1,626 research outputs found
An exact fluid model for relativistic electron beams: The many moments case
An interesting and satisfactory fluid model has been proposed in literature
for the the description of relativistic electron beams. It was obtained with 14
independent variables by imposing the entropy principle and the relativity
principle. Here the case is considered with an arbitrary number of independent
variables, still satisfying the above mentioned two principles; these lead to
conditions whose general solution is here found. We think that the results
satisfy also a certain ordering with respect to a smallness parameter
measuring the dispersion of the velocity about the mean; this
ordering generalizes that appearing in literature for the 14 moments case
Calculations for Extended Thermodynamics of dense gases up to whatever order and with all the symmetries
The 14 moments model for dense gases, introduced in the last years by Arima,
Taniguchi Ruggeri, Sugiyama, is here considered. They have found the closure of
the balance equations up to second order with respect to equilibrium; here the
closure is found up to whatever order with respect to equilibrium, but for a
more constrained system where more symmetry conditions are imposed and this in
agreement with the suggestion of the kinetic theory. The results, when
restricted at second order with respect to equilibrium, are the same of the
previously cited model but under the further restriction of full symmetries.Comment: arXiv admin note: substantial text overlap with arXiv:1410.405
Comparison of contact parameters measured with two different friction rigs for nonlinear dynamic analysis
The accurate measurement of contact interface parameters is of great importance for nonlinear dynamic response computations since there is a lack of predictive capabilities for such input parameters. Several test rigs have been developed at different institutions, and a series of measurements published, but their reliability remains unknown due to a lack of direct comparisons. To somehow address this issue, a Round-Robin test campaign was performed including the high frequency friction rigs of Imperial College London and Politecnico di Torino. Comparable hysteresis loops were recorded on specimen pairs manufactured from the same batch of raw stainless steel, for a wide range of test conditions, including varying normal loads, sliding distances and nominal areas of contact. Measurements from the two rigs were compared to quantify the level of agreement between the two very different experimental setup, showing a reasonably good matching in the results, but also highlighting some differences. Results also demonstrated that loading conditions can strongly affect the contact parameters, and consequently their effect must be included in future nonlinear dynamic simulations for more reliable predictions
Enhanced Recovery after Bariatric Surgery: 202 Consecutive Patients in an Italian Bariatric Center
Background: Enhanced Recovery After Surgery (ERAS) pathways have been shown to improve postoperative outcomes. However, its application in bariatric surgery is still limited. The aim of the study was to define the safety of ERAS in bariatric patients with regard to postoperative complications, length of hospital stay (LOS), and readmission rates within 30\ua0days from surgery. Methods: The effectiveness and safety of an ERAS protocol was prospectively investigated in morbidly obese patients who underwent bariatric surgery in a single-institute experience over a 2-year period. Results: Between June 2016 and September 2018, a total of 89 laparoscopic sleeve gastrectomy (SG), 105 Roux-en-Y gastric bypass (RYGB), and 8 one-anastomosis gastric bypass (OAGB) were performed. Twenty patients (9.9%) were revisional cases. Mean (standard deviation, SD) BMI and age at time of surgery were 43.2 (\ub1 6.2)\ua0kg/m2 and 46 (\ub1 11.3)\ua0years, respectively. Median (range) surgical time was 118 (45\u2013255) minutes. Overall postoperative complication rate was 7.4%, with 6 (3.0%) patients developing grade III\u2013IV complications according to the Clavien-Dindo classification. Median (range) LOS was 2 (1\u201350)\ua0days, with mean (SD) LOS of 2.3 (\ub1 3.6)\ua0days. Overall, 36.6% of patients were discharged by first postoperative day and 77.7% by second postoperative day. Readmission rate was 4.5%. No mortality was observed during the study period. Conclusions: According to the results of the present study, ERAS in primary and revisional bariatric surgery is safe and feasible, with short LOS, low morbidity and readmission rates, and no mortality. A significant reduction of mean LOS was progressively noted over the study period
The general exact solution for the many moments macroscopic approach to extended thermodynamics of polyatomic gases
A new model for Polyatomic and for Dense Gases has been proposed in literature in the last five years in
the framework of Extended Thermodynamics. The case with an arbitrary but fixed number of moments has been
recently studied, both with the kinetic approach than with the macroscopic approach; this last one is
more general and includes the results of the kinetic approach only as a particular case. \\
Scope of the "closure problem" is to find the expression of some arbitrary functions which appear in the
balance equations. Up to now only a recurrence procedure has been published which outlines how to find
the solution of this problem with the macroscopic approach; by using this procedure, a numberable set
of solutions has been found and written explicitly, while we find here the most general exact
solution. It is determined except for some arbirary terms and it is interesting that these terms appear
also in the 24 moments model; so we find here that they are transmitted from the model with 24 moments
to those with an arbitrary number of moments, without any further arbitrary term
Extended Thermodynamics for Dense Gases up to Whatever Order and with Only Some Symmetries
Extended Thermodynamics of dense gases is characterized by two hierarchies of field
equations, which allow one to overcome some restrictions on the generality of the previous
models. This idea has been introduced by Arima, Taniguchi, Ruggeri and Sugiyama. In~the
case of a 14-moment model, they have found the closure of the balance equations up to
second order with respect to equilibrium. Here, the closure is obtained up to whatever
order and imposing only the necessary symmetry conditions. It comes out that the first
non-symmetric parts of the higher order fluxes appear only at third order with respect to
equilibrium, even if Arima, Taniguchi, Ruggeri and Sugiyama found a non-symmetric part
proportional to an arbitrary constant also at first order with respect to equilibrium.
Consequently, this constant must be zero, as Arima, Taniguchi, Ruggeri and Sugiyama assumed
in the applications and on an intuitive ground
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