8,376 research outputs found
Large, long range tensile forces drive convergence during
Indirect evidence suggests that blastopore closure during gastrulation of anamniotes, including amphibians such as Xenopus laevis, depends on circumblastoporal convergence forces generated by the marginal zone (MZ), but direct evidence is lacking. We show that explanted MZs generate tensile convergence forces up to 1.5 mN during gastrulation and over 4 mN thereafter. These forces are generated by convergent thickening (CT) until the midgastrula and increasingly by convergent extension (CE) thereafter. Explants from ventralized embryos, which lack tissues expressing CE but close their blastopores, produce up to 2 mN of tensile force, showing that CT alone generates forces sufficient to close the blastopore. Uniaxial tensile stress relaxation assays show stiffening of mesodermal and ectodermal tissues around the onset of neurulation, potentially enhancing long-range transmission of convergence forces. These results illuminate the mechanobiology of early vertebrate morphogenic mechanisms, aid interpretation of phenotypes, and give insight into the evolution of blastopore closure mechanisms. © Shook et al
Working Notes from the 1992 AAAI Workshop on Automating Software Design. Theme: Domain Specific Software Design
The goal of this workshop is to identify different architectural approaches to building domain-specific software design systems and to explore issues unique to domain-specific (vs. general-purpose) software design. Some general issues that cut across the particular software design domain include: (1) knowledge representation, acquisition, and maintenance; (2) specialized software design techniques; and (3) user interaction and user interface
Ohio Agribusiness Compensation Study: 1986
Exact date of working paper unknown.Information about competitive wage and compensation packages is important to attracting and maintaining a productive workforce. A 1986 survey of compensation practices of Ohio Agribusiness firms revealed that bonuses and profit-sharing plans play a more important role in determining pay level than they did in 1982. Larger firms, measured by gross annual sales, still pay more than smaller firms; but trends by geographic location are not as distinct as they were in 1982. Non-managerial agribusiness employees still earn less than their metropolitan counterparts, but the gap is decreasing
Polarization Modeling and Predictions for DKIST Part 2: Application of the Berreman Calculus to Spectral Polarization Fringes of Beamsplitters and Crystal Retarders
We outline polarization fringe predictions derived from a new application of
the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder
optics. The DKIST retarder baseline design used 6 crystals, single-layer
anti-reflection coatings, thick cover windows and oil between all optical
interfaces. This new tool estimates polarization fringes and optic Mueller
matrices as functions of all optical design choices. The amplitude and period
of polarized fringes under design changes, manufacturing errors, tolerances and
several physical factors can now be estimated. This tool compares well with
observations of fringes for data collected with the SPINOR spectropolarimeter
at the Dunn Solar Telescope using bi-crystalline achromatic retarders as well
as laboratory tests. With this new tool, we show impacts of design decisions on
polarization fringes as impacted by anti-reflection coatings, oil refractive
indices, cover window presence and part thicknesses. This tool helped DKIST
decide to remove retarder cover windows and also recommends reconsideration of
coating strategies for DKIST. We anticipate this tool to be essential in
designing future retarders for mitigation of polarization and intensity fringe
errors in other high spectral resolution astronomical systems.Comment: Accepted for publication in JATI
Length-Length and Length-Weight Relationships of Oilfish (Ruvettus pretiosus), Escolar (Lepidocybium flavobrunneum), Snake Mackerel (Gempylus serpens), and Longnose Lancetfish (Alepisaurus ferox) From the Gulf of Mexico and the Western North Atlantic Ocean
Oilfish, escolar, snake mackerel (order Aulopiformes, family Gempylidae), and longnose lancetfish (order Perciformes, family Alepisauridae) sampled from the western North Atlantic and the Gulf of Mexico were analyzed for length–weight and length–length relationships. These species are encountered as occasional bycatch of pelagic longline fisheries. The fish (161 specimens, 19.0–149.1 cm TL) were collected over a 3-year period (January 2007–January 2010) from pelagic longline gear targeting swordfish and tuna. For each species, 95% confidence limits (CI) of parameters b and log a and regression coefficients (r2) were calculated for log-transformed length–weight relationships. The length–weight parameter b for all species ranged from 2.881 to 3.358, with regression coefficients (r2) ranging from 0.75 to 0.98. Linear relationships between fork lengths, standard lengths, and total lengths were also calculated
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Clinical Utility of Echocardiography in Former Preterm Infants with Bronchopulmonary Dysplasia.
BackgroundThe clinical utility of echocardiography for the diagnosis of pulmonary vascular disease (PVD) in former preterm infants with bronchopulmonary dysplasia (BPD) is not established. Elevated pulmonary vascular resistance (PVR) rather than pulmonary artery pressure (PAP) is the hallmark of PVD. We evaluated the utility of echocardiography in infants with BPD in diagnosing pulmonary hypertension and PVD (PVR >3 Wood units × m2) assessed by cardiac catheterization.MethodsA retrospective single center study of 29 infants born ≤29 weeks of gestational age with BPD who underwent cardiac catheterization and echocardiography was performed. PVD was considered present by echocardiography if the tricuspid valve regurgitation jet peak velocity was >2.9 m/sec, post-tricuspid valve shunt systolic flow velocity estimated a right ventricular systolic pressure >35 mm Hg, or systolic septal flattening was present. The utility (accuracy, sensitivity, and positive predictive value [PPV]) of echocardiography in the diagnosis of PVD was tested. Subgroup analysis in patients without post-tricuspid valve shunts was performed. Echocardiographic estimations of right ventricular pressure, dimensions, function, and pulmonary flow measurements were evaluated for correlation with PVR.ResultsThe duration between echocardiography and cardiac catheterization was a median of 1 day (interquartile range, 1-4 days). Accuracy, sensitivity, and PPV of echocardiography in diagnosing PVD were 72%, 90.5%, and 76%, respectively. Accuracy, sensitivity, and PPV increased to 93%, 91.7%, and 100%, respectively, when infants with post-tricuspid valve shunts were excluded. Echocardiography had poor accuracy in estimating the degree of PAP elevation by cardiac catheterization. In infants without post-tricuspid valve shunts, there was moderate to good correlation between indexed PVR and right ventricular myocardial performance index (rho = 0.89, P = .005), systolic to diastolic time index (0.84, P < .001), right to left ventricular diameter ratio at end systole (0.66, P = .003), and pulmonary artery acceleration time (0.48, P = .05).ConclusionsEchocardiography performs well in screening for PVD in infants with BPD and may be diagnostic in the absence of a post-tricuspid valve shunt. However, cardiac catheterization is needed to assess the degree of PAP elevation and PVR. The diagnostic utility of echocardiographic measurements that correlate with PVR should be evaluated prospectively in this patient population
The Aquarius Co-Moving Group is Not a Disrupted Classical Globular Cluster
We present a detailed analysis of high-resolution, high S/N spectra for 5
Aquarius stream stars observed with the MIKE spectrograph on the Magellan Clay
telescope. Our sample represents one third of the 15 known members in the
stream. We find the stream is not mono-metallic: the metallicity ranges from
[Fe/H] = -0.63 to -1.58. No anti-correlation in Na-O abundances is present, and
we find a strong positive Mg-Al relationship, similar to that observed in the
thick disk. We find no evidence that the stream is a result of a disrupted
classical globular cluster, contrary to a previously published claim. High
[(Na, Ni, alpha)/Fe] and low [Ba/Y] abundance ratios in the stream suggests it
is not a tidal tail from a disrupted dwarf galaxy, either. The stream is
chemically indistinguishable from Milky Way field stars with the exception of
one candidate, C222531-145437. From its position, velocity, and detailed
chemical abundances, C222531-145437 is likely a star that was tidally disrupted
from omega-Centauri. We propose the Aquarius stream is Galactic in origin, and
could be the result from a disk-satellite perturbation in the Milky Way thick
disk on the order of a few Gyr ago: derived orbits, UVW velocities, and angular
momenta of the Aquarius members offer qualitative support for our hypothesis.
Assuming C222531-145437 is a tidally disrupted member of omega-Centauri, this
system is the most likely disk perturber. In the absence of compelling chemical
and/or dynamical evidence that the Aquarius stream is the tidal tail of a
disrupted satellite, we advocate the "Aquarius group" as a more appropriate
description. Like the Canis Major over-density, as well as the Hercules and
Monoceros groups, the Aquarius group joins the list of kinematically-identified
substructures that are not actually accreted material: they are simply part of
the rich complexity of the Milky Way structure.Comment: Accepted to MNRAS. Updated to journal versio
The effect of multiple sclerosis on carotid baroreflex control of heart rate and blood pressure
Multiple sclerosis (MS) is marked by conduction abnormalities within the central nervous system that can lead to impaired blood pressure regulation. However, the impact of this disease on dynamic neural control—responsiveness and timing (i.e., latency)—of blood pressure has not been examined. Utilizing a variable neck chamber system, we tested the hypothesis that patients with MS (MS: n=4) exhibit an altered response following baroreflex perturbation compared to sex and age matched healthy controls (CON: n=4). At rest, 5-sec pulses of neck suction (NS; -60 Torr) and neck pressure (NP; +40 Torr) were applied to simulate carotid hypertension and hypotension, respectively. Mean arterial pressure (MAP; Finometer) and heart rate (HR) were continuously measured in response to the perturbations. Carotid baroreflex (CBR) latencies (i.e., time-to-peak responses) were examined using carotid-cardiac (peak HR responses), carotid-vasomotor (peak MAP responses), and change in MAP at the peak HR response of the corresponding stimuli (MAP@HRpeak), all of which were not significant for both NP and NS. Following NS, responses in MAP (MS: -12±5, CON: -10±3 mmHg; p=0.43) and HR (MS: -9±3, CON: -8±4 BPM; p=0.58) were similar between groups. Following administration of NP, HR responses (MS: 4±2, CON: 5±4 BPM; p=0.47) were no different. However, the differences found in MAP were significant (MS: 5±2, CON: 8±2 mmHg; p=0.05), providing some evidence that baroreceptor responsiveness may be compromised when faced with a hypotensive challenge
The Effect of Type II Diabetes Mellitus on Oxygen Uptake Kinetics during Heavy Exercise
The kinetics of oxygen uptake (Vo2) during the rest to exercise transition are thought to be modulated by intracellular metabolic processes. Diabetes has been shown to slow Vo2 kinetics, likely due to the impact of diabetes upon microvascular oxygen exchange (Padilla et al, 2007). However, to date, recovery from exercise has yet to be studied in these patients. Thus, the purpose of this study was to test the hypothesis that the existence of diabetes would hamper Vo2 kinetics during transitions to and from heavy leg cycling (H: Supra-LT). Nine subjects (4 control, 5 diabetic) completed three separate H exercise bouts. Vo2 was measured continuously at the mouth during exercise and recovery for each bout. During the on-transient, the total amplitude was decreased (Atot: Control 2.16±0.29 vs Diabetic 1.33±0.42 L/min, p=0.01). In an attempt to correct for differences in Atot, the rate of change in Vo2 (A1/T1 ) was calculated. This variable was significant reduced in diabetics during both the on-(A1/T1: Control 0.059±0.03 vs Diabetic 0.016±0.01, p=0.02), and off-transients (Control -0.10±0.10 vs Diabetic 0.035±0.012, p=0.09). In addition, the time constant during the on-transition was greatly slowed in diabetes (Tau: Control 24.07±8.39 vs Diabetic 76.76±37.94 sec, p=0.03). These findings suggest strongly that diabetes and it’s sequelae lead to impairments in oxidative metabolism during both exercise and recovery, which would serve to cause a faster rate of fatigue and a longer temporal course of recovery
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