Principles of the Photoacoustic Effect

Principles of the Photoacoustic Effect photothermal and photoacoustic Photothermam science encompasses a wide range of techniques and phenomena based upon the conversion of absorbed optical energy into heat. Optical energy is absorbed and eventually converted into thermal energy by an enormous number of material –solids, liquids, and gases. In fact, the optical energy is absorbed, the excited states in atoms or molecules lose their excition energy by a series of non- radiative transitions that result in a general heating in the material. The underlying principles of the photoacoustic effect have been studied for more then a century. it was named photocoustic because the photothermal heating effect was detected by an indirect acoustic method in 1880. Alexander Grshsm Bell (cited in Favier J.P.1997) had discovered the early concept of the photoacoustic effect when he tried to explain the operation of his photophone. He had done a lot of experiments on photoacoustic effect with solids, gases and liquids, where modulated light was used to illuminate the sample. through the experiments, Bell discovered that when a periodically interrupted beam of sunlight shines on a solid in an enclosed cell, an audible sound could be heard by means of hearing tube attached to the cell. the photoacoustic effect discovered by Bell was regarded as a part of the family of photothermal phenomena encompassing many effect produced by the heat generated in a sample due to the absorption of electromagnetic energy. In 1881,both Tyndah and Withem Roentgen (cited in Favier J.P. 1997) confirmed Bells experiment on gases. they found that an acoustic signal could also be produced when a gas in an enclosed cell is illuminated with modulation light. But due to the limitation of hearing tubes as detectors in the early experiment, progress in the field of photoacoustic died down. therefore, the photoacoustic technique had lay dormant for almost 50 years, until the advent of a microphone 50 years later the photoacoustic effect with gases was reexamined. then it had become a well-established technique for gas analysis. photons in the photoacoustic cell absorbed by the gas was converted into kinetic energy of the gas molecules, thus it gives rise to pressure fluctuations within the cell. All the discoveries in the photoacoustic effect originate from 1938 was entirely limited to gases only. the phoyoacoustic effect on solid matter did not occur until the early of 1970. it is almost 90 years after Bells discovery, since 1973, photoacoustic effect has strongly reemerged on the solid sample. ti has revived with the development of a very useful technique spectroscopic investigation of solid material. The photoacoustic effect in condensed matter may be detected by microphone absorption of modulated light by a solid sample produce a modulated heating of the sample surface. This heating cause pressure waves to be created in a gas in contact with the sample, producing an acoustic signal in the gas, which may be detected by a microphone. the sample, coupling gas, and the microphone are enclosed in a gas light photoacoustic cell. the cell acoustically isolates the microphone from external noise and contains a window enabling the modulated light to illuminate the sample (Almond and Patel 1996) Bells first experiment on a condensed matter sample, revealed the fact that the loudest signal were produced by sample with the darkest colours. a few other experiments were performed in the years following, however condensed matter photoacoustic died out until the 1970 Parker (1073) carried out the experiment about to measure the phootoacoustic effect in solid when he tried to carry out the experiment on the photoacoustic effect in gases. in his experiment, he worked on gas phase photoacoustic, attributed an anomalously large PA signal to absorption of light by the windows of his cell. Three years later, Rosencwing and Gersho (1976) derived the one-dimensional theory for a photoacoustic effect from asolid material, which has become known as the R-G theory and which has basis for the most other theories on microphone photoacoustic detection from a solid sample. in his hypothesis, the primary source of the photoacoustic signal result from a periodic heat flow from the solid to the surrounding gas. these can be explained when the beam of light falls onto sample, the heat produced by the light absorbed in the sample will diffuse from the sample to the gas through the sample –gas interface. by modulating the light beam, we are actually causes the expansions of the gas layer which near to the sample and this will finally create a sound wave. The R-G theory has been shown to be agood model by subsequent experiment work. Therefore, it led to direct expansions in photoacoustic research in 1970. The publication of the R-G theory, stimulated work in photoacoutic and number of papers have been written on the subject, describing various light sources, sample, cells, modulation technique and frequencies, detection methods and signal processing apparatus. This theory will be discussed in detail in the next chapter The photothermal and photoacoustic research was investigated since 1970 due to three major factors. i) Devlopment of intense light sources, such as laser and high pressure  arc lamps,such as xenon arc lamps. ii) Development of sensitive detection equipment, such as condenser and electret microphones and piezoelectric detectors iii) Development of more sensitive signal processing equipment such as filters and sensitive lock -in amplifiers. The improvement in the above three areas enabled the photoacoustic effect to be studied and hence higher sensitivity photoacoustic spectroscopy could be performed. Schemes of Photoacoustic Detection. All photothermal system employ a modulated source of electromagnetic radiation usually a light source, to generate modulated heating in a sample medium. the system rely on the absorption by the medium of electromagnetic energy and its subsequent conversion into thermal energy. this heating result in a number of physical changes in  and around the sample, figure 1.1 is schematic illustration of the phenomena resulting from the exposure of sample surface to a localized periodically modulated light source. in addition to a change in the temperature of the sample, it is also produced infrared, acoustic waves, surface expansion, thermoelastic waves, surface reflectivity modulation and refractive index gradient in the medium in contact with the heated surface. all of these effects could be used to probe the photothermal response of an enormous number of materials –solids, liquids, and gases. the thermal wave detection method were classified in to acoustic and thermal detection techniques. acoustic detection technique employ either a gas condenser microphone for the detection of pressure variation in air or a piezoelectric transducer for the detection of thermoelastic waves in solid media. thermal detection method includes the use of thermocoupe or pyroelectric transducers (photopyroelectric detection, PPE)to detect waves directly. (Murphy et al. 1992) Incident Refractive index gradient Infrared emission Surface Reflectivity modulation Acoustic waves Surface expansion thermal thermoelastic waves waves sample figure 1.1 photothremal effect caused by illumination of a surface by a modulated beam of light (Almond and Patel 1997) 1.3 Objective of the present study. CHAPTER 2 THEORY 2.1 Introduction. In this chapter, will discuss the theory of photoacoustic effect in the condensed matter.the formulation of Rosencwaing -Gersho (R-G)theory from the acoustic detection technique employ a gas condenser microphone for the detection of pressure variation in air are described. According to R-G model,when heat is created by means of non radiative transition with a boundary layer of the gas in the cell. Since the light is chopped, the photoacoustic signal is generated due to an acoustic pressure disturbance at the sample -gas interface transferred from the gas medium to the microphone. 2.2 Rosencwaing -Gersho Theory The Rosencwaing -Gersho theory, known as R-G theory, is an one -dimensional analysis of the production of a photoacoustic (PA) signal in a simple cylindrical cell resulting from the absorbed light energy. The model is schematically shown in figure 2.1 from the figure, the photoacoustic cell has a diameter D and length L . It is assumed that the length L is small compare to the wavelength of the acoustic waves and the microphone detecte the average pressure produced in the cell. In the present case, they also assumed that the light is not absorbed by the gas and backing material. The sample has thickness and diameter D. The sample is mounted so that its front surface is expose to the gas (air)within the cell and back surface is against a backing material of thickness . the length. . Of the gas volume is given by. = When a sinusoidally chopped monochromatic high passing through are window of the cell and incident upon the solid sample, the intensity I at the depth x is given by

Organisation culture Essay -- Business and Management Studies

Organisation culture Organisation culture can be defined as the collection of relatively uniform and enduring beliefs, values, customs, traditions and practices which are shared by an organisation’s members and which are transmitted from one generation of employees to the next. One view in the field of organisation culture is the culture metaphor. A metaphor is a word or phrase applied to an object or action which it does not literally denote.1 Metaphor can be powerful means of communicating ideas and are in common use in many organisations. It asserts that culture is a mental state that has to be tolerated since it is incapable of being changed by management. It adopted a phenomenological standpoint and conceptualised culture as a ‘process of enactment’ – not as something that exists ‘out there’ separate from people, but which was actually manufactured by company employees as they interacted with one another on a daily basis within the workplace.2 In highlighting the symbolic significance of virtually every aspect of organisation life, the culture metaphor thus focuses attention on a human side of organisation that other metaphors ignore or gloss over. The culture metaphor opens the way to a reinterpretation of many traditional managerial concepts and processes. It also helps to reinterpret the nature and significance of organisation environment relations. Culture of the organisation plays a key role in determining a structure that would suit. The organisation stance towards participation and risk-taking will have an impact on the decision pertaining to number of levels and delegation of authority. Congruence between culture and structure is important. Lack of congruence can result in mixed signals across the organisation. Organisational culture is based on differences in norms and shared practices which are learned in the workplace and are considered as valid within the boundaries of a particular organisation. Therefore the efficiency of an organization structure is determined by how well it fits into the culture in which it is set. The environments affect the structures chosen by organizational decision-makers through their society’s cultural expectations. Organisational structures are designed to insure survival through social legitimacy by reflecting the surrounding culture’s values and beliefs (Birnbaum-More a... ...se of authority here. For the most part individuals are encouraged to perform their tasks with few questions asked though important decisions are likely to be made as a result of political manoeuvring. The greatest strength of power cultures is their ability to react quickly but their success largely depends on the abilities of the person or people at the centre. In conclusion, organisational culture exercises a potent form of control over the interaction of organisational members with each other and outsiders. By supplying people with a toolbox of values, norms, and rules that tell them how to behave, organisation culture is instrumental in determining how they interpret and react to a situation. Thus, an organisation’s culture can be a source of competitive advantage. References 1. Andrew Brown.1995, ‘Organisational Culture’ Chap1, p13 2. David Buchanan & Andrzej Huczynski. 1997, ‘Organizational Behaviour’ Chap 18, p514 3. David Buchanan & Andrzej Huczynski. 1997, ‘Organizational Behaviour’ Chap 22, p681 Additional References l Gaeth Morgan. 1986 ‘Images of Organization’ 2 Laurie J Mullins. 2005 ‘Management and Organisational Behaviour’

Health Care Hall of Fame Museum Proposal Essay

Healthcare has existed for centuries. As a society we have gone from primitive treatments like casting spells to revolutionary disease breakthroughs. The United States has held steadfast in the evolution of healthcare delivery causing the delivery of healthcare to increase by magnitude proportions. The 1900’s was a time that changes in healthcare and the delivery of it began to emerge in the United States. Scientists started taking an increase interest in diseases. Cardiology developments have helped with the treatment of heart disease, monitoring and prevention. â€Å"Heart Disease is the number one leading cause of death in America.† (American Heart Association, www.heart.org). Heart disease goes as far back as Egyptian Pharaohs, British monarchs and American Presidents. Unhealthy behaviors causing an increase in the risk factors amongst Americans have greatly affected the health of our society as a whole. Americans lead with sedentary lifestyles and the â€Å"supers ize mentality†. Early interventions to reduce the risk factors that cause heart disease are essential. Mental illness has been frowned upon since ancient history. The United States was no different. Some people feel that mental illness is not a physical problem and is just a behavioral or spiritual problem that can be controlled. The mentally ill have been maltreated and put through deplorable, inhumane conditions. Introduction of antipsychotic medication in the 1950’s helped in the recovery and helped those who were mentally ill live in the community. Mental health became a priority and care in institutions and hospitals started to improve. â€Å"The Mental Health Act 1986 (the Act) provides a legislative framework for the care, treatment and protection of people with mental illness for psychiatrists to implement.† (Treatment plans under the Mental Health Act). The National Institute of Mental health has a mission to transform the understanding and treatment of mental illnesses. Better healthcare choices can be made with the use of biotechnology. Biotechnology is not a new science. It goes as far back as 500 B.C. It is beneficial with the development of medication, research on drugs, stem cell research, gene testing and therapy. â€Å"Modern biotechnology provides breakthrough products and technologies to combat debilitating and rare diseases, reduce our environmental footprint, feed the hungry, use less and cleaner energy, and have safer, cleaner and more efficient industrial manufacturing processes.† (What is Biotechnology? http://www.bio.org/articles/what-biotechnology). Biotechnology has made major strides in healthcare like the eradication of small pox or gene therapy to help people battle auto immune diseases. Public Health is concerned with disease prevention and wellness promotion for the community as a whole. Epidemics, pand emic and outbreaks make public health an essential part of healthcare. Public health dates back to Biblical times. An example of this is the isolation of a contagious disease like leprosy. Lillian Wald the mother of Public Health Nursing led the crusade of helping provide medical care to the poor in the United States. The increase awareness of health and the healthcare coverage that would be needed led the United States to develop HMOs. HMOs provide medical treatment for patients on a prepaid basis. HMO members pay a fixed monthly fee, more often than not through an employer regardless of how much medical care is needed in a given month. A wide variety of medical services are provided after the fee is paid, from office visits to hospitalization and surgery. There are benefits to having an HMO. â€Å"Preventive and well-care services, such as routine physicals and pediatric care, are provided at no additional cost. Co-payments apply to doctor’s office visits, prescriptions, hospital admissions, emergency room visits and some other services. You generally do not need to submit claim forms, except in cases when emergency care takes place outside of your coverage area.† Research on diseases, health maintenance, and wellness continues to progress. Public Health continues to be an advocate for health and safety in the community. The United States continues to evolve in healthcare delivery. References American Heart Association, Disease Information. (2000). Retrieved from http://my.americanheart.org/professional/Research/Disease-Information_UCM_459537_Article.jsp Future of Biotechnology in Healthcare, Chapter Nine. (2011, August). Retrieved from http://www.amgenscholars.com/images/uploads/contentImages/biotechnology-future.pdf Institute of Mental Health. About NIMH. (October 6, 2014). Retrieved from http://www.nimh.nih.gov/about/index.shtml Public health history time line. (2014, September 6). Retrieved from http://www.sphtc.org/resources.html

The benefits of preschool Essay - 1323 Words

Everyone has his or her own first day of kindergarten experiences. Some might have been more memorable while others still trying to forget. Mine was merely an observance and evaluation period. After I gave my mother a kiss goodbye, and placed my belongings in the cubbyhole I was ready to learn, but unfortunately the majority of the other students were not. Considering one can not get too accomplished over many loud high-pitched cries, I was forced to be patient and suffer silently from boredom. nbsp;nbsp;nbsp;nbsp;nbsp;Preschool is a beneficial tool for children because they learn social skills and gain an appreciation at an early age for the education system. The prefix â€Å"pre-â€Å" means before or prior to. Preschool education refers to†¦show more content†¦Not only did these findings lead to an increase in the number of schools but also now there are over eight million enrolled between the ages of three and five (Boyer 47). nbsp;nbsp;nbsp;nbsp;nbsp;I believe that group work better introduces the material and leaves a lasting impression for most people. Preschool provides a place where children can meet new friends and learn to get along with other children on an individual basis, and group (Kranyik 92). Taking turns to do things, exchanging ideas, and learning to cooperate with others are important qualities. They are able to be in a safe environment rich in learning and play experiences, supervised by an adult. A preschool gives children endless opportunities to practice speaking. Teachers involve them in storytelling, creative dramatics, and other experiences that will teach them new words and offer a chance to communicate with eachother. Preschools are spacious enough to allow a lot of movement and play indoors and out. The teacher encourages children to be more independent of adults by providing them with choices. They are able to choose what they will do and for how long. They are responsible for m aterials and their own behavior within the limits of the teacher. Children learn social, interaction, and manners inShow MoreRelatedEssay on The Benefits of Preschool1430 Words   |  6 PagesThe Benefits of Preschool Preschool isnt just a place for parents to drop off their children while they are at work for the day. It is in preschool where children learn the necessary skills needed to succeed in school and in life. With high-quality preschools and qualified teachers the possibilities are endless. 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