Publication11

The electron spin resonance (esr) of C60.Ox and C60.HMTTEF (hexamethylentetratellurafulvalene) has been investigated at 9.36 GHz as a function of temperature, T (298 ≥ T ≥ 4 K). C60.Ox shows an esr absorption of equal 'g' value to that of C6 0 exposed to O2 and light but is more intense. The C60 in its pure form is in a singlet state. The impurity sites introduced by O2 produce the esr absorption. The Curie - Weiss plots of inverse esr absorption intensity versus temperature indicate an antiferromagnetic Θ ≈ 50 for air exposed C60 and 90K for C60Ox. From the esr intensity at room temperature, the calculated number of free spins (S = 1/2) is ≈ 1/3 per mole of C60.Ox. In case of C60.HMTTEF, there is a very weak esr absorption at room temperature suggesting that the room temperature form is diamagnetic with very small charge transfer between C6 0 and HMTTEF. This conclusion is consistent with the structure and magnetic susceptibility of this cocrystal. As the temperature is lowered, the equilibrium: AD <=> A*- + D*+ is displaced towards the formation of free radical species, A*- and D*+.

Fiber pull-out resistance is an important mechanism of energy absorption during the failure of fiber-reinforced composite materials. This paper deals with axial stress distribution in the fiber during a pull-out. The frictional constraint between the fiber and the matrix is modeled with a perturbed Lagrangian approach and Coulomb's law of friction. Stress distribution has been determined for three cases, using the finite element method. The first case deals with the pull out of a fully embedded fiber. The second determines the stress distribution during fiber pull-out in the presence of a broken-embedded fiber. The third model attempts to solve the pull out of a coated fiber. The results for the first case compares favorably with those in existing literature. A local “pinching” effect, due to the matrix collapse behind the pulled fiber, is brought out clearly by this model. The second study indicates that the "plug" effect may not be significant in affecting the stress distribution. Lastly, the effects of coating stiffness and thickness are investigated. © 1996 ASME.

In the context of large deformation analysis for metal forming processes a new one-pass approach for the frictional contact is proposed. This approach eliminates the short comings of traditional one-pass and two-pass approaches both from the constraint requirement and solution convergence points of view. Implemented in an updated Lagrangian framework with the Perturbed Lagrangian formulation of Ju and Taylor for non-linear frictional contact, a patch test and typical examples have been worked out to prove the validity of the proposed approach. It is observed that a finer surface discretization of the slave and master surfaces is no longer needed to enforce contact constraint.

In this paper, the results of an experimental programme carried out on model pile groups have been reported. Lateral load tests were carried out on instrumented model aluminum pipe piles embedded in a marine clay at embedment depth ratios of 20, 30 and 40. Two pile and three pile groups were arranged in series and parallel configurations with varied spacing between the piles. The test results reveal that the capacities increase with spacing between the piles up to a certain value. Further there is an improvement in lateral capacities with increase in the embedment. Bending moments measured along the length of the piles indicate higher values for the rear piles. These test results obtained are found to be fairly in good agreement with the published results.

The paper investigates the influence of propellant composition, fuel, oxidizer, and binder content on ducted rocket performance as well as the influence of primary chamber fuel to oxidizer ratio and secondary chamber fuel to air ratio. Also the influence of some geometric and flight parameters like air inlet angle, inlet cross-section and flight Mach number can be treated. Primary and secondary combustion chamber reaction products composition and temperatures are computed, too. A simple model of a solid propellant ramrocket based on chemical equilibrium thermodynamics is developed by dividing the ducted rocket is into seven sections. These are characteristic for flight conditions like flight Mach number, flight velocity and atmospheric conditions, exit conditions of the air inlets, gas generator nozzle exit conditions, secondary combustion chamber conditions and the corresponding secondary combustion chamber nozzle throat and exit conditions. The results show the appearance of large amounts of C(gr) and hydrogen together with metal oxides and metal carbides in the exhaust gas of the primary combustor. The results also show that there is a second maximum in the dependence of primary chamber combustion temperature on fuel to air ratio. The flight range was up to 40 percent higher for propellants which contained high energy ingredients like boron and cubane as compared to a non-metallized propellant based on HTPB for a sea level mission.

The novel compounds Sr13NbAs11 and Eu13NbAs11 have been synthesized from SrAs, Eu5As4, Sr, Nb and As in niobium ampoules at 1173-1273 K. The tetragonal tI 200 phases are defect variants of the Ca14AlSb11 structure (space group I41/acd (no. 142); Sr13□NbAs11: a = 1649.8(2) and c = 2214.1(3); Eu13□NbAs11: a = 1632.9(8) and c = 2197.3(8) pm; Z = 8). The structures are built from the cations Sr2+, and Eu2+, respectively, and from the anions [NbAs4]7-, As3-, and the linear polyanion [As3]7-. This polyanion (isosteric to I3-) is asymmetric with d(As-As) = 273.0 and 346.0pm (Sr) and 274.7 and 335.6pm (Eu), respectively. The bond lengths in the tetrahedral anions are d(Nb-As) = 250.8 and 251.1 pm. The complete structural arrangement is related to that of Cu2O by forming two interpenetrating networks. The oxygen atoms are substituted by niobium centered As4 tetrahedra, and the Cu atoms are substituted by As6 octahedra (centered by Sr, Eu). The central As atoms of the polyanions connect the nets. Both As networks are enveloped by the remaining cations forming cubes, tetragonal antiprisms and capped trigonal prisms. © Johann Ambrosius Barth 1996.

Variable structure (VS) stabilizers possess the advantages of better transient response, insensitivity to plant parameter variations, etc. In general, variable structure controls involve measurements from all the states, which is not possible in a multimachine power system (MMPS). In this paper, the switching planes for the variable structure stabilizers are selected in such a way that computation of switching planes involves local state variables only. The coefficients of the switching plane equation are determined using the Riccati equation approach. Through the approximation of neglecting non-diagonal blocks of the state space matrix, at the design stage, a decentralized Variable Structure stabilizer (VS stabilizer) is obtained. To accept the switching plane so obtained, a check of the closed loop eigenvalues is made with the actual state space matrix. After computation of the switching plane, the variable gains are also selected in such a way that control signal computation involves only local state variables. This is possible as the gains of nonlocal state variables are small compared with local variables. The response of the system with variable structure stabilizers indicates that the system performance is improved. Copyright © 1996 Elsevier Science Ltd.

Maximizing bandwidth utilization and providing performance guarantees, in the context of multimedia networking, are two incompatible goals. Heterogeneity of the multimedia sources calls for effective traffic control schemes to satisfy their diverse Quality of Service (QoS) requirements. These include admission control at connection set up, traffic control at the source ends and efficient scheduling schemes at the switches. The emphasis in this paper is on traffic control at the source end. Most multimedia sources are bursty in nature. Traffic shapers have been mainly studied hitherto from the point of view of their effectiveness in smoothing the burstiness. The Leaky Bucket (LB) scheme, to cite an example, is a mean rate policer smoothing at the token generation rate. Studies on bursty sources show that burstiness promotes statistical multiplexing at the cost of possible congestion. Smoothing, on the other hand, helps in providing guarantees at the cost of utilization. Thus need for a flexible scheme which can provide a reasonable compromise between utilization and performance is imminent. Recent studies have also questioned the suitability of LB for policing real-time traffic due to the excessive delays. We argue for a policy which is less stringent on short term burstiness than the LB. We propose a new traffic shaper which can adjust the burstiness of the input traffic to obtain reasonable bandwidth utilization while maintaining statistical service guarantees. The performance study is conducted in two parts. In the first part, we study the effect of varying the shaper parameters on the input characteristics. In the second part, we dimension our scheme and a LB equivalently and compare the mean and peak rate policing behavior with delay and loss as the performance parameters. Adopting a less stringent attitude towards short term burstiness is shown to result in considerable advantage while policing real-time traffic. Future research possibilities in this topic are explored. © 1996 Elsevier Science B.V. All rights reserved.

Logical clocks and vector clocks were proposed in the past to capture causality between events of different processes of a distributed computation. However, these clocks could not capture intraprocess concurrency. Later, bitmatrix clocks and hierarchical clocks were developed to capture interprocess concurrency as well as intraprocess concurrency. The major disadvantages of these clocks are the associated storage and communication overheads. To overcome these disadvantages, the authors introduce the concept of difference clocks. The difference clocks maintain minimal information about the differences among various local clocks. It is shown that they can be used to reconstruct the bit-matrix clocks and result in substantial reduction in storage space and communication overhead. © IEE, 1996.

A finite element method is used to study the effect of flow past a circular cylinder with an integral wake splitter. A fractional step algorithm is employed to solve the Navier-Stokes and Energy equations with a Galerkin weighted residual formulation. The vortex shedding process is simulated and the effect of splitter addition on the time period of shedding is studied at a Reynolds number of 200 and a blockage ratio of 0.25. The effect of splitter and the Strouhal number and heat transfer augmentation per unit pressure drop has been investigated.

A cycle C passing through two specific vertices s and t of a biconnected graph is said to be an st-ambitus if its bridges do not interlace in some special way. We present algorithms for st-ambitus for planar biconnected graphs, which are much simpler than the one known for general graphs [MT]. Our algorithm runs in O(n) time on a sequential machine and (log n) parallel time using O(n/log n) processors on an EREW PRAM.

Solutions, within the framework of linear uncoupled thermoelasticity, are presented for certain problems of flexure of composite laminates. Benchmark numerical results, useful for the validation or otherwise of approximate laminate models, are tabulated. Finally, these results are used to examine the accuracy of the classical lamination theory based on Kirchhoff's hypothesis. Copyright © 1996 Elsevier Science Limited.

Level of service (LOS) is a qualitative measure of traffic flow from the users' perspectives. This paper presents a new methodology to find LOS of urban roads by taking users' perceptions and analyzing them through fuzzy set theory. Speed, volume and acceleration noise (defined as the standard deviation of accelerations) are taken as the evaluating criteria. The six categories of LOS A to F of the Highway Capacity Manual are assigned linguistic terms. The users have been divided into two age groups. Their perceptions, recorded through primary surveys, have been used to establish membership functions for different fuzzy sets and to arrive at importance factors assigned to them. Four important corridors of movement in the Metropolitan City of Madras formed the backdrop of the study. © 1996 OPA (Overseas Publishers Association) Amsterdam B.V. Published in The Netherlands under license by Gordon and Breach Science Publishers.

Coral islands are tiny and are scattered in deep seas throughout the world, hundreds of kilometres away from the mainland. For construction activities in these islands, coral shingles and coral sand are the main locally available materials. A review indicates that only a few investigations have been undertaken on the properties of coral aggregates and concrete made with them. This paper discusses the results of a systematic investigation of the physical, chemical and mechanical properties of coral shingles and coral sand. Their suitability as aggregate for concrete making has been studied through comparison with the results of tests on conventional crushed granite aggregate and river sand. The workability, density and compressive strength characteristics of different nominal mixes of conventional aggregate concrete and coral concrete with various water-cement ratios have been compared and discussed.

With the growth in multimedia applications, it is necessary to understand the characteristics of these applications and derive the Quality of Service (QoS) parameters. The multiple media streams and the synchronization across the media underline each application and its QoS requirements. These are normally negotiated upfront with the network service provider in the form of hard or soft guarantees. But the flow sequence of the streams, their interrelationships and the QoS may be affected by the changes made by the network service provider or the user interaction. This necessitates a systematic study of generic requirements of typical multimedia applications and specification of generic solutions in the form of protocol services in any network. This paper addresses these concerns by studying the network QoS requirements of multimedia presentation application. We use the idea of streams to characterize the multimedia application. An application sub-layer protocol called Multimedia Application Protocol (MMAP), which uses runtime support algorithms and provides services for QoS negotiation and for handling user interaction, is proposed. We present an example from orchestrated multimedia applications to show as to how the MMAP services can be used for implementing distributed multimedia applications.

This paper presents a broadband multiple access protocol for bidirectional hybrid fiber-coax (HFC) networks. The Adaptive Digital Access Protocol (ADAPt+) supports a full range of subscriber services via HFC networks with tree and branch topologies. The protocol efficiently accommodates different circuit- and packet-based access modes, such as synchronous transfer mode (STM), asynchronous transfer mode (ATM), and inherently variable length (VL) native data (for example, the Internet protocol [IP]). ADAPt+ allocates the available bandwidth efficiently and adapts to the changing traffic mix. In addition, the paper describes the medium access control (MAC) protocol for upstream and multiplexing/demultiplexing for downstream communication, its applicability to STM, ATM, and other native data applications, and its performance with respect to throughput, latency, and bandwidth efficiency. While discussed in the context of an HFC network, many aspects of ADAPt+ have relevance to wireless, fiber to the curb (FTTC), and fiber to the home (FTTH).

The problem of selecting the variables to be measured in order to maximize process reliability was tackled in our previous articles (Ali and Narasimhan, 1993, 1995). In this article, this approach is extended to the optimal design of sensor networks for bilinear processes. Diverse processes, such as a mineral beneficiation plant, a separation system of a synthetic juice plant, and a crude preheat train of a refinery are used to illustrate the utility of this approach.

In the field of robotic control, impedance control is seen as an efficient method of position and force control during operations where there is a dynamic interaction between the robot and the environment. An impedance control strategy using an electrohydraulic servosystem for such tasks is described. The impedance of the robotic manipulator is varied by varying the damping in the hydraulic servosystem appended to the manipulator, which acts as a controller in the physical domain. Theoretical and experimental investigations carried out on a typical system are described. Bond graph as well as block diagram approaches are used for analysis of the system. Copyright © 1996 Elsevier Science Ltd.

This paper presents a numerical method of evaluating view factors between planar surfaces which is computationally efficient and quite general to program on a computer. The method, which is based on Gaussian quadrature to perform the contour integration is extended to surfaces with curved boundaries. The performance of various quadrature formulas viz. trapezoidal, Simpson and Gaussian, have been compared for performance by applying them to sample problems. The Gaussian quadrature method with nonlinear transformation to map the boundary has been found to be the most accurate, computationally faster and very general. As an application, the shape factor between two elliptic surfaces has been evaluated.

Planning for urban solid waste management within the framework of sustainable development raises several intra-and inter-generational issues such as public health, livelihood of actors in the informal recycling sector, present and future cost to society, conservation of resources both renewable and nonrenewable, and environmental impacts of waste disposal. It is essential that planners seek to address the above issues 'interactively' by exploring various 'soft' alternatives, instead of 'preactively' extending conventional 'hard' solutions. Such an integrated approach, however, should be developed through consensus among various actors. This paper proposes a Critical Operational Research (COR) framework to facilitate consensus/conflict resolution among actors, and also aid in learning. The nonlinear goal programming model developed within the COR framework provides a platform for discussion among actors involved in urban solid waste management. Its utility as a 'learning' tool is demonstrated by applying it to a typical metropolitan city in India. The exercise highlights the limitations of techno-managerial solutions usually adopted in developing countries, and the scope for the informal sector in urban solid waste management. Copyright © 1996 Elsevier Science Ltd.