Abstract We study the analog of Snell's law for particles moving across the interface of two regions with two different potential energies, from two different points of view. First, a simple demonstration involving marbles and a potential step is shown. Then, from a theoretical point of view, this law describing mechanical refraction is derived from the Maupertuis and Jacobi variational principles, in close analogy with the well known derivation of Snell's law for refraction from Fermat's least time principle. Finally, the relativistic version of mechanical refraction is obtained by the Maupertuis principle, by trading the Newtonian dispersion relation with the relativistic one. The pedagogical significance of this treatment is discussed.

BACKGROUND: Ticks are vectors and important reservoirs for microbial agents that cause disease in humans and animals. Among these pathogens, the members of Rickettsia species play an important role in public health. AIM AND METHODS: One hundred twenty-nine ticks belonging to four tick species (Ixodes ricinus,Rhipicephalus turanicus,Dermacentor marginatus, and Haemaphysalis punctata) were collected at different sites of the Insugherata Natural Reserve, localized in the urban area of Rome, Italy. Questing ticks were tested by PCR for Rickettsia spp., amplifying partial gene of ompA. RESULTS: Forty-six ticks were found to be infected with Rickettsia species. Five SFG rickettsiae were identified: three human pathogens Rickettsia conorii, Rickettsia massiliae and Rickettsia aeschlimannii, and two putative new strains Rickettsia sp. strain RM1 and Rickettsia sp. strain RM2. The phylogenetic analysis of partial gene sequences of ompA, gltA, and 17-kd antigen showed that they clustered with several rickettsiae with unidentified pathogenicity. However, Rickettsia sp. strain RM1 and Rickettsia sp. strain RM2 clustered in a statistically supported clade with R. massiliae, and R. monacensis, respectively. CONCLUSION: Our findings suggest that Rickettsia species other than R. conorii are implicated in human disease in Italy.

Introduction. This study represents a preliminary inquiry on tick fauna composition carried out in Maremma, Central Italy, where very few data are available. Materials and methods. The study area was selected in the limestone hills surrounding Tarquinia town, on the base of suitable elements directly affecting the tick occurrence and the possible circulation of tick-borne pathogens, such as wild cattle rearing, kind of vegetation and human activities. Since a proper understanding of tick ecology is critical in predicting the risk of tick-borne pathogen transmission in a given area, a series of surveys was planned in such area in 2011. Results. One hundred fifty-four ticks belonging to 4 genera and 6 species, namely Ixodes ricinus (n. = 109; 70%), Rhipicephalus bursa (n. = 18; 12%), Rhipicephalus turanicus (n. = 14; 9%), Rhipicephalus sanguineus (n. = 6; 4%), Hyalomma marginatum (n. = 4; 3%) and Dermacentor marginatus (n. = 3; 2%) were identified and reported for the area. Discussion. The results of this acarological research represent a significant contribution to the knowledge of the tick fauna of rural areas in Northern Lazio Region, as first step toward a future molecular investigation on pathogen circulation.