Evaluation of a servo settling algorithm

The aim of this work is to discuss methods of friction identification and provide experimental evaluation of a novel control algorithm that enhances settling after point-to-point motion. This algorithm is called the Nonlinear Integral Action Settling Algorithm or NIASA. As the name suggests, the integral gain is nonlinear, and is based upon a Dahl friction model. The settling resulting from PID + NIASA control is nearly exponential, and governed by a time constant that is specified in the control design. As the NIASA algorithm requires, friction parameters must be identified for the servo under test. Two methods of friction identification (Step Tests and Identification Profile) are contrasted and found to provide comparable results, although the latter can provide advantages. The identified friction parameters are in turn used to perform four sets of control experiments; two PID controllers (standard factory tuning and high performance PID with acceleration feedforward) are tested both with and without NIASA compensation. In the case study with a factory tuned PID controller, servo settling times to within ±3-100 nm, are reduced by between 80.5 and 87.4 when NIASA compensation is added. When the NIASA compensator is added to the high performance PID controller, servo settling time is still reduced by between 50.5 and 73.0. Although the NIASA compensator was designed to increase settling performance for relatively large point-to-point motions, similar positive results are achieved when the method is applied to smaller step motions that do not leave the pre-rolling friction regime. Frequency domain analyses demonstrated the nonlinear loop-gain of the plant, with a clear distinction between the rolling and pre-rolling friction cases. As expected, the nonlinear loop gain was found to lower the bandwidth for smaller motions. Adding NIASA control was observed to increase the bandwidth for small motions by a factor of 3-6, while having little effect for large motions. © 2012 Published by Elsevier Inc. All rights reserved

Nonlinear control algorithm for improving settling time in systems with friction

A nonlinear control algorithm that greatly reduces settling time in precision instruments with rolling element bearings is proposed. Reductions of 80.5%-87.4% in settling time were achieved when settling to within 3-100 nm of the commanded position. Final settling of such systems is typically impacted by the nonlinearity in the pre-rolling friction regime, which manifests as a hysteretic stiffness. Consequently, the integral term in the controller can take a long time to respond. In this paper, a nonlinear integral action settling algorithm is presented. The nonlinear integral gain takes the form of a Dahl friction model. Since the integral gain mimics hysteretic stiffness, the output of the integral control term is instantaneously set to a large value after each direction change, greatly improving settling response. A nearly first-order error dynamic results, which has a user-definable time constant. Before the algorithm can be implemented, the Coulomb friction and initial contact stiffness in the Dahl model must be experimentally determined for the stage. A sensitivity study is performed on the initial contact stiffness, which was found in other works to dictate the stability of the algorithm. © 1993-2012 IEEE

Evaluation of a servo settling algorithm

The aim of this work is to discuss methods of friction identification and provide experimental evaluation of a novel control algorithm that enhances settling after point-to-point motion. This algorithm is called the Nonlinear Integral Action Settling Algorithm or NIASA. As the name suggests, the integral gain is nonlinear, and is based upon a Dahl friction model. The settling resulting from PID + NIASA control is nearly exponential, and governed by a time constant that is specified in the control design. As the NIASA algorithm requires, friction parameters must be identified for the servo under test. Two methods of friction identification (Step Tests and Identification Profile) are contrasted and found to provide comparable results, although the latter can provide advantages. The identified friction parameters are in turn used to perform four sets of control experiments; two PID controllers (standard factory tuning and high performance PID with acceleration feedforward) are tested both with and without NIASA compensation. In the case study with a factory tuned PID controller, servo settling times to within ±3-100 nm, are reduced by between 80.5 and 87.4 when NIASA compensation is added. When the NIASA compensator is added to the high performance PID controller, servo settling time is still reduced by between 50.5 and 73.0. Although the NIASA compensator was designed to increase settling performance for relatively large point-to-point motions, similar positive results are achieved when the method is applied to smaller step motions that do not leave the pre-rolling friction regime. Frequency domain analyses demonstrated the nonlinear loop-gain of the plant, with a clear distinction between the rolling and pre-rolling friction cases. As expected, the nonlinear loop gain was found to lower the bandwidth for smaller motions. Adding NIASA control was observed to increase the bandwidth for small motions by a factor of 3-6, while having little effect for large motions. © 2012 Published by Elsevier Inc. All rights reserved

Microplastics disrupt hermit crab shell selection

Microplastics (plastics < 5 mm) are a potential threat to marine biodiversity. However, the effects of microplastic pollution on animal behaviour and cognition are poorly understood. We used shell selection in common European hermit crabs (Pagurus bernhardus) as a model to test whether microplastic exposure impacts the essential survival behaviours of contacting, investigating and entering an optimal shell. We kept 64 female hermit crabs in tanks containing either polyethylene spheres (n = 35) or no plastic (n = 29) for 5 days. We then transferred subjects into suboptimal shells and placed them in an observation tank with an optimal alternative shell. Plastic-exposed hermit crabs showed impaired shell selection: they were less likely than controls to contact optimal shells or enter them. They also took longer to contact and enter the optimal shell. Plastic exposure did not affect time spent investigating the optimal shell. These results indicate that microplastics impair cognition (information-gathering and processing), disrupting an essential survival behaviour in hermit crabs

Measurement of the branching fraction and CP content for the decay B(0) -> D(*+)D(*-)

This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APS.We report a measurement of the branching fraction of the decay B0→D*+D*- and of the CP-odd component of its final state using the BABAR detector. With data corresponding to an integrated luminosity of 20.4  fb-1 collected at the Υ(4S) resonance during 1999–2000, we have reconstructed 38 candidate signal events in the mode B0→D*+D*- with an estimated background of 6.2±0.5 events. From these events, we determine the branching fraction to be B(B0→D*+D*-)=[8.3±1.6(stat)±1.2(syst)]×10-4. The measured CP-odd fraction of the final state is 0.22±0.18(stat)±0.03(syst).This work is supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the A.P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation

Search for rare quark-annihilation decays, B --> Ds(*) Phi

We report on searches for B- --> Ds- Phi and B- --> Ds*- Phi. In the context of the Standard Model, these decays are expected to be highly suppressed since they proceed through annihilation of the b and u-bar quarks in the B- meson. Our results are based on 234 million Upsilon(4S) --> B Bbar decays collected with the BABAR detector at SLAC. We find no evidence for these decays, and we set Bayesian 90% confidence level upper limits on the branching fractions BF(B- --> Ds- Phi) Ds*- Phi)<1.2x10^(-5). These results are consistent with Standard Model expectations.Comment: 8 pages, 3 postscript figues, submitted to Phys. Rev. D (Rapid Communications

Influence of soil water content and atmospheric conditions on leaf water potential in cv. "Touriga Nacional" deep-rooted vineyards

Abstract In this study, the influence of soil and atmosphere conditions on noon and basal leaf water potential of vines ‘‘Touriga Nacional’’ in the Da˜o region submitted to different irrigation treatments is analysed. Both indicators showed to be dependent on environmental conditions at the time of measurement. Leaf water potential at noon of fully watered plants was linearly related with atmospheric conditions, with values registered when vapour pressure deficit (VPD) was higher than approximately 3 kPa being no different from the values registered in stressed plants. Therefore, this indicator cannot be reliably used to distinguish different plant water stress levels when atmospheric conditions induce high evaporative demands. The basal leaf water potential (wb) was also influenced by VPD at the time of measurement for all soil water conditions. In well irrigated plants, it was even possible to establish a baseline that can therefore be used to identify nonwater stressed conditions (wb (MPa) = -0.062–0.0972 VPD (kPa), r2 = 0.78). A good correlation was found between soil humidity and wb. However, more than the average value of the whole thickness of soil monitored, the wb values were dependent on the distribution of soil humidity, with the plants responding to the presence of wet layers

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Observation of associated near-side and away-side long-range correlations in √sNN=5.02 TeV proton-lead collisions with the ATLAS detector

Two-particle correlations in relative azimuthal angle (Δϕ) and pseudorapidity (Δη) are measured in √sNN=5.02  TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1  μb-1 of data as a function of transverse momentum (pT) and the transverse energy (ΣETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Δη|<5) “near-side” (Δϕ∼0) correlation that grows rapidly with increasing ΣETPb. A long-range “away-side” (Δϕ∼π) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ΣETPb, is found to match the near-side correlation in magnitude, shape (in Δη and Δϕ) and ΣETPb dependence. The resultant Δϕ correlation is approximately symmetric about π/2, and is consistent with a dominant cos⁡2Δϕ modulation for all ΣETPb ranges and particle pT

Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV

The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of √s = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT≥20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60≤pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2≤{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration