Robust designs for Poisson regression models

We consider the problem of how to construct robust designs for Poisson regression models. An analytical expression is derived for robust designs for first-order Poisson regression models where uncertainty exists in the prior parameter estimates. Given certain constraints in the methodology, it may be necessary to extend the robust designs for implementation in practical experiments. With these extensions, our methodology constructs designs which perform similarly, in terms of estimation, to current techniques, and offers the solution in a more timely manner. We further apply this analytic result to cases where uncertainty exists in the linear predictor. The application of this methodology to practical design problems such as screening experiments is explored. Given the minimal prior knowledge that is usually available when conducting such experiments, it is recommended to derive designs robust across a variety of systems. However, incorporating such uncertainty into the design process can be a computationally intense exercise. Hence, our analytic approach is explored as an alternative

Spin Dynamics in the Magnetic Chains Arrays of Sr14Cu24O41: a Neutron Inelastic scattering Investigation

Below about 150 K, the spin arrangement in the chain arrays of Sr14Cu24O41 is shown to develop in two dimensions (2D). Both the correlations and the dispersion of the observed elementary excitations agree well with a model of interacting dimers. Along the chains, the intra- and inter-dimer distances are equal to 2 and about 3 times the distance (c) between neighboring Cu ions. While the intra-dimer coupling is J about 10 meV, the inter-dimer couplings along and between the chains are of comparable strenght, J// about -1.1 meV and Jperp about 1.7 meV, respectively. This remarkable 2D arrangement satisfies the formal Cu valence of the undoped compound. Our data suggest also that it is associated with a relative sliding of one chain with respect to the next one, which, as T decreases, develops in the chain direction. A qualitative analysis shows that nearest inter-dimer spin correlations are ferromagnetic, which, in such a 2D structure, could well result from frustration effects.Comment: 4 pages, 5 figures, submitted to Phys.Rev.B, date of receipt 29 June 199

The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System

We describe the layout and unique features of the focal plane system for MIRI. We begin with the detector array and its readout integrated circuit (combining the amplifier unit cells and the multiplexer), the electronics, and the steps by which the data collection is controlled and the output signals are digitized and delivered to the JWST spacecraft electronics system. We then discuss the operation of this MIRI data system, including detector readout patterns, operation of subarrays, and data formats. Finally, we summarize the performance of the system, including remaining anomalies that need to be corrected in the data pipeline

The ARIEL Instrument Control Unit design for the M4 Mission Selection Review of the ESA's Cosmic Vision Program

The Atmospheric Remote-sensing Infrared Exoplanet Large-survey mission (ARIEL) is one of the three present candidates for the ESA M4 (the fourth medium mission) launch opportunity. The proposed Payload will perform a large unbiased spectroscopic survey from space concerning the nature of exoplanets atmospheres and their interiors to determine the key factors affecting the formation and evolution of planetary systems. ARIEL will observe a large number (>500) of warm and hot transiting gas giants, Neptunes and super-Earths around a wide range of host star types, targeting planets hotter than 600 K to take advantage of their well-mixed atmospheres. It will exploit primary and secondary transits spectroscopy in the 1.2-8 um spectral range and broad-band photometry in the optical and Near IR (NIR). The main instrument of the ARIEL Payload is the IR Spectrometer (AIRS) providing low-resolution spectroscopy in two IR channels: Channel 0 (CH0) for the 1.95-3.90 um band and Channel 1 (CH1) for the 3.90-7.80 um range. It is located at the intermediate focal plane of the telescope and common optical system and it hosts two IR sensors and two cold front-end electronics (CFEE) for detectors readout, a well defined process calibrated for the selected target brightness and driven by the Payload's Instrument Control Unit (ICU).Comment: Experimental Astronomy, Special Issue on ARIEL, (2017

Phases of two coupled Luttinger liquids

A model of two interacting one--dimensional fermion systems (``Luttinger liquids'') coupled by single--particle hopping is investigated. Bosonization allows a number of exact statements to be made. In particular, for forward scattering only, the model contains two massless boson sectors and an Ising type critical sector. For general interactions, there is a spin excitation gap and either s-- or d--type pairing fluctuations dominate. It is shown that the same behavior is also found for strong interactions. A possible scenario for the crossover to a Fermi liquid in a many chain system is discussed.Comment: revised version, some changes, 11 pages, no figures, RexTeX3.

Antiferromagnetic S=1/2 Heisenberg Chain and the Two-flavor Massless Schwinger Model

An antiferromagnetic S=1/2 Heisenberg chain is mapped to the two-flavor massless Schwinger model at \theta=\pi. The electromagnetic coupling constant and velocity of light in the Schwinger model are determined in terms of the Heisenberg coupling and lattice spacing in the spin chain system.Comment: 3 pages. LaTex2

Magnetic excitations and structural change in the S=1/2 quasi-one-dimensional magnet Sr_{14-x}Y_{x}Cu_{24}O_{41} (0<x<1)

Neutron scattering measurements have been performed on the S=1/2 quasi-one-dimensional system Sr_{14-x}Y_{x}Cu_{24}O_{41}, which has both simple chains and two-leg ladders of copper ions. We observed that when a small amount of yttrium is substituted for strontium, which is expected to reduce the number of holes, the dimerized state and the structure in the chain are changed drastically. The inelastic peaks originating from the dimerized state of the chain becomes broader in energy but not in momentum space. This implies that the dimerized state becomes unstable but the spin correlations are unchanged with yttrium substitution. Furthermore, it was observed that nuclear Bragg peak intensities originating from the chain show strong temperature and x dependence, which suggests that the chains slide along the c axis as temperature and x are varied.Comment: 5 pages, 6 figures, to appear in Phys. Rev.

Measurement techniques for the verification of excess weapons materials

The end of the superpower arms race has resulted in an unprecedented reduction in stockpiles of deployed nuclear weapons. Numerous proposals have been put forward and actions have been taken to ensure the irreversibility of nuclear arms reductions, including unilateral initiatives such as those made by President Clinton in September 1993 to place fissile materials no longer needed for a deterrent under international inspection, and bilateral and multilateral measures currently being negotiated. For the technologist, there is a unique opportunity to develop the technical means to monitor nuclear materials that have been declared excess to nuclear weapons programs, to provide confidence that reductions are taking place and that the released materials are not being used again for nuclear explosive programs. However, because of the sensitive nature of these materials, a fundamental conflict exists between the desire to know that the bulk materials or weapon components in fact represent evidence of warhead reductions, and treaty commitments and national laws that require the protection of weapons design information. This conflict presents a unique challenge to technologists. The flow of excess weapons materials, from deployed warheads through storage, disassembly, component storage, conversion to bulk forms, and disposition, will be described in general terms. Measurement approaches based on the detection of passive or induced radiation will be discussed along with the requirement to protect sensitive information from release to unauthorized parties. Possible uses of measurement methods to assist in the verification of arms reductions will be described. The concept of measuring attributes of items rather than quantitative mass-based inventory verification will be discussed along with associated information-barrier concepts required to protect sensitive information

Quasi-two-dimensional hole ordering and dimerized state in the CuO2-chain layers in Sr14Cu24O41

Neutron scattering experiments have been performed on Sr$_{14}$Cu$_{24}$O$_{41}$ which consists of both chains and ladders of copper ions. We observed that the magnetic excitations from the CuO$_2$ chain have two branches and that both branches are weakly dispersive along the $a$ and $c$ axes. The $\omega$-$Q$ dispersion relation as well as the intensities can be reasonably described by a random phase approximation with intradimer coupling between next-nearest-neighbor copper spins $J$=11 meV, interdimer coupling along the c axis $J_c$=0.75 meV, and interdimer coupling along the a axis $J_a$=0.75 meV. The dimer configuration indicates a quasi-two-dimensional hole ordering, resulting in an ordering of magnetic Cu$^{2+}$ with spin-1/2 and nonmagnetic Cu, which forms the Zhang-Rice singlet. We have also studied the effect of Ca substitution for Sr on the dimer and the hole ordering.Comment: 7 pages, Revtex, 10 figures, Submitted to Phys. Rev.

Recurrent Variational Approach to the Two-Leg Hubbard Ladder

We applied the Recurrent Variational Approach to the two-leg Hubbard ladder. At half-filling, our variational Ansatz was a generalization of the resonating valence bond state. At finite doping, hole pairs were allowed to move in the resonating valence bond background. The results obtained by the Recurrent Variational Approach were compared with results from Density Matrix Renormalization Group.Comment: 10 pages, 14 Postscript figure