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71.
Jörg Mayer Hong-Viet V. Ngo Heinz Georg Schuster 《Journal of statistical physics》2012,148(4):676-685
We study the discrete dynamics of a fully connected network of threshold elements interacting via dynamically evolving synapses displaying spike timing dependent plasticity. Dynamical mean-field equations, which become exact in the thermodynamical limit, are derived to study the behavior of the system driven with uncorrelated and correlated Gaussian noise input. We use correlated noise to verify that our model gives account to the fact that correlated noise provides stronger drive for synaptic modification. Further we find that stochastic independent input leads to a noise dependent transition to the coherent state where all neurons fire together, most notably there exists an optimal noise level for the enhancement of synaptic potentiation in our model. 相似文献
72.
Force-extension curves (FECs), which quantify the response of a variety of biomolecules subject to mechanical force (f), are often quantitatively fit using worm-like chain (WLC) or freely jointed chain (FJC) models. These models predict that the chain extension, x, normalized by the contour length increases linearly at small f and at high forces scale as x ~ (1 - f(-α)), where α = 0.5 for WLC and unity for FJC. In contrast, experiments on single-stranded DNA (ssDNA) show that over a range of f and ionic concentration, x scales as x ~ ln f, which cannot be explained using WLC or FJC models. Using theory and simulations we show that this unusual behavior in FEC in ssDNA is due to sequence-independent polyelectrolyte effects. We show that the x ~ ln f arises because in the absence of force the tangent correlation function, quantifying chain persistence, decays algebraically on length scales on the order of the Debye length. Our theory, which is most appropriate for monovalent salts, quantitatively fits the experimental data and further predicts that such a regime is not discernible in double-stranded DNA. 相似文献
73.
Single-enzyme-based amperometric assay for phosphate ion 总被引:1,自引:0,他引:1
T. T. Ngo 《Applied biochemistry and biotechnology》1986,13(2):127-131
An amperometric assay for phosphate ion, using a single enzymatic process, has been developed. The enzyme used was pyruvate
oxidase, which catalyzes the oxidation of pyruvate in the presence of oxygen and phosphate ion. The products of the enzymatic
reaction are acetyl phosphate, carbon dioxide, and hydrogen peroxide. The latter was monitored by means of a hydrogen peroxide
electrode and an oxidase meter. Phosphate ion in the concentration range of 50–500 μM can be measured within 4 min. Anions,
such as pyrophosphate, sulfate, nitrate, nitrite, and acetate, gave only marginal responses. 相似文献
74.
That T. Ngo 《Applied biochemistry and biotechnology》1985,11(4):257-268
An ultrasensitive chromogenic system for horseradish peroxidase (HRP) is described. The chromogenic substrate system consists
of 3-methyl-2-benzothiazolinone hydrazone (MBTH) andN-phenyldiethanolamine (PDEA). The oxidative coupling of MBTH and PDEA using H2O2 and HRP, respectively, as the oxidant and catalyst, yields a blue chromophore that most likely is an indamine dye. The chromophore
has a rather broad absorption band, with an absorption maximum at 602 nm. In 0.1M phosphate, 0.1M citrate buffer, pH 7.5,
the optimal concentrations of MBTH, PDEA, and H2O2 are, respectively, 0.5, 25, and 8 mM. Using this assay system, HRP can be determined in lower picomolar levels by either
a rate or fixed-time method. 相似文献
75.
It is shown that a semiperfect ring is quasi-Frobenius if and only if every closed submodule of is non-small, where denotes the direct sum of copies of the right -module and is the first infinite ordinal.
76.
Chiral porous hybrid solids for practical heterogeneous asymmetric hydrogenation of aromatic ketones 总被引:3,自引:0,他引:3
Chiral porous zirconium phosphonates containing Ru-BINAP-DPEN moieties were synthesized via a molecular building-block approach, and characterized by a variety of techniques including TGA, adsorption isotherms, XRD, SEM, IR, and microanalysis. These hybrid solids were used for enantioselective heterogeneous asymmetric hydrogenation of aromatic ketones with remarkably high ee values of up to 99.2%. These solid catalysts can also be easily recycled and reused for eight times without the loss of activity and enantioselectivity. Ready tunability of such a molecular building-block approach will allow the optimization of these hybrid materials and promise to lead to other practically useful heterogeneous asymmetric catalysts. 相似文献
77.
Bouby M Geckeis H Manh TN Yun JI Dardenne K Schäfer T Walther C Kim JI 《Journal of chromatography. A》2004,1040(1):97-104
The combination of asymmetrical flow field-flow fractionation (AsFlFFF) with the laser-induced breakdown detection (LIBD) is presented as a powerful tool for the determination of colloid size distribution at trace particle concentrations. Detection limits (D1) of 1, 4, and 20 microg/L have been determined for a mixture of polystyrene reference particles with 20, 50, and 100 nm in size, respectively. This corresponds to injected masses of 1, 4, and 20 pg, which is lower than found in a previous study with the symmetrical FlFFF (SyFlFFF). The improvement is mainly due to the lower colloid background discharged from the AsFlFFF channel. The combined method of AsFlFFF-LIBD is then applied to the analysis of iron oxi/hydroxide colloids being considered as potential carriers for the radionuclide migration from a nuclear waste repository. Our LIBD arrangement is less sensitive for iron colloid detection as compared to reference polystyrene particles which results in a detection limit of approximately 240 microg/L FeOOH for the AsFlFFF-LIBD analysis. This is superior to the detection via UV-Vis absorbance and comparable to ICP-MS detection. Size information (mean size 11-18 nm) for different iron oxi/hydroxide colloids supplied by the present method is comparable to that obtained by sequential ultrafiltration and dynamic light scattering. A combined on-line ICP-MS detection is used to gain insight into the colloid-borne main and trace elements. 相似文献
78.
Transport of tervalent REEs — Sc, Y, Ce, Eu, Gd, Tm, Yb — from nitrate medium through a liquid membrane containing TBP in n-dodecane, impregnated on a flat-sheet nucleoporous support, has been studied as a function of time and initial metal concentration, salting-out agent concentration and pH of the feed phase. Influences of various complexing agents dissolved in the strip phase was investigated, too. Adding a suitable amount of EDTA into the feed phase, separation of binary mixtures of REEs was experimentally achieved. 相似文献
79.
[reaction: see text] A new synthesis of enantiopure 3,3-disubstituted oxindoles by stereoselective Mukaiyama aldol reaction of 3-substituted 2-siloxyindoles and chiral, enantiopure aldehydes having nitrogen or oxygen substituents at the alpha carbon is described. When the C3 substituent of the prochiral nucleophile is aryl or heteroaryl, stereoselectivity is high (10-80:1). 相似文献
80.
A new technique for conducting a separation-free amperometric enzyme immunoassay is described using DNP-aminocaproic acid
as the analyte. The technique is based on the combined use of a recently described separation-free enzyme immunoassay (19) and an electrode system that senses H2O2. Oxidation of glucose to gluconate and H2O2 by the enzyme reconstituted from DNP-conjugate apoglucose oxidase (DPN-CAGO) and FAD was continuously measured amperometrically.
The reconstitution was inhibited by preincubation with anti-DNP antibody before adding FAD. This antibody-induced inhibition
of the reconstituting of the holoenzyme was reversed by adding DNP-amino caproic acid to DNP-CAGO before adding the antibody
to DNP-CAGO. Based on (a) the antibody-induced inhibition of holoenzyme reconstitution, (b) a specific ligand-induced reversal
of the inhibition, and (c) an electrochemical system that measures H2O2, we developed a separation-free (homogeneous) amperometric enzyme immunoassay. 相似文献