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Open Access Publications from the University of California

Scholarly Works (14 results)

  • Article
  • Peer Reviewed
UC Santa Barbara Previously Published Works (2005)

Understanding the key ecological factors that moderate the relationship between biodiversity and the productivity of ecosystems is a major challenge for ecological research. Here we show that the relationship between the species richness of primary producers and net rates of biomass production in streams depends on the history of discharge-related disturbances. Using common methods to study 83 streams in the mid-Atlantic United States, we demonstrate that a positive relationship between producer richness and the net production of biomass only occurs in streams characterized by highly variable, unpredictable discharge regimes that represent frequently disturbed environments to benthic organisms. This pattern is partly explained by predictable changes in the composition of species assemblages among disturbed streams. The pattern also results because, in disturbed systems, species have faster rates of biomass accumulation when they are a part of species-rich assemblages. We discuss several possible explanations for this result. Our study supports qualitative predictions from theoretical and small-scale experimental work that the strength of the diversity-productivity relationship will depend explicitly on the disturbance regime of an ecosystem. The results have important implications for the management and conservation of aquatic resources as they suggest that changes to the productivity and diversity of streams may have their greatest impacts on organisms and systems that are most sensitive to disturbance.

    Cover page: Diversity-productivity relationships in streams vary as a function of the natural disturbance regime
    • Article
    Western Journal of Emergency Medicine: Integrating Emergency Care with Population Health, Volume 19, Issue 4.1 (2018)
      Cover page: Experience Introducing Physician Assistant Students into a Medical Student Emergency Medicine ClerkshipCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      LBL Publications (2016)
      The international Muon Ionization Cooling Experiment aims to demonstrate the transverse cooling of a muon beam by ionization interaction with absorbers and re-acceleration in RF cavities. The final MICE cooling channel configuration has two RF modules, each housing a 201 MHz RF cavity to compensate the longitudinal energy loss in the absorbers. The RF modules will be assembled and tested at LBNL before being shipped to and installed at RAL. This paper reports the recent progress on the manufacturing and testing of the RF module components, as well as the preparation for the final module assembly.
        Cover page: Progress on the MICE RF module at LBNL
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2022)
        Demonstrating the viability of Advanced Accelerator Concepts (AAC) relies on experimental validation. Over the last three decades, the U.S. has maintained a portfolio of advanced and novel accelerator test facilities to support research critical to AAC. The facilities have enabled pioneering developments in a wide variety of beam and accelerator physics, including plasma-wakefield and structure-wakefield acceleration. This paper provides an overview of the current portfolio of U.S. facilities possessing charged particle drive beams with high energies, on the order of tens of joules per pulse, or drive lasers with high peak powers, on the order of a petawatt, and are actively conducting AAC research.
          Cover page: U.S. advanced and novel accelerator beam test facilitiesCreative Commons 'BY-NC' version 4.0 license
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2019)
          The generation of X-rays and γ-rays based on synchrotron radiation from free electrons, emitted in magnet arrays such as undulators, forms the basis of much of modern X-ray science. This approach has the drawback of requiring very high energy, up to the multi-GeV-scale, electron beams, to obtain the required photon energy. Due to the limit in accelerating gradients in conventional particle accelerators, reaching high energy typically demands use of instruments exceeding 100's of meters in length. Compact, less costly, monochromatic X-ray sources based on very high field acceleration and very short period undulators, however, may enable diverse, paradigm-changing X-ray applications ranging from novel X-ray therapy techniques to active interrogation of sensitive materials, by making them accessible in energy reach, cost and size. Such compactness and enhanced energy reach may be obtained by an all-optical approach, which employs a laser-driven high gradient accelerator based on inverse free electron laser (IFEL), followed by a collision point for inverse Compton scattering (ICS), a scheme where a laser is used to provide undulator fields. We present an experimental proof-of-principle of this approach, where a TW-class CO2 laser pulse is split in two, with half used to accelerate a high quality electron beam up to 84 MeV through the IFEL interaction, and the other half acts as an electromagnetic undulator to generate up to 13 keV X-rays via ICS. These results demonstrate the feasibility of this scheme, which can be joined with other techniques such as laser recirculation to yield very compact photon sources, with both high peak and average brilliance, and with energies extending from the keV to MeV scale. Further, use of the IFEL acceleration with the ICS interaction produces a train of high intensity X-ray pulses, thus enabling a unique tool synchronized with a laser pulse for ultra-fast strobe, pump-probe experimental scenarios.
            Cover page: An inverse free electron laser acceleration-driven Compton scattering X-ray source
            • Article
            • Peer Reviewed
            Faculty Publications (2013)

            The evolution of ocean temperature measurement systems is presented with a focus on the development and accuracy of two critical devices in use today (expendable bathythermographs and conductivity-temperature-depth instruments used on Argo floats). A detailed discussion of the accuracy of these devices and a projection of the future of ocean temperature measurements are provided. The accuracy of ocean temperature measurements is discussed in detail in the context of ocean heat content, Earth's energy imbalance, and thermosteric sea level rise. Up-to-date estimates are provided for these three important quantities. The total energy imbalance at the top of atmosphere is best assessed by taking an inventory of changes in energy storage. The main storage is in the ocean, the latest values of which are presented. Furthermore, despite differences in measurement methods and analysis techniques, multiple studies show that there has been a multidecadal increase in the heat content of both the upper and deep ocean regions, which reflects the impact of anthropogenic warming. With respect to sea level rise, mutually reinforcing information from tide gauges and radar altimetry shows that presently, sea level is rising at approximately 3 mm yr−1 with contributions from both thermal expansion and mass accumulation from ice melt. The latest data for thermal expansion sea level rise are included here and analyzed.

              Cover page: A review of global ocean temperature observations: Implications for ocean heat content estimates and climate changeCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2024)
              It is widely accepted that the next lepton collider beyond a Higgs factory would require center-of-mass energy of the order of up to 15 TeV. Since, given reasonable space and cost restrictions, conventional accelerator technology reaches its limits near this energy, high-gradient advanced acceleration concepts are attractive. Advanced and novel accelerators (ANAs) are leading candidates due to their ability to produce acceleration gradients on the order of 1-100 GV/m, leading to compact acceleration facilities. However, intermediate energy facilities (IEF) are required to test the critical technology elements on the way towards multi-TeV-class collliders. Here a science case for a 20-100 GeV center-of-mass energy ANA-based lepton collider that can be a candidate for an intermediate energy facility is presented. The IEF can provide numerous opportunities for high energy physics studies including precision Quantum Chromodynamics and Beyond the Standard Model physics measurements, investigation of charged particle interactions with extreme electromagnetic fields, and exploring muon and proton beam acceleration. Possible applications of this collider include the studies of γγ and electron beam-fixed target/beamdump collider designs. Thus, the goal of the proposed IEF is to both carry out particle physics measurements in the 20-100 GeV ranges as well as to serve as an ANA demonstrator facility.
                Cover page: The science case for an intermediate energy advanced and novel accelerator linear collider facilityCreative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                LBL Publications (2017)
                Muon beams of low emittance provide the basis for the intense, well-characterized neutrino beams necessary to elucidate the physics of flavor at a neutrino factory and to provide lepton-antilepton collisions at energies of up to several TeV at a muon collider. The international Muon Ionization Cooling Experiment (MICE) aims to demonstrate ionization cooling, the technique by which it is proposed to reduce the phase-space volume occupied by the muon beam at such facilities. In an ionization-cooling channel, the muon beam passes through a material in which it loses energy. The energy lost is then replaced using rf cavities. The combined effect of energy loss and reacceleration is to reduce the transverse emittance of the beam (transverse cooling). A major revision of the scope of the project was carried out over the summer of 2014. The revised experiment can deliver a demonstration of ionization cooling. The design of the cooling demonstration experiment will be described together with its predicted cooling performance.
                  Cover page: Lattice design and expected performance of the Muon Ionization Cooling Experiment demonstration of ionization cooling
                  • Article
                  • Peer Reviewed
                  LBL Publications (2019)
                  The Muon Ionization Cooling Experiment (MICE) collaboration seeks to demonstrate the feasibility of ionization cooling, the technique by which it is proposed to cool the muon beam at a future neutrino factory or muon collider. The emittance is measured from an ensemble of muons assembled from those that pass through the experiment. A pure muon ensemble is selected using a particle-identification system that can reject efficiently both pions and electrons. The position and momentum of each muon are measured using a high-precision scintillating-fibre tracker in a 4 T solenoidal magnetic field. This paper presents the techniques used to reconstruct the phase-space distributions in the upstream tracking detector and reports the first particle-by-particle measurement of the emittance of the MICE Muon Beam as a function of muon-beam momentum.
                    • Article
                    • Peer Reviewed
                    LBL Publications (2020)
                    The use of accelerated beams of electrons, protons or ions has furthered the development of nearly every scientific discipline. However, high-energy muon beams of equivalent quality have not yet been delivered. Muon beams can be created through the decay of pions produced by the interaction of a proton beam with a target. Such 'tertiary' beams have much lower brightness than those created by accelerating electrons, protons or ions. High-brightness muon beams comparable to those produced by state-of-the-art electron, proton and ion accelerators could facilitate the study of lepton-antilepton collisions at extremely high energies and provide well characterized neutrino beams1-6. Such muon beams could be realized using ionization cooling, which has been proposed to increase muon-beam brightness7,8. Here we report the realization of ionization cooling, which was confirmed by the observation of an increased number of low-amplitude muons after passage of the muon beam through an absorber, as well as an increase in the corresponding phase-space density. The simulated performance of the ionization cooling system is consistent with the measured data, validating designs of the ionization cooling channel in which the cooling process is repeated to produce a substantial cooling effect9-11. The results presented here are an important step towards achieving the muon-beam quality required to search for phenomena at energy scales beyond the reach of the Large Hadron Collider at a facility of equivalent or reduced footprint6.
                      Cover page: Demonstration of cooling by the Muon Ionization Cooling Experiment
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