Free and forced wave propagation in a Rayleigh-beam grid: flat bands, Dirac cones, and vibration localization vs isotropization

In-plane wave propagation in a periodic rectangular grid beam structure, which includes rotational inertia (so-called 'Rayleigh beams'), is analyzed both with a Floquet-Bloch exact formulation for free oscillations and with a numerical treatment (developed with PML absorbing boundary conditions) for forced vibrations (including Fourier representation and energy flux evaluations), induced by a concentrated force or moment. A complex interplay is observed between axial and flexural vibrations (not found in the common idealization of out-of-plane motion), giving rise to several forms of vibration localization: 'X-', 'cross-' and 'star-' shaped, and channel propagation. These localizations are triggered by several factors, including rotational inertia and slenderness of the beams and the type of forcing source (concentrated force or moment). Although the considered grid of beams introduces an orthotropy in the mechanical response, a surprising 'isotropization' of the vibration is observed at special frequencies. Moreover, rotational inertia is shown to 'sharpen' degeneracies related to Dirac cones (which become more pronounced when the aspect ratio of the grid is increased), while the slenderness can be tuned to achieve a perfectly flat band in the dispersion diagram. The obtained results can be exploited in the realization of metamaterials designed to control wave propagation.Comment: 25 pages, 20 figure

Prestress tuning of negative refraction and wave channeling from flexural sources

The quest for wave channeling and manipulation has driven a strong research effort on topological and architected materials, capable of propagating localized electromagnetical or mechanical signals. With reference to an elastic structural grid, which elements can sustain both axial and flexural deformations, it is shown that material interfaces can be created with structural properties tuned by prestress states to achieve total reflection, negative refraction, and strongly localized signal channeling. The achievement of a flat lens and topologically localized modes is demonstrated and tunability of the system allows these properties to hold for a broad range of wavelengths. An ingredient to obtain these effects is the use, suggested here and never attempted before, of concentrated pulsating moments. The important aspect of the proposed method is that states of prestress can be easily removed or changed to tune with continuity the propagational characteristics of the medium, so that a new use of vibration channeling and manipulation is envisaged for elastic materials.Comment: 10 pages, 5 figure

The usefulness of c-Kit in the immunohistochemical assessment of melanocytic lesions

C-Kit (CD117), the receptor for the stem cell factor, a growth factor for melanocyte migra- tion and proliferation, has shown differential immunostaining in various benign and malig- nant melanocytic lesions. The purpose of this study is to compare c-Kit immunostaining in benign nevi and in primary and metastatic malignant melanomas, to determine whether c-Kit can aid in the differential diagnosis of these lesions. c-Kit immunostaining was per- formed in 60 cases of pigmented lesions, including 39 benign nevi (5 blue nevi, 5 intra- dermal nevi, 3 junctional nevi, 15 cases of pri- mary compound nevus, 11 cases of Spitz nevus), 18 cases of primary malignant melanoma and 3 cases of metastatic melanoma. The vast majority of nevi and melanomas examined in this study were posi- tive for c-Kit, with minimal differences between benign and malignant lesions. C-Kit cytoplasmatic immunoreactivity in the intraepidermal proliferating nevus cells, was detected in benign pigmented lesions as well as in malignant melanoma, increasing with the age of patients (P=0.007) in both groups. The patient’s age at presentation appeared to be the variable able to cluster benign and malignant pigmented lesions. The percentage of c-Kit positive intraepidermal nevus cells was better associated with age despite other vari- ables (P=0.014). The intensity and percentage of c-Kit positivity in the proliferating nevus cells in the dermis was significantly increased in malignant melanocytic lesions (P=0.015 and P=0.008) compared to benign lesions (compound melanocytic nevi, Spitz nevi, intradermal nevi, blue nevi). Immunostaning for c-Kit in metastatic melanomas was nega- tive. Interestingly in two cases of melanoma occurring on a pre-existent nevus, the melanoma tumor cells showed strong cytoplas- matic and membranous positivity for c-kit, in contrast with the absence of any immunoreac- tivity in pre-existent intradermal nevus cells. C-Kit does not appear to be a strong immuno- histochemical marker for distinguishing melanoma from melanocytic nevi, if we consid- er c-Kit expression in intraepidermal prolifer- ating cells. The c-Kit expression in proliferat- ing melanocytes in the dermis could help in the differential diagnosis between a superfi- cial spreading melanoma (with dermis inva- sion) and a compound nevus or an intradermal nevus. Finally, c-Kit could be a good diagnostic tool for distinguishing benign compound nevi from malignant melanocytic lesions with der- mis invasion and to differentiate metastatic melanoma from primary melanoma

The Use of Barbed Suture for Intracorporeal Mechanical Anastomosis During a Totally Laparoscopic Right Colectomy: Is It Safe? A Retrospective Nonrandomized Comparative Multicenter Study

Background. A totally laparoscopic right colectomy could be perceived as a more challenging procedure over a laparoscopic-assisted right colectomy owing to the difficulty of intracorporeal anastomosis and the closure of the enterotomy. The aim of this study is to evaluate the safety and efficacy of the barbed auto-locking absorbable suture for the closure of an anastomotic stapler-access enterotomy during a totally laparoscopic right colectomy. Methods. From January 2010 to April 2016, data from patients who had undergone a laparoscopic right colectomy in 2 different departments of 2 institutions (the Department of General and Minimally Invasive Surgery, San Camillo Hospital in Trento and the Department of Surgical Specialties and Nephrology, University Federico II in Naples) were retrospectively analyzed. We compared the data of patients in whom the stapler-access enterotomy was closed through a conventional absorbable suture (Group A), with the data of patients in whom a stapler-access enterotomy was closed through a V-Loc 180 suture (Group B). Biometric features and intraoperative and postoperative data were collected and analyzed. Results. The 2 groups (Group A: 40 patients; Group B: 40 patients) were comparable for biometric features and postoperative outcomes. The anastomosing time was lower in Group B. A statistically significant difference was noted in the mean operative time between Groups A and B (Group A = 134.92 ± 34.17; Group B = 120.92 ± 23.27, P =.035). Only one anastomotic leakage per group was recorded, each treated with an anastomosis redo. During the reoperations, we find in both groups an intact stapler-access enterotomy. Conclusion. On retrospective analysis, barbed suture appears to be safe and efficient for closure of the stapler-access enterotomy during totally laparoscopic right colectomy

Effect of influenza-induced fever on human bioimpedance values

BACKGROUND AND AIMS: Bioelectrical impedance analysis (BIA) is a widely used technique to assess body composition and nutritional status. While bioelectrical values are affected by diverse variables, there has been little research on validation of BIA in acute illness, especially to understand prognostic significance. Here we report the use of BIA in acute febrile states induced by influenza. METHODS: Bioimpedance studies were conducted during an H1N1 influenza A outbreak in Venezuelan Amerindian villages from the Amazonas. Measurements were performed on 52 subjects between 1 and 40 years of age, and 7 children were re-examined after starting Oseltamivir treatment. Bioelectrical Impedance Vector Analysis (BIVA) and permutation tests were applied. RESULTS: For the entire sample, febrile individuals showed a tendency toward greater reactance (p=0.058) and phase angle (p=0.037) than afebrile individuals, while resistance and impedance were similar in the two groups. Individuals with repeated measurements showed significant differences in bioimpedance values associated with fever, including increased reactance (p<0.001) and phase angle (p=0.007), and decreased resistance (p=0.007) and impedance (p<0.001). CONCLUSIONS: There are bioelectrical variations induced by influenza that can be related to dehydration, with lower extracellular to intracellular water ratio in febrile individuals, or a direct thermal effect. Caution is recommended when interpreting bioimpedance results in febrile states