A condenser is an optical lens which renders a divergent beam from a point source into a parallel or converging beam to illuminate an object. Condensers are an essential part of any imaging device, such as microscopes, slide projectors, telescopes; the concept is applicable to all kinds of radiation undergoing optical transformation, such as electrons in electron microscopy, neutron radiation and synchrotron radiation optics. Condensers are located above the light source and under the sample in an upright microscope, above the stage and below the light source in an inverted microscope, they act to gather light from the microscope's light source and concentrate it into a cone of light that illuminates the specimen. The aperture and angle of the light cone must be adjusted for each different objective lens with different numerical apertures. Condensers consist of a variable-aperture diaphragm and one or more lenses. Light from the illumination source of the microscope passes through the diaphragm and is focused by the lens onto the specimen.
After passing through the specimen the light diverges into an inverted cone to fill the front lens of the objective. The first simple condensers were introduced on pre-achromatic microscopes in the 17th century. Robert Hooke used a combination of a salt water filled globe and a plano-convex lens, shows in the'Micrographia' that he understands the reasons for its efficiency. Makers in the 18th century such as Benjamin Martin and Jones understood the advantage of condensing the area of the light source to that of the area of the object on the stage; this was a simple plano-convex or bi-convex lens, or sometimes a combination of lenses. With the development of the modern achromatic objective in 1829, by Joseph Jackson Lister, the need for better condensers became apparent. By 1837, the use of the achromatic condenser was introduced in France, by Felix Dujardin, Chevalier. English makers early took up this improvement, due to the obsession with resolving test objects such as diatoms and Nobert ruled gratings.
By the late 1840s, English makers such as Ross and Smith. It is erroneously stated that these developments were purely empirical - no-one can design a good achromatic, spherically corrected condenser relying only on empirics. On the Continent, in Germany, the corrected condenser was not considered either useful or essential due to a misunderstanding of the basic optical principles involved, thus the leading German company, Carl Zeiss in Jena, offered nothing more than a poor chromatic condenser into the late 1870s. French makers, such as Nachet, provided excellent achromatic condensers on their stands; when the leading German bacteriologist, Robert Koch, complained to Ernst Abbe, that he was forced to buy a Seibert achromatic condenser for his Zeiss microscope, in order to make satisfactory photographs of bacteria, Abbe produced a good achromatic design in 1878. There are three types of condenser: The chromatic condenser, such as the Abbe where no attempt is made to correct for spherical or chromatic aberration.
It contains two lenses that produce an image of the light source, surrounded by a blue and red color at its edges. The aplanatic condenser is corrected for spherical aberration; the compound achromatic condenser is corrected for both chromatic aberrations. The Abbe condenser is named for its inventor Ernst Abbe, who developed it in 1870; the Abbe condenser, designed for Zeiss, is mounted below the stage of the microscope. The condenser concentrates and controls the light that passes through the specimen prior to entering the objective, it has two controls, one which moves the Abbe condenser closer to or further from the stage, another, the iris diaphragm, which controls the diameter of the beam of light. The controls can be used to optimize brightness, evenness of illumination, contrast. Abbe condensers are difficult to use for magnifications of above 400X, as the aplanatic cone is only representative of a numerical aperture of 0.6. This condenser is composed of two lenses, a plano-convex lens somewhat larger than a hemisphere and a large bi-convex lens serving as a collecting lens to the first.
The focus of the first lens is traditionally about 2mm away from the plane face coinciding with the sample plane. A pinhole cap can be used to align the optical axis of the condenser with that of the microscope; the Abbe condenser is still the basis for most modern light microscope condenser designs though its optical performance is poor. An aplanatic condenser corrects for spherical aberration in the concentrated light path, while an achromatic compound condenser corrects for both spherical and chromatic aberration. Dark field and phase contrast setups are based on an Abbe, aplanatic, or achromatic condenser, but to the light path add a dark field stop or various size phase rings; these additional elements are housed in various ways. In most modern microscope, such elements are housed in sliders that fit into a slot between the illuminator and the condenser lens. Many older microscopes house these elements in a turret-type condenser, these elements are housed in a turret below the condenser lens and rotated into place.
Specialised condensers are used as part of Differential Interference Contrast and Hoffman Modulation Contrast systems, which aim to improve contrast and visibility of transparent specimens. In epifluorescence microscopy, the objective lens acts not only as a magnifier for the light emitted by the fluorescing object, but as a condenser for the incident light; the Arlow-Abbe condenser is a modified Abbe condenser that replaces the iris dia
Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water in plant and algal cells. They use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of other functions, including fatty acid synthesis, much amino acid synthesis, the immune response in plants; the number of chloroplasts per cell varies from one, in unicellular algae, up to 100 in plants like Arabidopsis and wheat. A chloroplast is a type of organelle known as a plastid, characterized by its two membranes and a high concentration of chlorophyll. Other plastid types, such as the leucoplast and the chromoplast, contain little chlorophyll and do not carry out photosynthesis. Chloroplasts are dynamic—they circulate and are moved around within plant cells, pinch in two to reproduce.
Their behavior is influenced by environmental factors like light color and intensity. Chloroplasts, like mitochondria, contain their own DNA, thought to be inherited from their ancestor—a photosynthetic cyanobacterium, engulfed by an early eukaryotic cell. Chloroplasts cannot be made by the plant cell and must be inherited by each daughter cell during cell division. With one exception, all chloroplasts can be traced back to a single endosymbiotic event, when a cyanobacterium was engulfed by the eukaryote. Despite this, chloroplasts can be found in an wide set of organisms, some not directly related to each other—a consequence of many secondary and tertiary endosymbiotic events; the word chloroplast is derived from the Greek words chloros, which means green, plastes, which means "the one who forms". The first definitive description of a chloroplast was given by Hugo von Mohl in 1837 as discrete bodies within the green plant cell. In 1883, A. F. W. Schimper would name these bodies as "chloroplastids".
In 1884, Eduard Strasburger adopted the term "chloroplasts". Chloroplasts are one of many types of organelles in the plant cell, they are considered to have originated from cyanobacteria through endosymbiosis—when a eukaryotic cell engulfed a photosynthesizing cyanobacterium that became a permanent resident in the cell. Mitochondria are thought to have come from a similar event, where an aerobic prokaryote was engulfed; this origin of chloroplasts was first suggested by the Russian biologist Konstantin Mereschkowski in 1905 after Andreas Schimper observed in 1883 that chloroplasts resemble cyanobacteria. Chloroplasts are only found in plants and the amoeboid Paulinella chromatophora. Cyanobacteria are considered the ancestors of chloroplasts, they are sometimes called blue-green algae though they are prokaryotes. They are a diverse phylum of bacteria capable of carrying out photosynthesis, are gram-negative, meaning that they have two cell membranes. Cyanobacteria contain a peptidoglycan cell wall, thicker than in other gram-negative bacteria, and, located between their two cell membranes.
Like chloroplasts, they have thylakoids within. On the thylakoid membranes are photosynthetic pigments, including chlorophyll a. Phycobilins are common cyanobacterial pigments organized into hemispherical phycobilisomes attached to the outside of the thylakoid membranes. Somewhere around 1 to 2 billion years ago, a free-living cyanobacterium entered an early eukaryotic cell, either as food or as an internal parasite, but managed to escape the phagocytic vacuole it was contained in; the two innermost lipid-bilayer membranes that surround all chloroplasts correspond to the outer and inner membranes of the ancestral cyanobacterium's gram negative cell wall, not the phagosomal membrane from the host, lost. The new cellular resident became an advantage, providing food for the eukaryotic host, which allowed it to live within it. Over time, the cyanobacterium was assimilated, many of its genes were lost or transferred to the nucleus of the host. From genomes that originally contained over 3000 genes only about 130 genes remain in the chloroplasts of contemporary plants.
Some of its proteins were synthesized in the cytoplasm of the host cell, imported back into the chloroplast. Separately, somewhere around 500 million years ago, it happened again and led to the amoeboid Paulinella chromatophora; this event is called endosymbiosis, or "cell living inside another cell with a mutual benefit for both". The external cell is referred to as the host while the internal cell is called the endosymbiont. Chloroplasts are believed to have arisen after mitochondria, since all eukaryotes contain mitochondria, but not all have chloroplasts; this is called serial endosymbiosis—an early eukaryote engulfing the mitochondrion ancestor, some descendants of it engulfing the chloroplast ancestor, creating a cell with both chloroplasts and mitochondria. Whether or not primary chloroplasts came from a single endosymbiotic event, or many independent engulfments across various eukaryotic lineages, has long been debated, it is now held that organisms with primary chloroplasts share a single ancestor that took in a cyanobacterium 600–2000 million years ago.
It has been proposed. The exception is the amoeboid Paulinella chromatophora, which descends from an ancestor that took in a Prochlorococcus cyanobacterium 90–500 million years ago; these chloroplasts
In optics, a diaphragm is a thin opaque structure with an opening at its center. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture, thus it is called a stop. The diaphragm is placed in the light path of a lens or objective, the size of the aperture regulates the amount of light that passes through the lens; the centre of the diaphragm's aperture coincides with the optical axis of the lens system. Most modern cameras use a type of adjustable diaphragm known as an iris diaphragm, referred to as an iris. See the articles on aperture and f-number for the photographic effect and system of quantification of varying the opening in the diaphragm. A natural optical system that has a diaphragm and an aperture is the human eye; the iris is the diaphragm, the opening in the iris of the eye is the aperture. An analogous dev in a photographic lens is called an iris diaphragm. In the early years of photography, a lens could be fitted with one of a set of interchangeable diaphragms as brass strips known as Waterhouse stops or Waterhouse diaphragms.
The iris diaphragm in most modern still and video cameras is adjusted by movable blades, simulating the iris of the eye. The diaphragm has two to twenty blades, depending on price and quality of the device in which it is used. Straight blades result in polygon shape of the diaphragm opening, while curved blades improve the roundness of the iris opening. In a photograph, the number of blades that the iris diaphragm has can be guessed by counting the number of diffraction spikes converging from a light source or bright reflection. For an odd number of blades, there are twice as many spikes. In case of an number of blades, the two spikes per blade will overlap each other, so the number of spikes visible will be the number of blades in the diaphragm used; this is most apparent in pictures taken in the dark with small bright spots, for example night cityscapes. Some cameras, such as the Olympus XA or lenses such as the MC Zenitar-ME1, use a two-bladed diaphragm with right-angle blades creating a square aperture.
Out-of-focus points of light appear as polygons with the same number of sides as the aperture has blades. If the blurred light is circular it can be inferred that the aperture is either round or the image was shot "wide-open"; the shape of the iris opening has a direct relation with the appearance of the blurred out-of-focus areas in an image called bokeh. A rounder opening produces more natural out-of-focus areas; some lenses utilize specially shaped diaphragms. This includes the diffusion discs or sieve aperture of the Rodenstock Tiefenbildner-Imagon and Sima soft focus lenses, the sector aperture of Seibold's Dreamagon, or the circular apodization filter in the Minolta/Sony Smooth Trans Focus or Fujifilm APD lenses; some modern automatic point-and-shoot cameras do not have a diaphragm at all, simulate aperture changes by using an automatic ND filter. Unlike a real diaphragm, this has no effect on depth of field. A real diaphragm when more-closed will cause the depth of field to increase and if the diaphragm is opened up again the depth of field will decrease.
In his 1567 work La Pratica della Perspettiva Venetian nobleman Daniello Barbaro described using a camera obscura with a biconvex lens as a drawing aid and points out that the picture is more vivid if the lens is covered as much as to leave a circumference in the middle. In 1762, Leonhard Euler says with respect to telescopes that, "it is necessary to furnish the inside of the tube with one or more diaphragms, perforated with a small circular aperture, the better to exclude all extraneous light." In 1867, Dr. Désiré van Monckhoven, in one of the earliest books on photographic optics, draws a distinction betweens stops and diaphragms in photography, but not in optics, saying: "Let us see what takes place when the stop is removed from the lens to a proper distance. In this case the stop becomes a diaphragm. * In optics and diaphragm are synonyms. But in photographic optics they are only so by an unfortunate confusion of language; the stop reduces the lens to its central aperture. According to Rudolf Kingslake, the inventor of the iris diaphragm is unknown.
Others credit Joseph Nicéphore Niépce for this device, around 1820. Mr. J. H. Brown, a member of the Royal Microscopical Society, appears to have invented a popular improved iris diaphragm by 1867. Kingslake has more definite histories for some other diaphragm types, such as M. Noton's adjustable cat eye diaphragm of two sliding squares in 1856, the Waterhouse stops of John Waterhouse in 1858. Aperture f-number Shutter Leaf shutter Diffraction spike
Safranin is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring all cell nuclei red; this is the classic counterstain in both Gram stains, endospore staining. It can be used for the detection of cartilage and mast cell granules. Safranin has the chemical structure shown at right. There is trimethyl safranin, which has an added methyl group in the ortho- position of the lower ring. Both compounds behave identically in biological staining applications, most manufacturers of safranin do not distinguish between the two. Commercial safranin preparations contain a blend of both types. Safranin is used as redox indicator in analytical chemistry. Safranines are the azonium compounds of symmetrical 2,8-dimethyl-3,7-diaminophenazine, they are obtained by the joint oxidation of one molecule of a para-diamine with two molecules of a primary amine. They are crystalline solids showing a characteristic green metallic lustre, they form stable monacid salts.
Their alcoholic solution shows a yellow-red fluorescence. Phenosafranine is not stable in the free state, it can be diazotized, the diazonium salt when boiled with alcohol yields aposafranine or benzene induline, C18H12N3. F. Kehrmann showed that aposafranine could be diazotized in the presence of cold concentrated sulfuric acid, the diazonium salt on boiling with alcohol yielded phenylphenazonium salts. Aposafranone, C18H12N2O, is formed by heating aposafranine with concentrated hydrochloric acid; these three compounds are to be represented as ortho- or as para-quinones. The "safranine" of commerce is an ortho-tolusafranine; the first aniline dye-stuff to be prepared on a manufacturing scale was mauveine, obtained by Sir William Henry Perkin by heating crude aniline with potassium bichromate and sulfuric acid. Mauveine was converted to parasafranine by Perkin in 1878 by oxidative/reductive loss of the 7N-para-tolyl group. Another well known safranin is phenosafranine used as a histological dye and redox probe.
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed.. "Safranine". Encyclopædia Britannica. Cambridge University Press
Polarization is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, transverse sound waves in solids. In some types of transverse waves, the wave displacement is limited to a single direction, so these do not exhibit polarization. An electromagnetic wave such as light consists of a coupled oscillating electric field and magnetic field which are always perpendicular.
In linear polarization, the fields oscillate in a single direction. In circular or elliptical polarization, the fields rotate at a constant rate in a plane as the wave travels; the rotation can have two possible directions. Light or other electromagnetic radiation from many sources, such as the sun and incandescent lamps, consists of short wave trains with an equal mixture of polarizations. Polarized light can be produced by passing unpolarized light through a polarizer, which allows waves of only one polarization to pass through; the most common optical materials are isotropic and do not affect the polarization of light passing through them. Some of these are used to make polarizing filters. Light is partially polarized when it reflects from a surface. According to quantum mechanics, electromagnetic waves can be viewed as streams of particles called photons; when viewed in this way, the polarization of an electromagnetic wave is determined by a quantum mechanical property of photons called their spin.
A photon has one of two possible spins: it can either spin in a right hand sense or a left hand sense about its direction of travel. Circularly polarized electromagnetic waves are composed of photons with only one type of spin, either right- or left-hand. Linearly polarized waves consist of photons that are in a superposition of right and left circularly polarized states, with equal amplitude and phases synchronized to give oscillation in a plane. Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology and microwaves. Impacted are technologies such as lasers and optical fiber telecommunications, radar. Most sources of light are classified as incoherent and unpolarized because they consist of a random mixture of waves having different spatial characteristics, frequencies and polarization states. However, for understanding electromagnetic waves and polarization in particular, it is easiest to just consider coherent plane waves. Characterizing an optical system in relation to a plane wave with those given parameters can be used to predict its response to a more general case, since a wave with any specified spatial structure can be decomposed into a combination of plane waves.
And incoherent states can be modeled stochastically as a weighted combination of such uncorrelated waves with some distribution of frequencies and polarizations. Electromagnetic waves, traveling in free space or another homogeneous isotropic non-attenuating medium, are properly described as transverse waves, meaning that a plane wave's electric field vector E and magnetic field H are in directions perpendicular to the direction of wave propagation. By convention, the "polarization" direction of an electromagnetic wave is given by its electric field vector. Considering a monochromatic plane wave of optical frequency f, let us take the direction of propagation as the z axis. Being a transverse wave the E and H fields must contain components only in the x and y directions whereas Ez = Hz = 0. Using complex notation, the instantaneous physical electric and magnetic fields are given by the real parts of the complex quantities occurring in the following equations; as a function of time t and spatial position z these complex fields can be written as: E → =
The optical properties of all liquid and solid materials change as a function of the wavelength of light used to measure them. This change as a function of wavelength is called the dispersion of the optical properties; the graph created by plotting the optical property of interest by the wavelength at which it is measured is called a dispersion curve. The dispersion staining is an analytical technique used in light microscopy that takes advantage of the differences in the dispersion curve of the refractive index of an unknown material relative to a standard material with a known dispersion curve to identify or characterize that unknown material; these differences become manifest as a color when the two dispersion curves intersect for some visible wavelength. This requires no stains or dyes to produce the color, its primary use today is in the confirmation of the presence of asbestos in construction materials but it has many other applications. There are five basic optical configurations of the microscope used for dispersion staining.
Each configuration has its disadvantages. The first two of these, Becke` line dispersion staining and oblique dispersion staining, were first reported in the United States by F. E. Wright in 1911 based on work done by O. Maschke in Germany during the 1870s; the five dispersion staining configurations are: Colored Becke` Line Dispersion Staining Oblique Illumination Dispersion Staining Darkfield Dispersion Staining Phase Contrast Dispersion Staining Objective Stop Dispersion Staining All of these configurations have the same requirements for the preparation of the sample to be examined. First, the substance of interest must be in intimate contact with the known reference material. In other words, the clean solid must be mounted in a reference liquid, one mineral phase must be in intimate contact with the reference mineral phase, or the homogenous liquid must contain the reference solid. Most applications involve a solid mounted in a reference liquid. Second, dispersion colors will only be present if the two materials have the same refractive index for some wavelength in the visible spectrum and they have different dispersions curves for the refractive index.
The sample must be properly mounted under a coverslip to minimize any other optical effect that could complicate the interpretation of the color seen. Once these criteria are met the sample is ready to be examined; the starting configuration of the microscope for all of these methods is properly adjusted Köhler illumination. Some additional adjustments are required for each of the methods; the Becke' Line method takes advantage of the fact that particles behave like lenses because they tend to be thinner at the edges than they are at the center. If the particle has a higher refractive index than the liquid surrounding it it behaves as a convex lens and focuses a parallel beam of light on the side opposite the source of the light. Looking through the microscope this is seen as a bright ring of light, the Becke` Line, moving in from the edge as the particle is dropped out of focus by increasing the distance between the stage of the microscope and the objective. If the stage is moved closer to the objective the particle behaves like a magnifying glass and the image of the Becke` Line is magnified and it appears outside the particle.
A requirement for this method is. This requires the closing down of the sub-stage condenser iris. Closing the sub-stage condenser iris decreases the resolution of the particle and increases the depth of field over which other objects may interfere with the effect seen. For large particles this is not a significant limitation but for small particles it is a problem; when the conditions for dispersion staining are met the particle has a high refractive index in the red part of the spectrum and a lower refractive index in the blue. This is; as a result, when the particle is dropped out of focus the red wavelengths are focused inward. For the blue wavelengths the particle behaves like a concave lens and the blue Becke` Line moves out into the liquid; the color of these two bands of light will vary depending on where the particle and liquid match in refractive index, the location of λo. If the match is near the blue end of the spectrum the Becke' Line moving into the particle will contain nearly all of the visible wavelengths except blue and will appear as a pale yellow.
The Becke` Line moving out will appear a dark blue. If the match is near the red end of the spectrum the Becke` Line moving into the particle will appear dark red and the Becke` Line moving out will appear pale blue. If the λo is near the middle of the visible wavelengths the Becke` Line moving into the particle will be orange and the Becke` Line moving out will be sky blue; the colors seen can be used to precisely determine the refractive index of the unknown or confirm the identity of the unknown, as in the case of asbestos identification. Examples of this type of dispersion staining and the colors shown for different λo’s can be seen at http://microlabgallery.com/gallery-dsbecke.aspx. The presence of two colors helps to bracket the wavelength at which the refractive index matches for the two materials; the Becke' Line method of dispersion staining is used as an exploratory technique. As a particle field is scanne
Tissue paper or tissue is a lightweight paper or, light crêpe paper. Tissue can be made from recycled paper pulp. Key properties are absorbency, basis weight, bulk, stretch and comfort. Tissues are napkins. Tissue paper is produced on a paper machine that has a single large steam heated drying cylinder fitted with a hot air hood; the raw material is paper pulp. The Yankee cylinder is sprayed with adhesives to make the paper stick. Creping is done by the Yankee's doctor blade, scraping the dry paper off the cylinder surface; the crinkle is controlled by the strength of the adhesive, geometry of the doctor blade, speed difference between the Yankee and final section of the paper machine and paper pulp characteristics. Tissue Paper Converting Machines with Jumbo Rolls attached; the highest water absorbing applications are produced with a through air drying process. These papers contain high amounts of NBSK and CTMP; this gives a bulky paper with good water holding capacity. The TAD process uses about twice the energy compared with conventional drying of paper.
The properties are controlled by crêping and additives. The wet strength is an important parameter for tissue. Hygienic tissue paper is used for facial tissue, bathroom tissue and household towels. Paper has been used for hygiene purposes for centuries, but tissue paper as we know it today was not produced in the United States before the mid-1940s. In Western Europe large scale industrial production started in the beginning of the 1960s. Facial tissue refers to a class of soft, disposable paper, suitable for use on the face; the term is used to refer to the type of facial tissue sold in boxes, designed to facilitate the expulsion of nasal mucus although it may refer to other types of facial tissues including napkins and wipes. The first tissue handkerchiefs were introduced in the 1920s, they have been refined over the years for softness and strength, but their basic design has remained constant. Today each person in Western Europe uses about 200 tissue handkerchiefs a year, with a variety of'alternative' functions including the treatment of minor wounds, the cleaning of face and hands and the cleaning of spectacles.
The importance of the paper tissue on minimising the spread of an infection has been highlighted in light of fears over a swine flu epidemic. In the UK, for example, the Government ran a campaign called “Catch it, bin it, kill it”, which encouraged people to cover their mouth with a paper tissue when coughing or sneezing. Paper towels are the second largest application for tissue paper in the consumer sector; this type of paper has a basis weight of 20 to 24 g/m2. Such paper towels are two-ply; this kind of tissue can be made from 100% chemical pulp to 100% recycled fibre or a combination of the two. Some long fibre chemical pulp is included to improve strength. Wrapping tissue is a type of thin, translucent tissue paper used for wrapping/packing various articles & cushioning fragile items. Custom-printed wrapping tissue is becoming a popular trend for boutique retail businesses. There are various on-demand custom printed wrapping tissue paper available online. Sustainably printed custom tissue wrapping paper are printed on acid-free paper.
Rolls of toilet paper have been available since the end of the 19th century. Today, more than 20 billion rolls of toilet tissue are used each year in Western Europe. Table napkins can be made of tissue paper; these are made from one up to four plies and in a variety of qualities, folds and patterns depending on intended use and prevailing fashions. The composition of raw materials varies a lot from deinked to chemical pulp depending on quality. Colored paper napkins can be a source of carcinogenic primary aromatic amines when used as a wrapper for food as a result of degradation of Azo compounds used as paper dyes. In the late 1970s and early 1980s, a sound recording engineer named Bob Clearmountain was said to have hung tissue paper over the tweeter of his pair of Yamaha NS-10 speakers to tame the over-bright treble coming from it; the phenomenon became the subject of hot debate and an investigation into the sonic effects of many different types of tissue paper. The authors of a study for Studio Sound magazine suggested that had the speakers' grilles been used in studios, they would have had the same effect on the treble output as the improvised tissue paper filter.
Another tissue study found inconsistent results with different paper, but said that tissue paper demonstrated an undesirable effect known as "comb filtering", where the high frequencies are reflected back into the tweeter instead of being absorbed. The author derided the tissue practice as "aberrant behavior", saying that engineers fear comb filtering and its associated cancellation effects, suggesting that more controllable and less random electronic filtering would be preferable. Tissue paper, in the form of standard single-ply toilet paper, is used in road repair to protect crack sealants; the sealants require upwards of 40 minutes to cure enough to not stick onto passing traffic. The application of toilet paper removes the stickiness and keeps the tar in place, allowing the road to be reopened and increasing road repair crew productivity; the paper disappears in the following days. The use has been credited to Minnesota Department of Transportation employee Fred Muellerleile, who came up with the idea in 1970 after trying standard office paper, which worked, but d