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The presence of elongated streaks of high and low streamwise velocity in the shear layer of circular jets breaks the axisymmetry of their steady-state solution. If the streaks are considered to be part of the base flow, for the purpose of linear instability analysis, the instability eigenmodes are thus affected by their presence. The resulting changes of growth rate and spatial shapes of eigenmodes, related to the shear instability in jets, are investigated here for parallel base flows. Optimal streamwise vortices (‘rolls’) with prescribed azimuthal periodicity are computed, such that the transient temporal growth of the streaks that they produce is maximal. The presence of finite-amplitude streaks requires the formulation of eigenvalue problems in a two-dimensional cross-plane. Sinuous rolls and streaks are found to have a stabilising effect on the Kelvin–Helmholtz instability, whereas the varicose rolls and streaks have a destabilising effect. Absolute instability is not found to occur. This work shows that the effects of rolls and streaks need to be taken into account for more precise modelling of jet instability.
We extend the resolvent-based estimation approach recently introduced by Towne etal. (J. Fluid Mech., vol. 883, 2020, A17) to obtain optimal, non-causal estimates of time-varying flow quantities from low-rank measurements. We derive optimal transfer functions between the measurements and certain nonlinear terms that act as a forcing on the linearised Navier–Stokes equations, and show that the resulting transfer function to the flow state is equivalent to a multiple-input, multiple-output Wiener filter if the colour of the forcing statistics is known. A matrix-free implementation is developed based on integration of the direct and adjoint linearised Navier–Stokes operators, enabling application to the large systems encountered for transitional and turbulent flows without the need for a priori model reduction. Using a linearised Ginzburg–Landau problem, we show that the non-casual resolvent-based method outperforms a casual Kalman filter for general sensor configurations and recovers the Kalman filter transfer function in specific cases, leading to causal estimates at a significantly reduced computational cost. Additionally, our method is shown to be more accurate and robust than popular approaches based on truncation of the resolvent operator to its leading modes. The applicability of the method to transitional and turbulent flows is demonstrated via application to a (linearised) transitional boundary layer and a (nonlinear) turbulent channel flow. Errors on the order of 2 % are achieved for the boundary layer, and the channel flow case highlights the need to account for the forcing colour to achieve accurate flow estimates. In practice, our method can be used as a post-processing tool to reconstruct unmeasured quantities from limited experimental data, and, in cases where the transfer function can be accurately truncated to its causal components, as a low-cost estimator for flow control.
Voluntary selection between response alternatives belong to cognitive abilities controlling and regulating goal-directed behaviour. Voluntary selection processes are associated with increased neural activity, especially in medial and lateral frontal brain regions as well as the inferior parietal gyrus. However, the precise function of each brain region as well as the spatiotemporal characteristic of the brain regions involved is not yet clear. The aim of the present study was to disentangle distinct aspects of voluntary selection and their underlying neural processes. Hence, event-related potentials (ERPs) and functional MRI data were acquired simultaneously. Brain regions modulated by the task-induced amplitude variation of ERPs (N2, P3) were indentified. The results showed N2-related hemodynamic responses, especially in medial and lateral frontal brain regions. Among other things, medial frontal brain regions are related to conflict monitoring, control of voluntary action and decision making. By contrast, the P3-amplitude proved to be predominantly related to increased BOLD responses in the temporo-parietal junction [TPJ] and lateral frontal brain regions. These brain regions are thought to play a decisive role in an attentional network involved in detecting auditory and visual stimuli.
Overall, the results of the study indicated a whole network of brain regions to be associated with voluntary selection processes. In addition, at least some frontal brain regions seemed to be involved at an earlier stage than temporo-parietal regions, probably indicating a top-down process.
Executive functions comprise various cognitive abilities including the inhibition of prepotent responses and voluntary decisions. Several studies showed medial-frontal activations in tasks with the free selection of responses. The inhibition of prepotent response tendencies seems to be associated with medial frontal as well as lateral frontal BOLD responses. The aim of this simultaneous EEG and fMRI study was to discriminate the neural correlates of behavioural control processes in ADHD.
8 adults with ADHD and 8 matched healthy subjects performed a go/nogo task comprising three different conditions: during the go condition, subjects were instructed to press a response button as fast as possible; during the nogo condition, this response was to be inhibited. In the voluntary selection task participants were allowed to freely decide, whether to press the response button or not.
The fMRI protocol used a gradient-echo EPI pulse sequence. Further analyses were done with using the BrainVoyager software package (Goebel, Maastricht). EEG signals were simultaneously recorded (Brain Products, Munich).
Electrophysiologically, the nogo task and voluntary decision task led to a negative decline especially in fronto-central brain regions (N2) in both groups. Regarding the functional MRI data we found inhibition-associated BOLD responses especially medial-frontal in the pre-SMA and activations in the medial part of BA 8 for the voluntary selection. ADHD patients showed a reduced contribution of frontal brain regions during free responses compared to controls.
The results may indicate that selection processes are related with dysfunctions predominantly in frontal brain regions in ADHD patients.
Studies of schizophrenia with functional MRI showed hyper- and hypoactivations in various brain regions including the prefrontal cortex. Functional abnormalities have also been reported in first-degree relatives of schizophrenic patients. The aim of this study was to examine working memory related brain functions in healthy subjects, schizophrenic patients and unaffected relatives and to determine the influence of psychopathology on these processes.
A parametric n-back working memory task and functional MRI were used to examine 61 schizophrenic patients on antipsychotic medication, 11 nonpsychotic relatives of schizophrenic patients and a comparison group of 61 healthy subjects. The task difficulty was incrementally increased using a parametric task (0-back, 1-back, 2-back, and 3-back) to examine the relationship between working memory load, performance, and brain activity.
The results indicated that during the attention task (0-back) behavioral responses of patients and healthy subjects hardly differed but BOLD responses were considerably enhanced in schizophrenic patients. With increasing task difficulty differences between groups in BOLD responses diminished whereas behavioral deficits of patients increased. The examination of attention-independent working memory-functions (2- vs. 0-back) produced hypoactivations in patients, especially in frontal, temporal and subcortical brain regions. Behavioral performance and neural responses of unaffected relatives of schizophrenic patients were intermediate between schizophrenic patients and controls indicating slight brain dysfunctions. In addition, compensatory strategies were demonstrated.
These findings suggest that the genetic risk for schizophrenia is accompanied by neural inefficiency which is associated with cognitive deficits, especially in difficult tasks.
Scientific literature reviews aim to summarize the state of knowledge and published empirical evidence. In contrast, medical guidelines are intervention tools that aim to improve physician behaviour and patient outcome. They can have positive effects, but they can also have negative effects. Their effects must be tested by research.
In a randomized controlled trial, 103 psychiatrists in private practice were either provided with the WHO depression guideline only (information group), or provided with the WHO depression guideline and trained for one day in this guideline (intervention group), or left uninformed (control group). They then treated a total of 497 patients according to individual clinical considerations and the needs of the patients. Observation of routine treatment lasted 12 weeks. Physicians and patients documented the course of illness and treatment, including the patient–physician interaction.
Psychiatrists in the intervention group saw more psychosocial stressors in their patients, prescribed higher dosages of medication, had fewer drop-outs, and rated treatment outcome as better. The ratings of patient–physician interactions indicated more strain in their relationships.
The results show both positive and negative effects of guideline exposure, but only in the training group and not in the information group. Guidelines should be empirically tested before being called “evidence based”. Every guideline should also explain how it can or must be implemented in order to become effective.
We use numerical simulations from the Community Coordinated Modeling Center to provide, for the first time, a coherent temporal description of the magnetic reconnection process of two dayside Electron Diffusion Regions (EDRs) identified in Magnetospheric Multiscale Mission data. The model places the MMS spacecraft near the separator line in these most intense and long-lived events. A listing of 31 dayside EDRs identified by the authors is provided to encourage collaboration in analysis of these unique encounters.
The objective of this study was to determine whether altered maternal energy supply during mid-gestation results in differences in muscle histology or genes regulating fetal adipose and muscle development. In total, 22 Angus cross-bred heifers (BW=527.73±8.3 kg) were assigned randomly to the three dietary treatments providing 146% (HIGH; n=7), 87% (INT; n=7) or 72% (LOW; n=8) of the energy requirements for heifers from day 85 to day 180 of gestation. Fetuses were removed via cesarean section at day 180 of gestation and longissimus muscle (LM) and subcutaneous fat were collected and prepared for analysis of gene expression. Samples from the LM and semitendinosus (ST) were evaluated for muscle fiber diameter, area and number. The right hind limb was dissected and analyzed to determine compositional analysis. Fetal growth and muscle histology characteristics of the LM and ST were similar among treatments. Preadipocyte factor-1 expression was up-regulated in fetal LM (P<0.05) of HIGH fetuses as compared with INT, whereas LOW fetuses showed increased CCAAT/enhancer-binding protein-β (C/EBP-β) expression in LM as compared with INT (P<0.05). Peroxisome proliferator-activated receptor γand C/EBP-α did not differ as a result of dietary treatment in LM or subcutaneous fat samples. There was a tendency for increased expression of fatty acid synthase in LM of LOW fetuses as compared with INT (P<0.10). Myogenin was more highly expressed (P<0.05) in LM of the LOW fetuses, whereas μ-calpain expression was increased in the HIGH treatment compared with INT. A tendency for increased expression of IGF-II was observed for both LOW and HIGH fetuses compared with INT (P<0.10). Expression of stearoyl-CoA desaturase, myoblast determination protein 1, myogenic factor 5, myogenic regulatory factor-4, m-calpain, calpastatin, IGF-I and myostatin was similar between treatments. Collectively, these results suggest that fetal growth characteristics are not affected by the level of maternal nutritional manipulation imposed in this study during mid-gestation. However, differences in expression of fetal genes regulating adipose and muscle tissue growth and development could lead to differences in postnatal composition and warrants further investigation.
We have conducted a LABOCA 870 μm follow-up of ten massive lensing clusters of the Herschel Lensing Survey (HLS, Egami et al. 2010) aiming at unveiling the yet hidden part of dusty star formation in the distant Universe. Among these clusters, A2744 and AS1063 are part of the Frontier Fields HST program. We also obtained 2 mm bolometer observations of A2744 and A370 with the GISMO array at the IRAM 30 m. We detected sources that are undetected with Herschel (PACS and SPIRE) implying either a very high redshift (z > 4) or a very low dust temperature (T<25 K). Their flux also imply a low intrinsic luminosity, LFIR < 1012L⊙. Some of them are extended and could correspond to multiple sources or to multiple images of a lensed source. Substructures in the Sunyaev-Zeldovich effect could also contribute this very red submm emission. An ALMA program is ongoing to unveil the nature of these sources.
Airbus and Boeing are cooperatively presenting this topic dealing with transport aircraft stalls. The paper will begin by defining a stall, followed by a review of requirements, predictive validation and flight testing. There are various ways of designing modern jet transports for the stall regime such as aerodynamic approaches, flight deck indications, and augmentation control laws to deal with the high angle-of-attack (α) arena. The goal of augmented control laws for high α is common – no full aerodynamic stall or loss of climb performance should occur in the operational flight envelope, in Normal flight control modes. The validation techniques employed in preparation for a flight test campaign will follow. These include flight characteristic predictions based on wind-tunnel data as well as pilot-in-the-loop simulation rehearsals. The preparation for flight testing will be reviewed from both the engineer and pilot viewpoints. This will be followed by a review of various flight testing that has been conducted. The paper will close with a brief foray into what the future of transport stalls could be – perhaps protection features in degraded flight control modes? What are the benefits as well as drawbacks to increased augmentation for high α?