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 $k$-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 $10^{38}$ determinants) in 250 core hours, substantially quicker than the $\sim$10$^{36}$ 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

Chemiluminescent Tags for Tracking Insect Movement in Darkness: Application to Moth Photo-Orientation

The flight tracks of Manduca sexta (Lepidoptera: Sphingidae) flying toward a 5 watt incandescent light bulb were recorded under low light conditions with the aid of a camera-mounted photomultiplier and a glowing marker technique. Small felt pads bearing a chemiluminescent (glowi ma­erial, Cyalume®, were affixed to the abdomens of free-flying moths. insects orienting to a dim incandescent bulb were easily visible to the naked eye and were clearly captured on videotape. On their initial approach to the light source, M. sexta were found to orient at a mean angle of -0.220 ± 2.70 (mean ± SEM). The speed of the initial approach flight (OA ± 0.03 m/s) was significantly faster than the speed immediately after passing the light (0.29 ± 0.02 m/s; t =6.4, PM. sexta initially fly approximately at a light source and only after passing it, do they engage in circular flight around the source. M. sexta flight to lights does not entirely match any paths predicted by several light orientation mechanisms, including the commonly invoked light compass theory

Coordination and Sustainability of River Observing Activities in the Arctic

To understand and respond to changes in the world’s northern regions, we need a coordinated system of long-term Arctic observations. River networks naturally integrate across landscapes and link the terrestrial and ocean domains. Changes in river discharge reflect changes in the terrestrial water balance, whereas changes in water chemistry are linked to changes in biogeochemical processes and water flow paths. Sustained measurements of river water discharge and water chemistry are therefore essential components of an Arctic observing network. As we strive to establish and sustain long-term observations in the Arctic, these two measurements must be coupled. Although river discharge and chemistry measurements are already coupled to some extent within national boundaries, this is not done in a consistent and coordinated fashion across the pan-Arctic domain. As a consequence, data quality and availability vary widely among regions. International coordination of river discharge and chemistry measurements in the Arctic would be greatly facilitated by formal commitments to maintain a set of core sites and associated measurements that are mutually agreed upon among pan-Arctic nations. Involvement of the agencies currently operating river discharge gauges around the Arctic and establishment of an overarching coordination entity to implement shared protocols, track data quality, and manage data streams would be essential in this endeavor. Focused studies addressing scale-dependent relationships between watershed characteristics and water chemistry, in-stream processes, and estuarine and coastal dynamics are also needed to support interpretation and application of Arctic river observing data as they relate to land and ocean change

A Custom Robotic System for Inspecting HEPA Filters in the Payload Changeout Room at the NASA Kennedy Space Center

In this paper, the prime objective is to describe a custom 4-dof (degree-of-freedom) robotic arm capable of autonomously or telerobotically performing systematic HEPA filter inspection and certification in the Shuttle Launch Pad Payload Changeout Rooms (PCR's) on pads A and B at the Kennedy Space Center, Florida. This HEPA filter inspection robot (HFIR) has been designed to be easily deployable and is equipped with the necessary sensory devices, control hardware, software and man-machine interfaces needed to implement HEPA filter inspection reliably and efficiently without damaging the filters or colliding with existing PCR structures or filters. The main purpose of the HFIR is to implement an automated positioning system to move special inspection sensors in pre-defined or manual patterns for the purpose of verifying filter integrity and efficiency. This will ultimately relieve NASA Payload Operations from significant problems associated with time, cost and personnel safety, impacts realized during non-automated PCR HFIR filter certification

Repurposing of Meropenem and Nadifloxacin for Treatment of Burn Patients?

The escalating number of multidrug resistant pathogens has demanded the swift development of new and potent antibiotics (ref. 2). Metallo-[beta]-lactamases (MBLs) continue to evolve, rendering the latest generation of carbapenem antibiotics useless (ref. 8). SPM-1, a recently discovered MBL, was isolated from a juvenile leukemia patient residing in a hospital in San Palo, Brazil just prior to the patient succumbing to septicemia brought on by Pseudomonas aeruginosa expressing SPM-1 (ref. 8). Screening of the Johns Hopkins Compound library of 1,514 FDA or FAD approved drugs (ref. 1) identified a novel SPM-1 inhibitor that is synergistically compatible with meropenem. Using clinically achievable concentrations, meropenem coupled with nadifloxacin inhibits Pseudomonas aeruginosa expressing SPM-1. This shotgun approach to new drug discovery provided a prompt solution to the grave problem of antibiotic resistant pathogens that are thriving in hospitals today

Searching for Hydrogen in Type Ib Supernovae

We present synthetic spectral fits of the typical Type Ib SN 1999dn and the Hydrogen Rich Ib SN 2000H using the generalized non-local thermodynamic equilibrium stellar atmospheres code \phx. We fit model spectra to five epochs of SN 1999dn ranging from ten days pre-maximum light to 17 days post-maximum light and the two earliest epochs of SN 2000H available, maximum light and six days post-maximum. Our goal is to investigate the possibility of hydrogen in Type Ib Supernovae (SNe Ib), specifically a feature around 6200\AA\ which has previously been attributed to high velocity H-alpha. In earlier work on SN 1999dn we found the most plausible alternative to H-alpha to be a blend of Si II and Fe II lines which can be adjusted to fit by increasing the metallicity. Our models are simple; they assume a powerlaw density profile with radius, homologous expansion, and solar compositions. The helium core is produced by burning 4H --> He in order to conserve nucleon number. For models with hydrogen the outer skin of the model consists of a shell of solar composition. The hydrogen mass of the standard solar composition shell is M_H less than about 0.001 times the mass of the sun in SN 1999dn and M_H less than about 0.2 times the mass of the sun for SN 2000H. Our models fit the observed spectra reasonably well, successfully reproducing most features including the characteristic He I absorptions. The hydrogen feature in SN 1999dn is clear, but much more pronounced in SN 2000H. We discuss a possible evolutionary scenario that accounts for the dichotomy in the hydrogen shell mass between these two supernovae.Comment: 20 pages, 11 figures, ApJ, in pres

San Juan County Agriculture Profile

This publication includes a report that gives agricultural facts and statistics pertaining to San Juan County

Sublethal exposure, insecticide resistance, and community stress

Insecticides are an invaluable pest management tool and anthropogenic stressors of widespread environmental occurrence that are subject to biased perceptions based on the targeted application, market value of use, and regulatory requirements. As a result, short-term and simplistic efforts focusing on lethal effects toward individual species and populations prevail. Holistic and comprehensive studies exploring rather common sublethal insecticide exposures are rare, particularly considering their potential role in structuring populations and communities in diverse environmental settings and potentially interfering in a range of ecological interactions. Studies on insecticide resistance, for example, do not go beyond population-based studies, disregarding temporal and spatial effects in the associated community, and rarely considering the whole of sublethal exposure. Some of these knowledge gaps are here recognized and explored

Sublethal exposure, insecticide resistance, and community stress

Insecticides are an invaluable pest management tool and anthropogenic stressors of widespread environmental occurrence that are subject to biased perceptions based on the targeted application, market value of use, and regulatory requirements. As a result, short-term and simplistic efforts focusing on lethal effects toward individual species and populations prevail. Holistic and comprehensive studies exploring rather common sublethal insecticide exposures are rare, particularly considering their potential role in structuring populations and communities in diverse environmental settings and potentially interfering in a range of ecological interactions. Studies on insecticide resistance, for example, do not go beyond population-based studies, disregarding temporal and spatial effects in the associated community, and rarely considering the whole of sublethal exposure. Some of these knowledge gaps are here recognized and explored