Small Drift Research Articles

Simultaneous frequency and phase corrections of single-shot MRS data using cross-correlation.

The objective of this study was to propose a novel preprocessing approach to simultaneously correct for the frequency and phase drifts in MRS data using cross-correlation technique. The performance of the proposed method was first investigated at different SNR levels using simulation. Random frequency and phase offsets were added to a previously acquired STEAM human data at 7 T, simulating two different noise levels with and without baseline artifacts. Alongside the proposed spectral cross-correlation (SC) method, three other simultaneous alignment approaches were evaluated. Validation was performed on human brain data at 3 T and mouse brain data at 16.4 T. The results showed that the SC technique effectively corrects for both small and large frequency and phase drifts, even at low SNR levels. Furthermore, the mean square measurement error of the SC algorithm was comparable to the other three methods used, with much faster processing time. The efficacy of the proposed technique was successfully demonstrated in both human brain MRS data and in a noisy MRS dataset acquired from a small volume-of-interest in the mouse brain. The study demonstrated the availability of a fast and robust technique that accurately corrects for both small and large frequency and phase shifts in MRS.

Contourite-drift archive links Late Devonian bioevents with periodic anoxic shelf water cascading

Analysis of a Devonian contourite depositional system in the eastern Anti-Atlas of Morocco reveals the formation of widespread erosional hiatuses and organic-rich bioclastic contourites (ORCs) coinciding with the expansion of an anoxic water mass during Frasnian bioevents, ultimately culminating in the Kellwasser crisis (Frasnian-Famennian extinction event). The identified contourite terrace formed on the uppermost slope of the northern passive margin of Gondwana. Its inner part was bounded by an along-slope contourite channel and a small mounded drift at its downslope margin. Facies- and drift-scale contourite features evidence northwest-directed bottom currents driven by repeated overflows of dense, highly saline, anoxic water originating from the northern Gondwana Epicontinental Sea. These periodic overflows were channeled through the Ougarta trough, then deflected westward over the Tafilalt contourite terrace by the Coriolis force and cascaded downslope until reaching a density equilibrium level, probably forming an intermediate water mass. The cascading of dense, anoxic shelf water supports the photic-zone eutrophication (top-down) model proposed for the Kellwasser crisis and related Devonian anoxic events. We propose a direct link between the anoxic overflows and the Devonian evolutionary events.

Field stability of an Alvarez-type drift tube linear accelerator with small drift tubes

This study presents theoretical, simulation and experimental investigations of the field stability of a 7 MeV Alvarez-type drift tube linear accelerator (DTL) with small drift tubes (DTs). Although technical advances in permanent magnet quadrupoles make smaller DTs possible, resulting in higher shunt impedance, it is widely recognized that the DT-to-wall spacing must lie between ∼0.90 and ∼1.03 times a quarter wavelength (λ/4) to achieve field stability through post couplers (PCs). To enhance the shunt impedance of a DTL cavity, we decrease the outer diameter of the DTs and increase the inner diameter of the cavity, resulting in a DT-to-wall spacing of 1.16 times λ/4. A low-power experiment confirms that when the global tilt sensitivity slope is zero, the PC-to-DT distance is larger and there exists a stronger coupling between the PCs, resulting in a disturbed distribution of PC modes, where the frequencies of lower-order modes are overwhelmed by higher-order modes. The observed result is consistent with the analysis result given by the equivalent circuit theory and three-dimensional simulation. After field tuning by the trial-and-error method, the relative error of the axial electric field is within ±1.9% and the tilt sensitivity is within ±70%/MHz.

High-Resolution and Large-Dynamic Range Fiber-Optic Sensors Based on Dual-Mode Direct Spectrum Interrogation Method

Conventional optical fiber temperature/strain sensors often have to make compromises between the resolution and the dynamic range. Here we present a new method that meets the measurement requirements for both high resolution and large dynamic range. A high-quality optical fiber Fabry-Perot Interferometer (FPI) constructed using a pair of chirped fiber Bragg gratings is employed as the sensor and a dual-mode direct spectrum interrogation method is proposed to identify the small drift of external temperature or strain. As a proof-of-concept illustration, a temperature resolution of 0.2 °C within 30–130 °C is demonstrated. For strain sensing, the resolution can be 10 µε within 0–1000 µε. The measurement resolution can be improved further by routinely increasing the reflectivity of the CFBG and the cavity length and the sensor can also be mass-produced. This new sensing schema not only resolves the conflict between the resolution and the dynamic range of fiber-optic temperature/strain sensors but can also be extended to other sensors and measurands.

Seismic performance of recentering energy dissipation bracing with pendulum in prefabricated steel frame structure systems

This research introduces the recentering energy dissipation bracing with a pendulum in prefabricated steel frame (REBP-PSF) structures. The primary objective of this study is to mitigate potential severe damage to steel frames during seismic events and to expedite postearthquake rehabilitation. This innovative system harnesses energy dissipation through friction between structural members and facilitates recentering through the cable pretensioning force. Consequently, this may make postearthquake repairs minimal or even unnecessary. Three REBP-PSF structures and a prefabricated steel frame with cantilever beam splices (PSF-CBS) were meticulously modeled using the ABAQUS finite element method to evaluate the seismic performance of this novel system. The study investigated the effects of pretensioning parameters and varied structural morphologies on seismic performance metrics, including failure modes, hysteresis performance, energy dissipation capacity, and residual displacements. This paper introduced a simplified method to simulate the restoring force model of REBP using the connection element method. Subsequently, a model for the REBP-RSF overall structure was established, enabling nonlinear dynamic time-history analysis, which was then compared with the rigid steel frame (RSF) structure. The results showed that the REBP-PSF structure outperformed the PSF-CBS in terms of initial stiffness, yield load, ultimate load, and energy dissipation capability. The bearing and energy dissipation capacities of the REBP-PSF structure were enhanced by augmenting the cable pretensioning force within this structure. The proposed connection element method could accurately simulate the hysteretic behavior of REBP. Compared with the RSF structure, the REBP-RSF demonstrated superior seismic performance, characterized by small story drift and residual displacements during seismic activities. Furthermore, a notable augmentation was observed in the lateral stiffness and torsional rigidity of the proposed structure.

Reference-free dual-comb spectroscopy with inbuilt coherence.

We demonstrate a simple system for dual-comb spectroscopy based on two inherently coherent optical frequency combs generated via seeded parametric downconversion. The inbuilt coherence is established by making the two combs share a common comb line. We show that the inbuilt coherence makes it possible to use a simple numerical post-processing procedure to compensate for small drifts of the dual-comb interferogram arrival time and phase. This enables long-time coherent averaging of the interferograms.

Seismic behavior of precast segmental bridge columns confined by grouted glass fiber reinforced plastic tubes

The application of precast segmental bridge columns (PSBCs) is still restricted in seismicity areas due to concerns such as lower lateral stiffness and column base bearing capacity. To enhance the applicability of PSBCs, this study proposed a novel approach of confining them with grouted GFRP tubes. Four novel and one reference specimens were tested under low cyclic loading to evaluate the effects of energy dissipation (ED) bars ratios, concrete interlayer strength, type of segment concrete, and concrete pouring methods within the outer GFRP tube (OGT) on the seismic behavior. Experimental results reveal that the failure modes of all specimens were triggered by the yielding of ED bars and the break of OGT at the top of ED bars. No crushed concrete at column bases or cracks at the segment joint were observed during the test due to the good confinement of GFRP tubes. All the specimens exhibited stable hysteretic behavior with small residual drift ratios and low strength degradation. Furthermore, finite element models (FEMs) were generated to predict the hysteretic behavior of novel specimens. The effects of some parameters such as OGT thickness, ED bars diameter, and concrete strength were further studied.

Propagation characteristics of the Bessel-Gaussian beams in turbulent plasma sheath surrounding the hypersonic aerocraft

To investigate the transmission characteristics of the Bessel-Gaussian beams in a turbulent plasma sheath, the flow field around a hypersonic vehicle is numerically simulated and analyzed according to the Navier-Stokes (N-S) equation and turbulence model. Then, utilizing the characteristics of the thickness of the plasma flow field around the supersonic vehicle at the centimeters level, the double fast Fourier transform (D-FFT) algorithm based on the Fresnel diffraction integral is used for the first time to predict the propagation characteristics of the Bessel-Gaussian beams in the turbulent plasma sheath. The results show that the lower the height and the higher the velocity, the smaller the thickness of the plasma sheath shock layer. The refractive index variance, the wavelength and the waist-radius are essential factors affecting the transmission quality of the Bessel-Gaussian beams. When compared to the Gaussian beams, the Bessel-Gaussian beams have smaller drift and scintillation index, which have the advantage in suppressing turbulence.

A likelihood-based adaptive CUSUM for monitoring linear drift of Poisson rate with time-varying sample sizes

Several weighted cumulative sum (CUSUM) and adaptive CUSUM (ACUSUM) control charts have been developed to address the challenge of time-varying sample sizes in detecting the incidence rates of Poisson count data. However, the known post-drift parameters in the CUSUM chart make it less realistic. Additionally, the adaptive component in the ACUSUM chart cannot integrate with time-varying sample sizes naturally. Furthermore, the existing charts predominantly address step drift, neglecting linear drift. Hence, this study introduces a Poisson ACUSUM chart that considers both linear drift and integration issues. Detailed comparisons are made among the proposed control chart, CUSUM control charts, and other ACUSUM control charts. Results demonstrate the proposed method's superior robustness and ability to effectively detect small drifts. Finally, the empirical results of the mortality data are employed to further validate the effectiveness of the proposed method.

Generalize for Future: Slow and Fast Trajectory Learning for CTR Prediction

Deep neural networks (DNNs) have achieved significant advancements in click-through rate (CTR) prediction by demonstrating strong generalization on training data. However, in real-world scenarios, the assumption of independent and identically distributed (i.i.d.) conditions, which is fundamental to this problem, is often violated due to temporal distribution shifts. This violation can lead to suboptimal model performance when optimizing empirical risk without access to future data, resulting in overfitting on the training data and convergence to a single sharp minimum. To address this challenge, we propose a novel model updating framework called Slow and Fast Trajectory Learning (SFTL) network. SFTL aims to mitigate the discrepancy between past and future domains while quickly adapting to recent changes in small temporal drifts. This mechanism entails two interactions among three complementary learners: (i) the Working Learner, which updates model parameters using modern optimizers (e.g., Adam, Adagrad) and serves as the primary learner in the recommendation system, (ii) the Slow Learner, which is updated in each temporal domain by directly assigning the model weights of the working learner, and (iii) the Fast Learner, which is updated in each iteration by assigning exponentially moving average weights of the working learner. Additionally, we propose a novel rank-based trajectory loss to facilitate interaction between the working learner and trajectory learner, aiming to adapt to temporal drift and enhance performance in the current domain compared to the past. We provide theoretical understanding and conduct extensive experiments on real-world CTR prediction datasets to validate the effectiveness and efficiency of SFTL in terms of both convergence speed and model performance. The results demonstrate the superiority of SFTL over existing approaches.

Seismic strengthening of deficient ground soft-story RC frames with inadequate lap splice using chevron brace

Deficient RC frames with ground soft-story irregularity have been constructed in many countries. Past earthquakes have shown that such structures are vulnerable and must be retrofitted. This study investigated the cyclic response of two one-bay, two-story, 1/2.5-scaled RC frames with inadequate lap splice length through experimental works and numerical simulations. One of the frames was kept as the reference, and the other was strengthened using a chevron brace system. The frames were subjected to displacement-controlled quasi-static cyclic loading, and their cyclic responses were recorded and compared. Besides, the lumped plasticity model was used to investigate the effect of the strength of infill walls on the force-displacement response of the retrofitted frame. The experimentally obtained results indicated that the employed chevron brace system significantly enhanced the cyclic response of the reference frame. The retrofitted frame exhibited a 171% greater ultimate strength than the reference frame. Besides, the retrofitted frame's initial and post-yield stiffness were 2.2 and 6.9 times greater than that of the reference frame. At a 3.5% drift ratio, the retrofitted frame dissipated 233% more energy than the reference frame. In small drift ratios, the retrofitted frame exhibited a faster decay in the lateral stiffness; however, at large drift ratios, both frames showed a comparable stiffness degradation rate. Numerical simulations showed that the infill wall's lateral strength could alter the retrofitted frame's failure mode and significantly affect its force-displacement response.

Dense Stacking of Millimeter‐Sized Perovskite Single Crystals for Sensitive and Low‐Bias Hard X‐Ray Detection

AbstractMetal halide perovskite single crystals are promising for hard X‐ray detection, but growth of large‐sized thin single crystals and inhibition of halide ion migration under high bias are challenging. Herein, the preparation of dense stacking of oriented millimeter‐sized perovskite single crystals with capability of large‐area fabrication, controlled thickness, and high ion migration activation energy (Ea)is reported. The oriented growth results in absence of grain boundaries parallel with the substrates, leading to large carrier mobility‐lifetime (µτ) product of 2.7 × 10−3 cm2 V−1, which is comparable to values of many perovskite bulk single crystals. Under low bias, hard X‐ray detectors exhibit high sensitivity of 1.2 × 104 µC Gy−1 cm−2 and low detection limit of 87.5 nGy s−1, which are comparable to those of many single‐crystal hard X‐ray detectors under high bias. Moreover, combination of low bias and high Ea results in weak halide ion migration and small dark current drift of 3.2 × 10−4 nA cm−1 s−1 v−1. Benefited from the superior detector performance, high‐contrast hard X‐ray imaging can be obtained at a low dose rate of 1.26 µGy s−1. The work may promote the application of perovskite hard X‐ray detectors in practical imaging area.

Dynamics of Lotka-Volterra Competition Patch Models in Streams with Two Branches.

Streams may have many branches and form complex river networks. We investigate two competition patch models associated with two different river network modules, where one is a distributary stream with two branches at the downstream end, and the other is a tributary stream with two branches at the upstream end. Treating one species as resident species and the other one as mutant species, it is shown that, for each model, there exists a invasion curve such that the mutant species can invade when rare if and only if its dispersal strategy is below this curve, but the shapes of the invasion curves are different. Moreover, we show that the global dynamics of the two models can be similar or different depending on river networks. Especially, if the drift rates of the two species are equal, then the global dynamics are similar for small drift rate and different for large drift rate. Our results also confirm a conjecture in Jiang et al. (Bull Math Biol 82:131, 2020).

Исследование кварцевых резонаторов в миниатюрных металлокерамических корпусах с целью дальнейшего применения в термокомпенсированных генераторах

With the advent of new technologies, the requirements for the sources of reference vibrations are becoming more stringent. They must be compact, quickly reach frequency, operate in a wide temperature range and have a small relative frequency drift in the operating temperature range. Changes in ambient temperature are the most destabilizing factor for the oscillator output frequency. Ensuring frequency stability over a wide temperature range is a pressing task. Thermal compensation allows increasing frequency stability over a wide range of operating temperatures. This is achieved by compensating for the effect of the destabilizing factor on the generator so that the frequency drift tends to zero as the temperature changes. Temperature-compensated quartz oscillators are highly stable and have a short readiness time. However, to create generators with a frequency stability of ± 0,1 ppm, imported components are required, which makes their production difficult in modern conditions. A technological chain is created at the JSC «LIT-PHONON», which allows producing a quartz resonator using only Russian components. The goal is to use these resonators in temperature-compensated oscillators with frequency stability of ± 0,1 ppm. However, the analysis showed that the resonators have problems with frequency drift over time during operation at a maximum operating temperature of + 85 ºС. Additional adjustment of generators during operation is required. It is also revealed that some Russian components are not ideally suited to the developed technological process, which may negatively affect the yield of suitable products. The measuring setup also has an error of ± 0,5 ppm, which does not allow an accurate assessment of the frequency stability of the resonators.

Assessing the acclimatisation to the wild of stocked European graylings Thymallus thymallus by monitoring lipid dynamics and food consumption

This study investigated how 2+-year-old stocked pond-reared European graylings (Thymallus thymallus) acclimatised to a wild environment during six months (May–October 2019) after released. We examined the quantity and composition of lipids in the liver, muscles and visceral adipose tissues (VAT), as well as size parameters, condition factors and stomach contents. Our results showed a low post-stocking recapture rate (5.17%) of stocked fish after 6 months suggesting a poor acclimation to the wild environment. During the six months of monitoring, stocked fishes exhibited a sharp decrease in lipid content in all examined tissues, and, in the final month, lipid content was well below those of wild conspecifics. Stocked graylings preferred risky foraging behaviour and consumed numerous small drift preys with occasional hyperphagic events, thus experiencing strong bioenergetic challenges. Our study reveals that fish cultivated for extended periods struggle to acclimatise to the wild environment and that this commonly used stocking practice seems unsuccessful when aimed at strengthening wild grayling populations.

Effect of the axial compression ratio on the seismic behavior of resilient concrete walls with concealed column stirrups

Abstract The axial compression ratio is one of the important factors affecting the seismic performance of reinforced concrete (RC) walls. Thus, the axial compression ratio is critical in the seismic design of RC walls. In addition to the axial compression ratio, the other significant experimental parameter is the stirrup form of the boundary elements. To study the effect of the axial compression ratio and the stirrup form on the seismic behavior of ductile RC walls reinforced by prestressed concrete strands, four full-scale concrete walls were constructed and subjected to reversed cyclic lateral loading while experiencing constant axial compression, with axial load ratios set at 0.17 and 0.26. The considered stirrup forms of the boundary elements are circular and compound, respectively. All specimens exhibit significant drift-hardening capability with a small residual drift and a small crack width. The ultimate capacity, ductility, stiffness and attenuation process, hysteretic characteristics, energy dissipation capacity, residual deformation, and maximum and residual crack width of the shear walls are compared and analyzed. The experimental results and comparisons between the two groups of shear walls with different axial compression ratios and stirrup forms of concealed columns are presented. The characteristics of the envelope curve are also analyzed, and a simplified bilinear envelope curve model is proposed to better fit the test results.

Experimental investigation of deficient RC frames retrofitted by RSFJ-toggle bracing systems

This paper investigates the performance of the new retrofitting system, consisting of self-centreing damper resilient slip friction joint (RSFJ)-toggle bracing system. The RSFJ-toggle bracing system can be activated within small drift values of the frame and preserve the frame from excessive damage. Two scaled deficient RC frames representing typical pre-1970s RC moment resisting frames were constructed and tested to investigate the performance of such retrofitting system. Material testing of the concrete and steel rebars as well as the damper component testing were conducted and recommendations regarding the proper design of various aspects of this retrofitting system were provided. The experimental observations demonstrate the improved behaviour of the frame in terms of energy dissipation and enhanced stiffness and strength for the upgraded RC frame. As per the findings of this study, the proposed retrofit solution can strengthen the frames within a limited drift and improve the frame’s damping with a repeatable semi-flag shape hysteresis performance.

Unidirectional Electron-Tunnelling Flexible PDMS Strain Sensor with Aligned Carbon Nanotubes.

High-aspect-ratio carbon nanotubes can be directly mixed into polymers to create piezoresistive polymers. Reducing the cross-sensitivity and creating unidirectional sensitive sensors can be achieved by aligning the nanotubes before they are cured in the polymer layer. This research presents and characterises this alignment of carbon nanotubes inside polydimethylsiloxane and gives the corresponding strain sensor results. The influence on the alignment method, as well as the field strength, frequency and time is shown. An analytical model is created to investigate the sensor's behaviour and determine the effect of electron-tunnelling in the sensor. A numerical model gives insight into the necessary applied field strength, frequency and time to facilitate alignment in viscous liquids. The experimental data show a two-phase piezoresistive response; first, a linear strain response, after which the more dominant electron-tunnelling piezoresistive phase starts with high gauge factors up to k ≈ 4500 in the preferential direction, depending on the carbon nanotube concentration. Gauge factors in the orthogonal direction remain low (k ≈ 22). Finally, the dynamic stability of the sensors is proven by exposing the sensors to a cyclic strain. Small initial drifts are observed but appear to stabilise after several cycles.

Thermal stability and high speed for optoelectronic hybrid phase-change memory based on Cr doped Ge2Sb2Te5 thin film

Non-volatile memory, which can simultaneously store data and compute in memory, is a promising candidate to break through “memory bottleneck”. However, its operation speed and thermal stability are still contradictory and difficult to meet the requirement of in-memory computing especially in high-temperature applications. In this work, optoelectronic hybrid phase-change memory based on Cr doped Ge2Sb2Te5 material is proposed, where the picosecond laser is used to perform the information recording/erasing operation based on the reversible phase-change characteristics while resistance signal is detected to realize the information readout. Results imply that the Cr doped Ge2Sb2Te5 film with Cr concentration of 10.7 at. % has high crystallization temperature (289 °C) and ten-year data-retention temperature (221 °C), low density-change rate (2.3%) and small resistance drift coefficients (0.022 at 85 °C, 0.056 at 120 °C, 0.070 at 150 °C, and 0.00131 for the laser induced SET state). The corresponding memory device has the SET/RESET operation speeds of as fast as 1820 ps/13 ps accompanied by the RESET/SET resistance ratio of higher than two orders of magnitude. The structural analyses indicate that Cr doping can suppress the growth of grains and reduce the grain size, improving the thermal stability of amorphous Ge2Sb2Te5 thin film while the octahedral/defective octahedral motif ensures its fast phase-change speed. Therefore, Cr doped Ge2Sb2Te5 based optoelectronic hybrid phase-change memory with superior thermal stability and ultrafast operation speed may be one of the promising solutions for in-memory computing.

X-Site Substituted 2D Cs2 Pb(SCN)2 Br2 Perovskites for X-Ray Detection.

2D Ruddlesden-Popper (RP) perovskites have been intensively investigated due to their superior stability and outstanding optoelectrical properties. However, investigations on 2D RP perovskites are mainly focused on A-site substituted perovskites and few reports are on X-site substituted perovskites especially in X-ray detection field. Here, X-site substituted 2D RP perovskite Cs2 Pb(SCN)2 Br2 polycrystalline wafers are prepared and systematically studied for X-ray detection. The obtained wafers show a large resistivity of 2.0 × 1010 Ω cm, a high ion activation energy of 0.75eV, a small current drift of 2.39 × 10-6 nA cm-1 s-1 V-1 , and charge carrier mobility-lifetime product under X-ray as high as 1.29 × 10-4 cm2 V-1 . These merits enable Cs2 Pb(SCN)2 Br2 wafer detectors with a sensitivity of 216.3 µC Gyair -1 cm-2 , a limit of detection of 42.4 nGyair s-1 , and good imaging ability with high spatial resolution of 1.08 lp mm-1 . In addition, Cs2 Pb(SCN)2 Br2 wafer detectors demonstrate excellent operational stability under high working field up to 2100V cm-1 after continuous X-ray irradiation with a total dose of 45.2 Gyair . The promising features such as short octahedral spacing and weak ion migration will open up a new perspective and opportunity for SCN-based 2D perovskites in X-ray detection.