Fractional Frequency Change Research Articles

Doppler effect in the ripple tank: further experiments with a moving source

In this paper, we extend some recent works about the Doppler effect in surface waves on water. We improve the experimental set up by exploring several situations: source in motion with constant velocity and receiver at rest, source at rest and receiver in motion with constant velocity, as well as both source and receiver in motion. Thereby we produce fractional frequency changes of the order of 40%–50%, far larger than those obtained by more traditional sound experiments. The experimental setup, the data collection and the data analysis also allow to highlight some aspects relevant from a didactic point of view, in particular, the experimental results clearly show the nonlinearity of the Doppler shift with the moving source velocity.

Magnetar spin-down glitch clearing the way for FRB-like bursts and a pulsed radio episode

Magnetars are a special subset of the isolated neutron star family, with X-ray and radio emission mainly powered by the decay of their immense magnetic fields. Many attributes of magnetars remain poorly understood: spin-down glitches or the sudden reductions in the star’s angular momentum, radio bursts reminiscent of extragalactic fast radio bursts (FRBs) and transient pulsed radio emission lasting months to years. Here we unveil the detection of a large spin-down glitch event (fractional change in spin frequency $$| {{\Delta }}\nu /\nu | =5.{8}_{-1.6}^{+2.6}\times 1{0}^{-6}$$ ) from the magnetar SGR 1935+2154 on 5 October 2020 (±1 day). We find no change to the source-persistent surface thermal or magnetospheric X-ray behaviour, nor is there evidence of strong X-ray bursting activity. Yet, in the subsequent days, the magnetar emitted three FRB-like radio bursts followed by a month-long episode of pulsed radio emission. Given the rarity of spin-down glitches and radio signals from magnetars, their approximate synchronicity suggests an association, providing pivotal clues to their origin and triggering mechanisms with ramifications to the broader magnetar and FRB populations. We postulate that impulsive crustal plasma shedding close to the magnetic pole generates a wind that combs out magnetic field lines, rapidly reducing the star’s angular momentum while temporarily altering the magnetospheric field geometry to permit the pair creation needed to precipitate radio emission. An abrupt slow-down in a magnetar’s rotation rate (a ‘glitch’) may be related to the subsequent emission of three radio bursts (resembling fast radio bursts) and a month-long episode of pulsed radio emission.

Constraints on wide-band radiative changes after a glitch in PSR J1452–6036

ABSTRACT We present high-sensitivity, wide-band observations (704–4032 MHz) of the young to middle-aged radio pulsar J1452–6036, taken at multiple epochs before and, serendipitously, shortly after a glitch occurred on 2019 April 27. We obtained the data using the new ultra-wide-bandwidth low-frequency (UWL) receiver at the Parkes radio telescope, and we used Markov chain Monte Carlo techniques to estimate the glitch parameters robustly. The data from our third observing session began 3 h after the best-fitting glitch epoch, which we constrained to within ∼4 min. The glitch was of intermediate size, with a fractional change in spin frequency of 270.52(3) × 10−9. We measured no significant change in spin-down rate and found no evidence for rapidly decaying glitch components. We systematically investigated whether the glitch affected any radiative parameters of the pulsar and found that its spectral index, spectral shape, polarization fractions, and rotation measure stayed constant within the uncertainties across the glitch epoch. However, its pulse-averaged flux density increased significantly by about 10 per cent in the post-glitch epoch and decayed slightly before our fourth observation a day later. We show that the increase was unlikely caused by calibration issues. While we cannot exclude that it was due to refractive interstellar scintillation, it is hard to reconcile with refractive effects. The chance coincidence probability of the flux density increase and the glitch event is low. Finally, we present the evolution of the pulsar’s pulse profile across the band. The morphology of its polarimetric pulse profile stayed unaffected to a precision of better than 2 per cent.

Investigation of Single-Crystal Niobium for Microwave Kinetic Inductance Detectors

The Advanced Technology Centre (ATC) of National Astronomical Observatory of Japan is developing microwave kinetic inductance detectors (MKIDs) for large-array pixel cameras for millimeter and sub-millimeter astronomy. We investigated single-crystal Nb thin layers to form superconducting microresonators. We compared the performances of MKIDs based on crystalline Nb structure and those based on polycrystalline Nb. We carried out the entire manufacture of the detectors in the ATC clean room. DC magnetron sputtering is used to grow single-crystal Nb films on r-plane sapphire substrates at an elevated temperature of 800 °C. The residual resistivity ratio (RRR) measured on these single-crystal Nb layers reached values ranging from 40 to 80. We made MKIDs with this crystalline Nb layer, and we measured internal quality factors of the detectors up to 106. The measurement of the noise power spectral density of these MKIDs gave a low value of − 95 dBc/Hz from 100 Hz to 100 kHz. The internal quality factor Qi and the fractional resonance frequency change δfr/fr of MKIDs with respect to the temperature variation are usually following the extended Mattis–Bardeen equations. However, we noticed a deviation from the theoretical prediction for temperature lower than 1 K (in our case). This deviation has already been observed on Al MKIDs and explained by a theory taking into account the Kondo effect and the kinetic inductance contribution. We demonstrated that our measurements on single-crystal Nb MKIDs are also in agreement with the same theory.

Noise Spectroscopy Analysis for Estimation of a Specific Biomolecule in a Complex Mixture Using Solid-State Nanopore

This paper presents a noise spectroscopy analysis of the current traces recorded in a functionalized silicon oxide nanopore in presence of specific antigen (Hep-B), nonspecific antigen (BSA), and their complex mixture for the first time. It is observed that though the on and off dwell times can differentiate nonspecific antigen from specific antigen in pure buffer, an approximate quantification of the specific antigen with low-dissociation constant of the receptor–ligand pair, becomes almost impossible in complex mixture. This has been ascribed to the significant overlap in the current blockade sensitivity values between the different concentration ranges of the specific antigen. On the contrary, a noise spectroscopy analysis shows a Lorentzian spectrum in presence of specific antigen with a distinct shift in the roll-off frequency, such that upto 1-nM BSA concentration; it has been possible to estimate the concentration of the specific antigen even for 1-pM Hep-B. However, for BSA concentration greater than 1 nM, the roll-off frequency for a particular concentration of specific antigen starts deviating from its value in pure buffer and overlaps with other concentration range. This problem has been addressed by processing the fractional change in current blockade and roll-off frequency by a partial least square-discriminant analysis based multivariate statistical model. It has been observed that the learning model yields 91.5% correct classification with the solutions, and has been able to predict the concentration of Hep-B quite closely even for a low value of 1 pM in presence of 100 nM concentration of BSA.

Reversible sulfuric acid doping of graphene probed by in-situ multi-wavelength Raman spectroscopy

Since lattice strain and charge density affect various material properties of graphene, a reliable and efficient method is required for quantification of the two variables. While Raman spectroscopy is sensitive and non-destructive, its validity towards precise quantification of chemical charge doping has not been tested. In this work, we quantified in-situ the fractional frequency change of 2D and G peaks in response of charge density induced by sulfuric acid solution as well as native lattice strain. Based on the experimental data and theoretical corroboration, we presented an optical method that simultaneously determines strain and chemically-induced charge density for three popular excitation wavelengths of 457, 514 and 633 nm. In order to expedite intercalation of dopant species through the graphene-SiO2 substrates, dense arrays of nanopores were precisely generated in graphene by thermal oxidation. The nano-perforated graphene membrane system was robust for multiple cycles of doping and undoping processes, and will be useful in studying various types of chemical interactions with graphene.

On the acceleration sensitivity and its active reduction by edge electrodes in AT-cut quartz resonators.

Incremental piezoelectric equations for small vibrations superposed on initial deformations are presented. The equations are implemented in COMSOL finite element models (FEA). Equations are validated by comparing the results for the force sensitivity coefficient Kf of a circular quartz plate subjected to a pair of diametrical forces with measured data. The model results show a consistent trend with the experimental results, and the relative difference between our FEA results and Ballato's measured result is about 13%. A detailed study of the acceleration sensitivity of a rectangular AT-cut quartz plate is presented. The plate resonator is fixed along one edge as a cantilever. For AT-cut quartz resonators with the crystal digonal X-axis perpendicular to plate X-axis, the in-plane acceleration sensitivity is found to be negligible compared with the out-of-plane (Y-axis) acceleration sensitivity. For AT-cut quartz resonators with the crystal digonal X-axis parallel to plate X-axis, the Y-axis acceleration sensitivity is found to be rectified, that is the fractional change in frequency is positive with respect to both positive and negative Y-axis accelerations. The Y-axis acceleration sensitivity is small in comparison with the in-plane acceleration sensitivity for small body forces. However, for large body forces, the Y-axis acceleration sensitivity dominates because it increases nonlinearly with the Y-axis acceleration. The resonator rectified acceleration sensitivity is confirmed by phase noise measurements. For reduced acceleration sensitivity, two pairs of electrodes along the plate edges reduce the bending of the plate resonator and subsequently reduce acceleration sensitivity. We present a new method using these edge electrodes in which a dc bias field is employed to control the resonant frequency of resonator subjected to g body forces. A dc bias field with an appropriate dc bias voltage could potentially yield a reduction of acceleration sensitivity in Y-axis direction of about two orders of magnitude.

Fourth-Order Contour Mode ZnO-on-SOI Disk Resonators for Mass Sensing Applications

In this work, we have investigated the design, fabrication and testing of ZnO-on-SOI fourth-order contour mode disk resonators for mass sensing applications. This study aims to unveil the possibility for real-time practical mass sensing applications by using high-Q ZnO-on-SOI contour-mode resonators while taking into account their unique modal characteristics. Through focused ion beam (FIB) direct-write metal deposition techniques, the effects of localized mass loading on the surface of three extensional mode devices have been investigated. Ten microfabricated 40 mm-radius disk resonators, which all have a 20 mm-thick silicon device layer and 1 mm-thick ZnO transducer layer but varied anchor widths and numbers, have exhibited resonant frequencies ranging from 84.9 MHz to 86.7 MHz with Q factors exceeding 6000 (in air) and 10,000 (in vacuum), respectively. It has been found that the added mass at the nodal locations leads to noticeable Q-factor degradation along with lower induced frequency drift, thereby resulting in reduced mass sensitivity. All three measured devices have shown a mass sensitivity of ~1.17 Hz·fg−1 at the maximum displacement points with less than 33.3 ppm of deviation in term of fractional frequency change. This mass sensitivity is significantly higher than 0.334 Hz·fg−1 at the nodal points. Moreover, the limit of detection (LOD) for this resonant mass sensor was determined to be 367 ag and 1290 ag (1 ag = 10−18 g) for loaded mass at the maximum and minimum displacement points, accordingly.

Damage Identification of Multimember Structure using Improved Neural Networks

A novel two stage Improved Radial Basis Function (IRBF) neural network for the damage identification of a multimember structure in the frequency domain is presented. The improvement of the proposed IRBF network is carried out in two stages. Conventional RBF network is used in the first stage for preliminary damage prediction and in the second stage reduced search space moving technique is used to minimize the prediction error. The network is trained with fractional frequency change ratios (FFCs) and damage signature indices (DSIs) as effective input patterns and the corresponding damage severity values as output patterns. The patterns are searched at different damage levels by Latin hypercube sampling (LHS) technique. The performance of the novel IRBF method is compared with the conventional RBF and Genetic algorithm (GA) methods and it is found to be a good multiple member damage identification strategy in terms of accuracy and precision with less computational effort.

Development and Characterization of Isotropic Magnetorheological Elastomer

Magneto rheological elastomer (MRE) is a new kind of smart materials. Its dynamic mechanical performances can be controlled by controlling an applied magnetic field. MRE is usually used as stiffness - changeable spring in the semi-active vibration absorber. In order to get perfect vibration control effect, low dynamic damping of MRE is needed. This paper presents a new method of fabricating isotropic MREs under normal temperature and pressure conditions. In the absence of a magnetic field, a variety of MR elastomer samples were prepared using Sylard’s184 silicone elastomer along with un-annealed electrolytic iron power 500 mesh and 15 micron size. Their dynamic characteristics like fractional change in resonant frequency and fractional change in have been studied. The effects of iron particles and the applied magnetic field were investigated. This study is also expected to provide a good guide for designing and preparing new MR elastomers.

Structural Damage Identification Using Improved RBF Neural Networks in Frequency Domain

This paper presents a novel two stage improved Radial basis function (RBF) neural network for the damage identification of multimember structures in the frequency domain. The improvement of the proposed RBF network is carried out in two stages, viz. (i) first stage damage prediction by conventional RBF network trained with effective input-output patterns and (ii) in the second stage, minimization of the prediction error below the predefined error tolerance (3%) by training the network with patterns from reduced search space located after the first stage prediction. The network effective input patterns are fractional frequency change ratios (FFCs) and damage signature indices (DSIs), and the corresponding output patterns are stiffness values or damage severity of the structure at different damage levels. A Latin hypercube search (LHS) technique is used for finding the effective input-output patterns from the search space to improve the training efficiency. The numerical simulation of structural damage identification for two multimember structures; a six-storey steel structure and a nine-member frame structure, are evaluated with and without addition of 5% random noise to the input patterns using the proposed network. The novel improved RBF network is shown to be a good damage identification strategy for multiple member structures compared to conventional RBF and existing hybrid methods in terms of accuracy and computational effort.

A Resonator for Tunable Superconducting Power Filters with Cavities for 5 GHz Band

A design of the tunable superconducting power filter is described. The filter consists of superconducting microwave cavities with a mechanical tuning method. The electromagnetic simulations using niobium cavity suggested that there were conditions where the resonator with high-unloaded Q can realize a fractional center frequency change of more than ±10% by using a Nb rod moving in the cavity. The simulations approximated the resonant frequency dependence of the rod moved by a cryogenic actuator in the tunable cavity experiment. In addition, the simulation of the power handling capability showed a feasibility of the value more than 50 dB W.

Unusual glitch activity in the RRAT J1819−1458: an exhausted magnetar?

We present an analysis of regular timing observations of the high-magnetic-field Rotating Radio Transient (RRAT) J1819$-$1458 obtained using the 64-m Parkes and 76-m Lovell radio telescopes over the past five years. During this time, the RRAT has suffered two significant glitches with fractional frequency changes of $0.6\times10^{-6}$ and $0.1\times10^{-6}$. Glitches of this magnitude are a phenomenon displayed by both radio pulsars and magnetars. However, the behaviour of J1819$-$1458 following these glitches is quite different to that which follows glitches in other neutron stars, since the glitch activity resulted in a significant long-term net decrease in the slow-down rate. If such glitches occur every 30 years, the spin-down rate, and by inference the magnetic dipole moment, will drop to zero on a timescale of a few thousand years. There are also significant increases in the rate of pulse detection and in the radio pulse energy immediately following the glitches.

Glitches in Anomalous X‐Ray Pulsars

We report on 8.7 and 7.6 yr of Rossi X-Ray Timing Explorer (RXTE) observations of the anomalous X-ray pulsars (AXPs) RXS J170849.0–400910 and 1E 1841–045, respectively. These observations have allowed us to study the long-term timing, pulsed flux, and pulse profile evolution of these objects. We report on four new glitches, one from RXS J170849.0–400910 and three from 1E 1841–045. With nearly all known persistent AXPs now seen to glitch, such behavior is clearly generic to this source class. We show that in terms of fractional frequency change, AXPs are among the most actively glitching neutron stars, with glitch amplitudes in general larger than in radio pulsars. However, in terms of absolute glitch amplitude, AXP glitches are unremarkable. Unlike radio pulsar glitches, AXP glitches can sometimes, though not always, be accompanied by radiative events. We show that the largest observed AXP glitches have recoveries that are unusual among those of radio pulsar glitches, with the combination of recovery time scale and fraction yielding changes in spin-down rates following the glitch similar to, or larger than, the long-term average. We also observed a large long-term fractional increase in the magnitude of the spin-down rate of 1E 1841–045, following its largest glitch, with $Δ d{ν }/d{ν } = 0.1$ -->. These observations are challenging to interpret in standard glitch models, as is the frequent occurence of large glitches given AXPs' high measured temperatures. We speculate that the stellar core may be involved in the largest AXP glitches.

Long‐Term Phase‐coherent X‐Ray Timing of PSR B0540−69

We present a new phase-coherent timing analysis for the young, energetic pulsar PSR B0540-69 using 7.6 yr of data from the Rossi X-Ray Timing Explorer. We measure the braking index, n=2.140+/-0.009, and discuss our measurement in the context of other discordant values reported in the literature. We present an improved source position from the phase-coherent timing of the pulsar, to our knowledge, the first of its kind from X-ray pulsar timing. In addition, we detect evidence for a glitch which has been previously reported but later disputed. The glitch occured at MJD 51335+/-12 with a fractional change in frequency of (1.4+/-0.2)E{-9} and a fractional change in frequency derivative of (1.33+/-0.02)E{-4}. We calculate that the glitch activity parameter for PSR B0540-69 is two orders of magnitude smaller than that of the Crab pulsar which has otherwise very similar properties. This suggests that neutron stars of similar apparent ages, rotation properties and inferred dipolar B fields can have significantly different internal properties.

A Frequency Glitch in an Accreting Pulsar

Frequency glitches have been observed so far only in radio pulsars and anomalous X-ray pulsars. Here we present evidence of a glitch in a neutron star accreting from a Be companion. The transient KS 1947+300 reappeared in 2000 October as a moderately strong X-ray source that exhibited 18.7 s pulsations, leading to an identification with the BATSE source GRO J1948+32, last detected in 1994. We have analyzed Rossi X-Ray Timing Explorer (RXTE) observations taken during the 2000-2001 outburst, as well as additional observations taken during a smaller outburst in 2002 July. Orbital Doppler shifts are apparent in the temporal variation of the pulse frequency. A joint fit of the RXTE data together with BATSE measurements from an outburst in 1994 yields the orbital period Porb = 40.415 ± 0.010 days, the projected orbital radius aX sin i = 137 ± 3 lt-s, and the eccentricity e = 0.033 ± 0.013. This degree of eccentricity is unexpectedly low for such a wide orbit. Pulse timing results also show that the intrinsic pulse frequency increased from 53.30 to 53.47 mHz at a rate approximately proportional to the X-ray flux. This is about the degree of spin-up expected from the accretion torques that must be present when the X-ray luminosity reaches ~1038 ergs s-1. On one occasion during the 2000-2001 outburst, the pulse frequency increased by ~1.8 × 10-6 Hz in 10 hr over and above the mean trend seen around that time, without any indication of a correspondingly large increase in X-ray flux. The fractional change in frequency of 3.7 × 10-5 during this event is significantly larger than the values observed in the glitches in radio pulsars and anomalous X-ray pulsars. We discuss other similarities and differences between these events.

A Microglitch in the Millisecond Pulsar PSR B1821-24 in M28

We report on the observation of a very small glitch observed for the first time in a millisecond pulsar, PSR B1821-24, located in the globular cluster M28. Timing observations were mainly conducted with the Nancay radio telescope (France), and confirmation comes from the 140 ft radio telescope at Green Bank and the new Green Bank Telescope data. This event is characterized by a rotation frequency step of 3 nHz, or 10-11 in fractional frequency change, along with a short duration limited to a few days or a week. A marginally significant frequency derivative step was also found. This glitch follows the main characteristics of those in the slow-period pulsars but is 2 orders of magnitude smaller than the smallest ever recorded. Such an event must be very rare for millisecond pulsars since no other glitches have been detected when the cumulated number of years of millisecond pulsar timing observations up to 2001 is around 500 for all these objects. However, pulsar PSR B1821-24 is one of the youngest among the old recycled ones, and there is likely a correlation between age, or a related parameter, and timing noise. While this event happens on a much smaller scale, the required adjustment of the star to a new equilibrium figure as it spins down is a likely common cause for all glitches.

LGX pure shear horizontal SAW for liquid sensor applications

This paper reports predicted and measured properties of the pure shear horizontal (SH) mode for the LGX family of crystals, which includes langasite (LGS), langanite (LGN), and langatate (LGT). These crystals are of the trigonal class 32 group, as quartz, and they exhibit the SH symmetry type uncoupling for the Euler angles (0/spl deg/, /spl theta/, 90/spl deg/). This surface acoustic mode, also known as surface transverse wave (STW), is especially attractive for liquid sensing due to the moderate damping observed in liquid or viscous environments. Numerical and experimental propagation data presented for the SH mode on LGX (0/spl deg/, /spl theta/, 90/spl deg/) includes phase velocity (v/sub p/), electromechanical coupling coefficient (K/sup 2/), temperature coefficient of delay (TCD), fractional change in frequency with respect to temperature (/spl Delta/f/fo), penetration depth, metal strip reflectivity, and excitation of spurious plate modes as a function of /spl theta/. High electromechanical coupling and zero temperature coefficient of delay (TCD) along LGX Euler angles (0/spl deg/, /spl theta/, 90/spl deg/), /spl theta/ between 10/spl deg/ and 25/spl deg/, with penetration depths comparable to surface acoustic wave (SAW) devices are disclosed. In particular, along LGT (0/spl deg/, 13.5/spl deg/, 90/spl deg/), the experimental results reported with resonators and delay line structures verify the high electromechanical coupling (0.8%) for a SH SAW mode, about 10 times stronger than the 36/spl deg/ Y rotated quartz SH orientation, and the existence of zero TCD around 140/spl deg/C. The phase velocity of 2660 m/s is within 0.2% of the calculated value, which is about 55% below the phase velocity of 36/spl deg/ Y quartz, thus leading to smaller STW devices. The penetration depth of 6.5 wavelengths is eight times more shallow than 36/spl deg/ Y quartz, thus providing significant SH mode energy trapping close to the surface. With such positive predicted and measured coupling and propagation characteristics, these orientations are appropriate for the fabrication of high coupling, zero TCD, smaller, and highly sensitive STW devices for filtering, frequency control, and liquid sensor applications.

Discovery of a 270 Hertz X-Ray Burst Oscillation in the X-Ray Dipper 4U 1916−053

We report the discovery of a highly coherent oscillation in a type I X-ray burst observed from 4U 1916-053 by the Rossi X-Ray Timing Explorer (RXTE). The oscillation was most strongly detected ≈1 s after the burst onset at a frequency of 269.4 Hz, and it increased in frequency over the following 4 s of the burst decay to a maximum of 272 Hz. The total measured drift of 3.58 ± 0.41 Hz (1 σ) represents the largest fractional change in frequency (1.32% ± 0.15%) yet observed in any burst oscillation. If the asymptotic frequency of the oscillation is interpreted in terms of a decoupled surface burning layer, the implied neutron star spin period is around 3.7 ms. However, the expansion of the burning layer required to explain the frequency drift during the burst is around 80 m, substantially larger than expected theoretically (assuming rigid rotation). The oscillation was not present in the persistent emission before the burst, nor in the initial rise. When detected, its amplitude was 6%-12% (rms) with a roughly sinusoidal profile. The burst containing the oscillation showed no evidence for photospheric radius expansion, while at least five of the other nine bursts observed from the source by RXTE during 1996 and 1998 did. No comparable oscillations were detected in the other bursts. A pair of kilohertz quasi-periodic oscillations (kHz QPOs) has been previously reported from this source with a mean separation of 348 ± 12 Hz. 4U 1916-053 is the first example of a source where the burst oscillation frequency is significantly smaller than the frequency separation of the kHz QPOs.

Relativistic effects for Doppler measurements near solar conjunction

The authors consider the relativistic corrections to the Doppler effect in a metric theory of gravity, in the weak field and slow motion approximation, for a source and a receiver at great distances from, but near alignment with, the perturbing body (i.e. near conjunction). They also work in the approximation of a thin screen and paraxial rays, and apply this formalism to an ideal experiment, related to that of the deflection of light rays by the solar mass. They then introduce a differential Doppler technique, which allows some new and interesting developments in the field of experimental gravitation. With a spacecraft equipped with a hydrogen maser on board, one can measure the difference between the fractional frequency shifts in both directions. Near conjunction it is possible to have information, for example, on the angular momentum of the Sun or on a possible effect of a privileged cosmological frame of reference. This technique also allows a drastic reduction of the effect due to the plasma of the solar corona. The maximum fractional frequency change induced by the angular momentum of the Sun is about 7*10-16, which is barely consistent with the stability of hydrogen masers currently available.