4,121 research outputs found
Multiple man-machine interfaces
The multiple man machine interfaces inherent in military pilot training, their social implications, and the issue of possible negative feedback were explored. Modern technology has produced machines which can see, hear, and touch with greater accuracy and precision than human beings. Consequently, the military pilot is more a systems manager, often doing battle against a target he never sees. It is concluded that unquantifiable human activity requires motivation that is not intrinsic in a machine
Experimental and modal verification of an integral equation solution for a thin-walled dichroic plate with cross-shaped holes
In order to add the capability of an X-band uplink onto the 70-m antenna, a new dichroic plate is needed to replace the Pyle-guide-shaped dichroic plate currently in use. The replacement dichroic plate must exhibit an additional passband at the new uplink frequency of 7.165 GHz, while still maintaining a passband at the existing downlink frequency of 8.425 GHz. Because of the wide frequency separation of these two passbands, conventional methods of designing air-filled dichroic plates exhibit grating lobe problems. A new method of solving this problem by using a dichroic plate with cross-shaped holes is presented and verified experimentally. Two checks of the integral equation solution are described. One is the comparison to a modal analysis for the limiting cross shape of a square hole. As a final check, a prototype dichroic plate with cross-shaped holes was built and measured
Carrier dynamics and coherent acoustic phonons in nitride heterostructures
We model generation and propagation of coherent acoustic phonons in
piezoelectric InGaN/GaN multi-quantum wells embedded in a \textit{pin} diode
structure and compute the time resolved reflectivity signal in simulated
pump-probe experiments. Carriers are created in the InGaN wells by ultrafast
pumping below the GaN band gap and the dynamics of the photoexcited carriers is
treated in a Boltzmann equation framework. Coherent acoustic phonons are
generated in the quantum well via both deformation potential electron-phonon
and piezoelectric electron-phonon interaction with photogenerated carriers,
with the latter mechanism being the dominant one. Coherent longitudinal
acoustic phonons propagate into the structure at the sound speed modifying the
optical properties and giving rise to a giant oscillatory differential
reflectivity signal. We demonstrate that coherent optical control of the
differential reflectivity can be achieved using a delayed control pulse.Comment: 14 pages, 11 figure
Recommended from our members
The impact of COVID-19 on small business outcomes and expectations
To explore the impact of coronavirus disease 2019 (COVID-19) on small businesses, we conducted a survey of more than 5,800 small businesses between March 28 and April 4, 2020. Several themes emerged. First, mass layoffs and closures had already occurred—just a few weeks into the crisis. Second, the risk of closure was negatively associated with the expected length of the crisis. Moreover, businesses had widely varying beliefs about the likely duration of COVID-related disruptions. Third, many small businesses are financially fragile: The median business with more than $10,000 in monthly expenses had only about 2 wk of cash on hand at the time of the survey. Fourth, the majority of businesses planned to seek funding through the Coronavirus Aid, Relief, and Economic Security (CARES) Act. However, many anticipated problems with accessing the program, such as bureaucratic hassles and difficulties establishing eligibility. Using experimental variation, we also assess take-up rates and business resilience effects for loans relative to grants-based programs. © 2020 National Academy of Sciences. All rights reserved
Polarization dependence of coherent phonon generation and detection in highly-aligned single-walled carbon nanotubes
We have investigated the polarization dependence of the generation and
detection of radial breathing mode (RBM) coherent phonons (CP) in
highly-aligned single-walled carbon nanotubes. Using polarization-dependent
pump-probe differential-transmission spectroscopy, we measured RBM CPs as a
function of angle for two different geometries. In Type I geometry, the pump
and probe polarizations were fixed, and the sample orientation was rotated,
whereas, in Type II geometry, the probe polarization and sample orientation
were fixed, and the pump polarization was rotated. In both geometries, we
observed a very nearly complete quenching of the RBM CPs when the pump
polarization was perpendicular to the nanotubes. For both Type I and II
geometries, we have developed a microscopic theoretical model to simulate CP
generation and detection as a function of polarization angle and found that the
CP signal decreases as the angle goes from 0 degrees (parallel to the tube) to
90 degrees (perpendicular to the tube). We compare theory with experiment in
detail for RBM CPs created by pumping at the E44 optical transition in an
ensemble of single-walled carbon nanotubes with a diameter distribution
centered around 3 nm, taking into account realistic band structure and
imperfect nanotube alignment in the sample
Timing of surgical intervention for developmental dysplasia of the hip: a randomised controlled trial (Hip 'Op)
Background: Developmental dysplasia of the hip (DDH) is a very common congenital disorder, and
late-presenting cases often require surgical treatment. Surgical reduction of the hip may be complicated
by avascular necrosis (AVN), which occurs as a result of interruption to the femoral head blood supply
during treatment and can result in long-term problems. Some surgeons delay surgical treatment until the
ossific nucleus (ON) has developed, whereas others believe that the earlier the reduction is performed,
the better the result. Currently there is no definitive evidence to support either strategy.
Objectives: To determine, in children aged 12 weeks to 13 months, whether or not delayed surgical
treatment of a congenitally dislocated hip reduces the incidence of AVN at 5 years of age. The main
clinical outcome measures were incidence of AVN and the need for a secondary surgical procedure during
5 years’ follow-up. In addition, to perform (1) a qualitative evaluation of the adopted strategy and (2) a
health economic analysis based on NHS and societal costs.
Design: Phase III, unmasked, randomised controlled trial with qualitative and health economics analyses.
Participants were randomised 1 : 1 to undergo either early or delayed surgery.
Setting: Paediatric orthopaedic surgical centres in the UK.
Participants: Children aged 12 weeks to 13 months with DDH, either newly diagnosed or following failed
splintage, and who required surgery. We had a target recruitment of 636 children.
Interventions: Surgical reduction of the hip performed as per the timing allocated at randomisation.
Main outcome measures: Primary outcome – incidence of AVN at 5 years of age (according to the
Kalamchi and MacEwen classification). Secondary outcomes – need for secondary surgery, presence or
absence of the ON at the time of primary treatment, quality of life for the main carer and child, and a
health economics and qualitative analysis.
Results: The trial closed early after reaching < 5% of the recruitment target. Fourteen patients were
randomised to early treatment and 15 to delayed treatment. Implementation of rescue strategies did not
improve recruitment. No primary outcome data were collected, and no meaningful conclusions could be
made from the small number of non-qualitative secondary outcome data. The qualitative work generated
rich data around three key themes: (1) access to, and experiences of, primary and secondary care; (2) the
impact of surgery on family life; and (3) participants’ experiences of being in the trial.
Limitations: Overoptimistic estimates of numbers of eligible patients seen at recruiting centres during the
planning of the trial, as well as an overestimation of the recruitment rate, may have also contributed to
unrealistic expectations on achievable patient numbers.
Future work: There may be scope for investigation using routinely available data.
Conclusions: Hip ’Op has highlighted the importance of accurate advance information on numbers of
available eligible patients, as well as support from all participating investigators when conducting surgical
research. Despite substantial consultation with parents of children in the planning stage, the level of
non-participation experienced during recruitment was much higher than anticipated. The qualitative work
has emphasised the need for appropriate advice and robust support for parents regarding the ‘real-life’
aspects of managing children with DDH.
Trial registration: Current Controlled Trials ISRCTN76958754.
Funding: This project was funded by the National Institute for Health Research (NIHR) Health Technology
Assessment programme and will be published in full in Health Technology Assessment; Vol. 21, No. 63.
See the NIHR Journals Library website for further project information
Posttraumatic growth as positive personality change: evidence, controversies and future directions
This target article focuses on the construct of post-traumatic growth—positive psychological change experienced as a result of the struggle with highly challenging life circumstances. Prominent theories of post-traumatic growth define it in terms of personality change, and as a result, this area of research should be of great interest to personality psychologists. Despite this fact, most of the research on this topic has not been sufficiently informed by relevant research in personality psychology, and much of the extant research suffers from significant methodological limitations. We review the literature on post-traumatic growth, with a particular focus on how researchers have conceptualized it and the specific methodological issues associated with these conceptualizations. We outline some ways in which personality science can both be enriched by the study of this phenomenon and inform rigorous research on post-traumatic growth and provide a series of guidelines for future research of post-traumatic growth as positive personality change
Resonant Coherent Phonon Spectroscopy of Single-Walled Carbon Nanotubes
Using femtosecond pump-probe spectroscopy with pulse shaping techniques, one
can generate and detect coherent phonons in chirality-specific semiconducting
single-walled carbon nanotubes. The signals are resonantly enhanced when the
pump photon energy coincides with an interband exciton resonance, and analysis
of such data provides a wealth of information on the chirality-dependence of
light absorption, phonon generation, and phonon-induced band structure
modulations. To explain our experimental results, we have developed a
microscopic theory for the generation and detection of coherent phonons in
single-walled carbon nanotubes using a tight-binding model for the electronic
states and a valence force field model for the phonons. We find that the
coherent phonon amplitudes satisfy a driven oscillator equation with the
driving term depending on photoexcited carrier density. We compared our
theoretical results with experimental results on mod 2 nanotubes and found that
our model provides satisfactory overall trends in the relative strengths of the
coherent phonon signal both within and between different mod 2 families. We
also find that the coherent phonon intensities are considerably weaker in mod 1
nanotubes in comparison with mod~2 nanotubes, which is also in excellent
agreement with experiment.Comment: 21 pages, 22 figure
Products of a reciprocal chromosome translocation involving the c-myc gene in a murine plasmacytoma.
In-Situ Infrared Transmission Study of Rb- and K-Doped Fullerenes
We have measured the four IR active molecular vibrations in
as a function of doping . We observe
discontinuous changes in the vibrational spectra showing four distinct phases
(presumably , and 6). The and modes
show the largest changes shifting downward in frequency in four steps as the
doping increases. Several new very weak modes are visible in the phase
and are possibly Raman modes becoming weakly optically active. We present
quantitative fits of the data and calculate the electron-phonon coupling of the
IR mode.Comment: 3 pages, Figure 1 included, 3 more figures available by request.
REVTEX v3.0 IRC60DO
- …