Effect of gluon-exchange pair-currents on the ratio G(E(P))/G(M(P))

The effect of one-gluon-exchange (OGE) pair-currents on the ratio $\mu_p G_E^p/G_M^p$ for the proton is investigated within a nonrelativistic constituent quark model (CQM) starting from $SU(6) \times O(3)$ nucleon wave functions, but with relativistic corrections. We found that the OGE pair-currents are important to reproduce well the ratio $\mu_p G_E^p/G_M^p$. With the assumption that the OGE pair-currents are the driving mechanism for the violation of the scaling law we give a prediction for the ratio $\mu_n G_E^n/G_M^n$ of the neutron.Comment: 5 pages, 4 figure

Mechanical Properties of Dual-Cured Resin Luting Agents for Ceramic Restoration

Purpose: The aim of the present study was to evaluate the mechanical properties including surface hardness, flexural strength, and flexural modulus of two dual-cured resin luting agents (New Resin Cement [NRC] and Variolink II [VLII]) irradiated through four different thickness of leucite ceramics (0, 1, 2, and 3 mm) and their shear bond strength to zirconia ceramic (Cercon) using each ceramic primer. Materials and Methods: Knoop hardness was measured on a thin layer of resin luting agent on the ceramic surface. Three-point bending tests were performed after 24 h storage at 37°C. Two different-shaped zirconia ceramic specimens with or without sandblasting with alumina were treated with each primer. The specimens were then cemented together with each resin luting agent. Half of the specimens were stored in water at 37°C for 24 h and the other half were thermocycled 5,000 times. Results: VLII revealed statistically higher Knoop hardness and flexural modulus than NRC for each thickness of ceramic. No significant differences in flexural strength were observed between VLII and NRC for each ceramic spacer. Reduction of the mechanical properties with increase of ceramic thickness varied for each property. However, these properties were similar between the two materials. Blasting with alumina was significantly effective for increasing shear bond strength of both resin luting agents before and after thermal cycling. The use of New Ceramic Primer showed the highest shear bond strength and maintained bond durability after 5,000 thermocycles. Conclusion: Mechanical properties of NRC dual-cured resin luting agent appear adequate for ceramic restorations.This is an electronic version of an Article published in Journal of Prosthodontics 16(5): 370-376, 2007

Design and analysis of cross vaults along history

The history of cross vaults began almost 2,000 years ago with a widespread use during the Middle Ages and Renaissance, becoming nowadays one of the most diffused and fascinating structural typologies of the European building cultural heritage. However, conversely to the undeniable excellence achieved by the ancient masons, the structural behavior of these elements is still at the center of the scientific debate. In this regard, with the aim of reviewing the knowledge on this subject as a concise and valuable support for researchers involved in conservation of historical buildings, with a focus on design rules and structural analysis, the present study firstly introduces the cross vaults from a historical perspective, by describing the evolution of the main geometrical shapes together with basic practical rules used to size them. Then, the article deals with the subsequent advancements in structural analysis methods of vaults, until the development of modern limit analysis.This work was partially carried out under the program "Dipartimento di Protezione Civile - Consorzio RELUIS", signed on 2013-12-27.info:eu-repo/semantics/publishedVersio

Porcelain bonding to titanium with two veneering principles and two firing temperatures

Dental literature, as well as dental laboratories, has described problems with ceramic veneering of titanium, while clinical and in vitro studies have reported good results. The objective of this study was to investigate the effect of firing temperature, thermo cycling, and veneering methods on bond strength between porcelain and titanium. Eighty titanium specimens were prepared with one of two methods:a bonding agent firing or an oxidation firing. During veneering, half of the specimens in each group were fired at 30 C above and half at the manufacturer's recommended temperature. In the bonding agent group and in the oxidation group, half of each firing group was thermocycled. Bond strength was calculated in a three-point bending test. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the titanium and the porcelain fracture surfaces of one specimen from each subgroup was used in order to study the composition of the interface between titanium and porcelain surfaces after fracture. No significant difference in bond strength was found when firing at a higher temperature compared with firing at the recommended temperature. An oxidation firing before veneering yielded significantly higher bond strength in a three-point bending test than when firing with a bonding agent. SEM and EDS analyses indicated a higher frequency of titanium oxide fractures in the oxidation than in the bonding agent group. The main finding is that firing at 30 degrees C above the recommended temperature does not significantly affect bond strength between titanium and porcelain. SEM and EDS analysis indicate that fractures occur in the titanium oxide layer by oxidation firing and in the interface between titanium oxide layer and veneering material by bonding agent firing. This finding might indicate that three-point bending test is not a relevant method for determining bond strength in this case, since the firing methods might influence the ductility of the samples

Porcelain bonding to titanium with two veneering principles and two firing temperatures

Dental literature, as well as dental laboratories, has described problems with ceramic veneering of titanium, while clinical and in vitro studies have reported good results. The objective of this study was to investigate the effect of firing temperature, thermo cycling, and veneering methods on bond strength between porcelain and titanium. Eighty titanium specimens were prepared with one of two methods:a bonding agent firing or an oxidation firing. During veneering, half of the specimens in each group were fired at 30 C above and half at the manufacturer\u27s recommended temperature. In the bonding agent group and in the oxidation group, half of each firing group was thermocycled. Bond strength was calculated in a three-point bending test. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the titanium and the porcelain fracture surfaces of one specimen from each subgroup was used in order to study the composition of the interface between titanium and porcelain surfaces after fracture. No significant difference in bond strength was found when firing at a higher temperature compared with firing at the recommended temperature. An oxidation firing before veneering yielded significantly higher bond strength in a three-point bending test than when firing with a bonding agent. SEM and EDS analyses indicated a higher frequency of titanium oxide fractures in the oxidation than in the bonding agent group. The main finding is that firing at 30 degrees C above the recommended temperature does not significantly affect bond strength between titanium and porcelain. SEM and EDS analysis indicate that fractures occur in the titanium oxide layer by oxidation firing and in the interface between titanium oxide layer and veneering material by bonding agent firing. This finding might indicate that three-point bending test is not a relevant method for determining bond strength in this case, since the firing methods might influence the ductility of the samples