Types performance

Actual heat-transfer coefficients encountered ia evaporators cover a wide range, depending on the physical properties of the solution, its fouling characteristics, the type of evaporator employed, the boiling temperature, and the temperature difference. Only ia the submerged-tube forced circulation and the falling-film evaporator can heat-transfer coefficients easily be calculated from theory (2). For other types, performance estimates are usually based on earlier experience with the same or a similar Hquor. In general, coefficients range from a low of about 175 J/(m -s-K) (100 Btu/(h-ft - F)) to a high of about 3500 (2000). The lowest coefficients are encountered at low temperatures and low ATs ia film-type or natural circulation evaporators, or at very high viscosities. The highest coefficients are encountered when employing doubly fluted tubes. These high coefficients are possible only when fouling resistances are very low, eg, when handling seawater that has been properly treated for scale prevention and deaerated.  [c.478]

Before we can explore how reactor conditions can be chosen, we require some measure of reactor performance. For polymerization reactors, the most important measure of performance is the distribution of molecular weights in the polymer product. The distribution of molecular weights dictates the mechanical properties of the polymer. For other types of reactors, three important parameters are used to describe their performance  [c.22]

We distinguish on one hand the physical properties that establish the correct fuel feed for a vehicle (starting up, warm up, cold and hot operation) and on the other hand the chemical properties essentially related to the octane numbers, acting to achieve optimum performance for the motor without risking abnormal combustion. The first items are largely the result of each country climatic conditions and can not therefore be made uniform over a wide geographical area on the other hand, they are identical for each type of gasoline (regular, premium, with or without lead). The second group of properties establish the classification of gasolines by types such as regular or premium they depend mostly on a compromise taking into account refining capacities, the options taken by the automobile manufacturers, and traffic conditions, etc. We observe that in this case, slightly different situations in the United States, Europe, and Japan for example.  [c.187]

Many oil and gas companies use contract staff to perform the part of a project between preliminary design and commissioning. This is either because they do not immediately have the staff or the skills to perform these tasks, or it is cheaper to pass the work to a contractor. Contracting out tasks is not limited to project work, and affects most departments in a company, from the drilling department through the training department to the cleaning services. The fraction of a company s expenditure directed to contract services may be very significant, especially when major projects are being performed. Every contract needs to be managed, and this section outlines some of the reasons for contracting out work and the main types of contract used in the oil and gas industry.  [c.291]

Since this is a purely mechanical operation it can be performed using the above equation, or by looking up the appropriate discount factor in discount tables. Two types of discount factors are presented for full year and half year discounting.  [c.320]

The aim of the work we present in this paper is to optimize the control parameters used in particles magnetic and interpret the obtained results. Experiments are performed on samples of welds or materials containing known defects. The realized and tested defects are grooves situated at different depths with variables dimensions. Other types of defects have been studied (inclusions, lack of penetration, etc.).  [c.635]

To determine the influence degree on both types of structure and volume of structural heterogeneity on the frequency spectrum characteristics of an ultrasonic pulse, research work using angle beam and straight beam probes was performed  [c.731]

In [66], we have reported inelastic and reactive transition probabilities. Here, we only present the reactive case. Five different types of probabilities will be shown for each transition (a) Probabilities due to a full tri-state calculation carried out within the diabatic representation (b) Probabilities due to a two-state calculation (for which T] = 0) performed within the diabatic representation (c) Probabilities due to a single-state extended BO equation for the N = 3 case (to, = 2) (d) Probabilities due to a single-state extended BO equation for the N = 2 case (coy =1) (e) Probabilities due to a single-state ordinary BO equation when coy = 0.  [c.71]

Such an analysis of the Hterature for assigning reaction types to different reaction schemes definitely has merits. However, it does not say anything about the importance of a reaction type, such as how frequently it is actually performed in the laboratory.  [c.189]

Clearly, such statistics are impossible to obtain on a worldwide basis. However, it is quite dear that organic reaction types that follow reaction scheme R1 (Table 3-3, Figure 3-13) are among the most frequently performed. This shifts the balance even further in the direction of this reaction scheme, lending overwhelming importance to it.  [c.189]

I)(. p end ing upon the parameters chosen, simulations performed using the Gay-Berne potential show behaviour typical of liquid crystaUine materials. Moreover, by modifying the potential, 111. can determine what contributions affect the liquid crystalline properties and so help to suggest what types of molecule should be made in order to attain certain properties.  [c.243]

Defect calculations are traditionally performed using an empirical potential function, but there are some types of problem for which a quantum mechanical model is required, such as when the defect formation is accompanied by a transition to an excited electronic state. The obvious drawback to this is that the quantum mechanical method is computationally more expensive than the empirical potentials that are typically used in Mott-Littleton or supercell calculations. As a consequence, the number of atoms that can be treated quantum mechanically is often limited to the defect and its immediate neighbours. It is then necessary in some way to incorporate the effects of the surrounding region. In the embedded cluster approach this outer region provides a representation of the electrostatic potential due to the surrounding lattice, most easily simulated using point charges placed at the appropriate lattice sites. In more sophisticated approaches, the influence of the defect on the surrounding region can be taken into account in a manner similar to the Mott-Littleton approach [Grimes et al. 1989 Pisani 1999].  [c.642]

Another basis technique that is popular for modeling crystals is the use of plane wave basis functions. Plane waves were proposed because they reflect the infinite symmetry of a crystal. There have been several different plane wave techniques proposed. The earliest plane wave calculations assumed the Schrodinger equation was spherically symmetric in a region around each atom (dubbed a muffin tin potential), but suffered from an inability to conserve charge. These muffin tin calculations gave reasonable results for ionic crystals. They are no longer performed since algorithms and computer hardware improvements make more accurate and reliable calculations feasible. A technique still used is the augmented plane wave (APW) technique, which is a cellular calculation over the Vigner-Seitz cell. There are many other basis function methods that are used for certain types of problems.  [c.268]

There are two types of Cl calculations implemented in Hyper-Chem — singly excited Cl and microstate CL The singly excited Cl which is available for both ab initio and semi-empirical calculations may be used to generate UV spectra and the microstate Cl available only for the semi-empirical methods in HyperChem is used to improve the wave function and energies including the electronic correlation. Only single point calculations can be performed in HyperChem using CL  [c.39]

HyperChem performs a number of different types of calculations such as geometry optimization, molecular dynamics, etc. Each of these types of calculations is designed to be, as far as is possible, independent of the technology that produces the potential energy surface. The technology that produces the potential energy surface is referred to here as a force-energy generator. Thus, geometry optimization of a molecule is fed by routines that compute the potential energy V (R) and its derivatives d (R)/dR, d (R)/dR, etc. without concern whether these force-energy generators are molecular mechanics or semi-empirical quantum mechanics. New force-energy generators could, in principle, be added easily. An example would be the addition of an ab initio force-energy generator for which all the other methodology of HyperChem, such as molecular dynamics, would become available.  [c.166]

When no explicitly correct force constant is found, HyperChem proceeds to stage two and finally to stage three. In stage two, you can use wildcards to relax the explicitness of the match between the atom types of the torsion in question and the available MM-t parameters. In the torsional case, as many as three searches of the mmp.par file are performed. If the exact match between A-X-Y-B and entries in mmp.par fails, then a search in mmp.par looks for an entry labeled, -X-Y- where is the designation for wildcard, don t-care, any-atom-type, unknown, etc. This search looks  [c.205]

Unfortunately, this description ignores the unique perspective that analytical chemists bring to the study of chemistry. The craft of analytical chemistry is not in performing a routine analysis on a routine sample (which is more appropriately called chemical analysis), but in improving established methods, extending existing methods to new types of samples, and developing new methods for measuring chemical phenomena.  [c.2]

The second set of experiments describes the application of high-performance liquid chromatography. These experiments encompass a variety of different types of samples and a variety of common detectors.  [c.612]

Quantitative information about a chemical reaction can be made using any of the techniques described in the preceding chapters. For reactions that are kineti-cally slow, an analysis may be performed without worrying about the possibility that significant changes in concentration occur while measuring the signal. When the reaction s rate is too fast, which is usually the case, significant errors may be introduced if changes in concentration are ignored. One solution to this problem is to stop, or quench, the reaction by suitably adjusting experimental conditions. For example, many reactions involving enzymes show a strong pli dependency and may be quenched by adding a strong acid or strong base. Once the reaction is stopped, the concentration of the desired species can be determined at the analyst s convenience. Another approach is to use a visual indicator that changes color after the reaction occurs to a fixed extent. You may recall that this variable-time method is the basis of the so-called clock reactions commonly used to demonstrate kinetics in the general chemistry classroom and laboratory. Finally, reactions with fast kinetics may be monitored continuously using the same types of spectroscopic and electrochemical detectors found in chromatographic instrumentation.  [c.634]

Linked scan at constant (B/E)(l - E). A linked scan at constant (B/E)(l - E) can be performed on a sector instrument that incorporates at least one electric sector plus one magnetic sector. It involves holding the accelerating voltage fixed and scanning the magnetic field (B) and electric field (E) simultaneously to maintain the quantity (B/E)(l - E) at a constant value. This constant value is equal to Bj/Eq, where Eg and Bj are, respectively, the electric-sector field and magnetic-sector field required to transmit m3 ions in the main ion beam m3 represents the mass (mj - mj) of the selected neutral fragment whose precursor (parent) ion spectrum is required. The observed fragmentation reactions occur in a field-free region traversed before the two sectors scanned in this way. This term should not be used without prior explanation of the meanings of B, E, and Eg. The term (B/E)(l - E) linked scan is not recommended. The above three definitions are merely examples of the types of linked scan that might be used. Other linked scans can readily be defined in a similar manner.  [c.434]

The throw of Blake jaw crushers is determined by the hardness of the ore as well as the size of the machine [Mollick et al,. Engineering Mining]., 181(6), 69-171 (1980)], It may vary from V4 in for hard but friable ores to 3 in for resilient material. The Big Bite jaw crusher (Kue-Ken Div, Process Technology Inc.) is a Blake double-toggle type in which the fulcrum pinion is positioned well over the center or the grinding chamber [Anon, Quarry Management, 18(1), 25-7 (1991)], This increases the throw at the top of the jaw opening, allowing it to better crush large rocks. It can be shipped in sections. Capacities of Kue-Ken jaw crushers (Blake type) are given in Table 20-8, including both standard and Big Bite types. Performance data of overhead eccentric crushers with straight jaw plates are given in Table 20-9,  [c.1842]

In order to identify the signature of the AE signals, a parametric cluster analysis study was performed for different combinations of AE descriptors and different combinations of clustering parameters Tf, Tm and N ,i . The selection of the most pronounced partition was based on separability criteria and comparative evaluation of the resulting cumulative plots of each class vs. the applied pressure. The results presented herein were obtained by taking into account the following six features in the pattern vector Rise Time (RT), Counts (CNTS), Duration (DUR), Amplitude (AMP), Decay Angle (DAN) and Rise to Total Area (RTA). The Max-Min Distance clustering algorithm for Tm=0.2 resulted in 17 classes, 8 of which composed of one or two patterns. Further optimisation of the initial partition by means of Forgy algorithm with T =0.25 and Nmin=4, resulted in 10 classes which correspond to the signature of 10 different types of AE hits/signals.  [c.41]

In this paper we present a neural network based spectrum elassifier (NSC) and its application to ultrasonic resonance spectroscopy. The use of an Artificial Neural Network (ANN) is proposed to meet the requirements of high sensitivity for small but relevant changes in the spectra, and simultaneous robustness against measurement noise. Provided with enough training examples, the ANNs are known to be able to find features representative for different classes and to generalize in order to cope with the measurement noise. Among several types of ANNs that could be used for classifying the spectra we have chosen a multi-layer perceptron (MLP). Although the MLP itself can perform feature extraction, we included an optional pre-processor for this purpose. The NSC is essentially model free and can be trained using real and modeled spectra. The classifier uses both amplitude and phase information in the spectra. The performance of the classifier has been verified using a number of practical applications, here we present results of its application to detection of disbonds in adhesively joint multi-layer aerospace structures using Fokker Bond Tester resonance instrument. In this case the classifier is capable of detecting very small disbonds (larger than 25% of the sensor area) and correct identifying their position in the structure (identifying the defected joint).  [c.105]

Direct three-dimensionai (or volumetric) imaging have been performed e.g. by Sire et al. [7]. In their work the whole specimen is insonified by a cone beam and reconstructed directly. In the present work the three-dimensional information was obtained by constructing two-dimensional reflection tomograms and stacking these in multiple continues planes in the third dimension, as indicated in Fig. 4. This approach needs less processing time and data storage than for direct reconstruction. Therefore, the stacking technique has been adopted for this NDE study. Once the data are mapped into a volumetric matrix composed of cubic voxels it can be numerically dissected in any plane. Fig. 4 also shows the six discontinuity types, i.e., (a)-(f) in an increasing axial distance from the edge of the 50 mm long cylinder.  [c.204]

Abstract At the Institute fuer Theoretische Nachrichtentechnik uiid Informationsver-arbeituiig at the University of Hannover investigations were carried out in cooperation with the Institute of Nuclear Engineering and Non-Destructive Testing concerning 3D analysis of internal defects using stereoradioscopy based on camera modelling. A camera calibration approach is used to determine 3D position and volume of internal defects using only two different X-ray images recorded from arbitrary directions. The volume of defects is calculated using intensity evaluation considering polychromatic radiation of microfocus X-ray tubes. The system performance was determined using test samples with different types of internal defects. Using magnifications between 1.1 and 1.4 the system achieves an accuracy of 0.5mm calculating the 3D positions of defects using samples rotated only 10° between two views and an accuracy of 0.3mm using 25° rotation. During calibration the distortion inherent in the image detector system is reduced from a maximum of 3.8mm to less than 0.1mm (0.3 pixel). The defect volumes are calculated with an overall accuracy of 10%. Additional results will be presented using the system to analyse casting defects.  [c.484]

A new system for automated ultrasonic inspection has been described. The key element of the new system is the remotely controlled front end processor, which includes ultrasonics, digital conversion and processing electronics, as well as scanner control electronics. The system operation and image analysis is performed on a portable industrial laptop computer. Data communication between the front end processor and the computer takes place by means of an ethemet connection through a cable which may be several hundred metres long. An inspection may include simultaneous execution of more inspection types in a single scanning P-scan, T-scan. Through Transmission, TOFD and A-scan. Data storage in frill 3D and off-line reconstruction of data is supported.  [c.789]

The following table lists some of the types of interfacial tensions that occur in systems of practical importance. Each row corresponds to a different system not all of the types of interfacial tensions are necessarily present in a given system, and of those present there may be some that, from the nature of the situation, are not under control (i.e., from a practical point of view cannot be modified). For each system certain changes are indicated that constitute a desired goal for that situation, for example, wetting, and detergency. Thus inc (dec) means that it is desirable for good performance to introduce a surfactant that will increase (decrease) the particular surface tension involved. For each case state which practical situation is involved and discuss briefly why the indicated modifications in surface tension should be desired.  [c.489]

The present high cost of full CASSCF direct dynamics means that it is not possible to use such calculations to run large numbers of trajectories. As a result it cannot be used to build up experience of the types of effects to be found in dynamical studies of organic photochemistry, and in their interpretation. This problem can be remedied by performing calculations using the MMVB force field [63,64].  [c.301]

Neural networks have been applied to IR spectrum interpreting systems in many variations and applications. Anand [108] introduced a neural network approach to analyze the presence of amino acids in protein molecules with a reliability of nearly 90%. Robb and Munk [109] used a linear neural network model for interpreting IR spectra for routine analysis purposes, with a similar performance. Ehrentreich et al. [110] used a counterpropagation network based on a strategy of Novic and Zupan [111] to model the correlation of structures and IR spectra. Penchev and co-workers [112] compared three types of spectral features derived from IR peak tables for their ability to be used in automatic classification of IR spectra.  [c.536]

The Ewald method has been widely used to study highly polar or charged systems. Its use is considered routine for many types of solid-state materials. It is increasingly used foi calculations on much larger molecular systems, such as proteins and DNA, due both tc the increases in computer performance and to the new methodological advances we have just discussed [Darden et al. 1999]. For example, an early application of the peirticle-mesl Ewald method was the molecular dynamics simulation of a crystal of tlie protein bovine pancreatic trypsin inhibitor [York et al. 1994]. The full crystal environment was reproduced with four protein molecules in the unit cell, together with associated water molecules anc chloride counterions. Over the course of the 1 ns simulation the deviation of the simulated structures from the initial crystallographic structure was monitored. Once equilibrium was achieved this deviation (measured as the root-mean-square positional deviation) settled down to a value of 0.63 A for all non-hydrogen atoms and 0.52 A for the backbone atoms alone. By contrast, an equivalent simulation run with a 9 A residue-based cutoff showed e deviation of more than 1.8 A. In addition, the atomic fluctuations calculated from the Ewald simulation were in close agreement with those derived from the crystallographic temperature factors, unlike the non-Ewald simulation, which was significantly overestimated due to the use of the electrostatic cutoff. The highly cheirged nature of DNA makes it particularly important to deal properly with the electrostatic interactions and simulations using the particle-mesh Ewald approach are often much more stable, with the trajectories remaining much closer to the experimental structures [Cheatham et al. 1995].  [c.353]

Once a protein model has been constructed, it is important to examine it for flaws. Much ( this analysis can be performed automatically using computer programs that examine tl structure and report any significant deviations from the norm. A simple test is to genera a Ramachandran map, in order to determine whether the amino acid residues occupy tl energetically favourable regions. The conformations of side chains can also be examine to identify any significant deviations from the structures commonly observed in X-ray stru tures. More sophisticated tests can also be performed. One popular approach is Eisenberg 3D profiles method [Bowie et al. 1991 Liithy et al. 1992]. This calculates three properties f( each amino acid in the proposed structure the total surface area of the residue that is burie in the protein, the fraction of the side-chain area that is covered by polar atoms and the loc secondeiry structure. These three parameters are then used to allocate the residue to one ( eighteen environment classes. The buried surface area and fraction covered by polar aton give six classes (Figure 10.25) for each of the three types of secondary structure (a-helix, / sheet or coil). Each amino acid is given a score that reflects the compatibility of that amir acid for that environment, based upon a statistical analysis of known protein structure Specifically, the score for a residue i in an environment is calculated using  [c.559]

The molecular mechanics force helds available are AMBER95 and CFIARMM. The molecular mechanics and dynamics portion of the code is capable of performing very sophisticated calculations. This is implemented through a large number of data hies used to hold different types of information along with keywords to create, use, process, and preprocess this information. This results in having a very hexible program, but it makes the input for simple calculations unnecessarily complex. QM/MM minimization and dynamics calculations are also possible.  [c.330]

AMPAC supports a number of semiempirical methods AMI, SAMI, SAMl/d, MNDO, MNDO/d, MNDOC, MINDO/3, and PM3. The solvation methods available are SM1-SM3 and COSMO. Types of calculation available include single-point energies, geometry optimization, frequency calculation, IRC, and a reaction path and an annealing algorithm. It incorporates some transition structure finding algorithms that are not in other semiempirical programs, such as the CHAIN and TRUST algorithms. A simulated annealing algorithm is available for conformation searching. The code incorporates many alternative algorithms and settings to control how the calculation is performed. Property prediction functions include ESR and nonlinear optical properties.  [c.341]

Types of Chelometric Titrations. Chelometric titrations may be classified according to their manner of performance direct titrations, back titrations, substitution titrations, redox titrations, or indirect methods.  [c.1167]

Ions produced in an ion source can be separated into their m/z values by a variety of analyzers. The resultant set of m/z values, along with the numbers (abundances) of ions, forms the mass spectrum. The separation of ions into their individual m/z values has been effected by analyzers utilizing magnetic fields or RF (radio frequency) electric fields. For example, the mass analysis of ions by instruments using a magnetic field is well known, as are instruments having quadru-pole RF electric fields (quadrupole, ion trap). Ions can also be dispersed in time, so their m/z values are measured according to their flight times in a time-of-flight (TOF) instrument. These individual pieces of equipment have their own characteristics and are commonly used in mass spectrometry. In addition, combinations of sectors have given rise to hybrid instruments. The earliest of these was the double-focusing mass spectrometer having an electric. sector to focus ions according to their energies and then a magnetic sector to separate the individual m/z values. There is now a whole series of hybrid types, each with some advantage over nonhybrids. Ion collectors have seen a similar improvement in performance, and any of the above analyzers may be used with ion detectors based on single-electron multipliers or, in the case of magnetic sectors, on arrays of multipliers, or, in the case of ion cyclotron resonance (ICR), on electric-field frequencies.  [c.195]

See pages that mention the term Types performance : [c.62]    [c.108]    [c.298]    [c.205]    [c.47]    [c.122]    [c.462]    [c.466]    [c.482]    [c.536]    [c.608]    [c.661]    [c.726]    [c.333]    [c.232]   
Applied Process Design for Chemical and Petrochemical Plants, Volume 1 (1999) -- [ c.297 ]