Determination of absorption length of CO2 and high power diode laser radiation for ordinary Portland cement and its influence on the depth of melting

The laser beam absorption lengths of CO2 and a high power diode laser (HPDL) radiation for concrete have been determined. By employing Beer-Lambert’s law the absorption lengths for concrete of CO2 and a HPDL radiation were 47022 m and 17715 m respectively. Indeed, this was borne out somewhat from a cross-sectional analysis of the melt region produced by both lasers which showed melting occurred to a greater depth when the CO2 laser was used

Determination of the absorption length of CO2, Nd:YAG and high power diode laser radiation for a selected grouting material

The laser beam absorption lengths of CO2, Nd:YAG and a high power diode laser (HPDL) radiation for a newly developed SiO2/Al2O3-based tile grout have been determined through the application of Beer-Lambert’s law. The findings revealed marked differences in the absorption lengths despite the material having similar beam absorption coefficients for the lasers. The absorption lengths for the SiO2/Al2O3-based tile grout for CO2, Nd:YAG and HPDL radiation were calculated as being 23211 m, 1934 m and 1838 m respectively. Moreover, this method of laser beam absorption length determination, which has hitherto been used predominantly with lasers operated in the pulsed mode, is shown to be valid for use with lasers operated in the continuous wave (CW) mode, depending upon the material being treated

The importance of asking “how and why?” in natural product structure elucidation

This review highlights why careful consideration of the biosynthetic origin (the how) and the biological function (the why) of a natural product can be so useful during the determination of its structure.</p

The impacts of commercial woodland management on butterfly biodiversity.

Although the effects on biodiversity in woodland managed for conservation have been studied for a range of species, there is very little empirical data on the potential impacts of commercial woodland management on biodiversity in the UK. This study measured species richness and abundance of diurnal butterflies as a proxy for the habitat quality of three different woodland management techniques in the Morecambe Bay limestone woodland region. Butterflies were sampled at two sites; Gait Barrows and Witherslack, where three woodland management techniques were carried out: low management woodland (woodland with no recent intervention); traditional coppice management for conservation; and commercial woodland management. Both coppice management for conservation and commercial management had significantly higher butterfly species richness and abundance when compared to low management woodland; neither butterfly species richness nor abundance were significantly different between the traditional coppice management for conservation and commercial woodland management. UK Biodiversity Action Plan fritillary species (high brown fritillary Argynnis adippe; pearl bordered fritillary Boloria euphrosyne; and small pearl bordered fritillary Boloria selene) were not significantly different between the traditional coppice management for conservation and commercial management.UKER

Dark matter halos in the multicomponent model. II. Density profiles of galactic halos

The multicomponent dark matter model with self-scattering and inter-conversions of species into one another is an alternative dark matter paradigm that is capable of resolving the long-standing problems of $\Lambda$CDM cosmology at small scales. In this paper, we have studied in detail the properties of dark matter halos with $M \sim 4-5 \times10^{11} M_{\odot}$ obtained in $N$-body cosmological simulations with the simplest two-component (2cDM) model. A large set of velocity-dependent cross-section prescriptions for elastic scattering and mass conversions, $\sigma_s(v)\propto v^{a_s}$ and $\sigma_c(v)\propto v^{a_c}$, has been explored and the results were compared with observational data. The results demonstrate that self-interactions with the cross-section per particle mass evaluated at $v=100$ km s$^{-1}$ being in the range of $0.01\lesssim \sigma_0/m\lesssim 1$ cm$^2$g$^{-1}$ robustly suppress central cusps, thus resolving the core-cusp problem. The core radii are controlled by the values of $\sigma_0/m$ and the DM cross-section's velocity-dependent power-law indices $(a_s,a_c)$, but are largely insensitive to the species' mass degeneracy. These values are in full agreement with those resolving the substructure and too-big-to-fail problems. We have also studied the evolution of halos in the 2cDM model with cosmic time.Comment: 17 pages, 13 figure

Natural product anticipation through synthesis

Natural product synthesis remains one of the most vibrant and intellectually rewarding areas of chemistry, although the justifications for pursuing it have evolved over time. In the early years, the emphasis lay on structure elucidation and confirmation through synthesis, as exemplified by celebrated studies on cocaine, morphine, strychnine and chlorophyll. This was followed by a phase where the sheer demonstration that highly complex molecules could be recreated in the laboratory in a rational manner was enough to justify the economic expense and intellectual agonies of a synthesis. Since then, syntheses of natural products have served as platforms for the demonstration of elegant strategies, for inventing new methodology ‘on the fly’ or to demonstrate the usefulness and scope of methods established with simpler molecules. We now add another aspect that we find fascinating, viz. ‘natural product anticipation’. In this Review, we survey cases where the synthesis of a compound in the laboratory has preceded its isolation from nature. The focus of our Review lies on examples where this anticipation of a natural product has triggered a successful search or where synthesis and isolation have occurred independently. Finally, we highlight cases where a potential natural product structure has been suggested as a result of synthetic endeavours but not yet confirmed by isolation, inviting further collaborations between synthetic and natural product chemists

Reactions of dioxygen and nitric oxide with iron(II) compounds : models for chemistry occuring in the active sites of non-heme iron enzymes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1995.Vita.Includes bibliographical references.by Andrew L. Feig.Ph.D

Modification of the wettability characteristics of polymethyl methacrylate (PMMA) by means of CO2, Nd:YAG, excimer and high power diode laser radiation

The surface of the bio-material polymethyl methacrylate (PMMA) was treated with CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation. The laser radiation was found to effect varying degrees of change to the wettability characteristics of the material depending upon the laser used. It was observed that interaction with CO2, Nd:YAG and HPDL effected very little change to wettability characteristics of the PMMA. In contrast, interaction of the PMMA with excimer laser radiation resulted an increase in a marked improvement in the wettability characteristics. After excimer laser treatment the surface O2 content was found to have increased and the material was seen to be more polar in nature. The work has shown that the wettability characteristics of the PMMA could be controlled and/or modified with laser surface treatment. However, a wavelength dependence of the change of the wetting properties could not be deduced from the findings of this work

Is Higgs inflation ruled out?

We consider the status of Higgs inflation in light of the recently announced detection of B modes in the polarization of the cosmic microwave background radiation by the BICEP2 Collaboration. In order for the primordial B-mode signal to be observable by BICEP2, the energy scale of inflation must be high: Vinf≈2×1016-GeV. Higgs inflation generally predicts a small amplitude of tensor perturbations, and therefore it is natural to ask if Higgs inflation might accommodate this new measurement. We find that the answer is essentially no, unless one considers either extreme fine-tuning or possibly adding new beyond the Standard Model fields, which remove some of the more attractive features of the original idea. We also explore the possible importance of a factor that has not previously been explicitly incorporated, namely the gauge dependence of the effective potential used in calculating inflationary observables (e.g., nS and r), to see if this might provide additional wiggle room. Such gauge effects are comparable to the effects of Higgs mass uncertainties and other observables already considered in the analysis, and therefore they are relevant for constraining models. However, they are therefore too small to remove the apparent incompatibility between the BICEP2 observation and the predictions of Higgs inflation