Pair distribution function and structure factor of spherical particles

The availability of neutron spallation-source instruments that provide total scattering powder diffraction has led to an increased application of real-space structure analysis using the pair distribution function. Currently, the analytical treatment of finite size effects within pair distribution refinement procedures is limited. To that end, an envelope function is derived which transforms the pair distribution function of an infinite solid into that of a spherical particle with the same crystal structure. Distributions of particle sizes are then considered, and the associated envelope function is used to predict the particle size distribution of an experimental sample of gold nanoparticles from its pair distribution function alone. Finally, complementing the wealth of existing diffraction analysis, the peak broadening for the structure factor of spherical particles, expressed as a convolution derived from the envelope functions, is calculated exactly for all particle size distributions considered, and peak maxima, offsets, and asymmetries are discussed.Comment: 7 pages, 6 figure

Immobilization of pyrene - adorned N - heterocyclic carbene complexes of rhodium (I) on reduced graphene oxide and study of catalytic activity

Twopyrene-tagged N-heterocyclic carbene (NHC) complexes of rhodium(I) wereobtained and characterized. Thetwo complexes were supported onto reduced graphene oxide (rGO), generating two new materials in which the molecular complexes are immob ilized by p–p stacking interactions onto the surfaceofthe solid. The catalytic activity of both complexes and solid hybrid materials were studied in the 1,4-addition of phenylboronic acid to cyclohex-2-one, and in the hydrosilylation of terminal alkynes. The studies showed that for both reactions,the dimetallic complex displayed better catalytic performances than the monometallic one. This accounted for both the reactions performed in homogeneous conditions and for the reactions performed with the solid. In the case of the addition of phenylboronic acid to cyclohexanone,the solid containing the dimetallic catalystcould be effectively recycled up to five times, with negligible loss of activity,whereas the monometallic catalyst rapidlybecame inactive. In the hydrosilylation of terminal alkynes, the selectivity towards the b-(Z)-vinylsilane was improved if the immobilized dimetallic catalyst was used, although the catalyst startedtolose activity after the second run

The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

One-step, low temperature synthesis of reduced graphene oxide decorated with ZnO nanocrystals using galvanized iron steel scrap

Production of a ZnO-rGO composite, using a novel one-pot method consisting in continuously flowing argon into a GO aqueous suspension heated at 80 C, in the presence of galvanized iron steel scrap is presented. FTIR shows the complete disappearance of GO functional groups and only the C=C band remained, indicating extensive GO reduction. Raman spectra indicated sp2 character increase after reaction and the presence of the E2h mode of ZnO. SEM showed submicron crystals identified by XRD as ZnO in the hexagonal phase, while TEM images indicate ZnO nanoparticles decorate mainly the rGO borders. Optical band gap of 3.5 eV corresponding to ZnO, and optical transitions at 4.1 and 5.5 eV related with n → π and π → π∗ were observed. Electrochemical characterization by cyclic voltammetry shows an specific capacitance of 4.7 F g-1 at a scan rate of 5 mVs-1, which drops to ca. 0.8 F g-1 at 200 mVs-1. By electrochemical impedance spectroscopy, the relaxation time was ca. 5 ms. The proposed mechanism for the materials' synthesis includes Zn dissolution from scrap, galvanic displacement of oxygen moieties at the GO sheet, Zn deposition onto the carbon surface, and further oxidation and growth of ZnO nanocrystals.</p

One-step, low temperature synthesis of reduced graphene oxide decorated with ZnO nanocrystals using galvanized iron steel scrap

Production of a ZnO–rGO composite, using a novel one-pot method consisting in continuously flowing argon into a GO aqueous suspension heated at 80 °C, in the presence of galvanized iron steel scrap is presented. FTIR shows the complete disappearance of GO functional groups and only the C=C band remained, indicating extensive GO reduction. Raman spectra indicated sp ^2 character increase after reaction and the presence of the E _2h mode of ZnO. SEM showed submicron crystals identified by XRD as ZnO in the hexagonal phase, while TEM images indicate ZnO nanoparticles decorate mainly the rGO borders. Optical band gap of 3.5 eV corresponding to ZnO, and optical transitions at 4.1 and 5.5 eV related with n →  π and π  →  π * were observed. Electrochemical characterization by cyclic voltammetry shows an specific capacitance of 4.7 F g ^−1 at a scan rate of 5 mVs ^−1 , which drops to ca. 0.8 F g ^−1 at 200 mVs ^−1 . By electrochemical impedance spectroscopy, the relaxation time was ca. 5 ms. The proposed mechanism for the materials‘ synthesis includes Zn dissolution from scrap, galvanic displacement of oxygen moieties at the GO sheet, Zn deposition onto the carbon surface, and further oxidation and growth of ZnO nanocrystals

EXPERIMENTAL AND THEORETICAL STUDY OF CdS DEPOSITION BY CHEMICAL BATH

In this work experimental data from a chemical bath deposition process for CdS growth were compared against simulated data of the evolution of the concentration curves of Cd2+, S2-, and cadmium complexes (CdnOHm, Cdn(NH4)m2+, CdClm), obtained with HySS speciation software. We considered equilibrium reactions of complexes from atmospheric CO2 hydrolysis like HCO3- and CO32- on CdS formation mechanism. Series of CdS thin films were prepared in a bath containing 0.02M CdCl2, 0.5M KOH, 1.5M NH4NO3, 0.2M SC(NH2)2 at 65 ºC, compared with another growth with only CdCl2 + KOH + NH4NO3 to compare CdCO3 formation non related with thiourea hydrolysis. The model was initially feed with experimental data from the chemical bath, i.e. [NO3-] was determined by Raman spectroscopy, pH, pCd2+ and pS2- from potentiometric data. The pH evolution was reproduced almost exactly with the proposed model. Films were characterized by XRD and UV-Vis spectroscopy, Film thickness was calculated by using SCOUT software from transmittance data. CdCO3 was identified by XRD confirming the influence of atmospheric CO2 and also the data indicate an important role of the nitrate complexes in the film growth kinetics

SONOCHEMICAL-ASSISTED CuInSe2 ELECTRODEPOSITION AND ELECTROCHEMICAL POST-SELENIZATION TREATMENTS

CuInSe2 films have been prepared onto Cu substrates by an electrochemical, ultrasonic-assisted method, using a home-made potentiostat and deposition cell. Films were prepared by sweeping the potential at 5 mVs-1from 0 to -1500 mV vs SSC and left there during 15 min with ultrasonic agitation. The electrolytic bath composition was varied in order to study its effect on the phases present in the films. The precursor solutions were mixed in Cu:In:Se ratios of 1:1:1, 1:2:1 and 1:2.5:1, while the precursor concentration was varied from 1.5 mM to 4 mM, with respect to Cu. A 1 M NaCl solution was used as supporting electrolyte when needed. An electrochemical selenization procedure was done after film deposition, by immersing the films in a 1.5 mM Se electrolyte and sweeping the potential from -200 to -800 mV vs SSC and left there during 5 min. The effect of thermal annealing in N2-flux on the film structure was also assessed. Films were characterized by X-ray diffraction, Raman spectroscopy and atomic force microscopy. Ultrasonic agitation leads to compact, uniform films. Raman spectra of the as-grown films indicate the presence of In-Se and CIS in the tetragonal and cubic forms. In-rich films were obtained at the higher In ratios and precursor concentrations. The selenization treatment showed to affect the phase composition, while thermal treatment increased the crystallinity