Nitric acid, HNOj. See separate entry.  [c.279]

Running casing is the process by which 40 toot sections of steel pipe are screwed together on the rig floor and lowered into the hole. The bottom two joints will contain a guide shoe, a protective cap which facilitates the downward entry of the casing string through the borehole. Inside the guide shoe is a one way valve which will open when cement / mud is pumped down the casing and is displaced upwards on the outside ot the string. The valve is necessary because the at the end of the cementing process the column of cement slurry filling the annulus will be heavier than the mud inside the casing and U tubing would occur without it. To have a second barrier in the string, a float collar s inserted in the joint above the guide shoe. The float collar also catches the bottom plug and top plug between which the cement slurry is placed. The slurry of  [c.54]

The advantages of surface sampling and recombination are that large samples may be taken, that stabilised conditions can be established over a number of hours prior to sampling, and that costly wireline entry into the well is avoided. The subsurface sampling requirements also apply to surface sampling if P is below P,, then it is probable that an unrepresentative volume of gas will enter the wellbore, and even good surface sampling practice will not obtain a true reservoir fluid sample.  [c.113]

Example. We reproduce the entry for iron in Table III-l as follows. First = 1880-(1808) (-0.43) = 2657 ergs/cm. Next, estimating V to be about 7.1 cm /mol and taking/ to be unity, A = (6.02 x 10 ) / (7.1) / = 3.1 x 10 cm /mol whence E = (2657)(3.1 X 10 )/(4.13 x 10 ) = 20.100 cal/mol.  [c.52]

In addition to AP being large, it is also desirable in promoting capillary penetration that the rate of entry be large. For the case of horizontal capillaries or, in general, where gravity can be neglected, Washburn [45] gives the following equation for the rate of entry of a liquid into a capillary radius r  [c.470]

Each entry is the product of first applying the permutation at the top of the column and then applying the permutation at the left end of the row.  [c.144]

Each entry is the product of first applying the operation at the top of the column and then applying the operation at the left end of the row.  [c.146]

The multiplication table of has the entries EE = E,E 2) = 2)E =(12) and (12)(12) = E. If, in the  [c.148]

Wlien one speaks of a spectrum , the dispersed array of colours from a luminous body comes to mind however, in the most general sense, a spectrum is a record of the energy and probability of transitions between states of a substance. In electron spectroscopy the spectrum takes the fonn of the energy distribution of electrons emanating from a sample. Electron spectroscopies are classified according to the phenomena giving rise to these electrons historically, each teclmique has acquired an acronym until today one finds a veritable alphabet soup of electron spectroscopies m the scientific literature. For example, PES refers to photoelectron spectroscopy, a technique in which the detected electrons are emitted after the absorption of a photon induces transitions into the continuum beyond the first ionization potential of the sample. Electron-impact spectroscopies, the subject of this entry, entail the excitation of a transition by an electron impinging upon a sample with the subsequent measurement of the energy of the scattered electron. The spectrum is the scattered-electron intensity as a fiinction of the difference between the incident- and scattered-electron energies—the energy loss.  [c.1306]

In order to obtain a more realistic description of reorientational motion of intemuclear axes in real molecules in solution, many improvements of the tcf of equation Bl.13.11 have been proposed [6]. Some of these models are characterized in table Bl.13.1. The entry number of tenns refers to the number of exponential fiinctions in the relevant tcf or, correspondingly, the number of Lorentzian temis in the spectral density fiinction.  [c.1504]

In the following we shall describe various applications of mesoscopic models to complex fluids. The examples extend from applications that are quite close to the atomistic level (e.g., coarse-grained polymer models) to highly idealized models (e.g., effective interface Hamiltonians or Ginzburg-Landau models). Moreover, we restrict ourselves mainly to the description of tliennodynamic equilibrium. The remainder of this entry is organized as follows. In section B3.6.2 we discuss applications of coarse-grained models to systems involving homopolymers. Mesoscopic models for the description of self-repelling chains, polymer solutions, polymer melts and binary blends are introduced. From these models, more coarse-grained descriptions can be derived in temis of Ginzburg-Landau expansions or effective interface Hamiltonians. Section B3.6.3 then considers amphiphilic molecules. Their co-operative behaviour on the supramolecular level has been explored in the framework of models with various degrees of detail. Chain models retain the salient features of the amphiphile s architecture while lattice models or continuum models yield a description in temis of a spatially varying concentration. On even larger scales, the statistical mechanics of interfaces has been investigated via random interface models. This article closes with a brief look at the application of mesoscopic and continuum models to dynamical phenomena.  [c.2364]

An examination of the crystal structure of the rat qj thyroid hormone receptor (TR) ligand binding domain bound with a thyroid hormone agonist (Wagner et al., 1995) suggests three entry/exit points for the hormone as shown in Fig. 5a. By applying an external force to the ligand to facilitate its unbinding from the protein, the three possible pathways were explored. In the simulations, the protein-ligand system was surrounded by a water bath. One atom of the hormone was harmonically restrained K = 10 kcal/molA 695 pN/A) to a point moving with a constant velocity V = 0.08 A/ps in a chosen direction. The investigation is still ongoing and presently only preliminary conclusions can be drawn from the SMD data.  [c.48]

We have chosen to study the extraction of the xenon atom from its binding site inside the hydrophobic cavity in mutant T4 lysozyme as a simple system in which to model the ligand extraction process. The internal binding site in this mutant is hydrophobic and excludes water as a result, an important source of friction in the extraction of a ligand (the simultaneous entry of water molecules) is absent. On the other hand, this system shares with the avidin-biotin system the requirement for a distortion of the geometry at the exit point in order to permit the ligand to escape. With long, but feasible, simulations it may therefore be possible to approach conditions of very slow extraction and hence small friction, in which the extraction force is dominated by the change in free energy (Cf. eq. 4). We describe first the interactive simulations in which we located an exit path for the xenon atom, and then the results of a scries of extractions performed at different rates.  [c.141]

In Tables 2 and 3 we show the error percentages of the LN energy components (and kinetic temperature) with respect to the explicit Langevin trajectories at At = 0.5 fs for BPTI and lysozyme simulations. The Reference column shows energy means and variances for the explicit trajectory (produced by the BBK scheme), and the LN columns (each corresponding to a different fe2 value, as indicated in the heading) show the percentage error of each entry (mean energy component and associated variance) with respect to the reference values. Here, Atm — 3 fs, so the LN variants shown (fe2 = 1, 3, 6, 12, 24, 48, and 96) correspond to outer timesteps At of 3, 9, 18, 36, 72, 144, and 288 fs, respectively.  [c.253]

The errors in the variance values (reflecting the fluctuations about the means) are larger for the total energy, variance errors can be as large as 7% for large 2 (the potential energy is the source rather than the kinetic energy) most other entries for energy components are less than 3%, except for two van der Waals values (LN 96 for BPTI and LN 3 for lysozyme) and all electrostatic entries. Note, however, that for the electrostatic energy the variance of the reference trajectory is a very small percentage of the mean value, namely 1% for BPTI. Thus, for example, the LN 96 variance (worst case for BPTI) for the electrostatic energy is still 1% of the reference energy mean although the value in the table is 33% (indicating an absolute energy variance of 16x 1.33 kcal/mol.). Thus, the values shown in Tables 2 and 3 still reflect a satisfactory agreement between LN trajectories and small-timestep analogs of the same Langevin equation. See [88] for many other examples of thermodynamic and geometric agreement.  [c.254]

Herein, H = H q) and Tg denote 2x2 Hermitian matrices, the entries of H being potential operators and Tg being diagonal  [c.389]

In 1986, David Weininger created the SMILES Simplified Molecular Input Line Entry System) notation at the US Environmental Research Laboratory, USEPA, Duluth, MN, for chemical data processing. The chemical structure information is highly compressed and simplified in this notation. The flexible, easy to learn language describes chemical structures as a line notation [20, 21]. The SMILES language has found widespread distribution as a universal chemical nomenclature  [c.26]


Walden inversion A phenomenon discovered in 1895 by Walden. When one of the atoms or groups attached to the asymmetric carbon atom in an optically active compound is replaced by a different atom, the product is sometimes a derivative of the optical isomer of the original compound. It is thus possible to pass from one isomer to the other without the formation and separation of a racemic compound. ( + )-Malic acid, when treated with PCI5 gives (— )-chlorosuccinic acid, which may be converted to ( —)-malic acid by AgjO or back to (-f)-malic acid by KOH. Similarly, ( —)-malic acid is converted to (-l-)-chloro-succinic acid which undergoes similar changes. A Walden inversion occurs at a tetrahedral carbon atom when the entry of the reagent and the departure of the leaving group are synchronous - the so-called bimolecular nucleophilic substitution mechanism. Since the reagent must approach from the side of the molecule opposite to that of the leaving group an inversion of optical configuration results.  [c.424]

The ideal comprehensive guide to written and spoken English the world over, with detailed etymologies and a wide selection of colloquial and idiomatic usage. There are over 100,000 entries and thousands of examples of how words are actually used - all clear, precise and up-to-date.  [c.438]

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]

During periodic surveys the Surveyor makes a close-up visual inspection and witnesses thickness measurements and crack detection inspections. In cases where a specific problem has been advised additional inspections may be made at the request of the Surveyor. When cracks are found during surveys the Surveyor will agree the repair procedure which, depending upon the severity of the crack, is most likely to be veeing out and welding. The Surveyor s report will be used to update the database maintained in HQ enabling defect trends to be identified. When cracks have been reported during Special Surveys the details will be recorded for entry into the Executive Hull Summary of the survey, a document issued by HQ to the Shipowner and kept on board the ship.  [c.1050]

In conclusion, we attempt to provide a snapshot of current research in Raman spectroscopy. Since any choice of topics must be necessarily incomplete, and certainly would reflect our own scientific bias, we choose, instead, an arbitrary approach (at least one not that is not biased by our own specialization). Thus an abbreviated sunnnary of the topics just presented in die keynote/plenary lectures at ICORSXVI in Cape Town, South Africa, is presented. Each of the 22 lectures appears in the Proceedings (and Supplement) of the 16th International Conference on Raman Spectroscopy (1998), edited by A M Heyns (Chichester Wiley) in a four-page fonnat, almost all containing a short list of references. Rather than ourselves searching for seminal citations, we instead give the e-mail address of the principal author, when available. Though the intent in this procedure is to expose the wide scope of current Raman activity, it is hoped that the reader who is looking for more details will not hesitate to seek out the author in this fashion, and that the authors will not feel put upon by this maimer of directing people to their work. To relate to table B 1.3.1 and tableBl.3.2. the acronym is given for the principal Raman spectroscopy that is used for each entry.  [c.1217]

The first microscopic theory for the phenomenon of nuclear spin relaxation was presented by Bloembergen, Purcell and Pound (BPP) in 1948 [2]. They related the spin-lattice relaxation rate to the transition probabilities between tire nuclear spin energy levels. The BPP paper constitutes the foundation on which most of the subsequent theory has been built, but contains some faults which were corrected by Solomon in 1955 [3]. Solomon noted also that a correct description of even a very simple system containing two interacting spins, requires introducing the concept of cross-relaxation, or magnetization exchange between the spins. The subsequent development has been rich and the goal of this entry is to provide a flavour of relaxation theory (sectionbl.13.2). experimental teclmiques (sectionbl.13.3) and applications (sectionbl.13.4).  [c.1500]

The fiirther reading list for this entry contains five monographs, a review volume and two extensive reviews from the early 1990s. The monographs cover the basic NMR theory and the theoretical aspects of NMR relaxation. The review volume covers many important aspects of modem NMR experiments in general and relaxation measurements in particular. The two reviews contain more than a thousand references to application papers, mainly from the eighties. The number of literature references provided in this entry is limited and, in particular in the theory and experiments sections, priority is given to reviews rather than to original articles.  [c.1500]

In the following entry we shall restrict ourselves to discussing mesoscopic and continuum models for complex fluids in chemical physics. The wide span of time and length scales in these materials is illustrated in figure B3.6.1 for a blend of two polymers. On the atomistic scale each polymer consists of chemical repeat units joined together to fomi the chain molecule. The length scale is set by the distance between the atoms along the backbone of the polymer, typically in the range of 1-2 A. The vibrations of the atoms occur on the timescale of picoseconds. In a dense melt, the flexible chain molecules adopt a random-walk-like confomiation. The step length of the random walk, or persistence length b, is typically of the order of a few nanometres. Since several thousands of repeat units fomi a polymer, the overall size of a single molecule, as specified by its radius of gyration, exceeds the persistence length by 1-3 orders of magnitude. On this range of length scales the structure of the polymer is self-similar. If the two components of tire blend are not miscible, as it is generally the case, one species fomis droplets that are dispersed in a matrix of the other species. The size of the droplets is in the micrometre range. On even larger length scales (say 1 nun) the material appears homogeneous. Clearly the properties on the mesoscopic length scale are important for application properties. A decrease of the droplet size or even the fomiation of a coimected morphology (i.e. a microemulsion) improves tlie mechanical properties of the composite material. A similar span of time and length scales is encountered in many other systems (e.g., mixtures of oil, water and surfactant or glassy materials) and this behaviour is rather typical for complex fluids.  [c.2361]

The observation of the universality and self-similarity of tlie large-length-scale properties has a theoretical basis. In 1972 de Geimes [H] related the stmcture of a polymer chain in a good solvent to a field theory of a n component vector model in the limit n —> 0. This class of models (see the entry on phase transitions and critical phenomena A2.5) exliibits a continuous phase transition and the properties close to this critical point have been investigated extensively with renomialization group calculations [8, 9 and 10]. The inverse chain length plays the role of the distance from the critical point of the n = 0 component vector model. As in the theory of critical phenomena, the behaviour in the vicinity of this critical point (i.e. 1/A<1) is governed by a universal scaling behaviour that is brought about by only a few relevant interactions. The relation between the behaviour of polymer chains in the limit of A—> oo and the critical behaviour justifies the use of highly coarsegrained models that incorporate only two relevant interactions connectivity along the chain and binary segmental interactions.  [c.2364]

Monte Carlo schemes generate a stochastic trajectory tlnough phase space (see the entry about statistical mechanical simulations B3.3). If the Monte Carlo moves resemble the configrirational changes in a realistic dynamics (e.g., tlie confonnations evolve via small displacements of particles) some dynamical infonnation can be gained. Since there is no momentum in Monte Carlo simulations the dynamics is difhisive. However, many Monte Carlo algoritlnns employ moves that involve rather large changes in the system confonnation (e.g., deletion of a molecule and subsequent insertion at a random position). These imphysicaT moves are  [c.2382]

The seope of this entry ineludes a deseription of tribologieal phenomena and the modem tools that are spurring developments in our understanding of tribology. The goal is to provide the reader with a basie understanding of the eoneepts, an understanding of their limitations and a perspeetive on the breadth and seope of phenomena that are ineluded under the umbrella of tribology.  [c.2741]

The key of constructing vibronic coupling terms for doubly degenerate states and modes to an arbibary order is the use of a complex representation. The fomial essence of the method is that in the complex representation U EEE xyz) is nonzero only for a single z- (In Table I there is only one entry in a row. Figuratively speaking All coupled coaches travel to a unique train station and all trains in that station consist of coupled coaches. Moreover, this goes also for the coupling of coupled trains, and so on. From our result, we conclude that the Berry phase around more than one conical intersection is not uniquely given by the number of conical intersections enclosed, but is model dependent. This has consequences for experimental Pacing of the phase, as well as for computations of line integrals with the purpose of obtaining non-adiabatic surface jumping in chemical reanangernent processes (e.g., in [186-195,300,301]) and as discussed in Section n.  [c.144]

We will not discuss here in detail our atomic model of the unbinding process derived from our simulations and sketched in Fig. 7, but restrict ourselves to two unexpected features. One is that the rupture of the initially very strong hydrogen bonds between the ligand and the residues of the binding pocket (Fig. 7 A) does not entail immediate unbinding. Rather, the complex is stabilized by a transient network of water bridges and other transient hydrogen bonds, which form during the unbinding process (Fig. 7 B and C). Only after subsequent rupture of these hydrogen bonds the maximum force — the rupture force — is reached and the biotin rapidly moves out of the entry of the binding pocket (Fig. 7 D). As another feature we observed, towards the end of the unbinding process, a second force maximum, which we attribute to a strong transient hydrogen bond and several water bridges between biotin and the entry of the binding pocket (Fig. 7 E). Crossing of that second barrier, which cannot yet be resolved in the AFM experiment, completes the unbinding process.  [c.87]

Fig. 3 shows the evolution of the charge distribution calculated with the PB equation of a set BPTI structures generated from the 200 ps MD simulation in solution. In this simulation the total charge of the protein was set to 5 e, by neutralization of the protein N-terminal group and the use of standard protonation states for all other protonation sites. However, the starting x-ray structure (PDB entry code [12] 4pti) is consistent with fractional ionization of the N-terminal group of 0.6 which indicates that for this structure the probability for this group of being neutral is slightly smaller than that of being charged. It is seen that at the initial stage of simulation (0-100 ps) the maximum net charge was about 5.8 e, in agreement with the fact that the starting structure taken for the simulation favored a larger charge than 5 e. The total charge becomes, however, very rapidly centered at the value of 5 e, so the distribution at 100-200 ps is nearly unimodal around that value, indicating an excellent agreement with the imposed charge during the MD simulation. The result presented in Fig. 3 shows that even a single charge mutation can substantially change the protein conformations explored during the MD simulation. This result not only emphasizes the need for the careful protein charge assigment, but also points out the direction of future development of the MD simulation techniques which would allow for modifying the titration state of a protein during the simulations.  [c.189]

Although the current multithreaded implementation of sequencers works well and provides a clearly visible algorithm, threads have several drawbacks. Extra memory is required for multiple stacks, there is overhead from contextswitching between threads, and a running sequencer cannot migrate between processors along with its patch. These problems will be addressed by using the Structured Dagger coordination language [22], which enables programmers to specify partial order between entry methods of an object. Using constructs such as overlap, forall, and when-blocks, one can easily express dependencies between entry methods of an object while letting the system do the buffering, bookkeeping, etc. required for the specified flow of control.  [c.480]

See pages that mention the term Entry : [c.9]    [c.65]    [c.279]    [c.421]    [c.77]    [c.166]    [c.39]    [c.364]    [c.381]    [c.578]    [c.526]    [c.2073]    [c.2370]    [c.2382]    [c.2815]    [c.45]    [c.46]    [c.46]   
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