A number of features of the research design and analyses imposed challenges to making causal claims about this relationship, including the fact that the data (2007 Trends in International Mathematics and Science Study) were cross-sectional and observational.
"The secreting of objects in rectal or genital areas becomes in this situation an imposing challenge to nerves and agility," Judge Frankel wrote.
As the lowest-ranked of the 32 nations in the field, North Korea faces an imposing challenge to become one of two teams advancing from the so-called Group of Death, which also includes Brazil, a five-time champion; Portugal, a 2006 semifinalist; and the Ivory Coast, an African power led by one of the world's best forwards, Didier Drogba.
This situation also imposes challenges to testing CLT as a theory.
However, the behaviors of two-phase heat transfer fluids impose challenges to simulating and developing process control schemes.
However, the long piston stroke length, high operating frequency and system nonlinearity impose challenges to precise piston motion control.
When simulating the geothermal convection with phase change phenomena, this imposes challenges to the numerical models.
The fluctuating and stochastic characteristics of wind power output impose challenges to supply adequacy in power systems, while the weak ability of wind turbines to mitigate and ride through grid disturbances imposes challenges to operation stability in a power system.
This imposes challenges to experimentalists, and compromises have to be made to maximize the beam density after deceleration.
Additionally, national variations in citizenship legislation impose challenges to the aim of mapping historical patterns of Olympic migration.
On the other hand, the increasing penetration of renewable energy sources as well as the popularization of plug-in EVs will introduce significant uncertainties, and impose challenges to the optimal operation of distribution systems.
