91,439 research outputs found
The sign problem in full configuration interaction quantum Monte Carlo: Linear and sub-linear representation regimes for the exact wave function
We investigate the sign problem for full configuration interaction quantum
Monte Carlo (FCIQMC), a stochastic algorithm for finding the ground state
solution of the Schr\"odinger equation with substantially reduced computational
cost compared with exact diagonalisation. We find -space Hubbard models for
which the solution is yielded with storage that grows sub-linearly in the size
of the many-body Hilbert space, in spite of using a wave function that is
simply linear combination of states. The FCIQMC algorithm is able to find this
sub-linear scaling regime without bias and with only a choice of Hamiltonian
basis. By means of a demonstration we solve for the energy of a 70-site
half-filled system (with a space of determinants) in 250 core hours,
substantially quicker than the 10 core hours that would be
required by exact diagonalisation. This is the largest space that has been
sampled in an unbiased fashion. The challenge for the recently-developed FCIQMC
method is made clear: expand the sub-linear scaling regime whilst retaining
exact on average accuracy. This result rationalizes the success of the
initiator adaptation (i-FCIQMC) and offers clues to improve it. We argue that
our results changes the landscape for development of FCIQMC and related
methods.Comment: 6 pages, 4 figures. The mentioned supplementary material is included
as "Ancillary files". Comments welcom
Habeas Corpus and the Penalty of Death
Adolescence is associated with high impulsivity and risk taking, making adolescent individuals more inclined to use drugs. Early drug use is correlated to increased risk for substance use disorders later in life but the neurobiological basis is unclear. The brain undergoes extensive development during adolescence and disturbances at this time are hypothesized to contribute to increased vulnerability. The transition from controlled to compulsive drug use and addiction involve long-lasting changes in neural networks including a shift from the nucleus accumbens, mediating acute reinforcing effects, to recruitment of the dorsal striatum and habit formation. This study aimed to test the hypothesis of increased dopamine release after a pharmacological challenge in adolescent rats. Potassium-evoked dopamine release and uptake was investigated using chronoamperometric dopamine recordings in combination with a challenge by amphetamine in early and late adolescent rats and in adult rats. In addition, the consequences of voluntary alcohol intake during adolescence on these effects were investigated. The data show a gradual increase of evoked dopamine release with age, supporting previous studies suggesting that the pool of releasable dopamine increases with age. In contrast, a gradual decrease in evoked release with age was seen in response to amphetamine, supporting a proportionally larger storage pool of dopamine in younger animals. Dopamine measures after voluntary alcohol intake resulted in lower release amplitudes in response to potassium-chloride, indicating that alcohol affects the releasable pool of dopamine and this may have implications for vulnerability to addiction and other psychiatric diagnoses involving dopamine in the dorsal striatum
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Targeting inflammatory pathways in axial spondyloarthritis.
The triggers and pathogenesis of axial spondyloarthritis (axSpA) are not yet completely understood. However, therapeutic agents targeting tumor necrosis factor-α and interleukin-17 inflammatory pathways have proven successful in suppressing many of the clinical symptoms and signs of axSpA, giving us an indication of which pathways are responsible for initiating and maintaining the inflammation. The mechanisms that eventuate in syndesmophytes and ankyloses are less clear. This review addresses these two critical pathways of inflammation, discussing their nature and these factors that may activate or enhance the pathways in patients with axSpA. In addition, genetic and other markers important to the inflammatory pathways implicated in axSpA are explored, and prognostic biomarkers are discussed. Treatment options available for the management of axSpA and their associated targets are highlighted
Evaluating the Long-run Impacts of the 9/11 Terrorist Attacks on US Domestic Airline Travel
Although the US airline industry began 2001 with 24 consecutive profitable quarters, including net profits in 2000 totaling $7.9 billion, the impact of the 9/11 event on the industry was substantial. Whereas the recession that began in early 2001 signaled the end of profitability, the 9/11 terrorist attacks pushed the industry into financial crisis after air travel dropped 20% over the September–December 2001 period compared to the same period in 2000. Given the decline in domestic air travel, an important question is whether the detrimental impact of the attacks was temporary or permanent. That is, did airline travel return to the trend that existed prior to the terrorist attacks? There are theoretical reasons to the believe that it would not. Economists have long viewed travel-mode choices as the outcome of a comparison of opportunity costs and benefits. Thus, anything that permanently raises the opportunity cost of travel, holding benefits constant, should reduce the level of travel volume. To determine whether air travel was permanently reduced, we use econometric and time-series forecasting models to generate a counter-factual forecast of air travel volume in the absence of the terrorist attacks. These dynamic forecasts are compared to actual air travel levels to determine the impact of the terrorist attacks. The findings suggest that domestic air travel did not return to the levels that would have existed in the absence of the attack
Photon molecules in atomic gases trapped near photonic crystal waveguides
Realizing systems that support robust, controlled interactions between
individual photons is an exciting frontier of nonlinear optics. To this end,
one approach that has emerged recently is to leverage atomic interactions to
create strong and spatially non-local interactions between photons. In
particular, effective interactions have been successfully created via
interactions between atoms excited to Rydberg levels. Here, we investigate an
alternative approach, in which atomic interactions arise via their common
coupling to photonic crystal waveguides. This technique takes advantage of the
ability to separately tailor the strength and range of interactions via the
dispersion engineering of the structure itself, which can lead to qualitatively
new types of phenomena. As an example, we discuss the formation of correlated
transparency windows, in which photonic states of a certain number and shape
selectively propagate through the system. Through this technique, we show in
particular that one can create molecular-like potentials that lead to molecular
bound states of photon pairs
The strong U.S. dollar: A dilemma for foreign monetary authorities
Dollar, American ; Money ; Foreign exchange
Use of a Theoretical Flow Model to Correlate Data for Film Cooling or Heating an Adiabatic Wall by Tangential Injection of Gases of Different Fluid Properties
No abstract availabl
Loads and Aeroelasticity Division research and technology accomplishments for FY 1986 and plans for FY 1987
The Loads and Aeroelasticity Division's research accomplishments for FY 86 and research plans for FY 87 are presented. The work under each Branch (technical area) is described in terms of highlights of accomplishments during the past year and highlights of plans for the current year as they relate to five year plans for each technical area. This information will be useful in program coordination with other government organizations and industry in areas of mutual interest
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