共查询到20条相似文献，搜索用时 46 毫秒
1.
Ages of fossil bones were determined by electron spin resonance spectroscopy. The electron spin resonance signal is associated with lattice defects or trapped centers produced by natural radiation in the bones and gives a measure of the total dose of natural radiation, or the archeological dose. Archeological doses were determined for samples of known age from a variety of sites and used to estimate apparent average annual rates of natural radiation at the sites. The method has the advantage that the sample need not be ground or heated, and it should be useful for dating biological materials. 相似文献
2.
Kato Y Myers RC Driscoll DC Gossard AC Levy J Awschalom DD 《Science (New York, N.Y.)》2003,299(5610):1201-1204
We present a scheme that enables gigahertz-bandwidth three-dimensional control of electron spins in a semiconductor heterostructure with the use of a single voltage signal. Microwave modulation of the Landé g tensor produces frequency-modulated electron spin precession. Driving at the Larmor frequency results in g-tensor modulation resonance, which is functionally equivalent to electron spin resonance but without the use of time-dependent magnetic fields. These results provide proof of the concept that quantum spin information can be locally manipulated with the use of high-speed electrical circuits. 相似文献
3.
Hemoglobin M variants, M Iwate, M Boston, M Saskatoon are easily and accurately identified by electron spin resonance with small amounts of patients' blood. In hemoglobin M Iwate and M Boston the electron spin resonance of both fresh blood (unprocessed) and isolated pure ferrihemoglobin M revealed similar signal shapes; whereas that of hemoglobin M Saskatoon was doublet in fresh blood and triplet in pure ferrihemoglobin M. 相似文献
4.
Individual pentacene-d(14) molecules doped into a p-terphenyl-d(14) host crystal have been studied by optically detected electron paramagnetic resonance spectroscopy. The magnetic resonance transitions between the triplet sublevels of the pentacene molecule and the splitting of the resonance lines for a molecule that contains a carbon-13 nucleus have been observed in an external magnetic field. This splitting is caused by the hyperfine interaction of the triplet electron spin with the single carbon-13 nuclear spin. 相似文献
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We demonstrate the ability to create spin order by using a magnetic resonance force microscope to harness the naturally occurring statistical fluctuations in small ensembles of electron spins. In one method, we hyperpolarized the spin system by selectively capturing the transient spin order created by the statistical fluctuations. In a second method, we took a more active approach and rectified the spin fluctuations by applying real-time feedback to the entire spin ensemble. The created spin order can be stored in the laboratory frame for a period on the order of the longitudinal relaxation time of 30 seconds and then read out. 相似文献
7.
秦九红 《信阳农业高等专科学校学报》2011,21(3):129-131
一氧化氮(nitric oxide,NO)在机体很多生理过程如血压调节、机体防御和神经信号传导等过程中发挥着重要的作用。本文综述了一氧化氮的常用检测方法,例如Griess试剂法、ESR自旋捕集技术、化学发光法和电化学检测法等。 相似文献
8.
Proton magnetic resonance spectra (220-megahertz field) of an isolated rabbit sciatic nerve in its native state have been observed and assigned to the extracellular water, intracellular water, and phospholipids of the nerve. This study indicates that the nerve fibers contain fluid-like hydrophobic regions, in agreement with the results of recent electron spin resonance spin-labeled studies of excitable membranes of nerve and muscle. 相似文献
9.
Borbat PP Costa-Filho AJ Earle KA Moscicki JK Freed JH 《Science (New York, N.Y.)》2001,291(5502):266-269
We provide a review of current electron spin resonance (ESR) techniques for studying basic molecular mechanisms in membranes and proteins by using nitroxide spin labels. In particular, nitroxide spin label studies with high-field/high-frequency ESR and two-dimensional Fourier transform ESR enable one to accurately determine distances in biomolecules, unravel the details of the complex dynamics in proteins, characterize the dynamic structure of membrane domains, and discriminate between bulk lipids and boundary lipids that coat transmembrane peptides or proteins; these studies can also provide time resolution to studies of functional dynamics of proteins. We illustrate these capabilities with recent examples. 相似文献
10.
Lancaster JR 《Science (New York, N.Y.)》1982,216(4552):1324-1325
Methanobacterium bryantii was grown in medium supplemented with nickel-61, an isotope with a nuclear spin of 3/2. The appearance of nuclear hyperfine structure in the electron paramagnetic resonance spectrum of a cell extract identified a previously observed signal as nickel(III) in an environment of octahedral coordination with rhombic distortions. 相似文献
11.
黄瓜叶片在水分胁控下随着胁迫程度的加深，细胞膜透性增加。表现出PSⅡ荧光激发光谱特征峰峰值的降低。同时其PSⅡ电子传递速率及PSⅡ氧化则DCIP光还原活性下降。通过对PSⅡ的^57Fe穆斯堡尔谱及其参数进行分析显示；水分胁迫使PSⅡ的^57FeMossbauer谱的Ⅱ，Ⅵ子谱2套双峰消失；铁醌复合物（Fe-Q)、细胞色素b559(Cytb559)由还原态向氧化态转化。以上结果表明：铁醌复合体、Cytb559因光能在PSⅡ色素分子之间共振效率降低及PSⅡ氧化侧的电子受到抑制、不能及时得珐其氧化侧传来的电子，而以高自旋Fe^3 -Q复合物及低自旋氧化型Cytb559的形式存在。致使PSⅡ电子由于含铁复合物的Fe^2 /Fe^3 氧还电热的变化而受到阻抑。 相似文献
12.
P Gilch F Pollinger-Dammer C Musewald ME Michel-Beyerle UE Steiner 《Science (New York, N.Y.)》1998,281(5379):982-984
The recombination dynamics of a transition metal redox system monitored by femtosecond pump-probe spectroscopy are shown to be sensitive to high magnetic fields at times shorter than 10 picoseconds. The effect, based on coherent population beats of different spin states, is quantitatively accounted for and allows direct access to spin relaxation rates far beyond the time resolution of the fastest electron paramagnetic resonance technique. The presence of this ultrafast magnetic field effect helps in understanding complex reaction schemes in transition metal chemistry, which occur in a wide range of fields, such as bioinorganic chemistry and catalysis. 相似文献
13.
Willard JE 《Science (New York, N.Y.)》1973,180(4086):553-561
Free radicals, hydrogen atoms, and electrons produced in rigid organic glasses at sufficiently low temperatures have lifetimes of minutes to years. They can be studied by their electron spin resonance spectra and, in the case of electrons, by their optical spectra, recombination luminescence, and electrical conductivity. The decay kinetics of these reaction intermediates serve to distinguish those trapped as geminate pairs or in spurs of high concentration from those formed with random distributions. Electron spin resonance studies of relaxation times and of the spectra of radical pairs provide further evidence on geometrical distributions. The decay rates of radicals combining with reactive geminate partners are dependent on the size and shape of the radical, the temperature, and the nature of the matrix. Decay is much slower in deuterated matrices than in protiated matrices. The factors that control the physical trapping of electrons in organic glasses are under intensive investigation. There is evidence that many electrons trapped relatively weakly during irradiations at 4 degrees K deepen their traps by orientation of dipoles when the matrix is warmed; that most electrons are trapped in the field of the geminate positive ion; that in some matrices the traps have a bound excited state to which the electron can be promoted without detrapping; and that trapped electrons can tunnel to solute molecules with a higher electron affinity than the trap depth. 相似文献
14.
Direct addition of O-H radicals at room temperature to the carbon No.5 of the uracil ring has been proved by measurement of the proton hyperfine structure in the electron spin resonance of the resulting uracil + O-H radicals. Upon addition of the OH, the H originally bound to carbon No. 5 shifts to No. 6, thus forming a methylene group at carbon No. 6, with the two protons having equivalent coupling of 28 gauss. The spin density on carbon No. 5 is O.64. The radicals were produced when powdered samples of uracil were subjected to a low-velocity beam of O-H radicals coming from either hydrogen peroxide or water vapor under reduced pressure and subjected to an electric discharge. 相似文献
15.
Under certain conditions nerves (such as the frog sciatic) exhibit electron spin resonance signals with several unusual properties: (i) variable g value and linewidth, (ii) anisotropic g tensor, and (iii) g value dependence on temperature. Such a signal must be due to a small ferromagnetic crystal formed when the nerve is subjected to pressure, such as that due to mechanical injury. 相似文献
16.
When moist, oriented DNA is gamma-irradiated and its electron spin resonance spectrum is recorded at 77 degrees K, an unresolved spectrum is obtained, the amplitude of which is strongly dependent on the angle between the direction of the DNA helices and the field. Annealing at 199 degrees K gives an eight-line thymine-like spectrum which also has a marked angular dependence. For dry, oriented DNA, the unresolved spectrum dominates even at room temperature, and the spectra exhibit lower degrees of anisotropy. 相似文献
17.
Eumelanins and pheomelanins: characterization by electron spin resonance spectroscopy 总被引：3，自引：0，他引：3
Synthetic dopa melanin and cysteinyldopa melanin have different electron spin resonance spectra. Data are reported for mixtures of these melanins and for dopa-cysteinyldopa copolymers, which are spectroscopically similar. A simple parameterization of the spectra allows estimation of the relative amounts of (i) dopa melanin and cysteinyldopa melanin in mixtures and of (ii) dopa and cysteinyldopa incorporated into copolymers. Several natural eumelanins and pheomelanins have been characterized and shown to be copolymers. 相似文献
18.
V Madhavan W Chen T Jamneala MF Crommie NS Wingreen 《Science (New York, N.Y.)》1998,280(5363):567-569
The Kondo effect arises from the quantum mechanical interplay between the electrons of a host metal and a magnetic impurity and is predicted to result in local charge and spin variations around the magnetic impurity. A cryogenic scanning tunneling microscope was used to spatially resolve the electronic properties of individual magnetic atoms displaying the Kondo effect. Spectroscopic measurements performed on individual cobalt atoms on the surface of gold show an energetically narrow feature that is identified as the Kondo resonance-the predicted response of a Kondo impurity. Unexpected structure in the Kondo resonance is shown to arise from quantum mechanical interference between the d orbital and conduction electron channels for an electron tunneling into a magnetic atom in a metallic host. 相似文献
19.
NN Kuzma P Khandelwal SE Barrett LN Pfeiffer KW West 《Science (New York, N.Y.)》1998,281(5377):686-690
Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state nu = 13. Below 0.5 kelvin, the spectra provide evidence that spin-reversed charged excitations of the nu = 13 ground state are localized over the NMR time scale of about 40 microseconds. Furthermore, by varying NMR pulse parameters, the electron spin temperature (as measured by the Knight shift) could be driven above the lattice temperature, which shows that the value of the electron spin-lattice relaxation time tau1s is between 100 microseconds and 500 milliseconds at nu = 13. 相似文献
20.
Greilich A Shabaev A Yakovlev DR Efros AL Yugova IA Reuter D Wieck AD Bayer M 《Science (New York, N.Y.)》2007,317(5846):1896-1899
The hyperfine interaction of an electron with the nuclei is considered as the primary obstacle to coherent control of the electron spin in semiconductor quantum dots. We show, however, that the nuclei in singly charged quantum dots act constructively by focusing the electron spin precession about a magnetic field into well-defined modes synchronized with a laser pulse protocol. In a dot with a synchronized electron, the light-stimulated fluctuations of the hyperfine nuclear field acting on the electron are suppressed. The information about electron spin precession is imprinted in the nuclei and thereby can be stored for tens of minutes in darkness. The frequency focusing drives an electron spin ensemble into dephasing-free subspaces with the potential to realize single frequency precession of the entire ensemble. 相似文献