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Nanoscope
The scanning helium microscope (SHeM) is a novel form of microscopy that uses low-energy (5–100 meV) neutral helium atoms to image the surface of a sample without any damage to the sample caused by the imaging process. Since helium is inert and neutral, it can be used to study delicate and insulating surfaces. Images are formed by rastering a sample underneath an atom beam and monitoring the flux of atoms that are scattered into a detector at each point. The technique is different from a scanning helium ion microscope, which uses charged helium ions that can cause damage to a surface. Motivation Microscopes can be divided into two general classes: those that illuminate the sample with a beam, and those that use a physical scanning probe. Scanning probe microscopies raster a small probe across the surface of a sample and monitor the interaction of the probe with the sample. The resolution of scanning probe microscopies is set by the size of the interaction region betwe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ShEM Diagram2
Shem (; he, שֵׁם ''Šēm''; ar, سَام, Sām) ''Sḗm''; Ge'ez: ሴም, ''Sēm'' was one of the sons of Noah in the book of Genesis and in the book of Chronicles, and the Quran. The children of Shem were Elam, Ashur, Arphaxad, Lud and Aram, in addition to unnamed daughters. Abraham, the patriarch of Jews, Christians, and Muslims, was one of the descendants of Arphaxad. Islamic literature describes Shem as one of the believing sons of Noah. Some sources even identify Shem as a prophet in his own right and that he was the next prophet after his father. Shem is mentioned several times in Genesis 5-11 as well as 1 Chronicles 1:4. In the Bible Genesis 10 Genesis 10:21 refers to relative ages of Shem and his brother Japheth, but with sufficient ambiguity to have yielded different English translations. The verse is translated in the King James Version as: "Unto Shem also, the father of all the children of Eber, the brother of Japheth the elder, even to him were ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SHeM Contrast Mechanism Tree
Shem (; he, שֵׁם ''Šēm''; ar, سَام, Sām) ''Sḗm''; Ge'ez: ሴም, ''Sēm'' was one of the sons of Noah in the book of Genesis and in the book of Chronicles, and the Quran. The children of Shem were Elam, Ashur, Arphaxad, Lud and Aram, in addition to unnamed daughters. Abraham, the patriarch of Jews, Christians, and Muslims, was one of the descendants of Arphaxad. Islamic literature describes Shem as one of the believing sons of Noah. Some sources even identify Shem as a prophet in his own right and that he was the next prophet after his father. Shem is mentioned several times in Genesis 5-11 as well as 1 Chronicles 1:4. In the Bible Genesis 10 Genesis 10:21 refers to relative ages of Shem and his brother Japheth, but with sufficient ambiguity to have yielded different English translations. The verse is translated in the King James Version as: "Unto Shem also, the father of all the children of Eber, the brother of Japheth the elder, even to him were ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Airy Disk
In optics, the Airy disk (or Airy disc) and Airy pattern are descriptions of the best- focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light. The Airy disk is of importance in physics, optics, and astronomy. The diffraction pattern resulting from a uniformly illuminated, circular aperture has a bright central region, known as the Airy disk, which together with the series of concentric rings around is called the Airy pattern. Both are named after George Biddell Airy. The disk and rings phenomenon had been known prior to Airy; John Herschel described the appearance of a bright star seen through a telescope under high magnification for an 1828 article on light for the ''Encyclopedia Metropolitana'': Airy wrote the first full theoretical treatment explaining the phenomenon (his 1835 "On the Diffraction of an Object-glass with Circular Aperture"). Mathematically, the diffraction pattern is characterized by the wavelen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Full Width At Half Maximum
In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve measured between those points on the ''y''-axis which are half the maximum amplitude. Half width at half maximum (HWHM) is half of the FWHM if the function is symmetric. The term full duration at half maximum (FDHM) is preferred when the independent variable is time. FWHM is applied to such phenomena as the duration of pulse waveforms and the spectral width of sources used for optical communications and the resolution of spectrometers. The convention of "width" meaning "half maximum" is also widely used in signal processing to define bandwidth as "width of frequency range where less than half the signal's power is attenuated", i.e., the power is at least half the maximum. In signal processing terms, this is at most −3 dB of attenuatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fraunhofer Diffraction
In optics, the Fraunhofer diffraction equation is used to model the diffraction of waves when plane waves are incident on a diffracting object, and the diffraction pattern is viewed at a sufficiently long distance (a distance satisfying Fraunhofer condition) from the object (in the far-field region), and also when it is viewed at the focal plane of an imaging lens. In contrast, the diffraction pattern created near the diffracting object (in the near field region) is given by the Fresnel diffraction equation. The equation was named in honor of Joseph von Fraunhofer although he was not actually involved in the development of the theory. This article explains where the Fraunhofer equation can be applied, and shows Fraunhofer diffraction patterns for various apertures. A detailed mathematical treatment of Fraunhofer diffraction is given in Fraunhofer diffraction equation. Equation When a beam of light is partly blocked by an obstacle, some of the light is scattered around the o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fresnel Number
The Fresnel number (''F''), named after the physicist Augustin-Jean Fresnel, is a dimensionless number occurring in optics, in particular in diffraction, scalar diffraction theory. Definition For an electromagnetic wave passing through an aperture and hitting a screen, the Fresnel number ''F'' is defined as : F = \frac where : a is the characteristic size (e.g. radius) of the aperture : L is the distance of the screen from the aperture : \lambda is the incident wavelength. Conceptually, it is the number of half-Periodic function, period zones in the wavefront amplitude, counted from the center to the edge of the aperture, as seen from the observation point (the center of the imaging screen), where a half-period zone is defined so that the wavefront Phase (waves), phase changes by \pi when moving from one half-period zone to the next. An equivalent definition is that the Fresnel number is the difference, expressed in half-wavelengths, between the ''slant'' distance from the obs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geometrical Optics
Geometrical optics, or ray optics, is a model of optics that describes light propagation in terms of ''rays''. The ray in geometrical optics is an abstraction useful for approximating the paths along which light propagates under certain circumstances. The simplifying assumptions of geometrical optics include that light rays: * propagate in straight-line paths as they travel in a homogeneous medium * bend, and in particular circumstances may split in two, at the interface between two dissimilar media * follow curved paths in a medium in which the refractive index changes * may be absorbed or reflected. Geometrical optics does not account for certain optical effects such as diffraction and interference. This simplification is useful in practice; it is an excellent approximation when the wavelength is small compared to the size of structures with which the light interacts. The techniques are particularly useful in describing geometrical aspects of imaging, including optical aberra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinhole Main 2-eps-converted-to
A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of engineering. Depending on the material and the placement, a hole may be an indentation in a surface (such as a hole in the ground), or may pass completely through that surface (such as a hole created by a hole puncher in a piece of paper). Types Holes can occur for a number of reasons, including natural processes and intentional actions by humans or animals. Holes in the ground that are made intentionally, such as holes made while searching for food, for replanting trees, or postholes made for securing an object, are usually made through the process of digging. Unintentional holes in an object are often a sign of damage. Potholes and sinkholes can damage human settlements. Holes can occur in a wide variety of materials, and at a wide ran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ionization Energy
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected. Uses Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps. It is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber. The ionizati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Constraint (mathematics)
In mathematics, a constraint is a condition of an optimization problem that the solution must satisfy. There are several types of constraints—primarily equality constraints, inequality constraints, and integer constraints. The set of candidate solutions that satisfy all constraints is called the feasible set. Example The following is a simple optimization problem: :\min f(\mathbf x) = x_1^2+x_2^4 subject to :x_1 \ge 1 and :x_2 = 1, where \mathbf x denotes the vector (''x''1, ''x''2). In this example, the first line defines the function to be minimized (called the objective function, loss function, or cost function). The second and third lines define two constraints, the first of which is an inequality constraint and the second of which is an equality constraint. These two constraints are hard constraints, meaning that it is required that they be satisfied; they define the feasible set of candidate solutions. Without the constraints, the solution would be (0,0), whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Resolution
Optical resolution describes the ability of an imaging system to resolve detail, in the object that is being imaged. An imaging system may have many individual components, including one or more lenses, and/or recording and display components. Each of these contributes (given suitable design, and adequate alignment) to the optical resolution of the system; the environment in which the imaging is done often is a further important factor. Lateral resolution Resolution depends on the distance between two distinguishable radiating points. The sections below describe the theoretical estimates of resolution, but the real values may differ. The results below are based on mathematical models of Airy discs, which assumes an adequate level of contrast. In low-contrast systems, the resolution may be much lower than predicted by the theory outlined below. Real optical systems are complex, and practical difficulties often increase the distance between distinguishable point sources. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereophotogrammetry
Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant imagery and other phenomena. The term photogrammetry was coined by the Prussian architect Albrecht Meydenbauer, which appeared in his 1867 article "Die Photometrographie." There are many variants of photogrammetry. One example is the extraction of three-dimensional measurements from two-dimensional data (i.e. images); for example, the distance between two points that lie on a plane parallel to the photographic image plane can be determined by measuring their distance on the image, if the scale of the image is known. Another is the extraction of accurate color ranges and values representing such quantities as albedo, specular reflection, metallicity, or ambient occlusion from photographs of materials for the purposes of physically based re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
