bluuebunny/crossref_metadata_2025 huggingface dataset:
ACCUMULATIVE ROLL BONDING OF AZ31 MAGNESIUM ALLOY
Authors: FATEMI-VARZANEH S. M. , ZAREI-HANZAKI A. , HAGHSHENAS M.
Published: August 2008

This work conducted to investigate the effects of accumulative roll bonding (ARB) method on achieving the ultra-fine grain microstructure in AZ31 alloy. Accordingly, a number of ARB routes at 400°C, applying thickness reductions per pass of 35%, 55%, and 85% were performed. The results indicate that both the final grain size and the degree of bonding have been dictated by the thickness reduction per pass. The larger pass reductions promote a higher degree of bonding. Increasing the total strain stimulates the formation of a more homogeneous ultra fine grain microstructure.
INFLUENCE OF STRAIN ACCUMULATION ON MICROSTRUCTURE OF ALUMINUM 1100 IN THE TWIST EXTRUSION
Authors: AKBARI MOUSAVI S. A. A. , SHAHAB A. R.
Published: August 2008

Nowadays, Severe Plastic Deformation (SPD) methods are at the focus of material researchers and among these methods, Twist Extrusion (TE) is one of promising ones to pave the way of commercialization. In this Investigation the magnitude of strain distribution along 4 selected paths of sample after 3 passes of Twist Extrusion were investigated by computer simulation and its influence on aluminum 1100 microstructure by experimental tests. ABAQUS 6.5 software based on FEM was applied for the former and 70 mm length samples with cross-section of 18*28 mm were exploited for the latter. According to the simulation results, corner, middle of small side, middle of long side and center of the cross-section are placed from maximum to minimum magnitude of strain respectively. Theses achievements were verified with metallographic images in aspect of metal flow and grain size as well.
MICROSTRUCTURE AND HARDNESS OF FRICTION STIR PROCESSED AZ31 WITH SiCP
Authors: NAJAFI M. , NASIRI A. M. , KOKABI A. H.
Published: August 2008

Friction stir processing (FSP) is a novel technique to produce ultrafine grained materials. Most of the researches conducted on FSP focus on aluminum alloys. Despite the potential weight reduction that can be achieved by using magnesium alloys, a few researches have been reported on FSP of magnesium alloys. In this work, the possibility of using FSP with and without SiC particles to modify the microstructure and hardness of commercial AZ31 is examined. SiC particles were uniformly dispersed into an AZ31 matrix by FSP. The mean grain size of the stir zone with the SiC particles was obviously smaller than the same zone without the SiC particles. SiC reinforced magnesium matrix composites created by FSP with cooling rapidly the plate that exhibit ultrafine grain size approximately 1μm and nearly doubled the hardness of the base material.
BULK AMORPHOUS AND NANOSTRUCTURED MATERIALS BY HIGH ENERGY BALL MILLING
Authors: POLITIS CONSTANTIN
Published: August 2008

Mechanical alloying by high energy ball milling is a promising method for the production of bulk metallic glasses, amorphous alloys and nanostructured materials. Amorphous alloys reinforced by nanocrystals represent a big step in the optimization of new ultra high strength materials. Nano-scale W-Y solid solutions were synthesized by high energy ball milling. Only 1 at. % oxygen can stabilize the bulk metallic glassy state of Zr54Cu19Ni8Al8Si5Ti5O1to higher Txand to large supercooled liquid range Δ Txg.
EFFECT OF MECHANICAL ALLOYING PROCESS PARAMETERS ON CHARACTERISTICS OFAl-B4CNANOCOMPOSITE-NANOCRYSTLLINE POWDER PARTICLES
Authors: KHAKBIZ MEHRDAD , AKHLAGHI FARSHAD
Published: August 2008

In the present work the effect of milling time (2-16h), milling speed (320 and 420rpm), as-received aluminum particle size (21 and 71 μm), B4C size (90, 700 and 1200nm) and its content (5% and 10%) on the characteristics of Al - B4C powder particles during milling was investigated by scanning electron microscopy (SEM) and laser particle size (LPS) analyzer. X-ray diffraction was used to investigate the crystal size and internal strains within the processed aluminum particles at different conditions. It was concluded that powder particles size increased after 4h milling but further milling (up to 16h) resulted in decreased powder particles size. By increasing milling speed from 320rpm to 420rpm, finer aluminum powder particle sizes were obtained in any specific milling time. XRD results confirmed that nanocrystalline structures with the size of 80nm for aluminum powder particles can be achieved in different milling conditions. SEM micrographs and EDX maps of Al - B4C mixtures confirmed that milling at optimum conditions breaks the reinforcement particle clusters and a homogenous distribution of B4C nanoparticles in Al - B4C powder mixture can be achieved after milling.
HEAT TREATMENT EFFECTS ON STRUCTURE AND PROPERTIES OF SYNTHESIZED NANOCRYSTALLINE NiTi INTERMETALLIC BY MECHANICAL ALLOYING
Authors: MOUSAVI T. , ABBASI M. H. , KARIMZADEH F. , ENAYATI M. H.
Published: August 2008

NiTi intermetallic with nanocrystalline structure was produced by mechanical alloying of the elemental powders and the effect of subsequent heat treatment was investigated. The products were characterized using X-ray diffraction and microhardness measurements. The results showed that after 60 h of mechanical alloying, disordered B 2- NiTi phase can be obtained as a metastable phase at room temperature with grain size of 25 nm, lattice strain and high microhardness of 1.2% and 922 HV, respectively.

After heat treatment, disordered structure transformed to ordered NiTi and a small amount of NiTi 2 and Ni 3 Ti phases. The long range order parameters of nanocrystalline NiTi were obtained to be 0.63 and 0.94 after annealing for 30 and 60 mins respectively. After 30 mins of heat treatment, 81.5% of Ni (or Ti ) atoms were on the right sites and after 60 mins it increased to 97%. Grain growth and decrease of microhardness and lattice strain were also observed after heat treatment. After 60 mins of heat treatment the grain size, lattice strain and microhardness of NiTi were 95, 0.09 and 624 HV respectively.
HARD AND TOUGH NANOCOMPOSITE TiN-Ni COATINGS DEPOSITED BY REACTIVE ION BEAM ASSISTED DEPOSITION
Authors: AKBARI ALIREZA , RIVIERE JEAN PAUL , TEMPLIER CLAUDE
Published: August 2008

A new category of hard nanocomposite coatings with adjustable improved hardness or enhanced toughness consisting of nanocrystalline (nc-) titanium nitride grains embedded in an amorphous (a-) metallic intergranular nickel phase i.e. nc - TiN / a - Ni type has been produced and investigated. Coatings were deposited at 573K on different substrates using a reactive dual ion beam sputtering (RDIBS) technique. A composite Ti - Ni target was sputtered with 1.2 keV Ar + ions and the growing films were bombarded with a mixture of 50 eV Ar ++ N 2++ N + ions. XRD, nanoindentation, high load indentation and pin-on-disk tests were used to characterize structural and mechanical properties. By adjusting Ni content enhanced hardness or toughness is obtained with an important improvement in wear resistance corresponding to the coatings exhibiting the highest toughness than highest hardness.
THE CORROSION BEHAVIOR OF ELECTROLESS Ni-P-SiC NANO-COMPOSITE COATING
Authors: BIGDELI FARYAD , ALLAHKARAM SAEED REZA
Published: August 2008

Composite coatings constitute a new class of materials which are mostly used for mechanical and tribological applications. The corrosion resistance of these composite coatings, however, has not been systematically studied and compared. In this study, electroless Ni – P composite coatings are formed on St 37 steel through the addition of nano-scale SiC particles to the plating bath. This work aimed to investigate the corrosion characteristics of electroless nickel composite coatings using electrochemical measurements which include polarization and electrochemical impedance spectroscopy tests. The morphology and structure of the composite coatings were studied by scanning electron microscopy (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The results showed that both electroless nickel and electroless nickel composite coatings demonstrated significant improvement of corrosion resistance in salty atmosphere.
A STUDY ON THE ELECTRODEPOSITION MECHANISM OF COBALT-NICKEL/COPPER MULTILAYER FROM SULFATE SOLUTION
Authors: MAHSHID S. S. , DOLATI A.
Published: August 2008

The cobalt-nickel/copper multilayer films were prepared by electrodeposition process in sulfate solution using a three electrode cell. Cyclic voltammetry and double chronoampermetry techniques were utilized to characterize the multilayer system and to obtain the nucleation and growth mechanism. The cyclic voltammograms determined the reduction potential range of the three components and also clearly emphasized that electrodeposition of cobalt-nickel alloy was controlled by a kinetic process, while copper ions were reduced with diffusion-controlled mechanism. These results were confirmed with those which were extracted from the chronoampermetry curves. In addition, the current transients revealed that nucleation mechanism was a typical three-dimensional nucleation process. The Atomic Force Microscope images (AFM) of these multilayers also confirmed the three-dimensional nucleation mechanism. The compositional analysis of these multilayers was carried out by Atomic Absorption Spectroscopy (AAS) and X-ray Photoelectron Spectroscopy (XPS) methods. The bulk and surface compositional analysis both revealed that the amount of Copper component within the cobalt-nickel layers is less than 3%.
THE EFFECT OF Ph ON THE PROPERTIES OF Ni-Mo NANOCRYSTALLINE ELECTRODEPOSITS
Authors: MOUSAVI R. , RAEISSI K. , SAATCHI A.
Published: August 2008

Nanocrystalline pure metals with grain size below 10nm are very difficult to prepare. Alloying enables the production of such a fine grains, even down to an amorphous state. In this work, Ni - Mo nanocrystalline coatings were electrodeposited from a citrate-ammonia base solution using a direct current (DC) technique. The grain sizes were estimated from X-ray line broadening. Mo content of the coatings was determined by energy dispersive X-ray analysis (EDS). The results showed that the grain size decreased when the Mo content of alloy was increased through reducing the bath pH. The microhardness measurements showed an increase in hardness with decreasing the pH, a maximum hardness of 820 Vickers was obtained for the coating deposited at pH9 with a 17 wt% Mo . Although, at pH values lower than 9, alloys with higher than 17wt% Mo were obtained, a softening effect was observed despite the decrease in grain size which is the result of transition from a nanocrystalline to amorphous structure.
NANO HYDROXYAPATITE COATING ON STAINLESS STEEL 304 BY ELECTROCHEMICAL METHOD
Authors: SAREMI M. , SABET F. HAGHIGHAT
Published: August 2008

Hydroxyapatite and other calcium phosphates are the most important mineral parts of human bone. HA is applied on 304 stainless steel using cathodic electrodeposition in an electrolyte consisting of Ca ( NO 3)2 and NH 4 H 2 PO 4. The effect of electrodeposition parameters such as voltage, temperature and current density on the morphology and adhesion of the deposits were examined. Needle-like structure with nano width was obtained at 80°C and 2V while higher operating voltage resulted in flake type and coarse needle-like deposits. In fact, the lower voltage can change the electronation and diffusion of acting species. The adhesion of the coating, examined by tape test, improved by this method. TEM and SEM images showed the needle-like structure with nanometric width which is very similar to structure of natural bone. Corrosion resistance of the deposits was checked using polarization method and confirmed better performance of the nano HA coating.
MECHANOCHEMICAL SYNTHESIS OF FLUORIDATED HYDROXYAPATITE NANOPOWDER
Authors: FATHI M. H. , ZAHRANI E. MOHAMMADI
Published: August 2008

Recently fluoridated hydroxyapatite (FHA) has been developed since it possesses lower solubility than pure hydroxyapatite (HA), while maintaining the comparable bioactivity and biocompatibility in dental and orthopedic application. The aim of this work was to synthesize and characterize the FHA nanopowder via mechanochemical activation method. Mechanochemical reaction was performed in the planetary ball mill at 300 rpm rotation speed by using 8 balls with 2 cm diameter. XRD technique was used to evaluate phase and composition and determine the grain size of prepared FHA nanopowder. FTIR spectroscopy was utilized to identify the functional groups and to compare obtained powder with bone apatite. The results showed that the synthesis of FHA after 6 hr ball milling at 300 rpm was completed. Fluorhydroxyapatite grain size was almost 37nm after 6 hr of milling.
SYNTHESIS OF NANO CRYSTALLINE BARIUM HEXAFERRITE IN THE PRESENCE OF SALT CATALYSTS
Authors: HASSANIRAD ATEFEH , ATAIE A. , NIKKHAH-MOSHAEE R.
Published: August 2008

Nano crystalline barium hexaferrite, BaFe 12 O 19, were synthesized from mixture of barium acetate and iron oxide by conventional mixed oxide ceramic method. The mixture of precursors together with a 3wt% salt-catalyst (ammonium and sodium chlorides) was intensively milled by high energy ball mill for 10 hr. The influence of addition of catalyst on the synthesis process has been studied by XRD, SEM, DTA/TG and TEM techniques. Analysis of the XRD patterns indicates that salt-catalysts can strongly alter the morphology and phase composition of ball milled powder particles. Sample with 3wt% NH 4 Cl after milling for 10 hr and annealing at 900°C for 1 hr exhibited single phase barium hexaferrite with mean crystallite size of 20 nm.
EFFECTS OF PROCESSING CONDITIONS ON THE CHARACTERISTICS OF NANO-CRYSTALLINE BARIUM HEXAFERRITE PREPARED BY MECHANICAL ALLOYING METHOD
Authors: NAZARI M. HONARVAR , ATAIE A. , EBRAHIMI S. A. SEYYED
Published: August 2008

In this research, the effect of milling time and annealing temperature on a heat activated synthesis of barium hexaferrite from mechanically activated mixture of hematite and barium acetate was investigated. The properties of samples were examined by XRD, DTA/TGA, SEM and VSM methods. The initial mixture with Fe / Ba molar ratio of 11 was milled for 24–48 h and then annealed at 800–1100°C. The XRD results showed the reflections of hematite as a major phase and barium hydroxide as a minor phase during mechanical milling in all three samples. It was observed that the specimen milled for 48 h exhibits the smallest mean crystallite size of 25 nm for hematite, as major phase. XRD results showed that annealing at 1100°C produces more pure barium hexaferrite phase comparing to lower temperatures. So, it was concluded that single phase BaFe 12 O 19 can be achieved by milling for 48 h and then annealing at 1100°C. The sample processed at these conditions exhibited nano-crystalline barium hexaferrite powders with a mean crystallite size of 46 nm, mean particle size of about 200 nm and high coercivity of 334.2 kA/m.
OPTIMIZATION OF Sr-HEXAFERRITE DYNAMIC GASEOUS HEAT TREATMENT BY CARBON MONOXIDE
Authors: YOURDKHANI A. , EBRAHIMI S. A. SEYYED , KOOHDAR H. R.
Published: August 2008

In this research the influence of dynamic carbon monoxide heat treatment on Sr -hexaferrite has been investigated. Sr -hexaferrite is a hard magnetic material which under gaseous heat treatment, its phase composition and particles size and morphology change significantly. Due to these changings, the magnetic nature of the material changes from hard to soft. Strontium hexaferrite was prepared by conventional route with calcination of Sr -carbonat and hematite at 1100°C for 1 hour. Then Sr -hexaferrite was isothermally heat treated in carbon monoxide dynamic atmosphere at various temperatures and gas flows for different times. The rate of heating and cooling were 10°C/min. The optimum conditions was obtained at 850°C and 20cc/min flow for 0.5 hour. The effect of gaseous heat treatment on phase composition and particles size and morphology characterized by XRD and SEM. The results show the decomposition of Sr -hexaferrite and reduction of the resultant hematite mainly to iron. The crystallite size of the resultant powder was also measured below 50nm.
LOW TEMPERATURE CRYSTALLIZATION OF BARIUM FERRITE NANO-PARTICLES VIA CO-PRECIPITATION METHOD USING DIETHYLENE GLYCOL
Authors: MONTAZERI-POUR M. , ATAIE A.
Published: August 2008

Nano-crystalline particles of barium ferrite have been prepared by co-precipitation route using aqueous and non-aqueous solutions of iron and barium chlorides with a Fe/Ba molar ratio of 11. Water and a mixture of diethylene glycol and water with volume ratio of 3:2 were used as solvents in the process. Co-precipitated powders were annealed at various temperatures for 1 h. Phase composition of the samples was evaluated by XRD while their morphology was studied by TEM and SEM techniques. The XRD results showed that the single phase barium ferrite obtained at 750°C when diethylene glycol/water mixture was used as a solvent. This temperature increased to 900°C when the starting materials dissolved in water. Nano-size particles of barium ferrite with mean particle size of almost 50 and 80 nm were observed in the SEM micrographs of the samples synthesized in diethylene glycol/water solution after annealing at 750°C and 800°C for 1 h, respectively. The corresponding mean crystallite size measured by TEM for sample annealed at 800°C was 40 nm.
AN INVESTIGATION ON THE FORMATION OF STRONTIUM HEXAFERRITE NANO-POWDER BY A SOL-GEL AUTO-COMBUSTION METHOD IN THE PRESENCE OF SURFACTANT USING DIFFERENT BASIC AGENTS
Authors: ALAMOLHODA S. , EBRAHIMI S. A. SEYYED , BADIEI A.
Published: August 2008

Strontium hexaferrite is a hard magnetic material and has been extensively used as a permanent magnet. In this work a novel sol-gel auto-combustion method was used to synthesize ultra fine strontium hexaferrite. The investigations show that the model of combustion changes with the change of basic agent. The XRD results show that using ammonia or trimethylamine does not change the composition of the combustion product and it also shows that the surfactant burns completely during the combustion process. The average crystallite size of hexaferrite powders was also measured by X-ray line broadening technique employing Scherrer formula. The results show that changing the basic agent makes the particle size of the final product much smaller. Basic agent also affects the formation temperature of the single phase strontium hexaferrite.
SYNTHESIS, CHARACTERIZATION AND SINGLE-BEAM Z-SCAN MEASUREMENT OF THE THIRD-ORDER OPTICAL NONLINEARITIES OF ZnO NANO-PARTICLES
Authors: ARA M. H. MAJLES , DEHGHANI Z. , IRANIZAD S. SAIEVAR
Published: August 2008

Nano-particle materials with large optical nonlinearities are in great need for the development of nonlinear optical technology and are being studied intensively in recent years. ZnO nanoparticles have been synthesized by precipitation from zinc acetate in a series of n-alkanols from ethanol to 1-hexanol as a function of temperature. The formation and microstructure of ZnO particles were monitored by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectrum and z-scan technique. We studied the optical limiting effect of ZnO nano-particles. Using a CW He - Ne laser at 632.8 nm. The UV-Visible spectrum of this material shows a 373.5 nm peak. Using the UV-Visible, the band gap of this nano-particle is obtained about 3.31 eV. Also the XRD spectroscopy indicates that the structure is wurtzite hexagonal. Average particle size obtained from SEM analysis about 43nm. Furthermore the nonlinear refractive index, n 2, and nonlinear absorption coefficient, β, were measured using close and open aperture z-scan respectively, at peak laser irradiation of 1.743 kW/cm2. Then the nonlinear refraction index of this nano-particle was measured in order of 10-7 (cm2/W) with negative sign and the nonlinear absorption coefficient was obtained in order of 10-3 (cm/W).
SYNTHESIS OF NANO-SIZE MgO POWDER BY CHEMICAL DEPOSITION OF LOW COST RAW MATERIALS
Authors: AHMADZADEH M. , BAHARVANDI H. R. , ABDIZADEH H. , HADIAN A. M.
Published: August 2008

Nanostructured MgO powders have been synthesized using chemical methods. Ammonium oxalate and Magnesium sulphate were used as the precursor materials. The weight ratios of the raw materials (ammonium oxalate/Magnesium sulphate) were 0.9, 1, 1.1, 1.2, 1.3, and 1.4. As a result of chemical reaction (between them), Magnesium oxalate was synthesized. Produced samples were analyzed by XRD and SEM. The results show that the best ratio (for ammonium oxalate/Magnesium sulphate) is 1.4. Produced Magnesium oxalate powder was heated at 450 and 550°C. The final product was MgO nanopowder. XRD studies indicate that the highest ratio of MgO was observed in the specimen heated at 450°C.
EFFECTS OF CONCENTRATION OF TTIP PRODUCER AGENT ON ZrO2/NANOTiO2 POWDER SYNTHESIS
Authors: MOHAMMADI E. , ABDIZADEH H. , BAHARVANDI H. R. , HADIAN A. M.
Published: August 2008

Ceramic materials based on zirconium titanate prepared by sol-gel method are used extensively in microwave, telecommunications and catalysis. In order to investigate the effects of concentration of TTIP, a series of ZrO 2– TiO 2 mixed oxides was prepared by a modified sol–gel method and varying mole fraction of TTIP from 0.002, to 0.1. The samples were characterized by XRD, TG/DTA, and SEM. The XRD pattern of 370°C calcined samples showed the formation of TiO 2 phase. The optimum concentration of TTIP in the zirconia-titania mixed oxide in the precipitation solution was 0.032 for obtaining complete coating. Each oxide was calcined between 250 and 620°C. The results showed that concentration of TTIP have a pronounced effect on particle size of the calcined zirconium titanate ( ZT ) powders. The results showed that the surface area of the composite powder increased proper to monolithic ZrO 2 powder.
EFFECTS OF PROCESSING TEMPERATURE AND FABRICATION METHOD ON MICROSTRUCTURE AND DENSITY OF MULTILAYER AL2O3-ZRO2 NANOCOMPOSITES
Authors: MIRHASHEMI S. , BAHARVANDI H. R. , ABDIZADEH H. , EHSANI N.
Published: August 2008

Relatively low strength and fracture toughness of ceramics have restricted their applications. Various solutions have been studied to overcome the abovementioned drawbacks. One of the most sophisticated and promising solution is production of multilayer ceramic composites. High hardness, heat and wear resistance, low electrical and thermal conductivity, and resistance to chemical attacks are the most important characteristics of Al 2 O 3. Therefore, it is a common candidate for various industrial applications. Multilayer alumina-zirconia composites were made using two methods of isostatic and hydraulic compaction of dry ceramic powders. The green articles were conventionally sintered at 1420, 1550 and 1650°C for 3h. The microstructure and density of composites were investigated. The results show that the pressing method and sintering temperature have a relatively moderate effect on the microstructure and density of the sintered samples.
THE REASON FOR THE HIGH EMISSION EFFICIENCY OF GaInN/GaN BASED LEDS
Authors: HITZEL F. , HANGLEITER A.
Published: August 2008

We explain the mechanism of defect screening in GaInN/GaN quantum wells, which are used as active layers in white and blue light emitting diodes (LEDs). Despite the fact that these devices have now been commercially available for some time, the reason for the high luminescence efficiency had not been really understood. The high defect densities in these devices commonly would not allow the use as an optical emitter. We present the mechanism turning an actually poor-quality material into a powerful optical emitter.
EFFECTS OF CATALYST PREPARATION CONDITIONS ON NANO-GOLD DEPOSITED ON ZSM-5 FOR CO OXIDATION
Authors: KOOTENAEI A. H. SHAHBAZI , KAZEMEINI M. , KAZEMIAN H.
Published: August 2008

Calcined Na - ZSM -5 zeolite was directly reacted with the chloroauric acid solution in different concentrations and pH for gold loading process. The synthesized Au / ZSM -5 catalyst was then characterized using XRD, BET, SEM, TEM and EDS techniques. In order to evaluate its catalytic activity, effect of temperature on CO conversion was investigated.
ADVANCED-DELAY DIFFERENTIAL EQUATION FOR AEROELASTIC OSCILLATIONS IN PHYSIOLOGY
Authors: LUCERO JORGE C.
Published: August 2008

This article analyzes a mathematical model for some aeroelastic oscillators in physiology, based on a previous representation for the vocal folds at phonation. The model characterizes the oscillation as superficial wave propagating through the tissues in the direction of the flow, and consists of a functional differential equation with advanced and delay arguments. The analysis shows that the oscillation occurs at a Hopf bifurcation, at which the energy absorbed from the flow overcomes the energy dissipated in the tissues. The bifurcation value of the flow pressure increases linearly with the tissue damping and the oscillation frequency. Also, it is minimum when the phase delay of the superficial wave to travel along the tissues is π, and increases indefinitely when the delay tends to 0 and to 2π.
ASSESSING THE SPATIAL PROPAGATION OF WEST NILE VIRUS
Authors: MAIDANA NORBERTO A. , YANG HYUN M.
Published: August 2008

In this work we study a spatial model for the West Nile Virus (WNV) propagation across the USA from the east to the west. WNV is an arthropod-borne flavivirus that appeared at first time in New York city in the summer of 1999 and then spread prolifically within birds. Mammals, as human and horse, do not develop sufficiently high bloodstream titers to play a significant role in transmission, which is the reason to consider the mosquito-bird cycle. The proposed model aims to study this propagation in a system of partial differential reaction-diffusion equations considering the mosquito and the avian populations. The diffusion is allowed to both populations, being greater in avian than in the mosquito. When a threshold value R0, depending on the model's parameters, is greater than one, the disease remains endemic and could propagate to regions previously free of disease. The travelling wave solutions of the model are studied to determine the speed of the disease propagation. This wave speed is obtained as a function of the model's parameters, for instance, vertical transmission rate and avian diffusion coefficient.
ON TURING-HOPF INSTABILITIES IN REACTION-DIFFUSION SYSTEMS
Authors: RICARD MARIANO RODRÍGUEZ
Published: August 2008

We examine the appearance of Turing instabilities of spatially homogeneous periodic solutions in reaction-diffusion equations when such periodic solutions are consequence of Hopf bifurcations. First, we asymptotically develop limit cycle solutions associated to the appearance of Hopf bifurcations in reaction systems. Particularly, we will show conditions to the appearance of multiple limit cycles after Hopf bifurcation. Then, we propose expansions to normal modes associated with Turing instabilities from spatially homogeneous periodic solutions associated to limit cycles which appear as a consequence of a Hopf bifurcation. Finally, we discuss examples of reaction-diffusion systems arising in biology and chemistry in which can be observed spatial and time-periodic patterning.
GEODESIC CURVES FOR BIOMOLECULAR STRUCTURE MODELLING
Authors: MONDAINI RUBEM P.
Published: August 2008

The present literature has several contributions to the understanding of biomolecular structure by adopting helix curves through the atom sites as a paradigm. In the present contribution we introduce the weaker paradigm of geodesic curves of the manifold along ordered sets of points. This alternative allows us to use many interesting curves with some basic properties of helices in the modelling of protein and DNA structures.
AGENT-BASED MODELS OR DIFFERENTIAL EQUATIONS: TWO WAYS TO LEARN ABOUT SELECTION MECHANISMS IN GERMINAL CENTRES
Authors: MEYER-HERMANN MICHAEL
Published: August 2008

The germinal centre reaction selects B cells from a large diversity of clones in order to optimise the efficiency of an immune response. We discuss two rather different approaches to tackle the puzzle of selection mechanisms in germinal centres with mathematical methods. A space-averaged differential equation approach is compared to a space-resolved agent-based approach. The same two novel selection mechanisms could be localised with both methods which increases the predictive power of the result. In addition, the comparison of both methods allows interesting conclusions about the suitability of diverse approaches in Theoretical Biology.
Roles of Thermal Adaptation and Chemical Ecology inLiriomyzaDistribution and Control
Authors: Kang Le , Chen Bing , Wei Jia-Ning , Liu Tong-Xian
Published: August 2008

Many Liriomyza species are pests of agricultural and ornamental plants. In the past two decades, the occurrence and distribution of certain Liriomyza species have changed dramatically, leading to an extensive body of research papers. First, we review the association of thermal tolerance with population dynamics, geographic distribution, and species displacement. Differences in thermal tolerances between species result in their differential geographic locations and overwintering ranges. Displacements among Liriomyza species are associated with their temperature adaptation. We examine the chemical linkage of plants, Liriomyza, and their parasitoids. Chemical compounds from host and nonhost plants mediate the behavior of Liriomyza and their parasitoids. Liriomyza and their parasitoids use chemical cues to locate their hosts. Induced compounds can be used as attractants of parasitoids or repellents of Liriomyza. Thus, understanding the thermal tolerances and chemical ecology of Liriomyza may enable researchers to predict geographic distribution and to develop novel control strategies.
Microelectromechanical Systems–Based Feedback Control of Turbulence for Skin Friction Reduction
Authors: Kasagi Nobuhide , Suzuki Yuji , Fukagata Koji
Published: August 2008

This article focuses on the feedback control of turbulence for skin friction reduction and reviews the state of the art of control algorithms and distributed microsensors and microactuators. From a viewpoint of possible practical applications, we discuss only the control schemes based on the wall-surface sensing of shear stress and pressure fluctuations with their assessment in direct numerical simulation. The rapid development of microelectromechanical systems (MEMS) flow sensors/actuators is sketched, and a prototype feedback control system assembled for a turbulent channel flow is introduced. Finally, several major remaining issues in control algorithms and massive fabrication of microdevices are discussed.
Adaptation to intermittent stress promotes maintenance of β-cell compensation: comparison with food restriction
Authors: Bates Holly E. , Sirek Adam , Kiraly Michael A. , Yue Jessica T. Y. , Riddell Michael C. , Matthews Stephen G. , Vranic Mladen
Published: August 2008

Intermittent restraint stress delays hyperglycemia in ZDF rats better than pair feeding. We hypothesized that intermittent stress would preserve β-cell mass through distinct mechanisms from food restriction. We studied temporal effects of intermittent stress on β-cell compensation during pre-, early, and late diabetes. Six-week-old obese male ZDF rats were restraint-stressed 1 h/day, 5 days/wk for 0, 3, 6, or 13 wk and compared with age-matched obese ZDF rats that had been food restricted for 13 wk, and 19-wk-old lean ZDF rats. Thirteen weeks of stress and food restriction lowered cumulative food intake 10–15%. Obese islets were fibrotic and disorganized and not improved by stress or food restriction. Obese pancreata had islet hyperplasia and showed evidence of neogenesis, but by 19 wk old β-cell mass was not increased, and islets had fewer β-cells that were hypertrophic. Both stress and food restriction partially preserved β-cell mass at 19 wk old via islet hypertrophy, whereas stress additionally lowered α-cell mass. Concomitant with maintenance of insulin responses to glucose, stress delayed the sixfold decline in β-cell proliferation and reduced β-cell hypertrophy, translating into 30% more β-cells per islet after 13 wk. In contrast, food restriction did not improve insulin responses or β-cell hyperplasia, exacerbated β-cell hypertrophy, and resulted in fewer β-cells and greater α-cell mass than with stress. Thus, preservation of β-cell mass with adaptation to intermittent stress is related to β-cell hyperplasia, maintenance of insulin responses to glucose, and reductions in α-cell mass that do not occur with food restriction.
Molecular Substrates Mediating Lanthanide-Evoked Neurotransmitter Release in Central Synapses
Authors: Chung ChiHye , Deák Ferenc , Kavalali Ege T.
Published: August 2008

Noncanonical secretagogues such as hypertonicity or α-latrotoxin have been extremely informative in studying neurotransmission. Lanthanum and lanthanides can also trigger neurotransmitter release through an unknown mechanism. Here, we studied the effect of lanthanides on neurotransmission in hippocampal cultures. Application of 2 mM La3+ caused rapid and robust neurotransmitter release within seconds. In addition, transient application of La3+ uncovered a sustained facilitation of miniature neurotransmission. The response to La3+ was detectable at 2 μM and increased in a concentration-dependent manner ≤2 mM. Rapid effect of La3+ was independent of extracellular and intracellular Ca2+ and did not require La3+ entry into cells or activation of phospholipaseCβ. Synapses deficient in synaptobrevin-2, the major synaptic vesicle soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein in the brain, did not display any rapid release in response to La3+, whereas the slow facilitation of release detected after La3+ removal remained intact. In contrast, preincubation with intracellular Ca2+ chelators selectively attenuated the delayed release triggered by La3+. Moreover, synapses deficient in synaptotagmin-1 maintained a rapid response to La3+, suggesting that La3+-triggered neurotransmitter release does not require synaptotagmin-1 as a sensor. Therefore La3+ has two separate effects on synaptic transmission. For its rapid action, La3+ interacts with a target on the surface membrane, and unlike other forms of release, it triggers strictly synaptobrevin-2–dependent fusion, implying that in central synapses synaptobrevin-2 function is secretagogue specific. For the delayed action, La3+ may act intracellularly after its entry or through intracellular Ca2+ via a mechanism that does not require synaptobrevin-2.
The Cerebellum in Chiari Type II Malformation
Authors: Salman Michael S.
Published: August 2008

Chiari type II malformation (CII) is a congenital deformity of the brainstem and cerebellum. In CII, the size of the posterior fossa is small and its contents are crowded. The cerebellar weight, volume, and cell content are reduced in CII. However, this reduction is not uniform and appears to involve the cerebellar hemispheres more than the vermis. The anatomical location of the vermis allows it to expand upwards, downwards, and along the ventral-dorsal axis when it is compressed in CII. This expansion seems to leave its ocular motor functions intact unlike the cerebellar hemispheres, which have no room for expansion and therefore undergo atrophy with consequent impairment of their functions.
Use of Fluorescence Fundus Angiography to Assess Variations in Retinal Circulation in Myopic Patients of Different Ages
Authors: Ying Xi , Wu Yan , Wang Yi , Ran Li , Yew David T.
Published: August 2008

To investigate the variation in retinal circulation in patients with different degrees of myopia and different age by fluorescence fundus angiography (FFA). Thirty myopic patients (60 eyes), 20–54 years of age, with various degrees of myopia were evaluated. All patients underwent fundus photography and FFA using a standard technique. Patients with other ophthalmologic diseases possibly affecting the retrobulbar circulation and those with a history of laser treatment or intraocular surgery were excluded. Vascular filling patterns at arterial phase, arterial-venous phase and venous phase were reviewed. The average filling times at each phase were significantly delayed in severe myopia, but there was no difference between eyes with mild and medium myopia. There was no statistically significant correlation between mean filling time and age. The findings indicated a significant correlation between the intraocular blood circulation and the degree of myopia.
Synergism of CPT-11 and Apo2L/TRAIL against Two Differentially Sensitive Human Colon Tumor Xenografts
Authors: Sugamura Kenji , Gibbs John F. , Belicha-Villanueva Alan , Andrews Christopher , Repasky Elizabeth A. , Hylander Bonnie L.
Published: August 2008

Objective: The ability to sustain and grow portions of human tumors as xenografts in SCID mice provides a valuable preclinical opportunity to test the response of human tumors to treatments, both individually and in combination. Using this model, our laboratory has previously demonstrated that the growth of several human adenocarcinomas can be inhibited by Apo2L/TRAIL. Apo2L/TRAIL triggers apoptosis in many types of tumor cells, and when combined with various chemotherapeutic agents results in enhanced inhibition of tumor growth in many xenograft models. Methods: To gain further insight into the antitumor potential of Apo2L/TRAIL in combination with chemotherapy, we compared the responses of 2 human colon adenocarcinomas, both of which were sensitive to CPT-11 while one was sensitive and the other comparatively resistant to Apo2L/TRAIL. Results: In both cases, a greater degree of growth inhibition was achieved when these agents were used in combination. Western blot analysis demonstrated that in the Apo2L/TRAIL-sensitive tumor total cellular expression of Apo2L/TRAIL death receptors (DR4 and DR5) as well as protein expression of the pro-apoptotic molecule BAX were higher and the anti-apoptotic molecule Bcl-2 was lower in comparison to the Apo2L/TRAIL-resistant tumor. Conclusion: These results indicate that both Apo2L/TRAIL-sensitive and -resistant colon tumors will respond to a combination of CPT-11 and Apo2L/TRAIL and predict that this will be useful in the treatment of human colon cancers in a clinical setting.
Silencing of Polo-Like Kinase (Plk) 1 via siRNA Causes Inhibition of Growth and Induction of Apoptosis in Human Esophageal Cancer Cells
Authors: Bu Youquan , Yang Zhengmei , Li Quanhai , Song Fangzhou
Published: August 2008

Esophageal cancer ranks among one of the most frequent causes of cancer death in the world. Polo-like kinase 1 (Plk1) is overexpressed in human tumors and has prognostic value in many cancers including esophageal cancer, indicating its potential as a therapeutic target. In this study, we investigated the therapeutic potential of Plk1 in esophageal cancer using the technique of RNA silencing via small interfering RNA (siRNA). Synthetic siRNA duplexes against Plk1 were introduced into 4 esophageal cancer cell lines, which subsequently resulted in a significant inhibition in Plk1 expression in the cells. We found that the targeted depletion of Plk1 caused a dramatic mitotic catastrophe (mitotic cell cycle arrest as well as defects in several mitotic events such as incomplete separation of sister chromatids and failure of cytokinesis) followed by massive apoptotic cell death, and eventually resulted in a significant decrease in growth and viability of all 4 esophageal cancer cell lines studied. In addition, our results also indicated that the mitotic arrest induced by Plk1 depletion is mediated by the inactivation of the cdc2/cyclin B1 complex. Taken together, our study strongly suggests that Plk1 may serve as a potential therapeutic target in human esophageal cancer.
Human and Mouse Enamel Phenotypes Resulting from Mutation or Altered Expression of AMEL, ENAM, MMP20 and KLK4
Authors: Wright J. Timothy , Hart Thomas C. , Hart P. Suzanne , Simmons Darrin , Suggs Cynthia , Daley Bill , Simmer Jim , Hu Jan , Bartlett John D. , Li Yong , Yuan Zhi-An , Seow W. Kim , Gibson Carolyn W.
Published: August 2008

Amelogenesis imperfecta (AI) is caused by AMEL, ENAM, MMP20 and KLK4 gene mutations. Mice lacking expression of the AmelX, Enam and Mmp20 genes have been generated. These mouse models provide tools for understanding enamel formation and AI pathogenesis. This study describes the AI phenotypes and relates them to their mouse model counterparts. Human AI phenotypes were determined in a clinical population of AI families and published cases. Human and murine teeth were evaluated using light and electron microscopy. A total of 463 individuals from 54 families were evaluated and mutations in the AMEL, ENAM and KLK4 genes were identified. The majority of human mutations for genes coding enamel nonproteinase proteins (AMEL and ENAM) resulted in variable hypoplasia ranging from local pitting to a marked, generalized enamel thinning. Specific AMEL mutations were associated with abnormal mineralization and maturation defects. Amel and Enam null murine models displayed marked enamel hypoplasia and a complete loss of prism structure. Human mutations in genes coding for the enamel proteinases (MMP20 and KLK4) cause variable degrees of hypomineralization. The murine Mmp20 null mouse exhibits both hypoplastic and hypomineralized defects. The currently available Amel and Enam mouse models for AI exhibit enamel phenotypes (hypoplastic) that are generally similar to those seen in humans. Mmp20 null mice have a greater degree of hypoplasia than humans with MMP20 mutations. Mice lacking expression of the currently known genes associated with the human AI conditions provide useful models for understanding the pathogenesis of these conditions.
Sorafenib: Tolerance in Patients on Chronic Hemodialysis
Authors: Maroto Rey Pablo , Villavicencio Humberto
Published: August 2008

Background/Objective: Improved understanding of renal cell carcinomas (RCC) and recent contributions in the field of RCC biology led to the development of a novel class of drugs, i.e. multiple-kinase inhibitors, targeting growth factor receptors (e.g. sorafenib). Sorafenib has proven significant benefit in terms of progression-free survival in a phase II trial in RCC patients. A subsequent randomized phase III study (Treatment Approaches in Renal Cancer Global Evaluation Trial) confirmed the significantly prolonged progression-free survival and improvement in the quality of life compared to patients receiving placebo. In the USA and Europe, sorafenib has been approved for the treatment of advanced RCC. Patients: Two RCC patients on chronic hemodialysis were treated with sorafenib. Results: Both patients responded to sorafenib treatment. Apart from high blood pressure, a major adverse effect of sorafenib treatment, treatment was well tolerated, in agreement with previous results. Conclusion: The results of our study confirm the beneficial effect of sorafenib in the treatment of RCC in our 2 patients on dialysis.
Inhibition of Hydroxyapatite Dissolution by Ovalbumin as a Function of pH, Calcium Concentration, Protein Concentration and Acid Type
Authors: Hemingway C.A. , Shellis R.P. , Parker D.M. , Addy M. , Barbour M.E.
Published: August 2008

Hydroxyapatite is the main constituent of the dental hard tissues, and in vivo its dissolution in acids leads to the pathological condition of dental erosion. Food proteins which inhibit hydroxyapatite dissolution may find application as erosion-reducing agents in food and drink products. The aim of this study was to investigate the egg protein ovalbumin as a potential inhibitor of hydroxyapatite dissolution in acidic solutions, with conditions representative of dental erosion. The dissolution rate of hydroxyapatite discs was measured in an acidic solution as a function of pH, calcium concentration, ovalbumin concentration and acid type. All experiments were performed in triplicate. 0.2% w/v ovalbumin significantly reduced the dissolution rate in citric acid by 50–75% over the pH range 2.80–4.00, and by 45–60% in solutions with calcium concentrations of up to 20 mM (p < 0.05). The effect was persistent for several rinses after the initial exposure to the protein. 0.02% w/v ovalbumin significantly reduced the dissolution of hydroxyapatite in citric acid by 30–55%. Ovalbumin did not, however, statistically significantly reduce the hydroxyapatite dissolution rate in malic or lactic acids. The effect is ascribed to adsorption and partial, reversible denaturation of ovalbumin on the hydroxyapatite surface. There may be some interaction between ovalbumin and the citrate ion which promotes the adsorption of protein in the presence of citric acid. Ovalbumin shows promise as a potential erosion-reducing additive to citrus-based drinks.
Self-Reported Adherence to Treatment and Quality of Life in Mild to Moderate Acne
Authors: Jones-Caballero María , Pedrosa Emilio , Peñas Pablo F.
Published: August 2008

Background: Adherence to treatment is a mayor issue in dermatology, and its relationship to quality of life has barely been studied. Objective: To evaluate the relationship between scores on the Skindex-29 skin disease assessment scale and adherence to treatment in patients with acne. Methods: An observational, prospective study of 1,628 patients carried out by 252 clinicians in Spain. Results: Adherence was related to better objective and subjective severity index scores and better Skindex-29 scale scores at the end of the study. Young, male and unemployed patients had the worst adherence scores. Baseline and final Skindex-29 scale scores were significantly worse in non-adherent females, while non-adherent males scored better. Reasons for non-adherence were side effects for older patients and forgetfulness for younger ones. Conclusion: Dermatologists should explain that adherence to treatment is linked to better outcomes and better quality of life. Young females with high Skindex-29 scale scores and males with low Skindex scores are especially prone to non-adherence.
Nutritional Intake of Children and Adolescents with Insulin-Dependent Diabetes Mellitus in Crete, Greece
Authors: Papadaki A. , Linardakis M. , Codrington C. , Kafatos A.
Published: August 2008

Background/Aims: The incidence of childhood insulin-dependent diabetes mellitus (IDDM) is rapidly increasing in Greece. The aim of this study was to examine nutrient patterns of children and adolescents with IDDM in Crete. Methods: A case-control survey of eating habits was conducted among 41 children and adolescents, aged 6–17 years, with IDDM (cases) and healthy sex- and age-matched controls, recruited from Heraklion University Hospital and the village of Rouvas, Crete, respectively. Dietary data was based on 24-hour recall records. Results: Dietary intake was similar between the groups. Both groups exceeded the recommendations for total and saturated fat and consumed lower than recommended amounts of dietary fibre and total carbohydrates. Children with IDDM consumed more dairy products and vegetables and less meats and cereals. Vegetables were consumed by a relatively high proportion of children and adolescents in both groups, but there was a higher proportion of fruit consumers amongst the IDDM group. For those who ate fruit and vegetables, intake approximated current recommendations of 400 g/day. Conclusions: The need to increase complex carbohydrates and reduce the consumption of total and saturated fat, in order to approach the traditional dietary pattern of Crete for this population, should be addressed via appropriate nutrition education programmes.