79 research outputs found
Seebeck effect in the conducting LaAlO_{3}/SrTiO_{3} interface
The observation of metallic behavior at the interface between insulating
oxides has triggered worldwide efforts to shed light on the physics of these
systems and clarify some still open issues, among which the dimensional
character of the conducting system. In order to address this issue, we measure
electrical transport (Seebeck effect, Hall effect and conductivity) in
LaAlO_{3}/SrTiO_{3} interfaces and, for comparison, in a doped SrTiO_{3} bulk
single crystal. In these experiments, the carrier concentration is tuned, using
the field effect in a back gate geometry. The combined analysis of all
experimental data at 77 K indicates that the thickness of the conducting layer
is ~7 nm and that the Seebeck effect data are well described by a
two-dimensional (2D) density of states. We find that the back gate voltage is
effective in varying not only the charge density, but also the thickness of the
conducting layer, which is found to change by a factor of ~2, using an electric
field between -4 and +4MV/m at 77K. No enhancement of the Seebeck effect due to
the electronic confinement and no evidence for two-dimensional quantization
steps are observed at the interfaces.Comment: 15 pages, 5 figure
Two-dimensional quantum oscillations of the conductance at LaAlO3/SrTiO3 interfaces
We report on a study of magnetotransport in LaAlO3/SrTiO3 interfaces
characterized by mobilities of the order of several thousands cm/Vs. We
observe Shubnikov-de Haas oscillations that indicate a two-dimensional
character of the Fermi surface. The frequency of the oscillations signals a
multiple sub-bands occupation in the quantum well or a multiple valley
configuration. From the temperature dependence of the oscillation amplitude we
extract an effective carrier mass \,. An electric field
applied in the back-gate geometry increases the mobility, the carrier density
and the oscillation frequency.Comment: 4 pages, 4 figure
Origin of interface magnetism in BiMnO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures
Possible ferromagnetism induced in otherwise non-magnetic materials has been
motivating intense research in complex oxide heterostructures. Here we show
that a confined magnetism is realized at the interface between SrTiO3 and two
insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent
x-ray absorption spectroscopy, we find that in both cases the magnetic order is
stabilized by a negative exchange interaction between the electrons transferred
to the interface and local magnetic moments. These local magnetic moments are
associated to Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+
ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetic
moments are quenched by annealing in oxygen, suggesting a decisive role of
oxygen vacancies in the stabilization of interfacial magnetism.Comment: 5 pages, 4 figure
Predictors of falls and hospitalization outcomes in elderly patients admitted to an acute geriatric unit
Two-dimensional superconductivity at a Mott-Insulator/Band-Insulator interface: LaTiO3/SrTiO3
Transition metal oxides display a great variety of quantum electronic
behaviours where correlations often play an important role. The achievement of
high quality epitaxial interfaces involving such materials gives a unique
opportunity to engineer artificial structures where new electronic orders take
place. One of the most striking result in this area is the recent observation
of a two-dimensional electron gas at the interface between a strongly
correlated Mott insulator LaTiO3 and a band insulator SrTiO3. The mechanism
responsible for such a behaviour is still under debate. In particular, the
influence of the nature of the insulator has to be clarified. Here we show that
despite the expected electronic correlations, LaTiO3/SrTiO3 heterostructures
undergo a superconducting transition at a critical temperature Tc=300 mK. We
have found that the superconducting electron gas is confined over a typical
thickness of 12 nm. We discuss the electronic properties of this system and
review the possible scenarios
Signatures of polaronic excitations in quasi-one-dimensional LaTiO
The optical properties of quasi-one-dimensional metallic LaTiO are
studied for the polarization along the and axes. With decreasing
temperature modes appear along both directions suggestive for a phase
transition. The broadness of these modes along the conducting axis might be due
to the coupling of the phonons to low-energy electronic excitations across an
energy gap. We observe a pronounced midinfrared band with a temperature
dependence consistent with (interacting) polaron models. The polaronic picture
is corroborated by the presence of strong electron-phonon coupling and the
temperature dependence of the dc conductivity.Comment: 5 pages, 5 figure
The Intracellular DNA Sensor IFI16 Gene Acts as Restriction Factor for Human Cytomegalovirus Replication
Human interferon (IFN)-inducible IFI16 protein, an innate immune sensor of intracellular DNA, modulates various cell functions, however, its role in regulating virus growth remains unresolved. Here, we adopt two approaches to investigate whether IFI16 exerts pro- and/or anti-viral actions. First, the IFI16 gene was silenced using specific small interfering RNAs (siRNA) in human embryo lung fibroblasts (HELF) and replication of DNA and RNA viruses evaluated. IFI16-knockdown resulted in enhanced replication of Herpesviruses, in particular, Human Cytomegalovirus (HCMV). Consistent with this, HELF transduction with a dominant negative form of IFI16 lacking the PYRIN domain (PYD) enhanced the replication of HCMV. Second, HCMV replication was compared between HELFs overexpressing either the IFI16 gene or the LacZ gene. IFI16 overexpression decreased both virus yield and viral DNA copy number. Early and late, but not immediate-early, mRNAs and proteins were strongly down-regulated, thus IFI16 may exert its antiviral effect by impairing viral DNA synthesis. Constructs with the luciferase reporter gene driven by deleted or site-specific mutated forms of the HCMV DNA polymerase (UL54) promoter demonstrated that the inverted repeat element 1 (IR-1), located between â54 and â43 relative to the transcription start site, is the target of IFI16 suppression. Indeed, electrophoretic mobility shift assays and chromatin immunoprecipitation demonstrated that suppression of the UL54 promoter is mediated by IFI16-induced blocking of Sp1-like factors. Consistent with these results, deletion of the putative Sp1 responsive element from the HCMV UL44 promoter also relieved IFI16 suppression. Together, these data implicate IFI16 as a novel restriction factor against HCMV replication and provide new insight into the physiological functions of the IFN-inducible gene IFI16 as a viral restriction factor
A Review of Dietary Prevention of Human Papillomavirus-Related Infection of the Cervix and Cervical Intraepithelial Neoplasia
The natural history of cervical cancer suggests that prevention can be achieved by modification of the host's immune system through a nutrient-mediated program. This study reviews the preventive role of dietary intake on cervical intraepithelial neoplasia (CIN) induced by human papillomavirus (HPV). Electronic databases were searched using relevant keywords such as, but not limited to, human papillomavirus infection, cervical intraepithelial neoplasia, lifestyle factors, nutrients intake, and diet. High consumption of fruit and vegetables appears to be protective against CIN. The findings also highlight the possibility of consuming high levels of specific nutrients, vitamins, and minerals, and retaining sufficient level of these elements in the body, especially those with high antioxidants and antiviral properties, to prevent progression of transient and persistent HPV infections to high-grade CIN 2 and 3 (including in situ cervical cancer). The protective effect is not significant for high-risk HPV persistent infections and invasive cervical cancer. Although it appears that intake of specific nutrients, vitamins, and minerals may be good in CIN prevention, there is lack of evidence from controlled trial to confirm this. Health professionals shall focus on implementation of a balanced-diet prevention strategy at an early stage for cervical cancer prevention
Comportamiento de los cultivares de papaya Sunset, Sunrise y de los genotipos Baixinho de Santa Amalia y BH - 65 en la zona sur de la isla de Tenerife
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