1,478 research outputs found
Recommended from our members
Seshat: The Global History Databank
The vast amount of knowledge about past human societies has not been systematically organized and, therefore, remains inaccessible for empirically testing theories about cultural evolution and historical dynamics. For example, what evolutionary mechanisms were involved in the transition from the small-scale, uncentralized societies, in which humans lived 10,000 years ago, to the large-scale societies with an extensive division of labor, great differentials in wealth and power, and elaborate governance structures of today? Why do modern states sometimes fail to meet the basic needs of their populations? Why do economies decline, or fail to grow? In this article, we describe the structure and uses of a massive databank of historical and archaeological information, Seshat: The Global History Databank. The data that we are currently entering in Seshat will allow us and others to test theories explaining how modern societies evolved from ancestral ones, and why modern societies vary so much in their capacity to satisfy their membersâ basic human needsPeer reviewedFinal Published versio
The Roots of Diversity: Below Ground Species Richness and Rooting Distributions in a Tropical Forest Revealed by DNA Barcodes and Inverse Modeling
F. Andrew Jones is with the Smithsonian Tropical Research Institute, David L. Erickson is with the Smithsonian Institution, Moises A. Bernal is with the Smithsonian Tropical Research Institute and UT Austin, Eldredge Bermingham is with the Smithsonian Tropical Research Institute, W. John Kress is with the Smithsonian Institution, Edward Allen Herre is with the Smithsonian Tropical Research Institute, Helene C. Muller-Landau is with the Smithsonian Tropical Research Institute, Benjamin L. Turner is with the Smithsonian Tropical Research Institute.Background -- Plants interact with each other, nutrients, and microbial communities in soils through extensive root networks. Understanding these below ground interactions has been difficult in natural systems, particularly those with high plant species diversity where morphological identification of fine roots is difficult. We combine DNA-based root identification with a DNA barcode database and above ground stem locations in a floristically diverse lowland tropical wet forest on Barro Colorado Island, Panama, where all trees and lianas >1 cm diameter have been mapped to investigate richness patterns below ground and model rooting distributions. Methodology/Principal Findings -- DNA barcode loci, particularly the cpDNA locus trnH-psba, can be used to identify fine and small coarse roots to species. We recovered 33 species of roots from 117 fragments sequenced from 12 soil cores. Despite limited sampling, we recovered a high proportion of the known species in the focal hectare, representing approximately 14% of the measured woody plant richness. This high value is emphasized by the fact that we would need to sample on average 13 m2 at the seedling layer and 45 m2 for woody plants >1 cm diameter to obtain the same number of species above ground. Results from inverse models parameterized with the locations and sizes of adults and the species identifications of roots and sampling locations indicates a high potential for distal underground interactions among plants. Conclusions -- DNA barcoding techniques coupled with modeling approaches should be broadly applicable to studying root distributions in any mapped vegetation plot. We discuss the implications of our results and outline how second-generation sequencing technology and environmental sampling can be combined to increase our understanding of how root distributions influence the potential for plant interactions in natural ecosystems.FAJ acknowledges the support of a Tupper postdoctoral fellowship in tropical biology and the National Science Foundation (DEB 0453665). Funding was provided by the Smithsonian Institution Global Earth Observatory, the Smithsonian Tropical Research Institute/Center for Tropical Forest Sciences endowment fund, and the Smithsonian Tropical Research Institute/Frank Levinson fund. We would like to thank Autoridad Nacional del Ambiente and the Smithsonian Tropical Research Institute for processing research permits. We thank S. Hubbell and R. Condit for access to plot data, S. Schnitzer for liana census data (NSF DEB 0613666), and L. Comita and S. Hubbell for access to seedling data (NSF DEB 0075102 and DEB 0823728). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Marine Scienc
Overexpression of Carnitine Palmitoyltransferase-1 in Skeletal Muscle Is Sufficient to Enhance Fatty Acid Oxidation and Improve High-Fat DietâInduced Insulin Resistance
OBJECTIVEâSkeletal muscle insulin resistance is associated with lipid accumulation, but whether insulin resistance is due to reduced or enhanced flux of long-chain fatty acids into the mitochondria is both controversial and unclear. We hypothesized that skeletal muscleâspecific overexpression of the muscle isoform of carnitine palmitoyltransferase 1 (CPT1), the enzyme that controls the entry of long-chain fatty acyl CoA into mitochondria, would enhance rates of fatty acid oxidation and improve insulin action in muscle in high-fat diet insulin-resistant rats
On the reliability of inflaton potential reconstruction
If primordial scalar and tensor perturbation spectra can be inferred from
observations of the cosmic background radiation and large-scale structure, then
one might hope to reconstruct a unique single-field inflaton potential capable
of generating the observed spectra. In this paper we examine conditions under
which such a potential can be reliably reconstructed. For it to be possible at
all, the spectra must be well fit by a Taylor series expansion. A complete
reconstruction requires a statistically-significant tensor mode to be measured
in the microwave background. We find that the observational uncertainties
dominate the theoretical error from use of the slow-roll approximation, and
conclude that the reconstruction procedure will never insidiously lead to an
irrelevant potential.Comment: 16 page LaTeX file with eight postscript figures embedded with epsf;
no special macros neede
Positron Propagation and Fluxes from Neutralino Annihilation in the Halo
Supersymmetric neutralinos are one of the most promising candidates for the
dark matter in the Universe. If they exist, they should make up some fraction
of the Milky Way halo. We investigate the fluxes of positrons expected at the
Earth from neutralino annihilation in the halo. Positron propagation is treated
in a diffusion model including energy loss. The positron source function
includes contributions from both continuum and monochromatic positrons. We find
that, for a "canonical" halo model and propagation parameters, the fluxes are
generally too low to be visible. Given the large uncertainties in both
propagation and halo structure, it is however possible to obtain observable
fluxes. We also investigate the shapes of the positron spectra, including fits
to a feature indicated by the results of the HEAT experiment.Comment: 16 pages, 19 figures, uses revte
On the gravitational production of superheavy dark matter
The dark matter in the universe can be in the form of a superheavy matter
species (WIMPZILLA). Several mechanisms have been proposed for the production
of WIMPZILLA particles during or immediately following the inflationary epoch.
Perhaps the most attractive mechanism is through gravitational particle
production, where particles are produced simply as a result of the expansion of
the universe. In this paper we present a detailed numerical calculation of
WIMPZILLA gravitational production in hybrid-inflation models and
natural-inflation models. Generalizing these findings, we also explore the
dependence of the gravitational production mechanism on various models of
inflation. We show that superheavy dark matter production seems to be robust,
with Omega_X h^2 ~ (M_X / (10^11 GeV))^2 (T_RH / (10^9 GeV)), so long as M_X <
H_I, where M_X is the WIMPZILLA mass, T_RH is the reheat temperature, and H_I
is the expansion rate of the universe during inflation.Comment: 26 pages, 7 figures; LaTeX; submitted to Physical Review D; minor
typographical error correcte
The cosmic ray positron excess and neutralino dark matter
Using a new instrument, the HEAT collaboration has confirmed the excess of
cosmic ray positrons that they first detected in 1994. We explore the
possibility that this excess is due to the annihilation of neutralino dark
matter in the galactic halo. We confirm that neutralino annihilation can
produce enough positrons to make up the measured excess only if there is an
additional enhancement to the signal. We quantify the `boost factor' that is
required in the signal for various models in the Minimal Supersymmetric
Standard Model parameter space, and study the dependence on various parameters.
We find models with a boost factor greater than 30. Such an enhancement in the
signal could arise if we live in a clumpy halo. We discuss what part of
supersymmetric parameter space is favored (in that it gives the largest
positron signal), and the consequences for other direct and indirect searches
of supersymmetric dark matter.Comment: 11 pages, 6 figures, matches published version (PRD
The Randomised Evaluation of early topical Lidocaine patches In Elderly patients admitted to hospital with rib Fractures (RELIEF): feasibility trial protocol
Background: Topical lidocaine patches, applied over rib fractures, have been suggested as a non-invasive method of local anaesthetic delivery to improve respiratory function, reduce opioid consumption and consequently reduce pulmonary complications. Older patients may gain most benefit from improved analgesic regimens yet lidocaine patches are untested as an early intervention in the Emergency Department (ED). The aim of this trial is to investigate uncertainties around trial design and conduct, to establish whether a definitive randomised trial of topical lidocaine patches in older patients with rib fractures is feasible. Methods: RELIEF is an open label, multicentre, parallel group, individually randomised, feasibility randomised controlled trial with economic scoping and nested qualitative study. Patients aged ℠65 years presenting to the ED with traumatic rib fracture(s) requiring admission will be randomised 1:1 to lidocaine patches (intervention), in addition to standard clinical management, or standard clinical management alone. Lidocaine patches will be applied immediately after diagnosis in ED and continued daily for 72 hours or until discharge. Feasibility outcomes will focus on recruitment, adherence and follow-up data with a total sample size of 100. Clinical outcomes, such as 30-day pulmonary complications, and resource use will be collected to understand feasibility of data collection. Qualitative interviews will explore details of the trial design, trial acceptability and recruitment processes. An evaluation of the feasibility of measuring health economics outcomes data will be completed. Discussion: Interventions to improve outcomes in elderly patients with rib fractures are urgently required. This feasibility trial will test a novel early intervention which has the potential of fulfilling this unmet need. The Randomised Evaluation of early topical Lidocaine patches In Elderly patients admitted to hospital with rib Fractures (RELIEF) feasibility trial will determine whether a definitive trial is feasible. ISRCTN Registration: ISRCTN14813929 (22/04/2021)
The medical student
The Medical Student was published from 1888-1921 by the students of Boston University School of Medicine
Relating Spectral Indices to Tensor and Scalar Amplitudes in Inflation
Within an expansion in slow-roll inflation parameters, we derive the complete
second-order expressions relating the ratio of tensor to scalar density
perturbations and the spectral index of the scalar spectrum. We find that
``corrections'' to previously derived formulae can dominate if the tensor to
scalar ratio is small. For instance, if or if
m_{Pl}^2/(4\pi) ~|V'''/V'|\ga 1, where is the inflaton potential
and is the Planck mass, then the previously used simple relations
between the indices and the tensor to scalar ratio fails. This failure occurs
in particular for natural inflation, Coleman--Weinberg inflation, and
``chaotic'' inflation.Comment: 18 pages, LaTeX, no figures, FNAL--PUB--94/046-A; CfPA 94-th-14
(small revisions only, esp. examples for hybrid inflation
- âŠ