18,379 research outputs found
Query Complexity of Derivative-Free Optimization
This paper provides lower bounds on the convergence rate of Derivative Free
Optimization (DFO) with noisy function evaluations, exposing a fundamental and
unavoidable gap between the performance of algorithms with access to gradients
and those with access to only function evaluations. However, there are
situations in which DFO is unavoidable, and for such situations we propose a
new DFO algorithm that is proved to be near optimal for the class of strongly
convex objective functions. A distinctive feature of the algorithm is that it
uses only Boolean-valued function comparisons, rather than function
evaluations. This makes the algorithm useful in an even wider range of
applications, such as optimization based on paired comparisons from human
subjects, for example. We also show that regardless of whether DFO is based on
noisy function evaluations or Boolean-valued function comparisons, the
convergence rate is the same
Chelator-facilitated removal of iron from transferrin: Relevance to combined chelation therapy
Current iron chelation therapy consists primarily of DFO (desferrioxamine),
which has to be administered via intravenous infusion,
together with deferiprone and deferasirox, which are orally-active
chelators. These chelators, although effective at decreasing the
iron load, are associated with a number of side effects. Grady
suggested that the combined administration of a smaller bidentate
chelator and a larger hexadentate chelator, such as DFO, would
result in greater iron removal than either chelator alone [Grady,
Bardoukas and Giardina (1998) Blood 92, 16b]. This in turn
could lead to a decrease in the chelator dose required. To test
this hypothesis, the rate of iron transfer from a range of bidentate
HPO (hydroxypyridin-4-one) chelators to DFO was monitored.
Spectroscopic methods were utilized to monitor the decrease in
the concentration of the FeâHPO complex. Having established
that the shuttling of iron from the bidentate chelator to DFO
does occur under clinically relevant concentrations of chelator,
studies were undertaken to evaluate whether this mechanism of
transfer would apply to iron removal from transferrin. Again, the
simultaneous presence of both a bidentate chelator and DFO was
found to enhance the rate of iron chelation from transferrin at
clinically relevant chelator levels. Deferiprone was found to be
particularly effective at âshuttlingâ iron from transferrin to DFO,
probably as a result of its small size and relative low affinity for
iron compared with other analogous HPO chelators
Increase of reactive oxygen species by desferrioxamine during experimental Chagas' disease.
Oxidative stress is common in inflammatory processes associated with many diseases including Chagas' disease. The aim of the present study was to evaluate, in a murine model, biomarkers of oxidative stress together with components of the antioxidant system in order to provide an overview of the mechanism of action of the iron chelator desferrioxamine (DFO). The study population comprised 48 male Swiss mice, half of which were treated daily by intraperitoneal injection of DFO over a 35-day period, while half were administered sterile water in a similar manner. On the 14th day of the experiment, 12 DFO-treated mice and an equal number of untreated mice were experimentally infected with Trypanosoma cruzi. Serum concentrations of nitric oxide and superoxide dismutase and hepatic levels of total glutathione, thiobarbituric acid reactive species and protein carbonyl, were determined on days 0, 7, 14 and 21 post-infection. The results obtained revealed that DFO enhances antioxidant activity in the host but also increases oxidative stress, indicating that the mode of action of the drug involves a positive contribution to the host together with an effect that is not beneficial to the parasite
Supply Management and Price Ceilings on Production Quota Values: Future or Folly?
This paper examines and contrasts two policies instituted by the Dairy Farmers of Ontario (DFO) in reaction to the escalation of production quota values on the provincial quota exchange, which regulates the transfer of dairy production quota among producers in the province of Ontario.Supply Management, DFO, Production Quota, Provincial Quota Exchange, Price ceiling, Progressive Transfer Assessment, Agricultural and Food Policy, Livestock Production/Industries, Production Economics,
Understanding the Impact of Meteorological Spatiotemporal Variability on Distant Focusing Overpressure Risk
Since the 1950s, the amplification of blast energy from explosions has been understood to be a significant hazard to public safety at launch ranges. Historically, the risk assessment of the Distant Focusing Overpressure (DFO) hazard started with a single temperature and wind profile (e.g., a radiosonde launch) as input to acoustic 1-D ray tracing models. By analyzing rays propagation and performing ray tracing, population centers under high DFO risk can be identified. Although this method is useful, less is known about how the blast waves can be focused when the spatiotemporal variability of the input profiles are considered. In summary, this work aims to consider how realistic atmospheric boundary layer variability (e.g., turbulence, land-surface contrasts) may affect blast waves propagation and focusing and, as a result, DFO risk assessment results
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