Spatio-temporal development of the long and short-wave vortex-pair instabilities

International audienceWe consider the spatio-temporal development of the long-wave and short-wave instabilities in a pair of counter-rotating vortices in the presence of a uniform axial advection velocity. The stability properties depend upon the aspect ratio a/b of the vortex pair, where a is the core radius of the vortices and b their separation, and upon W0/U0 the ratio between the self-induced velocity of the pair and the axial advection velocity. For sufficiently small W0/U0, the instabilities are convective, but an increase of W0/U0 may lead to an absolute instability. Near the absolute instability threshold, spatial growth rates are larger than those predicted by temporal stability theory. Considering aeronautical applications, it is shown that instabilities of the type considered in this communication cannot become absolute in farfield wakes of high aspect ratio wings. © 2000 American Institute of Physics

Resolvent Analysis: With or Without Eddy Viscosity?

International audienceIn this study, estimations of the spatio-temporal power cross-spectral density based on the resolvent operator are compared to those obtained by direct numerical simulation (DNS) in the turbulent plane channel flow at Re τ = 1007 by analysing separately the contribution of each temporal frequency ω. The comparison is performed for spatial scales characteristic of buffer-layer and large-scale motions. Good agreement between the resolvent-based estimates and the statistics obtained by DNS is found when the resolvent operator is based on a linear model which includes the effect of an eddy-viscosity modelling the effect of turbulent Reynolds stresses. The agreement is further improved when a colored noise matching the measures is used instead of white noise in the forcing modelling. Such a good agreement is not observed when the eddy-viscosity terms are not included in the linear model. In this case, the estimation based on the resolvent is unable to select the right peak frequency and wall-normal location of buffer-layer motions

Toward a well defined monopole creation operator

The lattice implementation of monopole creation operator proves to have problems related to bulk transitions that can possibly affect the interpretation of its mean value as an order parameter for monopole condensation. Preliminary evidence is presented that these unexpected behaviours are in fact only due to lattice artefacts and do not spoil the physical interpretation of the monopole operator

Chiral symmetry restoration, eigenvalue density of Dirac operator and axial U(1) anomaly at finite temperature

We reconsider constraints on the eigenvalue density of the Dirac operator in the chiral symmetric phase of 2 flavor QCD at finite temperature. To avoid possible ultra-violet(UV) divergences, we work on a lattice, employing the overlap Dirac operator, which ensures the exact "chiral" symmetry at finite lattice spacings. Studying multi-point correlation functions in various channels and taking their thermodynamical limit (and then taking the chiral limit), we obtain stronger constraints than those found in the previous studies: both the eigenvalue density at the origin and its first and second derivatives vanish in the chiral limit of 2 flavor QCD. In addition we show that the axial U(1) anomaly becomes invisible in susceptibilities of scalar and pseudo scalar mesons, suggesting that the 2nd order chiral phase transition with the O(4) scaling is not realized in 2 flavor QCD. Possible lattice artifacts when non-chiral lattice Dirac operator is employed are briefly discussed.Comment: 39 pages, 1 figure(2 eps files), a version published in PR

Ergodic sampling of the topological charge using the density of states

In lattice calculations, the approach to the continuum limit is hindered by the severe freezing of the topological charge, which prevents ergodic sampling in configuration space. In order to significantly reduce the autocorrelation time of the topological charge, we develop a density of states approach with a smooth constraint and use it to study SU(3) pure Yang Mills gauge theory near the continuum limit. Our algorithm relies on simulated tempering across a range of couplings, which guarantees the decorrelation of the topological charge and ergodic sampling of topological sectors. Particular emphasis is placed on testing the accuracy, efficiency and scaling properties of the method. In their most conservative interpretation, our results provide firm evidence of a sizeable reduction of the exponent z related to the growth of the autocorrelation time as a function of the inverse lattice spacing

Stress response in mesoangioblast stem cells

Stem cells are presumed to survive various stresses, since they are recruited to areas of tissue damage and regeneration, where inflammatory cytokines and cytotoxic cells may result in severe cell injury. We explored the ability of mesoangioblasts to respond to different cell stresses such as heat, heavy metals and osmotic stress, by analyzing heat shock protein (HSP)70 synthesis as a stress indicator. We found that the A6 mesoangioblast stem cells constitutively synthesize HSP70 in a heat shock transcription factor (HSF)-independent way. However, A6 respond to heat shock and cadmium treatment by synthesizing HSP70 over the constitutive expression and this synthesis is HSF1 dependent. The exposure of A6 to copper or to a hypertonic medium does neither induce HSP70 synthesis nor activation of HSF1, while a constitutive binding of constitutive heat shock element binding factor was found. Together, these data suggest that mesoangioblasts constitutively express HSP70 as an 'a priori' activation mechanism, while they maintain the ability to respond to stress stimuli. © 2006 Nature Publishing Group. All rights reserved

Attention Capture by Direct Gaze is Robust to Context and Task Demands

The final publication is available at Springer via https://dx.doi.org/10.1007/s10919-011-0128-z.Eye-tracking was used to investigate whether gaze direction would influence the visual scanning of faces, when presented in the context of a full character, in different social settings, and with different task demands. Participants viewed individual computer agents against either a blank background or a bar scene setting, during both a free-viewing task and an attractiveness rating task for each character. Faces with a direct gaze were viewed longer than faces with an averted gaze regardless of body context, social settings, and task demands. Additionally, participants evaluated characters with a direct gaze as more attractive than characters with an averted gaze. These results, obtained with pictures of computer agents rather than real people, suggest that direct gaze is a powerful attention grabbing stimulus that is robust to background context or task demands.103305-1/Canadian Institutes of Health Research89822-1/Canadian Institutes of Health Research103305-1/PHS HHS/United States89822-1/PHS HHS/United State

The positive impact of cisternostomy with cisternal drainage on delayed hydrocephalus after aneurysmal subarachnoid hemorrhage.

Hydrocephalus is one of the major complications of aneurysmal subarachnoid haemorrhage (aSAH). In the acute setting, an external ventricular drain (EVD) is used for early management. A cisternal drain (CD) coupled with the micro-surgical opening of basal cisterns can be an alternative when the aneurysm is clipped. Chronic hydrocephalus after aSAH is managed with ventriculo-peritoneal (VP) shunt, a procedure associated with a wide range of complications. The aim of this study is to analyse the impact of micro-surgical opening of basal cisterns coupled with CD on the incidence of VP shunt, compared to patients treated with EVD. The authors conducted a retrospective review of 89 consecutive cases of patients with aSAH treated surgically and endovascularly with either EVD or CD between January 2009 and September 2021. Patients were stratified into two groups: Group 1 included patients with EVD, Group 2 included patients with CD. Subgroup analysis with only patients treated surgically was also performed. We compared their baseline characteristics, clinical outcomes and shunting rates. There were no statistically significant differences between the two groups in terms of epidemiological characteristics, WFNS score, Fisher scale, presence of intraventricular hemorrhage (IVH), acute hydrocephalus, postoperative meningitis or of clinical outcomes at last follow-up. Cisternostomy with CD (Group 2) was associated with a statistically significant reduction in VP-shunt compared with the use of an EVD (Group 1) (9.09% vs 53.78%; p < 0.001). This finding was confirmed in our subgroup analysis, as among patients with a surgical clipping, the rate of VP shunt was 43.7% for the EVD group and 9.5% for the CD group (p = 0.02). Cisternostomy with CD may reduce the rate of shunt-dependent hydrocephalus. Cisternostomy allows the removal of subarachnoid blood, thereby reducing arachnoid inflammation and fibrosis. CD may enhance this effect, thus resulting in lower rates of chronic hydrocephalus

Early impairment of contractility reserve in patients with insulin resistance in comparison with healthy subjects

Background: Insulin resistance (IR) is currently considered a crucial cardiovascular (CV) risk factor, which seems to play a dominant role in the evolution toward cardiac and vascular impairment. Early IR-induced cardiac dysfunction can be assessed by Doppler-derived myocardial systolic strain rate (SR) index, measured at baseline and after dobutamine stress echocardiography (DSE).Methods: Thirty IR patients (HOMA-IR = 7 ± 5.2, age 52.6 ± 2.1 years), and 20 healthy, age and sex matched controls were studied. IR had been diagnosed in all patients in the 3 months preceding the study. Dobutamine echocardiography was performed in all subjects to exclude ischemic heart disease, and left ventricular contractile reserve (LVCR) was then assessed. LVCR was evaluated as an increase in the peak of an average longitudinal SR, measured in the basal and mid segments of 2 and 4 chamber ventricular walls.Results: No significant differences between the 2 groups were revealed by baseline echocardiography. In contrast, after DSE a significant decrease of Delta SR was found in the IR group in comparison to the controls (0.54 ± 0.31 s-1vs 1.14 ± 0.45 s-1; p < 0.0001).Conclusions: Our results show that IR, even if isolated and arising within a short time period, not only represents the initial phase of future diabetes, but may adversely affect heart function, as evidenced by the depressed LVCR. Our data strengthen the need for attention to be paid to IR state and for an early therapeutic approach