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81.
Edward E. Allen Gregory S. Warrington 《Journal of Combinatorial Theory, Series A》2008,115(7):1127-1155
Garsia-Haiman modules C[Xn,Yn]/Iγ are quotient rings in the variables Xn={x1,x2,…,xn} and Yn={y1,y2,…,yn} that generalize the quotient ring C[Xn]/I, where I is the ideal generated by the elementary symmetric polynomials ej(Xn) for 1?j?n. A bitableau basis for the Garsia-Haiman modules of hollow type is constructed. Applications of this basis to representation theory and other related polynomial spaces are considered. 相似文献
82.
Susumu Takahashi Dan G. Allen Jason Seifter Gerald Ramian Mark S. Sherwin Louis-Claude Brunel Johan van Tol 《Infrared Physics & Technology》2008,51(5):426-428
We describe the first free-electron laser (FEL)-based pulsed electron paramagnetic resonance (EPR) system designed to study spin dynamics and structure changes of proteins in aqueous solution with nano-second of time resolution. This novel approach opens up the possibility for high-power sub-THz and THz pulsed EPR spectroscopy. 相似文献
83.
Maurice J. Marks Nikhil E. Verghese K. James Hrovat Anamari Laboy‐Bollinger James C. Buck James A. Rabon Jr. Carol L. O'connell Lisa Allen 《Journal of Polymer Science.Polymer Physics》2008,46(15):1632-1640
Five families of new controlled epoxy thermosets (CENs) using three monophenol chain terminators were prepared to study systematic changes in the structure and amount of the monophenol and the initial molecular weight between crosslinks (Mc,i) on the properties of epoxy thermosets. Glass transition temperature (Tg) decreases with monophenol mole fraction (χ) in proportion to both the concentration and flexibility of the chain terminator. Distinct serial relations for Tg depression were observed for the three Mc,i families. Dynamic mechanical analysis (DMA) shows significant perturbations of the relaxation behavior with added terminator as evidenced by decrease in peak tan δ and in post Tg damping. The rubbery coefficients of thermal expansion (CTE) increases with monophenol concentration only at χ > 0.05 and shows distinct curvature versus temperature, but is largely invariant with monophenol flexibility. The thermal stability of terminated CENs decreases only slightly with χ and little difference was found with monophenol structure. Most surprisingly, fracture toughness decreases markedly and discontinuously with χ depending on Mc,i. The values of the critical monophenol concentration at which fracture toughness markedly decreases (χc) are inversely proportional to Mc,i but are independent of monophenol flexibility. No correlation of χc with any of the calculated network structure parameters was apparent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1632–1640, 2008 相似文献
84.
Paul Allen Margaret A. Brimble Peter Turner 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(1):95-96
The crystal structure of antibiotic CP44,161, 6-(7-{2-ethyl-2-[5-(1-hydroxymethyl)-5-methyl-2,3,4,5-tetrahydro-2-furyl]-4,10,-12-trimethyl-1,6,8-trioxadispiro[4.1.5.3]pentadec-13-en-9-yl}-4-hydroxy-3,5-dimethyl-6-oxononyl)-2-hydroxy-3-methylbenzoic acid monohydrate, C43H66O10·H2O, has been determined by X-ray crystallography. The molecule adopts a cyclic conformation, with a centrally located water molecule contributing to the stability of the conformation through hydrogen-bonding interactions. 相似文献
85.
86.
Most writers on frequency assignment algorithms have described the details of a single algorithm, and evaluated the algorithm on selected data sets. There has been relatively little emphasis on describing the common features that are important if an algorithm is to have good performance. This paper describes the key features, with particular emphasis on algorithms for weighted fixed spectrum problems. The use of algorithms handling weighted constraints has become increasingly common in recent years. The advantages and disadvantages of weighting constraints are demonstrated. 相似文献
87.
88.
A discrete-time model for an age-structured population in a patch-type environment is presented and analyzed. Comparison techniques for difference equations are used to find sufficient conditions for population persistence or extinction. The persistence and extinction theorem is used to define the critical patch number, the threshold for population persistence. Several examples are presented which illustrate the results of the theorems. The model is applied to a watersnake population. 相似文献
89.
Kevin Buckley Jemma G. Kerns Anthony W. Parker Allen E. Goodship Pavel Matousek 《Journal of Raman spectroscopy : JRS》2014,45(2):188-192
The decomposition of spatially offset Raman spectra for complex multilayer systems, such as biological tissues, requires advanced techniques such as multivariate analyses. Often, in such situations, the decomposition methods can reach their limits of accuracy well before the limits imposed by signal‐to‐noise ratios. Consequently, more effective reconstruction methods could yield more accurate results with the same data set. In this study we process spatially offset Raman spectroscopy (SORS) data with three different multivariate techniques (band‐target entropy minimization (BTEM), multivariate curve resolution and parallel factor analysis (PARAFAC)) and compare their performance when analysing a spectrally challenging plastic model system and an even more challenging problem, the analysis of human bone transcutaneously in vivo. For the in vivo measurements, PARAFAC's requirement of multidimensional orthogonal data is addressed by recording SORS spectra both at different spatial offsets and at different anatomical points, the latter providing added dimensionality through the variation of skin/soft tissue thickness. The BTEM and PARAFAC methods performed the best on the plastic system with the BTEM more faithfully reconstructing the major Raman bands and PARAFAC the smaller more heavily overlapped features. All three methods succeeded in reconstructing the bone spectrum from the transcutaneous data and gave good figures for the phosphate‐to‐carbonate ratio (within 2% of excised human tibia bone); the PARAFAC gave the most accurate figure for the mineral‐to‐collagen ratio (20% less than excised human tibia bone). Previous studies of excised bones have shown that certain bone diseases (such as osteoarthritis, osteoporosis and osteogenesis imperfecta) are accompanied by compositional abnormalities that can be detected with Raman spectroscopy, the utility of a technique which could reconstruct bone spectra accurately is manifest. The results have relevance on the use of SORS in general. © 2014 Crown copyright. Journal of Raman Spectroscopy published by John Wiley & Sons, Ltd. 相似文献
90.
Jack T. Skinner Ryan K. Robison Christopher P. Elder Allen T. Newton Bruce M. Damon C. Chad Quarles 《Magnetic resonance imaging》2014
Perfusion-based changes in MR signal intensity can occur in response to the introduction of exogenous contrast agents and endogenous tissue properties (e.g. blood oxygenation). MR measurements aimed at capturing these changes often implement single-shot echo planar imaging (ssEPI). In recent years ssEPI readouts have been combined with parallel imaging (PI) to allow fast dynamic multi-slice imaging as well as the incorporation of multiple echoes. A multiple spin- and gradient-echo (SAGE) EPI acquisition has recently been developed to allow measurement of transverse relaxation rate (R2 and R2?) changes in dynamic susceptibility contrast (DSC)-MRI experiments in the brain. With SAGE EPI, the use of PI can influence image quality, temporal resolution, and achievable echo times. The effect of PI on dynamic SAGE measurements, however, has not been evaluated. In this work, a SAGE EPI acquisition utilizing SENSE PI and partial Fourier (PF) acceleration was developed and evaluated. Voxel-wise measures of R2 and R2? in healthy brain were compared using SAGE EPI and conventional non-EPI multiple echo acquisitions with varying SENSE and PF acceleration. A conservative SENSE factor of 2 with PF factor of 0.73 was found to provide accurate measures of R2 and R2? in white (WM) (rR2 = [0.55–0.79], rR2? = [0.47–0.71]) and gray (GM) matter (rR2 = [0.26–0.59], rR2? = [0.39–0.74]) across subjects. The combined use of SENSE and PF allowed the first dynamic SAGE EPI measurements in muscle, with a SENSE factor of 3 and PF factor of 0.6 providing reliable relaxation rate estimates when compared to multi-echo methods. Application of the optimized SAGE protocol in DSC-MRI of high-grade glioma patients provided T1 leakage-corrected estimates of CBV and CBF as well as mean vessel diameter (mVD) and simultaneous measures of DCE-MRI parameters Ktrans and ve. Likewise, application of SAGE in a muscle reperfusion model allowed dynamic measures of R2′, a parameter that has been shown to correlate with muscle oxy-hemoglobin saturation. 相似文献