Velocity Modulation Research Articles

Dispersion tuning and route reconfiguration of acoustic waves in valley topological phononic crystals.

The valley degree of freedom in crystals offers great potential for manipulating classical waves, however, few studies have investigated valley states with complex wavenumbers, valley states in graded systems, or dispersion tuning for valley states. Here, we present tunable valley phononic crystals (PCs) composed of hybrid channel-cavity cells with three tunable parameters. Our PCs support valley states and Dirac cones with complex wavenumbers. They can be configured to form chirped valley PCs in which edge modes are slowed to zero group velocity states, where the energy at different frequencies accumulates at different designated locations. They enable multiple functionalities, including tuning of dispersion relations for valley states, robust routing of surface acoustic waves, and spatial modulation of group velocities. This work may spark future investigations of topological states with complex wavenumbers in other classical systems, further study of topological states in graded materials, and the development of acoustic devices.

Application of particle image velocimetry measurement technique to study pulsating flow in a rod bundle channel

The flow rate of the primary coolant in a nuclear reactor will fluctuate during accident conditions or in floating reactors that are affected by inertial forces in the ocean. These fluctuations may have a substantial impact on heat transfer by the primary coolant in the reactor. In the current research, the flow field distribution and turbulence structure at different planes of a 5 × 5 rod bundle under pulsating flow conditions were measured using phase-locked particle image velocimetry and matching index refractive. The local ensemble-averaged velocity and root-mean-square (RMS) component distributions of different pulsating flow phases were obtained from the measurement results. This experimental study covered a pulsation period T range of 3 – 7 s and an imposed pulsation amplitude Au range of 0.31 – 0.65. For quasi-steady, intermediate-frequency, and high-frequency pulsating flows, the ensemble-averaged velocity of different phases and the distribution of velocity amplitude modulation in different subchannels were studied. Moreover, the phase shifts of the velocity modulation amplitude and RMS components of the rod bundle channel relative to the imposed pulsating flow with different pulsation parameters (Au, T) were also analyzed. Results for the rod bundle channel under the pulsating flow condition and for a conventional channel were compared; the discrepancies and agreements are discussed in detail. These research results can help to understand pulsating flow in a rod bundle channel better, and the experimental results can provide reference and validation data for numerical simulations.

Perfect valley filter controlled by Fermi velocity modulation in graphene

In this work we investigate the effects of a Fermi velocity modulation in a valley filter in graphene created by a combination of a magnetic and electric barrier. With the effective Dirac equation of the system, we use the transfer matrix formalism to obtain the transmittance. We verify that the valley transport in graphene is very sensitive to a Fermi velocity modulation, which is able to choose which valley will be filtered with perfect filtering. Also, it is possible to use a Fermi velocity modulation to filter both valleys or to make the valley filter transparent. It reveals that the Fermi velocity is a powerful tool that can be used to tune a graphene valley filter, since it has a total control in its transport properties.

Weakly Nonlinear Magnetic Convection in a Nonuniformly Rotating Electrically Conductive Medium Under the Action of Modulation of External Fields

In this paper we studied the weakly nonlinear stage of stationary convective instability in a nonuniformly rotating layer of an electrically conductive fluid in an axial uniform magnetic field under the influence of: a) temperature modulation of the layer boundaries; b) gravitational modulation; c) modulation of the magnetic field; d) modulation of the angular velocity of rotation. As a result of applying the method of perturbation theory for the small parameter of supercriticality of the stationary Rayleigh number nonlinear non-autonomous Ginzburg-Landau equations for the above types of modulation were obtaned. By utilizing the solution of the Ginzburg-Landau equation, we determined the dynamics of unsteady heat transfer for various types of modulation of external fields and for different profiles of the angular velocity of the rotation of electrically conductive fluid.

The magnetic field and accretion regime of CI Tau

ABSTRACT This paper exploits spectropolarimetric data of the classical T Tauri star CI Tau collected with ESPaDOnS at the Canada–France–Hawaii Telescope, with the aims of detecting and characterizing the large-scale magnetic field that the star hosts, and of investigating how the star interacts with the inner regions of its accretion disc through this field. Our data unambiguously show that CI Tau has a rotation period of 9.0 d, and that it hosts a strong, mainly poloidal large-scale field. Accretion at the surface of the star concentrates within a bright high-latitude chromospheric region that spatially overlaps with a large dark photospheric spot, in which the radial magnetic field reaches −3.7 kG. With a polar strength of −1.7 kG, the dipole component of the large-scale field is able to evacuate the central regions of the disc up to about 50 per cent of the co-rotation radius (at which the Keplerian orbital period equals the stellar rotation period) throughout our observations, during which the average accretion rate was found to be unusually high. We speculate that the magnetic field of CI Tau is strong enough to sustain most of the time a magnetospheric gap extending to at least 70 per cent of the co-rotation radius, which would explain why the rotation period of CI Tau is as long as 9 d. Our results also imply that the 9 d radial velocity (RV) modulation that CI Tau exhibits is attributable to stellar activity, and thus that the existence of the candidate close-in massive planet CI Tau b to which these RV fluctuations were first attributed needs to be reassessed with new evidence.

Slowing ribosome velocity restores folding and function of mutant CFTR.

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR), with approximately 90% of patients harboring at least one copy of the disease-associated variant F508del. We utilized a yeast phenomic system to identify genetic modifiers of F508del-CFTR biogenesis, from which ribosomal protein L12 (RPL12/uL11) emerged as a molecular target. In the present study, we investigated mechanism(s) by which suppression of RPL12 rescues F508del protein synthesis and activity. Using ribosome profiling, we found that rates of translation initiation and elongation were markedly slowed by RPL12 silencing. However, proteolytic stability and patch-clamp assays revealed RPL12 depletion significantly increased F508del-CFTR steady-state expression, interdomain assembly, and baseline open-channel probability. We next evaluated whether Rpl12-corrected F508del-CFTR could be further enhanced with concomitant pharmacologic repair (e.g., using clinically approved modulators lumacaftor and tezacaftor) and demonstrated additivity of these treatments. Rpl12 knockdown also partially restored maturation of specific CFTR variants in addition to F508del, and WT Cftr biogenesis was enhanced in the pancreas, colon, and ileum of Rpl12 haplosufficient mice. Modulation of ribosome velocity therefore represents a robust method for understanding both CF pathogenesis and therapeutic response.

Discovery of a Red Supergiant Donor Star in SN2010da/NGC 300 ULX-1

Abstract SN2010da/NGC 300 ULX-1 was first detected as a supernova impostor in 2010 May and was recently discovered to be a pulsating ultraluminous X-ray source. In this Letter, we present Very Large Telescope/X-shooter spectra of this source obtained in 2018 October, covering the wavelength range 350–2300 nm. The J- and H-bands clearly show the presence of a red supergiant (RSG) donor star that is best matched by a MARCS stellar atmosphere with T eff = 3650–3900 K and log(L bol/L ⊙) = 4.25 ± 0.10, which yields a stellar radius R = 310 ± 70R ⊙. To fit the full spectrum, two additional components are required: a blue excess that can be fitted either by a hot blackbody (T ≳ 20,000 K) or a power law (spectral index α ≈ 4) and is likely due to X-ray emission reprocessed in the outer accretion disk or the donor star; and a red excess that is well fitted by a blackbody with a temperature of ∼1100 K, and is likely due to warm dust in the vicinity of SN2010da. The presence of an RSG in this system implies an orbital period of at least 0.8–2.1 yr, assuming Roche-lobe overflow. Given the large donor-to-compact object mass ratio, orbital modulations of the radial velocity of the RSG are likely undetectable. However, the radial velocity amplitude of the neutron star is large enough (up to 40–60 km s−1) to potentially be measured in the future, unless the system is viewed at a very unfavorable inclination.

Dynamical Confirmation of a Black Hole in MAXI J1820+070

Abstract We present time-resolved 10.4 m Gran Telescopio Canarias and 4.2 m William Herschel Telescope intermediate resolution spectroscopy of the X-ray transient MAXI J1820+070 (=ASASSN-18ey) obtained during its decline to the quiescent state. Cross-correlation of the 21 individual spectra against late-type templates reveals a sinusoidal velocity modulation with a period of 0.68549 ± 0.00001 day and semi-amplitude of 417.7 ± 3.9 km s−1. We derive a mass function f(M) = 5.18 ± 0.15 M ⊙, dynamically confirming the black hole (BH) nature of the compact object. Our analysis of the stellar absorption features supports a K3-5 spectral classification for the donor star, which contributes ≈20% of the total flux at 5200–6800 Å. The photometric 0.703 ± 0.003 day periodicity observed during outburst is 2.6% longer than the orbital period supporting the presence of a superhump modulation in the outburst light curves. In line with this interpretation, we constrain the binary mass ratio to be q ≃ 0.12. In addition, we observe a sharp increase in the Hα emission line equivalent width during inferior conjunction of the donor star that we interpret as a grazing eclipse of the accretion disk and allows us to constrain the binary inclination to i ≳ 69°. On the other hand, the absence of X-ray eclipses during outburst imply i ≲ 77°. These inclination limits, together with our dynamical solution, lead to a BH mass in the range 7–8 M ⊙. We also measure a systemic velocity γ = −21.6 ± 2.3 km s−1, which, combined with the Gaia second data release proper motion and parallax, implies a large peculiar velocity ∼100 km s−1.

Collision Avoidance for an Unmanned Aerial Vehicle in the Presence of Static and Moving Obstacles

A new collision-avoidance procedure for an unmanned aerial vehicle (UAV) in the presence of static and moving obstacles is presented. The proposed procedure is based on a new form of local parameterized guidance vector fields, called collision-avoidance vector fields, which produce smooth and intuitive maneuvers around obstacles. These vector fields are generated from a decomposition of UAV kinematics and a proximity-based velocity modulation. The proposed kinematic decomposition encodes both collision avoidance and constant-speed motion for the UAV. As such, the resulting maneuvers follow nominal collision-free paths, which are referred to as streamlines of the collision-avoidance vector fields, with constant speed. Next, in accordance with the computed guidance vector fields, different collision-avoidance controllers that generate collision-free maneuvers are developed. Furthermore, it is shown that any tracking controller with convergence guarantees can be used with the avoidance controllers to track the streamlines of the collision-avoidance vector fields. Finally, numerical simulations demonstrate the efficacy of the proposed approach and its ability to avoid collisions with static and moving pop-up threats in different practical scenarios.

Single-shot velocity mapping by rewinding of velocity encoding with Echo-Planar Imaging.

The ability of single-shot NMR imaging methods to follow the time evolution of a velocity distribution within an object is strongly limited by the phase errors accumulated as velocity maps are acquired. In the particular case of Carr-Purcell based sequences combined with Echo Planar Imaging acquisition, phase accumulates through subsequent images, hampering the possibility to acquire several velocity maps, which would be useful to determine transient behavior. In this work, we propose the use of a rewinding velocity encoding module applied after the acquisition of each image during the CPMG echo train. In this way, the first velocity module imparts a velocity dependent phase prior to the image acquisition and the second pair cancels this phase out before the next refocusing radiofrequency pulse is applied. The performance and limits of this method are studied by acquiring 100 images of a co-rotating Couette cell over a period of 1.6 s as a function of the rotation speed. The method is applied to determine the kinematic viscosity of a water/alcohol mixture, which is a relevant topic in many physical, chemical and biological processes.

Estimation of the porosity of clay soils using seismic P- and S-wave velocities

Seismic waves are commonly used to investigate how the soils behave during the earthquake. The goal of this study is to predict the porosity of shallow clay soils from seismic wave velocities investigated the dynamic properties of the soil and to develop the porosity graphs depending on geotechnical properties of the soils. The parameters used to determine porosity are compressional (P) and shear (S) wave velocities, seismic velocity ratio, Poisson ratio, bulk modulus, shear modulus. This study calculates bulk modulus, shear modulus and Poisson ratio from P- and S-wave velocities obtained by using the seismic-refraction method, and porosity values using grain and dry densities of core samples obtained from several boreholes within the study area. The study area is located in western Turkey, and has predominantly clay-silt-sand-gravel deposits. The data of the clay soils within the area were separately arranged based on the values of the Poisson ratio, seismic P wave velocity, seismic velocity ratio (Vp/Vs) and the stiffness of the clay soils. Using these parameters, new multi-parameter relationships were established among shear modulus, Poisson ratio, seismic velocities and porosity of clay soils. The errors of the parameters used for each relationship were determined using the error norm technique. According to the results of the error norm technique, the shear wave velocity and shear module have lowest error for estimating porosity. Consequently, the proposed relationships are recommended to estimate porosity of shallow clay soils. These relationships, in addition to estimate the porosity of clay soil, can be interpreted whether the liquid and/or gas saturation of pores of this soil. Also, the experimental results show that if the ratio of Vp/Vs < 1.53, the pores spaces of the clay soil are filled with gas.

Base-pairing interactions between substrate RNA and H/ACA guide RNA modulate the kinetics of pseudouridylation, but not the affinity of substrate binding by H/ACA small nucleolar ribonucleoproteins.

H/ACA small nucleolar ribonucleoproteins (snoRNPs) pseudouridylate RNA in eukaryotes and archaea. They target many RNAs site-specifically through base-pairing interactions between H/ACA guide and substrate RNA. Besides ribosomal RNA (rRNA) and small nuclear RNA (snRNA), H/ACA snoRNPs are thought to also modify messenger RNA (mRNA) with potential impacts on gene expression. However, the base pairing between known target RNAs and H/ACA guide RNAs varies widely in nature, and therefore the rules governing substrate RNA selection are still not fully understood. To provide quantitative insight into substrate RNA recognition, we systematically altered the sequence of a substrate RNA target by the Saccharomyces cerevisiae H/ACA guide RNA snR34. Time courses measuring pseudouridine formation revealed a gradual decrease in the initial velocity of pseudouridylation upon reducing the number of base pairs between substrate and guide RNA. Changing or inserting nucleotides close to the target uridine severely impairs pseudouridine formation. Interestingly, filter binding experiments show that all substrate RNA variants bind to H/ACA snoRNPs with nanomolar affinity. Next, we showed that binding of inactive, near-cognate RNAs to H/ACA snoRNPs does not inhibit their activity for cognate RNAs, presumably because near-cognate RNAs dissociate rapidly. We discuss that the modulation of initial velocities by the base-pairing strength might affect the order and efficiency of pseudouridylation in rRNA during ribosome biogenesis. Moreover, the binding of H/ACA snoRNPs to near-cognate RNAs may be a mechanism to search for cognate target sites. Together, our data provide critical information to aid in the prediction of productive H/ACA guide—substrate RNA pairs.

Dual cardiac and respiratory gated thoracic imaging via adaptive gantry velocity and projection rate modulation on a linear accelerator: A Proof-of-Concept Simulation Study.

Cardiac motion is typically not accounted for during pretreatment imaging for central lung and mediastinal tumors. However, cardiac induced tumor motion averages 5.8mm for esophageal tumors and 3-5 mm for some lung tumors, which can result in positioning errors. Our aim is to reduce both cardiac- and respiratory-induced motion artifacts in thoracic cone beam computed tomography (CBCT) images through gantry velocity and projection rate modulation on a standard linear accelerator (linac). The acquisition of dual cardiac and respiratory gated CBCT thoracic images was simulated using the XCAT phantom with patient-measured respiratory and ECG traces. The gantry velocity and projection rate were modulated based on the cardiac and respiratory signals to maximize the angular consistency between adjacent projections in the gated cardiac-respiratory bin. The mechanical limitations of a gantry-mounted CBCT system were investigated. For our protocol, images were acquired during the 60%-80% window of cardiac phase and 20% displacement either side of peak exhale of the respiratory cycle. The comparator method was the respiratory-only gated CBCT acquisition with constant gantry speed and projection rate in routine use for respiratory correlated four-dimensional (4D) CBCT. All images were reconstructed using the Feldkamp-Davis-Kress (FDK) algorithm. The methods were compared in terms of image sharpness as measured using the edge response width (ERW) and contrast as measured using the contrast to noise ratio (CNR). The effects of the total number of projections acquired and magnitude of cardiac motion on scan time and image quality were also investigated. Median total scan times with our protocol ranged from 117s (40 projections) through to 296s (100 projections), compared with 240s for the conventional protocol (1320 projections). The scan times were dictated by the number of projections acquired, heart rate, length of the respiratory cycle and mechanical constraints of the CBCT system. Our protocol was able to provide between 8% and 43% decrease in the median value of the ERW in the anterior/posterior (AP) direction across the 17 traces when there was 0.5cm of cardiac motion and between 35% and 64% decrease when there was 1.0cm of cardiac motion over conventional acquisition. In the superior-inferior (SI) direction, our protocol was able to provide between 22% and 26% decrease in the median value of the ERW across the 17 traces when there was 0.5cm of cardiac motion and between 30% and 35% decrease when there was 1.0cm of cardiac motion over conventional acquisition. The magnitude of the cardiac motion did not have an observable effect on the median value of the CNR. Across all 17 traces, our adaptive protocol produced noticeably more consistent, albeit lower CNR values compared with conventional acquisition. For the first time, the potential of adapting CBCT image acquisition to changes in the patient's cardiac and respiratory rates simultaneously for applications in radiotherapy was investigated. This work represents a step towards thoracic imaging that reduces the effects of both cardiac and respiratory motion on image quality.

Beat to Beat Modulation of Arterial Pulse Wave Velocity Induced by Vascular Smooth Muscle Tone.

The level of smooth muscle activation or `tone' (VSMT) can be defined as an intrinsic spontaneous level of vasoconstriction that may change in response to biomechanical stimuli such as flow, pressure, hormonal stimuli, neural stimuli, and drugs. Arteries can actively modify arterial pressure pulse wave velocity (PWV) by changing smooth muscle tone and diameter with little change in the mean arterial blood pressure. To evaluate the influence of aortic VSMT in terms of beat to beat PWV variations. Aortic pressure-diameter (P-D) relationships were invasively evaluated in five conscious animals. An `incremental' PWV was directly derived from the P-D loops, both in purely elastic conditions as well as in the presence of VSMT. Beat to beat PWV waveform variations showed different behavior, where mean PWV values were higher when VSMT was included in the P-D evaluation. Changes in incremental beat to beat PWV could be attributed to the influence of VSMT.

Motion tracking of parents' infant- versus adult-directed actions reveals general and action-specific modulations.

Parents tend to modulate their movements when demonstrating actions to their infants. Thus far, these modulations have primarily been quantified by human raters and for entire interactions, thereby possibly overlooking the intricacy of such demonstrations. Using optical motion tracking, the precise modulations of parents’ infant‐directed actions were quantified and compared to adult‐directed actions and between action types. Parents demonstrated four novel objects to their 14‐month‐old infants and adult confederates. Each object required a specific action to produce a unique effect (e.g. rattling). Parents were asked to demonstrate an object at least once before passing it to their demonstration partner, and they were subsequently free to exchange the object as often as desired. Infants’ success at producing the objects’ action‐effects was coded during the demonstration session and their memory of the action‐effects was tested after a several‐minute delay. Indicating general modulations across actions, parents repeated demonstrations more often, performed the actions in closer proximity and demonstrated action‐effects for longer when interacting with their infant compared to the adults. Meanwhile, modulations of movement size and velocity were specific to certain action‐effect pairs. Furthermore, a ‘just right’ modulation of proximity was detected, since infants’ learning, memory, and parents’ prior evaluations of their infants’ motor abilities, were related to demonstrations that were performed neither too far from nor too close to the infants. Together, these findings indicate that infant‐directed action modulations are not solely overall exaggerations but are dependent upon the characteristics of the to‐be learned actions, their effects, and the infant learners.

Internal gravity and infrasound waves during a hurricane in Moscow On May 29, 2017

The results of recording of internal gravity waves (IGWs) and infrasound waves from the warm and cold fronts associated with the atmospheric storm passing through Moscow on May 29, 2017 are presented. The waves were recorded by a network of 4 microbarographs IFA–MGU–MSR–ZNS located in Moscow and Moscow region, and compared with the data of measurements of the parameters of infrasound waves at infrasound station IS43 in Dubna. We study the temporal changes in the characteristics of IGWs and infrasound waves (coherence, direction of propagation,phase velocities, characteristic periods and frequency spectra) with the passage of warm and cold fronts through the network. The transition from the gravity to the acoustic dispersive branch of acoustic-gravity waves due to an increase in frequency and the temporal modulation of the phase velocity of infrasound waves caused by IGWs are also studied. The measurement data for PM10 aerosol concentrations and NO2 gas concentrations at various locations in Moscow during a passage of atmospheric storm are presented. The possibility of detecting wave precursors of atmospheric storms simultaneously in variations of atmospheric pressure, wind velocity and aerosol concentrations is studied.

Surface-acoustic-wave resonators with Ti, Cr, and Au metallization on GaAs

Surface-acoustic-wave (SAW) resonators, which confine SAW phonons in a small region between two Bragg reflectors, are attractive for studying the acoustic analog of cavity quantum electrodynamics. We have investigated characteristics of SAW resonators fabricated by patterning a metal film of Ti, Cr, and Au on GaAs and AlGaAs/GaAs heterostructure surfaces. The resonator modes and the acoustic band gap are identified by measuring the radio-frequency reflection spectrum and local piezoelectric potential with a quantum point contact. Ti metallization, showing a large band gap and small velocity modulation, is the best choice for designing a high-quality SAW resonator for GaAs.

Oversized coaxial relativistic extended interaction oscillator with gigawatt-level output at Ka-band

In this paper, an oversized coaxial relativistic extended interaction oscillator (OCREIO) with gigawatt-level output at the Ka-band is proposed. We adopt a four-gap buncher cavity and a three-gap output cavity to increase the power capability and improve the electronic efficiency of the OCREIO. The beam-loading conductance for each mode existing in the buncher cavity is derived based on a small-signal theory. The beam-wave interaction and power capability for the 2π/3 and π modes exciting in the buncher cavity are analyzed. The operation mode 2π/3 is chosen by considering the beam-loading conductance and power capability. In addition, an improved method is proposed to mitigate the electric field intensity of the buncher cavity so as to moderate velocity modulation. The weak velocity modulation offers enough distance to make density modulation, thereby obtaining a relatively high fundamental harmonic current amplitude. Our study on the device performance of the proposed OCREIO, using the particle-in-cell simulation code CHIPIC, predicts an output power of 922.7 MW and a high electronic efficiency of 32.9% at 30.5 GHz, as well as the relatively less time of frequency-lock of self-oscillation <20 ns. The simulated results of the proposed OCREIO motivate us to practically develop the device in the near future.

Spectroscopic confirmation of the binary nature of the hybrid pulsator KIC 5709664 found with the frequency modulation method

We started a program to search for companions around hybrid $\delta$ Sct/$\gamma$ Dor stars with the frequency modulation method using Kepler data. Our best candidate was KIC 5709664, where we could identify Fourier peaks with sidelobes, suggesting binary orbital motion. We determined the orbital parameters with the phase modulation method and took spectroscopic measurements to confirm unambiguously the binary nature with radial velocities. The spectra show that the object is a double-lined spectroscopic binary, and we determined the orbital solutions from the radial velocity curve fit. The parameters from the phase modulation method and the radial velocity fits are in good agreement. We combined a radial velocity and phase modulation approach to determine the orbital parameters as accurately as possible. We determined that the pulsator is a hybrid $\delta$ Sct/$\gamma$ Dor star in an eccentric binary system with an orbital period of ~95 d and an eccentricity of 0.55. The measured mass ratio is 0.67. We analysed the pulsation content and extracted 38 frequencies with amplitudes greater than 20 $\mu$mag. At low frequencies, we found broad power excesses which are likely attributed to spots on the rotating surface of the lower-mass component. We inferred rotation periods of 0.56 and 2.53 d for the primary and secondary, respectively.

Multistable Free States of an Active Particle from a Coherent Memory Dynamics.

We investigate the dynamics of a deterministic self-propelled particle endowed with coherent memory. We evidence experimentally and numerically that it exhibits several stable free states. The system is composed of a self-propelled drop bouncing on a vibrated liquid driven by the waves it emits at each bounce. This object possesses a propulsion memory resulting from the coherent interference of the waves accumulated along its path. We investigate here the transitory regime of the buildup of the dynamics which leads to velocity modulations. Experiments and numerical simulations enable us to explore unchartered areas of the phase space and reveal the existence of a self-sustained oscillatory regime. Finally, we show the coexistence of several free states. This feature emerges both from the spatiotemporal nonlocality of this path memory dynamics as well as the wave nature of the driving mechanism.