Magnetic frustration in the spinel compounds Ge Co_2 O_4 and Ge Ni_2 O_4

In both spinel compounds GeCo$_2$O$_4$ and GeNi$_2$O$_4$ which order antiferromagnetically (at $T_N = 23.5 K$ and $T_{N_1} = 12.13 K$, $T_{N_2} = 11.46 K$) with different Curie Weiss temperatures ($T_{CW}$=80.5 K and -15 K), the usual magnetic frustration criterion $f=|T_{CW}|/T_N>>1$ is not fulfilled. Using neutron powder diffraction and magnetization measurements up to 55 T, both compounds are found with a close magnetic ground state at low temperature and a similar magnetic behavior (but with a different energy scale), even though spin anisotropy and first neighbor exchange interactions are quite different. This magnetic behavior can be understood when considering the main four magnetic exchange interactions. Frustration mechanisms are then enlightened.Comment: submitted to Phys.Rev.B (2006

Hidden magnetic frustration by quantum relaxation in anisotropic Nd-langasite

The static and dynamic magnetic properties of the Nd$_3$Ga$_5$SiO$_{14}$ compound, which appears as the first materialization of a rare-earth kagome-type lattice, were re-examined, owing to contradictory results in the previous studies. Neutron scattering, magnetization and specific heat measurements were performed and analyzed, in particular by fully taking account of the crystal electric field effects on the Nd$^{3+}$ ions. One of the novel findings is that the peculiar temperature independent spin dynamics observed below 10 K expresses single-ion quantum processes. This would short-circuit the frustration induced cooperative dynamics, which would emerge only at very low temperature

SIRT7 mediates L1 elements transcriptional repression and their association with the nuclear lamina

Altres ajuts: La Marató de TV3.Long interspersed elements-1 (LINE-1, L1) are retrotransposons that hold the capacity of self-propagation in the genome with potential mutagenic outcomes. How somatic cells restrict L1 activity and how this process becomes dysfunctional during aging and in cancer cells is poorly understood. L1s are enriched at lamin-associated domains, heterochromatic regions of the nuclear periphery. Whether this association is necessary for their repression has been elusive. Here we show that the sirtuin family member SIRT7 participates in the epigenetic transcriptional repression of L1 genome-wide in both mouse and human cells. SIRT7 depletion leads to increased L1 expression and retrotransposition. Mechanistically, we identify a novel interplay between SIRT7 and Lamin A/C in L1 repression. Our results demonstrate that SIRT7-mediated H3K18 deacetylation regulates L1 expression and promotes L1 association with elements of the nuclear lamina. The failure of such activity might contribute to the observed genome instability and compromised viability in SIRT7 knockout mice. Overall, our results reveal a novel function of SIRT7 on chromatin organization by mediating the anchoring of L1 to the nuclear envelope, and a new functional link of the nuclear lamina with transcriptional repression

Frequency metrology in quantum degenerate helium: Direct measurement of the 2 3S1 - 2 1S0 transition

Precision spectroscopy of simple atomic systems has refined our understanding of the fundamental laws of quantum physics. In particular, helium spectroscopy has played a crucial role in describing two-electron interactions, determining the fine-structure constant and extracting the size of the helium nucleus. Here we present a measurement of the doubly-forbidden 1557-nanometer transition connecting the two metastable states of helium (the lowest energy triplet state 2 3S1 and first excited singlet state 2 1S0), for which quantum electrodynamic and nuclear size effects are very strong. This transition is fourteen orders of magnitude weaker than the most predominantly measured transition in helium. Ultracold, sub-microkelvin, fermionic 3He and bosonic 4He atoms are used to obtain a precision of 8.10^{-12}, providing a stringent test of two-electron quantum electrodynamic theory and of nuclear few-body theory.Comment: 14 pages, 6 figure

Reversal of Cancer Cachexia and Muscle Wasting by ActRIIB Antagonism Leads to Prolonged Survival

SummaryMuscle wasting and cachexia have long been postulated to be key determinants of cancer-related death, but there has been no direct experimental evidence to substantiate this hypothesis. Here, we show that in several cancer cachexia models, pharmacological blockade of ActRIIB pathway not only prevents further muscle wasting but also completely reverses prior loss of skeletal muscle and cancer-induced cardiac atrophy. This treatment dramatically prolongs survival, even of animals in which tumor growth is not inhibited and fat loss and production of proinflammatory cytokines are not reduced. ActRIIB pathway blockade abolished the activation of the ubiquitin-proteasome system and the induction of atrophy-specific ubiquitin ligases in muscles and also markedly stimulated muscle stem cell growth. These findings establish a crucial link between activation of the ActRIIB pathway and the development of cancer cachexia. Thus ActRIIB antagonism is a promising new approach for treating cancer cachexia, whose inhibition per se prolongs survival.PaperCli

Kitaev interactions in the Co honeycomb antiferromagnets Na3Co2SbO6 and Na2Co2TeO6

Co$^{2+}$ ions in an octahedral crystal field, stabilise a j$_{eff}$ = 1/2 ground state with an orbital degree of freedom and have been recently put forward for realising Kitaev interactions, a prediction we have tested by investigating spin dynamics in two cobalt honeycomb lattice compounds, Na$_2$Co$_2$TeO$_6$ and Na$_3$Co$_2$SbO$_6$, using inelastic neutron scattering. We used linear spin wave theory to show that the magnetic spectra can be reproduced with a spin Hamiltonian including a dominant Kitaev nearest-neighbour interaction, weaker Heisenberg interactions up to the third neighbour and bond-dependent off-diagonal exchange interactions. Beyond the Kitaev interaction that alone would induce a quantum spin liquid state, the presence of these additional couplings is responsible for the zigzag-type long-range magnetic ordering observed at low temperature in both compounds. These results provide evidence for the realization of Kitaev-type coupling in cobalt-based materials, despite hosting a weaker spin-orbit coupling than their 4d and 5d counterparts

Triterpene Saponins from the Aerial Parts of Trifolium medium L. var. sarosiense

Seven previously unreported triterpene glycosides (1−7) were isolated from methanol extract of the aerial parts of Trifolium medium var. sarosiense (zigzag clover). Their structures were established by the extensive use of 1D and 2D NMR experiments along with ESI-MS and HRMS analyses. Compounds 1−7 are oleanane derivatives characterized by the presence of a keto group at C-22 of an aglycone and a primary alcoholic function at C-24 and differing functions at C-30. Among these, compounds 1−3 and 6 showed a secondary alcoholic function at C-11, which is methoxylated in compounds 4 and 7. Compound 5 was shown to possess a known aglycone, wistariasapogenol A; however, it is described here for the first time as a saponin constituent of the Trifolium genus. Some aspects of taxonomic classification of zigzag clover are also discussed

Osteoprotegerin: A Novel Secreted Protein Involved in the Regulation of Bone Density

AbstractA novel secreted glycoprotein that regulates bone resorption has been identified. The protein, termed Osteoprotegerin (OPG), is a novel member of the TNF receptor superfamily. In vivo, hepatic expression of OPG in transgenic mice results in a profound yet nonlethal osteopetrosis, coincident with a decrease in later stages of osteoclast differentiation. These same effects are observed upon administration of recombinant OPG into normal mice. In vitro, osteoclast differentiation from precursor cells is blocked in a dose-dependent manner by recombinant OPG. Furthermore, OPG blocks ovariectomy-associated bone loss in rats. These data show that OPG can act as a soluble factor in the regulation of bone mass and imply a utility for OPG in the treatment of osteoporosis associated with increased osteoclast activity

The 18 kDa Translocator Protein (Peripheral Benzodiazepine Receptor) Expression in the Bone of Normal, Osteoprotegerin or Low Calcium Diet Treated Mice

The presence of the translocator protein (TSPO), previously named as the mitochondrial or peripheral benzodiazepine receptor, in bone cells was studied in vitro and in situ using RT-qPCR, and receptor autoradiography using the selective TSPO ligand PK11195