Induced-Moment Weak Antiferromagnetism and Orbital Order on the Itinerant-Localized Duality Model with Nested Fermi Surface: A Possible Origin of Exotic Magnetism in URu2{}_{2}Si2_{2}

The weak antiferromagnetism of URu${}_{2}$Si${}_{2}$ is discussed on the basis of a duality model which takes into account salient features of both itinerant fermions and "localized" component of spin degrees of freedom. The problem is analyzed in the framework of induced-moment mechanism by taking a singlet-singlet crystal field scheme together with the nesting property of partial Fermi surface of itinerant fermions . It is shown that the extremely small ordered moment $m$ of ${\cal O}$($10^{-2}$$\times$$\mu_{B}$) can be compatible with the large specific-heat jump at the transition temperature $T_{N}$. Analysis performed in the presence of external magnetic field shows that the field dependence of $m$ in the limit T\to 0 and T_{N}$ do not scale except very near the critical field B which is consistent with a recent observation by Mentink. It is also shown that the antiferromagnetic magnetic order gives rise to a tiny amount of antiferromagnetic orbital order of f-electrons.Comment: 14 pages, 2 figure PS file, accepted J. Phys. Soc. Jp

Neuronal Na+ Channels Are Integral Components of Pro-Arrhythmic Na+/Ca2+ Signaling Nanodomain That Promotes Cardiac Arrhythmias During β-Adrenergic Stimulation

SummaryAlthough triggered arrhythmias including catecholaminergic polymorphic ventricular tachycardia (CPVT) are often caused by increased levels of circulating catecholamines, the mechanistic link between β-adrenergic receptor (AR) stimulation and the subcellular/molecular arrhythmogenic trigger(s) is unclear. Here, we systematically investigated the subcellular and molecular consequences of β-AR stimulation in the promotion of catecholamine-induced cardiac arrhythmias. Using mouse models of cardiac calsequestrin-associated CPVT, we demonstrate that a subpopulation of Na+ channels, mainly the neuronal Na+ channels (nNav), colocalize with ryanodine receptor 2 (RyR2) and Na+/Ca2+ exchanger (NCX) and are a part of the β-AR-mediated arrhythmogenic process. Specifically, augmented Na+ entry via nNav in the settings of genetic defects within the RyR2 complex and enhanced sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA)-mediated SR Ca2+ refill is both an essential and a necessary factor for arrhythmogenesis. Furthermore, we show that augmentation of Na+ entry involves β-AR–mediated activation of CAMKII, subsequently leading to nNav augmentation. Importantly, selective pharmacological inhibition as well as silencing of Nav1.6 inhibit myocyte arrhythmic potential and prevent arrhythmias in vivo. Taken together, these data suggest that the arrhythmogenic alteration in Na+/Ca2+ handling evidenced ruing β-AR stimulation results, at least in part, from enhanced Na+ influx through nNav. Therefore, selective inhibition of these channels and of Nav1.6 in particular can serve as a potential antiarrhythmic therapy

Animal Behavior Frozen in Time: Gregarious Behavior of Early Jurassic Lobsters within an Ammonoid Body Chamber

Direct animal behavior can be inferred from the fossil record only in exceptional circumstances. The exceptional mode of preservation of ammonoid shells in the Posidonia Shale (Lower Jurassic, lower Toarcian) of Dotternhausen in southern Germany, with only the organic periostracum preserved, provides an excellent opportunity to observe the contents of the ammonoid body chamber because this periostracum is translucent. Here, we report upon three delicate lobsters preserved within a compressed ammonoid specimen of Harpoceras falciferum. We attempt to explain this gregarious behavior. The three lobsters were studied using standard microscopy under low angle light. The lobsters belong to the extinct family of the Eryonidae; further identification was not possible. The organic material of the three small lobsters is preserved more than halfway into the ammonoid body chamber. The lobsters are closely spaced and are positioned with their tails oriented toward each other. The specimens are interpreted to represent corpses rather than molts. The lobsters probably sought shelter in preparation for molting or against predators such as fish that were present in Dotternhausen. Alternatively, the soft tissue of the ammonoid may have been a source of food that attracted the lobsters, or it may have served as a long-term residency for the lobsters (inquilinism). The lobsters represent the oldest known example of gregariousness amongst lobsters and decapods in the fossil record. Gregarious behavior in lobsters, also known for extant lobsters, thus developed earlier in earth's history than previously known. Moreover, this is one of the oldest known examples of decapod crustaceans preserved within cephalopod shells

Behavioural palaeobiology and taphonomy of the Late Jurassie calcareous sponge Elasmostoma fomes W. Muller, 1984

Calcareous sponges Elastostoma !'omes W MUller, 1984, from the Lower Kimmeridgian marly onkolitic limestones exposed at Karsy in the Holy Cross Mountains, Central Poland, are studied in terms of their settlement, growth, behaviour, and resulting phenotypy. The lichen-shaped auriculate specimens are interpreted as growing upwardly, at a higher angle to the bottom surface, in order to involve passive flow carrying suspended nutrients up on which they fed. Unstable bottom and hydrodynamie conditions, under which the growth of sponges progressed, we re basic prerequisites that controlled ecophenotypic variability of the studied specimens, A peculiar case of regeneration is discussed, to postulaie the skeleton parts having been lithified during the sponge's life, and healed after an accidental injury. Aviolent event that caused catastrophic burial of the studied sponge assemblage is ascribed to high-energy agents, most likely of storm origin

Tiered burrows of alpheid shrimps and their eco-taphonomic significance in the Oxfordian and Kimmeridgian of the Holy Cross Mountains

To the activity of alpheid shrimps genus Alpheus Weber, 1795) ascribed are the tiered burrows of a gridlike appearance from Lower Kimmeridgian oolitic shoals and Middle Oxfordian nearshore micritic limestones of the Holy Cross Mountains, Central Poland. The burrow networks are confined to beds of the soft or hard bottom type, the upper parts of which are more or less deeply truncated, to indicate erosional events of storm agitation. At low stand, the open burrows served as traps for solutions derived from the nearby hypersaline lagoons of the sabkha type, to cause precipitation either of dolomite, or of silica gel. At high stand, the open burrows, exemplified by the Małogoszcz section (Lower Kimmeridgian), became taphonomic traps and/or crevice habitats for diverse biota, the echinoderms in particular, to form their graveyards (EchinodermenlagerstŹtten). In these, represented are echinoids (tests, some spine-coated, all either empty, or sediment-filled; broken tests and their fragments, spines) stalkless crinoids (cusps, centrodorsals, radials, brachials, cirrals), stalked crinoids (columnals, pluricolumnals), starfish (marginalia, ambulacral plates), and ophiuroids (vertebrae, arm plates). Eco-taphonomic pathways for particular echinoderms (21 taxa taxonomically recognised) are interpreted since their death to burial in open burrows. Spine-coated echinoids were entrapped alive, others were swept into during successive storms which acted as a lethal agent. The storms, catastrophic for echinoderm communities, have prevailed through a longer timespan, when the alpheid-burrowed shoal evolved from the soft bottom to the hard ground colonized by a successive echinoderm community dominated by stalked crinoids

Disease and trauma in Jurassic invertebrate animals of Poland – an updated review

The parasitism of, and predation upon, the diverse Middle and Late Jurassic invertebrates of Poland, personally recognised by the authors, are reviewed. All cases are discussed either in the biological (anatomical, ethological), or ecological terms, to show the mode of infection, or injury, and the relationship between the engaged taxa. The preys to parasites are exemplified by the prosopid crabs infested by bopyrid isopods, the crinoids infested by myzostomid polychaetes (both disk-shaped, and wormlike), and the echinoids attacked by copepod arthropods involving either swellings of spines, or gall-shaped cysts upon the test outerly. Of traumatic events, discussed is regeneration of injuries in the belemnite hooked guards, and in the ammonite shells of distorted ribbing. The pearl-like structures in belemnite guards (the “belemnite pearls”) are interpreted as caused by a tiny parasite encapsulated during further growth of the belemnite. Heaps of ammonite shell hash are thought to represent the ,“kitchen middens” of a larger predator which has feasted upon the fleshy tidbits alone, the beaten shell having been left. The post mortem damage of shells is remarked (taphonomic feedback and/or aftermath) to be distinguished from that one acted in shells of alive specimens of the Middle and Late Jurassic of Poland

Coral lumps in Early Kimmeridgian oyster shellbeds and oolites ot Małogoszcz

Scleractinian corals occurring scarcely in the Lower Kimmeridgian Actinostl'eon (=Lopha, =Alectryonia) shellbeds at Malogoszcz in the Holy Cross Mountains, Central Poland, are represented by abraded colonies densely riddled by rock-boring bivalves (Lithophaga inclusa Phillips, GastTOchaena sp.) and polychaetes (potamilla sp.). The taxonomically recognised specimens include C01nplexastrea bUJ'gundiae (de Blainville, 1830), D 'imorphocoenia sp., Ovalastrea caryophylloides (Goldfuss, 1826), and Thamnasteria graeilis (Miinster, 1826). AlI colonies are preserved in the form of hollows, the wall s of which bear moulds of coral calyces, and of bivalve and polychaete borings. Taking into account the structural features of shellbeds and their faunistic content (uprooted crinoids Apioerinites, dug-out deeply-infaunal bivalves), stormy agitation is postulated as a basic agent responsible for damaging AeUnostreon communities, and their associates. The studied corals are thought to have lived aside the Aetinostreon gardens, up on a muddy bottom, from where they have been stirred-up during the storm cataclysm, having been then abraded and riddled by rock-borers repeatedly until laid down in a shellbed and transferred in to the fossil record. The extremely shallow-water conditions, under which the ostreid Actinostreon has lived, suggest the typically opportunistic nature or the associated corals, the same as of Ovalastrea caryophylloides (Goldfuss, 1826) from oolitic shoals, and the only colony of which completes the coral assemblage of Malogoszcz. The opportunism or ali these corals differs them from the habit of hermatypie forms from coeval and Oxfordian patch-reef communities of the Holy Cross Mountains (ef. Roniewicz & Roniewicz 1968, 1971)