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301.
The effects of atorvastatin and simvastatin on hydroxy methylglutary (HMG)-CoA reductase activity and mRNA abundance were
studied in guinea pigs randomized to three groups: untreated animals and those treated with 20 mg/kg of atorvastatin or simvastatin.
Guinea pigs were fasted for 0, 6, 12, or 18 h in an attempt to remove the drug from their systems. Reductase activity and
mRNA levels were analyzed after each time point. Reductase inhibitor treatment resulted in 50–60% lower cholesterol concentrations
compared to untreated guinea pigs (P<0.0001), while plasma triacylglycerol (TAG) concentrations did not differ among groups. Plasma cholesterol and TAG were 50–70%
lower after 18 h fasting in the three groups (P<0.001). In the nonfasting state, simvastatin and atorvastatin treatment did not affect HMG-CoA reductase activity compared
with untreated animals. However, after 6 h of fasting, simvastatin-treated guinea pigs had higher HMG-CoA reductase activity
than untreated animals (P<0.01), suggesting that the drug had been removed from the enzyme. In contrast, atorvastatin-treated guinea pigs maintained
low enzyme activity even after 18 h of fasting. Further, HMG-CoA reductase mRNA abundance was increased by sevenfold after
atorvastatin treatment and by twofold after simvastatin treatment (P<0.01). These results suggest that sinvastatin and atorvastatin
have different half-lives, which may affect HMG-CoA reductase mRNA levels. The increase in reductase activity by simvastatin
during fasting could be related to an effect of this statin in stabilizing the enzyme. In contrast, atorvastatin, possibly
due to its longer half-life, prolonged inhibition of HMG-CoA reductase activity and resulted in a greater increase in mRNA
synthesis. 相似文献
302.
Yliès Falcone Laurent Mounier Jean-Claude Fernandez Jean-Luc Richier 《Formal Methods in System Design》2011,38(3):223-262
Runtime enforcement is a powerful technique to ensure that a program will respect a given set of properties. We extend previous
work on this topic in several directions. Firstly, we propose a generic notion of enforcement monitors based on a memory device
and finite sets of control states and enforcement operations. Moreover, we specify their enforcement abilities w.r.t. the
general Safety-Progress classification of properties. Furthermore, we propose a systematic technique to produce a monitor from the automaton recognizing a given safety, guarantee, obligation or response property.
Finally, we show that this notion of enforcement monitors is more amenable to implementation and encompasses previous runtime
enforcement mechanisms. 相似文献
303.
304.
305.
A. Fahim M. Fernandez 《The International Journal of Advanced Manufacturing Technology》1988,3(4):63-72
Current robot designs utilise a fixed counterweight approach to balance the robot arm. The different links are generally equipped
with counterweights so as to increase their load carrying capacity for a given link actuating motor. The counterweights are
either designed to balance the link alone, in which case the torque due to the load is carried by the link actuating motor,
or is designed to balance the link plus a portion of the maximum load intended. While this fixed counterweight approach is
adequate for the majority of industrial and manufacturing applications, it fails to provide adequate balancing for high performance
applications where large loads and high operating speeds are involved.
This paper describes an active counterbalancing system that provides advantageous balancing to the robot arm links throughout
the operation cycle, thus enhancing the load carrying capacity and the operation speed. A simplified dynamic analysis of a
robot arm equipped with this counterweight system is presented. The paper also presents the control scheme necessary for the
operation of the active counterweight. 相似文献
306.
307.
June Zhou Michael J. Keenan Sun Ok Fernandez‐Kim Paul J. Pistell Donald K. Ingram Bing Li Anne M. Raggio Li Shen Hanjie Zhang Kathleen L. McCutcheon Richard T. Tulley Marc R. Blackman Jeffrey N. Keller Roy J. Martin 《Molecular nutrition & food research》2013,57(11):2071-2074
Resistant starch (RS) is a dietary fiber that exerts multiple beneficial effects. The current study explored the effects of dietary RS on selected brain and behavioral functions in adult and aged rodents. Because glucokinase (GK) expression in hypothalamic arcuate nucleus and area postrema of the brainstem is important for brain glucose sensing, GK mRNA was measured by brain nuclei microdissection and PCR. Adult RS‐fed rats had a higher GK mRNA than controls in both brain nuclei, an indicator of improved brain glucose sensing. Next, we tested whether dietary RS improve selected behaviors in aged mice. RS‐fed aged mice exhibited (i) an increased eating responses to fasting, a behavioral indicator of improvement in aged brain glucose sensing; (ii) a longer latency to fall from an accelerating rotarod, a behavioral indicator of improved motor coordination; and (iii) a higher serum active glucagon‐like peptide‐1 (GLP‐1). Then, GLP‐1 receptor null (GLP‐1RKO) mice were used to test the role of GLP‐1 in brain glucose sensing, and they exhibited impaired eating responses to fasting. We conclude that in rodents (i) dietary RS improves two important indicators of brain function: glucose sensing and motor coordination, and (ii) GLP‐1 is important in the optimal feeding response to a fast. 相似文献
308.
309.
Specific rheological and electrical features of carbon nanotube dispersions in an epoxy matrix 总被引:1,自引:0,他引:1
M. Chapartegui N. Markaide S. Florez C. Elizetxea M. Fernandez A. Santamaría 《Composites Science and Technology》2010
The rheological analysis of epoxy pre-polymer/MWCNT dispersions indicates that a physical network is formed. This is destroyed with an imposed shear, giving a viscoplastic and shear thinning behavior. Such destruction is not reflected in dynamic viscoelastic experiments, due to the very rapid recovery of the MWCNT network in the pre-polymer matrix. This responds to the observed lower electrical than rheological percolation threshold. Electrical conductivity results fulfill electron hopping/tunnelling mechanism, which implies a tube–tube distance close to 5 nm. However, rheological percolation requires nanotubes should touch each other, since no polymer chains are implied in the network. 相似文献
310.
A series of experiments are described in which helium was released at a constant rate into a 1.5 m × 1.5 m × 0.75 m enclosure designed as a 1/4-scale model of a two-car garage. The purpose was to provide reference datasets for testing and validating computational fluid dynamics (CFD) models and to experimentally characterize the effects of a number of variables on the mixing behavior within an enclosure and the exchange of helium with the outside surroundings. Helium was used as a surrogate for hydrogen, and the total volume released was scaled as the amount that would be released by a typical hydrogen-fueled automobile with a full tank. Temporal profiles of helium were measured at seven vertical locations within the enclosure during and following 1-h and 4-h releases. Idealized vents in one wall sized to provide air exchange rates typical of actual garages were used. The effects of vent size, number, and location were investigated using three different vent combinations. The dependence on leak location was considered by releasing helium at three different points within the enclosure. 相似文献