Mach number methane

Laboratory sieves are made from woven wire of standard square apertures that foUow a geometric progression from one screen to the next. The sieve size is designated in micrometers or mesh number. The latter denotes the number of openings per linear inch. In the laboratory deterrnination of size distribution of a cmshed or ground product, standard sieves in the desired size range are stacked. Successively smaller apertures are arranged from top to bottom, the cmshed or ground material is placed on the coarsest sieve at the top, and the entire stack is shaken on vibratory equipment providing both vertical and circular motion to the particles. Material retained on each screen is then weighed, and the weight percent passing each screen is plotted against the sieve size. This is typically a log—log plot, but many other techniques have been developed (2). Wet screening is usually conducted before final dry sieving to remove very fine particles, which tend to adhere to coarse particles or to each other during dry sieving and lead to errors.  [c.398]

The helical-lobe compressor is further divided into a dry and a flooded form. The dry fonn uses timing gears to hold a prescribed timing to tlie relative motion of the rotors the flooded form uses a liquid media to keep the rotors from touching. The helical-lobe compressor is the most sophisticated and versatile of the rotary compressor group and operates at the highest rotor tip Mach number of any of the compressors in the rotary family. This compressor is usually referred to as the screw compressor or the SRM compressor.  [c.6]

In Fig. A.l, high-pressure steam is generated and fed to the high-pressure mains. The medium- and low-pressure mains are fed by expansion through steam turbines to generate power. Figure A.l shows three mains with typical mains pressures, but these vary in both number and pressure from site to site. Figure A. 1 also shows the possibility of using a condensing turbine, which is used when there is a desire to generate power but the exhaust steam from a backpressure turbine is not needed. Letdown stations are used to control the mains pressures. Because the letdown from high-pressure to lower-pressure mains creates steam with a large superheat, boiler feedwater is injected directly to reduce the superheat. As discussed in Example A.3.1, although steam for process heating is preferred saturated, if it is fed through the mains saturated, this leads to excessive condensation in the mains due to heat losses, which is undesirable. Hence steam is fed to the mains with some superheat. Another feature shown in Fig. A.l is that when water (blowdown or condensate) is reduced in pressure, flash steam is recovered. Although as much condensate as practicable and economical should be returned to the deaerator, levels of condensate return tend to be on the order of 50 percent but can be significantly higher.  [c.413]

Figure Bl.14.11. Amplitude-weighted images of (temporally) uncorrelated motions in a quail egg at an incubation period at about 140 h. A standard gradient echo sequence supplemented with strong bipolar gradient pulses for motion weighting was used. A high number of transients (N = 490) was acquired for each phase-encoding step to adequately average out temporal fluctuation of the motion. The intensity in the images shown corresponds to the signal ratio with and without motion weighting. Light grey shades hence represent no signal attenuation, darker shades strong signal attenuation due to uncorrelated motion. Pixels with signal below the noise level are set black as is the case in the egg yolk (black region in the middle of the egg) due to comparatively short T. The white double arrows indicate the probed velocity component. Both images show signal attenuation due to strong motion in the region above the egg yolk where the embryo presumably is located. Furthennore, the attenuation of the signal appears to be much stronger for the y-velocity component than for the v-component indicating strongly anisotropic motion. The white bar represents 2 mm. (From [32].) Figure Bl.14.11. Amplitude-weighted images of (temporally) uncorrelated motions in a quail egg at an incubation period at about 140 h. A standard gradient echo sequence supplemented with strong bipolar gradient pulses for motion weighting was used. A high number of transients (N = 490) was acquired for each phase-encoding step to adequately average out temporal fluctuation of the motion. The intensity in the images shown corresponds to the signal ratio with and without motion weighting. Light grey shades hence represent no signal attenuation, darker shades strong signal attenuation due to uncorrelated motion. Pixels with signal below the noise level are set black as is the case in the egg yolk (black region in the middle of the egg) due to comparatively short T. The white double arrows indicate the probed velocity component. Both images show signal attenuation due to strong motion in the region above the egg yolk where the embryo presumably is located. Furthennore, the attenuation of the signal appears to be much stronger for the y-velocity component than for the v-component indicating strongly anisotropic motion. The white bar represents 2 mm. (From [32].)
V), for producing a given final quantum state of the bath acceptor molecule, such as OO O, J, V, with a specific vibrational (OO O), rotational (J) and velocity (V) signature. In order to turn such a distribution into a P(E, E ) distribution, some method of identifying the initial state of the bath molecule must be found so that the energy change EE = E - E occurring during the collision can be detennined. (The conventional way to define AE gives it a negative sign for energy loss (E < E) from the donor.) The initial state of the bath molecule consists of a Boltzmann distribution of velocities and rotational state populations described by the cell temperature T. Thus, each final state of the bath molecule can arise from a number of different initial states leading to a distribution of AE values. Fortunately, for large A E, this spread is not too significant because the initial distribution for cell temperatures near T= 300 K is not large. In addition, by studying the final P 0(fi0,J, V) distributions as a function of cell temperature, the initial states of the bath that contribute significant population to a given scattered 00 0 J, V state can be narrowed still further [15,16]. Second, in the case of translational motion, the quantify of interest is the energy transferred in the centre-of-mass frame that takes into account the recoil of both the bath acceptor and the donor. Thus, the data obtained in the experiments that measures the laboratory frame recoil velocities of the bath molecules, as described here, must be transfonned into the centre-of-mass frame. The procedure for doing this is lengthy and has been described elsewhere [9,12]. Third, the results for collision-induced scattering into a large number of different final states of the bath molecule must be summed in order to obtain the complete distribution function P(E, E ). Finally, there is no way at present to take into account (no experimental measure of) the change in rotational energy of the donor molecule during the collision. For heavy donors, this is not expected to cause much error in the detennination of the distribution functions because angular-momentum constraints limit the maximum change in angular momentum during the collision [9, 20].  [c.3011]

While experiments by their very nature are carried out in a laboratory coordinate frame, theory commonly proceeds via the introduction of internal coordinates in terms of molecule fixed axes. Done properly, this means that the kinetic energy of the center-of-mass motion is first separated from the other degrees of freedom. The origin of the internal coordinates, of course, can be chosen in a number of ways. The center of mass of the nuclei is a convenient choice that does not introduce kinetic energy coupling terms between electronic and nuclear degrees of freedom. No matter what is the choice of origin of the internal system of coordinates the result is a set of modified kinetic energy operators with reduced particle masses and so-called mass polarization terms. The latter, which are sums of products of momenta of different particles, are as a rule small and usually neglected.  [c.220]

Hybrid Monte Carlo In standard MC only single particle moves are tried and accepted or rejected. Attempts to make many particle moves of the sys-tc in before applying the Metropolis acceptance criterion leads to such small acceptance probabilities that this method is not efficient. Moreover it requires the recalculation of the whole potential after each attempted move, a costly computation especially when the move is likely to be rejected. One efficient method for generating collective moves is the Hybrid Monte Carlo method invented by Duane and Kennedy. [12] In this method one starts with a configuration of the system and samples momenta of the particles from a Maxwell distribution. Molecular dynamics is used to move the whole system for a time At and, because this time may be sufficiently large as to cause a reasonable energy change due the lack of strict energy conservation, one then accepts or rejects the move using the Metropolis criterion based on exp(—/3i/) where H is the hamiltonian of the system. This step is repeated over and over. In HMC, bad MD is used to generate efficient MC. It is important that the integrator used for generating the solution to the equations of motion be reversible because only then will this method satisfy detailed balance and only then will the method generate the canonical distribution and the Boltzmann distribution. A number of authors have further elaborated the HMC method. [60, 61, 62, 63[  [c.313]

By looking more closely at how molecules move, we find that bonds between two atoms can vibrate, angles between three atoms can bend, and torsions between four atoms can twist. These types of elementary motions can be combined for groups of atoms, leading to the motion of substituents (e.g., the rotation of a methyl group) or even whole domains (e.g., in proteins). If we want to simulate how these motions occur, our protocol must allow the sampling of the fastest possible movement of an atom within the system under consideration. These are the vibrations of bonds involving a hydrogen atom (e.g., a C-H bond in a methyl group), taking between 10 and 100 fs. Therefore, the integration steps when the equations of motion are being solved numerically must be at least one order of magnitude smaller than the fastest motion, i.e., about 1 fs. Otherwise, one would run into problems concerning the numerical stability of the algorithms used. Considering the fact that the rotation around a single bond needs about 100 ps (of course, the number depends strongly on the rotational barrier modulated not only by the atoms involved, but also on the environment), the simulation of this elementary process needs about 10 integration steps. The time necessary for one step depends mainly on the size of the molecule, because the energy of the whole system has to be recalculated for the actual geometry. If one is interested in complex systems like proteins, the calculation of the energy for a specific geometry (a single point) may increase up to 1 s. Additionally, complex motions in proteins occur on a much larger time scale. The folding of some proteins from the denatured state to the active conformation may last about 1 s (or 10 integration steps). Taking these facts into account it is easy to understand that the simulation of such an event is not possible with the computer power and algorithms currently available.  [c.360]

The first section of this chapter discusses various ways that chemical properties are computed. Then a number of specific properties are addressed. The final section is on visualization, which is not so much a property as a way of gaining additional insight into the electronic structure and motion of molecules.  [c.107]

In practice the laser can operate only when n, in Equation (9.2), takes values such that the corresponding resonant frequency v lies within the line width of the transition between the two energy levels involved. If the active medium is a gas this line width may be the Doppler line width (see Section 2.3.2). Figure 9.3 shows a case where there are twelve axial modes within the Doppler profile. The number of modes in the actual laser beam depends on how much radiation is allowed to leak out of the cavity. In the example in Figure 9.3 the output level has been adjusted so that the so-called threshold condition allows six axial modes in the beam. The gain, or the degree of amplification, achieved in the laser is a measure of the intensity.  [c.342]

Once the culture is actively growing, the environment in the fermentor changes in part because of the depletion of medium components and in part because of the production of metaboHtes by the fermenting mass. In order to maximize productivity, a number of parameters must be maintained within close predeterrnined limits. The temperature is usually maintained at 0.5° C from the set point. Thermocouples (TC) or platinum resistance thermometer devices (RTD) are typically used to measure the temperature. The set point for the larger portion of the fermentation is often a few degrees lower than that used to grow the culture, and such changes or profiles are typically controlled by a computer or microprocessor based on time or some off-line measurement such as culture density, oxygen uptake rate, or carbon dioxide evolution rate. Experience has shown that in very large (250 m ) fermentors when the culture is actively growing, such fine control is not normally possible and transient temperatures of a few degrees above the set point can be attained because the fermentation broth produces heat at a greater rate than can be removed by the cooling process employed. Cooling is achieved by pumping chilled water through coils submerged inside the vessel or by the half-pipe design using external coHs. Cooling jackets are rarely employed on large-scale production fermentors.  [c.180]

The medium is the binder which provides for the adhesion of pigments. The most important types are the temper media (glue, egg, and gum), the oils, and wax. In addition, for wall painting there is the tme fresco technique, where the pigments are laid down in a fresh, wet plaster preparation layer. Several other media have been used, but much less frequendy, eg, casein temper. In modem paints, a number of synthetic resins are used for this purpose. Contemporary artist paints are often based on acryhc polymers (see Acrylic ester polymers Paints).  [c.420]

A more quantitative description can be obtained by dividing the field conceptually into three regions a turbulent core in which momentum, heat, and mass are readily transported radially by strong eddying motions a thin, nearly laminar, sublayer hugging the wall and a somewhat thicker transition or buffer layer bridging the two. Within the laminar sublayer, viscous stresses are important and the steady-state Navier-Stokes equations are valid. In the other regions they are inadequate. The fluctuating velocities in these regions can be described by the time-dependent Navier-Stokes equations, but the solution is enormously complex. It has been estimated that modem computers would require a time equal to the age of the universe to adequately describe turbulent pipe flow at a Reynolds number of 10. To avoid this complexity, the time-dependent equations can be averaged in the manner originally suggested by Reynolds. This yields equations that are similar to those for laminar flow, but which contain additional terms involving time-averaged  [c.89]

Turbulence Modeling. The time-dependent Navier-Stokes equations are generally considered adequate to represent turbulent flows. Direct numerical solution (DNS) of these equations is limited to low Reynolds numbers. At higher Reynolds numbers, the number of grid points required to resolve small eddies and the small time step size needed to obtain meaningful results make the computation of turbulent flows encountered in engineering practice by DNS outside the capabiUty of present computers. A less computationally intensive technique called large eddy simulation (LES) calculates the three-dimensional time-dependent details of the largest scales of motion using a simple subgrid scale model for the smaller eddies. However, the method is stiU very computationally intensive. Both DNS and LES are used primarily for studying the physics of turbulence, but LES has the potential of becoming an engineering tool in the near future.  [c.101]

The sputtering yield is proportional to the number of displaced atoms. In the linear cascade regime that is appUcable for medium mass ions (such as argon), the number of displaced atoms, E (E, is proportional to the energy deposited per unit depth as a result of nuclear energy loss. The sputtering yield Y for particles incident normal to the surface can be expressed as foUows (31).  [c.395]

An excellent tutorial on evaluating the costs and benefits of LIMS has been presented (11). The tutorial explains how to perform a cost—benefit analysis using a pragmatic approach to the economics involved. To assist in the analysis, a detailed Hst of specific LIMS costs and benefits from the tutorial is included here (see Tables 1—3) (12—14). The size of the system, based on the number of samples and analyses per year, can be used to approximate the cost. Table 4 summarizes the respective costs for small, medium, and large systems (15). Although the tutorial is a good starting point for accurately assessing the costs of a proposed system, the task of measuring the value of the benefits can be much more subjective in nature.  [c.518]

A mass spectrometer consists of four basic parts a sample inlet system, an ion source, a means of separating ions according to the mass-to-charge ratios, ie, a mass analyzer, and an ion detection system. AdditionaUy, modem instmments are usuaUy suppUed with a data system for instmment control, data acquisition, and data processing. Only a limited number of combinations of these four parts are compatible and thus available commercially (Table 1).  [c.539]

Natural mbber as obtained from Hevea brasiliensis is i7j -l,4-polyisoprene with small amounts of nonmbber produced by the tree. Although the double-bond stmcture is useful for chemical modification purposes, it does not benefit natural mbber s heat resistance. Natural mbber is relatively unstable compared to the more modem almost fully saturated elastomers, such as EPDM mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). In terms of physical properties, the strain crystallizing nature of natural mbber gives it high tensile and tear strengths, and it exhibits both low heat buildup and low rolling resistance. These latter two features make it especially attractive for tire manufacture. However, unless modified, it shows extensive swelling in oils, is relatively permeable to gases, and is not generally suitable for damping appHcations. In the majority of appHcations, natural mbber is used in blends and, until fairly recentiy (31), remarkably Httie was known about the distribution of cross-links in such blends. Modem techniques have been adapted to look into this subject, with a consequent improvement in properties brought about by achieving a better balance of cross-links in the blend. In latex appHcations, a large proportion of the industry has moved out to the Ear East, for example to Malaysia, if only because it is logical to ship the final product to the end user country rather than the latex, which contains 40% water. In general terms, the proportion of natural mbber in the total mbber market is slowly increasing (ca 1996), partly because it is technically necessary in tires for radial sidewalls, low rolling resistance, and low temperature behavior, and partly because the mbber industry is moving to the Ear East, where the bulk of natural mbber is grown and is more easily available.  [c.269]

Perforate Basket Centrifuges. The simplest and most common form of centrifugal filter is a perforate-waH basket centrifuge, consisting of a cylindrical bowl having a diameter ranging from about 100—2400 mm and a diameter-to-height ratio ranging from 1—3. The wall is perforated with a large number of holes, more than adequate for the drainage of most Hquid loads, and is lined with a filter medium. In the simplest case, the medium is a single layer of fabric or metal cloth or screen. In high speed basket centrifuges, one or more backup screens of relatively large mesh support a finer mesh filter surface. The method of discharging accumulated soHds distinguishes three types of basket centrifuge those that are stopped for discharge, those that are decelerated to a very low speed for discharge, and those that discharge at full speed (34).  [c.413]

The median particle diameter is the diameter which divides half of the measured quantity (mass, surface area, number), or divides the area under a frequency curve ia half The median for any distribution takes a different value depending on the measured quantity. The median, a useful measure of central tendency, can be easily estimated, especially when the data are presented ia cumulative form. In this case the median is the diameter corresponding to the fiftieth percentile of the distribution.  [c.127]

The North American P-51 Mustang, designed at the outset of World War II, was the first production aircraft to employ a laminar flow airfoil. Flowever, laminar flow is a sensitive phenomenon it readily gets unstable and tries to change to turbulent flow. For example, the slightest roughness of the airfoil surface caused by such real-life effects as protruding rivets, imperfections in machining, and bug spots can cause a premature transition to turbulent flow in advance of the design condition. Therefore, most laminar flow airfoils used on production aircraft do not yield the extensive regions of laminar flow that are obtained in controlled laboratory tests using airfoil models with highly polished, smooth surfaces. From this point of view, the early laminar flow airfoils were not successful. However, they were successful from an entirely different point of view namely, they were found to have excellent high-speed properties, postponing to a higher flight Mach number the large drag rise due to shock waves and flow separation encountered near Mach 1. As a result, the early laminar flow airfoils were extensively used on jet-propelled airplanes during the 1950s and 1960s and are still employed today on some modem high-speed aircraft.  [c.10]

The general question of the spectral manifestations of classical chaos and of non-classical processes, and their interplay in complex quantum systems, is a profound subject worthy of great current and fliture interest. Molecular spectra can provide an immensely important laboratory for the exploration of these questions. Molecules provide all the necessary elements a mixture of regular and chaotic classical motion, with ample complexity for the salient phenomena to make their presence known and yet sufficient simplicity and control in the number of degrees of freedom to yield intelligible answers. In particular, tlie fantastic simplification afforded by the polyad constants, together with their gradual breakdown, may well make the spectroscopic study of internal molecular motions an ideal arena for a fiindamental investigation of the quantum-classical correspondence.  [c.76]

At this point it is important to make some clarifying remarks (1) clearly one caimot regard dr in the above expression, strictly, as a mathematical differential. It caimot be infinitesimally small, since dr much be large enough to contain some particles of the gas. We suppose instead that dr is large enough to contain some particles of the gas but small compared with any important physical lengtii in the problem under consideration, such as a mean free path, or the length scale over which a physical quantity, such as a temperature, might vary. (2) The distribution fiinction / (r,v,t) typically does not describe the exact state of the gas in the sense that it tells us exactly how many particles are in the designated regions at the given time t. To obtain and use such an exact distribution fiinction one would need to follow the motion of the individual particles in the gas, that is, solve the mechanical equations for the system, and then do the proper countmg. Since this is clearly impossible for even a small number of particles in the container, we have to suppose that / is an ensemble average of the microscopic distribution fiinctions for a very large number of identically prepared systems. This, of course, implies that kinetic theory is a branch of the more general area of statistical mechanics. As a result of these two remarks, we should regard any distribution fiinction we use as an ensemble average rather than an exact expression for our particular system, and we should be carefiil when examining the variation of the distribution with space and time, to make sure that we are not too concerned with variations on spatial scales that are of the order or less than the size of a molecule, or on time scales that are of the order of the duration of a collision of a particle with a wall or of two or more particles with each other.  [c.666]

When a system is not in equilibrium, the mathematical description of fluctuations about some time-dependent ensemble average can become much more complicated than in the equilibrium case. However, starting with the pioneering work of Einstein on Brownian motion in 1905, considerable progress has been made in understanding time-dependent fluctuation phenomena in fluids. Modem treatments of this topic may be found in the texts by Keizer [21] and by van Kampen [22]. Nevertheless, the non-equilibrium theory is not yet at the same level of rigour or development as the equilibrium theory. Here we will discuss the theory of Brownian motion since it illustrates a number of important issues that appear in more general theories.  [c.687]

The basic system described above can be easily modified to study many processes. Figure A3.5.7 shows an example of a modem ion-molecule flow tube [93] with a number of interesting features. First, ions are created external to the flow tube. Any suitable ion source can be used, including high- and low-pressure electron-impact ion sources, a supersonic-expansion source (shown) or a flow-tube source. Once created the ions are injected mto a quadmpole mass spectrometer and only ions with the proper mass are injected into the flow tube through a Venturi mlet. Under favourable circumstances, only one ion species enters the flow tube. This configuration is called the selected-ion flow tube (SIFT) [89, 99 and 91]- Alternatively, ions can be created in the carrier-gas flow by a filament or discharge. Neutral reagents are added tluough a variety of inlets.  [c.809]

Scherer et al [205. 206] showed how to prepare, using interferometric methods, pairs of laser pulses with known relative phasing. These pulses were employed in experiments on vapour phase I2, in which wavepacket motion was detected in tenns of fluorescence emission. A more general approach, which can be used in principle to generate pulse sequences of any type, is to transfomi a single input pulse into a shaped output profile, with the intensity and phase of the output under control tln-oughout. The idea being exploited by a number of investigators, notably Warren and Nelson, is to use a programmable dispersive delay line constructed from a pair of diffraction gratings spaced by an active device that is used either to absorb or phase shift selectively the frequency-dispersed wavefront. The approach favoured by Warren and co-workers exploits a Bragg cell driven by a radio-frequency signal obtained from a frequency synthesizer and a computer-controlled arbitrary wavefomi generator [207]. Nelson and co-workers use a computer-controlled liquid-crystal pixel array as a mask [208]. In the fiiture, it is likely that one or both of these approaches will allow execution of currently impossible nonlinear spectroscopies with highly selective infomiation content. One can take inspiration from the complex pulse sequences used in modem multiple-dimension NMR spectroscopy to suppress unwanted interfering resonances and to enliance selectively the resonances from targeted nuclei.  [c.1990]

As these methods are explored, it is quickly realized that the numerical effort in the theoretical description grows prohibitively large with the number of atoms in a molecule. The difficulty lies in precisely what makes molecular motion fiindamentally qiiasi-classical, i.e. the large molecular masses (relative to the mass of the electron). Consequently, a molecular wavefiinction has many oscillations and is difficult to model numerically. There have been many attempts at developing alternate approaches for representing quantum wavefiinctions and observables without the use of large grids or basis sets, ranging from approximations to patli-mtegral descriptions. The basics of these approaches are described in Sections B3.4.8. Later, Sections B3.4.9. describes the issues involved in the study of non-adiabatic phenomena.  [c.2291]

The modem era of biochemistry and molecular biology has been shaped not least by the isolation and characterization of individual molecules. Recently, however, more and more polyfunctional macromolecular complexes are being discovered, including nonrandomly codistributed membrane-bound proteins [41], These are made up of several individual proteins, which can assemble spontaneously, possibly in the presence of a lipid membrane or an element of the cytoskeleton [42] which are themselves supramolecular complexes. Some of these complexes, e.g. snail haemocyanin [4o], are merely assembled from a very large number of identical subunits vimses are much larger and more elaborate and we are still some way from understanding the processes controlling the assembly of the wonderfully intricate and beautiful stmctures responsible for the iridescent colours of butterflies and moths [44].  [c.2822]

Given tire weak coupling, we still have incoherent energy transfer, but now tire photon tliat conveys tire energy has to be conceptualized as a virtual quantity—its involvement can only be inferred, and tire energy transfer is for all practical purjDoses radiationless. This kind of energy transfer was first investigated by Forster in 1948 [1], and addressed with a perturbation tlieory based on dipole-dipole interaction between tire excited donor and unexcited acceptor. Later tire tlieory was rectified in a number of works [2, 3] and became tire proven worklrorse for much of tire modem research on energy transfer in condensed matter [4, 5].  [c.3018]

A number of independent tiajectories, with up to 10 spawns each, were run to study the dynamics after excitation, with the initial conditions taken from the Wigner distribution. The results shows that initial motion is along the torsional motion to form the Dm twisted conformation. After a slight lag of 50-250 fs, this structm e starts to distort by pyramidalization of one of the ethylene groups. Crucially for the system dynamics, this leads to a conical intersection between Si and So- At this point, the system relaxes to the ground-state, but with an efficiency much less than 100% per pass of the intersection region. Interestingly, the character of the wave function at this point indicates that in fact the molecule is in the Z state, which in the distorted structure lies lower than the V. A study of the ethylene PES using more sophisticated quantum chemical methods [248] supports the observations from the dynamics that the relaxation mechanism for this system is not from the twisted structure as conventionally thought.  [c.309]

The splitting of the quantum propagator negatively effects the efficiency of the scheme especially if m/M is small, i.e., if the quantum oscillation are much faster than the classical motion and the number n of substeps is becoming inefficiently large.  [c.402]

Ra.tlo Sc Ig-. The ratio scale has name, order, distance, and a meaningful origin. A zero value on the scale means the absence of any of the property, eg, zero Kelvin means the absence of motion and gives meaning to the gas law, PV = nRT, whereas zero Celsius is arbitrary and meaningless in terms of the gas law. The mathematical form of Stevens law has been used to argue that a ratio scale could be developed to measure flavor intensity (14). The magnitude estimation method yields a ratio scale when the data foHow certain rules. In this method a paneHst is instmcted to associate the flavor intensity of a second flavor with a number, Y, that is perceived to be a multiple of the flavor intensity, X, of the first sample. If the ratio of X to Y is always the same no matter what the value of X given for the first sample, then the paneHst is estimating the flavor intensity on a ratio scale. However, if the difference between X and Y is constant for different values for X the flavor is being estimated on an interval scale. Zero on a ratio scale means the absence of the perception being measured and this is a controversial conclusion for some psychologists (25). Nevertheless, magnitude estimation is frequently used and often defended as an appropriate scaling method for sensory data (24). There has been considerable discussion (26—29) of the many psychological scales used to quantitate sensory perceptions, motivated by the desire to devise analytical methods that are consistent with the demands of Weber s and Stevens laws and appropriate for the use of parametric statistical methods. Although the method of magnitude estimation has some theoretical appeal, data produced with nine-point interval and graphical line marking scales are much easier to obtain and are statisticaHy similar. An important consideration is that interval data should be used in models without a fixed intercept or defined origin whereas ratio scaled data requires the inclusion of a zero intercept in most models (29).  [c.2]

Glasses are metastable and, under the appropriate conditions, revert to a thermodynamically more stable state. Glasses particularly susceptible to uncontrolled crystal growth or phase separation have traditionally created problems for their manufacturer. However, glass is also a good medium for controlled crystalli2a tion (50), and has become the basis for a number of unique crystalline materials known as glass-ceramics (qv). The separation of a single glass iato multiple glassy phases can make the article cloudy and adversely affect its chemical durabiUty. Controlled phase separation, however, can produce opaque, white opal glass or, after a leaching step, lead to new materials such as porous glass or 96% siUca glass. The colloidal suspension of multiple phases ia transparent glass produces precise colors for products such as optical filters (qv). Furthermore, photosensitive and photochromic glasses change their optical transmission and color, sometimes reversibly, upon stimulus by a combination of light and heat treatment (see Chromogenic MATERIALS, photochromic). ah these transformations generally depend on the phenomena of diffusion, nucleation, and growth.  [c.289]

Ca.ta.lysis, The use of rare earths is mentioned in a number of catalytic reactions (18), but only two areas are considered as industrial apphcations. One is the stabilization of the zeoHtes used as catalysts in petroleum (qv) cracking appHcations, where rare earths (added as chlorides) allow the catalyst to keep a strong acidity, even in the harsh medium in which it is involved (see Molecularsieves). Acidity is in fact essential for industrially exploitable conversion of high weight molecules into useflil lighter species (19). The second usage is in automotive post-combustion, where cerium oxide is a component of the three-way catalysts planned for usage in all cars before the year 2000. These catalytic systems lower the level of pollutant emissions from cars through selective reduction of nitrogen oxides (NO ) into nitrogen and water, and simultaneous oxidation of unbumt carbon monoxide and hydrocarbons into carbon dioxide and water vapor. Owing to redox properties, Ce02 acts as an oxygen reservoir to ensure the buffering effect necessary to control the composition of the exhaust gas, particularly to allow the oxidation of CO and hydrocarbons when the medium is globally reducing. Catalysts are made of precious metal (100—3000 ppm Pd, Rh, or Pt) dispersed on alumina to which 20 wt % of cerium oxide is added. Besides being a buffering agent, and owing to its high thermal stabiHty at the elevated (>800 °C) temperatures in the catalytic muffler, cerium oxide allows alumina to keep a strong surface stabiHty at these temperatures in the catalytic muffler, and gives the metallic particles a good dispersion, avoiding sintering which would make them inactive (20,21). Special grades of cerium oxides, with thermally stable high surface area are developed for this appHcation (see Exhaust control, automotive).  [c.547]

Although IL-1 protects a number of normal tissues against radiation injury, its effects on BM are the best characterized. IL-1 provides varying degrees of protection, depending on the timing - 20 h prior to irradiation is optimal (164). Synergy has been found with other cytokines, most notably TNF- a, IL-6, and SCF. Multiple daily injections of IL-1 a preceding irradiation are more effective than single doses in promoting both BM progenitor cell survival and granulocyte recovery (165). Protection may involve a number of mechanisms. One is the stimulation of BM progenitor cells such that more of these are in the radioresistant S-phase of the cell cycle (151). Another is the induction by IL-1 of a number of radioprotective substances such as prostaglandins (PGs), metaHothionein, scavenging acute-phase proteins, GSH, and SOD, as well as other hemopoietic growth factors (151). The protective effects of preirradiation IL-1 in murine BM cells and human cell lines correlate closely with the induction of MnSOD (126), and growth factors induced from accessory cells that constitute the hemopoietic microenvironment can enhance repopulation of the immune and hemopoietic systems after irradiation. Possible effects of IL-1 on radiation-induced apoptosis in tissues have yet to be reported, but cytokines can clearly affect the tendency of cells to undergo this form of death. The abiUty of IL-1 to accelerate the reconstitution of murine BM following lethal doses of radiation, which may be through stimulating production of CSFs, can also impact survival. Although IL-1 can protect mice from acute lethaUty and from CFU-GM damage caused by TBI, it has no significant effect on immediate CFU-GM survival or on the level of radiation-induced DNA strand breaks in BM cells (166).  [c.494]

See pages that mention the term Mach number methane : [c.33]    [c.62]    [c.80]    [c.595]    [c.1063]    [c.2174]    [c.2977]    [c.400]    [c.371]    [c.384]    [c.643]    [c.125]    [c.289]    [c.408]    [c.491]   
Pressure safety design practices for refinery and chemical operations (1998) -- [ c.104 , c.295 ]