905 research outputs found
Visum repertum über den Leichnam des seligen Herrn Hofraths Senckenberg des Stifters des Bürgerhospitals
No full textHandschriftlicher Leichenschaubericht über den verunglückten Johann Christian Senckenberg: 18.11.1772. Unterzeichnet von den Ärzten: Behrends, I. A. ; Krisner, I.C. ; Müller, F. S. ; Giese, J. G. ; Behrends, J. C. ; Jonas, A. I. G. ; Meyer, C. F. ; Bucher, J. L. ; Grasemann, Ch. F
Structural isomerization and molecular motions of liquid n-alkanes. Ultrasonic and high-frequency shear viscosity relaxation
No full textBetween 20 and 120 MHz, the complex shear viscosity of n-tetradecane, n-pentadecane, n-hexadecane, and a n-eicosane/n-tetradecane mixture has been measured using a shear impedance spectrometer. The data are compared to ultrasonic absorption spectra of the liquids as measured between 1 MHz and 2 GHz. Relaxational behavior has been found. The extrapolated high-frequency shear viscosity eta(s)(infinity) is distinctly smaller than the static shear viscosity eta(s)(0). The shear viscosity relaxation time is discussed in light of literature data of the orientational correlation time from depolarized Rayleigh scattering and also of the collision time as resulting from dielectric spectrometry. The assumption appears to be likely that the shear viscosity relaxation is due to rotational isomerizations of the chain molecules. A damped torsional oscillator model has been used to evaluate the spectra. The reasonable number of three carbon atoms per oscillator unit results. The activation energies and enthalpies are derived from measurements at different temperatures
Molecular dynamics and conformational kinetics of mono- and disaccharides in aqueous solution
No full textAcoustical attenuation spectra between 10 kHz and 2 GHz, complex dielectric spectra between 300 kHz and 40 GHz, and time-resolved non-equilibrium measurements are reported for aqueous solutions of various mono- and disaccharides with and without 2:1 valent salts. The spectra reveal a variety of relaxation regimes with relaxation times between 1 mu s and 10 ps. In addition, the time-resolved observations enable the study of the mutarotation with relaxation times on the order of 10(3) s. Variation of the concentration and temperature as well as a careful choice of the saccharides allow a discussion of the relaxation processes in terms of a chair-chair ring inversion, two modes of pseudorotation, an exocyclic hydroxymethyl group rotation, a carbohydrate-carbohydrate association, and, in the disaccharide solutions, a rotation of the rings relative to another. Salt-containing solutions show also relaxation phenomena reflecting different steps cation-carbohydrate association and variations in the carbohydrate conformational isomerizations and associations due to interactions with cations
Cambios en la estructura del gen NirK y en variables edáficas como consecuencia de la historia de uso de la tierra en Lajitas (Salta)
No full textFil: Behrends Kraemer, Filipe. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina.Fil: Montecchia, Marcela S. S. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina.Fil: Fernández, Patricia L. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina.Fil: Correa, Olga S. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina.Fil: Chagas, Celio I. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina
Hydrogen bonding and chain conformational isomerization of alcohols probed by ultrasonic absorption and shear impedance spectrometry
No full textThe acoustical absorption spectra between 300 kHz and 3 GHz and the complex shear viscosity spectra between 6 and 120 MHz for some monohydric alcohols are reported. The acoustical spectra exhibit two relaxation regions, one located at frequencies around some hundred MHz and the other one around some GHz. The shear viscosity spectra reveal a relaxation process in conformity with the low-frequency acoustical relaxation. This relaxation is assigned to fluctuations in the structure of hydrogen bonded alcohol clusters. The high-frequency acoustical relaxation is discussed in terms of a damped torsional oscillator model of allkyl chain isomerization, corresponding with the rotational isomerization of n-alkanes. The high frequency (>5 GHz) shear viscosity of the alcohols is estimated and found in the same order (1 mPa s) as that for n-alkanes
Author Correction: A prospective observational study of post-COVID-19 chronic fatigue syndrome following the first pandemic wave in Germany and biomarkers associated with symptom severity (Nature Communications, (2022), 13, 1, (5104), 10.1038/s41467-022-3
No full textIn the author list of this article, the names of the authorswere incorrectly listed with initials and family name only. The incorrect author list read as “C. Kedor, H. Freitag, L. Meyer-Arndt, K. Wittke, L. G. Hanitsch, T. Zoller, F. Steinbeis, M. Haffke, G. Rudolf, B. Heidecker, T. Bobbert, J. Spranger, H. D. Volk, C. Skurk, F. Konietschke, F. Paul, U. Behrends, J. Bellmann-Strobl and C. Scheibenbogen”. The author list has now been amended to include the given and family names in the HTML and PDF versions of the article. The corrected author list reads as “Claudia Kedor, Helma Freitag, Lil Meyer-Arndt, Kirsten Wittke, Leif G. Hanitsch, Thomas Zoller, Fridolin Steinbeis, Milan Haffke, Gordon Rudolf, Bettina Heidecker, Thomas Bobbert, Joachim Spranger, Hans- Dieter Volk, Carsten Skurk, Frank Konietschke, Friedemann Paul, Uta Behrends, Judith Bellmann-Strobl and Carmen Scheibenbogen”
Acoustical properties of aqueous solutions of urea: Reference data for the ultrasonic spectrometry of liquids
No full textThe density, sound velocity, and ultrasonic attenuation coefficient of aqueous solutions of urea were measured at temperatures between 10 degreesC and 35 degreesC and at concentrations ranging from 0 to 9 mol/L (equivalent to21.7 mol %) urea. The data are correlated using simple empirical expressions, and the isentropic compressibilities are calculated. These urea solutions provide a favorable set of reference data for acoustical measurements of liquids with sound velocity between 1500 m(.)s(-1) and 1700 m(.)s(-1)
Critical slowing in lipid bilayers
No full textUltrasonic attenuation spectra (100 kHz to 2 GHz) and complex dielectric spectra (300 kHz to 40 GHz) of aqueous solutions of 1,2-dimyristoyl-L-3-phosphatidylcholine vesicles are reported and are discussed in view of their behavior near the main phase transition of the lipid. The relaxation terms in the spectra are assigned to the domain structure fluctuations of the membranes, the structural isomerization of alkyl chains, the axial diffusion of lipid molecules within the membrane, and the reorientational motions of the zwitterionic phospholipid headgroups. The relaxation times of the alkyl chain isomerization and of the headgroup motions on the bilayer surfaces show a steplike change at the transition temperature, T-m. The axial diffusion and the domain fluctuations exhibit substantial effects of slowing near T-m as characteristic for critically demixing liquids at their consolute point
The binary system triethylamine-water near its critical consolute point: An ultrasonic spectrometry, dynamic light scattering, and shear viscosity study
No full textUltrasonic attenuation spectra between 100 kHz and 500 MHz, mutual diffusion coefficients and shear viscosities of the triethylamine/water mixture of critical composition have been measured at various temperatures near the critical one. The broadband ultrasonic spectra reveal two relaxation terms with discrete relaxation time and a term that is subject to a broad relaxation time distribution. The former have been discussed to be due to a protolysis reaction and a structural isomerization. The latter term has been evaluated in the light of the Bhattacharjee-Ferrell dynamic scaling theory, relating the sonic spectrum to fluctuations in the local mixture concentrations. The relaxation rate of the Bhattacharjee-Ferrell term follows power law behavior. However, its amplitude (Gamma(0)=45x10(9) s(-1)) is considerably smaller than that derived from the dynamic light scattering and shear viscosity measurements (Gamma(0)=96x10(9) s(-1)). This result is assumed to be due to a shear viscosity relaxation. Using density and heat capacity measurements from the literature, the adiabatic coupling constant g of the triethylamine/water system has been derived from the amplitude of the Bhattacharjee-Ferrell term in the ultrasonic spectra and from a thermodynamic relation as well. Again, a discrepancy is found. The ultrasonic spectra yield g=0.19, whereas g=0.98 follows otherwise. This difference in the g values is taken as an indication of the limitations of the Bhattacharjee-Ferrell model. It had been derived assuming a small amplitude in the singular part of the heat capacity, a precondition which is clearly not fulfilled with the triethylamine/water system. (C) 2002 American Institute of Physics
Critical fluctuations of the micellar triethylene glycol monoheptyl ether-water system
No full textUsing the equal volume criterion and also the pseudospinodal conception the critical demixing point of the triethylene glycol monoheptyl ether/water system (C7E3/H2O) has been determined as Y-crit=0.1 and T-crit=296.46 K (Y, mass fraction of surfactant). From density measurements the critical micelle concentration (cmc) followed as Y-cmc=0.007 at 288.15 K and Y-cmc=0.0066 at 298.15 K. The (static) shear viscosity eta(s) and the mutual diffusion coefficient D of the C7E3/H2O mixture of critical composition have been evaluated to yield their singular and background parts. From a combined treatment of both quantities the relaxation rate Gamma of order parameter fluctuations has been derived. Gamma follows power law with universal critical exponent and amplitude Gamma(0)=3.1x10(9) s(-1). Broadband ultrasonic spectra of C7E3/H2O mixtures exhibit a noncritical relaxation, reflecting the monomer exchange between micelles and the suspending phase, and a critical term due to concentration fluctuations. The former is subject to a relaxation time distribution that broadens when approaching the critical temperature. The latter can be well represented with the aid of the dynamic scaling model by Bhattacharjee and Ferrell (BF) [Phys. Rev. A. 31, 1788 (1985)]. The half-attenuation frequency in the scaling function of the latter model is noticeably smaller (Omega(BF)(1/2)approximate to 1) than the theoretically predicted value Omega(BF)(1/2)=2.1. This result has been taken as an indication of a coupling between the fluctuations in the local concentration and the kinetics of micelle formation, in correspondence with the idea of a fluctuation controlled monomer exchange [T. Telgmann and U. Kaatze, Langmuir 18, 3068 (2002)]. (c) 2006 American Institute of Physics
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