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471.
R.H. Austin N. Darnton R. Huang J. Sturm O. Bakajin T. Duke 《Applied Physics A: Materials Science & Processing》2002,75(2):279-284
We have constructed microfabricated devices, designed to have asymmetry in their physical structures, in order to fractionate
objects under continuous-flow conditions. The fractionation of particles with the inclusion of diffusion and asymmetric structures
requires a knowledge of not only statistical mechanics but also the external forces acting on the particles, since thermal
Brownian fluctuations alone cannot serve to separate particles. We explicitly examine this problem in a device designed to
fractionate biomolecules dissolved in water, and show that boundary conditions that influence the direction of the applied
force are quite important in determining the efficiency of the device.
Received: 11 December 2001 / Accepted: 11 February 2002 / Published online: 22 April 2002 相似文献
472.
Reinhard Noll Volker Sturm Ümit Aydin Daniel Eilers Christoph Gehlen Manuela Höhne André Lamott Joachim Makowe Jens Vrenegor 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
This paper presents R&D activities to explore new laser parameter ranges in pulse energy, time and space for laser-induced breakdown spectroscopy. The collinear double pulse effect, which is well studied for pulses of typically several 100 mJ energy can also be observed for laser pulses having a pulse energy two orders of magnitude lower. In this case, maximum line emission intensity occurs at interpulse separations of a few 100 ns. Temporal pulse tailoring to improve the performance of LIBS is only a first step. A comprehensive approach includes spatial pulse shaping to generate craters with predefined shape or to improve spatial averaging for the analysis of inhomogeneous samples. High performance components for LIBS systems such as spectrometers, electronics and sample stands are required to enable industrial applications. Latest developments offer wide-band single spectra acquisition with a high spectral resolution at a measuring frequency of up to 500 Hz. The next generation of multi-channel integrator electronics for Paschen–Runge spectrometers equipped with PMT detectors will further push the measuring speed to up to 5 kHz, thus opening a new area of high-speed LIBS microanalysis. Novel LIBS devices for various industrial applications presented include analysis of metallic process control samples with scale layers, on-site analysis of slag samples in secondary metallurgy, high-speed identification of Al scrap, mix-up detection of pipe fittings as well as recent work towards in-process identification of hot coils in a rolling mill. 相似文献
473.
Inglis DW Morton KJ Davis JA Zieziulewicz TJ Lawrence DA Austin RH Sturm JC 《Lab on a chip》2008,8(6):925-931
In this work we demonstrate a new microfluidic method for the rapid assessment of platelet size and morphology in whole blood. The device continuously fractionates particles according to size by displacing them perpendicularly to the fluid flow direction in a micro-fabricated post array. Whole blood, labeled with the fluorescent, platelet specific, antibody PE-anti-CD41, was run through the device and the positions of fluorescent objects noted as they exited the array. From this, histograms of platelet size were created which show marked increases in size after exposure to thrombin or a temperature of 4 degrees C. We infer that the well known morphological changes that occur during activation are causing the observed increase in size. 相似文献
474.
Ma X Schulzke C Schmidt HG Noltemeyer M 《Dalton transactions (Cambridge, England : 2003)》2007,(18):1773-1780
The first crystallographically characterized molybdenum(vi) selenoether complex [Mo(2)O(4)(OC(3)H(6)SeC(3)H(6)O)(2)] and its thioether analogue [Mo(2)O(4)(OC(3)H(6)SC(3)H(6)O)(2)] were synthesised. Their structural, electrochemical and oxygen atom transfer properties are compared. This is relevant for the molybdenum cofactors of the DMSO reductase family where the coordination of the active site metal occurs through O (serine/aspartate), S (cysteine) or Se (selenocysteine). Both structures are almost identical except for those parameters that are directly derived from the different sizes of the varied ligand atoms (Se and S). No trans influence was observed. The metal centered redox process (Mo(V)<-->Mo(VI)) is at slightly lower voltage for the sulfur than for the selenium complex. The selenium compound catalyses the oxygen atom transfer from DMSO to PPh(3) by a different mechanism and at a higher rate than the sulfur compound, which is an indication that cysteine and selenocysteine might be used for a purpose in the different molybdenum and tungsten cofactors. 相似文献
475.
Dr. Avijit Maiti Benedict J. Elvers Dr. Sachinath Bera Felix Lindl Dr. Ivo Krummenacher Prof. Prasanta Ghosh Prof. Dr. Holger Braunschweig Prof. Cem B. Yildiz Prof. Dr. Carola Schulzke Dr. Anukul Jana 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(28):e202104567
Herein, we disclose cyclic(alkyl)(amino)carbenes (CAACs) to be one-electron reductants under the formation of a transient radical cation as indicated by EPR spectroscopy. The disclosed CAAC reducing reactivity was used to synthesize acyclic(amino)(aryl)carbene-based Thiele and Chichibabin hydrocarbons, a new class of Kekulé diradicaloids. The results demonstrate CAACs to be potent organic reductants. Notably, the acyclic(amino)(aryl)carbene-based Chichibabin's hydrocarbon shows an appreciable population of the triplet state at room temperature, as evidenced by both variable-temperature NMR and EPR spectroscopy. 相似文献
476.
The running of the effective electromagnetic coupling is for many electroweak observables the dominant correction. It plays an important role for deriving constraints on the Standard Model in the context of electroweak precision measurements. We compute the four-loop QED corrections to the running of the effective electromagnetic coupling and perform a numerical evaluation of the different gauge invariant subsets. 相似文献
477.
The reaction of alkynes with tetracarbonyl[methoxy(2,4-dimethoxyphenyl)carbene]-chromium, followed by oxidation, gives naphthoquinones as well as other cyclized products. This has been utilized in the preparation of (3) an intermediate in the synthesis of 7-methoxyeleutherin. 相似文献
478.
The influence of sulfur versus selenium coordination to molybdenum on the oxo transfer reaction mechanisms of functional models for oxidoreductases has been studied. The solution structure of the dimeric molybdenum compound with tridentate bis-anionic ligands containing a thioether function (−O(CH2)3S(CH2)3O−) has been determined using EXAFS spectroscopy to be able to compare a feature of its solution structure to that of its selenoether analogue. A significant difference is found for the solution structures of the two compounds. The thioether group remains coordinated in solution, whereas the selenoether does not. The influence of this difference on the catalytic oxo transfer has been investigated in detail by following the catalytic transition of PPh3 to OPPh3 with DMSO as oxygen donor with variation of both substrate concentrations. 相似文献
479.
Ruibing Chen Limei Hui Robert M. Sturm Lingjun Li 《Journal of the American Society for Mass Spectrometry》2009,20(6):1068-1077
Imaging mass spectrometry is emerging as a powerful tool that has been applied extensively for the localization of proteins,
peptides, pharmaceutical compounds, metabolites, and lipids in biological tissues. In this article, a three-dimensional mass
spectral imaging (3D MSI) technique was developed to examine distribution patterns of multiple neuropeptide families and lipids
in the brain of the crab Cancer borealis. Different matrix/solvent combinations were compared for preferential extraction and detection of neuropeptides and lipids.
Combined with morphological information, the distribution of numerous neuropeptides throughout the 3D structure of brain was
determined using matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF/TOF MS). Different
localization patterns were observed for different neuropeptide families, and isoforms displaying unique distribution patterns
that were distinct from the common family distribution trends were also detected. In addition, multiple lipids were identified
and mapped from brain tissue slices. To confirm their identities, MS/MS fragmentation was performed. Different lipid species
displayed distinct localization patterns, suggesting their potential different functional roles in the nervous system. 相似文献
480.
Junhua Wang Xiaoyue JiangRobert M. Sturm Lingjun Li 《Journal of chromatography. A》2009,1216(47):8283-8288
In this study we report an improved protocol that combines simplified sample preparation and micro-scale separation for mass spectrometric analysis of neuropeptides from individual neuroendocrine organs of crab Cancer borealis. A simple, one-step extraction method with commonly used matrix-assisted laser desorption/ionization (MALDI) matrix, 2,5-dihydroxybenzoic acid (DHB), in saturated aqueous solution, is employed for improved extraction of neuropeptides. Furthermore, a novel use of DHB as background electrolyte for capillary electrophoresis (CE) separation in the off-line coupling of CE to MALDI-Fourier transform mass spectrometric (FT-MS) detection is also explored. The new CE electrolyte exhibits full compatibility with MALDI-MS analysis of neuropeptides in that both the peptide extraction process and MALDI detection utilize DHB. In addition, enhanced resolving power and improved sensitivity are also observed for CE-MALDI-MS of peptide mixture analysis. Collectively, the use of DHB has simplified the extraction and reduced the sample loss by elimination of homogenizing, drying, and desalting processes. In the mean time, the concurrent use of DHB as CE separation buffer and subsequent MALDI matrix offers improved spectral quality by eliminating the interferences from typical CE electrolyte in MALDI detection. 相似文献