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71.
72.
We study quantum dynamical tunneling between two symmetry-related islands of stability in the phase space of a classically chaotic system. The setting for these experiments is the motion of carefully prepared samples of cesium atoms in an amplitude-modulated standing wave of light. We examine the dependence of the tunneling dynamics on the system parameters and indicate how the observed features provide evidence for chaos-assisted (three-state) tunneling. We also observe the influence of a noisy perturbation of the standing-wave intensity, which destroys the tunneling oscillations, and we show that the tunneling is more sensitive to the noise for a smaller value of the effective Planck constant. 相似文献
73.
H. Yüksel Guney Taner Oskay H. Sinan
zkan 《Journal of Polymer Science.Polymer Physics》1995,33(7):985-991
The ultrasonic properties of PVC (S-27/R63) in the glassy region have been investigated as a function of temperature. The propagation velocities and absorption of the longitudinal and transverse ultrasonic waves have been measured at constant frequency of 2 MHz and at temperatures varying between ?5°C and 75°C, using the ultrasonic immersion technique. The variation of the elastic moduli with temperature has been derived from these measurements. The results thus obtained have been compared to those previously published in the literature for different PVC and other polymer samples. ©1995 John Wiley & Sons, Inc. 相似文献
74.
J.E. Stalnaker S.A. Diddams T.M. Fortier K. Kim L. Hollberg J.C. Bergquist W.M. Itano M.J. Delany L. Lorini W.H. Oskay T.P. Heavner S.R. Jefferts F. Levi T.E. Parker J. Shirley 《Applied physics. B, Lasers and optics》2007,89(2-3):167-176
We report the technical aspects of the optical-to-microwave comparison for our recent measurements of the optical frequency
of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. Over
the course of six years, these measurements have resulted in a determination of the mercury single-ion frequency with a fractional
uncertainty of less than 7×10-16, making it the most accurately measured optical frequency to date. In this paper, we focus on the details of the comparison
techniques used in the experiment and discuss the uncertainties associated with the optical-to-microwave synthesis based on
a femtosecond laser frequency comb. We also present our most recent results in the context of the previous measurements of
the mercury single-ion frequency and arrive at a final determination of the mercury single-ion optical frequency: f(Hg+)=1 064 721 609 899 145.30(69) Hz.
PACS 06.30.Ft; 42.62.Eh; 32.30.Jc 相似文献
75.
Fortier TM Ashby N Bergquist JC Delaney MJ Diddams SA Heavner TP Hollberg L Itano WM Jefferts SR Kim K Levi F Lorini L Oskay WH Parker TE Shirley J Stalnaker JE 《Physical review letters》2007,98(7):070801
We report tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground state hyperfine splitting in 133Cs. Analysis of the frequency ratio of the two clocks, extending over 6 yr at NIST, is used to place a limit on its fractional variation of <5.8x10(-6) per change in normalized solar gravitational potential. The same frequency ratio is also used to obtain 20-fold improvement over previous limits on the fractional variation of the fine structure constant of |alpha/alpha|<1.3x10(-16) yr-1, assuming invariance of other fundamental constants. Comparisons of our results with those previously reported for the absolute optical frequency measurements in H and 171Yb+ vs other 133Cs standards yield a coupled constraint of -1.5x10(-15)相似文献
76.
Subha Chakraborty Caglar Ataman Daniel G. Courtney Simon Dandavino Herbert Shea 《Journal of the American Society for Mass Spectrometry》2014,25(8):1364-1373
We report on the development of a time-of-flight (ToF) mass spectrometer with a highly efficient electrostatic ion guide for enhancing detectability in ToF mass spectrometry. This 65-cm long ion guide consists of 13 cascaded stages of Einzel lens to collect a large fraction of emitted charges over a wide emission angle and energy spread for time-of-flight measurements. Simulations show that the ion guide can collect 100% of the charges with up to 23° emission half-angle or 30% energy spread irrespective of their specific charge. We demonstrate this ion guide as applied to electrospray ion sources. Experiments performed with tungsten needle electrospraying the ionic liquid EMI-BF4 showed that up to 80% of the emitted charges could be collected at the end of the flight tube. Flight times of monomers and dimers emitted from the needles were measured in both positive and negative emission polarities. The setup was also used to characterize the electrospray from microfabricated silicon capillary emitters and nearly 30% charges could be collected even from a 40° emission half-angle. This setup can thus increase the fraction of charge collection for ToF measurement and spray characteristics can be obtained from a very large fraction of the emission in real time. 相似文献
77.
Single-atom optical clock with high accuracy 总被引:1,自引:0,他引:1
Oskay WH Diddams SA Donley EA Fortier TM Heavner TP Hollberg L Itano WM Jefferts SR Delaney MJ Kim K Levi F Parker TE Bergquist JC 《Physical review letters》2006,97(2):020801
For the past 50 years, atomic standards based on the frequency of the cesium ground-state hyperfine transition have been the most accurate time pieces in the world. We now report a comparison between the cesium fountain standard NIST-F1, which has been evaluated with an inaccuracy of about 4 x 10(-16), and an optical frequency standard based on an ultraviolet transition in a single, laser-cooled mercury ion for which the fractional systematic frequency uncertainty was below 7.2 x 10(-17). The absolute frequency of the transition was measured versus cesium to be 1,064,721,609,899,144.94 (97) Hz, with a statistically limited total fractional uncertainty of 9.1 x 10(-16) the most accurate absolute measurement of an optical frequency to date. 相似文献
78.
Melike Sever‐Bahcekapili Canelif Yilmaz Altan Demirel Mustafa Cemil Kilinc Ihsan Dogan Yusuf Sukru Caglar Mustafa O. Guler Ayse B. Tekinay 《Macromolecular bioscience》2021,21(1)
The highly complex nature of spinal cord injuries (SCIs) requires design of novel biomaterials that can stimulate cellular regeneration and functional recovery. Promising SCI treatments use biomaterial scaffolds, which provide bioactive cues to the cells in order to trigger neural regeneration in the spinal cord. In this work, the use of peptide nanofibers is demonstrated, presenting protein binding and cellular adhesion epitopes in a rat model of SCI. The self‐assembling peptide molecules are designed to form nanofibers, which display heparan sulfate mimetic and laminin mimetic epitopes to the cells in the spinal cord. These neuroactive nanofibers are found to support adhesion and viability of dorsal root ganglion neurons as well as neurite outgrowth in vitro and enhance tissue integrity after 6 weeks of injury in vivo. Treatment with the peptide nanofiber scaffolds also show significant behavioral improvement. These results demonstrate that it is possible to facilitate regeneration especially in the white matter of the spinal cord, which is usually damaged during the accidents using bioactive 3D nanostructures displaying high densities of laminin and heparan sulfate‐mimetic epitopes on their surfaces. 相似文献
79.
The trans-bis(saccharinato)nickel(II) complexes with 2-aminomethylpyridine (ampy) and 2-aminoethylpyridine (aepy) have been prepared and characterized by elemental analyses, i.r., u.v.–vis., magnetic measurements and single crystal X-ray diffraction. Both structures consist of discrete molecules of the title complexes, in which the nickel(II) ion lies on an inversion centre and is octahedrally coordinated by two bidentate (N,N) ampy or aepy ligands and two anionic sac ligands, occupying trans positions. The most interesting feature of the complexes is the coordination of sac. In [Ni(sac)2(ampy)2], sac is N-bonded, whereas it is O-coordinated in [Ni(sac)2(aepy)2]. The i.r. spectra and thermal behaviour of both complexes are discussed in detail. 相似文献