Sobhi Mejjaouli

Critical minerals such as rare earth elements and battery metals combine geographically concentrated supply, long capacity lead times and growing strategic demand, yet the policy levers that address the resulting risk (primary capacity, recycling, stockpiling, supplier diversification, substitution research and environmental mitigation) are usually analysed separately. We formulate a continuous-time optimal control model with eight state variables and six policy controls in which a planner minimises discounted cost while imports and unmet demand clear the market, and we solve it by direct multiple shooting with CasADi and IPOPT using an illustrative parameter set of the magnitude of a mid-sized mineral market. The model was implemented through a case study where different scenarios along with sensitivity analysis were conducted. The reported results show that: First, diversification of suppliers, rather than reduction of import volumes, is the economically optimal response to import-concentration risk. Second, a recycled-content requirement is costly only above a certain recycled materiel share (11%) of demand. Finally, meaningful precautionary stockpiling against an uncertain disruption requires the simultaneous presence of a binding constraint on emergency supply-response speed and sufficient lead time before the earliest plausible disruption date; policy designed around either condition alone is unlikely to induce the gradual, precautionary behavior it is presumably intended to encourage.

Control-relevance-aware sensor integrity (CRASI) combines heuristic relevance, common-evidence subtraction, finite trust retention and bias tracking. We evaluate an internally specified 2520-episode DC-motor surrogate campaign calibrated from Proteus characterization. In the held-out modeled 70% load domain, CRASI reduced integral absolute error (IAE) versus residual-plus-uncertainty by 37.6% for encoder bias, 19.9% for drift, 15.9% for current under-read and 4.4% for current bias. Fixed control performed better for drift/current bias, under-read matched fixed, and dropouts were effectively null; adaptive Huber was 2.0% better for drift. Revision diagnostics identify comparator-dependent attribution, simultaneous-fault blindness, current self-masking, inactive position-uncertainty derating, and no hard-safety superiority. Matched-observer, detection/recovery, parameter-sensitivity and guard-stress analyses therefore restrict mechanism claims. A revision-era direct Proteus audit is not treated as validation because its acquisition/analysis gates were amended after partial outcome inspection and protection trips materially affected several 50% cells; the audit is retained only as a transparent research record and is not used as evidence for the manuscript conclusions. Findings support selective tracking comparisons under modeled sensor/plant confounding, while fresh pre-specified direct Proteus/HIL/physical validation remains necessary.

Tourism is a major driver of the global economy, accounting for approximately 10% of global GDP; however, the literature highlights that unsustainable tourism growth can lead to economic volatility and overdependence, making sustainable approaches essential for ensuring long-term stability and resilience. This paper presents the development of a nonlinear model predictive control (MPC) framework that incorporates key state variables, such as the number of tourists and average spending per tourist, along with control variables including investment in facilities and services and human capital development, in addition to the formulation of the cost function and system dynamics. Numerical experiments demonstrate that the proposed MPC framework effectively manages the complex interactions inherent in tourism systems, achieving sustained growth in tourist arrivals, spending, and employment without instability, stabilizing experience quality despite congestion effects, maintaining a controlled decline in affordability within feasible bounds, and producing smooth, interpretable policy trajectories consistent with institutional constraints. To evaluate the robustness of the framework and identify the most critical governing parameters, a sensitivity analysis was conducted using the Morris screening method.

Vision–Language–Action (VLA) policies promise flexible long-horizon manipulation, but deployment under domain shift requires both reliable uncertainty estimates and a workable runtime-assurance policy. We study a model-agnostic uncertainty-calibrated safety-gating wrapper that estimates online failure risk and routes control among policy execution, pause-and-reobserve, and a fallback planner. Using a cleaned and consistently aggregated benchmark pipeline, we evaluate two long-horizon manipulation tasks in NVIDIA Isaac Sim 5.0 under lighting, texture, occlusion, sensor, and combined shifts. Relative to an ungated VLA baseline, calibrated gating improves mean shifted success from 57.5% to 77.2% and reduces aggregate expected calibration error from 0.303 to 0.100. The largest success gains occur under occlusion and combined shift, including improvements from 48.3% to 85.2% on the drawer task and from 59.4% to 87.8% on clutter sort. The results also expose a systems trade-off: an aggressive uncalibrated threshold baseline attains stronger raw success and collision metrics, but requires nearly twice as many interventions per shifted episode (21.6 vs. 11.5). The main contribution is, therefore, an empirical characterization of the reliability–intervention trade-off created by calibrated supervision, not a claim that the calibrated supervisor is universally the best terminal controller. We frame calibrated gating as a better-calibrated, lower-intervention supervisor that materially improves robustness relative to an ungated VLA while revealing the open problem of mapping calibrated risk into efficient intervention policies. Additional threshold-sensitivity, signal-diagnostic, overhead, and residual-failure analyses show that the selected operating point is meaningful but not universal: the calibrated risk threshold captures most shifted failures in retrospective logs, yet residual contacts still arise during pause and fallback states. These findings provide controlled simulation evidence for trustworthy VLA supervision under distribution shift and clarify the reliability–intervention frontier that future embodied-control systems must navigate.

The proposed model derives closed-form solutions for investment efforts in both product development and its associated production processes while balancing economic profit, product quality, and marginal production costs. The system dynamics, including state and control variables, as well as the relevant constraints, are explicitly formulated. To demonstrate the practical utility of the framework, a numerical example is investigated. Simulation results illustrate adaptive strategies that anticipate future market conditions, manage product–process innovation trade-offs, and respond effectively to changing innovation returns. In the baseline numerical scenario, the model achieves a cumulative profit of 7850 with an average period profit of 196. Finally, a sensitivity analysis is conducted to examine the impact of key model parameters on system performance.

Work–family conflict (WFC) is a worldwide and timeless dilemma that negatively and significantly impacts the performance of employees, families, and organizations. It intensifies when the career is engineering, the employee is female, and the job environment requires heavy-duty and field tasks. The present study investigates the WFC in an engineering environment for female engineers and studies many women-related issues in Yemen. Three questionnaires targeted 130 female engineer graduates, 60 senior engineers, and 20 female engineers’ husbands. The results indicated that marriage is strongly and negatively correlated to educational performance, job opportunities, and job continuity. The present study suggests that, in conservative societies, disruptions from family-to-work are more pronounced compared to work-to-family. Several external factors, including low stipends, economic downturns, and political crises, have a negative impact on job opportunities and job spillover. A significant finding revealed that the average wage of female engineers in Yemen is USD 145, which is 3.822 times lower than that of their male counterparts. The survey results indicated that only single female engineers, but not married female engineers, are currently employed in the industrial and construction sector. Most female engineering graduates are working in jobs unrelated to engineering. Employed females face balancing professional responsibilities, household tasks, and social commitments. Society needs to implement policies that alleviate the pressure on women’s work and promote and support dual-earning couples to enhance family income. The present study recommends organizations offer flexible work schedules, allow remote work options, and create a healthy work environment to address the work–family imbalance, particularly in male-dominated environments.

Serious concerns have been raised over the consistent academic underperformance of Yemeni students at almost all levels of university studies. This paper investigates the impact of various socioeconomic factors on the academic performance of engineering students in Taiz State, Yemen, an impoverished and unstable society. Our quantitative methodology employed a 5-point Likert scale questionnaire and targeted 596 female/male students from three engineering colleges in Taiz State. Data were analyzed using SPSS software and simple and multiple regression models to examine the impact of socioeconomic variables on academic achievement while moderating financial condition and gender. This study measured academic achievement through GPAs, student attendance, and English level. Many socioeconomic influences have been examined against academic performance, such as gender, family income, family stability, family openness, marital status, co-education, part-time jobs, and stimulant use. The results accurately specified that students’ gender considerably impacts the studied variables; moreover, low-income features of families negatively affect students’ academic performance. The outcome of this study indicated that socioeconomic variables matched well with GPA, attendance rate, and English level, but with higher matching to the attendance rate. This study highlights that university students in impoverished and unstable societies, like Yemen, are significantly affected by socioeconomic factors. It recommends coordinated efforts among government authorities, educational institutions, and community leaders to mitigate the negative impact on academic achievement and implement appropriate technologies to enhance performance. Additionally, conducting similar studies in other disciplines and communities within the country is recommended for a deeper understanding of this issue.

In this research work, a problem related to the most expensive cut that is purchase (Tenderloin) by food service operations company has been analyzed. The monthly relevant data such related to fixed and variable costs was collected. The monthly demand and average selling price of Tenderloin observed. The breakeven point, Sensitive analysis and Monte Carlo simulation were done. The risk associated with the loss (22%) has been observed and recommendations were given to enhance the price.

This report shows an economic analysis of fuel track transportation options for gas stations. The study of transportation options and defining the fixed, operation, and variable costs which will affect the transportation. The result shows breakeven point of when the Outsourcing, Own, or Rent to won method is the most valuable with its equations.