143 research outputs found
Edge-functionalized and substitutional doped graphene nanoribbons: electronic and spin properties
Graphene nanoribbons are the counterpart of carbon nanotubes in
graphene-based nanoelectronics. We investigate the electronic properties of
chemically modified ribbons by means of density functional theory. We observe
that chemical modifications of zigzag ribbons can break the spin degeneracy.
This promotes the onset of a semiconducting-metal transition, or of an
half-semiconducting state, with the two spin channels having a different
bandgap, or of a spin-polarized half-semiconducting state -where the spins in
the valence and conduction bands are oppositely polarized. Edge
functionalization of armchair ribbons gives electronic states a few eV away
from the Fermi level, and does not significantly affect their bandgap. N and B
produce different effects, depending on the position of the substitutional
site. In particular, edge substitutions at low density do not significantly
alter the bandgap, while bulk substitution promotes the onset of
semiconducting-metal transitions. Pyridine-like defects induce a
semiconducting-metal transition.Comment: 12 pages, 5 figure
Shortening the length of stay and mechanical ventilation time by using positive suggestions via MP3 players for ventilated patients
Long stay in intensive care unit (ICU) and prolonged ventilation are deleterious for subsequent quality of life and surcharge financial capacity. We have already demonstrated the beneficial effects of using suggestive communication on recovery time during intensive care. The aim of our present study was to prove the same effects with standardized positive suggestive message delivered by an MP3 player. Patients ventilated in ICU were randomized into a control group receiving standard ICU treatment and two groups with a standardized pre-recorded material delivered via headphones: a suggestive message about safety, self-control, and recovery for the study group and a relaxing music for the music group. Groups were similar in terms of age, gender, and mortality, but the SAPS II scores were higher in the study group than that in the controls (57.8 ± 23.6 vs. 30.1 ± 15.5 and 33.7 ± 17.4). Our post-hoc analysis results showed that the length of ICU stay (134.2 ± 73.3 vs. 314.2 ± 178.4 h) and the time spent on ventilator (85.2 ± 34.9 vs. 232.0 ± 165.6 h) were significantly shorter in the study group compared to the unified control. The advantage of the structured positive suggestive message was proven against both music and control groups
Felföldy Lajos (1920–2016)
Felföldy Lajos (1920–2016) magyar botanika Ă©s hidrobiolĂłgia egyik legsokoldalĂşbb Ă©s legeredetibb egyĂ©nisĂ©ge volt. Pályáját SoĂł RezsĹ‘ irányĂtásával kezdte, 1938 Ă©s 1946 között aktĂvan rĂ©szt vett a debreceni Ă©s 1941–1942 között a kolozsvári Tudományegyetem NövĂ©nytani TanszĂ©kĂ©n folyĂł geobotanikai kutatásokban. Számos tudományterĂĽleten maradandĂłt alkotott. A lĂ©gszennyezĂ©snek az epifiton zuzmĂłkra gyakorolt hatását vizsgálĂł kutatásai (1942) világviszonylatban is az elsĹ‘k közĂ© tartoznak. A Raunkiaer-fĂ©le növĂ©nyi Ă©letforma-rendszeren belĂĽl elkĂĽlönĂtette a kĂ©tĂ©vesek (Hemitherophyta) Ă©letforma-tĂpusát az egyĂ©vesekĂ©tĹ‘l (1942). ĂšttörĹ‘ szerepet játszott Magyarországon a vadon Ă©lĹ‘ növĂ©nyfajok citolĂłgiai (kariolĂłgiai) vizsgálatában (1947–1949). Foglalkozott növĂ©nyĂ©lettannal (1951–1959), vizekben folyĂł primer produkciĂłval Ă©s algatenyĂ©sztĂ©ssel (1958–1960). 1972-ban Ă©letre hĂvta Ă©s 1990-ig szerkesztette a VĂzĂĽgyi HidrobiolĂłgia sorozatot. Megalapozta a magyarországi vĂzminĹ‘sĂ©g-vĂ©delmet, amely a mai napig meghatározza a magyar hidrobiolĂłgusok szemlĂ©letĂ©t. 14 Ă©s 89 Ă©ves kora között legalább tĂzezer herbáriumi lapot gyűjtött. NyugdĂjba vonulása után a MTM NövĂ©nytár Ă©s az ELTE FĂĽvĂ©szkert herbáriumi anyagának rendezĂ©sĂ©vel, revĂziĂłjával foglalkozott, aktĂvan rĂ©szt vett az Ăšj Magyar FĂĽvĂ©szkönyv elkĂ©szĂtĂ©sĂ©nek munkálataiban. Munkáira egyszerre jellemzĹ‘ a termĂ©szet iránti mĂ©ly tisztelet, az elmĂ©leti megalapozottság Ă©s a gyakorlatiasság.</jats:p
Chemically active substitutional nitrogen impurity in carbon nanotubes
We investigate the nitrogen substitutional impurity in semiconducting zigzag
and metallic armchair single-wall carbon nanotubes using ab initio density
functional theory. At low concentrations (less than 1 atomic %), the defect
state in a semiconducting tube becomes spatially localized and develops a flat
energy level in the band gap. Such a localized state makes the impurity site
chemically and electronically active. We find that if two neighboring tubes
have their impurities facing one another, an intertube covalent bond forms.
This finding opens an intriguing possibility for tunnel junctions, as well as
the functionalization of suitably doped carbon nanotubes by selectively forming
chemical bonds with ligands at the impurity site. If the intertube bond density
is high enough, a highly packed bundle of interlinked single-wall nanotubes can
form.Comment: 4 pages, 4 figures; major changes to the tex
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