Fact sheet: Canopy cover and forest conditions

Canopy cover and how it relates to other forest attributes as an indicator of forest conditions

Logistics and Benefits of Using Mathematical Models of Hydrologic and Water Resource Systems; Selected Papers from an International Symposium, October 24-26,1978

The use of the mathematical models for the simulation, analysis, and control of water resource systems has spread rapidly in recent years. The basic structure and the mathematical formulation of these models have been widely discussed, but relatively little attention has been paid to the operational aspects and logistics of model use. To stimulate the exchange of ideas, knowledge, and experience about the use of hydrologic and water resource models, this Symposium was convened by the International Institute for Applied Systems Analysis (IIASA) and cosponsored by the World Meteorological Organization (WMO) and the IBM Scientific Center (Pisa). The Symposium concentrated on model identification and use. Logistic issues, such as computer requirements, support staff and data needed, and cost-benefit analysis of the use of models in practical work, were examined in particular detail. This book contains an introductory chapter on model structure and use, fourteen selected papers from the Symposium, and a summary of the more important points raised during the Symposium discussions

Phase Separation of Rigid-Rod Suspensions in Shear Flow

We analyze the behavior of a suspension of rigid rod-like particles in shear flow using a modified version of the Doi model, and construct diagrams for phase coexistence under conditions of constant imposed stress and constant imposed strain rate, among paranematic, flow-aligning nematic, and log-rolling nematic states. We calculate the effective constitutive relations that would be measured through the regime of phase separation into shear bands. We calculate phase coexistence by examining the stability of interfacial steady states and find a wide range of possible ``phase'' behaviors.Comment: 23 pages 19 figures, revised version to be published in Physical Review

Current Research of the Leiden-Turin Archaeological Mission in Saqqara. A Preliminary Report on the 2018 Season

In 2015, the Museo Egizio in Turin joined the Leiden expedition to Saqqara, in the area south of the Unas causeway. This report presents the expedition’s new approach as well as some first results of this new cooperation. In the 2018 season, the Leiden-Turin expedition worked in the northern sector of its concession, covering an area of ca. 250 sqm just north of the tomb of Maya. Here Late Antique layers overlie a windblown deposit containing some simple burials and numerous “embalmers’ caches”, some of which yielded marl clay cups with hieratic labels. An overview of both the pottery and the human remains found during this season is provided in the present report. Below the wind-blown deposit is a level with Ramesside funerary chapels and shafts. One of them has a remarkable decoration including six small-format figures carved in high relief in the middle of its back wall. The shaft of another chapel was also excavated, revealing several plundered chambers which yielded only scanty finds. A large mud-brick wall exposed during the previous season turned out to belong to the outer wall and pylon entrance of a monumental tomb, whose owner’s name has not been found yet.A photogrammetric survey by a team of the Politecnico di Milano yielded a 3D model of the dig (included in the web version of this report), as well as several 3D models of the monumental tombs (completed or in the making). During the season, conservation work was carried out on several tombs and on the newly discovered Ramesside chapel.Middle Eastern Studie

Berry phases and pairing symmetry in Holstein-Hubbard polaron systems

We study the tunneling dynamics of dopant-induced hole polarons which are self-localized by electron-phonon coupling in a two-dimensional antiferro- magnet. Our treatment is based on a path integral formulation of the adia- batic approximation, combined with many-body tight-binding, instanton, con- strained lattice dynamics, and many-body exact diagonalization techniques. Our results are mainly based on the Holstein-$tJ$ and, for comparison, on the Holstein-Hubbard model. We also study effects of 2nd neighbor hopping and long-range electron-electron Coulomb repulsion. The polaron tunneling dynamics is mapped onto an effective low-energy Hamiltonian which takes the form of a fermion tight-binding model with occupancy dependent, predominant- ly 2nd and 3rd neighbor tunneling matrix elements, excluded double occupan- cy, and an effective intersite charge interactions. Antiferromagnetic spin correlations in the original many-electron Hamiltonian are reflected by an attractive contribution to the 1st neighbor charge interaction and by Berry phase factors which determine the signs of effective polaron tunneling ma- trix elements. In the two-polaron case, these phase factors lead to polaron pair wave functions of either $d_{x^2-y^2}$-wave symmetry or p-wave symme- try with zero and nonzero total pair momentum, respectively. Implications for the doping dependent isotope effect, pseudo-gap and Tc of a superconduc- ting polaron pair condensate are discussed/compared to observed in cuprates.Comment: 23 pages, revtex, 13 ps figure

Solar Wind Turbulence and the Role of Ion Instabilities

International audienc

Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

Relating the microscopic rules in coalescence-fragmentation models to the macroscopic cluster size distributions which emerge

Coalescence-fragmentation problems are of great interest across the physical, biological, and recently social sciences. They are typically studied from the perspective of the rate equations, at the heart of such models are the rules used for coalescence and fragmentation. Here we discuss how changes in these microscopic rules affect the macroscopic cluster-size distribution which emerges from the solution to the rate equation. More generally, our work elucidates the crucial role that the fragmentation rule can play in such dynamical grouping models. We focus on two well-known models whose fragmentation rules lie at opposite extremes setting the models within the broader context of binary coalescence-fragmentation models. Further, we provide a range of generalizations and new analytic results for a well-known model of social group formation [V. M. Eguiluz and M. G. Zimmermann, Phys. Rev. Lett. 85, 5659 (2000)]. We develop analytic perturbation treatment of the original model, and extend the mathematical to the treatment of growing and declining populations