The role of shear in dissipative gravitational collapse

In this paper we investigate the physics of a radiating star undergoing dissipative collapse in the form of a radial heat flux. Our treatment clearly demonstrates how the presence of shear affects the collapse process; we are in a position to contrast the physical features of the collapsing sphere in the presence of shear with the shear-free case. By employing a causal heat transport equation of the Maxwell-Cattaneo form we show that the shear leads to an enhancement of the core temperature thus emphasizing that relaxational effects cannot be ignored when the star leaves hydrostatic equilibrium.Comment: 15 pages, To appear in Int. J. Mod. Phys.

The dynamics and control of large flexible space structures, 2. Part A: Shape and orientation control using point actuators

The equations of planar motion for a flexible beam in orbit which includes the effects of gravity gradient torques and control torques from point actuators located along the beam was developed. Two classes of theorems are applied to the linearized form of these equations to establish necessary conditions for controlability for preselected actuator configurations. The feedback gains are selected: (1) based on the decoupling of the original coordinates and to obtain proper damping, and (2) by applying the linear regulator problem to the individual model coordinates separately. The linear control laws obtained using both techniques were evaluated by numerical integration of the nonlinear system equations. Numerical examples considering pitch and various number of modes with different combination of actuator numbers and locations are presented. The independent model control concept used earlier with a discretized model of the thin beam in orbit was reviewed for the case where the number of actuators is less than the number of modes. Results indicate that although the system is controllable it is not stable about the nominal (local vertical) orientation when the control is based on modal decoupling. An alternate control law not based on modal decoupling ensures stability of all the modes

'Slippage' : The Bane of Rural Drinking Water Sector (A Study of Extent and Causes in Andhra Pradesh)

Slippage is one of the main bottlenecks of achieving full coverage of water and sanitation services in India. Slippage is the term often used to reflect unsustainable service delivery of water, sanitation and hygiene (WASH) services, especially in rural areas. Off late slippage is attracting attention at the policy level though slippage is as old as the coverage of water supply services. This paper makes an attempt to identify the causes of slippage in a systematic manner. The broad objectives of the paper include : i) assess the extent of slippage at the national and state level; ii) identify the causes of slippage at various levels; and iii) provide some pointers for policy based on the analysis. The extent of slippage is quite substantial even at the aggregate level. The situation is alarming in some of the states where the extent of slippage is as high as 60 percent. Our analysis at the national, state and habitation levels suggests strongly that policy makers should look beyond the often repeated supply sided strategies. As evident from the experience of Andhra Pradesh, the demand side and governance factors play an equally, if not more, important role in addressing the sustainability issues. So far the experiences are that large investments in water sector would not automatically lead to increase in coverage. The sector also needs a sound policy and capacity so that money is spent effectively and leads to increased water security. The policy should also address resource sustainability and behavioural change goals instead of relying upon a one-sided target driven approach. These aspects are highlighted in the proposed guidelines and their effective implementation needs to be ensured.slippage, India, supply side strategies, policy

The dynamics and control of large flexible space structures, 8

A development of the in plane open loop rotational equations of motion for the proposed Spacecraft Control Laboratory Experiment (SCOLE) in orbit configuration is presented based on an Eulerian formulation. The mast is considered to be a flexible beam connected to the (rigid) shuttle and the reflector. Frequencies and mode shapes are obtained for the mast vibrational appendage modes (assumed to be decoupled) for different boundary conditions based on continuum approaches and also preliminary results are obtained using a finite element representation of the mast reflector system. The linearized rotational in plane equation is characterized by periodic coefficients and open loop system stability can be examined with an application of the Floquet theorem. Numerical results are presented to illustrate the potential instability associated with actuator time delays even for delays which represent only a small fraction of the natural period of oscillation of the modes contained in the open loop model of the system. When plant and measurement noise effects are added to the previously designed deterministic model of the hoop column system, it is seen that both the system transient and steady state performance are degraded. Mission requirements can be satisfied by appropriate assignment of cost function weighting elements and changes in the ratio of plant noise to measurement noise