102 research outputs found
Spatiotemporal Analysis of Prior Appropriations Water Calls
A spatiotemporal model is developed to examine prior appropriations–based water curtailment in Idaho’s Snake River Plain Aquifer. Using a 100 year horizon, prior appropriations–based curtailment supplemented with optimized water use reductions is shown to produce a spatial distribution of water use reductions that differs from that produced by regulatory curtailment based strictly on initial water right assignments. Discounted profits over 100 years of crop production are up to 7% higher when allocation is optimized. Total pumping over 100 years is 0.3%, 3%, and 40% higher under 1, 10, and 100 year prior appropriations–based regulatory curtailment, respectively
Diffractive imaging of dissociation and ground state dynamics in a complex molecule
We have investigated the structural dynamics in photoexcited
1,2-diiodotetrafluoroethane molecules (C2F4I2) in the gas phase experimentally
using ultrafast electron diffraction and theoretically using FOMO-CASCI excited
state dynamics simulations. The molecules are excited by an ultra-violet
femtosecond laser pulse to a state characterized by a transition from the
iodine 5p orbital to a mixed 5p|| hole and CF2 antibonding orbital, which
results in the cleavage of one of the carbon-iodine bonds. We have observed,
with sub-Angstrom resolution, the motion of the nuclear wavepacket of the
dissociating iodine atom followed by coherent vibrations in the electronic
ground state of the C2F4I radical. The radical reaches a stable classical
(non-bridged) structure in less than 200 fs.Comment: 13 pages, 11 figure
Ultrafast manipulation of mirror domain walls in a charge density wave
Domain walls (DWs) are singularities in an ordered medium that often host
exotic phenomena such as charge ordering, insulator-metal transition, or
superconductivity. The ability to locally write and erase DWs is highly
desirable, as it allows one to design material functionality by patterning DWs
in specific configurations. We demonstrate such capability at room temperature
in a charge density wave (CDW), a macroscopic condensate of electrons and
phonons, in ultrathin 1T-TaS. A single femtosecond light pulse is shown to
locally inject or remove mirror DWs in the CDW condensate, with probabilities
tunable by pulse energy and temperature. Using time-resolved electron
diffraction, we are able to simultaneously track anti-synchronized CDW
amplitude oscillations from both the lattice and the condensate, where
photo-injected DWs lead to a red-shifted frequency. Our demonstration of
reversible DW manipulation may pave new ways for engineering correlated
material systems with light
Investigating dissociation pathways of nitrobenzene via mega-electron-volt ultrafast electron diffraction
As the simplest nitroaromatic compound, nitrobenzene is an interesting model
system to explore the rich photochemistry of nitroaromatic compounds. Previous
measurements of nitrobenzene's photochemical dynamics have probed structural
and electronic properties, which, at times, paint a convoluted and sometimes
contradictory description of the photochemical landscape. A sub-picosecond
structural probe can complement previous electronic measurements and aid in
determining the photochemical dynamics with less ambiguity. We investigate the
ultrafast dynamics of nitrobenzene triggered by photoexcitation at 267 nm
employing megaelectronvolt ultrafast electron diffraction with femtosecond time
resolution. We measure the first 5 ps of dynamics and, by comparing our
measured results to simulation, we unambiguously distinguish the lowest singlet
and triplet electronic states. We observe ground state recovery within 160 +/-
60 fs through internal conversions and without signal corresponding to
photofragmentation. Our lack of dissociation signal within the first 5 ps
indicates that previously observed photofragmenation reactions take place in
the vibrationally "hot" ground state on timescales considerably beyond 5 ps.Comment: 5 pages, 3 figures, and 1 tabl
Dual-stage structural response to quenching charge order in magnetite
The Verwey transition in magnetite (Fe_{3}O_{4} ) is the prototypical metal-insulator transition and has eluded a
comprehensive explanation for decades. A major element of the challenge is the complex interplay between
charge order and lattice distortions. Here we use ultrafast electron diffraction (UED) to disentangle the roles of
charge order and lattice distortions by tracking the transient structural evolution after charge order is melted via
ultrafast photoexcitation. A dual-stage response is observed in which X_{3}, X_{1}, and Delta5-type structural distortions
occur on markedly different timescales of 0.7–3.2 ps and longer than 3.2 ps. We propose that these distinct
timescales arise because X_{3}-type distortions strongly couple to the trimeron charge order, whereas the Delta5-
distortions are more strongly associated with monoclinic to cubic distortions of the overall lattice. Our work aids
in clarifying the charge-lattice interplay using UED method and illustrates the disentanglement of the complex
phases in magnetite
Dual-stage structural response to quenching charge order in magnetite
The Verwey transition in magnetite (Fe3O4 ) is the prototypical
metal-insulator transition and has eluded a comprehensive explanation for
decades. A major element of the challenge is the complex interplay between
charge order and lattice distortions. Here we use ultrafast electron
diffraction (UED) to disentangle the roles of charge order and lattice
distortions by tracking the transient structural evolution after charge order
is melted via ultrafast photoexcitation. A dual stage response is observed in
which X3, X1, and Delta5 type structural distortions occur on markedly
different timescales of 0.7 to 3.2 ps and longer than 3.2 ps. We propose that
these distinct timescales arise because X3 type distortions strongly couple to
the trimeron charge order, whereas the Delta5-distortions are more strongly
associated with monoclinic to cubic distortions of the overall lattice. Our
work aids in clarifying the charge lattice interplay using UED method and
illustrates the disentanglement of the complex phases in magnetite.Comment: 7 figures and 7 table
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