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71.
This work deals with tests of the RCA C-70045 photomultipliers in a delayed coincidence apparatus. Illuminating the photocathode of the photomultiplier with constant height light pulses, resolving time measurements are performed. Prompt resolution curves are then measured using two photomultipliers of this type associated with two plastic scintillators. A time resolution of 1.85×1O-10s (f.w. h.m.) was obtained with Co60. 相似文献
72.
The asymptotic physical optic (APO) formulation for the scattered fields from a paraboloid has been found to give results which agree with experiment except in the rear region. The disagreement here is due to the inexact nature of the assumed geometric optic (GO) edge currents as used in APO. A means of correcting for the error in these currents is given here by appealing to the equivalent half plane problem of Sommerfeld. This correction method is called CAPO ("corrected" APO). The resulting corrected diffraction coefficients are shown to be numerically indistinguishable from those of GTD. Comparisons of predictedE - andH -plane field patterns, based on these corrected results, with measurements in the rear region are given and shown to be quite acceptable; the corrections having negligible effect elsewhere. The "static" nature (in the sense of implicitly ignoring slope diffraction) of APO, GTD, and CAPO is discussed. 相似文献
73.
The ELM erythroleukemia is novel in that long-term survival of leukemic cells in culture (ELM-D cells) is dependent on contact with a bone marrow-derived stromal feeder cell layer. However, a number of stroma-independent (ELM-I) mutants that vary in their ability to differentiate in vitro in response to erythropoietin and interleukin-3 have been derived. We have attempted to define the genetic changes responsible for these different phenotypes. At the p53 locus in the primary leukemic cells, one copy of the gene has been lost whereas the other contains an 18-bp depletion, implicating its mutation as an early step in the development of the leukemia. Changes in ets gene expression have also been found. The Fli-1 gene region is rearranged in the primary tumor because of the insertion of a retrovirus inserted upstream of one Fli-1 allele, but this does not result in Fli-1 gene activation in any of the ELM-D or ELM-I cell lines except one. It seems significant that this line is the only one to have lost the ability to differentiate in response to erythropoietin. In addition, up-regulation of erg is associated with stromal cell-independent growth, since all ELM-I mutants have moderate levels of erg mRNA, whereas only low or undetectable levels are found in primary leukemic cells in vivo or in ELM-D cells in vitro. This up-regulation of erg mRNA seems to be important for stromal cell-independent growth, since ELM-D cells show elevated expression of the erg gene after separation from stromal cells. This seems to be made permanent in ELM-I mutants, since they do not down-regulate erg mRNA when grown in contact with stromal cells. We therefore propose that ets family members regulate both the survival and differentiation of erythroid cells. 相似文献
74.
Li Meng Verena Coleman Yu Zhao Mario Ost Anja Voigt Annelies Bunschoten Jaap Keijer Katja Teerds Susanne Klaus 《International journal of molecular sciences》2021,22(7)
In the present investigation, we examined whether a change in whole body energy fluxes could affect ovarian follicular development, employing mice ectopically expressing uncoupling protein 1 in skeletal muscle (UCP1-TG). Female UCP1-TG and wild-type (WT) mice were dissected at the age of 12 weeks. Energy intake and expenditure, activity, body weight and length, and body composition were measured. Plasma insulin, glucose, leptin, plasma fibroblast growth factor 21 (FGF21) and plasma insulin-like growth factor 1 (IGF1) levels were analyzed and ovarian follicle and corpus luteum numbers were counted. IGF1 signaling was analyzed by immunohistochemical staining for the activation of insulin receptor substrate 1/2 (IRS1/2) and AKT. UCP1-TG female mice had increased energy expenditure, reduced body size, maintained adiposity, and decreased IGF1 concentrations compared to their WT littermates, while preantral and antral follicle numbers were reduced by 40% and 60%, respectively. Corpora lutea were absent in 40% of the ovaries of UCP1-TG mice. Phospho-IRS1, phospho-AKT -Ser473 and -Thr308 immunostaining was present in the granulosa cells of antral follicles in WT ovaries, but faint to absent in the antral follicles of UCP1-TG mice. In conclusion, the reduction in circulating IGF1 levels due to the ectopic expression of UCP1 is associated with reduced immunostaining of the IRS1-PI3/AKT pathway, which may negatively affect ovarian follicle development and ovulation. 相似文献
75.
Thomas van Groen Dr. Inga Kadish Dr. Katja Wiesehan Dr. Susanne A. Funke Dr. Dieter Willbold Prof. Dr. 《ChemMedChem》2009,4(2):276-282
Plaque visualisation : We identified three different D ‐enantiomeric peptides that bind to Alzheimer's amyloid β (Aβ1‐42). As there is currently no definitive pre‐mortem diagnosis for Alzheimer's disease, we investigated the peptides' suitability as molecular probes for in vivo imaging in transgenic mouse models.
76.
This work identifies electrical field-induced concentration polarization (CP) as a key physical mechanism influencing the retention behavior of charged analytes in electrochromatography with fixed beds of porous adsorbent particles. Due to an insufficient screening of intraparticle surface charge, under most general conditions the porous (permeable) particles become charge-selective. CP is caused by coupled mass and charge transport normal to the charge-selective external surface of the permeable particles, which leads to concentration gradients of ionic species in the adjoining interparticle electrolyte solution. Cation-exchange (cation-selective) particles were employed to investigate the influence of applied voltage on the retention factor of counterionic, i.e., positively charged, analytes. It is demonstrated by macroscopic retention data and microscopic studies resolving the CP phenomenon on a particle scale that the dependence of CP on electrical field and mobile-phase ionic strengths is directly reflected in concomitant changes of analyte retention. The CP zones that develop at the interface between interparticle and intraparticle pore space are recognized by charged, but not electroneutral analytes while entering or leaving the particles. The intensity of these convective-diffusion boundary layers (CP zones) depends on the applied field strength and charge selectivity of a particle. Thus, it is the charge-selective transport between the interparticle and intraparticle pore space in packed beds that prevails under typical experimental conditions in electrochromatography and that forms the physical basis for a general electrical field dependence of the retention factor of charged analytes. 相似文献
77.
For the analysis of the 16 PAH (EFSA-PAH), which are classified as priority for different food groups by the Scientific Committee
on Food (SCF) and the Joint FAO/WHO Experts Committee on Food Additives (JECFA) in tea, a sensitive analytical Fast-GC/HRMS
method was used. The sample preparation included accelerated solvent extraction (ASE) and the highly automated clean up steps,
gel permeation chromatography and solid phase extraction. The analytical parameters, limit of detection (0.01–0.02 μg/kg)
and limit of quantification (0.03–0.06 μg/kg), were determined. The repeatability (RSD, n = 3) of different PAH in fruit tea ranged from 0.1 to 11%. It was observed that the total contents of the 16 PAH in tea samples
ranged from 14 to 2,662 μg/kg. The analysed tea samples showed an increasing presence of PAH in the following order: herbal
and fruit tea (n = 7) < black tea (n = 11) < green tea (n = 11) < white tea (n = 3) < mate-tea (n = 8). The correlation coefficient (R) between BaP and the sum of the 16 EFSA-PAH was established considering the contamination
amount in all the 40 tea samples analysed. 相似文献
78.
Beate Kettlitz Gabriele Scholz Viviane Theurillat Jrg Cselovszky Neil R. Buck Sue O Hagan Eva Mavromichali Katja Ahrens Karin Kraehenbuehl Gabriella Scozzi Markus Weck Claudia Vinci Marta Sobieraj Richard H. Stadler 《Comprehensive Reviews in Food Science and Food Safety》2019,18(3):738-752
The acceptance of many foods is related to traditional cooking practices, which create taste and texture and are important to digestibility, preservation, and the reduction of foodborne illnesses. A wide range of compounds are formed during the cooking of foods, a number of these have been shown to lead to adverse effects in classical toxicological models and are known as food processing contaminants (FPC). It is essential that the presence and effects of such compounds alone and in combination within the diet are understood such that proportionate risk management measures can be developed, while taking a holistic view across the whole value chain. Furan and alkylfurans (principally 2‐ and 3‐methylfuran) are highly volatile FPC, which are formed in a wide range of foods at low amounts. The focus of research to‐date has been on those foods, which have been identified to be most consequential in terms of being sources of exposure, namely jarred and canned foods for infants and young children (meals and drinks) and coffee (roast and ground, soluble). This report presents (i) new industry data on the occurrence of furan and methylfurans in selected food categories following previous coffee studies, (ii) the most salient parameters that impact furan formation, and (iii) aspects of importance for the risk assessment. 相似文献
79.
Dr. Maja Marušič Dr. Judith Schlagnitweit Prof. Dr. Katja Petzold 《Chembiochem : a European journal of chemical biology》2019,20(21):2685-2710
An ever-increasing number of functional RNAs require a mechanistic understanding. RNA function relies on changes in its structure, so-called dynamics. To reveal dynamic processes and higher energy structures, new NMR methods have been developed to elucidate these dynamics in RNA with atomic resolution. In this Review, we provide an introduction to dynamics novices and an overview of methods that access most dynamic timescales, from picoseconds to hours. Examples are provided as well as insight into theory, data acquisition and analysis for these different methods. Using this broad spectrum of methodology, unprecedented detail and invisible structures have been obtained and are reviewed here. RNA, though often more complicated and therefore neglected, also provides a great system to study structural changes, as these RNA structural changes are more easily defined—Lego like—than in proteins, hence the numerous revelations of RNA excited states. 相似文献
80.
Crispie F Alonso-Gómez M O'Loughlin C Klostermann K Flynn J Arkins S Meaney W Paul Ross R Hill C 《The Journal of dairy research》2008,75(3):374-384
In the accompanying article, we demonstrated that a live culture of Lactococcus lactis compares favourably with antibiotics for treatment of bovine mastitis in two initial field trials. In an effort to explain the mechanism involved, this study investigated the effect of culture administration on the local immune response. In this respect we initially observed that infusion of the live culture Lactococcus lactis stimulated substantial recruitment of polymorphonucleocytes (PMN) and lymphocytes to the udder. For instance, in one assay, quarters infused with the probiotic experienced a dramatic increase (approximately 20,000-fold) in neutrophils over the first 48-h period from an average value of 83.6 cells/ml pre-treatment to 1.78 x 106 cells/ml 48 h post-infusion. Levels of the acute phase proteins haptaglobin and milk amyloid A were also elevated significantly in comparison with controls following infusion of the culture. The results of flow cytometric assays also demonstrated that while infusion of a live lactococcal culture led to an enhanced recruitment of PMN to the udder (from 1.85 x 104 cells/ml pre-infusion to 1.45 x 106 cells/ml 24 h post-infusion) cell-free supernatant from the same culture was not able to do so, indicating that live Lc. lactis can specifically trigger the mammary immune response to elicit PMN accumulation. These results suggest that the mechanism responsible for this probiotic treatment of mastitis is associated with stimulation of the host intramammary immune system. 相似文献