Opposite Amplitude Research Articles

The timescape of the city: Example of spatial interactions based on big data

The paper develops the concept of a timescape of a city based on empirical analysis of geospatial big data. We understand the timescape as the temporal shape of a city, which reflects temporal dynamics of a city structure and rhythms based on aggregated time-space behaviour of individuals. The paper uses the concepts of rhythmanalysis and spatial interactions as theoretical basis. We analyse two data types: mobile phone location data and taxi trajectory data, and the city of Prague is taken as the example. The data capture the population mobility peak before the Covid-19 pandemic has burst out. We examine both the temporal (weekly and daily rhythms) and spatial (intra urban and ‘extra’ urban flows) hierarchies of the city time-space. We have confirmed the existence of distinct differences between workdays and weekend days. It has also been shown that the mobility based on taxi trajectories has specific temporal distribution. Based on ‘extra’ urban flows, rhythms and thus on the present population of the city we have identified two hierarchically different time waves, long (weekly) and short (daily), when the latter has opposite amplitude and span during workdays and during weekend days.

Differences of Electric Field Parameters for Lightning Strikes on Tall Towers and Nonelevated Objects

In this article, we analyzed the far electric field parameters of cloud-to-ground (CG) lightning striking tall towers in Guangzhou at the distance of 20–70 km, and compared with lightning striking nonelevated objects from the same thunderstorm near the tall towers. By comparing the waveform characteristics, we found that the far-field waveform of tall tower exhibits the characteristics of early narrow undershoot, zero crossing, oscillation damping attenuation and there is a secondary peak after the opposite polarity peak, which is absent in the CG lightning. The GM values of 10%–90% rise time, fall time and zero-crossing time of lightning strikes on tall towers are 1.6, 2.0, and 8.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s which are far less than 2.5 (1.8 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s), 7.9 (6.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s), and 28.1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s (28.7 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s) of the first return stroke (subsequent return stroke) of CG lightning. In addition, the initial electric field peak, the ratio of the opposite polarity overshoot amplitude to the initial peak, and the time interval between initial electric field peak and second peak of the lightning striking on tall tower are larger than those of the CG lightning.

Ultrafast Optical Probe of Coherent Acoustic Phonons in Dirac Semimetal Cd3As2 Film Epitaxied on GaAs(111)B Substrate.

Coherent longitudinal acoustic phonon (CAP) generation in epitaxial Dirac semimetal Cd3As2 films with different thicknesses was investigated by a time-resolved reflectance technique. The short-lived weak CAP oscillations can be observed only in the thicker Cd3As2 films, and their central frequency of 0.039 THz has no dependence on sample thickness, but is nearly inversely proportional to the probe wavelength. For the 20 nm thin film, the observed long-lived CAP with a central frequency of 0.049 THz is generated in the GaAs(111)B substrate underneath. A sound velocity of 3800 m/s for the Cd3As2 film and 5360 m/s for the GaAs(111)B substrate is thus deduced. In addition, the opposite CAP amplitude and lifetime dependence on temperature further confirms the electronic and thermal stress origination of CAP generated in GaAs(111)B and Cd3As2 film, respectively, based on the propagating strain pulse model. The central frequency of CAP is found to be stable with increasing pumping fluence and temperature, which makes Cd3As2 a potential material for thermoelectric device applications.

Contrasting Phase Changes of Precipitation Annual Cycle Between Land and Ocean Under Global Warming

AbstractWe report a land‐ocean contrast in the phase change of precipitation annual cycle in multimodel ensemble simulations as climate warms, with a robust delay over land (0–40°N/S) versus an advance (0–40°N/S) or no clear (0–25°N/S) phase changes over ocean. The robust delay over land is caused by the increased effective atmospheric heat capacity CA. Over ocean, the increased CA favors a phase delay, while the land‐ocean precipitation contrast during the peak rainy season favors a phase advance. The latter overwhelms the former and causes a seasonal advance over 0–40°N/S, while the two factors cancel out and result in no phase changes over 0–25°N/S. Under the atmospheric energetic constraint, the land‐ocean precipitation contrast in the peak rainy season is related to their opposite amplitude changes of surface temperature annual cycle: Seasonally different wind changes enhance the amplitude over ocean, while increased CA and surface cooling feedback reduce the amplitude over land.

Vector speckle grid: instantaneous incoherent speckle grid for high-precision astrometry and photometry in high-contrast imaging

Context. Photometric and astrometric monitoring of directly imaged exoplanets will deliver unique insights into their rotational periods, the distribution of cloud structures, weather, and orbital parameters. As the host star is occulted by the coronagraph, a speckle grid (SG) is introduced to serve as astrometric and photometric reference. Speckle grids are implemented as diffractive pupil-plane optics that generate artificial speckles at known location and brightness. Their performance is limited by the underlying speckle halo caused by evolving uncorrected wavefront errors. The speckle halo will interfere with the coherent SGs, affecting their photometric and astrometric precision. Aims. Our aim is to show that by imposing opposite amplitude or phase modulation on the opposite polarization states, a SG can be instantaneously incoherent with the underlying halo, greatly increasing the precision. We refer to these as vector speckle grids (VSGs). Methods. We derive analytically the mechanism by which the incoherency arises and explore the performance gain in idealised simulations under various atmospheric conditions. Results. We show that the VSG is completely incoherent for unpolarized light and that the fundamental limiting factor is the cross-talk between the speckles in the grid. In simulation, we find that for short-exposure images the VSG reaches a ∼0.3–0.8% photometric error and ∼3−10 × 10−3λ/D astrometric error, which is a performance increase of a factor ∼20 and ∼5, respectively. Furthermore, we outline how VSGs could be implemented using liquid-crystal technology to impose the geometric phase on the circular polarization states. Conclusions. The VSG is a promising new method for generating a photometric and astrometric reference SG that has a greatly increased astrometric and photometric precision.

A Simplified Approach to Identify Sectional Deformation Modes of Thin-Walled Beams with Prismatic Cross-Sections

In this paper, a simplified approach to identify sectional deformation modes of prismatic cross-sections is presented and utilized in the establishment of a higher-order beam model for the dynamic analyses of thin-walled structures. The model considers the displacement field through a linear superposition of a set of basis functions whose amplitudes vary along the beam axis. These basis functions, which describe basis deformation modes, are approximated from nodal displacements on the discretized cross-section midline, with interpolation polynomials. Their amplitudes acting in the object vibration shapes are extracted through a modal analysis. A procedure similar to combining like terms is then implemented to superpose basis deformation modes, with equal or opposite amplitude, to produce primary deformation modes. The final set of the sectional deformation modes are assembled with primary deformation modes, excluding the ones constituting conventional modes. The derived sectional deformation modes, hierarchically organized and physically meaningful, are used to update the basis functions in the higher-order beam model. Numerical examples have also been presented and the comparison with ANSYS shell model showed its accuracy, efficiency, and applicability in reproducing three-dimensional behaviors of thin-walled structures.

Tunable high-order single-sideband signal generator with optical carrier suppression using dual-parallel Mach–Zehnder modulator

A tunable high-order single-sideband signal generator with optical carrier suppression (SSB-OCS generator) is proposed, which is based on frequency multiplication operation using dual-parallel Mach–Zehnder modulator (DPMZM) and Mach–Zehnder interferometer (MZI). By changing all the modulators at maximum or minimum transmission point simultaneously, the amplitude of input radio frequency (RF) signals and the phase difference between input RF signals, two high-order even or odd signals with opposite amplitude of one sideband, are generated by upper DPMZM and lower DPMZM, respectively. Then, two optical signals are coupled to reserve one sideband, and the coupled SSB-OCS signal is injected into an MZI to suppress high-order intermodulation components. The simulated results show that the first-, second-, and third-order SSB-OCS signals can be achieved, and the suppression ratio is over 30 dB, which agrees well with the theoretical prediction. This scheme is featured by the capability to generate tunable high-order SSB-OCS signal with high suppression ratio, and the operation is simple and flexible. Finally, an experiment was carried out to demonstrate the feasibility of the proposed scheme, and a first- and second-order SSB-OCS signal were obtained, respectively, and the suppression ratio is over 24 dB.

Comparative study for convective heat transfer of counter-flow wavy double-layer microchannel heat sinks in staggered arrangement

This study proposes a modification of double-layer Microchannel Heat Sinks (DMHSs) into wavy configuration with swap of upper and lower layer design. The design can effectively improve the comparatively low cooling effectiveness at the upper layer, yet the swap of flow can promote re-developing of flow field and heat transfer accordingly. Both parallel and counter flow arrangements of the proposed configurations are examined in details. It is found that the staggered wavy DMHSs with opposite amplitude shows superior heat transfer enhancement. Regardless of the types of heat sink being investigated, the maximum temperature for all parallel flow arrangement always occurs at the exit while the maximum temperature for counter flow is in the interior of heat sink but is close to the exit. Interestingly, the swap design of counter flow arrangement (parallel channel or wavy) shows two maximum temperatures in the first and second half of the heat sink. Basically, the counter flow of straight staggered DMHS has the best overall thermal performance among the counter flows of straight parallel DMHS, synclastic wavy staggered DMHS and opposite wavy staggered DMHS. This is because the wavy staggered DMHS incur more pressure drop and pumping power accordingly.

Double Hyperbolic Reaching Law With Chattering-Free and Fast Convergence

This paper proposes a novel continuous reaching law for chattering-free sliding mode control by using two hyperbolic functions with similar changing rate and opposite amplitude characteristics. The first function is an inverse hyperbolic sine function, which can guarantee the fast convergence as the initial value of the sliding mode variable is far away from the equilibrium. When the sliding mode variable is approaching to zero, the second hyperbolic tangent function can ensure the sliding mode variable be infinitely close to zero rather than cross the zero. With the proposed reaching law, the fast convergence and chattering-free property can be both guaranteed, and the satisfactory convergence performance of the reaching phase is achieved with an approximation method. Moreover, the steady state error bound is analyzed in details when considering external disturbances. A simple example is provided to demonstrate the effectiveness of the proposed method.

Non-Feynman Deterministic Pulsing Ratchet Based on a Symmetric Periodic Potential with Harmonic Time Modulation

The deterministic mechanism of directed particle motion in a symmetric periodic potential with harmonic time modulation is theoretically examined. We show that directed particle motion can be established with a symmetric potential in the absence of thermal motion, provided the spatial particle shift is synchronized with the period of temporal change in the potential and the characteristic time required for the particle to pass through the interval between neighboring extremes in potential is equal to the half-period of the time modulation. Ratchet behavior is demonstrated using a simple symmetric force potential consisting of a square wave with opposite but equal amplitude regions. By establishing spatiotemporal synchronization between the particle shift in space and the time modulation, nonreversible directed particle motion is provided by inertia that is maintained as the potential profile approaches zero in the time modulation process.

Detecting quantum non-Gaussianity of noisy Schrödinger cat states

Highly quantum nonlinear interactions between different bosonic modes lead to the generation of quantum non-Gaussian states, i.e. states that cannot be written as mixtures of Gaussian states. A paradigmatic example is given by Schrödinger's cat states, that is, coherent superpositions of coherent states with opposite amplitude. We here consider a novel quantum non-Gaussianity criterion recently proposed in the literature and prove its effectiveness on Schrödinger cat states evolving in a lossy bosonic channel. We prove that the quantum non-Gaussianity can be effectively detected for high values of losses and for large coherent amplitudes of the cat states.

Research on LCR Filter in the Link of Shunt Active Power Filter in Electrical Power System

Shunt active power filter (APF) is an electric equipment which effectively optimizes harmonic waves. By measuring the load current, it produces compensated current with opposite amplitude to the load current in order to improve the power quality of the power grid. Little has been reported on how to effectively design the LPF employed in the link of shunt APF and power system. The paper theoretically analyzes constrains for parameters of the LCR output filter, and then determines the optimal LRC filter parameters by comparing different output filter (OF) functions. At last, the experiment results further verify the correctness of the design method.

Electrophysiological observations on the effects of potassium ions on the response of intradental nerves to dentinal tubular flow in the cat

Objective To determine the effects of K + on the sensitivity of sensory receptors in teeth to fluid flow through dentine. Methods Evoked discharges were recorded from intradental nerves in anaesthetised cats during the application of 5 s hydrostatic pressure stimuli to exposed dentine through either normal Ringer's or Ringer's containing up to 255 mmol/l K +. The stimuli ranged between −500 and +500 mm Hg. Results The number of impulses evoked by a positive pressure stimulus increased, and the latency of the response decreased, as either the pressure or the K + concentration of the Ringer's was increased. The response to a negative pressure stimulus applied 2 s after a positive pressure pulse of equal but opposite amplitude decreased as either the intensity of the stimulus or the K + concentration of the Ringer's was increased. Conclusions Potassium ions that were transported into the dentine and pulp by bulk flow during the application of positive pressure stimuli increased the sensitivity of the receptors to inward tubular flow but decreased their sensitivity to outward flow.

Photothermal radiometry and modulated luminescence examination of demineralized and remineralized dental lesions

Dental caries involves continuous challenges of acid-induced mineral loss and a counteracting process of mineral recovery. As an emerging non-destructive methodology, photothermal radiometry and modulated luminescence (PTR-LUM) has shown promise in measuring changes in tooth mineral content. Human molars (n=37) were subjected to demineralization in acid gel (pH 4.5, 10 days), followed by incubation in remineralisation solutions (pH 6.7, 4 weeks) without or with fluoride (1 or 1000 ppm). PTR-LUM frequency scans (1 Hz – 1 kHz) were performed prior to and during demineralization and remineralization treatments. Transverse Micro-Radiography (TMR) analysis followed at treatment conclusion. The non-fluoridated group exhibited opposite amplitude and phase trends to those of the highly fluoridated group: smaller phase lag and larger amplitude. These results point to a complex interplay between surface and subsurface processes during remineralization, confining the thermal-wave centroid toward the dominating layer.

Space-time correlations in inflationary spectra: A wave-packet analysis

The inflationary mechanism of mode amplification predicts that the state of each mode with a given wave vector is correlated to that of its partner mode with the opposite vector. This implies nonlocal correlations which leave their imprint on temperature anisotropies in the cosmic microwave background. Their spatial properties are best revealed by using local wave packets. This analysis shows that all density fluctuations giving rise the large scale structures originate in pairs which are born near the reheating. In fact each local density fluctuation is paired with an oppositely moving partner with opposite amplitude. To obtain these results we first apply a ``wave packet transformation'' with respect to one argument of the two point correlation function. A finer understanding of the correlations is then reached by making use of coherent states. The knowledge of the velocity field is required to extract the contribution of a single pair of wave packets. Otherwise, there is a two-folded degeneracy which gives three aligned wave packets arising from two pairs. The applicability of these methods to observational data is briefly discussed.

The MACHO Project Large Magellanic Cloud Variable Star Inventory. XI. Frequency Analysis of the Fundamental‐Mode RR Lyrae Stars

We have frequency-analyzed 6391 variables classified earlier as fundamental-mode RR Lyrae (RR0) stars in the MACHO database on the Large Magellanic Cloud (LMC). The overwhelming majority (i.e., 96%) of these variables have been proved to be indeed RR0 stars, whereas the remaining ones have fallen into one of the following categories: single- and double-mode Cepheids, binaries, first-overtone and double-mode RR Lyrae stars, and nonclassified variables. Special attention has been paid to the properties of the amplitude- and phase-modulated RR0 stars (the Blazhko stars). We found altogether 731 Blazhko variables showing either a doublet or an equidistant triplet pattern at the main pulsation component in their frequency spectra. This sample overwhelmingly exceeds the number of Blazhko stars known in all other systems combined. The incidence rate of the Blazhko variables among the RR0 stars in the LMC is 11.9%, which is 3 times higher than their rate among the first-overtone RR Lyrae stars. No difference is found in the average brightness between the single-mode and Blazhko variables. However, the latter ones show a somewhat lower degree of skewness in their average light curves and a concomitant lower total amplitude in their modulation-free light curves. From the frequency spectra we found that variables with larger modulation amplitudes at the higher frequency side of the main pulsation component are 3 times more common than the ones showing the opposite amplitude pattern. A search for a modulation component with the Blazhko period in the average brightness of the individual variables showed the existence of such a modulation with an overall amplitude of ≈0.006 mag. On the other hand, a similar search for quadruple modulation patterns around the main pulsation component has failed to clearly detect such components at the ≈0.004 mag level. This means that the amplitudes of the quadruple components (if they exist) should be, on average, at least 10 times smaller than those of the triplet components. This finding and the existence of Blazhko variables with highly asymmetric modulation amplitudes not only question the validity of the magnetic oblique rotator model but also put stringent constraints on models based on mode-coupling theories.

Telomeres and Telomerase Activity Are Regulated as a Complex System in Cultured Hepatoma Cells

Non-linear dynamics, often chaotic, are now accepted as the normal way in which major physiological functions proceed, allowing adaptation. The length of telomeres, the chromosome endings, is critical in limiting cell lifespan and in controlling subsets of downstream genes. Telomere length dynamics in tumoral cells is the net result of mitotic erosion of telomeric DNA and telomere repair by the enzyme telomerase. We observed telomere length oscillations in the long-lived hepatoma Fao cell line, for forty three 6-day passages in culture. Telomerase activity oscillated with similar frequency and opposite amplitude. We mapped the combined data of telomere erosion and telomerase activity. There was reverse symmetry between consecutive periods of 10 passages. Thus, telomere length and telomerase activity can be considered to be a single complex system with strong reciprocal regulation.

On the Difficulty of Detecting Streaming Potentials Generated at Depth

— In order to investigate how a streaming potential coefficient measured in the laboratory, at a typical scale of 10 cm, can be incorporated into a field model, with a typical scale of 1 to 10 km, we measured the electric field induced by water flows forced at 150 m depth through a 10-m wide granite fractured zone. The water flows were obtained by pumping cyclically 10 m of water from a borehole that cut the fractured zone at depth, and contemporaneously reinjecting it into another borehole located 50 m away. After one day a steady-state fluid flow regime was reached, with pumping cycles lasting 45 minutes, indicating a hydraulic conductivity of 10−5 m s−1 and a specific storage coefficient of 3.25×10−6 m−1. The expected self-potential at the surface was an anomaly with two maxima of opposite sign and 2μV amplitude each, both located 160 m away from the middle of the borehole heads, the signal being divided by two 500 m away from the middle of the borehole heads (in agreement with Wurmstich and Morgan, 1994). Instead, we observed an electrical signal of 8 mV midway between the borehole heads, and smaller than 5 mV, 33 m away from the borehole heads. The discrepancy observed between the data and the model can be explained by fluid flow leakages that occurred close to the water-table head, represented about 20% of the total water flow, and activated smaller but closer electric sources. This experiment thus illustrates the practical difficulty of detecting streaming potentials generated at depth. It shows in particular that in fractured zones, and hence in the vicinity of a major active fault small water flows located distantly from an energetic targeted source, but close to some of the electrodes of the network, can sometimes drastically distort the shape of the expected anomaly. Models of possible electrical earthquake precursors therefore turn out to be more speculative than expected.

Vestibuloocular reflex signal modulation during voluntary and passive head movements.

The vestibuloocular reflex (VOR) effectively stabilizes the visual world on the retina over the wide range of head movements generated during daily activities by producing an eye movement of equal and opposite amplitude to the motion of the head. Although an intact VOR is essential for stabilizing gaze during walking and running, it can be counterproductive during certain voluntary behaviors. For example, primates use rapid coordinated movements of the eyes and head (gaze shifts) to redirect the visual axis from one target of interest to another. During these self-generated head movements, a fully functional VOR would generate an eye-movement command in the direction opposite to that of the intended shift in gaze. Here, we have investigated how the VOR pathways process vestibular information across a wide range of behaviors in which head movements were either externally applied and/or self-generated and in which the gaze goal was systematically varied (i.e., stabilize vs. redirect). VOR interneurons [i.e., type I position-vestibular-pause (PVP) neurons] were characterized during head-restrained passive whole-body rotation, passive head-on-body rotation, active eye-head gaze shifts, active eye-head gaze pursuit, self-generated whole-body motion, and active head-on-body motion made while the monkey was passively rotated. We found that regardless of the stimulation condition, type I PVP neuron responses to head motion were comparable whenever the monkey stabilized its gaze. In contrast, whenever the monkey redirected its gaze, type I PVP neurons were significantly less responsive to head velocity. We also performed a comparable analysis of type II PVP neurons, which are likely to contribute indirectly to the VOR, and found that they generally behaved in a quantitatively similar manner. Thus our findings support the hypothesis that the activity of the VOR pathways is reduced "on-line" whenever the current behavioral goal is to redirect gaze. By characterizing neuronal responses during a variety of experimental conditions, we were also able to determine which inputs contribute to the differential processing of head-velocity information by PVP neurons. We show that neither neck proprioceptive inputs, an efference copy of neck motor commands nor the monkey's knowledge of its self-motion influence the activity of PVP neurons per se. Rather we propose that efference copies of oculomotor/gaze commands are responsible for the behaviorally dependent modulation of PVP neurons (and by extension for modulation of the status of the VOR) during gaze redirection.

A neural correlate for vestibulo-ocular reflex suppression during voluntary eye-head gaze shifts.

The vestibulo-ocular reflex (VOR) is classically associated with stabilizing the visual world on the retina by producing an eye movement of equal and opposite amplitude to the motion of the head. Here we have directly measured the efficacy of VOR pathways during voluntary combined eye-head gaze shifts by recording from individual vestibular neurons in monkeys whose heads were unrestrained. We found that the head-velocity signal carried by VOR pathways is reduced during gaze shifts in an amplitude-dependent manner, consistent with results from behavioral studies in humans and monkeys. Our data support the hypothesis that the VOR is not a hard-wired reflex, but rather a pathway that is modulated in a manner that depends on the current gaze strategy.