Publications by authors named "Doak P"

Recent empirical studies have quantified correlation between survival and recovery by estimating these parameters as correlated random effects with hierarchical Bayesian multivariate models fit to tag-recovery data. In these applications, increasingly negative correlation between survival and recovery has been interpreted as evidence for increasingly additive harvest mortality. The power of these hierarchal models to detect nonzero correlations has rarely been evaluated, and these few studies have not focused on tag-recovery data, which is a common data type.

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Longitudinal studies of marked animals provide an opportunity to assess the relative contributions of survival and reproductive output to population dynamics and change. Cassin's auklets are a long-lived seabird that maximizes annual reproductive effort in resource-rich years through a behaviour called double brooding, the initiation of a second breeding attempt following the success of the first during the same season. Our objective was to explore whether double brooding influenced population change by contributing a greater number of future recruits.

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We review recent advances in the capabilities of the open source ab initio Quantum Monte Carlo (QMC) package QMCPACK and the workflow tool Nexus used for greater efficiency and reproducibility. The auxiliary field QMC (AFQMC) implementation has been greatly expanded to include k-point symmetries, tensor-hypercontraction, and accelerated graphical processing unit (GPU) support. These scaling and memory reductions greatly increase the number of orbitals that can practically be included in AFQMC calculations, increasing the accuracy.

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The factors leading to changes in the organization of microbial assemblages at fine spatial scales are not well characterized or understood. However, they are expected to guide the succession of community development and function toward specific outcomes that could impact human health and the environment. In this study, we put forward a combined experimental and agent-based modeling framework and use it to interpret unique spatial organization patterns of H1-Type VI secretion system (T6SS) mutants of .

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Bulk molecular ionic solids exhibit fascinating electronic properties, including electron correlations, phase transitions, and superconducting ground states. In contrast, few of these phenomena have been observed in low-dimensional molecular structures, including thin films, nanoparticles, and molecular blends, not in the least because most of such structures have been composed of nearly closed-shell molecules. It is therefore desirable to develop low-dimensional ionic molecular structures that can capture potential applications.

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Article Synopsis
  • Large changes in vibrational energies of PCBM are observed when influenced by voltage in experiments using transport and SERS on PCBM-gold junctions.
  • The study finds a mix of linear and quadratic shifts in these energies, analyzed alongside similar experiments with C60-gold junctions.
  • Theoretical models indicate that both the vibrational Stark effect and junction charging explain these energy shifts, with PCBM showing notable linear Stark shifts due to its electric dipole moment.
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Attachment of difluoroborylcobaloxime catalysts to a polymer-brush-modified GaP semiconductor allows improved hydrogen production levels and photoelectrochemical performance under aqueous acidic conditions (pH = 4.5) as compared to the performance of electrodes without catalyst treatment. The catalytic assembly used in this work incorporates a boron difluoride (BF2) capping group on the glyoximate ligand of the catalyst, a synthetic modification previously used to enhance the stability of nonsurface-attached complexes toward acid hydrolysis and to shift the cobalt reduction potentials of the complex to less negative, and thus technologically more relevant, values.

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Vibrational modes of molecules are fundamental properties determined by intramolecular bonding, atomic masses, and molecular geometry, and often serve as important channels for dissipation in nanoscale processes. Although single-molecule junctions have been used to manipulate electronic structure and related functional properties of molecules, electrical control of vibrational mode energies has remained elusive. Here we use simultaneous transport and surface-enhanced Raman spectroscopy measurements to demonstrate large, reversible, voltage-driven shifts of vibrational mode energies of C60 molecules in gold junctions.

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Functional hybrid interfaces between organic molecules and semiconductors are central to many emerging information and solar energy conversion technologies. Here we demonstrate a general, empirical parameter-free approach for computing and understanding frontier orbital energies - or redox levels - of a broad class of covalently bonded organic-semiconductor surfaces. We develop this framework in the context of specific density functional theory (DFT) and many-body perturbation theory calculations, within the GW approximation, of an exemplar interface, thiophene-functionalized silicon (111).

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For many insect herbivores, maternal host selection is a critical determinant of offspring survival; however, maternal fitness is also affected by adult resources such as food availability. Consequently, adult resources may promote oviposition in sub-optimal locations when measured in terms of offspring performance. We tested whether oviposition site preference is primarily shaped by proximity to adult food resources or offspring performance in the aspen leaf miner (Phyllocnistis populiella).

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We investigated the overwintering physiology and behavior of Phyllocnistis populiella Chambers, the aspen leaf miner, which has caused severe and widespread damage to aspen in Alaska over the past 10 yr. Active P. populiella moths caught in spring and summer supercooled to an average temperature of -16°C, whereas dormant moths excavated from hibernacula in the leaf litter during fall and winter supercooled to an average of -32°C.

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Expression of foliar secondary compounds and extrafloral nectaries (EFNs) within the same leaves may be incompatible if secondary compounds repel beneficial insects that might otherwise be attracted to EFNs. This study examined the within-plant distributions of phenolic glycosides and EFNs in trembling aspen, Populus tremuloides, and their relationships to herbivore damage. Populus tremuloides expresses extrafloral nectaries (EFNs) on a subset of its leaves.

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The effects of plant defenses on herbivory can differ among spatial scales. This may be particularly common with indirect defenses, such as extrafloral nectaries (EFNs), that attract predatory arthropods and are dependent on predator distribution, abundance, and behavior. We tested the defensive effects of EFNs in quaking aspen (Populus tremuloides Michx.

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We studied the effect of epidermal leaf mining on the leaf chemistry of quaking aspen, Populus tremuloides, during an outbreak of the aspen leaf miner, Phyllocnistis populiella, in the boreal forest of interior Alaska. Phyllocnistis populiella feeds on the epidermal cells of P. tremuloides leaves.

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Transport fluctuations and variations in a series of metal-molecule-metal junctions were quantified through measurements of their thermopower. Thiol bound aromatic molecules of various lengths and degrees of freedom were chosen to understand the magnitude and origins of the variations. Junction thermopower was determined by measuring the voltage difference across molecules trapped between two gold contacts held at different temperatures.

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Transport in metal-molecule-metal junctions is defined by the alignment and coupling of molecular orbitals with continuum electronic states in the metal contacts. Length-dependent changes in molecular orbital alignment and coupling with contact states were probed via measurements and comparisons of thermopower (S) of a series of phenylenes and alkanes with varying binding groups. S increases linearly with length for phenylenediames and phenylenedithiols while it decreases linearly in alkanedithiols.

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The aspen leaf miner, Phyllocnistis populiella, feeds on the contents of epidermal cells on both top (adaxial) and bottom (abaxial) surfaces of quaking aspen leaves, leaving the photosynthetic tissue of the mesophyll intact. This type of feeding is taxonomically restricted to a small subset of leaf mining insects but can cause widespread plant damage during outbreaks. We studied the effect of epidermal mining on aspen growth and physiology during an outbreak of P.

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Thermopower measurements offer an alternative transport measurement that can characterize the dominant transport orbital and is independent of the number of molecules in the junction. This method is now used to explore the effect of chemical structure on the electronic structure and charge transport. We interrogate junctions, using a modified scanning tunneling microscope break junction technique, where: (i) the 1,4-benzenedithiol (BDT) molecule has been modified by the addition of electron-withdrawing or -donating groups such as fluorine, chlorine, and methyl on the benzene ring; and (ii) the thiol end groups on BDT have been replaced by the cyanide end groups.

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We have found that racemic mixtures of chiral single-walled nanotubes (SWNTs) wrapped with d(GT)20 DNA oligomer exhibit circular dichroism (CD). We attribute the CD signal to induced CD arising from the coupling of transition moments of the SWNTs and the DNA. Although the nanotube mixture appears to contain both enantiomers in equal amounts, DNA-SWNT transition moment interaction is more constructive for one SWNT enantiomer over the other, resulting in an overall CD signal.

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For the majority of insects, a female's choice of oviposition site(s) greatly influences both the success of individual offspring and her own total fitness. Theory predicts that females most strongly limited by egg number will employ greater oviposition site discrimination than those predominately subject to time limitation. The reproductive success of the butterfly Pieris virginiensis at our Connecticut, USA, field site is strongly time constrained on two fronts.

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Despite extensive research on parasitoid-prey interactions and especially the effects of heterogeneity in parasitism on stability, sources of heterogeneity other than prey density have been little investigated. This research examines parasitism rates by three parasitoid species in relationship to prey density and habitat spatial pattern. The herbivore Itame andersoni (Geometridae) inhabits a subdivided habitat created by patches of its host plant, Dryas drummondii, in the Wrangell Mountains of Alaska.

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There have been encouraging reports of the use of recombinant tissue plasminogen activator (tPA) in established veno-occlusive disease (VOD). Haemodialysis has been considered a contraindication to this therapy in view of the potential haemostatic complications. We report a case of a woman who developed moderately severe VOD complicated by anuria following an allogeneic bone marrow transplant for relapsed acute myeloid leukaemia.

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This study investigates the use of polymerase chain reaction (PCR) in comparison with viral culture and serology for monitoring of cytomegalovirus (CMV) infection in 21 consecutive renal allograft recipients treated with a quadruple immunosuppression protocol. In addition, an attempt is made to explore the significance of quantitation of CMV signals obtained from peripheral blood leucocytes. CMV infection developed in 16 patients with seven of these patients having organ involvement.

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Recipients of live related and first cadaveric renal allografts were retrospectively reviewed before and after institution of a standardized regimen incorporating greater immunosuppression, (by the addition of antilymphocyte preparations). The two review groups were comparable with 11 live related and 27 first cadaver grafts in each. Despite a small advantage in terms of graft survival and diminished rejection, this was at the expense of septic morbidity.

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The contributions of pre-selected predictions of outcome for survival and renal function following acute post infectious glomerulonephritis were tested in a group of 41 adults, followed up for a mean of 13 years 5 months (range: 2 weeks to 15 years 2 months), using a proportional hazards model. The best predictor of outcome was the severity of the renal lesion, as judged by histology obtained at renal biopsy. The extent of functional deterioration during the acute phase and the aetiology were also related to outcome, though less significantly.

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