Stability of multiplanet systems in binaries

When exploring the stability of multiplanet systems in binaries, two parameters are normally exploited: the critical semimajor axis ac computed by Holman and Wiegert (1999) within which planets are stable against the binary perturbations, and the Hill stability limit Delta determining the minimum separation beyond which two planets will avoid mutual close encounters. Our aim is to test whether these two parameters can be safely applied in multiplanet systems in binaries or if their predictions fail for particular binary orbital configurations. We have used the frequency map analysis (FMA) to measure the diffusion of orbits in the phase space as an indicator of chaotic behaviour. First we revisited the reliability of the empirical formula computing ac in the case of single planets in binaries and we find that, in some cases, it underestimates by 10-20% the real outer limit of stability. For two planet systems, the value of Delta is close to that computed for planets around single stars, but the level of chaoticity close to it substantially increases for smaller semimajor axes and higher eccentricities of the binary orbit. In these configurations ac also begins to be unreliable and non linear secular resonances with the stellar companion lead to chaotic behaviour well within ac, even for single planet systems. For two planet systems, the superposition of mean motion resonances, either mutual or with the binary companion, and non linear secular resonances may lead to chaotic behaviour in all cases. We have developed a parametric semiempirical formula determining the minimum value of the binary semimajor axis, for a given eccentricity of the binary orbit, below which stable two planet systems cannot exist.Comment: Accepted on A&

The Actual Future is Open

Open futurism is the indeterministic position according to which the future is \u2018open\u2019, i.e., there is now no fact of the matter as to what future contingent events will actually obtain. Many open futurists hold a branching conception of time, in which a variety of possible futures exist. This paper introduces two challenges to branching-time open futurism, which are similar in spirit to a challenge posed by Fine to (standard) tense realism. The paper argues that, to address the new challenges, (branching-time) open futurists must (1) adopt an objective, non-perspectival notion of actuality and (2) subscribe to an A-theoretic, dynamic conception of reality. Moreover, given a natural understanding of \u201cactual future\u201d, (3) it is perfectly sensible for open futurists to hold that a unique, objectively actual future exists, contrary to a common assumption in the current debate. The paper also contends that recognising the existence of a unique actual future helps open futurists to avoid potential misconceptions

An Experimental Method to Add New Prosthetic Teeth in the Removable Partial Denture Framework: TIG Cold Welding and Preformed Pins

The need to modify removable partial dentures equipped with a metal framework in order to add other prosthetic teeth to replace natural teeth lost by the patient could lead to laboratory procedures so complex as to require the creation of new prostheses with a heavy economic burden. The creation of preformed metal pins to be welded using the economical TIG cold welding method could represent a valid alternative solution with the aim of modifying the prostheses using a rein-forced resin capable of adequately resisting masticatory loads. This study evaluates and compares the mechanical robustness and the clinical reliability of these modified prostheses in cases of junctions of one or two contiguous prosthetic teeth. The 6-month follow-up demonstrated the total validity of the method via the absence of significant breakages or detachments in all of the patients analyzed; on the other hand, the prostheses modified using the traditional method and used as controls showed a high incidence of fractures

The Freehand Technique: The Ability of the Human Eye to Identify Implant Sites on the Patient

In implantology, among the key choices, to obtain predictable results, it is essential to establish, using cone beam computed tomography (CBCT), the bone site and where to insert the implants; during the surgical phase, these sites must be identified on the oral mucosa. Surgical templates are a valid aid, especially in complex cases which require the insertion of more than three or four implants. In cases of a single implant, on the other hand, surgical guides are rarely used, and the implant is often inserted freehand; therefore, the identification of the implant site on the oral mucosa (after choosing the location on the CBCT) is more difficult. For this reason, the clinician uses the teeth in the arch as a reference. This study evaluates the ability of the human eye to identify, on the oral mucosa, where the implant collars will be positioned, the position of which has previously been chosen on the CBCT, in cases where the hands-free surgical technique (without surgical guides) is used. The verification of this precision is carried out using particular thermo-printed templates which contain radiopaque metal spheres. The results show that, in the freehand technique, it is difficult to precisely identify the implant sites (chosen via X-ray) on the mucosa, especially when they are far from natural teeth adjacent to the edentulous area. In case of monoedentulism, the freehand implant technique seems to be applicable by expert implantologists with a reduced risk of error; in fact, clinical experience helps to find the correct correspondence between the implant site chosen on the CBCT and its identification on the mucosa. The level of experience is fundamental in the clinician’s decision about whether or not to use surgical guides; in fact, doctors with little experience should use surgical guides even in the simplest cases to reduce the risk of error

Uvulopalatopharyngoplasty with tonsillectomy in the treatment of severe OSAS

Objective: To establish the efficacy of uvulopalatopharyngoplasty with tonsillectomy for treating selected patients with severe obstructive sleep apnea syndrome Methodology: Retrospective study of patients who underwent clinical/instrumental evaluation and surgical treatment. Setting: University ENT division with a tertiary snoring referral center Participants: Twenty-two patients with normal body mass index affected by severe obstructive sleep apnea syndrome- Main outcome measures: Pre and post operative cardiopulmonary monitoring during sleep, daytime sleepiness evaluation, post treatment complication recording. Results: Complete response to therapy was obtained in 78% of patients. Four patients had relief of symptoms but retained apnea-hypopnea index scores greater than 5 Conclusions: Uvulopalatopharyngoplasty associated with tonsillectomy can be employed safely to treat patients with normal body mass index who suffer from severe obstructive sleep apne

Fatigue behavior and cyclic damage of peek short fiber reinforced composites

Fatigue strength and failure mechanisms of short fiber reinforced (SFR) PEEK have been investigated in the past by several research groups. However some relevant aspects of the fatigue behavior of these materials, like cyclic creep and fatigue damage accumulation and modeling, have not been studied yet, in particular in presence of both fillers and short fibers as reinforcement. In the present research these aspects were considered by carrying out uni-axial fatigue tests in load control (cycle ratio R = 0) on neat PEEK and PEEK based composites reinforced either with short carbon fibers only or with addition of fillers (graphite and PTFE). For each material stress-life curves were obtained and compared. Fatigue fracture surfaces were analyzed to identify failure mechanisms in presence of different reinforcement types. The evolution of cyclic creep strain was also monitored as a function of the number of cycles, thus allowing investigation on the correlation between cyclic creep parameters and fatigue life. The evolution of cyclic damage with loading cycles was then compared by defining a damage parameter related to the specimen stiffness reduction observed during the tests. Progressive cyclic damage evolution of short fiber reinforced PEEK composites presented significantly different patterns depending on applied stress level and on the presence of different reinforcement typologies. In order to reproduce the different fatigue damage kinetics and stages of progressive damage accumulation observed experimentally, a cyclic damage model was finally developed and implemented into a finite element code by which a satisfactory agreement between numerical prediction and experimental data at different stress levels for each examined material