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51.
Fluorescence resonance energy transfer in CdSe/ZnS-DNA conjugates: probing hybridization and DNA cleavage 总被引:3,自引:0,他引:3
Nucleic-acid-functionalized CdSe/ZnS quantum dots (QDs) were hybridized with the complementary Texas-Red-functionalized nucleic acid. The hybridization was monitored by following the fluorescence resonance energy transfer from the QDs to the dye units. Treatment of the QD/dye DNA duplex structure with DNase I resulted in the cleavage of the DNA and the recovery of the fluorescence properties of the CdSe/ZnS QDs. The luminescence properties of the QDs were, however, only partially recovered due to the nonspecific adsorption of the dye onto the QDs. Similarly, nucleic-acid-functionalized Au nanoparticles (Au NPs) were hybridized with the complementary Texas-Red-labeled nucleic acid. The hybridization was followed by the fluorescence quenching of the dye by the Au NPs. Treatment of the Au NP/dye DNA duplex with DNase I resulted in the cleavage of the DNA and the partial recovery of the dye fluorescence. The incomplete recovery of the dye fluorescence originated from the nonspecific binding of the dye units to the Au NPs. The nonspecific binding of the dye to the CdSe/ZnS QDs and the Au NPs is attributed to nonprotected surface vacancies in the two systems. 相似文献
52.
In this study we sought the detection and characterization of bacterial membrane domains. Fluorescence generalized polarization (GP) spectra of laurdan-labeled Escherichia coli and temperature dependencies of both laurdan's GP and fluorescence anisotropy of 1,3-diphenyl-1,3,5-hexatriene (DPH) (rDPH) affirmed that at physiological temperatures, the E. coli membrane is in a liquid-crystalline phase. However, the strong excitation wavelength dependence of rlaurdan at 37 degrees C reflects membrane heterogeneity. Time-resolved fluorescence emission spectra, which display distinct biphasic redshift kinetics, verified the coexistence of two subpopulations of laurdan. In the initial phase, <50 ps, the redshift in the spectral mass center is much faster for laurdan excited at the blue edge (350 nm), whereas at longer time intervals, similar kinetics is observed upon excitation at either blue or red edge (400 nm). Excitation in the blue region selects laurdan molecules presumably located in a lipid domain in which fast intramolecular relaxation and low anisotropy characterize laurdan's emission. In the proteo-lipid domain, laurdan motion and conformation are restricted as exhibited by a slower relaxation rate, higher anisotropy and a lower GP value. Triple-Gaussian decomposition of laurdan emission spectra showed a sharp phase transition in the temperature dependence of individual components when excited in the blue but not in the red region. At least two kinds of domains of distinct polarity and order are suggested to coexist in the liquid-crystalline bacterial membrane: a lipid-enriched and a proteolipid domain. In bacteria with chloramphenicol (Cam)-inhibited protein synthesis, laurdan showed reduced polarity and restoration of an isoemissive point in the temperature-dependent spectra. These results suggest a decrease in membrane heterogeneity caused by Cam-induced domain dissipation. 相似文献
53.
This paper studies some new properties of set functions (and, in particular, “non-additive probabilities” or “capacities”) and the Choquet integral with respect to such functions, in the case of a finite domain. We use an isomorphism between non-additive measures on the original space (of states of the world) and additive ones on a larger space (of events), and embed the space of real-valued functions on the former in the corresponding space on the latter. This embedding gives rise to the following results: the Choquet integral with respect to any totally monotone capacity is an average over minima of the integrand; the Choquet integral with respect to any capacity is the difference between minima of regular integrals over sets of additive measures; under fairly general conditions one may define a “Radon-Nikodym derivative” of one capacity with respect to another; the “optimistic” pseudo-Bayesian update of a non-additive measure follows from the Bayesian update of the corresponding additive measure on the larger space. We also discuss the interpretation of these results and the new light they shed on the theory of expected utility maximization with respect to non-additive measures. 相似文献
54.
We construct N=1 supersymmetric (SUSY) field theory in 4+2 dimensions compatible with the theoretical framework of two-time (2T) physics and its gauge symmetries. The fields are arranged into 4+2 dimensional chiral and vector supermultiplets, and their interactions are uniquely fixed by SUSY and 2T physics gauge symmetries. In a particular gauge the 4+2 theory reduces to ordinary supersymmetric field theory in 3+1 dimensions without any Kaluza-Klein remnants, but with some additional constraints in 3+1 dimensions of interesting phenomenological relevance. This construction is another significant step in the development of 2T physics as a structure that stands above 1T physics. 相似文献
55.
Itzhak Dotan Anthony J. Midey A. A. Viggiano 《Journal of the American Society for Mass Spectrometry》1999,10(9):815-820
We have measured the rate constants for the reactions of Ar+ with CO2 and SO2 from 300 to 1500 K in a high temperature flowing afterglow. For the reaction with CO2, we have found that all modes of energy, i.e., translation, rotation, and vibration, affect the rate constant to the same degree up to a total energy of 0.4 eV. Above 0.4 eV total energy, internal energy decreases the rate constants more effectively than does translational energy. For the reaction of Ar+ with SO2, the rate constants go through a minimum at about 900 K. By comparing our results to drift tube data, we derive rate constants for reaction from the υ=0 and υ>0 vibrational levels. At low energy, the vibrationally excited SO2 molecules react with Ar+ approximately twice as fast as the ground state molecules. Both vibrational modes have similar temperature dependences. 相似文献
56.
Itzhak Fried 《Magnetic resonance imaging》1995,13(8):1163-1170
Advances in magnetic resonance imaging (MRI) techniques have had an important impact on the decision-making process leading to surgical resection for chronic seizures. The MRI is now obtained relatively early in the work-up, and, when it shows abnormality, it assumes a crucial role in the detection of specific surgically remediable syndromes. These syndromes, when diagnosed by MR and other confirmatory studies such as electroencephalography (EEG), positron emission tomography (PET), magnetoencephalography (MEG), and neuropsychological testing, define the essential part of the surgical plan; that is, removal of the disease substrate. The availability of a host of MR techniques enable us to investigate epilepsy not only as a structural pathology but as physiological pathology reflected in abnormal blood flow, metabolism, and synaptic transmission. The mainstay of surgical treatment is the removal of the anatomic pathology, but other MR techniques may be helpful in the delineation of dual pathology in lesional cases, in appreciation of the full extent of microscopic pathology in developmental lesions, and in the imposition of restrictions on the resection based upon functional mapping. Finally, functional and anatomic maps obtained preoperatively can be related directly to the spatial coordinates of the exposed brain in the operating room using MRI-based frameless stereotactic methods. The final outcome, then, is the removal of the disease substrate without injury to adjacent, functionally salient cortical regions. 相似文献
57.
Elish Eyal Brandis Michal Haquin Gustavo Hershko Itzhak Yungrais Zohar Aviv Ofer Moyal Amiram Assulin Maor Nawi Yehuda Solomon Oren Zakon Yevgeni Rubinshtein Arnon Astrachan Boaz 《Journal of Radioanalytical and Nuclear Chemistry》2021,329(1):51-60
Journal of Radioanalytical and Nuclear Chemistry - An orphan radium-beryllium (Ra–Be) neutron source (Nuclear Chicago Corporation) detected inside a scrap metal shipping container, was seized... 相似文献
58.
59.
Itzhak Dana 《General Relativity and Gravitation》1981,13(8):807-811
Retardation features of rigid motion, in flat two-dimensional space-time, are interpreted in terms of a consistent picture of signals. A similar analysis is adopted to effect a natural transition from rigid to nonrigid frames for which a degree of rigidity, having a simple physical meaning, can be defined. 相似文献
60.
Itzhak Venezia 《European Journal of Operational Research》1985,19(2):191-200
This paper presents a statistical rationale for the existence of the learning curve phenomenon. We consider a firm which allocates a fixed amount of input into several activities under uncertainty concerning the values of the parameters of the production function. It is shown, under fairly reasonable assumptions, that if the firm learns about the parameters of the production function from previous observations of allocations and outputs, then a learning curve phenomenon will emerge. This result occurs since the estimates of the parameters become more precise over time, and thus the allocation of the production factor into the various activities becomes more efficient (i.e. closer to the optimum allocation that would have been determined if the parameters were known with certainty). Output, therefore, increases and inputs per unit of output decrease as a function of time (and cumulative output), and a learning curve emerges.‘Plateauing’ of the learning curve is discussed, as are the conditions sufficient for the existence of this phenomenon, for which the model presented herein is offered as a possible explanation. 相似文献