arXiv subjects

Seyit Hocuk

Publications and source records attributed to Seyit Hocuk.

6 recordsLinked to original sources

arXiv2024

Combining the Strengths of Dutch Survey and Register Data in a Data Challenge to Predict Fertility (PreFer)

The social sciences have produced an impressive body of research on determinants of fertility outcomes, or whether and when people have children. However, the strength of these determinants and underlying theories are rarely evaluated on their predictive ability on new data. This prevents us from systematically comparing studies, hindering the evaluation and accumulation of knowledge. In this paper, we present two datasets which can be used to study the predictability of fertility outcomes in the Netherlands. One dataset is based on the LISS panel, a longitudinal survey which includes thousands of variables on a wide range of topics, including individual preferences and values. The other is based on the Dutch register data which lacks attitudinal data but includes detailed information about the life courses of millions of Dutch residents. We provide information about the datasets and the samples, and describe the fertility outcome of interest. We also introduce the fertility prediction data challenge PreFer which is based on these datasets and will start in Spring 2024. We outline the ways in which measuring the predictability of fertility outcomes using these datasets and combining their strengths in the data challenge can advance our understanding of fertility behaviour and computational social science. We further provide details for participants on how to take part in the data challenge.

cs.LG↗

arXiv2022

The Cosmic-Ray Induced Sputtering Process On Icy Grains

In molecular cloud cores, the cosmic ray (CR) induced sputtering via CR ion-icy grain collision is one of the desorption processes for ice molecules from mantles around dust grains. The efficiency of this process depends on the incident CR ion properties as well as the physicochemical character of the ice mantle. Our main objective is the examination of the sputtering efficiency for H$_2$O and CO ices found in molecular cloud cores. In the calculation routine, we consider a multi-dimensional parameter space that consists of thirty CR ion types, five different CR ion energy flux distributions, two separate ice mantle components (pure H$_2$O and CO), three ice formation states, and two sputtering regimes (linear and quadratic). We find that the sputtering behavior of H$_2$O and CO ices is dominated by the quadratic regime rather than the linear regime, especially for CO sputtering. The sputtering rate coefficients for H$_2$O and CO ices show distinct variations with respect to the adopted CR ion energy flux as well as the grain size-dependent mantle depth. The maximum radius of the cylindrical latent region is quite sensitive to the effective electronic stopping power. The track radii for CO ice are much bigger than H$_2$O ice values. In contrast to the H$_2$O mantle, even relatively light CR ions ($Z \geq 4$) may lead to a track formation within the CO mantle, depending on ${\rm S_{\rm e,eff}}$. We suggest that the latent track formation threshold can be assumed as a separator between the linear and the quadratic regimes for sputtering.

astro-ph.EP↗

arXiv2019

Dust temperature and time-dependent effects in the chemistry of photodissociation regions

When studying the chemistry of PDRs, time dependence becomes important as visual extinction increases, since certain chemical timescales are comparable to the cloud lifetime. Dust temperature is also a key factor, since it significantly influences gas temperature and mobility on dust grains, determining the chemistry occurring on grain surfaces. We present a study of the dust temperature impact and time effects on the chemistry of different PDRs, using an updated version of the Meijerink PDR code and combining it with the time-dependent code Nahoon. We find the largest temperature effects in the inner regions of high $G$$_{\mathrm{0}}$ PDRs, where high dust temperatures favour the formation of simple oxygen-bearing molecules (especially that of O$_2$), while the formation of complex organic molecules is much more efficient at low dust temperatures. We also find that time-dependent effects strongly depend on the PDR type, since long timescales promote the destruction of oxygen-bearing molecules in the inner parts of low $G$$_{\mathrm{0}}$ PDRs, while favouring their formation and that of carbon-bearing molecules in high $G$$_{\mathrm{0}}$ PDRs. From the chemical evolution, we also conclude that, in dense PDRs, CO$_2$ is a late-forming ice compared to water ice, and confirm a layered ice structure on dust grains, with H$_2$O in lower layers than CO$_2$. Regarding steady state, the PDR edge reaches chemical equilibrium at early times ($\lesssim$10$^5$ yr). This time is even shorter ($<$10$^4$ yr) for high $G$$_{\mathrm{0}}$ PDRs. By contrast, inner regions reach equilibrium much later, especially low $G$$_{\mathrm{0}}$ PDRs, where steady state is reached at $\sim$10$^6$-10$^7$ yr.

astro-ph.GA↗

arXiv2017

The first frost in the Pipe Nebula

Spectroscopic studies of ices in nearby star-forming regions indicate that ice mantles form on dust grains in two distinct steps, starting with polar ice formation (H2O rich) and switching to apolar ice (CO rich). We test how well the picture applies to more diffuse and quiescent clouds where the formation of the first layers of ice mantles can be witnessed. Medium-resolution near-infrared spectra are obtained toward background field stars behind the Pipe Nebula. The water ice absorption is positively detected at 3.0 micron in seven lines of sight out of 21 sources for which observed spectra are successfully reduced. The peak optical depth of the water ice is significantly lower than those in Taurus with the same visual extinction. The source with the highest water-ice optical depth shows CO ice absorption at 4.7 micron as well. The fractional abundance of CO ice with respect to water ice is 16+7-6 %, and about half as much as the values typically seen in low-mass star-forming regions. A small fractional abundance of CO ice is consistent with some of the existing simulations. Observations of CO2 ice in the early diffuse phase of a cloud play a decisive role in understanding the switching mechanism between polar and apolar ice formation.

astro-ph.GA↗

arXiv2016

The role of ices in star-forming clouds

Ices play a critical role during the evolution of interstellar clouds. Their presence is ubiquitous in the dense molecular medium and their impact is not only limited to chemistry. Species adsorbed onto dust grains also affect cloud thermodynamics. It all depends on the interstellar conditions, the chemical parameters, and the composition of ice layers. In this work, I study the formation of ices by focusing on the interplay between gas and solid phase to determine their role on cloud evolution and star formation. I show that while the formation of ices greatly impacts the cloud chemistry, their role on the thermodynamics is more conservative, and their influence on star formation is only marginal.

astro-ph.GA↗

arXiv2010

The impact of metallicity and X-rays on star formation

Star formation is regulated through a variety of feedback processes. In this study, we treat feedback by metal injection and a UV background as well as by X-ray irradiation. Our aim is to investigate whether star formation is significantly affected when the ISM of a proto-galaxxy enjoys different metallicities and when a star forming cloud resides in the vicinity of a strong X-ray source. We perform cosmological Enzo simulations with a detailed treatment of non-zero metallicity chemistry and thermal balance. We also perform FLASH simulations with embedded Lagrangian sink particles of a collapsing molecular cloud near a massive, 10^{7} M\odot, black hole that produces X-ray radiation. We find that a multi-phase ISM forms for metallicites as small as 10^{-4} Solar at z = 6, with higher (10^{-2}Z\odot) metallicities supporting a cold (< 100 K) and dense (> 10^{3} cm^{-3}) phase at higher (z = 20) redshift. A star formation recipe based on the presence of a cold dense phase leads to a self-regulating mode in the presence of supernova and radiation feedback. We also find that when there is strong X-ray feedback a collapsing cloud fragments into larger clumps whereby fewer but more massive protostellar cores are formed. This is a consequence of the higher Jeans mass in the warm (50 K, due to ionization heating) molecular gas. Accretion processes dominate the mass function and a near-flat, non-Salpeter IMF results.

astro-ph.CO↗