30 research outputs found

    USPOREDNA RAČUNOVODSTVENA STRUKTURNA ANALIZA FINANCUSKIH IZVJEŠTAJA U DJELATNOSTI "HOTELI I RESTORANI" U CILJU EFIKASNIJEG UPRAVLJANJA

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    Djelatnost "Hoteli i restorani" sastoji se od nekoliko poddjelatnosti od kojih je najznačajnija "Hoteli". U radu se utvrđuju strukturni odnosi između pojedinih poddjelatnosti i financijsko stanje i profitabilnost poslovanja na razini djelatnosti i poddjelatnosti. Financijsko je stanje kod većina poddjelatnosti uneravnoteženo, što znači da nije uspostavljena ni dugoročna ni kratkoročna uravnoteženost. Profitabilnost pojedinih poddjelatnosti u razmatranom razdoblju je negativna. Sve to upućuje na zaključak da je stanje u djelatnosti "Hoteli i restorani" teško što podrazumijeva hitnu intervenciju na makro i na mikro području. Računovodstvena analiza je temelj na osnovu kojeg je moguće donijeti adekvatne odluke

    Layer-stacking irregularities in C36-type Nb-Cr and Ti-Cr laves phases and their relation with polytypic phase transformations.

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    International audienceSpecific layer-stacking irregularities have been identified in C36 (4H) Nb-Cr and Ti-Cr Laves-phases on the basis of X-ray diffraction line-profile analysis and high resolution transmission-electron microscopy. Domain boundaries and transformation errors within domains could be distinguished. The layer-stacking irregularities in both C36-NbCr2 and C36-TiCr2 can be associated with a preceding C14 (2H) -> C36 (4H) phase transformation carried out by glide of mobile synchro-Shockley partial dislocation dipoles in an ordered fashion. The stacking irregularities observed can be interpreted as deviations from such perfect "ordered glide". The interpretation is supported by the observation that in case of C36-NbCo2, where no preceding C14 -> C36 transformation occurs, different layer-stacking irregularities are observed

    Ultrathin 2D coordination polymer nanosheets by surfactant-mediated synthesis

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    Amine-Linked Covalent Organic Frameworks as a Platform for Postsynthetic Structure Interconversion and Pore-Wall Modification

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    Covalent organic frameworks have emerged as a powerful synthetic platform for installing and interconverting dedicated molecular functions on a crystalline polymeric backbone with atomic precision. Here, we present a novel strategy to directly access amine-linked covalent organic frameworks, which serve as a scaffold enabling pore-wall modification and linkage-interconversion by new synthetic methods based on Leuckart–Wallach reduction with formic acid and ammonium formate. Frameworks connected entirely by secondary amine linkages, mixed amine/imine bonds, and partially formylated amine linkages are obtained in a single step from imine-linked frameworks or directly from corresponding linkers in a one-pot crystallization-reduction approach. The new, 2D amine-linked covalent organic frameworks, rPI-3-COF, rTTI-COF, and rPy1P-COF, are obtained with high crystallinity and large surface areas. Secondary amines, installed as reactive sites on the pore wall, enable further postsynthetic functionalization to access tailored covalent organic frameworks, with increased hydrolytic stability, as potential heterogeneous catalysts

    High-pressure synthesis and characterization of Li<inf>2</inf>Ca <inf>3</inf>[N<inf>2</inf>]<inf>3</inf> - An uncommon metallic diazenide with [N<inf>2</inf>]<sup>2-</sup> ions

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    Dinitrogen (N2) ligation is a common and well-characterized structural motif in bioinorganic synthesis. In solid-state chemistry, on the other hand, homonuclear dinitrogen entities as structural building units proved existence only very recently. High-pressure/high-temperature (HP/HT) syntheses have afforded a number of binary diazenides and pernitrides with [N 2]2- and [N2]4- ions, respectively. Here, we report on the HP/HT synthesis of the first ternary diazenide. Li 2Ca3[N2]3 (space group Pmma, no. 51, a = 4.7747(1), b = 13.9792(4), c = 8.0718(4) Å, Z = 4, wRp = 0.08109) was synthesized by controlled thermal decomposition of a stoichiometric mixture of lithium azide and calcium azide in a multianvil device under a pressure of 9 GPa at 1023 K. Powder X-ray diffraction analysis reveals strongly elongated N-N bond lengths of dNN = 1.34(2)-1.35(3) Å exceeding those of previously known, binary diazenides. In fact, the refined N-N distances in Li2Ca3[N2]3 would rather suggest the presence of [N2]3·- radical ions. Also, characteristic features of the N-N stretching vibration occur at lower wavenumbers (1260-1020 cm-1) than in the binary phases, and these assignments are supported by first-principles phonon calculations. Ultimately, the true character of the N2 entity in Li 2Ca3[N2]3 is probed by a variety of complementary techniques, including electron diffraction, electron spin resonance spectroscopy (ESR), magnetic and electric conductivity measurements, as well as density-functional theory calculations (DFT). Unequivocally, the title compound is shown to be metallic containing diazenide [N2] 2- units according to the formula (Li+) 2(Ca2+)3([N2]2-) 3·(e-)2. © 2013 American Chemical Society

    Conductivity mechanism in ionic 2D carbon nitrides: from hydrated ion motion to enhanced photocatalysis

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    Carbon nitrides are among the most studied materials for photocatalysis, however, limitations arise from inefficient charge separation and transport within the material. Here, this aspect is addressed in the 2D carbon nitride poly(heptazine imide) (PHI) by investigating the influence of various counterions, such as M = Li+, Na+, K+, Cs+, Ba2+, NH4+ and tetramethyl ammonium, on the material’s conductivity and photocatalytic activity. These ions in the PHI pores affect the stacking of the 2D layers, which further influences the predominantly ionic conductivity in M-PHI. Na-containing PHI outperforms the other M-PHI in various relative humidity (RH) environments (0-42 %RH) in terms of conductivity, likely due to pore channel geometry and size of the (hydrated) ion. With increasing RH, the ionic conductivity increases by 4-5 orders of magnitude (for Na-PHI up to 10-5 S cm-1 at 42 %RH). At the same time, the highest photocatalytic hydrogen evolution rate is observed for Na-PHI, which is mirrored by increased photo-generated charge carrier lifetimes, pointing to efficient charge carrier stabilization by mobile ions. These results indicate that ionic conductivity is an important parameter that can influence the photocatalytic activity. Besides, RH-dependent ionic conductivity is of high interest for separators, membranes, or sensors
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