Optical probing of supersonic aerodynamic turbulence

Laser quasi-schlieren system and laser shadow-correlation system retrieve flow-related signals sufficient for computing accurate, reproducible correlation peaks. Statistical method for obtaining one-shot measurements of the decay history of turbulent structures in a stationary frame of reference is discussed

TVL₁shape approximation from scattered 3D data

With the emergence in 3D sensors such as laser scanners and 3D reconstruction from cameras, large 3D point clouds can now be sampled from physical objects within a scene. The raw 3D samples delivered by these sensors however, contain only a limited degree of information about the environment the objects exist in, which means that further geometrical high-level modelling is essential. In addition, issues like sparse data measurements, noise, missing samples due to occlusion, and the inherently huge datasets involved in such representations makes this task extremely challenging. This paper addresses these issues by presenting a new 3D shape modelling framework for samples acquired from 3D sensor. Motivated by the success of nonlinear kernel-based approximation techniques in the statistics domain, existing methods using radial basis functions are applied to 3D object shape approximation. The task is framed as an optimization problem and is extended using non-smooth L1 total variation regularization. Appropriate convex energy functionals are constructed and solved by applying the Alternating Direction Method of Multipliers approach, which is then extended using Gauss-Seidel iterations. This significantly lowers the computational complexity involved in generating 3D shape from 3D samples, while both numerical and qualitative analysis confirms the superior shape modelling performance of this new framework compared with existing 3D shape reconstruction techniques

The GeV-TeV Connection in Galactic gamma-ray sources

Recent observations with atmospheric Cherenkov telescope systems such as H.E.S.S. and MAGIC have revealed a large number of new sources of very-high-energy (VHE) gamma-rays from 100 GeV - 100 TeV, mostly concentrated along the Galactic plane. At lower energies (100 MeV - 10 GeV) the satellite-based instrument EGRET revealed a population of sources clustering along the Galactic Plane. Given their adjacent energy bands a systematic correlation study between the two source catalogues seems appropriate. Here, the populations of Galactic sources in both energy domains are characterised on observational as well as on phenomenological grounds. Surprisingly few common sources are found in terms of positional coincidence and spectral consistency. These common sources and their potential counterparts and emission mechanisms will be discussed in detail. In cases of detection only in one energy band, for the first time consistent upper limits in the other energy band have been derived. The EGRET upper limits are rather unconstraining due to the sensitivity mismatch to current VHE instruments. The VHE upper limits put strong constraints on simple power-law extrapolation of several of the EGRET spectra and thus strongly suggest cutoffs in the unexplored energy range from 10 GeV - 100 GeV. Physical reasons for the existence of cutoffs and for differences in the source population at GeV and TeV energies will be discussed. Finally, predictions will be derived for common GeV - TeV sources for the upcoming GLAST mission bridging for the first time the energy gap between current GeV and TeV instruments.Comment: (1) Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), Stanford, USA (2) Stanford University, W.W. Hansen Experimental Physics Lab (HEPL) and KIPAC, Stanford, USA (3) ICREA & Institut de Ciencies de l'Espai (IEEC-CSIC) Campus UAB, Fac. de Ciencies, Barcelona, Spain. (4) School of Physics and Astronomy, University of Leeds, UK. Paper Submitted to Ap

On the principles of a digital text corpus : New opportunities in working on heroic epics of the Shors

This essay will use the Shor corpus as its main example, though the Teleut, Evenki, or Nenets corpora might easily have been chosen instead. The reasoning behind this choice is the fact that the whole project arose out of my long-term study of the Shor epics. Additionally, the Shor (like the Teleut) materials belong for the most part to me, and I am the primary individual who has been working with them within the frame of this project. It is my hope that this single example will help readers better understand what our Corpus is able to do and how it has been organized.Not

Resource allocation for acorn production: A comparison across species pairs of oaks with contrasting acorn production patterns and water use strategies

Mast seeding, or masting, is a phenomenon where inter-annual seed production by individuals is synchronized across a population of plants. Masting is hypothesized to confer a selective advantage to plants by increasing rates of pollination or by decreasing rates of seed predation. Masting can also play a crucial role in ecosystem functioning as fluctuations in annual seed crops correspond with fluctuations in seed predator populations, which in turn have consequences that ripple throughout food webs. The mechanism(s) that causes masting is unresolved, but the high variability in seed production of masting plants is hypothesized to be caused, in part, by resource limitation. One hypothesized mechanism for masting that has gained support in recent years is known as the resource budget model (RBM). The RBM hypothesizes that plants store up resources across years until a threshold is reached, after which they flower and set seed, which depletes resources. It is still unknown how common the RBM is in masting species, and it is unknown whether the RBM describes a pattern of resource allocation that is distinctive of masting species, or if non-masting plants exhibit similar patterns. In this dissertation, we seek to resolve some of this uncertainty by comparing patterns of resource allocation and seed production among four species of California oak trees and shrubs. In Chapter 1, we test predictions of the RBM in two shrub species, one masting and one non-masting, in the Klamath Mountains of northern California. In chapter 2, we explore the carbon demands for acorn development of the masting species used in Chapter 1, in order to learn more about whether carbohydrates are limiting for seed production in this species. In Chapter 3, we use two masting tree species in central coastal California with contrasting water use strategies to test for resource limitation to flowering and seed production, and to compare which nutrients are the most important for each species. Overall, we found evidence for resource-limited reproduction in all three masting species. Furthermore, differences in patterns of seed production and in species traits matter for how resources are used for seed production. Advisor: Johannes M. H. Knop