771 research outputs found
Global linear stability of the non-parallel Batchelor vortex
International audienceLinear stability of the non-parallel Batchelor vortex is studied using global modes. This family of swirling wakes and jets has been extensively studied under the parallel-flow approximation, and in this paper we extend to more realistic non-parallel base flows. Our base flow is obtained as an exact steady solution of the Navier-Stokes equations by direct numerical simulation (with imposed axisymmetry to damp all instabilities). Global stability modes are computed by numerical simulation of the linearized equations, using the implicitly restarted Arnoldi method, and we discuss fully the numerical and convergence issues encountered. Emphasis is placed on exploring the general structure of the global spectrum, and in particular the correspondence between global modes and local absolute modes which is anticipated by weakly non-parallel asymptotic theory. We believe that our computed global modes for a weakly non-parallel vortex are the first to display this correspondence with local absolute modes. Superpositions of global modes are also studied, allowing an investigation of the amplifier dynamics of this unstable flow. For an illustrative case we find global non-modal transient growth via a convective mechanism. Generally amplifier dynamics, via convective growth, are prevalent over short time intervals, and resonator dynamics, via global mode growth, become prevalent at later times. © 2009 Cambridge University Press
The effects of heat stress on the development of the foetal lamb
Environmental heat stress in tropical sheep suppressed lamb birth weight, but the animals which did not experience hyperthermia under natural environmental conditions gave birth to significantly heavicr (P<0.01) lambs than their less adapted counterparts. Climate chamber studies designed to simulate the rectal temperature patterns of tropical sheep demonstrated that, without nutritional intervention, heat stress during the last month of pregnancy significantly retarded foetal growth (birth weight 2.3 kg v. 3.4 kg; P< 0.01) and maturation of wool follicles (P< 0.01). By comparison, severe nutritional restrictions during the last 3 months of pregnancy also caused a significant reduction in lamb birth weight (3.2 kg v. 3.9 kg; P<O.01), but this difference was not so marked
Magnetic field diagnostics and spatio-temporal variability of the solar transition region
Magnetic field diagnostics of the transition region from the chromosphere to
the corona faces us with the problem that one has to apply extreme UV
spectro-polarimetry. While for coronal diagnostic techniques already exist
through infrared coronagraphy above the limb and radio observations on the
disk, for the transition region one has to investigate extreme UV observations.
However, so far the success of such observations has been limited, but there
are various projects to get spectro-polarimetric data in the extreme UV in the
near future. Therefore it is timely to study the polarimetric signals we can
expect for such observations through realistic forward modeling.
We employ a 3D MHD forward model of the solar corona and synthesize the
Stokes I and Stokes V profiles of C IV 1548 A. A signal well above 0.001 in
Stokes V can be expected, even when integrating for several minutes in order to
reach the required signal-to-noise ratio, despite the fact that the intensity
in the model is rapidly changing (just as in observations). Often this
variability of the intensity is used as an argument against transition region
magnetic diagnostics which requires exposure times of minutes. However, the
magnetic field is evolving much slower than the intensity, and thus when
integrating in time the degree of (circular) polarization remains rather
constant. Our study shows the feasibility to measure the transition region
magnetic field, if a polarimetric accuracy on the order of 0.001 can be
reached, which we can expect from planned instrumentation.Comment: Accepted for publication in Solar Physics (4.Mar.2013), 19 pages, 9
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Remote sensing of inland waters: Challenges, progress and future directions
Monitoring and understanding the physical, chemical and biological status of global inland waters are immensely
important to scientists and policy makers alike.Whereas conventional monitoring approaches tend to be limited
in terms of spatial coverage and temporal frequency, remote sensing has the potential to provide an invaluable
complementary source of data at local to global scales. Furthermore, as sensors,methodologies, data availability
and the network of researchers and engaged stakeholders in this field develop, increasingly widespread use of
remote sensing for operational monitoring of inland waters can be envisaged. This special issue on Remote Sensing
of Inland Waters comprises 16 articles on freshwater ecosystems around the world ranging from lakes and
reservoirs to river systems using optical data from a range of in situ instruments as well as airborne and satellite
platforms. The papers variably focus on the retrieval of in-water optical and biogeochemical parameters as well as
information on the biophysical properties of shoreline and benthic vegetation.Methodological advances include
refined approaches to adjacency correction, inversion-based retrieval models and in situ inherent optical property
measurements in highly turbid waters. Remote sensing data are used to evaluate models and theories of environmental
drivers of change in a number of different aquatic ecosystems. The range of contributions to the special
issue highlights not only the sophistication of methods and the diversity of applications currently being developed,
but also the growing international community active in this field. In this introductory paper we briefly
highlight the progress that the community has made over recent decades as well as the challenges that remain.
It is argued that the operational use of remote sensing for inland water monitoring is a realistic ambition if we can
continue to build on these recent achievements
Prevention of fracture at the distal locking site of the gamma nail. A biomechanical study
To investigate the origin of fractures at the distal locking site of the
Gamma nail, we loaded ten paired human cadaver femora fixed with a Gamma
nail in torsion until they fractured. When an awl was hammered in to start
the hole for distal locking a fissure appeared in the lateral cortex of
all the femora, and the mean torsional load to create a fracture was
reduced by 57.8% compared with that in a control group in which the distal
locking hole had been started with a centre drill. When an additional
drill hole was made, the mean failure load in torsion decreased by 35.7%.
We strongly recommend that an awl should not be used at the distal locking
site of the Gamma nail; we recommend the use of a centre drill. Additional
drill holes should be avoided because they act as stress raisers
Psychological profile and self-administered relaxation in patients with craniofacial pain: a prospective in-office study
Introduction: The objective of this study was to evaluate the psychological profile of craniofacial pain sufferers and the impact of patient subtype classification on the short-time effectiveness of a self-administered relaxation training. Methods: One hundred unselected in-office patients (67% females) suffering from chronic facial pain and/or headache with the presumptive diagnose of temporo-mandibular disorder (TMD) completed a questionnaire battery comprising craniofacial pain perception, somatic complaints, irrational beliefs, and pain behavior and were classified into subtypes using cluster analysis. They underwent a self-administered progressive relaxation training and were re-evaluated for pain perception after 3 months. Results: Pain was mild to moderate in the majority of patients. Symptom domains comprised parafunctional activities, temporo-mandibular pain and dysfunction, fronto-temporal headache, head/neck and neck/back pain. Three patient subtypes were identified regarding symptom/dysfunction level: (i) low burden (mild/moderate), (ii) psychosocial dysfunction (moderate/high), (iii) adaptive coping (moderate/mild). Self-rated adherence to the recommended relaxation training was moderate throughout the sample, but self-rated relief was significantly different between clusters. At follow-up, pain intensity was significantly decreased in all patients, whereas pain-related interference was improved only in dysfunctional and adaptive patients. Improvement of symptom domains varied between clusters and was most comprehensive in adaptive patients. Conclusions: In conclusion, craniofacial pain sufferers can be divided in meaningful subtypes based on their pain perception, irrational beliefs, and pain behaviour. A self-administered relaxation training generally yielded positive effects on pain perception, however the benefit may be greater in patients with more marked symptom impact (both dysfunctional and adaptive).<br
Association of dentoskeletal morphology with incisor inclination in angle class II patients: a retrospective cephalometric study
Introduction: The purpose of this study was to identify possible dentoskeletal parameters associated with variation of anterior tooth inclination in Angle Class II subdivisions. Methods: Pre-treatment lateral radiographs of 144 Class II patients (68 males, 76 females) aged 9 to 17 years were classified for upper incisor inclination into three groups (proclined, normally inclined, retroclined) homogeneous for gender and skeletal jaw relationship. The effect of age on the 22 cephalometric variables was controlled by covariance analysis. Results: Multivariate analysis of the cephalometric parameters indicated significant inter-group differences. Systematic associations with incisor inclination were revealed using rank correlation: Lower incisor proclination, Wits appraisal and gonial angle significantly decreased (0.04 ≥ p ≥ 0.002), while intercisal angle, mandibular total and corpus length and nasolabial angle increased (0.04 ≥ p ≥ 0.001) with decreasing incisor proclination. Conclusions: Clear-cut classification criteria and control of confounding effects may clarify conflicting previous findings on dentoskeletal differences between Class II subdivisions in the mixed dentition. Only minor dentoskeletal differences appear to be associated with incisor inclination. The increased interincisal and nasolabial angle in Class II division 2 subjects are due to reclination of both upper and lower incisors. Jaw positions and chin prominence are not significantly different between the subdivisions. However, Wits appraisal is decreased in Class II division 2. The increased mandibular length observed in Class II division 2 requires further scrutinization.<br
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