Tris(dipivalomethanato)holmium Induced NMR Shifts

Paramagnetic complexes of praseodymium and europium with 1,1,l,2,2,3,3- -heptafluoro-7, 7 ~dimethyl-4,6-octanedione [Pr(fod)3 and Eu(fod)3]1 and with 2,2,6,6-tetramethyl-3,5-heptanedione [Pr(DPM)3 and Eu(DPM)3] or sometimes ab:breviated as [Pr(tmhd)3 and Eu(tmhd)3]Z--5 have shown to !be very useful NMR shift reagents which can greatly s~mplify spectra of compounds having functional gro1ups with lone pair electrons. The only other lanthanide oormplex used for this :purpose was Yb(DPM)3 6>7 • However, Yb(DPM)3 exhibited a shift power between that of Pr(DPM)3 and Eu(DPM)3 and also strong line broadening8 and therefore did not offer any substantial advantage

Absorption characteristics of a quantum dot array induced intermediate band: implications for solar cell design

We present a theoretical study of the electronic and absorption properties of the intermediate band (IB) formed by a three dimensional structure of InAs/GaAs quantum dots (QDs) arranged in a periodic array. Analysis of the electronic and absorption structures suggests that the most promising design for an IB solar cell material, which will exhibit its own quasi-Fermi level, is to employ small QDs (~6–12 nm QD lateral size). The use of larger QDs leads to extension of the absorption spectra into a longer wavelength region but does not provide a separate IB in the forbidden energy gap

Synthesis of the Four Structural Isomeric L-Pentapeptides of Ala. Glu. Lys. Ala. Ala. Sequence: Characterization and Correlation with the L-D-L-D-D-lsomer Related to the Peptidoglycan Peptide Chain

The synthesis of the four L-pentapeptides containing the Ala. Glu. Lys. Ala. Ala. sequence, which differ with regard to the \u27sHe of linkage between the glutamyl-lysyl residues, is described. In each case the chain was built by coupHng the protected N- termi:nal dipeptide N-hydroxysuccinimide esiter (II or IV) with the C-terminal tripeptide benzyl ester (VIII or X). The sequentially .identical L-D-L-D-D-pentapeptide having the y-carboxy-group of D-glutamic acid residue involved in the .peptide ·bond, was prepared after the same general pattern. Complete deprotection of the isomers i111 two successive steps gave the free pentapeptides which were characterized as solid di-trifluoroacetate salts by analytical, optical and proton NMR spectral data. The isomers were compared by paper electrophoresis at different pH values. The alantne methyl resonances in the NMR spectra of the a-a L-pentapeptide XVIII and the y-a L-D-L-D-D-pentapeptide XXII were assigned by observing the shift in spectral lines with varying pH

Olovo i kadmij u cigaretama i dimnom kondenzatu

The cigarettes of three commercial brands (belonging to JUS quality classes E, II and IV) were analysed for cadmium and lead in tobacco, butts and crude smoke condensate. Metal fractions transferred from the cigarette tobacco to the smoke as well as metal retentions in the butts were calculated from the analytical results. Statistical analyses revealed a significant dependence of all observables on the cigarette quality class.Metodom inverzne voltammetrije na visećoj živinoj kapi (DPASV) određene su količine kadmija i olova u cigaretama triju vrsta (kvalitetni razredi prema JUS-u: Extra, II i IV). Pored duhana, papira i filtarskih čepića analizirani su i opušci i sirovi dimni kondenzat. Iz analističkih rezultata izračunana je frakcija prijenosa metala iz duhana u dimni kondenzat kao J retencija metala u opušku. Statističkim analizama utvrđena je ovisnost svili opservabli o kvalitetnom razredu cigarete

Collective Charge Excitations below the Metal-to-Insulator Transition in BaVS3

The charge response in the barium vanadium sulfide (BaVS3) single crystals is characterized by dc resistivity and low frequency dielectric spectroscopy. A broad relaxation mode in MHz range with huge dielectric constant ~= 10^6 emerges at the metal-to-insulator phase transition TMI ~= 67 K, weakens with lowering temperature and eventually levels off below the magnetic transition Tchi ~= 30 K. The mean relaxation time is thermally activated in a manner similar to the dc resistivity. These features are interpreted as signatures of the collective charge excitations characteristic for the orbital ordering that gradually develops below TMI and stabilizes at long-range scale below Tchi.Comment: 6 pages, 3 figures, submitted to PR

Change of the image of the city in process of using traffic infrastructure

Unique urban image cannot be experienced without moving within its structure. This paper deals with phenomenology considering changes of images of the city and influential factors closely related to it. Infrastructure gives basic structural scheme of every city, so its planning requires a high level proficiency. Some changes in these images can be observed during longer period of time. Sometimes it includes rapid changes of temporal layers, generated by building new urban elements on the exact same place where the old ones existed; while lighter change during the time passing is a regular occurrence. Creating completely new urban frames, caused by expanding the city, represents its dynamical variant. Topography is a significant factor, giving distinctive feature to the urbanity. This paper considers factors identified as generators of the change of the urban image, based on research so far. The structural elements are considered with the utmost attention. The importance of the city landmark, monumental complexes not possessing these features but having the importance in image of the city stability (as well as the inhabitants' memory) are crucial elements of identifying its picture. Another significant factor is related to individual personal experience. However, there are also certain factors of significance features, but not considered within this paper. One such factor is change in coloring, being the special topic itself. The purpose of this work is to indicate that urban planning requires special attention in order to keep continuous nature of the urban image for the city to preserve its visual identity

Recent Advances in Unconventional Density Waves

Unconventional density wave (UDW) has been speculated as a possible electronic ground state in excitonic insulator in 1968. Recent surge of interest in UDW is partly due to the proposal that the pseudogap phase in high T_c cuprate superconductors is d-wave density wave (d-DW). Here we review our recent works on UDW within the framework of mean field theory. In particular we have shown that many properties of the low temperature phase (LTP) in alpha-(BEDT-TTF)_2MHg(SCN)_4 with M=K, Rb and Tl are well characterized in terms of unconventional charge density wave (UCDW). In this identification the Landau quantization of the quasiparticle motion in a magnetic field (the Nersesyan effect) plays the crucial role. Indeed the angular dependent magnetoresistance and the negative giant Nernst effect are two hallmarks of UDW.Comment: 18 pages, 12 figure

Local atomic structure and discommensurations in the charge density wave of CeTe3

The local structure of CeTe3 in the incommensurate charge density wave (IC-CDW) state has been obtained using atomic pair distribution function (PDF) analysis of x-ray diffraction data. Local atomic distortions in the Te-nets due to the CDW are larger than observed crystallographically, resulting in distinct short and long Te-Te bonds. Observation of different distortion amplitudes in the local and average structures are explained by the discommensurated nature of the CDW since the PDF is sensitive to the local displacements within the commensurate regions whereas the crystallographic result averages over many discommensurated domains. The result is supported by STM data. This is the first quantitative local structural study within the commensurate domains in an IC-CDW system.Comment: 4 pages, 4 figure

Molecular Mechanics and SCF MO Conformational Analysis of Indol-3-ylacetic Acid Phytohormone (Auxin)

Conformational analysis of indol-3-ylacetic acid (IAA)-plant growth hormone has been performed using molecular mechanics and the ab initio SCF MO theory. The equilibrium geometry of IAA has been determined. Relative energies of alternative conformations, their charge distribution, dipole moment and energy barriers between them have been calculated. The position of the carboxyl group relative to the indole ring depends on two torsion angles, Tl(C2-C3-C8-C9) and T2(C3-C8-C9=02). Rotational barriers for these two angles were explored and it emerged that both rotations (about the C3-C8and C8-C9 bonds) can be accomplished in a reasonable time period at room temperature (the barrier height is about 4.6-10.9 (TI) and 1.7-3.8 (T2) kJ/mol respectively, according to ab initio calculations. Ab initio (GAMESS)and molecular mechanics (DISCOVER (CVFF and cff91), SYBYL(TRIPOS) and MM2(87), calculations revealed qualitatively the same shape of potential energy surface (E =f(Tl, T2)). However, energy differences between various conformations depend on the basis set (ab initio calculations) and force field (molecular mechanics) used