Controlling the uncontrolled: Are there incidental experimenter effects on physiologic responding?

The degree to which experimenters shape participant behavior has long been of interest in experimental social science research. Here, we extend this question to the domain of peripheral psychophysiology, where experimenters often have direct, physical contact with participants, yet researchers do not consistently test for their influence. We describe analytic tools for examining experimenter effects in peripheral physiology. Using these tools, we investigate nine data sets totaling 1,341 participants and 160 experimenters across different roles (e.g., lead research assistants, evaluators, confederates) to demonstrate how researchers can test for experimenter effects in participant autonomic nervous system activity during baseline recordings and reactivity to study tasks. Our results showed (a) little to no significant variance in participants' physiological reactivity due to their experimenters, and (b) little to no evidence that three characteristics of experimenters that are well known to shape interpersonal interactions-status (using five studies with 682 total participants), gender (using two studies with 359 total participants), and race (in two studies with 554 total participants)-influenced participants' physiology. We highlight several reasons that experimenter effects in physiological data are still cause for concern, including the fact that experimenters in these studies were already restricted on a number of characteristics (e.g., age, education). We present recommendations for examining and reducing experimenter effects in physiological data and discuss implications for replication

Nitrogen Mineralization from Root Residues of Subterranean Clover and Lucerne

To understand why crops grown in the first or second year after lucerne (Medicago sativa L.) yielded less than crops grown after subterranean clover (Trifolium subterraneum L.) despite greater nitrogen (N) fixation by the lucerne, we studied the N mineralization patterns of their root residues in soil incubation assays. Fine roots of both species produced more mineral N than the control soil with no root residues. In contrast, coarse roots mineralized less N than the control soil. These differences in N mineralization were not explained by the physical size and therefore surface area differences between fine and coarse roots. Rather, the differences in N mineralization were explained by differences in the carbon to nitrogen ratio (C:N) of fine and coarse roots. Fine roots of both species had a C:N of about 11, while the C:N of coarse roots ranged from 28 to 37. Empirical evidence suggests that a mineralization / immobilization threshold occurs at a C:N of 20 to 30, and these results are in accordance with this interpretation. However, subterranean clover had mainly fine roots giving a weighted average C:N of 19 for the whole root system, while lucerne had mainly coarse roots giving an average C:N of 26, suggesting that root residues of subterranean clover result in a net mineralization of N while lucerne roots cause a net immobilization of N

Advanced-stage cervix cancer: rapid tumour growth rather than late diagnosis

Either diagnostic delay or tumour biology are possible factors governing the degree of spread at diagnosis of cervical cancer. To try to identify the most important parameter contributing to advanced stage, the duration of symptoms were recorded from patients scheduled for radiotherapy (n = 141) or radical hysterectomy (n = 36). In 146 cases tumour proliferation rates were evaluated following in vivo labelling with the DNA precursor BrdUrd. For symptomatic patients there was no association between duration of symptoms and stage at presentation. There was a significant trend for patients with increasing tumour stage to have more rapidly proliferating tumours with higher mean labelling index (LI) measurements (P = 0.001) and a shorter mean potential doubling time (Tpot) (P = 0.023). Socio economic deprivation may be associated with shorter Tpot values. The conclusion from this data is that stage at diagnosis is more dependent on the biological behaviour of the tumour, as expressed by proliferation rates, than delay in presentation. © 2000 Cancer Research Campaig

Meeting Highlights of the 11th Annual Scientific Sessions of the Society for Cardiovascular Magnetic Resonance, Los Angeles, February 1–3, 2008

This paper features the most interesting presentations and discussions of the 2008 Annual Sessions of the Society for Cardiovascular Magnetic Resonance, which were held in Los Angeles from February 1 to 3, 2008

Polychromatic gap solitons and breathers in nonlinear waveguide arrays

We predict the spatial localization of multiple wavelength components in the form of stationary polychromatic gap solitons and dynamic multi-gap breathers, and observe experimentally tunable spatio-spectral trapping of supercontinuum radiation in nonlinear periodic photonic structures