Unconstrained Submodular Maximization with Constant Adaptive Complexity

In this paper, we consider the unconstrained submodular maximization problem. We propose the first algorithm for this problem that achieves a tight $(1/2-\varepsilon)$-approximation guarantee using $\tilde{O}(\varepsilon^{-1})$ adaptive rounds and a linear number of function evaluations. No previously known algorithm for this problem achieves an approximation ratio better than $1/3$ using less than $\Omega(n)$ rounds of adaptivity, where $n$ is the size of the ground set. Moreover, our algorithm easily extends to the maximization of a non-negative continuous DR-submodular function subject to a box constraint and achieves a tight $(1/2-\varepsilon)$-approximation guarantee for this problem while keeping the same adaptive and query complexities.Comment: Authors are listed in alphabetical orde

Data from: Stimulus salience as an explanation for imperfect mimicry

The theory of mimicry explains how a mimic species gains advantage by resembling a model species . Selection for increased mimic-model similarity should then result in accurate mimicry, yet there are many surprising examples of poor mimicry in the natural world. The existence of imperfect mimics remains a major unsolved conundrum. We propose and experimentally test a novel explanation of the phenomenon. We argue that predators perceive prey as having several traits, but the traits differ in their importance for learning. When predators learn to discriminate prey, high-salience traits overshadow other traits, leaving them under little or no selection for similarity, and allow imperfect mimicry to succeed. We tested this idea experimentally, using blue tits as predators and artificial prey with three prominent traits: color, pattern and shape. We found that otherwise imperfect color mimics were avoided about as much as perfect mimics, whereas pattern and shape mimics did not gain from their similarity to the model. All traits could separately be perceived and learned by the predators, but the color trait was learned at a higher rate, implying that it had higher salience. We conclude that difference in salience between components of prey appearance is of major importance in explaining imperfect mimicry

User preferences for communication channels on energy conservation: a case study within Malaysian government office buildings

Purpose: The purpose of this paper is to identify the preferred communication channels to foster energy conservation behaviour among office building users. Energy demand from the commercial sector in Malaysia is, at 33.2 per cent, the highest after the industry sector, at 45.1 per cent. The country’s progress in actively practising energy conservation is lacking, despite various energy conservation programmes having been launched in recent years. A large amount of energy is wasted by users’ poor energy conservation behaviour. To market voluntary energy conservation behaviour, the delivery of energy conservation messages using the appropriate communication channels remains an important strategy. Design/methodology/approach: This paper involves two-stage data collection. The communication categories associated with a set of channels identified from expert interview serve as the basis for the second stage of empirical data gathering using conjoint analysis. A choice-based conjoint analysis assisted by Sawtooth Software is used to analyse the 525 usable empirical data gathered from a final questionnaire survey among the office building users in Malaysia. Findings: This paper has identified five communication categories associated with a total of 19 channels. The mass media is acknowledged as the most preferred communication channel among office building users in the marketing of energy conservation behaviour, while the least preferred channel to communicate energy conservation information is audio-visual media. Originality/value: This study contributes to existing literature with a novel case in Malaysia office building by identifying the preferred combination of communication channels in fostering energy conservation behaviour. The findings could benefit the building managers in marketing energy conservation behaviour among office building users to effectively achieve the desired change for sustainable development

generalisation_data

The file contains the number of attacks on rewarded (non-model) artificial prey in the generalization part of an experiment on imperfect mimicry

salience_data

The file contains the number of attacks on rewarded artificial prey in the salience testing part of an experiment on imperfect mimicry

discr_train_data

The file contains the number of attacks on rewarded (non-model) artificial prey in the discrimination training part of an experiment on imperfect mimicry

Membrane Tubulation in Lipid Vesicles Triggered by the Local Application of Calcium Ions

Experimental and theoretical studies on ion–lipid interactions predict that binding of calcium ions to cell membranes leads to macroscopic mechanical effects and membrane remodeling. Herein, we provide experimental evidence that a point source of Ca²⁺ acting upon a negatively charged membrane generates spontaneous curvature and triggers the formation of tubular protrusions that point away from the ion source. This behavior is rationalized by strong binding of the divalent cations to the surface of the charged bilayer, which effectively neutralizes the surface charge density of outer leaflet of the bilayer. The mismatch in the surface charge density of the two leaflets leads to nonzero spontaneous curvature. We probe this mismatch through the use of molecular dynamics simulations and validate that calcium ion binding to a lipid membrane is sufficient to generate inward spontaneous curvature, bending the membrane. Additionally, we demonstrate that the formed tubular protrusions can be translated along the vesicle surface in a controlled manner by repositioning the site of localized Ca²⁺ exposure. The findings demonstrate lipid membrane remodeling in response to local chemical gradients and offer potential insights into the cell membrane behavior under conditions of varying calcium ion concentrations

Membrane Tubulation in Lipid Vesicles Triggered by the Local Application of Calcium Ions

Experimental and theoretical studies on ion–lipid interactions predict that binding of calcium ions to cell membranes leads to macroscopic mechanical effects and membrane remodeling. Herein, we provide experimental evidence that a point source of Ca²⁺ acting upon a negatively charged membrane generates spontaneous curvature and triggers the formation of tubular protrusions that point away from the ion source. This behavior is rationalized by strong binding of the divalent cations to the surface of the charged bilayer, which effectively neutralizes the surface charge density of outer leaflet of the bilayer. The mismatch in the surface charge density of the two leaflets leads to nonzero spontaneous curvature. We probe this mismatch through the use of molecular dynamics simulations and validate that calcium ion binding to a lipid membrane is sufficient to generate inward spontaneous curvature, bending the membrane. Additionally, we demonstrate that the formed tubular protrusions can be translated along the vesicle surface in a controlled manner by repositioning the site of localized Ca²⁺ exposure. The findings demonstrate lipid membrane remodeling in response to local chemical gradients and offer potential insights into the cell membrane behavior under conditions of varying calcium ion concentrations