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1988 (183)
141Author    SalimM. KhalilRequires cookie*
 Title      
 Abstract    MINDO-Forces calculations are performed, after complete optimization of geometry, on a, ß, y-methylphenylallyl cations. It is found that the substituents affect only the geometrical parameters of the allyl and show no influence on the phenyl ring. The positive charges at the carbon atoms of the phenyl ring decrease on methyl substitutions. A methyl substituent at carbon atom C9 (E, E and E,Z isomers) stabilizes the phenylallyl cation, while all other substituents al CI and C8 are destabi­ lizing. The calculations predict no (1,9) ^-interaction in the methyl substituted phenylallyl cations. 
  Reference    Z. Naturforsch. 43a, 868—872 (1988); received July 11 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0868 
 Volume    43 
142Author    Stefanie Brummer, Helmut Paulus, Alarich WeissRequires cookie*
 Title      
 Abstract    The 35C1 NQR spectra of 2,4,4,6-tetrachloro-3,5-dimethyl-cyclohexadiene-2,5-one-l and 2,4,4,6-tetrachloro-cyclohexadiene-2,5-one-l were studied from 77 K up to the decomposition temperature, their crystal structure having been determined by single crystal X-ray diffraction. The first com­ pound crystallizes in the monoclinic space group C2h-P2!/m with two molecules in the unit cell. The lattice constants are a = 887.2 (3) pm, b = 704.8 (3) pm c = 824.0 (3) pm, y? = 96.10(1)°. The sec­ ond compound crystallizes orthorhombic, space group D^-Cmca, with 8 molecules in the unit cell which has the dimensions a = 711.2(2) pm, b = 1388.4(3) pm, c = 1729.8(4) pm. The structures deter­ mined belong to the stable phases of the title compounds as seen from the NQR spectra as a function of temperature which show no sign for a phase transition between the melting point and 77 K. In both title compounds the molecules are planar. Their symmetry is compared with other chloro-cyclohexadiene-2,5-ones-l and chloro-cyclohexadiene-2,5-diones-l,4. The intramolecular distances d,c_ci) of the sp2 carbon atoms and the 35C1 NQR frequencies assigned to the corresponding CI atoms correlate quite well according to the theory: v(35Cl) ~(4c-ci))"3-th e relation is v(35C1)/MHz = 2 +174 • 106-(d/pm)"3. 
  Reference    Z. Naturforsch. 43a, 873—884 (1988); received July 20 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0873 
 Volume    43 
143Author    W. Klämke, W. HaaseRequires cookie*
 Title     
 Abstract    -r a y S tu d ie s o n L a y e r S ta c k in g a n d O r d e r in g in a L iq u id C ry s ta llin e D is u b s titu te d B ip h e n y lc y c lo h e x a n e X-ray measurements on disubstituted biphenylcyclohexane BCH 52 show a crystalline smectic B phase with an ABCA layer stacking in bulk samples when cooled from the nematic to the smectic phase. No temperature dependence of this stacking can be seen. When cooling freely suspended thin films (below 20 |im) from the nematic to the smectic B phase, the obtained X-ray reflexes indicate an arrangement of the molecules in an orthorhombic F like stacking. 
  Reference    Z. Naturforsch. 43a, 885—888 (1988); received July 27 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0885 
 Volume    43 
144Author    B. N. Brunvoll, S. J. Cyvin, CyvinRequires cookie*
 Title      
 Abstract    Benzenoid systems and their A values are studied. Here A is the absolute magnitude of the difference between the numbers of black and white vertices. The systems with maximum A at a given h (number of hexagons) are treated in particular. TP benzenoids are defined as consisting of fused triangulenes and phenalenes only. All benzenoids with A = zlm ax = 1,2,3,... for h = 3,6,9,..., re­ spectively, are TP benzenoids. By means of a computer program all benzenoid systems with A = hi3 up to h — 15 are generated. In conclusion, a number of supplementary data to the enumerations of benzenoids are reported. 
  Reference    Z. Naturforsch. 43a, 889—894 (1988); received November 19 1987 
  Published    1988 
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 Identifier    ZNA-1988-43a-0889 
 Volume    43 
145Author    ZdzislawT. LalowiczRequires cookie*
 Title    2H -N M  
 Abstract    R S p e c tr o s c o p y o f T u n n e lin g A m m o n iu m I o n : G e n e r a l S ite S y m m e try 2H-NMR powder spectra of tunneling ammonium-d4 ions are computed. A representation of the tunneling Hamiltonian is worked out in the basis of simple product spin wavefunctions. Secular parts of quadrupole and dipole Hamiltonians are taken into account. Examples of spectra are given for tunneling about one C2 or C3 axis, as well as for overall rotations in potentials of higher symmetry. Ranges of tunneling frequencies measurable from the spectra are given for each case. Characteristic shapes of the spectra allow recognition of various ground torsional level structures. Possible further applications and available data are discussed. PACS number 76.60 
  Reference    Z. Naturforsch. 43a, 895—907 (1988); received July 19 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0895 
 Volume    43 
146Author    W. I. Jung, O. LutzRequires cookie*
 Title    Volume Selective N M R Spectroscopy by Coded Slice Excitation (C O D E X )  
 Abstract    A method for volume selective nuclear magnetic resonance spectroscopy has been developed and implemented on an 1.5 T whole body imager for in vivo investigations. Four single experiments produce different magnetizations in the same slice, and a special subtract scheme yields the signal of only the volume of interest, which is accurately defined. The resolution of the spectra and the stability of the method have been verified with a water phantom containing acetone, ethanol, methanol, and oil vessels. 
  Reference    Z. Naturforsch. 43a, 909—9 (1988); received September 22, 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0909 
 Volume    43 
147Author    K. Hau, P. Frodl, F. Sommer, F. WahlRequires cookie*
 Title      
 Abstract    A microscopic theory of a single hydrogen centre embedded in a Niobium crystal lattice is given. The electronic structure is investigated on the basis of a special energy difference procedure devel­ oped by Wahl et al. This procedure, here applied in its lowest approximation, yields the change in the electronic energy and electronic density distribution due to the embedded hydrogen atom. From these quantities, the dipole force tensor, the displacement of the ions close to the interstitial (nearest and next nearest neighbours) and the heat of solution are calculated. The computed results show good agreement with experimental data. A M ic ro s c o p ic T h e o ry o f a S in g le H y d r o g e n C e n tr e in N io b iu m * 
  Reference    Z. Naturforsch. 43a, 914—922 (1988); received August 10. 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0914 
 Volume    43 
148Author    F. T. Sommer, K. Hau, P. Frodl, F. WahlRequires cookie*
 Title     
 Abstract    a lc u la tio n o f th e E x c ita tio n E n e rg ie s o f a H y d r o g e n Im p u rity in N io b iu m Recent calculations of the electronic structure of a hydrogen atom in niobium using microscopic first principles are extended in that the dynamical behaviour of a hydrogen impurity centre in Nb is considered quantummechanically. The calculated excitation energies are in good agreement with experimental values of time of flight-spectra taken from NbH0 05. 
  Reference    Z. Naturforsch. 43a, 923—929 (1988); received December 10 1987 
  Published    1988 
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 Identifier    ZNA-1988-43a-0923 
 Volume    43 
149Author    B. Bruhn, B. P. KochRequires cookie*
 Title      
 Abstract    The Melnikov method is used to discuss the parameter dependence of homoclinic and heteroclinic bifurcations for the rf SQUID system. Also the case of strong damping is treated. Because of the complicated potential the resulting integrals have to be evaluated numerically. For some selected parameter sets the theoretical predictions are compared with numerical solutions of the equation of motion. Very good agreement of both methods is found. Key words: Nonlinear dynamics, Josephson effect, chaos, homoclinic and heteroclinic bifurcations H o m o c lin ic a n d H e te ro c lin ic B ifu rc a tio n s in r f S Q U I D s 
  Reference    Z. Naturforsch. 43a, 930—938 (1988); received September 1 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0930 
 Volume    43 
150Author    Requires cookie*
 Title     
 Abstract    o p o lo g ic a l P r o p e r tie s o f B e n z e n o id S y s te m s . L I. H o s o y a In d e x o f M o le c u le s C o n ta in in g a P o ly a c e n e F r a g m e n t 
  Reference    Z. Naturforsch. 43a, 939 (1988) 
  Published    1988 
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 Identifier    ZNA-1988-43a-0939 
 Volume    43 
151Author    A. Lakhtakia, R. Messier, V. V. Varadan, V. K. VaradanRequires cookie*
 Title      
 Abstract    c o m m e n s u r a te N u m b e rs , C o n tin u e d F r a c tio n s , a n d F r a c t a l I m m itta n c e s Continued fractions have a rich tradition in the theory of numbers; e.g., non-terminating con­ tinued fractions represent irrational numbers. It will be shown that a class of continued fractions possess the property of self-referential decomposition, and their interpretation in the form of non-terminating ladder circuits gives rise to fractal immittances with potential analogies to rough surfaces, thin cermet films, as well as to the internal void network structure of thick films. 
  Reference    Z. Naturforsch. 43a, 943—955 (1988); received June 10 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0943 
 Volume    43 
152Author    H. D. Försterling, H. SchreiberRequires cookie*
 Title      
 Abstract    The reaction HBr02 + Br " + H + -»2 HOBr, which is the most important control reaction in the Belousov-Zhabotinsky (BZ) system, is investigated in competition to the AgBr precipitation reaction Ag+ + Br" — ► AgBr. It turns out that the bromite-bromide reaction starts even in the presence of Ag^ in high concentration; the rate of consumption of bromite by bromide, however, is slowed down significantly if silver ions are present in the system. The experiments reveal that the AgBr precipita­ tion reaction proceeds in a series of several steps, starting with a fast equilibrium. This way different experimental results on the influence of silver ions on the kinetics of the BZ reaction may now be better understood. 
  Reference    Z. Naturforsch. 43a, 956—960 (1988); received August 8 1988 
  Published    1988 
  Keywords    Belousov-Zhabotinsky Reaction, Bromous Acid, Bromide, Silver Bromide 
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 Identifier    ZNA-1988-43a-0956 
 Volume    43 
153Author    Akira Endoh, Toshio Yamaguchi, Yusuke Tamura, Osamu Odawara, Isao Okada, Hitoshi Ohtaki, Masakatsu MisawaRequires cookie*
 Title     
 Abstract    t r u c t u r a l S tu d y o n M o lte n (7L i, K)C 1 a n d (7L i, N a , K)C 1 o f th e E u te c tic C o m p o s itio n by P u ls e d N e u tro n D if fr a c tio n Pulsed neutron diffraction measurements have been performed on molten (7Li, K)C1 and (7Li, Na, K)C1 mixtures of the eutectic composition to determine the nearest neighbour distance between Li+ and Cl~ ions. Owing to the negative scattering length of the 7 Li nucleus, this contribu­ tion becomes negative in the radial distribution function and can be separated from the other contributions. The nearest neighbour distance between Li+ ion and CP ion is found to be 240 pm in both the binary and ternary mixtures. 
  Reference    Z. Naturforsch. 43a, 961—964 (1988); received August 28 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0961 
 Volume    43 
154Author    ChrL. Teske, Hk Müller-BuschbaumRequires cookie*
 Title     
 Abstract    h e rm o a n a ly tis c h e U n te rs u c h u n g e n z u r R ü c k o x id a tio n von B a 2Y C u 30 6 + :c Thermoanalytical Investigations about the Reoxidation of Ba2YCu3Ob + x The reoxidation reaction of Ba,YCu30 6+x forming the superconducting ceramic material Ba2YCu30 6 93 is studied by thermoanalytical methods (DTA and TG). The exothermal oxygen uptake in pure 0 2-atmosphere is at a maximum rate in the range of 230-330 C (% 150 min). The reoxidation temperature can be lowered by treatment of Ba2YCu3Oe 0 in Ar: H2 = 1:1 atmosphere but the uptake of greater amounts of hydrogen prevents the material from becoming super-conducting again at low reoxidation temperatures. The process has an activation energy Ea = 70.9 + 2kJ/Mol and a reaction enthalpy AH = — 86.7kJ/Mol Ba2YCu30 6 0 (normalized to a 1/2 0 2 basis) which is estimated from DTA-data. 
  Reference    Z. Naturforsch. 43a, 965—970 (1988); eingegangen am 8. August 1988 
  Published    1988 
  Keywords    Ba2YCu30 6 + x, Thermoanalysis, Reoxidation, Activation Energy, Reaction Enthalpy 
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 Identifier    ZNA-1988-43a-0965 
 Volume    43 
155Author    Joachim Gripp, Helmut DreizlerRequires cookie*
 Title      
 Abstract    th e M ic ro w a v e S p e c tru m o f E th y l I o d id e : N u c le a r Q u a d r u p o le a n d S p in R o ta tio n C o u p lin g Some rotational transitions of ethyl iodide, CH3CH2I, have been reinvestigated by microwave Fourier transform (MWFT) spectroscopy. The iodine hyperfine structure splittings were first ana­ lyzed using a direct diagonalization procedure of the complete quadrupole Hamiltonian matrix. The results of this analysis showed deviations from our measurements up to 60 kHz. A new analysis using additional spin rotation coupling matrix elements reproduces our measurements within the experi­ mental error limit and decreases the standard deviation of the least squares fit from 28 kHz to only 4 kHz. 
  Reference    Z. Naturforsch. 43a, 971—976 (1988); received August 20 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0971 
 Volume    43 
156Author    SurjyaP. Das, Burghard Wittekopf, KonradG. WeilRequires cookie*
 Title      
 Abstract    Silver nitrate can form homogeneous liquid phases with some organic nitriles and water, even when there is no miscibility between the pure liquid components. We determined the shapes of the single phase regions in the ternary phase diagram for the following systems: silver nitrate/RCN/H,0 with R = CH3, C3H7, C6H5, and C6H5CH2 at room temperature and for R = C6H5 also at 60 C and 0°C. Furthermore we studied kinematic viscosities, electrical conductivities, and densities of mixtures containing silver nitrate, RCN, and water with the mole ratios X/4/1 (0.2 ^ X S 3.4). In these cases also R = C2H5 and C4H9 were studied. The organic nitriles show different dependences of viscosity and conductivity on the silver nitrate content from the aliphatic ones. P h a s e E q u ilib ria a n d T r a n s p o r t P r o p e r tie s 
  Reference    Z. Naturforsch. 43a, 977—982 (1988); received August 8 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-0977 
 Volume    43 
157Author    G. Pirzer, G. Gliemann, L. Chassot, A. Von ZelewskyRequires cookie*
 Title     
 Abstract    in g le C r y s ta l L u m in e sc e n c e o f D im e ric C is -b is (2 -p h e n y lp y rid in e)p la tin u m (II) a t H ig h P r e s s u r e The emission spectrum of single-crystal cis-bis(2-phenylpyridine)-platinum(II) has been measured at room temperature under high pressures up to 60 kbar. The observed red shift of the emission is on the order of —15 cm"7kbar and can be explained by a reduction of the Pt-Pt distance in the dimeric units with increasing pressure. 
  Reference    Z. Naturforsch. 43a, 983—986 (1988) 
  Published    1988 
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 Identifier    ZNA-1988-43a-0983 
 Volume    43 
158Author    Gerold Baier, Peter Urban, Klaus WegmannRequires cookie*
 Title     
 Abstract    N e w M o d e l S y s te m fo r th e S tu d y o f C o m p le x D y n a m ic a l E n z y m e R e a c tio n s . I. A N o n lin e a r E n z y m e R e a c tio n in a C h e m ic a l G r a d ie n t An experimental system for the study of biochemical reaction dynamics is introduced and de­ scribed. A one-enzyme reaction is extended by an artificial feedback loop in an electrochemical device. Cyclic voltammetry is used to show that the reaction rate depends nonlinearly on the amount of cosubstrate offered. For some sets of fixed parameter values a damped oscillatory approach of the steady state was observed. The usefulness of the systems theoretical concepts is discussed. 
  Reference    Z. Naturforsch. 43a, 987—994 (1988); Received August 22 1988 
  Published    1988 
  Keywords    Reaction-diffusion Systems, Peroxidase, Feedback, Nonlinearity, Damped Oscillations 
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 Identifier    ZNA-1988-43a-0987 
 Volume    43 
159Author    Gerold Baier, Peter Urban, Klaus WegmannRequires cookie*
 Title     
 Abstract    f C o m p le x D y n a m ic a l E n z y m e R e a c tio n s . I I . O s c illa tio n s in a R e a c tio n -D iffu s io n -C o n v e c tio n S y s te m A nonlinear enzyme reaction in a chemical gradient with an artificial feed-back loop is modified by the application of a constant temperature gradient leading to laminar convective motion of the fluid at an electrode. The complete system is shown to undergo a bifurcation into a limit cycle as a function of the applied temperature gradient. The effect of other parameters on the oscillation is described. More complicated types of behavior are expected in parameter space. A N e w M o d e l S y s te m f o r th e S tu d y 
  Reference    Z. Naturforsch. 43a, 995—1001 (1988); received August 22 1988 
  Published    1988 
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 TEI-XML for    default:Reihe_A/43/ZNA-1988-43a-0995.pdf 
 Identifier    ZNA-1988-43a-0995 
 Volume    43 
160Author    Yutaka Tai, Ishikawa Atsushi, Horiuchi*. Keizo, Asaji Tetsuo, Daiyu Nakamura, Ryuichi IkedaRequires cookie*
 Title    35C1  
 Abstract    N u c le a r Q u a d r u p o le R e la x a tio n in P y rid in iu m H e x a c h lo r o s ta n n a te (IV) The temperature dependence of the 35C1 quadrupole spin-lattice relaxation time T10 is reported for the three known resonance lines of pyridinium hexachlorostannate (IV). With increasing temper­ ature, a sharp decrease of T1Q is observed below the phase transition temperature of 331 K. This decrease can be explained by reorientational motions of the complex anions. The activation energy for the motions is determined as 97 and 63 kJmol-1 from the T\q data obtained from the highest-frequency resonance line and the remaining two lines, respectively. The two different barriers observed for the reorientation of a single anion suggest the existence of anisotropy of the anionic motion. An anomalous T1Q vs. T_1 relation observed in an intermediate-temperature region is discussed by referring to the cationic motion. 
  Reference    Z. Naturforsch. 43a, 1002 (1988); received July 26 1988 
  Published    1988 
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 Identifier    ZNA-1988-43a-1002 
 Volume    43 
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