Belt-like Structure Research Articles

Coupling between the N- and C- Termini of Kir2.1 is Critical for Cholesterol Modulation

In recent years, cholesterol has been emerging as a major regulator of ion channel function. The most common effect of cholesterol on ion channels is a decrease in channel activity that may include a decrease in the open probability, in the unitary conductance and/or in the number of active channels in the membrane. Yet, the mechanism by which cholesterol affects channel function is unclear.Here we focus on Kir2 channels, a subfamily of constitutively active, strongly inwardly rectifying K+ channels that set the resting membrane potential and modulate membrane excitability.We have previously shown that the function of Kir2 channels is suppressed by the elevation of membrane cholesterol and enhanced by cholesterol depletion. Furthermore, our earlier studies have shown that cholesterol sensitivity of Kir2 channels critically depends on a group of residues that form a belt-like structure around the cytosolic pore of the channel in proximity to the transmembrane domain. Surprisingly, however, each of the mutations of the cholesterol sensitivity belt residues that abrogated the cholesterol sensitivity of Kir2.1 also converted these residues to the corresponding residue in Kir2.2. This was completely unexpected because cholesterol sensitivities of Kir2.1 and Kir2.2 channels are very similar.In this study, we used this phenomenon to gain further insights into cholesterol sensitivity of Kir2 channels. Focusing on the L222I mutation, we screened the differences in the cytosolic domain between Kir2.1 and Kir2.2. Our analysis led to the identification of residues in the N-terminus and in the EF and GA loops of the C-terminus that reversed the effect of the L222I mutation on the cholesterol sensitivity of Kir2.1. These results indicate that an allosteric coupling between the N- and C- termini plays a critical role in cholesterol modulation of Kir2 channels.

Relaxation Dynamics and Structural Characterization of Organic Nanobelts with Aggregation-Induced Emission

We prepared the fluorescent nanobelts of cyano-substituted 1,4-distyrylbenzene derivative (CNDSB) with the reprecipitation method. CNDSB is nonemissive in solution but with strong aggregation-induced emission (AIE) in belt-like structure. The molecular structure predicted by quantum chemical calculations indicates a twisted conformation of CNDSB monomer, while the solid-state X-ray structure of the CNDSB crystal features herringbone-type arrangement and three benzene rings arrange in nearly planar conformation. Femto- and picosecond time-resolved fluorescence spectroscopy are implemented to study the photophysics and the origin of the AIE effect in CNDSB nanobelts. The fluorescence quenching of CNDSB in THF solution arises from the efficient nonradiative isomerization channel. In this study, the fluorescence decay of CNDSB embedded in poly(methyl methacrylate) matrix is slowed down due to the restriction of intramolecular motions in the solid matrix. In nanobelt structure, the fluorescence lifetime further increases due to the intermolecular interaction between H-type aggregates. Both the steady-state and time-resolved studies suggests that there are at least two different packing structures might exist in nanobelts, and the relative composition of these two different structures gradually changes in different sizes of nanobelts.

Alcohol Increases the Permeability of Airway Epithelial Tight Junctions in Beas‐2B and NHBE Cells

Tight junctions form a continuous belt-like structure between cells and act to regulate paracellular signaling. Protein kinase C (PKC) has been shown to regulate tight junction assembly and disassembly and is activated by alcohol. Previous research has shown that alcohol increases the permeability of tight junctions in lung alveolar cells. However, little is known about alcohol's effect on tight junctions in epithelium of the conducting airways. We hypothesized that long-term alcohol exposure reduces zonula occluden-1 (ZO-1) and claudin-1 localization at the cell membrane and increases permeability through a PKC-dependent mechanism. To test this hypothesis, we exposed normal human bronchial epithelial (NHBE) cells, cells from a human bronchial epithelial transformed cell line (Beas-2B), and Beas-2B expressing a PKCα dominant negative (DN) to alcohol (20, 50, and 100 mM) for up to 48 hours. Immunofluorescence was used to assess changes in ZO-1, claudin-1, claudin-5, and claudin-7 localization. Electric cell-substrate impedance sensing was used to measure the permeability of tight junctions between monolayers of NHBE, Beas-2B, and DN cells. Alcohol increased tight junction permeability in a concentration-dependent manner and decreased ZO-1, claudin-1, claudin-5, and claudin-7 localization at the cell membrane. To determine a possible signaling mechanism, we measured the activity of PKC isoforms (alpha, delta, epsilon, and zeta). PKCα activity significantly increased in Beas-2B cells from 1 to 6 hours of 100 mM alcohol exposure, while PKCζ activity significantly decreased at 1 hour and increased at 3 hours. Inhibiting PKCα with Gö-6976 prevented the alcohol-induced protein changes in both ZO-1 and claudin-1 at the cell membrane. PKCα DN Beas-2B cells were resistant to alcohol-induced protein alterations. These results suggest that alcohol disrupts ZO-1, claudin-1, claudin-5, and claudin-7 through the activation of PKCα, leading to an alcohol-induced "leakiness" in bronchial epithelial cells. Such alcohol-induced airway-leak state likely contributes to the impaired airway host defenses associated with acute and chronic alcohol ingestion.

A facile process to prepare copper oxide thin films as solar selective absorbers

Copper oxide thin films as solar selective absorbers were conveniently prepared by one-step chemical conversion method. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis–NIR spectra and Fourier transform infrared (FTIR) spectra were employed to characterize the composition, structure and optical properties of thin films. The results indicated that the composition, structure and optical properties of thin films were greatly influenced by reaction temperature, time and concentration of NaOH. When reaction temperature was fixed at 40 °C, the as-prepared films consist of pure cubic Cu 2O. The surface morphology of thin films was changed from square-like structure (reaction time ≤ 25 min) to porous belt-like structure (reaction time ≥ 30 min) with the elongation of reaction time. While for thin films prepared at 60 °C and 80 °C, single Cu 2O was observed after 5 min reaction. When reaction time is longer than 5 min, CuO appears and the content of CuO is increasing with the elongation of reaction time. With the increase of reaction temperature, the belt-like structure was easily formed for 60 °C/10 min and 80 °C/5 min. Decreasing concentration of NaOH also could result in the formation of CuO and porous belt-like structure. Simultaneously, the film thickness is increasing with the increase of reaction time, temperature and concentration. Films containing CuO with belt-like structure exhibited high absorptance (>0.9), and the emissivity of films increased with elongation of reaction time. Combination of the composition, structure and optical properties, it can be deduced that the porous belt-like structure like as a light trap can greatly enhance absorbance ( α), while the composition, thickness and roughness of thin films can greatly influence the emissivity ( ɛ). The highest photo-thermal conversion efficiency was up to 0.86 ( α/ ɛ = 0.94/0.08) for thin films prepared at 80 °C/5 min, which proved that the CuO x thin films can be served as high performance solar selective absorbers.

Preparation and Electrochemical Properties of VO<sub>2</sub>(B) Nano-Belts

The VO2(B) nanobelts with monoclinic phase were synthesized by a hydrothermal method at 220°C for 48 h in the absence of any surfactants. The electron energy loss spectrum (EELS) demonstrates that vanadium exists only in the 4+ oxidation state. The SEM and TEM images reveal a belt-like structure of the VO2(B) with the length of several micrometers, the width of 140 nm and the thickness of around 20nm and growth along the [110] crystal direction. Cyclic voltammetry (CV) and galvanostatic charge/discharge demonstrate that VO2(B) nano-belts electrode exhibits desirable electrochemical properties and the specific capacitance reaches up to 632.6F•g-1.

1H, 13C, and 15N resonance assignment of the first PDZ domain of mouse ZO-1

Zonula occludens-1 (ZO-1) is a scaffolding molecule critical to the formation of intercellular adhesion structures, such as tight junctions (TJs) and adherens junctions (AJs). ZO-1 contains three PDZ domains followed by a GUK domain and a ZU5 domain. The first PDZ of ZO-1 (ZO-1(PDZ1)) serves as a protein-protein interaction module and interacts with the C-termini of almost all claudins to initiate the formation of a belt-like structure on the lateral membranes, thereby promoting TJ formation. It has been recently reported that approximately 15% of all PDZ domains bind phosphoinositides, and ZO-1(PDZ1) is the one of these. Here we report the (15)N, (13)C, and (1)H chemical shift assignments of the first PDZ domain of mouse ZO-1. The resonance assignments obtained in this work may contribute in clarifying the interplay between the two binary interactions, ZO-1(PDZ1)-claudins and ZO-1(PDZ1)-phospholipids, and suggesting a novel regulation mechanism underlying the formation and maintenance of cell-cell adhesion machinery downstream of the phospholipid signaling pathways.

A theoretical survey on the structures, energetics, and isomerization pathways of the B5O radical

Boron-centered radicals have received growing interest. Recently, two groups reported density functional theory investigations (GGA-PW91 and B3LYP) on a hexa-atomic boron-oxide radical, B(5)O, which has led to great discrepancies on the type of low-lying structures. In this article, we not only explore the energetics of doublet and quartet B(5)O isomers at high electron-correlated levels (CCSD(T)/6-311+G(2df), CCSD(T)/aug-cc-pVTZ, and G3B3) but also investigate the isomerization and fragmentation stability of the low-lying B(5)O isomers. All the high-level studies consistently show that the B(5)O radical possesses a belt-like ground structure (2)01 in doublet electronic state followed by isomer (2)02 with an exocyclic - BO moiety at around 3.0 kcal/mol. Kinetically, (2)01 and (2)02 are separated by a considerable barrier of about 20 kcal/mol. Thus, the two isomeric forms of B(5)O radical should be very promising for isolation in laboratory. However, the other four isomers reported recently are all kinetically unstable toward conversion to (2)01 and (2)02. The high thermodynamic and kinetic stability of (2)01 and (2)02 might make them as important building cores in the growth of boron-oxide clusters. This results would also help deeply understand the oxidation and doping mechanism of pure boron clusters.

Electrospun SnO2 nanofiber mats with thermo-compression step for gas sensing applications

SnO2 nanofiber mats fabricated through electrospinning followed by thermo-compression and subsequent calcination steps exhibited unique morphologies facilitating efficient gas transport into the layers combined with high surface area (∼73.5 m2/g, measured by BET) and small grain size (∼5–15 nm), which are well suited for ultrasensitive gas detection. Single SnO2 nanofibers were found to have a belt-like structure of closely packed nanocrystallites, facilitating excellent adhesion to the substrate and good electrical contact to the electrodes. I–V measurements of single SnO2 nanofibers displayed ohmic behavior with electrical conductivity of 1.5 S/cm. Gas sensor prototypes comprising a random network of SnO2 fibers exhibited high sensitivity when exposed to NO2 at 225°C and CO at 300°C. A detection limit of 150 ppb NO2 at 185°C was estimated by extrapolating the sensitivity results obtained on exposure to higher gas concentrations, demonstrating potential of achieving ultra-sensitive gas detection at low operating temperatures enabled by the present synthesis method.

Tight Junctions in Salivary Epithelium

Epithelial cell tight junctions (TJs) consist of a narrow belt-like structure in the apical region of the lateral plasma membrane that circumferentially binds each cell to its neighbor. TJs are found in tissues that are involved in polarized secretions, absorption functions, and maintaining barriers between blood and interstitial fluids. The morphology, permeability, and ion selectivity of TJ vary among different types of tissues and species. TJs are very dynamic structures that assemble, grow, reorganize, and disassemble during physiological or pathological events. Several studies have indicated the active role of TJ in intestinal, renal, and airway epithelial function; however, the functional significance of TJ in salivary gland epithelium is poorly understood. Interactions between different combinations of the TJ family (each with their own unique regulatory proteins) define tissue specificity and functions during physiopathological processes; however, these interaction patterns have not been studied in salivary glands. The purpose of this review is to analyze some of the current data regarding the regulatory components of the TJ that could potentially affect cellular functions of the salivary epithelium.

Exploration of structure, potential energy surface, and stability of planar C3B3

The geometrical structures, potential energy surface, stability, and bonding character of low-energy isomers of planar C(3)B(3) were systematically explored and investigated at the B3LYP/6-311+G(d)// CCSD(T)/6-311+G(d) level for the first time. A large number of planar structures for low-energy isomers of C(3)B(3) are located and reported. In particular, isomers 1 (C(s),(2)A') and 2 (C(s),(2)A'), with a belt-like structure corresponding to the lowest-energy structures of planar C(3)B(3), are revealed. Based on molecular orbital (MO) and natural bond orbital (NBO) analyses, delocalized sigma MOs, multi-centered sigma MOs, and delocalized pi MOs play an important role in stabilizing the structures of low-energy isomers of C(3)B(3). It is interesting to note from isomerization analysis that the interconversion of isomers 2 and 7 can be realized through two isomerization channels. The results demonstrate that isomers 1, 2, 3, 4, 7, 9, 12, 17, 19, and 20 of C(3)B(3) are stable both thermodynamically and kinetically at the B3LYP/ 6-311+G(d)//CCSD(T)/ 6-311+G(d) level, and that they are observable in the laboratory, which is helpful for future experimental studies of C(3)B(3).

Structure and catalytic activity of a hexarhenium cluster-supported copper cubanes [{Cu4(μ-OH)4(NH3)7}2{Re6Se8(CN)6}][Re6Se8(CN)6] · 2H2O

The first hexarhenium cluster-supported Cu4(OH)4 cubanes had been synthesized. The complex displayed a belt-like one-dimensional structure with dangling Cu4 cubanes. As a heterogeneous catalyst, the complex showed a high catalytic activity in the transesterification of a range of esters with methanol under the mild conditions. Moreover, it can be reused without any loss of activity through five runs with ester, which suggests that this catalyst is an efficient, mild, and easily recyclable one for the alcoholysis of esters.

High-Temperature Deformation of Si3N4/Si3N4-SiC Hybrid Composites with Belt-Like Network Structure of Si3N4-SiC Composites

Superplastic deformation and creep resistance of Si3N4/Si3N4-SiC hybrid composites that formed belt-like network structure by Si3N4-SiC composite domain (the second domain) were investigated with tensile tests at 1873K and with bending tests at 1473K, respectively. The supserplastic elongation of Si3N4/Si3N4-SiC hybrid composites was dramatically improved with decreasing in SiC contents of the second domain from 20wt% to 10wt%. As the results, the Si3N4/Si3N4-SiC hybrid composites exhibited superplastic elongation more than 200% at 1873K. Furthermore, the hybrid composites exhibited the high-performance in both of the superplasitc deformation and the creep resistance.

Environmentally Friendly Chemical Route to Vanadium Oxide Single-Crystalline Nanobelts as a Cathode Material for Lithium-Ion Batteries

Orthorhombic V(2)O(5) single-crystalline nanobelts with widths of 100-300 nm, thicknesses of 30-40 nm, and lengths up to tens of micrometers have been synthesized on a large scale in a hydrogen peroxide aqueous solution by an environmentally friendly chemical route. Such nanobelts grow along the direction of [010]. The influence of the reaction time on the crystal structures and morphologies of the resulting products are investigated. A probable dehydration-recrystallization-cleavage mechanism for the formation of V(2)O(5) nanobelts is proposed. The experiments demonstrate that the use of a nanosized belt-like structure can considerably enhance the specific discharge capacity in lithium-ion batteries.

Hubble Space TelescopeSTIS Spectrum of RW Aurigae A: Evidence for an Ionized Beltlike Structure and Mass Ejection in Timescales of a Few Hours

Profiles of the UV semiforbidden lines of C III](1908) and Si III](1892) of RW Aur have been obtained with the Hubble Space Telescope (HST) STIS. The C III](1908) profile shows two high-velocity components at upsilon = +/-170 km s(-1) and a central one. The Si III](1892) profile is very broad (FWHM = 293 km s(-1)), and the high-velocity components are unresolved. The high-velocity components are most probably produced in a rotating belt similar to that detected in other sources of bipolar outflows. A radius between 2.7 R-* and the corotation radius (6.1 R-*) is derived, and a log T-e(K) similar or equal to 4.7 and log n(e)(cm(-3)) = 11.6 are estimated. The belt is clumpy, and the most likely source of heating is local X-ray radiation, probably associated with the release of magnetic energy. In addition, profiles of the optical lines of He I, Fe II, and Halpha retrieved from the HST archive have been analyzed. The spectra were obtained by shifting the STIS slit between exposures in the transverse direction to the flow. Two features vary from one exposure to another: a blueshifted emission feature (detected in the Fe II and He I lines) and a redshifted absorption feature (detected in Halpha), which are observed at the velocity of the blueshifted and redshifted components of the jet, respectively. There is a clear-cut correlation between the equivalent widths of these two components. These components are not associated with the flaring activity of the source, since they remain stable timescales of similar or equal to40 minutes. They are most likely associated with variations in the stellar/circumstellar environment in timescales of a few (similar or equal to5) hours, consistent with reports by other authors for variations of the veiling and the appearance of shell signatures in the optical spectrum.

The Structure of the Oxygen-rich Supernova Remnant G292.0+1.8 from [ITAL]Chandra[/ITAL] X-Ray Images: Shocked Ejecta and Circumstellar Medium

We present results from the observation of the young Galactic supernova remnant (SNR) G292.0+1.8 with the Advanced CCD Imaging Spectrometer (ACIS) on board the {\it Chandra X-ray Observatory}. In the 0.3 $-$ 8 keV band, the high resolution ACIS images reveal a complex morphology consisting of knots and filaments, as well as the blast wave around the periphery of the SNR. We present equivalent width (EW) maps for the elemental species O, Ne, Mg, and Si, which allow us to identify regions of enhanced metallicity in the SNR. G292.0+1.8 is bright in O, Ne, and Si; weaker in S and Ar; with little Fe. The EW and broad-band images indicate that the metal-rich ejecta are distributed primarily around the periphery of the SNR. The central belt-like structure has normal solar-type composition, strongly suggesting that it is primarily emission from shocked circumstellar medium rather than metal-rich ejecta. We propose that the belt traces its origin to enhanced mass loss in the star's equatorial plane during the slow, red supergiant phase. We also identify thin filaments with normal composition, centered on and extending nearly continuously around the outer boundary of the SNR. These may originate in a shell caused by the stellar winds from the massive progenitor in the red/blue supergiant phases, over-run by the blast wave.

A conserved motif in Crumbs is required for E-cadherin localisation and zonula adherens formation in Drosophila.

Specialised cell junctions in epithelia serve as cell-cell adhesion sites and thus contribute to the maintenance of tissue integrity. The Drosophila gene crumbs encodes a transmembrane protein that is required for the biogenesis of the zonula adherens, a belt-like structure encircling the apex of epithelial cells. As previously shown, expression of just the short membrane-bound cytoplasmic domain is sufficient to rescue major defects associated with the loss of crumbs function. The cytoplasmic domain of Crumbs is highly conserved in two putative crumbs homologues in Caenorhabditis elegans. To assess the significance of conserved residues, various point mutations and deletions were introduced into this region. Two functional domains were revealed, an amino-terminal region and the carboxy-terminal amino acids EERLI. Both are necessary for rescue of the crumbs phenotype. The EERLI motif interacts with Discs Lost, a cytoplasmic protein containing PDZ domains. Overexpression of the Crumbs cytoplasmic domain induces a transition from the single-layered epithelium to a multilayered tissue. This transition is associated with redistribution of the Drosophila homologue of the cell adhesion molecule E-cadherin, and depends on the presence of the EERLI motif. We propose a model in which the interaction of the Crumbs carboxyl terminus with Discs Lost organises a membrane-associated protein complex in the apical cytocortex of epithelial cells. This scaffold mediates the localisation and stabilisation of the zonula adherens component DE-cadherin, a crucial component for the maintenance of epithelial cell polarity and tissue integrity.

Relevant criteria for detecting microsporidia in stool specimens.

By using different staining techniques, 479 stool specimens from 212 diarrheic patients with AIDS were examined for microsporidian spores. Calcofluor fluorescence staining of 119 specimens revealed fluorescent ovoid structures of microsporidian size. Staining of these samples according to the method of Weber et al. (R. Weber, R. T. Bryan, R. L. Owen, C. M. Wilcox, L. Gorelkin, and G. S. Visvesvara, N. Engl. J. Med. 326:161-166, 1992) with trichrome produced six specimens with pinkish spores containing the characteristic microsporidian belt-like structure. The 6 specimens were processed for transmission electron microscopy, as were another 21 specimens which did not present the belt-like structure after trichrome staining but which looked highly suspicious after fluorescence staining. In these 21 samples, only fungal spores and, particularly, bacterial Clostridium spores were demonstrated, whereas in the 6 samples diagnosed positive after trichrome staining, the existence of microsporidia could be verified by electron microscopy. Based on our observations, we propose that the belt-like structure seen with the Weber stains in microsporidian spores corresponds to structures existing in priming-stage spores. The results suggest that routine microscopical fecal diagnosis for microsporidian infection should include a screening by fluorescence staining and, subsequently, a confirmatory viewing of fluorescence-positive samples after trichrome staining.

ISOLATION, CHARACTERIZATION, AND CHROMOSOME MAPPING OF AN ACTIN GENE FROM THE PRIMITIVE GREEN ALGA, NANNOCHLORIS BACILLARIS (CHLOROPHYCEAE)

Historically, the genus Nannochloris has been classified using the morphology of cell division, although the mechanics of division remain relatively poorly understood. Nannochloris bacillaris reproduces by binary fission. Microscopic observation with fluorescein isothiocyanate‐phalloidin showed that actin filaments localized near the nucleus and appeared as a ring‐ or beltlike structure in the septum‐forming area in the middle of the cell during cell division. In primitive unicellular Chlorophyta such as N. bacillaris, actin is also thought to play important roles in nuclear migration and cell division. The N. bacillaris actin gene has three exons and two introns defined by two exon–intron junctions with splice site consensus sequences. The two introns are located at codons specifying amino acids 3/4 and 47/48. One of these, intron position 3/4, is conserved in the actin gene of Saccharomyces cerevisiae. The actin gene product was predicted to be 378 amino acids long with an estimated molecular weight of 42 kDa. There is only one copy of the actin gene in the N. bacillaris genome. Nannochloris bacillaris has 14 chromosomes that range in size from 230 kb to 3000 kb, and the total size of the genome was estimated to be 20.3 Mb. The actin gene is on either chromosome XI or XII. In a phylogenetic tree based on the actin gene sequence, N. bacillaris diverged before the divergence of Volvox, Chlamydomonas, and higher plants, and very shortly after the radiation of the Rhodophyta.

Apolipoprotein(a) binds to low-density lipoprotein at two distant sites in lipoprotein(a).

Lipoprotein(a) [Lp(a)] consists of low-density lipoprotein (LDL) and apolipoprotein(a) [apo(a)] linked with a disulfide bond. Scanning force microscopy (SFM) of Lp(a) showed, for the first time, a belt-like structure of apo(a) with both ends attached to a spherical LDL. The two ends of apo(a) were bound to the LDL sphere at two distant sites. Occasionally, the ends were attached to two touching spheres. Under the same imaging conditions, LDL appeared as individual spheres. Electron microscopy (EM) studies of Lp(a) by several groups over the past decade failed to reveal this belt-like structure of apo(a). Images of isolated apo(a) in air or in phosphate buffer showed apo(a) as individual belts, and these belts tended to crowd together. Lp(a) formed leaf-like aggregates; apo(a) aggregates were fishnet-like, whereas LDL aggregates were less characteristic. Quantitative analysis of Lp(a) showed the diameter of the LDL to be 24.8 +/- 8.7 nm (n = 46), which is close to the reported value of 24.2 +/- 4.2 nm found with EM. The length of the belts attached to the spheres was measured to be 173.5 +/- 6.6 nm (n = 15). I also found, by using a functionalized tip, that the interaction force between apo(a) and its ligand, lysine, was related to the ionic strength of the bulk solution. This force can be reduced by the presence of epsilon-aminocaproic acid.

Earthquake precursors in magnetically conjugated ionosphere regions

It is known that the highly conducting geomagnetic field flux tube and quasitrapped energetic particles provide strong electrodynamic coupling between magnetically conjugated regions in the ionosphere. Such a connection is likely to cause ionospheric disturbances before a pending earthquake not only over the epicentral zone but also in the opposite hemisphere. Data from the INTERCOSMOS-18 and ALOUETTE satellites were analyzed from this point of view. Earthquake precursors in magnetically-conjugated ionosphere regions were found in very low frequency (VLF) emission and F2-peak parameters. F2-precursors appear some days before the earthquake, and manifest themselves as an Appleton-type anomaly if the epicenter of the future earthquake is situated near the magnetic equator. Estimation of the electric field magnitude necessary to generate the observed anomaly was made. It was shown that an electric field of less than one mV/m must be generated in the ionosphere. VLF precursors appearance some hours before the earthquake is localized close to the magnetic shell corresponding to the future earthquake epicenter and have a belt-like structure (longitudealigned for more than some tens thousands kilometers) in both hemispheres. VLF precursors are followed by energetic particle (electrons energy W>40 keV) precipitation.