Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session W1: Plenary Session III |
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Sponsoring Units: APS Chair: Natalie Roe, Berkeley National Laboratory Room: Hyatt Regency Jacksonville Riverfront Grand 4-5 |
Tuesday, April 17, 2007 8:30AM - 9:06AM |
W1.00001: The 21cm Background: A Probe of Reionization and the Dark Ages Invited Speaker: Observations of the redshifted 21cm line of neutral hydrogen have the potential to probe the processes of structure formation and reionization in a unique way, complementing other techniques in cosmology. The high redshift means that observations have to be done at frequencies of 200 MHz and below, a part of the spectrum plagued by radio frequency interference. I will review the status of the first-generation experiments that currently are under construction. Even modest collecting areas should be capable of detecting the power spectrum of fluctuations and the largest ``bubbles'' around quasars. Second generation experiments could in principle map structures on a wide range of spatial scales and, through sensitive power spectrum measurements, serve as a new probe of cosmological models and of dark matter. [Preview Abstract] |
Tuesday, April 17, 2007 9:06AM - 9:42AM |
W1.00002: Global Warming: The Threat to the Planet Invited Speaker: Paleoclimate data show that the Earth's climate is remarkably sensitive to global forcings. Positive feedbacks predominate. This allows the entire planet to be whipsawed between climate states. One feedback, the `albedo flip' property of water substance, provides a powerful trigger mechanism. A climate forcing that `flips' the albedo of a sufficient portion of an ice sheet can spark a cataclysm. Ice sheet and ocean inertia provides only moderate delay to ice sheet disintegration and a burst of added global warming. Recent greenhouse gas (GHG) emissions place the Earth perilously close to dramatic climate change that could run out of our control, with great dangers for humans and other creatures. CO$_2$ is the largest human-made climate forcing, but CH$_4$, O$_3$, N$_2$O and black carbon (BC) are important. Only intense simultaneous efforts to slow CO$_2$ emissions and reduce non-CO$_2$ forcings can keep climate within or near the range of the past million years. Some forcings are especially effective at high latitudes, so concerted efforts to reduce their emissions could still ``save the Arctic,'' while also having major benefits for human health, agricultural productivity, and the global environment. [Preview Abstract] |
Tuesday, April 17, 2007 9:42AM - 10:18AM |
W1.00003: New Results from RHIC on the Spin Structure of the Proton Invited Speaker: In addition to accelerating heavy ion beams to ultrarelativistic energies, RHIC is the world's first polarized proton collider. It facilitates study of spin observables for hard partonic interactions tractable by perturbative QCD (pQCD), in order to extract information on the non-perturbative spin structure of the proton. The pp collisions offer distinct advantages and complementarity to deep inelastic lepton scattering experiments for the determination of the helicity preferences of gluons, the flavor-dependence of sea antiquark polarizations, and parton transverse motion or spin orientation preferences inside polarized protons. I will review the latest results from the RHIC spin program, with emphasis on measurements for the production in 200 GeV pp collisions of hadrons, jets, di-jets and direct photons. I will summarize the constraints implied by these results on the gluon contribution to proton spin and on the origin of transverse spin asymmetries. I will also briefly describe the near-term prospects for mapping the gluon polarization as a function of Bjorken $x$ via coincidence measurements and for determining the flavor-dependence of sea-antiquark polarizations via W$^{\pm }$ production. [Preview Abstract] |
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