Polar Expansion Research Articles

Magnetopause erosion during the 17 March 2015 magnetic storm: Combined field‐aligned currents, auroral oval, and magnetopause observations

AbstractWe present multimission observations of field‐aligned currents, auroral oval, and magnetopause crossings during the 17 March 2015 magnetic storm. Dayside reconnection is expected to transport magnetic flux, strengthen field‐aligned currents, lead to polar cap expansion and magnetopause erosion. Our multimission observations assemble evidence for all these manifestations. After a prolonged period of strongly southward interplanetary magnetic field, Swarm and AMPERE observe significant intensification of field‐aligned currents. The dayside auroral oval, as seen by DMSP, appears as a thin arc associated with ongoing dayside reconnection. Both the field‐aligned currents and the auroral arc move equatorward reaching as low as ~60° magnetic latitude. Strong magnetopause erosion is evident in the in situ measurements of the magnetopause crossings by GOES 13/15 and MMS. The coordinated Swarm, AMPERE, DMSP, MMS and GOES observations, with both global and in situ coverage of the key regions, provide a clear demonstration of the effects of dayside reconnection on the entire magnetosphere.

Climate change and polar range expansions: Could cuttlefish cross the Arctic?

Climate change can have major effects on the distribution of species. In marine ecosystems, the cold waters of the Arctic have restricted warmer water species from crossing between Eurasia and North America. However, with Arctic waters becoming warmer, various marine species have expanded their distribution. Cuttlefish are fast-growing, voracious predators and are absent in American waters. The European cuttlefish Sepia officinalis is the most northerly distributed cuttlefish, with potential to expand its range and cross to the American continent, potentially causing changes in shelf food webs. Climate model predictions suggest that the S. officinalis could potentially reach American shores, by 2300 via the north Atlantic with medium mitigation of greenhouse gas concentrations; we predict that adult dispersal of cuttlefish across the Atlantic sector would require a migration distance of over 1400 km at depths below 200 m and temperatures above 7 °C (temperature below which cuttlefish can not maintain routine metabolic processes physiologically). For temperatures above 9.5 °C (temperature above which cuttlefish can grow), 2500 km would be required, and such conditions will possibly exist by the year 2300. If they reach American shores they could have large impacts on coastal marine ecosystems, due to their wide diet (e.g. diet covers many shallow-water crustacean and fish species) and its potential as prey, and due to their short life-history strategy of “live fast, die young”.

ChemInform Abstract: Visible‐Light Photoredox‐Catalyzed Semipinacol‐Type Rearrangement: Trifluoromethylation/Ring Expansion by a Radical—Polar Mechanism.

Abstract19 examples

Constitutive Expresser of Pathogenesis Related Genes 1 Is Required for Pavement Cell Morphogenesis in Arabidopsis.

For over 50 years, researchers have focused on the mechanisms underlying the important roles of the cytoskeleton in controlling the cell growth direction and cell expansion. In our study, we performed ethyl methane sulfonate mutagenesis on Col-0 background and identified two new CONSTITUTIVE EXPRESSER OF PATHOGENESIS RELATED GENES 1 (CPR1) alleles with pavement cell (PC) morphogenetic defects. Morphological characterizations showed that polar growth initiation and expansion of PCs are seriously suppressed in cpr1. Closer cytoskeleton investigation showed that the directional arrangement of microtubules (MTs) during PC development is defective and the cortical fine actin filaments cannot be aggregated effectively to form actin cable networks in cpr1 mutants. These results suggest that the abnormal PC morphogenesis in cpr1 is accompanying with the aberrant arrangement of cytoskeleton. Site-directed mutagenesis and knockout within the F-box-associated (FBA) domain, which is reported to be a motif for recognizing particular substrates of CPR1, proved that the FBA domain is indispensable for normal CPR1 regulation of the PC morphogenesis. Further genetic analysis indicated that the defects on PC morphogenesis of cpr1 depend on two lipase-like proteins, ENHANCED DISEASE SUSCEPTIBILITY 1 and PHYTOALEXIN DEFICIENT 4. Our results provide further insights into the relationship between the cytoskeleton and PC morphogenesis, and suggest that the cytoskeleton-mediated PC morphogenesis control might be tightly linked to plant defense responses.

Development of efficient models of Magnetic Braking Systems of railway vehicles

In modern railway vehicles, the use of Magnetic Braking Systems is continuously increasing, because they are characterized by high braking performances and low energy consumptions. Hence, the study and the accurate modelling of Magnetic Braking Systems is a very important issue, because they significantly affect the dynamics of vehicle and electrical supply circuit. Usually, the performances of Magnetic Braking Systems are evaluated on test-rigs in order to reduce times and costs of testing phases. For this reason, the authors focus on the development of a complete 3D model of Magnetic Brake System test-rig (built in COMSOL), including all the electromagnetic, circuital and mechanical parts. These parts are often studied separately in the literature; however, a combined analysis is crucial to correctly describe the behaviour of the whole system. The proposed model is highly modular (to describe different Magnetic Brake System test-rig layouts characterized by a different number of magnetic polar expansions) and aims at obtaining a compromise between accuracy and numerical efficiency. Subsequently, a second simplified lumped parameter model derived from the complete one and built in MATLAB is developed, to further reduce the computational load without decreasing the results accuracy. In this work, both the models have been developed and validated in collaboration Ferrovie dello Stato and compared with other simplified models present in the literature.

The microtubule plus-end tracking proteins SPR1 and EB1b interact to maintain polar cell elongation and directional organ growth in Arabidopsis.

The microtubule plus-end tracking proteins (+TIPs) END BINDING1b (EB1b) and SPIRAL1 (SPR1) are required for normal cell expansion and organ growth. EB proteins are viewed as central regulators of +TIPs and cell polarity in animals; SPR1 homologs are specific to plants. To explore if EB1b and SPR1 fundamentally function together, we combined genetic, biochemical, and cell imaging approaches in Arabidopsis thaliana. We found that eb1b-2 spr1-6 double mutant roots exhibit substantially more severe polar expansion defects than either single mutant, undergoing right-looping growth and severe axial twisting instead of waving on tilted hard-agar surfaces. Protein interaction assays revealed that EB1b and SPR1 bind each other and tubulin heterodimers, which is suggestive of a microtubule loading mechanism. EB1b and SPR1 show antagonistic association with microtubules in vitro. Surprisingly, our combined analyses revealed that SPR1 can load onto microtubules and function independently of EB1 proteins, setting SPR1 apart from most studied +TIPs in animals and fungi. Moreover, we found that the severity of defects in microtubule dynamics in spr1 eb1b mutant hypocotyl cells correlated well with the severity of growth defects. These data indicate that SPR1 and EB1b have complex interactions as they load onto microtubule plus ends and direct polar cell expansion and organ growth in response to directional cues.

RISAP is a TGN-associated RAC5 effector regulating membrane traffic during polar cell growth in tobacco.

RAC/ROP GTPases coordinate actin dynamics and membrane traffic during polar plant cell expansion. In tobacco (Nicotiana tabacum), pollen tube tip growth is controlled by the RAC/ROP GTPase RAC5, which specifically accumulates at the apical plasma membrane. Here, we describe the functional characterization of RISAP, a RAC5 effector identified by yeast (Saccharomyces cerevisiae) two-hybrid screening. RISAP belongs to a family of putative myosin receptors containing a domain of unknown function 593 (DUF593) and binds via its DUF593 to the globular tail domain of a tobacco pollen tube myosin XI. It also interacts with F-actin and is associated with a subapical trans-Golgi network (TGN) compartment, whose cytoplasmic position at the pollen tube tip is maintained by the actin cytoskeleton. In this TGN compartment, apical secretion and endocytic membrane recycling pathways required for tip growth appear to converge. RISAP overexpression interferes with apical membrane traffic and blocks tip growth. RAC5 constitutively binds to the N terminus of RISAP and interacts in an activation-dependent manner with the C-terminal half of this protein. In pollen tubes, interaction between RAC5 and RISAP is detectable at the subapical TGN compartment. We present a model of RISAP regulation and function that integrates all these findings.

Using monoclonal antibodies to label living root hairs: a novel tool for studying cell wall microarchitecture and dynamics in Arabidopsis.

BackgroundThe Arabidopsis root hair represents a valuable cell model for elucidating polar expansion mechanisms in plant cells and the overall biology of roots. The deposition and development of the cell wall is central to the root hair expansion apparatus. During this process, incorporation of specific wall polymers into the growing wall architecture constitutes a critical spatio-temporal event that controls hair size and growth rate and one that is closely coordinated with the cell’s endomembrane, cytoskeletal and signal transduction apparatuses.ResultsIn this study, the protocol for live cell labeling of roots with monoclonal antibodies that bind to specific wall polymers is presented. This method allows for rapid assessment of root hair cell wall composition during development and assists in describing changes to cell wall composition in transgenic mutant lines. Enzymatic “unmasking” of specific polymers prior to labeling allows for refined interpretation of cell wall chemistry. Live cell immunofluorescence data may also be correlated with transmission electron microscopy-based immunogold labeling.ConclusionsLive Arabidopsis root hairs may be labeled with cell wall polymer-specific antibodies. This methodology allows for direct visualization of cell wall dynamics throughout development in stable transgenic plant lines. It also provides an important new tool in the elucidation of the specific interactions occurring between membrane trafficking networks, cytoskeleton and the cell wall deposition/remodeling mechanism.

Asymptotics of the exchange-splitting energy for a diatomic molecular ion from a volume-integral formula of symmetry-adapted perturbation theory

The exchange splitting energy $J$ of the lowest \emph{gerade} and \emph{ungerade} states of the H$_2^+$ molecular ion was calculated using a volume integral expression of symmetry-adapted perturbation theory and standard basis set techniques of quantum chemistry. The performance of the proposed expression was compared to the well known surface integral formula. Both formulas involve the primitive function which we calculated employing either the Hirschfelder-Silbey perturbation theory or the conventional Rayleigh-Schr\"odinger perturbation theory (the polarization expansion). Our calculations show that very accurate values of $J$ can be obtained using the proposed volume integral formula. When the Hirschfelder-Silbey primitive function is used in both formulas the volume formula gives much more accurate results than the surface integral expression. We also show that using the volume integral formula with the primitive function approximated by Rayleigh-Schr\"odinger perturbation theory, one correctly obtains only the first four terms in the asymptotic expansion of the exchange splitting energy.

Electronic interactions in 1D-π-assemblies from TLS analysis of thermal motion

Advanced features of TLS analysis within Olex2 program package allow for a detailed analysis of electronic redistribution in supramolecular systems. Particularly, the possibility of calculating TLS tensors in user-defined coordinate systems along with qualitative graphical representation of difference thermal motion are especially useful for analysis of atomic asphericity and intra- and inter-molecular electron redistribution. In addition, these features allow for a directional dynamic analysis of intermolecular motions from variable-temperature experiments. We explored the exciting new possibilities analyzing supramolecular assemblies closely resembling modern electronic materials for a series of electron donor-acceptor complexes and ion-radical salts based on aromatic octamethyl-anthracene and anti-aromatic octamethyl-biphenylene substrates. The difference TLS analysis revealed intimate details of chemical bond polarization and electronic shell expansion for acceptor components along with electronic shell contraction for donor components of the complexes indicative of intra- and intermolecular charge transfer. Also, the variable-temperature analysis of relative thermal motion of the complex components in the crystals revealed some widening of the potential-energy minima in direction of the electronic overlap as a result of intermolecular pi-orbital coupling both in charge-transfer and charge-resonance supramolecular assemblies. A theoretical interpretation of the observed peculiarities was undertaken supported by respective spectroscopic data.

Salt marshes

Salt marshes are unique ecosystems that are brimming with diversity, and provide crucial shelter to coastal communities.

Low Temperature Dielectric Properties of (Rb1-xKx)2ZnI4 Mixed Crystals

Rb2ZnI4 shows phase transitional anomalies at about 4 K and about 62 K in the temperature dependence of the dielectric constant. To investigate those, the mixed systems (Rb1-xKx)2ZnI4 and Rb2Zn1-xCdxI4 were prepared by both evaporation from the aqueous solution and Czochralski method from the melt. Dielectric constant, spontaneous polarization and thermal expansion measurements were performed for such mixed systems. For (Rb1-xKx)2ZnI4, the phase diagram was completed over full range of concentration x.

The cortical cytoskeletal network and cell-wall dynamics in the unicellular charophycean green alga Penium margaritaceum.

Penium margaritaceum is a unicellular charophycean green alga with a unique bi-directional polar expansion mechanism that occurs at the central isthmus zone prior to cell division. This entails the focused deposition of cell-wall polymers coordinated by the activities of components of the endomembrane system and cytoskeletal networks. The goal of this study was to elucidate the structural organization of the cortical cytoskeletal network during the cell cycle and identify its specific functional roles during key cell-wall developmental events: pre-division expansion and cell division. Microtubules and actin filaments were labelled during various cell cycle phases with an anti-tubulin antibody and rhodamine phalloidin, respectively. Chemically induced disruption of the cytoskeleton was used to elucidate specific functional roles of microtubules and actin during cell expansion and division. Correlation of cytoskeletal dynamics with cell-wall development included live cell labelling with wall polymer-specific antibodies and electron microscopy. The cortical cytoplasm of Penium is highlighted by a band of microtubules found at the cell isthmus, i.e. the site of pre-division wall expansion. This band, along with an associated, transient band of actin filaments, probably acts to direct the deposition of new wall material and to mark the plane of the future cell division. Two additional bands of microtubules, which we identify as satellite bands, arise from the isthmus microtubular band at the onset of expansion and displace toward the poles during expansion, ultimately marking the isthmus of future daughter cells. Treatment with microtubule and actin perturbation agents reversibly stops cell division. The cortical cytoplasm of Penium contains distinct bands of microtubules and actin filaments that persist through the cell cycle. One of these bands, termed the isthmus microtubule band, or IMB, marks the site of both pre-division wall expansion and the zone where a cross wall will form during cytokinesis. This suggests that prior to the evolution of land plants, a dynamic, cortical cytoskeletal array similar to a pre-prophase band had evolved in the charophytes. However, an interesting variation on the cortical band theme is present in Penium, where two satellite microtubule bands are produced at the onset of cell expansion, each of which is destined to become an IMB in the two daughter cells after cytokinesis. These unique cytoskeletal components demonstrate the close temporal control and highly coordinated cytoskeletal dynamics of cellular development in Penium.

IMF effect on the polar cap contraction and expansion during a period of substorms

Abstract. The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase. In addition, we suggest that the IMF Bz component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further.

Polar Expansion Dynamics in the Plant Kingdom: A Diverse and Multifunctional Journey on the Path to Pollen Tubes.

Polar expansion is a widespread phenomenon in plants spanning all taxonomic groups from the Charophycean Green Algae to pollen tubes in Angiosperms and Gymnosperms. Current data strongly suggests that many common features are shared amongst cells displaying polar growth mechanics including changes to the structural features of localized regions of the cell wall, mobilization of targeted secretion mechanisms, employment of the actin cytoskeleton for directing secretion and in many cases, endocytosis and coordinated interaction of multiple signal transduction mechanisms prompted by external biotic and abiotic cues. The products of polar expansion perform diverse functions including delivery of male gametes to the egg, absorption, anchorage, adhesion and photo-absorption efficacy. A comparative analysis of polar expansion dynamics is provided with special emphasis on those found in early divergent plants.

Nonlinear polarization response of a gaseous medium in the regime of atom stabilization in a strong radiation field

The nonlinear polarization response of a quantum system modeling a silver atom in the field of high-intensity radiation in the IR and UV spectral ranges has been studied by direct numerical integration of a nonstationary Schrodinger equation. The domains of applicability of perturbation theory and polarization expansion in powers of the field intensity are determined. The contribution of excited atoms and electrons in a continuum to the atomic polarization response at the field frequency, which arises due to the radiation-induced excitation and photoionization processes, is analyzed. Features of the nonlinear response to an external field under conditions of atom stabilization are considered.

Optimisation of Fixed Polarity Canonical Or-Coincidence Expansions

An efficient minimisation method is presented to find the best polarity of fixed polarity canonical or-coincidence (COC) expansions. The method derives one COC fixed polarity expansion from another adjacent polarity expansion. To reduce CPU time, it utilises bitwise operation and Gray code. Furthermore, it counts the number of “0”s in the polarity matrix rather than polarity matrix multiplication. As a result, it makes minimisation for large functions within reasonable time practical. The space complexity of the proposed algorithm is O( M ) and time complexity is O(2 n ( M log M + M )) ( n and M are the number of input variables and the number of on-set COC maxterms).

Polar expansion during cytokinesis

Vesicle trafficking and new membrane addition at the cleavage furrow have been extensively documented. However, less clear is the old idea that expansion at the cell poles occurs during cytokinesis. We find that new membrane is added to the cell poles during anaphase, causing the plasma membrane to expand coincident with the constriction of the contractile ring and may provide a pushing force for membrane ingression at the furrow. This membrane addition occurs earlier during mitosis than membrane addition at the furrow and is dependent on actin and astral microtubules. The membrane that is added at the polar regions is compositionally distinct from the original cell membrane in that it is devoid of GM(1) , a component of lipid rafts. These findings suggest that the growth of the plasma membrane at the cell poles during cell division is not due to stretching as previously thought, but due to the addition of compositionally unique new membrane.

Image region duplication detection based on circular window expansion and phase correlation

Region duplication forgery is one of the tampering techniques that are frequently used, where a part of an image is copied and pasted into another part of the same image. In this paper, a phase correlation method based on polar expansion and adaptive band limitation is proposed for region duplication forgery detection. Our method starts by calculating the Fourier transform of the polar expansion on overlapping windows pair, and then an adaptive band limitation procedure is implemented to obtain a correlation matrix in which the peak is effectively enhanced. After estimating the rotation angle of the forgery region, a searching algorithm in the sense of seed filling is executed to display the whole duplicated region. Experimental results show that the proposed approach can detect duplicated region with high accuracy and robustness to rotation, illumination adjustment, blur and JPEG compression while rotation angle is estimated precisely for further calculation.

THE EVOLUTION OF PLASMA PARAMETERS ON A CORONAL SOURCE SURFACE AT 2.3R☉DURING SOLAR MINIMUM

We analyze data from the Solar and Heliospheric Observatory to produce global maps of coronal outflow velocities and densities in the regions where the solar wind is undergoing acceleration. The maps use UV and white light coronal data obtained from the Ultraviolet Coronagraph Spectrometer and the Large Angle Spectroscopic Coronagraph, respectively, and a Doppler dimming analysis to determine the mean outflow velocities. The outflow velocities are defined on a sphere at 2.3 R☉ from Sun-center and are organized by Carrington Rotations during the solar minimum period at the start of solar cycle 23. We use the outflow velocity and density maps to show that while the solar minimum corona is relatively stable during its early stages, the shrinkage of the north polar hole in the later stages leads to changes in both the global areal expansion of the coronal hole and the derived internal flux tube expansion factors of the solar wind. The polar hole areal expansion factor and the flux tube expansion factors (between the coronal base and 2.3 R☉) start out as super-radial but then they become more nearly radial as the corona progresses away from solar minimum. The results also support the idea that the largest flux tube expansion factors are located near the coronal hole/streamer interface, at least during the deepest part of the solar minimum period.