Can dust coagulation trigger streaming instability?

Streaming instability can be a very efficient way of overcoming growth and drift barriers to planetesimal formation. However, it was shown that strong clumping, which leads to planetesimal formation, requires a considerable number of large grains. State-of-the-art streaming instability models do not take into account realistic size distributions resulting from the collisional evolution of dust. We investigate whether a sufficient quantity of large aggregates can be produced by sticking and what the interplay of dust coagulation and planetesimal formation is. We develop a semi-analytical prescription of planetesimal formation by streaming instability and implement it in our dust coagulation code based on the Monte Carlo algorithm with the representative particles approach. We find that planetesimal formation by streaming instability may preferentially work outside the snow line, where sticky icy aggregates are present. The efficiency of the process depends strongly on local dust abundance and radial pressure gradient, and requires a super-solar metallicity. If planetesimal formation is possible, the dust coagulation and settling typically need ~100 orbits to produce sufficiently large and settled grains and planetesimal formation lasts another ~1000 orbits. We present a simple analytical model that computes the amount of dust that can be turned into planetesimals given the parameters of the disk model.Comment: 12 pages, 6 figures, 1 table, accepted for publication in A&A (minor corrections with respect to v1

Planetesimal formation during protoplanetary disk buildup

Models of dust coagulation and subsequent planetesimal formation are usually computed on the backdrop of an already fully formed protoplanetary disk model. At the same time, observational studies suggest that planetesimal formation should start early, possibly even before the protoplanetary disk is fully formed. In this paper, we investigate under which conditions planetesimals already form during the disk buildup stage, in which gas and dust fall onto the disk from its parent molecular cloud. We couple our earlier planetesimal formation model at the water snow line to a simple model of disk formation and evolution. We find that under most conditions planetesimals only form after the buildup stage when the disk becomes less massive and less hot. However, there are parameters for which planetesimals already form during the disk buildup. This occurs when the viscosity driving the disk evolution is intermediate ($\alpha_v \sim 10^{-3}-10^{-2}$) while the turbulent mixing of the dust is reduced compared to that ($\alpha_t \lesssim 10^{-4}$), and with the assumption that water vapor is vertically well-mixed with the gas. Such $\alpha_t \ll \alpha_v$ scenario could be expected for layered accretion, where the gas flow is mostly driven by the active surface layers, while the midplane layers, where most of the dust resides, are quiescent.Comment: 6 pages, 5 figures, accepted for publication in A&A, minor changes due to language editio

Production of single-domain magnetite throughout life by sockeye salmon, Oncorhynchus nerka

Although single-domain particles of biogenic magnetite have been found in different species of pelagic fishes, nothing is known about when it is synthesized, or about whether the time during life when it is produced is correlated with the development of responses to magnetic field stimuli. We have investigated production of biogenic magnetite suitable for use in magnetoreception in different life stages of the sockeye salmon, Oncorhynchus nerka (Walbaum). Sockeye salmon were chosen because responses in orientation arenas to magnetic field stimuli have been demonstrated in both fry and smolt stages of this species. We found significant quantities of single-domain magnetite in connective tissue from the ethmoid region of the skull of adult (4-year-old) sockeye salmon. The ontogenetic study revealed an orderly increase in the amount of magnetic material in the same region of the skull but not in other tissues of sockeye salmon fry, yearlings and smolts. The physical properties of this material closely matched those of magnetite particles extracted from the ethmoid tissue of the adult fish. We suggest that single-domain magnetite particles suitable for use in magnetoreception are produced throughout life in the ethmoid region of the skull in sockeye salmon. Based on theoretical calculations, we conclude that there are enough particles present in the skulls of the fry to mediate their responses to magnetic field direction. By the smolt stage, the amount of magnetite present in the front of the skull is sufficient to provide the fish with a magnetoreceptor capable of detecting small changes in the intensity of the geomagnetic field. Other tissues of the salmon, such as the eye and skin, often contained ferromagnetic material, although the magnetizations of these tissues were usually more variable than in the ethmoid tissue. These deposits of unidentified magnetic material, some of which may be magnetite, appear almost exclusively in adults and so would not be useful in magnetoreception by young fish. We suggest that tissue from within the ethmoid region of the skull in pelagic fishes is the only site yet identified where magnetite suitable for use in magnetoreception is concentrated

A tunnel and a traffic jam: How transition disks maintain a detectable warm dust component despite the presence of a large planet-carved gap

We combined hydrodynamical simulations of planet-disk interactions with dust evolution models that include coagulation and fragmentation of dust grains over a large range of radii and derived observational properties using radiative transfer calculations. We studied the role of the snow line in the survival of the inner disk of transition disks. Inside the snow line, the lack of ice mantles in dust particles decreases the sticking efficiency between grains. As a consequence, particles fragment at lower collision velocities than in regions beyond the snow line. This effect allows small particles to be maintained for up to a few Myrs within the first astronomical unit. These particles are closely coupled to the gas and do not drift significantly with respect to the gas. For lower mass planets (1$M_{\rm{Jup}}$), the pre-transition appearance can be maintained even longer because dust still trickles through the gap created by the planet, moves invisibly and quickly in the form of relatively large grains through the gap, and becomes visible again as it fragments and gets slowed down inside of the snow line. The global study of dust evolution of a disk with an embedded planet, including the changes of the dust aerodynamics near the snow line, can explain the concentration of millimetre-sized particles in the outer disk and the survival of the dust in the inner disk if a large dust trap is present in the outer disk. This behaviour solves the conundrum of the combination of both near-infrared excess and ring-like millimetre emission observed in several transition disks.Comment: Accepted for publication in A&A (including acknowledgments

ESTIMATION OF SOIL EROSION TIME PATHS: THE VALUE OF SOIL MOISTURE AND TOPSOIL DEPTH INFORMATION

Rates of soil erosion in the dryland cropping region of Saskatchewan are investigated under alternative cropping strategies. Chemical fallow is examined as an alternative to tillage fallow for moisture and soil conservation. Conclusions include: (a) flexible cropping increases net discounted returns and substantially reduced soil erosion compared to the predominant crop rotation; (b) chemical fallow is a viable alternative to tillage fallow but only when topsoil already has been eroded substantially; and (c) an increase in the discount rate is soil conserving, since it causes producers to plant more often rather than fallow.Land Economics/Use,

Komnas HAM dan HAM di Bawah Rejim Otoritarian

Pada saat pernbentukannya, Komnas HAM dipandang tidak berbeda dengan lembaga korparads negara Iainnya, yakni menjadi agen pemerintah untuk para anggotanya. khususnya para aktivis HAM dan meted tuntutan penegakkan HAM di Indonesia yang saat itu terus menguat. Melalui tulisan ini ditunjukkan bahwa Komnas HAM mampu mandiri dari penetrasi pernerintah, dan bersikap kritis terhadap pernerintah dalam kasus politik yang sangat senskif sekalipun. Sumbangan energi untuk membangun kemandirian tersebut terutama terletak pada komitmen dan kredibilitas individu anggota Komnas HAM, variasi keahlian dan akses, serta kemampuan untuk mengembangkan etika organisasi yang kondusif bagi pelaksanaan togas penegakkan HAM Namun demikian, penulis berargumentasi bahwa demi menjaga komitmen dan kemandinan lembaga, Komnas HAM menghadapi beberapa permasalahan serius yang harus segera ditangani. Pertama, menyangkut status hukum lembaga itu. Kedua, menyangkut sumber energi yang selama ini masih menekankan pada kapasitas individual Ketiga, menyangkut perlunya pengembangan mekanisme rekrutmen anggota baru yang lebih terbuka di mana opini publik Baru terhamba

Modeling and Compensation of Nonlinear Distortion in Horn Loudspeakers

Horn loaded compression drivers are widely used in the area where high sound pressure levels together with good directivity characteristics are needed. Major disadvantage of this kind of drivers is the considerable amount of nonlinear distortion. Due to the quite high air pressures in the driver the air is driven into its nonlinear range. This paper describes a technique to reduce the distortion caused by this phenomenon. Using a Digital Signal Processor (DSP), a feedforward compensation technique, based on an equivalent lumped parameter circuit, is implemented and tested in real–time in series with the loudspeaker. Measurement and simulation results are given. The overall conclusion is that a distortion reduction is obtained in the frequency span from 600 to 1050 Hz