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61.
Thomas L. Osborne und Isaak F. Harris 《Fresenius' Journal of Analytical Chemistry》1904,43(5):299-301
Ohne ZusammenfassungNach einem gütigst zugesandten Abdruck aus dem Journal of the American chemical Society25, Nr. 5. übersetzt und bearb. von Dr. Griessmayer. 相似文献
62.
63.
Vladimir P. Toshchevikov Yuli Ya. Gotlib Isaak A. Torchinskii Vladimir A. Shevelev 《Macromolecular Symposia》2005,220(1):139-154
We discuss the relaxation properties of polymer networks possessing either short-scale ordering caused by rigidity of network strands or long-scale liquid crystalline order. The main topics of the paper are the equilibrium and local dynamic properties of a polymer network ordered due to nematic-like interactions of the network segments with included rod-like particles. A simplified three chain network model is used. Lagrange multipliers in the equations of motion of hard rods are replaced by their averaged values. This approximation corresponds to modelling the rod-like particles by elastic Gaussian springs, their mean-square lengths independent of the ordering. Nematic-like interactions between network segments and rods are taken into account in terms of the Maier-Saupe mean-field approximation. Nematic ordering of rods induces ordering of the network segments. Relaxation spectrum of the ordered network splits into two main branches for the parallel and perpendicular components of the chain segments with respect to the director. We calculate the relaxation times of a polymer network as functions of the wave number. The relaxation spectrum of an isotropic network and that of the ordered network with included rods are compared. 相似文献
64.
S. Withington K. G. Isaak S. A. Kovtonyuk R. A. Panhuyzen T. M. Klapwijk 《Infrared Physics & Technology》1995,36(7):1059-1075
Superconducting tunnel-junction direct detectors are considered in some detail. For frequencies below twice that of the gap there is some bias voltage for which the input impedance is real, the responsivity quantum limited, and the dynamic range high. A susperconducting detector saturates for two reasons: intrinsic saturation due to the relative increase in two-photon tunnelling processes, and extrinsic saturation due to the input match changing with bias voltage. The responsivity of a detector with a resistive RF source is least sensitive to bias-voltage changes and has the greatest dynamic range when operating with a sloping load line. In the case of an inductive source, the dynamic range can be higher than the intrinsic saturation rate would suggest. Ideally, superconducting tunnel-junction detectors should be biased in a constant-voltage mode. If the responsivity is to be depressed by no more than a few percent, the photon step should have a height which is no more than one quarter of the total current turn-on at the gap. Superconducting direct detectors can be used to make precise and well-calibrated optical measurements at submillimetre wavelengths. 相似文献
65.
H.S. Pruys R. Engfer R. Hartmann E.A. Hermes H.P. Isaak F.W. Schlepuetz U. Sennhauser W. Dey K. Hess H.-J. Pfeiffer H.K. Walter W. Hesselink 《Nuclear Physics A》1981,352(3):388-398
Energy spectra of charged particles (p, d, t, 3He, α) emitted following the absorption of stopped π? in 12C, 59Co and 197Au have been measured. The results are compared with results from neutron spectroscopy and discussed in the context of the quasi-deuteron model of π? absorption. 相似文献
66.
67.
The deep blue organoclay color pigment (OCCP), naphthylazonaphthylammonium–montmorillonite, was synthesized in an aqueous
suspension by treating montmorillonite with naphthylammonium chloride followed after 2 h by NaNO2. The reddish-brown azo dye naphthylazonaphthylamine (commercial name “Solvent Brown 3”) was synthesized in an aqueous solution
in the absence of clay from the same reagents. X-ray diffraction and thermo-infrared (IR) spectroscopy of organoclay prepared
by treating montmorillonite with naphthylammonium chloride showed that the organoclay contained two types of tactoids with
intercalated naphthylammonium cations and with naphthylammonium–naphthylamine associations. Naphthylammonium clay was obtained
after thoroughly washing the latter organoclay. IR spectra of naphthylamine, naphthylammonium chloride, naphthylammonium clay,
naphthylammonium–naphthylamine clay (with some naphthylammonium-clay), OCCP, and Solvent Brown 3 in KBr disks were recorded
before and after thermal treatments up to 120 °C. IR spectrum of the OCCP was similar to that of Solvent Brown 3. An NH3
+ group was identified in the spectrum of the OCCP but not in that of Solvent Brown 3. In the latter spectrum, an NH2 group was identified, suggesting that the amine group of the azo dye in the OCCP was protonated. It appears that the difference
in color between OCCP and Solvent Brown 3 resulted from the protonation of the azo molecule in the interlayer space of the
clay. 相似文献
68.
Isaak Beyer Dr. Nasrollah Rezaei‐Ghaleh Dr. Hans‐Wolfgang Klafki Dr. Olaf Jahn Dr. Ute Haußmann Prof. Dr. Jens Wiltfang Prof. Dr. Markus Zweckstetter Prof. Dr. Hans‐Joachim Knölker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8685-8693
In addition to the prototypic amyloid‐β (Aβ) peptides Aβ1–40 and Aβ1–42, several Aβ variants differing in their amino and carboxy termini have been described. Synthetic availability of an Aβ variant is often the key to study its role under physiological or pathological conditions. Herein, we report a protocol for the efficient solid‐phase peptide synthesis of the N‐terminally elongated Aβ‐peptides Aβ?3–38, Aβ?3–40, and Aβ?3–42. Biophysical characterization by NMR spectroscopy, CD spectroscopy, an aggregation assay, and electron microscopy revealed that all three peptides were prone to aggregation into amyloid fibrils. Immunoprecipitation, followed by mass spectrometry, indicated that Aβ?3–38 and Aβ?3–40 are generated by transfected cells even in the presence of a tripartite β‐site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitor. The elongated Aβ peptides starting at Val(?3) can be separated from N‐terminally‐truncated Aβ forms by high‐resolution isoelectric‐focusing techniques, despite virtually identical isoelectric points. The synthetic Aβ variants and the methods presented here are providing tools to advance our understanding of the potential roles of N‐terminally elongated Aβ variants in Alzheimer's disease. 相似文献
69.
Mouhib H Jelisavac D Sutikdja LW Isaak E Stahl W 《The journal of physical chemistry. A》2011,115(2):118-122
We observed the microwave spectrum of ethyl isovalerate by molecular beam Fourier transform microwave spectroscopy. The rotational and centrifugal distortion constants of the most abundant conformer were determined. Its structure was investigated by comparison of the experimental rotational constants with those obtained by ab initio methods. In a first step, the rotational constants of various conformers were calculated at the MP2/6-311++G** level of theory. Surprisingly, no agreement with the experimental results was found. Therefore, we concluded that in the case of ethyl isovalerate more advanced quantum chemical methods are required to obtain a reliable molecular geometry. Ab initio calculations carried out at MP3/6-311++G**, MP4/6-311++G**, and CCSD/6-311++G** levels and also density functional theory calculations using the B3LYP/6-311++G** method gave similar results for the rotational constants, but they were clearly distinct from those obtained at the MP2/6-311++G** level. With use of these more advanced methods, the rotational constants of the lowest energy conformer were in good agreement with those obtained from the microwave spectrum. 相似文献
70.
Dydek EV Zaltzman B Rubinstein I Deng DS Mani A Bazant MZ 《Physical review letters》2011,107(11):118301
We revisit the classical problem of diffusion-limited ion transport to a membrane (or electrode) by considering the effects of charged sidewalls. Using simple mathematical models and numerical simulations, we identify three basic mechanisms for overlimiting current in a microchannel: (i)?surface conduction carried by excess counterions, which dominates for very thin channels, (ii)?convection by electro-osmotic flow on the sidewalls, which dominates for thicker channels, and (iii) transitions to electro-osmotic instability on the membrane end in very thick channels. These intriguing electrokinetic phenomena may find applications in biological separations, water desalination, and electrochemical energy storage. 相似文献