Cumulant functions in optical coherence theory

Cumulant functions are introduced to describe the statistical state of a radiation field. These functions are simply related to the optical coherence functions but have some interesting features. It is shown that if the cumulant functions of all orders greater than some numberN ₀ vanish then they also vanish for all orders greater than 2. Thermal field is the only field having this property. This property holds whether the field is described by a classical stochastic process or by a quantum density operator. Further the particular operator ordering used in defining these cumulant functions for the quantized field affects only the second order cumulant function. To describe the statistical state of a vector field such as partially polarized or unpolarized radiation, one would need to introduce cumulant tensors.     

Gas phase activation energy for unimolecular dissociation of biomolecular ions determined by focused RAdiation for gaseous multiphoton ENergy transfer (FRAGMENT)

We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd.     

Mammalian DNA δ15N exhibits 40‰ intramolecular variation and is unresponsive to dietary protein level

We report the first high‐precision characterization of molecular and intramolecular δ¹⁵N of nucleosides derived from mammalian DNA. The influence of dietary protein level on brain amino acids and deoxyribonucleosides was determined to investigate whether high protein turnover would alter amino acid ¹⁵ N or ¹³ C values. Pregnant guinea pig dams were fed control diets, or high or low levels of dietary protein throughout gestation, and all pups were fed control diets. The cerebellar DNA of offspring was extracted at 2 and 120 days of life, nucleosides isolated and δ¹⁵N and δ¹³C values characterized. Mean diet δ¹⁵N was 0.45 ± 0.33‰, compared with cerebellar whole tissue and DNA δ¹⁵N = +4.1 ± 0.7‰ and ?4.5 ± 0.4‰, respectively. Cerebellar deoxythymidine (dT), deoxycytidine (dC), deoxyadenosine (dA), and deoxyguanosine (dG) δ¹⁵N were +1.4 ± 0.4, –2.1 ± 0.9, –7.2 ± 0.3, and ?10.4 ± 0.5‰, respectively. There were no changes in amino acid or deoxyribonucleoside δ¹⁵N values due to dietary protein level. Using known metabolic relationships, we developed equations to calculate the intramolecular δ¹⁵N values originating from aspartate (asp) in purines (pur) or pyrimidines (pyr), glutamine (glu), and glycine (gly) to be δ¹⁵N_ASP‐PUR, δ¹⁵N_ASP‐PYR, δ¹⁵N_GLN, and δ¹⁵N_GLY +11.9 ± 2.3‰, +7.0 ± 2.0‰, –9.1 ± 2.4‰, and ?31.8 ± 8.9‰, respectively. A subset of twelve amino acids from food and brain had mean δ¹⁵N values of 4.3 ± 3.2‰ and 13.8 ± 3.1‰, respectively, and δ¹⁵N values for gly and asp were 12.6 ± 2.2‰ and 15.2 ± 0.8‰, respectively. A separate isotope tracer study detected no significant turnover of cerebellar DNA in the first six months of life. The large negative δ¹⁵N difference between gly and cerebellar purine N at the gly (7) position implies either that there is a major isotope effect during DNA synthesis, or that in utero gly has a different isotope ratio during rapid growth and metabolism from that in adult life. Our data show that cerebellar nucleoside intramolecular δ¹⁵N values vary over more than 40‰ and are not influenced by dietary protein level or age. Copyright © 2011 John Wiley & Sons, Ltd.     

The first high-pressure high-resolution NMR probe for a normal bore cryomagnet1

Abstract

We describe a high-pressure high-resolution NMR probe fitting into a 4.7 Tesla normal bore (50 mm Ø) cryomagnet used with a Bruker AC-200 spectrometer. The probe is designed for a pressure range from 0.1 to 200 MPa and can be used in a temperature domain from -50 to + 120°C. Eguipped with a double tuned frequeney adapter circuit the probe is used for ¹H (200 MHz) observation and ²H (30.7 MHz) field locking for easy homogeneity adjustment. The resolution obtained routinely is better than 1 Hz (< 5′10^?9). Other frequencies, e.g. 27.1 MHz for ¹⁷O observation, can easily be obtained by changing and according the frequency adapter box.     

铌酸锶钡薄膜的微结构与电光性能的研究

本文叙述了使用溶胶凝胶法在MgO(0 0 1)的衬底上制备铌酸锶钡薄膜的过程 ,膜层厚度可达 5 μm。通过X射线衍射、摇摆曲线、扫描、拉曼散射光谱等方法研究了薄膜的微结构性能 ,实验发现 ,铌酸锶钡薄膜具有了较好的 (0 0 1)方向的优先取向性能 ,并且随着薄膜厚度的增加 ,其晶体取向性也会随之不断改进。熔石英的透明衬底上生长的SBN薄膜具有较大的电致双折射效应 ,其有效电光系数能够高达 6 6 2× 10 -11m/V。