Theoretical Studies of CO Adsorption on Si(100)-2 × 1 Surface

Ab initio molecular orbital and density functional calculations have been carried out to investigate the adsorption of CO on the Si(100)-2 × 1 surface using the Si 9 H 12 and Si 13 H 20 cluster models of the surface. It was found that B3LYP/6-31G(d) is a reasonable level of theory for calculation of the geometries of the clusters and adsorbates, as well as energetics of the adsorbates of the CO/Si(100)-2 × 1 surface. The addition of a doubly contracted polarizarion d-function for the non-hydrogen atoms changes the calculated CO desorption energy by 1 kcal/mol. Increasing the size of the cluster from Si 9 H 12 to Si 13 H 20 , in general, increases the CO desorption energy by 1-2 kcal/mol, while it does not change the Si d -Si d , Si d -Si sub , and Si sub -Si sub bond distances, which suggests that the Si 9 H 12 cluster is a good model for the single-dimer cluster. Interaction of the CO molecule with the surface dramatically changes the Si d -Si d and Si d -Si sub bond distances corresponding to the silicon dimer on the surface and that between the first-and second-layer atoms, respectively. These results suggest that the geometry relaxation of the cluster upon interaction with gas molecules should be taken into account. Different adsorption geometries of CO on the silicon surface dimer have been studied. The adsorbed CO is most stable when bonded perpendicularly to the surface dimer with the C atom attached to one of the Si atoms. The calculated CO desorption energy at the B3LYP/6-311G(2d) level, 10.5 kcal/mol, is in good agreement with the experimental value, 11.4 kcal/mol. Vibrational frequencies of the different CO adsorption isomers have been analyzed. For the OC-normal adsorption process, an extensive search for its transition state failed to locate it; this suggests that the adsorption reaction is a nonactivated process with zero barrier

Observational Constraints on Potassium Synthesis during the Formation of Stars of the Galactic Disk

The non-LTE potassium abundances in the atmospheres of 33 Galactic-disk stars are derived and the parameters of the atmospheres of 23 of the stars are determined. Neglecting departures from LTE results in a systematic overestimation of the potassium abundances and an increase in their dispersion, even for differential analyses relative to the Sun. The non-LTE corrections are significant ((-0.2)-(-0.6) dex) and depend on the surface gravities and effective temperatures of the stars. The mean potassium abundance for a sample of ten stars with [Fe/H] ∼ 0.0 is in agreement with the solar and meteoritic abundances (log ε ⊙ (K) = 5.12). As the stellar metallicity increases from [Fe/H] = (-1.0) to (0.2) dex, the [K/Fe] ratio decreases systematically from 0.3 dex to -0.1 dex. The derived dependence [K/Fe]-[Fe/H] is in agreement with the results of published model calculations of the chemical evolution of the Galaxy. This indicates the dominance of explosive oxygen burning in massive type II supernovae during the synthesis of potassium in the Galactic disk. © 2003 MAIK "Nauka/Interperiodica"

Duality Invariant M-theory: Gauged supergravities and Scherk-Schwarz reductions

We consider the reduction of the duality invariant approach to M-theory by a U-duality group valued Scherk-Schwarz twist. The result is to produce potentials for gauged supergravities that are normally associated with non-geometric compactifications. The local symmetry reduces to gauge transformations with the gaugings exactly matching those of the embedding tensor approach to gauged supergravity. Importantly, this approach now includes a nontrivial dependence of the fields on the extra coordinates of the extended space.Comment: 22 pages Latex; v2: typos corrected and references adde

Agenesis of the putamen and globus pallidus caused by recessive mutations in the homeobox gene GSX2

Basal ganglia are subcortical grey nuclei that play essential roles in controlling voluntary movements, cognition and emotion. While basal ganglia dysfunction is observed in many neurodegenerative or metabolic disorders, congenital malformations are rare. In particular, dysplastic basal ganglia are part of the malformative spectrum of tubulinopathies and X-linked lissencephaly with abnormal genitalia, but neurodevelopmental syndromes characterized by basal ganglia agenesis are not known to date. We ascertained two unrelated children (both female) presenting with spastic tetraparesis, severe generalized dystonia and intellectual impairment, sharing a unique brain malformation characterized by agenesis of putamina and globi pallidi, dysgenesis of the caudate nuclei, olfactory bulbs hypoplasia, and anomaly of the diencephalic-mesencephalic junction with abnormal corticospinal tract course. Whole-exome sequencing identified two novel homozygous variants, c.26C>A; p.(S9*) and c.752A>G; p.(Q251R) in the GSX2 gene, a member of the family of homeobox transcription factors, which are key regulators of embryonic development. GSX2 is highly expressed in neural progenitors of the lateral and median ganglionic eminences, two protrusions of the ventral telencephalon from which the basal ganglia and olfactory tubercles originate, where it promotes neurogenesis while negatively regulating oligodendrogenesis. The truncating variant resulted in complete loss of protein expression, while the missense variant affected a highly conserved residue of the homeobox domain, was consistently predicted as pathogenic by bioinformatic tools, resulted in reduced protein expression and caused impaired structural stability of the homeobox domain and weaker interaction with DNA according to molecular dynamic simulations. Moreover, the nuclear localization of the mutant protein in transfected cells was significantly reduced compared to the wild-type protein. Expression studies on both patients' fibroblasts demonstrated reduced expression of GSX2 itself, likely due to altered transcriptional self-regulation, as well as significant expression changes of related genes such as ASCL1 and PAX6. Whole transcriptome analysis revealed a global deregulation in genes implicated in apoptosis and immunity, two broad pathways known to be involved in brain development. This is the first report of the clinical phenotype and molecular basis associated to basal ganglia agenesis in humans

An action for F-theory: SL(2)R+ exceptional field theory

DSB is supported by the STFC grant ST/L000415/1 'String Theory, Gauge Theory and Duality'. CB is supported in part by the Belgian Federal Science Policy Office through the Interuniversity Attraction Pole P7/37 'Fundamental Interactions', and in part by the 'FWO-Vlaanderen' through the project G.0207.14N and by the Vrije Universiteit Brussel through the Strategic Research Program 'High-Energy Physics'. EM is supported by the ERC Advanced Grant "Strings and Gravity' (Grant No. 32004). FJR is supported by an STFC studentship

MINPP1 prevents intracellular accumulation of the chelator inositol hexakisphosphate and is mutated in Pontocerebellar Hypoplasia

Inositol polyphosphates are vital metabolic and secondary messengers, involved in diverse cellular functions. Therefore, tight regulation of inositol polyphosphate metabolism is essential for proper cell physiology. Here, we describe an early-onset neurodegenerative syndrome caused by loss-of-function mutations in the multiple inositol-polyphosphate phosphatase 1 gene (MINPP1). Patients are found to have a distinct type of Pontocerebellar Hypoplasia with typical basal ganglia involvement on neuroimaging. We find that patient-derived and genome edited MINPP1−/− induced stem cells exhibit an inefficient neuronal differentiation combined with an increased cell death. MINPP1 deficiency results in an intracellular imbalance of the inositol polyphosphate metabolism. This metabolic defect is characterized by an accumulation of highly phosphorylated inositols, mostly inositol hexakisphosphate (IP6), detected in HEK293 cells, fibroblasts, iPSCs and differentiating neurons lacking MINPP1. In mutant cells, higher IP6 level is expected to be associated with an increased chelation of intracellular cations, such as iron or calcium, resulting in decreased levels of available ions. These data suggest the involvement of IP6-mediated chelation on Pontocerebellar Hypoplasia disease pathology and thereby highlight the critical role of MINPP1 in the regulation of human brain development and homeostasis

Loss of the sphingolipid desaturase DEGS1 causes hypomyelinating leukodystrophy.

Sphingolipid imbalance is the culprit in a variety of neurological diseases, some affecting the myelin sheath. We have used whole-exome sequencing in patients with undetermined leukoencephalopathies to uncover the endoplasmic reticulum lipid desaturase DEGS1 as the causative gene in 19 patients from 13 unrelated families. Shared features among the cases include severe motor arrest, early nystagmus, dystonia, spasticity, and profound failure to thrive. MRI showed hypomyelination, thinning of the corpus callosum, and progressive thalamic and cerebellar atrophy, suggesting a critical role of DEGS1 in myelin development and maintenance. This enzyme converts dihydroceramide (DhCer) into ceramide (Cer) in the final step of the de novo biosynthesis pathway. We detected a marked increase of the substrate DhCer and DhCer/Cer ratios in patients' fibroblasts and muscle. Further, we used a knockdown approach for disease modeling in Danio rerio, followed by a preclinical test with the first-line treatment for multiple sclerosis, fingolimod (FTY720, Gilenya). The enzymatic inhibition of Cer synthase by fingolimod, 1 step prior to DEGS1 in the pathway, reduced the critical DhCer/Cer imbalance and the severe locomotor disability, increasing the number of myelinating oligodendrocytes in a zebrafish model. These proof-of-concept results pave the way to clinical translation

Production of nanoparticles from natural hydroxylapatite by laser ablation

Laser ablation of solids in liquids technique has been used to obtain colloidal nanoparticles from biological hydroxylapatite using pulsed as well as a continuous wave (CW) laser. Transmission electron microscopy (TEM) measurements revealed the formation of spherical particles with size distribution ranging from few nanometers to hundred nanometers and irregular submicronic particles. High resolution TEM showed that particles obtained by the use of pulsed laser were crystalline, while those obtained by the use of CW laser were amorphous. The shape and size of particles are consistent with the explosive ejection as formation mechanism