5 research outputs found
Finite temperature Casimir effect in piston geometry and its classical limit
We consider the Casimir force acting on a -dimensional rectangular piston
due to massless scalar field with periodic, Dirichlet and Neumann boundary
conditions and electromagnetic field with perfect electric conductor and
perfect magnetic conductor boundary conditions. It is verified analytically
that at any temperature, the Casimir force acting on the piston is always an
attractive force pulling the piston towards the interior region, and the
magnitude of the force gets larger as the separation gets smaller. Explicit
exact expressions for the Casimir force for small and large plate separations
and for low and high temperatures are computed. The limits of the Casimir force
acting on the piston when some pairs of transversal plates are large are also
derived. An interesting result regarding the influence of temperature is that
in contrast to the conventional result that the leading term of the Casimir
force acting on a wall of a rectangular cavity at high temperature is the
Stefan--Boltzmann (or black body radiation) term which is of order ,
it is found that the contributions of this term from the interior and exterior
regions cancel with each other in the case of piston. The high temperature
leading order term of the Casimir force acting on the piston is of order ,
which shows that the Casimir force has a nontrivial classical
limit
Normal and Lateral Casimir Forces between Deformed Plates
The Casimir force between macroscopic bodies depends strongly on their shape
and orientation. To study this geometry dependence in the case of two deformed
metal plates, we use a path integral quantization of the electromagnetic field
which properly treats the many-body nature of the interaction, going beyond the
commonly used pairwise summation (PWS) of van der Waals forces. For arbitrary
deformations we provide an analytical result for the deformation induced change
in Casimir energy, which is exact to second order in the deformation amplitude.
For the specific case of sinusoidally corrugated plates, we calculate both the
normal and the lateral Casimir forces. The deformation induced change in the
Casimir interaction of a flat and a corrugated plate shows an interesting
crossover as a function of the ratio of the mean platedistance H to the
corrugation length \lambda: For \lambda \ll H we find a slower decay \sim
H^{-4}, compared to the H^{-5} behavior predicted by PWS which we show to be
valid only for \lambda \gg H. The amplitude of the lateral force between two
corrugated plates which are out of registry is shown to have a maximum at an
optimal wavelength of \lambda \approx 2.5 H. With increasing H/\lambda \gtrsim
0.3 the PWS approach becomes a progressively worse description of the lateral
force due to many-body effects. These results may be of relevance for the
design and operation of novel microelectromechanical systems (MEMS) and other
nanoscale devices.Comment: 20 pages, 5 figure
Safety and efficacy of non-steroidal anti-inflammatory drugs to reduce ileus after colorectal surgery
Background: Ileus is common after elective colorectal surgery, and is associated with increased adverse events and prolonged hospital stay. The aim was to assess the role of non-steroidal anti-inflammatory drugs (NSAIDs) for reducing ileus after surgery. Methods: A prospective multicentre cohort study was delivered by an international, student- and trainee-led collaborative group. Adult patients undergoing elective colorectal resection between January and April 2018 were included. The primary outcome was time to gastrointestinal recovery, measured using a composite measure of bowel function and tolerance to oral intake. The impact of NSAIDs was explored using Cox regression analyses, including the results of a centre-specific survey of compliance to enhanced recovery principles. Secondary safety outcomes included anastomotic leak rate and acute kidney injury. Results: A total of 4164 patients were included, with a median age of 68 (i.q.r. 57\u201375) years (54\ub79 per cent men). Some 1153 (27\ub77 per cent) received NSAIDs on postoperative days 1\u20133, of whom 1061 (92\ub70 per cent) received non-selective cyclo-oxygenase inhibitors. After adjustment for baseline differences, the mean time to gastrointestinal recovery did not differ significantly between patients who received NSAIDs and those who did not (4\ub76 versus 4\ub78 days; hazard ratio 1\ub704, 95 per cent c.i. 0\ub796 to 1\ub712; P = 0\ub7360). There were no significant differences in anastomotic leak rate (5\ub74 versus 4\ub76 per cent; P = 0\ub7349) or acute kidney injury (14\ub73 versus 13\ub78 per cent; P = 0\ub7666) between the groups. Significantly fewer patients receiving NSAIDs required strong opioid analgesia (35\ub73 versus 56\ub77 per cent; P < 0\ub7001). Conclusion: NSAIDs did not reduce the time for gastrointestinal recovery after colorectal surgery, but they were safe and associated with reduced postoperative opioid requirement