Magneto-optical behaviour of EuIn_2P_2

We report results of a magneto-optical investigation of the Zintl-phase compound EuIn$_2$P$_2$. The compound orders magnetically at $T_C$=24 K and exhibits concomitant large magnetoresistance effects. For $T\le$50 K and increasing magnetic fields we observe a transfer of spectral weight in $\sigma_1(\omega)$ from energies above 1 eV into the low-energy metallic component as well as into a mid-infrared signal centered at about 600 cm$^{-1}$. This latter absorption is reminiscent to what has been seen in a large variety of so-called Kondo materials and ascribed to excitations across the hybridization gap. The observed gain of Drude weight upon increasing magnetic field suggests an enhancement of the itinerant charge-carrier concentration due to the increasing magnetization, a phenomenon that was previously observed in other compounds which exhibit colossal magnetoresistive effects.Comment: 13 pages, 4 figure

Mutation in the MICOS subunit gene APOO (MIC26) associated with an X-linked recessive mitochondrial myopathy, lactic acidosis, cognitive impairment and autistic features.

BACKGROUND: Mitochondria provide ATP through the process of oxidative phosphorylation, physically located in the inner mitochondrial membrane (IMM). The mitochondrial contact site and organising system (MICOS) complex is known as the 'mitoskeleton' due to its role in maintaining IMM architecture. APOO encodes MIC26, a component of MICOS, whose exact function in its maintenance or assembly has still not been completely elucidated. METHODS: We have studied a family in which the most affected subject presented progressive developmental delay, lactic acidosis, muscle weakness, hypotonia, weight loss, gastrointestinal and body temperature dysautonomia, repetitive infections, cognitive impairment and autistic behaviour. Other family members showed variable phenotype presentation. Whole exome sequencing was used to screen for pathological variants. Patient-derived skin fibroblasts were used to confirm the pathogenicity of the variant found in APOO. Knockout models in Drosophila melanogaster and Saccharomyces cerevisiae were employed to validate MIC26 involvement in MICOS assembly and mitochondrial function. RESULTS: A likely pathogenic c.350T>C transition was found in APOO predicting an I117T substitution in MIC26. The mutation caused impaired processing of the protein during import and faulty insertion into the IMM. This was associated with altered MICOS assembly and cristae junction disruption. The corresponding mutation in MIC26 or complete loss was associated with mitochondrial structural and functional deficiencies in yeast and D. melanogaster models. CONCLUSION: This is the first case of pathogenic mutation in APOO, causing altered MICOS assembly and neuromuscular impairment. MIC26 is involved in the assembly or stability of MICOS in humans, yeast and flies

Cooling quasiparticles in A(3)C(60) fullerides by excitonic mid-infrared absorption

Long after its discovery, superconductivity in alkali fullerides A(3)C(60) still challenges conventional wisdom. The freshest inroad in such ever-surprising physics is the behaviour under intense infrared excitation. Signatures attributable to a transient superconducting state extending up to temperatures ten times higher than the equilibrium T-c similar to 20 K have been discovered in K3C60 after ultra-short pulsed infrared irradiation-an effect which still appears as remarkable as mysterious. Motivated by the observation that the phenomenon is observed in a broad pumping frequency range that coincides with the mid-infrared electronic absorption peak still of unclear origin, rather than to transverse optical phonons as has been proposed, we advance here a radically new mechanism. First, we argue that this broad absorption peak represents a 'super-exciton' involving the promotion of one electron from the t(1u) half-filled state to a higher-energy empty t(1g) state, dramatically lowered in energy by the large dipole-dipole interaction acting in conjunction with the Jahn-Teller effect within the enormously degenerate manifold of (t(1u))(2)(t(1g))(1) states. Both long-lived and entropy-rich because they are triplets, the infrared-induced excitons act as a sort of cooling mechanism that permits transient superconductive signals to persist up to much higher temperatures

Particle Simulation of Granular Flows in Electrostatic Separation Processes

Abstract—In waste processing technology, the recent Corona Elec-trostatic Separation (CES) method is used to separate conductive from non-conductive particles in recycling streams. This paper proposes an innovative simulation approach based on non-smooth dynamics. In this context, a differential-variational formulation is used to implement a scalable and efficient time integrator that allows the large-scale simulation of trajectories of particles with different properties under the effect of particle-particle interactions and frictional contacts. Issues related to performance optimization, fast collision detection and parallelization of the code are discussed. Keywords–Granular flows, particles, waste processing I

Monotonic Doping-Dependence in the Anisotropy of the Drude Weight and Scattering Rate of Detwinned Ba(Fe1-x Co (x) )(2)As-2 Established from the Optical Conductivity

We investigate the anisotropic metallic response in the optical conductivity of fully detwinned Ba(Fe1−x Co x )2As2 in their underdoped regime. We estimate the Drude weight and the scattering rates of the itinerant charge carriers across the structural (at T s ) and magnetic (at T N ) phase transition. Our findings support a monotonic doping dependence of the anisotropy of both parameters determining the transport properties, opposite to the non-monotonic anisotropy of the dc resistivity between the crystallographic axes. The capability of optical methods to address a broad energy interval extending far away from the Fermi level allows emphasizing the prominent role of the electronic structure rather than the impurity scattering when establishing a direct connection with the long-range ferro-orbital and antiferromagnetic orders.ISSN:1557-1939ISSN:0896-1107ISSN:1557-1947ISSN:1572-9605ISSN:1557-194

Saccharomyces cerevisiae as a model to study the role of mutations in SDHA gene associated to hereditary optic neuropathies

Hereditary optic neuropathies (HON) are genetic diseases which lead to the loss of central vision and it has been estimated that in Europe they affect more than 50.000 people. HON are characterized by selective loss of retinal ganglion cells (RGCs), leading to optic nerve atrophy and different degrees of visual impairment and blindness. Thanks to next generation sequencing, three heterozygous mutations in SDHA gene were identified in patients, that could be associated with these pathologies. SDHA encodes for one of the four subunits of the succinate dehydrogenase complex, involved in both the Krebs cycle and the mitochondrial electron transport chain. To evaluate whether these mutations are the specific cause of the pathology, it was necessary to validate them. The yeast Saccharomyces cerevisiae is extensively used to prove with high confidence the link between novel mutations and mitochondrial diseases, since yeast can survive without mitochondrial DNA or with large deletions of it, and can grow on fermentable carbon sources in absence of an oxidative metabolism. Besides, several human genes encoding for mitochondrial proteins are present and often conserved in yeast, giving the chance to introduce the mutation in the yeast orthologous gene or to introduce the human pathological allele in a strain disrupted in its orthologue. SDHA and SDH1, its yeast orthologue, encodes for proteins which share more than 60% of identity, and the three variants found in patients affect amino acids which are conserved in most organisms, including fungi and mammals. The three mutations were introduced in SDH1, and these mutant alleles were inserted in a SDH1-disrupted strain. Our results showed that the presence of mutant alleles leads to a decrease of the oxidative growth and of the oxygen consumption rate compared to the strain harboring SDH1 wild type allele. Furthermore, a strong depletion in the succinate dehydrogenase activity was also observed. Western blots showed that the steady state levels of the mutant proteins were similar or slightly reduced compared to the levels of wild type Sdh1, whereas Sdh2, the second subunit of the complex which interacts directly with Sdh1, is absent or strongly decreased. These results suggest that the substitutions in Sdh1/SDHA are pathological and that affects the stability of the complex. Besides, through the construction of heterozygous diploid strains, we demonstrated that two of three mutations are dominant negative, thus explaining the observation that the patients are heterozygous for each of these mutations

Yeast, worm, patient’s fibroblasts and zebrafish as models for drug repositioning of molecules targeting POLG-related diseases

The mitochondrial DNA (mtDNA) is replicated by the DNA polymerase gamma (POLG) and its accessory unit POLG2, both encoded by nuclear genes. To date, more than 300 mutations in POLG have been identified as a major cause of mitochondrial disorders with a spectrum of clinical presentations, ranging from infantile-onset epilepsies, liver failure, polyneuropathy, ataxia, dilated/hypertrophic cardiomyopathy to late-onset ophthalmoplegia and muscle weakness, all associated with multiple deletions and/or depletion of the mitochondrial DNA (mtDNA). The therapeutic treatment of POLG diseases is currently limited to symptom management. Based on the conservation of mitochondrial function from yeast to human, we used Saccharomyces cerevisiae harboring mutations in MIP1, the yeast POLG orthologous gene, as a tool to identify drugs already approved by the FDA for other pathologies, for their ability to suppress mtDNA instability. Twelve molecules were found in such drug repurposing analysis. Seven of them, called MRS (MIP1 rescuing substance) 1,8-13, have been characterized in this study. We characterized the MRS effects on the extended mtDNA mutability, the respiratory activity, the MIP1 mRNA levels and the Mip1 protein levels. We found that four MRS molecules decreased significantly the petite frequency and increased the respiratory activity of the yeast mutant strains. Treatment with these drugs strongly increased the levels of Mip1 protein, without increasing the levels of MIP1 mRNA, suggesting that these drugs stabilize Mip1. In addition, some drugs had an additive effect, indicating that they likely suppress the mtDNA defects acting on different pathways. The effects of the positive drugs have been further tested on a Caenorhabditis elegans models deleted for polg-1, in which a rescue of the detrimental phenotype was observed for several of them. A positive effect for one of such molecules, MRS8, was also observed in patients’ fibroblasts in which mtDNA depletion was induced by treatment with EtBr. One of the twelve drugs, clofilium tosylate (CLO), has been already previously characterized in yeast, worm and patients’ fibroblasts. However, a potential use in human therapy needs a validation in a vertebrate model. To reach this aim, we used a zebrafish-based model harboring homozygous Polg mutations associated to mtDNA depletion and complex I deficiency. We found that CLO is able to increase the mtDNA levels in such model as well as in a wild type zebrafish line with EtBr-induced mtDNA depletion