29,154 research outputs found

    Can grain growth explain transition disks?

    Full text link
    Aims: Grain growth has been suggested as one possible explanation for the diminished dust optical depths in the inner regions of protoplanetary "transition" disks. In this work, we directly test this hypothesis in the context of current models of grain growth and transport. Methods: A set of dust evolution models with different disk shapes, masses, turbulence parameters, and drift efficiencies is combined with radiative transfer calculations in order to derive theoretical spectral energy distributions (SEDs) and images. Results: We find that grain growth and transport effects can indeed produce dips in the infrared SED, as typically found in observations of transition disks. Our models achieve the necessary reduction of mass in small dust by producing larger grains, yet not large enough to be fragmenting efficiently. However, this population of large grains is still detectable at millimeter wavelengths. Even if perfect sticking is assumed and radial drift is neglected, a large population of dust grains is left behind because the time scales on which they are swept up by the larger grains are too long. This mechanism thus fails to reproduce the large emission cavities observed in recent millimeter-wave interferometric images of accreting transition disks.Comment: 11 pages, 5 figures, accepted to A&

    Containerless low gravity processing of glass forming and immiscible alloys

    Get PDF
    Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedimentation of the more dense of the immiscible liquid phases. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the 100 meter drop tube under low gravity, containerless conditions to determine the feasibility of producing dispersed structures. Three alloy compositions were utilized. Alloys containing 10 percent by volume of the gold-rich hypermonotectic phase exhibited a tendency for the gold-rich liquid to wet the outer surface of the samples. This wetting tendency led to extensive segregation in several cases. Alloys containing 80 and 90 percent by volume of the gold-rich phase possessed completely different microstructures from the 10 percent samples when processed under low-g, containerless conditions. Several samples exhibited microstructures consisting of well dispersed 2 to 3 microns diameter rhodium-rich spheres in a gold-rich matrix

    Generalized Clustering Conditions of Jack Polynomials at Negative Jack Parameter α\alpha

    Full text link
    We present several conjectures on the behavior and clustering properties of Jack polynomials at \emph{negative} parameter α=k+1r1\alpha=-\frac{k+1}{r-1}, of partitions that violate the (k,r,N)(k,r,N) admissibility rule of Feigin \emph{et. al.} [\onlinecite{feigin2002}]. We find that "highest weight" Jack polynomials of specific partitions represent the minimum degree polynomials in NN variables that vanish when ss distinct clusters of k+1k+1 particles are formed, with ss and kk positive integers. Explicit counting formulas are conjectured. The generalized clustering conditions are useful in a forthcoming description of fractional quantum Hall quasiparticles.Comment: 12 page

    Quantitying the Effects of Traffic Calming on Emissions Using on-road Measurement

    Get PDF
    The objective of this work was to determine the effect of one form of traffic calming on emissions. Traffic calming is aimed at reducing average vehicle speeds, especially in residential neighborhoods, often using physical road obstructions such as speed bumps, but it also results in a higher number of acceleration/deceleration events which in turn yield higher emissions. Testing was undertaken by driving a warmed-up Euro-1 spark ignition passenger car over a set of speed bumps on a level road, and then comparing the emissions output to a noncalmed level road negotiated smoothly at a similar average speed. For the emissions measurements, a novel method was utilized, whereby the vehicle was fitted with a portable Fourier Transform Infrared (FTIR) spectrometer, capable of measuring up to 51 different components in real-time on the road. The results showed that increases in emissions were much greater than was previously reported by other researchers using different techniques. When traffic-calmed results were compared to a smooth non-calmed road, there were substantial increases in CO2 (90%), CO (117%), NOx (195%) and THC (148%). These results form the basis for a good argument against traffic calming using speed bumps, especially for aggressive drivers. Slowing traffic down with speed restrictions enforced by speed cameras is a more environmentally friendly option

    Properties of Non-Abelian Fractional Quantum Hall States at Filling ν=kr\nu=\frac{k}{r}

    Full text link
    We compute the physical properties of non-Abelian Fractional Quantum Hall (FQH) states described by Jack polynomials at general filling ν=kr\nu=\frac{k}{r}. For r=2r=2, these states are identical to the ZkZ_k Read-Rezayi parafermions, whereas for r>2r>2 they represent new FQH states. The r=k+1r=k+1 states, multiplied by a Vandermonde determinant, are a non-Abelian alternative construction of states at fermionic filling 2/5,3/7,4/9...2/5, 3/7, 4/9.... We obtain the thermal Hall coefficient, the quantum dimensions, the electron scaling exponent, and show that the non-Abelian quasihole has a well-defined propagator falling off with the distance. The clustering properties of the Jack polynomials, provide a strong indication that the states with r>2r>2 can be obtained as correlators of fields of \emph{non-unitary} conformal field theories, but the CFT-FQH connection fails when invoked to compute physical properties such as thermal Hall coefficient or, more importantly, the quasihole propagator. The quasihole wavefuntion, when written as a coherent state representation of Jack polynomials, has an identical structure for \emph{all} non-Abelian states at filling ν=kr\nu=\frac{k}{r}.Comment: 2 figure

    The transient response of global-mean precipitation to increasing carbon dioxide levels

    Get PDF
    The transient response of global-mean precipitation to an increase in atmospheric carbon dioxide levels of 1% yr(-1) is investigated in 13 fully coupled atmosphere-ocean general circulation models (AOGCMs) and compared to a period of stabilization. During the period of stabilization, when carbon dioxide levels are held constant at twice their unperturbed level and the climate left to warm, precipitation increases at a rate of similar to 2.4% per unit of global-mean surface-air-temperature change in the AOGCMs. However, when carbon dioxide levels are increasing, precipitation increases at a smaller rate of similar to 1.5% per unit of global-mean surface-air-temperature change. This difference can be understood by decomposing the precipitation response into an increase from the response to the global surface-temperature increase (and the climate feedbacks it induces), and a fast atmospheric response to the carbon dioxide radiative forcing that acts to decrease precipitation. According to the multi-model mean, stabilizing atmospheric levels of carbon dioxide would lead to a greater rate of precipitation change per unit of global surface-temperature change

    Fetomaternal outcome in women with hemolysis, elevated liver enzymes and low platelet count syndrome: a retrospective study

    Get PDF
    Background: HELLP (hemolysis, elevated liver enzymes and low platelet count) syndrome which is a variant form of severe preeclampsia is an important cause of maternal and fetal mortality and morbidity. The importance lies in the early diagnosis and timely intervention for better fetal and maternal outcome. The objective of this study was to assess the maternal and fetal outcome in pregnancies complicated with HELLP syndrome.Methods: This is a retrospective study analyzing fetomaternal outcome in 63 women diagnosed with HELLP syndrome in the department of obstetrics and gynecology, Government Medical College, Thrissur from 1st January 2014 to 31st December 2016. Details were collected from data records library.Results: Among 7,566 deliveries, 63 women (0.83%) had HELLP syndrome. Mean age was 29.5 years. 47.6% (n=30) women developed HELLP syndrome at gestational age less than 34 weeks. Maternal complications were abruption (27.78%), acute kidney injury (16.67%), DIC (16.67%), sepsis (11.11%) and postpartum hemorrhage (11.11%). In this study, HELLP syndrome lead to one maternal death (1.58%). The perinatal mortality was 25.75%.Conclusions: HELLP syndrome is an alarming complication, which brings high maternal and perinatal morbidity and mortality

    Real-world comparison of probe vehicle emissions and fuel consumption using diesel and 5 % biodiesel (B5) blend.

    Get PDF
    An instrumented EURO I Ford Mondeo was used to perform a real-world comparison of vehicle exhaust (carbon dioxide, carbon monoxide, hydrocarbons and oxides of nitrogen) emissions and fuel consumption for diesel and 5% biodiesel in diesel blend (B5) fuels. Data were collected on multiple replicates of three standardised on-road journeys: (1) A simple urban route; (2) A combined urban/inter-urban route; and, (3) An urban route subject to significant traffic management. At the total journey measurement level, data collected here indicate that replacing diesel with a B5 substitute could result in significant increases in both NOx emissions (8-13%) and fuel consumption (7-8%). However, statistical analysis of probe vehicle data demonstrated the limitations of comparisons based on such total journey measurements, i.e., methods analogous to those used in conventional dynamometer/drive cycle fuel comparison studies. Here, methods based on the comparison of speed/acceleration emissions and fuel consumption maps are presented. Significant variations across the speed/acceleration surface indicated that direct emission and fuel consumption impacts were highly dependent on the journey/drive cycle employed. The emission and fuel consumption maps were used both as descriptive tools to characterise impacts and predictive tools to estimate journey-specific emission and fuel consumption effects
    corecore