8,707 research outputs found
Stress relief as the driving force for self-assembled Bi nanolines
Stress resulting from mismatch between a substrate and an adsorbed material
has often been thought to be the driving force for the self-assembly of
nanoscale structures. Bi nanolines self-assemble on Si(001), and are remarkable
for their straightness and length -- they are often more than 400 nm long, and
a kink in a nanoline has never been observed. Through electronic structure
calculations, we have found an energetically favourable structure for these
nanolines that agrees with our scanning tunneling microscopy and photoemission
experiments; the structure has an extremely unusual subsurface structure,
comprising a double core of 7-membered rings of silicon. Our proposed structure
explains all the observed features of the nanolines, and shows that surface
stress resulting from the mismatch between the Bi and the Si substrate are
responsible for their self-assembly. This has wider implications for the
controlled growth of nanostructures on semiconductor surfaces.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Improving Retail Supply Flexibility using Buyer-Supplier Relational Capabilities
Purpose
This study investigates the mediating role of three important relational capabilities -
Absorptive Capacity, Transactive Memory Systems, and Organizational Interoperability; on
the flexibility of buyer-supplier relationships and performance in retail supply chains.
Drawing on the Relational view of strategic management, the impact of relational capabilities
on two forms of supply chain flexibility is examined – (a) Configuration Flexibility for
switching suppliers with minimal penalties and (b) Planning and Control Flexibility for
altering supply schedules, quality, and delivery lead-time.
Design/methodology/approach
Strategic and tactical level managers from 211 retail stores in the UK were surveyed. We
validated a measurement model with structural equation modeling, and tested four hypotheses
on the mediating role of relational capabilities on supply chain flexibility and retail
performance, controlling for size, duration of relationship and market segment.
Findings
Results showed that the three relational capabilities partially mediated the positive effect of
configuration flexibility and planning and control flexibility on operational performance in
big-middle and niche retailers. Examining the interaction effect of the forms of flexibility on
the relational capabilities and performance, we found positive interaction effects on
Transactive Memory Systems and Organizational Interoperability but a non-significant effect
on Absorptive Capacity.
Practical Implications
In addition to providing novel theoretical insights on supply chain flexibility, our findings
have practical implications for supplier selection and buyer-supplier relationship
management.
Originality/value
Overall, the study highlights the impacts of relational capabilities on adopted operational
strategies such as flexibility, buyer-supplier relationships, and retail performanc
Self-reported domain-specific and accelerometer-based physical activity and sedentary behaviour in relation to psychological distress among an urban Asian population
Background: The interpretation of previous studies on the association of physical activity and sedentary behaviour with psychological health is limited by the use of mostly self-reported physical activity and sedentary behaviour, and a focus on Western populations. We aimed to explore the association of self-reported and devise-based measures of physical activity and sedentary behaviour domains on psychological distress in an urban multi-ethnic Asian population.
Methods: From a population-based cross-sectional study of adults aged 18-79 years, data were used from an overall sample (n = 2653) with complete self-reported total physical activity/sedentary behaviour and domain-specific physical activity data, and a subsample (n = 703) with self-reported domain-specific sedentary behaviour and accelerometry data. Physical activity and sedentary behaviour data were collected using the Global Physical Activity Questionnaire (GPAQ), a domain-specific sedentary behaviour questionnaire and accelerometers. The Kessler Screening Scale (K6) and General Health Questionnaire (GHQ-12) were used to assess psychological distress. Logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals, adjusted for socio-demographic and lifestyle characteristics.
Results: The sample comprised 45.0% men (median age = 45.0 years). The prevalence of psychological distress based on the K6 and GHQ-12 was 8.4% and 21.7%, respectively. In the adjusted model, higher levels of self-reported moderate-to-vigorous physical activity (MVPA) were associated with significantly higher odds for K6 (OR = 1.47 [1.03-2.10]; p-trend = 0.03) but not GHQ-12 (OR = 0.97 [0.77-1.23]; p-trend = 0.79), when comparing the highest with the lowest tertile. Accelerometry-assessed MVPA was not significantly associated with K6 (p-trend = 0.50) nor GHQ-12 (p-trend = 0.74). The highest tertile of leisure-time physical activity, but not work- or transport-domain activity, was associated with less psychological distress using K6 (OR = 0.65 [0.43-0.97]; p-trend = 0.02) and GHQ-12 (OR = 0.72 [0.55-0.93]; p-trend = 0.01). Self-reported sedentary behaviour was not associated with K6 (p-trend = 0.90) and GHQ-12 (p-trend = 0.33). The highest tertile of accelerometry-assessed sedentary behaviour was associated with significantly higher odds for K6 (OR = 1.93 [1.00-3.75]; p-trend = 0.04), but not GHQ-12 (OR = 1.34 [0.86-2.08]; p-trend = 0.18).
Conclusions: Higher levels of leisure-time physical activity and lower levels of accelerometer-based sedentary behaviour were associated with lower psychological distress. This study underscores the importance of assessing accelerometer-based and domain-specific activity in relation to mental health, instead of solely focusing on total volume of activity
Reticle management analysis for the photolithography sector of a semiconductor fabrication facility
Reticle management analysis for the photolithography sector of a semiconductor fabrication facilit
Quantum control and process tomography of a semiconductor quantum dot hybrid qubit
The similarities between gated quantum dots and the transistors in modern
microelectronics - in fabrication methods, physical structure, and voltage
scales for manipulation - have led to great interest in the development of
quantum bits (qubits) in semiconductor quantum dots. While quantum dot spin
qubits have demonstrated long coherence times, their manipulation is often
slower than desired for important future applications, such as factoring.
Further, scalability and manufacturability are enhanced when qubits are as
simple as possible. Previous work has increased the speed of spin qubit
rotations by making use of integrated micromagnets, dynamic pumping of nuclear
spins, or the addition of a third quantum dot. Here we demonstrate a new qubit
that offers both simplicity - it requires no special preparation and lives in a
double quantum dot with no added complexity - and is very fast: we demonstrate
full control on the Bloch sphere with -rotation times less than 100 ps in
two orthogonal directions. We report full process tomography, extracting high
fidelities equal to or greater than 85% for X-rotations and 94% for
Z-rotations. We discuss a path forward to fidelities better than the threshold
for quantum error correction.Comment: 6 pages, excluding Appendi
A Wave Function Describing Superfluidity in a Perfect Crystal
We propose a many-body wave function that exhibits both diagonal and
off-diagonal long-range order. Incorporating short-range correlations due to
interatomic repulsion, this wave function is shown to allow condensation of
zero-point lattice vibrations and phase rigidity. In the presence of an
external velocity field, such a perfect crystal will develop non-classical
rotational inertia, exhibiting the supersolid behavior. In a sample calculation
we show that the superfluid fraction in this state can be as large as of order
0.01 in a reasonable range of microscopic parameters. The relevance to the
recent experimental evidence of a supersolid state by Chan and Kim is
discussed.Comment: final version to be published in Journal of Statistical Mechanics:
Theory and Experimen
Electronic states and optical properties of PbSe nanorods and nanowires
A theory of the electronic structure and excitonic absorption spectra of PbS
and PbSe nanowires and nanorods in the framework of a four-band effective mass
model is presented. Calculations conducted for PbSe show that dielectric
contrast dramatically strengthens the exciton binding in narrow nanowires and
nanorods. However, the self-interaction energies of the electron and hole
nearly cancel the Coulomb binding, and as a result the optical absorption
spectra are practically unaffected by the strong dielectric contrast between
PbSe and the surrounding medium. Measurements of the size-dependent absorption
spectra of colloidal PbSe nanorods are also presented. Using room-temperature
energy-band parameters extracted from the optical spectra of spherical PbSe
nanocrystals, the theory provides good quantitative agreement with the measured
spectra.Comment: 35 pages, 12 figure
- …