A precise formulation of the third law of thermodynamics

The third law of thermodynamics is formulated precisely: all points of the state space of zero temperature $\Gamma_0$ are physically adiabatically inaccessible from the state space of a simple system. In addition to implying the unattainability of absolute zero in finite time (or "by a finite number of operations"), it admits as corollary, under a continuity assumption, that all points of $\Gamma_0$ are adiabatically equivalent. We argue that the third law is universally valid for all macroscopic systems which obey the laws of quantum mechanics and/or quantum field theory. We also briefly discuss why a precise formulation of the third law for black holes remains an open problem.Comment: 24 pages, no figure

Three-dimensional quantum electrodynamics as an effective interaction

We obtain a Quantum Electrodynamics in 2+1 dimensions by applying a Kaluza--Klein type method of dimensional reduction to Quantum Electrodynamics in 3+1 dimensions rendering the model more realistic to application in solid-state systems, invariant under translations in one direction. We show that the model obtained leads to an effective action exhibiting an interesting phase structure and that the generated Chern--Simons term survives only in the broken phase.Comment: 10 pages in Plain Te

Compact extra-dimensions as solution to the strong CP problem

We show that the strong CP problem can, in principle, be solved dynamically by adding extra-dimensions with compact topology. To this aim we consider a toy model for QCD, which contains a vacuum angle and a strong CP like problem. We further consider a higher dimensional theory, which has a trivial vacuum structure and which reproduces the perturbative properties of the toy model in the low-energy limit. In the weak coupling regime, where our computations are valid, we show that the vacuum structure of the low-energy action is still trivial and the strong CP problem is solved. No axion-like particle occur in this setup and therefore it is not ruled out by astrophysical bounds.Comment: Discussion adde

Experimental and Finite Element Analysis of the Pressure Carrying Capacity of Reinforced Composite Thick-Walled Material Tubes

Presently modern composites using continuous fibers in a resin matrix are important candidate materials for cylindrical structures like pipes and pressure vessels. These materials are lighter, stronger, corrosion resistance and more cost effective when compared with the traditional materials like metals. These structures are commonly subjected to internal pressure and there are some applications where structures subjected to complex loading conditions which are resulted from internal pressurization and superimposed axial loads during installation and/or operation. Most of the previous works were concentrated on the thin shell structures while less work was carried out on thick shell structures under internal pressure loading. The use of hybrid structures in this application is limited and also a limited research work is available for multi-directional tubular composite structures compared with single lay-up configuration. The effects of the different winding angle, different materials and hybridization, different number of layers and different stacking sequence of multi-layered angles on the carrying capacity of thick shell composite tube under internal pressure loading have been studied. The composite materials used were glass/epoxy and carbon/epoxy. In this study it was found that the optimum winding angle for filament wound pipes depends primarily on the loading modes applied. The experimental results showed that the optimum winding angle is 550 for biaxial pressure loading (mode II), 750 for hoop pressure loading (mode I) while 850 is suitable for biaxial pressure with axial compressive loading (mode III). The test results also show that the carrying capacity of the composite tube increases as the number of the number of layers increase and the percentage difference for all loading modes is about 46% and 63% for four layers and six layers compared by two layers of glass/epoxy respectively. Changing the stacking sequence of multi-layered composite tube enhance the internal pressure carrying capacity for different loading modes and the percentage difference for all loading modes is about 5% and 13%. Using different materials for the composite tube shows that the internal pressure carrying capacity is enhanced. The carrying capacity is about 9% to 19% increased if hybrid composite tube made from two different materials; glass/epoxy and carbon/epoxy are used compared with composite tube made from glass/epoxy alone for all loading modes. On the other hand the carrying capacity is increased by 32% to 38% for the composite tube wound with two and four layers of carbon/epoxy compared with composite tube wound with two and four layers of glass/epoxy for all loading modes. The finite element analysis has been used to analyze the composite tube under internal pressure load for different loading modes. ANSYS finite element software was used to perform the numerical analysis for the different arrangements of composite tubes. The predicted results gave good agreement with the experimental results, the percentage differences between the experimental and the finite element analysis results are approximately 4%-25% for different loading modes

Static Strength of Elliptical Chords T-Tubular Joints Subjected to Mechanical Loading

T-Tubular joints of elliptical and circular cross-section tubes for the main tube (chord) with circular cross-section tubes for the braces have been studied. Experimental tests for the joint strength of these welded T-joints under tension, compression, in plane bending and out of plane bending have been carried out. A rig has been designed and built for that purpose. Three cases of T-joint connections were selected. For Case 1, the brace was perpendicular to the circular chord outer diameter. For Case 2, the brace was perpendicular to elliptical chord minor diameter and for Case 3, the brace was perpendicular to elliptical chord major diameter. The chord was held as fixed-fixed for all cases. The material used for all tubes was mild steel. The ultimate loads and ultimate moments obtained from the tests are converted to non-dimensional strengths throughout this investigation. This was done to make efficient comparisons. Finite element models for similar T -joints have been developed and used to analyze the effect of axial loading and bending moment. Tension, compression, in plane bending and out-of-plane bending load modes were studied. A comparison between experimental results and finite element analysis was also carried out. Another comparison between experimental results and existing empirical equation results for similar circular chords tubular joints was also carried out. The results extracted from this study for tension, compression, in-plane bending and out-of-plane bending modes for the ultimate loads and moments of Case 1, are 53.85 kN, 25.43 kN, 0.76 kN.m and 0.40 kN.m respectively. On the other hand, the results for Case 2 of the ultimate loads and moments are 42.48 kN, 1 8.39 kN, 0.63 kN.m and 0.37 kN.m respectively. While for Case 3 the ultimate loads and moments are 64.86 kN, 28.95 kN, 1.00 kN.m and 0.55 kN.m respectively. The results obtained show that for axial tension and compression loading modes, Case 3 increases by 17.0% and 12.2% respectively when compared to Case 1 while 24.0% and 27.3% increase were found for in-plane and out-of-plane bending load modes respectively. This shows a significant improvement in the static strength for elliptical chords tubular joints (Case 3) under different loading modes when compared to circular chords tubular joints (Case 1)

Solution for a local straight cosmic string in the braneworld gravity

In this work we deal with the spacetime shaped by a straight cosmic string, emerging from local gauge theories, in the braneworld gravity context. We search for physical consequences of string features due to the modified gravitational scenario encoded in the projected gravitational equations. It is shown that cosmic strings in braneworld gravity may present significant differences when compared to the general relativity predictions since its linear density is modified and the deficit angle produced by the cosmic string is attenuated. Furthermore, the existence of cosmic strings in that scenario requires a strong restriction to the braneworld tension: $\lambda \geq 3 \times 10^{-17}$, in Planck units.Comment: 7 pages, 3 figure