Ground ice hydrochemical composition of permafrost core ICDP5011-3

The continuous sediment record from Lake El'gygytgyn in the northeastern Eurasian Arctic spans the last 3.6 Ma and for much of this time permafrost dynamics and lake level changes have likely played a crucial role for sediment delivery to the lake. Changes in the ground-ice hydrochemical composition (d18O, dD, pH, electrical conductivity, Na+, Mg2+, Ca2+, K+, HCO3-, Cl-, SO4-) of a 141 m long permafrost record from the western crater plain are examined to reconstruct repeated periods of freeze and thaw at the lake edge. Stable water isotope and major ion records of ground ice in the permafrost reflect both a synsedimentary palaeo-precipitation signal preserved in the near-surface permafrost (0.0-9.1 m core depth) and a post-depositional record of thawing and refreezing in deeper layers of the core (9.1-141.0 m core depth). These lake marginal permafrost dynamics were controlled by lake level changes that episodically flooded the surfaces and induced thaw in the underlying frozen ground. During times of lake level fall these layers froze over again. At least three cycles of freeze and thaw are identified and the hydrochemical data point to a vertical and horizontal talik refreezing through time. Past permafrost thaw and freeze may have destabilised the basin slopes of Lake El'gygytgyn and this has probably promoted the release of mass movements from the lake edge to the deeper basin as known from frequently occurring turbidite layers in the lake sediment column.

Seawater carbonate chemistry and community metabolism during an experiment with a coral reef, 2003

The effect of elevated pCO2 on the metabolism of a coral reef community dominated by macroalgae has been investigated utilizing the large 2650 m3 coral reef mesocosm at the Biosphere-2 facility near Tucson, Arizona. The carbonate chemistry of the water was manipulated to simulate present-day and a doubled CO2 future condition. Each experiment consisted of a 1-2 month preconditioning period followed by a 7-9 day observational period. The pCO2 was 404 ± 63 ?atm during the present-day pCO2 experiment and 658 ± 59 ?atm during the elevated pCO2 experiment. Nutrient levels were low and typical of natural reefs waters (NO3? 0.5-0.9 ?M, NH4+ 0.4 ?M, PO43? 0.07-0.09 ?M). The temperature and salinity of the water were held constant at 26.5 ± 0.2°C and 34.4 ± 0.2 ppt. Photosynthetically available irradiance was 10 ± 2 during the present-day experiment and 7.4 ± 0.5 mol photons m?2 d?1 during the elevated pCO2 experiment. The primary producer biomass in the mesocosm was dominated by four species of macroalgae; Haptilon cubense, Amphiroa fragillisima, Gelidiopsis intricata and Chondria dasyphylla. Algal biomass was 10.4 mol C m?2 during the present-day and 8.7 mol C m?2 and during the elevated pCO2 experiments. As previously observed, the increase in pCO2 resulted in a decrease in calcification from 0.041 ± 0.007 to 0.006 ± 0.003 mol CaCO3 m?2 d?1. Net community production (NCP) and dark respiration did not change in response to elevated pCO2. Light respiration measured by a new radiocarbon isotope dilution method exceeded dark respiration by a factor of 1.2 ± 0.3 to 2.1 ± 0.4 on a daily basis and by 2.2 ± 0.6 to 3.9 ± 0.8 on an hourly basis. The 1.8-fold increase with increasing pCO2 indicates that the enhanced respiration in the light was not due to photorespiration. Gross production (GPP) computed as the sum of NCP plus daily respiration (light + dark) increased significantly (0.24 ± 0.03 vs. 0.32 ± 0.04 mol C m?2 d?1). However, the conventional calculation of GPP based on the assumption that respiration in the light proceeds at the same rate as the dark underestimated the true rate of GPP by 41-100% and completely missed the increased rate of carbon cycling due to elevated pCO2. We conclude that under natural, undisturbed, nutrient-limited conditions elevated CO2 depresses calcification, stimulates the rate of turnover of organic carbon, particularly in the light, but has no effect on net organic production. The hypothesis that an increase pCO2 would produce an increase in net production that would counterbalance the effect of decreasing saturation state on calcification is not supported by these data.

Recent advances in laser-driven neutron sources

Due to the limited number and high cost of large-scale neutron facilities, there has been a growing interest in compact accelerator-driven sources. In this context, several potential schemes of laser-driven neutron sources are being intensively studied employing laser-accelerated electron and ion beams. In addition to the potential of delivering neutron beams with high brilliance, directionality and ultra-short burst duration, a laser-driven neutron source would offer further advantages in terms of cost-effectiveness, compactness and radiation confinement by closed-coupled experiments. Some of the recent advances in this field are discussed,
showing improvements in the directionality and flux of the laser-driven neutron beams.

Multi-Tenant Virtual GPUs for Optimising Performance of a Financial Risk Application

Graphics Processing Units (GPUs) are becoming popular accelerators in modern High-Performance Computing (HPC) clusters. Installing GPUs on each node of the cluster is not efficient resulting in high costs and power consumption as well as underutilisation of the accelerator. The research reported in this paper is motivated towards the use of few physical GPUs by providing cluster nodes access to remote GPUs on-demand for a financial risk application. We hypothesise that sharing GPUs between several nodes, referred to as multi-tenancy, reduces the execution time and energy consumed by an application. Two data transfer modes between the CPU and the GPUs, namely concurrent and sequential, are explored. The key result from the experiments is that multi-tenancy with few physical GPUs using sequential data transfers lowers the execution time and the energy consumed, thereby improving the overall performance of the application.

Corrosion resistance of self-growing TiC coating on SIMP steel in LBE at 600 °C

SIMP steel was newly developed as a candidate structural material for the accelerator driven subcritical system. The serious decarburization of SIMP steel because of the high Si content was used to successfully form a self-growing TiC coating on the surface, after the Ti deposition as a first step. This TiC layer can effectively protect the surface from the static liquid lead-bismuth eutectic (LBE) corrosion at 600 °C up to 2000 h in the low oxygen LBE. However, in the oxygen saturated LBE, the TiC coating is oxidized into porous TiO2 after only 500 h and fails to protect. Therefore, the self-growing TiC coating is desired only when the oxygen content of LBE is strictly controlled on a low level.

Demonstration of passive plasma lensing of a laser wakefield accelerated electron bunch

We report on the first demonstration of passive all-optical plasma lensing using a two-stage setup. An intense femtosecond laser accelerates electrons in a laser wakefield accelerator (LWFA) to 100 MeVover millimeter length scales. By adding a second gas target behind the initial LWFAstage we introduce a robust and independently tunable plasma lens. We observe a density dependent reduction of the LWFA electron beam divergence from an initial value of 2.3 mrad, down to 1.4 mrad (rms), when the plasma lens is in operation. Such a plasma lens provides a simple and compact approach for divergence reduction well matched to the mm-scale length of the LWFA accelerator. The focusing forces are provided solely by the plasma and driven by the bunch itself only, making this a highly useful and conceptually new approach to electron beam focusing. Possible applications of this lens are not limited to laser plasma accelerators. Since no active driver is needed the passive plasma lens is also suited for high repetition rate focusing of electron bunches. Its understanding is also required for modeling the evolution of the driving particle bunch in particle driven wake field acceleration.

Sedimentology, structure and age estimate of five continental slope submarine landslides, eastern Australia

Sedimentological and accelerator mass spectrometry (AMS) 14C data provide estimates of the structure and age of five submarine landslides (∼0.4–3 km3) present on eastern Australia's continental slope between Noosa Heads and Yamba. Dating of the post-slide conformably deposited sediment indicates sediment accumulation rates between 0.017 m ka–1 and 0.2 m ka–1, which is consistent with previous estimates reported for this area. Boundary surfaces were identified in five continental slope cores at depths of 0.8 to 2.2 m below the present-day seafloor. Boundary surfaces present as a sharp colour-change across the surface, discernible but small increases in sediment stiffness, a slight increase in sediment bulk density of 0.1 g cm–3, and distinct gaps in AMS 14C ages of at least 25 ka. Boundary surfaces are interpreted to represent a slide plane detachment surface but are not necessarily the only ones or even the major ones. Sub-bottom profiler records indicate that: (1) the youngest identifiable sediment reflectors upslope from three submarine landslides terminate on and are truncated by slide rupture surfaces; (2) there is no obvious evidence for a post-slide sediment layer draped over, or burying, slide ruptures or exposed slide detachment surfaces; and (3) the boundary surfaces identified within the cores are unlikely to be near-surface slide surfaces within an overall larger en masse dislocation. These findings suggest that these submarine landslides are geologically recent (<25 ka), and that the boundary surfaces are either: (a) an erosional features that developed after the landslide, in which case the boundary surface age provides a minimum age for the landslide; or (b) detachment surfaces from which slabs of near-surface sediment were removed during landsliding, in which case the age of the sediment above the boundary surface indicates the approximate age of landsliding. While an earthquake-triggering mechanism is favoured for the initiation of submarine landslides on the eastern Australian margin, further evidence is required to confirm this interpretation.

Extração de blocos graníticos nas pedreiras de Cinza Ariz e Amarelo Macieira da empresa Polimagra – Granitos, S.A

A perfuração em maciços rochosos desempenha um papel fundamental na área da exploração e extração de rocha ornamental, nomeadamente em granitos. Para esse efeito, e como irá ser abordado neste trabalho, são utilizados pela empresa Polimagra – Granitos, S.A, nas pedreiras que explora, dois sistemas de perfuração: perfuração hidráulica e perfuração pneumática. Sendo um dos objetivos deste trabalho perceber qual o tipo de perfuração que apresenta maior rentabilidade, torna-se importante perceber as principais características dos dois sistemas de perfuração em estudo. Para isso, com a realização deste estágio curricular na empresa Polimagra – Granitos, S.A, foi possível comparar as principais diferenças dos dois sistemas utilizados, através do acompanhamento dos trabalhos de lavra em pedreiras, da cronometragem de tempos de perfuração em maciço rochoso granítico e da realização de um estudo de fracturação nas pedreiras de Cinza Ariz e Amarelo Macieira. Durante este tempo do estágio foi ainda possível acompanhar os diferentes métodos de transformação utilizado sobre os diferentes granitos obtidos, nas instalações fabris da empresa Polimagra – Granitos, S.A. De destacar ainda, e dentro da área da transformação do granito, a utilização de um sistema robótico de tecnologia de ponta, para corte, acabamento e embalamento de produtos em granito.

Interview with Charles W. Peck

Interview in five sessions, October-November 2003, with Charles W. Peck, professor of physics (now emeritus) in the Division of Physics, Mathematics, and Astronomy. He recalls his early life in South Texas and his interest in radio; first year of college at Texas Arts & Industries; three more years at New Mexico College of Agriculture & Mechanical Arts. Recalls graduate studies at Caltech with Murray Gell-Mann, H. P. Robertson, Robert Walker, Richard A. Dean, W. R. Smythe. Works on increasing intensity and stability of the Caltech synchrotron, with Walker, Matt Sands, and Alvin Tollestrup; 1964 thesis on K-lambda photoproduction. Joins the faculty as an assistant professor in 1965. Discusses his various teaching assignments, including an embarrassing moment when Richard Feynman attended one of his freshman physics lectures. Discusses his research at the Stanford Linear Accelerator Center and Lawrence Radiation Laboratory’s Bevatron. Collaboration with UC Berkeley and SLAC on “crystal ball” detector for SLAC’s SPEAR storage ring. Taking the crystal ball to DESY, in Hamburg. Works with Barry Barish at Gran Sasso laboratory in Italy, on MACRO; search for magnetic monopoles. He also discusses his administration work at Caltech, as executive officer for physics (1983-1986) and as PMA division chair from 1993 to 1998, when he immediately had to deal with the troubles plaguing LIGO [Laser Interferometer Gravitational-wave Observatory]. Detailed discussion of the LIGO contretemps and how it was settled, and of turning Big Bear Solar Observatory over to the New Jersey Institute of Technology. Advent of David Baltimore as Caltech president; attempt to recruit Ed Witten.

Conversor de energia das ondas em energia elétrica com dispositivo de coluna de água oscilante: simulação numérica e estudo geométrico

Os oceanos representam um dos maiores recursos naturais, possuindo expressivo potencial energético, podendo suprir parte da demanda energética mundial. Nas últimas décadas, alguns dispositivos destinados à conversão da energia das ondas dos oceanos em energia elétrica têm sido estudados. No presente trabalho, o princípio de funcionamento do conversor do tipo Coluna de Água Oscilante, do inglês Oscillating Water Colum, (OWC) foi analisado numericamente. As ondas incidentes na câmara hidro-pneumática da OWC, causam um movimento alternado da coluna de água no interior da câmara, o qual produz um fluxo alternado de ar que passa pela chaminé. O ar passa e aciona uma turbina a qual transmite energia para um gerador elétrico. O objetivo do presente estudo foi investigar a influência de diferentes formas geométricas da câmara sobre o fluxo resultante de ar que passa pela turbina, que influencia no desempenho do dispositivo. Para isso, geometrias diferentes para o conversor foram analisadas empregando modelos computacionais 2D e 3D. Um modelo computacional desenvolvido nos softwares GAMBIT e FLUENT foi utilizado, em que o conversor OWC foi acoplado a um tanque de ondas. O método Volume of Fluid (VOF) e a teoria de 2ª ordem Stokes foram utilizados para gerar ondas regulares, permitindo uma interação mais realista entre o conversor, água, ar e OWC. O Método dos Volumes Finitos (MVF) foi utilizado para a discretização das equações governantes. Neste trabalho o Contructal Design (baseado na Teoria Constructal) foi aplicado pela primeira vez em estudos numéricos tridimensionais de OWC para fim de encontrar uma geometria que mais favorece o desempenho do dispositivo. A função objetivo foi a maximização da vazão mássica de ar que passa através da chaminé do dispositivo OWC, analisado através do método mínimos quadrados, do inglês Root Mean Square (RMS). Os resultados indicaram que a forma geométrica da câmara influencia na transformação da energia das ondas em energia elétrica. As geometrias das câmaras analisadas que apresentaram maior área da face de incidência das ondas (sendo altura constante), apresentaram também maior desempenho do conversor OWC. A melhor geometria, entre os casos desse estudo, ofereceu um ganho no desempenho do dispositivo em torno de 30% maior.