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Manufacturing Metallic Parts with Designed Mesostructure via Three-Dimensional Printing of Metal Oxide Powder
Cellular materials, metallic bodies with gaseous voids, are a promising class of materials that offer
high strength accompanied by a relatively low mass. In this paper, the authors investigate the use of ThreeDimensional Printing (3DP) to manufacture metallic cellular materials by selectively printing binder into a
bed of metal oxide ceramic powder. The resulting green part undergoes a thermal chemical post-process in
order to convert it to metal. As a result of their investigation, the authors are able to create cellular
materials made of maraging steel that feature wall sizes as small as 400 µm and angled trusses and channels
that are 1 mm in diameter.Mechanical Engineerin
Elf: computer automation and error correction for a microwave network analyzer
A microwave measurement system has been developed that combines a personal computer (PC) and an conventional vector network analyzer to yield a full complex-error-corrected automatic network analyzer. The system consists of a Hewlett-Packard HP 8410C network analyzer, an HP 8350B sweep oscillator, and an IBM PC. A program called Elf runs on the PC, performing calibration and measurement algorithms and providing a flexible, menu-oriented user interface. The system, when calibrated, achieves a worst-case measurement error vector of magnitude ≤ 0.02 for transmission and reflection coefficient measurements over the 2-12.4-GHz frequency range and has a measurement speed of three frequency points/s. Elf provides an inexpensive method for upgrading the HP 8410 to achieve the high accuracy of an automatic network analyzer
Puff, an Interactive Microwave Computer Aided Design Program for Personal Computers
We will demonstrate a CAD program designed for the lay out
and analysis of microstrip circuits. The program runs on the
IBM PC or AT. Circuit elements are selected from a parts list
and drawn on the screen using the cursor keys. The analysis
may then be performed, directly from the screen drawing. Puff
has been used by microwave students in classes at the California
Institute of Technology and the University of California at Los
Angeles
Introducing Challenging Modeling Problems Early with Chebfun Add-Ons for MATLAB
Early introduction of challenging and meaningful problems can significantly enhance learning. In a beginning ODEs course, many instructors shy away from “messy modeling problems” because they often require significant numerical work to get meaningful results. But with the chebfun add-ons for MATLAB, much of the numerical “overhead” for solving these problems can be lessened or even eliminated. I will briefly demonstrate the use of the chebfun add-ons and then discuss some examples of challenging modeling exercises which can be completed as lab projects in a first ODEs course with minimal additional support beyond the typical course material. (The chebfun add-ons are open-source and available freely from their authors at www.chebfun.org
Mercury accumulation in fishes from tropical aquatic ecosystems in the Niger Delta, Nigeria
Fishes are important biomarkers of trace elements in
aquatic ecosystems, and are used to evaluate the status
of water pollution by mercury in tropical aquatic ecosystems in Nigeria. Common fishes, Chrysichthys nigrodigitatus,Brycinus nurse, Hemichromis fasciatus,
Lutianus ava, Oreochromis nilotica, Pomadasys jubelini,
Stellifer stellifer and Tilapia guineensis were analysed
for Hg accumulation using the cold vapour atomic absorption spectrophotometry technique. The results
showed that Hg concentration in P. jubelini was relatively
the highest, with a mean concentration of 0.063 ± 0.03 mg kg–1. Other concentration values were 0.044 ± 0.031 mg kg–1 for O. nilotica, 0.026 ± 0.013 mg kg–1 for B. nurse, 0.034 ± 0.034 mg kg–1 for H. fasciatus, 0.023 ± 0.020 mg kg–1 for C. nigrodigitatus and 0.33 ± 0.016 mg kg–1 for L. ava. Concentrations of Hg accumulated by the fishes were low and within internationally accepted limit, not likely to cause mercury poisoning. Because of the high Hg accumulating potential of P. jubelini, it is recommended as a biomarker for assessment of Hg toxicity in a tropical aquatic environment
Nanoarrays for the generation of complex optical wave-forms
Light beams with unusual forms of wavefront offer a host of useful features to extend the repertoire of those developing new optical techniques. Complex, non-uniform wavefront structures offer a wide range of optomechanical applications, from microparticle rotation, traction and sorting, through to contactless microfluidic motors. Beams combining transverse nodal structures with orbital angular momentum, or vector beams with novel polarization profiles, also present new opportunities for imaging and the optical transmission of information, including quantum entanglement effects. Whilst there are numerous well-proven methods for generating light with complex wave-forms, most current methods work on the basis of modifying a conventional Hermite-Gaussian beam, by passage through suitably tailored optical elements. It has generally been considered impossible to directly generate wave-front structured beams either by spontaneous or stimulated emission from individual atoms, ions or molecules. However, newly emerged principles have shown that emitter arrays, cast in an appropriately specified geometry, can overcome the obstacles: one possibility is a construct based on the electronic excitation of nanofabricated circular arrays. Recent experimental work has extended this concept to a phase-imprinted ring of apertures holographically encoded in a diffractive mask, generated by a programmed spatial light modulator. These latest advances are potentially paving the way for creating new sources of structured light
Approximate Green's Function Coupled Cluster Method Employing Effective Dimension Reduction
The Green's function coupled cluster (GFCC) method is a powerful many-body
tool for computing the electronic structure of molecular and periodic systems,
especially when electrons of the system are strongly correlated. However, for
the GFCC to be routinely used in the electronic structure calculations, robust
numerical techniques and approximations must be employed to reduce its high
computational overhead. In our recent studies, we demonstrated that the GFCC
equations can be solved directly in the frequency domain using iterative linear
solvers, which can be easily distributed in a massively parallel environment.
In the present work, we demonstrate a successful application of
model-order-reduction (MOR) techniques in the GFCC framework. Briefly, for a
frequency regime which requires high resolution spectral function, instead of
solving GFCC linear equation of full dimension for every single frequency
point, an efficiently-solvable linear system model of a reduced dimension may
be built upon projecting the original GFCC linear system onto a subspace. From
this reduced order model is obtained a reasonable approximation to the full
dimensional GFCC linear equations in both interpolative and extrapolative
spectral regions. Here, we show that the subspace can be properly constructed
in an iterative manner from the auxiliary vectors of the GFCC linear equations
at some selected frequencies within the spectral region of interest. During the
iterations, the quality of the subspace and the linear system model can be
systematically improved. The method is tested in terms of the efficiency and
accuracy of computing spectral functions for some typical molecular systems
such as carbon monoxide, 1,3-butadiene, benzene, and adenine. As a byproduct,
the obtained reduced order model may provide a high quality initial guess which
improves the convergence rate for the existing iterative linear solver.Comment: 29 pages, 8 figure
Root Growth Potential and Field Survival of Container Loblolly Pine Seedlings Fall Fertilized with Nitrogen
Two studies investigated the effects of fall nitrogen fertilizer applications on the root growth potential (RGP) and field performance of container loblolly pine seedlings (Pinus taeda L.). The seedlings were sampled at 4 chilling levels ranging from 100 to 550 hours (0 to 8\u27 C). Seedlings propagated for the first study may have had a hidden nutrient deficiency and therefore the fall diammonium phosphate (DAP) application at rates of 202 kg N/ha and 67 kg N/ha increased RGP 43% and 32%, respectively. The growing season mineral fertilizer application rate was increased in the second study which may explain why nitrogen applications at 202 kg N fall/ha did not increase RGP. In general, RGP increased as exposure to chilling hours increased. Fall fertilization increased total seedling weight. Analysis of covariance indicated that RGP may be a function of total seedling weight and not a direct response to fertilizer treatment or chilling level. For the first study, survival was not significantly affected by the fall DAP treatments
Effects of Fall Fertilizer Applications of Mitotic Index and Bud Dormancy of Loblolly Pine Seedlings
A series of studies examined the effects of fall fertilization with diammoniwn phosphate (DAP) on mitotic index and bud donnancy [as measured by mean days to budbreak (DBB)] of two half-sib seed sources of loblolly pine. The first study tested different rates of DAP (0, 67, and 202 kg Nlha), the second study compared DAP with ammoniwnnitrate, and the third study examined the effect of different application dates (September 28, October 19, and November 9). An increase in mitotic index of unfertilized seedlings was observed during October and was due to developmental activity which follows initial budset. Differences in mitotic index were observed between families in all three studies.Overall, the Georgia family has a higher mitotic index, but in one study, the Virginia family had higher values in the spring. Both families tended to reach a minimum level of mitotic index at the same time (mid- to late December). However, the Virginia family reached maximum rest (as measured by days to bud break) about 1 to 2 weeks prior to the Georgia
family. Fertilization with DAP in the fall (after bud set in September) did not delay the progression of the bud dormancy cycle as measured by days to bud break in a greenhouse. The overall effect of fall fertilization on increasing the mitotic index was temporary and only lasted for about three weeks after fertilization. These findings indicated that a direct relationship may not exist between the bud dormancy cycle and mitotic index
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