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Active Brownian Particle
An active Brownian particle (ABP) is a model of self-propelled motion in a dissipative environment. It is a nonequilibrium generalization of a Brownian particle. The self-propulsion results from a force that acts on the particle's center of mass and points in the direction of an intrinsic body axis (the particle orientation). It is common to treat particles as spheres, though other shapes (such as rods) have also been studied. Both the center of mass and the direction of the propulsive force are subjected to white noise, which contributes a diffusive component to the overall dynamics. In its simplest version, the dynamics is overdamped and the propulsive force has constant magnitude, so that the magnitude of the velocity is likewise constant (speed-up to terminal velocity is instantaneous). The term ''active Brownian particle'' usually refers to this simple model and its straightforward extensions, though some authors have used it for more general self-propelled particle models ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-propelled Particles
Self-propelled particles (SPP), also referred to as self-driven particles, are terms used by physicists to describe autonomous agents, which convert energy from the environment into directed or persistent motion. Natural systems which have inspired the study and design of these particles include walking, swimming or flying animals. Other biological systems include bacteria, cells, algae and other micro-organisms. Generally, self-propelled particles often refer to artificial systems such as robots or specifically designed particles such as swimming Janus colloids, bimetallic nanorods, nanomotors and walking grains. In the case of directed propulsion, which is driven by a chemical gradient, this is referred to as chemotaxis, observed in biological systems, e.g. bacteria quorum sensing and ant pheromone detection, and in synthetic systems, e.g. enzyme molecule chemotaxis and enzyme powered hard and soft particles. Overview Self-propelled particles interact with each other, which c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Probability Density Function
In probability theory, a probability density function (PDF), or density of a continuous random variable, is a function whose value at any given sample (or point) in the sample space (the set of possible values taken by the random variable) can be interpreted as providing a ''relative likelihood'' that the value of the random variable would be close to that sample. Probability density is the probability per unit length, in other words, while the ''absolute likelihood'' for a continuous random variable to take on any particular value is 0 (since there is an infinite set of possible values to begin with), the value of the PDF at two different samples can be used to infer, in any particular draw of the random variable, how much more likely it is that the random variable would be close to one sample compared to the other sample. In a more precise sense, the PDF is used to specify the probability of the random variable falling ''within a particular range of values'', as opposed to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Active Matter
Active matter is matter composed of large numbers of active "agents", each of which consumes energy in order to move or to exert mechanical forces. Such systems are intrinsically out of thermal equilibrium. Unlike thermal systems relaxing towards equilibrium and systems with boundary conditions imposing steady currents, active matter systems break time reversal symmetry because energy is being continually dissipated by the individual constituents. Most examples of active matter are biological in origin and span all the scales of the living, from bacteria and self-organising bio-polymers such as microtubules and actin (both of which are part of the cytoskeleton of living cells), to schools of fish and flocks of birds. However, a great deal of current experimental work is devoted to synthetic systems such as artificial self-propelled particles. Active matter is a relatively new material classification in soft matter: the most extensively studied model, the Vicsek model, dates fro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Langevin Equation
In physics, a Langevin equation (named after Paul Langevin) is a stochastic differential equation describing how a system evolves when subjected to a combination of deterministic and fluctuating ("random") forces. The dependent variables in a Langevin equation typically are collective (macroscopic) variables changing only slowly in comparison to the other (microscopic) variables of the system. The fast (microscopic) variables are responsible for the stochastic nature of the Langevin equation. One application is to Brownian motion, which models the fluctuating motion of a small particle in a fluid. Brownian motion as a prototype The original Langevin equation describes Brownian motion, the apparently random movement of a particle in a fluid due to collisions with the molecules of the fluid, m\frac=-\lambda \mathbf+\boldsymbol\left( t\right). Here, \mathbf is the velocity of the particle, and m is its mass. The force acting on the particle is written as a sum of a viscous force ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Janus Particle
Janus particles are special types of nanoparticles or microparticles whose surfaces have two or more distinct physical property, physical properties. This unique surface of Janus particles allows two different types of chemistry to occur on the same particle. The simplest case of a Janus particle is achieved by dividing the particle into two distinct parts, each of them either made of a different material, or bearing different functional groups. For example, a Janus particle may have one-half of its surface composed of hydrophile, hydrophilic groups and the other half hydrophobe, hydrophobic groups, the particles might have two surfaces of different color, fluorescence, or magnetic properties. This gives these particles unique properties related to their asymmetric structure and/or functionalization. History The term "Janus Particle" was coined by author Leonard Wibberley in hi1962 novelThe Mouse on the Moon (novel), The Mouse on the Moon as a science-fictional device for space ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Run-and-tumble Motion
Run-and-tumble motion is a movement pattern exhibited by certain bacteria and other microscopic agents. It consists of an alternating sequence of "runs" and "tumbles": during a run, the agent propels itself in a fixed (or slowly varying) direction, and during a tumble, it remains stationary while it reorients itself in preparation for the next run. The tumbling is erratic or "random" in the sense of a stochastic process—that is, the new direction is sampled from a probability density function, which may depend on the organism's local environment (e.g., chemical gradients). The duration of a run is usually random in the same sense. An example is wild-type ''E. coli'' in a dilute aqueous medium, for which the run duration is exponentially distributed with a mean of about 1 second. Run-and-tumble motion forms the basis of certain mathematical models of self-propelled particles, in which case the particles themselves may be called run-and-tumble particles. Description Many bacteri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pseudomonas Citronellolis
''Pseudomonas citronellolis'' is a Gram-negative, bacillus bacterium that is used to study the mechanisms of pyruvate carboxylase. It was first isolated from forest soil, under pine trees, in northern Virginia, United States. Characteristics ''Pseudomonas citronellolis'' a Gram-negative, bacillus bacterium. It was first isolated from forest soil, under pine trees, in northern Virginia, United States. It has one polar flagellum allowing it to be motile. Relationship with plants On agar, ''P. citronellolis'' forms round white colonies that produce fluorescent green pigments. It also produces a biofilm and is resistant to most antibiotics. The bacteria has a biotic relationship with its plant host (either with pine trees or basil). It produces a type of hormone that induces plant cell elongation and division, leading to an increase of local available nutrients. Metabolic potential The study of P. citronellolis is important because it could be used as a model to research meta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shewanella Putrefaciens
''Shewanella putrefaciens'' is a Gram-negative pleomorphic bacterium. It has been isolated from marine environments, as well as from anaerobic sandstone in the Morrison Formation in New Mexico. ''S. putrefaciens'' is also a facultative anaerobe with the ability to reduce iron and manganese metabolically; that is, it can use iron and manganese as the terminal electron acceptor in the electron transport chain (in contrast to obligate aerobes which must use oxygen for this purpose). It is also one of the organisms associated with the odor of rotting fish, as it is a marine organism which produces trimethylamine (hence the species name putrefaciens, from putrid). In both solid and liquid media, ''S. putrefaciens'' is often recognizable by its bright pink color. On solid media, the colonies are round, fast-growing, and pink. The organism is also fast-growing in liquid media, and there will give the liquid an overall pink hue. On blood agar plates, the colonies are typically convex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pseudoalteromonas Haloplanktis
''Pseudoalteromonas haloplanktis'' is a Gram-negative, psychrophilic marine bacterium Marine prokaryotes are marine bacteria and marine archaea. They are defined by their habitat as prokaryotes that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. All cellular .... References External linksType strain of ''Pseudoalteromonas haloplanktis'' at Bac''Dive'' - the Bacterial Diversity Metadatabase Alteromonadales Bacteria described in 1944 Psychrophiles Gram-negative bacteria Marine microorganisms {{Alteromonadales-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pseudomonas Putida
''Pseudomonas putida'' is a Gram-negative, rod-shaped, saprotrophic soil bacterium. Based on 16S rRNA analysis, ''P. putida'' was taxonomically confirmed to be a ''Pseudomonas'' species (''sensu stricto'') and placed, along with several other species, in the ''P. putida'' group, to which it lends its name. However, phylogenomic analysis of complete genomes from the entire ''Pseudomonas'' genus clearly showed that the genomes that were named as ''P. putida'' did not form a monophyletic clade, but were dispersed and formed a wider evolutionary group (the putida group) that included other species as well, such as ''P. alkylphenolia, P. alloputida, P. monteilii, P. cremoricolorata, P. fulva, P. parafulva, P. entomophila, P. mosselii, P. plecoglossicida'' and several genomic species (new species which are currentely not validely defined as new species. A variety of ''P. putida'', called multiplasmid hydrocarbon-degrading ''Pseudomonas'', is the first patented organism in th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Myxococcus Xanthus
''Myxococcus xanthus'' is a gram-negative, rod-shaped species of myxobacteria that exhibits various forms of self-organizing behavior in response to environmental cues. Under normal conditions with abundant food, it exists as a predatory, saprophytic single-species biofilm called a swarm. Under starvation conditions, it undergoes a multicellular development cycle. Colony growth A swarm of ''M. xanthus'' is a distributed system, containing millions of bacteria that communicate among themselves in a non-centralized fashion. Simple patterns of cooperative behavior among the members of the colony combine to generate complex group behaviors in a process known as "stigmergy". For example, the tendency for one cell to glide only when in direct contact with another results in the colony forming swarms called "wolf-packs" that may measure up to several inches wide. This behavior is advantageous to the members of the swarm, as it increases the concentration of extracellular digestive enz ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Separation
Phase separation is the creation of two distinct phases from a single homogeneous mixture. The most common type of phase separation is between two immiscible liquids, such as oil and water. Colloids are formed by phase separation, though not all phase separations forms colloids - for example oil and water can form separated layers under gravity rather than remaining as microscopic droplets in suspension. Phase separation in cold gases A mixture of two helium isotopes (helium-3 and helium-4) in a certain range of temperatures and concentrations separates into parts. The initial mix of the two isotopes spontaneously separates into ^He-rich and ^3He-rich regions. Phase separation also exists in ultracold gas systems. It has been shown experimentally in a two-component ultracold Fermi gas case. The phase separation can compete with other phenomena as vortex lattice formation or an exotic Fulde-Ferrell-Larkin-Ovchinnikov phase. See also * Biomolecular condensate * Collo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
