Kim Il-sung University

ABSTRACT This paper presents the feasible direction (FD) method for calculating equilibrium compositions in combustion systems via Gibbs free energy minimization under mass balance constraints. The method was used to calculate the adiabatic flame temperature and the equilibrium composition of combustion products from combustion reactions of two types. The results of the present work are compared with those obtained using the Lagrange multipliers method. The proposed algorithm demonstrated robust convergence at the complicated multicomponent equilibrium calculation involving the condensed products as well as the simple chemical equilibrium problem. In addition, we simulated the equilibrium compositions and thermodynamic properties of combustion products depending on the temperature.

Statement of the problem. Winter concrete construction requires antifreeze admixtures that prevent freezing while maintaining strength development. Conventional nitrite- and chloride-based antifreezes face high costs and corrosion concerns. Industrial by-products like cement kiln dust (CKD) offer potential for sustainable antifreeze production, yet their application in nitrate-sulfate composite systems remains unexplored. A CKD-based nitrate-sulfate composite antifreeze was synthesized by reacting CKD-lime suspension with mixed HNO₃:H₂SO₄ (1:1 ratio) to yield a 40 % solids suspension containing KNO₃, Ca(NO₃)₂, K₂SO₄, CaSO₄, and 0.05 % triethanolamine. Performance was evaluated at three temperature ranges (–4 to –6 °C, –9 to –11 °C, and –14 to –16 °C)against four commercial antifreeze formulations through standardized testing of compressive strength, setting time, water absorption, frost resistance, and outdoor durability. Economic analysis compared production costs with commercial alternatives. Results. At –9 to –11°C, 5—6 % dosage prevented freezing and achieved 28-day strengths of 6.2 MPa, comparable to commercial calcium nitrate-based antifreeze (6.0 MPa) and superior to potassium carbonate-based (5.7 MPa) and calcium chloride-based (5.9 MPa) products. Setting time decreased by 50 %, water absorption reduced by 15 %, and freeze-thaw resistance improved from 28 to 46—47 cycles. Production costs of $95—105 per metric ton represent 78—82 % savings compared to commercial antifreezes ($420—480 per ton), translating to $735 savings per 100 m³ concrete. Conclusions. The CKD-based composite antifreeze demonstrates comparable or superior performance to commercial products while achieving substantial cost reduction through industrial waste valorization. Recommended dosages are 3—5 %, 5—7 %, and 8—10 % by cement weight for –4, –10, and –15 °C environments, respectively.

Background and Aim: Osteoporosis is an important type of metabolic bone disease in chronic cholangiogenic liver disease, with an incidence of up to maximum 72%. Osteoporosis and osteomalacia in patients with chronic liver disease are collectively referred to as "hepatic osteodystrophy," which is commonly found in patients with intestinal malabsorption and progressive primary biliary cirrhosis. To deal with the induction of osteoporosis by chronic cholestasis, we aimed to investigate the following: The aim of the study was to investigate the effect of iron intake on chronic cholestatic osteoporosis by surgical CBD partial ligation. Methods: Forty rats including weanling male rats weighing 70-80 g and adult male rats weighing 150-160 g were used. First, the rats were anesthetized with intraperitoneal ketamine injection, and then the CBD (Common Bile Duct) was exposed by surgical procedures, complete and partial ligation was performed, and then the abdomen was closed. Partial ligation was performed by ligating different thicknesses of the suture needles with the common bile duct and then removing the suture needle. In the case of using suture needle 5-0, 85-90% of the common bile duct is considered to be obstructed and 75-80% for 4-0. After ligation of the common bile duct, naturally proceeding rats were included as contrast group and rats receiving oral administration of 6 mg/ kg/day of folate iron were included as experimental group. After 8 weeks, liver function tests (ALT, AST, ZTT) and histopathological observation of the femur (H-E stained samples) were performed in the contrast and experimental groups, respectively. The significance test for viability and prevalence of osteoporosis following CBD ligation was performed by using the chi-square test, and the significance test for liver function test values was performed by using the t-test. Results: Experimental osteoporosis is induced at 8 weeks after surgical CBD partial ligation (85-90% occlusion). Conclusion: Iron intake significantly suppressed the development of osteoporosis by chronic cholestasis.

A rapid, accurate, and cost-effective spectrophotometric method has been developed for determining the degree of acetylation (DA) of cellulose acetate (CA). The method is based on the ferric hydroxamate principle. A mixed solvent system of dichloromethane and methanol (7 : 3, v/v) was optimized via Hansen solubility parameter theory to ensure complete dissolution of CA across a wide DA range (1.83-2.95). The reaction of CA with hydroxylamine to form the corresponding hydroxamic acid was systematically optimized, achieving >98.8% conversion within 20 minutes at 25 °C. Subsequent complexation with Fe(III) ions produced a stable, purple-colored chelate with a maximum absorbance at 520 nm. The method obeys Beer-Lambert law over a concentration range of 0.05-2.5 mg mL-1, with a molar absorptivity of 1.09 × 103 L mol-1 cm-1 and a correlation coefficient (r) of 0.999. The limits of detection and quantification were 0.012 mg mL-1 and 0.036 mg mL-1, respectively. Validation studies confirmed excellent precision (RSD < 2%), high accuracy (recovery 98.5-101.2%), and no significant statistical difference compared to the standard titration method (t-test and F-test, p > 0.05). This method offers a simple, reliable, and inexpensive alternative to conventional techniques for the routine analysis of CA acetylation.

Osteoporosis is an important type of metabolic bone disease in chronic cholangiogenic liver disease, with an incidence of up to maximum 72%. Osteoporosis and osteomalacia in patients with chronic liver disease are collectively referred to as "hepatic osteodystrophy," which is commonly found in patients with intestinal malabsorption and progressive primary biliary cirrhosis. To deal with the induction of osteoporosis by chronic cholestasis, we aimed to investigate the following: The aim of the study was to investigate the effect of iron intake on chronic cholestatic osteoporosis by surgical CBD partial ligation. Forty rats including weanling male rats weighing 70-80g and adult male rats weighing 150-160g were used. First, the rats were anesthetized with intraperitoneal ketamine injection, and then the CBD (common bile duct) was exposed by surgical procedures, complete and partial ligation was performed, and then the abdomen was closed. Partial ligation was performed by ligating different thicknesses of the suture needles with the common bile duct and then removing the suture needle. In the case of using suture needle 5-0, 85-90% of the common bile duct is considered to be obstructed and 75-80% for 4-0. After ligation of the common bile duct, naturally proceeding rats were included as contrast group and rats receiving oral administration of 6 mg/kg/day of folate iron were included as experimental group. After 8 weeks, liver function tests (ALT, AST, ZTT) and histopathological observation of the femur (H-E stained samples) were performed in the contrast and experimental groups, respectively. The significance test for viability and prevalence of osteoporosis following CBD ligation was performed by using the chi-square test, and the significance test for liver function test values was performed by using the t-test. Experimental osteoporosis is induced at 8 weeks after surgical CBD partial ligation (85-90% occlusion). Iron intake significantly suppressed the development of osteoporosis by chronic cholestasis.

We use the truncated-unity functional renormalization group (TUFRG) to study many-body instabilities of correlated electrons in graphene doped near the van Hove singularity (VHS). The system is described by an extended Hubbard model including several Coulomb repulsions between neighboring sites. With the repulsion parameters, which turn out to be suitable for low-energy consideration of graphene, we find a spin-bond-order phase in the vicinity of the VHS. This phase gives way to a spin-density-wave phase when involving a weak additional screening. The ground-state phase diagram is presented in the space of the doping level and the screening parameter. We describe in detail both of these spin-ordered states by using recently developed TUFRG + MF scheme, i.e., a combined approach of TUFRG and mean-field (MF) theory. The collinear states are energetically preferable in both cases of the spin bond order and the spin-density wave. But if the third-nearest-neighbor hopping is absent, these spin orders become chiral. The band structures of two collinear spin-ordered states are presented, revealing the metallic behavior of the system.