排序方式: 共有63条查询结果,搜索用时 15 毫秒
21.
Epitaxial La1−x
Pb
x
MnO3 (LPMO) thin films, grown on (100) SrTiO3 substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical
and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature
(T
MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa2Cu3O
x
/La1−x
MnO3 heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated. 相似文献
22.
Besenius P Cormack PA Ludlow RF Otto S Sherrington DC 《Chemical communications (Cambridge, England)》2008,(24):2809-2811
Translocating solution-phase molecular recognition of oppositely charged hosts and guests to the solid phase represents a major challenge; we report a successful immobilisation strategy which allows selective host-guest interactions in water unencumbered by unwanted ion exchange-type interactions. 相似文献
23.
Zelevinsky T Boyd MM Ludlow AD Ido T Ye J Ciuryło R Naidon P Julienne PS 《Physical review letters》2006,96(20):203201
With ultracold 88Sr in a 1D magic wavelength optical lattice, we performed narrow-line photoassociation spectroscopy near the 1S0 - 3P1 intercombination transition. Nine least-bound vibrational molecular levels associated with the long-range 0u and 1u potential energy surfaces were measured and identified. A simple theoretical model accurately describes the level positions and treats the effects of the lattice confinement on the line shapes. The measured resonance strengths show that optical tuning of the ground state scattering length should be possible without significant atom loss. 相似文献
24.
Blatt S Ludlow AD Campbell GK Thomsen JW Zelevinsky T Boyd MM Ye J Baillard X Fouché M Le Targat R Brusch A Lemonde P Takamoto M Hong FL Katori H Flambaum VV 《Physical review letters》2008,100(14):140801
The 1S0-3P0 clock transition frequency nuSr in neutral 87Sr has been measured relative to the Cs standard by three independent laboratories in Boulder, Paris, and Tokyo over the last three years. The agreement on the 1 x 10(-15) level makes nuSr the best agreed-upon optical atomic frequency. We combine periodic variations in the 87Sr clock frequency with 199Hg+ and H-maser data to test local position invariance by obtaining the strongest limits to date on gravitational-coupling coefficients for the fine-structure constant alpha, electron-proton mass ratio mu, and light quark mass. Furthermore, after 199Hg+, 171Yb+, and H, we add 87Sr as the fourth optical atomic clock species to enhance constraints on yearly drifts of alpha and mu. 相似文献
25.
The development and change of surface ruggedness in chars was studied at conditions typical in a pulverized coal furnace. The fractal dimension, a measure of surface ruggedness, of chars was measured using physisorption techniques. By adjusting the temperature encountered (1173 to 1773 K) and residence time (0.1 to 1.5 s) of the synthetic coal (sized to 46–106 μm diameter), chars at different stages of combustion were prepared in a laminar flow (drop-tube) furnace. The particles were quickly cooled and quenched in an inert atmosphere. The samples were examined using a scanning electron microprobe, and their fractal dimensions were determined using gas physisorption. The adsorption data were used to test if the char surface was fractal on a molecular scale, to determine the fractal dimension, and to quantify changes in the fractal dimension during combustion. The fractal dimension of the unburned synthetic coal was approximately 2. The fractal dimension increased as high as 2.85 as the carbon matrix burned away and exposed mineral moieties. However, as combustion continued the carbon burned completely away leaving a mineral fly ash particle with a fractal dimension as low as 2.47. 相似文献
26.
K
β-to-K
α X-ray intensity ratios of Fe and Ni in pure metals and in Fe
x
Ni1−x
alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a 241Am point source, to understand as to why the properties of permalloy Fe0.2Ni0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe0.2Ni0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties. 相似文献
27.
The study of complex mixtures of interacting synthetic molecules has historically not received much attention from chemists, even though research into complexity is well established in the neighbouring fields. However, with the huge recent interest in systems biology and the availability of modern analytical techniques this situation is likely to change. In this tutorial review we discuss some of the incentives for developing systems chemistry and we highlight the pioneering work in which molecular networks are making a splash. A distinction is made between networks under thermodynamic and kinetic control. The former include dynamic combinatorial libraries while the latter involve pseudo-dynamic combinatorial libraries, oscillating reactions and networks of autocatalytic and replicating compounds. These studies provide fundamental insights into the organisational principles of molecular networks and how these give rise to emergent properties such as amplification and feedback loops, and may eventually shed light on the origin of life. The knowledge obtained from the study of molecular networks should ultimately enable us to engineer new systems with properties and functions unlike any conventional materials. 相似文献
28.
By varying the density of an ultracold 88Sr sample from 10(9) to>10(12) cm(-3), we make the first definitive measurement of the density-related frequency shift and linewidth broadening of the 1S0-3P1 optical clock transition in an alkaline earth system. In addition, we report the most accurate measurement to date of the 88Sr 1S0-3P1 optical clock transition frequency. Including a detailed analysis of systematic errors, the frequency is [434 829 121 312 334+/-20(stat)+/-33(syst)] Hz. 相似文献
29.
A. V. Taichenachev V. I. Yudin C. W. Oates Z. W. Barber N. D. Lemke A. D. Ludlow U. Sterr Ch. Lisdat F. Riehle 《JETP Letters》2010,90(11):713-717
We have extended Ramsey spectroscopy by stepping the probe frequency during the two Ramsey excitation pulses to compensate
frequency shifts induced by the excitation itself. This makes precision Ramsey spectroscopy applicable even for transitions
that have Stark and Zeeman shifts comparable to the spectroscopic resolution. The method enables a new way to evaluate and
compensate key frequency shifts, which benefits in particular, optical clocks based on magnetic field-induced, spectroscopy,
two-photon transitions, or heavily forbidden transitions. 相似文献
30.
Sherman JA Lemke ND Hinkley N Pizzocaro M Fox RW Ludlow AD Oates CW 《Physical review letters》2012,108(15):153002
Presently, the Stark effect contributes the largest source of uncertainty in a ytterbium optical atomic clock through blackbody radiation. By employing an ultracold, trapped atomic ensemble and high stability optical clock, we characterize the quadratic Stark effect with unprecedented precision. We report the ytterbium optical clock's sensitivity to electric fields (such as blackbody radiation) as the differential static polarizability of the ground and excited clock levels α(clock) = 36.2612(7) kHz?(kV/cm)(-2). The clock's uncertainty due to room temperature blackbody radiation is reduced by an order of magnitude to 3×10(-17). 相似文献