Search

Connexin proteins are the hemichannels that form gap junctions to regulate the intercellular communication. Connexin 43 (Cx43) is the most common gap junction protein that expresses in many cell types, including the olfactory sensory neurons. Phosphorylation is a crucial step to regulate the function of Cx43. Gap junction was found to modulate the odor response, but the specific role is still elusive. Here, we report that gap junctions play a role in odor-evoked calcium response in both heterologous cell system and primary olfactory sensory neurons. This regulation is mediated through gap junction protein Cx43. Overexpression of full length Cx43 can counteract the inhibitory effect of gap junction or connexin blockers on odor-evoked [Ca 2+ ]i increase in hana3A cells. Carboxy-terminal of Cx43 (Cx43CT) has the similar function as the full length of Cx43. Furthermore, we found that expression level of phosphorylation of Cx43 at S368 is dynamic with the stimulation of odor in hana3A cells. Expression level of phosphorylated Cx43 at S368 was decreased when gap junction or connexin inhibitors were applied. Phosphorylation of Cx43 during odor or inhibitor stimulation may be mediated by ERK and JNK signaling pathway. Altogether our data suggest that expression of Cx43 can regulate the odor response. This study provides a clue to indicate the possible protective mechanism of gap junction in odor response.

Local acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave-particle interaction and quasi-linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth's magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB), a code that models the Earth's ring current and provides a realistic modeling of the Earth's magnetic field. By applying quasi-linear theory, the bounce- and Magnetic Local Time (MLT)-averaged electron pitch angle, mixed-term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (∼1 MeV) and ring current (∼100 keV) electrons, it is shown that at some MLTs the bounce-averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth's magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons.

The Notch signaling pathway regulates stem cell proliferation and differentiation in multiple tissues and organs, and is required for tissue maintenance. However, the role of Notch in regulation of olfactory epithelium (OE) progenitor/stem cells to maintain tissue function is still not clear. A recent study reported that leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) is expressed in globose basal cells (GBCs) localized in OE. Through lineage tracing in vivo, we found that Lgr5

A circuit analogy for Magnetosphere-Ionosphere current systems has two extremes for drivers of ionospheric currents: ionospheric electric fields/voltages constant while current/conductivity vary - the “voltage generator” - and current constant while electric field/conductivity vary - the “current generator”. Statistical studies of ground magnetometer observations associated with dayside Transient High Latitude Current Systems (THLCS) driven by similar mechanisms find contradictory results using this paradigm: some studies associate THLCS with voltage generators, others with current generators. We argue most of this contradiction arises from two assumptions used to interpret ground magnetometer observations: (1) measurements made at fixed position relative to the THLCS field-aligned current and (2) negligible auroral precipitation contributions to ionospheric conductivity. We use observations and simulations to illustrate how these two assumptions substantially alter expectations for magnetic perturbations associated with either a current or voltage generator. Our results demonstrate that before interpreting ground magnetometer observations of THLCS in the context of current/voltage generators, the location of a ground magnetometer station relative to the THLCS field-aligned current and the location of any auroral zone conductivity enhancements need to be taken into account.

Data assimilation using Kalman filters provides an effective way of understanding both spatial and temporal variations in the outer electron radiation belt. Data assimilation is the combination of in situ observations and physical models, using appropriate error statistics to approximate the uncertainties in both the data and the model. The global magnetic field configuration is one essential element in determining the adiabatic invariants for the phase space density (PSD) data used for the radiation belt data assimilation. The lack of a suitable global magnetic field model with high accuracy is still a long-lasting problem. This paper employs a physics-based magnetic field configuration for the first time in a radiation belt data assimilation study for a moderate storm event on 19 December 2002. The magnetic field used in our study is the magnetically self-consistent inner magnetosphere model RAM-SCB, developed at Los Alamos National Laboratory (LANL). Furthermore, we apply a cubic spline interpolation method in converting the differential flux measurements within the energy spectrum, to obtain a more accurate PSD input for the data assimilation than the commonly used linear interpolation approach. Finally, the assimilation is done using an ensemble Kalman filter (EnKF), with a localized adaptive inflation (LAI) technique to appropriately account for model errors in the assimilation and improve the performance of the Kalman filter. The assimilative results are compared with results from another assimilation experiment using the Tsyganenko 2001S (T01S) magnetic field model, to examine the dependence on a magnetic field model. Results indicate that the data assimilations using different magnetic field models capture similar features in the radiation belt dynamics, including the temporal evolution of the electron PSD during a storm and the location of the PSD peak. The assimilated solution predicts the energy differential flux to a relatively good degree when compared with independent LANL-GEO in situ observations. A closer examination suggests that for the chosen storm event, the assimilation using the RAM-SCB predicts a better flux at most energy levels during storm recovery phase but is slightly worse in the storm main phase than the assimilation using the T01S model.

Simulations from our newly expanded ring current-atmosphere interactions model with self-consistent magnetic field (RAM-SCB), now valid out to 9 RE, are compared for the first time with Van Allen Probes observations. The expanded model reproduces the storm time ring current buildup due to the increased convection and inflow of plasma from the magnetotail. It matches Magnetic Electron Ion Spectrometer (MagEIS) observations of the trapped high-energy (>50 keV) ion flux; however, it underestimates the low-energy ( 20 keV) energy are better reproduced using a high-resolution convection model. In agreement with Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations, RAM-SCB indicates that the large-scale magnetic field is depressed as close as ∼4.5 RE during even a moderate storm. Regions of electromagnetic ion cyclotron instability are predicted on the duskside from ∼6 to ∼9 RE, indicating that previous studies confined to geosynchronous orbit may have underestimated their scattering effect on the energetic particles.

We simulate substorm injections observed by the Van Allen Probes during the 17 March 2013 storm using a self-consistent coupling between the ring current model RAM-SCB and the global MHD model BATS-R-US. This is a significant advancement compared to previous studies that used artificially imposed electromagnetic field pulses to mimic substorm dipolarization and associated inductive electric field. Several substorm dipolarizations and injections are reproduced in the MHD model, in agreement with the timing of shape changes in the AE/AL index. The associated inductive electric field transports plasma sheet plasma to geostationary altitudes, providing the boundary plasma source to the ring current model. It is found that impulsive plasma sheet injections, together with a large-scale convection electric field, are necessary to develop a strong ring current. Comparisons with Van Allen Probes observations show that our model reasonably well captures dispersed electron injections and the global Dst index.

Capturing and subsequently modeling the influence of tail plasma injections on the inner magnetosphere is important for understanding the formation and evolution of the ring current. In this study, the ring current distribution is estimated with the Ring Current-Atmosphere Interactions Model with Self-Consistent Magnetic field (RAM-SCB) using, for the first time, data assimilation techniques and particle flux data from the Van Allen Probes. The state of the ring current within the RAM-SCB model is corrected via an ensemble based data assimilation technique by using proton flux from one of the Van Allen Probes, to capture the enhancement of the ring current following an isolated substorm event on July 18, 2013. The results show significant improvement in the estimation of the ring current particle distributions in the RAM-SCB model, leading to better agreement with observations. This newly implemented data assimilation technique in the global modeling of the ring current thus provides a promising tool to improve the characterization of particle distribution in the near-Earth regions.

Atorvastatin and its lactone form metabolite are reported to be associated with statin-induced myopathy (SIM) such as myalgia and life-threatening rhabdomyolysis. Though the statin-induced rhabdomyolysis is not common during statin therapy, its incidence will significantly increase due to pharmacokinetic drug-drug interactions (DDIs) with inhibitor drugs which inhibit atorvastatin’s and its lactone’s metabolism and hepatic uptake. Thus, the quantitative analysis of DDIs of atorvastatin and its lactone with cytochrome P450 3A4 (CYP3A4) and organic anion-transporting polypeptide (OATP) inhibitors is of great importance. This study aimed to predict pharmacokinetic DDIs possibly causing atorvastatin-induced rhabdomyolysis using Physiologically Based Pharmacokinetic (PBPK) Modelling. Firstly, we refined the PBPK models of atorvastatin and atorvastatin lactone for predicting the DDIs with CYP3A4 and OATP inhibitors. Thereafter, we predicted the exposure changes of atorvastatin and atorvastatin lactone originating from the case reports of atorvastatin-induced rhabdomyolysis using the refined models. The simulation results show that pharmacokinetic DDIs of atorvastatin and its lactone with fluconazole, palbociclib diltiazem and cyclosporine are significant. Consequently, clinicians should be aware of necessary dose adjustment of atorvastatin being used with these four inhibitor drugs.

Morphological features of the quiet/disturbed time variations in the Total Electron Content (TEC) at the polar cusp station Bharati (76.69°S MLAT) during a period of 5 years starting from February 2013 to December 2017 has been studied using GPS TEC measurements. The TEC at Bharati follows a diurnal pattern with its peak appearing close to local noon/magnetic noon during the summer/winter months. A nighttime enhancement in the TEC is seen around the magnetic midnight during winter. The plasma density at Bharati also exhibits semi-annual variation and a strong dependence on solar activity. A comparison of the IRI 2016 model derived TEC and the GPS TEC at Bharati shows significant differences with large underestimation of TEC especially during the nighttime period of the winter months. A two fold difference in magnitude between the GPS and modeled TEC is also observed in the summer months of the high solar activity period of 2013–2015. The response of the TEC to geomagnetic storms is found to depend on the onset time of the storm. We show that the morphological features in the temporal evolution of the plasma density at Bharati vary as the location of Bharati changes from being inside the polar cap, to the auroral region, and to the polar cusp in quick succession in a day. Our results highlight the fact that the dynamic nature of the location of Bharati with respect to the position of the polar cap plays an important role in deciding the plasma distribution at the polar cusp station.

[1] The ionospheric O+ outflow varies dramatically during geomagnetic activities, but the influence of its initial characteristics on the magnetospheric dynamics has not been well established. To expand a previous study on the impact of ionospheric heavy ions outflow originating from different source regions on the magnetotail dynamics and dayside reconnection rate, this study conducts two idealized numerical experiments with different O+ outflow densities to examine the consequent change in the magnetosphere system, especially on the solar wind-magnetosphere coupling efficiency. Results indicate that a larger O+ outflow is capable of triggering the Kelvin-Helmholtz instability (KHI) on the magnetopause flanks. The subsequent surface waves enhance the solar wind-magnetosphere coupling efficiency by transmitting more solar wind energy into the magnetosphere-ionosphere system, increasing the cross polar cap potential index. This index is initially reduced after the ionospheric mass loading owing to the direct depression in the dayside reconnection rate as commonly reported from earlier literature. The above KHI is generated under steady state solar wind conditions, suggesting that besides the commonly recognized cause, the elevated solar wind speed, ionospheric heavy ions outflow is another potential factor in disturbing the boundary by enhancing the mass density near the magnetopause and thus lowering the threshold for generating KHI. During storms, the increased ionospheric mass source causes an increased probability of KHI, which allows more solar wind plasma into the magnetosphere. This implies there is a possibility of even further nonlinear coupling between the magnetosphere and solar wind.

[1] This paper reports the metrics-based results of the Dst index part of the 2008–2009 GEM Metrics Challenge. The 2008–2009 GEM Metrics Challenge asked modelers to submit results for four geomagnetic storm events and five different types of observations that can be modeled by statistical, climatological or physics-based models of the magnetosphere-ionosphere system. We present the results of 30 model settings that were run at the Community Coordinated Modeling Center and at the institutions of various modelers for these events. To measure the performance of each of the models against the observations, we use comparisons of 1 hour averaged model data with the Dst index issued by the World Data Center for Geomagnetism, Kyoto, Japan, and direct comparison of 1 minute model data with the 1 minute Dst index calculated by the United States Geological Survey. The latter index can be used to calculate spectral variability of model outputs in comparison to the index. We find that model rankings vary widely by skill score used. None of the models consistently perform best for all events. We find that empirical models perform well in general. Magnetohydrodynamics-based models of the global magnetosphere with inner magnetosphere physics (ring current model) included and stand-alone ring current models with properly defined boundary conditions perform well and are able to match or surpass results from empirical models. Unlike in similar studies, the statistical models used in this study found their challenge in the weakest events rather than the strongest events.

[1] Heavy ions of ionospheric origin (O+) play an important role in altering global magnetospheric dynamics. While the heavy ions mainly originate from the dayside cusp and the nightside auroral region, the impact of these heavy ions on magnetospheric dynamics has not been differentiated. Controversy also remains on the role of heavy ions on tail stability and their energization mechanism in the magnetosphere. Two global MHD simulations are carried out to investigate the influence of heavy ion outflow from different source regions on reconnection rates, tail stability, and ring current energization. The local reconnection rate at the subsolar point and the total dayside reconnection rate are reduced after the outflow begins, but the decrease is more significant when the outflow comes out of the cusp region. Furthermore, the magnetotail is more disturbed when heavy ions flow out of the dayside cusp region as opposed to the nightside auroral zone. This implies that the role of O+ on tail stability is not definitively positive or negative; instead, the location of the source of heavy ions may be important in determining tail dynamics. Finally, the simulation reveals that the heavy ions originating from the dayside cusp region experience first adiabatic heating while traveling from the tail reconnection site toward the Earth and then further energization caused by flow braking near the outer boundary of the ring current.

The pitch angle distribution (PAD) of suprathermal electrons can have both spatial and temporal evolution in the magnetotail and theoretically can be an indication of electron energization/cooling processes there. So far, the spatial evolution of PAD has been well studied, leaving the temporal evolution as an open question. To reveal the temporal evolution of electron PAD, spacecraft should monitor the same flux tube for a relatively long period, which is not easy in the dynamic magnetotail. In this study, we present such an observation by Cluster spacecraft in the magnetotail behind a dipolarization front (DF). We find that the PAD of suprathermal electrons can evolve from pancake type to butterfly type during

We investigate variations of the location and intensity of auroral currents during two magnetic storm periods based on magnetic field measurements from CHAMP separately for both hemispheres, as well as for the dayside and nightside. The corresponding auroral electrojet current densities are on average enhanced by about a factor of 7 compared to the quiet time current strengths. The nightside westward current densities are on average 1.8 (2.2) times larger than the dayside eastward current densities in the Northern (Southern) Hemisphere. Both eastward and westward currents are present during the storm periods with the most intense electrojets appearing during the main phase of the storm, before the ring current maximizes in strength. The eastward and westward electrojet centers can expand to 55° MLat during intense storms, as is observed on 31 March 2001 with Dst=−387 nT. The equatorward shift of auroral currents on the dayside is closely controlled by the southward IMF, while the latitudinal variations on the nightside are better described by the variations of the Dst index. However, the equatorward and poleward motion of the nightside auroral currents occur earlier than the Dst variations. The Space Weather Modeling Framework (SWMF) can capture the general dynamics of the storm time current variations. Both the model and the actual data show that the currents tend to saturate when the merging electric field is larger than 10 mV/m. However, the exact prediction of the temporal development of the currents is still not satisfactory.

The Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin, MnIIITE-2-PyP5+ (AEOL-10113) has proven effective in treating oxidative stress-induced conditions including cancer, radiation damage, diabetes, and central nervous system trauma. The ortho cationic pyridyl nitrogens of MnTE-2-PyP5+ are essential for its high antioxidant potency. The exceptional ability of MnIIITE-2-PyP5+ to dismute O2.- parallels its ability to reduce ONOO- and CO3-. Decreasing levels of these species are considered its predominant mode of action, which may also involve redox regulation of signaling pathways. Recently, Ferrer-Sueta at al. (Free Radic. Biol. Med. 41:503-512; 2006) showed, with submitochondrial particles, thator=3 microM MnIIITE-2-PyP5+ was able to protect components of the mitochondrial electron transport chain from peroxynitrite-mediated damage. Our study complements their data in showing, for the first time that micromolar mitochondrial concentrations of MnIIITE-2-PyP5+ are obtainable in vivo. For this study we have developed a new and sensitive method for MnIIITE-2-PyP5+ determination in tissues. The method is based on the exchange of porphyrin Mn2+ with Zn2+, followed by the HPLC/fluorescence detection of ZnIITE-2-PyP4+. At 4 and 7 h after a single 10 mg/kg intraperitoneal administration of MnIIITE-2-PyP5+, the mice (8 in total) were anesthetized and perfused with saline. Mitochondria were then isolated by the method of Mela and Seitz (Methods Enzymol.55:39-46; 1979). We found MnIIITE-2-PyP5+ localized in heart mitochondria to 2.95 ng/mg protein. Given the average value of mitochondrial volume of 0.6 microL/mg protein, the calculated MnIIITE-2-PyP5+ concentration is 5.1 microM, which is sufficient to protect mitochondria from oxidative damage. This study establishes, for the first time, that MnIIITE-2-PyP5+, a highly charged metalloporphyrin, is capable of entering mitochondria in vivo at levels sufficient to exert there its antioxidant action; such a result encourages its development as a prospective therapeutic agent.

Neural stem cells (NSCs) are self-renewing and pluripotent, which can differentiate into neurons, astrocytes and oligodendrocytes. Due to these properties, NSCs are supposed to be an ideal candidate to clinical purpose while research on cell replacement therapy to treat neural diseases has been widely investigated recently. In this article, we demonstrated a new and efficient method to induce the generation of proliferative dopaminergic neurons from rat NSCs in the presence of bFGF, heparin and laminin both in vitro and in vivo. These cells were testified to survive in the grafted 6-Hydroxy-Dopamine (6-OHDA) lesioned rat for at least 1 month. More importantly, migration to close host tissue was observed on day 30 post-transplantation. In this regard, we anticipated that this technology may advance stem cell-based therapy to replace lost neurons in neural injury or neurodegenerative disorders.

Extracellular nucleotides are important neurotransmitters, neuromodulators and paracrine factors in the neural sensory system [16]. Most of purines and pyrimidines act on the associated purinergic cell-surface receptors to mediate sensory transduction and modulation. Previously, we reported a subgroup of heptaldehyde (H)/2-hepatanone (Ho)-responsive olfactory sensory neurons (H/Ho-OSNs) in the ventral endoturbinates [31]. Through the calcium image recording, we characterized that ATP elicited [Ca(2+)]i increase in the presence of extracellular calcium, while depletion of intracellular calcium stores blocked UTP-evoked [Ca(2+)]i increase. Pharmacological studies indicated that P2X3 was expressed in the H/Ho-OSNs, modulating both heptaldehyde (H) and 2-hepatanone (Ho)-induced responses. These data indicated that activation of purinergic receptor negatively modulated odor response, providing the evidence to support the possible protective effect of purinergic receptor in OSNs.

Mechanosensitive cells are essential for organisms to sense the external and internal environments, and a variety of molecules have been implicated as mechanical sensors. Here we report that odorant receptors (ORs), a large family of G protein-coupled receptors, underlie the responses to both chemical and mechanical stimuli in mouse olfactory sensory neurons (OSNs). Genetic ablation of key signaling proteins in odor transduction or disruption of OR–G protein coupling eliminates mechanical responses. Curiously, OSNs expressing different OR types display significantly different responses to mechanical stimuli. Genetic swap of putatively mechanosensitive ORs abolishes or reduces mechanical responses of OSNs. Furthermore, ectopic expression of an OR restores mechanosensitivity in loss-of-function OSNs. Lastly, heterologous expression of an OR confers mechanosensitivity to its host cells. These results indicate that certain ORs are both necessary and sufficient to cause mechanical responses, revealing a previously unidentified mechanism for mechanotransduction.

Using an extended MHD model including the Hall effect and finite Larmor radius effect, we reproduce multiple dipolarization fronts (DFs) associated with the interchange instability in the braking region of bursty bulk flow in the plasma sheet. Our simulations reveal that the multiple DFs produced by the interchange instability are “growing” type DFs because the maximum plasma flow speeds are behind the fronts. Both the earthward and tailward moving DFs can be produced by interchange instability in the near-Earth region. The Hall electric field is the dominant electric field component in the dip region and the DF layer. The convective and the electron pressure gradient electric field components are smaller. The sharp Bz changes in both the dip region and DF layer correspond to the oppositely directed currents that are primarily associated with electrons. The ion diamagnetic current due to the strong ion pressure gradient causes an intense downward current in the dip region, which can produce the dip ahead ...

[1] The validation of the magnetically self-consistent inner magnetospheric model RAM-SCB developed at Los Alamos National Laboratory is presented here. The model consists of two codes: a kinetic ring current–atmosphere interaction model (RAM) and a 3-D equilibrium magnetic field code (SCB). The validation is conducted by simulating two magnetic storm events and then comparing the model results against a variety of satellite in situ observations, including the magnetic field from Cluster and Polar spacecraft, ion differential flux from the Cluster/CODIF (Composition and Distribution Function) analyzer, and the ground-based SYM-H index. The model prediction of the magnetic field is in good agreement with observations, which indicates the model's capability of representing well the inner magnetospheric field configuration. This provides confidence for the RAM-SCB model to be utilized for field line and drift shell tracing, which are needed in radiation belt studies. While the SYM-H index, which reflects the total ring current energy content, is generally reasonably reproduced by the model using the Weimer electric field model, the modeled ion differential flux clearly depends on the electric field strength, local time, and magnetic activity level. A self-consistent electric field approach may be needed to improve the model performance in this regard.

The third adiabatic invariant L* plays an important role in modeling and understanding the radiation belt dynamics. The typical way to numerically calculate the L* value follows the method described by Roederer (1970), which is just a line integration method that is computationally slow and expensive. This work describes the application of an artificial neural network technique to a series of magnetospheric field models for calculating L* values in microseconds instead of seconds without losing significant accuracy, thereby delivering to the radiation belt community various L* neural networks. These neural networks will enable comprehensive solar-cycle long studies of radiation belt processes and can also help the development of operational radiation belt models because of the speed in calculating L*. The main focus of this work is to test the applicability of each L* neural network, an aspect not addressed in the previous studies, under different interplanetary and magnetospheric conditions. Specifically, we describe the conditions when the neural network is providing a good approximation to the full numerical calculation of L* and when the traditional but more time-consuming method should be used. These L* neural networks are available for download at http://lanlstar.net.

[1] The different responses of the magnetosphere to sudden solar wind density enhancements are investigated. The majority of the responses are observed to have two phases: the first is due to an inductive E field propagating through the system, while the second is due to a vortex formation in the magnetosphere. However, during some events, the system displays a single-phase response. In order to understand the controlling parameters in the system response, statistical analyses of several solar wind external characteristics as well as the internal index Dst are conducted. Results of these analyses show that none of those characteristics seem to be associated with the way the geospace system responds to the abrupt solar wind density increase. Owing to the lack of statistics in the analysis, simulations investigating the effect of the solar wind Alfven Mach number on the magnetospheric response have been conducted. The simulation results indicate that the two-phase response is always present but that a low solar wind Mach number causes an indistinct two-phase response, which is difficult to identify as having two phases. Compression signals following the sudden compression at the magnetopause are carried by a fast mode wave in the magnetosphere, which propagates toward the Earth and is reflected back toward the magnetopause by the plasmapause or ionosphere. The wave is subsequently reflected back again, leading to a secondary Earthward propagation. These multiple bounces of the fast mode wave result in two groups of the two-phase responses in the ionosphere, although the second group is extremely difficult to identify in ionospheric data.

[1] Many high‐latitude modeling studies utilize the horizontal ionospheric Hall current in calculating ground‐based magnetic perturbations, but low‐latitude and midlatitude studies should include current systems such as the magnetospheric, field‐aligned, and Pedersen currents. Recently, by including all these current systems, a more precise ground‐ based perturbation calculator has been implemented in the Space Weather Modeling Framework. Using this new method, ground‐based perturbations generated by different current systems are analyzed at low, middle, and high latitudes. As a result of the current systems, MLT‐UT maps of ground‐based perturbations are studied. Furthermore, nine storms events are simulated at more than 20 low‐latitude and midlatitude magnetometer locations and compared with observational ground‐based perturbations. These studies show that for specifying the northward component of the ground magnetic perturbations, the inclusion of magnetospheric, field‐aligned, and Pedersen current is important and improves the prediction significantly over the prediction only considering the Hall current in the calculation. The improvement is the most during the storm main phase. However, for the vertical and eastward components of the perturbations, which were typically smaller than the northward component, the inclusion of these current systems actually made the specifications worse because the ring current in the model rotates more toward the dayside than in reality.

[1] We use results from a global MHD simulation to study the interaction of an interplanetary shock with the Earth's magnetosphere for a northward interplanetary magnetic field orientation. We connect intensifications of the transient northward Bz (NBZ) and Region 1 currents in the ionosphere with the appearance of two strong dynamo regions in the magnetosphere: the first on the high-latitude magnetopause near and behind the cusps and the second near the equatorial plane on the flanks. The ionospheric and magnetospheric transients are well synchronized and move antisunward gradually. According to the results obtained, the source of energy for the transient NBZ current is related to shock-intensified lobe reconnection, while the transient Region 1 current corresponds to the reflected fast shock predicted by Samsonov et al. (2007). We speculate that the electric circuits for the quasi-stationary field-aligned currents are similar to the transient electric circuits obtained in this paper.

[1] A sudden southward turning of interplanetary magnetic field (IMF) is simulated by the University of Michigan's BATS-R-US model. The main goal of this study is to determine the time delay as well as physical processes between when an IMF discontinuity reaches the bow shock, when reconnection is initiated at the magnetopause, and when the ionosphere starts to react. While observations or empirical models might give an estimate of the time delay for the propagation of the discontinuity from the bow shock to the magnetopause, the global MHD simulation provides a more comprehensive insight of responses of the magnetosphere-ionosphere system. An idealized north-to-south IMF transition is modeled, using a solar wind velocity of 400 km/s. After the southward IMF encounters the bow shock, it takes about 6 min for the north-to-south IMF transition front to arrive at the subsolar geomagnetic field. The ionospheric response to this sudden southward IMF turning is delayed by another ∼4 min, during which the magnetosphere undergoes a conversion from cusp reconnection to subsolar reconnection and the Alfven wave propagation to the ionosphere takes place. Thereafter, changes in the ionosphere and ground magnetic perturbations associated with the southward IMF are observed. These responses appear to be globally onset as described in many other studies. The time it takes from the encounter of the IMF transition with the bow shock to when the ionospheric reaction takes place varies with the solar wind speed, ranging from nearly 15 min for a solar wind speed of 300 km/s to just over 6 min for solar wind speeds of 600 km/s.

[1] Geomagnetically induced currents (GICs) can disrupt power grid operations, causing significant interference for many people; therefore, predictions of ground-based magnetic perturbations and their time derivatives are quite important. This study quantifies how well the University of Michigan's Global MHD code predicts approximately 150 ground-based magnetometer traces for a number of storm-time intervals. It is found that in order to accurately represent the magnetic perturbation, Biot-Savart integrals over the entire hemisphere are needed, especially when calculating the vertical component. The 4 May 1998 storm is examined in detail. The code compares well with some stations, quantified by a normalized root mean squared error and cross correlation, while missing even the general trends for other stations. When multiple magnetometer station perturbations are averaged together, the model does an adequate job in the north and vertical components but reverses the trends in the eastward component. The code does significantly better when comparing an AL-like index but does not have as strong a variation as the actual data. Comparison of dB/dt in a wide window rather than simultaneously shows better model performance in capturing events but worse in yielding false alarms. It is further found that the MHD code models the magnetic perturbations better in the summer hemisphere than in the winter hemisphere.

Signal transducers and activator of transcription (STAT) proteins are activated in response to many cytokines and growth factors. Many studies indicated that regulation of STAT expression plays an important role in survival, growth, and differentiation of neurons and glias in response to ciliary neurotropic factor, including rehabilitation of rat cortical injury, nerve regeneration, gangliosides-mediated stimulation of rat and murine primary microglia, and differentiation of retinal neurons. In this study, we use olfactory bulb neurons as a useful model, which undergo strong neurogenesis throughout adulthood. Our research demonstrated that low level of STAT3 expression facilitates the terminal differentiation of olfactory bulb neurons as well as induces the generation of neurons from neural stem cells, which can be potentially used in future therapies. On the contrary, activation of STAT3 expression is essential to the maintenance of stem-like status in olfactory cells. This activation can be manipulated by leukemia inhibitory factor (LIF), a member of cytosolic tyrosine kinases. All these results implicate that STAT3 serves as a critical protein in regulating the differentiation state in neural cells.