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L Fishbein 《Journal of chromatography. A》1974,98(1):177-251
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Positron lifetime spectra were measured in 3He for temperatures 3–16 K and densities 120–432 amagat. Free positron and positron-3He clusters, as well as positronium induced cavities in the gas, are observed. Data are compared with previous work in 4He. 相似文献
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L Fishbein 《Journal of chromatographic science》1975,13(5):238-245
The utility of a variety of chromatographic procedures (GLC, TLC, and GLC/MS) has been described for the determination of a variety of methylene dioxyphenyl insecticide synergists. Particular focus was placed on chromatographic aspects of the principal synergist, piperonyl butoxide, in relation to its trace impurities, determination in formulations, metabolism, residues, and stability. 相似文献
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Determination of prostaglandins by gas-liquid chromatography 总被引:1,自引:0,他引:1
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Bi X Yang X Bostrom MP Bartusik D Ramaswamy S Fishbein KW Spencer RG Camacho NP 《Analytical and bioanalytical chemistry》2007,387(5):1601-1612
Assessment of subtle changes in proteoglycan (PG) and collagen, the primary macromolecular components of cartilage, which
is critical for diagnosis of the early stages of osteoarthritis (OA), has so far remained a challenge. In this study we induced
osteoarthritic cartilage changes in a rabbit model by ligament transection and medial meniscectomy and monitored disease progression
by infrared fiber optic probe (IFOP) spectroscopy, Fourier transform infrared imaging spectroscopy (FT-IRIS), and magnetic
resonance imaging (MRI) microscopy. IFOP studies combined with chemometric partial least-squares analysis enabled us to monitor
progressive cartilage surface changes from two to twelve weeks post-surgery. FT-IRIS studies of histological sections of femoral
condyle cartilage revealed that compared with control cartilage the OA cartilage had significantly reduced PG content 2 and
4 weeks post-surgery, collagen fibril orientation changes 2 and 4 weeks post-surgery, and changes in collagen integrity 2
and 10 weeks post-surgery, but no significant changes in collagen content at any time. MR microscopy studies revealed reduced
fixed charge density (FCD), indicative of reduced PG content, in the OA cartilage, compared with controls, 4 weeks post-surgery.
A non-significant trend toward higher apparent MT exchange rate, km, was also found in the OA cartilage at this time point, suggesting changes in collagen structural features. These two MR
findings for FCD and km parallel the FT-IRIS findings of reduced PG content and altered collagen integrity, respectively. MR microscopy studies of
the cartilage at the 12-week time point also found a trend toward longer T
2 values and reduced anisotropy in the deep zone of the OA cartilage, consistent with increased hydration and less ordered
collagen. These studies reveal that FT-IRIS and MR microscopy provide complementary data on compositional changes in articular
cartilage in the early stages of osteoarthritic degradation. 相似文献
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DJ Smith KW Ledingham RP Singhal T McCanny P Graham HS Kilic P Tzallas C Kosmidis AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1366-1373
With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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X Fang KW Ledingham P Graham DJ Smith T McCanny RP Singhal AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1390-1397
The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd. 相似文献