440 research outputs found
Early evolution of clumps formed via gravitational instability in protoplanetary disks; precursors of Hot Jupiters?
Although it is fairly established that Gravitational Instability (GI) should
occur in the early phases of the evolution of a protoplanetary disk, the fate
of the clumps resulting from disk fragmentation and their role in planet
formation is still unclear. In the present study we investigate
semi-analytically their evolution following the contraction of a synthetic
population of clumps with varied initial structure and orbits coupled with the
surrounding disk and the central star. Our model is based on recently published
state-of-the-art 3D collapse simulations of clumps with varied thermodynamics.
Various evolutionary mechanisms are taken into account, and their effect is
explored both individually and in combination with others: migration and tidal
disruption, mass accretion, gap opening and disk viscosity. It is found that,
in general, at least 50% of the initial clumps survive tides, leaving behind
potential gas giant progenitors after ~10^5 yr of evolution in the disk. The
rest might be either disrupted or produce super-Earths and other low mass
planets provided that a solid core can be assembled on a sufficiently short
timescale, a possibility that we do not address in this paper. Extrapolating to
million year timescales, all our surviving protoplanets would lead to close-in
gas giants. This outcome might in part reflect the limitations of the migration
model adopted, and is reminiscent of the analogous result found in
core-accretion models in absence of fine-tuning of the migration rate. Yet it
suggests that a significant fraction of the clumps formed by gravitational
instability could be the precursors of Hot Jupiters
Depth-First: Walking the Web of Chemical Information
U radu je prikazana mrežna stranica Depth-First (http://depth-first.com) koja sadrži članke o kemijskim alatima i softverima, online informacijskim izvorima i općenitijim aktualnim temama iz područja kemije. Detaljnije je prikazan članak o 32 besplatne kemijske baze podataka na dostupne na internetu
Baze podataka Europske unije za kemičare
Portal EnterEurope (www.entereurope.hr) projekt je Europskoga
dokumentacijskog centra (EDC, http://www.imo.hr/edc) pokrenut
krajem 2004. godine s ciljem ostvarivanja jednostavnijeg pristupa
informacijama o EU dostupnima na Internetu. EDC djeluje u sklopu
Instituta za meðunarodne odnose (http://www.imo.hr) u Zagrebu.
EnterEurope namijenjen je prvenstveno akademskoj i istraÞivaèkoj
zajednici, zaposlenima u državnoj upravi, ali i svoj zainteresiranoj
javnosti
Kemijski sadržaji na hrvatskom internetu
U radu su prikazane hrvatske internetske stranice sadržajno vezane za kemiju (poslužitelji, časopisi, strukovne udruge, referentna literatura, obrazovni sadržaji...)
American Elements
U radu su opisane mrežne stranice American Elements, tvrtke koja se bavi proizvodnjom i prodajom umjetnih materijala. Mrežne su stranice koristan i pregledan izvor informacija o kemijskim elementima i spojevima, svojim proizvodima te novostima i zanimljivostima iz nekoliko vezanih odabranih tema
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