498 research outputs found
Fracture characteristics of structural aerospace alloys containing deep surface flaws
Conditions controlling the growth and fracture of deep surface flaws in aerospace alloys were investigated. Static fracture tests were performed on 7075-T651 and 2219-T87 aluminum, and 6Ai-4V STA titanium . Cyclic flaw growth tests were performed on the two latter alloys, and sustain load tests were performed on the titanium alloy. Both the cyclic and the sustain load tests were performed with and without a prior proof overload cycle to investigate possible growth retardation effects. Variables included in all test series were thickness, flaw depth-to-thickness ratio, and flaw shape. Results were analyzed and compared with previously developed data to determine the limits of applicability of available modified linear elastic fracture solutions
Network governance for largeâscale natural resource conservation and the challenge of capture
Largeâscale natural resource conservation initiatives are increasingly adopting a network governance framework to respond to the ecological, social, and political challenges of contemporary environmental governance. A network approach offers new modes of management that allow resource managers and others to transcend a single institution, organization, resource, or landscape and engage in conservation that is multiâspecies and multiâjurisdictional. However, there are challenges to network governance in largeâscale conservation efforts, which we address by focusing on how special interests can capture networks and shape the goals, objectives, and outcomes of initiatives. The term ânetwork captureâ is used here to describe an array of strategies that direct the processes and outcomes of largeâscale initiatives in ways that advance a group\u27s positions, concerns, or economic interests. We outline how new stakeholders emerge from these management processes, and how the ease of information sharing can blur stakeholder positions and lead to competing knowledge claims. We conclude by reasserting the benefits of network governance while acknowledging the unique challenges that networks present
The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign
We present the results of a multisite photometric campaign on the pulsating
sdB star Balloon 090100001. The star is one of the two known hybrid hot
subdwarfs with both long- and short-period oscillations. The campaign involved
eight telescopes with three obtaining UBVR data, four B-band data, and one
Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal
resolution of 0.36microHz with a detection threshold of about 0.2mmag in
B-filter data.
Balloon 090100001 has the richest pulsation spectrum of any known pulsating
subdwarf B star and our analysis detected 114 frequencies including 97
independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz
region is most likely radial while the remaining ones in this region form two
nearly symmetric multiplets: a triplet and quintuplet, attributed to
rotationally split \ell=1 and 2 modes, respectively. We find clear increases of
splitting in both multiplets between the 2004 and 2005 observing campaigns,
amounting to 15% on average. The observed splittings imply that the rotational
rate in Bal09 depends on stellar latitude and is the fastest on the equator. We
use a small grid of models to constrain the main mode (f_1), which most likely
represents the radial fundamental pulsation. The groups of p-mode frequencies
appear to lie in the vicinity of consecutive radial overtones, up to the third
one. Despite the large number of g-mode frequencies observed, we failed to
identify them, most likely because of the disruption of asymptotic behaviour by
mode trapping. The observed frequencies were not, however, fully exploited in
terms of seismic analysis which should be done in the future with a larger grid
of reliable evolutionary models of hot subdwarfs.Comment: accepted for publication in MNRA
Static stretching of the hamstring muscle for injury prevention in football codes: a systematic review
Purpose: Hamstring injuries are common among football players. There is still disagreement regarding prevention. The aim of this review is to determine whether static stretching reduces hamstring injuries in football codes.
Methods: A systematic literature search was conducted on the online databases PubMed, PEDro, Cochrane, Web of Science, Bisp and Clinical Trial register. Study results were presented descriptively and the quality of the studies assessed were based on Cochraneâs ârisk of biasâ tool.
Results: The review identified 35 studies, including four analysis studies. These studies show deficiencies in the quality of study designs.
Conclusion: The study protocols are varied in terms of the length of intervention and follow-up. No RCT studies are available, however, RCT studies should be conducted in the near future
Intelligence in youth and mental health at age 50
Background:
Few cognitive epidemiology studies on mental health have focused on the links between pre-morbid intelligence and self-reports of common mental disorders, such as depression, sleep difficulties, and mental health status. The current study examines these associations in 50-year-old adults.
Methods:
The study uses data from the 5793 participants in the National Longitudinal Survey of Youth 1979 cohort (NLSY-79) who responded to questions on mental health at age 50 and had IQ measured with the Armed Forces Qualification Test (AFQT) when they were aged between 15 and 23 years in 1980. Mental health outcomes were: life-time diagnosis of depression; the mental component score of the 12-item short-form Health Survey (SF-12); the 7-item Center for Epidemiological Studies Depression Scale (CES-D); and a summary measure of sleep difficulty.
Results and conclusion:
Higher intelligence in youth is associated with a reduced risk of self-reported mental health problems at age 50, with age-at-first-interview and sex adjusted Bs as follows: CES-depression (B = â 0.16, C.I. â 0.19 to â 0.12, p < 0.001), sleep difficulties (B = â 0.11, C.I. â 0.13 to â 0.08, p < 0.001), and SF-12 mental health status (OR = 0.78, C.I. 0.72 to 0.85, p < 0.001; r = â 0.03 p = 0.075). Conversely, intelligence in youth is linked with an increased risk of receiving a diagnosis of depression by the age of 50 (OR 1.11, C.I. 1.01 to 1.22, p = 0.024; r = 0.03, p = 0.109). No sex differences were observed in the associations. Adjusting for adult SES accounted for most of the association between IQ and the mental health outcomes, except for having reported a diagnosis of depression, in which case adjusting for adult SES led to an increase in the size of the positive association (OR = 1.32, C.I. 1.16 to 1.51, p < 0.001)
The Simons Observatory: Cryogenic Half Wave Plate Rotation Mechanism for the Small Aperture Telescopes
We present the requirements, design and evaluation of the cryogenic
continuously rotating half-wave plate (CHWP) for the Simons Observatory (SO).
SO is a cosmic microwave background (CMB) polarization experiment at Parque
Astron\'{o}mico Atacama in northern Chile that covers a wide range of angular
scales using both small (0.42 m) and large (6 m) aperture telescopes. In
particular, the small aperture telescopes (SATs) focus on large angular scales
for primordial B-mode polarization. To this end, the SATs employ a CHWP to
modulate the polarization of the incident light at 8~Hz, suppressing
atmospheric noise and mitigating systematic uncertainties that would
otherwise arise due to the differential response of detectors sensitive to
orthogonal polarizations. The CHWP consists of a 505 mm diameter achromatic
sapphire HWP and a cryogenic rotation mechanism, both of which are cooled down
to 50 K to reduce detector thermal loading. Under normal operation the
HWP is suspended by a superconducting magnetic bearing and rotates with a
constant 2 Hz frequency, controlled by an electromagnetic synchronous motor.
The rotation angle is detected through an angular encoder with a noise level of
0.07. During a cooldown, the rotor is held in
place by a grip-and-release mechanism that serves as both an alignment device
and a thermal path. In this paper we provide an overview of the SO SAT CHWP:
its requirements, hardware design, and laboratory performance.Comment: 19 pages, 21 figures, submitted to RS
Characterizing Comment Types and Levels of Engagement in Video-Based Learning as a Basis for Adaptive Nudging
Video is frequently used as a learning medium in a variety of educational settings, including large online courses as well as informal learning scenarios. To foster learner engagement around instructional videos, our learning scenario facilitates interactive note taking and commenting similar to popular social video-sharing platforms. This approach has recently been enriched by introducing nudging mechanisms, which raises questions about ensuing learning effects. To better understand the nature of these effects, we take a closer look at the content of the comments. Our study is based on an ex post analysis of a larger data set from a recent study. As a first step of analysis, video comments are clustered based on a feature set that captures the temporal and semantic alignment of comments with the videos. Based on the ensuing typology of comments, learners are characterized through the types of comments that they have contributed. The results will allow for a better targeting of nudges to improve video-based learning
Emotion dysregulation mediates the relationship between nightmares and psychotic experiences: Results from a student population
Sleep-disruption is commonly associated with psychotic experiences. Whilst sparse, the literature to date highlights nightmares and related distress as prominent risk factors for psychosis in students. We aimed to further explore the relationship between specific nightmare symptoms and psychotic experiences in university students whilst examining the mediating role of emotion dysregulation. A sample (N=1273) of student respondents from UK universities completed measures of psychotic experiences, nightmare disorder symptomology, and emotion dysregulation. Psychotic experiences were significantly more prevalent in students reporting nightmares (n=757) relative to those who did not (n=516). Hierarchical linear regression analysis showed that psychotic experiences were significantly associated (Adjusted R2 = 32.4%) with perceived nightmare intensity, consequences and resulting awakenings, and with emotion regulation difficulties. Furthermore, multiple mediation analysis showed that the association between psychotic experiences and nightmare factors was mediated by emotion regulation difficulties. Adaptive regulation of dream content during rapid eye-movement sleep has previously been demonstrated to attenuate surges in affective arousal by controlling the intensity and variability of emotional content. Difficulties in emotion regulation may partially explain the experience of more intense and disruptive nightmares amongst individuals with psychotic experiences. Emotion regulation may represent an important control mechanism that safeguards dream content and sleep quality
Individual-environment interactions in swimming: The smallest unit for analysing the emergence of coordination dynamics in performance?
Displacement in competitive swimming is highly dependent on fluid characteristics,
since athletes use these properties to propel themselves. It is essential for sport
scientists and practitioners to clearly identify the interactions that emerge between
each individual swimmer and properties of an aquatic environment. Traditionally, the
two protagonists in these interactions have been studied separately. Determining the
impact of each swimmerâs movements on fluid flow, and vice versa, is a major
challenge. Classic biomechanical research approaches have focused on swimmersâ
actions, decomposing stroke characteristics for analysis, without exploring
perturbations to fluid flows. Conversely, fluid mechanics research has sought to
record fluid behaviours, isolated from the constraints of competitive swimming
environments (e.g. analyses in two-dimensions, fluid flows passively studied on
mannequins or robot effectors). With improvements in technology, however, recent
investigations have focused on the emergent circular couplings between swimmersâ
movements and fluid dynamics. Here, we provide insights into concepts and tools that
can explain these on-going dynamical interactions in competitive swimming within
the theoretical framework of ecological dynamics
- âŠ