Directly Indecomposables in Semidegenerate Varieties of Connected po-Groupoids

We study varieties with a term-definable poset structure, "po-groupoids". It is known that connected posets have the "strict refinement property" (SRP). In [arXiv:0808.1860v1 [math.LO]] it is proved that semidegenerate varieties with the SRP have definable factor congruences and if the similarity type is finite, directly indecomposables are axiomatizable by a set of first-order sentences. We obtain such a set for semidegenerate varieties of connected po-groupoids and show its quantifier complexity is bounded in general

The Pen Duick Escarpment off Morocco: A promising biogeochemically active carbonate mound laboratory (MiCROSYSTEMS)

Carbonate mud mounds, found in marine environments from shallow- to deep-water settings, span from Proterozoic to recent times. During the past decades, numerous active venting fields were discovered in deep marine environments and became a subject of extensive study for marine scientists. Mound building seems to be a fundamental but still enigmatic strategy for life. Various arguments suggest that microorganisms are playing a major role in the reef development, mound formation and biodiversity. Therefore, it is important to evaluate the microbial mediated processes of carbonate precipitation.Cold-water coral reefs thriving on carbonate mounds were discovered in the late 1990’s off western Ireland. An exploratory cruise of RV Belgica in 2002 off Morocco has led to the discovery of apparently juvenile mounds in water depths of 500-600 m, topping a cliff - the Pen Duick escarpment - flanked by giant mud volcanoes. Subsequent cruises have confirmed the colonization by deep-water corals and have unveiled extensive fields of seep-related carbonate crusts in the off-reef regions. Long cores taken in 2004 indicate that the ‘Pen Duick’ mounds, in which microbial action was demonstrated by a strong emission of hydrogen sulphide, may be considered as giant biogeochemical reactors. The mound sediments were dated 2 kyrs B.P. at the surface and 20 kyrs B.P. in a depth of 6 mbsf.A 450 cm long gravity core, coming from one of these juvenile mounds, was sampled and analyzed for mineralogy, stable isotopes composition, geochemistry, and microbial communities. Most of the sediment consists of calcite (coccoliths), quartz and dolomite. At a depth of 4 mbsf, we found hardened nodule-like structures, embedded in grey mud containing cold-water coral pieces. The presence of 20-30% of dolomite, in the carbonate phase, suggests a microbial influence during mineral formation. Preliminary results of the pore water geochemistry indicate a reactive sulphate – methane interface at 3.8 mbsf. In this layer we focused our studies on the microbial communities, such as methanogens, methanotrophs and sulphate reducers. The trend of the d13C values in digenetic carbonate supports the assumption of microbial activity in this section of the core. In order to define the primary microbial community involved in carbonate precipitation, we did direct culturing, DNA isolation and PCR analysis of three functional genes, the a subunit (mcrA) of the methyl-coenzyme M reductase (MCR), the a subunit (pmoA) of the particulate methane monooxygenase (MMO) and the a and ß subunits (dsrA and dsrB, respectively) of the dissimilatory sulfite reductase (DSR). These enzymes are involved in methanogenesis, methanotrophy and sulphate reduction biochemical pathways, respectively. In summary, our initial results demonstrate that the Pen Duick carbonate mound can be considered as a natural laboratory in which to study cold-water coral ecosystems associated with microbial activity

High frequency sound in superfluid 3He-B

We present measurements of the absolute phase velocity of transverse and longitudinal sound in superfluid 3He-B at low temperature, extending from the imaginary squashing mode to near pair-breaking. Changes in the transverse phase velocity near pair-breaking have been explained in terms of an order parameter collective mode that arises from f-wave pairing interactions, the so-called J=4- mode. Using these measurements, we establish lower bounds on the energy gap in the B-phase. Measurement of attenuation of longitudinal sound at low temperature and energies far above the pair-breaking threshold, are in agreement with the lower bounds set on pair-breaking. Finally, we discuss our estimations for the strength of the f-wave pairing interactions and the Fermi liquid parameter, F4s.Comment: 15 pages, 8 figures, accepted to J. Low Temp. Phy

Pyridazine-bridged cationic diiridium complexes as potential dual-mode bioimaging probes

A novel diiridium complex [(N^C^N)2Ir(bis-N^C)Ir(N^C^N)2Cl]PF6 (N^C^N = 2-[3-tert-butyl-5-(pyridin-2-yl)phenyl]pyridine; bis-N^C = 3,6-bis(4-tert-butylphenyl)pyridazine) was designed, synthesised and characterised. The key feature of the complex is the bridging pyridazine ligand which brings two cyclometallated Ir(III) metal centres close together so that Cl also acts as a bridging ligand leading to a cationic complex. The ionic nature of the complex offers a possibility of improving solubility in water. The complex displays broad emission in the red region (λem = 520–720 nm, τ = 1.89 μs, Φem = 62% in degassed acetonitrile). Cellular assays by multiphoton (λex = 800 nm) and confocal (λex = 405 nm) microscopy demonstrate that the complex enters cells and localises to the mitochondria, demonstrating cell permeability. Further, an appreciable yield of singlet oxygen generation (ΦΔ = 0.45, direct method, by 1O2 NIR emission in air equilibrated acetonitrile) suggests a possible future use in photodynamic therapy. However, the complex has relatively high dark toxicity (LD50 = 4.46 μM), which will likely hinder its clinical application. Despite this toxicity, the broad emission spectrum of the complex and high emission yield observed suggest a possible future use of this class of compound in emission bioimaging. The presence of two heavy atoms also increases the scattering of electrons, supporting potential future applications as a dual fluorescence and electron microscopy probe

Transition metal complexes as photosensitisers in one- and two-photon photodynamic therapy

Photodynamic therapy (PDT) exploits light-activated compounds for therapeutic use. It relies on a photosensitiser (PS) that is inactive in the absence of light. When irradiated, the PS absorbs light and is promoted to a higher energy, “excited” state (PS ∗ ), which is either toxic to cells in itself or triggers formation of other species which are toxic to cells, and hence particular wavelengths of light can be used to induce light-dependent cell killing. In PDT occurring via the so-called type I and type II mechanisms, the PS ∗ engages in energy transfer to dioxygen present in cells and tissues. This process generates highly reactive singlet oxygen ( 1 O 2 ) and/or other reactive oxygen species (ROS), which in turn cause damage in the immediate vicinity of the irradiation and ultimately can lead to cell death. Whilst the main focus of research for the last 50 years has been on organic molecules or porphyrins as sensitisers, there is now emerging interest in extending the use to transition metal (TM) complexes, which can display intense absorptions in the visible region, and many also possess high two-photon absorption cross-sections, enabling two-photon excitation with NIR light. As with any other type of photosensitiser, the issues to consider whilst designing a TM complex as a photosensitiser include cell permeability, efficient absorption of NIR light for deeper penetration, preferential affinity to cancer cells over healthy cells, targeted intracellular localisation and lack of side effects. This review summarises recent developments involving photosensitisers containing Ru(II), Os(II), Pt, Ir(III), and Re(I) ions, and the approaches used to address the above requirements. Several remarkable recent advances made in this area, including the first clinical trial of a metal complex as a photosensitiser, indicate the bright future of this class of compounds in PDT

Photodynamic killing of cancer cells by a Platinum(II) complex with cyclometallating ligand

Photodynamic therapy that uses photosensitizers which only become toxic upon light-irradiation provides a strong alternative to conventional cancer treatment due to its ability to selectively target tumour material without affecting healthy tissue. Transition metal complexes are highly promising PDT agents due to intense visible light absorption, yet the majority are toxic even without light. This study introduces a small, photostable, charge-neutral platinum-based compound, Pt(II) 2,6-dipyrido-4-methyl-benzenechloride, complex 1, as a photosensitizer, which works under visible light. Activation of the new photosensitizer at low concentrations (0.1–1 μM) by comparatively low dose of 405 nm light (3.6 J cm−2) causes significant cell death of cervical, colorectal and bladder cancer cell lines, and, importantly, a cisplatin resistant cell line EJ-R. The photo-index of the complex is 8. We demonstrate that complex 1 induces irreversible DNA single strand breaks following irradiation, and that oxygen is essential for the photoinduced action. Neither light, nor compound alone led to cell death. The key advantages of the new drug include a remarkably fast accumulation time (diffusion-controlled, minutes), and photostability. This study demonstrates a highly promising new agent for photodynamic therapy, and attracts attention to photostable metal complexes as viable alternatives to conventional chemotherapeutics, such as cisplatin

Metal-insulator transition and charge ordering in the extended Hubbard model at one-quarter filling

We study with exact diagonalization the zero temperature properties of the quarter-filled extended Hubbard model on a square lattice. We find that increasing the ratio of the intersite Coulomb repulsion, $V$, to the band width drives the system from a metal to a charge ordered insulator. The evolution of the optical conductivity spectrum with increasing $V$ is compared to the observed optical conductivity of several layered molecular crystals with the theta and beta'' crystal structures.Comment: 5 pages, 3 figure

Authigenic carbonates from cold-water carbonate mounds in the Gulf of Cadiz: Microbial diversity and imprint on carbonate minerals

The Pen Duick Escarpment off Morocco consists of recent carbonate mounds in water depths of 500-600 m, flanked by giant mud volcanoes. These mounds are covered by mainly lifeless cold-water corals and have been associated with extensive fields of seep-related carbonates in off-reef regions. Three piston cores (from 350 to 640 cm long), coming from different sites on these juvenile mounds, were sampled and analyzed for mineralogy, stable isotopic composition of carbonates, geochemistry, and microbial communities. Most of the sediment comprises pelagic calcite (coccoliths), detrital quartz and authigenic dolomite, often observed encasing coccoliths. The decalcification of the sediment resulted in a dolomite dominated matrix that showed stable carbon istotope values of as low as -30 permil in contrast to the bulk sample values of -7 to -15 permil, which implies the involvement of microbes in the production of bicarbonate ions. Initial results from 16S rRNA gene clone libraries support the theory, that anaerobic oxidation of methane is one of the most important biogeochemical process leading to carbonate precipitation. Preliminary results of stable carbon isotopes of bulk samples from different carbonate mounds from the same area, indicates that the sulphate-methane transition zone moves in depth through time. We will show and discuss multidisciplinary data obtained after several cruises aimed to elucidate the impact of microorganisms on the construction of these carbonate mounds. The special emphasis in this research will be on the correlation between microbial ecosystems and their metabolic influence on mineral formation and diagenesis

Spin polarons in triangular antiferromagnets

The motion of a single hole in a 2D triangular antiferromagnet is investigated using the t-J model. The one-hole states are described by strings of spin deviations around the hole. Using projection technique the one-hole spectral function is calculated. For large J/t we find low-lying quasiparticle-like bands which are well separated from an incoherent background by a gap of order J. However, for small J/t this gap vanishes and the spectrum becomes broad over an energy range of several t. The results are compared with SCBA calculations and numerical data.Comment: 4 pages, 6 figs, to be publish in PR