Assessment variations ranging from 2 to 3 dB are normal, even with well-trained ultrasonic inspectors. With longer work assignments or adverse external influences (cold, heat, dust, noises, etc.) considerably higher variations (12 dB and more) are often observed due to lack of concentration and to tiredness [1].  [c.774]

The encircling probe was characterised with its mirror in water. As we did not own very tiny hydrophone, we used a reflector with hemispherical tip with a radius of curvature of 2 mm (see figure 3c). As a result, it was possible to monitor the beam at the tube entrance and to measure the position of the beam at the desired angle relatively to the angular 0° position. A few acoustic apertures were verified. They were selected on an homogeneous criteria a good one with less than 2 dB of relative sensitivity variations, medium one would be 4 dB and a bad one with more than 6 dB.  [c.823]

If, instead of a configuration like that treated above, one had a 52 configuration, the above analysis would yield F, and symmetries (because the two 5 orbitals m values could be combined as 2 + 2, 2 - 2, -2 + 2, and -2 -2) the wavefunctions would be identical to those given above with the 7ii orbitals replaced by 82 orbitals and 71.1 replaced by 5.2. Likewise, dp- gives rise to H, and symmetries.  [c.263]

When the relative pressure falls to P2/p°, corresponding to r = 80 A, the second group of pores will have given up a volume of adsorbate equal to dv 22-But since the film thickness has now diminished to t2, there will have been an additional loss from the walls of group 1 the total loss from group 1 is therefore so that the total loss from both groups is  [c.144]

In mercury porosimetry the volume ti(Hg) of mercury taken up by the solid is measured as the applied pressure P (i.e. p — p ) is gradually increased. The value u,(Hg) at any value of applied pressure Pi, therefore gives the volume of all pores having a radius equal to or greater than rf and is termed the cumulative pore volume. This designation is the converse of that in gas adsorption porosimetry (Section 3.6) where the cumulative pore volume ) is the volume of all those pores of radius equal to or less than rf. Thus in mercury porosimetry the cumulative pore volume c(Hg) decreases as r increases, whereas in gas adsorption X( T) course increases with increasing r . In both techniques, however, the pore size distribution curves are obtained by differentiation of the curves of cumulative volume against r , giving curves of dv /dr against r .  [c.178]

Equation (2.3) describes a straight line of zero intercept if is plotted versus the velocity gradient. Such a plot is shown in Fig. 2.2. Since the coefficient of viscosity is the slope of this line, this quantity has a single value for Newtonian liquids. Liquids of low molecular weight compounds and their solutions are generally Newtonian, but quite a few different variations from this behavior are also observed. We shall not attempt to catalog all of these variations, but shall only consider the other pattern of behavior shown in Fig. 2.2. This example of non-Newtonian behavior is described as pseudoplastic and is often observed when the material under study is a fluid polymer. Since Eq. (2.3) defines the coefficient of viscosity as the slope of a plot of versus velocity gradient, it is clear from Fig. 2.2 that pseudoplastic substances are not characterized by a single viscosity. The apparent viscosity at a particular velocity gradient is given by the ratio a5/(dv/dy). Inspection of Fig. 2.2 reveals that pseudoplastic materials appear less viscous at high rates of shear than at low rates.  [c.78]

In the light of the difficulties described above, it is not surprising that in many areas of technology viscosity is measured with rotating devices for which the geometry deviates some from precisely coaxial cylinders. Instruments with modified geometry are simpler to construct and therefore open to such conveniences as interchangeable spindles as well as variable speeds. Although they may lack the precise geometry which permits the absolute determination of viscosity from experimentally measurable parameters, they are sturdy and versatile and permit reproducible observations to be made. These observations may serve as the basis for comparison of relative viscosities of samples measured with the same apparatus, or they may be caUbrated with substances of known viscosity so that unknown viscosities may be evaluated. Figure 2.4 is an example of one such commercial apparatus. The instrument shown is the Brookfield digital viscometer, and-with up to eight different speeds and seven different spindles—can measure 56 different average ranges for dv/dr.  [c.83]

The catalysts under consideration both initiate the polymerization and regulate the polymer formed. There is general agreement that the mechanism by which these materials exert their regulatory role involves coordination of monomer with the transition metal atom, but proposed details beyond this are almost as numerous and specific as the catalysts themselves. We shall return to a description of two specific mechanisms below. The general picture postulates an interaction between monomer and catalyst such that a complex is formed between the rr electrons of the olefin and the d orbitals of the transition metal. Figure 7.12 shows that the overlap between the filled orbitals of the monomer can overlap with vacant d 2 2 orbitals of the metal. Alternatively, hybrid orbitals may be involved on the metal. There is a precedent for such bonding in simple model compounds. It is known, for example, that Pt complexes with ethylene by forming a dsp hybrid-rr sigma bond and a dp hybrid-TT pi bond. A crucial consideration in this coordination is maximizing the overlap of the orbitals involved. Titanium III ions seem ideally suited for this function higher effective nuclear charge on the metal results in less spatial extension of d orbitals and diminished overlap.  [c.491]

Attenuation. The exceptional transparency, or low attenuation, of siUca-based glass fibers has made them the predominant choice for optical transmission because of the low level of absorption and scattering of light as it traverses the material. Together these comprise optical attenuation, or loss, measured in dB where  [c.251]

Suitable pretreatment of wood before pulping alters this behavior of hemiceUulose significantly. Saponification of the acetyl groups of softwood before sulfite cooking results in glucomannan retention in the final product (163,164). Those treatments that limit the peeling reaction during alkaline pulping processes (reductions with NaBH, H2S, or oxidations with chlorite, polysulfide, anthraquinone, etc), can result in polysaccharide retention (165). The pretreatment of wood with mineral acid or Uberated acids of wood at elevated temperatures (ie, 170°C for 30 min) diminishes the DP of hemiceUulose components sufficiently that they wUl be consumed mostly during a subsequent alkaline cook (166). The resulting pulp behaves more like cotton ceUulose in many industrial appUcations.  [c.33]

Having dynamic insertion loss in dB.  [c.315]

Test Methods. There is no standard test method for measuring transmissibihty or isolation efficiency of vibration isolation devices. The most common procedure is to measure the vibration transmitted to the supporting stmcture with the isolators in place and with the equipment supported on rigid blocking. From these measurements the insertion loss in dB is deterrnined by the following where T is the transmitted vibration with isolators in place and is the transmitted vibration with rigid supports.  [c.319]

Test Methods. There are no national standards for the measurement of vibration damping. The most useful and convenient technique is to measure the reverberation time or decay rate of a panel or bar. The sample is vibrated by noise from a transducer, the noise is abmpfly terminated, and the decaying vibrations are measured using an accelerometer to determine the decay rate A. The loss factor Tj is computed hy rj = Aj/27.3/ where A is the decay rate, dB/s and is the natural frequency of the sample, Hz (5). One significant difficulty encountered in making these measurements is how to prevent excessive energy dissipation by the supporting system, the transducer, the accelerometer, and related cables. The sample may be suspended from long strings the transducer should not contact the panel the accelerometer should be as low in mass as possible and the cables should be thin and flexible.  [c.320]

Crosstalk. This is a measure of the signal induced in a quiet pair by an excited pair. The excited signal could be voice, digital data, ringing, or noise. Crosstalk is expressed as a decibel (dB) loss, so the smaller the number, the less the crosstalk. Crosstalk becomes important when transmitting digital signals at high speeds.  [c.326]

The thmst of laser communications changed dramatically around 1970 with the development of optical fibers having low loss of signal (see Fiber optics). Light can be guided along the length of a glass fiber of small diameter. Medical instmments using bundles of glass fibers were developed for viewing portions of the interior of the human body. However, because the fibers had a high signal loss, thein appHcations were limited. Light propagating along the length of the fiber suffered attenuation greater than 1000 dB/km. Therefore practical appHcations could employ fibers at most a few meters long.  [c.16]

Natural polymers have also received attention as graft sites for carboxyflc monomers to produce detergent polymers (DP), though without great success. The synthetic portion of the graft is not usually biodegradable, although ia some cases attempts were made to meet molecular weight limitations (less than DP of ca 6—8). Acryhc grafts onto polysaccharides ia the presence of alcohol chain-transfer agents (220) were not completely biodegradable, nor were the ones based on initiation with Ce" " (221) and mercaptan (222,223). Proteia substrates (224) are expected to be similar to the starch grafts the fundamental problem is the need to control acryhc acid polymerization to the oligomer range, as iadicated earher, ia order to have complete bio degradabihty.  [c.482]

Ultrasonic Properties. Vitreous sihca of high purity, such as the synthetic type, has an unusually low attenuation of high frequency ultrasonic waves. The loss, is a linear function of frequency, up to the 30—40 MHz region and can be expressed a.s A = Bf, where B = 0.26 dB-MHz/m for shear waves and 0.16 dB-MHz/m for compressional waves (168).  [c.506]

Fabrication. Fabrication of titanium iato useful parts, such as tanks, heat exchangers, and pressure vessels, is comparable to the fabrication of austenitic steel ia method, degree of difficulty, and cost. Commercial-grade titanium can be bent 105° without cracking around a radius of 2—2.5 times the sheet thickness. The bend radius for alloys is as high as five times the sheet thickness. A loss of 15—25 degrees ia the iacluded bend angles is normal because of sptingback at room temperature related to the low elastic modulus. Heat is required to form most titanium alloy parts. Super plastic forming (SPF) is used to form complex shapes ia a—P-type alloys such as Ti—6A1—4V. The forming is conducted at ca 900°C where the alloy becomes super plastic, ie, elongates without necking. The process is sometimes combiaed with diffusion bonding (SPF/DB) to form complex stmctures (41).  [c.106]

DP Speed Factor. Pumping-speed efficiency depends on trap, valve, and system design. For gases having velocities close to the molecular velocity of the DP top jet, system-area utilization factors of 0.24 are the maximum that can be anticipated eg, less than one quarter of the molecules entering the system can be pumped away where the entrance area is the same as the cross-sectional area above the top jet (see Fig. 4). The system speed factor can be quoted together with the rate of contamination from the pump set. Utilization factors of <0.1 for N2 are common.  [c.370]

Self-Diffusivity—High Pressure The criterion of high pressure is vague at best. For most permanent gases, such as the major constituents of air, it would mean F > 70 atm. For less volatile components, the criterion would be lower. At present, accurate prediction of mutual diffusion coefficients for dense gas mixtures is not possible. One major reason for this is the scarcity of data. Most high-pressure diffusion experiments have measured the self-diffusion coefficient. The general observation is that the product DP is near constant at low pressure, is not constant at high pressure, but rather decreases as pressure increases. In addition, although there are usually neghgible composition effects on diffusivity of gases at low pressures, the effects are not negligible at high pressures.  [c.595]

The corresponding acoustic velocity /(dp/dp, ), is normally much less than the acoustic velocity for gas flow. The mixture density is given in terms of the individual phase densities and the quality (mass flow fraction vapor) x by  [c.655]

Minimum baffle spacing is generally one-fifth of the shell diameter and not less than 50.8 mm (2 in). Maximum baffle spacing is hm-ited by the requirement to provide adequate support for the tubes. The maximum unsupported tube span in inches equals 74 dP (where d is the outside tube diameter in inches). The unsupported tube span is reduced by about 12 percent for aluminum, copper, and their alloys.  [c.1072]

Cumulative mass % less lhan Dp  [c.1415]

The power for agitation of two-phase mixtures in vessels such as these is given by the cuiwes in Fig. 15-23. At low levels of power input, the dispersed phase holdup in the vessel ((j)/ ) can be less than the value in the feed (( )df) it will approach the value in the feed as the agitation is increased. Treybal Mass Transfer Operations, 3d ed., McGraw-HiU, New York, 1980) gives the following correlations for estimation of the dispersed phase holdup based on power and physical properties for disc flat-blade turbines  [c.1468]

In Fig. 2 an additional comparison with Lakestani (1992) is performed. This is a more difficult case because the centre depth of the crack is only 8 mm. It is still the pulse echo response from the lower edge of a 10 mm vertical strip-like crack that is shown. The probe has the size 20 mm by 22 mm, is of SV type with angle 60 and has centre frequency 2.04 MHz and an assumed bandwidth of 2 MHz. The calibration is by a side-drilled hole of diameter 9.5 mm and eentre depth 13 ram (the depth of the diffracting edge). The effects of the far field approximation for the probe is illustrated in the figure by giving curves for one, four and ten element probes. A single element probe is clearly insufficient although the peak location is correct and the peak value is only 6 dB too high. The difference between four and ten elements is for practical purposes negligible (the near field length of each element is less then 5 mm for the four element probe so this is not surprising). The agreement between UTDefect and the experiment is satisfactory, having in mind that the depth to the edge is about half the probe side so that the exact pressure distribution beneath the probe could be important.  [c.159]

Broadbanded probes having a high penetration capability are especially suitable for testing plastics, composites, cast material, austenitic steel and other materials showing strong sound attenuation. Depending on the application, composite probes have between 3 and 20 dB higher sensitivity and a clearly shorter sound pulse than comparable probes equipped with a classic piezoceramic element. Due to their low acoustic impedance, composite elements are especially advantageous on all probes equipped with plastic delay lines, such as dual element (TR) or angle beam probes, and on immersion probes. The use of composite probes has a particularly positive impact on automatic testing machines because the high sensitivity combined with an excellent resolution is often required in this application. The design with composite elements becomes considerably simpler in the case of arrays and paintbrush probes because a low impedance backing is enough in these cases to generate high resolution signals. This reduces the weight of the probe and makes it less susceptible to system dependent thermal and mechanical shock load.  [c.711]

Knowledge of the depolarization ratios allows one to classify easily the Raman modes of a molecule into synnnetric and asyimnetric vibrations. If a molecule is undergoing a totally syimnetric vibration, the depolarization ratio, P (p ) will be less than 3/4 (6/7) and we say that the vibration is polarized (p). On the other hand, for asyimnetric vibrations, the depolarization ratio will have a value close to 3/4 (6/7) and we say these vibrations are depolarized (dp) [34]. It should be stated that these values for p are only valid when the scattered radiation is collected at right angles to the direction of the incident light. If different geometry is used, p and p are accordingly changed (see the appendix).  [c.1195]

We present results on the F + D2 reaetion. Study of the reaetion of the D2 isotopie reagent was easier beeause the baekgroimd in the mass speetrometer was smaller at mass 21 (DF) than for mass 20 (FIF). Moreover, the masses of the DF and D are less dissimilar, so that the DF produet is less kinematieally eonstrained in the range of aeeessible laboratory seadering angles. Figure B2.3.4 presents the laboratory angular distribution and a veloeity veetor diagram for the reaetion, showing the aeeessible angular ranges for the produet vibrational levels. From this plot, it already appears that the bulk of the DF produets is made in the v = 3 and 4 vibrational levels that are seadered baekward in the CM frame with respeet to the ineident F atom beam.  [c.2067]

Ab initio FIF programs for crystals have been developed [106. 107] and have been applied to a wide variety of bulk and surface systems [108. 109]. As an example, a periodic FIF calculation using pseudopotentials and an LCAO basis predicted binding energies, lattice parameters, bulk moduli and central-zone phonon frequencies of 17 III-V and IV-IV semiconductors. The authors find that ... [o]n the whole, the FIF LCAO data appear no worse than other ab initio results obtamed with DF-based Flamiltonians [110]. They suggest that the largest part of the errors with respect to experiment is due to correlation effects and to a lesser extent due to the imperfections of the pseudopotentials [110]. More recently, the electronic and magnetic properties of transition metal oxides and halides such as perovskites, which had been a problem earlier, have been investigated witli spin-uiuestricted FIF [111]. In general, the periodic FIF method is best suited for the study of highly ionic, large band gap crystals because such systems are the least sensitive to the lack of electron correlation.  [c.2219]

Attenuation of less tlian 0.2 dB km is common for telecom quality fibre.) Since modal dispersion can be greatly mitigated by fibre design, real material dispersion is of greatest consequence. Silica is a dispersive media. There is a wavelengtli dependence to tire index of refraction, as a result an optical pulse of finite bandwidtli, >X, spreads as it propagates along tire core axis. This spread limits tire spacing of successive pulses and hence tire maximum transmission frequency. Figure C2.15.16 shows a plot of tire dispersion for silica as a function of w avelengtli witliin tire transmission window. Because tire zero dispersion point is at approximately 1.31 pm, tliis wavelengtli has become one of tire base telecom transmission bands. The otlier key telecom transmission wavelength, 1.54 pm, is near tire loss minimum of tire fibre.  [c.2871]

The dynamic range (1) is limited by the focal plane electronics which is an array of integrated circuits. The small pixels force the designer of the IC chip to use aggressive design rules to leave enough room for reasonable charge storage. Even so, the small capacitors result in a dynamic range of less than 60 dB. If for example the sensitivity is only 5 mK the dynamic range becomes 5 K and objects greater than 5 K different in temperature appear black or white on the display. The dynamic range problem is further compHcated by variations in emissivity of the radiating surfaces. Since manufactured materials have a wide range in emissivity, boundaries of stmctured objects are usually clearly defined in thermal imagery. The user selects between higher gain (displayed sensitivity) and higher contrast (displayed dynamic range). However when the emissivity is uniform (eg, bodies of water, mral scenes) high sensitivity is desired and good stabiUtyis critical.  [c.291]

Spinel Ferrites. The number of appHcations of spinel ferrites is very large and growing. Table 5 gives a schematic impression of the main appHcation areas and functions (93). In radio, television, and measuring equipment ferrite cores are extensively applied as inductors in LC-fHters. In telecommunication ferrites serve the same purpose, but have clearly higher demands on quaHty factor and temperature-plus-time stabiHty of the inductor. High -values requite a ferrite core having low energy losses, tan 5/at small signals in the relevant frequency ranges, and the temperature factor Ocp = (Ap /AT)/p , derived from the slope of the p (T) curve, has to be within very narrow limits. Because the inductance T is proportional to p, this also determines the temperature dependence of T, which has to be such that it compensates for the temperature drift of the capacitor in the filter. The inductance of a coil in a circuit can be fine-tuned by bridging the gap between two ferrite core halves with an inserted ferrite adjuster. If a ferrite experiences some kind of magnetic, thermal, or mechanical disturbance, the initial permeabiHty is instantaneously increased to an unstable value as a result of a changed configuration of magnetic domain walls. From that point it returns to its original level by relatively slow diffusion processes, often associated with preferred distribution of Fe ions or cation vacancies in the spinel stmcture (94,95). Filter AppHcations requite high stabiHty, expressed by a small disaccomodation factor Dp = A(p logjg 2/describing the relative change of p during a time interval fter a disturbance. Table 6 presents some specifications  [c.195]

Dimensiona.1 Ana.Iysis. Dimensional analysis is a mathematical technique that proceeds from the general principle that physical laws must be independent of the units of measurement used to express them. If one quantity is related to a group of other quantities, the quantities comprising the group must be related in such a manner that the net units or dimensions of the group are the same as those of the dependent quantity. A dimensionless group can then be formed immediately by division. A useful tool, the Pi theorem, asserts that the number of dimensionless groups needed to describe a situation is equal to the total number of variables less the number of fundamental dimensions needed to express them. Fundamental dimensions are generally taken to be length, time, mass, temperature, and heat content. The Pi theorem is a powerful tool because it limits the amount of experimental work needed to estabUsh a general relationship. For example, consider the problem of determining the drag force on a smooth sphere around which a Newtonian fluid is flowing. The diameter of the sphere and the fluid viscosity, density, and velocity may vary. Each of the five variables can be expressed using various combinations of the three dimensions mass, length, and time (force = mass times length per the square of time). The Pi theorem leads immediately to the conclusion that only two dimensionless numbers are needed to describe the relationship. These may be taken to be a drag coefficient 2F / AppV and a Reynolds number DV pj p. An accurate set of measurements for one sphere in one fluid provides a universal relationship between these numbers that is appHcable to all spheres in all Newtonian fluids.  [c.106]

The principal application of ZrF has been in the manufacture of HMFGs of which the most widely investigated is the system composed of Zr, Ba, La, Al, and Na, also popularly known as the ZBLAN glasses. This system has revolutionized the optics industry because of the significantly superior quahties of these glasses over conventional siUca glasses. The theoretical transmission losses for fluoride glass fibers are calculated to be 0.001 dB /km at 3.2 )Tm and 0.005 dB /km at 3.5 )Tm (6) (see Fiber optics). Transmission loss rates have been observed as low as 0.65 dB /km (4). Fluoride glasses, unlike the sihca glasses, are expected to transmit light in the range of 2—4 micrometers or in the infrared range. ZBLAN fibers transmit light at a 5 to 10 times lower optical loss than that of siUca fibers, and can be used for long distance data transmission, for use in mid-ir and multispectral optical components, ir domes, laser windows, laser hosts, for medical applications such as surgery and cauterization, and for nuclear radiation resistant transmitting devices (6—16).  [c.262]

CompositionaHy, the typical single-mode fiber contains a core with a diameter of about 8 ]lni (less than six times the wavelength of the light that it carries) and a cladding of 125 fim 1 fim diameter. The core, which has a step refractive index profile, is an 8 wt % Ge02 + 92 wt% Si02 glass. The germania raises the refractive index to about 1.4585. The refractive index of the pure siUca cladding is about 1.4534. That difference in refractive index is sufficient to guide the laser light with minimum distortion. Besides faciUtating strength and handleabiUty, the thickness of the cladding is required for minimum attenuation. The outside of the cladding is coated with two types of polymer to protect the pristine glass surface, theoretically maintaining its strength at upward of 4.8 GPa (700,000 psi). Another popular single-mode product is dispersion-shifted fiber, with attenuations of 0.20 dB /km at 1550 nm combined with minimum dispersion. This is the highest capacity fiber type and is used for carrying longer wavelength laser light over longer distances without amplifications. Some multimode fibers have larger cores (eg, 62.5 -lm), paraboHc index profiles, and higher refractive indexes.  [c.313]

Beginning around 1970, fibers were produced having much lower signal loss. Optical fibers with losses as low as 0.2 dB/km are available. This made possible long-distance communication with optical fibers. Using a repeater station every few kilometers, light can be propagated for great distances in fiber-optic Hghtguides. System performance is not affected by atmospheric factors. Fibers with continuous lengths of many kilometers are produced, in continuous fiber-drawing processes. Semiconductor diode lasers are employed as the light source. The early systems used AlGaAs lasers operating near 0.85 p.m, because the fiber loss was first reduced to low values near that wavelength. As the fiber loss was reduced at wavelengths near 1.3 and 1.55 p.m, InGaAsP lasers operating at those wavelengths have become widely used. Most installed fiber-optic communications systems operate at 1.3 p.m, but future installations are likely to be dominated by 1.55-p.m operation.  [c.16]

The dB/d/is limited to 6 T/s out of concern that larger values could cause nerve stimulation. The r-f exposure is limited to a specific absorption rate (SAR) of 0.4 W/kg for the whole body, 0.32 W/kg averaged over the head, and less than 8.0 W/kg spatial peakia any one gram of tissue. These numbers are designed to limit the temperature rise to less than 1°C and localized temperature of no greater than 38°C head, 39°C tmnk, and 40°C ia the extremities.  [c.56]

The role, design, and maintenance of creepproof barriers in traps, especially those in oil DPs, remain to be fully explored. In general, uncracked oil from a DP is completely inhibited from creeping by a surface temperature of <223 K. On the other hand, a cold trap, to perform effectively in an ordinary vacuum system, must be <173 K because of the vapor pressure of water, and <78 K because of the vapor pressure of CO2. For ultracontroUed vacuum environments, LN temperature or lower is required. CO2 accumulation on the trap surface must be less than one monolayer. The effectiveness of a LN trap can be observed by the absence of pressure pips on an ionization gauge when LN is replenished in the reservoir.  [c.378]

See pages that mention the term LACI-D1 : [c.251]    [c.135]    [c.681]    [c.721]    [c.179]    [c.249]    [c.30]    [c.544]    [c.366]    [c.378]    [c.1471]    [c.1586]    [c.1610]   
Introduction to protein structure (1999) -- [ c.361 , c.362 , c.362 ]