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We demonstrate that a current pulse of a non-uniform spin-polarized current density in a nanomagnet can drive, apart from magnetization reversal a static magnetic vortex. This vortex configuration can be achieved in low shape anisotropy spin valves of elliptical cross-sectional area. These non-uniform configurations exist also in presence of either ion mill damages below the nano-aperture or thermal effects at low temperature. We performed a numerical experiment of spin-torque driven ferromagnetic resonance in a magnetic vortex configuration, our results predict a frequency response with a few maxima and minima related to small oscillation of the vortex state around its equilibrium configuration.... Amplitude of the oscillations (D) of the x (solid line) and y (dotted line) component of the average normalized magnetization for a process γ0H=35mT, J=5.5×108A/cm2, d=30nm, and J0=0.25×108A/cm2 as function of fP. Inset: plot of the temporal evolution of y component of the average magnetization of the same process for fP=750MHz.
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Matertm/tm oocytes display an altered Ca2+ oscillation pattern following fertilization in vitro. (A) Zona-free metaphase II-arrested Mater+/+ and Matertm/tm oocytes were loaded with Fluo-4 AM, fertilized in vitro and Ca2+ oscillations were recorded every 20s for 2h following insemination. Fertilization was confirmed by visualization of the second polar body ~2h after insemination. Images were analysed by ImageJ and the representative graphs from each group are shown in (B). The bar graphs of amplitude and frequency in (C) indicate that Matertm/tm oocytes displayed a lower amplitude and higher frequency of Ca2+ oscillation patterns when compared to Mater+/+ oocytes (p<0.05). ... Ca2+ oscillations are a hallmark of mammalian fertilization and play a central role in the activation of development. The calcium required for these oscillations is primarily derived from the endoplasmic reticulum (ER), which accumulates in clusters at the microvillar subcortex during oocyte maturation. The migration of the ER to the cortex during maturation is thought to play an important role in rendering the ER competent to generate the calcium transients, and the redistribution of ER is believed to be primarily mediated by microtubules and microfilaments. We have previously shown that the oocyte- and early embryo-restricted maternal effect gene Mater (Nlrp5) localizes to, and is required for, formation of the oocyte cytoplasmic lattices, a tubulin-containing structure that appears to play an important role in organelle positioning and distribution during oocyte maturation. Given these observations, we hypothesized that Mater may also be required for ER redistribution and Ca2+ homeostasis in oocytes. To test this hypothesis, we first investigated ER localization in metaphase-II Matertm/tm (hypomorph) oocytes and found ER clusters to be less abundant at the microvillar cortex when compared to wild type oocytes. To examine the potential mechanisms by which MATER mediates ER redistribution, we tested whether tubulin expression levels and localization were affected in the mutant oocytes and found that the Triton-insoluble fraction of tubulin was significantly decreased in Matertm/tm oocytes. To identify potential functional defects associated with these ER abnormalities, we next set out to investigate if the pattern of Ca2+ oscillations was altered in Matertm/tm oocytes after fertilization in vitro. Intriguingly, Ca2+ oscillations in Matertm/tm oocytes exhibited a significantly lower first peak amplitude and a higher frequency when compared to wild type oocytes. We then found that the Ca2+ oscillation defect in Matertm/tm oocytes was likely caused by a reduced amount of Ca2+ in the ER stores. Taken together, these observations support the hypothesis that MATER is required for ER distribution and Ca2+ homeostasis in oocytes, likely due to defects in lattice-mediated ER positioning and/or redistribution.
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Emitted light intensity relative to mean intensity versus time. (a) Stable limit cycle; (b) Pulsation with rapid growth in amplitude leading to extinction. (c) Intermittent pulsations close to the marginal stability. (d) Pulsation with two competing frequencies. ... (a) Non-dimensional pulsation frequency versus relative Damköhler number. Open and solid symbols correspond to cases at constant inert composition and constant velocity, respectively. Symbol size is proportional to the amplitude ϵ. —-, f Dth/U2 =Da1/2. (b) Eq. (4) and data of Fig. 17a with C0=0.05. ... Measured cell size λc as a function diffusion length lD, determined with the thermal diffusivity and bulk velocity at the flame. (□, - - - corresponding to σ∗=1.75), variable inert composition at constant bulk velocity (average ϕ=0.45); (∘, — corresponding to σ∗=1.5, •), variable bulk velocity with pure CO2 as inert (average ϕ=0.62), the solid points representing oscillating cells. The error bars represent only the quantization error due to integer number of cells forming around the periphery of the inner quartz cylinder. ... Simultaneous traces of flame intensity (⊙) and position (□). (a) High frequency pulsations at 7.21Hz. (b) Low frequency pulsations at 0.86Hz. ... The recent development of a novel research burner at EPFL has opened the way for experimental investigations of essentially unstretched planar diffusion flames. In particular, it has become feasible to experimentally validate theoretical models for thermal-diffusive instabilities in idealized one-dimensional diffusion flames. In this paper, the instabilities observed close to the lean extinction limit are mapped in parameter space, notably as function of the two reactant Lewis numbers. Cellular and pulsating instabilities are found at low and high Lewis numbers, respectively, as predicted by linear stability analyses. The detailed investigation of these two types of instabilities reveals the dependence of cell size and pulsation frequency on the transport properties of the reactants and on flow conditions. The experimental scaling of the cell size is found in good agreement with linear stability. The comparison between experimental and theoretical pulsation frequencies, on the other hand, was hampered by the impossibility of experimentally reproducing the parameters of the stability calculations. Hence, a heuristic correlation between pulsation frequency and flow parameters, transport properties, in particular the Damköhler number, and oscillation amplitude has been developed and awaits theoretical interpretation.
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Oscillating flows... Schematic of fluid flow on the micromembrane-enhanced evaporating surfaces in region I. (a) Proposed fluid distribution in heat transfer region. ((b) and (c)) Bubble and meniscus distributions on the surfaces at the heat flux of 9.0W/cm2, respectively. ((d)–(h)) Hypothesized interactions between fluid and vapor inside microchannels. (i) The number of visible bubbles in a single channel, nb, and total number of visible bubbles in active channels, Nc nb, in the low heat flux region. (j) Oscillating frequency in a single channel, f, and the total frequency in the channel array, i.e., the product of active channel number and the frequency of a single channel, Nc·f, in the low heat flux region. ... Micromembrane-enhanced evaporating surfaces were developed to enhance capillary evaporation heat transfer coefficient (HTC) and critical heat flux (CHF). Micromembranes made of sintered single-layer copper mesh screen were diffusion bonded on microchannels to effectively promote capillary pressure and reduce flow resistance. Compared with mono-porous evaporating surfaces such as microchannels and copper woven mesh laminates in the same thickness under the similar working conditions, CHF was substantially increased by 83% and 198%, respectively, because of the separation of the capillary pressure generation and fluid transport process that was enabled by the micromembrane. The major features such as “M”-shaped capillary evaporation heat transfer curves and the associated heat transfer regions were identified. Oscillating flows induced by the bubble growth and collapse as well as the capillary flows induced by the receding menisci were observed and believed to play imperative roles in enhancing the heat transfer by inducing advections and improving evaporation and nucleate boiling.... Schematic of fluid flow on the micromembrane-enhanced evaporating surfaces in region III. (a) Hypothesized fluid low and liquid distributions inside the structure. ((b) and (c)) Bubble and meniscus distributions on the surfaces at the heat flux of 61.4W/cm2, respectively. (d) The number of visible bubbles in a single channel, nb, and total number of visible bubbles in active channels, Nc·nb, in the high heat flux region. (d) Bubble growth and collapse frequency, fgc, in the high heat flux region.
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Longitudinal flame oscillations for a 10vol.% H2 experiment, re-interpreted with the theoretical considerations given in previous sections. The white arrow indicates the moment when strong external noise affects the flame. ... Stability graphs for a 10vol.% H2–air mixture at normal conditions and an excitation frequency of 110Hz corresponding to the auto excitation of the flame (left) and 1000Hz corresponding to the major frequency of the horn (right). ... Longitudinal flame oscillations for the 10% H2 experiment. Time and distance along horizontal and vertical directions respectively. The white arrow indicates the moment when the strong external noise was turned on and subsequently started affecting the flame propagation. ... Stability graphs for H2–air mixtures at normal conditions. From left to right and from top to bottom: (a) 10, (b) 10.5, (c) 11, (d) 12, (e) 13 and (f) 14vol.% H2. Excitation frequencies are 110, 122, 121, 130, 145 and 170Hz respectively. ... This work addresses the experimental investigation and analytical interpretation of a flame subject to acoustic–parametric instability exited by self-generated pressure pulses. The research presented herein was carried out with lean hydrogen–air mixtures during flame propagation in a smooth channel with an open end. It was found that very lean mixtures with hydrogen concentrations in air of less than 14% vol. H2 generate acoustic oscillations due to flame instabilities, which, in turn, significantly influence the propagation of the flame. Above a 14% vol. H2 concentration in the air, the flame becomes relatively stable with respect to self-generated acoustic perturbations. It was also found that an external polychromatic sound with a dominant frequency of 1000Hz inhibits the instabilities and results in a reduced flame propagation velocity. Numerical solutions of the Searby and Rochwerger analytical formulation for the acoustic–parametric instability were utilized in order to analyze the experiments and study the influence of different parameters on the existence of a spontaneous transition from the acoustic to the parametric instability.... Positions and average velocity of the flame for 12% vol. H2 experiment. For clarity, the origin of coordinates for time and space was selected as the instant in which oscillations appear for the first time.
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Evolution with time of the inclination angle θ. Thick and thin lines for sliding and rolling, respectively. After a transitory state in which θ rises with large oscillations, it goes to a quasi-stationary oscillations state with decreasing frequencies (bottom left) and amplitudes (bottom right). ... A snap of a finger on an elongated cylinder produces on it a surprising fast spinning motion during which its mass center rises with very large oscillations. After that, the mass center goes to a long quasi-stationary oscillations state and eventually goes down very slowly. To explain this behavior we present a theoretical and numerical analysis of the dynamics of a spinning elongated cylinder moving with a single point of contact on a horizontal plane under the action of gravity. The study has been made taking into account the rolling and sliding dissipation as well as the Kutta–Joukowski airflow effect. The results of the simulations are in agreement qualitatively with the observed real motion.... Evolution with time for different initial conditions of the inclination angle θ with (gray (red in the online version)) and without (black (blue in the online version)) Kutta–Joukowski airflow effect. In all the cases we see that after a transitory state in which θ rises with large oscillations, it goes to a quasi-stationary oscillations state. Thick and thin lines for sliding and rolling, respectively. (For interpretation of the references to color in this figure caption, the reader is referred to the web version of this paper.)
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Amyloid β (Aβ) peptides play a central role in the pathophysiology of Alzheimer's disease (AD). The cellular mechanisms underlying Aβ toxicity, however, are poorly understood. Here we show that Aβ25-35 and Aβ1-40 acutely and differentially affect the characteristics of 3 classes of medial septum (MS) neurons in mice. In glutamatergic neurons Aβ increases firing frequency and blocks the A- and the M-current (IA and IM, respectively). While the IA block is similar in other MS neuron classes, the block of IM is specific to glutamatergic neurons. IM block and a simulated Aβ block mimic the Aβ-induced increase in spontaneous firing in glutamatergic neurons. Calcium imaging shows that under control conditions glutamatergic neurons rarely fire while nonglutamatergic neurons fire coherently at theta frequencies. Aβ increases the firing rate of glutamatergic neurons while nonglutamatergic neurons lose theta firing coherence. Our results demonstrate that Aβ-induced dysfunction of glutamatergic neurons via IM decrease diminishes MS rhythmicity, which may negatively affect hippocampal rhythmogenesis and underlie the memory loss observed in Alzheimer's disease.... Theta oscillations... Firing frequency in Vglut2 neurons in Vglut2-Cre mice is increased after amyloid β (Aβ) application. (A) Expression of GFP and ChAT in an MS/DB section of a Vglut2-Cre mouse. In this example, a GFP+ neuron (used for current clamp recordings) was filled with Alexa 555 (arrow). Scale bar, 50 μm. Right, gap-free current-clamp recording of the neuron marked by the arrows before and after the addition of 2 μM Aβ25-35. (B) Photomicrograph of an MS/DB section in which a neuron filled with neurobiotin expresses ChAT. Scale bar, 50 μm. Right, gap-free current-clamp recording of the neuron marked by the arrows on the left before and after the addition of 2 μM Aβ25-35 showing that some ChAT+ neurons can also exhibit increased firing frequency after Aβ25-35 application. (C) Photomicrograph (DIC image overlaid with tdTomato fluorescence of a GAD2-Cre slice) (scale bar, 50 μm). Right, gap-free current-clamp recording of the neuron patched on the left before and after the addition of 2 μM Aβ25-35. ... Amyloid β (Aβ) increases spontaneous firing frequency of VGLUT2+ neurons. Examples of gap-free current-clamp recordings (no injected current) of a VGLUT2+ (A), ChAT+ (B), and GAD2+ (C) neuron before and after the addition of 2 μM Aβ25-35 (right, typical firing patterns of neurons in response to a 200 pA depolarizing current step as well as agarose gel of PCR products of the recorded neurons in these examples). (D) Summary of firing frequencies of VGLUT2+, ChAT+, and GAD2+ neurons (* p = 0.01). (E) Summary of coefficient of variation (CV) of ChAT+ (dark circles, solid line) and GAD2+ neurons (open circles, dashed lines) (* p ≤ 0.02). (F) Diagram showing the approximate locations within the MS/DB of the ChAT+ (•), GAD2+ (x) and VGLUT2+ (☐) neurons shown in (D). Note the “core-and-mantel” distribution of ChAT+ and VGLUT2+ neurons, respectively.
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Gamma-oscillations elicited by a sentence-cue visuomotor task in a 17-year-old male with focal epilepsy (patient #10). Gamma-augmentation involved the lateral-polar occipital region 500msec prior to the onset of button-press, the inferior occipital-temporal region, and the Rolandic area immediately prior to the onset of button-press. The magnitude of gamma-augmentation was greater when the right hand (i.e.: contralateral hand) was used for motor responses, compared to when the left hand (i.e.: ipsilateral hand) was used. The lateral portion of the inferior occipital-temporal region had greater gamma-augmentation elicited by a sentence-cue, whereas the medial portion had greater gamma-augmentation elicited by a gesture-cue. ... We determined how visuomotor tasks modulated gamma-oscillations on electrocorticography in epileptic patients who underwent epilepsy surgery. Each visual-cue consisted of either a sentence or hand gesture instructing the subject to press or not to press the button. Regardless of the recorded hemisphere, viewing sentence and gesture cues elicited gamma-augmentation sequentially in the lateral-polar occipital and inferior occipital-temporal areas; subsequently, button-press movement elicited gamma-augmentation in the Rolandic area. The magnitudes of gamma-augmentation in the Rolandic and inferior occipital-temporal areas were larger when the hand contralateral to the recorded hemisphere was used for motor responses. A double dissociation was found in the left inferior occipital-temporal cortex in one subject; the lateral portion had greater gamma-augmentation elicited by a sentence-cue, whereas the medial portion had greater gamma-augmentation elicited by a gesture-cue. The present study has increased our understanding of the physiology of the human visuomotor system.... Gamma-oscillations elicited by a gesture-cue visuomotor task in a 17-year-old male with focal epilepsy (patient #10). Gamma-augmentation involved the lateral-polar occipital region 500msec prior to the onset of button-press, the inferior occipital-temporal region, and the Rolandic area immediately prior to the onset of button-press. The magnitude of gamma-augmentation was greater when the right hand (i.e.: contralateral hand) was used for motor responses, compared to when the left hand (i.e.: ipsilateral hand) was used. The medial portion of the inferior occipital-temporal region had greater gamma-augmentation elicited by a gesture-cue, whereas the lateral portion had greater gamma-augmentation elicited by a sentence-cue. ... Differential gamma-augmentation elicited by sentence- and gesture-cues in patient 10. Time-frequency ECoG matrixes relative to the onset of visual-cues revealed a functional double dissociation in patient 10. The sentence-cue visuomotor task resulted in gamma-augmentation in the lateral portion but not in the medial portion of the inferior occipital-temporal area (upper row). The gesture-cue visuomotor task resulted in gamma-augmentation in the medial and lateral portions of the inferior occipital-temporal area with greater intensity in the medial portion (middle row). Comparison of amplitudes between sentence- and gesture-cues revealed that the relatively lateral portion of inferior occipital-temporal area had significantly greater gamma-augmentation elicited by a sentence-cue (denoted by red areas in the bottom row), whereas the relatively medial portion had significantly greater gamma-augmentation elicited by a gesture-cue (denoted by blue areas in the bottom row). Please also see Videos S1 and S2 on the website.
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The following is the Supplementary material related to this article Video 1.Video 1Video clip showing the variation of wall shear stress (WSS) vector in four featured points located on the walls (see text for details) of the patient-specific side-to-end AVF model. Left: plot of WSS distribution (magnitude) on the whole surface of the AVF. Middle: the variation of WSS vector in the four featured points throughout the cardiac cycle; note that points P1 and P4 are behind the walls, which were set transparent, and that the WSS vectors are coloured by their magnitude (colour scale on the left panel). Right: zoomed view of P2–P4 WSS unit vectors; note that in this case the WSS vector was normalized (its length is always 1) and the colour scale of the oscillatory shear index (OSI) was changed respect to Figure 2 to distinct it from the WSS scale in the left side. The waveform of inflow blood velocity (U) in the proximal artery (PA) is shown in the upper right panel. Time unit is ms to capture the high frequency oscillations of the WSS vectors and the whole video duration is one cycle period (1s). Of note, respect to the point (P2) on DA where the WSS vector oscillates with low frequency (i.e., of the heart rate), the oscillations of the WSS vector at point (P3) on the inner side of SS have a very high frequency.... Actual surgical creation of vascular access has unacceptable failure rates of which stenosis formation is a major cause. We have shown previously in idealized models of side-to-end arteriovenous fistula that disturbed flow, a near-wall hemodynamic condition characterized by low and oscillating fluid shear stress, develops in focal points that corresponds closely to the sites of future stenosis. Our present study was aimed at investigating whether disturbed flow occurs in patient-specific fistulae, too.... Video clip showing the variation of wall shear stress (WSS) vector in four featured points located on the walls (see text for details) of the patient-specific side-to-end AVF model. Left: plot of WSS distribution (magnitude) on the whole surface of the AVF. Middle: the variation of WSS vector in the four featured points throughout the cardiac cycle; note that points P1 and P4 are behind the walls, which were set transparent, and that the WSS vectors are coloured by their magnitude (colour scale on the left panel). Right: zoomed view of P2–P4 WSS unit vectors; note that in this case the WSS vector was normalized (its length is always 1) and the colour scale of the oscillatory shear index (OSI) was changed respect to Figure 2 to distinct it from the WSS scale in the left side. The waveform of inflow blood velocity (U) in the proximal artery (PA) is shown in the upper right panel. Time unit is ms to capture the high frequency oscillations of the WSS vectors and the whole video duration is one cycle period (1s). Of note, respect to the point (P2) on DA where the WSS vector oscillates with low frequency (i.e., of the heart rate), the oscillations of the WSS vector at point (P3) on the inner side of SS have a very high frequency.
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a) Colloidal particle (black point adherent to bubbles) with different bubble development states: no bubble (plate used here is 10μm in diameter), bubble growth and maximum bubble size; b) Simulation (increased by factor 10 for presentation reasons) (for equation see theoretical section) of colloidal particle propulsion speed (red) upon bubble growth, maximum size and after bubble de-pining (acceleration, maximum speed, and deceleration) and real measurement (black) (error bars from five bubble life cycles measurements of two different particles with same frequency). The bubble radius used in the simulations is also shown (green and right Y axis). Please note that a) and b) are from different plates. A is from a plate with a slightly lower bubbling frequency than b) and frequency differences up to factor 10 were found. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) ... The collision phenomena of self-propelled micro-plate motors are significantly different from classical life-less particles. The Janus micro-plate motors used in this study are 5 and 10μm in diameter and driven by catalytic decomposition of hydrogen peroxide. Periodically oscillating oxygen bubbles drive the motor in rugged straight or spiral motion. Since the inertia effect of mass is no longer important for slow motion in low Reynold number liquid, the momentum law of collision shows some new characteristics due to the constant self-propelling force. We found a bounce back collision and a linear collision between the bubbles of one motor and the micromotor plates as well as between 2 microplates and present a basic theoretical concept. In addition we show experimentally that these 2D particles are able to destroy emerging gas bubbles. More complex collision dynamics may exist for a higher concentration of self-propelled motors.
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