513 research outputs found
Spin vortices and vacancies: interactions and pinning on a square lattice
The study gives a decisive answer to the recently risen question about the
type and origin of interaction between spin vortices and spin vacancies in 2D
spin models. The approach is based on the low-temperature approximation of the
2D XY model known as the Villain model and does not involve any additional
approximations, thus preserving the lattice structure. The exact form of the
Hamiltonian describing a system of topological charges and a vacant site
supports the attractive type of interaction between the vacancy and the
charges. The quantitative difference between the characteristics of the vortex
behavior in the 2D XY and Villain models due to the different energy of the
vortex "cores" in the two models is pointed out. This leads to a conclusion
that the interaction between a vortex and a spin vacancy and between a vortex
and the antivortex differs quantitatively for small separations in the two
mentioned models.Comment: 13 pages, 5 figure
Electronic states in arsenic-decapped MnAs (1100) films grown on GaAs(001): A photoemission spectroscopy study
3 pages, 2 figures.We examine the arsenic bonding in the near-surface region of initially arsenic-capped MnAs(1100)
films grown on GaAs(001) as it evolves upon arsenic decapping. Line-shape analyses of
high-resolution As 3d photoelectron emission spectra recorded at room temperature RT allow us
to identify electronically distinct As-bonding states associated to bulk MnAs phases, bulk arsenic,
and interfacial environments. Stable MnAs phases appear to be affected by the presence of a thin
arsenic coating, an effect that could be advantageously used to enhance the ferromagnetic properties
of MnAs films around RTWe thank the BESSY staff for support. This work has
been supported by the Spanish Ministry of Education and
Science (“Ramón y Cajal” and “Materials” Programs, 2005
call and MAT2004-05348 Grant, respectively) and by the
German Federal Ministry for Education and Research.Peer reviewe
Anisotropic Electronic Structure of the Two-Dimensional Electron Gas at the AlOx/KTaO3(110) interface
Oxide-based two-dimensional electron gases (2DEGs) have generated significant
interest due to their potential for discovering novel physical properties.
Among these, 2DEGs formed in KTaO3 stand out due to the recently discovered
crystal face-dependent superconductivity and large Rashba splitting, both of
which hold potential for future oxide electronics devices. In this work,
angle-resolved photoemission spectroscopy is used to study the electronic
structure of the 2DEG formed at the (110) surface of KTaO3 after deposition of
a thin Al layer. Our experiments revealed a remarkable anisotropy in the
orbital character of the electron-like dispersive bands, which form a Fermi
surface consisting of two elliptical contours with their major axes
perpendicular to each other. The measured electronic structure is used to
constrain the modeling parameters of self-consistent tight-binding slab
calculations of the band structure. In these calculations, an anisotropic
Rashba splitting is found with a value as large as 4 meV at the Fermi level
along the [-110] crystallographic direction. This large unconventional and
anisotropic Rashba splitting is rationalized based on the orbital angular
momentum formulation. These findings provide insights into the interpretation
of spin-orbitronics experiments and help to constrain models for
superconductivity in the KTO(110)-2DEG system
Atom-specific identification of adsorbed chiral molecules by photoemission
The study of chiral adsorbed molecules is important for an analysis of enantioselectivity in heterogeneous catalysis. Here we show that such molecules can be identified through circular dichroism in core-level photoemission arising from the chiral carbon atoms in stereoisomers of 2,3-butanediol molecules adsorbed on Si(100), using circularly polarized x rays. The asymmetry in the carbon 1s intensity excited by right and left circularly polarized light is readily observed, and changes sign with the helicity of the radiation or handedness of the enantiomers; it is absent in the achiral form of the molecule. This observation demonstrates the possibility of determining molecular chirality in the adsorbed phase
Process design for the manufacturing of soft X-ray gratings in single-crystal diamond by high-energy heavy-ion irradiation
This paper describes in detail a novel manufacturing process for optical gratings suitable for use in the UV and soft X-ray regimes in a single-crystal diamond substrate based on highly focused swift heavy-ion irradiation. This type of grating is extensively used in light source facilities such as synchrotrons or free electron lasers, with ever-increasing demands in terms of thermal loads, depending on beamline operational parameters and architecture. The process proposed in this paper may be a future alternative to current manufacturing techniques, providing the advantage of being applicable to single-crystal diamond substrates, with their unique properties in terms of heat conductivity and radiation hardness. The paper summarizes the physical principle used for the grating patterns produced by swift heavy-ion irradiation and provides full details for the manufacturing process for a specific grating configuration, inspired in one of the beamlines at the ALBA synchrotron light source, while stressing the most challenging points for a potential implementation. Preliminary proof-of-concept experimental results are presented, showing the practical implementation of the methodology proposed herein
Process design for the manufacturing of soft X-ray gratings in single-crystal diamond by high-energy heavy-ion irradiation
Artículo con 9 figurasThis paper describes in detail a novel manufacturing process for optical gratings suitable for use in the UV and soft X-ray regimes in a single-crystal diamond substrate based on highly focused swift heavy-ion irradiation. This type of grating is extensively used in light source facilities such as synchrotrons or free electron lasers, with ever-increasing demands in terms of thermal loads, depending on beamline operational parameters and architecture. The process proposed in this paper may be a future alternative to current manufacturing techniques, providing the advantage of being applicable to single-crystal diamond substrates, with their unique properties in terms of heat conductivity and radiation hardness. The paper summarizes the physical principle used for the grating patterns produced by swift heavy-ion irradiation and provides full details for the manufacturing process for a specific grating configuration, inspired in one of the beamlines at the ALBA synchrotron light source, while stressing the most challenging points for a potential implementation. Preliminary proof-of-concept experimental results are presented, showing the practical implementation of the methodology proposed herein.The authors acknowledge funding support by the following projects: PID2020-112770RB-C22 from the Spanish Ministry of Science
and Innovation, TechnoFusión (III)-CM (S2018/EMT-4437) from Comunidad de Madrid (cofinanced by ERDF and ESF), agreement between Community
of Madrid and Universidad Autónoma de Madrid (item “Excellence of University Professorate”). M.L.C. acknowledges financial support from the research
project “Captacion de Talento UAM” Ref: #541D300 supervised by the Vice-Chancellor of Research of Universidad Autónoma de Madrid (UAM). LOREA
beamline at ALBA is a project co-funded by the European Regional Development Fund (ERDF) within the Framework of the Smart Growth Operative
Programme 2014-2020. The authors acknowledge the support from The Centro de Microanálisis de Materiales (CMAM)—Universidad Autónoma de Madrid,
for the beam time proposal (demonstration of a grating profile for soft X-rays in diamond via ion lithography) with code IuB-005/21, and its technical staff
for their contribution to the operation of the accelerator. We also acknowledge P. Olivero for very useful comments on the manuscript draf
Synthesis, biological and in silico evaluation of pure nucleobase-containing spiro (Indane-Isoxazolidine) derivatives as potential inhibitors of MDM2-p53 interaction
Nucleobase-containing isoxazolidines spiro-bonded to an indane core have been synthesized in very good yields by regio- and diastereoselective 1, 3-dipolar cycloaddition starting from indanyl nitrones and N-vinylnucleobases by using environmentally benign microwave technology. The contemporary presence of various structural groups that are individually active scaffolds of different typology of drugs, has directed us to speculate that these compounds may act as inhibitors of MDM2-p53 interaction. Therefore, both computational calculations and antiproliferative screening against A549 human lung adenocarcinoma cells and human SH-SY5Y neuroblastoma cells were carried out to support this hypothesis
Process design for the manufacturing of soft X-ray gratings in single-crystal diamond by high-energy heavy-ion irradiation
The dataset that supports the findings of this study are archived in the Universidad Autónoma de Madrid data repository e‐cienciaDatos in https://doi.org/10.21950/ARZSJ1This paper describes in detail a novel manufacturing process for optical gratings suitable for use in the UV and soft X-ray regimes in a single-crystal diamond substrate based on highly focused swift heavy-ion irradiation. This type of grating is extensively used in light source facilities such as synchrotrons or free electron lasers, with ever-increasing demands in terms of thermal loads, depending on beamline operational parameters and architecture. The process proposed in this paper may be a future alternative to current manufacturing techniques, providing the advantage of being applicable to single-crystal diamond substrates, with their unique properties in terms of heat conductivity and radiation hardness. The paper summarizes the physical principle used for the grating patterns produced by swift heavy-ion irradiation and provides full details for the manufacturing process for a specific grating configuration, inspired in one of the beamlines at the ALBA synchrotron light source, while stressing the most challenging points for a potential implementation. Preliminary proof-of-concept experimental results are presented, showing the practical implementation of the methodology proposed herei
Novel Regioselective Synthesis of 1,3,4,5-Tetrasubstituted Pyrazoles and Biochemical Valuation on F1FO-ATPase and Mitochondrial Permeability Transition Pore Formation
An efficient, eco-compatible, and very cheap method for the construction of fully substituted pyrazoles (Pzs) via eliminative nitrilimine-alkene 1,3-dipolar cycloaddition (ENAC) reaction was developed in excellent yield and high regioselectivity. Enaminones and nitrilimines generated in situ were selected as dipolarophiles and dipoles, respectively. A deep screening of the employed base, solvent, and temperature was carried out to optimize reaction conditions. Recycling tests of ionic liquid were performed, furnishing efficient performance until six cycles. Finally, a plausible mechanism of cycloaddition was proposed. Then, the effect of three different structures of Pzs was evaluated on the F1FO-ATPase activity and mitochondrial permeability transition pore (mPTP) opening. The Pz derivatives’ titration curves of 6a, 6h, and 6o on the F1FO-ATPase showed a reduced activity of 86%, 35%, and 31%, respectively. Enzyme inhibition analysis depicted an uncompetitive mechanism with the typical formation of the tertiary complex enzyme-substrate-inhibitor (ESI). The dissociation constant of the ESI complex (Ki’) in the presence of the 6a had a lower order of magnitude than other Pzs. The pyrazole core might set the specific mechanism of inhibition with the F1FO-ATPase, whereas specific functional groups of Pzs might modulate the binding affinity. The mPTP opening decreased in Pz-treated mitochondria and the Pzs’ inhibitory effect on the mPTP was concentration-dependent with 6a and 6o. Indeed, the mPTP was more efficiently blocked with 0.1 mM 6a than with 1 mM 6a. On the contrary, 1 mM 6o had stronger desensitization of mPTP formation than 0.1 mM 6o. The F1FO-ATPase is a target of Pzs blocking mPTP formation
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