PHYSICS

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Control Works Modulus 4 Acoustics, Bioacoustics, Acoustobiology Problem. Estimate the intensity of sound which causes pain using Table 6.1. Answer: 10 W1m 2 • Problem. A point source emits sound waves with a power of 80 W. Find the intensity at a distance 3 m from the source. Answer: 0.707 W/m 2 • Problem. The bats of the Vespertilionidae family emit short high frequency pulses. Find the time of echo arrival after emission if the distance between the bat and insect is 10m. Answer: 58.8 ms. Example. Doppler ultrasound technique is able to measure blood velocity. If an artery has a typical blood velocity (about 1 m/s), what is the magnitude of the Doppler shift, if the velocity of ultrasound in the blood is 1500 m/s and the frequency is 5 MHz? Answer: 6.7 kHz. Animals Extremes! The sensitivity of cockroaches (Blattodeae) to vibrations is 10- 8 em - the amplitude of these vibrations is equal to the diameter of hydrogen atom. Most Powerful Sound - Finback whale (Balaenoptera) 10 W, within a range of 10000 km. Best Hearing - Barn Owl (Tyto alba) and Great Horned Owl (Bubo virginianusi, Chapter 10. MOLECULAR <strong>PHYSICS</strong> UllIn. _liM ., _w, • Ili~ 10.1. IDEAL GAS p V = nRT (10.1) where n = m/M is the number of moles, m is mass of gas, M is molecular weight of the substance (gjmole), and R is the universal gas constant (8.31 Jjmol·K = 0.0821 Latrn/rnol-K). The previous equation can be written as: p V = NkT (10.2) where N is the total number of molecules, and k the Boltzmann's constant (1.38.10- 23 JjK). 10.2. REAL GAS Real gases exhibit properties contrary to the ideal gas law; for example, real gas particles have a finite volume and measurable intermolecular forces. These two effects can be incorporated into a modified van der Waals' equation as: a (p + -2) (V - b) = RT (10.3) V where a and b are empirical constants. Isotherms for a real gas are presented in fig. P I 10.1. Below the critical temperature (Te>, the substance could be in a liquid, liquid-vapor, or Pc gaseous state, depending on the pressure and volume. Liquefaction technology for a real gas is related to isochoric (AB) and isobaric (Be) processes. Fig. 10.1. Isoterms ofa real gas: G - gas; V vapor; L - liquid; L + V liquid and vapor; I: critical temperature; Pc - critical pressure; ~ - critical volume An ideal gas is a hypothetical gas with molecules of negligible size and exert no intermolecular forces. Most gases at room temperature and atmospheric pressure behave as ideal gases. The equation of state for an ideal gas relates the pressure (p), temperature (1), and volume (V): 80 o /)11111111111'1>:""""= V ~ T 4 T=T 4 c T 2 T 1 v 81
10.3. HUMIDITY 10.3.1. Parameters of Humidity Water can exist in the atmosphere in three phases: gaseous, liquid and solid. It is called a vapor when in the gaseous phase and as water evaporates, the concentration of water molecules in the gas phase increases. Eventually an equilibrium is established when the number of molecules escaping from the liquid water equals the number being recaptured by the liquid. The equilibrium vapor pressure established between liquid water and water vapor in a closed system is known as the saturation vapor pressure (E). Humidity is the content of water vapor in the air and can be expressed several ways. Absolute humidity (a) is the mass (m) of water vapor (grams) per unit volume (II) of moist air (m'): a = m/V. Partial pressure (e) is defined as the pressure exerted by one gas in a mixture of gases. Relative humidity (r) is the ratio of the actual partial vapor pressure of water to the saturation vapor pressure at a given tempee rature: r = - . 100. E Vapor deficit (d) is the difference in vapor pressure between saturated and ambient air: d = E - e. Dew point (T) is the temperature to which, if unsaturated air is cooled, the water vapor becomes saturated. 10.3.2. Psychrometer Equation The psychrometer is the instrument used to determine air humidity. It consists of two thermometers - one measuring the air temperature To is the dry-bulb thermometer, and the second, the wet-bulb thermometer, has a muslin jacket which stands in a reservoir of water and measures the temperature T ' The wet bulb temperature is lower than that of the air due to w evaporation of water from the muslin. The relationshi p between the two thermometer readings can be written as a psychrometer equation: e = E] - A (To - Tjp (l0.4) A 82 where e is the water vapor pressure, E 1 the saturated vapor pressure at the temperature of the wet-bulb thermometer, A the psychrometric coefficient (6.62·10-4K-'), To the air temperature, T w the wet-bulb thermometer temperature, and PA the atmospheric pressure (mm Hg or Pa). Chapter 11. MOLECULAR BIO<strong>PHYSICS</strong> ~~~~t"""";-.';~o¥~~II!r';'*fii!!1~~~~'\1'.iI@a1U! .•& rr lUll' 11.1. CHEMORECEPTION Chemoreception is the ability of living organisms to perceive specific molecules in air and water. These molecules maybe important clues to the presence of specific objects in the environment and are essential to many animals in finding food, locating a mate and avoiding danger. Chemoreception is divided into two categories: gustation (taste) and olfaction (smell). Gustatory receptors respond to dissolved molecules that come in contact with the receptors. Olfactory receptors respond to airborne molecules from external sources that may be some distance away. Vertebtrates usually accomplish chemoreception by moving chemically rich air or water into a canal or sac that contains chemical receptors. Chemoreception is quite different between invertebrates and vertebrates. For example, planarians find food by following chemical gradients in their surroundings. Their simple chemoreceptors are found in pits on their bodies, over which they move water with cilia. Insects have chemoreceptors in their body surface, mouthparts, antennae and forelegs. Moths, for example, smell with thousands of sensory hairs on their antennae (fig. ILl). About 70 percent of the adult male receptors respond to only one compound (bombykol), a sex attractant released by fe . males of the species. The molecules enter the tiny pores of the hair, or sensillum, where the olfactory receptors are found. There is evidence that fish and turtles can distinguish the smell of the area (stream or beach) where they were born and use this information as a navigational tool. Salmon begin their lives in freshwater streams, where they stay from several months to as long as two years, depending upon the species. After they reach about an inch in length, the young fish swim downstream to the 83
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