732 research outputs found
Interspecific comparison of hydrodynamic performance and structural properties among intertidal macroalgae
Macroalgae use flexibility and reconfiguration, i.e. the alteration of shape, size and orientation as water velocity increases, to reduce the hydrodynamic forces imposed in the wave-swept rocky intertidal zone. Quantifying the effects of flexibility on hydrodynamic performance is difficult, however, because the mechanisms of reconfiguration vary with water velocity and the relationship between algal solid mechanics and hydrodynamic performance is poorly understood. In this study, the hydrodynamic performance, morphology and solid mechanics of 10 rocky shore macroalgal species were quantified to evaluate the influences of flexibility and morphology on reconfiguration. Hydrodynamic performance was measured in a flume by direct measurement of changes in size and shape during reconfiguration across a wide range of velocities, material stiffness was quantified with standard materials testing, and structural properties were calculated from material and morphological data. Hydrodynamic parameters varied significantly among species, indicating variation in the magnitude of reconfiguration and the velocities required for full reconfiguration. Structural properties also varied among species, and were correlated with hydrodynamic performance in some instances. The relationship between hydrodynamic and structural properties is velocity dependent, such that flexibility influences different aspects of reconfiguration at low and high velocities. Groups are identifiable among species based on hydrodynamic and structural properties, suggesting that these properties are useful for addressing functional-form hypotheses and the effects of hydrodynamic disturbance on macroalgal communities
The hydrodynamic effects of shape and size change during reconfiguration of a flexible macroalga
Rocky intertidal organisms experience large hydrodynamic forces due to high water velocities created by breaking waves. Flexible organisms, like macroalgae, often experience lower drag than rigid organisms because their shape and size change as velocity increases. This phenomenon, known as reconfiguration, has been previously quantified as Vogel\u27s E, a measure of the relationship between velocity and drag. While this method is very useful for comparing reconfiguration among organisms it does not address the mechanisms of reconfiguration, and its application to predicting drag is problematic. The purpose of this study was twofold: (1) to examine the mechanisms of reconfiguration by quantifying the change in shape and size of a macroalga in flow and (2) to build a mechanistic model of drag for reconfiguring organisms. Drag, frontal area and shape of the intertidal alga Chondrus crispus were measured simultaneously in a recirculating flume at water velocities from 0 to ∼2 m s–1. Reconfiguration was due to two separate mechanisms: whole-alga realignment (deflection of the stipe) at low velocities (\u3c0.2 m s–1) and compaction of the crown (reduction in frontal area and change in shape) at higher velocities. Change in frontal area contributed more to drag reduction than change in drag coefficient. Drag coefficient and frontal area both decrease exponentially with increasing water velocity, and a mechanistic model of drag was developed with explicit functions to describe these changes. The model not only provides mechanistic parameters with which to compare reconfiguration among individuals and species, but also allows for more reliable predictions of drag at high, ecologically relevant water velocities
Cognitive shifts within leader and follower teams:Where consensus develops in mental models during an organizational crisis
This empirical study investigates cognitive shifts in both leader and follower teams when developing consensus or agreement in how to resolve a slowly emerging organizational crisis over time. The cognitive maps of leaders and followers are analyzed in team settings to explain where consensus is formed. The findings indicate that consensus, or the agreement on the causal beliefs held to be critical to organizational adaptation and success, builds over time within both leader and follower teams. However, when comparing the development of consensus longitudinally, the findings confirm that the mental models of leadership teams converge towards follower teams, and not the other way around, during the crisis. The study provides new insights into the importance of the causal beliefs of follower teams when developing a vision to coordinate action to resolve a crisis
Vacuum stability of the standard model and BSM extensions
The Standard Model scalar potential contains a minimum at the Electroweak
scale, responsible for the masses of the weak gauge bosons
through the Higgs mechanism. However, if the Electroweak minimum is
only a local minimum, and there exists a global minimum at a higher
energy in the Higgs potential, then in a su ciently old universe we would
expect the vacuum expectation value to be at the global minimum. The
absence of a global minimum at higher energy is related to the condition
that the Higgs self coupling is greater than or equal to zero for all energies.
For any model that fails this, we expect new physics to enter before
the energy at which the coupling becomes negative. We developed tools
to automate the derivation of beta functions for renormalisable gauge
theories, and used these to carry out evolution of the renormalisation
group equations for the Standard Model and three extensions to the
Standard Model | the Standard Model with a fourth generation, the
Standard Model with right-handed neutrinos and a Left-Right Symmetric
Model. We conclude that of these four models, the Standard Model
is the only one in which all the couplings remain perturbative, and in
which the Electroweak minimum is a global minimum
Managing the Tensions at the Intersection of the Triple Bottom Line: A Paradox Theory Approach to Sustainability Management
Corporate sustainability management encompasses multiple dimensions: environmental, social, and economic. Companies are increasingly evaluated within the public sphere, and within their own organizations, according to the degree to which they are perceived to simultaneously promote this nexus of virtues. This article seeks to explore the tensions frequently faced by organizations that strive to manage these dimensions and the role of public policy in that pursuit. A multiple–case study approach is utilized in which the authors selected case organizations according to whether they were attempting to manage the three dimensions of sustainability. The authors utilize paradox theory and a typology provided by previous research to understand the nature of the tensions that emerge in the selected case study organizations. They extend this previous work by examining the role of public policy in providing the situational conditions to make these paradoxical tensions salient, and they examine organizational responses to these conditions. Directions for firms, policy makers, and future researchers are provided on the basis of this study’s findings
Managing the Tensions at the Intersection of the Triple Bottom Line: A Paradox Theory Approach to Sustainability Management
Corporate sustainability management encompasses multiple dimensions: environmental, social, and economic. Companies are increasingly evaluated within the public sphere, and within their own organizations, according to the degree to which they are perceived to simultaneously promote this nexus of virtues. This article seeks to explore the tensions frequently faced by organizations that strive to manage these dimensions and the role of public policy in that pursuit. A multiple–case study approach is utilized in which the authors selected case organizations according to whether they were attempting to manage the three dimensions of sustainability. The authors utilize paradox theory and a typology provided by previous research to understand the nature of the tensions that emerge in the selected case study organizations. They extend this previous work by examining the role of public policy in providing the situational conditions to make these paradoxical tensions salient, and they examine organizational responses to these conditions. Directions for firms, policy makers, and future researchers are provided on the basis of this study’s findings
A Contextual Inquiry of People with Vision Impairments in Cooking
Individuals with vision impairments employ a variety of strategies for object
identification, such as pans or soy sauce, in the culinary process. In
addition, they often rely on contextual details about objects, such as
location, orientation, and current status, to autonomously execute cooking
activities. To understand how people with vision impairments collect and use
the contextual information of objects while cooking, we conducted a contextual
inquiry study with 12 participants in their own kitchens. This research aims to
analyze object interaction dynamics in culinary practices to enhance assistive
vision technologies for visually impaired cooks. We outline eight different
types of contextual information and the strategies that blind cooks currently
use to access the information while preparing meals. Further, we discuss
preferences for communicating contextual information about kitchen objects as
well as considerations for the deployment of AI-powered assistive technologies.Comment: CHI 202
Some Two-Loop Corrections to the Finite Temperature Effective Potential in the Electroweak Theory
Perturbation theory at finite temperature suffers from well-known infrared
problems. In the standard model, as a result, one cannot calculate the
effective potential for arbitrarily small values of , the Higgs
expectation value. Because the Higgs field is now known not to be extremely
light, it is necessary to determine whether perturbation theory is a reliable
guide to properties of the weak phase transition. In this note, we evaluate the
most singular contributions to the potential at two loops as well as the
leading strong interaction contributions. Above the critical temperature, the
strong interaction corrections are reasonably small, while the weak corrections
are about 10\%, even for rather small values of the Higgs field. At the
critical temperature, the weak corrections have a more substantial effect,
rendering the transition significantly more first order, but not significantly
changing the upper bound on the Higgs mass required for baryogenesis.Comment: 13 pages, figures available on request, SCIPP 92/4
Once More on a Colour Ferromagnetic Vacuum State at Finite Temperature
The spontaneous vacuum magnetization at finite temperature is investigated in
SU(2) gluodynamics within a consistent effective potential approach including
the one-loop and the correlation correction contributions. To evaluate the
latter ones the high temperature limits of the polarization operators of
charged and neutral gluon fields in a covariantly constant magnetic field and
at high temperature are calculated.The radiation mass squared of charged gluons
is found to be positive. It is shown that the ferromagnetic vacuum state having
a field strength of order is spontaneously
generated at high temperature. The vacuum stability and some applications of
the results obtained are discussed.Comment: 16 pages, 2 figures, subm. to Nucl. Phys.
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