投稿者: yako77

What Is Sodium Salicylate?

Sodium salicylate, with molecular formula C7H5NaO3 and molecular weight 160.10, is a compound of salicylic acid with a sodium salt, and is a white crystal or crystalline powder at room temperature. It is extremely soluble in water, soluble in acetic acid (100), and slightly soluble in ethanol (95).

It is characterized by gradual coloration by light, and thus by sunlight and air, and especially by exposure to ammonia gas.

Industrially, it is obtained by synthesizing sodium phenoxide and carbon dioxide at high temperatures and pressures. Also called sodium salicylate, it is decomposed by heating to produce oxygen dioxide.

Uses of Sodium Salicylate

Sodium salicylate has long been used in medicine for its anti-inflammatory and analgesic properties. It is particularly applicable to symptomatic neuralgia (nerve pain with an obvious cause, such as trauma, pressure, inflammation, or infection) that tends to occur in limbs and joints.

It is also used as a denaturant and preservative in cosmetics. In the case of cosmetics, the amount of sodium salicylate that can be contained is small, so it is not a major problem.

However, those with a history of hypersensitivity to salicylic acid compounds (such as aspirin) may experience flare-ups of allergic symptoms such as asthma. It may also aggravate symptoms in patients with ulcerative colitis and Crohn’s disease.

In animal studies, teratogenic effects and weak ductus arteriosus contraction in fetuses have been reported, so pregnant women are advised to reduce the dosage due to the possibility of fetal effects.

Miscibility With Other Drugs

Sodium salicylate liberates salicylic acid in acidic solutions and precipitates with iron salts in neutral solutions, forming insoluble iron salicylate. It may also precipitate with alkaloid salts as insoluble salicylate alkaloid salts.

Discoloration occurs when mixed with alkalis, iron salts, and nitrites. Alkali bicarbonate turns reddish brown, and iron salts turn purple. The discoloration caused by iron salts does not change the therapeutic effect.

In aqueous solution, the alkali may cause photo-oxidation, resulting in coloration or precipitation, but this reaction is catalyzed by copper, iron, and manganese, and can be prevented by adding hydrogen sulfite or thiosulfate to the mixture.

Uses in the Medical Field

Sodium salicylate is thought to exert its analgesic and anti-inflammatory effects by inhibiting cyclooxygenase and decreasing the synthesis of prostaglandins and thromboxane precursors from arachidonic acid, but this remains unclear. Unlike aspirin, however, it does not inhibit platelet aggregation.

The exact mechanism of action of its anti-inflammatory and analgesic effects is unknown. It is thought to exert its effects by inhibiting the synthesis of prostaglandins or other factors in inflammatory tissues, thereby blocking the generation of nerve impulses.

What Is Asparagine?

Asparagine is a type of amino acid, isolated from the juice of the asparagus plant. It was also the first amino acid to be discovered. It is an amino acid that constitutes human proteins and can be biosynthesized, so nutritionally speaking, it is classified as a nonessential amino acid. It is an optically active compound, and as a protein-constituent amino acid, all asparagines are in the L form.

Asparagine helps to remove ammonia, which is harmful to the body, from the body and protects the central nervous system. Asparagine, together with aspartic acid, works with the TCA circuit, which produces energy in the body, to promote energy metabolism. As a result, its effect is to improve endurance during exercise.

Characteristics and Physicochemical Properties of Asparagine

1. Name

English name: L-Asparagine
IUPAC name: (S)-2,4-diamino-4-oxobutanic acid
3-letter abbreviation: Asn
1-letter abbreviation: N

2. Molecular Formula: C4h8n2o3

3. Molecular Weight: 132.12

4. Structural Formula: As in Figure 1 5. Melting Point: 234°C

5. Melting Point: 234~235°C

6. Solvent Solubility: Easily Soluble in Water, Insoluble in Ethanol

7. Taste: Bitter

Biosynthesis of Asparagine

In vivo, asparagine is biosynthesized from aspartic acid by asparagine synthetase.

Safety and Uses of Asparagine

Asparagine is a type of amino acid that exists in the human body. Therefore, it is a relatively safe substance. Asparagine is sometimes used in the food additive category.

It may also be used as a pharmaceutical product to supplement amino acids for hypoproteinemic and hypo-nutritional conditions, as it acts on the TCA circuit to promote energy metabolism.

Examples of Foods High in Asparagine

It is abundant in dairy products, whey, meat, seafood, eggs, nuts, brown rice, raisins, shrimp, potatoes, asparagus, and sprouted legumes.

What Is a Sound Power Level?

Sound power levels are the ratio of the total sound power of the energy that a sound produces in a unit of time to a reference sound power of 10 to the -12th power, converted to ordinary logarithm and multiplied by 10.

The unit is dB, and the same unit is used for sound pressure level, but the sound pressure level is defined differently. The sound pressure level is the ratio of the measured sound pressure to the reference 2 x 10 to the -5th power, converted to the ordinary logarithm and multiplied by 20. Sound power levels refer to the measured value at the source, while sound pressure levels represent the sound intensity at the point of measurement.

Usage of Sound Power Levels

Since sound power levels are independent of the measurement environment and location, they can be used to describe product specifications and indicate noise limits without specifying conditions. Once the sound power levels are known, the sound pressure power level due to distance attenuation can be calculated from them.

Since 1970, ISO standards have been created mainly in the United States, Germany, and France for general-purpose sound power levels measurement methods. First, sound power levels measurements were widely used in air conditioning equipment, construction machinery, and copying machines.

Principle of Sound Power Levels

Sound power levels can be measured by the following methods, depending on the sound field.

1. Practical Semi-Free Field Method (Method A)

This method is applied to a large room or an outdoor space with little resonance, which can be regarded as a semi-free sound field, and is measured with accuracy according to the precision method and corresponds to ISO3744.

2. Simple Semi-free-Field Method (Method B)

This method is used to measure the approximate sound power levels in a narrower room than Method A, where the measurement points can be placed according to the principle of the semi-free-field method, and where there is the influence of reflected sound.

3. Simple Diffuse Sound Field Method (C Method)

This is a simple method to measure sound power levels according to the principle of the diffuse sound field method in a room where boundary surfaces, such as walls, floors, and ceilings can be identified, assuming a situation where there is some degree of reverberation. There is no ISO standard that directly corresponds to this method; the C method was added so that it can be widely applied to measurements in machine rooms, general rooms, and factory test rooms in buildings and factories.

Each method can measure octave band sound power levels and A-weighted sound power levels, and only Method A can also measure 1/3 octave band sound power levels, directivity index, and directivity coefficient.

What Is a Copper Buss Bar?

Copper buss bars are copper materials used in the current-carrying parts of electrical equipment, and are made of tough pitch copper or oxygen-free copper, which has excellent electrical and thermal conductivity.

Tough pitch copper (C1100) is a metal with a Cu purity of 99.9% or higher. It has excellent electrical and thermal conductivity as well as corrosion resistance and workability. Due to the presence of a trace amount of oxygen inside, it may react with hydrogen at high temperatures, resulting in hydrogen embrittlement.

Oxygen-free copper (C1020) contains less oxygen than tough pitch copper and has less resistance and distortion, so oxygen-free copper may be used in environments where hydrogen embrittlement is a concern. Oxygen-free copper is also widely used in vacuum equipment because of its low gas emission.

Applications of Copper Buss Bars

Copper buss bars are used as conductors for carrying large currents at high voltage in a variety of applications, including power distribution boards and circuits for controlling electric vehicles and trains.

Compared to round conductors, copper buss bars have the advantage of better conductivity and require less wiring space. In addition, there is no need to caulk the terminals; simply drill holes directly through copper buss bars and bolt them to the equipment. When conductors are thicker, it is necessary to consider the bending radius, but this is not necessary with copper buss bars.

Features of Copper Buss Bars

Copper buss bars require a minimum cross-sectional area based on the current value. The cross-sectional area is calculated by dividing the current value by the current density as follows:

• 125A or less: 3.0 or less
• 125 to 250 A or less: 2.5 or less
• 250 to 400 A or less: 2.0 or less
• 400 to 600A or less: 1.7 or less

In designing the actual cross-sectional area, the cross-sectional area is determined by taking into account the chamfering and forming of the material and the current density increase +5%.

Copper buss bars have screw holes to fix them to equipment. If the cross-sectional area of the screw holes exceeds 1/2 of the cross-sectional area without screw holes, it is not necessary to adjust the cross-sectional area of the screw holes to the cross-sectional area determined by the calculation.

In addition to copper, copper buss bars may also be made of aluminum. Although aluminum has lower tensile strength and conductivity than copper, it is less expensive and may be considered as a cost reduction plan. On the other hand, aluminum has lower conductivity, so the conductor volume must be larger than that of copper buss bars.

What Is Bearing Steel?

Bearing steel is steel used for bearings.

Bearing steel is required to have “load carrying capacity,” “wear resistance,” “hardenability,” and “corrosion resistance.”

Depending on the environmental conditions in which it is used, carbon and chromium are added, and heat treatment and rolling are used to achieve high cleanliness, reduce the oxygen content in the steel, and refine non-metallic inclusions to increase the service life of bearings.

Applications of Bearing Steel

Bearings are used to support rotating parts and are mainly classified into roller bearings and ball bearings. Rollers are cylindrical and balls are spherical and roll in a cylindrical shape to support a rotating body.

The rollers and balls make linear or point contact with the weight of the rotating body, but the contact area is subject to high loads. Bearing Steel was developed to withstand high loads. The main processing methods are as follows:

• After the coarse cementite mesh structure is crushed by forging or rolling, it is heated to refine the crystal grains by recrystallization.
• Further spheroidizing annealing is followed by quenching or tempering at low temperature.

Other Information on Bearing Steel

Types of Materials Used in Bearings

The types of materials used for bearings are as follows:

1. High Carbon Chromium Bearing Steel
This material, called SUJ, is hardened not only on the surface but also internally. It is easy to temper, and its machinability is improved by spheroidizing and annealing.

SUJ2 is used for more than 90% of high-carbon chromium steels. SUJ3 is a type of SUJ2 with improved hardenability by increasing the ratio of Si and Mn and reducing the amount of Cr. It is suitable for large-sized balls, rollers, and races.

2. Hardened-Skin Alloy Steel for Bearings
By carburizing, this type of steel maintains the same hardness and wear resistance as high-carbon chromium bearings, but has an internal toughness.

3. Corrosion-Resistant Steel Bearing Steel
This type of steel has excellent corrosion and wear resistance and is used in chemical plants where materials are prone to corrosion.

4. Heat-Resistant Steel Bearing Steel
This is used in high-temperature environments with good dimensional stability.

5. Medium Carbon Steel Bearing Steel
Parts requiring high hardness are subjected to high-frequency quenching and are often used in hub unit bearings and linear motion bearings for automobiles.

What Is a Transmission Line?

Transmission lines are lines of misaligned atoms (defects) in metals.

Although it has been believed that all atoms in metals are regularly aligned, it has become clear that there are actually disarrangements in the alignment of atoms in some places.

When a group of atoms on a plane shifts in the same direction, the plane is called a slip plane, but it requires a considerably large amount of energy to shift a group of atoms at once. In reality, the metal begins to deform with very little force as a portion of the atoms are displaced in sequence along the slip surface. This theory was proposed by Taylor, Olowan, and others in 1934.

Uses of Transmission Lines

Dislocation lines are deformed by external forces caused by metal forging or plastic forming. Whenever deformation occurs, transmission lines are generated and move inside the metal. In order to strengthen metals, it is necessary to suppress the movement of dislocation lines.

Methods to suppress transmission lines include work hardening, precipitation strengthening, solid solution strengthening, and grain refinement.

Transmission lines are used to measure dislocation density by X-ray analysis. Dislocation density is the total length of dislocation lines. By measuring dislocation density, one can evaluate the degree to which a material has been strengthened. A greater dislocation density will create a greater strength material.

Other Information on Transmission Lines

1. Characteristics of Transmission Lines

Dislocation lines, which are linear lattice defects, are generated during plastic deformation of crystals and propagate to neighboring atoms, eventually reaching the surface of the crystal and displaying a step of one atom. Plastic deformation occurs inside the crystal as dislocation lines, which move to neighboring atoms step by step, so that no step is suddenly formed on the crystal surface.

An external shear force is required to cause dislocation migration, and this force is called the Peierls force. The Peierls force can be obtained from the spacing of slip surfaces, Burgers vector, Poisson’s ratio, and stiffness ratio.

2. Classification of Transmission Lines

The Burgers vector is a measure of the size or direction of dislocations. Transmission lines are classified into edge dislocations, helical dislocations, and mixed dislocations according to the relationship between transmission lines and Burgers vectors.

Edge Dislocations
This is an image of an atomic plane with one extra blade cut into the top or bottom half of the atomic plane in a row of many atomic planes. If there are slip planes at the top and bottom and a blade dislocation in the top half, the lattice is compressed at the top and expanded at the bottom, the condition is called “positive dislocation” and the opposite is called “negative dislocation”.

Helical Dislocation
When a line is defined in a metal, a 360° rotation around that line results in a displacement of the atomic layers in one plane. Depending on the direction of displacement, it is distinguished as right-handed or left-handed. In a blade dislocation, the Burgers vector and transmission lines are perpendicular to each other, while helical dislocations are parallel.

Mixed Dislocation
A dislocation is neither right-angled nor parallel and is a mixture of blade dislocations and helical dislocations.

What Is Super Duralumin?

Super duralumin is an aluminum alloy made by adding copper, magnesium, and other elements to aluminum.

It is stronger and easier to cut than duralumin, which is made by adding copper and other elements to aluminum. The hardness of super duralumin is 105HB, whereas that of super duralumin is about 120HB.

However, a disadvantage is that its corrosion resistance is reduced due to the high copper content.

Uses of Super Duralumin

Super duralumin has a specific gravity of about 1/3 that of steel. Taking advantage of its lightweight and high strength, it is used for various structural materials such as aircraft fuselages, bolt materials, and spindles.

Since weldability is inferior to other aluminum alloys, rivets and bolts are often used to join products made of super duralumin. In recent years, welding methods have advanced, and welding joints by resistance spot welding, etc. are used.

Principle of Duralumin

Pure aluminum is an extremely lightweight and workable material, but its disadvantage is its low strength. In general, “the strength of the base material increases when it contains copper. Super duralumin is an alloy in which copper is added to aluminum to improve strength and machinability.

In addition, super duralumin is made by adding copper and magnesium to aluminum. Compared to duralumin with the same composition, the amount of magnesium is increased to further increase strength.

The properties of aluminum alloys are greatly affected by heat treatment. Heat treatment is the process of heating a metal to a certain temperature and then cooling it. The heat treatment symbol T3 indicates that the alloy was cold worked after quenching, T4 indicates that the alloy was only quenched and left at room temperature for about 4 days to age-harden, and T6 indicates that the alloy was cold worked after quenching and then tempered.

The melting point of super duralumin is about 500-650℃, and it can be cast and processed relatively easily.

Types of Super Duralumin

There are three types of material known as super duralumin. Specifically, they are A2017 duralumin, A2024 super duralumin, and A7075 super duralumin. All of these materials are made by adding copper to aluminum to increase strength. They are precipitation-hardening alloys, in which inter-metallic compounds, such as copper precipitate and harden.

1. A2017 Duralumin

A2017 duralumin is an alloy of aluminum with copper and magnesium added. In Japan, industrial production of A2017 duralumin began in 1921 at Sumitomo Copper Works, and the following year, domestically produced duralumin was used in airplane structures.

With a specific gravity of 2.79, A2017 duralumin is characterized by its extremely lightweight, yet excellent strength and machinability. On the other hand, its corrosion resistance and weldability are inferior to those of other aluminum materials. It has the disadvantage of being prone to intergranular corrosion, and its high susceptibility to cracking makes it an extremely difficult material to weld.

A2017 duralumin is manufactured by adding 3.5-4.5% copper and 0.40-0.80% magnesium to aluminum. The addition of copper to aluminum increases its strength but makes it more susceptible to oxidation. The hardness of duralumin increases to 105HB compared to 65HB of aluminum.

A2017 duralumin is used in a wide range of fields, taking advantage of its lightweight and high strength. These include parts for aircraft and rockets, for ships, machine parts such as hydraulic equipment and gears, attaché cases, fastening members such as screws and rivets, and window frames of buildings.

2. A2024 Super Duralumin

A2024 super duralumin is an alloy similar to A2017 duralumin, but differs in the content of copper (3.8-4.9%) and magnesium (1.2-1.8%). It has a higher hardness than A2017 Duralumin, about 120 HB, and its strength increases. On the other hand, corrosion resistance is slightly lower due to the effect of increased copper content. It is also a material with excellent machinability.

A2024 super duralumin has the disadvantage of low weldability. The oxide film on the surface has a higher melting point than that of the base metal, requiring the removal of the oxide film in advance. Another disadvantage is that the heat from the base metal easily escapes, making the welding process unstable.

3. A7075 Duralumin

A7075 duralumin is an alloy of aluminum containing 1.2 to 2.0% copper, 2.1 to 2.9% magnesium, and 5.1 to 6.1% zinc.

It has a hardness of 160HB and is the strongest duralumin material. Its tensile strength is about 570 N/mm^2, which is a significant increase over the 425 N/mm^2 of A2017 duralumin and 470 N/mm^2 of A2024 super duralumin.

Applications for super duralumin include aircraft, rolling stock, and sporting goods. As with super duralumin, its corrosion resistance is inferior, so care must be taken in the environment in which it is used and in corrosion-proofing treatment.

What Is Short Fiber?

Short fiber is a general term for short fibers, which are the raw materials used to make yarn.

Most natural fibers such as cotton and hemp are examples. When making yarn, short fibers are twisted together, resulting in yarns with large volume and high bulk. When the yarn is created, the untwisted portions protrude, giving it a fluffy appearance. Yarns made from Short Fiber are also collectively called spun yarns.

Uses of Short Fiber

Short fiber is not used as it is. Short fibers are twisted together to make spun yarn before being used.

Spun yarns are widely known as sewing threads worldwide and are characterized by their good fit to fabrics and ease of sewing. Today, spun yarns are used for sewing a wide variety of fabrics, including knit products, clothing, and towels. Spun yarns with a strong fluffiness are said to have a gentler feel against the skin.

Types of Short Fiber

Short fiber is a type of fiber that is shorter in length. In general, when classifying fibers, they are divided into natural fibers and synthetic fibers.

Natural fibers are fibers derived from natural sources. Typical examples are cotton made from cotton, linen made from plant fibers, and wool made from wool. Chemical fibers are fibers produced by chemical synthesis. They are divided into three types: regenerated fibers, semi-synthetic fibers, and synthetic fibers.

Typical examples of regenerated fibers are cupro made from rayon or cotton linter. Semi-synthetic fibers are acetate, and synthetic fibers are nylon and polyester. Most of the natural fibers fall under the category of short fiber.

Synthetic fibers fall into the category of both short fiber and long fiber because it is possible to adjust the length of the fiber when it is made. Among natural fibers, silk falls under the category of long fibers and should be treated with caution.

What Is Sintering?

Sintering is an object that becomes dense when powdered metals are hardened and then joined together atoms at a temperature lower than their melting point.

In the initial stages of sintering, the powder particles form a neck that is bonded to each other. Diffusion of ions, atoms, and molecules on the surface of the neck causes the neck to grow larger and the surface area of the sintering object to decrease. At this point, the diameter of the neck is approximately 30% of the particle diameter.

The pores inside the sintering will change their shape to a tube-like structure and become connected to each other. Pores in this state are called open pores. Finally, the relative density exceeds 95% and the pores are dispersed within the sintered body, resulting in a closed pore state.

Uses of Sintering

Sintering is used to form materials that cannot be processed by plastic deformation, such as rolling and forging. For example, they are used in powder metallurgy and in the manufacture of ceramics. Compared to casting, where defects may or may not occur depending on the conditions of the mold and hot water, sintering offers more flexibility in shape and is therefore used for parts with complex shapes, such as automobile engine parts, drive train parts, small gears, and bearings.

Sintering can be used with almost any metal that can be made into powder. Therefore, sintering is also applied to parts made of tungsten and molybdenum, which have high melting points, and titanium, which easily reacts with other elements at high temperatures.

Other Information on Sintering

Characteristics of Sintering

The main sintering methods are atmospheric pressure sintering and pressure sintering, but research and development of electromagnetic field-assisted sintering as a new method is progressing, and some practical applications have begun.

1. Atmospheric Pressure Sintering
Atmospheric pressure sintering is a sintering method in which the atmosphere is at atmospheric pressure. There are two types of sintering methods: liquid phase sintering, in which a liquid phase is generated at high temperatures using additives to produce densification; and solid phase sintering, in which densification occurs through mass transfer between solid phases without generating a liquid phase.

2. Pressure Sintering
Pressure sintering is a method of densification by applying external pressure and includes hot press sintering and hot isostatic sintering. In hot press sintering, uniaxial pressure is applied to the powder, while in hot isostatic sintering, the powder is encapsulated in glass or metal and pressurized with gas to solidify.

3. Electromagnetic Field Assisted Sintering
Pulsed energized pressure sintering, microwave/millimeter wave sintering, and electric field assisted sintering are available. Pulsed current pressure sintering is a method of sintering by passing a pulse current of several thousand A through a conductive mold while applying pressure. Microwave and millimeter wave sintering are self-heating methods from the inside of the derivative, and heat treatment can be performed in a short time with high thermal efficiency. By raising the ambient temperature while energizing the powder compact directly, sintering can be performed at lower temperatures than with atmospheric pressure sintering.

What Is a Vibration Level?

Vibration levels are the acceleration of vibrations calculated from physical quantities plus a correction for human perception of vibrations.

The unit is a dB. Vibration can be measured in terms of displacement, velocity, and acceleration, but it is recognized that acceleration is more appropriate as the basis for vibration felt by the human body. Vibration levels are established to regulate vibration pollution.

Vibration has vertical and horizontal directions, and the way people perceive vibration differs according to the direction. Vertical vibration is felt more strongly than horizontal vibration. 

Applications of Vibration Levels

1. Specific Factories, Specific Construction Work

As a strain of rapid postwar economic growth, various types of pollution have occurred, and regulations have been enacted to deal with them. The vibration subject to regulation is specified factories, etc., specified construction work, and road traffic vibration. Vibration levels are determined based on the human body’s sensory perception during the daytime and nighttime.

Specified factories, etc., are factories and workplaces in designated areas set by local governments. Facilities that generate significant vibration are designated as specified facilities. Examples of specified facilities include metal processing machinery, large compressors, earth or mineral crushers, concrete block machines, injection molding machines for synthetic resin, and wood processing machinery. Vibration limits are established for each region.

Specified construction work is construction work that generates significant vibration; for example, piling machine work, work that destroys buildings, etc., and breaker work are subject to regulation. Vibration levels are set at the boundary of the site, depending on the area, time and duration of the work, and day of the work.

2. Road Traffic Vibration

Road traffic vibration is not directly regulated, but is required. If the living environment around a road is deemed to be significantly damaged, the mayor of the municipality will request the prefectural public safety commissioner to make improvements.

Principle of Vibration Levels

1. Calculation of Vibration Levels

Vibration Levels are calculated as the ordinary logarithm of the ratio of the effective vibration acceleration (a), corrected for vibration sensation, to the reference vibration acceleration (a0), times 20. The equation is shown below. The unit is dB.

　　VL = 20log10^(a/a0)

VL: Vibration Levels (dB), a: RMS value of vibration acceleration with vibration sensory correction (m/s^2), a0: Reference vibration acceleration (m/s^2)

For a0, the Japanese vibration code uses 10^-5m/s^2. Vibration levels are calculated using the ordinary logarithm because, according to Weber-Fechner’s law, the sensation of vibration is proportional to the logarithm of the intensity of the stimulus, as is the case with hearing.

The sensory correction used for vibration levels is more sensitive in the frequency bands of 4 to 8 Hz in the vertical direction and 1 to 2 Hz in the horizontal direction than in the other bands.

2. Guideline for Vibration Levels

Vibration levels are published by the Japan Meteorological Agency as seismic intensity classes in dB according to human senses as a guide; a level of 110 dB or higher is a level at which people are tossed about by the shaking and cannot act on their own volition, while a level of 55 dB or lower is a level at which people do not feel the shaking.

Other Information on Vibration Levels

1. Measurement of Vibration Levels

If the indicated value is irregular and fluctuates significantly, more than 100 measurements are taken at 5-second intervals, and the value is determined using the LV10 method. In the past, such a method was read by a human, but currently vibration levels meters can calculate it automatically; LV10 is a statistical value, meaning that it accounts for 10% of the time that it is measured.

2. Measurement of Ground Vibration

In principle, the measurement location for ground vibration is at the boundary of the site or property. However, if vibration is measured at the ground level, it may pick up abnormal vibration levels depending on the measurement location. The cause is due to the nature of the ground. It is necessary to measure vibration at multiple points to understand the propagation of vibration.