Avalanche Dynamics in Evolution, Growth, and Depinning Models

The dynamics of complex systems in nature often occurs in terms of punctuations, or avalanches, rather than following a smooth, gradual path. A comprehensive theory of avalanche dynamics in models of growth, interface depinning, and evolution is presented. Specifically, we include the Bak-Sneppen evolution model, the Sneppen interface depinning model, the Zaitsev flux creep model, invasion percolation, and several other depinning models into a unified treatment encompassing a large class of far from equilibrium processes. The formation of fractal structures, the appearance of $1/f$ noise, diffusion with anomalous Hurst exponents, Levy flights, and punctuated equilibria can all be related to the same underlying avalanche dynamics. This dynamics can be represented as a fractal in $d$ spatial plus one temporal dimension. We develop a scaling theory that relates many of the critical exponents in this broad category of extremal models, representing different universality classes, to two basic exponents characterizing the fractal attractor. The exact equations and the derived set of scaling relations are consistent with numerical simulations of the above mentioned models.Comment: 27 pages in revtex, no figures included. Figures or hard copy of the manuscript supplied on reques

Granular fluid thermostatted by a bath of elastic hard spheres

The homogeneous steady state of a fluid of inelastic hard spheres immersed in a bath of elastic hard spheres kept at equilibrium is analyzed by means of the first Sonine approximation to the (spatially homogeneous) Enskog--Boltzmann equation. The temperature of the granular fluid relative to the bath temperature and the kurtosis of the granular distribution function are obtained as functions of the coefficient of restitution, the mass ratio, and a dimensionless parameter $\beta$ measuring the cooling rate relative to the friction constant. Comparison with recent results obtained from an iterative numerical solution of the Enskog--Boltzmann equation [Biben et al., Physica A 310, 308 (202)] shows an excellent agreement. Several limiting cases are also considered. In particular, when the granular particles are much heavier than the bath particles (but have a comparable size and number density), it is shown that the bath acts as a white noise external driving. In the general case, the Sonine approximation predicts the lack of a steady state if the control parameter $\beta$ is larger than a certain critical value $\beta_c$ that depends on the coefficient of restitution and the mass ratio. However, this phenomenon appears outside the expected domain of applicability of the approximation.Comment: 16 pages, 7 figures; minor changes; to be published in Phys. Rev.

Infestazione da Dermanyssus gallinae nell'uomo: un problema di igiene urbana?

Gli Autori riportano 6 episodi di dermatite da Dermanyssus gallinae (De Geer, 1778) nell’uomo. Tutti i casi si sono verificati in ambiente cittadino ed hanno interessato persone che non avevano alcun contatto con il pollame, ritenuto il principale serbatoio dell’acaro. In prossimità degli ambienti infestati era sempre possibile riscontrare la presenza consistente di colombi di città o di loro nidi abbandonati. L’aumento incontrollato delle popolazioni di colombi è un problema oramai riconosciuto universalmente ed è diventato, in alcune città, una vera e propria emergenza. È noto che Dermanyssus gallinae circola tra questi animali con notevole frequenza, tanto da essere considerato il più diffuso ectoparassita ematofago della specie. La stretta promiscuità di questi uccelli con l’uomo, oramai costante in ambiente urbano, amplifica le occasioni di contatto tra Dermanyssus gallinae e persone ed induce a considerare questa parassitosi un problema emergente di sanità pubblica. L’acaro, infatti, in mancanza di uccelli su cui compiere il pasto di sangue, può compiere migrazioni alla ricerca di un ospite su cui alimentarsi, invadere le abitazioni e infestare l’uomo. Il mancato sospetto e/o riconoscimento della patologia dermatologica, peraltro caratterizzata da lesioni aspecifiche, al di fuori dei contesti rurali, in pazienti apparentemente lontani da animali portatori e la difficoltà di individuare precocemente il parassita nell’ambiente, per la peculiarità del suo ciclo biologico, sono i principali fattori che contribuiscono alla sottostima della infestazione in aree metropolitane

An urban outbreak of red mite dermatitis in Italy

In this paper an urban outbreak dermatitis is reported. Case reports of red mite dermatitis are rare, because it is difficult to detect and accurately identify red mites, and thus to relate symptoms to those parasites. There Is little mention of red mite dermatitis in medical textbooks. Physicians and dermatologists are keenly aware of dermatoses associated with the burrowing mites Sarcoptes scabiei. If dermatitis is caused by ectoparasites of zoonotic interest, it is often misdiagnosed. Indeed, it is common to see skin damage, but not to find arthropods on patients. Thus, the occurrence of red mite represents the principal ectoparasite acquired by humans in an hurban environment from feral pigeons, together with the pigeon tick, Argas reflex. Today, feral pigeons are among the most successful avian settlers in our cities, where they have few enemies and food is always abundant

Pseudoscabies caused by Dermanyssus gallinae in Italian city-dwellers: a new setting for an old dermatitis

Dermanyssus gallinae (De Geer 1778; the red poultry mite or chicken mite; fig. 1) is the most common mite associated with feral pigeons (Columba livia).1,2 It is a nocturnal blood-sucking ectoparasite and stays on the bird to feed only. During the daytime, it is usually foundin close proximity to the nest (1). In the absence of its usual host, the red mite can also infest mammals and cause a non-specific dermatitis associated with intense itching in humans. Infestations are often misdiagnosed and inevitably lead to failures in treatment. Figure 1. Figure 1. Open in figure viewerDownload Powerpoint slide D. gallinae, female: an egg is visible within the abdomen. This report outlines the importance of the red mite associated disease in humans through the report of seven episodes of pseudoscabies caused by D. gallinae in Italian cities, from 2001 to 2007. All cases shared common features. Particularly, all the patients lived and/or worked in urban environments but had no contact with animals or poultry farms. In five of the cases, people were infested in their homes and in the remaining two cases at work. Abandoned pigeon nests were always found in close proximity to the rooms infested by the mites. Medical consultations failed to solve the human dermatitis, which returned when symptomatic treatment with antihistamines and corticosteroids stopped. Indeed, diagnoses were consistently generic, and even when skin lesions were attributed to acariasis, the possibility of an animal to human cross-infection was not considered. Our experience confirms that most dermatologists have difficulty identifying ectoparasitoses, such as those that arise within new or atypical conditions. This is probably the main reason why similar cases of gamasidosis are more difficult to recognize than classical ones occurring in rural areas. The cases reported here give new insights into the sanitary role of D. gallinae infestation for humans living in urban areas. They also underline the need for dermatologists to be more aware of this threat and more familiar with its presentation and management. The meaning of these mites in public health also stems from their role as potential allergens and reservoirs of pathogens.1,3–5 Red mite is able to survive for long periods without a blood meal. This can lead to recurrent episodes of pruritic dermatitis (as has been observed in occasionaly-used buildings i.e. holiday homes). Therefore, the long-lasting absence of the human host does not guarantee the elimination of the mite from the environment, and a period of more than 9 months is necessary.6 In conclusion, the differential diagnosis of non-specific dermatitis in people living in urban settings should always include pseudoscabies caused by D. gallinae, particularly when the lesions develop in spring and the patients live and/or work on the upper floors of buildings. When the clinical presentation is non-specific and the arthropod cannot be found in cutaneous lesions, the environmental anamnesis could be a useful tool to diagnose successfully pseudoscabies. Dermatologists should provide the patients with complete instructions on how to inspect the living quarters and identify the mite (i.e. shape, colour, size of the mite; nocturnal feeding habits; typical hiding places), if suspicious elements emerge. The successful identification of the mite is absolutely fundamental to manage the clinical episodes correctly: specimens should be collected from the environment and sent to the laboratory of entomology for further identification. The involvement of a veterinary parasitologist can also be useful for a rapid diagnosis. Nowadays, the increase of synanthropic animals carries a high risk of zoonotic diseases and requires the collaboration of physicians and veterinarians as well as public health care officials