Phase Fluctuations Research Articles

Towards effective assessment of steady state performance in Java software: are we there yet?

Microbenchmarking is a widely used form of performance testing in Java software. A microbenchmark repeatedly executes a small chunk of code while collecting measurements related to its performance. Due to Java Virtual Machine optimizations, microbenchmarks are usually subject to severe performance fluctuations in the first phase of their execution (also known as warmup). For this reason, software developers typically discard measurements of this phase and focus their analysis when benchmarks reach a steady state of performance. Developers estimate the end of the warmup phase based on their expertise, and configure their benchmarks accordingly. Unfortunately, this approach is based on two strong assumptions: (i) benchmarks always reach a steady state of performance and (ii) developers accurately estimate warmup. In this paper, we show that Java microbenchmarks do not always reach a steady state, and often developers fail to accurately estimate the end of the warmup phase. We found that a considerable portion of studied benchmarks do not hit the steady state, and warmup estimates provided by software developers are often inaccurate (with a large error). This has significant implications both in terms of results quality and time-effort. Furthermore, we found that dynamic reconfiguration significantly improves warmup estimation accuracy, but still it induces suboptimal warmup estimates and relevant side-effects. We envision this paper as a starting point for supporting the introduction of more sophisticated automated techniques that can ensure results quality in a timely fashion.

A coupling strategy for comprehensive utilization of distillers’ grains towards energy recovery and carbon sequestration

This study investigated a coupling strategy for comprehensive utilization of distillers' grains (DGs), which integrated anaerobic digestion (AD) and chemical looping gasification (CLG) towards energy recovery and carbon sequestration. The AD and subsequent CLG performance on DGs were investigated, and the mass-energy flows and potential mechanisms in the coupling process were assessed. In the AD stage, all the fluctuations of solid, liquid and gas phases were concentrated in the first 6–8 days due to the limitation of the biodegradation of DGs. During the CLG stage, the volume fraction of syngas, gas yield and gasification efficiency were altered due to the consumption of the chemical components of DGs at different digestion days. Considering the overall assessment, the coupling strategy of 6-day AD and CLG was optimal, which could obtain 16.80 MJ/kg TS of energy recovery, 47.73 % of mass conversion, 55.06 % of carbon efficiency and 39.72 % of CO2 emissions. Correlation analysis showed that AD was more conducive to energy recover than CLG, and the biodegradable threshold of DGs was expected to be obtained in the AD stage for the coupling strategy. The normalization analysis showed that the variation of cellulose content can be used to determine the optimal AD time (6 Days), which could directly reflect the biodegradation of DGs with the strongest correlation (−0.9901). These findings provide a new strategy of green efficient energy and carbon recovery for the comprehensive utilization of biomass.

Autapse-induced logical resonance in the FitzHugh–Nagumo neuron

It was demonstrated that the chaos-driven FitzHugh–Nagumo (FHN) neuron can be considered as a logic system to implement the reliable logical operations through the mechanism of logical resonance. Autapse (meaning the self-synapse) widely exists in various kinds of neurons, and it significantly affects the neuronal dynamics and functionalities. However, the effects of autapse on logical resonance have not been reported yet. Here, we explore the effects of autapse on the reliability of AND & NAND logical operations based on the autaptic FHN neuron model with time-varying coupling intensity. The numerical results demonstrate that there are the optimal ranges of parameters (including autaptic time delay, amplitude, frequency and phase fluctuation of autaptic coupling intensity) at which the reliability of logical operations can be maximized. Namely, autapse-induced logical resonance can be realized in the autaptic FHN neuron model. More interestingly, multiple logical resonances can be obtained by regulating autaptic time delay, phase fluctuation of autaptic coupling intensity, as well as frequency ratio between and autaptic coupling intensity and external periodic driving force. Finally, an intuitive interpretation for autapse-induced logical resonance is given based on the motion of the particle in the potential landscape.

Arm locking in conjunction with time-delay interferometry

A crucial challenge to the ongoing endeavor of spaceborne gravitational wave (GW) detection resides in the laser phase noise, typically 7 to 8 orders of magnitude above the inevitable noise. The arm locking technique was proposed to suppress the noise in pre-stabilized laser beams. Based on the feedback control theory, it is implemented by appropriate design of the signal routing architecture, particularly the controllers' transfer functions. Theoretically and experimentally, the technique has been demonstrated to be capable of suppressing the laser phase noise by approximately 2-4 orders of magnitude while taking into account various aspects such as the gain and distribution of nulls in the Bode plot and the laser frequency pulling associated with the Doppler frequency subtraction. Consequently, the resultant noise floor is composed of the sources attributed to the clock jitter, optical bench motion, test mass fluctuations, shot-noise phase fluctuations at the photodetectors, whereas the magnitudes of these noises largely remain unchanged during the process. Besides, the original GW signals are deformed through the arm-locking control loop and therefore bear specific features governed by the associated arm-locking scheme. Nonetheless, the remaining laser phase noise from the arm-locking feedback routing settles within the capability threshold of the time-delay interferometry (TDI). In this regard, it is generally understood that the output of arm locking furnishes the input of TDI, through which the residual noise is further reduced to the desired level at a post-processing stage. In this work, we investigate the specific schemes regarding how the arm locking output is processed further by the TDI algorithm. Specific forms of the TDI combinations are derived in accordance with suppressed laser phase noise and deformed signals of GW.

Sign optimization and complex saddle points in one-dimensional QCD

We study one-dimensional QCD at finite quark density by using the sign optimization framework. The fermion sign problem is mitigated by deforming the path integral domain, $SU(3)$ to a complexified one ${\cal M} \subset SL(3)$, explicitly constructed to reduce the phase fluctuations. The complexification is constructed using the angular representation of $SU(3)$. We provide a physical explanation of the optimization procedure in terms of complex saddle points. This picture connects the sign optimization framework to the generalized Lefschetz thimbles.

Strength and ductility enhancement of high-entropy FeCoNi2Al0.9 alloy by ultrasonically refining eutectic structures

The solidification process of high-entropy FeCoNi2Al0.9 alloy was modulated by 20 kHz power ultrasound with maximum 13 μm amplitude. The statically solidified eutectic structures were composed of L12 and B2 phases growing by K-S synergistic relationship. With the increase of ultrasound amplitude, the eutectic cell width and regular lamellar spacing were significantly refined, the proportion of strictly semi-coherent L12/B2 interfaces increased, and the solute concentration fluctuation in each eutectic phase was obviously suppressed. The steady-state cavitation and acoustic flow displayed remarkable influences on eutectic microstructure evolution. The yield strength, ultimate strength, and total elongation were increased by 23%, 21%, and 19% as compared with statically solidified alloy. This provided an effective approach to promoting the mechanical properties and overcoming the strength-ductility trade-off for those high-entropy alloys with eutectic structures.

An interference iterative reconstruction algorithm based on a single off-axis digital hologram

Compared with in-line digital holography, off-axis digital holography can be used to image more kinds of objects without the limitation of weak phase and sparsity, but the resolution is lower. In this paper, we put forward a high-resolution iterative reconstruction algorithm for off-axis holography which requires only the recording of a single off-axis hologram. Interference and inverse interference processes are used to extract the object wave from the off-axis hologram. A frequency domain filter with increasing radius is used to improve the competitive advantage of low frequency information in the early iterations, while retaining the high frequency information. The constraints of total variation and positive absorption are implemented at the object plane to enhance the robustness of the algorithm. Numerical simulations and experiments show that the resolution of our method is higher than traditional off-axis digital holography. In addition, it is suitable for phase image when the object has a strong phase fluctuation, as well as for imaging dynamical objects.

Statistics of the instantaneous interaural parameters for dichotic tones in diotic noise (N0S ψ ).

Stimuli consisting of an interaurally phase-shifted tone in diotic noise-often referred to as N 0 S ψ -are commonly used to study binaural hearing. As a consequence of mixing diotic noise with a dichotic tone, this type of stimulus contains random fluctuations in both interaural phase- and level-difference. We report the joint probability density functions of the two interaural differences as a function of amplitude and interaural phase of the tone. Furthermore, a second joint probability density function for interaural phase differences and the instantaneous cross-power is derived. The closed-form expression can be used in future studies of binaural unmasking first to obtain the interaural statistics and then study more directly the relation between those statistics and binaural tone detection.

Hydrodynamic signatures and spectral properties of the quantum vortex

We characterize the low-lying excitations of a quantum vortex in a quasi-two-dimensional Bose-Einstein condensate (BEC) using the standard definition of the density of states (DOS) and a modified version that is sensitive to complementary aspects of the excitation's spectrum. The latter proves to be particularly relevant to studying the polaronic state realized when an impurity is embedded in a quantum vortex. We establish that the impurity becomes sensitive to the transversal fluctuations of the vortex, via its remnant kelvon mode, and to the phase fluctuations of the BEC Nambu-Goldstone mode. The presence of the vortex yields an anomalous excitation spectrum with a finite energy gap and non-linear DOS at low energies. We find that the high sensitivity of the kelvon mode to external potentials provides a channel of quantum-level control over impurities trapped in a vortex. This extra control channel may be of practical use for the proposal of using vortex-trapped impurities as qubit units for quantum information processing.

Compact and efficient radio frequency digital feedback control system for accelerator applications

The digital feedback (DFB) setup employed in a low-level radio frequency (LLRF) control system is crucial to ensure RF field stability in accelerating cavities, thus guaranteeing successful operation. To this end, a novel in-house and multi-purpose prototype DFB setup was developed for multiple applications at the Japan Proton Accelerator Research Complex (J-PARC). Being efficient, low-cost, and compact is key to achieving a cost-effective system that fulfills the performance specifications. It also reduces the production and maintenance costs of future DFB setups. A field-programmable gate array (FPGA)-based design with a digital signal processing (DSP) function uses an analog in-phase/quadrature-phase (I/Q) demodulator for RF-to-baseband signal conversion and an I/Q modulator to generate RF power. This arrangement compensates for RF phase fluctuations and amplitude modulations by employing a proportional and integral (PI) feedback controller. In addition, systematic errors are minimized by applying a hardware-error-compensation process. The system was utilized to conduct high-power tests on the interdigital H-mode drift-tube linac (IH-DTL) cavity of a muon linac for short RF pulses. The setup was also tested on a buncher cavity (Buncher-2) in the J-PARC linac, achieving efficient performance for longer RF pulses. The stability of the RF accelerating field in the IH-DTL was achieved at ±0.25% peak-to-peak (pp) in amplitude and ±0.36 degree pp in phase. For the Buncher-2, the amplitude stability of ±0.18% pp and phase stability of ±0.13 degree pp were obtained. Therefore, this DFB setup can be used to conduct high-power tests of RF cavities and klystrons. This study discusses the design aspects of a cost-effective DFB system and reports high-power measurements.

Free-space optical stealth communication based on wide-band spontaneous emission

We proposed and experimentally demonstrated a free-space optical stealth communication system that hides the stealth signal in wide-band spontaneous emission noise. Spontaneous emission light sources have been widely used for illuminations and has been recently deployed for short distance and indoor free-space optical communications, such as LiFi. Since free-space optical communication is a broadcasting network, the users’ privacy is exposed to eavesdropping attacks. In this paper, stealth communication is achieved by taking advantage of the existing properties of spontaneous emission light sources, random phase fluctuations, and protects users’ privacy in free-space communication networks. The keys to hide and recover the stealth signal are the optical delays at the transmitter and receiver. Only by matching the delay length with the pre-shared keys can the authorized receiver recover the stealth signal. Without the right key, the eavesdropper receives a constant power that is the same as illumination light sources and cannot detect the existence of the stealth signal.

Statistics of phase fluctuations of an acoustic wave propagating through a turbulent flow

We investigate the statistics of phase fluctuations of an acoustic wave propagating through a turbulent flow in line of sight (LOS) configuration. Experiments are performed on a closed von Kármán swirling flow whose boundaries are maintained at a constant temperature. In particular, we analyze the root mean square (RMS) and the power spectrum density (PSD) of phase fluctuations. A model is developed and analytical predictions obtained for these quantities using geometrical acoustics are shown to be in agreement with experimental observations.

움직이는 사람에 대한 비접촉식 생체신호추정 연구

The non-contact vital sign estimation of an individual using radar sensors has been widely researched. However, in the case of an individual with undesirable rigid-body motion of the torso, non-contact vital sign estimation may fail owing to extreme phase fluctuations caused by the larger rigid-body motion of the torso than the micro motion of the vital sign. To address this problem, we propose a rigid-body motion compensation method using the complex echo signals of the IR-UWB radar for the vital sign estimation of an individual with rigid-body motion. The proposed method extracts a complex signal vector using principal component analysis from complex echo signals in a radial range and pulse time domain. Next, compensation for the rigid-body motion is implemented by minimizing the entropy of the spectrum for the complex signal vector. In simulations using a point-scatterer model and experiments using IR-UWB commercial radar, we verified that our proposed method is capable of performing successful vital sign estimation of an individual with undesirable rigid-body motion.

Nonlinear chirped interferometry for frequency-shift measurement and χ(3) spectroscopy

Four-wave mixing processes are ubiquitous in ultrafast optics and the determination of the coefficients of the χ(3) tensor is thus essential. We introduce a novel time-resolved ultrafast spectroscopic method to characterize the third-order nonlinearity on the femtosecond time-scale. This approach, coined as “nonlinear chirped interferometry,” makes use of the variation of the optical group delay of a transmitted probe under the effect of an intense pump pulse in the nonlinear medium of interest. The observable is the spectral interference between the probe and a reference pulse sampled upstream and the metric is the transient swing of the probe group delay. We show that the detected signal is enhanced when the pulses are weakly chirped, and that, although interferometric, the method is intrinsically less sensitive to environmental phase fluctuations and drifts. By chirping adequately the reference pulse, the transient frequency shift of the probe pulses is also detected in the time domain and the detected nonlinear signal is enhanced. Nonlinear phase shifts as low as 10 mrad, corresponding to a frequency shift of 30 GHz, i.e., 0.01% of the carrier frequency, are detected without heterodyne detection or active phase-stabilization. The diagonal and/or non-diagonal terms of reference glasses (SiO2) and crystals (Al2O3, BaF2, CaF2) are characterized. The method is finally applied to measure the soft vibration mode of KTiOAsO4 (KTA).

Fast broadband cluster spin-glass dynamics in PbFe1/2Nb1/2O3

PbFe$_{1/2}$Nb$_{1/2}$O$_{3}$ (PFN) is a relaxor ferroelectric (T$_{c}$ $\sim$ 400 K) consisting of disordered magnetic Fe$^{3+}$ (S=${5\over2}$, L$\approx$0) ions resulting in a low temperature ``cluster glass" phase (W. Kleemann $\textit{et al.}$ Phys. Rev. Lett. ${\bf{105}}$, 257202 (2010)). We apply neutron scattering to investigate the dynamic magnetism of this phase in a large single crystal which displays a low temperature spin glass transition (T$_{g} \sim$ 15 K), but no observable spatially long-range antiferromagnetic order. The static response in the cluster glass phase (sampled on the timescale set by our resolution) is found to be characterized by an average magnetic spin direction that lacks any preferred direction. The dynamics that drive this phase are defined by a magnetic correlation length that gradually increases with decreasing temperature. However, below $\sim$ 50 K the spatial correlations gradually becoming more short range indicative of increasing disorder on cooling, thereby unravelling magnetism, until the low temperature glass phase sets in at T$_{g}$ $\sim$ 15 K. Neutron spectroscopy is used to characterize the spin fluctuations in the cluster glass phase and are found to be defined by a broadband of frequencies on the scale of $\sim$ THz, termed here ``fast" fluctuations. The frequency bandwidth driving the magnetic fluctuations mimics the correlation length and decreases until $\sim$ 50 K, and then increases again until the glass transition. Through investigating the low-energy acoustic phonons we find evidence of multiple distinct structural regions which form the basis of the clusters, generating a significant amount of local disorder. We suggest that random molecular fields originating from conflicting interactions between clusters is important for the destruction of magnetic order and the eventual formation of the cluster glass in PFN.

Classical route to ergodicity and scarring phenomena in a two-component Bose-Josephson junction

We consider a Bose-Josephson junction (BJJ) formed by a binary mixture of ultracold atoms to investigate the manifestation of coherent collective dynamics on ergodicity and quantum scars, unfolding the connection between them. By tuning the inter- and intra-species interaction, we demonstrate a rich variety of Josephson dynamics and transitions between them, which plays a crucial role in controlling the overall ergodic behavior. The signature of underlying classicality is revealed from the entanglement spectrum, which also elucidates the formation of quantum scars of unstable steady states and of periodic orbits leading to athermal behavior. The degree of ergodicity across the energy band and scarring phenomena can be probed from the auto-correlation function as well from the phase fluctuation of the condensates, which has relevance in cold atom experiments.

Diagonal and off-diagonal thermal conduction with resonant phonon scattering in Ni3TeO6

The coupling between phonon and magnon is ubiquitous in magnetic materials and plays a crucial role in many aspects of magnetic properties, most notably in spintronics. Yet, this academically and technologically interesting problem still poses a severe challenge to a general understanding of the issue in certain materials. We report that Ni3TeO6 exhibits clear evidence of significant magnon-phonon coupling in both longitudinal thermal conductivity ($\kappa_{xx}$) and thermal Hall coefficient ($\kappa_{xy}$). The Debye-Callaway model, a phenomenological description for phonon heat conduction, can explain the measured magnetic field dependence of $\kappa_{xx}(H)$: phonon scattering from spin fluctuation in the paramagnetic phase and additional scattering due to magnon-phonon coupling in the collinear antiferromagnetic phase. We further suggest that a similar approach could be applied to understand the finite $\kappa_{xy}$ values in $Ni_3TeO_6$.

Energy-length scaling of critical phase fluctuations in the cuprate pseudogap phase

The quantum origin of the cuprate pseudogap and its relationship to symmetry-breaking orders is a central conundrum of unconventional superconductors. The difficulty is deeply rooted in modeling simultaneous organizations in multiple degrees of freedom (including spin, momentum, and real space) generated by strong electron-electron correlations. Beyond early theories focusing on the description in spin and momentum space, recent studies turn to examine the spatial organization and intertwining mechanism of multiple orders. In this review, we summarize some progress in understanding the spatial organization of critical fluctuations and highlight the recent discovery of a universal energy-length scaling. This scaling quantitatively explains the nontrivial magnitude and doping dependence of the pseudogap energy and critical temperature and their relations to charge and superconducting ordering. We close with a prospect of the spatial organization mechanism of intertwined orders and its possible composite energy scaling.

Correlation analysis of normalized ROTI and S4 as observed during different geomagnetic conditions of the 2013 September equinox over the stations within EIA African sector

It has been a concern of space scientists and engineers for many decades to have a well-defined proxy to characterize the fluctuations experienced by radio-based signals propagating through the ionosphere. Scintillation indices were deduced using the signal intensity to show the level of fluctuations in phase and amplitude of radio signal passing through the ionosphere. Subsequently, more than two decades now, the rate of change of Total Electron Content (TEC) index (ROTI) was as well used to characterize the level of fluctuations associated to ionospheric irregularities on radio signals. This paper examines the level of relationship between the rate of change of TEC index (ROTI) and the ionospheric amplitude scintillation (S4) within the belt of equatorial ionization anomaly of West African sector. The study was carried out using the Scintillation Network Decision Aid (SCINDA) Global Positioning System (GPS) data obtained from ground-based stations located at Dakar (Senegal) and Cape Verde. The comparative analysis of ROTI and S4 was done with normalized ROTI. The results obtained have shown that the magnitude of normalized ROTI and S4 corresponds very well, higher in Cape Verde compared to Dakar. It was observed that the correlation coefficient could be ∼0.6 when all the satellites are used. However, the relationship increases with individual satellite in which the coefficient of correlation could be up to ∼0.97 and R2 ∼ 0.94. It can be concluded that the relationship between the S4 and ROTI depends on the location and the level of ionospheric disturbance condition as observed in this work.

Sound propagation and scattering in turbulent media

This presentation overviews sound propagation and scattering in turbulent media and pertinent acoustic remote sensing of turbulence. Although sound propagation through a turbulent atmosphere is mainly considered, the presented results apply to other media such as oceanic turbulence. Formulations are provided for various statistical characteristics of acoustic signals such as the scattering cross section, the variances of the phase and log-amplitude fluctuations, the spatial, temporal, and cross-frequency coherences, and the probability density functions. Monte Carlo simulation of sound propagation in a random medium is explained. Specifics of acoustic signals in turbulent media as compared to electromagnetic waves are highlighted. For example, sound waves are scattered by both the sound speed and medium velocity fluctuations, which are scalar and vector random fields, respectively, with different statistical properties. Also, fluctuations in the acoustic refractive index are much stronger than those in electromagnetic propagation, and sound can be scattered by humidity (or salinity) fluctuations. Finally, the Markov approximation, which is widely used for electromagnetic waves, might not be applicable for some statistical characteristics of acoustic signals. It is explained how these specifics of sound propagation are addressed in atmospheric acoustics.