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Disordered Hyperuniformity
Hyperuniform materials are mixed-component many-particle systems with unusually low fluctuations in component density at large scales, when compared to the distribution of constituents in common disordered systems, like a mixed ideal gas (air) or typical liquids or amorphous solids: A disordered ''hyperuniform'' system is statistically isotropic, like a liquid, but exhibits reduced long-wavelength density fluctuations, similar to crystals. All perfect crystals, perfect quasicrystals and special disordered systems are ''hyperuniform''. Quantitatively, a many-particle system is ''hyperuniform'' if the variance of the number of points within a spherical observation window grows more slowly than the volume of the observation window. This definition is equivalent to a vanishing of the structure factor in the long-wavelength limit. Disordered hyperuniform systems, were shown to be poised at an "inverted" critical point. They can be obtained via equilibrium or nonequilibrium routes, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Porous Medium
A porous medium or a porous material is a material containing pores (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid or gas). The skeletal material is usually a solid, but structures like foams are often also usefully analyzed using concept of porous media. A porous medium is most often characterised by its porosity. Other properties of the medium (e.g. permeability, tensile strength, electrical conductivity, tortuosity) can sometimes be derived from the respective properties of its constituents (solid matrix and fluid) and the media porosity and pores structure, but such a derivation is usually complex. Even the concept of porosity is only straightforward for a poroelastic medium. Often both the solid matrix and the pore network (also known as the pore space) are continuous, so as to form two interpenetrating continua such as in a sponge. However, there is also a concept of closed porosit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chickens
The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult male bird, and a younger male may be called a cockerel. A male that has been castrated is a capon. An adult female bird is called a hen and a sexually immature female is called a pullet. Humans now keep chickens primarily as a source of food (consuming both their meat and eggs) and as pets. Traditionally they were also bred for cockfighting, which is still practiced in some places. Chickens are one of the most common and widespread domestic animals, with a total population of 23.7 billion , up from more than 19 billion in 2011. There are more chickens in the world than any other bird. There are numerous cultural references to chickens – in myth, folklore and religion, and in language and literature. Genetic studies have pointed to mult ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eyes
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons (neurones). In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in molluscs, chordates and arthropods. The most simple eyes, pit eyes, ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoreceptor Cell
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential. There are currently three known types of photoreceptor cells in mammalian eyes: rods, cones, and intrinsically photosensitive retinal ganglion cells. The two classic photoreceptor cells are rods and cones, each contributing information used by the visual system to form an image of the environment, sight. Rods primarily mediate scotopic vision (dim conditions) whereas cones primarily mediate to photopic vision (bright conditions), but the processes in each that supports phototransduction is similar. A third class of mammalian photoreceptor cell was discovered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Waveguide (optics)
An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber waveguides, transparent dielectric waveguides made of plastic and glass, liquid light guides, and liquid waveguides. Optical waveguides are used as components in integrated optical circuits or as the transmission medium in local and long-haul optical communication systems. Optical waveguides can be classified according to their geometry (planar, strip, or fiber waveguides), mode structure (single-mode optical fiber, single-mode, multi-mode optical fiber, multi-mode), refractive index distribution (step or gradient index), and material (glass, polymer, semiconductor). Total internal reflection The basic principles behind optical waveguides can be described using the concepts of geometrical optics, geometrical or ray optics, as illustrated in the diagram. Light passing into a medium with higher refractive index bends towa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photonic Band Gap
A photonic crystal is an optical nanostructure in which the refractive index changes periodically. This affects the propagation of light in the same way that the structure of natural crystals gives rise to X-ray diffraction and that the atomic lattices (crystal structure) of semiconductors affect their conductivity of electrons. Photonic crystals occur in nature in the form of structural coloration and animal reflectors, and, as artificially produced, promise to be useful in a range of applications. Photonic crystals can be fabricated for one, two, or three dimensions. One-dimensional photonic crystals can be made of thin film layers deposited on each other. Two-dimensional ones can be made by photolithography, or by drilling holes in a suitable substrate. Fabrication methods for three-dimensional ones include drilling under different angles, stacking multiple 2-D layers on top of each other, direct laser writing, or, for example, instigating self-assembly of spheres in a matri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paul Steinhardt
Paul Joseph Steinhardt (born December 25, 1952) is an American theoretical physicist whose principal research is in cosmology and condensed matter physics. He is currently the Albert Einstein Professor in Science at Princeton University, where he is on the faculty of both the Departments of Physics and of Astrophysical Sciences. Steinhardt is best known for his development of new theories of the origin, evolution and future of the universe. He is also well known for his exploration of a new form of matter, known as quasicrystals, which were thought to exist only as man-made materials until he co-discovered the first known natural quasicrystal in a museum sample. He subsequently led a separate team that followed up that discovery with several more examples of natural quasicrystals recovered from the wilds of the Kamchatka Peninsula in far eastern Russia. Several years later, he and collaborators reported the accidental synthesis of a previously unknown type of quasicrystal in the r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Princeton University
Princeton University is a private university, private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial Colleges, fourth-oldest institution of higher education in the United States and one of the nine colonial colleges chartered before the American Revolution. It is one of the highest-ranked universities in the world. The institution moved to Newark, New Jersey, Newark in 1747, and then to the current site nine years later. It officially became a university in 1896 and was subsequently renamed Princeton University. It is a member of the Ivy League. The university is governed by the Trustees of Princeton University and has an endowment of $37.7 billion, the largest List of colleges and universities in the United States by endowment, endowment per student in the United States. Princeton provides undergraduate education, undergraduate and graduate education, graduate in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for by using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Colloids
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend the definition to include substances like aerosols and gels. The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word ''suspension'' is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). The dispersed phase particles have a diameter of approximately 1 nanometre to 1 micrometre. Some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color. Colloidal suspensions are the subject of interface and colloid science. This field of study was introduced in 1845 by Italian ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stable Marriage Problem
In mathematics, economics, and computer science, the stable marriage problem (also stable matching problem) is the problem of finding a stable matching between two equally sized sets of elements given an ordering of preferences for each element. A matching is a bijection from the elements of one set to the elements of the other set. A matching is ''not'' stable if: In other words, a matching is stable when there does not exist any pair (''A'', ''B'') which both prefer each other to their current partner under the matching. The stable marriage problem has been stated as follows: The existence of two classes that need to be paired with each other (heterosexual men and women in this example) distinguishes this problem from the stable roommates problem. Applications Algorithms for finding solutions to the stable marriage problem have applications in a variety of real-world situations, perhaps the best known of these being in the assignment of graduating medical students to th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
