Week 1 Essay Example | Topics and Well Written Essays - 250 words - 1

Week 1 - Essay Example The tool has automatic detection programs that keep history of a network system. In addition, the tool analyses all the activity and detect traffic in the network. It shows the period for which a program or application has been running and data usage for the same (Choudhary et al., 2013). Therefore, network analysers can elicit any operational challenges that can slow down or crash a system. Network analysers do detect not only viral software, but also test anti-malware programs. The analysers crosscheck the programs and monitor their operations. Network analysers equally pinpoint vulnerabilities in the anti-virus programs. After detection of suspicious software, network analysers notify a user through messages that pop up in the screen. Such messages could be in the form of warnings upon detection of any threats. Network analysers are vital in detecting unusual characteristics in a packet. The features of a system must remain standardised for efficient operations. Network analysers, therefore, compare progress activities of application and program to elicit any suspicions (Chih-Jung, 2013). Analysis of packets also entails identification of packet destinations and sources. Network analysers work through assessment of the general system or computer applications and programs (Chih-Jung, 2013). The analyses are crucial in the creation of plug-ins for specific applications. Monitoring of apps and user activities largely depend on consistent display of all the statistics on a control panel that is user-friendly. Choudhary, A. K., Harding, J., Camarinha-Matos, L. M., Lenny Koh, S., & Tiwari, M. K. (2013). Knowledge management and supporting tools for collaborative networks. International Journal Of Production Research, 51(7), 1953-1957.

Physics Project Essay Example for Free

Physics Project Essay Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement. In higher organisms the eye is a complex optical system which collects light from the surrounding environment; regulates its intensity through a diaphragm; focuses it through an adjustable assembly of lenses to form an image; converts this image into a set of electrical signals; and transmits these signals to the brain, through complex neural pathways that connect the eye, via the optic nerve, to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system.[1] Image-resolving eyes are present in molluscs, chordates and arthropods. [2] The simplest eyes, such as those in microorganisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment. Contents[hide] * 1 Overview * 2 Evolution * 3 Types of eye * 3.1 Normal eyes * 3.2 Pit eyes * 3.2.1 Spherical lensed eye * 3.2.2 Multiple lenses * 3.2.3 Refractive cornea * 3.2.4 Reflector eyes * 3.3 Compound eyes * 3.3.1 Apposition eyes * 3.3.2 Superposition eyes * 3.3.3 Parabolic superposition * 3.3.4 Other * 3.3.5 Nutrients of the eye * 4 Relationship to life requirements * 5 Visual acuity * 6 Perception of colours * 7 Rods and cones * 8 Pigmentation * 9 See also * 10 References * 10.1 Notes * 10.2 Bibliography * 11 External links| [edit] Overview Eye of the wisent, the European bison Complex eyes can distinguish shapes and colors. The visual fields of many organisms, especially predators, involve large areas of binocular vision to improve depth perception; in other organisms, eyes are located so as to maximize the field of view, such as in rabbits and horses, which have monocular vision. The first proto-eyes evolved among animals 600 million years ago, about the time of the Cambrian explosion.[3] The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the thirty-plus[4] main phyla.[1] In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for color) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby regulating the amount of light that enters the eye,[5] and reducing aberrations when there is enough light.[6] The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing vision is achieved by telescoping the lens—similar to how a camera focuses.[7] Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and which can give a full 360-degree field of visio n. Compound eyes are very sensitive to motion. Some arthropods, including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the brain, providing very different, high-resolution images. Possessing detailed hyperspectral color vision, the Mantis shrimp has been reported to have the worlds most complex color vision system.[8] Trilobites, which are now extinct, had unique compound eyes. They used clear calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes. The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of lenses in one eye. In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough image. Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot actually see in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and adapted to spot the infra-red light produced by the hot vents–in this way the bearers can spot hot springs and avoid being boiled alive.[9] [edit] Evolution Main article: Evolution of the eye Evolution of the eye Photoreception is phylogenetically very old, with various theories of phylogenesis.[10] The common origin (monophyly) of all animal eyes is now widely accepted as fact. This is based upon the shared anatomical and genetic features of all eyes; that is, all modern eyes, varied as they are, have their origins in a proto-eye believed to have evolved some 540 million years ago.[11][12][13] The majority of the advancements in early eyes are believed to have taken only a few million years to develop, since the first predator to gain true imaging would have touched off an arms race.[14] Prey animals and competing predators alike would be at a distinct disadvantage without such capabilities and would be less likely to survive and reproduce. Hence multiple eye types and subtypes developed in parallel. Eyes in various animals show adaption to their requirements. For example, birds of prey have much greater visual acuity than humans, and some can see ultraviolet light. The different forms of ey e in, for example, vertebrates and mollusks are often cited as examples of parallel evolution, despite their distant common ancestry. The very earliest eyes, called eyespots, were simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient brightness: they could distinguish light and dark, but not the direction of the lightsource.[15] Through gradual change, as the eyespot depressed into a shallow cup shape, the ability to slightly discriminate directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an effective pinhole camera that was capable of dimly distinguishing shapes.[16] The thin overgrowth of transparent cells over the eyes aperture, originally formed to prevent damage to the eyespot, allowed the segregated contents of the eye chamber to specialize into a transparent humour that optimized color filtering, blocked harmful radiation, improved the eyes refractive index, and allowed functionality outside of water. The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most species with the transparent crystallin protein.[17] The gap between tissue layers naturally formed a bioconvex shape, an optimally ideal structure for a normal refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive power and again eased circulatory problems. Formation of a nontransparent ring allowed more blood vessels, more circulation, and larger eye sizes.[17] [edit] Types of eye There are ten different eye layouts—indeed every way of capturing an image known to man, with the exceptions of zoom and Fresnel lenses. Eye types can be categorized into simple eyes, with one concave photoreceptive surface, and compound eyes, which comprise a number of individual lenses laid out on a convex surface.[1] Note that simple does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behavior or environment. The only limitations specific to eye types are that of resolution—the physics of compound eyes prevents them from achieving a resolution better than 1Â °. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures.[1] Eyes also fall into two groups on the basis of their photoreceptors cellular construction, with the photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomeric. These two groups are not monophyletic; the cnidaria also possess cilliated cells, [18] and some annelids possess both.[19] [edit] Normal eyes Human eyes are examples of normal eyes Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates, cephalopods, annelids, crustacea and cubozoa.[20] [edit Pit eyes Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eyespot, to allow the organism to deduce the angle of incoming light.[1] Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of simple eye. They are small, comprising up to about 100 cells covering about 100 Â µm.[1] The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.[1] [edit] Spherical lensed eye The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable.[1] The most basic form, still seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper image can be obtained using materials with a high refractive index, decreasing to the edges; this decreases the focal length and thus allows a sharp image to form on the retina.[1] This also allows a larger aperture for a given sharpness of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration.[1] Such an inhomogeneous lens is necessary in order for the focal length to drop from about 4 times the lens radius, to 2.5 radii.[1] Heterogeneous eyes have evolved at least eight times: four or more times in gastropods, once in the copepods, once in the annelids and once in the cephalopods.[1] No aquatic organisms possess homogeneous lenses; presumably the evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly outgrown.[1] This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimize the effect of eye motion while the animal moves, most such eyes have stabilizing eye muscles.[1] The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently they can never form a sharp image. This capitulates the function of the eye. Ocelli (pit-type eyes of arthropods) blur the image across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to the brain.[21] Focusing the image would also cause the suns image to be focused on a few receptors, with the possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce their sensitivity.[21] This fast response has led to suggestions that the ocelli of insects are used mainly in flight, because they can be used to detect sudden changes in which way is up (because light, especially UV light which is absorbed by vegetation, usually comes from above).[21] [edit] Multiple lenses Some marine organisms bear more than one lens; for instance the copepod Pontella has three. The outer has a parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another copepod, Copilias eyes have two lenses, arranged like those in a telescope.[1] Such arrangements are rare and poorly understood, but represent an interesting alternative construction. An interesting use of multiple lenses is seen in some hunters such as eagles and jumping spiders, which have a refractive cornea (discussed next): these have a negative lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.[1] [edit] Refractive cornea In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some insect larvae) the vitreous fluid has a higher refractive index than the air, relieving the lens of the function of reducing the focal length. This has freed it up for fine adjustments of focus, allowing a very high resolution to be obtained.[1] As with spherical lenses, the problem of spherical aberration caused by the lens can be countered either by using an inhomogeneous lens material, or by flattening the lens.[1] Flattening the lens has a disadvantage; the quality of vision is diminished away from the main line of focus, meaning that animals requiring all-round vision are detrimented. Such animals often display an inhomogeneous lens instead.[1] As mentioned above, a refractive cornea is only useful out of water; in water, there is no difference in refractive index between the vitreous fluid and the surrounding water. Hence creatures which have returned to the waterâ €”penguins and seals, for example—lose their refractive cornea and return to lens-based vision. An alternative solution, borne by some divers, is to have a very strong cornea.[1] [edit] Reflector eyes An alternative to a lens is to line the inside of the eye with mirrors, and reflect the image to focus at a central point.[1] The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same image that the organism would see, reflected back out.[1] Many small organisms such as rotifers, copeopods and platyhelminths use such organs, but these are too small to produce usable images.[1] Some larger organisms, such as scallops, also use reflector eyes. The scallop Pecten has up to 100 millimeter-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive lenses.[1] There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens, while that coming from below, by a curved mirror composed of many layers of small reflective plates made of g uanine crystals.[22] [edit] Compound eyes An image of a house fly compound eye surface by using Scanning Electron Microscope Anatomy of the compound eye of an insect Arthropods such as this carpenter bee have compound eyes A compound eye may consist of thousands of individual photoreceptor units or ommatidia (ommatidium, singular). The image perceived is a combination of inputs from the numerous ommatidia (individual eye units), which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarization of light.[23] Because the individual lenses are so small, the effects of diffraction impose a limit on the possible resolution that can be obtained. This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require compound eyes which would each reach the size of their head. Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image.[24] Compound eyes are common in arthropods, and are also present in annelids and some bivalved molluscs.[25] Compound eyes, in arthropods at least, grow at their margins by the addition of new ommatidia.[26] Structure of the ommatidia of apposition compound eyes [edit] Apposition eyes Apposition eyes are the most common form of eye, and are presumably the ancestral form of compound eye. They are found in all arthropod groups, although they may have evolved more than once within this phylum.[1] Some annelids and bivalves also have apposition eyes. They are also possessed by Limulus, the horseshoe crab, and there are suggestions that other chelicerates developed their simple eyes by reduction from a compound starting point.[1] (Some caterpillars appear to have evolved compound eyes from simple eyes in the opposite fashion.) Apposition eyes work by gathering a number of images, one from each eye, and combining them in the brain, with each eye typically contributing a single point of information. The typical apposition eye has a lens focusing light from one direction on the rhabdom, while light from other directions is absorbed by the dark wall of the ommatidium. In the other kind of apposition eye, found in the Strepsiptera, lenses are not fused to one another, and each forms an entire image; these images are combined in the brain. This is called the schizochroal compound eye or the neural superposition eye. Because images are combined additively, this arrangement allows vision under lower light levels.[1] [edit] Superposition eyes The second type is named the superposition eye. The superposition eye is divided into three types; the refracting, the reflecting and the parabolic superposition eye. The refracting superposition eye has a gap between the lens and the rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This kind is used mostly by nocturnal insects. In the parabolic superposition compound eye type, seen in arthropods such as mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes, which also have a transparent gap but use corner mirrors instead of lenses. [edit] Parabolic superposition This eye type functions by refracting light, then using a parabolic mirror to focus the image; it combines features of superposition and apposition eyes.[9] [edit] Other The compound eyes of a dragonfly Good fliers like flies or honey bees, or prey-catching insects like praying mantis or dragonflies, have specialized zones of ommatidia organized into a fovea area which gives acute vision. In the acute zone the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialized retina. The resulting eye is a mixture of a simple eye within a compound eye. Another version is the pseudofaceted eye, as seen in Scutigera. This type of eye consists of a cluster of numerous ocelli on each side of the head, organized in a way that resembles a true compound eye. The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole skin into a compound eye. The same is true of many chitons. [edit] Nutrients of the eye The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator muscle. The vitreous is the transparent, colorless, gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye.[27] It is produced by certain retinal cells. It is of rather similar composition to the cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as well as the hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid), no blood vessels, and 98-99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibers with the mucopolysaccharide hyaluronic acid, and also a wide array of proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye. [edit]Relationship to life requirements Eyes are generally adapted to the environment and life requirements of the organism which bears them. For instance, the distribution of photoreceptors tends to match the area in which the highest acuity is required, with horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of ganglia, with acuity decreasing outwards from the centre. Of course, for most eye types, it is impossible to diverge from a spherical form, so only the density of optical receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that reflects the region of highest data acquisition.[1]:23-4 Optical superposition eyes are constrained to a spherical shape, but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon, without altering the size or density of individual ommatidia.[28] Eyes of horizon-scanning organisms have stalks so they can be easily aligned to the horizon when this is inclined, for example if the animal is on a slope.[29] An extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to assist in the identification of prey.[28] In deep water organisms, it may not be the centre of the eye that is enlarged. The hyperiid amphipods are deep water animals that feed on organisms above them. Their eyes are almost divided into two, with the upper region thought to be involved in detecting the silhouettes of potential prey—or predators—against the faint light of the sky above. Accordingly, deeper water hyperiids, where the light against which the silhouettes must be compared is dimmer, have larger upper-eyes, and may lose the lower portion of their eyes altogether.[28] Depth perception can be enhanced by having eyes which are enlarged in one direction; distorting the eye slightly allows the distance to the object to be estimated with a high degree of accuracy.[9] Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential mates against a very large backdrop.[28] On the other hand, the eyes of organisms which operate in low light levels, such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be captured.[28] It is not only the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms, and this can act as a pressure on organisms to have more transparent eyes at the cost of function.[28] Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organisms carapace; this also allows them to track predators or prey without moving the head.[9] [edit] Visual acuity A hawks eye Visual acuity, or resolving power, is the ability to distinguish fine detail and is the property of cones.[30] It is often measured in cycles per degree (CPD), which measures an angular resolution, or how much an eye can differentiate one object from another in terms of visual angles. Resolution in CPD can be measured by bar charts of different numbers of white/black stripe cycles. For example, if each pattern is 1.75 cm wide and is placed at 1 m distance from the eye, it will subtend an angle of 1 degree, so the number of white/black bar pairs on the pattern will be a measure of the cycles per degree of that pattern. The highest such number that the eye can resolve as stripes, or distinguish from a gray block, is then the measurement of visual acuity of the eye. For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD[31] (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1 to 2 CPD.[32] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not match the high acuity of the human eyes central fovea region. Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of 3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7 arcminutes per line pair.[33] A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an optotype, corresponds to 20/20 (normal vision) in humans. [edit] Perception of colours Colour vision is the faculty of the organism to distinguish lights of different spectral qualities.[34] All organisms are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly between 400 and 700 nm.[35] This is a rather small section of the electromagnetic spectrum, probably reflecting the submarine evolution of the organ: water blocks out all but two small windows of the EM spectrum, and there has been no evolutionary pressure among land animals to broaden this range.[36] The most sensitive pigment, rhodopsin, has a peak response at 500 nm.[37] Small changes to the genes coding for this protein can tweak the peak response by a few nm;[2] pigments in the lens can also filter incoming light, changing the peak response.[2] Many organisms are unable to discriminate between colours, seeing instead in shades of grey; color vision necessitates a range of pigment cells which are primarily sensitive to smaller ranges of the spectrum. In primates, geckos, and other organisms, these take the form of cone cells, from which the more sensitive rod cells evolved.[37] Even if organisms are physically capable of discriminating different colours, this does not necessarily mean that they can perceive the different colours; only with behavioural tests can this be deduced.[2] Most organisms with colour vision are able to detect ultraviolet light. This high energy light can be damaging to receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets in the course of evolution, is to make the lens impervious to UV light — this precludes the possibility of any UV light being detected, as it does not even reach the retina.[37] [edit] Rods and cones The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones. Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision; they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina. Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light (often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours). The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are stimulated by light, the nerves send off impulses through these fibres to the brain.[37] [edit] Pigmentation The pigment molecules used in the eye are various, but can be used to define the evolutionary distance between different groups, and can also be an aid in determining which are closely related – although problems of convergence do exist.[37] Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the photoreceptor cells from light leaking in from the sides. The opsin protein group evolved long before the last common ancestor of animals, and has continued to diversify since.[2] There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells, and r-opsins, associated with rhabdomeric photoreceptor cells.[38] The eyes of vertebrates usually contain cilliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, an d that remnants survive in the eyes.[38] Likewise, c-opsins have been found to be expressed in the brain of some invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form.[38] C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins.[38] Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins but r-opsins are yet to be found in this group.[38] Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment.[38]

Mavis Gallants Bernadette :: essays research papers

Mavis Gallant's Bernadette Fear, it has a way of controlling everything that it comes in contact with. As young children we are introduced to this intimidating desire with intrigue and suspicion. As we age, the thoughts of fears become more like realities, ideas of loneliness and death enter the picture as comprehensible thoughts and views of the future. These issues make up the foundation of the Mavis Gallant story "Bernadette". In this story we are presented with the image of a young French Canadian girl, who finds herself pregnant and without a husband. The context of the story explores the relationships between the members of the household in a fear associated manner. The relationship between the Knights and Bernadette is the base of the story. These three people relate to each other in an intimidating fashion and this is what makes Bernadette's predicament so difficult to overcome. As well, the family ties between Nora and Robbie are explored. Their family relationship is one based on dependence, and without this one factor the connection between the two results in fearfulness of being alone. Fear has a way of attacking our judgment and this is what makes associations between people an apprehensive and hard act. The story is set in Quebec during the 1940-1950, when what you were was the definition of who you were. As the story opens we are presented with the main character Bernadette, who is concluding that she is one hundred and twenty-six days pregnant. At this time in history it was quit common for young rural girls to bare children at a young age. However, Bernadette is a single French Canadian girl who is working and living in a urban community, where things like that do not take place. We are here introduced to the first fear presented in the story: --How will Bernadette tell the Knights that she is pregnant? -- The answer to the question is what haunts her, and the reaction of the Knights is the anxiety that builds up inside of her. These intimidating fears places Bernadette in a compromising situation, she is in a position of abandonment by her family and the shame she thinks she has brought on to the Knights. These fears have forced her to react in an unusual fashion. Bernadette is so fearful of what they might think that she tries to hide herself in her work so that she is not placed in the position where she will have to interact with the Knights. The fear of failure and disappointment took control over her mind. When around the Knights she worked as a robot in order not to arouse ideas of

Abner and Sarty Snopes in Barn Burning :: Barn Burning Essays

Abner and Sarty Snopes The nature of the relationship between father and son in William Faulkner's Barn Burning is displayed in the first paragraph of the story. In general a father-son relationship would be built on genuine respect, love, loyalty, and admiration. These building blocks were absent in Abner and Sarty Snopes relationship. Sarty's loyalty to his father appeared to come from a long time fear of the consequences of not obeying his father's commands. The "nigger" that could place the blame on Abner was not to be found. Was Faulkner inferring by this statement that the individual had been killed? If Abner had so little moral value to destroy a man's property, surely to protect himself from persecution he could destroy a man's life. Sarty knew he "smelled cheese, and more." He smelled the "fierce pull of blood." His father's blood, the blood of the family name, Snopes. Sarty knew he was also the son of the "barn burner." A name he heard hissing as they passed by boys in town. Sarty fought to defend his father and when hurt, he seemed to need the blood to remain for a while as a reminder of why he stayed with the man. Sarty viewed his father at times as "bloodless" and cut from "tin." Sarty could usually convince himself why his father was this way. The fact that he had to be a horse trader for four years hiding from the blue and the gray armies to exist by stealing or "capturing" as he called it, horses. Was Sarty to become a man like his father? It seems to be the fear that Sarty may have worried about many times. Young boys usually acquire the desire at sometime in their life to simulate their fathers'actions, perspectives on life and mannerisms. Fathers are examples to how they would like their sons to be. Abner probably thought it was the only way to be. Abner's past was not Sarty's, his future was not to be Sarty's either. For their views on life and the people in it were quite different. Abner Snopes looked at the mansion of Major de Spain as a symbol of inequality. A fact that he had too much and Abner had so little . Sarty looked at the vast mansion as a picturesque scene of "the grove of oaks and cedars and flowering trees and shrubs" almost as if it was a rerun of something he had was coming to him.

Anti Imperialism Speech Against the Annexation of the Phillippines

Annexation of the Philippines – Argument Against I reflect on our own Declaration of Independence that states â€Å"Governments are instituted among Men, deriving their just powers from the consent of the governed. † We went to the Philippines to protect them from Spain and now here we are doing what we were keeping Spain from doing to these people. I ask you†¦ do we have their consent to annex them? Do they believe it is in their best interest to be annexed to our great country? And what measures are we taking to fund a continued military presence to care for these people? If the Filipinos are not in support of this annexation, they will most assuredly fight us that will result in unnecessary violence and bloodshed of both American soldiers and Filipinos, whether you think them civilized or uncivilized. This is hypocritical to what we ourselves claim in our ideals expressed in our Declaration of Independence†¦ the right to self govern. With this move of annexation are we not acting on the grounds of Imperialism which goes against our belief as a Republic? Are we conquerors, or are we liberators? I believe we should allow Aguinaldo, who we brought there from exile, to set up their own government and create a strong partnership that is agreeable for both the Philippines and the United States with mutual prosperity. Let us be the inspiration and model of their new venture and not force it upon them. This move will be viewed by eyes of other countries; it will impact their perception of our United States and the freedoms our nation values.

Definition and Examples of Subjects in English Grammar

Definition and Examples of Subjects in English Grammar In English grammar, the subject is the part of a sentence or clause that commonly indicates (a) what it is about, or (b) who or what performs the action (that is, the agent). The subject is typically a noun  (The dog . . .), a  noun phrase  (My sisters Yorkshire terrier . . .), or a  pronoun  (It . . .). The subject pronouns are  I, you, he, she, it, we, they, who,  and  whoever. In a declarative sentence, the subject usually appears before the verb (The dog  barks). In an interrogative sentence, the subject usually follows the first part of a verb (Does the dog  ever bark?). In an  imperative sentence, the subject is commonly  said to be you understood (Bark!).  Its etymology is from the Latin, to throw. How to Identify the Subject The clearest way of spotting the subject of a sentence is to turn the sentence into a yes-no question (by this we mean a question which can be answered with either yes or no). In English, questions are formed by reversing the order between the subject and the first verb which follows it. Look at the following example: He can keep a Tamagotchi alive for more than a week. The appropriate question here if we want a yes or no as an answer is: Can he keep a Tamagotchi alive for more than a week? Here he and can have changed places and that means that he must be the subject in the first sentence. . . .If there is no suitable verb in the original sentence, then use dummy do, and the subject is the constituent which occurs between do and the original verb.(Kersti Bà ¶rjars and Kate Burridge, Introducing English Grammar, 2010) Subject Examples and Observations The Grinch hated Christmas.(Dr. Seuss, How the Grinch Stole Christmas! 1957)We should take Bikini Bottom and push it somewhere else!(Patrick in Squid on Strike.  SpongeBob  SquarePants,  2001)Momma was preparing our evening meal, and  Uncle Willie leaned on  the door sill.(Maya Angelou, I Know Why the Caged Bird Sings. 1969)My master made me this collar. He is a good and smart master, and he made me this collar so that I may speak.(Dug in Up, 2009)The saber-toothed  tiger was prowling around the bottom of the tree, growling, as it looked for an easier way up. Then something caught its attention.(Damian Harvey, The Mudcrusts:  Saber-Toothed Terrors.  2010)Sophie was especially excited because she  and her friends were  performing the opening dance at the Misty Wood fair.(Lily Small, Sophie the Squirrel.  2017)Fettucini alfredo is macaroni and cheese for adults.(Mitch Hedberg)You cant try to do things; you simply must do them.(Ray Bradbury)Great spirits have alway s encountered violent opposition from mediocre minds.(Albert Einstein) Look at the circles under my eyes. I havent slept in weeks!(The Cowardly Lion in The Wizard of Oz, 1939)The orderly came back in a few minutes with a rifle and five cartridges, and meanwhile some Burmans had arrived and told us that the elephant was in the paddy fields below, only a few hundred yards away.(George Orwell, Shooting an Elephant. New Writing, 1936)Up to the farmhouse to dinner through the teeming, dusty field, the road under our sneakers was only a two-track road.(E.B. White, Once More to the Lake. Harpers, 1941)To do the thing properly, with any hope of ending up with a genuine duplicate of a single person, you really have no choice. You must clone them all.(Lewis Thomas, The Tucson Zoo)Every sentence has a truth waiting at the end of it, and the writer learns how to know it when he finally gets there.(Don DeLillo, Mao II. 1991) Challenging Traditional Definitions of a SubjectThe traditional definition of subject as referring to the doer of an action (or agent), though it is adequate for central or typical cases, will not work for all cases. For example, in passive sentences, such as John was attacked, the subject is John, but John is certainly not the doer of the attacking. Again, not all sentences, even those with transitive verbs, express any action. Examples are This book cost fifty francs and I loathe relativism. But such sentences have always traditionally been held to have subjects (in these cases, this book and I).(James R. Hurford, Grammar: A Students Guide. 1994) Subjects and Predicates in Poetry[Robert] Frosts Dust of Snow justifies its form by devoting one stanza to the grammatical subject and the other to the predicate: The way a crowShook down on meThe dust of snowFrom a hemlock treeHas given my heartA change of moodAnd saved some partOf a day I had rued. (Paul Fussell, Poetic Meter and Poetic Form, 1979)

The Alchemist by Paulo Coelho

The Alchemist by Paulo Coelho The book, The Alchemist, can be described as a metaphor of life. It is funny how dreams can mould a person’s life. It is a paradox such that people consider other lifestyles as better than theirs thereby striving to get that life that belongs to other cultures, through that lives are transformed.Advertising We will write a custom essay sample on The Alchemist by Paulo Coelho specifically for you for only $16.05 $11/page Learn More Dreams can also be seen as the driving forces behind an individual’s life, they bring about desires that mould an individual’s destiny because through them, then fate ceases to be the determinant of happenings in an individual’s life time. Santiago, a young shepherd, the main character in the story The Alchemist is portrayed by Paulo Coelho, as a go getter to some extent. He repeatedly gets a dream that haunts him and pushes him to follow it and thus his expedition in the story; he wants to achieve that dream (Coelho 34). Santiago gets the simple lessons of life of believing in the signs that one gets in life, even if it is just through dreams and following them till he achieves them. The crossing of cultures leads him to following his dreams which he finally achieves. The boy, Santiago is driven to search for the hidden treasure in Egypt making him cross many countries and even the wide Sahara desert whereby he meets different characters, both deceitful and truthful who shape his life, the same way the young Chinese man and other international students cross the borders to get to Melbourne to study, their treasure in this context, education. When the young man shows up in the author’s office with scratchy English (Coelho 45), it is evident that there is a bit of transformation from his past self to his present self. The young Chinese appreciated the author’s message that she had given him the first day he visited her office because she says so. In the same sprit of a ppreciation, the boy Santiago appreciated the advice given to him in the story which leads him to acquire the treasure that he set out to look for. For instance he gives the old man a share of his sheep, that is, a tenth of his flock and promises to give a tenth of his treasure to the old woman. The Chinese student on the other hand brings the tutor a painting of a well embroidered Chinese woman (Coelho 61). This therefore gives the importance of appreciating those who help us in our endeavors to acquire our different treasures in life.Advertising Looking for essay on literature languages? Let's see if we can help you! Get your first paper with 15% OFF Learn More Through the harsh experiences that he faces, the boy learns the value of being strong, patient, and persistent and being a hard working person. Regardless of the setbacks that he encounters a long the way, he does not give up. Just like Rachael, no potential was seen in her as a nurse, she was disco uraged by her tutors that she could not make it as a children’s nurse, but her so many visits to the Occupational Health Department which convinced the tutors that she was capable of becoming a nurse saw her through (Coelho 25). It took a year to convince them, and about fifteen visits and in the long run she was allowed to take up the career path that she had dreamt of and desired to do. Her desire and persistence to follow her dream made her accomplish her heart desires. Following a dream can sometimes seem too hard and expensive but the determination in it tells all about the conviction that one has. The boy in the story The Alchemist is portrayed by Coelho as humble and a brave character. The king tells him that when he wants something, the world will always conspire to help him achieve it, and now that he wants to get the treasure then he is going to get it as long as he is ready to face the challenges (Coelho 24). The challenges he faces in foreign lands can be likened to the challenges faced by those living in the outer suburbs of Melbourne. We are told that the further one lives away from the city, the more harsh life is for them because life there is a bit depressing and that there is little or even no amenities at all. The public transport system is also poor. The kinds of houses that are there are in a sorry state just like street lights are not in proper functioning conditions. Fitting into a new culture can be demoralizing more especially after relocation to a new place, but regardless of this, accepting the prevailing conditions in order to achieve one’s heart desires is reason enough to go on, the international students face problems of housing but with perseverance they the can achieve their ultimate goals and desires. The boy Santiago takes up every opportunity that comes his way, he wallows through so much problems that he encounters along his path of getting to the treasure, he worked hard towards his destiny because no problem was too big for him to deal with. We find that dreaming is one thing and following that dream is another, Rachael had a dream of becoming a nurse, she felt that she really needed to give back to the community and serve the people who had made a great difference in her life and that is why she really wanted to be a children’s nurse, she was laughed at told on several occasions that it was never going to happen because a nursing course was not suitable for her and that she was fit to a desk job (Coelho 25).Advertising We will write a custom essay sample on The Alchemist by Paulo Coelho specifically for you for only $16.05 $11/page Learn More Nevertheless, her desire to follow her dream was the driving force that led her to achieving it in the long run. Had she given up a long the way due to the words of discouragement from even her tutors she could not have become a voice to reckon to the parents of the sick children that she attended to at the Childr en’s Out-patient Department (Coelho 25). In the story, we are also brought to a level ground where freedom to choose what one wants to do should be embraced and given room to drive us. Freedom is the ability for one to do what he or she likes and that entails following one’s heart. Through this one is capable of exploiting his or her own potentialities and doing something that is self fulfilling, if one is made to do something that dictates his or her destiny in a forceful way then the end results will always be bitter. The boy chooses to travel the world because this is his inner calling other than studying theology and becoming a priest. He enjoys the life of adventure and travelling to new places. On her part, Rachael could have been forced to do a desk job because of her health something that she could have done regretfully thereby ending up a slave in a career path that on the contrary should have brought her inner peace and happiness. The boy was allowed to follo w his heart which led him later on to acquire his life experiences that are worthwhile, even more than he could have achieved material treasures. The challenges faced by adapting to a new culture can some times be too much to bear, but how ready is a person to bear with the challenges that come with it? At the same time, it can be hard to make a dream a reality but how persistent that can one be to catch up with that dream (Coelho 89)? Both parties therefore should equip themselves with the communication gear which most definitely is the vehicle that will enable one to get to his or her destiny. The individual will get room to express him/her self thereby appreciating each other as well as compromising with each other’s feelings where possible, that way the joy of learning will have come into play. Once a dream has been hatched then the determination and persistence that will be employed in making it a reality is what will determine whether it is going to be the destiny of an individual and that is what brings in the difference between destiny and fate. Though not sure of his destiny, he strives to get it no matter the challenges, and his life experiences show that everyone needs to work hard to achieve success, one need to strive for the good things in life. This simply inspires people to put effort in order to achieve our goals, for one to make his or her dreams become a reality, he or she is not just gong to sit there and wait for dreams to fall into place, one needs to risk the good things in life in order to achieve better ones (Coelho 100).Advertising Looking for essay on literature languages? Let's see if we can help you! Get your first paper with 15% OFF Learn More Coelho simply intends to bring to our attention that if one dreams and wishes for something then one should be persistent about it and be patient for long enough, one might loose an opportunity by getting tired at the last minute and give up so easily, and see the fruits after somebody else has achieved the fruits of our long suffering. Just like Santiago ones wishes can come in both material objects and life experiences, as for the case of Santiago, his journey to the Pyramids in Egypt, is his treasure. Coelho, Paulo. The Alchemist. New York. Harpertorch. 1993. pp. 1 – 163.