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181.
We present a practical method to determine femtosecond laser induced refractive index changes in transparent materials. Based on an iterative Fourier transform algorithm, this technique spatially resolves the refractive index of complex structures by combining the dimensions of the modified region with the corresponding phase change extracted from far-field intensity measurements. This approach is used to characterize optical waveguides written by a femtosecond laser in borosilicate glass. 相似文献
182.
Marta Gerowska Lucy Hall James Richardson Montserrat Shelbourne Tom Brown 《Tetrahedron》2012,68(3):857-864
A convenient method of oligonucleotide labeling using click chemistry has been developed. A 2′-mesyloxyethyl ribothymidine phosphoramidite monomer was incorporated into DNA at several loci during solid phase oligonucleotide synthesis and converted to 2′-azidoethyl ribothymidine in high yield on the synthesis resin. The resultant azide oligonucleotides were doubly and triply labeled with alkyne-modified cyanine dyes and their biophysical properties were studied. The influence of the dye structures and method of labeling on the fluorescence properties of the DNA probes is discussed and compared with a standard labeling method using active esters of Cy-Dyes. 相似文献
183.
Caitlin N. Rinke Mary R. Williams Christopher Brown Matthieu Baudelet Martin Richardson Michael E. Sigman 《Analytica chimica acta》2012
A method is described for performing discriminant analysis in the presence of interfering background signal. The method is based on performing target factor analysis on a data set comprised of contributions from analyte(s) and interfering components. A library of data from representative analyte classes is tested for possible contributing factors by performing oblique rotations of the principal factors to obtain the best match, in a least-squares sense, between test and predicted vectors. The degree of match between the test and predicted vectors is measured by the Pearson correlation coefficient, r, and the distribution of r for each class is determined. A Bayesian soft classifier is used to calculate the posterior probability based on the distributions of r for each class, which assist the analyst in assessing the presence of one or more analytes. The method is demonstrated by analyses performed on spectra obtained by laser induced breakdown spectroscopy (LIBS). Single and multiple bullet jacketing transfers to steel and porcelain substrates were analyzed to identify the jacketing materials. Additionally, the metal surrounding bullet holes was analyzed to identify the class of bullet jacketing that passed through a stainless steel plate. Of 36 single sample transfers, the copper jacketed (CJ) and non-jacketed (NJ) class on porcelain had an average posterior probability of the metal deposited on the substrate of 1.0. Metal jacketed (MJ) bullet transfers to steel and porcelain were not detected as successfully. Multiple transfers of CJ/NJ and CJ/MJ on the two substrates resulted in posterior probabilities that reflected the presence of both jacketing materials. The MJ/NJ transfers gave posterior probabilities that reflected the presence of the NJ material, but the MJ component was mistaken for CJ on steel, while non-zero probabilities were obtained for both CJ and MJ on porcelain. Jacketing transfer from a bullet to steel as the projectile passed through the steel also proved difficult to analyze. Over 50% of the samples left insufficient transfer to be identified. Transfer from NJ and CJ jacketing was successfully identified by posterior probabilities greater than 0.8. 相似文献
184.
C. J. Larsen M. Ortiz C. L. Richardson 《Archive for Rational Mechanics and Analysis》2009,193(3):539-583
Crack fronts play a fundamental role in engineering models for fracture: they are the location of both crack growth and the
energy dissipation due to growth. However, there has not been a rigorous mathematical definition of crack front, nor rigorous
mathematical analysis predicting fracture paths using these fronts as the location of growth and dissipation. Here, we give
a natural weak definition of crack front and front speed, and consider models of crack growth in which the energy dissipation
is a function of the front speed, that is, the dissipation rate at time t is of the form
where F(t) is the front at time t and v is the front speed. We show how this dissipation can be used within existing models of quasi-static fracture, as well as
in the new dissipation functionals of Mielke–Ortiz. An example of a constrained problem for which there is existence is shown,
but in general, if there are no constraints or other energy penalties, this dissipation must be relaxed. We prove a general
relaxation formula that gives the surprising result that the effective dissipation is always rate-independent. 相似文献
185.
In this paper an alternative approach for measurement of στ product for 4
F
3/2→4
I
11/2 transition of Nd3+ doped YVO4 crystal is reported. In this method a microchip laser is formed by keeping a small piece of the sample in plane-plane resonator
and a diode laser (808 nm) is used for pumping. The pump power induced thermal lensing effect is used to make the cavity stable.
The cavity mode area is estimated by measuring the thermal lens focal length at the threshold and the average pump area is
measured by Gaussian fit to the intensity profiles of the pump beam. The value of στ product of Nd:YVO4 crystal obtained by this method is within 10% of the reported values. The advantage of this method is that it is a simple
method for direct measurement of στ product of laser crystals. 相似文献
186.
David B. Lovejoy Des R. Richardson Paul V. Bernhardt 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):341-342
The potentially tridentate O,N,S‐donor ligand, 2‐hydroxy‐1‐naphthaldehyde 2‐methylthiosemicarbazone, C13H13N3OS, has been structurally characterized and the molecule is found to exhibit a distorted planar structure with the thiosemicarbazide moiety being twisted slightly out of the plane defined by the naphthyl ring. 相似文献
187.
R. Zhang H. Cao H. M. Chen P. Mallon T. C. Sandreczki J. R. Richardson Y. C. Jean B. Nielsen R. Suzuki T. Ohdaira 《Radiation Physics and Chemistry》2000,58(5-6):639-644
A variable mono-energetic positron beam with a computer-controlled system has recently been constructed at the University of Missouri–Kansas City for weathering studies of polymeric coatings. The beam is designed to measure the S-parameter from Doppler-broadening energy spectra and the sub-nanometer defect properties from positron annihilation lifetimes (PAL). Significant variations of S-parameter and ortho-positronium intensity in coatings, as obtained from the newly built beam and from the Electrotechnical Laboratory’s beam, respectively, are observed as a function of depth and exposure time due to the Xe-light irradiation. A high sensitivity of positron annihilation signal response to the early stage of degradation is observed. Development of positron annihilation spectroscopy to test accelerated weathering of polymeric coatings is discussed. 相似文献
188.
A necessary and sufficient condition is presented for a set to be a Pompeiu subset of any compact homogeneous space with a
finite invariant measure. The condition, which is expressed in terms of the intertwining operators of each primary summand
of the quasi-regular representation, is then interpreted in the case of the compact Heisenberg manifolds. Examples are presented
demonstrating that the condition to be Pompeiu in these manifolds is quite different from the corresponding condition for
a torus of the same dimension. This provides a contrast with the existing comparison between the Heisenberg group itself and
Euclidean space in terms of Pompeiu sets. In addition, the closed linear span of all translates of any square integrable function
on any compact homogeneous space is determined. 相似文献
189.
L.E. Topol D.H. Hengstenberg M. Blander R.A. Happe N.L. Richardson L.S. Nelson 《Journal of Non》1973,12(3):377-390
Glass spherules have been made by laser spin melting and free fall cooling techniques from ceramic rods. Thus, the materials were not in contact with a container at any time. Glasses of 100 to 800 μm diameter were formed from at least 80 wt% of the oxides Al2O3, Ga2O3, In2O3, La2O3, ZrO2, HfO2, Nb2O5 and Ta2O5 with 20 or less weight percent of CaO + SiO2. The best glass formers were in the Nb2O5- and Ta2O5-based systems. The indices of refraction of most of the glasses and Abbe numbers of many were measured. 相似文献
190.
Jeishla L. M. Matos Samantha A. Green Yuge Chun Vuong Q. Dang Russell G. Dushin Paul Richardson Jason S. Chen David W. Piotrowski Brian M. Paegel Ryan A. Shenvi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):13098-13103
Preparative reactions that occur efficiently under dilute, buffered, aqueous conditions in the presence of biomolecules find application in ligation, peptide synthesis, and polynucleotide synthesis and sequencing. However, the identification of functional groups or reagents that are mutually reactive with one another, but unreactive with biopolymers and water, is challenging. Shown here are cobalt catalysts that react with alkenes under dilute, aqueous, buffered conditions and promote efficient cycloisomerization and formal Friedel–Crafts reactions. The constraining conditions of bioorthogonal chemistry are beneficial for reaction efficiency as superior conversion at low catalyst concentration is obtained and competent rates in dilute conditions are maintained. Efficiency at high dilution in the presence of buffer and nucleobases suggests that these reaction conditions may find broad application. 相似文献