Relative Delay Research Articles

Hybrid Terahertz Emitter for Pulse Shaping and Chirality Control

AbstractTerahertz (THz) radiation (0.3 to 30 THz) fills the crucial gap between the microwave and infrared spectral range. THz technology is important for applications ranging from imaging to telecommunication to biosensing, but these applications often require precise control and manipulation of the THz frequency and polarization state, which typically requires modulators external to the THz source. A hybrid THz emitter that overcomes this limitation by integrating two THz emitters into a single device to enable pulse shaping and chirality control of the emitted radiation without any external components is demonstrated. The two sources are a spintronic emitter (SE) and a semiconductor photoconductive antenna (PCA). The two emitters respond independently to external parameters: the PCA is controlled by the applied bias voltage, while the SE is controlled by the applied magnetic field. Moreover, a dual‐wavelength excitation scheme allows for control of the relative time delay between the THz emission from each constituent. These properties of the hybrid emitter enable precise control of the mixing of the two signals to control the frequency, polarization, and chirality of the overall THz radiation. This on‐chip hybrid emitter thus provides a powerful platform for engineered THz radiation with wide‐ranging potential applications.

Fast measurement of group index variation with optimum precision using Hong–Ou–Mandel interferometry

Hong–Ou–Mandel (HOM) interferometry has emerged as a valuable means for quantum sensing applications, particularly in measuring physical parameters that influence the relative optical delay between photon pairs. Unlike classical techniques, HOM-based quantum sensors offer higher resolution due to the intrinsic dispersion cancellation property of correlated photon pairs. Due to the use of single photons, HOM-based quantum sensors typically involve a large integration time to acquire the signal and subsequent post-processing for high-resolution measurements, restricting their use for real-time operations. Based on our understanding of the relationship between measurement resolution and the gain medium length that produces photon pairs, we report here on the development of an HOM-based quantum sensor for high-precision group index measurements. Using a 1 mm long periodically poled KTP (PPKTP) crystal for photon-pair generation, we have measured the group index with a precision of ∼6.75×10−6 per centimeter of sample length at an integration time of 100 ms, surpassing the previous reports by 400%. Typically, the measurement range reduces with the increase in the resolution. However, using a novel scheme compensating photon delay due to group index changes stepwise with an optical delay stage, we have measured the group index variation of PPKTP crystal over a range of 3.5 × 10−3 for a temperature change from 25 to 200 °C, corresponding to an optical delay adjustment of ∼200 μm while maintaining the same precision (∼6.75×10−6 per centimeter of sample length). The current results establish the usefulness of HOM-interferometer-based quantum sensors for fast, precise, and long-range measurements in various applications, including quantum optical coherence tomography.

Generation of 10 kT axial magnetic fields using multiple conventional laser beams: A sensitivity study for kJ PW-class laser facilities

Strong multi-kilotesla magnetic fields have various applications in high-energy density science and laboratory astrophysics, but they are not readily available. In our previous work [Y. Shi et al., Phys. Rev. Lett. 130, 155101 (2023)], we developed a novel approach for generating such fields using multiple conventional laser beams with a twist in the pointing direction. This method is particularly well-suited for multi-kilojoule petawatt-class laser systems like SG-II UP, which are designed with multiple linearly polarized beamlets. Utilizing three-dimensional kinetic particle-in-cell simulations, we examine critical factors for a proof-of-principle experiment, such as laser polarization, relative pulse delay, phase offset, pointing stability, and target configuration, and their impact on magnetic field generation. Our general conclusion is that the approach is very robust and can be realized under a wide range of laser parameters and plasma conditions. We also provide an in-depth analysis of the axial magnetic field configuration, azimuthal electron current, and electron and ion orbital angular momentum densities. Supported by a simple model, our analysis shows that the axial magnetic field decays owing to the expansion of hot electrons.

Probing the solar system for dark matter using the Sagnac effect

This study investigates the potential of the Sagnac Effect for detecting dark matter in the Solar System, particularly within the Sun. Originating from the relative delay and interference of light beams traveling in opposite directions on rotating platforms, the effect can account for how varying gravitational conditions affect its manifestation. We analyze the Sagnac time in two static, spherically symmetric spacetimes: Schwarzschild and one incorporating dark matter, in the form of a perfect fluid. Comparing the relative deviations in Sagnac time calculated for these metrics in the reference frame of satellites orbiting our star, which serve as a rotating circular platform and emit laser beams in opposite directions, with the precision of onboard atomic clocks (about 10−11), allows us to evaluate the potential for detecting dark matter’s gravitational influence through this effect.

Frequency and amplitude dependence of nuclear displacement and phase delay in mechanical vibrations for determining cellular natural frequency

Cultured cells biochemically respond to mechanical vibrations. However, the mechanisms of sensing mechanical vibrations and transducing biochemical responses remain unclear. A previous study reported that the expression of the alkaline phosphatase gene of osteoblastic cell under mechanical vibrations peaks at 50 Hz, which seems like a resonance curve in the mechanical vibration theory. Since forced displacement excitation is a dynamic mechanical stimulus that differs from other static mechanical stimuli in that an external force is equivalent to inertia, force is apparently exerted on the mass element by considering the equation of motion. In this study, the method for obtaining the change of a nucleus’s relative displacement to an excited dish was refined, and the frequency and acceleration amplitude dependence of the nucleus’s relative displacement and phase delay under mechanical vibrations was demonstrated by regarding a cell model as a vibration system. The change of the relative displacement of a HeLa nucleus to an excited dish decreases with increasing frequency in the 12.5–100 Hz range at 0.5 G and increases with increasing acceleration amplitude in the 0.5–2.0 G range at 50 Hz. Phase reversal occurs between 12.5 Hz and 50 Hz, which suggests the existence of the natural frequency of the cell between 12.5 Hz and 50 Hz. The single actin filament tension estimated from the nucleus’s relative displacement change was 2.3–10 pN and can be a biochemical response of the mechanotransducer. These findings can contribute to clarifying the mechanism of cell mechanotransduction in dynamic mechanical stimuli.

Image formation near hyperbolic umbilic in strong gravitational lensing

Hyperbolic umbilic (HU) is a point singularity of the gravitational lens equation, giving rise to a ring-shaped image formation made of four highly magnified images, off-centred from the lens centre. Recent observations have revealed new strongly lensed image formations near HU singularities, and many more are expected in ongoing and future observations. Like fold/cusp, image formations near HU also satisfy magnification relation (), i.e., the signed magnification sum of the four images equals zero. Here, we study how deviates from zero as a function of area () covered by the image formation near HU and the distance ( d) of the central maxima image (which is part of the HU image formation) from the lens centre for ideal single- and double-component cluster-scale lenses. For lens ellipticity values ≥0.3, the central maxima image will form sufficiently far from the lens centre ( d≳5″), similar to the observed HU image formations with . We also find that, in some cases, double-component and actual cluster-scale lenses can lead to large cross-sections for HU image formations for sources at z≳5, effectively increasing the chances to observe HU image formation at high redshifts. Finally, we study the time delay distribution in the observed HU image formation, finding that not only are these images highly magnified, but the relative time delay between various pairs of HU characteristic image formation has a typical value of ∼100 days, an order of magnitude smaller than generic five-image formations in cluster lenses, making such image formations optimal targets for time delay cosmography studies.

Breast cancer: do the current policies mean anything?

Aim Breast cancer remains one of the most prevalent malignancies globally with a high mortality rate. South Africa has a number of policies in place designed to ensure that minimum delays are experienced by patients from first symptom to initial treatment. This study was initiated to determine where the longest delays occurred during the patient’s journey, from the first symptom to the first treatment. This information, combined with the existing policy, identifies shortfalls in the breast cancer diagnostic and treatment pathways that must be addressed. Methods A cross-sectional study was undertaken in the Department of Medical Oncology, University of Pretoria/Steve Biko Academic Hospital between April 2020 and August 2021, analysing six timelines from first symptom to first treatment in patients with newly diagnosed breast cancer. Data was obtained by the researchers from the patients on their first visit relating to the delays experienced from first symptom to final biopsy. Clinical information was obtained from the patients’ source records once a treatment decision had been reached and treatment started where applicable. Results The longest delays experienced were between the patients’ first visit to any medical facility to date of diagnostic biopsy. Delays due to COVID-19 were in the minority with 13/79 (16.4%) patients reporting having experienced COVID-19 related delays. Key Area 2 of the Breast Cancer Prevention and Control Policy makes provision for patients to be referred directly to a regional/tertiary/quaternary medical facility for further screening, diagnosis and treatment within 21-60 days from the first visit. In the study’s cohort, a mean of four months from first visit to diagnostic biopsy was recorded. Overall delays of longer than 12 months due to non-representative biopsies (range 1-3) were recorded in three patients. Twenty-nine patients (36.7%) presented to three medical facilities prior to diagnostic biopsy with 10/79 (12.6%) and 1/79 (1.2%) presenting to four and five institutions, respectively, before the diagnostic biopsy. Conclusions The delays patients experienced highlights the lack of knowledge about the urgency and correct referral of suspected malignancy cases. Despite the number of promulgated policies relating to fast track systems via specialist breast units, fiscal and human capital deficiencies negatively impact the attempts to diagnose and treat patients timeously and increase survival.

Feasibility and acceptability of a caregiver-mediated early support program, delivered online, for infants at elevated familial likelihood for autism: A feasibility randomized controlled trial.

Preliminary evidence indicates potential benefit of providing caregiver-mediated intervention, prior to diagnosis, for infants at elevated familial likelihood for autism and related developmental delays including language delay (EL-A). However, delivering such interventions online and in low-resource settings like India has not been reported. This study aimed to evaluate the feasibility and acceptability of delivering a novel manualized caregiver-mediated early support program, the "LiL' STEPS," online in India, for EL-A infants. LiL' STEPS stands for Language development & Intervention Lab's (LiL') Supporting Early social-communication and language by Promoting caregiver Sensitive responsiveness (STEPS). The program comprised 14 sessions with a focus on social-communication and language, conducted over 12-weeks using demonstration and video feedback. Families of 36 EL-A infants aged 9 to 15-months participated in this feasibility randomized controlled trial (RCT). Families were randomized in a 2:1 ratio (n = 24 LiL' STEPS and n = 12 care as usual groups). Information on feasibility and acceptability was collated following a mixed methods approach from caregiver interviews, fidelity forms, session notes, and study register. Findings indicated the LiL' STEPS study trial as feasible and acceptable with recruitment rate of 4 per month, 100% willingness for randomization, 8.3% attrition, and 3.03% loss of blinding. Interventionist and caregiver fidelity was maintained above 80%. Despite challenges like interruptions during sessions, 100% families found the program acceptable and satisfactory, 86% said they would recommend the program to others, and 71% preferred online modality. Caregivers' perspectives on beneficial components and experience attending the program have been described. Accordingly, recommendations for future definitive RCTs have been presented.

Emission control of entangled electrons in photoionisation of a hydrogen molecule

For photo-dissociation of a single hydrogen molecule (H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_2$$\\end{document}) with combined XUV and IR laser pulses, we demonstrate optical control of the emission direction of the photoelectron with respect to the outgoing neutral fragment (the H-atom). Depending on the relative delay between the two laser fields, adjustable with sub-femtosecond time resolution, the photoelectron is emitted into the same hemisphere as the H-atom or opposite. This emission asymmetry is a result of entanglement of the two-electron final-state involving the spatially separated bound and emitted electron.

Exploring Delays in Cardiac Care Processes Through Electronic Health Records.

Cardiovascular diseases are the leading cause of death globally. Timely health services are fundamental to the appropriate prevention, identification, care and rehabilitation of these diseases. This study aimed to explore the potential of using electronic health records as a data source to help identify health system -related delays in care processes of cardiac patients. This retrospective registry study is based on a sample of electronic health records of 200 cardiac patients admitted to one out of twenty wellbeing services counties in Finland during the years 2021-2022. A total of 426 health system -related delays were identified. All expressions were found in unstructured format and most of these (58.7%) were generated by nurses. These results show that the electronic health records contained a variety of information on health system -related patient care delays, and that most delays were associated with difficulties in finding a bed for the patient in a post-acute care facility (49.8%), but also in-hospital process delays were common (27.7%). These findings show great potential for exploring electronic health record data with natural language processing methods in the future for the development of tools to better identify and monitor different types of delays in care processes. Such tools may support leadership to respond to organisational procedures in need of improvement.

Forecast of strongly lensed supernovae rates in the China Space Station Telescope surveys

Strong gravitationally lensed supernovae (SNe) are a powerful probe for cosmology and stellar physics. The relative time delays between lensed SN images provide an independent way of measuring a fundamental cosmological parameter --- the Hubble constant ---, the value of which is currently under debate. The time delays also serve as a ``time machine'', offering a unique opportunity to capture the extremely early phase of the SN explosion, which can be used to constrain the SN progenitor and explosion mechanism. Although there are only a handful of strongly lensed SN discoveries so far, which greatly hinders scientific applications, the sample size is expected to grow substantially with next-generation surveys. In this work, we investigate the capability of detecting strongly lensed SNe with the China Space Station Telescope (CSST), a two-meter space telescope to be launched around 2026. Through Monte Carlo simulations, we predict that CSST can detect 1008.53 and 51.78 strongly lensed SNe from its Wide Field Survey (WFS, covering 17,500 deg$^2$) and Deep Field Survey (DFS, covering 400 deg$^2$) over the course of ten years. In both surveys, about 35<!PCT!> of the events involve Type Ia SNe as the background sources. Our results suggest that the WFS and DFS of CSST, although not designed or optimized for discovering transients, can still make a great contribution to the strongly lensed SNe studies.

JWST Spectroscopy of SN H0pe: Classification and Time Delays of a Triply Imaged Type Ia Supernova at z = 1.78

SN H0pe is a triply imaged supernova (SN) at redshift z = 1.78 discovered using the James Webb Space Telescope. In order to classify the SN spectroscopically and measure the relative time delays of its three images (designated A, B, and C), we acquired NIRSpec follow-up spectroscopy spanning 0.6–5 μm. From the high signal-to-noise spectra of the two bright images B and C, we first classify the SN, whose spectra most closely match those of SN 1994D and SN 2013dy, as a Type Ia SN. We identify prominent blueshifted absorption features corresponding to Si ii λ6355 and Ca ii H λ3970 and K λ3935. We next measure the absolute phases of the three images from our spectra, which allow us to constrain their relative time delays. The absolute phases of the three images, determined by fitting the three spectra to Hsiao07 SN templates, are 6.5−1.8+2.4 days, 24.3−3.9+3.9 days, and 50.6−15.3+16.1 days for the brightest to faintest images. These correspond to relative time delays between Image A and Image B and between Image B and Image C of −122.3−43.8+43.7 days and 49.3−14.7+12.2 days, respectively. The SALT3-NIR model yields phases and time delays consistent with these values. After unblinding, we additionally explored the effect of using Hsiao07 template spectra for simulations through 80 days instead of 60 days past maximum, and found a small (11.5 and 1.0 days, respectively) yet statistically insignificant (∼0.25σ and ∼0.1σ) effect on the inferred image delays.

Broadband rapid-scanning phase-modulated Fourier transform electronic spectroscopy.

We present a phase-modulated approach for ultrabroadband Fourier transform electronic spectroscopy. To overcome the bandwidth limitations and spatial chirp introduced by acousto-optic modulators (AOMs), pulses from a 1 µm laser are modulated using AOMs prior to continuum generation. This phase modulation is transferred to the continuum generated in a yttrium aluminum garnet crystal. Separately generated phase-modulated continua in two arms of a Mach-Zehnder interferometer interfere with the difference of their modulation frequencies, enabling physical under-sampling of the signal and the suppression of low-frequency noise. By interferometrically tracking the relative time delay of the continua, we perform continuous, rapid-scanning Fourier transform electronic spectroscopy with a high signal-to-noise ratio and spectral resolution. As proof of principle, we measure the linear absorption and fluorescence excitation spectra of a laser dye and various biological samples.

Robust Methods for Assessing the Characteristics of Locomotor Activity Based on Markerless Video Capture Data

Introduction. Analysis of locomotor activity is essential in a number of biomedical and pharmacological research designs, as well as environmental monitoring. The movement trajectories of biological objects can be represented by time series exhibiting a complex multicomponent structure and non-stationary dynamics, thus limiting the effectiveness of conventional correlation and spectral time series analysis methods. Recordings obtained using markerless technologies are typically characterized by enhanced noise levels, including both instrumental noise and anomalous errors associated with false estimates of the location of the points of interest, as well as gaps in the trajectories, promoting an urgent need in the development of robust methods to assess the characteristics of locomotor activity.Aim. Development of robust methods for assessing the characteristics of locomotor activity capable of efficient processing of noisy recordings obtained by markerless video-based motion capture systems.Materials and methods. In order to assess the characteristics of locomotor activity, the relative movements of body parts of laboratory animals were analyzed using the stability metrics of the mutual dynamics of their trajectories, their relative delays, as well as the relative duration of the recording fragments when relatively stable mutual dynamics could be observed. The local maxima of the cross-correlation function of two body fragments, the minima of the standard deviation of the difference between their Hilbert phases, as well as their relative delays, were used as the metrics of mutual dynamics.Results. The considered phase metrics were shown to explicitly reflect changes in locomotor activity, while the assessment of time delays using phase metric was shown to be prone to periodic error. The above limitation could be largely overcome using the correlation metrics, assuming that phase and correlation metrics could be combined.Conclusion. The proposed robust methods provide stable estimates of the characteristics of locomotor activity based on markerless video capture recordings, altogether increasing the efficiency of diagnostic procedures and assessment of the therapeutic effect during rehabilitation.

A large-aperture, high-power ultrawideband radiation system with beam broadening capacity.

Due to the limited maximum output power of the pulsers based on avalanche transistors, high-power ultrawideband (UWB) radiation systems usually synthesize plenty of modules simultaneously to achieve a high peak effective potential (rEp). However, this would lead to an increased aperture size as well as a narrower beam, which would limit their applications in intentional electromagnetic interference fields. In this paper, a high-power UWB radiation system with beam broadening capacity is developed. To achieve beam broadening in the time domain, a power-law time delay distribution method is proposed and studied by simulation, and then the relative excitation time delays of the modules are optimized to achieve higher rEp and avoid beam splitting in the beam broadening mode. In order to avoid false triggering of the pulser elements when implementing the beam broadening, the mutual coupling effect in the system is analyzed and suppressed by employing onboard high-pass filters, since the mutual coupling effect is much more severe in the low-frequency range. Finally, a radiation system with 36 modules is developed. Measuring results indicate that in the high-rEp mode, the developed system could achieve a maximum effective potential rEp of 313.6kV and a maximum pulse-repetition-rate of 20kHz. In the beam broadening mode, its half-peak-power beam width in the H-plane is broadened from the original value of 3.9° to 7.9°, with a maximum rEp of 272.9kV. The polarization direction of the system could be flexibly adjusted by a built-in motor.

Highly versatile, two-color setup for high-order harmonic generation using spatial light modulators.

We present a novel, interferometric, two-color, high-order harmonic generation setup based on a turn-key Ytterbium-doped femtosecond laser source and its second harmonic. Each interferometer arm contains a spatial light modulator with individual capabilities to manipulate the spatial beam profiles and to stabilize the relative delay between the fundamental and the second harmonic. In addition, separate control of the relative power and focusing geometries of the two color beams is implemented to conveniently perform automated scans of multiple parameters. A live diagnostics system gives continuous information during ongoing measurements.

Supernova Explosions of the Lowest-mass Massive Star Progenitors

We here focus on the behavior of supernovae that technically explode in 1D (spherical symmetry). When simulated in 3D, however, the outcomes of representative progenitors of this class are quite different in almost all relevant quantities. In 3D, the explosion energies can be 2 to 10 times higher, and there are correspondingly large differences in the 56Ni yields. These differences between the 3D and 1D simulations reflect in part the relative delay to explosion of the latter and in the former the presence of protoneutron star convection that boosts the driving neutrino luminosities by as much as ∼50% at later times. In addition, we find that the ejecta in 3D models are more neutron-rich, resulting in significant weak r-process and 48Ca yields. Furthermore, we find that in 3D the core is an interesting, though subdominant, source of acoustic power. In summary, we find that though a model might be found theoretically to explode in 1D, one must perform supernova simulations in 3D to capture most of the associated observables. The differences between 1D and 3D models are just too large to ignore.

Treacher Collins Syndrome (mandibulofacial dysostosis) – A case report

Background. Treacher-Collins Syndrome (TCS) (or mandibulofacial dysostosis) is a rare autosomal dominant genetic disorder involving 1st and 2nd branchial arches present with craniofacial deformities with variable expressivity. TCS commonly manifests as facial dysmorphism with varied presentations. In this case report, we demonstrate the typical CT (Computed Tomography) findings of the characteristic features. Case report. Here, we report an 8-year-old boy who presented for evaluation of uneven facial features. Upon a multidisciplinary evaluation, he was diagnosed with TCS, and the characteristic radiological features are described in this report. Conclusions. TCS has a variable degree of phenotypic expression with no related developmental delay or neurologic disorder. Proper counselling, planning, and surgical procedures are necessary for more promising results.

A Controllable Response Power Beam Localization Method and System Implementation

Sound source localization technology has gradually become one of the main methods for fault source target localization in dangerous and difficult-to-discover applications. In order to locate the target fault sound source more intuitively, accurately and in real time in practical applications, an audio-visual positioning system is developed. A 64-channel microphone array is designed, which is evenly distributed in a circular shape, and has a video acquisition target at the same time. The system uses GCC-PHAT to estimate the relative time delay between the signal source arriving at two microphones, and then uses SRP-PHAT algorithm to obtain weighted sum beamforming. A spatial grid search strategy based on spherical coordinate spatial contraction method is proposed. When the output power is maximum, the direction corresponding to the beam is regarded as the sound source direction. Using the same sound source signal, the proposed positioning method is compared with the direct Newton iterative method and the Cartesian coordinate scanning SRP-based maximum method. The simulation results show that the Cartesian coordinate value and spherical coordinate value of the positioning algorithm in this article are closer to the real coordinates of the sound source position than the other two methods, and the positioning operation time is the shortest. In addition, in the actual corona discharge power source positioning experiment, the system can accurately locate the insulator pollution discharge point, which is consistent with the infrared detection and positioning results and has good robustness. Therefore, the system location method can provide a new choice for sound source location applications.

DNS root server resolution anomaly detection

The DNS root server is at the top of the hierarchical structure of the DNS system and is the initial node that bootstraps all DNS queries. If the root server resolves abnormally, all domain name resolutions will fail, and many users cannot access the Internet. For this reason, this paper detects the root server itself resolution anomalies and non-self resolution anomalies by constructing high-confidence root zone file and anomaly judgment rules. First, we use the weighted voting statistics method to build high-confidence root zone file by calculating the confidence of multi-source root zone files. Based on high-confidence root zone files, we construct three types of anomaly detection judgment rules: (1) root-side resolution anomaly judgment rules based on feature value matching, (2) response hijacking judgment rules by correlating response anomaly features and resolution routing information, (3) root zone file synchronization anomaly judgment rules by calculating the relative synchronization delay of multi-source root zone files. Finally, using three anomaly judgment rules, we perform anomaly detection on the root resolution data obtained by active measurement. Our detection results show that root zone file synchronization delay distributions of different root server instances vary greatly. Some instances even show minute-level convergence, resulting in incorrect resolution for some TLDs. We also detect one response hijacking incident for 2 TLDs resolution, caused by the domain takeover mechanism adopted by the ISP to reduce inter-domain traffic settlement and decrease resolution latency. Except for the unresponsive exception caused by network packet loss, no root-side resolution anomaly is found, indicating that there is no artificial manipulation of TLD resolution on the root server and reflecting the responsibility of each root server operator aiming to maintain global Internet interconnection. The detection results show that the detection rules proposed in this paper can effectively achieve the anomaly detection of root server resolution and help to maintain the health and stability of the DNS system.