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Objective: The objective of the study was to evaluate the effect of artificial high- and low-density materials on Bone mineral density (BMD)scans in dual-energy X-ray absorptiometry (DXA) method and emergence of black-hole artifact through GATE Monte Carlo simulation. Materials and Methods: GATE Monte Carlo code was utilized to simulate the artifact encountered in clinical scans acquired by HOLOGIC[sup.®] bone densitometer. Two simplified phantoms were designed. The first one was a rectangular box with six smaller cubes inside and the second one was a body torso. Materials of cubes were spine bone, polymethyl methacrylate (PMMA), barium sulfate suspension in water, stainless steel, titanium alloy, and gold. The torso phantom contained objects of 5 vertebrae, bowel and 3 small spherical objects near the surface of the torso as piercing objects on the abdominal wall, each overlying the vertebrae. Using 100 and 140 kVp, spectral X-rays were generated to simulate DXA. For both phantoms, two simulations were carried out. The pair of projections acquired for each phantom were then subtracted and analyzed by curve fitting techniques. Results: Except for spine bone, in which radio-opacity decreases with increasing spectral X-ray energy (from 100 to 140 kVp), other squares exhibit little changes over different energies. PMMA shows consistently very low radio-opacity. Four other materials (barium sulfate in water, stainless steel alloy, titanium alloy, and gold), all attenuate the X-ray photons substantially. Except for spine bone, other materials are barely noticeable in pairwise subtracted images. In torso phantom, piercing objects are visualized as 'holes' in vertebrae. Conclusion: Both artificial high- and low-density materials, compared to bone, are eliminated during the subtraction of dual-energy X-ray profiles and therefore, can create black-hole artifact. Keywords: Artificial materials, 'black-hole' artifact, bone mineral densitometry, dual-energy X-ray absorptiometry, GATE Monte Carlo simulation, Author(s): Mohsen Qutbi (corresponding author) [1] INTRODUCTION As a crucial indicator of bone health, bone mineral density (BMD) is currently assessed and measured utilizing dual-energy X-ray absorptiometry (DXA) in bone [...]

Polymethylmethacrylate-co-methacrylic acid (PMMA-co-MAA) was utilized for surface improvement of silica to be used as reinforcement in self-healing natural rubber based on metal thiolate ionic network. The amount of PMMAco-MAA was varied at 1, 3, and 5 wt% of silica content and the optimized PMMA-co-MAA was utilized to investigate the self-healing NR/silica composites at different filler loading (5, 10, 20, and 30 phr). The graft polymerization of PMMA-co-MAA on silica was confirmed using FTIR spectroscopy and grafting percentage was determined by thermogravimetric analysis (TGA). Intermolecular diffusion occurred at the fractured area was detected using a scanning electron microscope (SEM) and the results revealed that the composite tensile and tear performance increased 22%-70% with healing efficiency percentage ranging between 70% and 97% depending on the silica loading. KEYWORDS Methacrylic acid, modified silica, natural rubber composites, reversible ionic network, self-healing, 1 | INTRODUCTION Natural rubber (NR) is an important raw material used in numerous industries, including the automotive, sporting goods, medical, and electrical fields. Their exceptional qualities, including strong chemical [...]

Within the framework of a coupled problem of thermoviscoelasticity, using the method of numerical modeling, we have studied the thermal instability of a rectangular prism, composed of copper and polyethylene or polymethylmethacrylate layers, in the course of its dissipative heating. The prism is subjected to high-frequency force or kinematic shear. We have established that, in the case of polyethylene, thermal instability occurs under conditions of force loading and is absent under a kinematic one. However, for polymethylmethacrylate, thermal instability takes place for both cases of loading. This effect is attributable to the existence of temperature intervals where the shear and volume loss compliances for each of the polymers increases with the temperature. We have also revealed that the critical values of thermal instability for a prism with metal layers are substantially higher than those for a homogeneous prism. In addition to thermal instability, thermal resonance instability is also possible. It is caused by the jump of the thermal state from the low- to high-temperature branch of the soft-type resonance characteristic. UDC 539.3, Vibratory heating induced by intense vibrations of viscoelastic solids can lead to a substantial growth of their temperature (8, 11, 14). Upon reaching the temperature of softening or melting of [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2009.05.008 Byline: Ahmet Sari (a), Cemil Alkan (a), Ali Karaipekli (a), Orhan Uzun (b) Keywords: PCM; Microencapsulation; Emulsion polymerization; n-Octacosane; Methylmethacrylate; Energy storage Abstract: This study deals with preparation and characterization of polymethylmetracrylate (PMMA) microcapsules containing n-octacosane as phase change material for thermal energy storage. The surface morphology, particle size and particle size distribution (PSD) were studied by scanning electron microscopy (SEM). The chemical characterization of PMMA/octacosane microcapsules was made by FT-IR spectroscopy method. Thermal properties and thermal stability of microencapsulated octacosane were determined using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The melting and freezing temperatures and the latent heats of the microencapsulated octacosane as PCM were measured as 50.6 and 53.2[degrees]C, 86.4 and -88.5J/g, respectively, by DSC analysis. TGA analysis indicated that the microencapsulated octacosane degrade in two steps and had good chemical stability. Thermal cycling test shows that the microcapsules have good thermal reliability with respect to the accelerated thermal cycling. Based on the results, it can be considered that the microencapsulated octacosane have good energy storage potential. Author Affiliation: (a) Department of Chemistry, GaziosmanpaAa University, 60240 Tokat, Turkey (b) Department of Physics, GaziosmanpaAa University, 60240 Tokat, Turkey Article History: Received 10 July 2008; Revised 22 December 2008; Accepted 18 May 2009 Article Note: (miscellaneous) Communicated by: Associate Editor Halime Paksoy

Intense gigawatt relativistic electron beam generation studies were carried out with a Perspex cathode holder. Purpose of the dielectric cathode holder was to minimize the prepulse voltage across the diode. The typical electron beam parameter was 180 kV, 26 kA, 100 ns, with a few hundreds of ampere per square centimeter current density. It was found that corrugated Perspex of length [greater than or equal to] 35 mm can eliminate the prepulse voltage but affects the rise time of the diode voltage. The diode voltage and current waveforms were analyzed with the bipolar space-charge limited flow model. The anode and cathode plasma expansion velocities were calculated using the perveance data. The plasma expands at 5.1 cm/ [micro]s for 18-mm anode-cathode gap and the plasma velocity increases for larger gap. Inserting a dielectric at the cathode holder could be a very effective method to reduce prepulse voltage at the electron beam diode, but it increases the rise time of the diode voltage and reduces the effective electron beam pulsewidth. The prepulse voltage reduces significantly ([less than or equal to] 10%) when an inductance is added to the charging circuit of the Blumlein line. Index Terms--Electron beam diode, perveance, plasma expansion, surface flashover.

Acoustoelasticity refers to the dependence of acoustic wave velocities on stresses or deformation in the material that the wave is propagating and this change in the acoustic wave velocities is known as the acoustoelastic effect. A transducer and measurement method is developed for exact measurement of surface wave velocity and this method is used to check the acoustoelastic effects for wave propagation on the polymethylmethacrylate.

Temperature gradient interaction chromatography (TGIC) was applied for the separation of stereoregular poly(ethyl methacrylate) (PEMA) according to the tacticity. The three PEMA samples with differing tacticity (rr triad content: 0, 53, and 91%) prepared by anionic polymerization were used. C18 bonded silica and a mixture of C[H.sub.2][Cl.sub.2] and C[H.sub.3]CN (30/70, v/v) were used as stationary and mobile phase, respectively. TGIC was able to separate the PEMA samples, showing the increasing retention in the order of decreasing rr triad contents; however TGIC elution peaks of the three PEMAs were not fully resolved but, rather, were partially overlapped. To isolate the tacticity effect from the molecular weight effect on the TGIC retention, the PEMA samples were fractionated by TGIC, and the accurate molecular weight of the fractions was determined by MALDI-TOF mass spectrometry. The fractions showed a much narrower molecular weight distribution than the mother PEMAs. The TGIC fractions of similar molecular weight but with different tacticity were fully resolved by TGIC, but mother PEMAs were not. These results indicate that the retention in TGIC is affected by both tacticity and molecular weight.

This paper composes the dynamic mechanical and dielectric relaxation properties for Poly (5-indanyl methacrylate) (P51M), a polymer with a bulky side chain. Measurements were carried out from about -100 ° C to near 250 ° C. A secondary loss peak was observed in dielectric measurements at room temperature (20 ° C at 0.1 Hz.), whereas nothing was resolved in the mechanical spectrum. A prominent [Alpha] relaxation associated with the glass transition was also observed near 107 ° C at 0.1 Hz. in the dielectric and the mechanical spectra. Dipolar dielectric loss overlapped with conductivity at high temperatures and low frequencies. A new method to split the conductive, interfacial, and dipolar contributions to the spectrum is proposed., INTRODUCTION Bulky side chain polymers are very interesting from different points of view. The bulkiness of the side chain enhances rigidity of the polymer mainly because of the steric hindrance, [...]

Polymethylacrylate (PMMA) and polyethyleneterephthalate (PET) surfaces treated with reactive and noble gas plasmas, contain well-defined surface conformations. Plasma ions use an ion-electron recombination method to decompose ester groups in PMMA. The decomposition is less in PET due to the protective effect of the PET phenyl ring. The ion current is the sole determinant of equilibrium between oxygen depletion and reactive species formation in the surfaces.

Scanning electron microscopic analysis of the charging mechanism of polymethylmethacrylate samples involves the use of a mirror image method. Classical Kepler equations are extended to compute total trapped charge, Q. A fitting procedure that lacking low accelerating voltage ability is used for Q calculations.

The end groups in poly(methyl methacrylate) (PMMA) macromonomers and their radically polymerized prepolymers were determined using a pyrolysis gas chromatograph (Py-GC) equipped with a simultaneous multidetection system. End groups associated with the initiator azobis(isobutyronitrile) (AIBN) and the chain transfer reagents such as thioglycolic acid and mercaptopropionic acid were of particular interest. Various characteristic pyrolyzates that reflected the end groups in the PMMAs were observed on the pyrograms. Pyrolysates that contain sulfur from the chain transfer reagent residues in the end groups were determined on the basis of the pyrograms simultaneously obtained by a sulfur-selective flame photometric detector and an ordinary flame ionization detector (FID). On the other hand, the cyano-group-containing end groups consisting of the AIBN residue were determined from the pyrograms simultaneously observed by FID and a nitrogen-phosphorus detector. The degree of polymerization estimated from the relative intensities of the end-group-specific pyrolyzates were comparable with those determined by size exclusion chromatography (SEC). Furthermore, the terminal ratio estimated by Py-GC proved to be in good agreement with those calculated from kinetic data.

The melt-quenched and annealed blend of 80 wt% polyvinylidene fluoride and 20 wt% polymethylmethacrylate has the beta crystal form of the polyvinylidene difluoride (PVDF). The PVDF has optical clarity and other properties desirable for a material with an optically nonlinear dye that is orientationally-stabilized by the strong poled electric field. The polarization distributions cause thermal pulses.

The fracture behavior of oriented poly (methyl methacrylate) (PMMA) has been investigated. The stress intensity factor K(sub IC), characteristic distance alpha, and angle theta of switching propagation direction decrease with increasing draw ratio in the range of 1.25 and 3.25. The microstructures such as the plastic zone and the features of morphology are in good agreement with the variations of these three variables, i.e., K(sub IC), alpha, and theta.

The laser ablation pf polymethyl methacrylate in ultraviolet and infrared lasers were compared. A pulse of visible laser light was used for the imaging of plume emergence. A large fraction of a solid polymer was identified by the UV laser pulses in the plume and was examined at high magnification. The importance of photochemical and photothermal mechanisms in laser ablation was established.

The rheological properties of polystyrene (PS) and poly(methyl methacrylate) (PMMA) composites filled with monodisperse sized crosslinked polymeric particles are sensitive to processing history and chemical composition. Particles compatible with the matrix, such as PMMA or copolystyrene-vinylphenol in a PMMA matrix, are randomly dispersed on mixing, yielding (almost) Newtonian fluids. Particles incompatible with the matrix, such as PS or copolystyrene-acetoxystyrene in PMMA, produce composites whose steady shear viscosities depend on shear rate and whose dynamic moduli are elevated at low frequency. Particles in incompatible composites tend to cluster, producing a structure that is destroyed at high shear rates and that reforms on aging at elevated temperatures.

A polymeric waveguide material with nonlinear optical properties is studied: crosslinked poly(methyl) methacrylate (PMMA) doped with N,N'-dihexyl-amino-nitrostilbene (DHANS). The fabrication and characterization of thin-film waveguides (2-4 [Mu] m) are demonstrated. The anisotropy of the refractive index and the damping of the films have been investigated by m-line spectroscopy and loss measurements. Thin polymeric multilayer structures, including a nonlinear optical core, sandwiched between buffer layers and electrodes have been produced. For these samples, the anisotropy of the refractive index in poled films are measured. Finally, two systems are compared: PMMA/DHANS and a side-chain polymer with the same nonlinear optical group.

The electrical breakdown process in polymethyl methacrylate for a point-to-plan gap configuration has been studied using an image convertor camera and a nanosecond rectangular HV pulse generator. The propagation velocity of the breakdown channel for positive polarity is estimated to be [approximately] 80 km/s. The velocity is of the same order as that of secondary fast streamers in several hydrocarbon liquids.

The temperatures and kinetics of phase separation have been studied as a function of filler concentration in a polymer mixture of poly(vinyl acetate)-poly(methyl methacrylate). The filler was shown to have a marked effect on the cloud point position and the phase separation kinetics at various temperatures. The effects observed are dependent upon the component ratio.

The modifications induced in haloaromatic, ArX (Ar, Nap, Phen, and An; X = Br and I), dopants dispersed within poly(methyl methacrylate) (PMMA) upon UV irradiation are examined. The results are well accounted for within a thermal model of the laser interaction with PMMA and the factors that controls the reactivity in the UV ablation of polymer substrates are illustrated.

A disposible plastic (poly(methyl methacrylate)) chip containing eight open channels (375 [micro]m in width, 300 [micro]m in depth, 1.25 cm in length) capable of performing sequential electrospray analysis is described. The channels were constructed by simply cutting the plastic chip with a sharp knife. One end of each channel was fabricated to a sharp end, while the other was connected to a sample well. The high voltage required for electrospray was introduced into the sample solution (70% methanol/ water) via a copper electrode inserted in the sample well. The solution in the sample well was continuously drawn to the sharp end of the channel by capillary action and by applying the electrospray voltage at the sample reservoir. A stable and fine Taylor cone was observed at the exit of the channel. Chemical modification on the surface of the channel was not required to decrease wettability. The octagonal plastic chip allowed sequential electrospray analyses of eight samples. The technique was also shown to be useful in rapidly determining active ingredient in a commercial tablet.

Photochormic dyes such as spiropyran, are finding wider applications such as in energy efficient smart windows, optical memories and optical switches when used as thin films in combination with inorganic [...]