Tribological behaviour of polyalphaolefins: wear and rolling contact fatigue tests

Polyalphaolefin fluids are gaining rapid acceptance as high-performance lubricants and functional fluids because they have certain inherent, and highly desirable, characteristics relative to mineral oils. One of these characteristics is their low toxicity. It combined with excellent viscometrics and lubricity, have made low-viscosity PAO fluids an important component in lubricant formulations. Typical data found in product specifications for lubricants are the kinematic viscosity and the viscosity index. These values do not give enough information to choose the optimum lubricant for a lubricated contact. In mechanical systems take place rolling, sliding and rolling/sliding contacts, therefore lubricants have to work the best possible in these operation conditions. In this study are experimentally determined the L50, L10 and Weibull´s slope () of polyalphaolefins with two different viscosities. This test was made on a four-ball machine (Stanhope Seta). Wear test also was made on a four-ball tester (Roxana) in order to measure the wear scar diameter (WSD), and the flash temperature parameter (FTP). Lubricants were identified through infrared spectroscopy, and ball´s pittings were observed with SEM

La incontinencia urinaria

Urinary incontinence, understood as any involuntary loss of urine, constitutes an important medical and social problem. It can be classified as stress urinary incontinence, urgent urinary incontinence or mixed urinary incontinence. The proportions of these three types of urinary incontinence are difficult to establish and vary notably between sources, but they might be about 40, 33 and 20% respectively. Its diagnosis requires a correct clinical history and physical exploration, together with some complementary explorations. The first therapeutic step consists of hygienicdietary measures and behaviour modification techniques. Pharmacological treatment is specific for each type of urinary incontinence, using anticholinergics and inhibitors of serotonin reuptake. Finally, different surgical techniques have a role in cases where conservative treatments fail or when dealing with severe urinary incontinence

Influence of Ultraviolet Radiation Exposure Time on Styrene-Ethylene-Butadiene-Styrene (SEBS) Copolymer

[EN] The effect of ultraviolet radiation on styrene-ethylene-butadiene-styrene (SEBS) has been studied at different exposures times in order to obtain a better understanding of the mechanism of ageing. The polymer materials were mechanically tested and then their surfaces were analyzed using a scanning electron microscope (SEM) and atomic force microscopy (AFM). Moreover, the optical analysis of contact angle (OCA) was used to evaluate the surface energy (gamma(s)) and the yellowing index (YI) and attenuated total reflectance infrared spectroscopy (ATR-FTIR) were used to observe structural and physical changes in aging SEBS. The results obtained for the SEBS, in relation to the duration of exposure, showed superficial changes that cause a decrease in the surface energy (gamma(s)) and, therefore, a decrease in surface roughness. This led to a reduction in mechanical performance, decreasing the tensile strength by about 50% for exposure times of around 200 hours.This work was supported by the Ministry of Economy and Competitiveness (MINECO) grant number MAT2017-84909-C2-2-R). Daniel Garcia-Garcia acknowledges Generalitat Valenciana (GVA) for financial support through a postdoctoral contract (APOSTD/2019/201).Garcia-Garcia, D.; Crespo, J.; Parres, F.; Samper, M. (2020). Influence of Ultraviolet Radiation Exposure Time on Styrene-Ethylene-Butadiene-Styrene (SEBS) Copolymer. Polymers. 12(4):1-14. https://doi.org/10.3390/polym12040862S114124Picchioni, F., Giorgi, I., Passaglia, E., Ruggeri, G., & Aglietto, M. (2001). Blending of styrene-block-butadiene-block-styrene copolymer with sulfonated vinyl aromatic polymers. Polymer International, 50(6), 714-721. doi:10.1002/pi.692Zhu, J., Birgisson, B., & Kringos, N. (2014). Polymer modification of bitumen: Advances and challenges. European Polymer Journal, 54, 18-38. doi:10.1016/j.eurpolymj.2014.02.005Gupta, S., Chandra, T., Sikder, A., Menon, A., & Bhowmick, A. K. (2008). Accelerated weathering behavior of poly(phenylene ether)-based TPE. Journal of Materials Science, 43(9), 3338-3350. doi:10.1007/s10853-008-2484-6Mamodia, M., Indukuri, K., Atkins, E. T., De Jeu, W. H., & Lesser, A. J. (2008). Hierarchical description of deformation in block copolymer TPEs. Journal of Materials Science, 43(22), 7035-7046. doi:10.1007/s10853-008-3030-2Allen, N. S., Edge, M., Wilkinson, A., Liauw, C. M., Mourelatou, D., Barrio, J., & Martı́nez-Zaporta, M. A. (2000). Degradation and stabilisation of styrene–ethylene–butadiene–styrene (SEBS) block copolymer. Polymer Degradation and Stability, 71(1), 113-122. doi:10.1016/s0141-3910(00)00162-2Costa, P., Ribeiro, S., Botelho, G., Machado, A. V., & Lanceros Mendez, S. (2015). Effect of butadiene/styrene ratio, block structure and carbon nanotube content on the mechanical and electrical properties of thermoplastic elastomers after UV ageing. Polymer Testing, 42, 225-233. doi:10.1016/j.polymertesting.2015.02.002Tomacheski, D., Pittol, M., Lopes, A. P. M., Simões, D. N., Ribeiro, V. F., & Santana, R. M. C. (2017). Effects of Weathering on Mechanical, Antimicrobial Properties and Biodegradation Process of Silver Loaded TPE Compounds. Journal of Polymers and the Environment, 26(1), 73-82. doi:10.1007/s10924-016-0927-8Singh, B., & Sharma, N. (2008). Mechanistic implications of plastic degradation. Polymer Degradation and Stability, 93(3), 561-584. doi:10.1016/j.polymdegradstab.2007.11.008White, C. C., Tan, K. T., Hunston, D. L., Nguyen, T., Benatti, D. J., Stanley, D., & Chin, J. W. (2011). Laboratory accelerated and natural weathering of styrene–ethylene–butylene–styrene (SEBS) block copolymer. Polymer Degradation and Stability, 96(6), 1104-1110. doi:10.1016/j.polymdegradstab.2011.03.003Allen, N. (2004). Photooxidation of styrene–ethylene–butadiene–styrene (SEBS) block copolymer. Journal of Photochemistry and Photobiology A: Chemistry, 162(1), 41-51. doi:10.1016/s1010-6030(03)00311-3Flaris, V., & Stachurski, Z. H. (1992). The effects of processing on the mechanical properties of a polyolefin blend. Polymer International, 27(3), 267-273. doi:10.1002/pi.4990270312Li, Y., Li, L., Zhang, Y., Zhao, S., Xie, L., & Yao, S. (2009). Improving the aging resistance of styrene-butadiene-styrene tri-block copolymer and application in polymer-modified asphalt. Journal of Applied Polymer Science, n/a-n/a. doi:10.1002/app.31458Xu, X., Yu, J., Xue, L., Zhang, C., He, B., & Wu, M. (2017). Structure and performance evaluation on aged SBS modified bitumen with bi- or tri-epoxy reactive rejuvenating system. Construction and Building Materials, 151, 479-486. doi:10.1016/j.conbuildmat.2017.06.102Si Bachir, D., Dekhli, S., & Ait Mokhtar, K. (2016). Rheological Evaluation of Ageing Properties of SEBS Polymer Modified Bitumens. Periodica Polytechnica Civil Engineering, 397-404. doi:10.3311/ppci.7853Awaja, F., Gilbert, M., Kelly, G., Fox, B., & Pigram, P. J. (2009). Adhesion of polymers. Progress in Polymer Science, 34(9), 948-968. doi:10.1016/j.progpolymsci.2009.04.007Poisson, C., Hervais, V., Lacrampe, M. F., & Krawczak, P. (2006). Optimization of PE/binder/PA extrusion blow-molded films. II. Adhesion properties improvement using binder/EVA blends. Journal of Applied Polymer Science, 101(1), 118-127. doi:10.1002/app.22407Zhang, H., Guo, W., Yu, Y., Li, B., & Wu, C. (2007). Structure and properties of compatibilized recycled poly(ethylene terephthalate)/linear low density polyethylene blends. European Polymer Journal, 43(8), 3662-3670. doi:10.1016/j.eurpolymj.2007.05.001Guerrica-Echevarría, G., Eguiazábal, J. I., & Nazábal, J. (2007). Influence of compatibilization on the mechanical behavior of poly(trimethylene terephthalate)/poly(ethylene–octene) blends. European Polymer Journal, 43(3), 1027-1037. doi:10.1016/j.eurpolymj.2006.11.036Chang, Y.-W., Shin, J.-Y., & Ryu, S. H. (2004). Preparation and properties of styrene–ethylene/butylene–styrene(SEBS)–clay hybrids. Polymer International, 53(8), 1047-1051. doi:10.1002/pi.1480Chen, W.-C., Lai, S.-M., & Chen, C.-M. (2008). Preparation and properties of styrene-ethylene-butylene-styrene block copolymer/clay nanocomposites: I. Effect of clay content and compatibilizer types. Polymer International, 57(3), 515-522. doi:10.1002/pi.2377Qin, R.-Y., & Schreiber, H. P. (1999). Adhesion at partially restructured polymer surfaces. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 156(1-3), 85-93. doi:10.1016/s0927-7757(99)00061-8Zhang, X., Xie, F., Pen, Z., Zhang, Y., Zhang, Y., & Zhou, W. (2002). Effect of nucleating agent on the structure and properties of polypropylene/poly(ethylene–octene) blends. European Polymer Journal, 38(1), 1-6. doi:10.1016/s0014-3057(01)00182-3Beholz, L. G., Aronson, C. L., & Zand, A. (2005). Adhesion modification of polyolefin surfaces with sodium hypochlorite in acidic media. Polymer, 46(13), 4604-4613. doi:10.1016/j.polymer.2005.03.086Kinloch, A. J. (1980). The science of adhesion. Journal of Materials Science, 15(9), 2141-2166. doi:10.1007/bf00552302Lippert, T., & Dickinson, J. T. (2003). Chemical and Spectroscopic Aspects of Polymer Ablation:  Special Features and Novel Directions. Chemical Reviews, 103(2), 453-486. doi:10.1021/cr010460qVan der Leeden, M. C., & Frens, G. (2002). Surface Properties of Plastic Materials in Relation to Their Adhering Performance. Advanced Engineering Materials, 4(5), 280-289. doi:10.1002/1527-2648(20020503)4:53.0.co;2-zPukánszky, B. (2005). Interfaces and interphases in multicomponent materials: past, present, future. European Polymer Journal, 41(4), 645-662. doi:10.1016/j.eurpolymj.2004.10.035Tjong, S. C., Xu, S.-A., & Mai, Y.-W. (2003). Journal of Materials Science, 38(2), 207-215. doi:10.1023/a:1021132725370Sanchis, R., Fenollar, O., García, D., Sánchez, L., & Balart, R. (2008). Improved adhesion of LDPE films to polyolefin foams for automotive industry using low-pressure plasma. International Journal of Adhesion and Adhesives, 28(8), 445-451. doi:10.1016/j.ijadhadh.2008.04.002Brockmann, W., & Hüther, R. (1996). Adhesion mechanisms of pressure sensitive adhesives. International Journal of Adhesion and Adhesives, 16(2), 81-86. doi:10.1016/0143-7496(96)89797-1Brovko, O., Rosso, P., & Friedrich, K. (2002). Journal of Materials Science Letters, 21(4), 305-308. doi:10.1023/a:1017936206578Court, R. S., Sutcliffe, M. P. F., & Tavakoli, S. M. (2001). Ageing of adhesively bonded joints—fracture and failure analysis using video imaging techniques. International Journal of Adhesion and Adhesives, 21(6), 455-463. doi:10.1016/s0143-7496(01)00022-7Komvopoulos, K. (2003). Adhesion and friction forces in microelectromechanical systems: mechanisms, measurement, surface modification techniques, and adhesion theory. Journal of Adhesion Science and Technology, 17(4), 477-517. doi:10.1163/15685610360554384Pijpers, A. ., & Meier, R. J. (2001). Adhesion behaviour of polypropylenes after flame treatment determined by XPS(ESCA) spectral analysis. Journal of Electron Spectroscopy and Related Phenomena, 121(1-3), 299-313. doi:10.1016/s0368-2048(01)00341-3Yu, S., Hu, H., Zhang, Y., & Liu, Y. (2008). Effect of transfer film on tribological behavior of polyamide 66-based binary and ternary nanocomposites. Polymer International, 57(3), 454-462. doi:10.1002/pi.2337Żenkiewicz, M. (2007). Comparative study on the surface free energy of a solid calculated by different methods. Polymer Testing, 26(1), 14-19. doi:10.1016/j.polymertesting.2006.08.005Kumar, S., & Misra, R. K. (2007). Analysis of Banana Fibers Reinforced Low‐density Polyethylene/Poly(Є‐caprolactone) Composites. Soft Materials, 4(1), 1-13. doi:10.1080/15394450600823040Fowkes, F. ., McCarthy, D. ., & Mostafa, M. . (1980). Contact angles and the equilibrium spreading pressures of liquids on hydrophobic solids. Journal of Colloid and Interface Science, 78(1), 200-206. doi:10.1016/0021-9797(80)90508-1Owens, D. K., & Wendt, R. C. (1969). Estimation of the surface free energy of polymers. Journal of Applied Polymer Science, 13(8), 1741-1747. doi:10.1002/app.1969.070130815Zhao, Y., Tang, S., Myung, S.-W., Lu, N., & Choi, H.-S. (2006). Effect of washing on surface free energy of polystyrene plate treated by RF atmospheric pressure plasma. Polymer Testing, 25(3), 327-332. doi:10.1016/j.polymertesting.2005.12.007Hänni‐Ciunel, K., Findenegg, G. H., & von Klitzing, R. (2007). Water Contact Angle On Polyelectrolyte‐Coated Surfaces: Effects of Film Swelling and Droplet Evaporation. Soft Materials, 5(2-3), 61-73. doi:10.1080/15394450701554452Radovanovic, E., Carone, E., & Gonçalves, M. . (2004). Comparative AFM and TEM investigation of the morphology of nylon6-rubber blends. Polymer Testing, 23(2), 231-237. doi:10.1016/s0142-9418(03)00099-0Drnovská, H., Lapčík, L., Buršíková, V., Zemek, J., & Barros-Timmons, A. M. (2003). Surface properties of polyethylene after low-temperature plasma treatment. Colloid and Polymer Science, 281(11), 1025-1033. doi:10.1007/s00396-003-0871-8Lehocký, M., Drnovská, H., Lapčı́ková, B., Barros-Timmons, A. ., Trindade, T., Zembala, M., & Lapčı́k, L. (2003). Plasma surface modification of polyethylene. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 222(1-3), 125-131. doi:10.1016/s0927-7757(03)00242-5Ortiz-Magán, A. B., Pastor-Blas, M. M., Ferrándiz-Gómez, T. P., Morant-Zacarés, C., & Martín-Martínez, J. M. (2001). Plasmas and Polymers, 6(1/2), 81-105. doi:10.1023/a:1011352903775Mailhot, B., & Gardette, J. L. (1992). Polystyrene photooxidation. 2. A pseudo wavelength effect. Macromolecules, 25(16), 4127-4133. doi:10.1021/ma00042a013Mailhot, B., Jarroux, N., & Gardette, J.-L. (2000). Comparative analysis of the photo-oxidation of polystyrene and poly(α-methylstyrene). Polymer Degradation and Stability, 68(3), 321-326. doi:10.1016/s0141-3910(00)00016-1Luengo, C., Allen, N. S., Edge, M., Wilkinson, A., Parellada, M. D., Barrio, J. A., & Santa, V. R. (2006). Photo-oxidative degradation mechanisms in styrene–ethylene–butadiene–styrene (SEBS) triblock copolymer. Polymer Degradation and Stability, 91(4), 947-956. doi:10.1016/j.polymdegradstab.2005.06.017Han, X., Zhou, L., Liu, H., & Hu, Y. (2007). Effect of in situ oxidization with potassium permanganate on the morphologies of SEBS membranes. Polymer Degradation and Stability, 92(1), 75-85. doi:10.1016/j.polymdegradstab.2006.09.006Allen, N. S., Edge, M., Mourelatou, D., Wilkinson, A., Liauw, C. M., Dolores Parellada, M., … Ruiz Santa Quiteria, V. (2003). Influence of ozone on styrene–ethylene–butylene–styrene (SEBS) copolymer. Polymer Degradation and Stability, 79(2), 297-307. doi:10.1016/s0141-3910(02)00293-8Fombuena, V., Balart, J., Boronat, T., Sánchez-Nácher, L., & Garcia-Sanoguera, D. (2013). Improving mechanical performance of thermoplastic adhesion joints by atmospheric plasma. Materials & Design, 47, 49-56. doi:10.1016/j.matdes.2012.11.031Sanchis, M. R., Calvo, O., Fenollar, O., Garcia, D., & Balart, R. (2008). Characterization of the surface changes and the aging effects of low-pressure nitrogen plasma treatment in a polyurethane film. Polymer Testing, 27(1), 75-83. doi:10.1016/j.polymertesting.2007.09.002Sheikhy, H., Shahidzadeh, M., Ramezanzadeh, B., & Noroozi, F. (2013). Studying the effects of chain extenders chemical structures on the adhesion and mechanical properties of a polyurethane adhesive. Journal of Industrial and Engineering Chemistry, 19(6), 1949-1955. doi:10.1016/j.jiec.2013.03.008Švab, I., Musil, V., Šmit, I., & Makarovič, M. (2007). Mechanical properties of wollastonite-reinforced polypropylene composites modified with SEBS and SEBS-g-MA elastomers. Polymer Engineering & Science, 47(11), 1873-1880. doi:10.1002/pen.20897Sanchis, M. R., Blanes, V., Blanes, M., Garcia, D., & Balart, R. (2006). Surface modification of low density polyethylene (LDPE) film by low pressure O2 plasma treatment. European Polymer Journal, 42(7), 1558-1568. doi:10.1016/j.eurpolymj.2006.02.001Ganguly, A., & Bhowmick, A. K. (2009). Effect of polar modification on morphology and properties of styrene-(ethylene-co-butylene)-styrene triblock copolymer and its montmorillonite clay-based nanocomposites. Journal of Materials Science, 44(3), 903-918. doi:10.1007/s10853-008-3183-

Effect of welding orientation in angular distortion in multipass GMAW

The use of the welding process on an industrial scale has become significant over the years and is currently among the main processes for joining metallic materials. Along the weld, structural changes occur in the vicinity of the joint. These thermal stresses and geometric distortions are mostly undesirable and are complex to predict with precision. Using S235JR steel as the base material, laboratory experiments were carried out using the multipass GMAW process, with the aim of investigating the influence of the welding direction on angular distortion. To measure the distortions, a methodology was applied using equipment to identify the coordinates in the operational space with metrological precision. Through metrological and statistical analyses, we found that the orientation factor significantly influenced the final distortions and that the alternated orientation sequence resulted in less distortions.This work has been supported by FCT—Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: CIMO (UIDB/00690/2020).info:eu-repo/semantics/publishedVersio

Scaling Flows and Dissipation in the Dilute Fermi Gas at Unitarity

We describe recent attempts to extract the shear viscosity of the dilute Fermi gas at unitarity from experiments involving scaling flows. A scaling flow is a solution of the hydrodynamic equations that preserves the shape of the density distribution. The scaling flows that have been explored in the laboratory are the transverse expansion from a deformed trap ("elliptic flow"), the expansion from a rotating trap, and collective oscillations. We discuss advantages and disadvantages of the different experiments, and point to improvements of the theoretical analysis that are needed in order to achieve definitive results. A conservative bound based on the current data is that the minimum of the shear viscosity to entropy density ration is that eta/s is less or equal to 0.5 hbar/k_B.Comment: 32 pages, prepared for "BCS-BEC crossoverand the Unitary Fermi Gas", Lecture Notes in Physics, W. Zwerger (editor), Fig. 5 corrected, note added; final version, corrected typo in equ. 9

Cellular-to-dendritic and dendritic-to-cellular morphological transitions in a ternary al-mg-si alloy

The study is focused on the influence of solidification thermal parameters upon the evolution of the microstructure (either cells or dendrites) of an Al-3wt%Mg-1wt%Si ternary alloy. It is well known that the application properties of metallic alloys will greatly depend on the final morphology of the microstructure. As a consequence, various studies have been carried out in order to determine the ranges of cooling rates associated with dendritic-cellular transitions in multicomponent alloys. In the present research work, directional solidification experiments were conducted using either a Bridgman (steady-state) device or another device that allows the solidification under transient conditions (unsteady-state). Thus, a broad range of cooling rates (dot T), varying from 0.003K/s to 40K/s could be achieved. This led to the identification of a complete series of cellular/dendritic/cellular transitions. For low cooling rate experiments, low cooling rate cells to dendrites transition happens. Moreover, at a high cooling rate, a novel transition from dendrites to high cooling rate cells could be observed for the Al-3wt%Mg-1wt%Si alloy. Additionally, cell spacing λC and primary dendritic spacing λ1 are related to the cooling rate by power function growth laws characterized by the same exponent (-0.55) for both steady-state and unsteady-state solidification conditions529CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP23038.000069/2015-042012/08494-0; 2012/16328-2; 2013/23396-7; 2014/25809-

Inflationary Cosmology with Five Dimensional SO(10)

We discuss inflationary cosmology in a five dimensional SO(10) model compactified on $S^1/(Z_2\times Z_2')$, which yields $SU(3)_c\times SU(2)_L\times U(1)_Y\times U(1)_X$ below the compactification scale. The gauge symmetry $SU(5)\times U(1)_X$ is preserved on one of the fixed points, while ``flipped'' $SU(5)'\times U(1)'_X$ is on the other fixed point. Inflation is associated with $U(1)_X$ breaking, and is implemented through $F$-term scalar potentials on the two fixed points. A brane-localized Einstein-Hilbert term allows both branes to have positive tensions during inflation. The scale of $U(1)_X$ breaking is fixed from $\delta T/T$ measurements to be around $10^{16}$ GeV, and the scalar spectral index $n=0.98-0.99$. The inflaton field decays into right-handed neutrinos whose subsequent out of equilibrium decay yield the observed baryon asymmetry via leptogenesis.Comment: 1+19 pages, improved discussion of 5D cosmology, Version to appear in PR

Calibration of Smearing and Cooling Algorithms in SU(3)-Color Gauge Theory

The action and topological charge are used to determine the relative rates of standard cooling and smearing algorithms in pure SU(3)-color gauge theory. We consider representative gauge field configurations on $16^3\times 32$ lattices at $\beta=5.70$ and $24^3\times 36$ lattices at $\beta=6.00$. We find the relative rate of variation in the action and topological charge under various algorithms may be succinctly described in terms of simple formulae. The results are in accord with recent suggestions from fat-link perturbation theory.Comment: RevTeX, 25 pages, 22 figures, full resolution jpeg version of Fig. 22 can be obtained from http://www.physics.adelaide.edu.au/cssm/papers_etc/SmearingComp.jp

N-body simulations of galaxies and groups of galaxies with the Marseille GRAPE systems

I review the Marseille GRAPE systems and the N-body simulations done with them. I first describe briefly the available hardware and software, their possibilities and their limitations. I then describe work done on interacting galaxies and groups of galaxies. This includes simulations of the formation of ring galaxies, simulations of bar destruction by massive compact satellites, of merging in compact groups and of the formation of brightest members in clusters of galaxies.Comment: 13 pages, 5 figures, to be published in "Non-linear Dynamics and Chaos in Astrophysics", eds. J.R. Buchler, S. Gottesman, J. Hunter and H. Kandrup, Annals of the New York Academy of Science

Vortex states in binary mixture of Bose-Einstein condensates

The vortex configurations in the Bose-Einstein condensate of the mixture of two different spin states |F=1,m_f=-1> and |2,1> of ^{87}Rb atoms corresponding to the recent experiments by Matthews et. al. (Phys. Rev. Lett. 83, 2498 (1999)) are considered in the framework of the Thomas-Fermi approximation as functions of N_2/N_1, where N_1 is the number of atoms in the state |1,-1> and N_2 - in the state |2,1>. It is shown that for nonrotating condensates the configuration with the |1,-1> fluid forming the shell about the |2,1> fluid (configuration "a") has lower energy than the opposite configuration (configuration "b") for all values of N_2/N_1. When the |1,-1> fluid has net angular momentum and forms an equatorial ring around the resting central condensate |2,1>, the total energy of the system is higher than the ground energy, but the configuration "a" has lower energy than the configuration "b" for all N_2/N_1. On the other hand, when the |2> fluid has the net angular momentum, for the lowest value of the angular momentum \hbar l (l=1) there is the range of the ratio N_2/N_1 where the configuration "b" has lower energy than the configuration "a". For higher values of the angular momentum the configuration "b" is stable for all values of N_2/N_1.Comment: minor changes, references adde