6,978 research outputs found
High-resolution antenna near-field imaging and sub-THz measurements with a small atomic vapor-cell sensing element
Atomic sensing and measurement of millimeter-wave (mmW) and THz electric
fields using quantum-optical EIT spectroscopy of Rydberg states in atomic
vapors has garnered significant interest in recent years towards the
development of atomic electric-field standards and sensor technologies. Here we
describe recent work employing small atomic vapor cell sensing elements for
near-field imaging of the radiation pattern of a K-band horn antenna at
13.49 GHz. We image fields at a spatial resolution of and measure
over a 72 to 240 V/m field range using off-resonance AC-Stark shifts of a
Rydberg resonance. The same atomic sensing element is used to measure sub-THz
electric fields at 255 GHz, an increase in mmW-frequency by more than one order
of magnitude. The sub-THz field is measured over a continuous 100 MHz
frequency band using a near-resonant mmW atomic transition
Evaluación de los efectos de la urbanización en los arroyos de Tierra del Fuego
We set out to understand how urbanization affects streams in Ushuaia, Tierra del Fuego. Paired ttestsand linear regressions were used to compare physico-chemical stream habitat variables (i.e., temperature,turbidity, conductivity, dissolved oxygen and pH) and benthic macroinvertebrate community structure (i.e.,density, taxonomic richness, Shannon-Weiner diversity) and function (functional feeding groups [FFG]) in fourwatersheds with urban and reference sites. We then calculated indices of biotic integrity for habitat (rapid visualassessment protocol [RVAP]) and benthos (Ephemeroptera, Plecoptera, Trichoptera richness [EPT], family bioticindex [FBI], rapid bioassessment protocol [RBP] and biotic monitoring Patagonian streams [BMPS]). Resultsindicated that urbanization negatively impacted these streams? underlying ecological condition, decreasingbenthic biodiversity and dissolved oxygen, while increasing conductivity and turbidity. FFG assemblagewas similar between both sites, but urbanization increased the existing dominance of collector-gatherers.Additionally, urban sites presented lower values in three of the benthic macroinvertebrate indices (EPT, RBP,BMPS, but not FBI) and also for habitat (RVAP). These data fill an existing gap in stream ecology for southernPatagonia and are useful to create monitoring tools. By incorporating urbanization as a driver of ecosystemchange, managers and planners will be better able to confront the issue of sustainable development in thisregion, which is considered one of the most pristine wilderness areas remaining on the planet but whosehuman population is concentrated in a few densely populated urban areas.Fil: Zagarola, Jean Paul A.. Bonneville Environmental Foundation; Estados UnidosFil: MartÃnez Pastur, Guillermo José. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro Austral de Investigaciones CientÃficas; ArgentinaFil: Lopez, MarÃa Eugenia. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro Austral de Investigaciones CientÃficas; ArgentinaFil: Anderson, Christopher Brian. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro Austral de Investigaciones CientÃficas; Argentin
Time resolved structural dynamics of butadiyne-linked porphyrin dimers
In this work the timescales and mechanisms associated with the structural dynamics of butadiyne-linked porphyrin dimers are investigated through time resolved narrowband pump / broadband probe transient absorption spectroscopy. Our results confirm previous findings that the broadening is partly due to a distribution of structures with different (dihedral) angular conformations. Comparison of measurements with excitations on the red and blue sides of the Q-band unravel the ground and excited state conformational re-equilibration timescales. Further comparison to a planarized dimer, through addition of a ligand, provide conclusive evidence for the twisting motion performed by the porphyrin dimer in solution
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