Electron–phonon coupling and superconductivity in a 2D Tl–Pb compound on Si(111)

[EN] Electron-phonon interaction in a single-layer Tl-Pb compound on Si(111) is investigated within the density-functional theory and linear-response approach in the mixed-basis pseudopotential representation. It is found that phonon-induced scattering of electrons at the Fermi level is primarily determined by surface electronic states responsible for bonding at the interface and by low-energy, predominantly shear-vertical vibrations of adatoms. The contribution of substrate-localized vibrations involved in the electron-phonon scattering turns out to be small. We have also estimated the superconducting transition temperature T-c by solving the linearized gap equation of the Eliashberg theory. An analysis of phonon-mediated transitions for a number of electronic states in the Tl-Pb surface bands showed that the strength of the coupling varies with the binding energy, increasing as it approaches the Fermi level, and significantly depends on the surface band to which the state belongs.This work was supported by the University of the Basque Country (Grants no. GIC07-IT-366-07 and No. IT-756-13) and the Spanish Ministry of Science and Innovation (Grant no. FIS2016-75862-P). The authors acknowledge support by the state of Baden-Wurttemberg through bwHPC

Formation of Surface and Quantum-Well States in Ultra Thin Pt Films on the Au(111) Surface

The electronic structure of the Pt/Au(111) heterostructures with a number of Pt monolayers n ranging from one to three is studied in the density-functional-theory framework. The calculations demonstrate that the deposition of the Pt atomic thin films on gold substrate results in strong modifications of the electronic structure at the surface. In particular, the Au(111) s-p-type Shockley surface state becomes completely unoccupied at deposition of any number of Pt monolayers. The Pt adlayer generates numerous quantum-well states in various energy gaps of Au(111) with strong spatial confinement at the surface. As a result, strong enhancement in the local density of state at the surface Pt atomic layer in comparison with clean Pt surface is obtained. The excess in the density of states has maximal magnitude in the case of one monolayer Pt adlayer and gradually reduces with increasing number of Pt atomic layers. The spin-orbit coupling produces strong modification of the energy dispersion of the electronic states generated by the Pt adlayer and gives rise to certain quantum states with a characteristic Dirac-cone shape.We acknowledge the Tomsk State University competitiveness programme (Project No. 8.1.01.2017) and partial support by the Saint Petersburg State University (Project No. 15.61.202.2015). I.V.S. acknowledges financial support from the Ministry of Education and Science of the Russian Federation within governmental program Megagrants (State Task No. 3.9003.2017/Pi 220 or 3.9003.2017/9.10). Y.M.K. acknowledges the Russian Foundation for Basic Research (Project No. 15-02-02717-a). E.V.C. acknowledges the Spanish Ministry of Science and Innovation (Grant No. FIS2016-75862-P). Calculations were performed at the SKIFCyberia supercomputer of Tomsk State University and at the Research park of St. Petersburg State University Computing Center (Russian Federation)

Hole-Phonon Relaxation and Photocatalytic Properties of Titanium Dioxide and Zinc Oxide: First-Principles Approach

First-principles calculations for the temporal characteristics of hole-phonon relaxation in the valence band of titanium dioxide and zinc oxide have been performed. A first-principles method for the calculations of the quasistationary distribution function of holes has been developed. The results show that the quasistationary distribution of the holes in TiO2 extends to an energy level approximately 1eV below the top of the valence band. This conclusion in turn helps to elucidate the origin of the spectral dependence of the photocatalytic activity of TiO2. Analysis of the analogous data for ZnO shows that in this material spectral dependence of photocatalytic activity in the oxidative reactions is unlikely.The authors acknowledge financial support from the Spanish MICINN (Grant no. FIS2010-19609-C02-01), the Departamento de Educacion del Gobierno Vasco, the University of the Basque Country (Grant no. GIC07-IT-366-07), and the Presidium of the Ural Branch of Russian Academy of Sciences (Grant no. 12-U-3-1001). The help of Professor L. Baker in the preparation of the paper is also greatly acknowledged. The calculations were performed using the URAN cluster of the Institute of Mathematics and Mechanics of the Russian Academy of Sciences, Yekaterinburg

El transplante de modelos de comunicación

The presence of giant diamagnetism in Au nanorods, NRs, is shown to be a possible consequence of field induced currents in the surface electrons. The distance, Delta , between quantum surface energy levels has been calculated as a function of the NRs radius. Note that those electrons occupying states for which Delta > k(B)T are steadily orbiting with constant orbital moment. The diamagnetic response induced when a field is turned on remains constant during the time the field is acting. As the NRs radius increases, Delta decreases and accordingly the electron fraction available to generate constant currents decreases, consequently the surface diamagnetic susceptibility decreases towards its bulk value. The surface electronic motion induced by the axial applied field on electrons confined into a cylindrical surface accounts with extremely good quantitative agreement for the giant diamagnetism recently measured and reported.We gratefully acknowledge financial support from the Spanish Ministerio de Innovacion, Ciencia y Tecnologia (grant numbers MAT2012-37109-C02-01 and FIS2010-21282-C02-02), the University of the Basque Country (grant no. IT-366-07), the Basque Government through the NANOMATERIALS project (grant IE05-151) under the ETORTEK Program (iNanogune). AH acknowledges to Dr J M Rojo helpful comments on gold surfaces

Study of proteins of biomedical pharmacentical interest

Η αντιγονοπαρουσίαση, που αποτελεί κλειδί στη σωστή λειτουργία του ανοσολογικού συστήματος, είναι μια αυστηρά ελεγχόμενη διαδικασία και ρυθμίζεται από πλήθος ανεξάρτητων παραγόντων. Ανάμεσα σε αυτούς τους παράγοντες σημαντική θέση κατέχουν τα τάξης Ι και ΙΙ αντιγόνα του Κυρίου Συμπλόκου Ιστοσυμβατότητας, η παρουσία των οποίων διασφαλίζει τη φόρτωση τους με αντιγονικά πεπτίδια. Η απώλεια των HLA αντιγόνων σε καρκινικά κύτταρα διαταράσσει την έναρξη και τη διατήρηση της ανοσολογικής απόκρισης μέσω πλημμελούς ενεργοποίησης των CD4+ λεμφοκυττάρων. Πολλά λευχαιμικά κύτταρα χρησιμοποιούν τέτοιους μηχανισμούς για να διαφύγουν της ανοσολογικής επαγρύπνησης ενώ επιπλέον σε ασθενείς με λευχαιμία ή λέμφωμα η έκφραση των τάξης ΙΙ μορίων του Κ ΣΙ συσχετίζεται με καλύτερη έκβαση και πρόγνωση της ασθένειας. Στην παρούσα εργασία εξετάσαμε τις λευχαιμικές σειρές K562 και HL-60 αναφορικά με την ενδοκυτταρική έκφραση τάξης ΙΙ μορίων. Η ανίχνευση πραγματοποιήθηκε με κυτταρομετρία ροής, συνεστιακή και ηλεκτρονική μικροσκοπία. Το πρωτεϊνικό προφίλ ελέγχθηκε επίσης, σε μοριακό επίπεδο, με πειράματα RT-PCR. Τα αποτελέσματα, που παρουσιάζονται στη συνέχεια έδειξαν ότι παρά την απουσία μεμβρανικών τάξης ΙΙ μορίων τα λευχαιμικά κύτταρα διαθέτουν ενδοκυτταρικά αποθέματα των DR και DM ενώ εκφράζουν συστηματικά την CD74 και την β αλυσίδα του DO. Οι διπλοί ανοσοφθορισμοί αποκάλυψαν τον συνεντοπισμό όλων αυτών των μορίων σε κυστίδια, που ταυτοποιούνται ως ώριμα ενδοσώματα από την έκφραση της πρωτεΐνης Rab7. Για να απαντήσουμε στο ερώτημα κατά πόσο η DOβ αλυσίδα από μόνη της μπορεί να εξέρχεται από το ενδοπλασματικό δίκτυο και να οδηγείται στα ενδοσώματα την κλωνοποιήσαμε στα Κ562 κύτταρα, συντηγμένη με τη φθορίζουσα πρωτεΐνη eGFP. Τα αποτελέσματα της συνεστιακής μικροσκοπίας επιβεβαίωσαν ότι πράγματι η συντηγμένη DOβ-eGFP μπορεί να οδηγείται στα ενδοσώματα απουσία της DOα αλυσίδας. Επιπλέον κλωνοποιήσαμε και την DOα αλυσίδα συντηγμένη με την dsRED και δημιουργήσαμε μονά και διπλά διαμολυσμένους πληθυσμούς. Οι χειρισμοί αυτοί μας έδωσαν τη δυνατότητα να παρακολουθούμε την έκφραση και τη μετακίνηση των μορίων χωρίς τη χρήση αντισωμάτων. Ακόμα μελετήσαμε το πρωτεϊνικό προφίλ αναφορικά με τα τάξης ΙΙ μόρια, των δύο λευχαιμικών σειρών κατόπιν επίδρασης για 6 ώρες με IFN-γ καθώς επίσης και των Κ562_CIITA διαμολυσμένων κυττάρων. Τα αποτελέσματα έδειξαν ότι και οι δύο παράγοντες (η IFN-γ και ο CIITA) μπορούν να επάγουν την έκφραση του DR στην πλασματική μεμβράνη. Τέλος πειράματα ηλεκτροφόρησης και western blotting αποκάλυψαν τη δημιουργία συμπλόκου ανάμεσα στα DR και DOβ. Συμπερασματικά μπορούμε να πούμε ότι τα λευχαιμικά κύτταρα, που εξετάσαμε παρά την απουσία επιφανειακών τάξης ΙΙ μορίων διαθέτουν ενδοκυτταρικά αποθέματα DR τα οποία μπορούν να μεταφερθούν στη μεμβράνη κατόπιν επίδρασης με IFN-γ. Η ταυτόχρονη παρουσία της DOβ αλυσίδας στα ίδια ενδοσώματα με τα τάξης ΙΙ μόρια δίνει νέες προοπτικές στο ρόλο του HLA-DO στην αντιγονοπαρουσίαση κάνοντας την περισσότερο πολύπλοκο θέμα από ότι πιστευόταν αρχικά. Βάση όλων αυτών των αποτελεσμάτων διατυπώνουμε έναν μηχανισμό ρύθμισης και διατήρησης του DR αρνητικού φαινοτύπου στα λευχαιμικά κύτταρα σύμφωνα με τον οποίο το DR εγκλωβίζεται στα ενδοσώματα δημιουργώντας απευθείας σύμπλοκο με το DO.Antigen presentation, a key event in the functioning of the immune system, is a well-controlled process, regulated by a number of independent factors. Among these factors the most important are the class I and II antigens of Major Histocompatibility Complex the presence of which ensures the proper antigen loading. Loss of expression of human leukocyte antigen (HLA) on tumor cells alters the onset and modulation of immune response through lack of activation on CD4+ lymphocytes. Most leukemia cells use such mechanism to escape immune surveillance. Moreover in patients with leukemia or lymphoma the expression o f H LA-class II molecules correlate with better survival. Here, K562 and HL-60 leukemia cells were examined as to intracellular HLA-DR,- DM,-DO and CD74 expression, if any. Cytoplasmic immunofluorescence of K562 was performed and the cells were analyzed by flow cytometry, confocal microscopy and transmission electron microscopy. The protein profile was also confirmed at molecular level by RT-PCR analysis. The results presented here showed that despite the negative HLA-DR surface expression, leukemia cells contain intracellular HLA-DR and DM molecules, while constitutively expressing the CD74 antigen and the DOβ chain. Double immunofluorescence experiments revealed the co-localization of all these molecules in endosomal compartments which were identified as late endosomes by the presence of Rab7 protein. To answer the question on how DOβ chain alone could leave ER and enter the endosomal compartments, stable transfectants of K562 with a DOβ-eGFP fusion construct were isolated. Confocal microscope analysis of the trasfectants verified the endosomal localization of the DOβ chain indicating that indeed this molecule can leave ER without the need of DOα chain. In addition transfectants of K562 with a DOα-dsRED and double tranfectants of K562 with DOαβ were constructed. These manipulations allowed the following up of DO α and β chains without the use of any antibody. We also analyze the antigens profile in K562 and HL-60 cells treated with IFN-γ for 6 h ours a s w ell as i n K 562 c ells t ransfected w ith a C IITA t ranscription factor construct. T he r esults s howed t hat b oth f actors c an l ead H LA-DR t o t he c ell s urface. SDS-page analysis followed by western blot assay detected a direct complex formation between HLA-DR/DO. We conclude that leukemia cells despite the absence of any surface class II antigen they contain intracellular HLA-DR molecules which can be transferred to the membrane upon stimulation with IFN-γ. The presence of DOβ chain in the same endosomal compartments with class II molecules provide new insights in the role of HLA-DO in antigen presentation showing that this is a more complicated issue than originally thought. We propose a new mechanism of regulation and maintenance of the negative MHC class II state in leukemia cells where HLA-DR retains in endosomal compartments forming a direct complex with HLA-DO

Role of occupied d bands in the dynamics of excited electrons and holes in Ag

The role that occupied d bands play in the inelastic lifetime of bulk and surface states in Ag is investigated from the knowledge of the quasiparticle self-energy. In the case of bulk electrons, sp bands are taken to be free-electron-like. For surface states, the surface band structure of sp states is described with the use of a realistic one-dimensional Hamiltonian. The presence of occupied d states is considered in both cases by introducing a polarizable background. We obtain inelastic lifetimes of bulk electrons that are in good agreement with first-principles band-structure calculations. Our surface-state lifetime calculations indicate that the agreement with measured lifetimes of both crystal-induced and image-potential-induced surface states on Ag(100) and Ag(111) is considerably improved when the screening of d electrons is taken into account

First-principles calculations of hot-electron lifetimes in metals

First-principles calculations' of the inelastic lifetime of low-energy electrons in Al, Mg, Be, and Cu are reported. Quasiparticle damping rates are evaluated from the: knowledge of the electron self-energy, which we compute within the GW approximation of many-body theory. Inelastic lifetimes are then obtained along various directions of the electron wave vector, with full inclusion of the band structure of the solid. Average lifetimes are also reported, as a function of the electron energy. In Al and Mg, splitting of the band structure over the Fermi level yields electron lifetimes that are smaller than those of electrons in a free-electron gas. Larger lifetimes are found in Be, as a result of the characteristic dip that this material presents in the density of states near the Fermi level. In Cu, a major contribution from d electrons participating in the screening of electron-electron interactions yields electron Lifetimes that are well above those of electrons in a free-electron gas with the electron density equal to that of valence (4s(1)) electrons