面向全体学生的物理——2006年美国全国物理教师协会"密立根奖"受奖演讲

我们物理教师必须将关注点从“面向物理学家和其他科学家的物理”扩大到“面向全体学生的物理”．理由正如美国科学促进协会说的那样：“没有一个具备科学素养的大众，美好世界的前景就没有指望．”面向全体学生的物理（包括为培养科学家而开设的初级课程）应该是概念性的，而不是技术性的．它应该把宇宙描述为我们今天所了解的宇宙，包括狭义和广义相对论、量子物理、近代宇宙学、核物理、粒子和相互作用的标准模型，以及量子场论．许多科学著作者已经向我们展示这是可以实现的．面向全体学生的物理应该强调科学的过程，并包含如全球变暖、核武器和伪科学等社会性话题，因为公众需要对这些问题做出明智的表决．     

Electron spin polarization of the excited quartet state of strongly coupled triplet-doublet spin systems

The electron spin polarization associated with electronic relaxation in molecules with trip-quartet and trip-doublet excited states is calculated. Such molecules typically relax to the lowest trip-quartet state via intersystem crossing from the trip doublet, and it is shown that when spin-orbit coupling provides the main mechanism for this relaxation pathway it leads to spin polarization of the trip quartet. Analytical expressions for this polarization are derived using first- and second-order perturbation theory and are used to calculate powder spectra for typical sets of magnetic parameters. It is shown that both net and multiplet contributions to the polarization occur and that these can be separated in the spectrum as a result of the different orientation dependences of the +/-1/2<-->+/-3/2 and +1/2<-->-1/2 transitions. The net polarization is found to be localized primarily in the center of the spectrum, while the multiplet contribution dominates in the outer wings. Despite the fact that the multiplet polarization is much stronger than the net polarization for individual orientations of the spin system, the difference in orientation dependence of the transitions leads to comparable amplitudes for the two contributions in the powder spectrum. The influence of this difference on the line shape is investigated in simulations of partially ordered samples. Because the initial nonpolarized state of the spin system is not conserved for the proposed mechanism, the net polarization can survive in the doublet ground state following electronic relaxation of the triplet part of the system.     

Raman spectroscopic analysis of breast cancer tissues: identifying differences between normal,invasive ductal carcinoma and ductal carcinoma in situ of the breast tissue

A relatively non‐destructive method employing Raman spectroscopy for the analysis of histopathological specimens is described. Raman spectroscopy has allowed qualitative analysis of the same specimen used for histopathological evaluation. Breast cancer tissues have been analysed to demonstrate the feasibility of the chemical changes taking place in the biological tissue, which can be identified precisely, and the results are reproducible. Raman analysis of tissue sections provides distinct spectra that can be used to distinguish between the nuclear grades of ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) of the breast. Sixty cases of breast carcinoma including DCIS and IDC and seven cases of normal breast tissues were studied employing the Raman spectroscopic technique. This study reports for the first time spectral differences between DCIS grades. It is concluded that Raman spectroscopy can objectively distinguish between DCIS and IDC grades and is non‐destructive and reproducible. It should become possible in future to use Raman spectroscopy as an informative and quantitative method suitable for classification of grades and diagnosis of breast carcinoma. Copyright © 2007 John Wiley & Sons, Ltd.     

Promising X-ray fluorescence tests for superconducting tunnel junction detector

The Advanced Photon Source (APS) looks forward to a period of growth in the coming years. Meanwhile, in April 2006, the APS reorganized its divisions, creating an X-ray Science Division (XSD), bringing science at the APS on a par with the accelerator, and sharing engineering and support services. The machine division, the Accelerator Systems Division, now includes all of the groups that operate and develop the machine and focus on future accelerator research.     

On Some Rational Triangles

We prove that every set of n ≥ 3 points in \mathbbR²{\mathbb{R}^2} can be slightly perturbed to a set of n points in \mathbbQ²{\mathbb{Q}^2} so that at least 3(n − 2) of mutual distances between those new points are rational numbers. Some special rational triangles that are arbitrarily close to a given triangle are also considered. Given a triangle ABC, we show that for each ε > 0 there is a triangle A′B′C′ with rational sides and at least one rational median such that |AA′|, |BB′|, |CC′| < ε and a Heronian triangle A′′B′′C′′ with three rational internal angle bisectors such that A^￠￠, B^￠￠, C^￠￠ ? \mathbbQ²{A^{\prime\prime}, B^{\prime\prime}, C^{\prime\prime} \in \mathbb{Q}^2} and |AA′′|, |BB′′|, |CC′′| < ε.     

Stimulated Electron Spin Polarization in Strongly Coupled Triplet–Doublet Spin Pairs

The possibility of stimulating electron spin polarization in a system consisting of a stable paramagnetic center and a chromophore that can be excited into its triplet state is discussed. In such systems, the doublet state of the paramagnetic center couples to the excited triplet state of the chromophore and if the coupling is larger than the difference in the precession frequencies of the doublet and triplet, the eigenstates of the coupled system are quartet and doublet states. The quartet state is usually the lowest energy excited state. Following light excitation, the initial electronic relaxation to the quartet state generates strong multiplet polarization if it is governed by the spin–orbit coupling that follows the molecular symmetry. It is shown that application of a selective π-pulse to the ±3/2 ↔ ±1/2 transitions of the quartet converts this multiplet polarization into net polarization. The magnitude and orientation dependence of the generated polarization is estimated on the basis of a simple analytical model. The experimental conditions required for this net polarization to be retained in the ground state after decay of the quartet state are discussed. The viability of using this as a method to enhance the signal strength of a spin label or metal center in selective excitation experiments is considered.     

Synthesis and photoluminescence properties of Sm-doped LaMgB5O10 and GdMgB5O10

Luminescence and reflection spectra as well as luminescence kinetics of the 1 mol% Sm³⁺-doped crystalline lanthanum magnesium meta borate (LaMgB₅O₁₀) and gadolinium magnesium meta borate (GdMgB₅O₁₀) were analyzed. Materials were synthesized by conventional solid state route and showed bright orange-red emission under UV excitation. Emission spectra contain sharp and well resolved Sm³⁺⁴G_5/2→⁶H_J transitions indicating a strong crystal-field effect. In case of gadolinium compound energy transfer between Gd³⁺ and Sm³⁺ was detected. The luminescent kinetics of the Sm³⁺ in analyzed powders is characterized by single exponential decay and experimental values vary in the range 2.2-2.4 ms.     

A Coordination Compound of Ge0 Stabilized by a Diiminopyridine Ligand

Reduction of the cationic Ge^II complex [dimpyrGeCl][GeCl₃] (dimpyr=2,6‐(ArN=CMe)₂NC₅H_3, Ar=2,6‐iPr₂C₆H₃) with potassium graphite in benzene affords an air sensitive, dark green compound of Ge⁰, [dimpyrGe], which is stabilized by a bis(imino)pyridine platform. This compound is the first example of a complex of a zero‐valent Group 14 element that does not contain a carbene or carbenoid ligand. This species has a singlet ground state. DFT studies revealed partial delocalization of one of the Ge lone pairs over the π*(C?N) orbitals of the imines. This delocalization results in a partial multiple‐bond character between the Ge atom and imine nitrogen atoms, a fact supported by the X‐ray crystallography and IR spectroscopy data.