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991.
Rosana M. Turtos Stefan Gundacker Marco T. Lucchini Lenka Procházková Václav Čuba Hana Burešová Jan Mrázek Martin Nikl Paul Lecoq Etiennette Auffray 《固体物理学:研究快报》2016,10(11):843-847
The implementation of nanocrystal‐based composite scintillators as a new generation of ultrafast particle detectors is explored using ZnO:Ga nanopowder. Samples are characterized with a spectral‐time resolved photon counting system and pulsed X‐rays, followed by coincidence time resolution (CTR) measurements under 511 keV gamma excitation. Results are comparable to CTR values obtained using bulk inorganic scintillators. Bringing the ZnO:Ga nanocrystal's timing performance to radiation detectors could pave the research path towards sub‐20 ps time resolution as shown in this contribution. However, an efficiency boost when placing nanopowders in a transparent host constitutes the main challenge in order to benefit from sub‐nanosecond recombination times. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
992.
The ac Stark effect was used to induce resonant energy transfer between translationally cold 85Rb Rydberg atoms. When a 28.5 GHz dressing field was set at specific field strengths, the two-atom dipole-dipole process 43d5/2+43d5/2-->45p3/2+41f was dramatically enhanced, due to induced degeneracy of the initial and final states. This method for enhancing interactions is complementary to dc electric-field-induced resonant energy transfer, but has more flexibility due to the possibility of varying the applied frequency. 相似文献
993.
Tvaskis V Christy ME Arrington J Asaturyan R Baker OK Blok HP Bosted P Boswell M Bruell A Cochran A Cole L Crowder J Dunne J Ent R Fenker HC Filippone BW Garrow K Gasparian A Gomez J Jackson HE Keppel CE Kinney E Lapikás L Liang Y Lorenzon W Lung A Mack DJ Martin JW McIlhany K Meekins D Milner RG Mitchell JH Mkrtchyan H Moreland B Nazaryan V Niculescu I Opper A Piercey RB Potterveld DH Rose B Sato Y Seo W Smith G Spurlock K van der Steenhoven G Stepanyan S Tadevosian V Uzzle A Vulcan WF Wood SA 《Physical review letters》2007,98(14):142301
We report on a study of the longitudinal to transverse cross section ratio, R=sigmaL/sigmaT, at low values of x and Q2, as determined from inclusive inelastic electron-hydrogen and electron-deuterium scattering data from Jefferson Laboratory Hall C spanning the four-momentum transfer range 0.06相似文献
994.
Interfaces moving in a disordered medium exhibit stochastic velocity fluctuations obeying universal scaling relations related to the presence or absence of conservation laws. For fluid invasion of porous media, we show that the fluctuations of the velocity are governed by a geometry-dependent length scale arising from fluid conservation. This result is compared to the statistics resulting from a nonequilibrium (depinning) transition between a moving interface and a stationary, pinned one. 相似文献
995.
Giraud N Blackledge M Böckmann A Emsley L 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,184(1):51-61
The effect of nitrogen-15 proton-driven spin diffusion on quantitative (15)N T(1) measurements in solid proteins is investigated, and the impact on the measurement of dynamic parameters is assessed. A simple model of exchange between neighboring nitrogens is used to reproduce the evolution of (15)N spin systems whose longitudinal relaxation rates and exchange rates are compatible with experimental measurements. We show that the induced error in the measured T(1) and its effect on the determination of dynamics parameters is likely to be less than the current experimental error. The use of deuterated protein samples is shown to have a small but sometimes visible effect, and may also considerably slow down or even suppress the exchange of magnetization due to spin diffusion. 相似文献
996.
We demonstrate the preparation and probing of the coherence between the hyperfine ground states |S(1/2),F=1> and |5S(1/2),F=2> of the Rb87 isotope. The effects of various coherence control techniques, i.e., fractional stimulated Raman adiabatic passage and coherent population return, on the coherence are investigated. These techniques are implemented using nearly degenerate pump and Stokes lasers at 795 nm (Rb D1 transition), which couple the two hyperfine ground states via the excited state |5P(1/2),F=1> through a resonant two-photon process in which a coherent superposition of the two hyperfine ground states is established. The medium is probed by an additional weak laser, which generates a four-wave mixing signal proportional to the ground state coherence and allows us to monitor its evolution in time. The experimental data are compared with numerical simulations. 相似文献
997.
We describe a method of optical refocusing for high numerical aperture (NA) systems that is particularly relevant for confocal and multiphoton microscopy. This method avoids the spherical aberration that is common to other optical refocusing systems. We show that aberration-free images can be obtained over an axial scan range of 70 mum for a 1.4 NA objective lens. As refocusing is implemented remotely from the specimen, this method will enable high axial scan speeds without mechanical interference between the objective lens and the specimen. 相似文献
998.
Levitt JM Hunter M Mujat C McLaughlin-Drubin M Münger K Georgakoudi I 《Optics letters》2007,32(22):3305-3307
Depth-resolved NADH autofluorescence images are shown to differentiate between normal and precancerous engineered tissues. An inverse power law behavior of the power spectral density (PSD) of these images is observed, indicating a self-affine organization of mitochondrial NADH at length scales 1-10 microm. Power exponents of the PSD functions vary significantly with tissue depth and precancerous state, giving insight into the morphological changes associated with precancerous lesions and providing substantial potential for noninvasive clinical diagnosis of squamous epithelial lesions and tumors. 相似文献
999.
Yankeelov TE Lepage M Chakravarthy A Broome EE Niermann KJ Kelley MC Meszoely I Mayer IA Herman CR McManus K Price RR Gore JC 《Magnetic resonance imaging》2007,25(1):1-13
PURPOSE: The objective of this study was to assess changes in the water apparent diffusion coefficient (ADC) and in pharmacokinetic parameters obtained from the fast-exchange regime (FXR) modeling of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) during neoadjuvant chemotherapy in breast cancer. MATERIALS AND METHODS: Eleven patients with locally advanced breast cancer underwent MRI examination prior to and after chemotherapy but prior to surgery. A 1.5-T scanner was used to obtain T1, ADC and DCE-MRI data. DCE-MRI data were analyzed by the FXR model returning estimates of K(trans) (volume transfer constant), v(e) (extravascular extracellular volume fraction) and tau(i) (average intracellular water lifetime). Histogram and correlation analyses assessed parameter changes post-treatment. RESULTS: Significant (P < .05) changes or trends towards significance (P < .10) were seen in all parameters except tau(i), although there was qualitative reduction in tau(i) values post-treatment. In particular, there was reduction (P < .035) in voxels with K(trans) values in the range 0.2-0.5 min(-1) and a decrease (P < .05) in voxels with ADC values in the range 0.99 x 10(-3) to 1.35 x 10(-3) mm2/s. ADC and v(e) were negatively correlated (r = -.60, P < .02). Parameters sensitive to water distribution and geometry (T(1), v(e), tau(i) and ADC) correlated with a multivariable linear regression model. CONCLUSION: The analysis presented here is sensitive to longitudinal changes in breast tumor status; K(trans) and ADC are most sensitive to these changes. Relationships between parameters provide information on water distribution and geometry in the tumor environment. 相似文献
1000.
OBJECTIVE: This study aimed to prospectively compare measurement precision of calf intramyocellular lipid (IMCL) quantification at 3.0 and 1.5 T using (1)H magnetic resonance spectroscopy ((1)H-MRS). MATERIALS AND METHODS: We examined the soleus and tibialis anterior (TA) muscles of 15 male adults [21-48 years of age, body mass index (BMI)=21.9-38.0 kg/m(2)]. Each subject underwent 3.0- and 1.5-T single-voxel, short-echo-time, point-resolved (1)H-MRS both at baseline and at 31-day follow-up. The IMCL methylene peak (1.3 ppm) was scaled to unsuppressed water peak (4.7 ppm) using the LCModel routine. Full width at half maximum (FWHM) and signal-to-noise ratios (SNRs) of unsuppressed water peak were measured using jMRUI software. Measurement precision was tested by comparing interexamination coefficients of variation (CV) between different field strengths using Wilcoxon matched pairs signed rank test in all subjects. Overweight subjects (BMI>25 kg/m(2)) were analyzed separately to examine the benefits of 3.0-T acquisitions in subjects with increased adiposity. RESULTS: No significant difference between 3.0 and 1.5 T was noted in CVs for IMCL of soleus (P=.5). CVs of TA were significantly higher at 3.0 T (P=.02). SNR was significantly increased at 3.0 T for soleus (64%, P<.001) and TA (62%, P<.001) but was lower than the expected improvement of 100%. FWHM at 3.0 T was significantly increased for soleus (19%, P<.001) and TA (7%, P<.01). Separate analysis of overweight subjects showed no significant difference between 3.0- and 1.5-T CVs for IMCL of soleus (P=.8) and TA (P=.4). CONCLUSION: Using current technology, (1)H-MRS for IMCL at 3.0 T did not improve measurement precision, as compared with 1.5 T. 相似文献