452 research outputs found
Interactive Space Generation through Play: Exploring Form Creation and the Role of Simulation on the Design Table
Fiscal Federalism and Foreign Transfers: Does Inter-Jurisdictional Competition Increase Foreign Aid Effectiveness?
Percutaneous fixation of acute scaphoid waist fractures: long-term patient-reported functional outcomes and satisfaction at a mean of 11 years following surgery.
Should Subsidies to Urban Passenger Transport be Increased? A Spatial CGE Analysis for a German Metropolitan Area
Symmetric and asymmetric action integration during cooperative object manipulation in virtual environments
Cooperation between multiple users in a virtual environment (VE) can take place at one of three levels. These
are defined as where users can perceive each other (Level 1), individually change the scene (Level 2), or
simultaneously act on and manipulate the same object (Level 3). Despite representing the highest level of
cooperation, multi-user object manipulation has rarely been studied. This paper describes a behavioral
experiment in which the piano movers' problem (maneuvering a large object through a restricted space) was
used to investigate object manipulation by pairs of participants in a VE. Participants' interactions with the object
were integrated together either symmetrically or asymmetrically. The former only allowed the common
component of participants' actions to take place, but the latter used the mean. Symmetric action integration was
superior for sections of the task when both participants had to perform similar actions, but if participants had to
move in different ways (e.g., one maneuvering themselves through a narrow opening while the other traveled
down a wide corridor) then asymmetric integration was superior. With both forms of integration, the extent to
which participants coordinated their actions was poor and this led to a substantial cooperation overhead (the
reduction in performance caused by having to cooperate with another person)
Lichens facilitate seedling recruitment in alpine heath
Abstract Questions How do mat thickness, physical structure and allelopathic properties of terricolous mat-forming lichens affect recruitment of vascular plants in dwarf-shrub and lichen heath vegetation?. Location The mountains of Dovrefjell, central Norway. Methods In autumn, seeds of ten vascular plant species were collected and sown in a common garden experiment with mats of six lichen species and bare-soil controls as experimental treatments. We recorded growing season soil temperature and moisture, and seedling recruitment and growth after one year. The effect of lichen secondary compounds on germination was tested in a growth chamber experiment and compared to the lichen-plant interactions detected under field conditions. Results The lichen mats buffered extreme soil temperatures and soil drying in dry weather, with soils below the thickest mats (Cladonia stellaris and C. rangiferina) experiencing the lowest temperature fluctuations. Seedling recruitment and seedling growth in the field and seed germination in the lab were species-specific. Seedling recruitment rates were overall higher within lichen mats than on bare soil, but the c. 6.5 cm thick mats of C. stellaris reduced recruitment of many species. The lab experiment suggested no overall strong effect of lichen allelopathy on seed germination, and effects on seed germination were only moderately correlated with the lichen-plant interactions observed for seedling recruitment in the field. Conclusions In harsh environments like alpine dwarf-shrub and lichen heaths, the presence of lichens and the resulting amelioration of the microclimate seems more important for vascular plant recruitment than are allelopathic effects often reported in lab experiments. We might therefore expect most terricolous lichens, depending on the plant species in focus, to facilitate rather than hamper the early stages of plant recruitment into lichen-dominated arctic-alpine heath vegetation. This article is protected by copyright. All rights reserved.Peer reviewe
- …