Systematic Errors in Future Weak Lensing Surveys: Requirements and Prospects for Self-Calibration

We study the impact of systematic errors on planned weak lensing surveys and compute the requirements on their contributions so that they are not a dominant source of the cosmological parameter error budget. The generic types of error we consider are multiplicative and additive errors in measurements of shear, as well as photometric redshift errors. In general, more powerful surveys have stronger systematic requirements. For example, for a SNAP-type survey the multiplicative error in shear needs to be smaller than 1%(fsky/0.025)^{-1/2} of the mean shear in any given redshift bin, while the centroids of photometric redshift bins need to be known to better than 0.003(fsky/0.025)^{-1/2}. With about a factor of two degradation in cosmological parameter errors, future surveys can enter a self-calibration regime, where the mean systematic biases are self-consistently determined from the survey and only higher-order moments of the systematics contribute. Interestingly, once the power spectrum measurements are combined with the bispectrum, the self-calibration regime in the variation of the equation of state of dark energy w_a is attained with only a 20-30% error degradation.Comment: 20 pages, 9 figures, to be submitted to MNRAS. Comments are welcom

Recursive dynamics for flexible multibody systems using spatial operators

Due to their structural flexibility, spacecraft and space manipulators are multibody systems with complex dynamics and possess a large number of degrees of freedom. Here the spatial operator algebra methodology is used to develop a new dynamics formulation and spatially recursive algorithms for such flexible multibody systems. A key feature of the formulation is that the operator description of the flexible system dynamics is identical in form to the corresponding operator description of the dynamics of rigid multibody systems. A significant advantage of this unifying approach is that it allows ideas and techniques for rigid multibody systems to be easily applied to flexible multibody systems. The algorithms use standard finite-element and assumed modes models for the individual body deformation. A Newton-Euler Operator Factorization of the mass matrix of the multibody system is first developed. It forms the basis for recursive algorithms such as for the inverse dynamics, the computation of the mass matrix, and the composite body forward dynamics for the system. Subsequently, an alternative Innovations Operator Factorization of the mass matrix, each of whose factors is invertible, is developed. It leads to an operator expression for the inverse of the mass matrix, and forms the basis for the recursive articulated body forward dynamics algorithm for the flexible multibody system. For simplicity, most of the development here focuses on serial chain multibody systems. However, extensions of the algorithms to general topology flexible multibody systems are described. While the computational cost of the algorithms depends on factors such as the topology and the amount of flexibility in the multibody system, in general, it appears that in contrast to the rigid multibody case, the articulated body forward dynamics algorithm is the more efficient algorithm for flexible multibody systems containing even a small number of flexible bodies. The variety of algorithms described here permits a user to choose the algorithm which is optimal for the multibody system at hand. The availability of a number of algorithms is even more important for real-time applications, where implementation on parallel processors or custom computing hardware is often necessary to maximize speed

Role of Universal Service Obligation Fund in Rural Telecom Services: Lessons from the Indian Experience

Despite the tremendous growth of mobile services in most developing countries, these have largely remained limited to urban areas. This has further aggravated the existing urban and rural divide. Policy makers and regulators perceive the need for an effective regulatory and policy environment to reduce the gap, as there are several market challenges in this endeavor, including low commercial viability. However, most such interventions have had little success. This paper outlines India.s experience of increasing rural teledensity, including its recent policy initiative to increase penetration through creation of a Universal Service Obligation Fund (USOF) that supported a variety of innovative initiatives. USOF.s most ambitious program to date had been the design and deployment of mobile services in rural areas. This paper analyses the outcomes of various programs, especially those of the mobile service provision component of USOF. Despite the innovative design of the USOF program, it had little impact on increasing rural teledensity. On the other hand, positive policy steps that reduced the costs for service provision (revenue shares, duties, ADC) and competition facilitated greater rural penetration. This raises the issue of role of government vis-�-vis private sector in increasing rural teledensities. The lack of accountability arising from the relationship between the government owned incumbent and the USOF administrator and proper evaluation of USOF, the non-ring fencing of the fund and poor quality project management contributed to the low impact. Non-involvement of private operators at an early stage, inability to suitably enforce any penalties for violation of contracts, and non-existent review and feedback mechanism have not allowed USOF to leverage the benefits of an early start. In Peru, strict penalties in non implementation of contracts led to more timely schedules (Cannock, 2001). Since USOF is a highly visible program, it is important to generate high impact outcomes. On the strategic front, USOF needs to be managed by an independent body that is made responsible for outcomes. Third party assessments and greater enforceability of contracts are necessary operational elements of thisdesign. Without this operational framework, the strategic elements of design will not provide the value that was envisaged. This paper also provides a framework for assessment of USOF and relates it to the experience in other countries. USOF must be treated as one among many instruments for increasing rural teledensities and efforts should be made to facilitate policy outcomes on a variety of dimensions.

Composite Fermions and Landau Level Mixing in the Fractional Quantum Hall Effect

The reduction of the energy gap due to Landau level mixing, characterized by the dimensionless parameter $\lambda = (e^2/\epsilon l_0)/\hbar\omega_c$, has been calculated by variational Monte Carlo for the fractional quantum Hall effect at filling fractions $\nu=1/3$ and 1/5 using a modified version of Jain's composite fermion wave functions. These wave functions exploit the Landau level mixing already present in composite fermion wave functions by introducing a partial Landau level projection operator. Results for the energy gaps are consistent with experimental observations in $n$-type GaAs, but we conclude that Landau level mixing alone cannot account for the significantly smaller energy gaps observed in $p$-type systems.Comment: 11 pages, RevTex, 2 figures in compressed tar .ps forma

Nonuniversal exponents in sandpiles with stochastic particle number transfer

We study fixed density sandpiles in which the number of particles transferred to a neighbor on relaxing an active site is determined stochastically by a parameter $p$. Using an argument, the critical density at which an active-absorbing transition occurs is found exactly. We study the critical behavior numerically and find that the exponents associated with both static and time-dependent quantities vary continuously with $p$.Comment: Some parts rewritten, results unchanged. To appear in Europhys. Let

Relevance of inter-composite fermion interaction to the edge Tomonaga-Luttinger liquid

It is shown that Wen's effective theory correctly describes the Tomonaga-Luttinger liquid at the edge of a system of non-interacting composite fermions. However, the weak residual interaction between composite fermions appears to be a relevant perturbation. The filling factor dependence of the Tomonaga-Luttinger parameter is estimated for interacting composite fermions in a microscopic approach and satisfactory agreement with experiment is achieved. It is suggested that the electron field operator may not have a simple representation in the effective one dimensional theory.Comment: 5 pages; accepted in Phys. Rev. Let