the mode profile of the he11 mode of a step index fiber can be approximated by a gaussian distribution with a 1 / e width w given by : where : d is the core diameter, and v is the v - number. for our f - sv fiber, for which v = 2, the gaussian width is approximately 28 % larger than the core diameter, so the light should be focused to a spot size 1. 28 times the core diameter at the fiber surface. for a gaussian laser beam, the required beam diameter d incident upon focusing lens of focal length f to produce a focused spot of diameter w is d = 4λf / ( πw ). given the laser beam waist and divergence, its easy to determine the distance needed between the focusing lens and the laser to expand the beam to the required diameter. the mode field diameter is now given to provide easier matching of lens to optical fiber for a gaussian beam. a high numerical aperture lens must collimate the diverging output beam of a laser diode. newports f - l series diode laser focusing lenses, are ar - coated for high transmittance at popular laser diode wavelengths and with numerical apertures up to 0. 5 are useful for collimating or focusing. mode scrambling and filtering many multimode fiber experiments are sensitive to the distribution of power among the fibers modes. this is determined by the launching optics, fiber perturbations, and the fibers length. mode scrambling is a technique that distributes the optical power in a fiber among all the guided modes. mode filtering simulates the effects of kilometer lengths of fiber by attenuating higher - order fiber modes. figure 8launching conditions in a multimode optical fiber. one scrambling technique is to splice a length of graded - index fiber between two pieces of step - index fiber this ensures that the downstream fibers core is overfilled regardless of launch conditions. mode filtering can be achieved by wrapping a fiber several times around a finger - sized mandrel ; bending sheds the high - order modes. one way to achieve both scrambling and filtering is to introduce microbending to cause rapid coupling between all fiber modes and attenuation of high - order modes. one approach is to place a stripped section of fiber in a box filled with lead shot. a more precise way is to use newports fm - 1 mode scrambler. this specially designed tool uses a calibrated mechanism to introduce microbending for mode scrambling and filtering. ( a )


of fiber in a box filled with lead shot. a more precise way is to use newports fm - 1 mode scrambler. this specially designed tool uses a calibrated mechanism to introduce microbending for mode scrambling and filtering. ( a ) overfilled ( b ) underfilledfigure 9a schematic of coupling of light into an optical fiberfigure 10mode scrambler for optical fibers. the bends tend to couple out higher - order and radiation modes and to distribute the light into a distribution of modes that will remain stable over long distances. cladding mode removal some light is invariably launched into a fibers cladding. though cladding modes dissipate rapidly with fiber length, they can interfere with measurements. for example, the output of a single - mode fiber will not have a gaussian distribution if light is propagating in the cladding. you can remove cladding modes by stripping a length of fiber coating and immersing the bare fiber in an index matching fluid such as glycerin. common optical parameters the following is a list of common optical parameters associated with fiber optic components. please call or visit newports website for application notes on how to measure these parameters. figure 11 port configuration : number of input ports x number of output ports. e. g. 2 x 2 coupling ratio : the ratio of the power at an output port to the launched power expressed in db. e. g. - 10log ( p2 / p1 ). isolation : the ratio of the power at an output port in the transmitted wavelength band to that in the extinguished wavelength band, expressed in db. directivity : the ratio of the power returned to any other input port to the launched power, expressed in db. e. g. - 10log ( p4 / p1 ). bandwidth : the range of operating wavelengths over which performance parameters are specified. excess loss : the ratio of the total power at all output ports to the launched power, expressed in db. e. g. - 10log [ ( p2 + p3 ) / p1 ]. uniformity : the difference between maximum and minimum insertion losses. extinction ratio : the ratio of the residual power in an extinguished polarization state to the transmitted power, expressed in db. return loss : the ratio of the power returned to the input port to the launched power, expressed in db. e. g. - 10log ( p5 / p1 ). polarization - dependent loss ( pdl ) : the maximum (


return loss : the ratio of the power returned to the input port to the launched power, expressed in db. e. g. - 10log ( p5 / p1 ). polarization - dependent loss ( pdl ) : the maximum ( peak - to - peak ) variation in insertion loss as the input polarization varies, expressed in db. fiber optic communications the theoretical bandwidth of optical fiber transmission in the 1550 nm window alone is on the order of terabits. current fiber optic systems have not even begun to utilize the enormous potential bandwidth that is possible. there are two methods that are employed to achieve an increase in bandwidth. the first is known as time division multiplexing or tdm. multiple channels are transmitted on a single carrier by increasing the modulation rate and allotting a time slot to each channel. however, more sophisticated high - speed electronics, at both the transmitting and receiving ends of the communications link, are required when increasing the bit rate of a system. and as the bit rate increases, inherent modulation limiting characteristics of optical fibers become dominant. chromatic and polarization mode dispersion cause pulse spreading, which affects the signal quality over longer transmission distances. an alternate method for increasing the capacity of fiber optic communications systems is known as wavelength division multiplexing, or wdm. by this method, capacity can be increased by using more than one optical carrier ( wavelength ) on a single fiber. therefore, adding a second transmitter and receiver to an optical fiber can double the bandwidth of that communications system. this method of increasing the capacity of an optical system has appeal for a variety of reasons. if a system were to increase in capacity using tdm alone, the existing transmitter and receiver would be replaced with a faster and more expensive transmitter / receiver pair. using wdm, the existing transmitter and receiver do not need to be replaced. a second transmitter / receiver pair of a different wavelength is simply added. this is done by coupling, or multiplexing the output of the two lasers into a single fiber. at the receiving end, the two wavelengths are then separated, or demultiplexed, and each optical carrier is routed to its own receiver. for transmission systems using a 1310 nm laser, a second laser at 1550 nm is usually added. the reason for choosing these wavelengths is that they lie in the windows or ranges of least attenuation. this allows the signal to travel a longer distance. the itu ( international telecommunication union ) has proposed a set of closely spaced wavelengths in the 1550 nm window. this method of w


that they lie in the windows or ranges of least attenuation. this allows the signal to travel a longer distance. the itu ( international telecommunication union ) has proposed a set of closely spaced wavelengths in the 1550 nm window. this method of wdm is known as dense wavelength division multiplexing, or dwdm. these different wavelengths or channels, are spaced 100 ghz apart, which is approximately 0. 8 nm. this set of channels is commonly known as the itu - t grid, and is specified in frequency. the reason the 1550 nm window was chosen by the itu is twofold : it is in one of the windows that has the smallest amount of attenuation ; and it also lies in the band in which erbium doped optical amplifiers operate. itu - t dwdm grid the following diagram is a conceptual example of a fiber optic network. the all - optical network the all - optical network will be the next evolution in optical communications. current dwdm systems are point - to - point links meaning that the signals have a single distinct starting and ending point. research is being performed to help these networks evolve into fully configurable networks, which are not limited to fixed point - to - point links. transparency in the optical layer opens many possibilities for the future. digital and analog transmission can occur on the same fiber. different bit rates using different protocols will all travel together. current research is being performed on reconfiguring an optical network in real time. wavelength selective switching allows wavelengths to be routed through the network individually. some of the applications of this are for network restoration and redundancy, which may reduce or entirely eliminate the need for an entire back up system to help the network recover from failures such as equipment malfunctions or fiber breaks. a reconfigurable network may offer bandwidth on demand to configure itself to optimize for traffic bottlenecks. the future may also include wavelength translation to convert traffic on one wavelength to another wavelength in the optical domain. all optical switching is still in the research phase ; however, researchers are looking for ways to create reliable, low loss switches with fast switching speeds. investigation into the possibility of optical packet switching and other novel technologies are currently underway. the all - optical network may be just around the corner. photonic crystal fibers ( pcfs ) photonic crystal fiber ( pcf ) is a subset of photonic crystals. the field of pcf was first explored in the latter half of 1990 ' s and quickly


network may be just around the corner. photonic crystal fibers ( pcfs ) photonic crystal fiber ( pcf ) is a subset of photonic crystals. the field of pcf was first explored in the latter half of 1990 ' s and quickly evolved into a commercial technology. pcfs are generally divided into two main categories : index guiding fibers that have a solid core, and photonic bandgap fibers that have periodic microstructured elements and a core of low index material ( e. g. hollow core ). they can provide characteristics that ordinary optical fiber cannot, such as : single - mode operation from the uv to ir with large mode - field diameters, exceptionally high nonlinearity, numerical aperture ( na ) ranging from very low to about 0. 9, and optimized dispersion properties. applications of pcfs are found in a wide range of research fields like spectroscopy, metrology, biomedicine, imaging, telecommunication, industrial machining, and military. fabrication and characteristicsfigure 12close - up view of pcf preform the typical starting point for manufacturing of an index guided pcf is an array of hollow capillary silica tubes bundled around a pure silica rod replacing the center capillary. for photonic bandgap ( pbg ) fibers, one or more capillary tubes may simply be left out in the center of the preform in order to create a hollow ' defect ' core. a sleeving tube surrounds the entire assembly that forms the preform. in a fiber draw tower, the preform is heated to around 2000°c and it is carefully pulled into fiber with the aid of gravity and pressure. typical outer fiber diameter is 125 µm, but diameters from 80 to around 700 µm are routinely fabricated. this fiber maintains the structure of the preform, but now on a microscopic scale. standard protective polymer coatings are applied to the fibers in order to improve handling characteristics. figure 13most pcf fiber can be connectorized too. call newport for more information. the dispersion characteristics of pcfs can be manipulated to create fibers having zero, low, or anomalous dispersion at visible wavelengths. the dispersion can also be flattened. combining these features with small mode field areas results in outstanding nonlinear fibers. by altering the pattern of air holes or the materials used, it is possible to manipulate other characteristics of pcfs, such as the single - mode cut - off wavelength, the na, and the nonlinear coefficient.


fiber technology, where the light is guided using solid glasses with different refractive indices, several new properties may be realized using pcf technology. for example : - fibers that are single - mode in a very broad spectral range ( in principle all wavelengths ) - very small mode sizes may be obtained ( down to approx. 1 µm ) - very large mode sizes may be obtained ( up to 25 µm or larger ) - zero dispersion wavelengths below 1300 nm is possible ( down to approx. 600 nm ) - exceptionally large birefringence close to 10 - 2 can be realized - very high numerical apertures up to 0. 9 may be obtained hence, pcfs are ideally suited for applications requiring large non - linearities, broadband operation with single - mode guidance, large mode areas, light collection from a large solid angle, etc. figure 17large mode area fiber ( f - sm series ) figure 18near field image of f - sm fiber at 1550 nmfigure 19mode structure of f - sm20 fiber formation of broad continuous spectra through propagation of short femto or picosecond - range high power pulses through nonlinear media ( also known as supercontinuum generation, or scg ) was first observed in 1970 and has since then been studied extensively in many different materials. the term supercontinuum does not cover a specific phenomenon but rather a plethora of nonlinear effects leading to considerable spectral broadening of optical pulses and thereby potentially octave - spanning output. the involved nonlinear effects depend on the dispersion in the material and count effects like self - phase modulation ( spm ), raman scattering, phase matching and solitons. results on scg in pcfs have previously been presented with pumping in the anomalous dispersion regime or at the zero - dispersion wavelength in both the visible and the infrared wavelength range. most experiments utilize femtosecond pumping as this results in spectacularly broad spectra. picosecond pumping yields more narrow spectra, but does so with far cheaper laser sources and is therefore commercially interesting. although scg can be observed in a drop of water given enough pumping power, pcfs are ideal media for scg as the dispersion can be designed to facilitate continuum generation in a specific region. in this way, it is possible to convert light to both higher and lower wavelength, just like super wide spectra covering more than an octave is achievable at previously unthinkable low power levels. practical super


contact : ken kingery, nscl, office : 517 - 908 - 7482, kingery @ nscl. msu. edu published january 4, 2012 for immediate release east lansing, mich. – the recent measurement of the mass of the short - lived rare isotope manganese - 66 has made it possible for nuclear astrophysicists to pin down the underlying heating elements of one of the universe ’ s most fantastic phenomena — accreting neutron stars. out in the cold depths of space, billions of the densest objects known to man sit quietly while their nuclear decomposition processes play out. but some of them are hungry. some neutron stars sit close enough to a neighboring star for its immense gravity to begin pulling matter from its neighbor into its own mass in an ongoing thermonuclear process. but sooner or later, the fuel for the neutron star is exhausted and it begins to cool rapidly. through observations of this cooling process and measurements taken at nuclear physics laboratories such as the national superconducting cyclotron laboratory ( nscl ), scientists can deduce the inner workings of neutron stars. in the recent experiment at nscl, researchers measured the mass of manganese - 66, which sits right next to iron - 66 on the nuclear chart. based on the newly discovered mass and previous measurements of iron - 66, scientists can determine where in the crust of a neutron star the layer of iron - 66 lies, which is one of two heating elements in neutron stars. “ on earth, iron - 66 is a rare short - lived isotope with a half - life of about 400 ms, ” said alfredo estrade, postdoctoral researcher with st. mary ’ s university in halifax, canada, and gsi in darmstadt, germany, and lead author of the study. “ however, it also is part of the crust of accreting neutron stars, where it becomes stable due to its high density and it heats the crust by capturing electrons. ” scientists at nscl calculated the mass of manganese - 66 by doing a time - of - flight experiment. krypton - 86 was accelerated up to 40 percent of the speed of light and smashed into a thin foil of beryllium. some of the ions shattered after hitting other nuclei in the foil, creating a smorgasborg of new isotopes and particles. the facility then filtered out about 100 desired types of isotopes, some of which they wanted to measure and others that they used for calibrations. the filtered isotopes traveled down


representative theory of perception, also known as indirect realism, epistemological dualism, and the veil of perception, is a philosophical concept. it states that we do not ( and cannot ) perceive the external world directly ; instead we know only our ideas or interpretations of objects in the world. thus, a barrier or a veil of perception prevents first - hand knowledge of anything beyond it. the " veil " exists between the mind and the existing world. the debate then occurs about where our ideas come from, and what this place is like. an indirect realist believes our ideas come from sense data of a real, material, external world ( unlike idealists ). the doctrine states that in any act of perception, the immediate ( direct ) object of perception is only a sense - datum that represents an external object. aristotle was the first to provide an in - depth description of indirect realism. in on the soul he describes how the eye must be affected by changes in an intervening medium rather than by objects themselves. he then speculates on how these sense impressions can form our experience of seeing and reasons that an endless regress would occur unless the sense itself were self aware. he concludes by proposing that the mind is the things it thinks. he calls the images in the mind " ideas ". the way that indirect realism involves intermediate stages between objects and perceptions immediately raises a question : how well do sense - data represent external objects, properties, and events? indirect realism creates deep epistemological problems, such as solipsism and the problem of the external world. nonetheless, indirect realism has been popular in the history of philosophy and has been developed by many philosophers including bertrand russell, baruch spinoza, rene descartes, and john locke. representationalism is one of the key assumptions of cognitivism in psychology. potential results of representative realism a problem with representationalism is that if simple data flow and information processing is assumed then something in the brain, described as a homunculus, must be viewing the perception. this suggests that some physical effect or phenomenon other than simple data flow and information processing might be involved in perception. this was not an issue for the rationalist philosophers such as descartes, since cartesian dualism held that there is a supernatural " homunculus " in the form of the soul. for those who doubt dualism, explaining precisely what it is that sees the representation is problematic. but if the transfer of information into a " mind " is thought to be the only explanation of how we


, i am referring to the process of interpreting the sense - data i am receiving from the eiffel tower in an act of mental representation. the term " eiffel tower " refers to the eiffel tower, and not to the mental representation of the tower, which is the result of the act of " seeing ". thus, both of us can refer to the same object while making our own unique representations of that object. representative realism does, unlike naive realism, take into account sense data ( the way in which the object is interpreted, not simply the objective, mathematical object ) - this induces the veil of perception wherein we are unsure the table we look at exists due to there being no direct objective proof of its existence. in other words, the table i ' m looking at appears to have a particular shape to me, due to my angle of vision, and to have a particular colour due to the way in which the light bounces off it relative to my position, and that appearance differs from the appearance of the table as seen by the person next to me. each of us sees not the actual table, but an appearance of it which merely represents an actual table out there. the representative theory of perception states that we do not perceive the external world directly ; instead we perceive our personal interpretation of an object by way of sense data. a naive realist assumes she sees the dog upon perceiving a dog, whereas a representative realist assumes she sees a sensory representation of the dog upon perceiving a dog. the external world is real and continues to exist unobserved. but we are only aware of it indirectly. our perception of the external world is mediated by way of sense data such as photons and sound waves. we perceive a representation of reality ( not the reality itself ) ; this has been given many names : ideas, sense data, percept or appearance. thus representative realism is the idea that our perceptions are directly caused by the intrinsic qualities of objects, and based on these perceptions we can infer things about these objects. the 17th century philosopher john locke most prominently advocated this theory. the term he used was not " sense - datum " but " idea. " " idea " as used in the theory of perception is a technical term, meaning roughly the same thing as sense - datum, and this article does not discuss any differences in meaning that the two terms might have. john locke thought objects had two classes of qualities : - primary qualities are qualities which are ' explanatorily basic


the same thing as sense - datum, and this article does not discuss any differences in meaning that the two terms might have. john locke thought objects had two classes of qualities : - primary qualities are qualities which are ' explanatorily basic ' - which is to say, they can be referred to as the explanation for other qualities or phenomena without requiring explanation themselves - and they are distinct in that our sensory experience of them resembles them in reality. ( for example, one perceives an object as spherical precisely because of the way the atoms of the sphere are arranged. ) primary qualities cannot be removed by either thought or physical action, and include mass, movement, and, controversially, solidity ( although later proponents of the distinction between primary and secondary qualities usually discount solidity ). - secondary qualities are qualities which one ' s experience does not directly resemble ; for example, when one sees an object as red, the sensation of seeing redness is not produced by some quality of redness in the object, but by the arrangement of atoms on the surface of the object which reflects and absorbs light in a particular way. secondary qualities include colour, smell, and taste. in contemporary philosophy, epistemological dualism has come under sustained attack by philosophers like wittgenstein ( the private language argument ) and wilfrid sellars in his seminal essay " empiricism and the philosophy of mind. " indirect realism is argued to be problematical because of ryle ' s regress and the apparent need for a homunculus. these problems have led some philosophers to abandon realism and suggest the existence of dualism and others to propose, or suggest through emergentism, that some form of new physics is operating in the brain such as quantum mind, space - time theories of consciousness - online papers on representationalism, by various authors, compiled by david chalmers - harold i. brown, " direct realism, indirect realism, and epistemology ". philosophy and phenomenological research, vol. 52, no. 2. ( jun., 1992 ), pp. 341 - 363. - what do we perceive and how do we perceive it? ( pdf file ) - neurological explanation for paranormal experiences - the representationalism web site - mccreery, c., " perception and hallucination : the case for continuity. ” oxford : oxford forum ( 2006 ). an analysis of empirical arguments for representationalism. online pdf


materials enable the ideas of scientists to meet the needs of engineers. research into the relationships between the atomic structure of materials and their physical and mechanical properties, both in the united states and elsewhere, is leading to exciting new alloys and compounds that can be designed to exhibit a wide range of useful properties. for this reason a number of federal agencies, including the department of energy, department of defense, department of commerce, and advisory bodies, such as the office of science and technology policy and the national research council, have identified materials as a critical technology vital to our nation ' s national security and economic competitiveness. the integrated materials research laboratory ( imrl ) enables sandia to develop new and superior materials that meet government and industrial needs. this 140, 000 square foot building houses most of the advanced materials research and development functions at sandia. the facility integrates research from the atomic scale, through the development of electronic devices, to full scale mechanical components. the experimental work is augmented by advanced computer modeling and simulation techniques, another area of sandia ' s expertise. a wide variety of types of materials will be investigated : advanced metallic alloys, semiconductors for electronic and photonic applications, high temperature superconductors, ceramics, metals with properties tailored for improved resistance to friction, wear, corrosion and erosion, etc., and laser, optical and dielectric materials. the imrl has been built outside of sandia ' s secure area to facilitate technical cooperation with researchers from industry and universities. the new four story building has permitted sandia to bring together some 250 materials researchers previously scattered about the campus. it also includes space for postdoctoral researchers and guests from other organizations, facilitating the collaborative generation of new ideas, and the subsequent transfer of novel pre - competitive technologies to practice. the imrl is strategically located with our microelectronics development, compound semiconductor research and robotics manufacturing science and engineering laboratories. this drives the integration of materials research with advanced microelectronic component development creating a set of leading edge facilities in what may be termed an integrated microsystems technology park. we have developed a variety of solution chemistry routes to ceramic powders in order to control such important powder properties as particle size, agglomerate structure, dopant levels, and impurities. the ability to control powder properties is important because the microstructural and electrical properties of ceramics are strongly influenced by the nature of the powder used in their fabrication. this solution processing approach is illustrated above for the sandia - developed process to prepare high field zno varisto


problems of philosophy chapter 5 - knowledge by acquaintance and knowledge by description after distinguishing two types of knowledge, knowledge of things and knowledge of truths, russell devotes this fifth chapter to an elucidation of knowledge of things. he further distinguishes two types of knowledge of things, knowledge by acquaintance and knowledge by description. we have knowledge by acquaintance when we are directly aware of a thing, without any inference. we are immediately conscious and acquainted with a color or hardness of a table before us, our sense - data. since acquaintance with things is logically independent from any knowledge of truths, we can be acquainted with something immediately without knowing any truth about it. i can know the color of a table " perfectly and completely when i see it " and not know any truth about the color in itself. the other type of knowledge of things is called knowledge by description. when we say we have knowledge of the table itself, a physical object, we refer to a kind of knowledge other than immediate, direct knowledge. " the physical object which causes such - and - such sense - data " is a phrase that describes the table by way of sense - data. we only have a description of the table. knowledge by description is predicated on something with which we are acquainted, sense - data, and some knowledge of truths, like knowing that " such - and - such sense - data are caused by the physical object. " thus, knowledge by description allows us to infer knowledge about the actual world via the things that can be known to us, things with which we have direct acquaintance ( our subjective sense - data ). according to this outline, knowledge by acquaintance forms the bedrock for all of our other knowledge. sense - data is not the only instance of things with which we can be immediately acquainted. for how would we recall the past, russell argues, if we could only know what was immediately present to our senses. beyond sense - data, we also have " acquaintance by memory. " remembering what we were immediately aware of makes it so that we are still immediately aware of that past, perceived thing. we may therefore access many past things with the same requisite immediacy. beyond sense - data and memories, we possess " acquaintance by introspection. " when we are aware of an awareness, like in the case of hunger, " my desiring food " becomes an object of acquaintance. introspective acquaintance is a kind of acquaintance with our own minds that may be understood as self - consciousness. however, this self - consciousness is really more


in the case of hunger, " my desiring food " becomes an object of acquaintance. introspective acquaintance is a kind of acquaintance with our own minds that may be understood as self - consciousness. however, this self - consciousness is really more like a consciousness of a feeling or a particular thought ; the awareness rarely includes the explicit use of " i, " which would identify the self as a subject. russell abandons this strand of knowledge, knowledge of the self, as a probable but unclear dimension of acquaintance. russell summarizes our acquaintance with things as follows : " we have acquaintance in sensation with the data of the outer senses, and in introspection with the data of what may be called the inner sense — thoughts, feelings, desires, etc. ; we have acquaintance in memory with things which have been data either of the outer senses or of the inner sense. further, it is probable, though not certain, that we have acquaintance with self, as that which is aware of things or has desires towards things. " all these objects of acquaintance are particulars, concrete, existing things. russell cautions that we can also have acquaintance with abstract, general ideas called universals. he addresses universals more fully later in chapter 9. russell allocates the rest of the chapter to explaining how the complicated theory of knowledge by description actually works. the most conspicuous things that are known to us by description are physical objects and other people ' s minds. we approach a case of having knowledge by description when we know " that there is an object answering to a definite description, though we are not acquainted with any such object. " russell offers several illustrations in the service of understanding knowledge by description. he claims that it is important to understand this kind of knowledge because our language uses depends so heavily on it. when we say common words or proper names, we are really relying on the meanings implicit in descriptive knowledge. the thought connoted by the use of a proper name can only really be explicitly expressed through a description or proposition. bismarck, or " the first chancellor of the german empire, " is russell ' s most cogent example. imagine that there is a proposition, or statement, made about bismarck. if bismarck is the speaker, admitting that he has a kind of direct acquaintance with his own self, bismarck might have voiced his name in order to make a self - referential judgment, of which his name is a constituent. in this simplest case, the " proper name has the direct use which it always wishes to have, as simply


own self, bismarck might have voiced his name in order to make a self - referential judgment, of which his name is a constituent. in this simplest case, the " proper name has the direct use which it always wishes to have, as simply standing for a certain object, and not for a description of the object. " if one of bismarck ' s friends who knew him directly was the speaker of the statement, then we would say that the speaker had knowledge by description. the speaker is acquainted with sense - data which he infers corresponds with bismarck ' s body. the body or physical object representing the mind is " only known as the body and the mind connected with these sense - data, " which is the vital description. since the sense - data corresponding to bismarck change from moment to moment and with perspective, the speaker knows which various descriptions are valid. still more removed from direct acquaintance, imagine that someone like you or i comes along and makes a statement about bismarck that is a description based on a " more or less vague mass of historical knowledge. " we say that bismarck was the " first chancellor of the german empire. " in order to make a valid description applicable to the physical object, bismarck ' s body, we must find a relation between some particular with which we have acquaintance and the physical object, the particular with which we wish to have an indirect acquaintance. we must make such a reference in order to secure a meaningful description. to usefully distinguish particulars from universals, russell posits the example of " the most long - lived of men, " a description which wholly consists of universals. we assume that the description must apply to some man, but we have no way of inferring any judgment about him. russell remarks, " all knowledge of truths, as we shall show, demands acquaintance with things which are of an essentially different character from sense - data, the things which are sometimes called ' abstract ideas ', but which we shall call ' universals '. " the description composed only of universals gives no knowledge by acquaintance with which we might anchor an inference about the longest - lived man. a further statement about bismarck, like " the first chancellor of the german empire was an astute diplomatist, " is a statement that contains particulars and asserts a judgment that we can only make in virtue of some acquaintance ( like something heard or read ). statements about things known by description function in our language as statements about the " actual thing described ; " that is, we intend to refer to that thing.


judgment that we can only make in virtue of some acquaintance ( like something heard or read ). statements about things known by description function in our language as statements about the " actual thing described ; " that is, we intend to refer to that thing. we intend to say something with the direct authority that only bismarck himself could have when he makes a statement about himself, something with which he has direct acquaintance. yet, there is a spectrum of removal from acquaintance with the relevant particulars : from bismarck himself, " there is bismarck to people who knew him ; bismarck to those who only know of him through history " and at a far end of the spectrum " the longest lived of men. " at the latter end, we can only make propositions that are logically deducible from universals, and at the former end, we come as close as possible to direct acquaintance and can make many propositions identifying the actual object. it is now clear how knowledge gained by description is reducible to knowledge by acquaintance. russell calls this observation his fundamental principle in the study of " propositions containing descriptions " : " every proposition which we can understand must be composed wholly of constituents with which we are acquainted. " indirect knowledge of some particulars seems necessary if we are to expressively attach meanings to the words we commonly use. when we say something referring to julius caesar, we clearly have no direct acquaintance with the man. rather, we are thinking of such descriptions as " the man who was assassinated on the ides of march " or " the founder of the roman empire. " since we have no way of being directly acquainted with julius caesar, our knowledge by description allows us to gain knowledge of " things which we have never experienced. " it allows us to overstep the boundaries of our private, immediate experiences and engage a public knowledge and public language. this knowledge by acquaintance and knowledge by description theory was a famous epistemological problem - solver for russell. its innovative character allowed him to shift to his moderate realism, a realism ruled by a more definite categorization of objects. it is a theory of knowledge that considers our practice of language to be meaningful and worthy of detailed analysis. russell contemplates how we construct a sense of meaning about objects remote from our experience. the realm of acquaintance offers the most secure references for our understanding of the world. knowledge by description allows us to draw inferences from our realm of acquaintance but leaves us in a more vulnerable position. since knowledge by description also depends on truths, we are prone to


of acquaintance offers the most secure references for our understanding of the world. knowledge by description allows us to draw inferences from our realm of acquaintance but leaves us in a more vulnerable position. since knowledge by description also depends on truths, we are prone to error about our descriptive knowledge if we are somehow mistaken about a proposition that we have taken to be true. critics of this theory have held that russell ' s hypothesis of knowledge by description is confusing. his comments when defining sense - data, that the physical world is unknowable to us, contradict his theory of knowledge by descriptions. he implies that " knowledge by description " is not really a form of knowledge since we can only know those things with which we are acquainted and we cannot be acquainted with physical objects. russell ' s theory amounts to the proposition that our acquaintance with mental objects appears related in a distant way to physical objects and renders us obliquely acquainted with the physical world. sense - data are our subjective representations of the external world, and they negotiate this indirect contact. while innovative, russell ' s theory of knowledge by description is not an attractive theory of knowledge. it is clearly unappealing because our impressions of the real world, on his view, are commensurate with muddy representations of reality. though we have direct access to these representations, it seems impossible to have any kind of direct experience of reality. reality, rather, consists in unconscious, inferential pieces of reasoning. readers ' notes allow users to add their own analysis and insights to our sparknotes — and to discuss those ideas with one another. have a novel take or think we left something out? add a readers ' note!


in a galaxy simultaneously, rather than observing one location at a time. stis can also record a broader span of wavelengths in the spectrum of a star at one time. as a result, stis is much more efficient at obtaining scientific data than the earlier hst spectrographs. a power supply in stis failed in august 2004, rendering it inoperable. during the servicing mission in 2009, astronauts successfully repaired the stis by removing the circuit card containing the failed power supply and replacing it with a new card. since stis was not designed for in - orbit repair of internal electronics, this task was a substantial challenge for the astronaut crew. near infrared camera and multi - object spectrometer the near infrared camera and multi - object spectrometer ( nicmos ) is an hst instrument providing the capability for infrared imaging and spectroscopic observations of astronomical targets. nicmos detects light with wavelengths between 0. 8 and 2. 5 microns - longer than the human - eye limit. the sensitive hgcdte arrays that comprise the infrared detectors in nicmos must operate at very cold temperatures. after its deployment, nicmos kept its detectors cold inside a cryogenic dewar ( a thermally insulated container much like a thermos bottle ) containing frozen nitrogen ice. nicmos is hst ' s first cryogenic instrument. the frozen nitrogen ice cryogen in nicmos was exhausted in early 1999, rendering the instrument inoperable at that time. an alternate means of cooling the nicmos was developed and installed in the march 2002 servicing mission. this device uses a mechanical cooler to cool the detectors to the low temperatures necessary for operations. the technology for this cooler was not available when the instrument was originally designed, but fortunately became available in time to support the reactivation of the instrument. since late 2008, the nicmos cooling system ( ncs ) has experienced difficulties maintaining the instrument ’ s nominal scientific operating state, in which the detectors are maintained at ~ 77k. repeated restart attempts have demonstrated that it is not possible to restart the ncs in a cold state immediately following safing events. the main culprit for the problems is believed to be water ice in the primary ( circulator ) loop of the ncs. an inefficient approach to this problem would be to put the ncs through a several - month warm - up / cooldown cycle and hope that there is an opportunity for science prior to the next payload safing event. the only feasible path towards satisfactory operation of nic


achieving quality the final piece of the puzzle properly calibrated testing equipment ensures quality in order for a business to generate a high - quality product or service, it is essential to obtain a quality measurement system that will be used to study the integrity of its finished product. in the certification industry, testing equipment is essential to measure the different variables that could potentially alter the quality of a raw material, finished product or final status on a certification report. the quality of a product or service is compromised if the test equipment used to measure the final quality is not reading accurate results. this is why a flawless calibration system is the final puzzle piece to achieving a high - quality product or service. what is calibration? in this article, calibration will be defined as the comparison between measurements. during the calibration of a test instrument, a device with a known magnitude or assigned correctness, known as a standard, will be used to check the measuring accuracy of a test instrument. calibration ensures that a measuring instrument is providing results for a sample that fall in an acceptable accurate range. accurate testing results allow manufacturers or certification agencies to eliminate or minimize factors that could cause inaccurate measurements during production or testing. calibration procedures naturally vary depending on the instrument being calibrated. generally, the test instrument is used to test calibrators, which are one or more test samples that have known values. the results are then used to establish a relationship between the measurement instrument and the known values. the calibration processes eliminate or “ zero out ” the current instrument error at the specified calibration points. this process basically “ teaches ” the instrument to produce more accurate results. after a test instrument is calibrated, it will provide more accurate results for unknown values tested during its everyday normal usage. to keep a successful calibration system, calibrations must be done consistently and on a systematic schedule. when is calibration needed? during the manufacturing or certification process of any product, there may be many different types of test instruments used to determine the quality of a product or service. the question of which test instruments need to be calibrated and which do not is answered by whether or not the test performed and the test instrument used affect the final quality of the product or service. there are situations in which a test instrument does not need to be calibrated. if the readings of the test instrument are for reference only, and the accuracy of the test results have little or no impact on the quality of the product or service


i said that there are n ^ 2 interactions and not ( n ^ 2 ) / 2? this is because each form factor is like a diode in that it only handles energy going in one direction : from a " source surface " to a " destination surface. " in this case, we ’ ll say that the source surfaces are index by columns and destination surfaces are indexed by rows. source surfaces will emit their energy to the destination surfaces. now lets solve the matrix. to do this, we simply visit each column ( source ) in the matrix and emit energy to each row ( destination ) in that column. when we do this, we ’ ll be placing some of that radiated energy ( from the source ) in the illumination value for the destination. but these surfaces are reflectors, which means they ’ re going to reflect some energy back into the scene. based on the surface ’ s reflectivity, we ’ ll add a little bit of energy to the destination ’ s radiative energy. this radiative energy will eventually make its way back into the scene ( i. e. to the other surfaces ) as we progress through the matrix. if the destination is a perfect reflector ( i. e. it reflects every single bit of energy it receives - a mirror ) then there will be no energy stored in the destination ’ s illumination, it would all go to its radiative energy. the inverse is also true : a perfectly black surface might not reflect any energy back into the scene, absorbing it all, so every bit of energy it receives is stored in its illumination value. if you ’ re starting to think that we ’ re making a black surface white, we ’ re not. remember, we ’ re dealing with light, so the color of a surface is ultimately multiplied by its illumination. in the case of the perfectly black surface, the surface remains visually black. once we ’ ve gone through the matrix once, we do it all over again. this is necessary because we we ’ re storing some energy as illumination, and some as radiative energy. now it ’ s time to go through the matrix again and start distributing that reflected radiative energy. we ’ ll go through this matrix over and over again until the total amount of radiative energy for all surfaces is relatively small. the next step if you made it this far without getting lost, you ’ re in the home stretch. there ’ s still a lot we haven ’ t covered yet, so let ’ s move on. i ’


element from its source element. ironically, this is called " gathering. " the progressive refinement approach reversed this and defined ( the other incredibly ironic term ) " shooting. " the basic idea behind progressive refinement starts by finding the surface with the most energy to contribute to the scene ( i. e. has the highest amount of radiative energy. ) this surface would then iterate through all other surfaces, distributing its energy along the way. after this process was completed, the image was then rendered for the user, and the process began again, finding the surface with the most energy to contribute to the scene. each pass would cause another render of the scene, allowing the user to progressively evaluate the progress. if the progress showed a problem along the way ( an illumination surface was in the wrong place or the wrong color ) they could stop the process and make the needed adjustments. during this process, the user would see a completely dark scene progress to a fully lit scene. to accommodate this sharp contrast in visual difference from beginning to end, the progressive refinement technique added something called the " ambient term ". before i continue, i want to point something out that is pretty important in radiosity. there is no such thing as ambient light in real life. ambient light is something that was invented to accommodate the need for what appears to be a " global light " in real life. but in reality, ambient light doesn ’ t exist. rather, light is always being reflected from surface to surface, which is how it finds its way into all the nooks and crannies of real - world detail. before the advent of radiosity, ambient light was the best thing available to the typical rendering architectures. it is safe to think of radiosity is a more accurate solution to ambient ( global ) light. this is why radiosity is considered a technique for " global illumination. " the ambient term starts off as a " differential area sum " of the radiative energy for the entire scene. what this means is that it ’ s a number that represents the average amount of light that each surface will receive throughout the processing of the entire radiosity solution. we can calculate that average without doing all the work simply because it ’ s an average amount of energy, not a specific amount of energy for a single surface. as each progressive pass emits the radiative energy for a surface, the ambient term is slowly decreased. as the total radiative energy of the scene approaches zero, so does the ambient term ( though


science fiction ( abbreviated sf or sci - fi with varying punctuation and capitalization ) is a broad genre of fiction that often involves speculations based on current or future science or technology. fiction is the telling of stories which are not real more specifically fiction is an imaginative form of narrative, one of the four basic rhetorical modes. science ( from the latin scientia, meaning " knowledge " or " knowing " is the effort to discover, and increase human understanding technology is a broad concept that deals with a species ' usage and knowledge of tools and crafts and how it affects a species ' ability to control and adapt science fiction is found in books, art, television, films, games, theater, and other media. in organizational or marketing contexts, science fiction can be synonymous with the broader definition of speculative fiction, encompassing creative works incorporating imaginative elements not found in contemporary reality ; this includes fantasy, horror, and related genres. speculative fiction is a term used as an inclusive descriptor covering a group of fiction genres that speculate about worlds that are unlike the real world in fantasy is a genre that uses magic and other supernatural forms as a primary element of plot, theme, and / or setting horror fiction is broadly fiction in any medium intended to scare unsettle or horrify the audience science fiction differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically established or scientifically postulated laws of nature ( though some elements in a story might still be pure imaginative speculation ). science fiction is largely based on writing entertainingly and rationally about alternate possibilities in settings that are contrary to known reality. these include : exploring the consequences of such differences is the traditional purpose of science fiction, making it a " literature of ideas ". outer space, often simply called space, comprises the relatively empty regions of the universe outside the escape velocities of celestial bodies. extraterrestrial life is life originating outside of the earth. this article details time travel itself for other uses see time traveler. psionics is the study and / or practice of using the mind to induce paranormal phenomena nanotechnology, sometimes shortened to nanotech, refers to a field of applied science whose theme is the control of matter on an atomic and molecular a robot is a mechanical or virtual artificial agent in practice it is usually an electro - mechanical system which by its appearance or movements science fiction is difficult to define, as it includes a wide range of subgenres and themes. a genre ( ˈʒɑːnrə


mechanical or virtual artificial agent in practice it is usually an electro - mechanical system which by its appearance or movements science fiction is difficult to define, as it includes a wide range of subgenres and themes. a genre ( ˈʒɑːnrə also / ˈdʒɑːnrə / from french " kind " or " sort " from latin : genus ( stem gener - ) is a loose set author and editor damon knight summed up the difficulty by stating that " science fiction is what we point to when we say it ". damon francis knight ( september 19, 1922 & ndash april 15, 2002 ) was an american science fiction author, vladimir nabokov argued that were we rigorous with our definitions, shakespeare ' s play the tempest would have to be termed science fiction. this page is about the novelist for his father the politician see vladimir dmitrievich nabokov. william shakespeare ( baptised the tempest is a comedy written by william shakespeare. it is generally dated to 1610 - 11 and accepted as the last play written solely by him although according to science fiction writer robert a. heinlein, " a handy short definition of almost all science fiction might read : realistic speculation about possible future events, based solidly on adequate knowledge of the real world, past and present, and on a thorough understanding of the nature and significance of the scientific method. robert anson heinlein ( july 7 1907 – may 8 1988 was an american novelist and science fiction writer. scientific method refers to bodies of techniques for investigating phenomena " rod serling ' s stated definition is " fantasy is the impossible made probable. rodman edward " rod " serling ( december 25, 1924 & ndash june 28, 1975 ) was an american screenwriter, best known science fiction is the improbable made possible. " lester del rey wrote, " even the devoted aficionado – or fan - has a hard time trying to explain what science fiction is, " and that the reason for there not being a " full satisfactory definition " is that " there are no easily delineated limits to science fiction. lester del rey ( june 2 1915 & ndash may 10 1993 ) was an american science fiction author and editor. " author mark c. glassy stated that the definition of science fiction was very much like the definition of porn ; you don ' t know what it is, but you know it when you see it. pornography or porn is the explicit depiction of sexual subject matter with the sole intention of sexually exciting the viewer forrest j. ac


physics ( greek physis - φυσις in everyday terms is the science of matter and its motion. astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties ( luminosity, chemistry ( from egyptian keme ( chem meaning " earth " ) is the science concerned with the composition structure and properties many accurate predictions of the future come from the hard science fiction subgenre, but numerous inaccurate predictions have emerged as well. hard science fiction is a category of science fiction characterized by an emphasis on scientific or technical detail or on scientific accuracy or on both for example, arthur c. clarke accurately predicted ( and invented the concept of ) geostationary communications satellites, but erred in his prediction of deep layers of moondust in lunar craters. sir arthur charles clarke, cbe ( 16 december 1917 – 19 march 2008 was a british science fiction author, inventor, and a geostationary orbit ( geo is a geosynchronous orbit directly above the earth ' s equator ( 0° latitude ) with a period equal to the earth ' s some hard sf authors have distinguished themselves as working scientists, including robert forward, gregory benford, charles sheffield, and geoffrey a. landis, while mathematician authors include rudy rucker and vernor vinge. this is about the physicist and science fiction writer you may be looking for his son robert d gregory benford ( born january 30, 1941 in mobile alabama ) is an american science fiction author and astrophysicist who is on the charles sheffield ( june 25, 1935 & ndash november 2, 2002 ) was an english - born mathematician physicist and science fiction geoffrey a landis works as a scientist and writer of science fiction. rudolf von bitter rucker ( born march 22, 1946 in louisville kentucky ) is an american computer scientist and science fiction vernor steffen vinge ( ˈvɪndʒi ( born october 2, 1944 in waukesha wisconsin, u other noteworthy hard sf authors include hal clement, joe haldeman, larry niven, jerry pournelle, kim stanley robinson, robert j. sawyer, and stephen baxter. harry clement stubbs ( may 30, 1922 in somerville massachusetts – october 29, 2003 in milton massachusetts ) better joe william haldeman is an american science fiction author. life and work haldeman was born in 1943 in oklahoma city oklahoma laurence van cott niven ( born april 30, 1938 los angeles california ) is a us science fiction author. jerry eugene pournelle (


of an ego, or as an eternal state of existence into which an ego or self enters or with which it merges. hence it is said : " mere suffering exists, no sufferer the deed is, but no doer of the deed is nibbana is, but not the man that enters the path is, but no traveler on it is literature : for texts on nibbana, see path, 36ff. - see vis. m. xvi. 64ff. - anatta and nibbana, by nyanaponika thera ( wheel 11 ) ; the buddhist doctrine of nibbana, by ven. p. vajiranana & f. story ' rebirth ', is a synonym for patisandhi ( q. v. ). - panna ) : ' morality ( concentration, wisdom ) connected with penetration ' ; s. hana - bhagiya - sila. of aversion ', is one of the 18 chief kinds of insight ; s. vipassana ( 4 ), samatha - vipassana ( 2 ), visuddhi ( vi, 5 ). perception ( or consciousness, or view ) of permanency, is one of the 4 perversions nihilistic view : natthika - ditthi ; exercise ' s. kasina. nimitta : mark, sign ; image ; target, object ; cause, condition. these meanings are used in, and adapted to, many contexts of which only the doctrinal ones are mentioned here. 1. ' mental ( reflex - ) image ', obtained in meditation. in full clarity, it will appear in the mind by successful practice of certain concentration - exercises and will then appear as vividly as if seen by the eye. the object perceived at the very beginning of concentration is called the preparatory image ( parikamma - nimitta ). the still unsteady and unclear image, which arises when the mind has reached a weak degree of concentration, is called the acquired image ( uggaha - nimitta ). an entirely clear and immovable image arising at a higher degree of concentration is the counter - image ( patibhaga - nimitta ). as soon as this image arises, the stage of neighbourhood ( or access ) concentration ( upacara - samadhi ) is reached. for further details, s. kasina, samadhi. 2. ' sign of ( previous ) kamma ' ( kamma - nimit


it is possible to use a hash function to construct a block cipher with a structure similar to des? because a hash function is one way and a block cipher must be reversible ( to decrypt ), how is it possible? migrated from security. stackexchange. com nov 8 ' 12 at 12 : 26 it is possible to build a block cipher out of a great many things. if you want to use a hash function, the classic trick is to follow a feistel structure, which is, incidentally, the same kind of structure than what des uses. the schematics on the wikipedia page are quite clear ; you would use the hash function for the " f " part, which combines one ( sub ) key and one half of the current block, to produce a value which is to be xored with the other half of the current block. the beauty of the scheme is that the " f " function is always invoked in the same direction, both for encryption and for decryption. therefore, it can be a one - way function, like a hash function. luby and rackoff have demonstrated in 1988 that the feistel scheme offers remarkable security with as little as four rounds, provided that the " f " function is " perfect " and that the cipher block size is big enough ( to get the standard " 128 - bit security " out of the luby - rackoff proof, you need 256 - bit blocks ). of course, any concrete hash function cannot be really " perfect " ( see for instance this answer ) and there are a lot of subtle details which can destroy the security of the best thought cipher structure. as usual, you are strongly advised not to build your own crypto ( unless you are quite clear with yourself that you do it for learning and not to actually protect any data of value ). also, if you build such a cipher, you will probably notice that the resulting performance is disappointing. with a secure hash function like sha - 256, you could expect an encryption bandwidth roughly 20 times lower than what aes would get you. it is possible to use a hash function like ( sha family, for instance ) in ofb or cfb ( and possibly ctr ), by using the hash function ( with the key as part of the input! ) in the place of the block cipher encryption. that said, thomas is right - - do not build your own crypto. just use a normal block cipher. you ' ll get better performance ( especially if it ' s


from wikipedia, the free encyclopedia | part of the politics series on | | communism portal | communism is a social structure in which classes are abolished and property is commonly controlled, as well as a political philosophy and social movement that advocates and aims to create such a society. karl marx, the father of communist thought, posited that communism would be the final stage in society, which would be achieved through a proletarian revolution and only possible after a socialist stage develops the productive forces, leading to a superabundance of goods and services. " pure communism " in the marxian sense refers to a classless, stateless and oppression - free society where decisions on what to produce and what policies to pursue are made democratically, allowing every member of society to participate in the decision - making process in both the political and economic spheres of life. in modern usage, communism is often used to refer to bolshevism or marxism - leninism and the policies of the various communist states which had government ownership of all the means of production and centrally planned economies. communist regimes, all inspired only by the leninist current, have historically been authoritarian, repressive, and coercive governments concerned primarily with preserving their own power. as a political ideology, communism is usually considered to be a branch of socialism ; a broad group of economic and political philosophies that draw on the various political and intellectual movements with origins in the work oftheorists of the industrial revolution and the french revolution. communism attempts to offer an alternative to the problems with the capitalist market economy and the legacy of imperialism and nationalism. marx states that the only way to solve these problems is for the working class ( proletariat ), who according to marx are the main producers of wealth in society and are exploited by the capitalist - class ( bourgeoisie ), to replace the bourgeoisie as the ruling class in order to establish a free society, without class or racial divisions. the dominant forms of communism, such as leninism, stalinism, maoism and trotskyism are based on marxism, as well as others forms of communism ( such as luxemburgism and council communism ), but non - marxist versions of communism ( such as christian communism and anarchist communism ) also exist. karl marx never provided a detailed description as to how communism would function as an economic system, but it is understood that a communist economy would consist of common ownership of the means of production, culminating in the negation of the concept of private ownership of capital, which referred to