Unfair Priority for HCC: A Problem Whose Ideal Solution Remains Unsolved

Unfair priority for HCC: A problem whose ideal solution remains unsolved.

Since the inception of the model for end-stage liver disease (MELD) liver transplant allocation system in 2002, it has been recognized that some diseases exist for which mortality risk is not adequately measured by MELD score. For this reason patients with hepatocellular carcinoma (HCC) have been assigned an exception MELD score. In this issue of AJT (1), Washburn and colleagues attempted to de...

The symbol grounding problem ... remains unsolved

Homologous chromosome pairing remains an unsolved problem: a test of a popular hypothesis utilizing maize meiosis.

A recently proposed and popular model for the mechanism of meiotic homologue pairing relies on prior association of nonhomologous chromosome arms of most similar length. According to this model, the diploid complement is organized into two genomic linear chains, each containing the various heterologues in the same sequence. At meiosis, then, appression of the two genomic chains could presumably...

Pigeons and the Ambiguous-Cue Problem: A Riddle that Remains Unsolved

The ambiguous-cue task is composed of two-choice simultaneous discriminations involving three stimuli: positive (P), ambiguous (A), and negative (N). Two different trial types are presented: PA and NA. The ambiguous cue (A) served as an S- in PA trials, but as an S+ in NA trials. When using this procedure, it is typical to observe a less accurate performance in PA trials than in NA trials. This...

Correcting for 16S rRNA gene copy numbers in microbiome surveys remains an unsolved problem

The 16S ribosomal RNA gene is the most widely used marker gene in microbial ecology. Counts of 16S sequence variants, often in PCR amplicons, are used to estimate proportions of bacterial and archaeal taxa in microbial communities. Because different organisms contain different 16S gene copy numbers (GCNs), sequence variant counts are biased towards clades with greater GCNs. Several tools have r...