3,602 research outputs found

    Error Compensation of Single-Qubit Gates in a Surface Electrode Ion Trap Using Composite Pulses

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    The fidelity of laser-driven quantum logic operations on trapped ion qubits tend to be lower than microwave-driven logic operations due to the difficulty of stabilizing the driving fields at the ion location. Through stabilization of the driving optical fields and use of composite pulse sequences, we demonstrate high fidelity single-qubit gates for the hyperfine qubit of a 171Yb+^{171}\text{Yb}^+ ion trapped in a microfabricated surface electrode ion trap. Gate error is characterized using a randomized benchmarking protocol, and an average error per randomized Clifford group gate of 3.6(3)×1043.6(3)\times10^{-4} is measured. We also report experimental realization of palindromic pulse sequences that scale efficiently in sequence length

    Mixed methods in land change research: towards integration

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/89580/1/j.1475-5661.2011.00482.x.pd

    The application of optical coherence tomography to image subsurface tissue structure of Antarctic krill Euphausia superba

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    Many small open ocean animals, such as Antarctic krill, are an important part of marine ecosystems. To discover what will happen to animals such as krill in a changing ocean, experiments are run in aquaria where conditions can be controlled to simulate water characteristics predicted to occur in the future. The response of individual animals to changing water conditions can be hard to observe, and with current observation techniques it is very difficult to follow the progress of an individual animal through its life. Optical coherence tomography (OCT) is an optical imaging technique that allows images at high resolution to be obtained from depths up to a few millimeters inside biological specimens. It is compatible with in vivo imaging and can be used repeatedly on the same specimens. In this work, we show how OCT may be applied to post mortem krill samples and how important physiological data such as shell thickness and estimates of organ volume can be obtained. Using OCT we find an average value for the thickness of krill exoskeleton to be (30±4) µm along a 1 cm length of the animal body. We also show that the technique may be used to provide detailed imagery of the internal structure of a pleopod joint and provide an estimate for the heart volume of (0.73±0.03) mm3

    Multicarrier CDMA systems with MIMO technology

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    The rapid demand for broadband wireless access with fast multimedia services initiated a vast research on the development of new wireless systems that will provide high spectral efficiencies and data rates. A potential candidate for future generation wireless systems is multi-carrier code division multiple access (MC-CDMA). To achieve higher user capacities and increase the system data rate, various multiple-input multiple-output (MIMO) technologies such as spatial multiplexing and spatial diversity techniques have been proposed recently and combined with MC-CDMA.This research proposes a chip level coded ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver for downlink MIMO MC-CDMA systems. As the conventional chip level OSIC receiver [1] is unable to overcome multiple access interference (MAI) and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference by requiring only the knowledge of the desired user's spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors [2] but also outperforms both the chip and symbol level OSIC receivers. In this work we also compare the error rate performance between our proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and we justify the comparisons with a pairwise error probability (PEP) analysis. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system loads whereas in high system loads, MIMO OFDMA outperforms MIMO MC-CDMA. However if all users' spreading sequences are used at the desired user receiver, MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.In the second part of this work, user grouping algorithms are proposed to provide power minimisation in grouped MC-CDMA and space-time block code (STBC) MC-CDMA systems. When the allocation is performed without a fair data rate requirement, the optimal solution to the minimisation problem is provided. However when some fairness is considered, the optimal solution requires high computational complexity and hence we solve this problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

    Krill biomass estimation : sampling and measurement variability

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    FB is funded by an EPSRC studentship (grant code: EP/R513337/1).Krill are the subject of growing commercial fisheries and therefore fisheries management is necessary to ensure long-term sustainability. Krill catch limits, set by Commission for the Conservation of Antarctic Marine Living Resources, are based on absolute krill biomass, estimated from acoustic-trawl surveys. In this work, we develop a method for determining an error budget for acoustic-trawl surveys of krill which includes sampling and measurement variability. We use our error budget method to examine the sensitivity of biomass estimates to parameters in acoustic target strength (TS) models, length frequency distribution and length to wetmass relationships derived from net data. We determined that the average coefficient of variation (CV) of estimated biomass was 17.7% and the average CV due from scaling acoustic observations to biomass density was 5.3%. We found that a large proportion of the variability of biomass estimates is due to the krill orientation distribution, a parameter in the TS model. Orientation distributions with narrow standard deviations were found to emphasise the results of nulls in the TS to length relationship, which has to potential to lead to biologically implausible results.Publisher PDFPeer reviewe

    Mediastinal Lymphangioma and Chylothorax: Thoracic Involvement of Gorham's Disease

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    We report a case of mediastinal lymphangioma associated with Gorham's disease in a 38-year-old man who had suffered recurrent clavicular fractures during a seven-year period. Mediastinal widening associated with osteolysis of the clavicles and the sternal manubrium was revealed by chest radiography, while computed tomography demonstrated a cystic anterior mediastinal mass infiltrating mediastinal fat and associated with osseous destruction of the clavicles and manubrium. Chylothorax recurred during the course of the disease

    Correction: Dynamic Remodeling of Dendritic Arbors in GABAergic Interneurons of Adult Visual Cortex

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    Chronic in vivo imaging of fluorescent-labeled neurons in adult mice reveals extension and retraction of dendrites in GABAergic non-pyramidal interneurons of the cerebral cortex

    Ising-like antiferromagnetism on the octahedral sublattice of a cobalt-containing garnet and the potential for quantum criticality

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    In this contribution, we report that CaY2Co2Ge3O12 exhibits an unusual anisotropic and chainlike antiferromagnetic arrangement of spins despite crystallizing in the highly symmetric garnet structure. Using low-temperature powder neutron diffraction and symmetry analysis, we identify a magnetic structure consisting of chainlike motifs oriented along the body diagonals of the cubic unit cell with moments pointing parallel to the chain direction due to the strong Ising character of the Co ions. Antiferromagnetic order sets in below 6 K and exhibits both temperature- and field-induced magnetic transitions at high fields. Combining the results, we present a magnetic phase diagram that suggests CaY2Co2Ge3O12 undergoes a quantum phase transition at low temperatures and moderate fields
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