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Biomedical subjects

E Sharon

Publications and source records attributed to E Sharon.

At least 19 recordsLinked to original sources
PubMed2001

Propagating solitary waves along a rapidly moving crack front.

A rapidly moving crack in a brittle material is often idealized as a one-dimensional object with a singular tip, moving through a two-dimensional material. However, in real three-dimensional materials, tensile cracks form a planar surface whose edge is a rapidly moving one-dimensional singular front. The dynamics of these fronts under repetitive interaction with material inhomogeneities (asperities) and the morphology of the fracture surface that they create are not yet understood. Here we show that perturbations to a crack front in a brittle material result in long-lived and highly localized waves, which we call 'front waves' These waves exhibit a unique characteristic shape and propagate along the crack front at approximately the Rayleigh wave speed (the speed of sound along a free surface). Following interaction, counter-propagating front waves retain both their shape and amplitude. They create characteristic traces along the fracture surface, providing cracks with both inertia and a new mode of dissipation. Front waves are intrinsically three-dimensional, and cannot exist in conventional two-dimensional theories of fracture. Because front waves can transport and distribute asperity-induced energy fluctuations throughout the crack front, they may help to explain how cracks remain a single coherent entity, despite repeated interactions with randomly dispersed asperities.

Journal Article↗
PubMed2000

Vaporization of melanin in oral tissues and skin with a carbon dioxide laser: a canine study.

PURPOSE: This study tested the efficacy of carbon dioxide (CO2) laser vaporization in ablating gingival, oral mucosal, and cutaneous melanin in dogs. MATERIALS AND METHODS: Three mongrel dogs with pigmentation of the oral mucosa, gingivae, and skin were used. Biopsy specimens from the melanin sites were obtained from all 3 dogs before laser application. Removal of the melanin sites was performed by using a 3 W continuous-wave CO2 laser. Biopsies of the treated areas were performed 1, 2, 4, and 6 weeks after laser treatment in all 3 dogs and also, at 11 weeks in 1 dog. The histologic sections were stained with hematoxylin and eosin and Masson-Fontana dye. A computerized morphometric program calculated the average percentage of the melanin layer in the Masson-Fontana-stained sections. RESULTS: Clinical and histologic examination showed the CO2 laser to be effective in eliminating the pigmented areas in all tissues treated. No recurrence of melanin was detected in either the oral mucosa or gingiva at any of the follow-up times. In the skin, however, a small amount of melanin repigmentation was noticeable. CONCLUSIONS: CO2 laser surgery proved an effective tool for obliterating superficial melanin discoloration. To prevent recurrence of the pigmentation, the area must be cleared completely of melanin, directing the laser beam carefully along the visible margins of the area.

Animals↗
PubMed2000

Analysis of lateral tooth movement during forced orthodontic eruption.

STATEMENT OF PROBLEM: Forced eruption is a prosthodontic procedure that enables the treatment of otherwise problematic restorative conditions. During the vertical orthodontic movement, the root may be moved laterally, affecting the position of a tooth in the arch. PURPOSE: This study quantified the degree of lateral movement possible during the eruptive procedure and addressed the significance of this movement from a theoretical and clinical standpoint. MATERIAL AND METHODS: A patient treatment, which demonstrated the movement in a single direction on the buccolingual axis, was isolated. On the basis of this theoretical model, a clinically relevant model was developed: A "worst-case" situation for each posterior tooth was calculated, from which clinical conclusions may be derived. RESULTS: . In a given extrusion angle of 30 degrees, a lateral movement/shift of 0.58 mm resulted per 1 mm of eruption distance. The lateral movement for every millimeter of eruption and the maximum extrusion angle for each of the maxillary and mandibular posterior teeth were calculated. CONCLUSION: The lateral movement that accompanies the forced eruption procedure may compromise or be used to esthetically enhance prosthodontic treatment.

Bicuspid↗
PubMed1998

Corneal thickness and curvature in normal-tension glaucoma.

PURPOSE: To determine whether normal-tension glaucoma, defined as a condition in which glaucomatous optic nerve and visual field changes exist without documentation of intraocular pressure greater than 21 mm Hg or other apparent cause for these changes, is overdiagnosed in patients with decreased central corneal thickness and curvature. METHODS: Twenty-one patients with normal-tension glaucoma were compared with 25 patients with primary open-angle glaucoma and 27 age-matched healthy subjects. Corneal thickness was determined by ultrasonic pachymetry. Corneal curvature was determined using a keratometer. Eyes with corneal pathology or previous intraocular surgery were excluded. RESULTS: Mean corneal thickness +/- SD in 21 eyes of 21 patients with normal-tension glaucoma was 0.521 +/- 0.037 mm, significantly (P = .0028) lower than in 25 eyes of 25 patients with primary open-angle glaucoma (0.556 +/- 0.035 mm) and 27 eyes of 27 healthy subjects (0.555 +/- 0.034). Mean corneal curvature in the three groups was not appreciably different: 43.90 +/- 1.81 diopters, 43.66 +/- 1.68 diopters, and 44.36 +/- 1.13 diopters in the patients with normal-tension glaucoma and primary open-angle glaucoma and the healthy subjects, respectively. CONCLUSIONS: Corneal thickness is significantly reduced in patients with normal-tension glaucoma compared with patients with primary open-angle glaucoma (P = .0028) and normal subjects (P = .0037). This may lead to underestimation of intraocular pressure and misdiagnosis in some of these patients. Corneal curvature was similar in patients with normal-tension glaucoma and primary open-angle glaucoma and in healthy subjects.

Aged↗
PubMed1997

Meloidogyne javanica surface proteins: characterization and lability.

Characterization of surface coat (SC) proteins including carbohydrate-binding proteins and glycoproteins of the plant-parasitic nematode Meloidogyne javanica 2nd-stage juvenile (J2) is reported. Extraction of surface proteins with sodium dodecyl sulfate (SDS) and separation by denaturing polyacrylamide gel electrophoresis (SDS-PAGE) results with bands at 6, 9, 14, 22, 26, 31, 46, 49, 58, 66, 80, 205 and 250 kDa. On Western blots, the neoglycoprotein, fucosylated-, mannosylated- and glucosylated-bovine serum albumin, reacted with the 14, 22, 26, 58 and 66 kDa bands. The lectins, Concanavalin A and wheat-germ agglutinin (WGA) labelled surface protein bands of 6, 9, 14, 31, 58 and 66 kDa; WGA also labelled the 22 and 26 kDA bands. Biotin reagents were used to specifically trace surface proteins on live J2. SDS-PAGE of biotinylated J2 extracts revealed only 2 specific biotin-protein bands at 46 and 49 kDa. The labile and transitory nature of Meloidogyne javanica SC was demonstrated by the dynamics of human red blood cells (HRBC) adherence to J2 of different ages. HRBC adherence was also used to demonstrate the SC recovery of detergent-treated J2, which was further exhibited in the SDS-PAGE profiles.

Animals↗
PubMed1995

Carbohydrate-recognition domains on the surface of phytophagous nematodes.

Human red blood cells (HRBC) adhered to preparasitic second-stage juveniles (J2) of Heterodera avenae, Heterodera schachtii, Meloidogyne javanica, Pratylenchus mediterraneus, Rotylenchulus reniformis, and Tylenchulus semipenetrans over the entire nematode body. Binding was conspicuously confined to the head and tail of Longidorus cohni, Xiphinema brevicolle, and Xiphinema index. Binding was Ca2+ and Mg2+ dependent. In contrast, HRBC did not adhere to Anguina tritici, Aphelenchoides subtenius, Ditylenchus dipsaci, M. javanica females, and Panagrellus redivivus, even in the presence of these cations. Incubation of M. javanica J2 with fucose, glucose, N-acetylglucosamine, mannose, or trypsin decreased the intensity of subsequent HRBC binding, while galactose and N-acetylgalactosamine increased binding intensity. HRBC binding was diminished when nematodes were pretreated with trypsin and eliminated when pretreatments with detergents removed the surface coat. HRBC adhered to nylon fibers coated with surface coat extracted from M. javanica J2; binding was Ca2+ and Mg2+ dependent and diminished when the nylon fibers were coated with bovine serum albumin or preincubated with fucose and mannose. These results demonstrate that HRBC adhesion involves carbohydrate moieties of HRBC and corresponding carbohydrate-recognition domains (CRD) distributed in the nematode surface coat. To our knowledge this is the first report of a surface CRD in the phylum Nematoda.

Animals↗
PubMed1975

Hyperuricosuria and increased tubular secretion of urate in sickle cell anemia.

Seven young adults with uric acid overproduction due to sickle cell anemia were normouricemic with a mean serum uric acid level of 4.9 mg/100 ml. Urate clearance was greater in these patients than in normal subjects or in patients with primary hyperuricemia due to uric acid overproduction. The increase in urate clearance was entirely accounted for by increased pyrazinamide suppressible urate clearance. Pyrazinamide administration abolished the uricosuric response to ribonucleic acid (RNA) feeding in these patients with sickle cell anemia, and maximal uricosuric response to the administration of probenecid was similar in the patients with sickle cell anemia and in normal subjects suggesting that reabsorption of both filtered and secreted urate was not impaired in sickle cell disease. Pyrazinamide suppressible urate clearance at maximal uricosuric response to probenecid was increased in patients with sickle cell disease suggesting increased tubular secretion of urate. This increase in urate secretion permits most young adults with urate overproduction due to sickle cell anemia to remain normouricemic and may account for the low frequency of secondary gout in this disease.

Adolescent↗