Melamine formaldehyde compounds. The active species in acid catalyzed reactions

Applying results from previously published kinetic investigations on the hydrolysis and condensation of methylol melamine compounds in acid solution a thorough analysis of the reaction mechanism is given. In the literature it has been discussed whether the acid catalysis takes place by protonation of the triazine ring, if it is a protonation of the methylol side groups or if both types of protonation are active.In the present paper strong support is given to a kinetic model where the side group activated species are the reactive ones. Ring protonation, on the other side, leads to deactivation. Included are also computer simulations in Matlab of the decomposition of tri- and hexa-methylol melamine in dilute solution, assuming the hydrolysis to take place by series first order reactions. The computer simulations allow us to calculate the relative composition of the reaction mixture as a function of time and to see the effect of changes in the experimental rate constant as the reaction proceeds.     

Short‐term extreme response analysis of a jacket supporting an offshore wind turbine

Wind turbines must be designed in such a way that they can survive in extreme environmental conditions. Therefore, it is important to accurately estimate the extreme design loads. This paper deals with a recently proposed method for obtaining short‐term extreme values for the dynamic responses of offshore fixed wind turbines. The 5 MW NREL wind turbine is mounted on a jacket structure (92 m high) at a water depth of 70 m at a northern offshore site in the North Sea. The hub height is 67 m above tower base or top of the jacket, i.e. 89 m above mean water level. The turbine response is numerically obtained by using the aerodynamic software HAWC2 and the hydrodynamic software USFOS . Two critical responses are discussed, the base shear force and the bending moment at the bottom of the jacket. The extreme structural responses are considered for wave‐induced and wind‐induced loads for a 100 year return‐period harsh metocean condition with a 14.0 m significant wave height, a 16 s peak spectral period, a 50 m s ^{? 1} (10 min average) wind speed (at the hub) and a turbulence intensity of 0.1 for a parked wind turbine. After performing the 10 min nonlinear dynamic simulations, a recently proposed extrapolation method is used for obtaining the extreme values of those responses over a period of 3 h. The sensitivity of the extremes to sample size is also studied. The extreme value statistics are estimated from the empirical mean upcrossing rates. This method together with other frequently used methods (i.e. the Weibull tail method and the global maxima method) is compared with the 3 h extreme values obtained directly from the time‐domain simulations. Copyright © 2012 John Wiley & Sons, Ltd.     

Response load extrapolation for wind turbines during operation based on average conditional exceedance rates

The paper explores a recently developed method for statistical response load (load effect) extrapolation for application to extreme response of wind turbines during operation. The extrapolation method is based on average conditional exceedance rates and is in the present implementation restricted to cases where the Gumbel distribution is the appropriate asymptotic extreme value distribution. However, two extra parameters are introduced by which a more general and flexible class of extreme value distributions is obtained with the Gumbel distribution as a subclass. The general method is implemented within a hierarchical model where the variables that influence the loading are divided into ergodic variables and time‐invariant non‐ergodic variables. The presented method for statistical response load extrapolation was compared with the existing methods based on peak extrapolation for the blade out‐of‐plane bending moment and the tower mudline bending moment of a pitch‐controlled wind turbine. In general, the results show that the method based on average conditional exceedance rates predicts the extrapolated characteristic response loads at the individual mean wind speeds well and results in more consistent estimates than the methods based on peak extrapolation. Copyright © 2011 John Wiley & Sons, Ltd.     

Mobile video literacy: negotiating the use of a new visual technology

In this article, we examine the practice of learning to produce video using a new visual technology. Drawing upon a design intervention at a science centre, where a group of teenagers tried a new prototype technology for live mobile video editing, we show how the participants struggle with both the content and the form of producing videos, i.e., what to display and how to do it in a comprehensible manner. We investigate the ways in which video literacy practices are negotiated as ongoing accomplishments and explore the communicative and material resources relied upon by participants as they create videos. Our results show that the technology is instrumental in this achievement and that as participants begin to master the prototype, they start to focus more on the narrative aspects of communicating the storyline of a science centre exhibit. The participants are explicitly concerned with such issues as how to create a comprehensible storyline for an assumed audience, what camera angles to use, how to cut and other aspects of the production of a video. We consider these observed activities to be candidate steps in an emerging mobile video literacy trajectory that involves developing a capacity to document and argue by means of this specific medium.     

The ductile-brittle transition of low-density polyethylene

The impact behavior of a low-density polyethylene was studied with an instrumented Charpy tester. A change from elastic or ductile response to brittle fracture was observed over a small temperature interval, usually within 1°C. This characteristic impact transition temperature (ITT) was highly sensitive to shallow, sharp notches. Whereas an unnotched test bar had a very low impact transition temperature of ?94°C, a razor cut with a depth of only 5 percent of the total thickness raised it to ?4°C. The impact transition temperature was effectively reduced by increasing the cooling rate during specimen preparation and by the addition of nonpolar liquids, On the other hand, impact properties were adversely affected by aging, annealing, and adding other thermoplastics.     

A probability density function for daily insolation within the temperate storm belts

Long-term insolation data are frequently obtainable either from recordings or from various empirical formulae. Many radiation-driven processes are, however, highly non-linear. The ability to model the correct long-term frequency distribution of a sequence of radiation events having a specified long-term mean insolation, is, therefore, valuable. This paper emphasizes that the “U-shaped” cloud cover frequency distribution, characteristic of the temperate storm belts, is “mapped” into the irradiation domain in a way that augments the number of “poor” and “excellent” days of sunshine at the expense of “average” days. An analytical and adjustable model is proposed, correlating the probability density of daily clearness index with the monthly average clearness index. This model is tuned to the two longest records of solar radiation in Norway, and it is verified against independent observations from the northern temperate storm belt.     

A probability density model for hourly total and beam irradiance on arbitrarily orientated planes

An analytical and adjustable model is proposed, by which the probability density of hourly global irradiance may be derived from long-term mean global irradiation. The model explicitly accounts for the bimodal character of the probability density of solar irradiance, and it is tuned to a developmental data sample and verified against an independent data base. In combination with previously published deterministic models this probability density model even forms a composite model which yields the probability density of hourly irradiance (total, beam or diffuse) on arbitrarily orientated planes. This composite model is also verified against the independent data base.     

The intensity of facial expression is determined by underlying affective state and social situation.

The present study concerned the influence of the presence of others on facial expressions of emotion. The proposition that facial expressive displays are better predicted by the social context than by emotional state (A. J. Fridlund, 1991) was tested in an experiment varying both the sociality of the context and the intensity of the emotion elicitor as well as the relationship between expressor and audience. The results indicate that the intensity of expressive displays cannot be satisfactorily predicted by either of these factors alone but is influenced by a complex interplay of all 3 factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Software Strategies and Hardware Upgrades to the PPL Data Acquisition System (DAS)

This paper describes upgrades to the Data Acquisition System for the Experimental Projects Department at PPPL, especially in support of the PBX-M upgrade to be completed this year. Hardware and software maintenance problems with the old configuration, consisting of a DEC KL-10 and eight PDP-11's, are described. The real-time software and hardware performance requirements and projections for CAMAC I/O and data analysis and display are presented. Described are three applications that have realtime requirements and are located on separate processors, connected to PPPL's VAX Cluster by an Ethernet link. Building upon a previous large software base, general-purpose subroutine libraries and utilities are being emphasized. The most useful of these are described. The use of software packages from DEC, third-party vendors, and the fusion community, is also described. The new approaches to software development that are being incorporated into the DAS efforts are discussed. Specific future challenges are also described.