Efficient calculation of formation energies of kink-pairs in BCC crystals

En materiales con estructura cristalina BCC el movimiento de dislocaciones de tipo tornillo a baja temperatura está asociado con la formación y el crecimiento de escalones en la línea de la dislocación. Para entender la movilidad de dislocaciones de tipo tornillo en estos materiales es muy importante la correcta predicción de las energías de nucleación de estos escalones. El cálculo a nivel atomístico de la mecánica de dislocaciones constituye un problema complicado desde el punto de vista tanto numérico como computacional. Este trabajo se centra en el cálculo de las energías de formación de distintas configuraciones de escalones dobles en cristales BCC y en ausencia de cargas exteriores. En nuestro modelo, basado en la teoría discreta de dislocaciones desarrollada por Ariza y Ortiz, la energía almacenada se calcula de forma eficiente mediante un algoritmo de programación basado en NVIDIA Compute Unified Device Architecture (CUDA). Los resultados obtenidos presentan un buen acuerdo con los calculados utilizando primeros principios y potenciales atomísticos, y los correspondientes a la teoría elástica de dislocaciones.Motion of screw dislocations in BCC materials at low temperature is believed to be related to the formation of mobile kinks on the dislocation line. Therefore, the accurate prediction of kink nucleation energies is required to fully describe mobility of screw dislocations in these materials. Studies of fundamental dislocation processes at atomic length scale are numerically and computationally intensive problems. This work studies the calculation of zero-stress formation energies of kink-pair configurations for BCC crystals. Our model for stored energy associated to a dislocation line configuration is based on the theory of discrete dislocations of Ariza and Ortiz. Its value is computed efficiently using an algorithm developed on the NVIDIA Compute Unified Device Architecture (CUDA). Results confirm those obtained using atomistic potentials and first principles calculations, and those based on the continuum theory of dislocations.Peer Reviewe

Multiple glomus tumors and segmental neurofibromatosis: there are no coincidences

Segmental neurofibromatosis is a rare subtype of neurofibromatosis type 1 (NF1). Glomus tumors are uncommon benign tumors. The authors report the association between these two rare conditions, not yet reported

Childhood hypopigmented mycosis fungoides: a commonly delayed diagnosis

Primary cutaneous lymphomas (PCLs) are exceedingly rare in children and adolescents, with mycosis fungoides (MF) being the most frequent PCL diagnosed in childhood. There are numerous unusual clinical variants of MF, including the hypopigmented type form (HMF). HMF is exceptional overall, but comparatively common among children. We present an 8-year-old boy with a 3-year history of progressive, generalised, scaly, hypopigmented round patches and few erythematous papules. He was first diagnosed with pityriasis alba (PA), and moisturisers were prescribed with no improvement. Skin biopsy showed typical features of MF, and the patient was successfully treated with narrowband ultraviolet B. HMF may simulate atopic dermatitis, PA, pityriasis lichenoides, tinea versicolour, vitiligo, postinflammatory hypopigmentation or leprosy. Therefore, persistent and unusual hypopigmented lesions should be biopsied to rule out this rare variant of MF

Paraneoplastic pemphigus with clinical features of lichen planus associated with low-grade B cell lymphoma

BACKGROUND: Neoplasia-induced lichen planus is described as a cell-mediated reaction to unknown epithelial antigens. Paraneoplastic pemphigus (PNP), characterized by the presence of a specific array of autoantibodies, probably represents a different form of presentation of the same autoimmune syndrome where the mucocutaneous expression depends on the dominant pathologic mechanism. METHODS: The authors report a case of PNP with predominant lichen planus-like lesions and review the relevant literature. We observed a 74-year-old female with vesico-bullous, erosive, target-shaped and flat papular lichenoid lesions on the lower legs, palms and soles, evolving for 3 weeks. Histopathology revealed a lichenoid dermatitis. Direct immunofluorescence showed C3 deposition around keratinocytes and epidermal IgG intranuclear deposition. Indirect immunofluorescence revealed circulating IgG with intercellular staining on rat bladder substrate. Immunoblotting demonstrated bands of 130, 190, 210 and 250 kDa antigens. A pararenal B cell lymphoma was found. RESULTS: Oral corticotherapy with 40 mg prednisolone daily was initiated with a good cutaneous response. Four months later, cyclophosphamide (50 mg/day) was introduced because of a discrete enlargement of the pararenal mass. The patient died on the seventh month of follow up as a result of respiratory insufficiency. CONCLUSION: PNP has different forms of presentation and the lack of a consensus about diagnostic criteria may contribute to underdiagnosed cases. Advances on the knowledge of the sensitivity and specificity of diagnostic criteria have allowed a better accuracy of diagnosis

Unilateral progressive osseous heteroplasia

A 50-year-old male patient presented with firm subcutaneous nodules and plaques with a gritty texture, unilaterally affecting the left side of the trunk and the left limbs. These lesions had had a progressive course since early childhood and caused functional impairment. There was no family history of similar disorders. No phospho-calcium metabolism abnormalities were observed. Biopsies of the affected areas demonstrated osteoma cutis. Analysis of DNA showed no mutation of the GNAS gene. The clinical features were consistent with progressive osseous heteroplasia, atypically presented in a unilateral form, probably revealing a mosaic distribution

Bowel-associated dermatosis-arthritis syndrome in an adolescent with short bowel syndrome

Bowel-associated dermatosis-arthritis syndrome (BADAS) is a neutrophilic dermatosis, characterized by the occurrence of arthritis and skin lesions related to bowel disease with or without bowel bypass. We report an unusual case of BADAS in a 15-year-old white male with congenital aganglionosis of the colon and hypoganglionosis of the small intestine and multiple bowel surgeries in childhood complicated by short bowel syndrome. He presented with recurrent peripheral polyarthritis, tenosynovitis, and painful erythematous subcutaneous nodules located on the dorsolateral regions of the legs and on the dorsa of the feet. Histological examination disclosed a neutrophilic dermatosis confirming the diagnosis of BADAS.Although an uncommon disease, especially at pediatric age, it is important to evoke the diagnosis of BADAS in children and adolescents with bowel disease, because treatment options and prognosis are distinct from other rheumatologic conditions

Pityriasis lichenoides et varioliformis acute: case report and review of the literature

We report a case of a 63-year-old man hospitalized for a polymorphous generalized eruption consisting of maculopapules with peripheral scaling, vesicopustules, and ulceronecrotic and crusted lesions measuring 5-20 mm, localized on his trunk and extremities, particularly exuberant in the flexural area. Histopathology showed necrotic keratinocytes with exocytosis of red blood cells and lymphocytes and a dermal perivascular and periadnexal inflammatory infiltrate, composed of CD8+/CD4-/CD30- T cells, indicating the clinical diagnosis of pityriasis lichenoides et varioliformis acuta. He was treated with erythromycin and methylprednisolone reduced gradually over 5 months, with a slow but complete response; the patient was without lesions after 2 years of follow-up. The authors want to remind of this rare entity which may present difficulties in diagnosis and therap