Sentence examples for proved difficult to demonstrate from inspiring English sources

Despite extensive research, however, it has proved difficult to demonstrate in nonhuman animals.

Although no one is suggesting that the first compartment had to be composed of phospholipids arranged in a bilayer, it has proved difficult to demonstrate exactly how a continued flow of genetic and/or metabolic precursors gained entry into the available abiotically generated amphiphiles.

In human cells, however, it is not clear that p14ARF levels are affected by or contribute significantly to senescence [62], [63] and it has proved difficult to demonstrate that ARF is subject to regulation by PcG complexes [27], [35], [64], [65].

This pathway is used for the transmission of head-direction information (Vann & Aggleton, 2004), though even here it has often proved difficult to demonstrate a close coupling between activity in the head-direction system and spatial learning (Dudchenko et al., 2005; Vann, 2005).

Such differences would be of great interest, but have proven difficult to demonstrate robustly [23].

Antigen-driven T cells responses have proven difficult to demonstrate.

Despite being a longstanding point of discussion, however, this idea has proven difficult to demonstrate empirically.

Moreover, having a small sample pool may prove difficult to demonstrate the validity of the findings [ 16].

Although sexual swellings have been proposed to reliably indicate female quality [ 29, 30], this has long proven difficult to demonstrate [ 31, 32].

It has, however, proven difficult to demonstrate the expression of eNOS protein in isolated human or murine platelets (rev. in (11).

It has thus proven difficult to demonstrate spatial variability in tephra leachate compositions from these datasets and, consequently, to unambiguously relate that variability to volcanic and/or depositional factors.