Audiology

What is the sound?

Seyyed Zia Taheri

It is as a lecture

Anatomy and physiology of the auditory tracts

Mohammadhosein Hekmatara

It is as a lecture

Anatomical changes in auditory system induced by sound

Seyyed Abdollah Mousavi

Sounds situated in a certain domain of intensity can evoke auditory system physiologically. Permanent and continuous stimulation which is produced by such sounds would not be harmful to hearing organ. This safe intensity is estimated 61 dB SPL. However one should pay attention that in case the intensity of mechanical sound wave increases (more than 75 dB SPL), the exposure time should be decreased unless the serious harm to auditory system is expected. Auditory system can be affected due to sound harms in two major types: Permanent threshold shift and temporary threshold shift which can be described as the changes in hearing status of human caused by the exposure to sententorian sounds. Numerous physiological factors can exacerbate the devastating effects of sounds that we are aimed at an overall description on this issue in the present review article.

Sound effects on human beings from a religous point of view

Mohammad Rabbani

Sounds are the creatures of God which are found in nature in diverse forms. In addition to sounds naturally exist in the environment there are artificial sounds that is hand-maid and we experience them in our daily life. Industrialization has had detrimental effect on manufacturing such sounds in the environment which in turn can affect our mental and physical state.The current article is taking sound from a religious point of view into account. We want to discuss the role of sounds in perceiving the meanings of related concepts and also will have an overall look on the devastating effects of noise and irritating sounds on human life and the human mental and physical health.

Sound and the biochemical changes in the auditory system

Ghasem Mohammad Khani

Many researchers have reported that after the sound trauma, RNA and DNA in the outer hair cells and ganglion cells will decrease. Some scientists have also mentioned the mitochondrial enzyme deficits in cochlear cells. Sound stimulation will induce the decrease of enzyme activities which are effective in the process of energy production. This process happens because of the reduced ATP synthesis and in turn the damage to receptors due to energy disruption. The moderate oxygen deficiency can also be considered as a potential factor in the amplitude changes of the potential of cochlear microphonic due to irrita6ing sounds. On the other hand, since the organ of corti is far from blood tissue, logically, Anaerobic Glycogen should be considered as the main factor in the metabolism of the organ of corti.In addition to that, there are evidences which demonstrate intense acoustical stimulation can increase Na+ and decrease K+ in endolymphatic fluid and a contrary effect in perylimphatic fluid in scala vestibule.

The pathogenesis of Noise Induced Hearing Loss

Seyyed Abbas Mir Vakili

NIHL occurs when too much sound intensity is transmitted into and through the auditory system and can be occur following a shot gun or the exposure to a moderately intense sound for a long period of time. NIHL caused by acoustic trauma refers to permanent cochlear damage from a one-time exposure to excessive sound pressure. This form of NIHL commonly results from exposure to high-intensity sounds such as explosions, gunfire, a large drum hit loudly and firecrackers.Meanwhile the sound intensity, duration of exposure and personal hearing thresholds as the effective factors in the amount of noise induced hearing loss should not be overlooked. Since numerous investigations have been performed about intense sudden sound we will discuss it in detail in the current article.

Contributing factors in inducing noise induced hearing loss

Saeid Farahani

The most common contributing factors in inducing hearing loss in adults are aging, exposure to noise and the interaction among these factors with other parameters. Individual parameters are also effective in the extent of hearing loss which is produced. Being aware of Vulnerability factors such as physical parameters, Auditory and non-auditory factors can be useful in considering a good hearing conservation program for noise induced hearing losses.In the current article we are aimed at introducing three important parameters and their sub-divisions pertaining to this issue.

Noise Induced Vestibular Damage

Maryam Emadi

There are increasing evidences about the vestibular damage caused by the exposure to noise. Histological and functional derangements of the vestibular system have been reported in laboratory animals exposed to high levels of noise. However, clinical series describe contradictory results with regard to vestibular disturbances in industrial workers and military personnel suffering from noise induced hearing loss (NIHL). Animal studies have proved that crista ampullaris bears the most disturbances, though some damages have been also detected in macula of the utricle and saccule and utricle. These changes have been induced due to acoustical pressure on the vestibular labyrinth. The findings from the experiments regarding vestibular function in patients suffering NIHL have shown a paramount diminish in vestibulo-occular Reflex (VOR). The correlation among NIHL, VOR and unilateral caloric weakness were statistically significant which can be due to a common mechanism of disturbances in the function of cochlea and vestibule.

The effect of sound on the Immune system

Mojgan Shaygan

The immune system protects body against disturbing factors such as pathogens and tumor cells by means of its special cell and biological structures. It has been divided based on its components and soluble factors into two groups of specific and non-specific immune system.Since sound is considered as a stressor it can affect dramatically on the immune system. Stress caused by noise can reduce the immune system response to chemical stimulators have decreased.In Stead, deep relaxation has consistently been proven to be very effective at increasing T-Cells and strengthening the immune system. In the current article, we want to have a look on the adverse effects of sound on the immune system.

The effect of noise on Fetus and Pregnancy of women working in noisy industrial workplace

Mahin Sedaie

Many pregnant women are exposed to noise in the workplace. Noise can affect both fetus and pregnancy of pregnant women. Hormonal disturbances and nanism are of devastating effects of noise. An increased risk of shortened gestation has been shown in four studies Results. In a third study showedthe length of gestation in female infants to be inversely correlatedto maternal residential noise exposure. Decreased birth weight has also been associated with noise exposure in pregnant women.Some of the adverse impacts of exposure to noise is discussed here as an investigation report.

Nuisance caused by aircraft noise in the vicinity of Tehran International Airport

Khodabakhsh Karami

Noise measurement and social questionnaire surveys in three residential areas around Mehrabad International Airport (Tehran, Iran) were based upon randomly selected dwellings in each area. A total of 193 individuals responded and many are annoyed and dissatisfied with aircraft noise and in consequence they would like to move. Aircraft noise is the strongest negative environmental factor affecting the residents in the vicinity of Mehrabad Airport and it could be a hazard for their health.

An acoustic design for control room

Masoud Rafie

Nowadays, sound is a critical part of our daily life and its unwanted and undesirable disturbances in the environment and in the workplace has induced much psychological and physical annoyance to human being and had also lessened the efficacy of the daily activities. Since the mechanical vibrations of molecules in the air had led in producing sound and considering profound damaging vibrations produced by the harsh sounds in the objects and instruments, we have studied the noise and the vibrations caused by it, together.With this introduction and Considering the potential devastating impact of noise and the need to keep staff which are working in the control room secure from this effects the power house of "Shahjid Madhaj" have proposed a project to control and limiting the noise in the control room by examining the diverse ways of transmitting sound into it. The project will be discussed here in details.

The mental and psychological deleterious effect of noise on the operators of Telecommunication Company

Mohammad Taheri

Nowadays, unwanted noise is present everywhere in the workplace and in the living environment and disturbs human peace and calm. In spite of the importance of the indirect impact of noise on human life, little is performed about this issue in our country. Therefore, the present study have been focused on the measurement of noise pollution that impose operators of the telecommunication company in addition to the evaluation of the psychological and mental effect of sound on the telecommunication operators.

Measuring the noise caused by Tehran Metro

Majid Abbas Pour

One of the most common and important sources of noise in the residential environments are vehicles such as airplanes and subways. Trafficking of vehicles in streets and highways, psychologically, have damaging impacts on people living close to such areas. The development and expansion of the trading and industrial units is another factor that causes more and more exposure to noise.We have aimed at measuring the noises caused by vibration of subways of the Line of Karaj-Tehran-Mehrshahr and its effect on its surrounding area.To study this effect we designed a mathematical model and put the information of this subway line in the mentioned model. Then we analyzed the findings.This model demonstrated that we can control the harsh noise of the subway by reducing the speed of the train to 60Km/h in some points and increase in other parts to 130Km/h.

noise and tinnitus

Mansoureh Adel Ghahraman

Tinnitus from the Latin word tinnire meaning ringing is the perception of sound within the human ear in the absence of corresponding external sound. The most common cause is noise induced hearing loss. Tinnitus may be induced by an acoustic trauma or a permanent noise in the workplace. In case that Tinnitus is induced by acoustic trauma the site of lesion is commonly the base of the cochlea. Tinnitus in the senile population is mostly accompanying presbycusis. Although the incidence of permanent tinnitus following noise exposure is high, little is published about this issue. In the current article we are aimed at studying the prevalence of tinnitus in Minoo and other manufactures.

Studying the effect of the noise of a 63.20KV transformer post in the residential area close to it

Fereydoon Sheikh Momeni

This study was designed to measure the noise caused by a 63.20KV transformer in the residential area close to it that consisted of 36 points inside the post and the surrounding area around it (including 29 points+30 points). the results demonstrated that noise caused by the function of the transformer t1 was 59.1dBA with the standard deviation of 6.89dBA and for transformer t2 was 59.89dBA with a standard deviation of 6.86dBA .The measured noise in the west residential area around the post was 54.95dBA with a standard deviation of 1.76dBA, in the east was 54.1dBA with a standard deviation of 2.52dBA and in the south was 49.71dBA with a standard deviation of 1.07dBA.The statistical measurements showed no significant difference in the measured noise around in the mentioned direction.The results of this measurements manifested that the noise measured in all residential areas close to the post was more than noise permitted in night.

a noise measurement study of the traffic in the Modarres High way In Tehran

Amir Hossein Izad Doustdar

We measured the noise caused by Vehicles and its subjective effects in the Modarres high way In Tehran. we examined 143 cases in 11 stations in the mentioned pathway with an accuracy of 95% and a standard deviation of 39%. The noise criteria of Leq and the number of vehicles were determined in dBA. The loudness contours were also measured in some stations to determine the subjective impacts of noise. Then the correlation of the responses of the interviewees with sound pressure level was measured. Based on our findings, decrease of the noise of traffic sources should be considered three levels: the first level is noise reduction at the level of source, e.g. the vehiclesthe second is Noise reduction at the traffic level and the third is noise reduction at the level of general activity.

Hearing aid and noise

Ahmad Reza Nazeri

Prescription of hearing aid is an extensive special category of knowledge in the field of audiology. This article is aimed at discussing the function of hearing aid and also management of patients in the noisy environments and presenting solutions to overcome problems regarding to this issue along with taking a look to the equipments prepared nowadays to cope with noisy situations.

the noise pollution caused by Pneumatic drills in city services

Rostam Gol Mohammadi

We designed this study to measure the Percussion caused by pneumatic drill( 32gram) which is used commonly in different in city services. this study have been performed in the summer of 1375 in Hamedan. The results demonstrated that the average background noise level (including environment and compressor) was 92.4 with standard deviation of 5.4 dBC, the average background noise level of the drills while working was 109.6 dBC with the standard deviation of about 2.2dBC and the average peaking factor was 18.6 with a standard deviation of 3.7dBC. the average background noise level of the drills while working in a distance of 5m, 10m and 20m from the source respectively were 98.6 dBA(with a standard deviation of 2.8dBA), 91.5dBA(with a standard deviation of2.6dBA) and 86.8dBA with a standard deviation of 2.8dBA).Based on the obtained results and the potential effects of exposure to noise which mainly can be summarized to damage to auditory system, interference with the communication skills, neural excitation, Hypertension and tachycardia the side effects of noise should be taken in to account seriously.Based on the mounting evidences regarding the adverse impact of working in the noisy environment and the damaging consequences of living in such atmospheres and the findings of the current study which confirms that the noise exposure level is more than allowed limit, the health of the workers and citizens is threaded by the noise pollution factors mentioned in the current study and serious considerations should be taken in to account.

Hearing conservation program for the workers of in municipality of Tehran exposed to high level of noise

Parviz Moshki

Workers in the Municipality of Tehran expose to high level of noises. The major sources of noise are the vehicles for garbage collection, Asphalt production and its usage in construction of pavements, Repairing motor vehicles, technical and constructive implementation including road and building construction , Forging, Concrete planning, Welding, Building structure and etc.Although most of such activities are performed by Contractors, many workers are exposed to high levels of noise during such processes. Since hearing conservation program is a duty for the Municipality, we have managed to use some new protocols to prepare a convenient and quiet environment for workers that is going to be discussed here in the present article

The continuing exposure to noise in workers in the society and living environment

Shahrokh Ehtesham zadeh

As the industry develops in the societies, human being is more likely to exposed to high level of noises and be at risk of hearing loss. Urbanism and working in the situation which are not in accordance with the personal nature make people even more susceptible to risk factors of hearing loss. Exposure of workers to industrial noise has been the subject to several studies and it seems that reconsidering the situations in both society and nature can be a key to change environment for decreasing noise in the society.For example in Tehran, geographically, the slope of the earth from north to south is 5-10% which is a main factor contributing in noise pollution.Moreover, the source of most outdoor noise worldwide is mainly construction and transportation systems including motor vehicles, air craft noises and rail noises. Poor urban planning may give rise to noise pollution, since side-by-side industrial and residential buildings can result in noise pollution in the residential area.In the current article we have examined both conditions in the hearing condition of workers with high levels of noise exposure.

Hearing evaluation in some veterans in the years between 1996-1997 in Hamedan

Faranak Emami

Background: Many Endogenic and exogenic factors can affect the individual&aposs susceptibility to noise exposure, for instance middle and outer ear characteristics, the amount of oxygen transmission, skin color, medical history, mental state and the patient&aposs attention, age, cigarette smoking and many otjher factors affect the amount of noise induced hearing loss and acoustic trauma.The current study was aimed at investigate the impact of various Endogenic and exogenic factors on the amount of PTS and TTS in veterans in Hamedan province.
Results: The results of the study manifested that:- Veterans with tinnitus suffered more hearing loss than patients without this symptom.- Extended intensity of noise and exposure time to war noises can exacerbate the amount of hearing loss in veterans who had fight more.- The degree of hearing loss in patients who had previously suffered middle ear infections or otitis or the familial history of hearing loss was more than people without such history
Discussion: The findings of our study in compatible with the results of other similar studies and confirms the effect of different pathologic and non-pathologic factors on the degree of noise induced hearing loss.

Evaluating the impact of spinning noise on the spinning workers of the first flat of Yarn Polyacryl

Javad Sanati

Background: workers in the spinning company were audiologically evaluated to estimate the impact of industrial noise of the factory on their hearing status.
Material & Method: subjects were 185 workers of the spinning post in the first flat of yarn. Hearing thresholds were compared at the beginning of their employment and after 1 to 19 years of work experience.
Results: the percent of hearing deficit was lower than the data reported by WHO.
Discussion: efficient application of hearing conservation devices has had a remarkable effect on hearing status of workers.

A descriptive study of the audiograms and Hearing aid prescription papers of Veterans

Mohammad reza Ranayie

In the current investigation we gathered information about the hearing thresholds, types of hearing loss, types of tinnitus, and also the prescribed tinnitus maskers for the veterans. We were aimed at determining the percentage of tinnitus, audiogram shape and its relationship with tinnitus, and the percentages of veterans using tinnitus maskers. The needed information was prepared by studying the audiograms and file of the patients. The results of the investigation have been prepared here in details.

Sound and the physiologic conservation of hearing system

Seyyed Hab toddin Borghehiea

It is as a lecture

Estimating sound intensity and its effect on the hearing status of the workers in an industrial shoe factory

Vida Ameri

Introduction: We estimated the noise in an industrial shoe factory to determine the effect of noise in the workplace on the hearing status of the workers in such environments.
Materials and method: the intensity of noise in dB in different parts of the factory was estimated. Then working people in each part was selected randomly and their hearing thresholds were evaluated by Conventional audiometry.
Results: The results demonstrated that 23% were required to estimate thresholds more precisely and 95 needed close examination by Otolaryngologist. Besides, 10% of the workers suffered sensory neural hearing loss whose 2% of them diagnosed as NIHL.
Discussion: Since the mentioned factory has good hearing conservation program for the workers, it seems that promoting the program can decline the number of noise induced hearing losses to the least numbers.

Music and its impact on musicians in broadcasting company

Mina Milani

Sound is an inseparable part of human life and provides us with lovely experiences such as listening to music. Musicians from classical orchestras to rock groups are exposed to high decibel of sounds. Musicians playing percussion musical instruments are exposed to high level of impact noise and players of Brass musical instruments are highly exposed to noise peaks higher than 100dB. Woodwind players are enduring the risk of posing directly in front of Brass players. Based on the above-mentioned risks for hearing loss clinical consideration of noise induced hearing loss in musicians is highly required.In the current study we were aimed at examining hearing stratus of classic and traditional musicians by means of pure tone audiometry in Islamic Republic of Iran Broadcasting. 33 subjects were evaluated aged between 22 to 59 years old. Their musical experience was variable between 6 to 45 years.The study demonstrated that most of the musicians in this study suffered bilateral high frequency hearing loss with a notch in the frequency range of 4-8 KHz.

Studying the amount of noise exposure and measuring the hearing loss in workers of door and window construction factory

Sadegh Hazrati

Material and method: by using a dosimeter we tried to study the amount of noise exposure each worker is exposed to the microphone was connected to the collar of the shirts and the dosimeter to the belt. The audiometric evaluations were performed before starting work in the factory.
Results: the years of experience in the factory has a significant correlation with amount of hearing loss in the workers of the noisy environments (based on the findings of the dosimetric measurements)
Conclusion: the findings of the current study demonstrated that workers of the door and window construction factory were exposed to high level of noises and their hearing thresholds were largely affected by the noise pollution. This is in accordance with results of the similar studies. This impact was mostly revealed in the forgers.

Estimating the amount of exposure to noise and hearing status in Dentists in Tehran

Rostam Sasani

Technology has made people to be exposed to a lot of sources of noise because of the instruments they use at workplace or at home. Dentists are a group of such people who are especially subject to different sources of noise such as high-speed air-turbine headpieces, operated at 300,000 to 400,000 revolutions per minute In the current study we were aimed at measuring noise at the dentists&apos office estimating hearing thresholds in dentists and determining the reason of hearing loss and finally determining the role that work experience e play in the hearing loss occurred.Dentists have been divided into groups based on the work experience and subjects were randomly selected from the dentists of various groups. Sound levels were measured in clinical settings and in a pre-clinical laboratory for estimation of hearing-damage risk among dentists,The findings demonstrated that all dentists regardless of age and gender suffered a notched hearing loss at 6000 Hz. Additionally hearing loss was worse in right ear.Since sound energy of high-speed air-turbine headpieces is mostly concentrated in high frequencies, it can lead in the most possible hearing loss at 6000Hz.

Industrial noise pollution and the need for applying protocols for its control and decrease

Parvin Nasiri

Industrialization has had many complications for human beings and has been a threat to social mental and physical health. Vibration induced noises in the workplace is one of the main devastating factor in producing hearing loss in workers.Recently, several investigations on the issue of noise pollution and noise dosimetry and also Noise induced hearing loss have been developed. In the current article we will have a look and sometimes reconsideration on the results and of these studies and will discuss the findings in regard to noise control and management in details.

sound in Ergonomics

Jebreil Seraji

The word of "Ergonomics "is composed of two separate parts: "Ergo" and" Nomos" and means the Human Factors Engineering. Indeed, Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance. It has applied different sciences such as Anatomy and physiology, anthropometry, engineering, psychology, biophysics and biochemistry from different ergonomics purposes.Sound when is referred as noise pollution can affect such balance in human life. The industrial noise caused by factories, traffic jam, media, and modern human activity can affect the health of the society.Here we are aimed at discussing sound from an ergonomic point of view.

Magnesium chlorate decrease the sound induced stress and control the concentration of Cortisol and glucose after hatching

Mahin Gharavi

We prepared 300 eggs from Isfahan Poultry farm industrial complex. All the eggs were fertilized and their average weight in the first turn was 61±2gr, in the second turn was 60±.5gr and in the third turn was 59.5±.5gr which was measured 6 hours after laying eggs. We were aimed at studying the effect of magnesium chlorate on the fetus chicken in preventing stress induced sound 6 weeks after birth.The eggs were divided into four groups and prepared magnesium chlorate with a concentration of 2.5 /100 ml. the first group contained of 25 eggs drilled in the air Sac with a small hole and 1cc of magnesium chlorate was injected and the hole was sealed with paraffin. The same procedure was performed for the second group in the 4^th embryonic age and in the two control groups. All groups were hatched in the days 21 and 22. The effect of sound was studied in all groups.our research demonstrated that the chickens who received magnesium chlorate during their embryonic stage had more resistance toward noise exposure.

The protective effect of oral magnesium ion on Noise Induced Hearing Loss

Zahra Jafari

Introduction: Several animal studies have been performed that demonstrates a relationship between the amount of magnesium ion in the plasma and the hearing thresholds following exposure to noise, Mg++ has been considered as an effective factor in prevention of noise induced hearing loss in animals.The aim of this study was to discover whether Mg for a long period of time have a protective effect on occurrence of Noise Induce Hearing loss.
Method: The subjects were randomly chosen among individuals who were under training in army service for two months. The subjects were treated in a double-blind manner by placebo and magnesium ion. Threshold estimation and blood examination was performed for all subjects before and after treatment. All subjects were exposed to noise during 8 weeks training in the army.
Results: The statistical difference between two groups which was treated with placebo and magnesium ion was significant.
Discussion: This study is compatible with previous in vivo observations and animal studies demonstrating the protective effects of magnesium on noise-induced impairment of inner ear.

Sound pollution caused by the industrial activity in Tehran

Fattah Ramezanali

Noise pollution is the problem of the industrial world that along with noised induced by traffic has become a problem in human life.This is more problematic in Tehran because of the traffic and the accumulation of small or large industries. People are profoundly exposed to the high level noises and there are increasing demands to solve the problem of noise in Tehran or at least alleviate it.In the current article we will have a brief and quick look to the noise making industries, the reason behind the noise pollution and the strategies for facing the disturbing industries.

The role that natural environment plays in reducing noise pollution

Nasim Saber Maash

Noise pollution is one of the major problems for the present time and it can affect the life of human being. Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life. Researchers have mentioned a lot of devastating effects of noise that can disrupt the physical and psychological health of human beings. Noise pollution has also been considered as an important issue which needs to be solved in industrial countries and also as a main factor that is required to be minimized in factory construction and also in producing machinery. In the current article we are aimed at discussing some solutions that natural environment can bring to mankind regarding the reduction of noise pollution.

Sound control in the physic lab in the polyacryl company and studying the noise reduction by means of different absorbents

Harandi

Studying noise effect at the workplace has more various aspects than other factors. So it is not surprising that its adverse impact on the physical and mental state of the society has been detected to some extent. There is a significant correlation between the hearing loss and the noise pollution of the workplaces. The most important ways to lessen and control the impact of noise are: substituting the noisy equipments with ones that produce less noise, correcting noise sources and isolating the sound source.In the current study we tried to control the noise level by using various sound absorbents and measured sound level by using these different substances. The results of these measurements have reported in the current article in details.

Insufficiencies in the Hearing Conservation Program

Seyyed Ali Akbar Tahayei

There are some insufficiencies in the Hearing Conservation Program that are exponentially exacerbated by lack of the standard and observation for this program and little interest in team work activities. Regarding the noise measurement instruments, limitation in the measurement lack of the equipments and also incomplete evaluation are clearly detected.The performed investigations have demonstrated that most of the industrial centers have no baseline auditory curve and sometimes do not intend in hearing screening evaluations. that is mainly because of the need for sound protected environment and calibrated instruments and also 14 hours of sound rest before the experiment.Her the problems in performing hearing conservation program is discussed in more details.

Studying the noise control engineering protocols in industry

Hamid Golshah

Today, sound is one of the detrimental factors in the workplace and its harmful impact has been so important that scientists have named it "Noise Pollutions".Hearing is one of the five senses of human being which is also a medium for communicating with other s and enjoying the pleasant feeling of listening to a piece of music. In spite of this, changes in the intensity and frequency of sound can make it annoying. Using Sound Level Meter to measure the dB of noise in the workplace and noise control principles will be discussed here.

selecting the protective ear plugs

Manouchehr Omidvari

Exposure to noise is a one of the common problems in any industrial places. Many solutions have been introduced to overcome the deleterious effects of noise pollution maintaining and repairing systems in the equipments, environmental control and hearing conservation systems are some of these solutions that could be mentioned.
There are various types of Hearing protection devices and each one is useful under special circumstances. Commonly, different Hearing protection devices have a particular brochure to introduce information about the manufacturers and the quality of noise reduction in that special production.
Three different methods are commonly used to determine the noise reduction factor in various Hearing protection devices. All these methods have been presented based on the mathematical evaluations and according to the spectral features of the sound existing in the environment and then the sound pressure level is determined in dBA. In the current article we will have a look on the mentioned arithmetic models and their special characteristics.