1,637 research outputs found
Mott metal-insulator transition on compressible lattices
The critical properties of the finite temperature Mott endpoint are
drastically altered by a coupling to crystal elasticity, i.e., whenever it is
amenable to pressure tuning. Similar as for critical piezoelectric
ferroelectrics, the Ising criticality of the electronic system is preempted by
an isostructural instability, and long-range shear forces suppress microscopic
fluctuations. As a result, the endpoint is governed by Landau criticality. Its
hallmark is thus a breakdown of Hooke's law of elasticity with a non-linear
strain-stress relation characterized by a mean-field exponent. Based on a
quantitative estimate, we predict critical elasticity to dominate the
temperature range DeltaT/Tc ~ 8% close to the Mott endpoint of
kappa-(BEDT-TTF)2X.Comment: 4 pages, 6 figure
Air–snowpack exchange of bromine, ozone and mercury in the springtime Arctic simulated by the 1-D model PHANTAS – Part 2: Mercury and its speciation
Atmospheric mercury depletion events (AMDEs) refer to a recurring depletion
of mercury occurring in the springtime Arctic (and Antarctic) boundary layer,
in general, concurrently with ozone depletion events (ODEs). To close some of
the knowledge gaps in the physical and chemical mechanisms of AMDEs and ODEs,
we have developed a one-dimensional model that simulates multiphase chemistry
and transport of trace constituents throughout porous snowpack and in the
overlying atmospheric boundary layer (ABL). This paper constitutes Part 2 of
the study, describing the mercury component of the model and its application
to the simulation of AMDEs. Building on model components reported in Part 1
("In-snow bromine activation and its impact on ozone"), we have developed a
chemical mechanism for the redox reactions of mercury in the gas and aqueous
phases with temperature dependent reaction rates and equilibrium constants
accounted for wherever possible. Thus the model allows us to study the
chemical and physical processes taking place during ODEs and AMDEs within a
single framework where two-way interactions between the snowpack and the
atmosphere are simulated in a detailed, process-oriented manner. Model runs
are conducted for meteorological and chemical conditions that represent the
springtime Arctic ABL characterized by the presence of "haze" (sulfate
aerosols) and the saline snowpack on sea ice. The oxidation of gaseous
elemental mercury (GEM) is initiated via reaction with Br-atom to form HgBr,
followed by competitions between its thermal decomposition and further
reactions to give thermally stable Hg(II) products. To shed light on
uncertain kinetics and mechanisms of this multi-step oxidation process, we
have tested different combinations of their rate constants based on published
laboratory and quantum mechanical studies. For some combinations of the rate
constants, the model simulates roughly linear relationships between the
gaseous mercury and ozone concentrations as observed during AMDEs/ODEs by
including the reaction HgBr + BrO and assuming its rate constant to be the
same as for the reaction HgBr + Br, while for other combinations the
results are more realistic by neglecting the reaction HgBr + BrO.
Speciation of gaseous oxidized mercury (GOM) changes significantly depending
on whether or not BrO is assumed to react with HgBr to form Hg(OBr)Br.
Similarly to ozone (reported in Part 1), GEM is depleted via bromine radical
chemistry more vigorously in the snowpack interstitial air than in the
ambient air. However, the impact of such in-snow sink of GEM is found to be
often masked by the re-emissions of GEM from the snow following the
photo-reduction of Hg(II) deposited from the atmosphere. GOM formed in the
ambient air is found to undergo fast "dry deposition" to the snowpack by
being trapped on the snow grains in the top ~1 mm layer. We
hypothesize that liquid-like layers on the surface of snow grains are
connected to create a network throughout the snowpack, thereby facilitating
the vertical diffusion of trace constituents trapped on the snow grains at
much greater rates than one would expect inside solid ice crystals.
Nonetheless, on the timescale of a week simulated in this study, the signal
of atmospheric deposition does not extend notably below the top 1 cm of the
snowpack. We propose and show that particulate-bound mercury (PBM) is
produced mainly as HgBr<sub>4</sub><sup>2−</sup> by taking up GOM into bromide-enriched
aerosols after ozone is significantly depleted in the air mass. In the
Arctic, "haze" aerosols may thus retain PBM in ozone-depleted air masses,
allowing the airborne transport of oxidized mercury from the area of its
production farther than in the form of GOM. Temperature dependence of
thermodynamic constants calculated in this study for Henry's law and
aqueous-phase halide complex formation of Hg(II) species is a critical factor
for this proposition, calling for experimental verification. The proposed
mechanism may explain observed changes in the GOM–PBM partitioning with
seasons, air temperature and the concurrent progress of ozone depletion in
the high Arctic. The net deposition of mercury to the surface snow is shown
to increase with the thickness of the turbulent ABL and to correspond well
with the column amount of BrO in the atmosphere
Formation of dispersive hybrid bands at an organic-metal interface
An electronic band with quasi-one dimensional dispersion is found at the
interface between a monolayer of a charge-transfer complex (TTF-TCNQ) and a
Au(111) surface. Combined local spectroscopy and numerical calculations show
that the band results from a complex mixing of metal and molecular states. The
molecular layer folds the underlying metal states and mixes with them
selectively, through the TTF component, giving rise to anisotropic hybrid
bands. Our results suggest that, by tuning the components of such molecular
layers, the dimensionality and dispersion of organic-metal interface states can
be engineered
Effect of cold-water irrigation on bacterial wilt pathogen of tomato.
Bacterial wilt caused by Ralstonia solanacearum is one of the most devastating bacterial diseases of plants worldwide. Management of bacterial wilt in tomato and other crops has been difficult, and so novel but easily implemented control methods are being sought. To evaluate the effect of cold-water irrigation on bacterial wilt of tomato, four treatments were used in which CF (chemically fertilized) soil and CF + FYM (chemical fertilizer + farmyard manure [FYM]) soil were inoculated with a bacterial suspension (R. solanacearum strain YU1Rif43) at 106 colony forming units (CFU) g−1 soil. Tomato seedlings were grown in Agri-pots in a plant growth chamber. The soil was irrigated with water that was kept at the same temperature in each treatment: 4, 10, 20, or 30°C. Incidence and severity of wilt, counting of the colonies of the culturable population of pathogen, and dry-mass and height of the plants were examined. After 45 days and in both kinds of soil, most of the plants had wilted in soil irrigated at 30°C. Wilt incidence was substantially reduced when transplanted seedlings were irrigated at lower temperatures (4–20°C). Survival of R. solanacearum was also reduced after being irrigated with water at lower temperatures, indicating that the reduced incidence of wilt was linked to reduced survival of the pathogen. Dry-mass and plant height were slightly higher under control conditions than in soils irrigated at lower temperatures. This study suggests that cold-water irrigation could significantly reduce bacterial wilt of tomato and have an adverse effect on survival of the wilt pathogen
Determining ethylene group disorder levels in -(BEDT-TTF)Cu[N(CN)]Br
We present a detailed structural investigation of the organic superconductor
-(BEDT-TTF)Cu[N(CN)]Br at temperatures from 9 to 300 K.
Anomalies in the dependence of the lattice parameters are associated with a
glass-like transition previously reported at = 77 K. From structure
refinements at 9, 100 and 300 K, the orthorhombic crystalline symmetry, space
group {\it Pnma}, is established at all temperatures. Further, we extract the
dependence of the occupation factor of the eclipsed conformation of the
terminal ethylene groups of the BEDT-TTF molecule. At 300 K, we find 67(2) %,
with an increase to 97(3) % at 9 K. We conclude that the glass-like transition
is not primarily caused by configurational freezing-out of the ethylene groups
- …