Substituent effects on the nitrogen-15 and carbon-13 shieldings of some N-arylguanidinium chlorides

The 13C and 15N chemical shifts of five N-arylguanidinium chlorides carrying polar substituents, ranging in character from 4-methoxy to 4-nitro groups, have been determined by NMR spectroscopy at the natural-abundance level of 13C and 15N in dimethyl sulfoxide solution. Comparison of the 13C shifts of these salts with those of monosubstituted benzenes shows that the guanidinium group induces an average downfield shift of -5.8 ppm of the resonance of the aryl carbon to which it is attached (C1), an average upfield shift of +4.2 ppm for C2 and C6, and a small upfield shift of +1.9 ppm for C4. The shifts of C3 and C5 are small and erratic relative to the corresponding carbons in monosubstituted benzenes. The 15N resonances of the guanidinium nitrogens are quite sensitive to electric effects resulting from substitution of polar groups at C4. The 15N shift of the ==NAr nitrogen relative to that of the salts suggests that the predominant tautomer for N-arylguanidines is (H2N)2C==NAr. The 15N shifts of the (NH2) 2 nitrogens correlate rather well with σp- parameters, whereas the shifts of the -NHAr nitrogens seem to correlate only with R values derived from the σp- substituent constants

Sustainability Reporting Practices In Portugal: Greenwashing Or Triple Bottom Line?

This paper examines the status of sustainability reporting in Portugal.  The Global Reporting Initiative’s (GRI) guidelines for sustainability reporting is an initiative that attempts to create a paradigm of triple bottom line reporting that encompasses the economic, environmental, and social performance of business. Measurement and reporting of environmental and social aspects are in their infancy compared to financial/economic reporting. The objective of the GRI’s framework is to elevate environmental and social reporting to the level of financial reporting by developing reporting principles and information qualities similar to those used in corporate financial reporting. In the post-Enron corporate reporting environment, such credibility may be tarnished and lead stakeholders to suspect corporations of greenwashing their reputations by issuing reports that are environmental window dressing.Currently 860 companies in a variety of industries worldwide are voluntarily listed as using the guidelines on the GRI’s web site; however, only five are from Portugal. Two of the five companies are GRI organizational stakeholders and one is listed as reporting 'in accordance' with the guidelines. Content analysis will be used to examine both the quantity and quality of information in the GRI reports of Portuguese companies. An additional issue regarding the transparency and credibility of the information provided is whether the reports have been verified (a more generic term than audit used for a similar assurance-type service relative to GRI Reports). The results of the content analysis will be used to shed some light on whether the companies generating these reports are bridging or widening the sustainability reporting expectations gap between companies and stakeholders

A Four Stage Approach to Community Archaeology, illustrated with cases studies from Dorset, England

This article presents an approach to guide the planning, development and evaluation of community archaeology. This will assist practitioners of all forms of community archaeology by providing a pathway to ethical practice that will benefit all. The approach focuses attention on four elements that are integral to community archaeology and which should always be considered: Who (the people involved); Why (their motivation); the Archaeology (in the broadest sense, including research questions and research methods); and How (the specific format the community engagement will take). This framework is applied to three case study community archaeology projects in Dorset, England, in order to demonstrate challenging examples of planned and reflexive community archaeology

The language of experience : a study in methodology

Cover title"April 30, 1955."At head of title: Communications"696"--handwritten on cover"Since the time this MS has been hectographed a few suggestions have been made, particularly by Ithiel de S. Pool, which will rather improve the paper and which will, therefore, be incorporated in the final copy. Further criticisms and suggestions will be appreciated."Includes bibliographical reference

Design and fabrication of highly efficient non-linear optical devices for implementing high-speed optical processing

We present the design and fabrication of micro-cavity semiconductor devices for enhanced Two-Photon-Absorption response, and demonstrate the use of these devices for implementing sensitive autocorrelation measurements on pico-second optical pulses

High-sensitivity two-photon absorption microcavity autocorrelator

A GaAs-AlAs microcavity device has been used as a photodetector in an autocorrelator for measuring the temporal pulsewidth of 1.5-/spl mu/m optical pulses. Enhancement of the two-photon absorption photocurrent due to the microcavity structure results in an autocorrelation (average power times peak power) sensitivity of 9.3/spl times/10/sup -4/ (mW)/sup 2/, which represents two orders of magnitude improvement when compared with conventional autocorrelators

Two-photon absorption in microcavities for optical autocorrelation and sampling

We have designed novel semiconductor microcavity structures for the enhancement of the two-photon absorption (TPA) photocurrent. We report a TPA autocorrelation technique for short optical pulses that uses the microcavity structure instead of a second harmonic generation crystal. Knowledge of these characteristics is important for implementation in applications such as optical switching and sampling in optical time division multiplexed (OTDM) communications systems

A novel approach towards two-photon absorption based detectors

Summary: We have demonstrated that the inherent inefficiency of the TPA process in semiconductors can be overcome by incorporating the semiconductor in a microcavity structure. Proof of concept devices with a 0.27μm Ga0.7Al0.3As active region and two Bragg reflectors with the cavity resonance of 890 nm were fabricated. We measured the TPA photocurrent of these devices and have demonstrated a factor of 12000 enhancement over a nonmicrocavity device at 890 nm. Our active length of 0.27 nm is as efficient as 5.4 mm without a microcavity, overcoming the very long detector lengths limiting the use of TPA in practical autocorrelators, optical switches and sampling devices for real telecommunication systems. The effect of the cavity is to enhance the intra-cavity optical intensity, which leads to an increase in the nonlinear response of the active region. We studied, theoretically and experimentally, the impact of the cavity on the temporal response and the sensitivity of the device, which are critical considerations for commercial applications. This cavity design has a 3 pico-second response time and the autocorrelation trace is comparable with the BBO crystal response for an input 1.6 ps pulse. Devices designed for 1550 nm have also been realised and our measurements indicate these two-photon absorption based detectors are potential candidates for optical autocorrelation of short optical pulses, and for optical switching and sampling in optical time division multiplexed (OTDM) communications systems