Sexual experiences among multicultural adolescents in Korea: evidence from the Korean Youth's Risk Behavior Survey.

Several studies have examined adolescent sexual behaviors by family immigration status, but most of these failed to account for heterogeneity within youths' multicultural backgrounds. To fill this gap in the literature, this paper draws data from the 2011 to 2022 rounds of the Korean Youth's Risk Behavior Survey (N = 769,160) and compares the likelihood of sexual intercourse across four groups of adolescents. Results from logistic regression indicate that the odds of having sexual contact increased 2.8 times for youths with a non-Korean father and Korean mother, compared with those from families with two Korean parents. When both father and mother are foreign-born, the odds of being sexually active increased 4.7 times. In both cases, the discrepancies might be primarily associated with the foreign fathers' lack of socioeconomic resources. Therefore, the father's role deserves more examination, and sex education in schools should be tailored to reflect multicultural adolescents' needs.

Reductive dechlorination of DNAPL mixtures with Fe(II/III)-L and Fe(II)-C: Evaluation using a kinetic model for the competitions.

A kinetic model for the competitions was applied to understand the reductive dechlorination of tertiary DNAPL mixtures containing PCE, TCE, and 1,1,1-TCA. The model assumed that the mass transfer rates were sufficiently rapid that the target compounds in the solution and the DNAPL mixture were in phase equilibrium. Dechlorination was achieved using either a mixture of Fe(II), Fe(III), and Ca(OH)2 (Fe(II/III)-L) or a mixture of Fe(II) and Portland cement (Fe(II)-C). PCE in the DNAPL mixtures was gradually reduced and it was reduced more rapidly using Fe(II)-C than Fe(II/III)-L. A constant total TCE concentration in the DNAPL mixtures was observed, which implied that the rate of loss of TCE by dechlorination and possibly other processes was equal to the rate of production of TCE by PCE dechlorination. On the other hand, 1,1,1-TCA in the DNAPL mixtures was removed rapidly and its degradation rate by Fe(II/III)-L was faster than by Fe(II)-C. The coefficients in the kinetic model (ki, Ki) were observed to decrease in the order 1,1,1-TCA>PCE>TCE, for both Fe(II/III)-L and Fe(II)-C. The concentrations of target compounds in solution were the effective solubilities, because of the assumption of phase equilibrium and were calculated with Rault's Law. The concentration changes observed were an increase and then a decrease for PCE, a sharp and then gradual increase for TCE, and a dramatic decrease for 1,1,1-TCA. The fraction of initial and theoretical reductive capacity revealed that Fe(II)-C had ability to degrade target compounds.

Continuous recovery of valine in a model mixture of amino acids and salt from Corynebacterium bacteria fermentation using a simulated moving bed chromatography.

The economical efficiency of valine production in related industries is largely affected by the performance of a valine separation process, in which valine is to be separated from leucine, alanine, and ammonium sulfate. Such separation is currently handled by a batch-mode hybrid process based on ion-exchange and crystallization schemes. To make a substantial improvement in the economical efficiency of an industrial valine production, such a batch-mode process based on two different separation schemes needs to be converted into a continuous-mode separation process based on a single separation scheme. To address this issue, a simulated moving bed (SMB) technology was applied in this study to the development of a continuous-mode valine-separation chromatographic process with uniformity in adsorbent and liquid phases. It was first found that a Chromalite-PCG600C resin could be eligible for the adsorbent of such process, particularly in an industrial scale. The intrinsic parameters of each component on the Chromalite-PCG600C adsorbent were determined and then utilized in selecting a proper set of configurations for SMB units, columns, and ports, under which the SMB operating parameters were optimized with a genetic algorithm. Finally, the optimized SMB based on the selected configurations was tested experimentally, which confirmed its effectiveness in continuous separation of valine from leucine, alanine, ammonium sulfate with high purity, high yield, high throughput, and high valine product concentration. It is thus expected that the developed SMB process in this study will be able to serve as one of the trustworthy ways of improving the economical efficiency of an industrial valine production process.

Development of a four-zone carousel process packed with metal ion-imprinted polymer for continuous separation of copper ions from manganese ions, cobalt ions, and the constituent metal ions of the buffer solution used as eluent.

A three-zone carousel process, in which Cu(II)-imprinted polymer (Cu-MIP) and a buffer solution were employed as adsorbent and eluent respectively, has been developed previously for continuous separation of Cu²âº (product) from Mn²âº and Co²âº (impurities). Although this process was reported to be successful in the aforementioned separation task, the way of using a buffer solution as eluent made it inevitable that the product stream included the buffer-related metal ions (i.e., the constituent metal ions of the buffer solution) as well as copper ions. For a more perfect recovery of copper ions, it would be necessary to improve the previous carousel process such that it can remove the buffer-related metal ions from copper ions while maintaining the previous function of separating copper ions from the other 2 impure heavy-metal ions. This improvement was made in this study by proposing a four-zone carousel process based on the following strategy: (1) the addition of one more zone for performing the two-step re-equilibration tasks and (2) the use of water as the eluent of the washing step in the separation zone. The operating conditions of such a proposed process were determined on the basis of the data from a series of single-column experiments. Under the determined operating conditions, 3 runs of carousel experiments were carried out. The results of these experiments revealed that the feed-loading time was a key parameter affecting the performance of the proposed process. Consequently, the continuous separation of copper ions from both the impure heavy-metal ions and the buffer-related metal ions could be achieved with a purity of 91.9% and a yield of 92.8% by using the proposed carousel process based on a properly chosen feed-loading time.

Determination of chromatographic separation parameters of tryptophan enantiomers on a Chirosil-SCA chiral stationary phase by using the inverse method based on the initial guesses estimated from elution by characteristic point method.

An effective chiral stationary phase (CSP) for enantioseparation of amino acids was established previously by bonding (18-crown-6)-2, 3, 11, 12-tetracarboxylic acid to silica gel. This CSP has recently been commercialized under the name of Chirosil-SCA. As a first step for developing a Chirosil-SCA simulated moving bed chromatographic process for separation of tryptophan enantiomers, the adsorption isotherm and mass-transfer parameters of each tryptophan enantiomer on the Chirosil-SCA CSP were determined in this study while using only water as a mobile phase. For this task, inverse method (IM) was applied on the basis of the initial guesses estimated from elution by characteristic point (ECP) method, which was found to be more advantageous in the aspects of both accuracy and computational efficiency than the case of utilizing individually only IM or ECP method. The results revealed that the adsorption behavior of each tryptophan enantiomer on the Chirosil-SCA could be well described by the Langmuir-Freundlich isotherm. The model predictions based on the determined parameter values were in close agreement with the experimental chromatograms from a series of single-component or mixture pulse tests that were performed under various feed concentrations and flow rates. It was also found that the Langmuir-Freundlich isotherm parameters of each enantiomer were largely affected by temperature. Such a marked dependence of the parameters on temperature was investigated quantitatively. The results of such an investigation indicated that as the temperature decreases, the adsorption affinities of both enantiomers become higher and the heterogeneity of the Chirosil-SCA becomes more pronounced.

Continuous separation of copper ions from a mixture of heavy metal ions using a three-zone carousel process packed with metal ion-imprinted polymer.

In this study, a three-zone carousel process based on a proper molecular imprinted polymer (MIP) resin was developed for continuous separation of Cu(2+) from Mn(2+) and Co(2+). For this task, the Cu (II)-imprinted polymer (Cu-MIP) resin was synthesized first and used to pack the chromatographic columns of a three-zone carousel process. Prior to the experiment of the carousel process based on the Cu-MIP resin (MIP-carousel process), a series of single-column experiments were performed to estimate the intrinsic parameters of the three heavy metal ions and to find out the appropriate conditions of regeneration and re-equilibration. The results from these single-column experiments and the additional computer simulations were then used for determination of the operating parameters of the MIP-carousel process under consideration. Based on the determined operating parameters, the MIP-carousel experiments were carried out. It was confirmed from the experimental results that the proposed MIP-carousel process was markedly effective in separating Cu(2+) from Mn(2+) and Co(2+) in a continuous mode with high purity and a relatively small loss. Thus, the MIP-carousel process developed in this study deserves sufficient attention in materials processing industries or metal-related industries, where the selective separation of heavy metal ions with the same charge has been a major concern.