Given a simple graph G = (V,E) with edge cost c ∈ℝ^|E| , a positive integer h, source s ∈ V and terminal t ∈ V , the hop-constrained cheapest path problem ( HCCPP ) seeks to find an s-t path of length at most h hops with the cheapest cost. This paper proposes a cut-based mixed integer programming (MIP) formulation, which has only one set of constraints that capture connectivity and hop constraints simultaneously, to solve the HCCPP when edge costs are nonnegative. As the only set of constraints of the formulation has exponentially many constraints, we show that their corresponding fractional separation problem is easy for h ∈{2,3} and hard for h ≥ 4 . We also propose a polytime algorithm for solving the integer separation problem. Furthermore, we show that our cut-based model is at least as strong as the jump-based model of Dahl (Operations Research Letters, 1999), which results in perfectness of our proposed model for h ∈{2,3} . We finally conduct a brief set of computational experiments to compare the performance of the cut formulation against the jump model.
RATIONALE:The migration of phthalate plasticizers from high-volume polymers, such as poly(vinyl chloride) (PVC), raises significant toxicological concerns, particularly when materials are subjected to aging and environmental stress. As traditional monitoring techniques rely on time-consuming solvent extraction and chromatographic methods that are often expensive and lack the throughput required for large-scale safety screening, this study intends to present a rapid screening method using direct analysis in real time coupled to high-resolution mass spectrometry (DART-HRMS) to monitor plasticizer migration in PVC films subjected to accelerated UV aging. Operational parameters, such as ionization gas temperature and grid voltage, were systematically optimized to balance desorption efficiency with molecular integrity. METHODS:DART-HRMS analysis of three commercial PVC films subjected to accelerated UV aging (ASTM G154-23) was performed after optimization of the operational parameters: ionization gas temperature: 250 °C, 350 °C, and 500 °C and grid voltage: 50 and 350 V were systematically optimized to balance desorption efficiency with molecular integrity. RESULTS:Analytical performance was strongly governed by source energy, with optimal conditions achieved at 350 °C and 50 V, yielding the highest signal stability and minimal in-source fragmentation. Elevated grid voltage (350 V) caused severe signal suppression and fragmentation, particularly for high-molecular-weight plasticizers such as DIDP and DINP. Application of the optimized method revealed formulation-dependent migration behavior during UV aging. Short-chain phthalates showed rapid and, in some cases, transient surface enrichment, whereas medium- and high-molecular-weight plasticizers exhibited delayed or limited migration, becoming detectable only after prolonged exposure. CONCLUSIONS:DART-HRMS provides a fast, robust, and solvent-free approach for screening plasticizer migration in PVC films. The optimized conditions enable sensitive detection while preserving molecular integrity, allowing differentiation of additive mobility as a function of molecular weight, formulation, and UV-induced degradation. This methodology offers a high-throughput alternative for assessing additive stability and potential release in consumer-grade PVC materials.
This work focuses on the nitration of nanocellulose to obtain products with potential advantages over traditional ones obtained from linter cellulose (LC). The material used was a sample of cellulose nanofibrils (CNF) commercially available as an aqueous suspension with a 3% solid content. The main objective of the research was to develop the reaction conditions for nitration, including the preparatory methods for the cellulose raw material, so that the properties on the nanometric scale were maintained. The dehydration of the CNF to concentrate the fibrils in suspension was investigated using different methods: gravity and vacuum filtration, centrifugation, oven, and freeze-drying. The nitration experiments were carried out with dehydrated CNF following a protocol based on methodologies reported in the literature. For comparative purposes, commercial samples of cotton LC and microcrystalline cellulose (MCC) were also evaluated. A complete characterization of the structural and thermal properties of the cellulose materials and their nitration products was carried out using the following techniques: size-exclusion chromatography, scanning electron microscopy, infrared spectroscopy, X-ray diffraction, simultaneous thermogravimetric analysis, and elemental analysis. The results of the analysis revealed that the chemical structure of the cellulose chains is neither altered by the removal of water nor by the temperature and pressure conditions. However, the agglomeration of the fibrils is favored due to the interconversion of hydrogen bonds between cellulose-water and cellulose-cellulose, as in the heating and freezing treatments, making the redispersion of the nanofibers impossible. Only dehydration by vacuum filtration was suitable for preparing CNF for the reaction to obtain nitrocellulose. Although the resulting degree of substitution was not yet suitable for energetic applications, it was possible to obtain nitrated products from the commercial cellulosic materials under study. Comparing the structural and thermal properties of the nitrated CNF with those of LC and MCC nitration products obtained under identical conditions, the results corroborated the work in the literature and the theories developed so far. Therefore, the study demonstrated the potential viability of the synthesis methodology developed for the nitration of cellulose of different origins, dimensions, and morphological types.
The use of hardwood species in glued laminated timber (glulam) production enables the utilization of native resources, with Parica (Schizolobium amazonicum) showing promising properties comparable to commonly used species in Brazil. The structural performance of glulam beams is strongly influenced by the quality of the interface, which is often assessed through macroscale tests. However, microscopic evaluation of the glue line is essential to fully understand bonding characteristics affecting performance. Despite the availability of several microscopy techniques, including polarized light microscopy (LM), fluorescence microscopy (FM), confocal laser scanning microscopy (CSLM), scanning electron microscopy (SEM), and X-ray microtomography (microCT), comparative studies on their effectiveness for glulam characterization are rare. This study compares five microscopy techniques for evaluating adhesive penetration in Parica glulam, analyzing three different adhesives. Results indicate that the microscopy methods are complementary, with each offering distinct advantages and limitations. Notably, microCT and CSLM provided the most comprehensive details about the glue line. The research presents a comparative overview and suggests a protocol for microscopy-based characterization of glued interfaces. To enhance assessment of bonding quality, it is recommended that, beyond conventional macroscale tests, at least two complementary microscopy analyses be carried out for a more complete structural evaluation of glulam beams.
Molecular dynamics (MD) simulations were performed to investigate high-pressure thermodynamic properties of CO2-hydrocarbon binary mixtures using different force field strategies - united atom, all atom, and hybrid combinations. Simulations were carried out in the isothermal-isobaric (NPT) ensemble to obtain molar volumes as a function of pressure and composition. As a preliminary step, four cubic equations of state were tested against available compressibility factor data, and Peng-Robinson (PR) was selected as the reference cubic framework for the subsequent analyses. MD-derived molar volumes were then coupled to PR in a hybrid workflow: compressibility factors were computed and benchmarked against experimental data, and PR-based fugacity coefficients were evaluated using either PR-predicted or MD-derived molar volumes to quantify the sensitivity of phi to the volume source under identical (P, T, y) conditions. The results show that force field choice significantly affects high-pressure volumetric predictions, with TraPPE-based descriptions providing the closest agreement with experimental compressibility factors for CO2 + CH4 over the investigated conditions. Finally, effective PR mixture parameters were inferred by nonlinear least-squares fitting of the molar-volume form of PR to volumetric datasets, demonstrating that MD-generated Vm(P, T, y) data can serve as an independent input for cubic-EoS parameter inference when experimental information or calibrated mixture parameters are limited.
