Angular Fluctuations Research Articles

Measuring the evolution of intergalactic gas from z = 0 to 5 using the kinematic Sunyaev–Zel’dovich effect

ABSTRACT A complete census of baryons in the late Universe is a long-standing challenge due to the intermediate temperate and rarefied character of the majority of cosmic gas. To gain insight into this problem, we extract measurements of the kinematic Sunyaev–Zel’dovich (kSZ) effect from the cross-correlation of angular redshift fluctuations maps, which contain precise information about the cosmic density and velocity fields, and cosmic microwave background maps high-pass filtered using aperture photometry; we refer to this technique as angular redshift fluctuations (ARF)–kSZ tomography. Remarkably, we detect significant cross-correlation for a wide range of redshifts and filter apertures using 6dF galaxies, BOSS galaxies, and SDSS quasars as tracers, yielding a 11σ detection of the kSZ effect. We then leverage these measurements to set constraints on the location, density, and abundance of gas inducing the kSZ effect, finding that this gas resides outside dark matter haloes, presents densities ranging from 10 to 250 times the cosmic average, and comprises half of cosmic baryons. Taken together, these findings indicate that ARF–kSZ tomography provides a nearly complete census of intergalactic gas from z = 0 to 5.

Density weighted angular redshift fluctuations: a new cosmological observable

ABSTRACT We propose the use of angular fluctuations in the galaxy redshift field as a new way to extract cosmological information in the Universe. This new probe $\delta z (\hat{\mathbf {n}})$ consists of the statistics of sky maps built by projecting redshifts under a Gaussian window of width σz centred upon a redshift zobs, and weighted by the galaxy density field. We compute the angular power spectrum of the $\delta z (\hat{\mathbf {n}})$ field in both numerical simulations and in linear perturbation theory. From these, we find that the $\delta z (\hat{\mathbf {n}})$ field (i) is sensitive to the underlying density and peculiar velocity fields; (ii) is highly correlated, at the $\gtrsim 60\, {{\ \rm per\ cent}}$ level, to the line-of-sight projected peculiar velocity field; (iii) for narrow windows (σz < 0.03), it is almost completely uncorrelated to the projected galaxy angular density field under the same redshift window; and (iv) it is largely unaffected by multiplicative and additive systematic errors on the observed number of galaxies that are redshift-independent over ∼σz. We conclude that $\delta z (\hat{\mathbf {n}})$ is a simple and robust tomographic measure of the cosmic density and velocity fields, complementary to angular clustering, that will contribute to more complete exploitations of current and upcoming galaxy redshift surveys.

Brownian fluctuations and hydrodynamics of a microhelix near a solid wall

We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix. From the analysis of mean squared displacements and time correlation functions we recover the components of the full mobility tensor. We find that Brownian motion displays correlations between angular and translational fluctuations from which we can directly measure the hydrodynamic coupling coefficient that is responsible for thrust generation. By varying the distance of the microhelices from a no-slip boundary we can systematically measure the effects of a nearby wall on the resistance matrix. Our results indicate that a rotated helix moves faster when a nearby no-slip boundary is present, providing a quantitative insight on thrust enhancement in confined geometries for both synthetic and biological microswimmers.

Swimmer Suspensions on Substrates: Anomalous Stability and Long-Range Order.

We present a comprehensive theory of the dynamics and fluctuations of a two-dimensional suspension of polar active particles in an incompressible fluid confined to a substrate. We show that, depending on the sign of a single parameter, a state with polar orientational order is anomalously stable (or anomalously unstable), with a nonzero relaxation (or growth) rate for angular fluctuations, not parallel to the ordering direction, at zero wave number. This screening of the broken-symmetry mode in the stable state does lead to conventional rather than giant number fluctuations as argued by Bricard etal., Nature 503, 95 (2013), but their bend instability in a splay-stable flock does not exist and the polar phase has long-range order in two dimensions. Our theory also describes confined three-dimensional thin-film suspensions of active polar particles as well as dense compressible active polar rods, and predicts a flocking transition without a banding instability.

Quantitative earthquake-like statistical properties of the flow of soft materials below yield stress

The flow behavior of soft materials below the yield stress can be rich and is not fully understood. Here, we report shear-stress-induced reorganization of three-dimensional solid-like soft materials formed by closely packed nematic domains of surfactant micelles and a repulsive Wigner glass formed by anisotropic clay nano-discs having ionic interactions. The creep response of both the systems below the yield stress results in angular velocity fluctuations of the shearing plate showing large temporal burst-like events that resemble seismic foreshocks-aftershocks data measuring the ground motion during earthquake avalanches. We find that the statistical properties of the quake events inside such a burst map on to the scaling relations for magnitude and frequency distribution of earthquakes, given by Gutenberg-Richter and Omori laws, and follow a power-law distribution of the inter-occurrence waiting time. In situ polarized optical microscopy reveals that during these events the system self-organizes to a much stronger solid-like state.

Research and experiment of a novel flower transplanting device using hybrid-driven mechanism

Aiming at decreasing the component complexity and cost of flower transplanting machine, an integrated transplanting method for picking and planting flower seedlings was proposed, and a hybrid-driven five-bar parallel mechanism was designed. A “beak-shaped” trajectory was designed for integrated transplanting requirements, and meantime, either the posture requirements of transplanting claw were determined. Based on the transplanting trajectory of the mechanism, a corresponding mathematical model for solving the link parameters was established, and then the five-bar mechanism was divided into two bar groups, optimization was conducted in two steps based on genetic algorithm and NSGA-II algorithm. Consequently, the optimal solution of the hybrid-driven five-bar parallel mechanism for flower seedling transplanting was obtained. Compared with similar designs, the trajectory displacement of the proposed mechanism is larger in the condition of smaller link size, which indicates that the mechanism can effectively decrease the machine size. The real-time controllable motor angular acceleration fluctuation is smaller and the commutation times are less, which has the advantage of reducing the difficulty of the mechanism control system. Subsequently, the correctness of the design method is verified by kinematics simulation. Finally, the synchronous linkage motion control methods of the two motors were designed, a transplanting experiment of the prototype was carried out, the picking success rate had reached 90%-93.4% and transplanting success rate was 80.5%-86.9% during experiment, which showed that the integrated operation of picking and planting flower seedlings can be realized by the proposed mechanism. Keywords: hybrid-driven mechanism, mechanism optimization, integrated operation of picking and planting, synchronous linkage motion control DOI: 10.25165/j.ijabe.20201302.5187 Citation: Zhao X, Zhang X S, Wu Q P, Dai L, Chen J N. Research and experiment of a novel flower transplanting device using hybrid-driven mechanism. Int J Agric & Biol Eng, 2020; 13(2): 92–100.

A possibility of Lorentz violation in the Higgs sector

In string theory, a scalar field often appears as a moduli of a geometrical configuration of D-branes in higher-dimensional space. In the low energy effective theory on D-branes, the distance between D-branes is translated into the energy scale of the gauge symmetry breaking. In this paper, we study a phenomenological consequence of a possibility that the Higgs field is such a moduli field and the D-brane configuration is stabilized by a stationary motion, in particular, revolution of D-branes on which we live. Then, due to the Coriolis force, Higgs mode is mixed with the angular fluctuation of branes and the Lorentz symmetry is violated in the dispersion relation of the Higgs boson. The Higgs boson mass measurements at LHC experiments give an upper bound [Formula: see text][Formula: see text][Formula: see text] GeV for the angular frequency of the revolution of D-branes.

Implications of a frame dependent dark energy for the spacetime metric, cosmography, and effective Hubble constant

In earlier papers we showed that a frame dependent effective action motivated by the postulates of three-space general coordinate invariance and Weyl scaling invariance exactly mimics a cosmological constant in Friedmann-Robertson-Walker (FRW) spacetimes, but alters the linearized equations governing scalar perturbations around a spatially flat FRW background metric. Here we analyze the implications of a frame dependent dark energy for the spacetime cosmological metric within both a perturbative and a non-perturbative framework. Both methods of calculation give a one-parameter family of cosmologies which are in close correspondence to one another, and which contain the standard FRW cosmology as a special case. We discuss the application of this family of cosmologies to the standard cosmological distance measures and to the effective Hubble parameter, with special attention to the current tension between determinations of the Hubble constant at late time, and the Hubble value obtained through the cosmic microwave background (CMB) angular fluctuation analysis.

Large angular scale fluctuations of near-infrared extragalactic background light based on the IRTS observations

Abstract We measure the spatial fluctuations of the Near-Infrared Extragalactic Background Light (NIREBL) from 2° to 20° in angular scale at the 1.6 and $2.2\, \mu \mathrm{m}$ using data obtained with Near-Infrared Spectrometer (NIRS) on board the Infrared Telescope in Space (IRTS). The brightness of the NIREBL is estimated by subtracting foreground components such as zodiacal light, diffuse Galactic light, and integrated star light from the observed sky. The foreground components are estimated using well-established models and archive data. The NIREBL fluctuations for the 1.6 and $2.2\, \mu \mathrm{m}$ connect well toward the sub-degree scale measurements from previous studies. Overall, the fluctuations show a wide bump with a center at around 1° and the power decreases toward larger angular scales with nearly a single power-law spectrum (i.e., ${F[\sqrt{l(l+1)C_l/2\pi }]} \sim \theta ^{-1}]$, indicating that the large-scale power is dominated by the random spatial distribution of the sources. After examining several known sources, contributors such as normal galaxies, high-redshift objects, intra-halo light, and far-IR cosmic background, we conclude that the excess fluctuation at around the 1° scale cannot be explained by any of them.

Design of a micro pole-climbing robot

Pole-climbing robots are increasingly needed to carry out high-risk tasks for human beings. A micro pole-climbing robot is designed in this article. A strategy of climbing pole is proposed, which has high precision in each stride. To enable the robot to sample the angle relative to the ground in real time, micro electro mechanical systems (MEMS) three-axis accelerometers are equipped on micro pole-climbing robot. Accelerometer measurements provide an absolute reference for the pitch-and-roll components of the estimated orientation, which are used as feedback input signal of proportional–integral–derivative algorithm. A supporting structure is installed at the joint of each gripper to assist the robot to clamp a pole. The support structure improves the load capacity of the robot. The maximum load of micro pole-climbing robot is 3.5 times its own weight. The climbing pole strategy includes the following sections: a Denavit–Hartenberg model is established and the inverse kinematic solution is analyzed; the flip locomotion is analyzed; and the parameters of KP, KI, and KD in the proportional–integral–derivative control method are obtained according to the Ziegler–Nichols controller. The performance of pole climbing based on micro pole-climbing robot prototype was tested. By using this strategy of climbing pole, the self-continuous climbing with controllable stride is realized, and the angular velocity fluctuation of the five-bar mechanism driven by steering gear is reduced. The average time of a single step is 27 s, the maximum relative error of step distance is 4.6%, and the average relative error is 2.8%. These results confirm that the structure scheme and the strategy of climbing pole are feasible.

Low voltage ride-through capability improvement of microgrid using a hybrid coordination control strategy

This paper proposes a hybrid coordination control strategy to improve the low voltage ride-through (LVRT) capability of microgrids. During microgrid external failure, the overcurrent and the voltage sag of the microgrid can be effectively suppressed. Compared with traditional control strategies, the microgrid transient performance can also be enhanced by adopting a generalized control algorithm, performing the active switching of the energy storage (ES) operation mode and triggering the inductance-type flux coupling fault current limiters (FCLs). Among them, according to the hierarchical control structure of the grid-connected inverter, the generalized control algorithm is applied to ES. Through the two degrees of freedom's control principle and inverse plant modeling techniques, the generalized control algorithm can make the control layer of the ES inverter operate in all control targets (i.e., PQ control, droop control and Vf control), with a single control structure. Also, it eliminates the effects of microgrid distortion voltage and ES surge current on the control system of the ES inverter. For the inverter application layer, by introducing microgrid voltage and angular frequency feedforward compensation, the voltage and frequency fluctuation of the microgrid can be suppressed efficiently under the fault conditions. Therefore, with the help of the generalized control algorithm, the active switching function of ES can be carried out successfully, which is the key technology for microgrids to realize their operational mode smooth switching. Meanwhile, the voltage sag and overcurrent of microgrids can be significantly mitigated through generating reactive power from microgrids and injecting it into inductance-type FCLs with lower cost. The related theoretical derivation and simulation analysis under various scenarios (including asymmetric faults) confirm that the proposed control strategy can not only enhance the LVRT capability, but also strengthen the microgrid transient performance.

Feasibility Study of a Small Field Detector Based on a Microfluidic Calorimeter

The widespread proliferation of modern external beam radiotherapy devices employing small or non-standard fields has created a number of challenges for accurate reference dosimetry measurements based on ionization chambers, as they require an ever increasing number of corrections. A miniature water-based calorimeter, on the other hand, would allow for direct measurement of absorbed dose to water that can be traced to standards entirely independent of radiation. In this study, a microfluidic calorimeter prototype developed at the Korea Advanced Institute of Science and Technology was assessed for its feasibility as a detector for measurement of absolute dose to water in small and composite fields. Using the GEANT4 Monte Carlo simulation toolkit, the detector design was examined for the water equivalence and the angular dependence of the absorbed dose to the active calorimeter volume inside three different radiation fields. The initial design exhibited poor water equivalence but this was remedied through a simple modification to the detector geometry. The modified design was subsequently re-tested and it showed a maximum water equivalence deviation of 1.15% while angular fluctuations remained within 1.1%, thus indicating that the modified microfluidic calorimeter is a promising concept for the construction of a calorimeter-based absorbed dose to water detector for absolute dosimetry.

Hydrodynamic performance of a vertical axis tidal current turbine with angular speed fluctuation

ABSTRACTThe angular speed of Vertical axis tidal current turbines (VATTs) should undulate in one periodic rotation given their inherent special structure. A coupled dynamic numerical simulation method is presented to study the effect of angular speed fluctuation on the performance of a VATT. The CFX User Fortran interface is applied to simultaneously solve the fluid conservation and rigid motion equations. The angular speed and acceleration of the turbine at specific time steps are determined by solving the moment equation of the rigid blade, and the force on the blade is obtained from the dynamic integral of the fluid field. The numerical simulation and experimental results suggest that coupled numerical simulation is necessary for small moment of inertia because the amplitude of the angular speed fluctuation is approximately 28% of the average value. Undulation of the load and the moment caused by unsteady angular speeds will reduce the turbine’s energy extraction.

Partially polarized black-body radiation

Angular temperature fluctuations in a photon gas generate fractional polarization of the black-body spectrum. The spectral density consists of two Planckians with different temperature variables representing orthogonal polarization states. The angular-dependent fluctuating temperature variables can be inferred from the Stokes parameters which have been measured, over the full solid angle, for the cosmic microwave background (CMB) radiation. The polarization matrix of a partially polarized photon gas is obtained by way of a unitary transformation of the annihilation and creation operators. The radiation is decomposed into a totally polarized and an unpolarized intensity component, and the polarization fraction is calculated, which is very small, of order ∼10−7, for the nearly isotropic CMB radiation. Spatial energy density autocorrelations induced by polarization and temperature anisotropy are derived and isotropized by an angular average. These correlations are long-range, exhibiting power-law decay ∝1∕r6 at large distance, and much stronger than the energy density correlation of an ideal photon gas which decays ∝1∕r8. As for the CMB radiation, the spatial energy density correlations are calculated from analytic Gaussian fits to the measured temperature and polarization power spectra, including the crossover from the short-distance regime to the asymptotic power-law decay.

Application of Instantaneous Rotational Speed to Detect Gearbox Faults Based on Double Encoders

Considerable studies have been carried out on fault diagnosis of gears, with most of them concentrated on conventional vibration analysis. However, besides the complexity of gear dynamics, the diagnosis results in terms of vibration signal are easily misjudged owing to the interference of sensor position or other components. In this paper, an alternative gearbox fault detection method based on the instantaneous rotational speed is proposed because of its advantages over vibration analysis. Depending on the timer/counter-based method for the pulse signal of the optical encoder, the varying rotational speed can be obtained effectively. Owing to the coupling and meshing of gears in transmission, the excitations are the same for the instantaneous rotational speed of the input and output shafts. Thus, the differential signal of instantaneous rotational speeds can be adopted to eliminate the effect of the interference excitations and extract the associated feature of the localized fault effectively. With the experiments on multistage gearbox test system, the differential signal of instantaneous speeds is compared with other signals. It is proved that localized faults in the gearbox generate small angular speed fluctuations, which are measurable with an optical encoder. Using the differential signal of instantaneous speeds, the fault characteristics are extracted in the spectrum where the deterministic frequency component and its harmonics corresponding to crack fault characteristics are displayed clearly.

Pressure characteristics of a novel double rotor hydraulic transformer

The hydraulic transformer is the core component when it works with the common pressure rail system, which integrates the functions of the pump and the motor, and thus possesses sensitive pressure characteristics. The rotating speed has significant influence on the pressure characteristics of a hydraulic transformer while it has not been considered previously. In this study, aimed at improving the working performance, a novel double rotor hydraulic transformer is proposed and a comprehensive mathematical model considering the dynamic characteristics of the cylinder block is established. At the same time, a prototype is made and the experiment is conducted. The test results show that the robust rotor structure enables a larger pressure range, and the numerical results exhibit a good match with the test results. The parameter sensitivity study shows that the delivery pressure is mainly subject to the valve plate control angle δ and, under the effects of the resistance torques, pressure loss will occur especially under a large control angle and a high rotating speed. The magnitude of the instantaneous angular velocity fluctuation increases sharply when the speed is lower than 400 r/min, which is the main reason for the serious pressure pulsation at a low speed. As a result of the improved low-speed stability and output flow uniformity, the pressure pulsation rate of the double rotor hydraulic transformer is greatly reduced. However, the pulsation rate is still high at an extremely low speed. In addition, when the rotating speed exceeds the capability of the damping grooves, the pressure undershoot becomes serious at the A-T transition region around the control angle of −30°. Consequently, from the perspective of pressure characteristics, the limitation on the rotating speed under small control angles is suggested for the design of the double rotor hydraulic transformer controller.

Enhanced locomotion, effective diffusion and trapping of undulatory micro-swimmers in heterogeneous environments.

Swimming cells and microorganisms must often move through complex fluids that contain an immersed microstructure such as polymer molecules or filaments. In many important biological processes, such as mammalian reproduction and bacterial infection, the size of the immersed microstructure is comparable to that of the swimming cells. This leads to discrete swimmer-microstructure interactions that alter the swimmer's path and speed. In this paper, we use a combination of detailed simulation and data-driven stochastic models to examine the motion of a planar undulatory swimmer in an environment of spherical obstacles tethered via linear springs to random points in the plane of locomotion. We find that, depending on environmental parameters, the interactions with the obstacles can enhance swimming speeds or prevent the swimmer from moving at all. We also show how the discrete interactions produce translational and angular velocity fluctuations that over time lead to diffusive behaviour primarily due to the coupling of swimming and rotational diffusion. Our results demonstrate that direct swimmer-microstructure interactions can produce changes in swimmer motion that may have important implications for the spreading of cell populations in or the trapping of harmful pathogens by complex fluids.

Temperature‐dependent local atomic structures in the traditional Fe65Ni35 Invar alloy by X‐ray fluorescence holography

Fe and Ni Kα X‐ray fluorescence holography measurements were conducted on a single crystal Fe65Ni35 Invar alloy at 100 and 300 K to investigate the temperature dependence of the 3‐dimensional local structures around the Fe and Ni atoms, respectively. Local structural information was obtained by detailed analyses using a L1‐regularized linear regression for the experimental data. At 100 K, the local atomic arrangements around both the elements show fcc structures. At 300 K, however, only the image around Fe shows a bcc‐like neighboring arrangement. From these X‐ray fluorescence holography data, we propose a model that with increasing temperature, an Fe atom with the low‐spin state enters at the central position of the fcc lattice and is stabilized. And then, large angular positional fluctuations are induced for the atoms at the face‐centered positions around the central Fe atom only.

End-to-end distance and contour length distribution functions of DNA helices.

I present a computational method to evaluate the end-to-end and the contour length distribution functions of short DNA molecules described by a mesoscopic Hamiltonian. The method generates a large statistical ensemble of possible configurations for each dimer in the sequence, selects the global equilibrium twist conformation for the molecule, and determines the average base pair distances along the molecule backbone. Integrating over the base pair radial and angular fluctuations, I derive the room temperature distribution functions as a function of the sequence length. The obtained values for the most probable end-to-end distance and contour length distance, providing a measure of the global molecule size, are used to examine the DNA flexibility at short length scales. It is found that, also in molecules with less than ∼60 base pairs, coiled configurations maintain a large statistical weight and, consistently, the persistence lengths may be much smaller than in kilo-base DNA.

Density correlations induced by temperature fluctuations in a photon gas

The impact of angular temperature variations on the thermodynamic variables and real-space correlation functions of black-body radiation are analyzed. In particular, the effect of temperature fluctuations on the number density and energy density correlations of the cosmic microwave background (CMB) is studied. The angular temperature fluctuations are modeled by an isotropic and homogeneous Gaussian random field, whose autocorrelation function is defined on the unit sphere in momentum space. This temperature correlation function admits an angular Fourier transform which determines the density correlations in real space induced by temperature fluctuations. In the case of the CMB radiation, the multipole coefficients of the angular power spectrum defining the temperature correlation function have been measured by the Planck satellite. The fluctuation-induced perturbation of the equilibrium variables (internal energy, entropy, heat capacity and compressibility) can be quantified in terms of the measured multipole coefficients by expanding the partition function around the equilibrium state in powers of the temperature random field. The real-space density correlations can also be extracted from the measured temperature power spectrum. Both the number density and energy density correlations of the electromagnetic field are long-range, admitting power-law decay; in the case of the energy density correlation, the fluctuation-induced correlation overpowers the isotropic equilibrium correlation in the long-distance limit.