134 research outputs found
Unidentified EGRET Sources and the Extragalactic Gamma-Ray Background
The large majority of EGRET point sources remain to this day without an
identified low-energy counterpart. Whatever the nature of the EGRET
unidentified sources, faint unresolved objects of the same class must have a
contribution to the diffuse gamma-ray background: if most unidentified objects
are extragalactic, faint unresolved sources of the same class contribute to the
background, as a distinct extragalactic population; on the other hand, if most
unidentified sources are Galactic, their counterparts in external galaxies will
contribute to the unresolved emission from these systems. Understanding this
component of the gamma-ray background, along with other guaranteed
contributions from known sources, is essential in any attempt to use gamma-ray
observations to constrain exotic high-energy physics. Here, we follow an
empirical approach to estimate whether a potential contribution of unidentified
sources to the extragalactic gamma-ray background is likely to be important,
and we find that it is. Additionally, we comment on how the anticipated GLAST
measurement of the diffuse gamma-ray background will change, depending on the
nature of the majority of these sources.Comment: 6 pages, 3 figures, to appear in proceedings of "The Multi-Messenger
Approach to High Energy Gamma-Ray Sources", Barcelona, 4-7 July 2006;
comments welcom
Book Reviews
Reviews of the following books: The Massachusetts Historical Society: A Bicentennial History, 1791-1991 by Louis Leonard Tucker; Interpreting Early American History Essays by Jack P. Greene; Molly Spotted Elk: A Penobscot in Paris by Bunny McBride; The Artist\u27s Mount Desert: American Painters on the Maine Coast by John Wilmerding; Politics of Conscience: A Biography of Margaret Chase Smith by Patricia Ward Wallace; Maine, A Peopled Landscape: Salt Documentary Photography, 1978 to 1995 edited by Hugh French, with essays by C. Stewart Doty, James C. Curtis and R. Todd Hoffman; Always Rachel: The Letters of Rachel Carson and Dorothy Freeman, 1952-1964 by Martha Free.man; Sarah Orne Jewett: Her World and Her Work by Paula Blanchar
Historical trends of sperm whale (Physeter macrocephalus) distribution in the Phoenix Archipelago
The Phoenix Archipelago in the Central Pacific is situated in what was once one of the most productive areas for capturing sperm whales (Physeter macrocephalus). These whales were the focal targets of American offshore whalers in the mid-19th century along the equator, an area known as the âon-the-lineâ whaling grounds. Now, as large-scale Marine Protected Areas (MPAs) have provided protection for marine mammals and their food sources, it is important to have a solid understanding of historical baselines so recovery distributions can be compared with pre-whaling distributions. The Phoenix Islands archipelago contains two large MPAs: the Phoenix Islands Protected Area (PIPA), established by Kiribati in 2008, and the Howland/Baker unit of the Pacific Remote Islands Marine National Monument (PRIMNM), established by the United States in 2009. Using historic whaling records from American whaling vessels operated through the wider Phoenix Archipelago region, we reconstructed information about the presence and distribution of P. microcephalus throughout the 1800s within and around PIPA and the Howland/Baker units of the PRIMNM. Historical data analyzed using ArcGIS showed that sperm whales were present year-round within the study area, which is consistent with 20th century records from the Ocean Biogeographic Information System (OBIS). A Getis Ord Giâ hotspot analysis also revealed sighting hotspots within PIPA and near Howland and Baker, suggesting that these two areas may be of long-term ecological importance to sperm whales in the central Pacific. The New England whaling fleet ceased whaling effort in the central Pacific in the late 1800s, and publicly available records since that time are scarce. There has been no modern systematic whale survey ever conducted within the Phoenix Archipelago, though anecdotal accounts and sightings have been compiled over the years. These intermittent accounts suggest that though whale populations have not recovered to pre-whaling baselines, large-scale MPAs may play a role in helping to foster a resurgence of marine mammal populations. As the network of large-scale MPAs continue to grow as part of the commitment to ocean conservation set forth by UNESCO, IUCN, and the UN Decade for Ocean Science, historical baselines will be critical as a âyardstickâ to measure population resurgence success for each MPA, and for populations overall.Published versio
Evolutionary and ecological forces influencing population diversification in Bornean montane passerines
The mountains of Borneo are well known for their high endemicity and historical role in preserving Southeast Asian rainforest biodiversity, but the diversification of populations inhabiting these mountains is poorly studied. Here we examine the genetic structure of 12 Bornean montane passerines by comparing complete mtDNA ND2 gene sequences of populations spanning the island. Maximum likelihood and
Bayesian phylogenetic trees and haplotype networks are examined for common patterns that might signal important historical events or boundaries to dispersal. Morphological and ecological characteristics of each species are also examined using phylogenetic generalized least-squares (PGLS) for correlation with population structure. Populations in only four of the 12 species are subdivided into distinct clades or haplotype groups. Although this subdivision occurred at about the same time in each species (ca. 0.6â
0.7 Ma), the spatial positioning of the genetic break differs among the species. In two species, northeastern
populations are genetically divergent from populations elsewhere on the island. In the other two species,
populations in the main Bornean mountain chain, including the northeast, are distinct from those on two isolated peaks in northwestern Borneo. We suggest different historical forces played a role in shaping these two distributions, despite commonality in timing. PGLS analysis showed that only a single characteristicâhand-wing indexâis correlated with population structure. Birds with longer wings, and
hence potentially more dispersal power, have less population structure. To understand historical forces influencing montane population structure on Borneo, future studies must compare populations across the entirety of Sundaland
Olber's Paradox for Superluminal Neutrinos: Constraining Extreme Neutrino Speeds at TeV-ZeV Energies with the Diffuse Neutrino Background
The only invariant speed in special relativity is c; therefore, if some
neutrinos travel at even tiny speeds above c, normal special relativity is
incomplete and any superluminal speed may be possible. I derive a limit on
superluminal neutrino speeds v >> c at high energies by noting that such speeds
would increase the size of the neutrino horizon. The increased volume of the
Universe visible leads to a brighter astrophysical neutrino background. The
nondetection of "guaranteed" neutrino backgrounds from star-forming galaxies
and ultrahigh energy cosmic rays (UHECRs) constrains v/c at TeV--ZeV energies.
I find that v/c <= 820 at 60 TeV from the nondetection of neutrinos from
star-forming galaxies. The nondetection of neutrinos from UHECRs constrains v/c
to be less than 2500 at 0.1 EeV in a pessimistic model and less than 4.6 at 4
EeV in an optimistic model. The UHECR neutrino background nondetection is
strongly inconsistent with a naive quadratic extrapolation of the OPERA results
to EeV energies. The limits apply subject to some caveats, particularly that
the expected pionic neutrino backgrounds exist and that neutrinos travel faster
than c when they pass the detector. They could be improved substantially as the
expected neutrino backgrounds are better understood and with new experimental
neutrino background limits. I also point out that extremely subluminal speeds
would result in a much smaller neutrino background intensity than expected.Comment: 13 pages, 2 figures, fixed titl
Corrigendum: the unknown and the unexplored: insights into the Pacific deep-sea following NOAA CAPSTONE expeditions
Published versio
The unknown and the unexplored: insights Into the Pacific deep-sea following NOAA CAPSTONE expeditions
Over a 3-year period, the National Oceanic and Atmospheric Administration (NOAA) organized and implemented a Pacific-wide field campaign entitled CAPSTONE: Campaign to Address Pacific monument Science, Technology, and Ocean NEeds. Under the auspices of CAPSTONE, NOAA mapped 597,230 km2 of the Pacific seafloor (with âŒ61% of mapped area located within US waters), including 323 seamounts, conducted 187 ROV dives totaling 891.5 h of ROV benthic imaging time, and documented >347,000 individual organisms. This comprehensive effort yielded dramatic insight into differences in biodiversity across depths, regions, and features, at multiple taxonomic scales. For all deep sea taxonomic groups large enough to be visualized with the ROV, we found that fewer than 20% of the species were able to be identified. The most abundant and highest diversity taxa across the dataset were from three phyla (Cnidaria, Porifera, and Echinodermata). We further examined these phyla for taxonomic assemblage patterns by depth, geographic region, and geologic feature. Within each taxa, there were multiple genera with specific distribution and abundance by depth, region, and feature. Additionally, we observed multiple genera with broad abundance and distribution, which may focus future ecological research efforts. Novel taxa, records, and behaviors were observed, suggestive of many new types of species interactions, drivers of community composition, and overall diversity patterns. To date, only 13.8% of the Pacific has been mapped using modern methods. Despite the incredible amount of new known and unknown information about the Pacific deep-sea, CAPSTONE is far from the culminating experience the name suggests. Rather, it marks the beginning of a new era for exploration that will offer extensive opportunities via mapping, technology, analysis, and insights.Published versio
Ensaios sobre a metodologia do estudo da influĂȘncia de trĂȘs herbicidas em Spirodela punctata (G.F.W. Meyer) Thompson (Lemnaceae)
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