8,676 research outputs found
Field Measurements of Photosynthesis and Leaf Growth Rates of Three Alpine Plant Species
Leaf photosynthetic measurements using a portable 14Co2 field system were carried out and correlative leaf relative growth rates, RGR, were determined at different leaf positions of three alpine plant species throughout the growing season. Initially there was a period of high leaf RGR associated with a period of increasing photosynthetic activity. Following this stage was a long period of no net change in length of the living leaf. During this period, photosynthetic activity generally increased to a maximum level and then decreased steadily. The final ontogenetic stage was a period of negative leaf RGR denoting leaf senescence which was associated with a marked decline in leaf Co2 uptake. Ontogenetic timing of these alpine species is geared with the surge and decline of individual leaf photosynthetic activity so that one to several leaves operating at near maximal photosynthetic capacity are always maintained during the growing season for each plant. These findings are discussed in relation to their adaptive significance for these species
Quantitative test of general theories of the intrinsic laser linewidth
We perform a first-principles calculation of the quantum-limited laser
linewidth, testing the predictions of recently developed theories of the laser
linewidth based on fluctuations about the known steady-state laser solutions
against traditional forms of the Schawlow-Townes linewidth. The numerical study
is based on finite-difference time-domain simulations of the semiclassical
Maxwell-Bloch lasing equations, augmented with Langevin force terms, and thus
includes the effects of dispersion, losses due to the open boundary of the
laser cavity, and non-linear coupling between the amplitude and phase
fluctuations ( factor). We find quantitative agreement between the
numerical results and the predictions of the noisy steady-state ab initio laser
theory (N-SALT), both in the variation of the linewidth with output power, as
well as the emergence of side-peaks due to relaxation oscillations.Comment: 24 pages, 10 figure
High On/Off Ratio Graphene Nanoconstriction Field Effect Transistor
We report a method to pattern monolayer graphene nanoconstriction field
effect transistors (NCFETs) with critical dimensions below 10 nm. NCFET
fabrication is enabled by the use of feedback controlled electromigration (FCE)
to form a constriction in a gold etch mask that is first patterned using
conventional lithographic techniques. The use of FCE allows the etch mask to be
patterned on size scales below the limit of conventional nanolithography. We
observe the opening of a confinement-induced energy gap as the NCFET width is
reduced, as evidenced by a sharp increase in the NCFET on/off ratio. The on/off
ratios we obtain with this procedure can be larger than 1000 at room
temperature for the narrowest devices; this is the first report of such large
room temperature on/off ratios for patterned graphene FETs.Comment: 18 pages, 6 figures, to appear in Smal
Comparing Fixed-amount and Progressive-amount DRO Schedules for Tic Suppression in Youth with Chronic Tic Disorders
Chronic tic disorders (CTDs) involve motor and/or vocal tics that often cause substantial distress and impairment. Differential reinforcement of other behavior (DRO) schedules of reinforcement produce robust, but incomplete, reductions in tic frequency in youth with CTDs; however, a more robust reduction may be needed to affect durable clinical change. Standard, fixedâamount DRO schedules have not commonly yielded such reductions, so we evaluated a novel, progressiveâamount DRO schedule, based on its ability to facilitate sustained abstinence from functionally similar behaviors. Five youth with CTDs were exposed to periods of baseline, fixedâamount DRO (DROâF), and progressiveâamount DRO (DROâP). Both DRO schedules produced decreases in tic rate and increases in intertic interval duration, but no systematic differences were seen between the two schedules on any dimension of tic occurrence. The DROâF schedule was generally preferred to the DROâP schedule. Possible procedural improvements and other future directions are discussed
Building capacity for dissemination and implementation research: One universityâs experience
Abstract Background While dissemination and implementation (D&I) science has grown rapidly, there is an ongoing need to understand how to build and sustain capacity in individuals and institutions conducting research. There are three inter-related domains for capacity building: people, settings, and activities. Since 2008, Washington University in St. Louis has dedicated significant attention and resources toward building D&I research capacity. This paper describes our process, challenges, and lessons with the goal of informing others who may have similar aims at their own institution. Activities An informal collaborative, the Washington University Network for Dissemination and Implementation Research (WUNDIR), began with a small group and now has 49 regular members. Attendees represent a wide variety of settings and content areas and meet every 6Â weeks for half-day sessions. A logic model organizes WUNDIR inputs, activities, and outcomes. A mixed-methods evaluation showed that the network has led to new professional connections and enhanced skills (e.g., grant and publication development). As one of four, ongoing, formal programs, the Dissemination and Implementation Research Core (DIRC) was our first major component of D&I infrastructure. DIRCâs mission is to accelerate the public health impact of clinical and health services research by increasing the engagement of investigators in later stages of translational research. The aims of DIRC are to advance D&I science and to develop and equip researchers with tools for D&I research. As a second formal component, the Washington University Institute for Public Health has provided significant support for D&I research through pilot projects and a small grants program. In a third set of formal programs, two R25 training grants (one in mental health and one in cancer) support post-doctoral scholars for intensive training and mentoring in D&I science. Finally, our team coordinates closely with D&I functions within research centers across the university. We share a series of challenges and potential solutions. Conclusion Our experience in developing D&I research at Washington University in St. Louis shows how significant capacity can be built in a relatively short period of time. Many of our ideas and ingredients for success can be replicated, tailored, and improved upon by others
Used-habitat calibration plots: a new procedure for validating species distribution, resource selection, and step-selection models
âSpecies distribution modelingâ was recently ranked as one of the top five âresearch frontsâ in ecology and the environmental sciences by ISI's Essential Science Indicators (Renner and Warton 2013), reflecting the importance of predicting how species distributions will respond to anthropogenic change. Unfortunately, species distribution models (SDMs) often perform poorly when applied to novel environments. Compounding on this problem is the shortage of methods for evaluating SDMs (hence, we may be getting our predictions wrong and not even know it). Traditional methods for validating SDMs quantify a model's ability to classify locations as used or unused. Instead, we propose to focus on how well SDMs can predict the characteristics of used locations. This subtle shift in viewpoint leads to a more natural and informative evaluation and validation of models across the entire spectrum of SDMs. Through a series of examples, we show how simple graphical methods can help with three fundamental challenges of habitat modeling: identifying missing covariates, non-linearity, and multicollinearity. Identifying habitat characteristics that are not well-predicted by the model can provide insights into variables affecting the distribution of species, suggest appropriate model modifications, and ultimately improve the reliability and generality of conservation and management recommendations
Comparison of the Symbiotic Fauna of the Family Plethodontidae in the Ouachita Mountains of Western Arkansas
During the spring of 1985, 101 salamanders representing six host species (29 Plethodon ouachitae, 25 P. caddoensis, 6 P. fourchensis, 23 P. serratus, 13 Desmognathus brimleyorum, and 5 P. glutinosus glutinosus) were collected from six localities in three counties in Arkansas (Polk, Scott, and Montgomery) and examined for symbionts. With the exception of Hannemania dunni, all symbionts recovered from the first five species listed constitute new host records, and the endoparasitic fauna in all species establish new locality records. Examinations revealed one or more species of parasites in 82% of the hosts. Eight species of symbionts (3 nematode, 1 trematode, 1 cestode, 1 protozoan, 1 arthropod, and 1 cystacanth acanthocephalon) were recovered. Conclusions are based on the three host species examined in the largest numbers. Thelandros magnavulvularis and H. dunni were the most commonly occurring parasites, found in five and four host species respectively. Cepedietta michiganensis was restricted to P. ouachitae and Brachycoelium storeriae to P. caddoensis. Hannemania dunni was absent in P. serratus
Heterotic AdS_3/CFT_2 duality with (0,4) spacetime supersymmetry
We discuss the AdS_3/CFT_2 duality of a heterotic three-charge model with
(0,4) target space supersymmetry. The worldsheet theory for heterotic strings
on the AdS_3 x S^3/Z_N x T^4 near-horizon geometry was constructed by Kutasov,
Larsen and Leigh in [hep-th/9812027]. We propose that the dual conformal field
theory is given by a two-dimensional (0,4) sigma model arising on the Higgs
branch of an orbifolded ADHM model. As a non-trivial consistency check of the
correspondence, we find that the left- and right-moving central charges of the
infrared conformal field theory agree with those predicted by the worldsheet
model. Moreover, using the entropy function formalism, we show that to
next-to-leading order the central charge can also be obtained from an
alpha'-corrected supergravity theory.Comment: 34 pages, 2 figures, references added, to be published in Nucl. Phys.
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