Constraints on the height of the inner disk rim in pre-main-sequence stars

The structure of inner region of protoplanetary disks around young pre-main-sequence stars is still poorly understood. This part of the disk is shaped by various forces that influence dust and gas dynamics, and by dust sublimation, which creates abrupt drops in the dust density. This region also emits strong near-infrared excess that cannot be explained by classical accretion disk models, which suggests the existence of some unusual dust distribution or disk shape. The most prevalent explanation to date is the puffed-up inner disk rim model, where the disk exhibits an optically thin cavity around the star up to the distance of dust sublimation. The critical parameter in this model is the inner disk rim height $z_{\rm max}$ relative to the rim distance from the star $R_{\rm in}$. Observations often require $z_{\rm max}/R_{\rm in}\gtrsim0.2$ to reproduce the near-infrared excess in the spectra. We compile a comprehensive list of processes that can shape the inner disk rim and combine them into a self-consistent model. Two of them, radiation pressure force and the gas velocity profile, have never been applied in this context before. The aim was to find the most plausible theoretical values of $z_{\rm max}/R_{\rm in}$. The results show that this value is $\lesssim$0.13 for Herbig Ae stars, $\lesssim$0.11 for T Tau stars, and $\lesssim$0.10 for young brown dwarfs. This is lower than the observational requirements for Herbig Ae stars. We argue that the same problem exists in T Tau stars as well. We conclude that the puffed-up inner rim model cannot be the sole explanation for the near-infrared excess in young pre-main-sequence stars.Comment: Research Note, accepted in Astronomy and Astrophysic

Temperature inversion on the surface of externally heated optically thick multigrain dust clouds

It was recently discovered that the temperature in the surface layer of externally heated optically thick gray dust clouds increases with the optical depth for some distance from the surface, as opposed to the normal decrease in temperature with distance in the rest of the cloud. This temperature inversion is a result of efficient absorption of diffuse flux from the cloud interior by the surface dust exposed to the external radiation. A micron or bigger size grains experience this effect when the external flux is of stellar spectrum. We explore what happens to the effect when dust is a mixture of grain sizes (multigrain). Two possible boundary conditions are considered: i) a constant external flux without constrains on the dust temperature, and ii) the maximum dust temperature set to the sublimation temperature. We find that the first condition allows small grains to completely suppress the temperature inversion of big grains if the overall opacity is dominated by small grains. The second condition enables big grains to maintain the inversion even when they are a minor contributor to the opacity. In reality, the choice of boundary condition depends on the dust dynamics. When applied to the physics of protoplanetary disks, the temperature inversion leads to a previously unrecognized disk structure where optically thin dust can exist inside the dust destruction radius of an optically thick disk. We conclude that the transition between the dusty disk and the gaseous inner clearing is not a sharp edge, but rather a large optically thin region.Comment: 8 pages, 10 figures, Accepted for publication in the Astrophysical Journa

Chemistry of 1,3-Dioxepins. XIV.1 Structural Studies of 4,7-Dihydro-(4,7-dihydro-1,3-dioxepin-2-yl)-1,3-dioxepin and Their Metal Complexes

The coordination properties and conformational behaviour of 4,7- dihydro-(4,7-dihydro-1,3-dioxepin-2-yl)-1,3-dioxepin 1, bis-(1,3-dioxepin), or C10H14O4 have been investigated. The crystal and molecular structures of bis-(1,3-dioxepin) (1), bis-(1,3-dioxepin) lithiumperchlorate (2:1) (2) and bis-(1,3-dioxepin) sodium-perchlorate (1:1) (3) complexes, as well as bis-(1,3-dioxepin) hexsaaquamagnesiumperchlorate (3:1) chlatrate (4), have been determined by X-ray diffraction. The molecule of bis-(1,3-dioxepin) is a bidentate ligand in mononuclear lithium complex 2, in contrast to its bridging mode in 2D polymeric sodium complex 3. The coordination environment around lithium in 2 is distorted octahedral with C2 symmetry, while around sodium in 3 it is quasi-pentagonal bipyramidal. Out of four possible conformations of bis-(1,3-dioxepin) molecule, twist-boattwist- boat centrosymmetric (tb-tb-c), twist-boat-twist-boat non-centrosymmetric (tb-tb), twist-boat-chair (tb-ch) and chair-chair (ch-ch), three have been found in the investigated crystal structures: ch-ch in 1, tb-tb in 2 and tb-tb-c in 3 and 4

Integral scales in the surface atmospheric boundary layer for Bora flows

Mnogi numerički i klimatski modeli za prognozu vremena koriste prognostički oblik jednadžbe turbulentne kinetičke energije (TKE). Mjera disipacije TKE se parametrizira odgovarajućim omjerom TKE i takozvanom integralnom skalom duljine, što je otežano određenim numeričkim koeficijentom. U znanstvenoj zajednici ne postoji dogovor o jedinstvenoj formulaciji takve integralne skale. Stoga, u literaturi nalazimo različite oblike integralne skale. Međutim, one se najčešće izvode iz autokorelacijske funkcije i Fourierovog spektra komponenti brzine vjetra. To su, takozvane skale 1/e i skala prelaska nule te skala za koju normalizirani Fourierov spektar postiže maksimum. Cilj ovog rada je procjena integralne skale turbulencije i pripadnog numeričkog koeficijenta, po prvi put, za buru. Za analizu koristimo podatke prikupljene „WindMaster“ ultrasoničnim anemometrima na visinama 2, 5 i 10 m, u neposrednoj blizini novog Masleničkog mosta, s čestinom uzrokovanja od 20 Hz. U razdoblju od 09. listopada 2015. do 09. listopada 2016. godine izdvojeno je 48 epizoda bura u trajanju od otprilike 1206 sati. Tako veliki set podataka nam omogućava procjenu navedene integralne skale i numeričkog koeficijenta u svrhu testiranja parametrizacije TKE i disipacije TKE u prizemnom sloju za buru. Takozvana skala 1/e se pokazala najboljom za procjenu integralne skale turbulencije za buru. U konačnici, na temelju analiziranih podataka uočeno je znatno odstupanje numeričkog koeficijenta za buru u odnosu na vrijednosti korištenih u znanstvenoj zajednici, koje predlažu npr. Cuxart i sur. (2006), to nam ostavlja prostora za daljnja detaljnija istraživanja u budućnosti.Many NWP and climate models use prognostic turbulence kinetic energy (TKE) equation. TKE dissipation ratio is parameterized via suitable ratio of TKE and so-called integral length scale for turbulence, which is weighted by a certain numerical coefficient. The scientific community does not have unique agreement on formulation of integral turbulence scales. Therefore, in literature we find various forms of those integral scales. However, usually they are derived from autocorrelation functions and Fourier spectra of wind speed components. These are the so-called 1/e and zero crossing scales and the scale at which a normalized Fourier spectra achieve their maximum value. The aim of this study is to evaluate integral turbulence scales and the related coefficient, for the first time for bora flows. For the analysis we used dana collected with „WindMaster“ ultrasonic anemometers at heights 2, 5 and 10 m, close to new Maslenica bridge, with a frequency sampling of 20 Hz. In the period from 09 October 2015 to 09 October 2016 recorded were 48 bora events with cumulative duration of 1206 hours. Such a large dataset gives us an opportunity to evaluate integral turbulence scales and the related numerical coefficient to test the parametrization of the TKE dissipation rate for the atmospheric surface boundary layer in bora flows. So-called 1/e scale proved to be the best estimate for the integral turbulence scale. At the end, based on the analyzed dataset, it has been observed a significant disagreement of the numerical coefficient for bora flows compared with values used in the literature, proposed by e.g. Cuxart et al. (2006). This leaves us space for further studies in future

Suvremeni trendovi u upravljanju proizvodnjom

U radu su analizirani suvremeni trendovi u proizvodnji. Najprije se govorilo o proizvodnom menadžmentu, proizvodnji i proizvodnim procesima. Izabrana je jedna tvrtka i njezin proizvodni proces te je na osnovu tog procesa izrađen dijagram tijeka i gantogram. Nakon analize, data su i moguća poboljšanja procesa. Predložena su poboljšanja na način da se uvede smjenski rad i da se poveća serija proizvoda. Na taj način bi se opisivani proizvodni proces mogao uvelike poboljšati

Milking hygiene

Higijena je veoma važan čimbenik uspješne proizvodnje mlijeka. Poznato je da količina i kakvoća mlijeka ovise o zdravlju mliječne žlijezde. Zbog toga se provode razni postupci čišćenja i dezinfekcije u svrhu smanjenja onečišćenja vimena, a s tim u vezi i higijene u staji, higijene pribora i prostora za mužnju te čistoće ruku muzača. Veoma značajan čimbenik u provođenju ovih mjera je educirani stočar (farmer) koji treba sustavno provoditi sve nove postupke i mjere koje nalaže struka. Samo će se na taj način doseći traženu razinu kakvoće svježeg mlijeka i zadovoljiti uvjete Pravilnika o kakvoći svježeg sirovog mlijeka (NN 102/2000.).Hygiene is a very important factor for successful milk production. It is known that the quantity and quality of milk depend on the health of the milk gland. Various techniques for cleaning and disinfection exist to reduce dirt and contamination of the udder, and to keep the hygiene of the cowshed, utensils and the milking area as well as to keep the hands of the milker clean. A very important factor in carrying out these measures is the trained farmer who must systematically follow all the new procedures and measures dictated by the profession. Only thus the required quality of fresh milk will be achieved and the conditions in the Regulations on raw fresh milk quality will be satisfied. (NN 102/200O)

Korištenje i prednosti Profinet komunikacijskog protokola u industriji

In complex industrial production processes it is necessary to introduce automation system with special consideration to process supervision. High number of automation devices in system will require great resources in quantity and speed of data transfer. The protocols such as Profibus or similar obviously will not satisfy all demands of these production processes since the high number of devices are used. The possibilities of combining standard methods of communication with industrial protocols are available by introducing the devices for supervision and eventually process management placed outside the industrial plant, such as engineers or plant manager offices, etc. One of the most popular such protocols are Profinet which uses Ethernet standard for industrial purposes, and is described in this paper.U složenim industrijskim procesima proizvodnje potrebno je ugraditi sustav automatizacije sa posebnim naglaskom na nadzor procesa. Veliki broj uređaja u automatizacijskom sustavu traži velike resurse u količini i brzini protoka podataka unutar sustava. Ukoliko se radi o velikom broju uređaja protokoli kao što su Profibus i slični očito ne mogu zadovoljiti sve potrebe takvog pogona. Uvođenje uređaja za nadzor i eventualno upravljanje pogonom u prostore koji nisu nužno vezani za samu proizvodnju, kao što su uredi inženjera, voditelja pogona, i slično, otvara se mogućnost kombinacije standardnih metoda komunikacije sa industrijskim protokolima. Jedan od najprihvaćenijih je Profinet koji koristi Ethernet standard u industrijske svrhe, i opisan je u ovom radu

Obrazovne asimetrije u nastajanju: natjecanja učenika kao indikatori ekonomskog razvoja

Croatia does not score well in the human development index, rate of employment, or development of the high tech sector – to mention only a few indicators that hinder good prospects for improvement. Also, Croatian high school students are at the bottom of European rankings on performance in science and mathematics and their interest in career in science is declining. Croatia needs more educated people, especially in the area of science and technology, and this can be achieved only if the youth become interested in science at an early age. Thus, science fair competitions are of an utmost importance for development of Croatia. This paper aims at investigating a relation of the Croatian counties’ development index and their students’ participation rates in the science fair competitions. This is done by including two development indexes in search for the relation with the counties’ participation rates in biology, chemistry, physics and mathematics competition, and with a reference to a previous research on astronomy competition. As is revealed, there is a growing trend of interconnection of the development index and participation rates at science competitions in all disciplines.Hrvatska ne stoji dobro na ljestvici indeksa razvijenosti, stope zaposlenosti, razvoja visokotehnološkog sektora, što su samo neki od indikatora koji ne daju perspektivu promjene na bolje. Također, hrvatski srednjoškolci su na dnu ljestvice u Europi po rezultatima na testovima znanosti, a opada i njihov interes za karijeru u znanosti. Hrvatska treba više obrazovanih ljudi, posebice u području znanosti i tehnologije, što se može postići jedino ukoliko se mlade u najranijoj dobi zainteresira za znanost. Stoga su natjecanja u pojedinim znanstvenim disciplinama od presudne važnosti za razvoj Hrvatske. Ovaj članak cilja ka istraživanju povezanosti indeksa razvijenosti županija sa stopom sudjelovanja učenika na natjecanjima. Navedeno će se postići uključenjem dvaju indeksa razvijenosti u traženje povezanosti sa stopama sudjelovanja u natjecanjima iz biologije, kemije, fizike i matematike, uz pregled prethodnog istraživanja za natjecanje iz astronomije. Kao što će se pokazati, postoji rastući trend međusobne povezanosti indeksa razvijenosti i stopa sudjelovanja učenika na natjecanjima po svim disciplinama