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51.
Larry J. Langley 《Discrete Applied Mathematics》1995,60(1-3):257-266
From a partially ordered set (X, <) one may construct the collection PS(X) consisting of a collection of subsets of X ordered by inclusion. We show that the interval dimension of X equals the dimension of PS(X) and give an O(n3) algorithm to determine whether X has interval dimension 2 and construct an interval realizer of X. 相似文献
52.
J. K. Langley 《Journal d'Analyse Mathématique》2005,97(1):357-396
Letf be a real meromorphic function of infinite order in the plane such thatf has finitely many poles. Then for eachk≥3, at least one off andf (k) has infinitely many non-real zeros. Together with a result of Edwards and Hellerstein, this establishes the analogue for higher derivatives of a conjecture going back to Wiman around 1911. 相似文献
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54.
This paper presents the results of investigating the effect of curvature and pitch on stress-wave propagation in helical springs. It supplements a previous paper in which the work carried out on a single spring of fixed curvature and pitch was described and the experimental results compared with theory. A short duration, wide-band pulse technique, described in the first paper, was used to investigate the nature of the propagation. Theoretical dispersion curves, appropriate to the springs used, were computed for comparison with the experimental results which were interpreted according to Kelvin's principle of stationary phase. 相似文献
55.
Greenwood JB Johnston IM McKenna P Williams ID Goodworth TR Sanderson JH Bryan WA El-Zein AA Newell WR Langley AJ Divall EJ 《Physical review letters》2002,88(23):233001
The interaction of an intense laser field with a beam of atomic ions has been investigated experimentally for the first time. The ionization dynamics of Ar+ ions and Ar neutrals in a 60 fs, 790 nm laser pulse have been compared and contrasted at intensities up to 10(16) W cm-2. Our results show that nonsequential ionization from an Ar+ target is strongly suppressed compared with that from the corresponding neutral target. We have also observed for the first time the strong field ionization of high lying target metastable levels in the Ar+ beam. 相似文献
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57.
It is well known that the power absorbed by a linear oscillator when excited by white noise base acceleration depends only on the mass of the oscillator and the spectral density of the base motion. This places an upper bound on the energy that can be harvested from a linear oscillator under broadband excitation, regardless of the stiffness of the system or the damping factor. It is shown here that the same result applies to any multi-degree-of-freedom nonlinear system that is subjected to white noise base acceleration: for a given spectral density of base motion the total power absorbed is proportional to the total mass of the system. The only restriction to this result is that the internal forces are assumed to be a function of the instantaneous value of the state vector. The result is derived analytically by several different approaches, and numerical results are presented for an example two-degree-of-freedom-system with various combinations of linear and nonlinear damping and stiffness. 相似文献
58.
Langley DB Brown DE Cheruzel LE Contakes SM Duff AP Hilmer KM Dooley DM Gray HB Guss JM Freeman HC 《Journal of the American Chemical Society》2008,130(25):8069-8078
The copper amine oxidase from Arthrobacter globiformis (AGAO) is reversibly inhibited by molecular wires comprising a Ru(II) complex head group and an aromatic tail group joined by an alkane linker. The crystal structures of a series of Ru(II)-wire-AGAO complexes differing with respect to the length of the alkane linker have been determined. All wires lie in the AGAO active-site channel, with their aromatic tail group in contact with the trihydroxyphenylalanine quinone (TPQ) cofactor of the enzyme. The TPQ cofactor is consistently in its active ("off-Cu") conformation, and the side chain of the so-called "gate" residue Tyr296 is consistently in the "gate-open" conformation. Among the wires tested, the most stable complex is produced when the wire has a -(CH2)4- linker. In this complex, the Ru(II)(phen)(bpy)2 head group is level with the protein molecular surface. Crystal structures of AGAO in complex with optically pure forms of the C4 wire show that the linker and head group in the two enantiomers occupy slightly different positions in the active-site channel. Both the Lambda and Delta isomers are effective competitive inhibitors of amine oxidation. Remarkably, inhibition by the C4 wire shows a high degree of selectivity for AGAO in comparison with other copper-containing amine oxidases. 相似文献
59.
Sergio Cancho-Gonzalez Paul Ferguson Julie M. Herniman G. John Langley 《Journal of separation science》2023,46(20):2300425
Poly(ethylene glycols) are complex polymers often added to pharmaceutical formulations to improve drug solubility and delivery. One of the main challenges when using chromatographic techniques coupled to mass spectrometry is the unselective ionization of poly(ethylene glycols) oligomers. Additionally, when the chain length is large enough, multiple charged species are formed, further complicating the mass spectra and processing. This study uses the advanced oligomer separation provided by supercritical fluid chromatography with a mass spectrometry approach that selectively ionizes poly(ethylene glycols) as ammoniated molecules to simplify data analysis and facilitate batch-to-batch comparisons. Several visual representations of the response of the ionization events based on the polymer molecular weight and the repeating unit were used to elucidate trends in ionization. Evaluation of the influence of the oligomer length and end-group on the electrospray ionization of the polymer allowed the development of a process to enable selective ionization for these complex polymers. 相似文献
60.
Philipp Stephan Chloe Langley Daniela Winkler Dr. Jérôme Basquin Dr. Lorenzo Caputi Prof. Dr. Sarah E. O'Connor Dr. Hajo Kries 《Angewandte Chemie (International ed. in English)》2023,62(35):e202304843
Engineering of biosynthetic enzymes is increasingly employed to synthesize structural analogues of antibiotics. Of special interest are nonribosomal peptide synthetases (NRPSs) responsible for the production of important antimicrobial peptides. Here, directed evolution of an adenylation domain of a Pro-specific NRPS module completely switched substrate specificity to the non-standard amino acid piperazic acid (Piz) bearing a labile N−N bond. This success was achieved by UPLC-MS/MS-based screening of small, rationally designed mutant libraries and can presumably be replicated with a larger number of substrates and NRPS modules. The evolved NRPS produces a Piz-derived gramicidin S analogue. Thus, we give new impetus to the too-early dismissed idea that widely accessible low-throughput methods can switch the specificity of NRPSs in a biosynthetically useful fashion. 相似文献