Why does low intensity, long-day lighting promote growth in Petunia, Impatiens, and tomato?

Numerous reports demonstrate that low intensity, long-day (LD) lighting treatments can promote growth. However, there are conflicting suggestions as to the mechanisms involved. This study examines the responses of Petunia, Impatiens, and tomato to LD lighting treatments and concludes that no single mechanism can explain the growth promotion observed in each case. Petunia showed the most dramatic response to photoperiod; up to a doubling in dry weight (DW) as a result of increasing daylength from 8 h d–1 to 16 h d–1.This could be explained by an increase in specific leaf area (SLA) comparable to that seen with shading. At low photosynthetic photon flux densities (PPFD), the increased leaf area more than compensated for any loss in photosynthetic capacity per unit leaf area. In Petunia, the response may, in part, have also been due to changes in growth habit. Impatiens and tomato showed less dramatic increases in DW as a result of LD lighting, but no consistent effects on SLA or growth habit were observed. In tomato, increased growth was accompanied by increased chlorophyll content, but this had no significant effect on photosynthesis. In both species, increased growth may have been due to a direct effect of LD lighting on photosynthesis. This is contrary to the generally held view that light of approx. 3 – 4 μmol m–2 s–1 is unlikely to have any significant impact on net photosynthesis. Nevertheless, we show that the relationship between PPFD and net photosynthesis is non-linear at low light levels, and therefore low intensity LD lighting can offset respiration very efficiently. Furthermore, a small increase in photosynthesis will have a greater impact when ambient light levels are low

Letter from W. S. Langton

Letter concerning a report of the athletic department at Utah Agricultural College

Universal Cellular Automata and Class 4

Wolfram has provided a qualitative classification of cellular automata(CA) rules according to which, there exits a class of CA rules (called Class 4) which exhibit complex pattern formation and long-lived dynamical activity (long transients). These properties of Class 4 CA's has led to the conjecture that Class 4 rules are Universal Turing machines i.e. they are bases for computational universality. We describe an embedding of a ``small'' universal Turing machine due to Minsky, into a cellular automaton rule-table. This produces a collection of $(k=18,r=1)$ cellular automata, all of which are computationally universal. However, we observe that these rules are distributed amongst the various Wolfram classes. More precisely, we show that the identification of the Wolfram class depends crucially on the set of initial conditions used to simulate the given CA. This work, among others, indicates that a description of complex systems and information dynamics may need a new framework for non-equilibrium statistical mechanics.Comment: Latex, 10 pages, 5 figures uuencode

Looking back at the stare-in-the-crowd effect: Staring eyes do not capture attention in visual search

The stare-in-the crowd effect refers to the finding that a visual search for a target of staring eyes among averted- eyesdistractersismoreefficientthanthesearchforan averted-eyes target among staring distracters. This finding could indicate that staring eyes are prioritized in the processing of the search array so that attention is more likely to be directed to their location than to any other. However, visual search is a complex process, which not only depends upon the properties of the target, but also the similarity between the target of the search and the distractor items and between the distractor items themselves. Across five experiments, we show that the search asymmetry diagnostic of the stare- in-the-crowd effect is more likely to be the result of a failure to control for the similarity among distracting items between the two critical search conditions rather than any special attention-grabbing property of staring gazes. Our results suggest that, contrary to results reported in the literature, staring gazes are not prioritized by attention in visual search

Parametric ordering of complex systems

Cellular automata (CA) dynamics are ordered in terms of two global parameters, computable {\sl a priori} from the description of rules. While one of them (activity) has been used before, the second one is new; it estimates the average sensitivity of rules to small configurational changes. For two well-known families of rules, the Wolfram complexity Classes cluster satisfactorily. The observed simultaneous occurrence of sharp and smooth transitions from ordered to disordered dynamics in CA can be explained with the two-parameter diagram

Atmospheric Circulation of Eccentric Hot Neptune GJ436b

GJ436b is a unique member of the transiting extrasolar planet population being one of the smallest and least irradiated and possessing an eccentric orbit. Because of its size, mass and density, GJ436b could plausibly have an atmospheric metallicity similar to Neptune (20-60 times solar abundances), which makes it an ideal target to study the effects of atmospheric metallicity on dynamics and radiative transfer in an extrasolar planetary atmosphere. We present three-dimensional atmospheric circulation models that include realistic non-gray radiative transfer for 1, 3, 10, 30, and 50 times solar atmospheric metallicity cases of GJ436b. Low metallicity models (1 and 3 times solar) show little day/night temperature variation and strong high-latitude jets. In contrast, higher metallicity models (30 and 50 times solar) exhibit day/night temperature variations and a strong equatorial jet. Spectra and light curves produced from these simulations show strong orbital phase dependencies in the 50 times solar case and negligible variations with orbital phase in the 1 times solar case. Comparisons between the predicted planet/star flux ratio from these models and current secondary eclipse measurements support a high metallicity atmosphere (30-50 times solar abundances) with disequilibrium carbon chemistry at play for GJ436b. Regardless of the actual atmospheric composition of GJ436b, our models serve to illuminate how metallicity influences the atmospheric circulation for a broad range of warm extrasolar planets.Comment: 25 pages, 13 figure

Cognitive demands of face monitoring: Evidence for visuospatial overload

Young children perform difficult communication tasks better face to face than when they cannot see one another (e.g., Doherty-Sneddon & Kent, 1996). However, in recent studies, it was found that children aged 6 and 10 years, describing abstract shapes, showed evidence of face-to-face interference rather than facilitation. For some communication tasks, access to visual signals (such as facial expression and eye gaze) may hinder rather than help children’s communication. In new research we have pursued this interference effect. Five studies are described with adults and 10- and 6-year-old participants. It was found that looking at a face interfered with children’s abilities to listen to descriptions of abstract shapes. Children also performed visuospatial memory tasks worse when they looked at someone’s face prior to responding than when they looked at a visuospatial pattern or at the floor. It was concluded that performance on certain tasks was hindered by monitoring another person’s face. It is suggested that processing of visual communication signals shares certain processing resources with the processing of other visuospatial information

Assessing the impact of verbal and visuospatial working memory load on eye-gaze cueing

Observers tend to respond more quickly to peripheral stimuli that are being gazed at by a centrally presented face, than to stimuli that are not being gazed at. While this gaze-cueing effect was initially seen as reflexive, there have also been some indications that top-down control processes may be involved. Therefore, the present investigation employed a dual-task paradigm to attempt to disrupt the putative control processes involved in gaze cueing. Two experiments examined the impact of working memory load on gaze cueing. In Experiment 1, participants were required to hold a set of digits in working memory during each gaze trial. In Experiment 2, the gaze task was combined with an auditory task that required the manipulation and maintenance of visuo-spatial information. Gaze cueing effects were observed, but they were not modulated by dual-task load in either experiment. These results are consistent with traditional accounts of gaze cueing as a highly reflexive process

A Study on Visual Focus of Attention Recognition from Head Pose in a Meeting Room

This paper presents a study on the recognition of the visual focus of attention (VFOA) of meeting participants based on their head pose. Contrarily to previous studies on the topic, in our set-up, the potential VFOA of people is not restricted to other meeting participants only, but includes environmental targets (table, slide screen). This has two consequences. Firstly, this increases the number of possible ambiguities in identifying the VFOA from the head pose. Secondly, due to our particular set-up, the identification of the VFOA from head pose can not rely on an incomplete representation of the pose (the pan), but requests the knowledge of the full head pointing information (pan and tilt). In this paper, using a corpus of 8 meetings of 8 minutes on average, featuring 4 persons involved in the discussion of statements projected on a slide screen, we analyze the above issues by evaluating, through numerical performance measures, the recognition of the VFOA from head pose information obtained either using a magnetic sensor device (the ground truth) or a vision based tracking system (head pose estimates). The results clearly show that in complex but realistic situations, it is quite optimistic to believe that the recognition of the VFOA can solely be based on the head pose, as some previous studies had suggested