Interface disorder and layer transitions in Ising thin films

The disorder and layer transitions in the interface between an Ising spin-1/2 film denoted $(n)$, and an Ising spin-1 film denoted $(m)$, are studied using Monte Carlo simulations. The effects of both an external magnetic field, acting only on the spin-1/2 film, and a crystal magnetic field acting only on the spin-1 film, are studied for a fixed temperature and selected values of the coupling constant $J_p$ between the two films. It is found that for large values of the constant $J_p$, the layers of the film $(n)$, as well as those of the film $(m)$, undergo a first order layering transition. On the other hand, the only disordered layer of the film $(n)$ is that one belonging to the interface films $(n)/(m)$, for any values of the crystal field $\Delta$. We show the existence of a critical value of the crystal field $\Delta_c$, above which this particular layer of the film $(n)$ is disordered. We found that $\Delta_c$ depends on the values of the constant coupling $(J_p)$ between the two films.Comment: 6 pages Latex, 13 figures Postscript forma

A Monte Carlo study of random surface field effect on layering transitions

The effect of a random surface field, within the bimodal distribution, on the layering transitions in a spin-1/2 Ising thin film is investigated, using Monte Carlo simulations. It is found that the layering transitions depend strongly on the concentration $p$ of the disorder of the surface magnetic field, for a fixed temperature, surface and external magnetic fields. Indeed, the critical concentration $p_c(k)$ at which the magnetisation of each layer $k$ changes the sign discontinuously, decreases for increasing the applied surface magnetic field, for fixed values of the temperature $T$ and the external magnetic field $H$. Moreover, the behaviour of the layer magnetisations as well as the distribution of positive and negative spins in each layer, are also established for specific values of $H_s$, $H$, $p$ and the temperature $T$. \\Comment: 5 pages latex, 6 figures postscrip

Filmmakers in North Africa have been preoccupied by radical Islam

As part of our series examining the origins of Africa’s War of Terror, Jamal Bahmad analyses the social origins of Islamic militancy and terrorism in North and West Africa through its depiction in film

Migraine associated with auditory-vestibular dysfunction

SummaryThe association between hearing and balance disorders with migraine is known since the times of the ancient Greeks, when Aretaeus from Cappadocia in 131 B.C, made an accurate and detailed description of this occurrence during a migraine episode. We present a broad review of migraine neurotological manifestations, using the most recent publications associated with epidemiology, clinical presentation, pathophysiology, diagnostic methods and treatment for this syndrome.Aimto describe the clinical entity: “Migraine associated with auditory-vestibular dysfunction” in order to help otorhinolaryngologists and neurologists in the diagnosis and management of such disorder.Final RemarksThere is a strong association between neurotological symptoms and migraine, and the auditory-vestibular dysfunction-associated migraine is the most common cause of spontaneous episodic vertigo (non-positional). Symptoms may vary broadly among patients, making it a diagnostic challenge to the otorhinolaryngologist. This entity usually presents with positional or spontaneous vertigo spells, lasting for seconds or days, associated with migraine symptoms. A better understanding of the relationship between central vestibular mechanisms and migraine mechanisms, besides the discovery of ionic channel disorders in some cases of migraine, ataxia and vertigo, may lead to a better understanding of migraine pathophysiology associated with audio-vestibular disorder