2,426 research outputs found
AMR on the CM-2
We describe the development of a structured adaptive mesh algorithm (AMR) for the Connection Machine-2 (CM-2). We develop a data layout scheme that preserves locality even for communication between fine and coarse grids. On 8K of a 32K machine we achieve performance slightly less than 1 CPU of the Cray Y-MP. We apply our algorithm to an inviscid compressible flow problem
Traversing probe Patent
Flow meter for measuring stagnation pressure in boundary layer around high speed flight vehicl
Oscillators and relaxation phenomena in Pleistocene climate theory
Ice sheets appeared in the northern hemisphere around 3 million years ago and
glacial-interglacial cycles have paced Earth's climate since then. Superimposed
on these long glacial cycles comes an intricate pattern of millennial and
sub-millennial variability, including Dansgaard-Oeschger and Heinrich events.
There are numerous theories about theses oscillations. Here, we review a number
of them in order to draw a parallel between climatic concepts and dynamical
system concepts, including, in particular, the relaxation oscillator,
excitability, slow-fast dynamics and homoclinic orbits. Namely, almost all
theories of ice ages reviewed here feature a phenomenon of synchronisation
between internal climate dynamics and the astronomical forcing. However, these
theories differ in their bifurcation structure and this has an effect on the
way the ice age phenomenon could grow 3 million years ago. All theories on
rapid events reviewed here rely on the concept of a limit cycle in the ocean
circulation, which may be excited by changes in the surface freshwater surface
balance. The article also reviews basic effects of stochastic fluctuations on
these models, including the phenomenon of phase dispersion, shortening of the
limit cycle and stochastic resonance. It concludes with a more personal
statement about the potential for inference with simple stochastic dynamical
systems in palaeoclimate science.
Keywords: palaeoclimates, dynamical systems, limit cycle, ice ages,
Dansgaard-Oeschger eventsComment: Published in the Transactions of the Philosophical Transactions of
the Royal Society (Series A, Physical Mathematical and Engineering Sciences),
as a contribution to the Proceedings of the workshop on Stochastic Methods in
Climate Modelling, Newton Institute (23-27 August). Philosophical
Transactions of the Royal Society (Series A, Physical Mathematical and
Engineering Sciences), vol. 370, pp. xx-xx (2012); Source codes available on
request to author and on http://www.uclouvain.be/ito
A chemical ionization mass spectrometer for continuous underway shipboard analysis of dimethylsulfide in near-surface seawater
A compact, low-cost atmospheric pressure, chemical ionization mass spectrometer ("mini-CIMS") has been developed for continuous underway shipboard measurements of dimethylsulfide (DMS) in seawater. The instrument was used to analyze DMS in air equilibrated with flowing seawater across a porous Teflon membrane equilibrator. The equilibrated gas stream was diluted with air containing an isotopically-labeled internal standard. DMS is ionized at atmospheric pressure via proton transfer from water vapor, then declustered, mass filtered via quadrupole mass spectrometry, and detected with an electron multiplier. The instrument described here is based on a low-cost residual gas analyzer (Stanford Research Systems), which has been modified for use as a chemical ionization mass spectrometer. The mini-CIMS has a gas phase detection limit of 220 ppt DMS for a 1 min averaging time, which is roughly equivalent to a seawater DMS concentration of 0.1 nM DMS at 20°C. The mini-CIMS has the sensitivity, selectivity, and time response required for underway measurements of surface ocean DMS over the full range of oceanographic conditions. The simple, robust design and relatively low cost of the instrument are intended to facilitate use in process studies and surveys, with potential for long-term deployment on research vessels, ships of opportunity, and large buoys
Risk factors and demographics for microtia in South America: a case-control analysis
BACKGROUND: The etiopathogenesis of microtia is still unknown in the majority of the cases, particularly for individuals presenting with isolated microtia. Our aim was to evaluate potential risk factors for this condition using a caseâcontrol approach. METHODS: We analyzed data from 1,194 live births with isolated microtia enrolled in the ECLAMC study (Estudio Colaborativo Latino Americano de Malformaciones CongĂ©nitas) from 1982 to 2011 and their respective controls. Odds ratios (ORs) were estimated with logistic regression models along with 95% confidence intervals for the resulting OR estimates controlling for the effects of potential confounders (sex, maternal age, hospital, and year of birth) for an adjusted OR (aOR). RESULTS: Multiparity was associated with a higher risk of microtia compared with primiparity (aOR, 1.5; 95% confidence interval [CI], 1.2â1.8), with women who had eight or more prior pregnancies having the highest risk (aOR, 2.8; 95% CI, 1.6â5.2). Women who presented with cold-like symptoms were at higher risk for microtia (aOR, 2.2; 95% CI, 1.2â3.9) as well as those that used tobacco or alcohol during pregnancy (aOR, 1.7; 95% CI, 1.1â2.6 and aOR, 1.4; 95% CI, 0.9â2.1, respectively). The association with alcohol use appeared to be limited to those women who reported binge drinking during pregnancy (aOR, 1.4; 95% CI, 0.7â3.1). Cases from hospitals at low altitude (<2500 m) tended to have more severe types of microtia than those from hospitals at high altitude. CONCLUSION: These results support the hypothesis that, in addition to teratogens, other nongenetic risk factors contribute to the occurrence of isolated microtia.Fil: Luquetti, Daniela. University of Washington; Estados Unidos. Seattle Children; Estados UnidosFil: Saltzman, Babette S.. Seattle Children; Estados UnidosFil: LĂłpez Camelo, Jorge Santiago. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. CEMIC-CONICET. Centro de Educaciones MĂ©dicas e Investigaciones ClĂnicas "Norberto Quirno". CEMIC-CONICET.; ArgentinaFil: Dutra, Maria da Graça. Instituto Oswaldo Cruz; BrasilFil: Castilla, Eduardo Enrique. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. CEMIC-CONICET. Centro de Educaciones MĂ©dicas e Investigaciones ClĂnicas "Norberto Quirno". CEMIC-CONICET.; Argentina. Instituto Nacional de GenĂ©tica MĂ©dica Populacional; Brasi
Air/Sea Transfer of Highly Soluble Gases Over Coastal Waters
The deposition of soluble trace gases to the sea surface is not well studied due to a lack of flux measurements over the ocean. Here we report simultaneous air/sea eddy covariance flux measurements of water vapor, sulfur dioxide (SO2), and momentum from a coastal North Atlantic pier. Gas transfer velocities were on average about 20% lower for SO2 than for H2O. This difference is attributed to the difference in molecular diffusivity between the two molecules (DSO2/DH2O = 0.5), in reasonable agreement with bulk parameterizations in air/sea gas models. This study demonstrates that it is possible to observe the effect of molecular diffusivity on air-side resistance to gas transfer. The slope of observed relationship between gas transfer velocity and friction velocity is slightly smaller than predicted by gas transfer models, possibly due to wind/wave interactions that are unaccounted for in current models
Methanesulfonate in the Greenland Ice Sheet Project 2 Ice Core
In this paper we present measurements of methanesulfonate in the Greenland Ice Sheet Project 2 (GISP2) ice core. Methanesulfonate is an atmospheric oxidation product of dimethylsulfide. The GISP2 methanesulfonate record contains information about the atmospheric loading of biogenic sulfur over the past 110 kyr and its relationship to climate change. The GISP2 data set supports the inferences made from the Renland ice core from Greenland that the glacial atmosphere over Greenland had reduced concentrations of biogenic sulfur compared with the present day [Hansson and Saltzman, 1993]. We conclude that the flux of biogenic sulfur from the North Atlantic Ocean must have been lower during glacial times and speculate that this decrease may have been related to differences in phytoplankton speciation. The data suggest that changes in direct radiative forcing from biogenic sulfur aerosols would act as negative feedback to the glacial/interglacial climate cycles in this region
The Aqueous Phase Yield Of Alkyl Nitrates From Roo+No: Implications For Photochemical Production In Seawater
Alkyl nitrates have been observed in remote oceanic regions of the troposphere and in the surface ocean. The mechanism for their production in the oceans is not known. A likely source is the reaction of ROO + NO (where R is an alkyl group). Steady-state laboratory experiments show that alkyl nitrates are produced in the aqueous phase via this reaction, with branching ratios of 0.23 +/- 0.04, 0.67 +/- 0.03, and 0.71 +/- 0.04 for methyl, ethyl, and propyl nitrate respectively. The branching ratios in aqueous solution are significantly higher than in the gas phase. Irradiation of surface seawaters yield rates of alkyl nitrate production on the order of 10(-18) mol cm(-3) s(-1), suggesting that the reaction of ROO and NO is an important source of alkyl nitrates in seawater
Listener expectations and the perceptual accommodation of talker variability: A pre-registered replication
Published: 04 May 2021Researchers have hypothesized that in order to accommodate variability in how talkers produce their speech sounds, listeners
must perform a process of talker normalization. Consistent with this proposal, several studies have shown that spoken word
recognition is slowed when speech is produced by multiple talkers compared with when all speech is produced by one talker (a
multitalker processing cost). Nusbaum and colleagues have argued that talker normalization is modulated by attention (e.g.,
Nusbaum & Morin, 1992, Speech Perception, Production and Linguistic Structure, pp. 113â134). Some of the strongest
evidence for this claim is from a speeded monitoring study where a group of participants who expected to hear two talkers
showed a multitalker processing cost, but a separate group who expected one talker did not (Magnuson & Nusbaum, 2007,
Journal of Experimental Psychology, 33[2], 391â409). In that study, however, the sample size was small and the crucial
interaction was not significant. In this registered report, we present the results of a well-powered attempt to replicate those
findings. In contrast to the previous study, we did not observe multitalker processing costs in either of our groups. To rule out the
possibility that the null result was due to task constraints, we conducted a second experiment using a speeded classification task.
As in Experiment 1, we found no influence of expectations on talker normalization, with no multitalker processing cost observed
in either group. Our data suggest that the previous findings of Magnuson and Nusbaum (2007) be regarded with skepticism and
that talker normalization may not be permeable to high-level expectations.This research was supported by NSF 1754284, NSF
IGERT 1144399 & NSF NRT 1747486 (PI: JSM) and NSF BCS
1554810 & NIH R01 DC013064 (PI: EBM). This research was also
supported in part by the Basque Government through the BERC 2018-
2021 program and by the Agencia Estatal de InvestigaciĂłn through
BCBL Severo Ochoa excellence accreditation SEV-2015-0490. SL was
supported by an NSF Graduate Research Fellowshi
DMS air/sea flux and gas transfer coefficients from the North Atlantic summertime coccolithophore bloom
Dimethylsulfide (DMS) atmospheric and oceanic concentrations and eddy covariance air/sea fluxes were measured over the N. Atlantic Ocean during July 2007 from Iceland to Woods Hole, MA, USA. Seawater DMS levels north of 55 degrees N ranged from 3 to 17 nM, with variability related to the satellite-derived distributions of coccoliths and to a lesser extent, chlorophyll. For the most intense bloom region southwest of Iceland, DMS air/sea fluxes were as high as 300 mu mol m(-2) d(-1), larger than current model estimates. The observations imply that gas exchange coefficients in this region are significantly greater than those estimated using most gas transfer parameterizations. South of 55 degrees N, DMS levels were lower and the gas transfer coefficients were similar to those observed in other regions of the ocean. The data suggest that DMS emissions from the bloom region may be significantly larger than current estimates. The anomalous gas exchange coefficients likely reflect strong near-surface, water column DMS gradients influenced by physical and biological processe
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