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ZusammenfassungIn diesem Artikel beschreiben wir den Fallbericht eines Gärtners mit allergischer Reaktion auf Pflanzeninhaltsstoffe, gehen kurz auf die unterschiedlichen Formen der Kontaktdermatitis (photo-/irritative/allergische) ein und bieten zudem eine Literaturübersicht über kürzlich erschienene Publikationen zum Thema pflanzenvermittelte Kontaktdermatitis.

Allergic contact dermatitis (ACD) is a chemical-induced inflammatory skin disease. Contact allergens are low-molecular-weight chemicals that must react with proteins in order to become immunogenic. This interaction leads to the activation of innate immune and stress responses and to the formation of antigenic epitopes for T cells which are the effector cells of ACD. Due to the multitude of chemicals that surround us in our daily life and their potential sensitizing capacity, it is crucial to identify contact sensitizers before these chemicals are used in consumer products. Appropriate in vitro assays for hazard identification are urgently needed to replace animal-based assays. The EU-wide ban on sensitization testing of cosmetic ingredients in animals is in effect since March 2009 and the necessity to test more than 30,000 already marketed chemicals for their sensitizing potential under the EU regulation REACh has intensified the worldwide efforts to replace animal testing. We summarize here the current strategies to develop a battery of assays which allows the identification of contact allergens by in vitro alternatives to animal testing. Our main focus lies on the test systems recently developed within the EU project Sens-it-iv in which we participate.

Viele Chemikalien konnen eine allergische Kontaktdermatitis verursachen. Diese wird von T-Zellen vermittelt, die Hautzellen schadigen. Voraussetzung fur die Aktivierung und Differenzierung kontaktallergenspezifischer T-Zellen ist die Aktivierung des angeborenen Immunsystems. Die daraus resultierende Hautentzundung ahnelt mechanistisch der angeborenen Immunantwort gegen Bakterien und Viren. Diese Ubersicht beschreibt die Orchestrierung der Hautentzundung bei der Kontaktallergie auf molekularer und zellularer Ebene.

The European mistletoe Viscum album L. is a plant used for remedies in cancer treatment. The benefit of commonly used aqueous extracts is controversial but the plant contains water insoluble triterpene acids providing interesting anticancer properties. Triterpene extracts (TE) from plants and single triterpenoids such as oleanolic acid (OA) or betulinic acid (BA) are known for their cytotoxic effects on cancer cell lines in vitro. We report here cytotoxic effects of a novel OA-rich triterpene extract from mistletoe (V. album L., Santalaceae) solubilized by 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) on B16.F10 mouse melanoma cells. The 2-HP-β-CD solubilized triterpene extract (STE) was highly cytotoxic by causing DNA fragmentation, followed by loss of membrane integrity and intracellular adenosine-5'-triphosphate (ATP). Blocking the caspase machinery by inhibitors aborted DNA fragmentation and delayed the cytotoxic effects but did not prevent cell death. The solubilization by 2-HP-β-CD allows a solvent-free application of triterpene extracts in the in vitro setting. These findings suggest the use of STE from mistletoe as a solvent-free anticancer drug for preclinical animal experiments and clinical trials.

The development of new tools to selectively deplete specific cell populations in vivo has enabled us to gain novel insights into the function of Langerhans cells (LC) in the sensitisation process of allergic contact hypersensitivity. To our great surprise and against the current dogma these models show that epidermal LC seem to be dispensible for contact sensitisation. A newly described population of Langerin+ dermal DC seems to be sufficient for the sensitisation process. Subsequent studies suggest that LC and dermal DC play complementary roles in the initiation of the adaptive immune response. The analysis of DC subpopulations isolated from human skin explants demonstrates a functional specialisation, in which epidermal LC preferentially act as inducer of cellular immune responses, while dermal DC preferentially induce humoral immune responses. Similar results are reported in mice, in which epidermal LC and Langerin+ dermal DC were demonstrated to be unrelated and to display distinct functions with regard to induction of humoral and cellular immune responses.

The 180-degree ambiguity in magnetic field direction along polarity reversal boundaries can be resolved often and reliably by the chiral method. The chiral method requires (1) identification of the chirality of at least one solar feature related to a polarity reversal boundary along which the field direction is sought and (2) knowledge of the polarity of the network magnetic field on at least one side of the polarity reversal boundary. In the context of the Sun, chirality is an observable signature of the handedness of the magnetic field of a solar feature. We concentrate on how to determine magnetic field direction from chirality definitions and illustrate the technique in eight examples. The examples cover the spectrum of polarity boundaries associated with filament channels and filaments ranging from those connected with active regions to those on the quiet Sun. The applicability of the chiral method to all categories of filaments supports the view that active region filaments and quiescent filaments are the extreme ends in a continuous spectrum of filaments.

Allergic contact dermatitis (ACD) is a T cell-mediated inflammatory skin disease. In order to activate the T cell response, the innate immune system has to generate an inflammation that activates skin cells and triggers allergen-loaded dendritic cells (DC) to migrate to the local lymph nodes. There, DC confer the information about their tissue of origin and the site of antigen encounter to T cells which are induced to upregulate skin-specific homing receptors. This enables the recruitment of allergen-specific effector T cells to the skin following allergen contact. Similar findings were made for the small intestine. Our recent studies in the mouse model show a crucial role for the tissue microenvironment both for the inflammatory response and for the transfer of the topographical information from the DC to the T cells. Thus, we have found that Toll-like receptors and the IL-12/IL-12R system are important for DC activation by contact allergens and imply a role for endogenous TLR ligands generated during ACD. Moreover, cells of the peripheral tissue microenvironment provide information via soluble factors and cell-cell contact which license DC emigrating from skin but also DC emigrating from the small intestine to confer topographical information to T cells by imprinting tissue-specific homing receptors on the T cells in the draining lymph nodes. Our results illustrate the crucial role of the tissue context and of the communication between tissue-specific cell types for the shaping of immune responses. These findings underline the necessity to take into account the unique tissue microenvironments upon analysis of immune responses.

CD8+-cytotoxic T cells play an important, often dominant role as effector cells in chemical or metal ion-induced contact dermatitis. The reason for the dominance of this T cell subset was unclear, especially since reactive chemicals simultaneously generate immunogenic structures for the activation of CD4+ and CD8+ T cells. Now, we have shown in vitro that the dominance of CD8+ T cells is caused by cytolysis of CD4+ T cells via a fas-dependent mechanism. Moreover, it was unknown how the CD8+ T cells differentiate to become tissue-specific effectors which migrate selectively to inflamed skin. Our studies have revealed that activation of naive T cells by tissue-specific dendritic cells in the microenvironment of skin-draining lymphnodes selectively induces the expression of skin-specific migration receptors. We could demonstrate, for the first time, that Langerhans cells induce these migration receptors on T cells in vitro. This identifies a previously unknown role for Langerhans cells which, besides presenting antigens from the skin to T cells in lymph nodes, also direct T cells selectively to the skin for efficient immunedefense or induction of allergy.

Prominence eruptions or disappearances observed with an Hα limb filtergraph can be classified into 3 categories, the eruptive prominence, the quasi-eruptive prominence , and the disappearing prominence . We investigated their mechanism by comparing the results of simultaneous observations by Yohkoh SXT and Hα. We found that soft X-ray features change in both eruptive prominences and quasieruptive prominences , whereas no significant change takes place in disappearing prominences . In one prominence eruption event soft X-ray cusp structure suggests that the reconnection point is just below the Hα prominence.

During the past five years at least six manifestations of a global organization of solar magnetic fields have been recognized. The magnetic chirality (handedness) of the following features shows a hemispheric preference: filament channels, quiescent filaments, sunspot whorls, superpenumbral fibrils, coronal arcades, and interplanetary clouds associated with CMEs. Although the patterns are clear in the data, their interpretation and their possible connection to the dynamo is open to question. This paper reviews the observations of the patterns, corrects some misinterpretations, and offers a scenario for the origin of the most marked pattern, the chirality of filaments. We suggest the pattern arises from the reconnection of coronal loops, under the influence of supergranulation and differential rotation. Unlike alternative scenarios, ours relies only on observable surface motions and fields.

We present observational evidence that eruptions of quiescent filaments and associated coronal mass ejections (CMEs) occur as a consequence of the destabilization of large-scale coronal arcades due to interactions between these structures and new and growing active regions. Both statistical and case studies have been carried out. In a case study of a 'bulge' observed by the High-Altitude Observatory Solar Maximum Mission coronagraph, the high-resolution magnetograms from the Big Bear Solar Observatory show newly emerging and rapidly changing flux in the magnetic fields that apparently underlie the bugle. For other case studies and in the statistical work the eruption of major quiescent filaments was taken as a proxy for CME eruption. We have found that two thirds of the quiescent-filament-associated CMEs occurred after substantial amounts of new magnetic flux emerged in the vicinity of the filament. In addition, in a study of all major quiescent filaments and active regions appearing in a 2-month period we found that 17 of the 22 filaments that were associated with new active regions erupted and 26 of the 31 filaments that were not associated with new flux did not erupt. In all cases in which the new flux was oriented favorably for reconnection with the preexisting large-scale coronal arcades; the filament was observed to erupt. The appearance of the new flux in the form of new active regions begins a few days before the eruption and typically is still occurring at the time of the eruption. A CME initiation scenario taking account of these observational results is proposed.

This paper reviews the major discussions and conclusions of the Flares 22 Workshop concerning the physical processes involved in mass ejecta events, with an emphasis on large-scale phenomena, especially Coronal Mass Ejections (CMEs). New insights have been gained from recent data obtained from the SMM andYohkoh spacecraft and from several new ground-based radio and optical instruments, as well as from theoretical advances concerning the origins, driving mechanisms and long-term evolution of CMEs.

Contact allergy is a skin disease that is caused by the reaction of the immune system to low molecular weight chemicals. A hallmark of contact allergens is their chemical reactivity, which is not exhibited by toxic irritants. Covalent binding of contact allergens to or complex formation with proteins is essential for the activation of the immune system. As a consequence antigenic epitopes are formed, which are recognized by contact allergen-specific T cells. The generation of effector and memory T cells causes the high antigen specificity and the repeated antigen-specific skin reaction of contact allergy. New findings reveal that the less specific reaction of the innate immune system to contact allergens closely resembles the reaction to an infection. Therefore, contact allergy can be viewed as an immunologic misunderstanding since the skin contact with chemical allergens is interpreted as an infection. The growing understanding of the molecular and cellular pathologic mechanisms of contact allergy can aid the development of specific therapies and of in vitro alternatives to animal testing for the identification of contact allergens.

The European mistletoe Viscum album L. is a plant used for remedies in cancer treatment. The benefit of commonly used aqueous extracts is controversial but the plant contains water insoluble triterpene acids providing interesting anticancer properties. Triterpene extracts (TE) from plants and single triterpenoids such as oleanolic acid (OA) or betulinic acid (BA) are known for their cytotoxic effects on cancer cell lines in vitro. We report here cytotoxic effects of a novel OA-rich triterpene extract from mistletoe (V. album L., Santalaceae) solubilized by 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) on B16.F10 mouse melanoma cells. The 2-HP-β-CD solubilized triterpene extract (STE) was highly cytotoxic by causing DNA fragmentation, followed by loss of membrane integrity and intracellular adenosine-5'-triphosphate (ATP). Blocking the caspase machinery by inhibitors aborted DNA fragmentation and delayed the cytotoxic effects but did not prevent cell death. The solubilization by 2-HP-β-CD allows a solvent-free application of triterpene extracts in the in vitro setting. These findings suggest the use of STE from mistletoe as a solvent-free anticancer drug for preclinical animal experiments and clinical trials.

Allergic contact dermatitis (ACD) is one of the most prevalent occupational skin diseases and causes severe and long-lasting health problems in the case of chronification. It is initiated by an innate inflammatory immune response to skin contact with low molecular weight chemicals that results in the priming of chemical-specific, skin-homing CD8(+) Tc1/Tc17 and CD4(+) Th1/Th17 cells. Following this sensitization step, T lymphocytes infiltrate the inflamed skin upon challenge with the same chemical. The T cells then exert cytotoxic function and secrete inflammatory mediators to produce an eczematous skin reaction. The recent characterization of the mechanisms underlying the innate inflammatory response has revealed that contact allergens activate innate effector mechanisms and signalling pathways that are also involved in anti-infectious immunity. This emerging analogy implies infection as a potential trigger or amplifier of the sensitization to contact allergens. Moreover, new mechanistic insights into the induction of ACD identify potential targets for preventive and therapeutic intervention. We summarize here the latest findings in this area of research.

The use of substituted cyclopropanes as conformationally constrained peptidomimetics has received considerable attention recently (1-6). The efforts from our laboratory in this area have focused on the use 1,2,3-trisubstituted cyclopropanes as novel isosteric replacements in several biological systems (7-10). A common theme of this program has been the use of trans-substituted cyclopropanes to enforce extended or "β-strand" secondary structure while orienting the amino acid side chain in a predictable conformation (11). In an effort to explore further the utility of this novel isostere, modeling and calculations suggested that a cis-substituted cyclopropane dipeptide subunit could stabilize a turn structure. The focus of this chapter is to describe the preparation of a novel cyclopropane-containing cis-substituted (-Glyψ[CHOH-cp-CONH]-) subunit, which replaces Gly(2)-Gly(3) subunit of the Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) framework shown in Fig. 1. Fig. 1. Leu-Enkephalin analog 1.

Extracellular ATP contributes to the pathogenesis of asthma via signalling at purinergic receptors. However, the precise purinergic receptors subtypes mediating the pro-asthmatic effects of ATP have not been identified, yet.In vivo studies were performed using the OVA-alum model. Functional expression of the P2Y(2) purinergic receptor subtype on human monocyte-derived dendritic cells and eosinophils was investigated using real-time PCR, migration assays, and production of reactive oxygen species.Compared to wild-type animals P2Y(2) -/- mice showed reduced allergic airway inflammation which can be explained by defective migration of blood myeloid DCs towards ATP in vitro and in vivo, whereas the influence of ATP on maturation and cytokine production was not changed. Additionally, ATP failed to induce migration of bone marrow-derived eosinophils from P2Y(2) R-deficient animals. The relevance of our findings for humans was confirmed in functional studies with human monocyte-derived DCs and eosinophils. Interestingly, stimulation of human DCs derived from allergic individuals with house dust mite allergen induced functional up-regulation of the P2Y(2) R subtype. Furthermore, eosinophils isolated from asthmatic individuals expressed higher levels of P2Y(2) R compared to healthy controls. This was of functional relevance as these eosinophils were more sensitive to ATP-induced migration and production of reactive oxygen metabolites.In summary, P2Y(2) R appears to be involved in asthmatic airway inflammation by mediating ATP-triggered migration of mDCs and eosinophils, as well as reactive oxygen species production. Together our data suggest that targeting P2Y(2) R might be a therapeutic option for the treatment of asthma.

Allergic contact dermatitis (ACD) is an inflammatory skin disease of great and steadily increasing importance as an occupational health problem. The disease is induced by chemicals and metal ions which penetrate the skin and form complexes with host proteins. This process is accompanied by a strong, allergen-induced inflammatory reaction and leads to the migration of allergen-carrying dendritic cells (DC) from the skin to regional lymph nodes, where they promote generation of allergen-specific T cells. The latter are the ultimate effector cells of the disease. Re-exposure to the causative agent leads to the recruitment of the T effector cells, which then elicit the typical skin inflammatory reaction at the site of contact. Although DC and effector T cells play a protagonistic role in the sensitization and elicitation phase of ACD, respectively, other cell types including keratinocytes, NK cells, mast cells and B cells contribute to the pathogenesis of the disease. In this review the authors summarize recent findings that identify stress responses and innate immune pathways triggered by contact allergens and review recent data regarding the adaptive T cell response. The new data were collected mainly from studies on contact hypersensitivity (CHS), the corresponding experimental mouse model of human ACD. The elucidation of the molecular events involved in contact allergen-induced innate responses will help to design new treatment strategies and may allow to develop predictive in vitro assays for the identification of contact allergens.

[1] On 20 March 2003, a forward shock was observed in the near-Earth solar wind, followed 8 hours later by an interplanetary magnetic cloud (IMC), in a configuration having several uncommon features: Both were parts of a 38-hour interval containing transient solar outflows that occurred in an extended high-speed stream from a Y-shaped extension of the south polar coronal hole. (In contrast, IMCs, and ejecta in general, were rarely observed within high-speed streams at low heliolatitudes during cycle 23.) The most likely solar source for the IMC is AR 10314, located at S15°, just above the “fork” of the Y-shaped coronal hole. Several solar flares occurred in this active region on 17–18 March, as well as a succession of four coronal mass ejections (CMEs). Velocity considerations narrow the most likely source of the 38-hour interval of activity to two CMEs on 17 March 2003 associated with solar flares at W33° and W39°. The IMC axis had a north-south orientation, which is unusual for IMCs during this solar cycle. Its left-handedness implies an association with a left-skewed coronal arcade, which is less common in the Southern Hemisphere. Considering the shock observed ahead of the IMC, we conclude based on orientation and ram pressure arguments that this shock was not driven by the IMC, as might be presumed, but was the flank of an unrelated shock that overtook the IMC approximately halfway between Sun and Earth, heating the plasma and accelerating particles within the IMC. The CME associated with the X-class flare, at 1208 UT on 18 March in AR 10314 appears to be the solar source for this shock.

[reaction: see text]. The Wittig reactions of alpha-alkoxyaldehydes and sugar lactols with stabilized ylides such as (alkoxycarbonylmethylene)triphenylphosphoranes typically proceed with low E-selectivities. However, we have discovered that the reaction of such aldehydes with (methoxycarbonylmethylene)tributylphosphorane in toluene in the presence of catalytic amounts of benzoic acid proceeds to give the E-alpha,beta-unsaturated esters with high selectivities and in high yields.

The phosphatidylcholine (PC)-preferring phospholipase C (PLC) from Bacillus cereus (PLC(Bc)) hydrolyzes various 1,2-diacyl derivatives of PC at different rates. Substrates with side chains having eight or more carbons are present in micellular form in aqueous media and are processed most rapidly. The catalytic efficiency (k(cat)/K(m)) for the hydrolyses of short-chain PCs at concentrations below their respective critical micelle concentrations also decreases as the side chains become shorter, and this loss of efficiency owes its origin to increases in K(m). In order to ascertain whether the observed increases in K(m) might arise from conformational changes in the glycerol backbone, nuclear magnetic resonance (NMR) experiments were performed in D(2)O to determine the (3)J(HH) and (3)J(CH) coupling constants along the glycerol subunit of 1, 2-dipropanoyl-sn-glycero-3-phosphocholine (K(m)=61 mM), 1, 2-dibutanoyl-sn-glycero-3-phosphocholine (K(m)=21.2 mM) and 1, 2-dihexanoyl-sn-glycero-3-phosphocholine (K(m)=2.4 mM). Using these coupling constants, the fractional populations for each rotamer about the backbone of each of substrate were calculated. Two rotamers, which were approximately equally populated, about the sn-1-sn-2 bond of each substrate were significantly preferred, and in these conformers, the oxygens on the sn-1 and sn-2 carbons of the backbone were synclinal to optimize intramolecular hydrophobic interactions between the acyl side chains. There was greater flexibility about the sn-2-sn-3 bond, and each of the three possible staggered conformations was significantly populated, although there was a slight preference for the rotamer in which the oxygen bearing the phosphate head group was synclinal to the oxygen at the sn-2 carbon and to the sn-1 carbon; in this orientation, the head group is folded back relative to the side chains. These studies demonstrate that there is no significant change in the conformation about the glycerol backbone as a function of side chain length in short-chain phospholipids. Thus, prior organization of the substrate seems an unlikely determinant of the catalytic efficiency of PLC(Bc), and other factors such as hydrophobic interactions or differential solvation/desolvation effects associated with the complexation of the substrate with PLC(Bc) may be involved.

We investigated the mechanism of the disparition brusque, i.e., the sudden disappearance of a prominence (e.g., Tandberg-Hanssen 1995), observed with an Hα limb filtergraph by comparing Yohkoh SXT observations and Hα observations.

The aim of this paper is to study the mechanism of the disparition brusque, i. e., the sudden disappearance of a prominence (e. g., Tandberg-Hanssen 1995) observed with an Hα limb filtergraph and compare Yohkoh SXT and Hα observations.

Solar prominences are sheets of relatively cool and dense gas embedded in the surrounding hotter corona. An erupting prominence can inject a mass of up to 1015 g into the solar wind1 as part of a coronal mass ejection. These eruptions must depend critically on the topology of the prominence's magnetic field. In all present models2,3, the prominence hangs on horizontal or helical field lines, while an overlying magnetic arcade temporarily restrains the prominence from erupting. Such models are inconsistent, however, with the slow upward vertical gas flows that are seen in prominences4,5,6,7,8,9,10,11,12,13,14. Here we report counter-streaming flows along closely spaced vertical regions of a prominence, between its top and the lower solar atmosphere. As the flows must be aligned with the magnetic field, this observation implies that a field connects the prominence directly to the photosphere, contrary to all existing models. These magnetic ‘tethers’ might help prevent a prominence from erupting.

A multiple entrance slit spectrograph was built for time-lapse photography of the spectra of flares and other transient solar phenomena. This spectrograph employs narrow-band filters to limit the wavelength range of the spectrograph to several angstroms centered at Hα or other spectral lines. The passband of the filter, and the dispersion of the spectrograph determine the number of parallel slits through which light may be passed to achieve multiple adjacent spectral displays. By using a 7 A filter, a dispersion of 10.8 A mm−1, and 35 mm film, adjacent Hα spectra are imaged from 30 parallel slits. A system of mirrors and relay lenses transfers the slitjaw image to the same film plane as the spectral image. A 2 frame camera is used to simultaneously record both images on adjacent frames. Filtering of the reference spatial image to 1.0 A allows the observer to see the position of the slits relative to the Hα centerline structure and to match the brightness of the spatial image to the spectral display. A polarizing beamsplitter, prior to the slits, provides a prefiltered second solar image to a narrow band Hα Doppler filter for simultaneous photography in the wings of the Hα line. The multislit monochromatic spectrograph and Hα Doppler system constitute a flexible instrument in which components may be substituted to achieve different passbands width, image scales, dispersions and corresponding numbers and spacings of adjacent spectra at a selected wavelength.

Revised temperature and density estimates are provided in a synthesis of previous studies of the two-ribbon solar flare of July 29, 1973 and results are compared with observations of a similar event by the Solar Maximum Mission on May 21, 1980. Photographs taken through X ray filters permitted determination of the spatial distribution of temperature and density in the loop system and variations over time. The entire growth process of the flare is detailed, including the magnetic field configurations and the enlargement of the Halpha flare ribbon separation distance. The temperature is revised to 8.8 million K during maximum soft X ray emission and 6.8 million K at the appearance of the last Halpha loops. The 1973 flare is noted to have occurred in an old, decaying spotless region, producing higher loops at lower density than the 1980 flare, which displayed ribbons imbedded in a sunspot group.

In a series of papers on the flare of 29 July 1973 (Nolte et al., 1979; Martin, 1979; Švestka et al., 1979) it has been shown that Hα “post-flare” loops are the cooled aftermath of previously hot coronal loops which were visible in x-rays in the same position earlier in the flare. Kopp and Pneuman (1976) have proposed that these post-flare loops are formed by a process of successive magnetic field reconnections of previously distended magnetic field lines as illustrated in Figure 1. Each successive reconnection of the magnetic field yields a closed magnetic loop that forms above and concentric with previously formed loops. A shock wave created during each sudden reconnection travels down both legs of each loop and provides energy for ionizing chromospheric mass at the footpoints of the loop. Subsequent condensation of the ionized mass at the tops of the loops renders them visible as this mass falls to the chromosphere.

The solar cycle has been defined in terms of a sequential periodic variation in sunspot numbers, the period being the interval between successive minima, currently averaging 11.2 years. But a number of observations have indicated that the activity cycle may begin at higher latitudes before the emergence of the first sunspots of the new cycle. Here we report results from sunspot cycle 21 concerning the ephemeral active regions, the coronal green-line emission and the torsional oscillation signal, which confirm the earlier suggestions. In particular, we report the appearance of a high-latitude population of ephemeral active regions in the declin-ing phase of sunspot cycle 21, with orientations that tend to favour those for cycle 22 rather than 21. Taken together, these data indicate that sunspot activity is simply the main phase of a more extended cycle that begins at high latitudes before the maximum of a given sunspot cycle and progresses towards the equator during the next 18–22 yr, merging with the conventional 'butterfly diagram' (the plot of the latitudes of emerging sunspots against time) as it enters sunspot latitudes. We suggest that this extended cycle may be understood in the perspective of a model of giant convective rolls that generate dynamo waves propagating from pole to equator.