Evolution of light domain walls interacting with dark matter, part 1

The evolution of domain walls generated in the early Universe is discussed considering an interaction between the walls and a major gaseous component of the dark matter. The walls are supposed able to reflect the particles elastically and with a reflection coefficient of unity. A toy Lagrangian that could give rise to such a phenomenon is discussed. In the simple model studied, highly non-relativistic and slowly varying speeds are obtained for the domain walls (approximately 10 (exp -2)(1+z)(exp -1)) and negligible distortions of the microwave background. In addition, these topological defects may provide a mechanism of forming the large scale structure of the Universe, by creating fluctuations in the dark matter (delta rho/rho approximately O(1)) on a scale comparable with the distance the walls move from the formation (in the model d less than 20 h(exp -1) Mpc). The characteristic scale of the wall separation can be easily chosen to be of the order of 100 Mpc instead of being restricted to the horizon scale, as usually obtained

Could the electroweak scale be linked to the large scale structure of the Universe?

We study a model where the domain walls are generated through a cosmological phase transition involving a scalar field. We assume the existence of a coupling between the scalar field and dark matter and show that the interaction between domain walls and dark matter leads to an energy dependent reflection mechanism. For a simple Yakawa coupling, we find that the vacuum expectation value of the scalar field is theta approx. equals 30GeV - 1TeV, in order for the model to be successful in the formation of large scale 'pancake' structures

Optical (VRI) Photometry in the Field of the Galaxy Cluster AC 118 at z=0.31

We present new photometric V-, R- and I-band data for the rich galaxy cluster AC 118 at z=0.31. The new photometry covers an area of 8.6x8.6 arcmin$^2$, corresponding to 2.9$\times$2.9 Mpc$^2$ (H$_0=50$ km s$^{-1}$ Mpc$^{-1}$, q$_0=0.5$ and $\Lambda = 0$). The data have been collected for a project aimed at studying galaxy evolution through the color-magnitude relation and the fundamental plane. We provide a catalogue including all the sources (N = 1206) detected in the cluster field. The galaxy sample is complete to V=22.8 mag (N_gal=574), R=22.3 mag (N_gal=649) and I=20.8 mag (N_gal=419). We give aperture magnitudes within a fixed aperture of 4.4 arcsec and Kron magnitudes. We also give photometric redshifts for 459 sources for which additional U- and K-band photometry is available. We derive and discuss the V- and R-band luminosity functions. The catalogue, which is distributed in electronic form, is intended as a tool for studies in galaxy evolution.Comment: 15 pages, 6 figures, A&A in pres

Light domain walls, massive neutrinos and the large scale structure of the Universe

Domain walls generated through a cosmological phase transition are considered, which interact nongravitationally with light neutrinos. At a redshift z greater than or equal to 10(exp 4), the network grows rapidly and is virtually decoupled from the matter. As the friction with the matter becomes dominant, a comoving network scale close to that of the comoving horizon scale at z of approximately 10(exp 4) gets frozen. During the later phases, the walls produce matter wakes of a thickness d of approximately 10h(exp -1)Mpc, that may become seeds for the formation of the large scale structure observed in the Universe

Aeroacústica de barras transversais de teto automotivas

Orientador: William Roberto WolfDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: Redução de ruído aeroacústico é uma crescente preocupação na indústria automotiva. Com a proliferação de Veículos Elétricos e Direção Autônoma, os ocupantes de um veículo estarão mais suscetíveis a ruídos aerodinâmicos. Os fenômenos aeroacústicos de natureza tonal são os mais severos em veículos automotores. Bagageiros de teto possuem uma barra transversal diretamente exposta ao escoamento e geram ruído em banda larga e um tonal aeólico característico. Atualmente, as soluções aplicadas ao ruído tonal são empíricas, sustentadas pelo fato de os perfis comerciais não serem rombudos como um cilindro, nem finos como um perfil de asa. O objetivo deste trabalho é investigar os mecanismos de geração de ruído em barras transversais de teto com perfil elíptico, através de medições acústicas em pista. Na primeira parte do projeto, medições de pressão e intensidade sonora feitas em pista e em túnel de vento aeroacústico foram correlacionadas com o objetivo de avaliar a precisão e repetitividade dos testes em pista. A medição de pressão sonora com um único microfone posicionado fora do veículo se demonstrou um método preciso na captura de efeitos de banda larga e estreita, apesar da condição não controlada do ruído de fundo. A interação da esteira da barra com o teto também foi avaliada através de medições acústicas de referência e visualização de escoamento. Na segunda parte, o ruído gerado por um perfil elíptico foi comparado ao ruído gerado por um cilindro circular e por um perfil NACA 0012 de mesma espessura e nas mesmas condições de operação. Os resultados mostraram que as características do ruído do perfil elíptico se aproximam às do cilindro circular em números de Reynolds mais baixos, e às do perfil NACA 0012 em velocidades mais altas. Na etapa seguinte, investigou-se o efeito de alterações geométricas do perfil elíptico no ruído gerado. Diferentes combinações de bordo de ataque e fuga foram testadas e demonstraram que o bordo de fuga é o principal contribuinte para o ruído tonal, enquanto que o bordo de ataque está associado ao ruído em banda larga. Bordos de fuga finos foram capazes de eliminar completamente o ruído tonal. Ângulos de incidência positivos e negativos apresentaram tendências contrárias em relação à redução de ruído, e se demonstraram soluções não efetivas em altas velocidades. Por final, soluções conhecidas como perturbação da camada limite foram testadas e comparadas com soluções inovadoras (Assopramento e Perfuração). Ambas técnicas reduziram efetivamente o ruído tonal mas apresentaram efeitos indesejados como a excitação de tons em alta frequênciaAbstract: Aeroacoustic noise reduction is one of the growing concerns in the automotive industry. With the advention of Electric Vehicles and Autonomous Driving, vehicle occupants will become more sensitive to aerodynamic noise. The most severe aeroacoustic phenomena in ground vehicles are the ones with a tonal nature. Roof carrier systems have a leading crossbar directly exposed to the airflow, generating broadband noise and a discrete aeolian tone. Nowadays, most of the applied solutions to aeolian tone are empirical, sustained by the fact that commercial crossbar profiles are not as blunt as a circular cylinder, neither as thin as a wing section. The objective of this project is to investigate the noise mechanisms involved in elliptical crossbars through actual acoustic measurements taken on track. The first part of the project correlated sound pressure and intensity measurements taken on track and in an aeroacoustic wind tunnel, with the objective of assessing track data accuracy and repeatability. Acoustic pressure taken outside the vehicle with a single microphone has demonstrated good accuracy in capturing both narrow and broadband noise effects, despite of the uncontrolled background noise. The crossbar wake interaction with the roof plane was also assessed through reference measurements and local flow visualization. The second part of the project compared the noise generated by an elliptical cylinder with that generated by a circular cylinder and a NACA 0012 airfoil with the same thicknesses and at the same operational conditions. Results have shown that the elliptical crossbar noise characteristics have similarities when compared to those of blunt bodies at low Reynolds numbers and wing sections at higher speeds. The following step investigated the effects of the ellipse geometry and angle of attack on the generated sound. Different leading and trailing edge combinations were tested and demonstrated that the trailing edge is the key contributor to the aeolian tone characteristics, while the leading edge affects primarily the broadband noise. Thin trailing edges were capable to completely eliminate the aeolian tone. Positive and negative incidence angles presented opposite trends towards noise reduction and have proven to be ineffective in higher speeds. Finally, industry-known solutions such as Boundary Layer Tripping (BLT) were assessed and compared to innovative solutions (Trailing Edge Blowing (TEB) and Perforation). Both TEB and Perforation were effective on reducing the aeolian tone but presented counter effects such as high frequency whistlingMestradoTermica e FluidosMestre em Engenharia Mecânic