Singular Points of Affine ML-Surfaces

We give a geometric proof of the fact that any affine surface with trivial Makar-Limanov invariant has finitely many singular points. We deduce that a complete intersection surface with trivial Makar-Limanov invariant is normal.Comment: 11 page

Book review: The prehistoric apprentice: Investigating apprenticeship, know-how and expertise in prehistoric technologies; L’apprenti préhistorique: Appréhender l’apprentissage, les savoir-faire et l’expertise à travers les productions techniques des soci

Describing cultural change and variability and inferring sociocultural dynamics about past people and communities may be among archaeology’s main goals as a field of practice. In this regard, the concept of skill has proved its usefulness to, time and again, expand the breath of archaeologists and lithic technologists’ analyses. It covers a wide range of applications, from apprenticeship, cognition, paleo-sociology, spatial organization. It is one of the main causes for material culture variability, up there with raw material constraints, design, technological organization or cultural norms. Yet, while skill has certainly been the focus of some research in the last decades, it remains quite peripheral, when considering how central the concept should be to technological inquiries. Whatever the reasons may be, this book, edited by Laurent Klaric and fully bilingual (French and English), aims at changing that, and argues for skill to become a central concern in lithic technology. Its chapters do so strongly and the end-result is a book that should become a reference for lithic technologists, whatever their research interests or schools of thought may be

Separation of random telegraph signals from 1/f noise in MOSFETs under constant and switched bias conditions

The low-frequency noise power spectrum of small dimension MOSFETs is dominated by Lorentzians arising from random telegraph signals (RTS). The low-frequency noise is observed to decrease when the devices are periodically switched 'off'. The technique of determining the statistical lifetimes and amplitudes of the RTS by fitting the signal level histogram of the time-domain record to two-Gaussian histograms has been reported in the literature. This procedure is then used for analysing the 'noisy' RTS along with the device background noise, which turned out to be 1/f noise. The 1/f noise of the device can then be separated from the RTS using this procedure. In this work, RTS observed in MOSFETs, under both constant and switched biased conditions, have been investigated in the time domain, Further, the 1/f noise in both the constant and the switched biased conditions is investigated

Modal analysis of a robot arm using the finite element analysis and modal testing

The objective of the present work was to study the technique of modal analysis using theoretical and experimental methods. A PUMA UNIMATION five axis robot was used as a model. The finite element analysis was performed using MacNeai Schwendler Corporation\u27s NASTRAN code. Intergraph\u27s Rand Micas pre- and post-processor was used to discretize the model and subsequently to display the animated mode shapes after the analysis was done with NASTRAN. The modal testing was performed using Structural Measurement Systems\u27 STAR software and Bruel & Kjaer\u27s instrumentation including a spectrum analyzer, accelerometer and hammer. Due to the size and weight of the structure it was not possible to test it in its free-free condition. Hence it was tested in its supported condition. The results from the two analyses were then compared. The first thirteen modes from both the analyses showed a one-to-one correspondence. The natural frequencies showed a deviation from 1% to 33%. Although the difference of 33% seems large, it was only for one mode which could reflect a computational error. For most of the modes, the variation was less than 10%. The comparison of mode shapes was done by observation of the displayed animated mode shapes. Also, a technique called Modal Assurance Criterion for numerical correlation of mode shapes is discussed. The experimental mode shapes showed an erratic behavior. This was probably due to the nonlinearities in the structure. The causes of the discrepancies between the finite element method and modal testing are discussed in the text. Similar patterns of deflection could be seen in the two analyses

Synthesis of 5-halo-3-methoxy-salicylaldiminato nickel catalysts and their use for ethylene polymerization in organic and aqueous media

In the present work, we have synthesized nickel salicylaldiminato catalysts based on a 5-halo-3-methoxy ligand framework. The structures of the 5-chloro analog and the 5-bromo analog were successfully confirmed using NMR spectroscopy and X-ray crystallography. These syntheses have the advantage that starting materials are commercially available and only two steps are required to obtain the targeted catalysts. Both catalysts have been applied for polymerization of ethylene in organic media (toluene) and aqueous media. For polymerization in organic medium, the effectiveness of the catalysts was evaluated under different reaction conditions such as different temperatures and catalyst concentrations. The appearance and structure of the polymers changed from amorphous to rubbery with increase in temperature. The polymers obtained were found to be branched, as determined by NMR spectroscopy. Distinct methyl doublets were observed in the H NMR spectra. As the polymerization temperature increased, the branching also increased with an accompanying decrease in melting point. Remarkably, as the temperature of the polymerization was increased between 30 and 50oC, the molecular weight of polymer obtained was found to increase. This was accounted for the catalyst activity increasing as well in this temperature range. As the temperature is increased from 50 to 70oC, the molecular weight decreases as expected for coordinative polymerizations. The optimum temperature to obtain high activity, high molecular weight and relatively low branching was determined to be 50oC. When tried in aqueous medium, the percentage of polyethylene formed seemed to be very low (1-2 %). This is due to the low solubility of ethylene at the relatively low pressures we could apply in the glass reactor. We also applied a known nickel enolate catalyst bearing a CF3-ligand for the aqueous emulsion polymerizations to determine how the polymerization parameters influence the particle size. We found that in particular an increase in the stirrer speed helped to reduce the particle size

Radiosensitization with Magnetic Nanoparticles

Radiation therapy, along with surgery and chemotherapy, are the major therapeutic strategies for cancer treatment. It involves the delivery of ionizing radiation with high accuracy to the tumor tissue, resulting in the death of tumor cells. Radiation sensitization is a process of enhancing the susceptibility of tumor tissues to injury by radiation exposure. Hence, radiation sensitizers are therapeutic or otherwise inert agents that enhance the effects of radiation therapy. Iron oxide nanoparticles, a type of magnetic nanoparticle (MNP), are amongst the nanomaterials which have been suggested as radiation sensitizers. Hyperthermia is a type of cancer treatment in which tissue is exposed to elevated temperatures. Hyperthermia is almost always used with other forms of cancer therapy, such as radiation therapy and chemotherapy. Hyperthermia may make some cancer cells more sensitive to radiation. When hyperthermia and radiation therapy are combined, they are often given within an hour of each other. MNP can induce localized hyperthermia when exposed to an alternating magnetic field (AMF). As MNP are potentially capable of producing two sensitization effects (x-ray interaction and hyperthermia generation) they are particularly attractive for this application

Impact of hot-carrier degradation on the low-frequency noise in MOSFETs under steady-state and periodic large-signal excitation

This letter reports the diagnostic power of the low-frequency noise analysis (steady-state and periodic large-signal excitation) in MOSFETs subjected to hot-carrier degradation. The LF noise under periodic large-signal excitation is shown to increase more rapidly than the LF noise in steady-state. Moreover the improvement in the LF noise performance due to periodic large-signal excitation, observed for fresh devices, gradually diminishes as the devices are subjected to hot-carrier stress