By using the KAM(Kolmogorov-Arnold-Moser) theory and time reversal symmetries, we investigate the stability of the equilibrium solutions of the system: x n + 1 = 1 y n , y n + 1 = β x n 1 + y n , n = 0 , 1 , 2 , … , where the parameter β > 0 , and initial conditions x 0 and y 0 are positive numbers. We obtain the Birkhoff normal form for this system and prove the existence of periodic points with arbitrarily large periods in every neighborhood of the unique positive equilibrium. We use invariants to find a Lyapunov function and Morse’s lemma to prove closedness of invariants. We also use the time reversal symmetry method to effectively find some feasible periods and the corresponding periodic orbits.

INTRODUCTION Occupational diseases are diseases caused by occupational exposures at the workplace, while diseases related to work are diseases caused by many factors, wherein the harmful work conditions are one of the possible causes. Dental medicine is a profession with a high risk of developing occupational diseases. The aim of this paper was to present the results of a survey about occupational health risks and health related habits among dental students at the School of Dental Medicine University of Zagreb and to show how this survey led to an improvement in education by introducing a new course into the dental curriculum. PARTICIPANTS AND METHODS Students of all years at the School of Dental Medicine University of Zagreb (total of 663) were offered to participate in a survey about occupational health risks and health related habits. RESULTS A questionnaire was completed by 351 students. 28.0% of male students and 22.5% of female students were smokers. During the first two years of study, up to 84.6% of students consumed alcoholic beverages at least once a week. Prior to enrollment in the university, 85.3% male and 77.6% female students were engaged in sports. The significant drop in the number of students who participated in sports was noticed in the first study year in both sexes. Student awareness of the health risks related to dental profession increases with the year of study. Most students believe that occupational diseases can be prevented. CONCLUSION The results have shown that students enter the School of Dental Medicine with a relatively low level of awareness of the health hazards of dental profession. Although the level of awareness increases with years of study, harmful habits such as smoking, alcohol consumption, and the lack of physical activity also remain present in the later years of study.

Medical emergencies that are life threatening can occur in dental practice. Complications may arise because of an underlying disease or a reaction to medication. Reactions to medications may be allergic and toxic. The most common reactions are toxic reactions to local anesthetics, whereas allergies occur mainly as a consequence of the application of antibiotics, usually penicillin. In response to stress, vasovagal syncope typically occurs. Other causes may be related to an underlying disease-specific pathology (such as acute asthma attack, diabetic ketoacidosis, hypoglycemia, or seizures) or accidents (aspiration of a foreign body causing obstruction of the respiratory system). For all the above conditions, guidelines have been established that need to be known. If complications occur or necessary measures are not taken, it can lead to cardiac and respiratory arrest. Therefore, cardiopulmonary resuscitation is needed. All procedures and dosages should be adapted to the age of the child.

To construct a sensing interface, in the present work, a conjugated polymer and core-shell magnetic nanoparticle containing biosensor was constructed for the pesticide analysis. The monomer 4,7-di(furan-2-yl)benzo[c][1,2,5]thiadiazole (FBThF) and core-shell magnetic nanoparticles were designed and synthesized for fabrication of the biosensing device. The magnetic nanoparticles were first treated with silica and then modified using carboxyl groups, which enabled binding of the biomolecules covalently. For the construction of the proposed sensor a two-step procedure was performed. First, the poly(FBThF) was electrochemically generated on the electrode surface. Then, carboxyl group modified magnetic nanoparticles (f-MNPs) and acetylcholinesterase (AChE), the model enzyme, were co-immobilized on the polymer-coated surface. Thereby, a robust and novel surface, conjugated polymer bearing magnetic nanoparticles with pendant carboxyl groups, was constructed, which was characterized using Fourier transform infrared spectrometer, cyclic voltammetry, scanning electron microscopy, and contact angle measurements. This novel architecture was then applied as an immobilization platform to detect pesticides. To the best of our knowledge, a sensor design that combines both conjugated polymer and magnetic nanoparticles was attempted for the first time, and this approach resulted in improved biosensor characteristics. Hence, this approach opens a new perspective in the field of enzyme immobilization and sensing applications. Paraoxon and trichlorfon were selected as the model toxicants. To obtain best biosensor performance, optimization studies were performed. Under optimized conditions, the biosensor in concern revealed a rapid response (5 s), a low detection limit (6.66 × 10(-3) mM), and high sensitivity (45.01 μA mM(-1) cm(-2)). The KM(app) value of poly(FBThF)/f-MNPs/AChE were determined as 0.73 mM. Furthermore, there was no considerable activity loss for 10 d for poly(FBThF)/f-MNPs/AChE biofilm.

A fundamental question about the complexity of corvid social cognition is whether behaviours exhibited when caching in front of potential pilferers represent specific attempts to prevent cache loss (cache protection hypothesis) or whether they are by-products of other behaviours (by-product hypothesis). Here, we demonstrate that Eurasian jays preferentially cache at a distance when observed by conspecifics. This preference for a ‘far’ location could be either a by-product of a general preference for caching at that specific location regardless of the risk of cache loss or a by-product of a general preference to be far away from conspecifics due to low intra-species tolerance. Critically, we found that neither by-product account explains the jays’ behaviour: the preference for the ‘far’ location was not shown when caching in private or when eating in front of a conspecific. In line with the cache protection hypothesis we found that jays preferred the distant location only when caching in front of a conspecific. Thus, it seems likely that for Eurasian jays, caching at a distance from an observer is a specific cache protection strategy.