Frictional Dermatosis in a Courier Driver.
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ABSTRACT:
SUBMITTER: Wollina U
PROVIDER: S-EPMC5535681 | biostudies-other | 2017 Jul
REPOSITORIES: biostudies-other
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Project description:ImportanceErosive pustular dermatosis (EPD) is a rare condition that typically affects actinically damaged skin of the scalp. Characterized by sterile pustules, erosions, and crusts, EPD is difficult to treat and heals slowly. The exact cause of EPD is unknown, although trauma is an inciting factor.ObjectiveTo describe 3 women who presented with prolonged facial erosions after cosmetic resurfacing procedures, specifically fully ablative carbon dioxide laser or medium-depth chemical peel.Design, setting, and participantsThis case series describes the clinical features, histopathological findings, laboratory results, and treatment of 3 patients with an ultimate diagnosis most consistent with facial EPD. Patients were evaluated between September 10, 2010, and May 6, 2016, in a dermatology clinic in an academic medical center. The patients were 3 women seeking diagnostic evaluation and therapeutic options for nonhealing facial erosions occurring after ablative procedures (carbon dioxide laser resurfacing or Jessner solution/trichloroacetic acid chemical peel).Main outcomes and measuresHistologic examination and wound culture from initial presentation as well as clinical follow-up documenting improvement with therapeutic interventions.ResultsAll 3 patients were women in their 50s or 60s for whom EPD was deemed to be the best diagnosis, after infection, immunobullous disorders, and other pustular dermatoses were considered. Histologic features were nonspecific. Treatment included a combination of topical and systemic therapies, such as corticosteroids, dapsone, isotretinoin, and/or antibiotics. Watchful waiting (tincture of time) appeared to be central to the healing process.Conclusions and relevanceAfter cosmetic resurfacing, patients may develop EPD isolated to the face. As a diagnosis of exclusion that should be considered in patients who have nonhealing wounds following ablative procedures, EPD is challenging to treat and may require the use of anti-inflammatory agents. Recognizing this condition is important, especially as cosmetic procedures become more widespread.
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Project description:Stiff scales adorn the exterior surfaces of fishes, snakes, and many reptiles. They provide protection from external piercing attacks and control over global deformation behavior to aid locomotion, slithering, and swimming across a wide range of environmental condition. In this report, we investigate the dynamic behavior of biomimetic scale substrates for further understanding the origins of the nonlinearity that involve various aspect of scales interaction, sliding kinematics, interfacial friction, and their combination. Particularly, we study the vibrational characteristics through an analytical model and numerical investigations for the case of a simply supported scale covered beam. Our results reveal for the first time that biomimetic scale beams exhibit viscous damping behavior even when only Coulomb friction is postulated for free vibrations. We anticipate and quantify the anisotropy in the damping behavior with respect to curvature. We also find that unlike static pure bending where friction increases bending stiffness, a corresponding increase in natural frequency for the dynamic case does not arise for simply supported beam. Since both scale geometry, distribution and interfacial properties can be easily tailored, our study indicates a biomimetic strategy to design exceptional synthetic materials with tailorable damping behavior.
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Project description:When two objects are in contact, the force necessary to overcome friction is larger than the force necessary to keep sliding motion going. This difference between static and dynamic friction is usually attributed to the growth of the area of real contact between rough surfaces in time when the system is at rest. We directly measure the area of real contact and show that it actually increases during macroscopic slip, despite the fact that dynamic friction is smaller than static friction. This signals a decrease in the interfacial shear strength, the friction per unit contact area, which is due to a mechanical weakening of the asperities. This provides a novel explanation for stick-slip phenomena in, e.g., earthquakes.
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Project description:During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or "pseudotachylytes." It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics.
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Project description:Recent experiments indicate that frictional sliding occurs by nucleation of detachment fronts at the contact interface that may appear well before the onset of global sliding. This intriguing precursory activity is not accounted for by traditional friction theories but is extremely important for friction dominated geophysical phenomena as earthquakes, landslides or avalanches. Here we simulate the onset of slip of a three dimensional elastic body resting on a surface and show that experimentally observed frictional precursors depend in a complex non-universal way on the sample geometry and loading conditions. Our model satisfies Archard's law and Amontons' first and second laws, reproducing with remarkable precision the real contact area dynamics, the precursors' envelope dynamics prior to sliding, and the normal and shear internal stress distributions close to the interfacial surface. Moreover, it allows to assess which features can be attributed to the elastic equilibrium, and which are attributed to the out-of-equilibrium dynamics, suggesting that precursory activity is an intrinsically quasi-static physical process. A direct calculation of the evolution of the Coulomb stress before and during precursors nucleation shows large variations across the sample, explaining why earthquake forecasting methods based only on accumulated slip and Coulomb stress monitoring are often ineffective.
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Project description:ImportancePyoderma gangrenosum and necrotizing Sweet syndrome are diagnostically challenging variants of neutrophilic dermatosis that can clinically mimic the cutaneous and systemic features of necrotizing fasciitis. Improved characterization of these rare variants is needed, as improper diagnosis may lead to inappropriate or delayed treatment and the potential for morbidity.ObjectiveTo determine the characteristics of necrotizing neutrophilic dermatosis to improve diagnostic accuracy and distinguish from infection.Design, setting, and participantsA case series of patients with necrotizing neutrophilic dermatosis treated at 3 academic hospitals (University of California San Francisco, Oregon Health and Science University, and University of Minnesota) from January 1, 2015, to December 31, 2017, was performed along with a literature review of related articles published between January 1, 1980, and December 31, 2017. Data were obtained from medical records as well as Medline and Embase databases. All patients had signs resembling necrotizing infection and had a final diagnosis of pyoderma gangrenosum with systemic features or necrotizing Sweet syndrome. Patients were excluded if a diagnosis other than neutrophilic dermatosis was made, if key clinical information was missing, and if reported in a non-English language.Main outcomes and measuresDescription of key characteristics of necrotizing neutrophilic dermatosis.ResultsOverall, 54 patients with necrotizing neutrophilic dermatosis were included, of which 40 had pyoderma gangrenosum with systemic features and 14 had necrotizing Sweet syndrome. Of the 54 patients, 29 (54%) were male and 25 (46%) were female, with a mean (SD) age of 51 (19) years. Skin lesions commonly occurred on the lower (19 [35%]) and upper (13 [24%]) extremities and developed after a surgical procedure (22 [41%]) or skin trauma (10 [19%]). Shock was reported in 14 patients (26%), and leukemoid reaction was seen in 15 patients (28%). Of the patients with necrotizing neutrophilic dermatosis, 51 (94%) were initially misdiagnosed as necrotizing fasciitis and subsequently received inappropriate treatment. Debridement was performed in 42 patients (78%), with a mean (SD) of 2 (2 [range, 1-12]) debridements per patient. Four amputations (7%) were performed. Forty-nine patients (91%) received antibiotics when necrotizing neutrophilic dermatosis was misdiagnosed as an infection, and 50 patients (93%) received systemic corticosteroids; all patients responded to immunosuppressants.Conclusions and relevanceA complex spectrum of clinical findings of pyoderma gangrenosum and Sweet syndrome with prominent systemic inflammation exists that defines a new subset of neutrophilic dermatoses, termed necrotizing neutrophilic dermatoses; recognizing the difference between this variant and severe infection may prevent unnecessary surgical procedures and prolonged disease morbidity associated with a misdiagnosis and may expedite appropriate medical management.
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