RSS saddle points


Steel, paint (matte surface) 0.90-0.95  [c.113]

However, the most widespread use of weathering steels in the U.K., and elsewhere, has been for buildings and bridges, especially where maintenance painting is particularly difficult, dangerous, inconvenient or expensive. Bridges over land, rivers, railways, roads and estuaries fall into this category, although in the last two cases care should be taken with respect to airborne salinity. Road bridges can be affected by salt-laden atmospheres or water, produced as a consequence of winter ice and snow clearing with deicing salt and grit. The chloride can be in the form of an airborne spray thrown up by passing vehicles or as a result of leaks in the bridge deck. In the presence of salt-water many materials, including steel, paint, reinforced concrete, aluminium, etc., deteriorate at an accelerated rate. Weathering steels are no exception, and higher than normal corrosion rates should be expected if they are exposed to saline waters or frequent spraying with salt. The important criterion is design. Many bridges have been built successfully from weathering steels but at the design stage it is important to consider the possible effects of road salt in order to obtain the maximum maintenance-free life.  [c.516]

Consider the molecule below. From an atomic point of view, an atom common to two structures, aromatic and naphthenic, or aromatic and paraffinic or still further naphthenic and paraffinic will be considered first of ill aromatic, then naphthenic, then paraffinic 2  [c.40]

In order to adapt an engine to a given fuel of a given octane number, the automobile manufacturer must consider the design and control parameters in order to prevent knocking in all possible operating conditions the variables at hand are essentially the compression ratio and ignition advance which in turn determine the motor performance (thermal efficiency and specific horsepower). Horsepower can always be maintained by technological devices such as cylinder displacement and transmission ratios but the thermal efficiency always remains closely tied to the octane number. This is illustrated by the following example a 6-point increase in octane number (RON or MON) —corresponding to an average difference between a premium gasoline and a regular gasoline— enables a one-point gain in compression ratio (from 9 to 10, for example), which results in an efficiency improvement of 6%. An average 1% efficiency gain per point of octane number increase is thereby obtained. This approach has led to the concept of Car Efficiency Parameter (CEP). For an engine with a compression ratio exactly adapted to the fuel used, the CEP represents the weight per cent change in consumption resulting from a one-point change in octane number. In the preceding example, the CEP equals 1. That is the value most often used in economic evaluation of the technology. Now if the manufacturer changes the system acting on not the compression ratio but the ignition advance, the preceding tendency still applies but with a lower CEP, between 0.5 and 1. As a  [c.198]

The smoke point corresponds to the maximum possible flame height (without smoke formation) from a standardized lamp (NF M 07-028). The values commonly obtained are between 10 and 40 mm and the specifications for TRO fix a minimum threshold of 25 mm. The smoke point is directly linked to the chemical structure of the fuel it is high, therefore satisfactory, for the linear paraffins, lower for branched paraffins and much lower still for naphthenes and aromatics.  [c.227]

The pour point is the lowest temperature at which an oil can still pour while it is cooled, without agitation, under standardized conditions. The pour point of paraffinic bases is linked to the crystallization of n-paraffins. The pour point of naphthenic bases is related to a significant viscosity increase at low temperatures. This property can be improved by additives.  [c.283]

The softening point is the temperature at which a bitumen becomes soft under standard conditions. The measurement uses the ring and ball method which is standardized in France (NF T 66-008) and in the USA (ASTM D 36). A steel ball of precisely defined dimensions and weight is placed on the bitumen sample that is surrounded by a metal ring also precisely defined. The assembly is heated gradually. When the bitumen sample becomes soft enough for the ball to pass through and travel a vertical distance of 2,5 cm, the corresponding temperature is called the softening point. This measurement is also related to the viscosity.  [c.289]

The aromatic extracts have been used in the paint industry to partially replace linseed oil. They are still used for producing printer s ink. In addition, they are finding a variety of applications as plasticizers in the rubber industry or for the manufacture of plastics such as PVC.  [c.291]

Although lubricant base stocks have been subjected to dewaxing processes, they still contain large amounts of paraffins that result in a high pour point for the oil. In the paragraph on the cold behavior of diesel fuels, additives were mentioned that modify the paraffin crystalline system and oppose the precipitation of solids.  [c.357]

The economic lifetime of a project normally terminates once its net cash flow turns permanently negative, at which moment the field is decommissioned. Since towards the end of field life the capital spending and asset depreciation are generally negligible, economic decommissioning can be defined as the point at which gross income no longer covers operating costs (and royalties). It is of course still technically possible to continue producing the field, but at a financial loss.  [c.7]

The gas processing options described in the previous section were designed primarily to meet on-site usage or evacuation specifications. Before delivery to the customer further processing would normally be carried out at dedicated gas processing plants, which may receive gas from many different gas and oil fields. Gas piped to such plants is normally treated to prevent liquid drop out under pipeline conditions (dew point control) but may still contain considerable volumes of natural gas liquids (NGL) and also contaminants.  [c.253]

Sealed metal-ceramic X-ray tubes are in use since the sixties. Whereas glass tubes still are the most common known form of X-ray tubes in the public, and are certainly the most used technology firom point of view of sold tubes per year, metal-ceramic X-ray tubes in lots of applications are state-of-the-art.  [c.532]

Surface SH Waves are considered to be great advantage" to detect surface and near subsurface defects. Architectural Institute of Japan specified the detection with surface SH Waves in Steel Structures. This method has been applied for detection of incomplete penetration at root of single bevel groove welded T-Joints with backing strip since 1996. Surface SH Waves vibrate in parallel with the test surface, therefore no mode conversion occurs and the echoes on CRT are simple and easy for evaluation. Couplants for SH Waves have recently been improved, and Surface SH Waves are available for much wider application in flaw detection. This paper describes the echo directivity of surface SH Wave probes and SH Wave angle probes. The echo directivity was evaluated, using side drilled holes of various depths. The echo height of side drilled holes was measured at a constant beam path length . The calculation for the echo height was based on a point sound source assumption on the test surface in different phases. The experimental results showed consistency with the calculation. The echo directivity was influenced by frequency, angle of refraction, and height of the transducer.  [c.902]

The most eomprehensive object from the diagnostic point of view still remains the human being with the variety of diagnostic parameters of his different organs, ills and ete.  [c.914]

Planar defects, espeeially if interpreted as craeks, are deemed non-aeeeptable in many codes. Although this may be understandable from a fracture mechanics point of view, this is not the only reason. The presence of planar defects goes beyond the aspect of checking the welder they might influence weld integrity. In addition, it is also the fact that conventional NDT methods had (and still have) their limitations that urged code makers to reject planar defects in general. Their detection indicates that something is very wrong with the weld, without being able to quantify the severity of the defect(s).  [c.947]

High frequency radar on the other hand is not affected by the amount of steel reinforcing at the measuring point. The transmission time for the reflected radar signal is registered and converted to distance using reflectors at known distances, or by knowing the wave speed for the given concrete.  [c.999]

The preceding discussion on site energy distributions has made the implicit assumption that each kind of site occurred in patches at least large enough that boundary effects could be neglected. In effect, each patch is treated as a small adsorption system within which lateral interaction between adsorbate molecules would occur. At the other extreme, sites of varying energy are randomly distributed on the surface, and only as lower energy sites b ame occupied would there be a developing probability of adjacent sites being occupied. A complete description of surface heterogeneity would have to include the distribution of site energies adjacent to a site of given energy. At this point there are probably too many variables to be extracted from adsorption data alone, although the comparison of isotherms for adsorbates of varying size may help (e.g., nitrogen versus butane—see Ref. 162). A formal statistical mechanical approach to the problem was made by Steel [166].  [c.660]

Stell G, Wu K C and Larsen B 1976 Critical point in a fluid of charged hard spheres Phys. Rev. Lett. 211 369  [c.555]

The integral under the heat capacity curve is an energy (or enthalpy as the case may be) and is more or less independent of the details of the model. The quasi-chemical treatment improved the heat capacity curve, making it sharper and narrower than the mean-field result, but it still remained finite at the critical point. Further improvements were made by Bethe with a second approximation, and by Kirkwood (1938). Figure A2.5.21 compares the various theoretical calculations [6]. These modifications lead to somewhat lower values of the critical temperature, which could be related to a flattening of the coexistence curve. Moreover, and perhaps more important, they show that a short-range order persists to higher temperatures, as it must because of the preference for unlike pairs the excess heat capacity shows a discontinuity, but it does not drop to zero as mean-field theories predict. Unfortunately these improvements are still analytic and in the vicinity of the critical point still yield a parabolic coexistence curve and a finite heat capacity just as the mean-field treatments do.  [c.636]

There are several different possible goals in controlling molecular dynamics. One goal can be the localization of excitations to a specific bond in a molecule, and the molecule could be broken along that bond [188]. Alternatively, one can try to transfer the molecule completely to an excited electronic state [186]. Another is the control of aligmnent (so that a molecule would pomt in a certain direction) [189. 190]. Still another goal would be the control of branching ratios for example, in a reaction of an atom with a diatom, A + BC, one may want to control the branching into  [c.2321]

Metal clusters are bonded by strong covalent or metallic bonds. Clusters of the low melting point metallic elements are produced using the thennal evaporation teclmique. With the laser vaporization teclmique, metal clusters from all the metallic elements in the periodic table can be made. Simple metal clusters include those main group elements whose cluster properties are dominated by the delocalized nature of their valence electrons. In contrast to the simple metal clusters, transition-metal clusters are extremely complicated. Because of the unfilled d orbitals, transition-metal clusters possess a high density of electronic states. Transition-metal clusters possess both metallic and covalent bonding characters and exhibit interesting chemical, magnetic and electronic properties. Studies of transition-metal clusters are directly relevant to heterogeneous catalysis, surface science, metal cluster chemistry and metal-metal bonding in inorganic chemistry [33]. Although accurate theoretical descriptions of transition-metal clusters still pose a tremendous challenge, improved experimental and theoretical teclmiques are expected to make significant progress in the investigation of transition-metal clusters.  [c.2391]

The simplest design of a spike electrode is represented by the Shepard rod in Fig. 3-18a, which uses the right-hand electrode simply as an auxiliary ground, and measures with the left electrode the grounding resistance of the insulated stainless steel tip, which is proportional to the soil resistivity. The Columbia rod (Fig. 3-18b) uses the shaft of the rod as a counter electrode. Since the rod usually moves sideways as it is driven down, this method can easily give values that are too high. Both methods presuppose that the steel point is always in good contact with the soil if this is not the case, too high values are obtained. To eliminate measuring errors at the electrode point, current and voltage electrodes are separated from each other on the Wenner rod as in Fig. 3-18c. Instead of Eq. (3-44), the following equation is valid for the Wenner rod because the current spreads out in all directions  [c.117]

In Chapter 5, this characteristic was applied to centrifugal compressors. The airplane wing analogy of stall was used, which is very directly applicable to the axial s airfoil-shaped blades. The incidence angle, described earlier, defines the onset of surge by stating that when the incidence exceeds the stall point, as developed from the cascade data, the foil ceases to produce a forward motion to the gas. When the gas cannot move forward, it moves in reverse, opposing the incoming flow. When the two collide, there is a noise, sometimes very loud. Recompression of the gas causes the temperamre to rise very high very quickly. There have been cases where, when the blades were sufficiently strong not to break from the unsteady forces, they melted. It is more normal with prolonged surge to experience catastrophic blade breakage. The axial can also exhibit a phenomenon referred to as rotating stall. Rotating stall (propagating stall) is generally encountered when the axial compressor is started or operated too near the surge limit. This is especially true for compressor with adjustable vanes with the vanes in their extreme open or closed position. Vane movement is limited in some cases to minimize this problem. A flow perturbation causes one blade to reach a stalled condition before tbe other blades. This stalled blade does not produce a sufficient pressure rise to maintain the flow around it, and an effective ilow blockage or a zone of reduced flow develops. This retarded flow diverts the flow around it so that the angle of attack increases or decreases on adjacent blades. These blades, with the increased angle of attack, stall and stay in a cell-like form. The cell then propagates around the stage or possibly two in which it occurs and at some fraction (40-75%) of rotor speed. Once begun, the cells continue to generate, causing inefficient perfonnance, and if not terminated, may continue until a blade failure occur - This is especially true if the cell s rotating speed coincides with  [c.237]

The penetration of unleaded fuels will continue rapidly in Europe in the coming years. Figure 5.8 portrays a scenario predicting the complete disappearance of leaded motor fuels by 2000-2005. Regular gasolines will also be eliminated very soon. The remaining uncertainty for unleaded fuels is the distribution between Eurosuper and Superplus. From a strictly regulatory point of view, the predictions lean towards a predominance of Eurosuper, defined by the European Directive of 20 March 1985, still in force. Nevertheless, the automobile manufacturers desire to have available, abundantly if possible, a motor fuel of high quality so that they can more easily reach their objective of reducing fuel consumption in the early years following 2000.  [c.210]

Although gas may have been partially dried and dew point controlled (for hydrocarbons and water) prior to evacuation from the site of production, some heavier hydrocarbons, water and other non-hydrocarbon components can still be present. Gas arriving at the gas plant may pass through a slug catcher , a device which removes any slugs of liquid which have condensed and accumulated in the pipeline during the journey. Following this, gas is dehydrated, processed to remove contaminants and passed through a demethaniser to isolate most of the methane component (for sales gas). Specifications for sales gas may accommodate small amounts of impurities such as CO2 (up to 3%), but gas feed for either LPG or LNG plants must be free of practically all water and contaminants.  [c.254]

For the substantiation of such possibility, destructive tests of the most applicable struetural steel speeimens were made in the civil engineering. In one case - the loading on the specimen was increased in a step like way, and, after each an increment of load, the coercive force, the measurement of eoercive force was measured in the direction along the tensile force. In the second case - the loading was increased in the same manner, but with the subsequent off - loading until zero point after every regular increment the coercive force is measured, as it was before, at each an increment of loading and after setting to zero. The coercive force values in the off - loading state are the aecumulation standard of the specimen s strain variations during every similar solitary loading, off-loading of the specimen. As a result, the possibility is to identify by the coercive force the particular points of Stress-Deformation diagram, such as yield point, ultimate strength, etc. It is determined unambiguously, to what area of diagram ( of elasticity, elasticity-ductility, destructive zone) corresponds the metal structure of the metalwork under inspection at that very instant.  [c.29]

In isotropic media, the pressure and shear wave slownesses are given by circles (see Fig. 4(a)). For the coupling of the trruasdiicer to transversely isotropic media the slowness diagram will change in the following way (see Fig. 5(a) and 6(a)) the upper part contains the circles of isotropic steel, because the transducer is designed for transmitting 45° shear waves into steel, and the lower part of the diagram shows the three non-circular curves for quasi pressure [qP), quasi shear verticcJ qSV) and shear horizontal SH) slownesses of transversely isotropic austenitic steel into which the wave is actually transmitted. Using the phase matching condition, it is seen that an incident shear wave under an angle of 45° (angles are counted counterclockwise from the normal pointing into the sample) will be transmitted into isotropic steel as a 45° shear vertical wave, into the anisotropic weld with perpendicular grain orientation under an angle of 35° and into the anisotropic weld with herringbone structure under an angle of 58° as a quasi shear vertical wave. It can also be seen that the phase velocity vector and the group velocity vector point in the isotropic case into the same direction, since the direction of the group velocity vector is obtained by drawing a line at right angles to a tangent to the respective slowness curve [9], because the group velocity vector is always perpendicular to the slowness curve. For both anisotropic cases the angle of the direction of the group velocity vector is smaller than 45°, i.e. 2° for perpendicular grain orientation and 25° for herringbone grain orientation.  [c.154]

To verify the modelling of the data eolleetion process, calculations of SAT 4, in the entrance window of the XRII was compared to measurements of RNR p oj in stored data as function of tube potential. The images object was a steel cylinder 5-mm) with a glass rod 1-mm) as defect. X-ray spectra were filtered with 0.6-mm copper. Tube current and exposure time were varied so that the signal beside the object. So, was kept constant for all tube potentials. Figure 8 shows measured and simulated SNR oproj, where both point out 100 kV as the tube potential that gives a maximum. Due to overestimation of the noise in calculations the maximum in the simulated values are normalised to the maximum in the measured values. Once the model was verified it was used to calculate optimal choice of filter materials and tube potentials, see figure 9.  [c.212]

Further instruments followed from our stable, the next was the HALEC crack detector in 1970, which again is still in use today and the engineer who designed it is still with the company. We were among the first to put microprocessors into instruments to replace front panel switches, and later to put menus on-screen with settings stored in memory. At one point we were working on a digital display technology which we knew we could not sell due to the high cost of memory. Imagine our feelings when at the end of the development project the cost of memory had fallen to a fraction of what it was at the beginning. We had a modest success on our hands, more by luck than anything else. But everyone needs to be lucky from time to time and we have enjoyed rather a good share of good fortune.  [c.273]

In order to predict the acoustic field generated by a given transducer configuration, a model based on Huygens principle has been employed [17]. This assumes that each finger may be represented as a series of point sources, the field at any point on the structure being obtained by summing the components from all the sources on the transducer. One particular interest has been to design interdigital transducers (IDTs) which have all round 360" vision of the surrounding structure. Fig 5(a) shows a typical sub-transducer, designed to excite the a, mode at 1.1 MHz In 1.2 mm thick steel plate. The complete transducer would have six such subtransducers arranged in a circle with a common focus, the idea being that each sub-transducer would generate a uniformly diverging beam to interrogate the 60" sector of structure in front of it. Fig 5(b) shows the Huygens prediction of the field from the sub-transducer. To investigate the beam divergence, an angular cross section is taken along the dotted line and plotted in Fig 5(c), where a comparison with experimental measurements is also shown. The agreement is not as good as has been obtained in other cases [17], but this is thought to be due to uneven bonding of the experimental IDT. However, both the experimental and predicted results indicate that the beam is uniform over around 40" and not the required 60", hence this particular transducer configuration was not suitable for the required purpose. Further work is in progress designing integrated IDTs which have a greater degree of overlap between the fields of their constituent sub-transducers.  [c.719]

Using the optimised parameters, rf signals from fatigue cracks with depths ranging from 7 mm to 28 mm in 56 mm thick carbon steel specimen and machined notches with depths ranging from 8 mm to 16 mm (width 1mm) in 150 mm thick carbon steel block were recorded. It is very essential in TOED method to measure the time-of-flight precisely. The beam entry point was determined by the back wall echo arrival time. Further, by applying easily implementable analytic signal and cross-correlation methods the peak amplitude of the rf signal was detected and the time-of-flight was calculated precisely [II]. Figure 6 shows the experimentally obtained depths of various surface breaking defects in carbon steel specimens and their actual depths. Despite scatter, a clear linear relationship was observed with a correlation coefficient of 0.997, thus establishing the possibility of using diffracted SH waves for quantitative defect sizing.  [c.725]

There is no doubt that the reduction of fi by such as the foregoing lubricants is due to a thin and perhaps monomolecular film of adsorbed material. Thus Frewing [48] found that, using a hemispherical steel rider, the coefficients of friction for various alcohols, esters, and acids were about the same whether an excess of lubricant was used or whether one or more monolayers were built up by means of the Langmuir-Blodgett technique (Section XV-7). Later, films of low-molecular-weight alcohols, aldehydes, paraffins, and water formed by vapor-phase adsorption on a steel surface were found to exhibit n values that decreased to a minimum as the monolayer point was reached [49]. Similarly, monolayers of halogenated compounds adsorbed on metal or glass slides from solution in aqueous or organic solvents or from the vapor phase led to values typical for boundary lubrication [47].  [c.445]

Although a separation of electronic and nuclear motion provides an important simplification and appealing qualitative model for chemistry, the electronic Sclirodinger equation is still fomiidable. Efforts to solve it approximately and apply these solutions to the study of spectroscopy, stmcture and chemical reactions fonn the subject of what is usually called electronic structure theory or quantum chemistry. The starting point for most calculations and the foundation of molecular orbital theory is the independent-particle approximation.  [c.31]

The divergences of the heat capacity Cj and of the compressibility K, for a one-component fluid are usually defined as along the critical isochore, but if the phase diagram is shown in field space (p versus T as in figure A2.5.1 or figure A2.5.11, it is evident that this is a special direction along the vapour pressure curve. Indeed any direction that lies within the coexistence curve (e.g. constant enthalpy etc) and intersects that curve at the critical point will yield the same exponents. Conversely any patli that intersects this special direction, such as the critical isobar, will yield different exponents. These other directions are not unique there is no such thing as orthogonality in thennodynamics. Along the critical isobar, the compressibility divergence is still strong, but the exponent is reduced by renonualization from y to y/ 35, nearly a 40% reduction. The weak divergence of Cj is reduced by a similar amount from a to a/(35.  [c.649]

Because of the general difficulty encountered in generating reliable potentials energy surfaces and estimating reasonable friction kernels, it still remains an open question whether by analysis of experimental rate constants one can decide whether non-Markovian bath effects or other influences cause a particular solvent or pressure dependence of reaction rate coefficients in condensed phase. From that point of view, a purely  [c.852]

For centrosynnnetric media the spatially local contribution to the second-order nonlinear response vanishes, as we have previously argued, providing the interface specificity of the method. This spatially local contribution, which arises in the quantum mechanical picture from the electric-dipole tenns, represents the dommant response of the medium. Flowever, if we consider the problem of probing interfaces closely, we recognize that we are comparing the nonlinear signal originating from an interfacial region of monolayer thickness with that of the bulk media. In the bulk media, the signal can build up over a thickness on the scale of the optical wavelength, as dictated by absorption and phase-matching considerations. Thus, a bulk nonlmear polarization that is much weaker than that of the dipole-allowed contribution present at the interface may still prove to be significant because of the larger volume contributing to the emission. Let us examine this point in a somewhat more quantitative fashion.  [c.1279]

The technology of focusing ions is still at the stage where the resolution of the NMP does not compete with the electron microprobe. A set of deflection plates allows movement or scaiming of the ion beam and, using computer control, the position of the bombarding beam is known. At each point of irradiation, analytical data are acquired. In this way, the analytical infomiation obtained can be presented as an image. NaPirally, the imaging capabilities of the NMP is limited by the sensitivity of each teclmique used shice an entire spectrum must be collected at each pixel in the image. For example, a 128 x 128 pixel image is equivalent to 16 384 single-point analyses. For this reason the analytical techniques used in imaging are mostly limited to PIXE hi the case of trace elements, RBS and forward recoil spectrometry (FRS) for depth infomiation and light elements and nuclear reaction analysis (NRA) to the detection of elements at high concentrations. Naturally the NMP can also be used in a point analysis mode, as for example in the case of geological applications [28]. Here the gram sizes that need to be analysed are often of the order of a few microns and a reasonably small bombarding beam is necessary to limit the analysis to a specific gram.  [c.1844]

Gas-phase kinetics studies are ideally concerned with the most fiindamental events of chemical reactions related to isolated, single molecules either as elementary unimolecular reactions, isolated bimolecular collisions, or trimolecular reactions. The experimental study of such fast elementary processes has progressed to a point where it is possible to prove a reaction mechanism by identifying each elementary reaction contributing to the total reactive flux and by demonstrating that any conceivable additional contribution to the total reactive flux must be negligible. In fact gas-phase kinetics studies have even gone beyond this fiindamental goal of reaction kinetics. By using the tecluriques of femtosecond spectroscopy and quantum-chemical kinetics from high-resolution spectroscopy it is possible to look into the very details of the primary processes that initiate chemical reactions. These fields are still in active development and most of the fruits from these fields still remain to be harvested.  [c.2145]

The neutron scattering data of figure C2.1.6 show tliat if tire excluded volume effects are activated by increasing tire temperature from tire 0 point, and tluis increasing tire goodness of tire solvent, tire transition from tire Gaussian chain behaviour into tliat of an expanded chain depends on tire lengtli scale. The transition from tire regime x q to oc occurs first for low values of q, i.e. for long distances, while below a temperature-dependent lengtli, referred to as tire tliennic correlation length, the chain is still Gaussian. The whole chain many be seen as a self-avoiding walk of Gaussian blobs (figure C2.1.7).  [c.2519]


See pages that mention the term RSS saddle points : [c.186]    [c.450]    [c.56]    [c.209]    [c.432]    [c.341]    [c.514]    [c.589]    [c.819]    [c.1265]    [c.1926]    [c.2531]   
Molecular modelling Principles and applications (2001) -- [ c.253 , c.280 , c.291 ]