1,370 research outputs found
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
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
Obstructive sleep apnoea syndrome (OSAS): effects on the vestibular system
Aim of the present study was to evaluate the effects of obstructive sleep apnoea syndrome (OSAS) on the peripheral and central vestibular
system, by means of a case series prospective study at the University referral centre of Otolaryngology Head and Neck Surgery; 45 consecutive
patients suffering from OSAS were compared with a control group of 30 volunteer subjects selected from among the department
employees. Severity of the disease was evaluated by means of cardio-respiratory function monitoring during sleep; the apnoea-hypopnoea
index was calculated. Both groups underwent: 1) head and neck examination; 2) fibre-optic examination; 3) pure tone audiometry; 4) evaluation
of eye movement disorders using oculomotility tests recorded with the help of video-nystagmography; 5) caloric vestibular responses
recorded with video-nystagmography; 6) auditory brainstem response. Results, when evaluating our data, showed that the peripheral vestibular
system may become asymmetric due to hypoxic damage while the central vestibular system corrects this disequilibrium
Management of benign paroxysmal positional vertigo of lateral semicircular canal by Gufoni's manoeuvre
Benign paroxysmal positional vertigo (BPPV) of lateral semicircular canal (LSC) is one of the rarer forms of BPPV as compared to posterior semicircular canal BPPV. Various particle repositioning manoeuvres have been described in the literature as a mode of treating this condition
Purpose: Evaluation and discussion of the procedure of the Gufoni\u2019s manoeuvre and its advantages in the treatment of BPPV of LSC
Material and methods: Prospective study of 58 patients affected by LSC BPPV who where office-treated with Gufoni\u2019s manoeuvre
Results: Seventy-nine percent of the patients so treated had complete resolution of symptons, and 6,9% did not show any improvement in their symptoms. The remaining 13,8% had a conversion into posterior semicircular canal BPPV during treatment and were successfully treated with Epley\u2019s or Semont\u2019s manoeuvre.
Conclusions: Gufoni\u2019s manoeuvre is effective in treating patients suffering from BPPV of LSC; it is simple to perform; there are not many movements to execute, it needs low timeof positioning, and positions are comfortable to the patien
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