scholarly journals Stratified Flows over and around Long Dynamically Tall Mountain Ridges

2019 ◽  
Vol 76 (5) ◽  
pp. 1265-1287 ◽  
Author(s):  
Arjun Jagannathan ◽  
Kraig Winters ◽  
Laurence Armi
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Stratified Flows ◽  
Half Width ◽  
Short Time Scale ◽  
Late Time ◽  
Low Level ◽  
Long Time ◽  
Flow Splitting ◽  
Short Time

Abstract Uniformly stratified flows approaching long and dynamically tall ridges develop two distinct flow components over disparate time scales. The fluid upstream and below a “blocking level” is stagnant in the limit of an infinite ridge and flows around the sides when the ridge extent is finite. The streamwise half-width of the obstacle at the blocking level arises as a natural inner length scale for the flow, while the excursion time over this half-width is an associated short time scale for the streamwise flow evolution. Over a longer time scale, low-level horizontal flow splitting leads to the establishment of an upstream layerwise potential flow beneath the blocking level. We demonstrate through numerical experiments that for sufficiently long ridges, crest control and streamwise asymmetry are seen on both the short and long time scales. On the short time scale, upstream blocking is established quickly and the flow is well described as a purely infinite-ridge overflow. Over the long time scale associated with flow splitting, low-level flow escapes around the sides, but the overflow continues to be hydraulically controlled and streamwise asymmetric in the neighborhood of the crest. We quantify this late-time overflow by estimating its volumetric transport and then briefly demonstrate how this approach can be extended to predict the overflow across nonuniform ridge shapes.

scholarly journals Techniques and Results of Observations of Rapid and Ultrarapid Variable Stars

1971 ◽  
Vol 15 ◽  
pp. 144-159 ◽  
Author(s):  
Brian Warner
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Variable Stars ◽  
Observational Evidence ◽  
Short Time Scale ◽  
Dwarf Novae ◽  
Stellar Objects ◽  
Blue Object ◽  
Flare Stars ◽  
Short Time

The inception of the present era of interest in rapidly varying stars may be identified with M. F. WALKER’s discovery in 1954 (WALKER 1954) of changes in the brightness of the blue object MacRae+43° 1 (now known as MVLyr), on a time scale of a few minutes. Outside of flare stars, few other stellar objects were suspected to vary on such a short time scale. GREENSTEIN’s (1954) spectra showed that MV Lyr resembles an old nova, which stimulated WALKER to look for light fluctuations in old, recurrent, and dwarf novae and related stars. His observational evidence that all members of these classes show variations of various amplitudes and time scales is summarized in the IAU Colloquium on non-stable stars (WALKER 1957). Most spectacular of his discoveries was the existence of 71 sec periodic variations in the light from the remnant of Nova Herculis 1934 (DQ Her) (WALKER 1956).

scholarly journals Short Time Scale Variability of Active Galactic Nuclei: Einstein IPC Observations of PKS 2155-304 - A Report of Rapid Variations of Instrumental Origin

1989 ◽  
Vol 134 ◽  
pp. 106-107
Author(s):  
J. H. Beall ◽  
W. A. Snyder ◽  
K. S. Wood
Keyword(s):  
Active Galactic Nuclei ◽  
Time Scales ◽  
Time Scale ◽  
Galactic Nuclei ◽  
Short Time Scale ◽  
Background Region ◽  
Rapid Changes ◽  
Source Models ◽  
The Mean ◽  
Short Time

The Einstein IPC observed the bright (5 mCrab) X-ray emitting BL Lac Object PKS 2155-304 on 1979 November 4th and 5th through 7th and on 1980 May 16th through 18th. A total of 17.4 hours were spent monitoring the source. Changes in intensity of between 10–50% are evident in the data for time scales of days and months. The source was constant to within 10% of the mean intensity on hourly time scales for all intervals of data except one. Repeated factor of 2 variations in intensity, occuring on 10–30 second time scales, were observed during the first 50 minutes of the 1979 Nov. 5th observation. These variations, however, were anticorrelated with variations seen in an adjacent background region. Concurrent MPC observations also failed to confirm the rapid changes, although they should have been readily detected. Thus, we conclude that the observed rapid variations are not intrinsic to the source, but originated in the IPC. These results can have implications for other IPC reports of short time scale variability for active galaxies and for source models based on such observations.

On Failure Mechanisms in Flip Chip Assembly—Part 2: Optimal Underfill and Interconnecting Materials

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Yoonchan Oh ◽  
C. Steve Suh ◽  
Hung-Jue Sue
Keyword(s):  
Time Scale ◽  
Flip Chip ◽  
Thermal Stresses ◽  
Failure Modes ◽  
Scale Effects ◽  
Short Time Scale ◽  
Long Time ◽  
Solder Joint Fatigue ◽  
Scale Properties ◽  
Short Time

The physics explored in this investigation enables short-time scale dynamic phenomenon to be correlated with package failure modes such as solder ball cracking and interlayer debond. It is found that although epoxy-based underfills with nanofillers are shown to be effective in alleviating thermal stresses and improving solder joint fatigue performance in thermal cycling tests of long-time scale, underfill material viscoelasticity is ineffective in attenuating short-time scale propagating shock waves. In addition, the inclusion of Cu interconnecting layers in flip chip area arrays is found to perform significantly better than Al layers in suppressing short-time scale effects. Results reported herein suggest that, if improved flip chip reliability is to be achieved, the compositions of all packaging constituent materials need be formulated to have well-defined short-time scale and long-time scale properties. Chip level circuit design layout also needs be optimized to either discourage or negate short-time wave propagation. The knowledge base established is generally applicable to high performance package configurations of small footprint and high clock speed. The approach along with the numerical procedures developed for the investigation can be a practical tool for realizing better device reliability and thus high manufacturing yield.

scholarly journals Behavioral evidence for nested central pattern generator control of Drosophila grooming

2020 ◽  
Author(s):  
Primoz Ravbar ◽  
Neil Zhang ◽  
Julie H. Simpson
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Neural Circuits ◽  
Central Pattern Generators ◽  
Repetitive Behaviors ◽  
Short Time Scale ◽  
Behavioral Experiments ◽  
Behavioral Evidence ◽  
Pattern Generators ◽  
Short Time

AbstractCentral pattern generators (CPGs) are neurons or neural circuits that produce periodic output without requiring patterned input. More complex behaviors can be assembled from simpler subroutines, and nested CPGs have been proposed to coordinate their repetitive elements, simplifying control over different time-scales. Here, we use behavioral experiments to establish that Drosophila grooming may be controlled by nested CPGs. On the short time-scale (5-7 Hz), flies execute periodic leg sweeps and rubs. More surprisingly, transitions between bouts of head cleaning and leg rubbing are also periodic on a longer time-scale (0.3 - 0.6 Hz). We examine grooming at a range of temperatures to show that the frequencies of both oscillations increase – a hallmark of CPG control – and also that the two time-scales increase at the same rate, indicating that the nested CPGs may be linked. This relationship also holds when sensory drive is held constant using optogenetic activation, but the rhythms decouple in spontaneously grooming flies, showing that alternative control modes are possible. Nested CPGs simplify generation of complex but repetitive behaviors, and identifying them in Drosophila grooming presents an opportunity to map the neural circuits that constitute them.

scholarly journals Mathematical modelling and application of frog choruses as an autonomous distributed communication system

2019 ◽  
Vol 6 (1) ◽  
pp. 181117 ◽  
Author(s):  
Ikkyu Aihara ◽  
Daichi Kominami ◽  
Yasuharu Hirano ◽  
Masayuki Murata
Keyword(s):  
Mathematical Model ◽  
Wireless Sensor Network ◽  
Mathematical Modelling ◽  
Sensor Network ◽  
Time Scale ◽  
Wireless Sensor ◽  
Multiple Time Scales ◽  
Short Time Scale ◽  
Long Time ◽  
Short Time

Interactions using various sensory cues produce sophisticated behaviour in animal swarms, e.g. the foraging behaviour of ants and the flocking of birds and fish. Here, we investigate the behavioural mechanisms of frog choruses from the viewpoints of mathematical modelling and its application. Empirical data on male Japanese tree frogs demonstrate that (1) neighbouring male frogs avoid call overlaps with each other over a short time scale and (2) they collectively switch between the calling state and the silent state over a long time scale. To reproduce these features, we propose a mathematical model in which separate dynamical models spontaneously switch due to a stochastic process depending on the internal dynamics of respective frogs and also the interactions among the frogs. Next, the mathematical model is applied to the control of a wireless sensor network in which multiple sensor nodes send a data packet towards their neighbours so as to deliver the packet to a gateway node by multi-hop communication. Numerical simulation demonstrates that (1) neighbouring nodes can avoid a packet collision over a short time scale by alternating the timing of data transmission and (2) all the nodes collectively switch their states over a long time scale, establishing high network connectivity while reducing network power consumption. Consequently, this study highlights the unique dynamics of frog choruses over multiple time scales and also provides a novel bio-inspired technology that is applicable to the control of a wireless sensor network.

scholarly journals Sliding of spherical ball on solid lubricating coating combined with wear process

2021 ◽  
Vol 93 (1) ◽  
pp. 39-50
Author(s):  
Marcin Białas ◽  
Jan Maciejewski ◽  
Stanisław Kucharski
Keyword(s):  
Steady State ◽  
Time Scale ◽  
Contact Region ◽  
Short Time Scale ◽  
Steady State Condition ◽  
Wear Process ◽  
Spherical Ball ◽  
Long Time ◽  
Short Time ◽  
Solid Lubricating Coating

In present paper we show results of ball-on-disk wear experiment of MoS2 film deposited on Ti6Al4V substrate. The ball materials is aluminum oxide. The tests are performed for different surrounding temperature conditions: 20 oC, 200 oC and 350 oC. It is shown that depth of the wear groove increases with increasing surrounding temperature. A finite element modeling approach is next developed to mimic the experimental observations of ball-on-disk wear process. It is based on the assumption of steady state condition developed during short time scale at contact region. The steady state results can next be applied to long time scale in which wear process is numerically simulated. Model results are compared with experimentally obtained wear groove and show satisfactory agreement.

scholarly journals The Mathematical Analysis On The Effect Of Strong Nonlinearity On Steady-State Self-Focusing And Filamentation Of Whistlers In A Plasma

2016 ◽  
Vol 5 (1) ◽  
pp. 18
Author(s):  
Ghanshyam Rai
Keyword(s):  
Time Scale ◽  
High Frequency ◽  
Small Scale ◽  
Nonuniform Heating ◽  
Short Time Scale ◽  
Strong Nonlinearity ◽  
Self Focusing ◽  
Long Time ◽  
Short Time ◽  
Very High

<div><p><em>A high-power Gaussian Whistler propagating in a magnatoplasma becomes self-focused because of (i) ponderomotive force and (ii) nonuniform heating nonlinearities (i) being dominant for t &lt;&lt; T and (ii) being dominant for t &gt; t<sub>E</sub>. On short time scale (t &lt;&lt; t<sub>E</sub> ) whistlers of all frequencies can be focused (the self – focusing length is very large for ω= </em><em> /2 and decreases rapidly on both sides), whereas on the long time scale (t &gt; t<sub>E</sub>) only high frequency whistlers (ω&gt; </em><em> /2) are focused. At very high powers the plasma is depleted almost completely from the axial region and self-focusing does not occur, rather, defocusing takes place. </em></p><p><em>            A plane uniform whistler of high intensity is seen to be unstable for small scale fluctuations, i.e., it must break up into filaments in course of it propagation. The growth rate increases with decreasing scale length of perturbation and is seen to be a saturating function of power density of the beam. </em></p></div>

scholarly journals The effects of driving time scales on heating in a coronal arcade

2020 ◽  
Vol 643 ◽  
pp. A85
Author(s):  
T. A. Howson ◽  
I. De Moortel ◽  
L. E. Fyfe
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Time Scales ◽  
Time Scale ◽  
Plasma Temperature ◽  
Short Time Scale ◽  
Heating Rates ◽  
Poynting Flux ◽  
Long Time

Context. The relative importance of alternating current (AC) and direct current (DC) heating mechanisms in maintaining the temperature of the solar corona is not well constrained. Aims. We aim to investigate the effects of the characteristic time scales of photospheric driving on the injection and dissipation of magnetic and kinetic energy within a coronal arcade. Methods. We conducted three-dimensional magnetohydrodynamic simulations of complex foot point driving imposed on a potential coronal arcade. We modified the typical time scales associated with the velocity driver to understand the efficiency of heating obtained using AC and DC drivers. We considered the implications for the injected Poynting flux and the spatial and temporal nature of the energy release in dissipative regimes. Results. For the same driver amplitude and complexity, long time scale velocity motions are able to inject a much greater Poynting flux of energy into the corona. Consequently, in non-ideal regimes, slow stressing motions result in a greater increase in plasma temperature than for wave-like driving. In dissipative simulations, Ohmic heating is found to be much more significant than viscous heating. For all drivers in our parameter space, energy dissipation is greatest close to the base of the arcade, where the magnetic field strength is strongest, and at separatrix surfaces, where the field connectivity changes. Across all simulations, the background field is stressed with random foot point motions (in a manner more typical of DC heating studies), and, even for short time scale driving, the injected Poynting flux is large given the small amplitude flows considered. For long time scale driving, the rate of energy injection was comparable to the expected requirements in active regions. The heating rates were found to scale with the perturbed magnetic field strength and not the total field strength. Conclusions. Alongside recent studies that show that power within the corona is dominated by low frequency motions, our results suggest that, in the closed corona, DC heating is more significant than AC heating.

scholarly journals Four-Types of IIT-Induced Group Integrity of Plecoglossus altivelis

Entropy ◽  
2020 ◽  
Vol 22 (7) ◽  
pp. 726
Author(s):  
Takayuki Niizato ◽  
Kotaro Sakamoto ◽  
Yoh-ichi Mototake ◽  
Hisashi Murakami ◽  
Takenori Tomaru ◽  
...  
Keyword(s):  
Time Scale ◽  
Brain Network ◽  
Collective Behaviour ◽  
Short Time Scale ◽  
Plecoglossus Altivelis ◽  
Global Parameter ◽  
Fish Schools ◽  
Long Time ◽  
Spatio Temporal ◽  
Short Time

Integrated information theory (IIT) was initially proposed to describe human consciousness in terms of intrinsic-causal brain network structures. Particularly, IIT 3.0 targets the system’s cause–effect structure from spatio-temporal grain and reveals the system’s irreducibility. In a previous study, we tried to apply IIT 3.0 to an actual collective behaviour in Plecoglossus altivelis. We found that IIT 3.0 exhibits qualitative discontinuity between three and four schools of fish in terms of Φ value distributions. Other measures did not show similar characteristics. In this study, we followed up on our previous findings and introduced two new factors. First, we defined the global parameter settings to determine a different kind of group integrity. Second, we set several timescales (from Δ t = 5 / 120 to Δ t = 120 / 120 s). The results showed that we succeeded in classifying fish schools according to their group sizes and the degree of group integrity around the reaction time scale of the fish, despite the small group sizes. Compared with the short time scale, the interaction heterogeneity observed in the long time scale seems to diminish. Finally, we discuss one of the longstanding paradoxes in collective behaviour, known as the heap paradox, for which two tentative answers could be provided through our IIT 3.0 analysis.

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