First report of partial albinism in genus Thrichomys (Rodentia: Echimyidae)

Reports about albinism in rodents are common. In the family Echimyidae, however, albinism is very rare. This is the second case of coat color variation reported within Echimyidae and the first for the genus Thrichomys. The pelages of Thrichomys pachyurus individuals with normal and variant coat color were observed under a fluorescent artificial light and were examined with a stereoscopic microscope. The descriptions of pelage color were based on the book "Color Standards and Color Nomenclature". The predominantly white pattern of coat color in individuals of T. pachyurus suggests a partial albinism caused by delay in migration time of melanoblasts from neural crest to epidermis. The habitat of T. pachyurus has a heavy vegetative cover, which offers natural protection against predators and high-quality nutrition.Registros de albinismo em roedores são comuns. Na família Echimyidae, no entanto, albinismo é muito raro. Este é o segundo caso de variação da cor da pelagem registrado para Echimyidae e o primeiro para o gênero Thrichomys. A pelagem de indivíduos de Thrichomys pachyurus com a cor normal e a variante foram observados sob luz fluorescente artificial e foram examinados com um microscópio estereoscópico. As descrições da cor da pelagem foram baseados no livro "Color Standards and Color Nomenclature". O padrão predominantemente branco da cor da pelagem no indivíduo de T. pachyurus sugere um abinismo parcial causado pelo atraso no tempo de migração dos melanoblastos da crista neural para a epiderme. O habitat de T. pachyurus tem uma densa cobertura vegetal, que oferece proteção natural contra predadores e nutrição de alta qualidade

First report of partial albinism in genus Thrichomys (Rodentia: Echimyidae)

Reports about albinism in rodents are common. In the family Echimyidae, however, albinism is very rare. This is the second case of coat color variation reported within Echimyidae and the first for the genus Thrichomys. The pelages of Thrichomys pachyurus individuals with normal and variant coat color were observed under a fluorescent artificial light and were examined with a stereoscopic microscope. The descriptions of pelage color were based on the book "Color Standards and Color Nomenclature". The predominantly white pattern of coat color in individuals of T. pachyurus suggests a partial albinism caused by delay in migration time of melanoblasts from neural crest to epidermis. The habitat of T. pachyurus has a heavy vegetative cover, which offers natural protection against predators and high-quality nutrition

Delay times and reflection in chaotic cavities with absorption

Absorption yields an additional exponential decay in open quantum systems which can be described by shifting the (scattering) energy E along the imaginary axis, E+i\hbar/2\tau_{a}. Using the random matrix approach, we calculate analytically the distribution of proper delay times (eigenvalues of the time-delay matrix) in chaotic systems with broken time-reversal symmetry that is valid for an arbitrary number of generally nonequivalent channels and an arbitrary absorption rate 1/\tau_{a}. The relation between the average delay time and the ``norm-leakage'' decay function is found. Fluctuations above the average at large values of delay times are strongly suppressed by absorption. The relation of the time-delay matrix to the reflection matrix S^{\dagger}S is established at arbitrary absorption that gives us the distribution of reflection eigenvalues. The particular case of single-channel scattering is explicitly considered in detail.Comment: 5 pages, 3 figures; final version to appear in PRE (relation to reflection extended, new material with Fig.3 added, experiment cond-mat/0305090 discussed

Electronic localization at mesoscopic length scales: different definitions of localization and contact effects in a heuristic DNA model

In this work we investigate the electronic transport along model DNA molecules using an effective tight-binding approach that includes the backbone on site energies. The localization length and participation number are examined as a function of system size, energy dependence, and the contact coupling between the leads and the DNA molecule. On one hand, the transition from an diffusive regime to a localized regime for short systems is identified, suggesting the necessity of a further length scale revealing the system borders sensibility. On the other hand, we show that the lenght localization and participation number, do not depended of system size and contact coupling in the thermodynamic limit. Finally we discuss possible length dependent origins for the large discrepancies among experimental results for the electronic transport in DNA sample

Analysis of symmetry breaking in quartz blocks using superstatistical random matrix theory

We study the symmetry breaking of acoustic resonances measured by Ellegaard et al., Phys. Rev. Lett. 77, 4918 (1996), in quartz blocks. The observed resonance spectra show a gradual transition from a superposition of two uncoupled components, one for each symmetry realization, to a single component well represented by a Gaussian orthogonal ensemble (GOE) of random matrices. We discuss the applicability of superstatistical random-matrix theory to the final stages of the symmetry breaking transition. A comparison is made between different formula of the superstatistics and a pervious work [Abd El-Hady et al, J. Phys. A: Math. Theor. 35, 2361 (2002)], which describes the same data by introducing a third GOE component. Our results suggest that the inverse-chi-square superstatistics could be used for studying the whole symmetry breaking process.Comment: 11 pages, 1 figur