Direct Rate Measurements Research Articles

Flow-induced nucleation in polymer melts: a study of the GO model for pure and bimodal blends, under shear and extensional flow

We present a rapid rescaling algorithm that enables a systematic comparison between the Graham and Olmsted (GO) model for flow-induced nucleation of polymer melts (Graham and Olmsted, Phys Rev Lett 103(11): 115702, 2009) and direct nucleation rate measurements from a flowing polymer melt. We consider polymer melts consisting of pure long chains and bimodal blends of long and short chains. We simulate the nucleation rate for a wide range of free energy barriers under a wide range of applied shear and extensional flows by using an accelerated nucleation algorithm. We then develop a semi-analytical technique to compute efficiently the nucleation rate under flow for monodisperse melts. We extend our approach to bimodal blends using a method to rescale reference data. This allows us to compare the GO model to experimentally measured nucleation rates at several different temperatures. The GO model is able to consistently account for the effect of temperature on flow-induced nucleation. Our modelling will also contribute to the derivation of computationally inexpensive molecular models of flow-induced nucleation in polymers.

Mixing process on the northeast coast of Hokkaido in summer

Direct measurements using a free-falling micro-profiler were conducted on the northeast coast of Hokkaido in the summer of 2007 to clarify the mixing process in the Soya Warm Current (SWC) region in terms of microstructure. The distribution of the Turner angle (Tu) showed that these regions have a high potential for double diffusive convection, but direct measurements of the turbulent dissipation rate (e) and dissipation of temperature variance (\( \chi_{T} \)) did not necessarily correspond to each other in the SWC region, especially in the offshore front of SWC and farther offshore. The mixing efficiency indicated that, even though the Turner angle (Tu) indicated a high potential for double diffusive convection, turbulent mixing was the main contributor to the mixing process in this region, and double-diffusive convection only contributed partially and sparsely, especially in the boundary off SWC water. The bottom mixed layer (BML) is known to thicken off the SWC. The vertical diffusivity coefficient was enhanced near the bottom (10−4–10−3 m2 s−1) off the SWC, and these results support that turbulence near the bottom off the SWC contributed to the thickening of the BML.

Attack Rates Assessment of the 2009 Pandemic H1N1 Influenza A in Children and Their Contacts: A Systematic Review and Meta-Analysis

BackgroundThe recent H1N1 influenza A pandemic was marked by multiple reports of illness and hospitalization in children, suggesting that children may have played a major role in the propagation of the virus. A comprehensive detailed analysis of the attack rates among children as compared with their contacts in various settings is of great importance for understanding their unique role in influenza pandemics.Methodology/Principal FindingsWe searched MEDLINE (PubMed) and Embase for published studies reporting outbreak investigations with direct measurements of attack rates of the 2009 pandemic H1N1 influenza A among children, and quantified how these compare with those of their contacts. We identified 50 articles suitable for review, which reported school, household, travel and social events. The selected reports and our meta-analysis indicated that children had significantly higher attack rates as compared to adults, and that this phenomenon was observed for both virologically confirmed and clinical cases, in various settings and locations around the world. The review also provided insight into some characteristics of transmission between children and their contacts in the various settings.Conclusion/SignificanceThe consistently higher attack rates of the 2009 pandemic H1N1 influenza A among children, as compared to adults, as well as the magnitude of the difference is important for understanding the contribution of children to disease burden, for implementation of mitigation strategies directed towards children, as well as more precise mathematical modeling and simulation of future influenza pandemics.

Velocity Relaxation in a Strongly Coupled Plasma

Collisional relaxation of Coulomb systems is studied in the strongly coupled regime. We use an optical pump-probe approach to manipulate and monitor the dynamics of ions in an ultracold neutral plasma, which allows direct measurement of relaxation rates in a regime where common Landau-Spitzer theory breaks down. Numerical simulations confirm the experimental results and display non-Markovian dynamics at early times.

A facility for simulating Titan’s environment

As a result of measurements acquired by the Cassini–Huygens mission of Titan’s near surface atmospheric composition and temperature, Titan conditions can now be simulated in the laboratory and samples can subsequently be subjected to those conditions. Titan demonstrates an active hydrological-like cycle with its thick atmosphere, dynamic clouds, polar lakes of methane and ethane, moist regolith, and extensive fluvial erosive features. Unlike Earth, Titan’s hydrological-like cycle likely involves several constituents, primarily methane and ethane. Here the properties of a new Titan simulation facility are presented, including conceptual methodology, design, implementation, and performance results. The chamber maintains Titan’s surface temperature and pressure, and the sample cryogenic liquids undergoing experimentation are condensed within the chamber itself. During the experiments, the evaporation rates of the sample liquids are directly determined by continually measuring mass. Constituents are analyzed utilizing a Fourier Transform Infrared Spectroscopy (FTIR), and vapor concentrations are determined using a gas chromatograph fitted with a Flame Ionization Detector (FID). All pertinent data is logged via computer. Under laboratory conditions, the direct measurements of the evaporation rates of methane, ethane, and mixtures thereof can be achieved. Among the processes to be studied are the effects of regolith on transport from the subsurface to the atmosphere, the freezing point depression effects of dissolved nitrogen, and the solubility of various relevant organic compounds.

Self-calibrated algorithms for diffuse optical tomography and bioluminescence tomography using relative transmission images

Reconstruction algorithms for diffuse optical tomography (DOT) and bioluminescence tomography (BLT) have been developed based on diffusion theory. The algorithms numerically solve the diffusion equation using the finite element method. The direct measurements of the uncalibrated light fluence rates by a camera are used for the reconstructions. The DOT is self-calibrated by using all possible pairs of transmission images obtained with external sources along with the relative values of the simulated data and the calculated Jacobian. The reconstruction is done in the relative domain with the cancelation of any geometrical or optical factors. The transmission measurements for the DOT are used for calibrating the bioluminescence measurements at each wavelength and then a normalized system of equations is built up which is self-calibrated for the BLT. The algorithms have been applied to a three dimensional model of the mouse (MOBY) segmented into tissue regions which are assumed to have uniform optical properties. The DOT uses the direct method for calculating the Jacobian. The BLT uses a reduced space of eigenvectors of the Green's function with iterative shrinking of the permissible source region. The reconstruction results of the DOT and BLT algorithms show good agreement with the actual values when using either absolute or relative data. Even a small calibration error causes significant degradation of the reconstructions based on absolute data.

High resolution of black carbon and organic carbon emissions in the Pearl River Delta region, China

A high-resolution regional black carbon (BC) and organic carbon (OC) emission inventory for the year 2009 was developed for the Pearl River Delta (PRD) region, China, based on the collected activity data and the latest emission factors. PM2.5, BC and OC emissions were estimated to be 303kt, 39kt and 31kt, respectively. Industrial processes were major contributing sources to PM2.5 emissions. BC emissions were mainly from mobile sources, accounting for 65.0%, while 34.1% of OC emissions were from residential combustion. The primary OC/BC ratios for individual cities in the PRD region were dependent on the levels of economic development due to differences in source characteristics, with high ratios in the less developed cities and low ratios in the central and southern developed areas. The preliminary temporal profiles were established, showing the highest OC emissions in winter and relatively constant BC emissions throughout the year. The emissions were spatially allocated into grid cells with a resolution of 3km×3km. Large amounts of BC emissions were distributed over the central–southern PRD city clusters, while OC emissions exhibited a relatively even spatial distribution due to the significant biomass burning emissions from the outlying area of the PRD region. Uncertainties in carbonaceous aerosol emissions were usually higher than in other primary pollutants like SO2, NOx, and PM10. One of the key uncertainty sources was the emission factor, due to the absence of direct measurements of BC and OC emission rates.

High precision measurements for the rp-process

The explosive nuclear burning of hydrogen at high temperatures and densities on the surface of accreting neutron stars, known as the rp-process, gives rise to a number of observable phenomena related to X-ray bursts. Recent astronomical observations provide unprecedented information, e.g. on atomic abundances in ejecta and time structure in X-ray bursts. To interpret these data requires an understanding of the nuclear processes during the explosive events and, therefore, information on the structure of unstable, proton-rich nuclei. Network model calculations show that the dominant burning processes, after breakout from the hot CNO cycles at sufficiently high temperatures, proceed via proton- and α-induced reactions. Since the reaction rates are very sensitive to the nuclear structure, shell- and statistical-model calculations are often insufficient in predicting exact reaction paths. Therefore, we have been conducting experiments using high-resolution spectrometers to search for resonances that play a role in the rp-process and determine the nuclear-structure, most importantly excitation energies, accurately above the particle thresholds. The techniques and examples of experimental results will be presented and discussed. The status and outlook of direct measurements of stellar reactions rates in inverse kinematics using planned recoil separators will be outlined.

Revising the human mutation rate: implications for understanding human evolution

It is now possible to make direct measurements of the mutation rate in modern humans using next-generation sequencing. These measurements reveal a value that is approximately half of that previously derived from fossil calibration, and this has implications for our understanding of demographic events in human evolution and other aspects of population genetics. Here, we discuss the implications of a lower-than-expected mutation rate in relation to the timescale of human evolution.

Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates

Abstract. Marine N2 fixing microorganisms, termed diazotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen (N2) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic cell counts or qPCR assays targeting the nifH genes) and N2 fixation rates. Biomass conversion factors are estimated based on cell sizes to convert abundance data to diazotrophic biomass. The database is limited spatially, lacking large regions of the ocean especially in the Indian Ocean. The data are approximately log-normal distributed, and large variances exist in most sub-databases with non-zero values differing 5 to 8 orders of magnitude. Reporting the geometric mean and the range of one geometric standard error below and above the geometric mean, the pelagic N2 fixation rate in the global ocean is estimated to be 62 (52–73) Tg N yr−1 and the pelagic diazotrophic biomass in the global ocean is estimated to be 2.1 (1.4–3.1) Tg C from cell counts and to 89 (43–150) Tg C from nifH-based abundances. Reporting the arithmetic mean and one standard error instead, these three global estimates are 140 ± 9.2 Tg N yr−1, 18 ± 1.8 Tg C and 590 ± 70 Tg C, respectively. Uncertainties related to biomass conversion factors can change the estimate of geometric mean pelagic diazotrophic biomass in the global ocean by about ±70%. It was recently established that the most commonly applied method used to measure N2 fixation has underestimated the true rates. As a result, one can expect that future rate measurements will shift the mean N2 fixation rate upward and may result in significantly higher estimates for the global N2 fixation. The evolving database can nevertheless be used to study spatial and temporal distributions and variations of marine N2 fixation, to validate geochemical estimates and to parameterize and validate biogeochemical models, keeping in mind that future rate measurements may rise in the future. The database is stored in PANGAEA (doi:10.1594/PANGAEA.774851).

The Application of Artificial Neural Networks for the Prediction of Oil Production Flow Rate

Estimation of oil production flow rate, where direct rate measurement is not feasible, is a challenge faced by petroleum engineers in some fields throughout the world. In such situations, oil flow rate is commonly estimated using empirical correlations. In some cases, significant error is inherent in application of the empirical correlations and yields inaccurate results. This study presents a new methodology for prediction of oil flow rate in two-phase flow of oil and gas through wellhead chokes using the artificial neural network technique. The developed model predicts oil flow rate as functions of choke upstream pressure, choke size, and producing gas to oil ratio. The accuracy of the developed model was compared with some popular empirical correlations. Results of comparison showed that oil flow rates predicted by the new model are in excellent agreement with actual measured data.

Shock tube/laser absorption studies of the decomposition of methyl formate

Reaction rate coefficients for the major high-temperature methyl formate (MF, CH3OCHO) decomposition pathways, MF→CH3OH+CO (1), MF→CH2O+CH2O (2), and MF→CH4+CO2 (3), were directly measured in a shock tube using laser absorption of CO (4.6μm), CH2O (306nm) and CH4 (3.4μm). Experimental conditions ranged from 1202 to 1607K and 1.36 to 1.72atm, with mixtures varying in initial fuel concentration from 0.1% to 3% MF diluted in argon. The decomposition rate coefficients were determined by monitoring the formation rate of each target species immediately behind the reflected shock waves and modeling the species time-histories with a detailed kinetic mechanism [12]. The three measured rate coefficients can be well-described using two-parameter Arrhenius expressions over the temperature range in the present study: k1=1.1×1013exp(−29556/T, K)s−1, k2=2.6×1012exp(−32052/T, K)s−1, and k3=4.4×1011exp(−29 078/T, K)s−1, all thought to be near their high-pressure limits. Uncertainties in the k1, k2 and k3 measurements were estimated to be ±25%, ±35%, and ±40%, respectively. We believe that these are the first direct high-temperature rate measurements for MF decomposition and all are in excellent agreement with the Dooley et al. [12] mechanism. In addition, by also monitoring methanol (CH3OH) and MF concentration histories using a tunable CO2 gas laser operating at 9.67 and 9.23μm, respectively, all the major oxygen-carrying molecules were quantitatively detected in the reaction system. An oxygen balance analysis during MF decomposition shows that the multi-wavelength laser absorption strategy used in this study was able to track more than 97% of the initial oxygen atoms in the fuel.

The effective Lagrangian of dark energy from observations

Using observational data on the expansion rate of the universe (H(z)) we constrain the effective Lagrangian of the current accelerated expansion. Our results show that the effective potential is consistent with being flat i.e., a cosmological constant; it is also consistent with the field moving along an almost flat potential like a pseudo-Goldstone boson. We show that the potential of dark energy does not deviate from a constant at more than 6% over the redshift range 0 < z < 1. The data can be described by just a constant term in the Lagrangian and do not require any extra parameters; therefore there is no evidence for augmenting the number of parameters of the LCDM paradigm. We also find that the data justify the effective theory approach to describe accelerated expansion and that the allowed parameters range satisfy the expected hierarchy. Future data, both from cosmic chronometers and baryonic acoustic oscillations, that can measure H(z) at the % level, could greatly improve constraints on the flatness of the potential or shed some light on possible mechanisms driving the accelerated expansion. Besides the above result, it is shown that the effective Lagrangian of accelerated expansion can be constrained from cosmological observations in a model-independent way and that direct measurements of the expansion rate H(z) are most useful to do so.

Direct measurement of ozone production rates in Houston in 2009 and comparison with two estimation methods

Abstract. Net ozone production rates, P(O3), were measured directly using the Penn State Measurement of Ozone Production Sensor (MOPS) during the Study of Houston Atmospheric Radical Precursors (SHARP, 2009). Measured P(O3) peaked in the late morning, with values between 15 ppbv h−1 and 100 ppbv h−1, although values of 40–80 ppbv h−1 were typical for higher ozone days. These measurements were compared against ozone production rates calculated using measurements of hydroperoxyl (HO2), hydroxyl (OH), and nitric oxide (NO) radicals, called "calculated P(O3)". The same comparison was done using modeled radicals obtained from a box model with the RACM2 mechanism, called "modeled P(O3)". Measured and calculated P(O3) had similar peak values but the calculated P(O3) tended to peak earlier in the morning when NO values were higher. Measured and modeled P(O3) had a similar dependence on NO, but the modeled P(O3) was only half the measured P(O3). The modeled P(O3) is less than the calculated P(O3) because the modeled HO2 is less than the measured HO2. While statistical analyses are not conclusive regarding the comparison between MOPS measurements and the two estimation methods, the calculated P(O3) with measured HO2 produces peak values similar to the measured P(O3) when ozone is high. Although the MOPS is new and more testing is required to verify its observations, the measurements in the SHARP field campaign show the potential of this new technique for contributing to the understanding of ozone-producing chemistry and to the monitoring of ozone's response to future air quality regulatory actions.

Femoral Arterial and Venous Catheterization for Blood Sampling, Drug Administration and Conscious Blood Pressure and Heart Rate Measurements

In multiple fields of study, access to the circulatory system in laboratory studies is necessary. Pharmacological studies in rats using chronically implanted catheters permit a researcher to effectively and humanely administer substances, perform repeated blood sampling and assists in conscious direct measurements of blood pressure and heart rate. Once the catheter is implanted long-term sampling is possible. Patency and catheter life depends on multiple factors including the lock solution used, flushing regimen and catheter material. This video will demonstrate the methodology of femoral artery and venous catheterization of the rat. In addition the video will demonstrate the use of the femoral venous and arterial catheters for blood sampling, drug administration and use of the arterial catheter in taking measurements of blood pressure and heart rate in a conscious freely-moving rat. A tether and harness attached to a swivel system will allow the animal to be housed and have samples taken by the researcher with minimal disruption to the animal. To maintain patency of the catheter, careful daily maintenance of the catheter is required using lock solution (100 U/ml heparinized saline), machine-ground blunt tip syringe needles and the use of syringe filters to minimize potential contamination. With careful aseptic surgical techniques, proper catheter materials and careful catheter maintenance techniques, it is possible to sustain patent catheters and healthy animals for long periods of time (several weeks).

Femoral Arterial and Venous Catheterization for Blood Sampling, Drug Administration and Conscious Blood Pressure and Heart Rate Measurements

In multiple fields of study, access to the circulatory system in laboratory studies is necessary. Pharmacological studies in rats using chronically implanted catheters permit a researcher to effectively and humanely administer substances, perform repeated blood sampling and assists in conscious direct measurements of blood pressure and heart rate. Once the catheter is implanted long-term sampling is possible. Patency and catheter life depends on multiple factors including the lock solution used, flushing regimen and catheter material. This video will demonstrate the methodology of femoral artery and venous catheterization of the rat. In addition the video will demonstrate the use of the femoral venous and arterial catheters for blood sampling, drug administration and use of the arterial catheter in taking measurements of blood pressure and heart rate in a conscious freely-moving rat. A tether and harness attached to a swivel system will allow the animal to be housed and have samples taken by the researcher with minimal disruption to the animal. To maintain patency of the catheter, careful daily maintenance of the catheter is required using lock solution (100 U/ml heparinized saline), machine-ground blunt tip syringe needles and the use of syringe filters to minimize potential contamination. With careful aseptic surgical techniques, proper catheter materials and careful catheter maintenance techniques, it is possible to sustain patent catheters and healthy animals for long periods of time (several weeks).

Nanocalorimetry of respiration in micro-organisms in natural waters

Two commercially available nanocalorimeters were assessed for direct measurement of respiration rates of micro-organisms in natural waters or liquid cultures as a function of temperature. Respiration heat rates were measured with isothermal and temperature-scanning nanocalorimeters in natural seawater and in cultures of microplankton and bacteria. The standard deviation of a measurement of metabolic heat rate by isothermal nanocalorimetry is ±25nW/mL and by temperature-scanning nanocalorimetry, ±150nW/mL as a continuous function of temperature. Although the absolute uncertainty of temperature scanning calorimetry is larger, the relative noise between data points is small and temperature scanning rapidly produces a curve of heat rate versus temperature that describes the metabolic response to temperature. Used together, the two methods are capable of generating a curve of metabolic heat rate versus temperature over the entire temperature range of respiratory activity in about 4h.

Estimating ocean heat transports and submarine melt rates in Sermilik Fjord, Greenland, using lowered acoustic Doppler current profiler (LADCP) velocity profiles

AbstractSubmarine melting at the ice–ocean interface is a significant term in the mass balance of marine-terminating outlet glaciers. However, obtaining direct measurements of the submarine melt rate, or the ocean heat transport towards the glacier that drives this melting, has been difficult due to the scarcity of observations, as well as the complexity of oceanic flows. Here we present a method that uses synoptic velocity and temperature profiles, but accounts for the dominant mode of velocity variability, to obtain representative heat transport estimates. We apply this method to the Sermilik Fjord–Helheim Glacier system in southeastern Greenland. Using lowered acoustic Doppler current profiler (LADCP) and hydrographic data collected in summer 2009, we find a mean heat transport towards the glacier of 29 × 109W, implying a submarine melt rate at the glacier face of 650 ma–1. The resulting adjusted velocity profile is indicative of a multilayer residual circulation, where the meltwater mixture flows out of the fjord at the surface and at the stratification maximum.

Patterns of interspecific variation in the heart rates of embryonic reptiles.

New non-invasive technologies allow direct measurement of heart rates (and thus, developmental rates) of embryos. We applied these methods to a diverse array of oviparous reptiles (24 species of lizards, 18 snakes, 11 turtles, 1 crocodilian), to identify general influences on cardiac rates during embryogenesis. Heart rates increased with ambient temperature in all lineages, but (at the same temperature) were faster in lizards and turtles than in snakes and crocodilians. We analysed these data within a phylogenetic framework. Embryonic heart rates were faster in species with smaller adult sizes, smaller egg sizes, and shorter incubation periods. Phylogenetic changes in heart rates were negatively correlated with concurrent changes in adult body mass and residual incubation period among the lizards, snakes (especially within pythons) and crocodilians. The total number of embryonic heart beats between oviposition and hatching was lower in squamates than in turtles or the crocodilian. Within squamates, embryonic iguanians and gekkonids required more heartbeats to complete development than did embryos of the other squamate families that we tested. These differences plausibly reflect phylogenetic divergence in the proportion of embryogenesis completed before versus after laying.

Applying Dalton’s law of potential evaporation rate over the territory of Russia and neighboring countries using long-term observation data

Parameters of the relationship between wind speed W and conductance G, used in Dalton’s law for potential evaporation rate, were estimated from the long-term field monitoring data on potential evaporation at 81 stations of the State Hydrological Institute. Linear dependence onWwas assumed, that is, G(W) = g1 + g2W. The estimation yielded g1 = 165.2 and g2 = 99.9. These parameters were employed for computation of potential evaporation rate from routine meteorological data for locations of 2460 meteorological stations of the former USSR territory. The computed estimates were then compared with some published calculated values and with the data of direct potential evaporation rate measurements at 254 geographical points. The comparison yielded satisfactory results.