Offset Fluctuations Research Articles

Mass transfer and mixing performance in jet-to-counterflow micromixer

As an important component of the fine organic microreaction system, micromixers can realize efficient mixing of different fluids within a short distance. In spite of great progress in micromixer design for high mixing performance over the last decade, micromixers are limited by the narrowness of channels, making it impossible to operate at high throughputs. Here, we propose a novel jet-to-counterflow (JTC) micromixer, which is based on the offset fluctuation jet mechanism to build a jet-to-counterflow zone and an annular liquid film zone to promote the rapid and efficient mixing of fluids. Micro-PIV and dye visualization experiments are used to investigate the internal flow behaviors and mixing performance of the JTC micromixer. The results show that in the “jet-to-counterflow mixing zone”, the jet undergoes the transition of three flow regimes i.e. “no offset jet − stable offset jet − fluctuating offset jet” with the increase of Re under the effects of wall effect and fluid inertia. When Re = 100, the fluctuating offset jet enhances the internal perturbation, which promotes the mixing index of the micromixer within 3 mm up to 78 %. In addition, the fluctuating offset jet intensifies the disturbance of the fluid flow in the annular liquid film zone, which further enhances the fluid mixing. A mixing efficiency of 97 % is achieved in mixing experiments over flow rates ranging from 0.075 – 37.66 mL/min−1. Our results demonstrate that fluctuating offset jet can be used to enhance microfluidic internal perturbation and mixing, which provide new insights into the design of novel micromixers.

Laser frequency stabilization in the 10 -14 range via optimized modulation transfer spectroscopy on the 87Rb D2 line.

We present a high-performance laser frequency stabilization method using modulation transfer spectroscopy (MTS) on the rubidium 87D2 transition line. A substantial improvement of the laser frequency stability was achieved by searching for the optimal diameter and intensity settings of the probe and pump beam. The frequency instability measured from the beat frequency of two locked external cavity diode lasers (ECDLs) reached a short-term stability of 4.5×10-14/τ and did not exceed 2 × 10-12 until 105 s, which is the best performance reported thus far with a D2 transition. The long-term stability is limited by the offset fluctuations of the baseline induced by the residual amplitude modulation (RAM), which can be further improved by reducing the current temperature variation of about 0.2 K by means of temperature stabilization or through a further reduction of the RAM.

Remote Photonic THZ Generation Using an Optical Frequency Comb and Multicore Fiber

This paper proposes and demonstrates a photonic THz generation technique based on an optical frequency comb and multicore fiber (MCF) transmission, with the advantage of remote generation with great reconfigurability and reduced digital signal processing (DSP). The feasibility of the proposed technique is evaluated experimentally comparing the performance when transmitting a data wavelength and a local oscillator for optical heterodyning over a single core or over different cores in a 1-km MCF link. The proposed remote photonic THz generation technique is demonstrated employing a 16QAM 12.5 GBd signal. A short wireless transmission at 183 GHz center frequency with 0.25 m antenna-separation is achieved after 1 km MCF, meeting the soft-decision decision forward error correction (SD-FEC) bit error rate (BER) recommendation of 210-2. The analysis includes the received photocurrent range for which the BER meets the standard hard-decision forward error correction (HD-FEC) recommendation of 3.810-3 BER. The BER performance is analyzed considering different DSP configurations, with and without frequency offset estimation (FOE) and decision-driven least mean squares (DD LMS) equalization. The performance of the remote photonic THz generation technique is evaluated comparatively against traditional free-running laser transmission over MCF, confirming the advantage of using comb generation to reduce the frequency offset fluctuation and simplify the DSP.

Accuracy assessment of the CNAO dose delivery system in the initial period of clinical activity and impact of later improvements on delivered dose distributions.

A retrospective analysis of the dose delivery system (DDS) performances of the initial clinical operation at CNAO (Centro Nazionale di Adroterapia Oncologica) is reported, and compared with the dose delivery accuracy following the implementation of a position feedback control. Log files and raw data of the DDS were analyzed for every field of patients treated with protons and carbon ions between January 2012 and April 2013 (~3800 fields). To investigate the DDS accuracy, the spot positions and the number of particles per spot measured by the DDS and prescribed by the treatment planning system were compared for each field. The impact of deviations on dose distributions was studied by comparing, through the gamma-index method, 2 three-dimensional (3D) physical dose maps (one for prescribed, one for measured data), generated by a validated dose computation software. The maximum gamma and the percentage of points with gamma≤1 (passing volume) were studied as a function of the treatment day, and correlated with the deviations from the prescription in the measured number of particles and spot positions. Finally, delivered dose distributions of same treatment plans were compared before and after the implementation of a feedback algorithm for the correction of small position deviations, to study the effect on the delivery quality. A double comparison of prescribed and measured 3D maps, before and after feedback implementation, is reported and studied for a representative treatment delivered in 2012, redelivered on a polymethyl methacrylate (PMMA) block in 2018. Systematic deviations of spot positions, mainly due to beam lateral offsets, were always found within 1.5mm, with the exception of the initial clinical period. The number of particles was very stable, as possible deviations are exclusively related to the quantization error in the conversion from monitor counts to particles. For the chosen representative patient treatment, the gamma-index evaluation of prescribed and measured dose maps, before and after feedback implementation, showed a higher variability of maximum gamma for the 2012 irradiation, with respect to the reirradiation of 2018. However, the 2012 passing volume is >99.8% for the sum of all fields, which is comparable to the value of 2018, with the exception of one day with 98.2% passing volume, probably related to an instability of the accelerating system. A detailed retrospective analysis of the DDS performances in the initial period of CNAO clinical activity is reported. The spot position deviations are referable to beam lateral offset fluctuations, while almost no deviation was found in the number of particles. The impact of deviations on dose distributions showed that the position feedback implementation and the increased beam control capability acquired after the first years of clinical experience led to an evident improvement in the DDS stability, evaluated in terms of gamma-index as a measure of the impact on dose distributions. However, the clinical effect of the maximum gamma variability found in the 2012 representative irradiation is mitigated by averaging along the number of fractions, and the high percentage of passing volumes confirmed the accuracy of the delivery even before the feedback implementation.

Optimal Sizing of Small Scale Liquefied Natural Gas Storage using Numerical Cascade Pinch Analysis

Increasing demand for liquefied natural gas (LNG) at the inaccessible area through pipeline has provided a solid platform for the emergence of new small scale LNG (ssLNG). The key challenges related to the ssLNG business are relatively expensive supply chain due to the diseconomy of small scale and meeting the security of supply and demand with limited supply alternatives available. Nevertheless, the market has increasingly become the preferred delivery method for natural gas (NG) because LNG can be produced at remote locations and distributed to end-users conveniently. To date, extensive works with a variety of objectives have been developed in an attempt to optimise the ssLNG supply chain in terms of conversion, transportation, and utilisation yet an optimal synthesis of LNG for small scale market has not been adequately investigated. The activity of loading and unloading of LNG in supply port terminals needs sufficient capacity of LNG storage tank. Designing an adequate capacity is necessary in order to secure reliable supplies of LNG as well as to offset fluctuations in the supply and demand of LNG. This work aims to ease industrial planner to design an optimal capacity of ssLNG storage by implementing a well established numerical cascade approach based on Pinch Analysis technique and proposed a new numerical approach of small scale LNG-Storage Cascade Analysis (ssLNG-SCA). Based on the proposed tool, the minimum amount of LNG supply for operation has been reduced from 2,100 m3 to 1,400 m3 due to the stored amount of excess LNG supply (700 m3) during start-up with the existence of ssLNG storage tank. The developed ssLNG-SCA in this work shows a significantly reduced storage capacity from 24,000 m3 to 6,300 m3 thus eliminate the need to provide for a larger and higher price of LNG storage tank. The storage offers delivery of NG to virtual trading hubs to meet end-user demand which inaccessible to the high-pressure pipeline.

Design and Development of a Reduced Form-Factor High Accuracy Three-Axis Teslameter

A novel three-axis teslameter and other similar machines have been designed and developed for SwissFEL at the Paul Scherrer Institute (PSI). The developed instrument will be used for high fidelity characterisation and optimisation of the undulators for the ATHOS soft X-ray beamline. The teslameter incorporates analogue signal conditioning for the three-axes interface to a SENIS Hall probe, an interface to a Heidenhain linear absolute encoder and an on-board high-resolution 24-bit analogue-to-digital conversion. This is in contrast to the old instrumentation setup used, which only comprises the analogue circuitry with digitization being done externally to the instrument. The new instrument fits in a volumetric space of 150 mm × 50 mm × 45 mm, being very compact in size and also compatible with the in-vacuum undulators. This paper describes the design and the development of the different components of the teslameter. Performance results are presented that demonstrate offset fluctuation and drift (0.1–10 Hz) with a standard deviation of 0.78 µT and a broadband noise (10–500 Hz) of 2.05 µT with an acquisition frequency of 2 kHz.

Ultra‐low‐voltage low‐power dynamic comparator with forward body bias scheme for SAR ADC

An ultra-low-voltage two-stage dynamic comparator is proposed with a forward body bias (FBB) scheme for successive approximation register (SAR) analogue-to-digital converters (ADCs). The proposed FBB scheme for a preamplifier and latch stage reduces the delay time remarkably under a low supply voltage. At 0.4 V, the power consumption is 4.48 nW, and the delay can be decreased to 593.9 ns for ΔV in = 0.1 mV and f clk = 100 kHz. The RMS equivalent input-referred noise of the comparator is 0.136 mV. The total offset is 13.7 mV, and offset fluctuation is 0.183 mV with the proposed structure. Both the input-referred noise and offset fluctuation are <0.5 least-significant bit for a 10-bit SAR ADC at 0.4 V.

Robust interferometry against imperfections based on weak value amplification

The optical interferometry has been widely used in various high precision applications. Usually, the minimum precision of an interferometry is limited by various technique noises in practice. To suppress such kind of noises, we propose a novel scheme, which combines the weak measurement with the standard interferometry. The proposed scheme dramatically outperforms the standard interferometry in the signal noise ratio and the robustness against noises caused by the optical elements' reflections and the offset fluctuation between two paths. A proof-of-principle experiment is demonstrated to validate the amplification theory.

Frequency stability characterization of a quantum cascade laser frequency comb

AbstractOptical frequency combs generated by quantum cascade lasers have recently been demonstrated in the mid and far infrared, but a detailed analysis of the possibility of a fine control of the emission to use them for high‐resolution spectroscopy and metrology applications is still missing. In this manuscript the attempt of frequency stabilizing a mid‐infrared quantum cascade laser comb (QCL‐comb) against a metrological mid‐infrared intracavity‐difference‐frequency‐generated comb through a single phase‐locking chain acting on the driving current is presented. Following a brief derivation, simple relations between the QCL‐comb frequency parameters and optical quantities such as the refractive index have been found and used to observe how the locking affects the physics of the system. The conclusion is that the current locking essentially acts on the effective refractive index to reduce the offset fluctuations (common noise), but does not sensitively affect the group refractive index and the mode spacing. Nonetheless, the overall single QCL‐comb tooth linewidth is reduced from 500 kHz down to values ranging from 1 to 23 kHz on a 40 ms time scale. image

Conceptual study of axial offset fluctuations upon stepwise power changes in a thorium–plutonium core to improve load-following conditions

The increased share of renewable energy, such as wind and solar power, will increase the demand for load-following power sources, and nuclear reactors could be one option. However, during rapid load-following events, traditional UOX cores could be restricted by the volatile oscillation of the power distribution. Therefore, a conceptual study on stability properties of Th-MOX PWR concerning axial offset power excursion during load-following events are investigated and discussed. The study is performed in SIMULATE-3 for a realistic PWR core (Ringhals-3) at the end of cycle, where the largest amplitude of the axial offset oscillations is expected. It is shown that the Th-MOX core possesses much better stability characteristics and shorter reactor dead time compared with a traditional UOX core, and the main reasons are the lower sensitivity to perturbations in the neutron spectrum, lower xenon poisoning and lower thermal neutron flux.

Cattle Ranchers and Agritourism in Oregon, USA: Motivations, Challenges and Opportunities from the Landowner's Perspective

Cattle ranches are cultural icons in many countries. Still, high costs to maintain ranches may force some ranchers to sell their operation. One income alternative is to diversify into agritourism. Empirical research on ranch agritourism is scarce. This study provides an overview of, and assesses the motivations for, and challenges to diversifying into agritourism from the ranchers' perspective. A survey of 400 Oregon ranchers in 2003 found that 21% of 177 respondents promoted agritourism and that it contributed 8% to their annual household income compared to an 84% contribution from livestock production. Working on the ranch and hunting/fishing were the most popular agritourism activities. Main motivations to diversify were to utilize ranch resources, capture additional income, and offset fluctuations in income. Key barriers were insurance and liability, lack of time, regulations, and lack of financial assistance and resources. Agritourism was a success for 79% of those involved; 73% of guests were repeat customers and 38% learned about the operation from friends and family. Most guests (82%) were from Oregon. Findings suggest that agritourism can be compatible with ranching and can help ranches to remain viable. Despite low adoption numbers at the time of this study, agritourism initiatives are likely to increase.

Threshold-variation-enhanced adaptability of response in a nanowire field-effect transistor network

Stochastic resonance in a summing network with varied thresholds was investigated using GaAs-based etched nanowire field-effect transistors having different threshold voltages. The network’s response adapted to input offset fluctuations in the range of the threshold voltage variation and the network could detect a weak signal without any adjustment of the input offset or the addition of high noise. The observed adaptability resulted from a widened dynamic range of the system due to signal decomposition and reconstruction by multiple thresholds together with the output summation process.

Novel dry electrodes for ECG monitoring

The development, fabrication and characterization of two novel dry bioelectrodes—conductive and capacitive ones—for biopotential monitoring are presented. The new electrodes have the potential to improve the applicability of dry electrodes in ambulant recording of ECG by reducing motion artifacts as well as the contact impedance to the skin. Furthermore, a passive filter network is integrated into the new electrodes to suppress slow offset fluctuation of the ECG signal caused e.g. by motions like breathing or changes in the electrode–skin interface properties. Compared to standard gel electrodes these new electrodes exhibit equivalent and superior contact impedances and biosignals. The integrated filter network effectively suppresses fluctuating offset potentials.

A background comparator calibration technique for flash analog-to-digital converters

This paper presents a background calibration technique for trimming the input-referred offsets of the comparators in a flash analog-to-digital converter (ADC) without interrupting the ADC's normal operation. For a random-chopping comparator, the polarity of its offset is detected by observing the code density of its comparison results. Binary feedback is then used to digitally adjust the comparator's offset so that the offset is minimized. All calibration procedures are performed in the digital domain. The calibration performance is characterized by the converging speed of the feedback loop and the offset fluctuation due to the disturbance of the ADC's input. These two performance indexes of a background-calibrated comparator (BCC) are determined by three parameters: the probabilistic distribution of the ADC's input, the BCC's offset quantized step size, and the threshold of an internal bilateral peak detector. The offset fluctuation of a BCC can be drastically reduced by employing a windowing mechanism. The use of windowed BCCs in a flash ADC can introduce nonmonotonic-threshold (NMT) effects which include an increase in calibration settling time and an increase in /spl sigma/(V/sub OS/). The use of uncorrelated random chopping for neighboring BCCs can ensure the validity of offset detection and mitigate the NMT effects.

Seasonal and diurnal patterns of soil water potential in the rhizosphere of blue oaks: evidence for hydraulic lift.

In a 3-year study, seasonal and daily soil water fluctuations in a California blue oak woodland were investigated by measuring soil water potential (Ψs) at hourly intervals. Soil water potential remained relatively high well into the annual summer drought, with values above -0.5MPa until June even in a dry year. As drought progressed, Ψs (at 25, 50, 75, and 100cm depth) decreased to less than -3MPa, providing evidence for continued blue oak root activity throughout the summer. We observed diurnal Ψs fluctuations (gradual increase at night and rapid decrease during daytime) characteristic of hydraulic lift, a process by which plant roots redistribute water from wet to dry soil layers. These diurnal fluctuations were observed at all four soil depths and began to appear when Ψs reached approximately -0.3MPa. When Ψs reached approximately -3MPa, fluctuations became "offset" from those typical of hydraulic lift. These offset fluctuations (apparent at low water potentials when temperature fluctuations were large) closely followed diurnal fluctuations in soil temperature. We propose that these offset patterns resulted from a combination of hydraulic lift cessation and an over-correction for temperature in the model used to calculate Ψs from raw sensor data. The appearance and disappearance of hydraulic lift fluctuations seemed to depend on Ψs. While soil temperatures and dates at which hydraulic lift appeared (and disappeared) were significantly different between wet and dry years, Ψs values associated with hydraulic lift appearance were not significantly different. Hydraulic lift occurred too late in summer to benefit annual forage grasses. However, water released by blue oak trees at night could slow the rate of soil water depletion and extend blue oaks' growing season.

Diffusion due to Beam-Beam Interaction and Fluctuating Fields in Hadron Colliders.

Random fluctuations in the tune, beam offsets and beam size in the presence of the beam-beam interaction are shown to lead to significant particle diffusion and emittance growth in hadron colliders. We find that far from resonances high frequency noise causes the most diffusion while near resonances low frequency noise is responsible for the large emittance growth observed. Comparison of different fluctuations shows that offset fluctuations between the beams causes the largest diffusion for particles in the beam core.