Balancing-compensation system for the vertically moving elements of the machine tools with numerical control

The main topic consists of enhancing the geometrical and positioning accuracy of the machine tools with numerical control. Currently, in order to minimize the errors met during the vertical motions of the moving elements in the structure of a machine tool, various systems are used that are relatively complex and whose adjustments are difficult to do. This work is presenting a balancing–compensation system of the elements moving vertically that includes three invention patents; it has a simple structure that is easily adaptable to various types of machine tools. The newness element of the balancing-compensation system is represented by the pressure regulator being used, whose operation principle and design is described into detail. The related results have been reified in increasing by approximately 10 times the geometrical accuracy and, by default, the positioning accuracy of the element moving in a vertical plane.     

Self contained enrichment cell for tritium

Tritiated water is probably the most mobile manmade nuclide found in the environment. The low-energy beta decay produces few health concerns except at extremely high concentrations of tritium. However, because of the ubiquitous nature of tritiated water, when identified in the bionetwork, it can be viewed as a precursor of nuclides with greater health risks. For this reason alone it becomes desirable to determine tritium concentrations many orders of magnitude below that considered a health concern. A devise is described that eliminates the need for large water-filled chest freezers used as coolers. The enrichment cells can be employed individually or in series.     

Determination of carbamate pesticides and some urea pesticides after derivatization with acetic anhydride by means of GC-MSD

Summary A simple method for the determination of several thermolabile carbamate and urea pesticides as acetyl derivatives by means of capillary gas chromatography is described. 10 carbamate and 6 urea pesticides yielded thermostable derivatives which can easily be analysed by GC-MSD at the relevant residue levels as demonstrated with food samples. The method was designed to be used in addition to a popular multimethod (S19 — DFG Pesticide Commission).Part of this paper was presented at the Seventh International Congress of Pesticide Chemistry, Hamburg, August 5–10, 1990     

A Note on Veraverbeke's Theorem

We give an elementary probabilistic proof of Veraverbeke's theorem for the asymptotic distribution of the maximum of a random walk with negative drift and heavy-tailed increments. The proof gives insight into the principle that the maximum is in general attained through a single large jump.     

Spatial Estimates for the Constrained Anisotropic Elastic Cylinder

This paper establishes spatial estimates in a prismatic (semi-infinite) cylinder occupied by an anisotropic homogeneous linear elastic material, whose elasticity tensor is strongly elliptic. The cylinder is maintained in equilibrium under zero body force, zero displacement on the lateral boundary and pointwise specified displacement over the base. The other plane end is subject to zero displacement (when the cylinder is finite, say). The limiting case of a semi-infinite cylinder is also considered and zero displacement on the remote end (at large distance) is not assumed in this case. A first approach is developed by considering two mean-square cross-sectional measures of the displacement vector whose spatial evolution with respect to the axial variable is studied by means of a technique based on a second-order differential inequality. Conditions on the elastic constants are derived that show the cross-sectional measures exhibit alternative behaviour and in particular for the semi-infinite cylinder that there is either at least exponential growth or at most exponential decay. A second approach considers cross-sectional integrals involving the displacement and its gradient and furnishes information upon the spatial evolution, without restricting the range of strongly elliptic elastic constants. Such models are principally based upon a first-order differential inequality as well as on one of second order. The general results are explicitly presented for transversely isotropic materials and graphically illustrated for a cortical bone.     

<Superscript>99m</Superscript>Tc-labeling and molecular modeling of short dipeptide glycyl-<Emphasis Type="SmallCaps">l</Emphasis>-proline

Glycyl-l-proline (Gly-l-Pro) is the main degradation product of collagen and is a good diagnostic tool in various pathological conditions. The aim of this work was to prepare dipeptide Gly-l-Pro labeled with ^99mTc. Complex preparation was carried out under alkaline reaction conditions and its stability was assessed 10 and 120 min after preparation. The formation of two types of complex compounds was observed. High-performance liquid chromatography, paper electrophoresis, paper chromatography and thin layer chromatography were employed to monitor the formation of different complexes. Molecular modeling (semi-empirical method) was used to design their structure and composition. First complex cI with formula [TcO(Gly-l-Pro)]⁻¹ is unstable. After 120 min cI is completely transformed to complex cII with formula Tc(Gly-l-Pro)₃.     

Study on the transesterification of methyl aryl phosphorothioates in methanol promoted by Cd(II), Mn(II), and a synthetic Pd(II) complex

Methanol solutions containing Cd(II), Mn(II), and a palladacycle, (dimethanol bis(N,N-dimethylbenzylamine-2C,N)palladium(II) (3), are shown to promote the methanolytic transesterification of O-methyl O-4-nitrophenyl phosphorothioate (2b) at 25 °C with impressive rate accelerations of 10(6)-10(11) over the background methoxide promoted reaction. A detailed mechanistic investigation of the methanolytic cleavage of 2a-d having various leaving group aryl substitutions, and particularly the 4-nitrophenyl derivative (2b), catalyzed by Pd-complex 3 is presented. Plots of k(obs) versus palladacycle [3] demonstrate strong saturation binding to form 2b:3. Numerical fits of the kinetic data to a universal binding equation provide binding constants, K(b), and first order catalytic rate constants for the methanolysis reaction of the 2b:3 complex (k(cat)) which, when corrected for buffer effects, give corrected (k(cat)(corr)) rate constants. A sigmoidal shaped plot of log(k(cat)(corr)) versus (s)(s)pH (in methanol) for the cleavage of 2b displays a broad (s)(s)pH independent region from 5.6 ≤ (s)(s)pH ≤ 10 with a k(minimum) = (1.45 ± 0.24) × 10(-2) s(-1) and a [lyoxide] dependent wing plateauing above a kinetically determined (s)(s)pK(a) of 12.71 ± 0.17 to give a k(maximum) = 7.1 ± 1.7 s(-1). Br?nsted plots were constructed for reaction of 2a-d at (s)(s)pH 8.7 and 14.1, corresponding to reaction in the midpoints of the low and high (s)(s)pH plateaus. The Br?nsted coefficients (β(LG)) are computed as -0.01 ± 0.03 and -0.86 ± 0.004 at low and high (s)(s)pH, respectively. In the low (s)(s)pH plateau, and under conditions of saturating 3, a solvent deuterium kinetic isotope effect of k(H)/k(D) = 1.17 ± 0.08 is observed; activation parameters (ΔH(Pd)(++) = 14.0 ± 0.6 kcal/mol and ΔS(Pd)(++)= -20 ± 2 cal/mol·K) were obtained for the 3-catalyzed cleavage reaction of 2b. Possible mechanisms are discussed for the reactions catalyzed by 3 at low and high sspH. This catalytic system is shown to promote the methanolytic cleavage of O,O-dimethyl phosphorothioate in CD3OD, producing (CD3O)2P═O(S(-)) with a half time for reaction of 34 min.     

Chemical potential perturbation: a method to predict chemical potentials in periodic molecular simulations

A new method, called chemical potential perturbation (CPP), has been developed to predict the chemical potential as a function of density in periodic molecular simulations. The CPP method applies a spatially varying external force field to the simulation, causing the density to depend upon position in the simulation cell. Following equilibration the homogeneous (uniform or bulk) chemical potential as a function of density can be determined relative to some reference state after correcting for the effects of the inhomogeneity of the system. We compare three different methods of approximating this correction. The first method uses the van der Waals density gradient theory to approximate the inhomogeneous Helmholtz free energy density. The second method uses the local pressure tensor to approximate the homogeneous pressure. The third method uses the Triezenberg-Zwanzig definition of surface tension to approximate the inhomogeneous free energy density. If desired, the homogeneous pressure and Helmholtz free energy can also be predicted by the new method, as well as binodal and spinodal densities of a two-phase fluid region. The CPP method is tested using a Lennard-Jones (LJ) fluid at vapor, liquid, two-phase, and supercritical conditions. Satisfactory agreement is found between the CPP method and an LJ equation of state. The efficiency of the CPP method is compared to that for Widom's method under the tested conditions. In particular, the new method works well for dense fluids where Widom's method starts to fail.     

Assessing Similarity of Random sets via Skeletons

Methodology and Computing in Applied Probability - The paper concerns a method for assessing similarity of realisations of random sets based on a construction of their morphological skeletons and a...