394 research outputs found

    Quantum-Information Processing with Semiconductor Macroatoms

    Get PDF
    An all optical implementation of quantum information processing with semiconductor macroatoms is proposed. Our quantum hardware consists of an array of semiconductor quantum dots and the computational degrees of freedom are energy-selected interband optical transitions. The proposed quantum-computing strategy exploits exciton-exciton interactions driven by ultrafast sequences of multi-color laser pulses. Contrary to existing proposals based on charge excitations, the present all-optical implementation does not require the application of time-dependent electric fields, thus allowing for a sub-picosecond, i.e. decoherence-free, operation time-scale in realistic state-of-the-art semiconductor nanostructures.Comment: 11 pages, 5 figures, to be published in Phys. Rev. Lett., significant changes in the text and new simulations (figure 3

    The Radio Sky at Meter Wavelengths: m-Mode Analysis Imaging with the Owens Valley Long Wavelength Array

    Get PDF
    A host of new low-frequency radio telescopes seek to measure the 21-cm transition of neutral hydrogen from the early universe. These telescopes have the potential to directly probe star and galaxy formation at redshifts 20z720 \gtrsim z \gtrsim 7, but are limited by the dynamic range they can achieve against foreground sources of low-frequency radio emission. Consequently, there is a growing demand for modern, high-fidelity maps of the sky at frequencies below 200 MHz for use in foreground modeling and removal. We describe a new widefield imaging technique for drift-scanning interferometers, Tikhonov-regularized mm-mode analysis imaging. This technique constructs images of the entire sky in a single synthesis imaging step with exact treatment of widefield effects. We describe how the CLEAN algorithm can be adapted to deconvolve maps generated by mm-mode analysis imaging. We demonstrate Tikhonov-regularized mm-mode analysis imaging using the Owens Valley Long Wavelength Array (OVRO-LWA) by generating 8 new maps of the sky north of δ=30\delta=-30^\circ with 15 arcmin angular resolution, at frequencies evenly spaced between 36.528 MHz and 73.152 MHz, and \sim800 mJy/beam thermal noise. These maps are a 10-fold improvement in angular resolution over existing full-sky maps at comparable frequencies, which have angular resolutions 2\ge 2^\circ. Each map is constructed exclusively from interferometric observations and does not represent the globally averaged sky brightness. Future improvements will incorporate total power radiometry, improved thermal noise, and improved angular resolution -- due to the planned expansion of the OVRO-LWA to 2.6 km baselines. These maps serve as a first step on the path to the use of more sophisticated foreground filters in 21-cm cosmology incorporating the measured angular and frequency structure of all foreground contaminants.Comment: 27 pages, 18 figure

    Interobserver Agreement in the Clinical Assessment of Children With Blunt Abdominal Trauma

    Full text link
    Objectives The objective was to determine the interobserver agreement of historical and physical examination findings assessed during the emergency department (ED) evaluation of children with blunt abdominal trauma. Methods This was a planned substudy of a multicenter, prospective cohort study of children younger than 18 years of age evaluated for blunt abdominal trauma. Patients were excluded if injury occurred more than 24 hours prior to evaluation or if computed tomography (CT) imaging was obtained at another hospital prior to transfer to a study site. Two clinicians independently recorded their clinical assessments of a convenience sample of patients onto data collection forms within 60 minutes of each other and prior to CT imaging (if obtained) or knowledge of laboratory results. The authors categorized variables as either subjective symptoms (i.e., patient history) or objective findings (i.e., physical examination). For each variable recorded by the two observers, the agreement beyond that expected by chance was estimated, using the kappa (κ) statistic for categorical variables and weighted κ for ordinal variables. Variables with 95% lower confidence limits (LCLs) κ ≥ 0.4 (moderate agreement or better) were considered to have acceptable agreement. Results A total of 632 pairs of physician observations were obtained on 23 candidate variables. Acceptable agreement was achieved in 16 (70%) of the 23 variables tested. For six subjective symptoms, κ ranged from 0.48 (complaint of shortness of breath) to 0.90 (mechanism of injury), and only the complaint of shortness of breath had a 95% LCL κ < 0.4. For the 17 objective findings, κ ranged from –0.01 (pelvis instability) to 0.82 (seat belt sign present). The 95% LCL for κ was <0.4 for flank tenderness, abnormal chest auscultation, suspicion of alcohol or drug intoxication, pelvis instability, absence of bowel sounds, and peritoneal irritation. Conclusions Observers can achieve at least acceptable agreement on the majority of historical and physical examination variables in children with blunt abdominal trauma evaluated in the ED. Those variables are candidates for consideration for development of a clinical prediction rule for intra‐abdominal injury in children with blunt trauma. Resumen Concordancia Interobservador en la Valoración Clínica de los Niños con Traumatismo Abdominal Cerrado Objetivos Determinar la concordancia interobservador de los hallazgos de la historia clínica y la exploración física obtenidos durante la valoración de los niños con traumatismo abdominal de alta energía en el servicio de urgencias (SU). Metodología Se diseñó un subestudio de un estudio de cohorte prospectivo y multicéntrico de niños de 18 años o menos evaluados por traumatismo abdominal cerrado. Se excluyeron los pacientes si el traumatismo había ocurrido más de 24 horas antes de la primera valoración, o si las imágenes de la tomografía computarizada (TC) se obtuvieron en otro hospital previamente a trasladarse al lugar del estudio. Dos clínicos recogieron de forma independiente su valoración clínica en un formulario de datos, de una muestra de conveniencia de pacientes, en los primeros 60 minutos, y previamente a las imágenes de la TC (si ésta se realizó) o al conocimiento de los resultados del laboratorio. Se clasificaron las variables como síntomas subjetivos (ej.: historia del paciente) o hallazgos objetivos (ej.: exploración física). Para cada variable recogida por los dos observadores, se estimó la concordancia más allá de la esperada por el azar usando el índice kappa (κ) para las variables categóricas y índice κ ponderado para las variables ordinales. Se consideró que existía una concordancia aceptable para las variables con una κ ≥ 0,4 (concordancia moderada o buena) en el límite inferior del intervalo de confianza del 95% (IC 95%). Resultados Se obtuvieron 632 pares de observaciones clínicas en 23 variables candidatas. Se alcanzó la concordancia aceptable en 16 (70%) de ellas. Para los seis síntomas subjetivos, el rango de κ fue de 0,48 (queja de dificultad respiratoria) a 0,90 (mecanismo de la lesión), y sólo la queja de dificultad respiratoria tuvo una κ < 0,4 en el límite inferior del IC 95%. Para los 17 hallazgos objetivos, el rango de κ fue desde ‐0,01 (inestabilidad pelvis) a 0,82 (presencia del signo del cinturón de seguridad). El dolor en el flanco, la auscultación torácica alterada, la sospecha de intoxicación por alcohol o tóxicos, la inestabilidad de pelvis, la ausencia de ruidos intestinales y la irritación peritoneal tuvieron una κ < 0,4 en el límite inferior del IC 95%. Conclusiones Los observadores pueden alcanzar al menos una concordancia aceptable en la mayoría de las variables de la historia clínica y la exploración física en los niños con traumatismo abdominal cerrado evaluado en el SU. Estas variables son candidatas para considerarse en el desarrollo de una regla de predicción clínica para la lesión intrabdominal en los niños con traumatismo de cerrado.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98339/1/acem12132.pd

    Control of Decoherence: Dynamical Decoupling versus Quantum Zeno Effect - a case study for trapped ions

    Get PDF
    The control of thermal decoherence via dynamical decoupling and via the quantum Zeno effect (Zeno control) is investigated for a model of trapped ion, where the dynamics of two low lying hyperfine states undergoes decoherence due to the thermal interaction with an excited state. Dynamical decoupling is a procedure that consists in periodically driving the excited state, while the Zeno control consists in frequently measuring it. When the control frequency is high enough, decoherence is shown to be suppressed. Otherwise, both controls may accelerate decoherence.Comment: 24 pages, 8 figure

    Simulating open quantum systems: from many-body interactions to stabilizer pumping

    Get PDF
    In a recent experiment, Barreiro et al. demonstrated the fundamental building blocks of an open-system quantum simulator with trapped ions [Nature 470, 486 (2011)]. Using up to five ions, single- and multi-qubit entangling gate operations were combined with optical pumping in stroboscopic sequences. This enabled the implementation of both coherent many-body dynamics as well as dissipative processes by controlling the coupling of the system to an artificial, suitably tailored environment. This engineering was illustrated by the dissipative preparation of entangled two- and four-qubit states, the simulation of coherent four-body spin interactions and the quantum non-demolition measurement of a multi-qubit stabilizer operator. In the present paper, we present the theoretical framework of this gate-based ("digital") simulation approach for open-system dynamics with trapped ions. In addition, we discuss how within this simulation approach minimal instances of spin models of interest in the context of topological quantum computing and condensed matter physics can be realized in state-of-the-art linear ion-trap quantum computing architectures. We outline concrete simulation schemes for Kitaev's toric code Hamiltonian and a recently suggested color code model. The presented simulation protocols can be adapted to scalable and two-dimensional ion-trap architectures, which are currently under development.Comment: 27 pages, 9 figures, submitted to NJP Focus on Topological Quantum Computatio

    Measuring the value of placements to employers: A cost-benefit approach

    Get PDF
    This article explores the concept and measurement of placement value, underexplored in theory and practice to date. The article makes a theoretical contribution to the placement value discourse by examining and articulating the placement value concept. It also offers a practical contribution by exploring a piloted tool to evaluate employer placement value, developed as part of a project funded by the Higher Education Funding Council for England. It examines the immaturity of the placement value concept against contemporary value discourse, including service- and goods-dominant logic frameworks (exploring value-in-use and value-in-exchange) and calls for greater attention to be paid to placement value to support the sustainable provision of placements.N/

    Penerapan Metode Scoring System untuk Penilaian Latihan Pemahaman Materi Ibadah Sholat Fardhu dan Sunnah

    Full text link
    Ibadah Sholat merupakan kewajiban yang harus senantiasa dikerjakan oleh umat muslim. Tidak hanya mengutamakan ibadah sholat fardhu, melainkan Allah juga menganjurkan untuk menyempurnakan dengan melakukan ibadah sholat sunnah. Dalam pelaksanaannya, umat muslim masih membutuhkan panduan mengenai tuntunan sholat tersebut secara praktis dan bersifat mobile, sementara mobilitas manusia semakin tinggi. Oleh karena itu, pada penelitian ini telah membangun aplikasi tuntunan sholat baik fardhu dan sunnah berbasis android yang dilengkapi dengan latihan kemampuan pemahaman materi mengenai sholat fardhu dan sunnah. Tujuannya adalah mampu meningkatkan kualitas setiap orang yang ingin belajar sholat dengan melakukan latihan kemampuan pemahaman materi tersebut. Sistem penilaiannya menggunakan metode pengukuran, yaitu metode scoring system. Metode scoring system adalah metode yang memberikan evaluasi terhadap kelayakan subyek tes dalam bentuk nilai. Dari hasil pengujian menunjukkan bahwasannya aplikasi penilaian latihan ini mampu menilai tingkat pemahaman materi berdasarkan hasil tes yang diperoleh menggunakan metode scoring system
    corecore