419 research outputs found
Plastic Strain Curl Theory
No full textThe main mechanisms for the hardening of metal materials are the multiplication, accumulation and interaction of dislocations. The dislocation density tensor can be decomposed into two parts: one is the plastic strain curl tensor and the other is the plastic curvature tensor. The influence of the plastic curvature can be characterized by the interaction between the Cauchy's stresses and the couple stresses. The plastic strain curl is supposed to play the most important role for the stress level. Three rotational degrees of freedom omega(i), named as micro rotation, are introduced besides the displacement components u(i). Micro rotations omega(i) have no direct dependence upon ui while the material rotation theta = Delta x u/2. The generalized normality law is used to describe constitutive relations of Cauchy's stresses versus strains and couple stresses versus curvatures. Plastic strain curl is incorporated into the instantaneous tangent modulus. In this way, the generalized equivalent stress is no longer a single-variable function of the generalized equivalent strain. The plastic strain energy density is no longer determined by the generalized equivalent strain solely, too. Based on the present theory, an FEM program is developed to simulate the microindentation tests on Copper and Tungsten. The calculated hardness is observed to elevate as the indent depth decreases. The calculated results agree well with the experimental data. The crack tip field for small scale yielding condition is also studied. The calculated results clearly show that the stress level near the crack tip with plastic strain curl effects is considerably higher than that in the conventional plasticity theory. The singularity of the mean stress near the crack tip is nearly equal to the square-root singularity, and the singularity of the effective stress field is slightly greater than the square-root singularity. Consequently, the singularity of stress components is also slightly greater than the square-root singularity. The J-integral is observed to be essentially path independent
Curl-conforming hierarchical vector bases for triangles and tetrahedra
No full textA new family of hierarchical vector bases is proposed for triangles and tetrahedra. These functions span the curl-conforming reduced-gradient spaces of Nédélec. The bases are constructed from orthogonal scalar polynomials to enhance their linear independence, which is a simpler process than an orthogonalization applied to the final vector functions. Specific functions are tabulated to order 6.5. Preliminary results confirm that the new bases produce reasonably well-conditioned matrice
Structural Modeling and Validation of Rep protein of Begomovirus Strains (TLCBV and TYLCTHV)
No full textHomology modeling involves taking a known sequence with an unknown structure and mapping it against a known structure of one or several similar (homologous) proteins. It would be expected that two proteins of similar origin and function would have reasonable structural similarity. Therefore it is possible to use the known structure as a template for modeling the structure of the unknown structure. Proteins that share the same function generally have similar structures. During alignment if two proteins show maximum sequence identity they also show a similar folding pattern. This principal has became the foundation of homology modeling. 
The Geminivirus taxonomic group of plant viruses is characterized by geminate particles and genomes consisting of single-stranded circular DNA molecules of about 2.5 to 2.8 kb in size. Agricultural plants are threatened by many diseases caused by whitefly-transmitted geminiviruses. Since these diseases are in a fast spreading phase, it is urgent to devise rapid diagnosis methods and to produce resistant plants. 

Fibre coupled difference frequency generation utilising ytterbium-doped fibre amplifier and periodically poled LiNbO3
No full textA new mid-infrared tunable spectroscopic source based on fibre coupled difference frequency generation in bulk periodically-poled LiNbO₃for trace gas detection is reported. The source mixes the outputs of a fibre coupled external cavity diode laser and a 1083 nm seeded Yb-doped fibre amplifier. Powers up to 0.8 μW are obtained in the 3.8-4.3 μm rangeD.G. Lancaster, L. Goldberg, J. Koplow, R.F. Curl and F.K. Titte
Mid-infrared difference-frequency generation source pumped by a 1.1-1.5-micrometres dual-wavelength fiber amplifier for trace-gas detection
No full textContinuous-wave mid-infrared radiation near 3.5 micrometers is generated by difference-frequency mixing of the output of a compact 1.1-1.5 micrometer dual-wavelength fiber amplifier in periodically poled LiNbO3. The diode side-pumped amplifier is constructed with double-cladding Yb-doped fiber followed by single-mode Er/Yb codoped fiber. Output powers of as much as 11 microW at 3.4 micrometers are obtained, and spectroscopic detection of CH4 and H2CO is demonstrated.L. Goldberg, J. Koplow, D.G. Lancaster, R.F. Curl, and F.K. Titte
Novel gas sensor based on difference frequency mixing using all fiber beam delivery
No full textA new infrared narrowband spectroscopic source based on difference frequency generation in periodically poled lithium niobate is presented. This system generates up to 1 μW of light which is tunable from 3.85 to 4.3 μm. It is pumped by a 16 mW fiber coupled external cavity diode laser with a tuning range of 845 to 865 nm and a Yb fiber amplifier which is seeded by a single longitudinal mode 1083 nm DBR diode. The suitability and bandwidth of this source for trace detection is demonstrated by conducting spectral scans of calibrated mixtures of 0.97 ppm CO2 and 1.0 ppm N2 in a 18 m pathlength multipass cell.D.G. Lancaster, R.F. Curl, F.K. Tittel, L. Goldberg and J. Koplo
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[Infrared tunable difference frequency laser source]. Final technical report, September 15, 1990--September 14, 1992
No full textPurpose of grant was to purchase equipment necessary to construct an infrared laser source based on difference frequency generation in AgGaS[sub 2]. This continuous wave, single frequency, tunable infrared source has been assembled and is being used for infrared kinetic spectroscopy of small free radicals important in combustion. Infrared spectra are given for the Q-branch of a combination band (11[sup 1]1) of N[sub 2]O, and for the transient in CO produced by flash photolysis of acetone in various vibrational states
Cover Story piece profiling Linda Greenlaw, 40, of Isle au Haut, author of Th
No full textCover Story piece profiling Linda Greenlaw, 40, of Isle au Haut, author of The Hungry Ocean
Spectral mimetic least-squares method for div-curl systems
No full text\u3cp\u3eIn this paper the spectral mimetic least-squares method is applied to a two-dimensional div-curl system. A test problem is solved on orthogonal and curvilinear meshes and both h- and p-convergence results are presented. The resulting solutions will be pointwise divergence-free for these test problems. For N> 1 optimal convergence rates on an orthogonal and a curvilinear mesh are observed. For N= 1 the method does not converge.\u3c/p\u3
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