The uptake and accumulation of cesium-137 by fishes from sea water was studied through the field studies for eight years (1963-1970). The concentrations of cesium-137 in marine fish muscles have decreased with time since 1963, and the concentration factors ranged from 11 to 81. On the other hand, the concentration factors of stable cesium remained in a narrow range between 34 and 52. The mean value of the observed ratio (OR) calculated by cesium-137 and potassium was 5.7 during the period from 1964 to 1970, and the OR value based on stable cesium was 5.9. The ratios between annual mean values of the specific activities of fish muscles and of sea water were found to be from 0.6 to 1.5.
The disk midplane temperature is potentially affected by the dust traps/rings. The dust depletion beyond the water snowline will cast a shadow. In this study, we adopt a detailed gas-grain chemical reaction network, and investigate the radial gas and ice abundance distributions of dominant carbon-, oxygen-, and nitrogen-bearing molecules in disks with shadow structures beyond the water snowline around a protosolar-like star. In shadowed disks, the dust grains at around $3-8$ au are predicted to have more than around $5-10$ times amounts of ices of organic molecules such as H$_{2}$CO, CH$_{3}$OH, and NH$_{2}$CHO, saturated hydrocarbon ices such as CH$_{4}$ and C$_{2}$H$_{6}$, in addition to H$_{2}$O, CO, CO$_{2}$, NH$_{3}$, N$_{2}$, and HCN ices, compared with those in non-shadowed disks. In the shadowed regions, we find that hydrogenation (especially of CO ice) is the dominant formation mechanism of complex organic molecules. The gas-phase N/O ratios show much larger spatial variations than the gas-phase C/O ratios, thus the N/O ratio is predicted to be a useful tracer of the shadowed region. N$_{2}$H$^{+}$ line emission is a potential tracer of the shadowed region. We conclude that a shadowed region allows the recondensation of key volatiles onto dust grains, provides a region of chemical enrichment of ices that is much closer to the star than within a non-shadowed disk, and may explain to some degree the trapping of O$_{2}$ ice in dust grains that formed comet 67P/Churyumov-Gerasimenko. We discuss that, if formed in a shadowed disk, Jupiter does not need to have migrated vast distances.
Tier 2 Emission standards enacted by the U.S. Environmental Protection Agency (EPA) require substantial emission reductions for new vehicles, including those with diesel engines. The standards are fuel neutral, and all light duty vehicles must eventually meet a fleet averaged emission level of Bin 5. To improve the emission capability for diesel engines, several advanced technologies have been investigated. These technologies include: common rail FIE with multi-injection capability, enhanced cooled EGR system with increased flow capability, variable geometry turbo charger, and a lower compression ratio piston. A new combustion approach using premixed diesel combustion was applied in the low load area for improving NO x and soot emissions significantly in the FTP-75 test cycle. Applying these technologies, engine out NO x was substantially reduced while maintaining similar soot levels . An aftertreatment system with lean NO x trap (LNT) catalysts and a catalyzed soot filter was studied on a demonstration vehicle. The aftertreatment system was prepared for evaluation by thermal aging to useful vehicle life. A regeneration strategy for the LNT has been developed which provides NO x reduction efficiency, while minimizing the fuel penalty and HC slip to the tail pipe. A new combustion approach using premixed diesel combustion was also applied to the rich composition in order to reduce HC slip and soot emission. After aging with a simulated 120kmile aging cycle, this system showed greater than 90% reduction for PM and 60% reduction for NO x emission in the FTP-75 test cycle.
Abstract We perform simulations of the dust and gas disk evolution to investigate the observational features of a dust pileup at the dead-zone inner edge. We show that the total mass of accumulated dust particles is sensitive to the turbulence strength in the dead zone, α dead , because of the combined effect of turbulence-induced particle fragmentation (which suppresses particle radial drift) and turbulent diffusion. For a typical critical fragmentation velocity of silicate dust particles of 1 m s −1 , the stress-to-pressure ratio α dead needs to be lower than 3 × 10 −4 for dust trapping to operate. The obtained dust distribution is postprocessed using the radiative transfer code RADMC-3D to simulate infrared scattered-light images of the inner part of protoplanetary disks with a dust pileup. We find that a dust pileup at the dead-zone inner edge, if present, casts a shadow extending out to ∼10 au. In the shadowed region the temperature significantly drops, which in some cases yields even multiple water snow lines. We also find that even without a dust pileup at the dead-zone inner edge, the disk surface can become thermally unstable, and the excited waves can naturally produce shadows and ring-like structures in observed images. This mechanism might account for the ring-like structures seen in the scattered-light images of some disks, such as the TW Hya disk.
Metropolitan cities in the world have long been suffering from serious air pollution problems. In Tokyo, the high levels of nitrogen oxides and ozone resulting from heavy traffic emission are of the greatest concern. However, the cost and size of the chemical analyzers have limited the number of environmental monitoring stations and, therefore, have resulted in insufficient spatial resolution in the measurement of pollutant distributions. The authors have been proposing a gas distribution analyzing system (GASDAS). The use of gas sensors enables compact and inexpensive sensing systems, and will lead to a significant increase in the density of monitoring sites. As a first step in the development of GASDAS, nitrogen dioxide and ozone monitoring systems have been developed. The experimental results have shown that the low-cost sensor systems with signal compensation features for the change in weather conditions can be used for the quantitative measurement of spatial pollutant distributions.
Midplane heating induced by disk accretion plays a key role in determining the disk temperature particularly at the inner disk midplane where planets form. However, the efficiency of accretion heating has been not well constrained by observations. We construct two-dimensional models of the Class II disk around CW Tau, taking into account the midplane heating. The models are compared with the ALMA dust continuum observations at Bands 4, 6, 7 and 8, with an angular resolution of 0.1 arcsec. The observed brightness temperatures are almost wavelength-indenpendent at $\lesssim$10 au. We find that if the maximum dust size $a_{\rm max}$ is $\lesssim100~{\rm \mu m}$, the brightness temperatures predicted by the model exceed the observed values, regardless of the efficiency of accretion heating. The low observed brightness temperatures can be explained if millimeter scattering reduces the intensity. If the disk is passive, $a_{\rm max}$ needs to be either $\sim150~{\rm \mu m}$ or $\gtrsim$ few ${\rm cm}$. The accretion heating significantly increases the brightness temperature particularly when $a_{\rm max}\lesssim300~{\rm \mu m}$, and hence $a_{\rm max}$ needs to be either $\sim300~{\rm \mu m}$ or $\gtrsim$ few ${\rm cm}$. The midplane temperature is expected to be $\sim$1.5-3 times higher than the observed brightness temperatures, depending on the models. The dust settling effectively increases the temperature of the dust responsible for the millimeter emission in the active disk, which makes the model with $300~{\rm \mu m}$-sized dust overpredicts the brightness temperatures when strong turbulence is absent. Porous dust (porosity of 0.9) makes the accretion heating more efficient so that some sort of reduction in accretion heating is required. Future longer wavelength and higher angular resolution observations will help us constrain the heating mechanisms of the inner protoplanetary disks.
Abstract Recent millimeter and infrared observations have shown that gap- and ring-like structures are common in both dust thermal emission and scattered light of protoplanetary disks. We investigate the impact of the so-called thermal wave instability (TWI) on the millimeter and infrared scattered light images of disks. We perform 1+1D simulations of the TWI and confirm that the TWI operates when the disk is optically thick enough for stellar light, i.e., small-grain-to-gas mass ratio of ≳0.0001. The midplane temperature varies as the waves propagate, and hence gap and ring structures can be seen in both millimeter and infrared emission. The millimeter substructures can be observed even if the disk is fully optically thick since it is induced by the temperature variation, while density-induced substructures would disappear in the optically thick regime. The fractional separation between TWI-induced ring and gap is Δ r / r ∼ 0.2–0.4 at ∼10–50 au, which is comparable to those found by the Atacama Large Millimeter/submillimeter Array. Due to the temperature variation, snow lines of volatile species move radially and multiple snow lines are observed even for a single species. The wave propagation velocity is as fast as ∼0.6 au yr −1 , which can be potentially detected with a multiepoch observation with a time separation of a few years.
Abstract Previous studies of the protoplanetary disk HD 163296 revealed that the morphology of its sub-au infrared emission encompasses the terminal sublimation front of dust grains, referred to as the inner rim, but also extends into the (supposedly) dust-free region within it. Here, we present a set of radiative hydrostatic simulations of the inner rim in order to assess how much the rim alone can contribute to the observed interferometric visibilities V , half-light radii R hl , and fractional disk fluxes F in the wavelength range 1.5–13 μ m. In our set of models, we regulate the cooling efficiency of the disk via the boundary condition for radiation diffusion and we also modify the shape of the sublimation front. We find that when the cooling efficiency is reduced, the infrared photosphere at the rim becomes hotter, leading to an increase in R hl sufficient to match the observations. However, the near-infrared disk flux is typically too low ( F≃0.25 at 1.5 μ m), resulting in H -band visibility curves located above the observed data. We show that the match to the H -band observations up to moderate baselines can be improved when a wall-shaped rather than curved sublimation front is considered. Nevertheless, our model visibilities always exhibit a bounce at long baselines, which is not observed, confirming the need for additional emission interior to the rim. In summary, our study illustrates how the temperature structure and geometry of the inner rim need to change in order to boost the rim’s infrared emission.
