385 research outputs found
Kondo effect in a few-electron quantum ring
A small quantum ring with less than 10 electrons was studied by transport
spectroscopy. For strong coupling to the leads a Kondo effect is observed and
used to characterize the spin structure of the system in a wide range of
magnetic fields. At small magnetic fields Aharonov-Bohm oscillations influenced
by Coulomb interaction appear. They exhibit phase jumps by at the
Coulomb-blockade resonances. Inside Coulomb-blockade valleys the Aharonov-Bohm
oscillations can also be studied due to the finite conductance caused by the
Kondo effect. Astonishingly, the maxima of the oscillations show linear shifts
with magnetic field and gate voltage.Comment: 4 pages, 4 figure
Aharonov-Bohm oscillations of a tunable quantum ring
With an atomic force microscope a ring geometry with self-aligned in-plane
gates was directly written into a GaAs/AlGaAs-heterostructure. Transport
measurements in the open regime show only one transmitting mode and
Aharonov-Bohm oscillations with more than 50% modulation are observed in the
conductance. The tuning via in-plane gates allows to study the Aharonov-Bohm
effect in the whole range from the open ring to the Coulomb-blockade regime.Comment: 3 pages, 3 figure
Understanding adhesion at as-deposited interfaces from ab initio thermodynamics of deposition growth: thin-film alumina on titanium carbide
We investigate the chemical composition and adhesion of chemical vapour
deposited thin-film alumina on TiC using and extending a recently proposed
nonequilibrium method of ab initio thermodynamics of deposition growth (AIT-DG)
[Rohrer J and Hyldgaard P 2010 Phys. Rev. B 82 045415]. A previous study of
this system [Rohrer J, Ruberto C and Hyldgaard P 2010 J. Phys.: Condens. Matter
22 015004] found that use of equilibrium thermodynamics leads to predictions of
a non-binding TiC/alumina interface, despite the industrial use as a
wear-resistant coating. This discrepancy between equilibrium theory and
experiment is resolved by the AIT-DG method which predicts interfaces with
strong adhesion. The AIT-DG method combines density functional theory
calculations, rate-equation modelling of the pressure evolution of the
deposition environment and thermochemical data. The AIT-DG method was
previously used to predict prevalent terminations of growing or as-deposited
surfaces of binary materials. Here we extent the method to predict surface and
interface compositions of growing or as-deposited thin films on a substrate and
find that inclusion of the nonequilibrium deposition environment has important
implications for the nature of buried interfaces.Comment: 8 pages, 6 figures, submitted to J. Phys.: Condens. Matte
Effective elastic properties of a van der Waals molecular monolayer at a metal surface
Adsorbing anthracene on a Cu(111) surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young\u27s modulus of 1.5 GPa and a Poisson ratio approximate to 0.1. These values suggest interpretation of the molecular monolayer as a porous material-in marked congruence with our microscopic observations
Effective elastic properties of a van der Waals molecular monolayer at a metal surface
Adsorbing anthracene on a Cu(111) surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young's modulus of 1.5 GPa and a Poisson ratio approximate to 0.1. These values suggest interpretation of the molecular monolayer as a porous material-in marked congruence with our microscopic observations
Unknown mutations and genotype/phenotype correlations of autosomal recessive congenital ichthyosis in patients from Saudi Arabia and Pakistan
Background Autosomal recessive congenital ichthyosis (ARCI) is a genetically and phenotypically heterogeneous skin disease, associated with defects in the skin permeability barrier. Several but not all genes with underlying mutations have been identified, but a clear correlation between genetic causes and clinical picture has not been described to date. Methods Our study included 19 families from Saudi Arabia, Yemen, and Pakistan. All patients were born to consanguineous parents and diagnosed with ARCI. Mutations were analyzed by homozygosity mapping and direct sequencing. Results We have detected mutations in all families in five different genes: TGM1, ABCA12, CYP4F22, NIPAL4, and ALOXE3. Five likely pathogenic variants were unknown so far, a splice site and a missense variant in TGM1, a splice site variant in NIPAL4, and missense variants in ABCA12 and CYP4F22. We attributed TGM1 and ABCA12 mutations to the most severe forms of lamellar and erythematous ichthyoses, respectively, regardless of treatment. Other mutations highlighted the presence of a phenotypic spectrum in ARCI. Conclusion Our results contribute to expanding the mutational spectrum of ARCI and revealed new insights into genotype/phenotype correlations. The findings are instrumental for a faster and more precise diagnosis, a better understanding of the pathophysiology, and the definition of targets for more specific therapies for ARCI
Testosterone production during puberty in two 46,XY patients with disorders of sex development and novel NR5A1 (SF-1) mutations
BACKGROUND: Steroidogenic factor 1 (SF-1, NR5A1) is a key transcriptional regulator of many genes involved in the hypothalamic–pituitary–gonadal axis and mutations in NR5A1 can result in 46,XY disorders of sex development (DSD). Patients with this condition typically present with ambiguous genitalia, partial gonadal dysgenesis, and absent/rudimentary Müllerian structures. In these cases, testosterone is usually low in early infancy, indicating significantly impaired androgen synthesis. Further, Sertoli cell dysfunction is seen (low inhibin B, anti-Müllerian hormone). However, gonadal function at puberty in patients with NR5A1 mutations is unknown.
SUBJECTS AND METHODS: Clinical assessment, endocrine evaluation, and genetic analysis were performed in one female and one male with 46,XY DSD who showed spontaneous virilization during puberty. The female patient presented at adolescence with clitoral hypertrophy, whereas the male patient presented at birth with severe hypospadias and entered puberty spontaneously. Molecular analysis of NR5A1 was performed followed by in vitro functional analysis of the two novel mutations detected.
RESULTS: Testosterone levels were normal during puberty in both patients. Analysis of NR5A1 revealed two novel heterozygous missense mutations in the ligand-binding domain of SF-1 (patient 1: p.L376F; patient 2: p.G328V). The mutant proteins showed reduced transactivation of the CYP11A promoter in vitro.
CONCLUSION: Patients with 46,XY DSD and NR5A1 mutations can produce sufficient testosterone for spontaneous virilization during puberty. Phenotypic females (46,XY) with NR5A1 mutations can present with clitoromegaly at puberty, a phenotype similar to other partial defects of androgen synthesis or action. Testosterone production in 46,XY males with NR5A1 mutations can be sufficient for virilization at puberty. As progressive gonadal dysgenesis is likely, gonadal function should be monitored in adolescence and adulthood, and early sperm cryopreservation considered in male patients if possible
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