The geoelectric field is the primary input used for estimation of geomagnetically induced currents (GICs) in conducting systems. We compare three methods for estimating the geoelectric field given ...the measured geomagnetic field at four locations in the U.S. during time intervals with average Kp in the range of 2–3 and when the measurements had few data spikes and no baseline jumps. The methods include using (1) a preexisting 1‐D conductivity model, (2) a conventional 3‐D frequency domain method, and (3) a robust and remote reference 3‐D frequency domain method. The quality of the estimates is determined using the power spectrum (in the period range 9.1 to 18,725 s) of estimation errors along with the prediction efficiency summary statistic. It is shown that with respect to these quality metrics, Method 1 produces average out‐of‐sample electric field estimation errors with a variance that can be equal to or larger than the average measured variance (due to underestimation or overestimation, respectively), and Method 3 produces reliable but slightly lower quality estimates than Method 2 for the time intervals and locations considered.
Key Point
Three methods for estimating the geoelectric field given the measured geomagnetic field at four locations in the U.S. are compared
This paper is the primary deliverable of the very first NASA Living With a Star Institute Working Group, Geomagnetically Induced Currents (GIC) Working Group. The paper provides a broad overview of ...the current status and future challenges pertaining to the science, engineering, and applications of the GIC problem. Science is understood here as the basic space and Earth sciences research that allows improved understanding and physics-based modeling of the physical processes behind GIC. Engineering, in turn, is understood here as the ''impact'' aspect of GIC. Applications are understood as the models, tools, and activities that can provide actionable information to entities such as power systems operators for mitigating the effects of GIC and government agencies for managing any potential consequences from GIC impact to critical infrastructure. Applications can be considered the ultimate goal of our GIC work. In assessing the status of the field, we quantify the readiness of various applications in the mitigation context. We use the Applications Readiness Level (ARL) concept to carry out the quantification.
Objective: To evaluate the results of surgical treatment options for chronic subdural haematoma in contemporary neurosurgery according to evidence based criteria. Methods: A review based on a Medline ...search from 1981 to October 2001 using the phrases “subdural haematoma” and “subdural haematoma AND chronic”. Articles selected for evaluation had at least 10 patients and less than 10% of patients were lost to follow up. The articles were classified by three classes of evidence according to criteria of the American Academy of Neurology. Strength of recommendation for different treatment options was derived from the resulting degrees of certainty. Results: 48 publications were reviewed. There was no article that provided class I evidence. Six articles met criteria for class II evidence and the remainder provided class III evidence. Evaluation of the results showed that twist drill and burr hole craniostomy are safer than craniotomy; burr hole craniostomy and craniotomy are the most effective procedures; and burr hole craniostomy has the best cure to complication ratio (type C recommendation). Irrigation lowers the risk of recurrence in twist drill craniostomy and does not increase the risk of infection (type C recommendation). Drainage reduces the risk of recurrence in burr hole craniostomy, and a frontal position of the drain reduces the risk of recurrence (type B recommendation). Drainage reduces the risk of recurrence in twist drill craniostomy, and the use of a drain does not increase the risk of infection (type C recommendation). Burr hole craniostomy appears to be more effective in treating recurrent haematomas than twist drill craniostomy, and craniotomy should be considered the treatment of last choice for recurrences (type C recommendation). Conclusions: The three principal techniques—twist drill craniostomy, burr hole craniostomy, and craniotomy—used in contemporary neurosurgery for chronic subdural haematoma have different profiles for morbidity, mortality, recurrence rate, and cure rate. Twist drill and burr hole craniostomy can be considered first tier treatment, while craniotomy may be used as second tier treatment. A cumulative summary of data shows that, overall, the postoperative outcome of chronic subdural haematoma has not improved substantially over the past 20 years.
A variety of observations have shown strong seasonal variations in a vast array of magnetosphere‐ionosphere parameters, including field‐aligned currents, cross polar cap potential, and precipitating ...electron energy flux. In this paper we examine how these variations are modeled in the Lyon‐Fedder‐Mobarry (LFM) global‐scale magnetohydrodynamic simulation of the coupled solar wind‐magnetosphere‐ionosphere system. In order to account for changes in the solar wind conditions caused by the seasonal variation of the Earth's dipole tilt we carefully select the solar wind parameters so that the effective driving conditions are the same across the March, June, and December intervals examined. The seasonal variation of the field‐aligned current strengths is in good agreement with observations, with the sunlit hemisphere having more current than the dark hemisphere in the June and December intervals. However, in order to bring the modeled precipitating electron energy flux into better agreement with the observations we need to utilize a modified current‐voltage relationship which includes a proxy for illumination effects. We provide a detailed description of the LFM's magnetosphere‐ionosphere coupling interface including how illumination effects are incorporated into the model. This methodology for including these effects does not allow for determining if changes in conductance or ionospheric density are responsible for the changes. In addition to improving the agreement with observations the new version of the current‐voltage relationship results in enhanced geomagnetic activity in the March interval examined and suppression of activity during the June interval.
This Letter presents the design of a low-profile and low-cost transmitarray antenna operating at 122 GHz. The transmitarray design is based on unit-cells with 1-bit phase resolution. A single RO4350B ...substrate layer is used to form the unit-cells resulting in a total thickness of 0.326 mm. A wideband shift in the transmission phase of $180^\circ $180° is generated by rotating one metal layer of the unit-cell by $180^\circ $180°. The simulation of the transmitarray with $30 \times 30$30×30 elements and a feed distance of 35 mm shows a maximum directivity of 28 dBi at 122 GHz. Steering angles of $0^\circ $0° and $15^\circ $15° are investigated. Measurements of the fabricated transmitarrays are performed with an open waveguide and a package antenna as feed showing similar results but slightly different maximum relative gain values of 11.8 and 9.5 dB for the $0^\circ $0° version. The measured main beam directions are in good agreement with the simulations and the design values.
Molecular subtypes of breast cancer are characterized by distinct patterns of gene expression that are predictive of outcome and response to therapy. The luminal breast cancer subtypes are defined by ...the expression of estrogen receptor-alpha (ERα)-associated genes, many of which are directly responsive to the transcription factor activator protein 2C (TFAP2C). TFAP2C participates in a gene regulatory network controlling cell growth and differentiation during ectodermal development and regulating ESR1/ERα and other luminal cell-associated genes in breast cancer. TFAP2C has been established as a prognostic factor in human breast cancer, however, its role in the establishment and maintenance of the luminal cell phenotype during carcinogenesis and mammary gland development have remained elusive. Herein, we demonstrate a critical role for TFAP2C in maintaining the luminal phenotype in human breast cancer and in influencing the luminal cell phenotype during normal mammary development. Knockdown of TFAP2C in luminal breast carcinoma cells induced epithelial-mesenchymal transition with morphological and phenotypic changes characterized by a loss of luminal-associated gene expression and a concomitant gain of basal-associated gene expression. Conditional knockout of the mouse homolog of TFAP2C, Tcfap2c, in mouse mammary epithelium driven by MMTV-Cre promoted aberrant growth of the mammary tree leading to a reduction in the CD24(hi)/CD49f(mid) luminal cell population and concomitant gain of the CD24(mid)/CD49f(hi) basal cell population at maturity. Our results establish TFAP2C as a key transcriptional regulator for maintaining the luminal phenotype in human breast carcinoma. Furthermore, Tcfap2c influences development of the luminal cell type during mammary development. The data suggest that TFAP2C has an important role in regulated luminal-specific genes and may be a viable therapeutic target in breast cancer.
Reconnection in the magnetotail occurs along so‐called X‐lines, where magnetic field lines tear and detach from plasma on microscopic spatial scales (comparable to particle gyroradii). In 2017–2020, ...the Magnetospheric MultiScale (MMS) mission detected X‐lines in the magnetotail enabling their investigation on local scales. However, the global structure and evolution of these X‐lines, critical for understanding their formation and total energy conversion mechanisms, remained virtually unknown because of the intrinsically local nature of observations and the extreme sparsity of concurrent data. Here, we show that mining a multi‐mission archive of space magnetometer data collected over the last 26 yr and then fitting a magnetic field representation modeled using flexible basis‐functions faithfully reconstructs the global pattern of X‐lines; 24 of the 26 modeled X‐lines match (Bz = 0 isocontours are within ∼2 Earth radii or RE) or nearly match (Bz = 2 nT isocontours are within ∼2RE) the locations of the MMS encountered reconnection sites. The obtained global reconnection picture is considered in the context of substorm activity, including conventional substorms and more complex events.
Plain Language Summary
Magnetic reconnection is a fundamental process in plasmas which couples microscopic scales (∼electron to proton gyroradii) to explosive macroscopic phenomena many orders of magnitude larger, such as solar flares and geomagnetic storms/substorms. Reconnection forms along “X‐lines”, rifts where oppositely directed magnetic field lines are forced together. In the Earth's magnetosphere, reconnection has been observed by satellites at isolated locations; however, the large‐scale structure of X‐lines and their time evolution remains unknown because of the rarity and local nature of observations. Here, ground based measurements of geomagnetic activity and solar wind measurements are used to data‐mine 26 yr of magnetometer data from 22 Earth‐orbiting satellites, which are then utilized to reconstruct the global magnetic field associated with X‐lines in Earth's magnetosphere. We show that these reconstructions pinpoint the reconnection locations by verifying their consistency with direct spacecraft observations.
Key Points
Global structure of magnetotail reconnection inferred from data mining matches its locations revealed by in situ observations
Reconstructed magnetotail reconnection structures include X‐ and O‐lines and magnetic nulls
Reconstructed multiscale current sheet structure is consistent with its formation mechanism by quasi‐adiabatic ion motions
A common assumption used when estimating geomagnetically induced currents (GICs) in a power system given a time series of nearby direct measurements or indirect estimates of the horizontal ...geoelectric field components Ex(t) and Ey(t) on Earth's surface is that the system is resistive. That is, the approximation GIC(t)=aoEx(t)+boEy(t) (Model 1) is used, where ao and bo are frequency‐independent power system coefficients. A first test of this assumption is made using GIC measurements in a 187 kV transformer connected to a ∼100 km power line in Memanbetsu, Japan and geoelectric field measurements made at the Memanbetsu Magnetic Observatory ∼9 km away. A second model (Model 2) is obtained using a frequency domain generalization of Model 1: GIC(ω)=a(ω)Ex(ω)+b(ω)Ey(ω). The coefficients a(ω) and b(ω) are shown to be frequency‐dependent, and this model provides significantly better estimates of the measured GIC than Model 1. Based on results using a simulated geoelectric field, it is suggested that the measurement‐derived frequency dependence of the system coefficients may be explained by spatial variations in the spectrum of the geoelectric field over the spatial extent of the power system. It is also shown that further improvements over Model 2 can be made using frequency‐dependent models with the geomagnetic field as an input.
Key Points
Power system coefficients derived from a time series of GIC and geoelectric field measurements are frequency dependent
A GIC model with frequency‐dependent system coefficients provides significantly better estimates of GIC than a frequency‐independent model
Data‐derived power system coefficients may differ significantly with those computed using power system configuration information
Aircraft borne optical in situ size distribution measurements were performed within Arctic boundary layer clouds with a special emphasis on the cloud top layer during the VERtical Distribution of Ice ...in Arctic clouds (VERDI) campaign in April and May 2012. An instrumented Basler BT-67 research aircraft operated out of Inuvik over the Mackenzie River delta and the Beaufort Sea in the Northwest Territories of Canada. Besides the cloud particle and hydrometeor size spectrometers the aircraft was equipped with instrumentation for aerosol, radiation and other parameters. Inside the cloud, droplet size distributions with monomodal shapes were observed for predominantly liquid-phase Arctic stratocumulus. With increasing altitude inside the cloud the droplet mean diameters grew from 10 to 20 μm. In the upper transition zone (i.e., adjacent to the cloud-free air aloft) changes from monomodal to bimodal droplet size distributions (Mode 1 with 20 μm and Mode 2 with 10 μm diameter) were observed. It is shown that droplets of both modes co-exist in the same (small) air volume and the bimodal shape of the measured size distributions cannot be explained as an observational artifact caused by accumulating data point populations from different air volumes. The formation of the second size mode can be explained by (a) entrainment and activation/condensation of fresh aerosol particles, or (b) by differential evaporation processes occurring with cloud droplets engulfed in different eddies. Activation of entrained particles seemed a viable possibility as a layer of dry Arctic enhanced background aerosol (which was detected directly above the stratus cloud) might form a second mode of small cloud droplets. However, theoretical considerations and model calculations (adopting direct numerical simulation, DNS) revealed that, instead, turbulent mixing and evaporation of larger droplets are the most likely reasons for the formation of the second droplet size mode in the uppermost region of the clouds.
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