共查询到20条相似文献，搜索用时 578 毫秒
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Dutt MV Childress L Jiang L Togan E Maze J Jelezko F Zibrov AS Hemmer PR Lukin MD 《Science (New York, N.Y.)》2007,316(5829):1312-1316
The key challenge in experimental quantum information science is to identify isolated quantum mechanical systems with long coherence times that can be manipulated and coupled together in a scalable fashion. We describe the coherent manipulation of an individual electron spin and nearby individual nuclear spins to create a controllable quantum register. Using optical and microwave radiation to control an electron spin associated with the nitrogen vacancy (NV) color center in diamond, we demonstrated robust initialization of electron and nuclear spin quantum bits (qubits) and transfer of arbitrary quantum states between them at room temperature. Moreover, nuclear spin qubits could be well isolated from the electron spin, even during optical polarization and measurement of the electronic state. Finally, coherent interactions between individual nuclear spin qubits were observed and their excellent coherence properties were demonstrated. These registers can be used as a basis for scalable, optically coupled quantum information systems. 相似文献
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Hillman GC Robins GV Oduwole D Sales KD McNeil DA 《Science (New York, N.Y.)》1983,222(4629):1235-1236
The thermal histories of archeological cereal grains were examined by electron spin resonance spectroscopy. Studies with modern samples of heated cereal grain showed that the parameters of the electron spin resonance signal characterize the maximum temperature to which the sample had previously been heated. This technique has applicability in archeology and other disciplines. 相似文献
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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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Transmembrane proteins serve important biological functions, yet precise information on their secondary and tertiary structure is very limited. The boundaries and structures of membrane-embedded domains in integral membrane proteins can be determined by a method based on a combination of site-specific mutagenesis and nitroxide spin labeling. The application to one polypeptide segment in bacteriorhodopsin, a transmembrane chromoprotein that functions as a light-driven proton pump is described. Single cysteine residues were introduced at 18 consecutive positions (residues 125 to 142). Each mutant was reacted with a specific spin label and reconstituted into vesicles that were shown to be functional. The relative collision frequency of each spin label with freely diffusing oxygen and membrane-impermeant chromium oxalate was estimated with power saturation EPR (electron paramagnetic resonance) spectroscopy. The results indicate that residues 129 to 131 form a short water-exposed loop, while residues 132 to 142 are membrane-embedded. The oxygen accessibility for positions 131 to 138 varies with a periodicity of 3.6 residues, thereby providing a striking demonstration of an alpha helix. The orientation of this helical segment with respect to the remainder of the protein was determined. 相似文献
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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
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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
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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
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The total dose of natural radiation and the age were determined from paramagnetic defects in quartz grains at a fractured fault zone. Young age at the fault indicates that the accumulated defects in rocks were destroyed by high stress or high temperature at the time of the last fault movement, setting the clock time to zero. The technique was applied to quartz grains crushed by uniaxial compression in the laboratory to verify this interpretation. 相似文献
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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
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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
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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
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Fagan PJ Krusic PJ McEwen CN Lazar J Parkert DH Herron N Wasserman E 《Science (New York, N.Y.)》1993,262(5132):404-407
Perfluoroalkylated nanospheres have been prepared by reaction of fullerenes with a variety of fluoroalkyl radicals. The latter are generated by thermal or photochemical decomposition of fluoroalkyl iodides or fluorodiacyl peroxides. Up to 16 radicals add to C(60) to afford easily isolable fluoroalkylated derivatives. The monosubstituted radical adducts were detected by electron spin resonance in the early stages of the fluoroalkylation reactions. These spheroidal molecules are thermally quite stable, soluble in fluoroorganic solvents, chemically resistant to corrosive aqueous solutions, and more volatile than the parent fullerenes. Films of the sublimed material display properties typical for a perfluoroalkylated material. 相似文献
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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
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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
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Light-enhanced free radical formation and trypanocidal action of gentian violet (crystal violet) 总被引：2，自引：0，他引：2
R Docampo S N Moreno R P Muniz F S Cruz R P Mason 《Science (New York, N.Y.)》1983,220(4603):1292-1295
Transmission of Chagas' disease by transfusion of blood containing Trypanosoma cruzi has often been reported, and gentian violet, a triarylmethane dye, is widely used by blood banks in attempts to eliminate such transmission. In a study of intact trypanosomes, gentian violet was found to undergo a one-electron reduction to produce a carbon-centered free radical as demonstrated by electron spin resonance spectroscopy. Either reduced nicotinamide adenine dinucleotide or the reduced dinucleotide phosphate could serve as a source of reducing equivalents for the production of this free radical by homogenates of Trypanosoma cruzi. The formation of this free radical, and the trypanocidal action of gentian violet, were enhanced by light. The enhanced free radical formation may be the basic cause of the selective toxicity of gentian violet to Trypanosoma cruzi. 相似文献
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不同作物辐射诱变适宜剂量的测定 总被引：2，自引：0，他引：2
室内快速测定VID_(50)(使种子发芽活力指数下降50%)的剂量值,可作为作物诱变适宜剂量。无性繁殖作物的诱变适宜剂量则可通过室内测定休眠芽条GRD_(60)(使萌芽率下降50%)的剂量值确定。测出了玉米、绿豆、红小豆、黍子、芝麻、大葱、银瓜,以VID_(50)作指标和山楂、玫瑰以GRD_(50)作指标的辐射诱变适宜剂量。 相似文献
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短时间不同剂量UV-B辐射处理对冬小麦幼苗生理指标的影响 总被引：1，自引：0，他引：1
[目的]研究短时间不同剂量UV—B辐射对冬小麦幼苗叶片生理指标的影响,为进一步研究植物应答短时间紫外线照射机理提供参考。[方法]以冬小麦为试验材料,采用15和30μW／cm^2的uV—B照射强度对冬小麦幼苗进行短时间照射处理,并测定色素含量、光合速率等生理指标。[结果]UV—B处理导致叶绿素、可溶性蛋白含量以及含水量都降低,且存在剂量效应,30μW／cm^2处理的降幅大于15μW／cm^2;UV—B辐射处理对类胡萝卜紊含量的影响与花青素相同,均表现为先下降后上升的趋势,2种剂量间差异不大;2种剂量的UV—B处理均抑制了PSⅡ的电子传递,尤其是处理2h的抑制作用最大,4、6和8h的抑制作用有所缓解,且存在剂量效应;2种剂量的UV-B辐射均抑制了叶片的光合速率。随着照射时间的延长抑制效应加大;高剂量UV—B处理对膜系统的损伤较大,低剂量UV—B处理结果不明显。[结论]短时间UV—B辐射处理对冬小麦幼苗叶片的影响具有剂量效应,高剂量比低剂量的作用效果大。且随着处理时间的延长,受害程度有所减轻,该结果与长时间UV—B照射的结果不同。 相似文献
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[目的]研究短时间不同剂量UV-B辐射对冬小麦幼苗叶片生理指标的影响,为进一步研究植物应答短时间紫外线照射的机理提供参考。[方法]以冬小麦为试验材料,采用15和30μW／cm^2。的UV—B照射强度对冬小麦幼苗进行短时间照射处理。测定指标包括：①反射光谱值。用Unispec光谱仪测定反射光谱,并计算所得参数,评价UV—B处理前后叶片叶绿素、花色素苷、类胡萝卜素含量、水分含量以及光合强度的变化,每处理测定10片叶;②可溶性蛋白含量。采用考马斯亮蓝G-250法测定叶片的可溶性蛋白含量,牛血清蛋白作为对照;③荧光参数（Fn／Fm）：将待测叶片暗反应20min后,用OS-30P荧光仪测定部位同叶色,每处理测定5片叶;④相对电导率。采用Martineau等的方法测定;⑤丙二醛（MDA）：采用邹琦的方法测定。测定项目②～⑤均重复5次。[结果】UV—B处理导致叶绿素、可溶性蛋白含量以及含水量都降低,且存在剂量效应,30μW／cm。的降幅大于15μW／cm^2;UV—B辐射导致花色素苷和类黄酮含量下降,尤其是处理后2h下降幅度最大,2种剂量的UV—B处理间差异不大。随着处理时间的延长,花色素苷含量呈逐渐上升趋势,其中,30μW／cm。处理的略高于15μW／cm。处理。UV—B辐射处理对类胡萝卜素含量的影响与花青素相同,均表现为先下降后上升的趋势,2种剂量间差异不大;2种剂量的UV—B处理均抑制了PSⅡ的电子传递,尤其是处理2h的抑制作用最大,4、6和8h的抑制有所缓解,且存在剂量效应;2种剂量的UV-B辐射均抑制了叶片的光合速率,随着照射时间的延长抑制效应加大;MDA和相对电导率在照射2h后明显增加,说明高剂量的UV—B处理对膜系统的损伤较大,低剂量的UV—B处理结果不明显。[结论]短时间的UV—B辐射处理对冬小麦幼苗叶片的影响具有剂量效应,高剂量比低剂量的作用效果大。且随着处理时间的延长,受害程度有所减轻,该结果与长时间UV—B照射的结果不同。 相似文献