387 research outputs found
Hyperfine induced spin and entanglement dynamics in Double Quantum Dots: A homogeneous coupling approach
We investigate hyperfine induced electron spin and entanglement dynamics in a
system of two quantum dot spin qubits. We focus on the situation of zero
external magnetic field and concentrate on approximation-free theoretical
methods. We give an exact solution of the model for homogeneous hyperfine
coupling constants (with all coupling coefficients being equal) and varying
exchange coupling, and we derive the dynamics therefrom. After describing and
explaining the basic dynamical properties, the decoherence time is calculated
from the results of a detailed investigation of the short time electron spin
dynamics. The result turns out to be in good agreement with experimental data.Comment: 10 pages, 8 figure
Perturbative regimes in central spin models
Central spin models describe several types of solid state nanostructures
which are presently considered as possible building blocks of future quantum
information processing hardware. From a theoretical point of view, a key issue
remains the treatment of the flip-flop terms in the Hamiltonian in the presence
of a magnetic field. We systematically study the influence of these terms, both
as a function of the field strength and the size of the spin baths. We find
crucial differences between initial states with central spin configurations of
high and such of low polarizations. This has strong implications with respect
to the influence of a magnetic field on the flip-flop terms in central spin
models of a single and more than one central spin. Furthermore, the
dependencies on bath size and field differ from those anticipated so far. Our
results might open the route for the systematic search for more efficient
perturbative treatments of central spin problems.Comment: 7 pages, 3 figure
Die Veränderung der urbanen Territorialität infolge der Videoüberwachung des öffentlichen Raumes : ein Vergleich unterschiedlicher räumlicher Funktionsweisen der Videoüberwachung
As a result of the anonymisation of parts of public space and increasing individualisation of social relations and forms of life, mechanisms of social regulation are changing within public space. Increases of private and public video surveillance were first seen in Great Britain and the United States, later in continental Europe. On the basis of a study of spatial distribution of video surveillance cameras in the context of public space in the city of Geneva, different strategies and forms of surveillance by video cameras are indicated. The investigation shows the degree to which the locality of a video surveillance camera reflects the economic activities in the area. Consequently, the implications of mostly privately owned video surveillance on the urban territoriality of different actors within public space could be analysed. Included in the research are the results of a public opinion poll involving 500 inhabitants of Olten on public perception of video surveillance. In this context, special attention was paid to video surveillance as a symbolic and material mediator, transforming social relations between individuals as well as their relationship with public space
Universal phase shift and non-exponential decay of driven single-spin oscillations
We study, both theoretically and experimentally, driven Rabi oscillations of
a single electron spin coupled to a nuclear spin bath. Due to the long
correlation time of the bath, two unusual features are observed in the
oscillations. The decay follows a power law, and the oscillations are shifted
in phase by a universal value of ~pi/4. These properties are well understood
from a theoretical expression that we derive here in the static limit for the
nuclear bath. This improved understanding of the coupled electron-nuclear
system is important for future experiments using the electron spin as a qubit.Comment: Main text: 4 pages, 3 figures, Supplementary material: 2 pages, 3
figure
Detection of vascularity in wrist tenosynovitis: power doppler ultrasound compared with contrast-enhanced grey-scale ultrasound
Equipment specification for a space rated radar altimeter Final technical report
Equipment specifications for GEOS C mission altimeter
Driven coherent oscillations of a single electron spin in a quantum dot
The ability to control the quantum state of a single electron spin in a
quantum dot is at the heart of recent developments towards a scalable
spin-based quantum computer. In combination with the recently demonstrated
exchange gate between two neighbouring spins, driven coherent single spin
rotations would permit universal quantum operations. Here, we report the
experimental realization of single electron spin rotations in a double quantum
dot. First, we apply a continuous-wave oscillating magnetic field, generated
on-chip, and observe electron spin resonance in spin-dependent transport
measurements through the two dots. Next, we coherently control the quantum
state of the electron spin by applying short bursts of the oscillating magnetic
field and observe about eight oscillations of the spin state (so-called Rabi
oscillations) during a microsecond burst. These results demonstrate the
feasibility of operating single-electron spins in a quantum dot as quantum
bits.Comment: Total 25 pages. 11 pages main text, 5 figures, 9 pages supplementary
materia
Developing a Critical Understanding of Smart Urbanism?
Smart urbanism is emerging at the intersection of visions for the future of urban places, new technologies and infrastructures. Smart urbanism discourses are deeply rooted in seductive and normative visions of the future where digital technology stands as the primary driver for change. Yet our understanding of the opportunities, challenges, and implications of smart urbanism is limited. Research in this field is in its infancy, fragmented along disciplinary lines and often based on single city case studies. As a result, we lack both the theoretical insight and empirical evidence required to assess the implications of this potentially transformative phenomenon. Given the significant implications of smart urbanism there is an urgent need to critically engage with why, how, for whom and with what consequences smart urbanism is emerging in different urban contexts. The aim of this review is to unpack the different logics and rationales behind smart urbanism discourses and proposals, and in this way understand the ways by which imaginaries of urban futures are currently being constructed, along with their socio-technical and political implications for future research priorities
EULAR Points to Consider for the use of imaging to guide interventional procedures in patients with rheumatic and musculoskeletal diseases (RMDs)
OBJECTIVES: To develop evidence-based Points to Consider (PtC) for the use of imaging modalities to guide interventional procedures in patients with rheumatic and musculoskeletal diseases (RMDs). METHODS: European Alliance of Associations for Rheumatology (EULAR) standardised operating procedures were followed. A systematic literature review was conducted to retrieve data on the role of imaging modalities including ultrasound (US), fluoroscopy, MRI, CT and fusion imaging to guide interventional procedures. Based on evidence and expert opinion, the task force (25 participants consisting of physicians, healthcare professionals and patients from 11 countries) developed PtC, with consensus obtained through voting. The final level of agreement was provided anonymously. RESULTS: A total of three overarching principles and six specific PtC were formulated. The task force recommends preference of imaging over palpation to guide targeted interventional procedures at peripheral joints, periarticular musculoskeletal structures, nerves and the spine. While US is the favoured imaging technique for peripheral joints and nerves, the choice of the imaging method for the spine and sacroiliac joints has to be individualised according to the target, procedure, expertise, availability and radiation exposure. All imaging guided interventions should be performed by a trained specialist using appropriate operational procedures, settings and assistance by technical personnel. CONCLUSION: These are the first EULAR PtC to provide guidance on the role of imaging to guide interventional procedures in patients with RMDs
Poor reproducibility of compression elastography in the Achilles tendon: same day and consecutive day measurements.
OBJECTIVE
To determine the reproducibility of compression elastography (CE) when measuring strain data, a measure of stiffness of the human Achilles tendon in vivo, over consecutive measures, consecutive days and when using different foot positions.
MATERIALS AND METHODS
Eight participants (4 males, 4 females; mean age 25.5 ± 2.51 years, range 21-30 years; height 173.6 ± 11.7 cm, range 156-189 cm) had five consecutive CE measurements taken on one day and a further five CE measures taken, one per day, at the same time of day, every day for a consecutive 5-day period. These 80 measurements were used to assess both the repeatability and reproducibility of the technique. Means, standard deviations, coefficient of variation (CV), Pearson correlation analysis (R) and intra-class correlation coefficients (ICC) were calculated.
RESULTS
For CE data, all CVs were above 53%, R values indicated no-to-weak correlations between measures at best (range 0.01-0.25), and ICC values were all classified in the poor category (range 0.00-0.11). CVs for length and diameter measures were acceptably low indicating a high level of reliability.
CONCLUSIONS
Given the wide variation obtained in the CE results, it was concluded that CE using this specific system has a low level of reproducibility for measuring the stiffness of the human Achilles tendon in vivo over consecutive days, consecutive measures and in different foot positions
- …