Surface science motivated by heating of trapped ions from the quantum ground state.

For the past two and a half decades, anomalous heating of trapped ions from nearby electrode surfaces has continued to demonstrate unexpected results. Caused by electric-field noise, this heating of the ions' motional modes remains an obstacle for scalable quantum computation with trapped ions. One of the anomalous features of this electric-field noise is the reported nonmonotonic behavior in the heating rate when a trap is incrementally cleaned by ion bombardment. Motivated by this result, the present work reports on a surface analysis of a sample ion-trap electrode treated similarly with incremental doses of Ar+ ion bombardment. Kelvin probe force microscopy and x-ray photoelectron spectroscopy were used to investigate how the work functions on the electrode surface vary depending on the residual contaminant coverage between each treatment. It is shown that the as-fabricated Au electrode is covered with a hydrocarbon film that is modified after the first treatment, resulting in work functions and core-level binding energies that resemble that of atomic-like carbon on Au. Changes in the spatial distribution of work functions with each treatment, combined with a suggested phenomenological coverage and surface-potential roughness dependence to the heating, appear to be related to the nonmonotonic behavior previously reported.

Crystallographic orientation dependence of work function: carbon adsorption on Au surfaces.

We investigate the work function (WF) variation of different Au crystallographic surface orientations with carbon atom adsorption. Ab initio calculations within density-functional theory are performed on carbon deposited (100), (110), and (111) gold surfaces. The WF behaviour with carbon coverage for the different surface orientations is explained by the resultant electron charge density distributions. The dynamics of carbon adsorption at sub-to-one- monolayer (ML) coverage depends on the landscape of the potential energy surfaces. At higher ML coverage, because of adsorption saturation, the WF will have weak surface orientation dependence. This systematic study has consequential bearing on studies of electric-field noise emanating from polycrystalline gold ion-trap electrodes that have been largely employed in microfabricated electrodes.

100-fold reduction of electric-field noise in an ion trap cleaned with in situ argon-ion-beam bombardment.

Motional heating of trapped atomic ions is a major obstacle to their use as quantum bits in a scalable quantum computer. The detailed physical origin of this heating is not well understood, but experimental evidence suggests that it is caused by electric-field noise emanating from the surface of the trap electrodes. In this study, we have investigated the role of adsorbates on the electrodes by identifying contaminant overlayers, implementing an in situ argon-ion-beam cleaning treatment, and measuring ion heating rates before and after treating the trap electrodes' surfaces. We find a 100-fold reduction in heating rate after treatment. The experiments described here are sensitive to low levels of electric-field noise in the MHz frequency range. Therefore, this approach could become a useful tool in surface science that complements established techniques.

Effect of airway pressure display on interobserver agreement in the assessment of vascular pressures in patients with acute lung injury and acute respiratory distress syndrome.

BACKGROUND: Previous investigations have identified significant interobserver variability in the measurements of central venous pressure and pulmonary artery occlusion pressure in critically ill patients. Large interobserver variability in the measurement of vascular pressures could potentially lead to inappropriate treatment decisions. OBJECTIVE: We postulated that adding an airway pressure signal (Paw) to pressure tracings of central venous pressure and pulmonary artery occlusion pressure would improve interobserver agreement by facilitating identification of end-expiration. DESIGN: To test this hypothesis, six independent experts used a standard protocol to interpret strip-chart recordings of central venous pressure and pulmonary artery occlusion pressure with or without Paw. Two observers were said to agree if their measurements were within 2 mm Hg of each other. SETTING/SUBJECTS/INTERVENTIONS: A total of 459 strip-chart recordings (303 without Paw and 156 with Paw) were obtained from 121 patients enrolled in the ARDSnet Fluids and Catheters Treatment Trial (FACTT) in 16 different hospitals. RESULTS: Agreement within 2 mm Hg between two measurements was 79% for central venous pressure strips without Paw vs. 86% with Paw. For pulmonary artery occlusion pressure, agreement increased from 71% without Paw to 83% with Paw. The increase in agreement with the addition of Paw was greater for strips demonstrating >8 mm Hg phasic respiratory variation compared with strips demonstrating less phasic respiratory variation. CONCLUSION: Paw display is a simple, inexpensive method to facilitate the identification of end-expiration that can significantly improve interobserver agreement.

Observation of quantum oscillations between a Josephson phase qubit and a microscopic resonator using fast readout.

We have detected coherent quantum oscillations between Josephson phase qubits and critical-current fluctuators by implementing a new state readout technique that is an order of magnitude faster than previous methods. These results reveal a new aspect of the quantum behavior of Josephson junctions, and they demonstrate the means to measure two-qubit interactions in the time domain. The junction-fluctuator interaction also points to a possible mechanism for decoherence and reduced fidelity in superconducting qubits.

Decoherence in josephson phase qubits from junction resonators.

Although Josephson junction qubits show great promise for quantum computing, the origin of dominant decoherence mechanisms remains unknown. Improving the operation of a Josephson junction based phase qubit has revealed microscopic two-level systems or resonators within the tunnel barrier that cause decoherence. We report spectroscopic data that show a level splitting characteristic of coupling between a two-state qubit and a two-level system. Furthermore, we show Rabi oscillations whose "coherence amplitude" is significantly degraded by the presence of these spurious microwave resonators. The discovery of these resonators impacts the future of Josephson qubits as well as existing Josephson technologies.

Recombinant human complement C5a receptor antagonist reduces infarct size after surgical revascularization.

OBJECTIVES: This study tested the hypothesis that a recombinant human C5a antagonist, CGS 32359, attenuates neutrophil activation and reduces infarct size in a porcine model of surgical revascularization. METHODS: CGS 32359 (0.16-16 micromol/L) dose-dependently inhibited superoxide production by human C5a-activated porcine neutrophils (18 +/- 3.7 vs 1.6 +/- 0.5 nmol/5 min/5 x 10(6) neutrophils; P <.05) and reduced neutrophil adherence to coronary endothelium from 194 +/- 9 to 43 +/- 6 neutrophils/mm(2) (P <.05). The left anterior descending coronary artery was occluded for 50 minutes, after which saline solution (n = 8), mannitol-buffer vehicle (n = 9, 102 mg/kg bolus, 102 mg. kg(-1). h(-1)), or CGS 32359 (CGS, n = 7, 60 mg/kg bolus, 60 mg. kg(-1). h(-1)) was infused. After ischemia, 1-hour arrest was achieved by means of multidose hypothermic (4 degrees C) blood cardioplegia, followed by 2.5 hours of off-bypass reperfusion. The ligature on the left anterior descending artery was released before the second infusion of cardioplegic solution. RESULTS: Area at risk was similar in all groups (saline solution, 27% +/- 2%; mannitol-buffer vehicle, 26% +/- 2%; CGS, 26% +/- 2% left ventricular mass). Infarct size (area necrosis/area at risk) was significantly reduced by CGS (18% +/- 6%, P <.05) versus saline solution (52% +/- 3%) and mannitol-buffer vehicle (60% +/- 4%). Postischemic systolic shortening (sonomicrometry) in the area at risk was significantly improved with CGS (0.8% +/- 0.9%) compared with saline solution (-3.7% +/- 1.1%) and mannitol-buffer vehicle (-6.4% +/- 1.0%). Myeloperoxidase activity from accumulated neutrophils was less in the ischemic zone of CGS (0.014 +/- 0.002 U/100 mg tissue; P <.05) than mannitol-buffer vehicle (0.133 +/- 0.012 U/100 mg tissue). CONCLUSIONS: We conclude that the recombinant human C5a receptor antagonist CGS 32359 inhibits surgical ischemia-reperfusion injury after coronary occlusion.

Catalase activity and hydrogen peroxide levels are inversely correlated in maize scutella during seed germination.

Temporal patterns of hydrogen peroxide (H2O2) levels and total catalase activity are presented for post-imbibition scutella from six maize inbred lines expressing variable catalase activity. In all lines examined, H2O2 levels were highest during the initial days post-imbibition (1-2 dpi) and decreased thereafter, while total catalase activity was lowest during early dpi (1-2 dpi) and reached maximal activity at 4-6 dpi. In three of the six lines tested, a simple inverse correlation between catalase activity and H2O2 level was significant by Spearman's rank (P < 0.01). In addition to the general decline in H2O2 level throughout the dpi period, a reproducible increase in H2O2 level was observed at 4-5 dpi in five of six lines examined. Mutant lines lacking CAT-3 activity demonstrated a temporal shift in the occurrence of this increase. The role of total catalase (and individual isozymes) in controlling H2O2 levels during germination and the role of H2O2 as a potential regulator of catalase expression during germination are discussed.

Evaluation of two approaches to the quantitative histochemical localization of sucrose-P synthase in leaves.

Two methods for determining the quantitative localization of sucrose-P synthase in plant tissues were evaluated. The single-cell method (rapid freezing, freeze-drying, microdissection, micro-analysis) was validated in several ways, including comparative biochemistry, comparative histochemistry, and kinetics. In contrast, bulk isolation of cells by protoplast-forming methods resulted in loss of sucrose-P synthase activity. This latter approach is widely used and, as far as we are aware, can be successfully used for measurement of other enzymes. Thus, our observations form the basis for a specific caution against the use of protoplast-forming methods in an assay protocol for sucrose-P synthase.

Enzymic potential for fructose 6-phosphate phosphorylation by guard cells and by palisade cells in leaves of the broad bean Vicia faba L.

Guard cells and palisade cells were dissected from freeze-dried leaflets of the broad bean, Vicia faba L. Individual cell samples (6-12 ng) were assayed for ATP-dependent and pyrophosphate-dependent phosphofructokinases. The assay indicator, NADH loss, was monitored in real time in oil droplets with a computer-driven microfluorometer. On a protein basis, both activities were 10-fold higher in guard cells than in palisade cells, indicating (i) elevated carbon metabolism in guard cells to meet demands for energy and carbon skeletons required during stomatal opening, and (ii) parallel glycolytic pathways in guard cells, one responsive to the potent regulatory metabolite fructose 2,6-bisphosphate and the other not. Future work will be devoted to clarifying the roles of the cytosolic and chloroplastic compartments in guard cells.

Inactivation of highly activated spinach leaf sucrose-phosphate synthase by dephosphorylation.

Spinach (Spinacia oleracea L.) leaf sucrose-phosphate synthase (SPS) can be phosphorylated and inactivated in vitro with [gamma-(32)P]ATP (JLA Huber, SC Huber, TH Nielsen [1989] Arch Biochem Biophys 270: 681-690). Thus, it was surprising to find that SPS, extracted from leaves fed mannose in the light to highly activate the enzyme, could be inactivated in an ATP-independent manner when desalted crude extracts were preincubated at 25 degrees C before assay. The "spontaneous" inactivation involved a loss in activity measured with limiting substrate concentrations in the presence of the inhibitor, Pi, without affecting maximum catalytic activity. The spontaneous inactivation was unaffected by exogenous carrier proteins and protease inhibitors, but was inhibited by inorganic phosphate, fluoride, and molybdate, suggesting that a phosphatase may be involved. Okadaic acid, a potent inhibitor of mammalian type 1 and 2A protein phosphatases, had no effect up to 5 micromolar. Inactivation was stimulated about twofold by exogenous Mg(2+) and was relatively insensitive to Ca(2+) and to pH over the range pH 6.5 to 8.5. Radioactive phosphate incorporated into SPS during labeling of excised leaves with [(32)P]Pi (initially in the dark and then in the light with mannose) was lost with time when desalted crude extracts were incubated at 25 degrees C, and the loss in radiolabel was substantially reduced by fluoride. These results provide direct evidence for action of an endogenous phosphatase(s) using SPS as substrate. We postulate that highly activated SPS contains phosphorylated residue(s) that increase activation state, and that spontaneous inactivation occurs by removal of these phosphate group(s). Inactivation of SPS in vivo caused by feeding uncouplers to darkened leaf tissue that had previously been fed mannose in the dark, may occur by this mechanism. However, there is no evidence that this mechanism is involved in light-dark regulation of SPS in vivo.

Removal of contaminating nucleoside diphosphates from commercial preparations of uridine diphosphoglucose.

Nucleoside diphosphate contamination in commercial preparations of UDP-Glc poses potential problems in activity assays for enzymes that use this substrate. For removing these contaminants, we report a simple, inexpensive, and rapid method that obviates the need for uncertain corrections in assay calculations.

Effect of labyrinthectomy on the dynamic vestibulo-ocular counterrol reflex in the rhesus monkey.

Timeline records of eyeball counterrotation to constant speed rotations about the line of sight were examined in the Rhesus monkey via a linear transformer measurement system using a contact lens. Normal monkeys exhibited a decrease in the amplitude ratio of eye-to-chair motion and an increasing phase lag between eye and chair as the frequency of the motion platform increased. Bilateral labyrinthectomy or prolonged dosage with streptomycin was found to nearly abolish the counterroll reflex. Unilateral damage to the vestibular system resulted in a decrease in the amplitude ratio of the eye-to-chair motion by approximately 50% 1 month after surgery.