Sliding on the surface: bacterial spreading without an active motor

Bacteria are able to translocate over surfaces using different types of active and passive motility mechanisms. Sliding is one of the passive types of movement since it is powered by the pushing force of dividing cells and additional factors facilitating the expansion over surfaces. In this review, we describe the sliding proficient bacteria that were previously investigated in details highlighting the sliding facilitating compounds and the regulation of sliding motility. Besides surfactants that reduce the friction between cells and substratum, other compounds including exopolysaccharides, hydrophobic proteins, or glycopeptidolipids where discovered to promote sliding. Therefore, we present the sliding bacteria in three groups depending on the additional compound required for sliding. Despite recent accomplishments in sliding research there are still many open questions about the mechanisms underlying sliding motility and its regulation in diverse bacterial species

Perirhinal Cortex Neuronal Activity is Actively Related to Working Memory in the Macaque

Lesion studies suggest that the perirhinai cortex plays a role in object recognition memory. To analyze its role, we recorded the activity of single neurons in the perirhinal cortex in a rhesus monkey (Macaca mulatta) performing a delayed matching-to-sample task with up to four intervening stimuli. Certain neurons (40 of 90 analyzed) showed a smaller response to an image when it was shown the second time within a trial (as a match image) than when it had been shown (as a sample image) the first time. A new finding was that the perirhinal cortex neurons were actively reset between trials: when a particular image was shown as a sample on a succeeding trial, the response was much larger than when it had been shown as a match image a short time previously on the previous trial. This resetting between trials appears to reflect the operation of an active working memory process rather than a passive temporal decay in a neuronal response. The results thus provide evidence that the perirhinal cortex plays an active role in visual working memory, perhaps in association with other brain areas such as the prefrontal cortex

The Floor Strategy: Wayfinding Cognition in a Multi-Level Building

This short paper is concerned with strategies and cognitive processes of wayfinding in public buildings. We conducted an empirical study in a complex multi-level building, comparing performance measures of experienced and inexperienced participants in different wayfinding tasks. Thinking aloud protocols provided insights into navigation strategies, planning phases, use of landmarks and signage. Three specific strategies for navigation in multi-level buildings were compared. The cognitively efficient floor strategy was preferred by experts over a central-point strategy or a direction strategy, and overall was associated to better wayfinding performance

Thermal effects on atomic friction

We model friction acting on the tip of an atomic force microscope as it is dragged across a surface at non-zero temperatures. We find that stick-slip motion occurs and that the average frictional force follows $|\ln v|^{2/3}$, where $v$ is the tip velocity. This compares well to recent experimental work (Gnecco et al, PRL 84, 1172), permitting the quantitative extraction of all microscopic parameters. We calculate the scaled form of the average frictional force's dependence on both temperature and tip speed as well as the form of the friction-force distribution function.Comment: Accepted for publication, Physical Review Letter

“You’re free from just a girl or a boy”:Nonbinary children’s understanding of their gender

BackgroundIn recent years, research on gender diversity in early childhood has increased significantly. However, much of the published literature still focuses on children whose experiences align with binary gender norms, inadvertently excluding nonbinary experiences from analysis.AimsWe seek to explore how nonbinary children, aged five to eight, perceive and understand their gender modality and experiences.MethodsNine American nonbinary children were interviewed using a semi-structured approach, which included two book readings, a drawing activity, and approximately 23 pre-determined questions. Inductive reflexive thematic analysis was utilized for developing, analyzing, and interpreting patterns across a qualitative dataset. All authors engaged in various aspects of reflexivity throughout the process, including personal, functional, and disciplinary reflexivity.AnalysisWe constructed five themes, which were evident across the accounts of participating children. The first one, Being nonbinary has different meanings for different people, illustrates the diverse interpretations of nonbinary identities. Gender is hard to describe but my pronouns help me make sense of it, highlights the challenges of explaining gender, yet pronouns help participants lucidly put their and others’ gender into words. People can change their gender for good or just for a little while, reflect participants’ view of gender as dynamic and fluid. “I have the agency to decide who I am with a little help of others”: feeling, learning, choosing and telling, explores participants’ journey in adopting the label “nonbinary”. Lastly, Being nonbinary is both easy and hard: easy because I am myself, hard because of other people, depicts the multifaceted experiences of being nonbinary, from the affirmation to bullying.DiscussionIn an era marked by a contentious political climate and ongoing debates about trans/nonbinary individuals, these young children defy conventional norms and establish themselves as active architects of their identity narratives, driven by their agency and self-determination

Crowd behaviour during high-stress evacuations in an immersive virtual environment

Understanding the collective dynamics of crowd movements during stressful emergency situations is central to reducing the risk of deadly crowd disasters. Yet, their systematic experimental study remains a challenging open problem due to ethical and methodological constraints. In this paper, we demonstrate the viability of shared 3D virtual environments as an experimental platform for conducting crowd experiments with real people. In particular, we show that crowds of real human subjects moving and interacting in an immersive 3D virtual environment exhibit typical patterns of real crowds as observed in real-life crowded situations. These include the manifestation of social conventions and the emergence of self-organized patterns during egress scenarios. High-stress evacuation experiments conducted in this virtual environment reveal movements characterized by mass herding and dangerous overcrowding as they occur in crowd disasters. We describe the behavioral mechanisms at play under such extreme conditions and identify critical zones where overcrowding may occur. Furthermore, we show that herding spontaneously emerges from a density effect without the need to assume an increase of the individual tendency to imitate peers. Our experiments reveal the promise of immersive virtual environments as an ethical, cost-efficient, yet accurate platform for exploring crowd behaviour in high-risk situations with real human subjects.Comment: 17 pages, 5 figure

Phase Transitions of an Oscillator Neural Network with a Standard Hebb Learning Rule

Studies have been made on the phase transition phenomena of an oscillator network model based on a standard Hebb learning rule like the Hopfield model. The relative phase informations---the in-phase and anti-phase, can be embedded in the network. By self-consistent signal-to-noise analysis (SCSNA), it was found that the storage capacity is given by $\alpha_c = 0.042$, which is better than that of Cook's model. However, the retrieval quality is worse. In addition, an investigation was made into an acceleration effect caused by asymmetry of the phase dynamics. Finally, it was numerically shown that the storage capacity can be improved by modifying the shape of the coupling function.Comment: 10 pages, 6 figure

A duo of Potassium-responsive Histidine Kinases govern the multicellular destiny of Bacillus subtilis

Multicellular biofilm formation and surface motility are bacterial behaviors considered mutually exclusive. However, the basic decision to move over or stay attached to a surface is poorly understood. Here, we discover that in Bacillus subtilis, the key root biofilm-controlling transcription factor Spo0A~Pi (phosphorylated Spo0A) governs the flagellum-independent mechanism of social sliding motility. A Spo0A-deficient strain was totally unable to slide and colonize plant roots, evidencing the important role that sliding might play in natural settings. Microarray experiments plus subsequent genetic characterization showed that the machineries of sliding and biofilm formation share the same main components (i.e., surfactin, the hydrophobin BslA, exopolysaccharide, and de novo-formed fatty acids). Sliding proficiency was transduced by the Spo0A-phosphorelay histidine kinases KinB and KinC. We discovered that potassium, a previously known inhibitor of KinC-dependent biofilm formation, is the specific sliding-activating signal through a thus-far-unnoticed cytosolic domain of KinB, which resembles the selectivity filter sequence of potassium channels. The differential expression of the Spo0A~Pi reporter abrB gene and the different levels of the constitutively active form of Spo0A, Sad67, in Δspo0A cells grown in optimized media that simultaneously stimulate motile and sessile behaviors uncover the spatiotemporal response of KinB and KinC to potassium and the gradual increase in Spo0A~Pi that orchestrates the sequential activation of sliding, followed by sessile biofilm formation and finally sporulation in the same population. Overall, these results provide insights into how multicellular behaviors formerly believed to be antagonistic are coordinately activated in benefit of the bacterium and its interaction with the host.Fil: Grau, Roberto Ricardo. Universidad Nacional de Rosario. Facultad de Cs.bioquimicas y Farmaceuticas. Departamento de Microbiologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: de Oña, Paula. Universidad Nacional de Rosario. Facultad de Cs.bioquimicas y Farmaceuticas. Departamento de Microbiologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kunert, Maritta. Instituto Max Planck Institut Fur Chemische Okologie; AlemaniaFil: Leñini, Cecilia Andrea. Universidad Nacional de Rosario. Facultad de Cs.bioquimicas y Farmaceuticas. Departamento de Microbiologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gallegos Monterrosa, Ramses. Universitat Jena; AlemaniaFil: Mhatre, Eisha. Universitat Jena; AlemaniaFil: Vileta, Darío. Universidad Nacional de Rosario. Facultad de Cs.bioquimicas y Farmaceuticas. Departamento de Microbiologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Donato, Veronica. Universidad Nacional de Rosario. Facultad de Cs.bioquimicas y Farmaceuticas. Departamento de Microbiologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hölscher, Theresa. Universitat Jena; AlemaniaFil: Boland, Wilhem. Instituto Max Planck Institut Fur Chemische Okologie; AlemaniaFil: Kuipers, Oscar P.. University of Groningen; Países BajosFil: Kovács, Ákos T.. Universitat Jena; Alemani