electron cloud mitigation efficiency has been settled, before definitely including porous surfaces in any cryogenic machine design, all the consequences of having a rough rather than a flat wall should be carefully evaluated

Nonstimulated early visual areas carry information about surrounding context

Even within the early sensory areas, the majority of the input to any given cortical neuron comes from other cortical neurons. To extend our knowledge of the contextual information that is transmitted by such lateral and feedback connections, we investigated how visually nonstimulated regions in primary visual cortex (V1) and visual area V2 are influenced by the surrounding context. We used functional magnetic resonance imaging (fMRI) and pattern-classification methods to show that the cortical representation of a nonstimulated quarter-field carries information that can discriminate the surrounding visual context. We show further that the activity patterns in these regions are significantly related to those observed with feed-forward stimulation and that these effects are driven primarily by V1. These results thus demonstrate that visual context strongly influences early visual areas even in the absence of differential feed-forward thalamic stimulation

SEY and low-energy SEY of conductive surfaces

Abstract The study of Secondary Electron Yield (SEY) is widely performed to address important properties of materials to be used in a very wide spectrum of applications. It is, therefore, extremely important to understand the SEY dependence on material type, surface contaminants, structural quality and surface damage. We review here our recent studies of such items performed by looking at some representative conductive materials as noble metals and carbon based surfaces. Polycrystalline Ag, Au and Cu samples have been studied as introduced in the ultra-high vacuum chamber (therefore with an significant surface contamination) and after having been cleaned by ion sputtering. The comparison between the curves confirms that the SEY behavior is strongly influenced by the chemical state of the metal surfaces. We demonstrate the ability of SEY to determine work function values with high accuracy if the experimental system allows using very slow primary electrons. We also investigated, for the Cu sample, the effect on SEY of minimal amount of contaminants in the sub-monolayer regime showing that SEY is highly sensitive to the presence of adsorbates even at such very low coverages, specially for low energy primary electrons. In the case of C surfaces we summarize here the effect that the structural ordering of the C lattice has on the macroscopic SEY properties of ultrathin C layers. In particular we followed the SEY evolution during the thermal graphitization of thin amorphous carbon layers and during the amorphization of highly oriented pyrolytic graphite by means of Ar+ bombardment. In the first case the SEY decrease observed with the progressive conversion of sp3 hybrids into six-fold aromatic domains was related to the electronic structure of the C-films close to the Fermi level. We found that a moderate structural quality of the C layer, corresponding to aromatic clusters of limited size, is sufficient to obtain a SEY as low as ∼1. For the bombarded graphite, the strong lattice damage remains limited to the near surface layer, where the high density of defects reduces the transport of incoming and secondary electrons. Then, the SEY curves resulted differently modified in the low and high primary energy regions, but their maximal values remained favorably low. Our findings demonstrate that SEY, besides being an indispensable mean to qualify technical materials in many technological fields, can be also used as a flexible and advantageous diagnostics to probe surfaces and interfaces

Src family kinases as therapeutic targets in advanced solid tumors. What we have learned so far

Src is the prototypal member of Src Family tyrosine Kinases (SFKs), a large non-receptor kinase class that controls multiple signaling pathways in animal cells. SFKs activation is necessary for the mitogenic signal from many growth factors, but also for the acquisition of migratory and invasive phenotype. Indeed, oncogenic activation of SFKs has been demonstrated to play an important role in solid cancers; promoting tumor growth and formation of distant metastases. Several drugs targeting SFKs have been developed and tested in preclinical models and many of them have successfully reached clinical use in hematologic cancers. Although in solid tumors SFKs inhibitors have consistently confirmed their ability in blocking cancer cell progression in several experimental models; their utilization in clinical trials has unveiled unexpected complications against an effective utilization in patients. In this review, we summarize basic molecular mechanisms involving SFKs in cancer spreading and metastasization; and discuss preclinical and clinical data highlighting the main challenges for their future application as therapeutic targets in solid cancer progression

Dataset of Electoral Volatility in the European Parliament elections since 1979

This dataset provides data on electoral volatility and its internal components in the elections for the European Parliament (EP) in all European Union (EU) countries since 1979 or the date of their accession to the Union. It also provides data about electoral volatility for both the class bloc and the demarcation bloc. This dataset will be regularly updated so as to include the next rounds of the European Parliament elections. How to cite this dataset? Emanuele, V., Angelucci, D., Marino, B., Puleo, L., and Vegetti, F. (2019), Dataset of Electoral Volatility in the European Parliament elections since 1979, Rome: Italian Center for Electoral Studies, http://dx.doi.org/10.7802/1905

Development of a Background-Oriented Schlieren Technique with Telecentric Lenses for Supersonic Flow

Background oriented schlieren (BOS) is a quantitative optical technique which exploits light deflection occurring in non-homogeneous transparent media. It allows to indirectly measure the density gradients by analysing the apparent displacement of features of a background pattern when imaged through the investigated flow. Thanks to its simple set-up and to the consolidated data reduction technique based on cross-correlation algorithms the BOS technique has progressively attracted the interest of the researchers. In this work a BOS system using a telecentric lens system has been set up in order to improve measurement accuracy and to avoid 3D effects arising from using conventional entocentric lenses. The design of the telecentric lens system is reported along with an analysis of its performance in term of spatial resolution. Some preliminary tests on a supersonic flows are also reported

Multicast Network Design Game on a Ring

In this paper we study quality measures of different solution concepts for the multicast network design game on a ring topology. We recall from the literature a lower bound of 4/3 and prove a matching upper bound for the price of stability, which is the ratio of the social costs of a best Nash equilibrium and of a general optimum. Therefore, we answer an open question posed by Fanelli et al. in [12]. We prove an upper bound of 2 for the ratio of the costs of a potential optimizer and of an optimum, provide a construction of a lower bound, and give a computer-assisted argument that it reaches $2$ for any precision. We then turn our attention to players arriving one by one and playing myopically their best response. We provide matching lower and upper bounds of 2 for the myopic sequential price of anarchy (achieved for a worst-case order of the arrival of the players). We then initiate the study of myopic sequential price of stability and for the multicast game on the ring we construct a lower bound of 4/3, and provide an upper bound of 26/19. To the end, we conjecture and argue that the right answer is 4/3.Comment: 12 pages, 4 figure

Inhibition of acetylpolyamine and spermine oxidases by the polyamine analogue chlorhexidine

""Acetylpolyamine and spermine oxidases are involved in the catabolism of polyamines. The discovery of selective. inhibitors of these enzymes represents an important tool for the development of novel anti-neoplastic drugs. Here, a. comparative study on acetylpolyamine and spermine oxidases inhibition by the polyamine analogue chlorhexidine. is reported. Chlorhexidine is an antiseptic diamide, commonly used as a bactericidal and bacteriostatic agent.. Docking simulations indicate that chlorhexidine binding to these enzymes is compatible with the stereochemical. properties of both acetylpolyamine oxidase and spermine oxidase active sites. In fact, chlorhexidine is predicted. to establish several polar and hydrophobic interactions with the active site residues of both enzymes, with binding. energy values ranging from −7.6 to −10.6 kcal\\\/mol. In agreement with this hypothesis, inhibition studies indicate that. chlorhexidine behaves as a strong competitive inhibitor of both enzymes, values of Ki being 0.10 μM and 0.55 μM for. acetylpolyamine oxidase and spermine oxidase, respectively."