bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation of magnetohydrodynamic slip flow of power-law nanofluid with temperature dependent viscosity and thermal conductivity over a permeable surface
Authors: Hussain Sajid , Aziz Asim , Khalique Chaudhry Masood , Aziz Taha
Published: January 2018

In this paper, a numerical investigation is carried out to study the effect of temperature dependent viscosity and thermal conductivity on heat transfer and slip flow of electrically conducting non-Newtonian nanofluids. The power-law model is considered for water based nanofluids and a magnetic field is applied in the transverse direction to the flow. The governing partial differential equations(PDEs) along with the slip boundary conditions are transformed into ordinary differential equations(ODEs) using a similarity technique. The resulting ODEs are numerically solved by using fourth order Runge-Kutta and shooting methods. Numerical computations for the velocity and temperature profiles, the skin friction coefficient and the Nusselt number are presented in the form of graphs and tables. The velocity gradient at the boundary is highest for pseudoplastic fluids followed by Newtonian and then dilatant fluids. Increasing the viscosity of the nanofluid and the volume of nanoparticles reduces the rate of heat transfer and enhances the thickness of the momentum boundary layer. The increase in strength of the applied transverse magnetic field and suction velocity increases fluid motion and decreases the temperature distribution within the boundary layer. Increase in the slip velocity enhances the rate of heat transfer whereas thermal slip reduces the rate of heat transfer.
"A difficult case": Pacioli and Cardano on the Chinese Rings
Authors: Heeffer Albrecht , Hinz Andreas M.
Published: January 2018

The Chinese rings puzzle is one of those recreational mathematical problems known for several centuries in the West as well as in Asia. Its origin is diffcult to ascertain but is most likely not Chinese. In this paper we provide an English translation, based on a mathematical analysis of the puzzle, of two sixteenth-century witness accounts. The first is by Luca Pacioli and was previously unpublished. The second is by Girolamo Cardano for which we provide an interpretation considerably different from existing translations. Finally, both treatments of the puzzle are compared, pointing out the presence of an implicit idea of non-numerical recursive algorithms.
A generalization of Trenkler’s magic cubes formula
Authors: Uko Livinus U. , Barron Terry L.
Published: January 2018

A Magic Cube of order p is a p×p×p cubical array with non-repeated entries from the set {1, 2, . . . , p3} such that all rows, columns, pillars and space diagonals have the same sum. In this paper, we show that a formula introduced in The Mathematical Gazette 84(2000), by M. Trenkler, for generating odd order magic cubes is a special case of a more general class of formulas. We derive sufficient conditions for the formulas in the new class to generate magic cubes, and we refer to the resulting class as regular magic cubes. We illustrate these ideas by deriving three new formulas that generate magic cubes of odd order that differ from each other and from the magic cubes generated with Trenkler’s rule.
Modelling Creep (Relaxation) of the Urinary Bladder
Authors: Zdravkovic Nebojsa , Rosic Mirko , Jankovic Nikola , Stojic Vladislava , Zdravkovic Natasa
Published: January 2018

We first present the results of an experiment in which the passive properties of the urinary bladder were investigated using strips of rabbit bladder. Under the assumption that the urinary bladder had orthopaedic characteristics, the strips were taken in the longitudinal and in the circumferential directions. The material was subjected to uniaxial tension, and stress-stretch curves were generated for various rates of deformation. We found that the rates did not have a significantly effect on the passive response of the material. Additionally, the stress-stretch dependence during relaxation of the material when exposed to isometric conditions was determined experimentally.

Next, we measured nonlinear stress-stretch dependence to determine the coefficients for this dependence in analytical form using a standard fitting procedure. The same approach was used to obtain the coefficients for the relaxation curves from the experimental data. Two constitutive laws, the nonlinear model for passive response and the creep model, were introduced within the shell finite element for geometrically and materially nonlinear analysis. We provide descriptions of the numerical procedures that were performed by considering the urinary bladder as a thin-walled shell structure subjected to pressure loading.

The developed numerical algorithm for the incremental-iterative solution was implemented into the finite element program, PAK. The response of the urinary bladder was calculated for continuous filling, and the numerical and experimental results were compared through cystometrograms (pressure-volume relationships). We also present comparisons of the shapes and volumes of the urinary bladder obtained numerically and experimentally. Finally, the numerical results of the creep response, when placed under constant internal pressure, are provided for various stages of deformation.
Analysis of Risk Factors for Development of Cognitive Disorders in Maintenance Hemodialysis Patients – Pilot Study
Authors: Jovanovic Milena , Todorovic Zeljko , Milovanovic Dragan , Draskovic Branislava , Todorovic Andreja , Petrovic Dejan
Published: January 2018

Prevalence of cognitive disorders is high in maintenance hemodialysis patients. Montreal cognitive assessment (MoCA) is used for detecting and evaluation of cognitive disorder degree in this patient population. In examined patient population, only 5 (12.5%) of them had normal cognitive function (MoCA ≥26). Mild cognitive impairment (MoCA 18-26) was found in 65.9% (29) patients, while moderate cognitive disorder (MoCA 10-17) was detected in 6 (21.6%) patients. Major cognitive disorder wasn’t detected in examined population. Statistically significant correlation was not established between laboratory parameters and overall MoCA score. Statistically significant correlation, however, was established between MoCA item that evaluates space and time orientation and intermediate secondary hyperparathyroidism and space and time orientation and severe secondary hyperparathyroidism. Hemodynamic instability during hemodialysis and silent ischemia of the brain are increasing risk of appearance of cognitive disorders in maintenance hemodialysis patients.
The improved design method of shear strength of reinforced concrete beams without transverse reinforcement
Authors: Vegera Pavlo , Vashkevych Rostyslav , Khmil Roman , Blikharskyy Zinoviy
Published: January 2018

In this article, results of experimental testing of reinforced concrete beams without transverse shear reinforcement are given. Three prototypes for improved testing methods were tested. The testing variable parameter was the shear span to the effective depth ratio. In the result of the tests we noticed that bearing capacity of RC beams is increased with the decreasing shear span to the effective depth ratio. The design method according to current codes was applied to test samples and it showed a significant discrepancy results. Than we proposed the improved design method using the adjusted value of shear strength of concrete CRd,c. The results obtained by the improved design method showed satisfactory reproducibility.
Costs of performance based maintenance for local roads: Case study Albania
Authors: Jokanović Igor , Grujić Bojana , Zeljić Dragana , Grujić Žarko , Svilar Mila
Published: January 2018

The provision and maintenance of road infrastructure is a major global business, consequently it is essential that road maintenance services are provided in the most cost effective manner. Without regular maintenance, roads can rapidly fall into disrepair, preventing realization of the longer term impacts of road improvements on development, such as increased agricultural production and growth in school enrollment, which is of particular importance for a network of local (access) roads. Inadequate local roads maintenance in Albania is proposed to be solved by implementing performance based maintenance approach for which the costing exercise is presented within the paper.
Keyhole surgery of pineal area tumors - personal experience in 22 patients
Authors: Kotwica Zbigniew , Saracen Agnieszka , Kasprzak Piotr
Published: January 2018

Background

Pineal area tumors are challenging for surgery due to their location. However, the removal of the lesion is critical for further treatment and survival of the patients

Material and methods

22 patients with pineal area tumors were surgically treated via keyhole medial suboccipital craniotomy and supracerebellar midline approach All the patients were operated in the sitting position with the use of operating microscope and microsurgical technique.

Results

All patients survived surgery in a perfect condition, and no one patient worsened after surgery. No complications due to the sitting position were noted.

Conclusions

Surgical removal of pineal area tumors via small suboccipital craniotomy is safe and with the use of microsurgical techniques the results of surgical treatment are excellent. The sitting position of the patients gives a better view to the surgeon. We did not observe any intraoperational complications due to the sitting position.
Piezoelectric Effects in GaN/AlGaN Multiple Quantum Wells Probed by Picosecond Time-Resolved Photoluminescence
Authors: Kim H. S. , Lin J. Y. , Jiang H. X. , Chow W. W. , Botchkarev A. , Morkoç H.
Published: January 2018

Piezoelectric effects in GaN/AlGaN multiple quantum wells (MQWs) have been directly probed by picosecond time-resolved photoluminescence (PL) spectroscopy. The time-resolved PL spectra of the 40 Å well MQWs reveal that the PL transition peak position is in fact blueshifted at early delay times due to the collective effects of quantum confinement of carriers, piezoelectric field, and Coulomb screening. However, the spectral peak position shifts toward lower energies as the delay time increases and becomes redshifted at longer delay times. By comparing experimental and calculation results, we have obtained a low limit of the piezoelectric field strength to be about 560 kV/cm in the 40 Å well GaN/Al0.15Ga0.85N MQWs.
Influence of Active Nitrogen Species on the Nitridation Rate of Sapphire
Authors: Ptak A.J. , Ziemer K.S. , Millecchia M.R. , Stinespring C.D. , Myers T.H.
Published: January 2018

The operating regimes of two rf-plasma sources, an Oxford CARS-25 and an EPI Unibulb, have been extensively characterized. By changing the exit aperture configuration and using an electrostatic deflector, the Oxford source could produce either primarily atomic nitrogen, atomic nitrogen mixed with low energy ions, or a large flux of higher energy ions (>65 eV) as the active species in a background of neutral molecular nitrogen. The EPI source produced a significant flux of metastable molecular nitrogen as the active species with a smaller atomic nitrogen component. Nitridation of sapphire using each source under the various operating conditions indicate that the reactivity was different for each type of active nitrogen. Boron contamination originating from the pyrolytic boron nitride plasma cell liner was observed.
Thermal Residual Stress Modeling in AlN and GaN Multi Layer Samples
Authors: Wang Kai , Reeber Robert R.
Published: January 2018

Thermal residual stresses can detrimentally affect the electronic and optical properties of epitaxial films thereby shortening device lifetime. Based on our earlier work on thermal expansion of nitrides, we provide a finite element modeling analysis of the residual stress distribution of multilayered GaN and AlN on 6H-SiC. The effects of thickness and growth temperatures are considered in the analysis.
Growth of Oriented Thick Films of Gallium Nitride from the Melt
Authors: Dyck Jeffrey S. , Kash Kathleen , Grossner Michael T. , Hayman Cliff C. , Argoitia Alberto , Yang Nan , Hong Moon-Hi , Kordesch Martin E. , Angus John C.
Published: January 2018

While significant strides have been made in the optimization of GaN-based devices on foreign substrates, a more attractive alternative would be homoepitaxy on GaN substrates. The primary motivation of this work is to explore the growth of thick films of GaN from the melt for the ultimate use as substrate material. We have previously demonstrated the synthesis of polycrystalline, wurtzitic gallium nitride and indium nitride by saturating gallium metal and indium metal with atomic nitrogen from a microwave plasma source. Plasma synthesis avoids the high equilibrium pressures required when molecular nitrogen is used as the nitrogen source. Here we report the growth of thick oriented GaN layers using the same technique by the introduction of (0001) sapphire into the melt to serve as a substrate. The mechanism of this growth is not established, but may involve transport of the metal as a liquid film onto the sapphire and subsequent reaction with atomic nitrogen. The films were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. X-ray diffraction showed that the GaN films were oriented with their c-axes parallel to the sapphire c-axis. The TEM analysis confirmed the orientation and revealed a dislocation density of approximately 1010 cm−2. The E2 Raman active phonon modes were observed in the GaN films.
Effects of Surface Preparation on Epitaxial GaN on 6H-SiC Deposited Via MOCVD
Authors: Xie Z. Y. , Wei C. H. , Li L. Y. , Edgar J. H. , Chaudhuri J. , Ignatiev C.
Published: January 2018

A comparison was made of 6H-SiC surfaces etched with H2, C2H4/H2, and HCl/H2, and the resulting crystal quality of epitaxial GaN films deposited on these substrates. To remove the many fine scratches and to smooth the rough surfaces typical of commercial SiC substrates, the Si-face 6H-SiC substrates were etched in H2, C2H4/H2, and HCl/H2 at 145 °C. GaN was subsequently deposited on these etched surfaces after first depositing a low temperature GaN buffer layer via metalorganic chemical vapor deposition (MOCVD). The surface morphologies after etching and after GaN deposition were characterized by atomic force microscopy and Normaski differential interference contrast microscopy, while the crystal quality of the GaN films was assessed by double crystal x-ray rocking curves and x-ray topography. 6H-SiC substrate surfaces were improved in terms of the removal of scratches and the reduction of surface roughness, and both surface morphology and crystal quality of the subsequently deposited GaN films were enhanced. However, the dislocation density was not decreased by the surface etching. The best GaN film was produced by etching the substrate in pure H2 for 40 minutes before growth. Recommendations for the optimum substrate treatment are made.
Disordering of InGaN/GaN Superlattices after High-Pressure Annealing
Authors: McCluskey M.D. , Romano L.T. , Krusor B.S. , Hofstetter D. , Bour D.P. , Kneissl M. , Johnson N.M. , Suski T. , Jun J.
Published: January 2018

Interdiffusion of In and Ga is observed in InGaN multiple-quantum-well superlattices for annealing temperatures of 1250 to 1400°C. Hydrostatic pressures of up to 15 kbar were applied during the annealing treatments to prevent decomposition of the InGaN and GaN. In as-grown material, x-ray diffraction spectra show InGaN superlattice peaks up to the fourth order. After annealing at 1400°C for 15 min, only the zero-order InGaN peak is observed, a result of compositional disordering of the superlattice. Composition profiles from secondary ion mass spectrometry indicate significant diffusion of Mg from the p-type GaN layer into the quantum well region. This Mg diffusion may lead to an enhancement of superlattice disordering. For annealing temperatures between 1250 and 1300°C, a blue shift of the InGaN spontaneous emission peak is observed, consistent with interdiffusion of In and Ga in the quantum-well region.
Structure of AlN on Si (111) Deposited with Metal Organic Vapor Phase Epitaxy
Authors: Rehder Eric , Zhou M. , Zhang L. , Perkins N. R. , Babcock S. E. , Kuech T. F.
Published: January 2018

The surface morphology and structure of AlN deposited by metal organic vapor phase epitaxy (MOVPE) on Si (111) at growth temperatures ranging from 825 to 1175°C was investigated. Transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) techniques were used to study the resulting film structure. Growth at high temperatures but less than ∼1100°C, resulted in a wire texture with some degree of in-plane alignment with (0001)AlN/ /(111)Si, < 10 0>AlN//< 11>Si, and 110>AlN//<10>Si. Deposition at temperatures greater than 1100°C results in single crystal films consisting of domains 60 nm across with an aspect ratio near unity. Growth below1100°C leads to degraded crystal quality with the grains developing random rotational misalignments around the AlN [0001] axis. Growth at lower temperatures produces islands elongated along the [110] direction. At the growth temperature of 825°C, the aspect ratio of the islands increased to 3 and a width of 25 nm. Cross-sectional TEM reveals that these islands are faceted due to slow growth on the {1 01}planes.
Comparative Growth of AlN on Singular and Off-Axis 6H and 4H-SiC by MOCVD
Authors: Wilson S. , Dickens C. S. , Griffin J. , Spencer M. G.
Published: January 2018

A comparison study of the growth of aluminum nitride (AlN) single crystal epitaxy on 6H-SiC and 4H-SiC substrates has been performed. The material has been characterized using atomic force microscopy (AFM) and reflective high energy electron diffraction (RHEED). AlN crystals were deposited on the following 6H-SiC substrates: singular with and without an initial SiC epilayer, and 3.5° off-axis with and without an initial SiC epilayer. AlN crystals were deposited on 8.0° off-axis 4H-SiC with and without initial SiC epilayers. AFM shows that the deposition of AlN on 6H-SiC and 4H-SiC with an initial SiC epilayer displays high quality quasi-two dimensional growth as atomically flat or step flow epitaxy.
Gallium Nitride Growth Using Diethylgallium Chloride as an Alternative Gallium Source
Authors: Zhang Ling , Zhang Rong , Boleslawski Marek P. , Kuech T.F.
Published: January 2018

Metal organic vapor phase epitaxy (MOVPE) of GaN has been carried out using diethyl gallium chloride (DEGaCl) and ammonia. The growth rate and efficiency of the DEGaCl-based growth decreases with increasing temperature when compared to trimethyl gallium (TMG)-based growth under similar conditions. Both low temperature buffer and the high temperature GaN layers were grown using the DEGaCl-NH3 precursor combination on the basal plane of sapphire and compared to similar structures grown using TMG and NH3. DEGaCl-based growth reveals an improved growth behavior under identical growth conditions to the conventional TMGa and ammonia growth. X-ray, Hall, and atomic force microscopy (AFM) measurements have been carried out on these samples providing a direct comparison of materials properties associated with these growth precursors. For the DEGaCl-based growth, the x-ray rocking curve line width, using the (0002) reflection, is as low as 300 arcsec on a 2.5-micron thick film. A RMS surface roughness of ∼0.5nm measured over a 10×10 micron area.
Piezoelectric Level Splitting in GaInN/GaN Quantum Wells
Authors: Wetzel C. , Takeuchi T. , Amano H. , Akasaki I.
Published: January 2018

Identification of the electronic band structure in AlInGaN heterostructures is the key issue in high performance light emitter and switching devices. In device-typical GaInN/GaN multiple quantum well samples in a large set of variable composition a clear correspondence of transitions in photo- and electroreflection, as well as photoluminescence is found. The effective band offset across the GaN/GaInN/GaN piezoelectric heterointerface is identified and electric fields from 0.23 - 0.90 MV/cm are directly derived. In the bias voltage dependence a level splitting within the well is observed accompanied by the quantum confined Stark effect. We furthermore find direct correspondence of luminescence bands with reflectance features. This indicates the dominating role of piezoelectric fields in the bandstructure of such typical strained layers.
Quantum-Confined Stark Effect and Recombination Dynamics of Spatially Indirect Excitons in MBE-Grown GaN-AlGaN Quantum Wells
Authors: Lefebvre Pierre , Gil Bernard , Allègre Jacques , Mathieu Henry , Grandjean Nicolas , Leroux Mathieu , Massies Jean , Bigenwald Pierre
Published: January 2018

We analyze the low-temperature photoluminescence decay times, for a series of MBE-grown samples embedding GaN-AlGaN quantum wells. We investigate a variety of configurations in terms of well widths, barrier widths and overall strain states. We find that not only the wells but also the barriers are submitted to large built-in electric fields. In the case of narrow barriers (5 nm), these fields favor the nonradiative escape of carriers from narrow wells into wider wells. When all wells have the same width, the field in such narrow barriers allow us to observe the recombination of long-lived “inter-well” excitons at energies close to those of the short-lived “intra-well” excitons. Our results also prove that the energies and the dynamics of excitonic recombinations depend on the parameters of the heterostructures in a complicated way, due to the interplay of piezoelectric and spontaneous polarizations.
Ion Channeling Analysis of Gallium Nitride Implanted with Deuterium
Authors: Wampler W. R. , Myers S. M.
Published: January 2018

Ion channeling and transmission electron microscopy were used to examine the microstructure of GaN implanted with deuterium (D) at high (>1 at. %) and low (< 0.1 at. %) D concentrations. At high concentrations, bubbles and basal-plane stacking faults were observed. Ion channeling showed the D was disordered relative to the GaN lattice, consistent with precipitation of D2 into bubbles. At low D concentrations, bubbles and stacking faults are absent and ion channeling shows that a large fraction of the D occupies sites near the center of the c-axis channel.
Growth and Characterization of BxGa1−xN on 6H-SiC (0001) by Movpe
Authors: Wei C. H. , Xie Z. Y. , Edgar J. H. , Zeng K. C. , Lin J. Y. , Jiang H. X. , Ignatiev C. , Chaudhuri J. , Braski D. N.
Published: January 2018

Boron was incorporated into GaN in order to determine its limits of solubility, its ability of reducing the lattice constant mismatch with 6H-SiC, as well as its effects on the structural and optical properties of GaN epilayers. BxGa1−xN films were deposited on 6H-SiC (0001) substrates at 950 °C by low pressure MOVPE using diborane, trimethylgallium, and ammonia as precursors. A single phase alloy with x=0.015 was successfully produced at a gas reactant B/Ga ratio of 0.005. Phase separation into pure GaN and BxGa1−xN alloy with x=0.30 was deposited for a B/Ga reactant ratio of 0.01. This is the highest B fraction of the wurtzite structure alloy ever reported. For B/Ga ratio ≥ 0.02, no BxGa1−xN was formed, and the solid solution contained two phases: wurtzite GaN and BN based on the results of Auger and x-ray diffraction. The band edge emission of BxGa1−xN varied from 3.451 eV for x=0 with FWHM of 39.2 meV to 3.465 eV for x=0.015 with FWHM of 35.1 meV. The narrower FWHM indicated that the quality of GaN epilayer was improved with small amount of boron incorporation.
Optical and Structural Properties of Er3+-Doped GaN Grown by MBE
Authors: Birkhahn R. H. , Hudgins R. , Lee D. S. , Lee B.K. , Steckl A. J. , Saleh A. , Wilson R. G. , Zavada J. M.
Published: January 2018

We report the morphological and compositional characteristics of Er-doped GaN grown by MBE on Si(111) substrates and their effect on optical properties. The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Er) and a plasma gas source for N2. The films emit by photoexcitation in the visible and near infrared wavelengths from the Er atomic levels. The morphology of the GaN:Er films was examined by AFM. Composition was determined by SIMS depth profiling that revealed a large Er concentration at 4.5×1021 atoms/cm3 accompanied by a high oxygen impurity concentration.
Defect Complexes and Non-Equilibrium Processes Underlying the P-Type Doping of GaN
Authors: Reboredo Fernando A. , Pantelides Sokrates T.
Published: January 2018

It is well known that hydrogen plays a key role in p-type doping of GaN. It is believed that H passivates substitutional Mg during growth by forming a Mgs-N-Hi complex; in subsequent annealing, H is removed, resulting in p-type doping. Several open questions have remained, however, such as experimental evidence for other complexes involving Mg and H and difficulties in accounting for the relatively high-temperature anneal needed to remove H. We present first principles calculations in terms of which we show that the doping process is in fact significantly more complex. In particular, interstitial Mg plays a major role in limiting p-type doping. Overall, several substitutional/interstitial complexes form and can bind H, with vibrational frequencies that account for hitherto unidentified observed lines. We predict that these defects, which limit doping efficiency, can be eliminated by annealing in an atmosphere of H and N prior to the final anneal that removes H.
Spectroscopy of Proton Implanted GaN
Authors: Weinstein M.G. , Stavola M. , Song C.Y. , Bozdog C. , Przbylinska H. , Watkins G.D. , Pearton S.J. , Wilson R.G
Published: January 2018

Vibrational spectroscopy, photoluminescence, and optically detected electron paramagnetic resonance (ODEPR) have been used to characterize the defects produced in undoped and Sidoped GaN by the implantation of hydrogen. Several new vibrational bands were found near 3100 cm−1 in GaN that had been implanted with protons. These frequencies are close to those predicted for VGa−Hn complexes, leading to the tentative assignment of the new lines to VGa defects decorated with different numbers of H atoms. The proton implantation also produces an infrared PL band centered at 0.95 eV and the ODEPR spectrum labeled LE1, both of which were seen previously for electron-irradiated GaN.
Gan Nanotubes
Authors: Mi Lee Seung , Hee Lee Young , Gyoo Hwang Yong , Elsner J. , Porezag Dirk , Frauenheim Thomas
Published: January 2018

We perform parametrized density-functional calculations to predict the stability and formation mechanism of GaN nanotubes. Strain energies of GaN nanotubes are comparable to those of carbon nanotubes, suggesting the possibility for the formation of GaN nanotubes. We note that an intermediate phase with [4,6,10] polygons exist at armchair tube edge, which may play as a nucleation seed of further tube growth.
Base Transit Time in Abrupt GaN/InGaN/GaN and AlGaN/GaN/AlGaN HBTs
Authors: Chiu Shean-Yih , Anwar A. F. M. , Wu Shangli
Published: January 2018

Base transit time, τb , in abrupt npn GaN/InGaN/GaN and AlGaN/GaN/AlGaN double heterojunction bipolar transistors (DHBTs) is reported. Base transit time strongly depends not only on the quasi-neutral base width, but also on the low field electron mobility, μn, in the neutral base region and the effective electron velocity, Sc, at the edge of base-collector heterojunction. μn and Sc are temperature-dependent parameters. A unity gain cut-off frequency of 10.6 GHz is obtained in AlGaN/GaN/AlGaN DHBTs and 19.1 GHz in GaN/InGaN/GaN DHBTs for a neutral base width of 0.05um. It is also shown that non-stationary transport is not required to study τb for neutral base width in the range of 0.05um for GaN-based HBTs.
Piezoelectric Field Effect on Optical Properties of GaN/GaInN/AlGaN Quantum Wells
Authors: Im Jin Seo , Kollmer H. , Gfrörer O. , Off J. , Scholz F. , Hangleiter A.
Published: January 2018

We designed and studied two sample groups: first, GaInN/AlGaN/GaN quantum wells with asymmetric barrier structure and secondly, GaInN/GaN quantum wells with asymmetrically doped barriers. Time-resolved measurements on the asymmetric structure reveal an enhanced oscillator strength when the AlGaN barrier is on top of the GaInN quantum well, indicating a better carrier confinement in such a structure. The photoluminescence emission energy of the GaInN/GaN quantum well with doped GaN barriers shifts towards higher energy than that of undoped samples due to screening, but only when the GaN barrier layer below the quantum well is doped. In contrast, the sample where only a GaN cap layer above the quantum well is doped, shows no blue-shift. These results, showing asymmetries in GaInN/GaN quantum wells, provide confirming evidence of the piezoelectric field effect and allow us to determine the sign of the piezoelectric field, which points towards the substrate in a compressively strained quantum well. Furthermore, we performed model calculations of the global band bending and the screening effect, which consistently explain our experimental findings.
Thermal Stability of GaN Investigated by Raman Scattering
Authors: Kuball M. , Demangeot F. , Frandon J. , Renucci M.A. , Grandjean N. , Briot O.
Published: January 2018

We have investigated the thermal stability of GaN using Raman scattering. Noninvasive optical monitoring of the degradation of GaN during high-temperature processing has been demonstrated. GaN samples grown by molecular-beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOCVD) were studied. Characteristic features in the Raman spectrum identify three thermal stability regimes: (1) annealing below 900°C does not affect the GaN Raman spectrum; (2) annealing between 900°C and 1000°C results in the appearance of disorder-induced Raman scattering between the E2 and A1(LO) phonon; (3) annealing at temperatures higher than 1000°C gives rise to distinct Raman modes at 630 cm−1, 656 cm−1 and 770 cm−1. The evolution of the Raman spectrum of GaN with increasing annealing temperature is discussed in terms of disorder-induced Raman scattering. We find clear indications for an interfacial reaction between GaN and sapphire for annealing temperatures higher than 1000°C.
Electroluminescence Properties of InGaN/AlGaN/GaN Light Emitting Diodes with Quantum Wells
Authors: Yunovich A.E. , Kudryashov V.E. , Turkin A.N. , Kovalev A.N. , Manyakhin F.I.
Published: January 2018

Electroluminescence spectra of light-emitting diodes based on InGaN/AlGaN/GaN heterostructures with single and multiple quantum wells (QWs) are analyzed by models of radiative recombination in 2D-structures with band tails. Equations of the model fit spectra quite good in a wide range of currents. Parameters of the fit are discussed and compared for single and multiple QWs. Tunnel effects play a sufficient role in blue LEDs with single QWs at low currents; they can be neglected in LEDs with multiple QWs. A new spectral band was detected at the high energy side of the spectra of green LEDs with multiple QWs; it is attributed with large scale inhomogenities of In distribution in InGaN QWs.*)
Ni/Si-Based Contacts to GaN: Thermally Activated Structural Transformations Leading to Ohmic Behavior
Authors: Kaminska E. , Piotrowska A. , Jasinski J. , Kozubowski J. , Barcz A. , Golaszewska K. , Thomson D.B. , Davis R.F. , Bremser M.D.
Published: January 2018

Structural transformations in Ni/Si-based contacts to GaN occurring under heat treatment have been studied using transmission electron microscopy and secondary ion mass spectrometry. Transition from non-ohmic to ohmic behavior correlates with reaction between Ni and Si, and decomposition of the initially formed interfacial Ni:Ga:N layer. Transport of dopant atoms from metallization into GaN testifies in favour of the SPR process of ohmic contact formation
LAJU RESPIRASI INDUK IKAN BLACKHEAD SEABREAM Acanthopagrus schlegelii PADA SUHU PEMELIHARAAN YANG BERBEDA
Authors: Prakoso Vitas Atmadi , Chang Young Jin
Published: January 2018

Laju respirasi hewan akuatik memiliki hubungan yang erat dengan metabolisme. Tingkat metabolisme hewan merupakan variabel yang dapat dipengaruhi faktor dalam maupun luar, salah satunya adalah suhu. Pada ikan, proses metabolisme juga berkorelasi dengan suhu. Salah satu jenis ikan yang perlu dikaji laju respirasinya adalah ikan blackhead seabream Acanthopagrus schlegelii yang merupakan spesies ikan laut yang popular di Korea Selatan, sehingga diperlukan lebih banyak informasi lagi mengenai laju respirasi ikan ini untuk mengoptimalkan metabolisme ikan ini dan berdampak kepada produktivitas budidaya. Penelitian ini bertujuan untuk mengevaluasi laju respirasi induk ikan blackhead seabream pada beberapa tingkatan suhu. Ikan blackhead seabream (panjang total 29,3 ± 2,2 cm dan bobot tubuh 538,3 ± 43,0 g) diteliti menggunakan respirometer dalam sistem resirkulasi. Tiga kelompok percobaan dilakukan untuk mengukur laju respirasi berdasarkan perubahan suhu pemeliharaan (15°C, 20°C, dan 25°C). Hasil penelitian menunjukkan bahwa kecenderungan laju respirasi meningkat secara linier dengan peningkatan suhu perlakuan, dengan nilai tertinggi sebesar 164,8 ± 30,7 mg O2/kg/jam pada 25°C dan nilai terendah sebesar 72,4 ± 8,1 mg O2/kg/jam pada 15°C. Sementara itu, frekuensi pernapasan berkorelasi positif terhadap kenaikan suhu. Berdasarkan penelitian ini, dapat disimpulkan bahwa perubahan suhu dari 15°C ke 25°C menyebabkan peningkatan laju respirasi pada induk ikan blackhead seabream.It is well known that a close relationship exists between respiration rate and metabolism in aquatic animal. In fish, the metabolic rate is influenced by internal or external factors, such as temperature. This research observed the respiration rate of blackhead seabream, Acanthopagrus schlegelii, which is one of the popular marine fish species in South Korea. Despite the fish popularity, very few information are available about the fish’s respiration rate which is important in order to optimize its metabolism and increase its aquaculture productivity. This study aimed to evaluate the respiration rate of adult blackhead seabream reared in media with different temperature settings. The fish (total length of 29.3 ±2.2 cm and body weight of 538.3 ± 43.0 g) were observed using a respirometer placed inside the recirculation systems. Three groups of experiments were set up to measure the fish’s respiration rate according to different rearing temperatures (15°C, 20°C, and 25°C). The results showed that there was a tendency of respiration rate increased linearly with the increase of temperature. The highest respiration rate was 164.8 ± 30.7 mg O2/kg/hour at 25°C and the lowest value was 72.4 ± 8.1 mg O2/kg/hour at 15°C which indicated that the respiratory rate positively correlated to the change in temperature. According to this study, it can be concluded that temperature changes from 15°C to 25°C led an increase in respiration rate of adult blackhead seabream
DAYA ADAPTASI TIGA SPESIES IKAN PATIN PADA LINGKUNGAN YANG BERBEDA
Authors: Tahapari Evi , Darmawan Jadmiko , Dewi Raden Roro Sri Pudji Sinarni
Published: January 2018

Penampilan fenotipe suatu organisme ditentukan oleh faktor genotipe dan faktor lingkungan tempat organisme tersebut hidup. Penelitian ini bertujuan untuk mempelajari daya adaptasi tiga spesies ikan patin yang dipelihara di lokasi berbeda. Ikan patin siam, patin jambal, dan patin pasupati dengan rataan bobot 20 g dipelihara di tiga lokasi yang berbeda, yaitu: kolam air tenang, tambak, dan keramba jaring apung. Pemeliharaan ikan dilakukan selama empat bulan. Selama pemeliharaan, ikan diberi pakan berupa pelet komersial dengan kadar protein 30%–32%. Jumlah pakan yang diberikan pada bulan kesatu sampai keempat secara berturut-turut adalah sebanyak 5%, 4%, dan 3% dari biomassa ikan per hari. Pakan diberikan dengan frekuensi tiga kali sehari. Hasil penelitian menunjukkan adanya interaksi yang signifikan antara genotipe ikan patin dengan lingkungan ekosistem yang berbeda dan daya adaptasi yang spesifik dari ketiga spesies ikan patin. Ketiga spesies ikan patin memiliki pertumbuhan sama bila dipelihara di kolam air tenang. Ikan patin jambal tumbuh dengan baik (P<0,05) jika dipelihara di keramba jaring apung (KJA) dan tambak, masing-masing dengan laju pertumbuhan spesifik (LPS) 2,51±0,15%/hari, dan LPS 2,39±0,04%/hari. Pertumbuhan ikan patin siam dan pasupati adalah sama pada ketiga lokasi penelitian (P>0,05). Ketiga spesies ikan patin mempunyai daya adaptasi lingkungan yang sempit sehingga budidayanya akan optimal jika dilakukan di lokasi tertentu saja.The phenotypic appearance of an organism is determined by genotypes and environmental factors in which the organism lives. This study aims to study the adaptability of three species of pangasiids reared in three different environments. Three species of catfish (Siamese pangasiid, jambal pangasiid, and pasupati) with an average weight of 20 gwere kept in stagnant water pond, brackishwater pond, and floating net cage). Fishes were reared for four months. During the rearing, fish were fed by commercial pellets with 30%-32% protein content. The amount of feed given in the first month to the fourth month was 5%, 4%, and 3% of the biomass per day. Feed was given three times a day. The results showed the significant interaction between pangasiid genotype and environment, and specific adaptability on three species of pangasiid. Jambal pangasiid grew better in floating net cage (SGR 2.51±0.15%/day). Pasupati pangasiid grew better in stagnant water pond (SGR 2.05±0.03%/day). Siamese pangasiid grew better in stagnant water pond (SGR 2.02±0.05%/day) and brackishwater pond (SGR 2.31±0.09%/day). The three species of catfish have a narrow environmental adaptability so that the cultured will be optimal if done in a particular location.
PEMANFAATAN PROBIOTIK KOMERSIAL PADA PEMBESARAN IKAN LELE (Clarias gariepinus)
Authors: Dewi Raden Roro Sri Pudji Sinarni , Tahapari Evi
Published: January 2018

Ikan lele Afrika (Clarias gariepinus) merupakan spesies asli Afrika yang telah diintroduksikan dan dibudidayakan secara komersial di Indonesia. Upaya peningkatan efisiensi produksi ikan lele terus ditingkatkan guna meningkatkan keuntungan. Salah satu upaya untuk meningkatkan efektivitas budidaya ikan lele adalah melalui penggunaan probiotik. Penelitian ini bertujuan untuk mengevaluasi pemanfaatan probiotik pada pembesaran ikan lele. Perlakuan yang diberikan berupa pemberian pakan hasil fermentasi probiotik dan pakan tanpa fermentasi (kontrol) dengan tiga ulangan. Pengujian dilakukan pada kolam terpal berukuran 3 m3 dengan padat tebar yang digunakan yaitu 500 ekor/wadah dan dipelihara selama 35 hari. Berdasarkan hasil pengujian, pemberian probiotik pada pakan dengan cara fermentasi mampu meningkatkan bobot dan biomassa panen secara signifikan (P<0,1). Bobot akhir ikan lele yang diberi pakan hasil fermentasi probiotik mencapai 76,9 ± 0,2 g; sedangkan kontrol 74,2 ± 0,2 g. Biomassa akhir ikan lele yang diberi pakan hasil fermentasi probiotik mencapai 37,91 ± 0,29 kg; sedangkan kontrol 34,65 ± 1,70 kg. Pemberian pakan yang difermentasi probiotik mampu meningkatkan retensi protein sebesar 1,02%; retensi karbohidrat sebesar 10,26%; dan retensi lemak sebesar 7,22%. Selain itu, penggunaan probiotik mampu menekan biaya produksi sebesar Rp 561,00/kg dan meningkatkan keuntungan sebesar 5%.African catfish (Clarias gariepinus) is a native African species that has been introduced and cultivated commercially in Indonesia. Efforts to increase the efficiency of catfish production were conducted in order to increase profit. One effort to increase the effectiveness of catfish farming is through the use of probiotics. This study was aimed to evaluate the use of probiotics in catfish farming. The treatments were fermented feed by probiotic and non fermented feed (control) and repeated three times. The experiment was conducted on a 3 m3 tarpaulin pond, with a density 500 fishes/pond, and reared for 35 days. Based on the results, the fermented feed by probiotic could increase the weight and biomass of harvested fish significantly. The weight of catfish fed with fermented feed reached 76.9 ± 0.2 g while the control was 74.2 ± 0.2 g. The final biomass of catfish fed with fermented feed reached 37.91 ± 0.29 kg while the control was 34.65 ± 1.70 kg. Feeding fermented feed by probiotic Gut Bio Aero increased the protein retention by 1.02%, carbohydrate retention by 10.26%, and lipid retention by 7.22%. The application of probiotic could reduce production cost by 561 IDR/kg and increased profit by 5%.
Polarização federativa do SUS nos anos 1990: uma interpretação histórico-institucionalista
Authors: Ouverney Assis Mafort , Fleury Sonia
Published: January 2018

Resumo Este artigo busca explicar a dinâmica político-institucional que produziu um quadro polarizado de relações federativas no SUS nos anos 1990, com base no arcabouço teórico do neoinstitucionalismo histórico. Nessa perspectiva, analisa-se a trajetória das relações intergovernamentais como o resultado de uma cadeia de decisões tomadas em contextos singulares dos governos Collor, Itamar e FHC, onde o jogo entre os atores políticos do SUS e as tendências do contexto federativo nacional estabeleceu a direção da estratégia de descentralização em cada etapa. A intensidade de institucionalização dependeu ainda das escolhas desses governos relativas à direção da política nacional e à estrutura de coordenação federativa do Ministério da Saúde, da estabilidade e do volume do financiamento setorial, e das capacidades institucionais de estados e municípios para assumirem novas responsabilidades.
Estrategias de apropiación y desviación de recursos en el Sistema Municipal de Planeación de Santiago de Cali
Authors: Pazos Leonardo Solarte , Olaya Álvaro Pío Gómez , Arias Luis Felipe Sánchez
Published: January 2018

Resumen A partir de algunos elementos que caracterizan un mecanismo de captura de élite mencionado en la literatura, este artículo compara cinco estrategias de apropiación de recursos realizadas por ciertos actores del Sistema Municipal de Planeación (SMP) participativa, de la tercera ciudad más poblada de Colombia, entre 1998 y 2008. Desde un enfoque de evaluación centrada en el uso, se abordaron los actores del SMP y sus alianzas que, aprovechando asimetrías informacionales, restringieron la participación y sesgaron el uso de los recursos. La investigación identificó, como causal básica de la captura, la desarticulación del SMP en tres subsistemas: la comunidad, las instancias de participación local y el Departamento de Planeación. El artículo describe igualmente la serie de ajustes institucionales desarrollados entre 2012 y 2015 (monitoreo, e-voting) buscando minimizar las posibilidades de captura.
Imunidade celular em vacas Holandesas soropositivas para o Vírus da Leucose Bovina (BLV) durante o período de transição
Authors: Gomes V. , Baldacim V.A.P. , Costa J.F.R. , Silva C.P. Costa e , Arcaro J.R.P. , Miranda M.S. , Sousa R.S. , Fagliari J.J. , Madureira K.M.
Published: January 2018

RESUMO Esta pesquisa avaliou a dinâmica dos leucócitos e das subpopulações de linfócitos em vacas Holandesas soropositivas para o BLV no período de transição. Amostras de sangue (n=72) provenientes de 12 vacas foram coletadas entre as semanas -2 e +3 para a realização do leucograma, imunofenotipagem, dosagem de cortisol e haptoglobina (Hp). O perfil leucocitário foi caracterizado por leucocitose, neutrofilia, monocitose e eosinopenia próximo ao parto. Linfocitose e elevada proporção de linfócitos B CD21+ foram achados constantes entre as semanas -2 e +3; assim, as vacas foram testadas e confirmadas soropositivas para o BLV. Os valores das subpopulações de linfócitos T apresentaram-se baixos durante o período de transição, observando-se dois picos máximos que coincidiram com as elevações nas concentrações de cortisol no parto (2,11µg/dL) e semana +3 (1,97µg/dL). Hp apresentou aumento crescente de -2 (166µg/mL) a +3 (576µg/mL), provavelmente associada à elevada taxa de infecções uterinas observadas nas semanas +2 e +3. As vacas soropositivas para o BLV apresentaram leucograma de estresse próximo ao parto, exceto para linfócitos. A linfocitose e as elevadas proporções de células B CD21+, associadas com as baixas proporções de células T, podem ser indicativo de imunossupressão e predisposição aos processos inflamatórios no período pós-parto.
Characterization of Staphylococcus spp. strains in milk from buffaloes with mastitis in Brazil: the need to identify to species level to avoid misidentification
Authors: Coimbra-e-Souza V. , Brito M.A.V.P. , Chamon R.C. , Laport M.S. , Giambiagi-deMarval M.
Published: January 2018

ABSTRACT Mastitis is an inflammation of the mammary gland that affects dairy cattle worldwide causing economic losses. Coagulase-negative staphylococci (CNS) are the predominant cause of this type of infection. We have recently showed that coagulase-positive staphylococci could be misidentified. So, the aim of this study was to characterize the Staphylococcus spp. strains initially classified as coagulase-negative Staphylococci, isolated from buffalo with subclinical mastitis. Milk of buffaloes with mastitis in herds was collected and 9 strains were identified as CNS by phenotypic tests. Molecular methodologies latter identified the strains as coagulase-negative Staphylococcus chromogenes (5), coagulase-positive Staphylococcus hyicus (2) and coagulase-positive Staphylococcus aureus (2). Our results strongly support the need to identify the isolates to a species level in order to avoid misidentification and to be aware of the classification using the coagulase test alone.
Parâmetros citológicos e bioquímicos do líquido cefalorraquidiano coletado de bovinos sadios em dois momentos, com intervalo de 96 horas
Authors: Cunha P.H.J. , Andrade D.G.A. , Oliveira-Filho J.P. , Badial P.R. , Passarelli D. , Takahira R.K. , Lisboa J.A.N. , Borges A.S.
Published: January 2018

RESUMO A análise do líquido cefalorraquidiano (LCR) é uma importante ferramenta no diagnóstico das doenças neurológicas dos bovinos. A coleta do LCR em diferentes momentos facilita o monitoramento do quadro clínico e/ou a avaliação da eficácia de tratamentos estabelecidos. Todavia, os efeitos de coletas consecutivas sobre os parâmetros citológicos e bioquímicos do LCR de bovinos saudáveis ainda não foram analisados. Dessa forma, o objetivo do presente estudo foi avaliar potenciais diferenças citológicas e bioquímicas no LCR de bovinos sadios, obtidos em dois momentos, com intervalo de 96 horas. O LCR foi submetido à análise citológica e à determinação do teor de proteína total. Na segunda coleta, verificou-se aumento significativo da celularidade, porém ainda dentro do intervalo de referência para a espécie, diminuição de linfócitos e elevação de células mononucleares em relação à primeira coleta. No entanto, os números de hemácias (/µL), células nucleadas (/µL), neutrófilos (%), eosinófilos (%) e a concentração da proteína total (mg/dL) continuaram dentro dos valores de referência 96 horas após a realização da primeira punção. Conclui-se que os procedimentos de coleta de LCR consecutivos não provocaram inflamação local detectável 96 horas após a primeira punção, o que sugere que, quando necessário, coletas de LCR seriadas, por si só, não interfeririam nos resultados do exame.