排序方式: 共有121条查询结果,搜索用时 15 毫秒
71.
David W. Podlesak Gabriel J. Bowen Shannon O'Grady Thure E. Cerling James R. Ehleringer 《Isotopes in environmental and health studies》2013,49(2):259-279
An understanding of the factors influencing the isotopic composition of body water is important to determine the isotopic composition of tissues that are used to reconstruct movement patterns of humans. The δ2H and δ18O values of body water (δ2Hbw and δ18Obw) are related to the δ2H and δ18O values of drinking water (δ2Hdw and δ18Odw), but clearly distinct because of other factors including the composition of food. Here, we develop a mechanistic geographical information system (GIS) model to produce spatial projections of δ2Hbw and δ18Obw values for the USA. We investigate the influence of gender, food, and drinking water on the predicted values by comparing them with the published values. The strongest influence on the predicted values was related to the source of δ2Hdw and δ18Odw values. We combine the model with equations that describe the rate of turnover to produce estimates for the time required for a non-resident to reach an isotopic equilibrium with a resident population. 相似文献
72.
J.E. Pollard D.J. Trevor J.E. Reutt Y.T. Lee D.A. Shirley 《Chemical physics letters》1982,88(4):434-438
The photoelectron asymmetry parameter for H+2(ν′ = 0) was measured for the S rotational branch at λ = 584 and 736 Å using supersonic beam of n-H2. Comparison with the theoretical β values of Itikawa demonstrates the importance of coupling between the p and f photoelectron waves at higher photon energy. 相似文献
73.
The Fokker-Planck approximation for n-dimensional nonmarkovian Langevin equations is discussed through an expansion in powers of the correlation time of the noise. Exact cases are considered and an application to brownian motion is presented. 相似文献
74.
Timothy P. Parr Richard Behrens Andrew Freedman Ronald R. Herm 《Chemical physics letters》1978,56(1):71-75
Laboratory (lab) angular and time-of-flight (TOF) recoil velocity spectra of SnCl product formed by crossing a thermal Sn beam with a Cl2 nozzle beam have been measured in a molecular beam apparatus equipped with an electron bombardment ionizer—quadrupole mass filter detector unit. Product center of mass (c.m.) recoil angle and energy distributions have been fit to the data by convoluting the c.m. → lab transformation over measured beam speed distributions and the instrumental TOF resolution. The inferred distributions for the Sn + Cl2 reaction are strikingly similar to those reported for the Li + Cl2 reaction. In addition, SnBr product was observed from crossed beams of Sn and Br2 which establishes a lower limit for D00 (SnBr) of 131 kJ/mole. 相似文献
75.
Michael O. Albertson 《Discrete Mathematics》1973,4(3):197-199
Sufficient conditions are established for Hadwiger's Conjecture to be valid in thecase r = 5. 相似文献
76.
The threshold behavior of Raman amplitudes for photon energies near dissociation of the intermediate potential surface of a diatomic molecule is determined. Structure in the Raman amplitudes is calculated and found to be due to resonance of the intermediate potential surface. 相似文献
77.
R.C. Haushalter C.J. OConnor A.M. Umarji G.K. Shenoy C.K. Saw 《Solid State Communications》1984,49(10):929-933
The amorphous alloys M2SnTe4 (M=Cr, Mn, Fe) are prepared by a new method involving the oxidation of main group polyanions (Zintl anions) by transition metal cations in solution at or below room temperature. The M2SnTe4 materials undergo a transition to a spin glass state at 12 K ? Tf ? 20 K and were characterized by dc magnetization, 57Fe and 119Sn Mossbauer and x-ray diffraction measurements as well as the behavior of the remanent magnetization. 相似文献
78.
Fluorescence from high vibrational levels of the first excited singlet state of chlorophyll-a in solution is observed at 77°K. The pronounced fluorescence efficiency dependence on pumping of specific vibrational levels may contribute to excitation-wavelength effects on photosynthesis. 相似文献
79.
Tributyltin (TBT), a biocidal antifoulant in many marine paints, was measured in near-surface and near-bottom water over a 25 h period at the entrance to a marina in San Diego Bay, USA. Surface water concentrations varied from 20 to 225 nanograms per liter (ng dm?3) as TBT chloride and bottom water varied from non-detectable (<1 ng dm?3) to 77 ng dm?3. Surface water concentrations varied, with highest concentrations associated with ebbing tides, and lowest concentrations with flooding tides, indicating that the yacht basin is a source of TBT. Bottom water TBT concentrations were almost always lower than corresponding surface water concentrations. The highest bottom water concentrations were associated with flooding tides and lowest surface water TBT concentrations. Physical water column measurements indicate that vertical stratification developed during ebbing tides and dissipated during flooding tides. This accounted for maximum bottom water and minimum surface water TBT concentrations during flooding tides, due, at least in part, to vertical mixing and dilution during flood tides. 相似文献
80.
Measurements of the Knight shift K and the nuclear spin-lattice relaxation rate of Zn67 are reported for liquid Zn. Measurements of K extend from 409°C (supercooled) to 700°C; measurements of cover the range 425 – 620°C. The Knight shift shows a weak positive temperature dependence attributed to thermal expansion. The reciprocal enhancement factor of the Korringa relation K(α) is found to increase with temperature from .77 ± .04 to .82 ± .04 in the range 425 – 620°C. The quadrupolar contribution to the relaxation rate was concluded to be very small with an estimated upper limit given by 相似文献