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Subsurface tropical Pacific nitrogen isotopic composition of nitrate: Biogeochemical signals and their transport
We report measurements of the nitrogen isotopic composition of nitrate (the δ15N of NO3â) across the equatorial Pacific, for zonal transects from 165°E to 95°W and meridional transects across 95° and 110°W. The δ15N of NO3â is similar in the equatorial thermocline (â100 m) and intermediate depth waters (â150 to 600 m), averaging (7.1 Âą 0.3)â° and (7.1 Âą 0.1)â°, respectively. These values are more than 2â° higher than subthermocline waters of the Southern and Atlantic Oceans and are â1â° higher than putative source waters in the high latitude South Pacific (Subantarctic Mode Water, SAMW). The combined constraints of nitrate concentration and δ15N of NO3âin the equatorial Pacific require (1) lateral exchange between the highâlatitude source waters and the zones of denitrification in the eastern tropical Pacific and (2) the accumulation of remineralized nutrients at depth. The zonal uniformity of the subsurface equatorial Pacificδ15N of NO3â indicates rapid transport within the equatorial zone, which works to homogenize the δ15N of NO3â across the Pacific basin. Against this backdrop of high δ15N of NO3âin the tropical Pacific, we find a discrete offâequatorial core of lowerδ15N of NO3â (5.5 Âą 0.3)â° concentrated at 5°S and 150 to 200 m along the 110° and 95°W transects and in apparent association with the Southern Subsurface Counter Current (SSCC). We propose that the remineralized products of nitrogen fixation, at the source of the SSCC in the western south Pacific, are the origin of the low δ15N of NO3â in these waters
Foraminiferal isotope evidence of reduced nitrogen fixation in the ice age Atlantic Ocean
Fixed nitrogen (N) is a limiting algal nutrient in the low
latitude ocean, and the oceanic N inventory has been
suggested to increase during ice ages so as to lower
atmospheric CO_2. In organic matter within planktonic
foraminifera shells in Caribbean Sea sediments, the
^(15)N/^(14)N from the last ice age is higher than that from the
current interglacial, indicating higher nitrate ^(15)N/^(14)N in
the Caribbean thermocline. This and species-specific
differences are best explained by less N fixation in the
Atlantic during the last ice age. The fixation decrease was
most likely a response to a known ice age reduction in
ocean N loss, and it would have worked to balance the
ocean N budget and to curb ice age-to-interglacial change
in the N inventory
An Efficient, Highly Flexible Multi-Channel Digital Downconverter Architecture
In this innovation, a digital downconverter has been created that produces a large (16 or greater) number of output channels of smaller bandwidths. Additionally, this design has the flexibility to tune each channel independently to anywhere in the input bandwidth to cover a wide range of output bandwidths (from 32 MHz down to 1 kHz). Both the flexibility in channel frequency selection and the more than four orders of magnitude range in output bandwidths (decimation rates from 32 to 640,000) presented significant challenges to be solved. The solution involved breaking the digital downconversion process into a two-stage process. The first stage is a 2 oversampled filter bank that divides the whole input bandwidth as a real input signal into seven overlapping, contiguous channels represented with complex samples. Using the symmetry of the sine and cosine functions in a similar way to that of an FFT (fast Fourier transform), this downconversion is very efficient and gives seven channels fixed in frequency. An arbitrary number of smaller bandwidth channels can be formed from second-stage downconverters placed after the first stage of downconversion. Because of the overlapping of the first stage, there is no gap in coverage of the entire input bandwidth. The input to any of the second-stage downconverting channels has a multiplexer that chooses one of the seven wideband channels from the first stage. These second-stage downconverters take up fewer resources because they operate at lower bandwidths than doing the entire downconversion process from the input bandwidth for each independent channel. These second-stage downconverters are each independent with fine frequency control tuning, providing extreme flexibility in positioning the center frequency of a downconverted channel. Finally, these second-stage downconverters have flexible decimation factors over four orders of magnitude The algorithm was developed to run in an FPGA (field programmable gate array) at input data sampling rates of up to 1,280 MHz. The current implementation takes a 1,280-MHz real input, and first breaks it up into seven 160-MHz complex channels, each spaced 80 MHz apart. The eighth channel at baseband was not required for this implementation, and led to more optimization. Afterwards, 16 second stage narrow band channels with independently tunable center frequencies and bandwidth settings are implemented A future implementation in a larger Xilinx FPGA will hold up to 32 independent second-stage channels
Two Modes of Change in Southern Ocean Productivity Over the Past Million Years
Export of organic carbon from surface waters of the Antarctic Zone of the Southern Ocean decreased during the last ice age, coinciding with declining atmospheric carbon dioxide (CO2) concentrations, signaling reduced exchange of CO2 between the ocean interior and the atmosphere. In contrast, in the Subantarctic Zone, export production increased into ice ages coinciding with rising dust fluxes, thus suggesting iron fertilization of subantarctic phytoplankton. Here, a new high-resolution productivity record from the Antarctic Zone is compiled with parallel subantarctic data over the past million years. Together, they fit the view that the combination of these two modes of Southern Ocean change determines the temporal structure of the glacial-interglacial atmospheric CO2 record, including during the interval of âlukewarmâ interglacials between 450 and 800 thousand years ago
Nitrogen isotope evidence for expanded ocean suboxia in the early Cenozoic
The million-year variability of the marine nitrogen cycle is poorly understood. Before 57 million years (Ma) ago, the ^(15)N/^(14)N ratio (δ^(15)N) of foraminifera shell-bound organic matter from three sediment cores was high, indicating expanded water column suboxia and denitrification. Between 57 and 50 Ma ago, δ^(15)N declined by 13 to 16 per mil in the North Pacific and by 3 to 8 per mil in the Atlantic. The decline preceded global cooling and appears to have coincided with the early stages of the Asia-India collision. Warm, salty intermediate-depth water forming along the Tethys Sea margins may have caused the expanded suboxia, ending with the collision. From 50 to 35 Ma ago, δ^(15)N was lower than modern values, suggesting widespread sedimentary denitrification on broad continental shelves. Î^(15)N rose at 35 Ma ago, as ice sheets grew, sea level fell, and continental shelves narrowed
Hierarchical Organization in Complex Networks
Many real networks in nature and society share two generic properties: they
are scale-free and they display a high degree of clustering. We show that these
two features are the consequence of a hierarchical organization, implying that
small groups of nodes organize in a hierarchical manner into increasingly large
groups, while maintaining a scale-free topology. In hierarchical networks the
degree of clustering characterizing the different groups follows a strict
scaling law, which can be used to identify the presence of a hierarchical
organization in real networks. We find that several real networks, such as the
World Wide Web, actor network, the Internet at the domain level and the
semantic web obey this scaling law, indicating that hierarchy is a fundamental
characteristic of many complex systems
Added sugar intake and metabolic syndrome in US adolescents: cross-sectional analysis of the National Health and Nutrition Examination Survey 2005â2012
ObjectiveTo examine the association between added sugar intake and metabolic syndrome among adolescents.DesignDietary, serum biomarker, anthropometric and physical activity data from the US National Health and Nutrition Examination Survey cycles between 2005 and 2012 were analysed using multivariate logistic regression models. Added sugar intake in grams per day was estimated from two 24 h standardized dietary recalls and then separated into quintiles from lowest to highest consumption. Multivariate logistic regression analyses were adjusted for physical activity, age, BMI Z-score and energy intake, and their interactions with race were included.SettingNationally representative sample, USA.SubjectsUS adolescents aged 12-19 years (n 1623).ResultsAdded sugar was significantly associated with metabolic syndrome. The adjusted prevalence odds ratios for having metabolic syndrome comparing adolescents in the third, fourth and fifth quintiles v. those in the lowest quintile of added sugar were 5¡3 (95 % CI 1¡4, 20¡6), 9¡9 (95 % CI 1¡9, 50¡9) and 8¡7 (95 % CI 1¡4, 54¡9), respectively.ConclusionsOur findings suggest that higher added sugar intake, independent of total energy intake, physical activity or BMI Z-score, is associated with increased prevalence of metabolic syndrome in US adolescents. Further studies are needed to determine if reducing intake of added sugar may help US adolescents prevent or reverse metabolic syndrome
Natural images from the birthplace of the human eye
Here we introduce a database of calibrated natural images publicly available
through an easy-to-use web interface. Using a Nikon D70 digital SLR camera, we
acquired about 5000 six-megapixel images of Okavango Delta of Botswana, a
tropical savanna habitat similar to where the human eye is thought to have
evolved. Some sequences of images were captured unsystematically while
following a baboon troop, while others were designed to vary a single parameter
such as aperture, object distance, time of day or position on the horizon.
Images are available in the raw RGB format and in grayscale. Images are also
available in units relevant to the physiology of human cone photoreceptors,
where pixel values represent the expected number of photoisomerizations per
second for cones sensitive to long (L), medium (M) and short (S) wavelengths.
This database is distributed under a Creative Commons Attribution-Noncommercial
Unported license to facilitate research in computer vision, psychophysics of
perception, and visual neuroscience.Comment: Submitted to PLoS ON
Helping and Cooperation in Children with Autism
Helping and cooperation are central to human social life. Here, we report two studies investigating these social behaviors in children with autism and children with developmental delay. In the first study, both groups of children helped the experimenter attain her goals. In the second study, both groups of children cooperated with an adult, but fewer children with autism performed the tasks successfully. When the adult stopped interacting at a certain moment, children with autism produced fewer attempts to re-engage her, possibly indicating that they had not formed a shared goal/shared intentions with her. These results are discussed in terms of the prerequisite cognitive and motivational skills and propensities underlying social behavior
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