Fundamental studies of the solid-particle erosion of silicon

The predictions of the theories of solid-particle erosion of brittle materials are compared to experimental results of studies in which angular Al2O3 particles with mean diameters D of 23 to 270 microns are used to erode (111) surfaces of silicon single crystals at impact angles alpha from 20 to 90 deg and velocities v from 30 to 150 m/s. The description of the steady state erosion rate by a power law, delta W varies directly as (v sin alpha)(n)D(m) must be modified to include threshold and plasticity effects. Furthermore the velocity exponent n depends on D. Results using abrasives of different sizes mixed together can be explained using a logarithmic-normal distribution. The results of transient experiments can be used to explain the synergistic effects which are observed using a biomodal distribution of abrasives

Erosion of Composite Ceramics

The theoretical basis to describe solid-particle erosion of monolithic ceramics is well developed. In many cases, the models can account for the impact velocity, impact angle and erodent-size dependencies of the steady-state erosion rate. In addition, the models account for effects of materials parameters such as fracture toughness and hardness. Steady-state erosion measurements on a wide variety of composite ceramics, including SiC whisker-reinforced Al{sub 2}O{sub 3}, Si{sub 3}N{sub 4} containing Si{sub 3}N{sub 4} or SiC whiskers, Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} reinforced with SiC whiskers, and duplex-microstructure Si{sub 3}N{sub 4} have been reported. The theories developed for monolithic ceramics are, however, less successful in describing the results for composites

Thermoelectric power factors of nanocarbon ensembles as a function of temperature

Thermoelectric power factors of nanocarbon ensembles have been determined as a function of temperature from 400 to 1200 K. The ensembles, composed of mixtures of nanographite or disperse ultrananocrystalline diamond with B 4 C B4C , are formed into mechanically rigid compacts by reaction at 1200 K with methane gas and subsequently annealed in an argon atmosphere at temperatures up to 2500 K. The ensembles were characterized using scanning electron microscopy, Raman, x-ray diffraction, and high resolution transmission electron microscopy techniques and found to undergo profound nanostructural changes as a function of temperature while largely preserving their nanometer sizes. The power factors increase strongly both as a function of annealing temperature and of the temperature at which the measurements are carried out reaching 1 µW/K 2 ¿cm 1 µW/K2¿cm at 1200 K without showing evidence of a plateau. Density functional “molecular analog” calculations on systems based on stacked graphene sheets show that boron substitutional doping results in a lowering of the Fermi level and the creation of a large number of hole states within thermal energies of the Fermi level [P. C. Redfern, D. M. Greun, and L. A. Curtiss, Chem. Phys. Lett. 471, 264 (2009)]. We propose that enhancement of electronic configurational entropy due to the large number of boron configurations in the graphite lattice contributes to the observed thermoelectric properties of the ensembles

Review and assessment of nanofluid technology for transportation and other applications.

This report provides a literature review on the research and development work contributing to the current status of nanofluid technology for heat transfer applications in industrial processes. Nanofluid technology is a relatively new field, and as such, the supporting studies are not extensive. Specifically, the experimental results and theoretical predictions regarding the enhancement of the thermal conductivity and convective heat transfer of nanofluids relative to conventional heat transfer fluids were reviewed and assessments were made of the current status to derive future research and development directions for industrial applications. Pertinent parameters were considered individually as to the current state of knowledge. Experimental results from multiple research groups were cast into a consistent parameter, 'the enhancement ratio,' to facilitate comparisons of data among research groups and identification of thermal property and heat transfer trends. The current state of knowledge is presented as well as areas where the data are currently inconclusive or conflicting. Heat transfer enhancement for available nanoparticles is known to be in the 15-40% range, with a few situations resulting in orders of magnitude enhancement. The direction of future research should be to substantiate the lower range results and to continue investigations into the higher enhancements. The focus of this study is primarily transportation applications. However, some attention is given to other industrial applications of nanofluid heat transfer. Also discussed are barriers to be addressed prior to commercialization of nanofluids

Erosion of a geopolymer.

Solid-particle erosion studies were conducted on a representative geopolymer. The test conditions were normal impact of 390-{micro}m angular Al{sub 2}O{sub 3} erodent particles moving at 50, 70, or 100 m/s. Steady-state erosion rates were obtained and the material-loss mechanism was studied by scanning electron microscopy. The geopolymer responded as a classic brittle material. Elastic-plastic indentation events led to formation of brittle cleavage cracks that resulted in spallation of material. The erosion rate was proportional to erodent velocity to the 2.3 power. The erosion rate and mechanism for the geopolymer were nearly identical to what has been observed for erosion of Si single crystals

Superplasticity and Joining of Zirconia-Based Ceramics

Steady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1,250 and 1,350 C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1,200 C

Selective inhibition of kindling development by intraventricular administration of TrkB receptor body.

Recent work has shown that neurotrophin gene expression is increased after seizures evoked in the kindling model of epilepsy, but whether neurotrophins regulate kindling development is as yet unclear. In this study, we attempted to block selectively the activation of distinct neurotrophin receptors throughout kindling development in the rat via chronic intracerebroventricular administration of trk receptor bodies. The efficacy and selectivity of the trk receptor bodies were established by inhibition of neurotrophin-induced trk receptor phosphorylation in pheochromocytoma (PC12) cells and primary cultures of cortical neurons. The intracerebroventricular infusion of trkB receptor body (trkB-Fc) inhibited development of kindling in comparison with that seen with saline or human IgG controls, trkA-Fc, or trkC-Fc. These results imply that activation of trkB receptors contributes to the development of kindling, a form of activitydependent behavioral plasticity in the adult mammalian brain

Relaxation Effects in the Transition Temperature of Superconducting HgBa2CuO4+delta

In previous studies on a number of under- and overdoped high temperature superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta}, the transition temperature T_c has been found to change with time in a manner which depends on the sample's detailed temperature and pressure history. This relaxation behavior in T_c is believed to originate from rearrangements within the oxygen sublattice. In the present high-pressure studies on HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation effects in strongly under- and overdoped samples ($T_c\simeq 40 - 50 K$) with an activation energy $E_{A}(1 bar) \simeq 0.8 - 0.9 eV$. For overdoped HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of +11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an anomalous result for high-T_c superconductors in the present pressure range, giving evidence for a change in the electronic and/or structural properties near 0.4 GPa

Peningkatan Prestasi Belajar CAD Mahasiswa Teknik Otomotif Non-Reguler FT UNY melalui Pembuatan “Pohon Kata” Perintah dalam Program AutoCAD

Penelitian ini bertujuan meningkatkan prestasi belajar mata kuliah Computer Aided Design (CAD) mahasiswa prodi Teknik Otomotif Non-Reguler yang dinyatakan dalam bentuk rerata nilai akhir semester yang berasal dari komponen nilai tugas harian, nilai ujian tengah semester dan nilai ujian akhir semester. Penelitian quasi-eksperimen ini terdiri dari tahapan penelitian diawali dengan penyusunan materi pembelajaran sejumlah pokok bahasan tertentu dalam satu job sheet (lembar kerja), dilanjutkan dengan pembuatan bantuan “Pohon Kata” perintah dalam Auto CAD kepada kelas eksperimen yang ditentukan secara random dari dua kelas peserta kuliah Auto CAD pada Semester Genap 2008/2009. Kedua kelas diamati prestasinya, baik kecepatan penyelesaiannya maupun kualitas kebenaran gambarnya. Prestasi belajar kedua kelas juga diukur melalui pemberian ujian tengah semester dan ujian akhir semester. Setelah data prestasi kedua kelas terkumpul dilanjutkan dengan analisis statistik melalui uji beda (t-test) setelah sebelumnya dilakukan uji persyaratan analisis yang ternyata dapat dipenuhi. Hasil penelitian ini disimpulkan bahwa: prestasi belajar CAD mahasiswa pada kelas yang diberi perlakuan strategi pembelajaran menggunakan “Pohon Kata” perintah dalam Program Auto CAD lebih baik dibanding prestasi belajar CAD mahasiswa pada kelas yang tidak diberi perlakuan (75,41>70,89), dengan demikian pembelajaran CAD menggunakan media “Pohon Kata” perintah dalam Program Auto CAD dapat meningkatkan prestasi belajar mahasiswa Teknik Otomotif Program Non-Reguler