Darryl Dixon - Academia.edu (original) (raw)

Papers by Darryl Dixon

Nondestructive Testing and Evaluation, 2007

A surface crack, close to a small, well-defined heated spot, impedes lateral heat flow and produc... more A surface crack, close to a small, well-defined heated spot, impedes lateral heat flow and produces alterations in the shape of the thermal spot image that can be monitored by thermography. Spot heating has been achieved using both cw and pulsed laser beam illumination on stainless steel and titanium samples and the technique has been found to be successful for

Hierarchical control of cognitive processes was studied by examining the relationship between seq... more Hierarchical control of cognitive processes was studied by examining the relationship between sequenceand task-level processing in the performance of explicit, memorized task sequences. In 4 experiments, switch costs in task-switching performance were perturbed by sequence initiation times that varied with sequence complexity, preparation time, and type of sequence transition (repetition or switch). Hierarchical control was inferred from these sequence initiation time effects and the recurrent finding of no switch cost at the first serial position across sequences, the point at which sequence-level processes are likely active in maintaining or instantiating a hierarchical control structure in working memory. These findings resonate with past research on motor programs and serial memory and provide new insights into the concepts of task set and control.

Endogenous retroviruses (ERVs) are the proviral phase of exogenous retroviruses that become integ... more Endogenous retroviruses (ERVs) are the proviral phase of exogenous retroviruses that become integrated into a host germ line. They can play an important role in the host genome. Bioinformatic tools have been used to detect ERVs in several vertebrates, primarily primates and rodents. Less information is available regarding ERVs in other mammalian groups, and the source of this information is basically experimental. We analyzed the genome of the cow (Bos taurus) using three different methods. A BLAST-based method detected 928 possible ERVs, LTR_STRUC detected 4,487 elements flanked by long terminal repeats (LTRs), and Retrotector detected 9,698 ERVs. The ERVs were not homogeneously distributed across chromosomes; the number of ERVs was positively correlated with chromosomal size and negatively correlated with chromosomal GC content. The bovine ERVs (BoERVs) were classified into 24 putative families, with 20 of them not previously described. One of these new families, BoERV1, was the most abundant family and appeared to be specific to ruminants. An analysis of representatives of ERV families from rodents, primates, and ruminants showed a phylogenetic relationship following their hosts' relationships. This study demonstrates the importance of using multiple methods when trying to identify new ERVs and shows that the number of bovine ERV families is not as limited as previously thought.

Antimicrobial Agents and Chemotherapy, 2002

Nature, 2004

The goal of the International HapMap Project is to determine the common patterns of DNA sequence ... more The goal of the International HapMap Project is to determine the common patterns of DNA sequence variation in the human genome and to make this information freely available in the public domain. An international consortium is developing a map of these patterns across the genome by determining the genotypes of one million or more sequence variants, their frequencies and the degree of association between them, in DNA samples from populations with ancestry from parts of Africa, Asia and Europe. The HapMap will allow the discovery of sequence variants that affect common disease, will facilitate development of diagnostic tools, and will enhance our ability to choose targets for therapeutic intervention.

Nature, 2003

The goal of the International HapMap Project is to determine the common patterns of DNA sequence ... more The goal of the International HapMap Project is to determine the common patterns of DNA sequence variation in the human genome and to make this information freely available in the public domain. An international consortium is developing a map of these patterns across the genome by determining the genotypes of one million or more sequence variants, their frequencies and the degree of association between them, in DNA samples from populations with ancestry from parts of Africa, Asia and Europe. The HapMap will allow the discovery of sequence variants that affect common disease, will facilitate development of diagnostic tools, and will enhance our ability to choose targets for therapeutic intervention.

Chemistry-a European Journal, 2009

Attempts to anchor metal complexes to supports to obtain highly uniform catalytic sites have ofte... more Attempts to anchor metal complexes to supports to obtain highly uniform catalytic sites have often been hindered by the non-uniformity of the support. Here we report the behavior of a catalyst with highly uniform active sites synthesized from Rh(C2H4)2(CH3COCHCOCH3) and a crystalline support, dealuminated Y zeolite. The supported catalyst consists of frameworkbound bis-ethylene Rh sites. Treatment of this supported metal complex catalyst with acetylene initiates the catalytic acetylene cyclotrimerization to benzene. We report characterization of the catalyst by NMR and EXAFS spectroscopies complemented by density functional theory (DFT), having determined structures of the observable supported complexes and elucidated the catalytic cycle theoretically, including transition states.

Nondestructive Testing and Evaluation, 2007

A surface crack, close to a small, well-defined heated spot, impedes lateral heat flow and produc... more A surface crack, close to a small, well-defined heated spot, impedes lateral heat flow and produces alterations in the shape of the thermal spot image that can be monitored by thermography. Spot heating has been achieved using both cw and pulsed laser beam illumination on stainless steel and titanium samples and the technique has been found to be successful for

Hierarchical control of cognitive processes was studied by examining the relationship between seq... more Hierarchical control of cognitive processes was studied by examining the relationship between sequenceand task-level processing in the performance of explicit, memorized task sequences. In 4 experiments, switch costs in task-switching performance were perturbed by sequence initiation times that varied with sequence complexity, preparation time, and type of sequence transition (repetition or switch). Hierarchical control was inferred from these sequence initiation time effects and the recurrent finding of no switch cost at the first serial position across sequences, the point at which sequence-level processes are likely active in maintaining or instantiating a hierarchical control structure in working memory. These findings resonate with past research on motor programs and serial memory and provide new insights into the concepts of task set and control.

Endogenous retroviruses (ERVs) are the proviral phase of exogenous retroviruses that become integ... more Endogenous retroviruses (ERVs) are the proviral phase of exogenous retroviruses that become integrated into a host germ line. They can play an important role in the host genome. Bioinformatic tools have been used to detect ERVs in several vertebrates, primarily primates and rodents. Less information is available regarding ERVs in other mammalian groups, and the source of this information is basically experimental. We analyzed the genome of the cow (Bos taurus) using three different methods. A BLAST-based method detected 928 possible ERVs, LTR_STRUC detected 4,487 elements flanked by long terminal repeats (LTRs), and Retrotector detected 9,698 ERVs. The ERVs were not homogeneously distributed across chromosomes; the number of ERVs was positively correlated with chromosomal size and negatively correlated with chromosomal GC content. The bovine ERVs (BoERVs) were classified into 24 putative families, with 20 of them not previously described. One of these new families, BoERV1, was the most abundant family and appeared to be specific to ruminants. An analysis of representatives of ERV families from rodents, primates, and ruminants showed a phylogenetic relationship following their hosts' relationships. This study demonstrates the importance of using multiple methods when trying to identify new ERVs and shows that the number of bovine ERV families is not as limited as previously thought.

Antimicrobial Agents and Chemotherapy, 2002

Nature, 2004

The goal of the International HapMap Project is to determine the common patterns of DNA sequence ... more The goal of the International HapMap Project is to determine the common patterns of DNA sequence variation in the human genome and to make this information freely available in the public domain. An international consortium is developing a map of these patterns across the genome by determining the genotypes of one million or more sequence variants, their frequencies and the degree of association between them, in DNA samples from populations with ancestry from parts of Africa, Asia and Europe. The HapMap will allow the discovery of sequence variants that affect common disease, will facilitate development of diagnostic tools, and will enhance our ability to choose targets for therapeutic intervention.

Nature, 2003

The goal of the International HapMap Project is to determine the common patterns of DNA sequence ... more The goal of the International HapMap Project is to determine the common patterns of DNA sequence variation in the human genome and to make this information freely available in the public domain. An international consortium is developing a map of these patterns across the genome by determining the genotypes of one million or more sequence variants, their frequencies and the degree of association between them, in DNA samples from populations with ancestry from parts of Africa, Asia and Europe. The HapMap will allow the discovery of sequence variants that affect common disease, will facilitate development of diagnostic tools, and will enhance our ability to choose targets for therapeutic intervention.

Chemistry-a European Journal, 2009

Attempts to anchor metal complexes to supports to obtain highly uniform catalytic sites have ofte... more Attempts to anchor metal complexes to supports to obtain highly uniform catalytic sites have often been hindered by the non-uniformity of the support. Here we report the behavior of a catalyst with highly uniform active sites synthesized from Rh(C2H4)2(CH3COCHCOCH3) and a crystalline support, dealuminated Y zeolite. The supported catalyst consists of frameworkbound bis-ethylene Rh sites. Treatment of this supported metal complex catalyst with acetylene initiates the catalytic acetylene cyclotrimerization to benzene. We report characterization of the catalyst by NMR and EXAFS spectroscopies complemented by density functional theory (DFT), having determined structures of the observable supported complexes and elucidated the catalytic cycle theoretically, including transition states.