ALEA: Fine-Grain Energy Profiling with Basic Block Sampling

Energy efficiency is an essential requirement for all contemporary computing systems. We thus need tools to measure the energy consumption of computing systems and to understand how workloads affect it. Significant recent research effort has targeted direct power measurements on production computing systems using on-board sensors or external instruments. These direct methods have in turn guided studies of software techniques to reduce energy consumption via workload allocation and scaling. Unfortunately, direct energy measurements are hampered by the low power sampling frequency of power sensors. The coarse granularity of power sensing limits our understanding of how power is allocated in systems and our ability to optimize energy efficiency via workload allocation.
We present ALEA, a tool to measure power and energy consumption at the granularity of basic blocks, using a probabilistic approach. ALEA provides fine-grained energy profiling via sta- tistical sampling, which overcomes the limitations of power sens- ing instruments. Compared to state-of-the-art energy measurement tools, ALEA provides finer granularity without sacrificing accuracy. ALEA achieves low overhead energy measurements with mean error rates between 1.4% and 3.5% in 14 sequential and paral- lel benchmarks tested on both Intel and ARM platforms. The sampling method caps execution time overhead at approximately 1%. ALEA is thus suitable for online energy monitoring and optimization. Finally, ALEA is a user-space tool with a portable, machine-independent sampling method. We demonstrate two use cases of ALEA, where we reduce the energy consumption of a k-means computational kernel by 37% and an ocean modelling code by 33%, compared to high-performance execution baselines, by varying the power optimization strategy between basic blocks.

The measurement of the dielectronic recombination in He-like Fe ions

We have studied the dielectronic recombination process in He-like Fe ions and have obtained the resonant strengths of the KLn (3 less than or equal to, n less than or equal to, 5) resonances. This measurement was performed with the use of an electron beam ion trap by measuring the x-ray energy emitted from highly charged ions simultaneously with the electron beam energy scanned during the measurement. The total resonant strengths obtained are 5.0 x 10(-19), 2.1 x 10(-19) and 1.1 X 10(-19) cm(2) eV, for KLM, KLN and KLO, respectively.

The measurement of the electron impact ionization cross-sections of hydrogen-like ions

We have measured electron impact ionization cross-sections of hydrogen-like iron and hydrogen-like molybdenum with an electron beam ion trap. The measurements were performed in the electron energy range between 13.5 and 40 keV for hydrogen-like iron and between 50 and 80 keV for hydrogen-like molybdenum. (C) 2003 Elsevier Science B.V. All rights reserved.

Spectroscopic measurements of phase-resolved electron energy distribution functions in RF-excited discharges

The reliable measurement of the electron energy distribution function (EEDF) of plasmas is one of the most important subjects of plasma diagnostics, because this piece of information is the key to understand basic discharge mechanisms. Specific problems arise in the case of RF-excited plasmas, since the properties of electrons are subject to changes on a nanosecond time scale and show pronounced spatial anisotropy. We report on a novel spectroscopic method for phase- and space-resolved measurements of the electron energy distribution function of energetic (> 12 eV) electrons in RF discharges. These electrons dominate excitation and ionization processes and are therefore of particular interest. The technique is based on time-dependent measurements during the RF cycle of excited-state populations of rare gases admixed in small fractions. These measurements yield � in combination with an analytical model � detailed information on the excitation processes. Phase-resolved optical emission spectroscopy allows us to overcome the difficulties connected with the very low densities (107�109 cm�3) and the transient character of the electrons in the sheath region. The EEDF of electrons accelerated in the sheath region can be described by a shifted Maxwellian with a drift velocity component in direction of the electric field. The method yields the high-energy tail of the EEDF on an absolute scale. The applicability of the method is demonstrated at a capacitively coupled RF discharge in hydrogen.

Measurement of Quenching Coefficients and Developement of Calibration Methods for Quantitative Spectroscopy of Plasma at Elevated Pressures

Measurements of collisional de-excitation (quenching) coefficients required for the interpretation of emission and fluorescence spectroscopic measurements are reported. Particular attention is turned on argon transitions which are of interest for actinometric determinations of atomic ground state populations and on fluorescence lines originating from excited atoms and noble gases in connection with two-photon excitation (TALIF) of atomic radicals. A novel method is described which allows to infer quenching coefficients for collisions with molecular hydrogen of noble gas states in the energy range up to 24 eV. The excitation is performed in these experiments by collisions of energetic electrons in the sheath of an RF excited hydrogen plasma during the field reversal phase which lasts about 10 ns. We describe in addition a calibration method - including quenching effects - for the determination by TALIF of absolute atomic radical densities of hydrogen, nitrogen and oxygen using two-photon resonances in noble gases close by the resonances of the species mentioned. The paper closes with first ideas on a novel technique to bypass quenching effects in TALIF by introducing an additional, controllable loss by photoionization that will allow quenching-free determination of absolute atomic densities with prevalent nanosecond laser systems in situations where collisional de-excitation dominates over spontaneous emission.

Application to argon ions of a new technique to measure the two-electron contribution to the ground state energy of helium-like ions

We have measured the two-electron contribution of the ground state energy of helium-like argon ions using an electron beam ion trap (EBIT). A two-dimensional map was measured showing the intensity of x-rays from the trap passing through a krypton-filled absorption cell. The independent axes of this map were electron beam energy and x-ray energy. From this map, we deduced the two-electron contribution of the ground state of helium-like argon. This experimentally determined Value (312.4 +/- 9.5 eV) was found to be in good agreement with our calculated values (about 303.35 eV) and previous calculations of the same quantity. Based on these measurements, we have shown that a ten-day absorption spectroscopy run with a super-EBIT should be sufficient to provide a new benchmark value for the two-electron contribution to the ground state of helium-like krypton. Such a measurement would then constitute a test of quantum electrodynamics to second order.

Measurement-based Method for Wind Farm Power System Oscillations Monitoring

The global increase in the penetration of renewable energy is pushing electrical power systems into uncharted territory, especially in terms of transient and dynamic stability. In particular, the greater penetration of wind generation in European power networks is, at times, displacing a significant capacity of conventional synchronous generation with fixed-speed induction generation and now more commonly, doubly fed induction generators. The impact of such changes in the generation mix requires careful monitoring to assess the impact on transient and dynamic stability. This study presents a measurement-based method for the early detection of power system oscillations, with consideration of mode damping, in order to raise alarms and develop strategies to actively improve power system dynamic stability and security. A method is developed based on wavelet-based support vector data description (SVDD) to detect oscillation modes in wind farm output power, which may excite dynamic instabilities in the wider system. The wavelet transform is used as a filter to identify oscillations in frequency bands, whereas the SVDD method is used to extract dominant features from different scales and generate an assessment boundary according to the extracted features. Poorly damped oscillations of a large magnitude, or that are resonant, can be alarmed to the system operator, to reduce the risk of system instability. The proposed method is exemplified using measured data from a chosen wind farm site.

Low-energy positron interactions with atoms and molecules

This paper is a review of low-energy positron interactions with atoms and molecules. Processes of interest include elastic scattering, electronic and vibrational excitation, ionization, positronium formation and annihilation. An overview is presented of the currently available theoretical and experimental techniques to study these phenomena, including the use of trap-based positron beam sources to study collision processes with improved energy resolution. State-resolved measurements of electronic and vibrational excitation cross sections and measurement of annihilation rates in atoms and molecules as a function of incident positron energy are discussed. Where data are available, comparisons are made with analogous electron scattering cross sections. Resonance phenomena, common in electron scattering, appear to be less common in positron scattering. Possible exceptions include the sharp onsets of positron-impact electronic and vibrational excitation of selected molecules. Recent energy-resolved studies of positron annihilation in hydrocarbons containing more than a few carbon atoms provide direct evidence that vibrational Feshbach resonances underpin the anomalously large annihilation rates observed for many polyatomic species. We discuss open questions regarding this process in larger molecules, as well as positron annihilation in smaller molecules where the theoretical picture is less clear.

MEASUREMENT AND CALCULATION OF ABSOLUTE SINGLE AND MULTIPLE CHARGE EXCHANGE CROSS SECTIONS FOR Feq+ IONS IMPACTING H2O

Charge exchange (CE) plays a fundamental role in the collisions of solar- and stellar-wind ions with lunar and planetary exospheres, comets, and circumstellar clouds. Reported herein are absolute cross sections for single, double, triple, and quadruple CE of Feq+ (q = 5-13) ions with H2O at a collision energy of 7q keV. One measured value of the pentuple CE is also given for Fe9+ ions. An electron cyclotron resonance ion source is used to provide currents of the highly charged Fe ions. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental cross sections are compared with new results of the n-electron classical trajectory Monte Carlo approximation. The radiative and non-radiative cascades following electron transfers are approximated using scaled hydrogenic transition probabilities and scaled Auger rates. Also given are estimates of cross sections for single capture, and multiple capture followed by autoionization, as derived from the extended overbarrier model. These estimates are based on new theoretical calculations of the vertical ionization potentials of H2O up to H2O10+.

Experimental setup and first measurement of DNA damage induced along and around an antiproton beam

Radiotherapy employs ionizing radiation to induce lethal DNA lesions in cancer cells while minimizing damage to healthy tissues. Due to their pattern of energy deposition, better therapeutic outcomes can, in theory, be achieved with ions compared to photons. Antiprotons have been proposed to offer a further enhancement due to their annihilation at the end of the path. The work presented here aimed to establish and validate an experimental procedure for the quantification of plasmid and genomic DNA damage resulting from antiproton exposure. Immunocytochemistry was used to assess DNA damage in directly and indirectly exposed human fibroblasts irradiated in both plateau and Bragg peak regions of a 126 MeV antiproton beam at CERN. Cells were stained post irradiation with an anti-gamma-H2AX antibody. Quantification of the gamma-H2AX foci-dose relationship is consistent with a linear increase in the Bragg peak region. A qualitative analysis of the foci detected in the Bragg peak and plateau region indicates significant differences highlighting the different severity of DNA lesions produced along the particle path. Irradiation of desalted plasmid DNA with 5 Gy antiprotons at the Bragg peak resulted in a significant portion of linear plasmid in the resultant solution.