Why Solve the Hamiltonian Constraint in Numerical Relativity?

The indefinite sign of the Hamiltonian constraint means that solutions to Einstein's equations must achieve a delicate balance--often among numerically large terms that nearly cancel. If numerical errors cause a violation of the Hamiltonian constraint, the failure of the delicate balance could lead to qualitatively wrong behavior rather than just decreased accuracy. This issue is different from instabilities caused by constraint-violating modes. Examples of stable numerical simulations of collapsing cosmological spacetimes exhibiting local mixmaster dynamics with and without Hamiltonian constraint enforcement are presented.Comment: Submitted to a volume in honor of Michael P. Ryan, Jr. Based on talk given at GR1

Impact of Changes in Management Regime on Fisheries: A Temporal Case Study of Dhir Beel in Assam

The floodplain wetlands (beels) constitute important fisheries resources of Assam. These resources are managed through a complex social framework. The state of this management regime determines the level and sustainable utilization with implications on fisheries and livelihoods. To find the impact of such management regime, a case study has been undertaken in the Dhir beel of Assam. The impact of the change in the management regime on the sustainability of fisheries and livelihoods of fishers has been evaluated. This change in the management regime has been due to immigration of a large number of people from the nearby areas since 1985. The study has compared the scenario that existed ‘before 1985’ (data of 1982-84) and “after 1985’ (data of 2004). There has been a significant increase in the fishing pressure with new fishing practices (1.5 to 5 times) as well as intensity of effort (3 to 7 times). The weakening of the regulating institutions has led to irrational practices which in turn, have resulted in a decline (22.32%) in the production and productivity of the beel. The decline has been more (31.79%) in terms of value than production of fish, indicating a definite decline in the quality of the fish available in these resources. In the changed scenario, the economics of the management has gone against the resource managers as they are to spend more money on monitoring and enforcing the rules. The livelihood of the fishers has also declined with the high degree of sharing of fish among the fishers.Resource /Energy Economics and Policy,

Fluctuation Cumulant Behavior for the Field-Pulse Induced Magnetisation-Reversal Transition in Ising Models

The universality class of the dynamic magnetisation-reversal transition, induced by a competing field pulse, in an Ising model on a square lattice, below its static ordering temperature, is studied here using Monte Carlo simulations. Fourth order cumulant of the order parameter distribution is studied for different system sizes around the phase boundary region. The crossing point of the cumulant (for different system sizes) gives the transition point and the value of the cumulant at the transition point indicates the universality class of the transition. The cumulant value at the crossing point for low temperature and pulse width range is observed to be significantly less than that for the static transition in the same two-dimensional Ising model. The finite size scaling behaviour in this range also indicates a higher correlation length exponent value. For higher temperature and pulse width range, the transition seems to fall in a mean-field like universality class.Comment: 5 pages, 8 eps figures, thoroughly revised manuscript with new figures, accepted in Phys. Rev. E (2003

Late Pleistocene stratigraphy and paleoceanography in the Chukchi Plateau, western Arctic Ocean

第3回極域科学シンポジウム/特別セッション「これからの北極研究」11月28日（水） 国立極地研究所 2階大会議

Phenomenology of the Gowdy Universe on T3×RT^3 \times R

Numerical studies of the plane symmetric, vacuum Gowdy universe on $T^3 \times R$ yield strong support for the conjectured asymptotically velocity term dominated (AVTD) behavior of its evolution toward the singularity except, perhaps, at isolated spatial points. A generic solution is characterized by spiky features and apparent ``discontinuities'' in the wave amplitudes. It is shown that the nonlinear terms in the wave equations drive the system generically to the ``small velocity'' AVTD regime and that the spiky features are caused by the absence of these terms at isolated spatial points.Comment: 19 pages, 21 figures, uses Revtex, psfi

Study of wear test on hybrid material reinforced Epoxy based Composites

In the present work, the hybrid nanomaterial such as Graphene – Multiwalled carbon nanotube reinforced epoxy composites are fabricated with dif ferent weight fraction of the reinforcement and are subjected to wear test. The mechanical properties of these composites are investigated and found posses decrease in wear rate, as the increased in weight fraction of the reinforcement there is reducing wear rate compared to the based matrix fabricated using the same process

Dimensional instability studies in machining of Inconel 718 nickel based superalloy as applied to aerogas turbine components

Inconel 718 alloy is used extensively in aerogas turbines and this alloy is most difficult to machine and highly prone to dimensional instability after machining. Such detrimental phenomenon poses an enormous problem in engine assembly and affects structural integrity. This paper highlights the systematic research work undertaken to study the plastic deformation characteristics of Inconel 718, and the effect of process variables on machined surface, subsurface, and dimensional instability. Also illustrated is the technique developed for simultaneous optimization of several process variables such as cutting speed, feed, depth of cut, rake angle, and tool nose radius to control the residual stresses and dimensional instability within the acceptable tolerance band of the component. Prediction equations were developed for residual stress, dimensional instability, tool life, surface finish, and material removal rate. Predicted data were validated experimentally. This paper also presents the qualitative and quantitative data on dimensional instability with specific case studies of jet engine components, and it clearly illustrates the approach followed to develop a technique to control such detrimental effect

Scoping biological indicators of soil quality Phase II. Defra Final Contract Report SP0534

This report presents results from a field assessment of a limited suite of potential biological indicators of soil quality to investigate their suitability for national-scale soil monitoring

IRRIGATION AND INTEGRATED NUTRIENT MANAGEMENT IN CASTOR (RICINUS COMMUNIS L.)

          The results of a two year's field experiment conducted at Junagadh (Gujarat) on clayey soils to evaluate the effect of irrigation (0.4 and 0.8 IW:CPE), biofertilizer (control and seed treatment with Pseudomonas striata), nitrogen (50, 75 and 100 kg N/ha) and phosphorus (0, 25 and 50 kg P2O5/ha) revealed that irrigation scheduled at 0.8 IW:CPE, seed inoculation with phosphate solubilizing bacteria, application of 100 kg N/ha and 50 kg P2O5/ha significantly increased growth and yield attributes, and yield of castor as well as also proved economical in terms of net realization.

Length and time scale divergences at the magnetization-reversal transition in the Ising model

The divergences of both the length and time scales, at the magnetization- reversal transition in Ising model under a pulsed field, have been studied in the linearized limit of the mean field theory. Both length and time scales are shown to diverge at the transition point and it has been checked that the nature of the time scale divergence agrees well with the result obtained from the numerical solution of the mean field equation of motion. Similar growths in length and time scales are also observed, as one approaches the transition point, using Monte Carlo simulations. However, these are not of the same nature as the mean field case. Nucleation theory provides a qualitative argument which explains the nature of the time scale growth. To study the nature of growth of the characteristic length scale, we have looked at the cluster size distribution of the reversed spin domains and defined a pseudo-correlation length which has been observed to grow at the phase boundary of the transition.Comment: 9 pages Latex, 3 postscript figure