Abstract

Abstract
This paper presents the conditions required for effective sensitivity amplification in the optical harmonic Vernier effect. Two distinct cases are analyzed: in the first, the sensor cavity is the shortest, while in the second, it is the longest. Based on the proposed theoretical model, supported by experimental results, it is concluded that, in the first case, the sensitivity associated with the spectral extremes increases with the order of the harmonic states. In contrast, in the second case, the sensitivity at the spectral extremes remains constant, regardless of the harmonic order. To evaluate the effectiveness of applying the optical Vernier effect and to differentiate between the two cases, a new formulation of the magnification factor (M-factor) is introduced. This leads to the definition of a novel figure of merit for the optical Vernier effect, denoted as (FoM(Vernier)). In Case 1, where harmonics are generated by increasing the reference cavity, the figure of merit assumes a value of (m + 1). In Case 2, where harmonics are generated by increasing the sensor cavity, the figure of merit remains constant at 1, regardless of the state order (whether fundamental or harmonic). This study also concludes that the observed increase in sensitivity is apparent rather than intrinsic, as the sensitivity curve produced by the optical Vernier effect mirrors that of a conventional interferometer.

Abstract
Over the past 18 months, we have performed hundreds of temperature characterizations of fiber Bragg gratings inscribed in different germanium-doped silica glass fibers. Under experimental conditions, the main conclusions are as follows: the temperature dependence of the temperature gauge factor or the normalized temperature sensitivity, K-T, was found to be quadratic in the -50-200 degrees C range, while it may be considered linear for the -20-100 degrees C range; K-T values at 20 degrees C vary from 5.176 x 10(-6) K-1, for a B/Ge co-doped fiber up to 6.724 x 10(-6) K-1, for a highly Ge-doped fiber; K-T does not depend on the hydrogen-loading process or the gratings coupling strength; K-T is essentially independent of wavelength in the 1500-1600 nm range, its value being accurately determined with a relative error similar to 0.2%; based on the accurate value of K-T = 6.165 x 10(-6) K-1, at 20 degrees C, obtained for gratings inscribed in the SMF-28 fiber, we calculated a value of 19.4 x 10(-6) K-1 for the thermo-optic coefficient of bulk germanium glass; and gratings produced by femtosecond-laser radiation and UV-laser radiation exhibit comparable values of K-T. The previous achievements allow, by having knowledge of K-T for a single grating, the accurate determination of the temperature dependence of the Bragg wavelength for any other grating inscribed in the same fiber; the presented methodology enables one to determine the unknown gratings' temperature sensitivity, typically with an error of 0.01 pm/degrees C, being, therefore, very useful in research labs and computer simulations. Thus, expressions for the temperature dependence of K-T for gratings inscribed in several fibers are given, as well as an expression for K-T as a function of the effective refractive index. We have also fully analyzed the potential sources of error in K-T determination.

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[No abstract available]

Abstract
In the competitive landscape of higher education, institutions increasingly rely on international rankings to secure funding, attract talent, and enhance their global reputation. Concurrently, these institutions have expanded their presence on social media, utilizing sophisticated posting strategies not only to disseminate information but also to boost recognition and engagement. This study examines the relationship between the rankings of Higher Education Institutions (HEIs) and their social media posting strategies. We collected and analyzed tweets from 22 HEIs featured in a consolidated ranking system, focusing on various features of their social media posts. The analysis identified six distinct clusters of posting strategies. This paper categorizes the HEIs into these clusters and discusses the implications of differing social media strategies on their rankings. The findings suggest a nuanced interaction between social media engagement and the perceived prestige of HEIs. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2026.

Abstract
This paper solves the resource-constrained project scheduling problem (RCPSP) with a satisfiability problem (SAT) solver. This paper builds further on various existing SAT models for this well-known project scheduling problem and extends them with two methods to satisfy the resource constraints. Specifically, we use the wellknown minimal forbidden sets and compare them with the so-called covers that are traditionally used in SAT implementations. Moreover, we also implement an existing binary decision trees approach under various settings and extend the model with networks with adders, so far never used for solving the RCPSP, to guarantee that resource constraints are satisfied. The algorithms are tested under different settings on a set of 13,413 project instances with diverse network and resource structures, and the experiments demonstrate that a combination of these approaches help in finding better solutions within a reasonable time. Moreover, 393 new lower bounds, 62 new upper bounds, and 290 optimally solved instances (including 18 from the PSPLIB) have been discovered, which, to the best of our knowledge, had not been found before. The strong performance of the new algorithm motivated additional experiments, and the preliminary results suggest several promising directions for future research.