402 research outputs found
Natural ocean carbon cycle sensitivity to parameterizations of the recycling in a climate model
Sensitivities of the oceanic biological pump within the GISS (Goddard Institute for Space Studies ) climate modeling
system are explored here. Results are presented from twin control simulations
of the air–sea CO<sub>2</sub> gas exchange using two different ocean models coupled
to the same atmosphere. The two ocean models (Russell ocean model and Hybrid
Coordinate Ocean Model, HYCOM) use different vertical coordinate systems, and
therefore different representations of column physics. Both variants of the
GISS climate model are coupled to the same ocean biogeochemistry module (the
NASA Ocean Biogeochemistry Model, NOBM), which computes prognostic
distributions for biotic and abiotic fields that influence the air–sea flux
of CO<sub>2</sub> and the deep ocean carbon transport and storage. In particular, the
model differences due to remineralization rate changes are compared to
differences attributed to physical processes modeled differently in the two
ocean models such as ventilation, mixing, eddy stirring and vertical
advection. GISSEH(GISSER) is found to underestimate mixed layer depth
compared to observations by about 55% (10%) in the Southern Ocean
and overestimate it by about 17% (underestimate by 2%) in the
northern high latitudes. Everywhere else in the global ocean, the two models
underestimate the surface mixing by about 12–34%, which prevents deep
nutrients from reaching the surface and promoting primary production there.
Consequently, carbon export is reduced because of reduced production at the
surface. Furthermore, carbon export is particularly sensitive to
remineralization rate changes in the frontal regions of the subtropical gyres
and at the Equator and this sensitivity in the model is much higher than the
sensitivity to physical processes such as vertical mixing, vertical advection
and mesoscale eddy transport. At depth, GISSER, which has a significant warm
bias, remineralizes nutrients and carbon faster thereby producing more nutrients and
carbon at depth, which eventually resurfaces with the global thermohaline
circulation especially in the Southern Ocean. Because of the reduced primary
production and carbon export in GISSEH compared to GISSER, the biological
pump efficiency, i.e., the ratio of primary production and carbon export at
75 m, is half in the GISSEH of that in GISSER, The Southern Ocean emerges as
a key region where the CO<sub>2</sub> flux is as sensitive to biological
parameterizations as it is to physical parameterizations. The fidelity of
ocean mixing in the Southern Ocean compared to observations is shown to be a
good indicator of the magnitude of the biological pump efficiency regardless
of physical model choice
The statistical neuroanatomy of frontal networks in the macaque
We were interested in gaining insight into the functional properties of frontal networks based upon their anatomical inputs. We took a neuroinformatics approach, carrying out maximum likelihood hierarchical cluster analysis on 25 frontal cortical areas based upon their anatomical connections, with 68 input areas representing exterosensory, chemosensory, motor, limbic, and other frontal inputs. The analysis revealed a set of statistically robust clusters. We used these clusters to divide the frontal areas into 5 groups, including ventral-lateral, ventral-medial, dorsal-medial, dorsal-lateral, and caudal-orbital groups. Each of these groups was defined by a unique set of inputs. This organization provides insight into the differential roles of each group of areas and suggests a gradient by which orbital and ventral-medial areas may be responsible for decision-making processes based on emotion and primary reinforcers, and lateral frontal areas are more involved in integrating affective and rational information into a common framework
Functional sex differences in human primary auditory cortex
Background We used PET to study cortical activation during auditory stimulation and found sex differences in the human primary auditory cortex (PAC). Regional cerebral blood flow (rCBF) was measured in 10 male and 10 female volunteers while listening to sounds (music or white noise) and during a baseline (no auditory stimulation). Results and discussion We found a sex difference in activation of the left and right PAC when comparing music to noise. The PAC was more activated by music than by noise in both men and women. But this difference between the two stimuli was significantly higher in men than in women. To investigate whether this difference could be attributed to either music or noise, we compared both stimuli with the baseline and revealed that noise gave a significantly higher activation in the female PAC than in the male PAC. Moreover, the male group showed a deactivation in the right prefrontal cortex when comparing noise to the baseline, which was not present in the female group. Interestingly, the auditory and prefrontal regions are anatomically and functionally linked and the prefrontal cortex is known to be engaged in auditory tasks that involve sustained or selective auditory attention. Thus we hypothesize that differences in attention result in a different deactivation of the right prefrontal cortex, which in turn modulates the activation of the PAC and thus explains the sex differences found in the activation of the PAC. Conclusion Our results suggest that sex is an important factor in auditory brain studies
The energy dependence of flow in Ni induced collisions from 400 to 1970A MeV
We study the energy dependence of collective (hydrodynamic-like) nuclear
matter flow in 400-1970 A MeV Ni+Au and 1000-1970 A MeV Ni+Cu reactions. The
flow increases with energy, reaches a maximum, and then gradually decreases at
higher energies. A way of comparing the energy dependence of flow values for
different projectile-target mass combinations is introduced, which demonstrates
a common scaling behaviour among flow values from different systems.Comment: 12 pages, 3 figures. Submitted to Physical Review Letter
Radial Flow in Au+Au Collisions at E=0.25-1.15 A GeV
A systematic study of energy spectra for light particles emitted at
midrapidity from Au+Au collisions at E=0.25-1.15 A GeV reveals a significant
non-thermal component consistent with a collective radial flow. This component
is evaluated as a function of bombarding energy and event centrality.
Comparisons to Quantum Molecular Dynamics (QMD) and Boltzmann-Uehling-Uhlenbeck
(BUU) models are made for different equations of state.Comment: 10 pages of text and 4 figures (all ps files in a uuencoded package)
Statistical signatures of critical behavior in small systems
The cluster distributions of different systems are examined to search for
signatures of a continuous phase transition. In a system known to possess such
a phase transition, both sensitive and insensitive signatures are present;
while in systems known not to possess such a phase transition, only insensitive
signatures are present. It is shown that nuclear multifragmentation results in
cluster distributions belonging to the former category, suggesting that the
fragments are the result of a continuous phase transition.Comment: 31 pages, two columns with 30 figure
Effects of Male Hypogonadism on Regional Adipose Tissue Fatty Acid Storage and Lipogenic Proteins
Testosterone has long been known to affect body fat distribution, although the underlying mechanisms remain elusive. We investigated the effects of chronic hypogonadism in men on adipose tissue fatty acid (FA) storage and FA storage factors. Twelve men with chronic hypogonadism and 13 control men matched for age and body composition: 1) underwent measures of body composition with dual energy x-ray absorptiometry and an abdominal CT scan; 2) consumed an experimental meal containing [3H]triolein to determine the fate of meal FA (biopsy-measured adipose storage vs. oxidation); 3) received infusions of [U-13C]palmitate and [1-14C]palmitate to measure rates of direct free (F)FA storage (adipose biopsies). Adipose tissue lipoprotein lipase, acyl-CoA synthetase (ACS), and diacylglycerol acetyl-transferase (DGAT) activities, as well as, CD36 content were measured to understand the mechanism by which alterations in fat storage occur in response to testosterone deficiency. Results of the study showed that hypogonadal men stored a greater proportion of both dietary FA and FFA in lower body subcutaneous fat than did eugonadal men (both p<0.05). Femoral adipose tissue ACS activity was significantly greater in hypogonadal than eugonadal men, whereas CD36 and DGAT were not different between the two groups. The relationships between these proteins and FA storage varied somewhat between the two groups. We conclude that chronic effects of testosterone deficiency has effects on leg adipose tissue ACS activity which may relate to greater lower body FA storage. These results provide further insight into the role of androgens in body fat distribution and adipose tissue metabolism in humans
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