Raman spectra of single crystals of adipic and sebacic acids and a study of the hydrogen bond vibrations in carboxylic acid dimers

Raman spectra of single crystals of adipic and sebacic acids have been photographed for the first time using λ 2537 excitation. The spectra have been divided into four regions: (a) internal frequencies; (b) summations and overtones; (c) external vibrations; and (d) low-frequency hydrogen bond oscillations. Tentative correlations have been given for all the internal frequencies and summations and overtones. A series of diffuse weak bands observed in the spectra of both these acids in the not, vert, similar2400–2800 cm−1 have been explained as a superposition of O---H frequencies lowered due to hydrogen bond formation over the summations and overtones of fundamentals mainly in the not, vert, similar1000–1500 cm−1 region. Rotatory type of external oscillations of the two formula units of these molecules in their unit cells have been identified at 76, 99, 118 and 165 cm−1 in adipic acid and 66, 95, 117 and 177 cm−1 in the spectrum of sebacic acid. A brief discussion of the low frequency hydrogen bond vibrations in these acids has been made. Making use of the Lippincott—Schroeder potential and assuming a highly anharmonic potential curve for the hydrogen bond, the vibrational frequencies of the bond have been theoretically evaluated. There is very good agreement between these and the experimental values. The results for adipic acid in cm−1 are: 304 (0 → 1), 270 (1 → 2), 241 (2 → 3), 222 (3 → 4) 201 (4 → 5), 183 (5 → 6). In the case of sebacic acid some of the intermediate and higher transitions are absent in the spectrum recorded by the author. From the above data for adipic acid the dissociation energy of the hydrogen bond was evaluated as 5·9 kcal/mole in fair agreement with the values derived from conventional methods.

Urey-Bradley potential function for the in-plane vibrations of boric acid

The Urey-Bradley force constants for the in-plane vibrations of the boric acid molecule are calculated using the Wilson's F-G matrix method. They are as follows: KO-H=5·23, KB-O=4·94, HBOH=0·36, {Mathematical expression}, F00=0·68 and FBH=0·98 in units of 105 dynes/cm. Using the force constants, the frequencies are recalculated and the calculated values agree with the observed values satisfactorily. The in-plane vibrational frequencies of deuterated boric acid are also calculated and again satisfactory agreement with the observed values is found.

Shaping of adherends in bonded joints

A method of analysis of adhesive bonded joints with arbitrary adherend shapes is developed and applied to their design for efficient load transfer. The formulation of the simplified physical model is essentially one dimensional. An efficient numerical procedure is developed and its applicability is demonstrated. Guide lines are indicated for choosing suitable shape functions.

Influence of Starch Polysaccharide on the Remolded Properties of 2 Indian clay Samples

The reported presence in marine clays and the recognized role of polysaccharide as a bonding agent provided the motivation to examine the role of starch polysaccharide in the remoulded properties of nonswelling (kaolinite) and swelling (bentonite) groups of clays. The starch polysaccharide belongs to a group of naturally occurring, large-sized organic molecules (termed polymers) and is built up by extensive repetition of simple chemical units called repeat units. The results of the study indicate that the impact of the starch polysaccharide on the remoulded properties of clays is dependent on the mineralogy of the clays. On addition to bentonite clay, the immensely large number of segments (repeat units) of the starch polysaccharide create several polymer segment - clay surface bonds that cause extensive aggregation of the bentonite units layers. The aggregation of the bentonite unit layers greatly curtails the available surface area of the clay mineral for diffuse ion layer formation. The reduction in diffuse ion layer thickness markedly lowers the consistency limits and vane shear strength of the bentonite clay. On addition to kaolinite, the numerous polymer segment - clay surface bonds enhance the tendency of the kaolinite particles to flocculate. The enhanced particle flocculation is responsible apparently for a small to moderate increase in the liquid limit and remoulded undrained strength of the nonswelling clay.

A Molecular Dynamics Study of Atomic Correlations in Glassy BzS3t

Glassy B&, the parent compound of the superionic conductor LiI-Li&B& has been studied by the molecular dynamics technique using a new potential model. The results suggest that the glass is made up of local units of four-membered B2S2 rings bridged by sulfur atoms, leading to a chainlike structure. Various pair correlation functions have been analyzed, and the B2Sz rings have been found to be planar. The calculated neutron structure factor shows a peak at 1.4 A-' which has been attributed to B-B correlations at 5.6 A. The glass transition temperature of the simulated system has been calculated to be around 800 K.

A Flexible Class of Regenerating Codes for Distributed Storage

In the distributed storage setting introduced by Dimakis et al., B units of data are stored across n nodes in the network in such a way that the data can be recovered by connecting to any k nodes. Additionally one can repair a failed node by connecting to any d nodes while downloading at most beta units of data from each node. In this paper, we introduce a flexible framework in which the data can be recovered by connecting to any number of nodes as long as the total amount of data downloaded is at least B. Similarly, regeneration of a failed node is possible if the new node connects to the network using links whose individual capacity is bounded above by beta(max) and whose sum capacity equals or exceeds a predetermined parameter gamma. In this flexible setting, we obtain the cut-set lower bound on the repair bandwidth along with a constructive proof for the existence of codes meeting this bound for all values of the parameters. An explicit code construction is provided which is optimal in certain parameter regimes.

Data compression by linear prediction for storage and transmission of EEG signals

The EEG time series has been subjected to various formalisms of analysis to extract meaningful information regarding the underlying neural events. In this paper the linear prediction (LP) method has been used for analysis and presentation of spectral array data for the better visualisation of background EEG activity. It has also been used for signal generation, efficient data storage and transmission of EEG. The LP method is compared with the standard Fourier method of compressed spectral array (CSA) of the multichannel EEG data. The autocorrelation autoregressive (AR) technique is used for obtaining the LP coefficients with a model order of 15. While the Fourier method reduces the data only by half, the LP method just requires the storage of signal variance and LP coefficients. The signal generated using white Gaussian noise as the input to the LP filter has a high correlation coefficient of 0.97 with that of original signal, thus making LP as a useful tool for storage and transmission of EEG. The biological significance of Fourier method and the LP method in respect to the microstructure of neuronal events in the generation of EEG is discussed.

Some Basic Aspects of Reaction Engineering of Precipitation Processes

Analysis of precipitation reactions is extremely important in the technology of production of fine particles from the liquid phase. The control of composition and particle size in precipitation processes requires careful analysis of the several reactions that comprise the precipitation system. Since precipitation systems involve several, rapid ionic dissociation reactions among other slower ones, the faster reactions may be assumed to be nearly at equilibrium. However, the elimination of species, and the consequent reduction of the system of equations, is an aspect of analysis fraught with the possibility of subtle errors related to the violation of conservation principles. This paper shows how such errors may be avoided systematically by relying on the methods of linear algebra. Applications are demonstrated by analyzing the reactions leading to the precipitation of calcium carbonate in a stirred tank reactor as well as in a single emulsion drop. Sample calculations show that supersaturation dynamics can assume forms that can lead to subsequent dissolution of particles that have once been precipitated.

An economical method for direct numerical simulation studies of transitional round jets

A pseudo-spectral method based on Fourier expansions in a Cartesian coordinate system is shown to be an economical method for direct numerical simulation studies of transitional round jets, Several characteristics of the solutions are presented to establish the validity of the solutions in spite of the unnatural choices. We show that neither periodicity, nor the use of a Cartesian system have adversely affected the simulations, Instead, there are benefits in terms of ease of computing and lack of the usual restrictions due to grid structure near the jet axis. By computing the simultaneous evolution of passive scalers, the process of reaction in round jet burners, between a fuel-laden jet and an ambient oxidizer, was also simulated. Some typical solutions are shown and then the results of analysis of these data are summarized. (C) 2001 Elsevier Science Ltd, All rights reserved.

Phase transitions in the anchored organic bilayers of long-chain alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4; n=12, 16, 18

The single perovskite slab alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4, n = 12, 16, 18, display two phase transitions, just above room temperature, associated with changes in the alkylammonium chains. We have followed these two phase transitions using scanning calorimetry, X-ray powder diffraction, and IR and Raman spectroscopies. We find the first phase transition to be associated with symmetry changes arising from a dynamic rotational disordering of the ammonium headgroup of the chain whereas the second transition, the melting of the chains in two dimensions, is characterized by an increased conformational disorder of the methylene units of the alkyl chains. We examine these phase transitions in light of the interesting optical properties of these materials, as well as the relevance of these systems as models for phase transitions in lipid bilayers.

Cu(II)-azide polymers with various molar equivalents of blocking diamine ligands: synthesis, structures, magnetic properties with DFT studies

Four new neutral copper-azido polymers [Cu(4)(N(3))(8)(Me-hmpz)(2)](n) (1), [Cu(4)(N(3))(8)(men)(2)](n) (2), [Cu(5)(N(3))(10)(N,N-dmen)(2)](n) (3) and [Cu(5)(N(3))(10)(N,N'-dmen)(5)](n) (4) [Me-hmpz = 1-methylhomopiperazine; men = N-methylethylenediamine; N, N-dmen = N, N-dimethylethylenediamine and N, N'-dmen = N, N'-dimethylethylenediamine] have been synthesized by using various molar equivalents of the chelating diamine ligands with Cu(NO(3))(2)center dot 3H(2)O and an excess of NaN(3). Single-crystal X-ray structures show that the basic asymmetric units of 1 and 2 are very similar, but the overall 1D structures were found to be quite different. Complex 3 with a different composition was found to be 2D in nature, while the 1D complex 4 with 1 : 1 metal to diamine ratio presented several new structural features. Cryomagnetic susceptibility measurements over a wide range of temperature were corroborated with density functional theory calculations (B3LYP functional) performed on the complexes 1-3 to provide a qualitative theoretical interpretation of their overall magnetic behavior.

Influence of Phase Connection and Terminal Conditions on Natural Frequencies of Three-Phase Transformer Windings

With the increasing use of extra high-voltage transmission in power system expansion, the manufacturers of power apparatus and the electric utilities are studying the nature of overvoltages in power systems due to lightning and, in particular, switching operations. For such analyses, knowledge of the natural frequencies of the windings of transformers under a wide variety of conditions is important. The work reported by the author in a previous paper is extended and equivalent circuits have been developed to represent several sets of terminal conditions. These equivalent circuits can be used to determine the natural frequencies and transient voltages in the windings. Comparison of the measured and the computed results obtained with a model transformer indicates that they are in good agreement. Hence, this method of analysis provides a satisfactory procedure for the estimation of natural frequencies and transient voltages in transformer windings.

Ship-Mounted Real-Time Surface Observational System on board Indian Vessels for Validation and Refinement of Model Forcing Fields

A network of ship-mounted real-time Automatic Weather Stations integrated with Indian geosynchronous satellites Indian National Satellites (INSATs)] 3A and 3C, named Indian National Centre for Ocean Information Services Real-Time Automatic Weather Stations (I-RAWS), is established. The purpose of I-RAWS is to measure the surface meteorological-ocean parameters and transmit the data in real time in order to validate and refine the forcing parameters (obtained from different meteorological agencies) of the Indian Ocean Forecasting System (INDOFOS). Preliminary validation and intercomparison of analyzed products obtained from the National Centre for Medium Range Weather Forecasting and the European Centre for Medium-Range Weather Forecasts using the data collected from I-RAWS were carried out. This I-RAWS was mounted on board oceanographic research vessel Sagar Nidhi during a cruise across three oceanic regimes, namely, the tropical Indian Ocean, the extratropical Indian Ocean, and the Southern Ocean. The results obtained from such a validation and intercomparison, and its implications with special reference to the usage of atmospheric model data for forcing ocean model, are discussed in detail. It is noticed that the performance of analysis products from both atmospheric models is similar and good; however, European Centre for Medium-Range Weather Forecasts air temperature over the extratropical Indian Ocean and wind speed in the Southern Ocean are marginally better.

Identification of source of heavy metal contamination in a site - a case study

Accidental spills and improper disposal of industrial effluent/sludge containing heavy metals onto the open land or into subsurface result in soil and water contamination. Detailed investigations are carried out to identify the source of contamination of heavy metals in an industrial suburb near Bangalore in India. Detailed investigation of ground water and subsurface soil analysis for various heavy metals has been carried out. Ground water samples were collected in the entire area through the cluster of borewells. Subsurface soil samples were collected from near borewells which were found to contain heavy metals. Water samples and soils samples (after acid digestion) were analysed as per APHO-standard method of analysis. While the results of Zn, Ni and Cd showed that they are within allowable limits in the soil, the ground water and soils in the site have concentration of Cr+6 far exceeding the allowable limits (up to 832 mg/kg). Considering the topography of the area, ground water movement and results of chromium concentration in the borewells and subsurface it was possible to identify the origin, zone of contamination and the migration path of Cr+6. The results indicated that the predominant mechanism of migration of Cr+6 is by diffusion.

The exploration of Kemp's triacid (KTA) as the core for the synthesis of 3-fold symmetric 2(3)-cyclophane, 2(2)-cyclophane and novel linker directed designs

For the first time, two units of KTA have been linked to three units of cyst-di-OMe. The reaction is noteworthy since it involves the formation of six amide bonds leading to a three-fold symmetric 23-cyclophane (3) harboring a cluster of three S-S bridges. The major product is a di-imide (4), arising from the interaction of a cystine NH with a neighbouring activated ester. A third reaction of tethering KTA with a single cyst-di-OMe unit afforded the flexible compound 6 and, with benzidine, the novel linker directed 7 with orthogonally disposed anchor modules.