北京同步辐射装置上的位相衬度成像

在北京同步辐射装置上首次用位相衬度成像方法对生物样品和复合材料进行研究,得到了非常清晰而精细的材料内部细观结构.其图像的清晰度和分辨率明显地优于吸收衬度成像 关键词： 位相衬度成像 相干光源 同步辐射硬X射线     

Parallel finite element splitting-up method for parabolic problems

An efficient method for solving parabolic systems is presented. The proposed method is based on the splitting-up principle in which the problem is reduced to a series of independent 1D problems. This enables it to be used with parallel processors. We can solve multidimensional problems by applying only the 1D method and consequently avoid the difficulties in constructing a finite element space for multidimensional problems. The method is suitable for general domains as well as rectangular domains. Every 1D subproblem is solved by applying cubic B-splines. Several numerical examples are presented.     

Mechanism of acetylcholinesterase inhibition by fasciculin: a 5-ns molecular dynamics simulation

Our previous molecular dynamics simulation (10 ns) of mouse acetylcholinesterase (EC 3.1.1.7) revealed complex fluctuation of the enzyme active site gorge. Now we report a 5-ns simulation of acetylcholinesterase complexed with fasciculin 2. Fasciculin 2 binds to the gorge entrance of acetylcholinesterase with excellent complementarity and many polar and hydrophobic interactions. In this simulation of the protein-protein complex, where fasciculin 2 appears to sterically block access of ligands to the gorge, again we observe a two-peaked probability distribution of the gorge width. When fasciculin is present, the gorge width distribution is altered such that the gorge is more likely to be narrow. Moreover, there are large increases in the opening of alternative passages, namely, the side door (near Thr 75) and the back door (near Tyr 449). Finally, the catalytic triad arrangement in the acetylcholinesterase active site is disrupted with fasciculin bound. These data support that, in addition to the steric obstruction seen in the crystal structure, fasciculin may inhibit acetylcholinesterase by combined allosteric and dynamical means. Additional data from these simulations can be found at http://mccammon.ucsd.edu/.     

Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges

Using silicon-on-insulator-based silicon-wire waveguides with submicrometer cross sections, we constructed ultrasmall channel-dropping lattice filters for 1.5-microm infrared systems. The waveguide's low-loss bends with 2.5-microm radius reduce the total length of the filter to less than 100 microm and enlarge the free spectral range to more than 80 nm. The measured spectra show fine channel-dropping characteristics, and the results agree well with numerical predictions. Moreover, we have succeeded in tuning the dropping wavelength by adjusting the lengths of the delay lines.     

The Moduli Space of Real Abelian Varieties with Level Structure

The moduli space of principally polarized Abelian varieties with real structure and with level N = 4m structure (with m1) is shown to coincide with the set of real points of a quasi-projective algebraic variety defined over , and to consist of finitely many copies of the quotient of the space GL(n, )/O(N) (of positive definite symmetric matrices) by the principal congruence subgroup of level N in GL(n, ).     

NIST reference materials to support accuracy in drug testing

Substance abuse is a major problem worldwide. There is considerable emphasis placed upon testing individuals for evidence of use of controlled substances. Because the consequences of a positive test can be quite severe, laboratories conducting such tests must rigorously follow a carefully designed quality assurance program. Such a QA program should include use of reference materials to assure that the methods used to detect and quantify drugs are providing accurate results. The National Institute of Standards and Technology (NIST) supports accuracy in drugs of abuse testing by providing Standard Reference Materials (SRMs) with certified concentrations of drugs of abuse in urine- and hair-based reference materials. NIST, working in collaboration with the College of American Pathologists (CAP), has developed urine-based SRMs for marijuana metabolite, cocaine metabolite, morphine and codeine, and morphine glucuronide and CAP Reference Materials for amphetamines and phencyclidine. Certification measurements performed at NIST involve two independent methods for each analyte, one of which always uses GC/MS with the other usually being an LC method with either MS or UV detection. Work has recently been completed on a seven component drug in urine SRM. In addition NIST conducts research in the analysis of hair for drugs of abuse. To assist laboratories testing hair for that purpose, NIST has developed two drugs in hair reference materials.College of American Pathologists Research Associate at NIST     

The crystal structures of α,ω-diaminoalkanecadmium(II) tetracyanonickelate(II)-aromatic molecule inclusion compounds. II. 1,6-diaminohexanecadmium(II) tetracyanonickelate(II)-o-toluidine (1/1): Cd(NH2(CH2)6NH2)Ni(CN)4.o-CH3C6H4NH2

The title inclusion compound crystallizes in monoclinic space group P2/m, with a=9.541(2), b=7.569(2), and c=7.199(1) Å, =100.3(1)^o, and Z=1. The structure has been refined to a conventional R=0.036 for 1973 independent reflections collected by counter method. The host metal complex has the structure similar to that of 1,4-diaminobutanecadmium(II) tetracyanonickelate(II)-2,5-xylidine (1/1) with respect to the two-dimensionally extended wavy cyanometal complex sheets bridged by the ,-diaminoalkane ligands at the respective Cd atoms in adjacent sheets providing a channel-like cavity with the guest aromatic molecule. The guesto-toluidine molecule is surrounded by four 1,6-diaminohexane bridges taking an all-trans conformation of the aliphatic chain and show disorder in the orientation in the cavity. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82021 (21 pages).