Origin of the activation barrier in the process of hydrogen abstraction: the perturbation treatment

The perturbation treatment previously given is extended to explain the process of hydrogen abstraction from the various hydrogen donor molecules by the triplet nπ* state of ketones or the ground state of the alkyl or alkoxy radical. The results suggest that, as the ionization energy of the donor bonds is decreased, the reaction is accelerated and it is not influenced by the bond strength of the donor bonds. The activation barrier in such reactions arises from a weakening of the charge resonance term as the ionization energy of the donor bond increases.

Micromechanisms of damage in a hypereutectic Ti-6Al-4V-B alloy

The tensile stress–strain response and fracture in a hypereutectic Ti–6Al–4V–1.7B (weight percent) alloy were investigated by employing interrupted tensile tests combined with acoustic emission measurements, with the aim to identify the cause for the observed low ductility in this alloy. These tests were complemented with microscopy. The alloy contains TiB whiskers of different length scales, the majority of which include micro-whiskers ( 5–10 μm length) and a few primary-whiskers ( 200–300 μm length). Although the fracture of both types of whiskers occur during deformation, the former leads to a gradual decrease in the secant modulus whereas initiation of the latter leads to a drastic drop in the modulus along with failure of the specimen, limiting the ductility.

Origin of the activation barrier in the process of hydrogen abstraction: the perturbation treatment

The perturbation treatment previously given is extended to explain the process of hydrogen abstraction from the various hydrogen donor molecules by the triplet nπ* state of ketones or the ground state of the alkyl or alkoxy radical. The results suggest that, as the ionization energy of the donor bonds is decreased, the reaction is accelerated and it is not influenced by the bond strength of the donor bonds. The activation barrier in such reactions arises from a weakening of the charge resonance term as the ionization energy of the donor bond increases.

The perturbational treatment of the process of hydrogen abstraction by ketones

The change in energy during hydrogen abstraction by ketones is estimated for different electronic states as a function of the intermolecular orbital overlap employing perturbation theory. The results suggest that ketones preferentially undergo the in-plane reaction and abstract a hydrogen atom in their triplet nπ* state. For ketones where the triplet ππ* state lies below the triplet nπ* state, hydrogen abstraction can take place in the ππ* state owing to the crossing of the zero order reaction surfaces of the nπ* and ππ* states.

Understanding the folding process of synthetic polymers by small-molecule folding agents

Two acceptor containing polyimides PDI and NDI carrying pyromellitic diimide units and 1,4,5,8-naphthalene tetracarboxy diimide units, respectively, along with hexa(oxyethylene) (EO6) segments as linkers, were prepared from the corresponding dianhydrides and diamines. These polyimides were made to fold by interaction with specifically designed folding agents containing a dialkoxynaphtha-lene (DAN) donor linked to a carboxylic acid group. The alkali-metal counter-ion of the donor carboxylic acid upon complexation with the EO6 segment brings the DAN unit in the right location to induce a charge-transfer complex formation with acceptor units in the polymer backbone. This two-point interaction between the folding agent and the polymer backbone leads to a folding of the polymer chain, which was readily monitored by NMR titrations. The effect of various parameters, such as structures of the folding agent and polymer, and the solvent composition, on the folding propensities of the polymer was studied.

The process of technological innovations in small enterprises: the Indian way

This paper probes how two small foundries in Belgaum, Karnataka State, India, have achieved technological innovations successfully based on their technological capability and customer needs, enabling them to sail through the competitive environment. This study brought out that technically qualified entrepreneurs of both the foundries have carried out technological innovations, mainly due to their self-motivation and self-efforts. Changing product designs, as desired or directed by the customers, cost reduction, quality improvement and import substitution through reverse engineering are the characteristics of these technological innovations. These incremental innovations have enabled the entrepreneurs of the two foundries to enhance competitiveness, grow in the domestic market and penetrate the international market and grow in size over time.

The process of technological innovations in small enterprises: the Indian way

This paper probes how two small foundries in Belgaum, Karnataka State, India, have achieved technological innovations successfully based on their technological capability and customer needs, enabling them to sail through the competitive environment. This study brought out that technically qualified entrepreneurs of both the foundries have carried out technological innovations, mainly due to their self-motivation and self-efforts. Changing product designs, as desired or directed by the customers, cost reduction, quality improvement and import substitution through reverse engineering are the characteristics of these technological innovations. These incremental innovations have enabled the entrepreneurs of the two foundries to enhance competitiveness, grow in the domestic market and penetrate the international market and grow in size over time.

Rapid localization of damage using a circular sensor array and Lamb wave based triangulation

A damage detection and imaging methodology based on symmetry of neighborhood sensor path and similarity of signal patterns with respect to radial paths in a circular array of sensors has been developed It uses information regarding Limb wave propagation along with a triangulation scheme to rapidly locate and quantify the severity of damage without using all of the sensor data. In a plate like structure, such a scheme can be effectively employed besides full field imaging of wave scattering pattern from the damage, if present in the plate. This new scheme is validated experimentally. Hole and corrosion type damages have been detected and quantified using the proposed scheme successfully. A wavelet based cumulative damage index has been studied which shows monotonic sensitivity against the severity of the damage. which is most desired in a Structural Health Monitoring system. (C) 2010 Elsevier Ltd. All rights reserved.

Evaluation of damage in foam sandwich components of aircraft

Tn the current set of investigations foam sandwich panels and some components of an aircraft comprising of two layer Glass Fiber Reinforced Plastic(GFRP) face sheets of thickness 1mm each with polyurethene foam as filler of thickness 8mm were examined for detection of debonds and defects. Known defects were introduced in the panels in the form of teflon insert, full foam removal,half foam removal and edge delamination by inserting a teflon and removing it after curing. Two such panels were subjected to acoustic impact and analysis was carried out in both time and frequency domains. These panels were ultrasonically scanned to obtain C-SCAN images as reference to evaluate Acoustic Impact Test (AIT) results. In addition both Fokker bond testing and AIT(woodpecker) were carried out on the same panels and also some critical joints on the actual component. The results obtained from these tests are presented and discussed in this paper.

Evidence for supramolecular organization of alkane and surfactant molecules in the process of forming mesoporous silica

Investigations of the pore expansion in mesoporous silica in the presence of n-alkanes suggest a cooperative organization of the surfactant and alkane molecules, involving additivity of chain lengths.

Understanding the building-up process of three dimensional open-framework metal phosphates: Acid degradation of the 3D structures to lower dimensional structures

Acid degradation of 3D zinc phosphates primarily yields a one-dimensional ladder compound, an observation that is significant considering that the latter forms 3D structures on heating in water.

An Empirical Model of the Process of Synthesis of Multiple State Mechanical Devices

Automated synthesis of mechanical designs is an important step towards the development of an intelligent CAD system. Research into methods for supporting conceptual design using automated synthesis has attracted much attention in the past decades. The research work presented here is based on the processes of synthesizing multiple state mechanical devices carried out individually by ten engineering designers. The designers are asked to think aloud, while carrying out the synthesis. The ten design synthesis processes are video recorded, and the records are transcribed and coded for identifying activities occurring in the synthesis processes, as well as for identifying the inputs to and outputs from the activities. A mathematical representation for specifying multi-state design task is proposed. Further, a descriptive model capturing all the ten synthesis processes is developed and presented in this paper. This will be used to identify the outstanding issues to be resolved before a system for supporting design synthesis of multiple state mechanical devices that is capable of creating a comprehensive variety of solution alternatives could be developed.

Ultrasonic Lamb wave based monitoring of corrosion type of damage in plate using a circular array of piezoelectric transducers

In this paper we propose a concept and report experimental results based on a circular array of Piezoelectric Wafer Active Sensors (PWASs) for rapid localization and parametric identification of corrosion type damage in metallic plates. Implementation of this circular array of PWASs combines the use of ultrasonic Lamb wave propagation technique and an algorithm based on symmetry breaking in the signal pattern to locate and monitor the growth of a corrosion pit on a metallic plate. Wavelet time-frequency maps of the sensor signals are employed to obtain an insight regarding the effect of corrosion growth on the Lamb wave transmission in time-frequency scale. We present here a method to eliminate the time scale, which helps in identifying easily the signature of damage in the measured signals. The proposed method becomes useful in determining the approximate location of the damage with respect to the location of three neighboring sensors in the circular array. A cumulative damage index is computed from the wavelet coefficients for varying damage sizes and the results appear promising. Damage index is plotted against the damage parameters for frequency sweep of the excitation signal (a windowed sine signal). Results of corrosion damage are compared with circular holes of various sizes to demonstrate the applicability of present method to different types of damage. (C) 2011 Elsevier Ltd. All rights reserved.