Micro‐ and nanoscale structures of mesiodens dentin: Combined study of FTIR and SAXS/WAXS techniques

A mesiodens is the most common type of supernumerary tooth present in conjunction to normal dentition. A mesiodens may commonly occur in the central region of the upper or lower jaw. A mesiodens is different from normal teeth in terms of structure and shape. The aim of this study is to evaluate the micro‐ and nanoscale structural properties of mesiodens dentin by combined small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and Fourier transform infrared (FTIR) spectroscopy. Five freshly extracted, noncarious mesiodens and five normal dentin disks prepared from human incisor teeth were compared. Using FTIR, the phosphate‐to‐amide I, carbonate‐to‐phosphate, and carbonate‐to‐amide I band area ratios and the crystallinity index were quantified. SAXS/WAXS were used to study the nanostructure of mesiodens. An increase in the mineral content in the mesiodens dentin with respect to the normal group was found. Crystallinity was also significantly increased and the protein content decreased in the mesiodens dentin compared with that of normal dentin. SAXS/WAXS results revealed that mesiodens dentin has a more calcified tissue. Further, SAXS analysis revealed a nonuniform distribution of dentin fibrils in mesiodens. Microsc. Res. Tech., 78:52–58, 2015. © 2014 Wiley Periodicals, Inc.     

Active only integrator and differentiator with tunable time constants

In this paper new active only current-mode integrator and differentiator with electronically tunable time constants are described. They are composed of one operational amplifier (OA) and two operational transconductance amplifiers (OTAs), and are suitable for monolithic implementation either with CMOS or bipolar technologies. No realizability conditions are imposed for the proposed circuits and all of the active sensitivities are low. The performances of the circuits are demonstrated on the PSPICE platform.     

Predicting crack propagation with peridynamics: a comparative study

The fidelity of the peridynamic theory in predicting fracture is investigated through a comparative study. Peridynamic predictions for fracture propagation paths and speeds are compared against various experimental observations. Furthermore, these predictions are compared to the previous predictions from extended finite elements (XFEM) and the cohesive zone model (CZM). Three different fracture experiments are modeled using peridynamics: two experimental benchmark dynamic fracture problems and one experimental crack growth study involving the impact of a matrix plate with a stiff embedded inclusion. In all cases, it is found that the peridynamic simulations capture fracture paths, including branching and microbranching that are in agreement with experimental observations. Crack speeds computed from the peridynamic simulation are on the same order as those of XFEM and CZM simulations. It is concluded that the peridynamic theory is a suitable analysis method for dynamic fracture problems involving multiple cracks with complex branching patterns.     

Effect of slip on entropy generation in a single rotating disk in MHD flow

In the present study, the effect of slip on entropy generation in magnetohydrodynamic (MHD) flow over a rotating disk is investigated by semi-numerical analytical solution technique. The nonlinear governing equations of flow and thermal fields are reduced to ordinary differential equations by the Von Karman approach, then solved via differential transform method (DTM), a recently-developed, powerful analytical method. Related entropy generation equations are derived and nondimensionalized using geometrical and physical flow field-dependent parameters. For a rotating surface the form of slip introduced into the governing equations is rarefaction. For comparison, slip and no-slip regimes in the range 0.1 > Kn > 0 and their interaction with magnetic effects are investigated by minimum entropy generation. While minimizing entropy generation, equipartitioning is encountered between fluid friction irreversibility and Joule dissipation.     

The performance of PCD tools in high-speed milling of Ti6Al4V

Tool performance of conventional tools is poor and a major constraint when used in milling titanium alloys at elevated cutting speeds. At these high cutting speeds, the chemical and mechanical properties of Ti6Al4V cause complex wear mechanisms. In this paper, a fine-grain polycrystalline diamond (PCD) end mill tool was tested, and its wear behavior was studied. The performance of the PCD tool has been investigated in terms of tool life, cutting forces, and surface roughness. The PCD tool yielded longer tool life than a coated carbide tool at cutting speeds above 100?m/min. A slower wear progression was found with an increase in cutting speeds, whereas the norm is an exponential increase in tool wear at elevated speeds. Observations based on scanning electron microscope (SEM) and energy dispersive spectroscopy (EDAX) analysis suggest that adhesion of the workpiece is the wear main type, after which degradation of the tools accelerates probable due to the combined effect of high temperature degradation coupled with abrasion.     

Hierarchically Structured Magnetic Nanoconstructs with Enhanced Relaxivity and Cooperative Tumor Accumulation

Iron oxide nanoparticles are formidable multifunctional systems capable of contrast enhancement in magnetic resonance imaging, guidance under remote fields, heat generation, and biodegradation. Yet, this potential is underutilized in that each function manifests at different nanoparticle sizes. Here, sub‐micrometer discoidal magnetic nanoconstructs are realized by confining 5 nm ultra‐small super‐paramagnetic iron oxide nanoparticles (USPIOs) within two different mesoporous structures, made out of silicon and polymers. These nanoconstructs exhibit transversal relaxivities up to ≈10 times (r ₂ ≈ 835 mm ^?1 s^?1) higher than conventional USPIOs and, under external magnetic fields, collectively cooperate to amplify tumor accumulation. The boost in r ₂ relaxivity arises from the formation of mesoscopic USPIO clusters within the porous matrix, inducing a local reduction in water molecule mobility as demonstrated via molecular dynamics simulations. The cooperative accumulation under static magnetic field derives from the large amount of iron that can be loaded per nanoconstuct (up to ≈65 fg) and the consequential generation of significant inter‐particle magnetic dipole interactions. In tumor bearing mice, the silicon‐based nanoconstructs provide MRI contrast enhancement at much smaller doses of iron (≈0.5 mg of Fe kg^?1 animal) as compared to current practice.     

Characterization of 5-HT receptors in rat proximal colon

Gastric leiomyoblastoma is a rare entity. In this report, we describe the magnetic resonance (MR) appearance of a recurrent gastric leiomyoblastoma 14 years after initial presentation. This tumor was heterogeneous and moderately low signal intensity on T1-weighted images and heterogeneous and moderately high signal intensity on T2-weighted images. The tumor also contained foci of low signal intensity on the post gadolinium images, consistent with areas of necrosis. The mass enhanced mildly and increased in enhancement on the delayed images, consistent with a hypovascular mass. Multiple liver metastases were noted. Magnetic resonance findings were confirmed with surgical specimens.     

Adhesion of lacquer to phosphated steel — A shear test evaluation

Measurement of the adhesion toughness of a fast cure thermosetting powder coating used for corrosion protection of cold-rolled steel has been attempted in a shear test under uniform plane stress loading conditions at the interface. A specially designed test specimen preparation procedure (by direct crosslinking) and geometry (symmetrical) was developed to enable proper mechanical behaviour under shear initiation of fracture and uniform plane stress loading in the significant section of the specimen — the interface. The shear test was designed to measure the nominal and the net ultimate shear stress values (USS)_n and (USS)_net' as well as the critical stress intensity factor (SIF) of interfaces. From experimentally measured critical load at which the adhesion failed, the ultimate shear stress values (USS_net N mm^–2) were calculated and used as a quantitative information of the bond toughness along the interfaces. The experimental results with a range of specimens revealed that the test can, indeed, discern subtle variations influencing adhesion such as type of cold-rolled steel, an iron phosphate pretreatment before coating or variation in stoving temperatures. Fractographic analysis of shear failed specimens on mating surfaces revealed generation of a microcrack network in most of the fracture pattern tested, indicating fracture mechanism transitions characteristic of pure shear for both iron phosphated free cold-rolled steel-lacquer (SL) as well as for iron phosphated cold-rolled steel-lacquer (SPL) specimens. The fractographs, however, indicate fracture propagation more difficult for SPL specimens and comparatively smooth fracture surface for SL specimens, obviously affected by variations in their respective interface structure and morphology. This behaviour correlates well with measurements of (USS)_net in test.