The band structure of single-layer black phosphorus and the effect of strain are predicted using density functional theory and tight-binding models. Having determined the localized orbital ...composition of the individual bands from first principles, we use the system symmetry to write down the effective low-energy Hamiltonian at the Γ point. From numerical calculations and arguments based on the crystal structure of the material, we show that the deformation in the direction normal to the plane can be used to change the gap size and induce a semiconductor-metal transition.
To understand the complex physics of a system with strong electron-electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the ...system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices. However, the material must be thin enough to avoid shielding of the electric field in the bulk material. Two-dimensional materials do not experience electrical screening, and their charge-carrier density can be controlled by gating. Octahedral titanium diselenide (1T-TiSe2) is a prototypical two-dimensional material that reveals a charge-density wave (CDW) and superconductivity in its phase diagram, presenting several similarities with other layered systems such as copper oxides, iron pnictides, and crystals of rare-earth elements and actinide atoms. By studying 1T-TiSe2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, we achieve unprecedented control over the CDW transition temperature (tuned from 170 kelvin to 40 kelvin), and over the superconductivity transition temperature (tuned from a quantum critical point at 0 kelvin up to 3 kelvin). Electrically driving TiSe2 over different ordered electronic phases allows us to study the details of the phase transitions between many-body states. Observations of periodic oscillations of magnetoresistance induced by the Little-Parks effect show that the appearance of superconductivity is directly correlated with the spatial texturing of the amplitude and phase of the superconductivity order parameter, corresponding to a two-dimensional matrix of superconductivity. We infer that this superconductivity matrix is supported by a matrix of incommensurate CDW states embedded in the commensurate CDW states. Our results show that spatially modulated electronic states are fundamental to the appearance of two-dimensional superconductivity.
2D materials and van der Waals heterostructures Novoselov, K. S.; Mishchenko, A.; Carvalho, A. ...
Science (American Association for the Advancement of Science),
07/2016, Letnik:
353, Številka:
6298
Journal Article
Recenzirano
Odprti dostop
The physics of two-dimensional (2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear (for ...instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices--such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes--are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.
The inflammatory response is critical to fight insults, such as pathogen invasion or tissue damage, but if not resolved often becomes detrimental to the host. A growing body of evidence places ...non-resolved inflammation at the core of various pathologies, from cancer to neurodegenerative diseases. It is therefore not surprising that the immune system has evolved several regulatory mechanisms to achieve maximum protection in the absence of pathology.
The production of the anti-inflammatory cytokine interleukin (IL)-10 is one of the most important mechanisms evolved by many immune cells to counteract damage driven by excessive inflammation. Innate immune cells of the central nervous system, notably microglia, are no exception and produce IL-10 downstream of pattern recognition receptors activation. However, whereas the molecular mechanisms regulating IL-10 expression by innate and acquired immune cells of the periphery have been extensively addressed, our knowledge on the modulation of IL-10 expression by central nervous cells is much scattered. This review addresses the current understanding on the molecular mechanisms regulating IL-10 expression by innate immune cells of the brain and the implications of IL-10 modulation in neurodegenerative disorders.
The regulation of IL-10 production by central nervous cells remains a challenging field. Answering the many remaining outstanding questions will contribute to the design of targeted approaches aiming at controlling deleterious inflammation in the brain.
Rationale
Whether asthma constitutes a risk factor for coronavirus disease‐2019 (COVID‐19) is unclear. Here, we aimed to assess whether asthma, the most common chronic disease in children, is ...associated with higher COVID‐19 risk or severity in pediatric populations.
Methods
We performed a systematic literature search in three stages: first, we reviewed PubMed, EMBASE, and CINAHL for systematic reviews of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) and COVID‐19 in pediatric populations, and reviewed their primary articles; second, we searched PubMed for studies on COVID‐19 or SARS‐CoV‐2 and asthma/wheeze, and evaluated whether the resulting studies included pediatric populations; third, we repeated the second search in BioRxiv.org and MedRxiv.org to find pre‐prints that may have information on pediatric asthma.
Results
In the first search, eight systematic reviews were found, of which five were done in pediatric populations; none of the 67 primary studies included data on pediatric asthma as a comorbidity for COVID‐19. In the second search, we found 34 results in PubMed, of which five reported asthma in adults, but none included data on children. In the third search, 25 pre‐prints in MedRxiv included data on asthma, but none on children. We found one report by the US Centers for Disease Control and Prevention stating that 40/345 (~11.5%) children with data on chronic conditions had “chronic lung diseases including asthma,” and one from a tertiary hospital in New York that reported asthma in 11/46 (~23.9%) children hospitalized for COVID‐19.
Conclusion
There is scarcely any data on whether childhood asthma (or other pediatric respiratory diseases) constitute risk factors for SARS‐CoV‐2 infection or COVID‐19 severity. Studies are needed that go beyond counting the number of cases in the pediatric age range.
Chromium and aluminium salphen complexes have been found to display remarkable catalytic activity in the synthesis of cyclic carbonates from a range of epoxides and carbon dioxide. The Al(salphen) ...complex is more reactive towards terminal epoxides at ambient temperature and pressure, whereas the Cr(salphen) complex exhibits higher catalytic activity towards more challenging internal epoxides at elevated temperature and pressure.
Have you got the metal for it? Diethylamino‐substituted chromium and aluminium salphen complexes both catalyse the synthesis of cyclic carbonates from epoxides and carbon dioxide, but show different substrate preferences. The chromium complex is best for internal epoxides whilst the aluminium complex is best for terminal epoxides.
Strongly bound excitons confined in two-dimensional (2D) semiconductors are dipoles with a perfect in-plane orientation. In a vertical stack of semiconducting 2D crystals, such in-plane excitonic ...dipoles are expected to efficiently couple across van der Waals gap due to strong interlayer Coulomb interaction and exchange their energy. However, previous studies on heterobilayers of group 6 transition metal dichalcogenides (TMDs) found that the exciton decay dynamics is dominated by interlayer charge transfer (CT) processes. Here, we report an experimental observation of fast interlayer energy transfer (ET) in MoSe2/WS2 heterostructures using photoluminescence excitation (PLE) spectroscopy. The temperature dependence of the transfer rates suggests that the ET is Förster-type involving excitons in the WS2 layer resonantly exciting higher-order excitons in the MoSe2 layer. The estimated ET time of the order of 1 ps is among the fastest compared to those reported for other nanostructure hybrid systems such as carbon nanotube bundles. Efficient ET in these systems offers prospects for optical amplification and energy harvesting through intelligent layer engineering.
Oxygen defects in phosphorene Ziletti, A; Carvalho, A; Campbell, D K ...
Physical review letters,
2015-Jan-30, Letnik:
114, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Surface reactions with oxygen are a fundamental cause of the degradation of phosphorene. Using first-principles calculations, we show that for each oxygen atom adsorbed onto phosphorene there is an ...energy release of about 2 eV. Although the most stable oxygen adsorbed forms are electrically inactive and lead only to minor distortions of the lattice, there are low energy metastable forms which introduce deep donor and/or acceptor levels in the gap. We also propose a mechanism for phosphorene oxidation involving reactive dangling oxygen atoms and we suggest that dangling oxygen atoms increase the hydrophilicity of phosphorene.
Cytochrome c (cyt c) is a small soluble heme protein characterized by a relatively flexible structure, particularly in the ferric form, such that it is able to sample a broad conformational space. ...Depending on the specific conditions, interactions, and cellular localization, different conformations may be stabilized, which differ in structure, redox properties, binding affinities, and enzymatic activity. The primary function is electron shuttling in oxidative phosphorylation, and is exerted by the so-called native cyt c in the intermembrane mitochondrial space of healthy cells. Under pro-apoptotic conditions, however, cyt c gains cardiolipin peroxidase activity, translocates into the cytosol to engage in the intrinsic apoptotic pathway, and enters the nucleus where it impedes nucleosome assembly. Other reported functions include cytosolic redox sensing and involvement in the mitochondrial oxidative folding machinery. Moreover, post-translational modifications such as nitration, phosphorylation, and sulfoxidation of specific amino acids induce alternative conformations with differential properties, at least in vitro. Similar structural and functional alterations are elicited by biologically significant electric fields and by naturally occurring mutations of human cyt c that, along with mutations at the level of the maturation system, are associated with specific diseases. Here, we summarize current knowledge and recent advances in understanding the different structural, dynamic, and thermodynamic factors that regulate the primary electron transfer function, as well as alternative functions and conformations of cyt c. Finally, we present recent technological applications of this moonlighting protein.
Four inflammatory diseases are strongly associated with Major Histocompatibility Complex class I (MHC-I) molecules: birdshot chorioretinopathy (HLA-A
29:02), ankylosing spondylitis (HLA-B
27), ...Behçet's disease (HLA-B
51), and psoriasis (HLA-C
06:02). The endoplasmic reticulum aminopeptidases (ERAP) 1 and 2 are also risk factors for these diseases. Since both enzymes are involved in the final processing steps of MHC-I ligands it is reasonable to assume that MHC-I-bound peptides play a significant pathogenetic role. This review will mainly focus on recent studies concerning the effects of ERAP1 and ERAP2 polymorphism and expression on shaping the peptidome of disease-associated MHC-I molecules in live cells. These studies will be discussed in the context of the distinct mechanisms and substrate preferences of both enzymes, their different patterns of genetic association with various diseases, the role of polymorphisms determining changes in enzymatic activity or expression levels, and the distinct peptidomes of disease-associated MHC-I allotypes. ERAP1 and ERAP2 polymorphism and expression induce significant changes in multiple MHC-I-bound peptidomes. These changes are MHC allotype-specific and, without excluding a degree of functional inter-dependence between both enzymes, reflect largely separate roles in their processing of MHC-I ligands. The studies reviewed here provide a molecular basis for the distinct patterns of genetic association of ERAP1 and ERAP2 with disease and for the pathogenetic role of peptides. The allotype-dependent alterations induced on distinct peptidomes may explain that the joint association of both enzymes and unrelated MHC-I alleles influence different pathological outcomes.
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