Practical Bayesian Optimization for Variable Cost Objectives

We propose a novel Bayesian Optimization approach for black-box functions with an environmental variable whose value determines the tradeoff between evaluation cost and the fidelity of the evaluations. Further, we use a novel approach to sampling support points, allowing faster construction of the acquisition function. This allows us to achieve optimization with lower overheads than previous approaches and is implemented for a more general class of problem. We show this approach to be effective on synthetic and real world benchmark problems.Comment: 8 pages, 7 figure

The Metagalactic Ionizing Radiation Field at Low Redshift

We compute the ionizing radiation field at low redshift, arising from Seyferts, QSOs, and starburst galaxies. This calculation combines recent Seyfert luminosity functions, extrapolated ultraviolet fluxes from our IUE-AGN database, and a new intergalactic opacity model based on Hubble Space Telescope and Keck Ly-alpha absorber surveys. At z = 0 for AGN only, our best estimate for the specific intensity at 1 Ryd is I_0 = 1.3 (+0.8/-0.5) x 10^-23 ergs/cm^2/s/Hz/sr, independent of H_0, Omega_0, and Lambda. The one-sided ionizing photon flux is Phi_ion = 3400 (+2100/-1300) photons/cm^2/s, and the H I photoionization rate is Gamma_HI = 3.2 (+2.0/-1.2) x 10^-14 s^-1 for alpha_s = 1.8. We also derive Gamma_ HI for z = 0 - 4. These error ranges reflect uncertainties in the spectral indexes for the ionizing EUV (alpha_s = 1.8 +/- 0.3) and the optical/UV (alpha_UV = 0.86 +/- 0.05), the IGM opacity model, the range of Seyfert luminosities (0.001 - 100 L*) and the completeness of the luminosity functions. Our estimate is a factor of three lower than the most stringent upper limits on the ionizing background (Phi_ion < 10^4 photons/cm^2/s) obtained from H-alpha observations in external clouds, and it lies within the range implied by other indirect measures. Starburst galaxies with a sufficiently large Lyman continuum escape fraction, f_ esc > 0.05, may provide a comparable background to AGN, I_0 (z=0) = 1.1 (+1.5/-0.7) x 10^{-23). An additional component of the ionizing background of this magnitude would violate neither upper limits from H-alpha observations nor the acceptable range from other measurements.Comment: 30 pages, 9 figures, accepted for Astronomical J. (Oct. 1999

The Rotation and Shear of a String

Whether a string has rotation and shear can be investigated by an anology with the point particle. Rotation and shear involve first covariant spacetime derivatives of a vector field and, because the metric stress tensor for both the point particle and the string have no such derivatives, the best vector fields can be identified by requiring the conservation of the metric stress. It is found that the best vector field is a non-unit accelerating field in x, rather than a unit non-accelerating vector involving the momenta; it is also found that there is an equation obeyed by the spacetime derivative of the Lagrangian. The relationship between membranes and fluids is looked at.Comment: version 3: some sub/superscript corrections on the internal labels of the Nambu-Goto string, version 2: 17 pages, result generalized and contact established with the approach of other

Stability transitions for axisymmetric relative equilibria of Euclidean symmetric Hamiltonian systems

In the presence of noncompact symmetry, the stability of relative equilibria under momentum-preserving perturbations does not generally imply robust stability under momentum-changing perturbations. For axisymmetric relative equilibria of Hamiltonian systems with Euclidean symmetry, we investigate different mechanisms of stability: stability by energy-momentum confinement, KAM, and Nekhoroshev stability, and we explain the transitions between these. We apply our results to the Kirchhoff model for the motion of an axisymmetric underwater vehicle, and we numerically study dissipation induced instability of KAM stable relative equilibria for this system.Comment: Minor revisions. Typographical errors correcte

Effect of H on the crystalline and magnetic structures of the YCo3-H(D) system. I. YCo3 from neutron powder diffraction and first-principles calculations

This paper reports investigations into the influence of hydrogen on the magnetic properties of the YCo3-H system. We report results on the magnetic structure and magnetic transitions of YCo3 using a combination of neutron powder diffraction measurements and first-principles full potential augmented plane wave + local orbital calculations under the generalized gradient approximation. The ferromagnetic and ferrimagnetic structures are examined on an equal footing. However, we identify that, no matter which structure is used as the starting point, the neutron diffraction data always refines down to the ferrimagnetic structure with the Co2 atoms having antiparallel spins. In the ab initio calculations, the inclusion of spin-orbit coupling is found to be important in the prediction of the correct magnetic ground state. Here, the results suggest that, for zero external field and sufficiently low temperatures, the spin arrangement of YCo3 is ferrimagnetic rather than ferromagnetic as previously believed. The fixed spin moment calculation technique has been employed to understand the two successive field-induced magnetic transitions observed in previous magnetization measurements under increasing ultrahigh magnetic fields. We find that the magnetic transitions start from the ferrimagnetic phase �0.61�B/Co� and terminate with the ferromagnetic phase �1.16�B/Co�, while the spin on the Co2 atoms progressively changes from antiparallel ferrimagnetic to paramagnetic and then to ferromagnetic. Our neutron diffraction measurements, ab initio calculations, and the high field magnetization measurements are thus entirely self-consistent

Ocean Winds and Turbulent Air-Sea Fluxes Inferred From Remote Sensing

Air-sea turbulent fluxes determine the exchange of momentum, heat, freshwater, and gas between the atmosphere and ocean. These exchange processes are critical to a broad range of research questions spanning length scales from meters to thousands of kilometers and time scales from hours to decades. Examples are discussed (section 2). The estimation of surface turbulent fluxes from satellite is challenging and fraught with considerable errors (section 3); however, recent developments in retrievals (section 3) will greatly reduce these errors. Goals for the future observing system are summarized in section 4. Surface fluxes are defined as the rate per unit area at which something (e.g., momentum, energy, moisture, or CO Z ) is transferred across the air/sea interface. Wind- and buoyancy-driven surface fluxes are called surface turbulent fluxes because the mixing and transport are due to turbulence. Examples of nonturbulent processes are radiative fluxes (e.g., solar radiation) and precipitation (Schmitt et al., 2010). Turbulent fluxes are strongly dependent on wind speed; therefore, observations of wind speed are critical for the calculation of all turbulent surface fluxes. Wind stress, the vertical transport of horizontal momentum, also depends on wind direction. Stress is very important for many ocean processes, including upper ocean currents (Dohan and Maximenko, 2010) and deep ocean currents (Lee et al., 2010). On short time scales, this horizontal transport is usually small compared to surface fluxes. For long-term processes, transport can be very important but again is usually small compared to surface fluxes

Estimation of Short-Term Tag-Induced Mortality in Horseshoe Crabs Limulus Polyphemus

Horseshoe crabs Limulus Polyphemus range along the East Coast of the United States and over 150,000 of them have been marked with U.S. Fish and Wildlife Service disk tags. It has been assumed that the tags do not harm the animals and are similar to common epibionts often found on the shells of the horseshoe crabs. We investigated whether newlv tagged adult female horseshoe crabs would exhibit higher short-term mortality rates than untagged adult females. All crabs were collected from a beach in Connecticut and then were transported to a laboratory for the experiment. Tagging involved drilling a small hole through the carapace in the lower back corner or the prosoma and then inserting the tag into the hole. Overall mortality of the tagged and untagged females held in flow-through raceways for 44 d was minimal (0% mortality among 53 tagged crabs; 4% mortality among 52 untagged crabs). None of the horseshoe crabs lost or shed their disk tags over the course of the experiment. In field mark-recapture studies of horseshoe crabs, typically between 11% and 20% of the initial numbers of tagged crabs are recaptured. Crabs that are recaptured but reported dead are unlikely to have died from the initial tagging process. Our results indicate that newly tagged adult horseshoe crabs have the potential to survive as well as untagged crabs through the Connecticut spawning season (~30-45 d). Recapture data also suggest that these crabs can survive for as long Its 8-10 years with the tags in place