Current Ring Research Articles

Statistical and numerical analysis on characteristics and influence factors of construction cracks of large-diameter underwater shield tunnel: a case study

Tunnel excavation is prone to segment cracks, which may lead to serious safety accidents. This work aims to investigate the type, location and occurrence time of cracks in a large-diameter underwater shield tunnel and also ascertain the causes of the cracks. The correlations between crack characteristics and shield tunneling parameters were analyzed. The effect of jack deflection and poor assembly on cracks were investigated using a refined finite element model of two consecutive rings with consideration of the assembly clearance and the constraint effect of the shield machine. The results confirmed that 93% of the cracks were formed between the current ring and the last ring jacking stage. Positive cracks induced by jack deflection occurred during the current ring jacking stage, while the lengths of the cracks, proportional to the constraint of the boring machine on the segments, remained constant during the subsequent construction process. The cracks caused by poor assembly quality arose during the current and next ring jacking stages. Furthermore, the cracks generated in the current ring jacking stage would propagate during the subsequent construction process. The type, length, and number of cracks were influenced by the assembly clearance. The inverted V-shape longitudinal joints caused more cracks than any other assembly defects. The finding of this study results and conclusions are expected to contribute to the reduction of cracks at the jacking stage of the large-diameter underwater shield tunnels with eccentricity force transfer platforms.

Effects of fragmentation on production at Peak mine Midlands, Zimbabwe

Over the years, the cost of production at Peak Mine Midlands, Zimbabwe, has been high due to oversized rock fragments. This led to increased mining costs far above what was planned by the mine. Initial investigations showed that valuable production hours were lost in trying to deal with the oversized rock fragments at the draw points. This study was conducted at Peak Mine Midlands, Zimbabwe, on 1210 level. The methods used to assess the effects of fragmentation on production at the mine included visual assessment, analysis of the drill and blasting costs of the production data, 2D image analysis, sieve analysis, time and motion studies, analysis of the explosive’s consumption, mining blasting trials and post-mine blast experiments. The results show that the current ring hole designs used in the sublevel open stopes at Peak Mine do not give optimal particle size distribution after the primary blasts as the sieve analyses show that 50% of the sizes of materials at the draw points are larger than 1,000 mm. While 4 secondary blasts were budgeted per shift to reduce the sizes of the boulders to sizes that will pass through the grizzly’s sieves, 7 secondary blasts were done per shift and this led to about 75% increase in the cost of explosives consumed by the mine. The results also show that 35.96 minutes of production time were lost on each secondary blast conducted. Four trial blasts conducted on different ring hole patterns show that ring #1 which has a burden of 1.2 m instead of 1.8 m in the other ring holes led to a significant reduction in drilling and blasting costs from USD $33.79 in trial #4 (the control case) to $28.80 in trial #1. The sieve analyses also show that the optimal fragment sizes from primary blasts are in the range of X = +200 mm and X = +300 mm. So, the designed ring hole patterns in the sublevel open stopes should produce particles with sizes in the range of  150 mm and  +350 mm from the primary blasts.

Improved SEM Current Ringing Suppressor for Maglev Trains

In electromagnetic suspension (EMS) systems, the air gap between the suspension electromagnet (SEM) and steel track is adjusted by changing the electromagnetic attraction force, which is accomplished by controlling the maglev chopper (MC). When switching the power electronic devices of the MC, SEM current ringing tends to occur, which is harmful to the whole EMS system. A conventional current ringing suppressor (CRS) deteriorates the SEM port voltage ringing, which may accelerate the aging process of SEM insulation or even directly result in a breakdown fault. Herein, to explore the generation mechanism of SEM current ringing, a third-order equivalent circuit model of the suspension electromagnet-maglev chopper (SEM-MC) system is established by using the field-circuit coupling analysis technique. A series of simulations and experiments have been undertaken to verify the validity of the built circuit model, and the deviation between the simulation and experimental results is acceptable. As the influencing factors of SEM current ringing are analyzed based on this third-order equivalent circuit model, an improved CRS, i.e., hybrid inductor-resistor CRS, is proposed to avoid deteriorating the SEM port voltage ringing and protect the SEM insulation. Finally, the feasibility of the proposed hybrid inductor-resistor CRS is verified by corresponding experiments.

Ultra-high voltage silicon pixel sensor with less soft-breakdown for X-ray free electron laser

X-ray free electron laser (XFEL) requires operation of an advanced silicon pixel sensor (SPS) under ultra-high voltage for detection of fast electron–hole pairs. In this study, a high-voltage tolerant SPS is designed and fabricated by considering suppressing the soft-breakdown of the current collection ring (CCR) and increasing the breakdown voltage of the pixel array after dicing the sensor. It is found that a soft-breakdown behavior of CCR in one diced SPS occurred before a hard breakdown happening in the pixel and it may cause the degradation of maximum hard breakdown voltage in pixel region, which, in particular, turns worse as the increasing of the number of guard rings. An optimized method with the expansion of the non-sensitive area is used to effectively prevent the occurrence of soft-breakdown and increase the operation voltage of the SPS. Ultimately, a high performance SPS with a maximum breakdown voltage exceeding 1000 V and reversed leakage of ∼1.5 pA per pixel at bias 500 V is obtained. Together with the optimized multi-guard ring structure, a record ultra-high avalanche breakdown voltage of over 2100 V is obtained, which provides a promising approach to develop ultra-fast detector in an XFEL.

New collimating shielded bellow for the connection of superconducting rf cavities in a high current storage ring

New collimating shielded bellow for the connection of superconducting rf cavities in a high current storage ring

Combining an Eddy Detection Algorithm with In-Situ Measurements to Study North Brazil Current Rings

North Brazil Current (NBC) rings are believed to play a key role in the Atlantic Ocean circulation and climate. Here, we use a new collection of high-resolution in-situ observations acquired during the EUREC4A-OA field experiment together with satellite altimetry to define, with unprecedented detail, the structure and evolution of these eddies. In-situ observations reveal a more complex structure than previously documented. In particular, we highlight a measurable impact of the Amazon outflow in creating a barrier layer over a large portion of the eddies. We show that this unprecedented data set allows us to estimate the accuracy of satellite altimetry gridded fields. The geostrophic velocities derived from satellite altimetry turn out to be considerably lower (up to 50% in amplitude) than the values measured by current meters. However, eddy properties as detected by TOEddies, a newly developed algorithm show to be relatively precise. For example, the eddy center and maximum azimuthal velocity contour fall within 25 ± 5 km and 16 ± 9 km, respectively, from the in-situ observed values. We apply TOEddies to 27 years of satellite altimetry to investigate the generic NBC rings behavior. We found a mean generation rate of 4.5 ± 1.1 rings per year, and a strong seasonal cycle in all eddy properties.

Highly Robust and Antiaromatic Rhenium(I) Rosarin.

1ReH•Cl, a highly robust and antiaromatic rhenium(I) complex of triarylrosarin, is synthesized. The 1H NMR spectrum of 1ReH•Cl shows upfield-shifted pyrrole protons and highly downfield-shifted inner protons that confirm its antiaromatic nature, with density functional theory calculations strongly supporting this interpretation. Antiaromatic 1ReH•Cl absorbs from the UV to near-IR region of the optical spectrum; cyclic voltammetry, thin-layer UV-vis spectroelectrochemistry, and spin-density distributions clearly reveal that the rosarin backbone of 1ReH•Cl undergoes redox chemistry. The X-ray structure of 1ReH•Cl shows a fully coordinated and protonated inner cavity that effectively prevents proton-coupled electron transfer when treated with an acid. A remarkably negative NICS(0) value, clockwise anisotropy of the induced current density ring current, and the aromatic shielded inner cavity in the 2D ICSS(0) map reveal that the T1 state of 1ReH•Cl is aromatic based on Baird's rule.

Transverse gradient undulator in a storage ring x-ray free electron laser oscillator

Modern electron storage rings produce bright x rays via spontaneous synchrotron emission, which is useful for a variety of scientific applications. The x-ray free-electron laser oscillator (XFELO) has the potential to amplify this output, both in terms of peak power and photon coherence. However, even current fourth generation storage rings (4GSRs) lack the requisite electron beam brightness to drive the XFELO due to its electron energy spread. The transverse gradient undulator (TGU) can overcome this issue, thus providing a practical means to couple the 4GSR to the XFELO. In this study, we first examine the theoretical basis of the TGU interaction by deriving the 3D TGU gain formula in the low gain approximation. Then, we perform an optimization study of the gain formula in order to determine optimal beam and machine parameters. Finally, we construct a hypothetical storage ring TGU-XFELO based on near-optimal parameters and report on its projected performance using multistage numerical simulation. We also discuss potential implementation challenges associated with the ring-FEL coupling.

Accelerated Aging Procedure and Online Method for Stator Insulation Monitoring of Induction Motors

Online methods for stator insulation monitoring have been investigated with increasing interest in the last 15 years. These methods rely on the high-frequency behavior of the electric machine. In converter-fed machines, the high-frequency behavior is visible through the current ringings occurring during the switching commutations of the power electronics. As the lifetime of electric machines can last several decades, a faster way to evaluate insulation monitoring methods is through accelerated aging tests. This work aims to perform an accelerated aging procedure on an induction motor to test an online insulation monitoring method. The motor has a randomly-wound stator winding and it is aged by means of thermal cycles without the need for an oven. A custom converter is employed during the accelerated aging procedure to apply the thermal cycles and to record the current ringings. The proposed insulation monitoring method is based on a metric that quantifies the current ringing variations in a simple manner, following the quasi-linear variation of the parasitic capacitances during the motor aging.

Participant experiences with a multipurpose vaginal ring for HIV and pregnancy prevention during a phase 1 clinical trial: learning from users to improve acceptability.

With high concurrent global rates of HIV incidence and unintended pregnancy, there is a need to provide options beyond condoms to enable users to simultaneously prevent HIV acquisition and pregnancy. Multiple vaginal rings are in development as "MPTs" (multipurpose prevention technologies) as they are shown to provide several co-occurring benefits such as discretion, convenience, reversibility and user control. In this Phase 1 trial of a 3-month MPT ring in the U.S., 25 participants (low-risk for HIV and pregnancy) were randomized to use the study ring for 90 days continuously or in 28-day cycles with 2-day removal periods in between. All participants completed in-depth interviews at the end of their study participation. Overall, the ring was well tolerated. Participants resoundingly endorsed the concept of an extended-use, dual-purpose vaginal ring, but reported too many functional challenges and side effects to endorse this particular ring. Participants assigned to the continuous regimen reported more positive experiences with ring use than those in the cyclic group. A minority of participants who experienced minimal side effects and did not experience challenges with vaginal retention of the ring found it appealing. However, the majority of participants experienced challenges (ring slippage, expulsions, side effects, vaginal bleeding changes) with product use that outweighed the potential benefits and led them to report that - in the future - they would not be interested in using this specific version of the ring in its current form. A subset expressed interest in using the current MPT ring under certain conditions (e.g., if fewer expulsions, less bleeding, higher risk for HIV/pregnancy). User feedback regarding participant experiences and challenges with the study ring was continuously shared with the product developer, underscoring the value of early-stage end-user feedback in product development.

Friction of Coated and Uncoated Rough Surfaces in Additive-Free and Fully Formulated Engine Oils Under Boundary and Mixed Lubrication Conditions

Abstract Downsizing in spark-ignited engines becomes one of the most effective concepts to achieve fuel economy and emissions requirements and drives operating conditions of major moving engine components into more mixed and boundary lubrication regimes. Piston ring design faces considerable challenge to reduce friction losses, oil consumption, blow-by, and wear. Surface coatings have received great attention in applications of automotive engine components due to their unique friction properties. In this study, an elastic–plastic contact model of rough surfaces with hard coatings is used to provide proper design of the ring coating thickness concerning the plasticity-yielding resistance of stiff coating. A diamond-like carbon (DLC) coating with surface hardness higher than current production ring coatings has been evaluated in additive-free base oil and fully formulated engine oil under boundary and mixed lubrication conditions. The friction behavior of the coated material relative to uncoated materials is compared in boundary and mixed lubrication regimes. A traction-merging rolling speed in the mixed lubrication regime is observed, at which friction coefficient is independent of applied loads. By using a mixed lubrication model previously published, calculations indicate that the lower the traction-merging rolling speed, the earlier the contact approaches elastohydrodynamic lubrication (EHL), therefore reducing the risk of asperity-interacting fatigue in boundary and mixed lubrication regimes. Effects of tribofilm on friction behavior for DLC coating and uncoated steel in fully formulated oil are investigated by using measured Stribeck curves in conjunction with the model. The results from this study analytically support one of the possible mechanisms of tribofilm-dependent friction enhancement in mixed lubrication conditions proposed in the earlier publication.

Development of cryogenic undulators and measurement equipment for PETRA IV

DESY is planning to upgrade its current storage ring PETRA III into the ultra-low emittance photon source PETRA IV. The current H6BA cell design for the PETRA IV lattice will allow for insertion devices of up to 4 m length in the standard straight sections. In order to allow some beamlines to not only benefit from the performance improvements by the machine but also from the undulators, we started looking into using advanced undulator schemes as well. We decided to start the design of cryogenically cooled permanent magnet undulators (CPMUs) based on (Nd,Pr)FeB magnets for PETRA IV, since this technique has already been proven successfully by various other facilities. We will present the planned design for the magnet keepers, the pole tuning mechanism as well as a testbed for keepers under cryogenic conditions. We will also show a preliminary design for the in-situ Hall-probe bench currently developed for the upcoming PETRA IV CPMUs.

Evaluation of High-Frequency Current Ringing Measurements for Insulation Health Monitoring in Electrical Machines

Condition monitoring of the insulation health of electric machines is usually performed with offline tests. In recent years, online condition monitoring methods for the groundwall insulation have been introduced. The majority of these works are based on leakage current measurements, requiring additional equipment compared to the standard one in converters. The condition monitoring method in this work instead relies on the high-frequency ringing of stator currents occurring after a converter switching transition. This work evaluates the method experimentally in a randomly-wound stator winding of an induction machine prototype equipped with taps. The insulation condition change is forced by inserting external capacitors. Through the analysis of different metrics for the health monitoring and a detailed discussion of the hardware and software requirements for an electric drive, a viable way forward for the practical implementation of the approach is proposed.

Reconstructing the Three-Dimensional Structure of Loop Current Rings from Satellite Altimetry and In Situ Data Using the Gravest Empirical Modes Method

The three-dimensional structure of Gulf of Mexico’s warm-core rings, detaching from the Loop Current, is investigated using satellite altimetry and a large set of ARGO float profiles. Reconstruction of the Loop Current rings (LCRs) vertical structure from sea surface height observations is made possible by the use of the gravest empirical modes method (GEM). The GEMs are transfer functions that associate a value of temperature and salinity for each variable pair {dynamic height; pressure}, and are computed by estimating an empirical relationship between dynamic height and the vertical thermohaline structure of the ocean. Between 1993 and 2021, 40 LCRs were detected in the altimetry and their three-dimensional thermohaline structure was reconstructed, as well as a number of dynamically relevant variables (geostrophic and cyclogeostrophic velocity, relative vorticity, potential vorticity, available potential energy and kinetic energy density, etc.). The structure of a typical LCR was computed by fitting an analytical stream function to the LCRs dynamic height signature and reconstructing its vertical structure with the GEM. The total heat and salt contents and energy of each LCR were computed and their cumulative effect on the Gulf of Mexico’s heat, salt and energy balance is discussed. We show that LCRs have a dramatic impact on these balances and estimate that residual surface heat fluxes of −13 W m−2 are necessary to compensate their heat input, while the fresh water outflow of the Mississippi river approximately compensates for their salt excess input. An average energy dissipation of O [10−10–10−9] W kg−1 would be necessary to balance their energy input.

Generation of Vorticity Near Topography: Anticyclones in the Caribbean Sea

AbstractMesoscale anticyclonic eddies dominate the sea‐surface height variability in the Caribbean Sea. Although it is well established that these anticyclones are formed near the eastern boundary of the Caribbean Sea, which is demarcated by the Lesser Antilles, the source of their anticyclonic vorticity remains unclear. To gain insight into this source, we analyze the fluxes of vorticity into the Caribbean at its eastern boundary using a high‐resolution numerical model. We find that the anticyclonic vorticity in the eastern Caribbean Sea predominantly originates from regions where intense ocean currents flow close to the Lesser Antilles. More specifically, St. Lucia and Grenada are hotspots for vorticity generation. The local generation rate scales with the amplitude of the volume transport through the passages between these islands. This finding is in contrast with the view that anticyclonic North Brazil Current (NBC) rings in the Atlantic Ocean are the main source of anticyclonic vorticity in the eastern Caribbean Sea. Our analyses reveal that the direct contribution of the vorticity of the NBC rings is of lesser importance than the local generation. However, the collision of upstream NBC rings with the Lesser Antilles increases the volume transport through the passages into the Caribbean Sea, so that their presence indirectly leads to enhanced local production of anticyclonic vorticity. This process is an example of the importance of vorticity generation near topography, which is ubiquitous in the oceans, and expected to be important whenever currents and steep topography meet.

Volume and Heat Transports by North Brazil Current Rings

A methodology that combines a 24-year long (January 1993 to December 2016) global dataset of eddy trajectories, derived from altimetry, with vertical temperature and salinity profiles from the EN4.2.0 database, derived from XBTs/MBTs, CTDs and Argo floats, was used to reconstruct the mean vertical structure of North Brazil Current (NBC) rings, and to calculate some of their properties. The number of NBC rings formed each year varied from 2 to 8, with an annual-mean formation of 5.3 ± 1.5. During the analyzed period, 112 rings were sampled at least once, at various distances from the center of the rings, leading to a total of 1323 (604) temperature (salinity) profiles available to compute the mean NBC ring, depicting a large, surface intensified, and relatively shallow ring, with intense temperature and salinity anomalies. The meridional volume transport was estimated in 1.3 Sv (1Sv = 106 m3s-1) per ring, leading to an annualized transport of ~7 ± 2 Sv. The amount of South Atlantic Water (SAW) within the mean ring was estimated in ~40 to 60% of the ring volume. According to these estimates, NBC rings may be responsible in different years for approximately 20 to 80% of the northward volume transport associated with the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and approximately 15 to 55% of the meridional heat transport in the tropical Atlantic.

Wintertime process study of the North Brazil Current rings reveals the region as a larger sink for CO<sub>2</sub> than expected

Abstract. The key processes driving the air–sea CO2 fluxes in the western tropical Atlantic (WTA) in winter are poorly known. WTA is a highly dynamic oceanic region, expected to have a dominant role in the variability in CO2 air–sea fluxes. In early 2020 (February), this region was the site of a large in situ survey and studied in wider context through satellite measurements. The North Brazil Current (NBC) flows northward along the coast of South America, retroflects close to 8∘ N and pinches off the world's largest eddies, the NBC rings. The rings are formed to the north of the Amazon River mouth when freshwater discharge is still significant in winter (a time period of relatively low run-off). We show that in February 2020, the region (5–16∘ N, 50–59∘ W) is a CO2 sink from the atmosphere to the ocean (−1.7 Tg C per month), a factor of 10 greater than previously estimated. The spatial distribution of CO2 fugacity is strongly influenced by eddies south of 12∘ N. During the campaign, a nutrient-rich freshwater plume from the Amazon River is entrained by a ring from the shelf up to 12∘ N leading to high phytoplankton concentration and significant carbon drawdown (∼20 % of the total sink). In trapping equatorial waters, NBC rings are a small source of CO2. The less variable North Atlantic subtropical water extends from 12∘ N northward and represents ∼60 % of the total sink due to the lower temperature associated with winter cooling and strong winds. Our results, in identifying the key processes influencing the air–sea CO2 flux in the WTA, highlight the role of eddy interactions with the Amazon River plume. It sheds light on how a lack of data impeded a correct assessment of the flux in the past, as well as on the necessity of taking into account features at meso- and small scales.

Fairy ring‐induced soil potassium depletion gradients reshape microbial community composition in a montane grassland

AbstractFairy rings promoting circular greening belts in the vegetation can shape soil microbial communities by altering soil conditions. Knowledge about soil variables involved in this process is incomplete. We characterised the soil microbial communities of six fairy rings in a montane grassland using phospholipid fatty acid (PLFA) profiling, and studied if changes in soil properties corresponded to changes in soil microbial PLFA patterns. Exchangeable potassium (K) decreased inside the current rings, while soil moisture increased in the zones where the greening belts were two years before sampling (R2015). Fairy ring associated changes in PLFA composition were highly related to soil K. Gram‐negative bacteria were associated with the zones outside the ring with the highest K content, whereas Gram‐positive bacteria proportions increased inside the ring‐affected zones. An environmental stress indicator, the iso to anteiso ratio of PLFA 17:0, decreased in the R2015 zones, coinciding with the highest soil moisture contents. Our findings highlight the unreported importance of soil K in fairy ring dynamics affecting microbial communities. This common omission could lead to incorrect conclusions. Hence, the effects of fairy rings on soil should be further tested.Highlights Exchangeable potassium (K) decreased inside the current fairy rings. Fairy ring associated changes in PLFA microbial composition were present related to soil K. Soil moisture increased in the zones where the rings were 2 years before sampling. An environmental stress indicator decreased in those areas.

A Performance Prediction Model for Permanent Magnet Eddy-Current Couplings Based on the Air-Gap Magnetic Field Distribution

In this article, a clear analytical model for predicting the performance of permanent magnet (PM) eddy current couplers is proposed. The interaction of the reaction magnetic fields between adjacent eddy current rings was considered for the first time. Based on a magnetic equivalent circuit (MEC) and the Ampere circuital theorem, the accurate distribution of the air gap magnetic field under different slip velocities was deduced in a 2-D model, and the analytical expression of the transmission torque was obtained. 3-D effects were also taken into account to calibrate the model. The validity of the analytical model was verified by comparison with results from the 3-D finite element method (FEM). The comparison shows that the analytical model can accurately predict the magnetic field distribution and transmission torque over a wide range of slip velocity variations. This model can greatly reduce the number of calculations required and save time, and it is suitable for the preliminary design and optimization of PM eddy current couplers.

Correlates of non-persistent endocrine disrupting chemical mixtures among reproductive-aged Black women in Detroit, Michigan

Some studies indicate that Black women have higher exposure to multiple non-persistent endocrine disrupting chemicals (EDCs) than white women, but little is known about correlates of exposure to EDC mixtures. Using baseline data from a prospective cohort study of reproductive-aged Black women (N = 751), we characterized profiles of EDC mixtures and identified correlates of exposure. At baseline, we quantified biomarkers of 16 phthalates, 7 phenols, 4 parabens, and triclocarban in urine and collected covariate data through self-administered questionnaires and interviews. We used principal component (PC) analysis and k-means clustering to describe EDC mixture profiles. Associations between correlates and PCs were estimated as the mean difference (β) in PC scores, while associations between correlates and cluster membership were estimated as the odds ratio (OR) of cluster membership. Personal care product use was consistently associated with profiles of higher biomarker concentrations of non-persistent EDCs. Use of nail polish, menstrual and vaginal products (e.g., vaginal powder, vaginal deodorant), and sunscreen was associated with a mixture of phthalate and some phenol biomarkers using both methods. Current vaginal ring use, a form of hormonal contraception placed inside the vagina, was strongly associated with higher concentrations of high molecular weight phthalate biomarkers (k-means clustering: OR = 2.42, 95% CI = 1.28, 4.59; PCA: β = −0.32, 95% CI = −0.71, 0.07). Several dietary, reproductive, and demographic correlates were also associated with mixtures of EDC biomarkers. These findings suggest that personal care product use, diet, and contraceptive use may be sources of exposure to multiple non-persistent EDCs among reproductive-aged Black women. Targeted interventions to reduce exposure to multiple EDCs among Black women are warranted.