Short Oscillation Period Research Articles

The electrohydrodynamic enhancement of heat transfer on interdigitated electrodes by a charge injection pump

Electrohydrodynamic pumps, as a representative type of nonmechanical pump, have received significant research attention due to their inherent advantages of having no moving parts and low power consumption. In particular, the planar charge injection pump has exhibited superior fluid driving performance, making it highly promising for applications in microscale flow driving and chip cooling. A sandwich structure pump with multiple pairs of planar interdigitated electrodes is numerically studied in this paper. The interaction of the flow, thermal, and electric fields is analyzed using the lattice Boltzmann method under different pump configurations, governing parameters, and convection mechanisms. The results reveal that the geometric configurations of the planar interdigitated electrodes have direct effects on the pumping performance and heat transfer rate. Specifically, an optimal configuration is achieved when the width of the collector is twice that of the emitter under two-pair electrode simulation conditions. More interestingly, competition between electric and thermal effects is observed, and the optimal threshold for heat transfer is found at an electric Rayleigh number of T = 300 for the considered cases. Finally, the interaction of the electric and thermal fields induces periodic oscillations. The single-vortex mechanism exhibits the longest oscillation period and inhibits heat transfer, while the multi-vortex mechanism has the shortest oscillation period and enhances heat transfer.

Nonlinear dynamic response analysis of marine risers under non-uniform combined unsteady flows

Considering the top-end platform surge induced by periodic wave, the encountered flow field of marine risers under the actual marine environment is approximate to a combined sheared and sheared-oscillatory flow, which is non-uniform in both time and spatial domains. A published time domain force-decomposition model is proposed to predict the riser's nonlinear dynamic response under non-uniform combined unsteady flows. A 90 m flexible riser is chosen as the simulated object, and a large amount of the combined flow cases with different oscillation periods and combined ratios are designed. With the fundamental study on a steady sheared flow case, the structural dynamic response characteristics under non-uniform combined flows are investigated systematically. The overall dynamic response presents travel wave pattern, and the high-frequency response is easier to be excited for the riser's top and bottom segments. Some time-sharing response characteristics like amplitude modulation, frequency transition and mode jumps are captured, and they are affected by the flow field parameters significantly. Under the long oscillation period cases, the intermittent dynamic response follows the accordant periodicity with the current velocity. While under the short oscillation period cases, the unstable structural vibration occurs persistently without clear regularity. The combined ratio also influences the RMS displacement, excited frequency bandwidth and travel wave propagation velocity evidently. Associated with VIV mechanism analysis, the individual response characteristics under different flow field parameter combinations are explained reasonably.

Apple pomace from variety “Blanca de Asturias” as sustainable source of pectin: Composition, rheological, and thermal properties

Pectin derived from pomace from the apple variety “Blanca de Asturias” was isolated by acidic extraction and characterized as an alternative source of pectin. The influence of solid:liquid ratio and the extraction time on the chemical, rheological and thermal properties were evaluated. The molecular weight (Mw) decreased from 865 kDa to 590 kDa due to the hydrolysis reaction, effect that is favored at higher extraction times and to the increment in the solid:liquid ratio. Rheological studies suggest that the chains of apple pomace pectin (APP) disentangled during a short period of oscillation at high frequency and were related to inter- and intra-interaction at the junction zones. The composition and rheological characteristics of APP from the variety “Blanca de Asturias” exhibited strong potential as a thickener and gelling agent in the food industry.

Reconstruction of sunspot activity, cold and warm events, and drought and flood events in the central plain of China during the northern Song Dynasty using historical documents

The Northern Song Dynasty was an important and prosperous dynasty in the history of China, and it existed during a period of climate abnormality. Climate change research for the Northern Song Dynasty era has significance for understanding the interaction between agricultural civilizations in the central plains and nomadic populations in northern China, transfer of the economic and cultural centers of China, and the vicissitudes of the Northern Song Dynasty. There is currently considerable disagreement regarding climate change in the Central Plain during the Northern Song Dynasty era. Many precious and valuable historical documents and records about the Northern Song Dynasty have been collected, and abundant records of sunspot activity, cold and warm weather, drought and flood events have been compiled. Using the Mann-Kendall test, wavelet analysis, R/S analysis, and frequency analysis etc. mathematical statistics methods, sunspot activity, cold and warm events, and drought and flood events were quantitatively reconstructed. There are 15 sunspot maximum years and 16 sunspot minimum years, the cycle length of sunspot activity is 8–14 years, and the average cycle length is 11 years. Hot years account for 11.3% of the total years; warm years account for 12.7%; cold years account for 20.7%; and freezing cold years account for 3.3%. Mann-Kendall test results show that cold and warm variations are natural fluctuations, and there is no indication of abrupt climate change during the Northern Song Dynasty. Morlet wavelet analysis indicates that there are weak high-frequency oscillations and short oscillation periods with three years before 1052 AD, and there are oscillation periods of six years and clear alternations between warmth and cold during 1060-1120 AD. R/S analysis indicates that the Hurst index (H) of cold and warm index series is 0.6155, and the fractal dimension (D) is 1.3845. Since 0.5 < H < 1 and 1 < D < 1.5, fractal structures are evident in the time series of cold and warm indexes, past increments are positively correlated with future increments, and the average cycle length in the time series for cold and warm indexes is 6 years. Temperatures first decreased rapidly followed by a slow increase with long-term fluctuations, and the mean temperature during the Northern Song Dynasty era is 0.4 °C higher than that in the period 1880–1979 AD. Severe drought, moderate drought, moderate flood, severe flood and normal years account for 15.3%, 25.3%, 11.3%, 6.7%, 41.4% of all years, respectively. Frequency analysis indicates that cooling, warming, drought and flood events show a close relationship to sunspot activity.

High-flux x-ray photon emission by a superluminal hybrid electromagnetic mode of intense laser in a plasma waveguide

The feasibility of several novel ultrafast x-ray sources has been demonstrated through the interaction between laser and a micro-structured target. However, the resulting photon flux is still deficient for some applications. Here, we proposed a new method to yield high-flux synchrotron radiation by adopting compact hollow plasma waveguide. We verified the method theoretically and numerically. Linearly polarized laser pulses propagating in the waveguide are mainly converted into the electromagnetic mode HE11 with a superluminal phase speed of 1.02c when the pulse is coupled with the waveguide. The mode fields lead to a strong oscillating force and short oscillation period for energetic electrons, which are accelerated via the longitudinal acceleration mechanism. Then, the short x-ray beam is generated with high yield of 1011–1012. The corresponding photon flux reaches 3.5 × 1021 photons s−1 · 0.1% bandwidth. The high-flux source can be even used for single shot ultrafast imaging or the ultrafast x-ray diffraction and absorption studies.

Numerical investigation on vortex-induced vibration response characteristics for flexible risers under sheared-oscillatory flows

Surge motion of top-end platform induced by periodic wave makes marine flexible riser encounter equivalent sheared-oscillatory flow, under which the Vortex-induced Vibration (VIV) response will be more complicated than pure sheared flow or oscillatory flow cases. Based on a time domain force-decomposition model, the VIV response characteristics under sheared-oscillatory flows are investigated numerically in this paper. Firstly, the adopted numerical model is validated well against laboratory experiments under sheared flow and oscillatory flow. Then, 20 sheared-oscillatory flow cases with different oscillation periods and top maximum current velocities are designed and simulated. Under long and short oscillation period cases, the structural response presents several similar features owing to the instantaneous sheared flow profile at each moment, but it also has some different patterns because of the differently varying flow field. Finally, the effects and essential mechanism of oscillation period and top maximum current velocity on VIV response are discussed systematically.

Autonomously Oscillating Hydrogel Microspheres with High-Frequency Swelling/Deswelling and Dispersing/Flocculating Oscillations.

Fast swelling/deswelling and dispersing/flocculating oscillations of autonomously oscillating hydrogel microspheres (microgels) at periods of single-order seconds were accomplished. The design of the oscillating microgels is based on the incorporation of neutral and hydrophilic acrylamide monomers into conventional microgels to suppress the irreversible aggregation of the microgels during oscillation at high substrate concentrations and high temperatures in the Belousov-Zhabotinsky (BZ) reaction. In contrast to conventional microgels, the aforementioned microgels can carry out the BZ reaction under optimized conditions without irreversible aggregation at higher temperature, resulting in short oscillation periods (∼7 s) that were obtained from optical transmittance measurements. Furthermore, a macrogel composed of organized microgels was prepared, which also showed a remarkably fast swelling/deswelling oscillation (oscillation period: ∼23 s). This new type of oscillating microgel could be applied to advanced materials, e.g. to autonomously oscillating micropumps that imitate the human heartbeat.

Faster redox fluctuations can lead to higher iron reduction rates in humid forest soils

Iron (Fe) minerals play an important role in carbon (C) and nutrient dynamics in redox fluctuating soils. We explored how the frequency of redox oscillations influence Fe reduction rates and C content in Puerto Rican soils. We hypothesized that iron reduction rates would be faster during short oscillation periods than in longer oscillation periods. Surface soils from an upland valley in a humid tropical forest were exposed to systematic redox oscillations over 49 days. The oxidation events were triggered by the introduction of air (21% O2), maintaining the time ratio under oxic or anoxic conditions at 1:6 (τox/τanox). After pre-conditioning the soil to fluctuating redox conditions for 1 month, we imposed 280- and 70-h (or 11.67- and 2.5-day) redox oscillations, measuring FeII every few days. We found that by the end of the experiment, Fe reduction rates were higher in the short oscillation period (τox = 10 h, τanox = 60 h) than in the long oscillation period (τox = 40 h, τanox = 240 h). Carbon and nitrogen loss however was similar for both treatments. These results suggest the characteristics of redox fluctuations can alter rates of Fe reduction and potentially influence ecosystem processes that depend on iron behavior.

Fluid pressure sensing with fiber-optic distributed acoustic sensing

Measurement of interwell hydraulic interference is a fundamental method of characterizing the permeability structure of geothermal, carbon sequestration, and petroleum reservoirs. A new system of pressure measurement is demonstrated that utilizes fiber-optic cable. In the laboratory, fiber-optic distributed acoustic sensing (DAS) was used to measure oscillating pressure signals employed at mHz frequencies. DAS measures oscillatory strain rate along the fiber-optic cable caused by oscillatory pressure changes. Pressure was measured in a water-filled reservoir subjected to an oscillating water level. Because the native measurement of the DAS system is strain rate, the quality of the measurement degrades with longer oscillation periods and smaller pressure changes. Tests showed a linear relationship between DAS strain and hydrostatic pressure for short oscillation periods (&lt;10 s), but a poor relationship for longer periods (&gt;100 s). The approach exhibits poor sensitivity to fluid pressure compared with piezoelectric transducers. However, because fiber-optic cable can withstand harsh environments and measurements are distributed (every 0.25 m along the fiber-optic cable), further refinement may make DAS useful for geofluid monitoring. This is especially true given that geomechanical, seismic, and temperature monitoring may be conducted along the same cable.

Modelling the effects of porous media deformation on the propagation of water-table waves in a sandy unconfined aquifer

This paper examines the influence of porous media deformation on water-table wave dispersion in an unconfined aquifer using a numerical model which couples Richards’ equation to the poro-elastic model. The study was motivated by the findings of Shoushtari et al. (J Hydrol 533:412–440, 2016) who were unable to reproduce the observed wave dispersion in their sand flume data with either numerical Richards’ equation models (assuming rigid porous media) or existing analytic solutions. The water-table wave dispersion is quantified via the complex wave number extracted from the predicted amplitude and phase profiles. A sensitivity analysis was performed to establish the influence of the main parameters in the poro-elastic model, namely Young’s modulus (E) and Poisson’s ratio (ν). For a short oscillation period (T = 16.4 s), the phase lag increase rate (k i) is sensitive to the chosen values of E and ν, demonstrating an inverse relationship with both parameters. Changes in the amplitude decay rate (k r), however, were negligible. For a longer oscillation period (T = 908.6 s), variations in the values of E and ν resulted in only small changes in both k r and k i. In both the short and long period cases, the poro-elastic model is unable to reproduce the observed wave dispersion in the existing laboratory data. Hence porous media deformation cannot explain the additional energy dissipation in the laboratory data. Shoushtari SMH, Cartwright N, Perrochet P, Nielsen P (2016) The effects of oscillation period on groundwater wave dispersion in a sandy unconfined aquifer: sand flume experiments and modelling. J Hydrol 533:412–440.

Influence of hysteresis on groundwater wave dynamics in an unconfined aquifer with a sloping boundary

In this paper, the influence of hysteresis on water table dynamics in an unconfined aquifer was examined using a numerical model to solve Richards’ unsaturated flow equation. The model was subject to simple harmonic forcing across a sloping boundary with a seepage face boundary condition. Time series from both hysteretic and non-hysteretic models were subject to harmonic analysis to extract the amplitude and phase profiles for comparison with existing sand flume data (Cartwright et al., 2004). The results from both model types show good agreement with the data indicating no influence of hysteresis at the oscillation period examined (T = 348 s). The models were then used to perform a parametric study to examine the relationship between oscillation period and hysteresis effects with periods ranging from 3 min to 180 min. At short oscillation periods, (T ≈ 180 s) the effects of hysteresis were negligible with both models providing similar results. As the oscillation period increased, the hysteretic model showed less amplitude damping than the non-hysteretic model. For periods greater than T = 60 min, the phase lag in the non-hysteretic model is greater than for the hysteretic one. For periods less than T = 60 min this trend is reversed and the hysteretic model produced a greater phase lag than the non-hysteretic model. These findings suggest that consideration of hysteresis dynamics in Richards’ equation models has no influence on water table wave dispersion for short period forcing such as waves (T ≈ 10 s) whereas for long period forcing such as tides (T ≈ 12.25 h) or storm surges (T ≈ days) hysteresis dynamics should be taken into account.

Determining the statistical weight of multicluster wave functions for light nuclei in a parametrized phase analysis

The experimental angular distributions of light alpha-cluster nuclei are described. Based on fitting, we find that the experimental angular distribution splits into two diffraction modes: the first has a short oscillation period on the nucleus as a whole, and the second has long oscillation periods on the alpha-cluster substructures. Fitting also reveals that the cross sections rising above the Rutherford level for light nuclei is explained by the additivity (modulation) of the alpha-particle mode of elastic scattering (the scattering of alpha particles on alpha-particle clusters).

First-order phase transitions in magnetization of Fe/Cr/Fe three-layer films

The possibility of appearing jumps in the magnetization curves of Fe/Cr multilayers has been predicted under the assumption that magnetic ordering in chromium interlayers has the form of a linearly polarized spin-density wave. This possibility has been analyz ed for an Fe/Cr/Fe three4ayer film with a conventional quality of Fe/Cr interfaces, which does not ensure a change in the ferromagnetic and antiferromagnetic orientations of the magnetizations of neighboring iron layers with a variation in the thickness of the chromium interlayer by one atomic layer (short oscillation period). The model used suggests that the wave vector of the spin-density wave is responsible for the experime ntally observed long period of these oscillations. Relationships have been derived for the range of thicknesses of chromium interlayers in which the appearance of the predicted effect can be expected, and the magnitude of the effect has been evaluated.

Electronic and vibrational population transfer in diatomic molecules as a function of chirp for different pulse bandwidths

We study the dynamics of two-photon nonresonant electronic excitation of diatomic molecules driven by chirped pulses. While the majority of the experimental results address the role of the chirp for fixed pulse bandwidth, we analyze the possibility of selective excitation for fixed time, as a function of the pulse bandwidth, depending on the sign of the chirp. With strong picosecond pulses and positive chirp it is shown that the dynamics always prepare the molecule in the ground vibrational level of the excited electronic state. The robustness of the dynamics inherits the properties of an effective Landau–Zener crossing. For negative chirp the final state is very sensitive to the specific pulse bandwidth. The dynamics of the system follow a complex convoluted behavior, and the final state alternates between low vibrational levels of the excited electronic state and excited vibrational levels of the ground potential, which become increasingly more excited with increasing bandwidth. The final electronic populations follow a double-period oscillatory behavior. We present a model based on sequential independent crossings which correlates the long-oscillation period with changes in the final vibrational state selected. We show that the short-oscillation period is related with nonadiabatic effects that give rise to fast dynamic Rabi flipping between the electronic states, providing only information of the field–molecule effective coupling. Although the short-oscillation period partially masks the expected results of the final populations, we show that it is still possible to retrieve information from the long-oscillation period regarding the frequencies of the electronic potentials. In order to do so, or in order to control the outcome of the dynamics, it is necessary to perform experiments scanning very different pulse bandwidths, and we propose a possible experimental implementation. All the numerical results of the paper are calculated for a model of the Na2 dimer.

The Desire to Belong Syndrome: Israel and Middle-Eastern Defense, 1948-1954

BECOMING A RECOGNIZED MEMBER OF the Middle-Eastern state system has been a permanent target of Israel since its foundation. Ostracized, however, by most Middle-Eastern countries, Israel has been compelled to leapfrog over the Arab circle and establish friendly relations with Western and Eastern states alike. Naturally, the question of foreign policy orientation was a major consideration for the newly-born state. Following a short period of oscillation between East and West (1948-1950)--a policy called non-identification'Israel's orientation gradually tilted toward the West.I As a result, it became more involved in world affairs, and its desire to play a part in Western defense plans proportionally increased. Thus, the question of Israel's participation in Western schemes for the defense of the Middle East became acute in the early 1950s. This article analyzes the Israeli attitude toward strategic cooperation with the West in the Middle East in the early 195os, and attempts to shed new light on a rather neglected topic, as well as to offer a new framework for understanding Israel's behavior.) The underlying assumption is that Israel's keen desire to associate itself with Western defense plans should be analyzed within the context of what I term--the desire to belong syndrome. Suffering from a growing sense of insecurity and isolation in the face of Arab animosity, Israel aimed to secure Western support in order to consolidate its position in the Middle East. Israel's immediate concerns were to obtain arms, to secure a guarantee of its boundaries as fixed in the armistice agreements (1949), and to be recognized as a major regional player. All these targets could be attained by Israel's association with Western regional defense schemes directed against the Soviet Union in the early I950s.

Confinement effects in electrical resistivity and spin-valve magnetoresistance in metallic layered structures

Quantum size effects in electronic transport properties of metallic trilayers are analysed theoretically. It is shown that electron confinement leads to oscillations in electrical resistivity with two different periodicities. The short oscillation period is determined by the appropriate Fermi wavelength, whereas the long period depends on the potential step at interfaces. When the outer films in the trilayer are ferromagnetic, then the oscillations in the resistivity give rise to similar oscillations in the spin-valve magnetoresistance.

Interlayer exchange coupling and interface reflectivities in Fe/Cu, Co/Cu and Ni/Cu (0 0 1) layers

We present ab inition calculations for the interlayer exchange coupling of FCC Fe, Co and Ni layers in Cu (0 0 1) which have been performed by a KKR-Green's function method for planar defects. The calculations show strong differences in the amplitudes for the short and long oscillation periods, which in a first approximation can be understood from the bulk band structures of Fe, Co and Ni. We discuss results for the quantum well states in the Cu spacer layers and their relation to interlayer coupling. We investigate in detail the effect of the finite thickness of the magnetic layers and present calculations for the reflectivity of a Cu Blochwave at a magnetic layer of finite thickness. We discuss the temperature dependence of the coupling and the transition from finite-to-infinite layer thickness.

Quantum-well states and the short period of oscillation in Cu/Co(001) multilayers.

We report a combined photoemission and inverse-photoemission study of the quantum-well states formed in copper thin films deposited on a fcc Co(001) substrate. In particular, we examine the k point that would correspond to the Fermi-surface crossing that would allow the quantum-well states to mediate the short period of exchange coupling in the associated magnetic multilayers. The states do not display a strong intensity in photoemission, an effect that we attribute to interfacial roughness. \textcopyright{} 1996 The American Physical Society.

On the variability of Mediterranean water flow into the Black Sea

Mediterranean water inflow into the Black Sea has been investigated using current measurements at the northern sill of the Strait of Istanbul (Bosphorus). Variability of the inflow and its relation to sea level and atmospheric factors were studied. Current and salinity spectra show internal variability with periods of 3.5 days. This is correlated with N-S wind component and sea level variations. During southerly wind episodes the lower layer flow increases and relatively well-mixed Mediterranean water reaches the Black Sea. During northeasterlies the bottom layer flow decreases and relatively undiluted Mediterranean water flows into the Black Sea. Dominant energy input is in the low frequency (<0.6 cpd) range in salinity and current speed variations. Current speed also displays variability in short period range. Short period of oscillation (21.3) h is attributed to internal and Black Sea diurnal tidal oscillations and sea breeze.

Trapped Coronal Magnetogravity Modes

Theoretical analyses suggest a physical scenario for the trapping of coronal magnetogravity wave modes above the solar transition region. The shortest oscillation period of coronal magnetogravity modes should be longer than about 1.5 hours. These long-period modes may be responsible for the unexpected low-frequency (1 to 140 microhertz) discrete modes recently discovered in interplanetary charged particle fluxes and magnetic field fluctuations. If the detected modes are caused by these magnetogravity modes rather than by gravity-mode oscillations in the solar interior, then the solar corona and the transition region may be probed from an entirely new perspective by helioseismological techniques. These coronal magnetogravity modes could reveal clues to the heating and dynamics of the solar corona.