2,304 research outputs found
Engineering transport by concatenated maps
We present a generalized kick rotor model in which the phase of the kick can
vary from kick to kick. This additional freedom allows one to control the
transport in phase space. For a specific choice of kick-to-kick phases, we
predict novel forms of accelerator modes which are potentially of high
relevance for future experimental studies
Geophysical and Biological Reconnaissance of Rock Habitats in Western Camden Bay, Beaufort Sea, Alaska
This report presents the results of a 10-day geophysical and
biological survey in western Camden Bay, in the Alaskan Beaufort Sea.
The primary objective of this survey was to confirm the existence of
boulders and cobbles on the seafloor as reported by Barnes (1981, 1982).
The survey area extended from the eastern edge of the Canning River (mud
flat area) to Kangigivik Point and seaward to the 14m contour line
(Fig. 1). A solid boundary of pack ice prevented any survey work
seaward of the 14m contour. We had proposed to examine the seabed to
the 18m contour.This work was
supported by the Bureau of Land Management through an interagency
agreement with the National Oceanic and Atmospheric Administration,
under which a multiyear program responding to needs of petroleum
development of the Alaskan Continental Shelf is managed by the Outer
Continental Shelf Environmental Assessment Program (OCSEAP) office
Elimination of swelling stresses from measurements of the equilibrium constant in silica
The reaction of water with silica is described by the equilibrium constant k. This property depends on temperature and is affected by stresses. The experimental determination of k is in most cases carried out in presence of swelling stresses. Knowledge of the reaction volume allows an elimination of the swelling stresses and the determination of an equilibrium constant for the case of a stress-free material. An analytical expression of k as a function of temperature, k=f(T), will be suggested
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Evaluating the Economic Response to Japan's Earthquake
This paper compares the 1995 Kobe earthquake with the more recent one in Tohoku. The impact of the recent earthquake on industrial production was much larger and long-lasting than that of the 1995 earthquake. We find that very little of this can be explained by differences in government expenditures or private consumption. However, we find very substantial differences in energy production in the wake of the two earthquakes. The substantial and persistent drop in energy output is likely to have exacerbated supply disruptions and may continue to slow the pace of recovery. Moreover, we provide some evidence that Japan‘s increasing reliance on fossil fuel sources of energy is likely to result in a large number of deaths and increases in morbidity due to increased air pollution. These results highlight the difficulties that Japan is likely to face in its move away from nuclear power
Crack-tip shielding in silica at room temperature
When water penetrates into silica surfaces near a crack tip, it reacts with the SiO network and generates hydroxyl SiOH. Due to the hydroxyl generation, the glass must expand. Since a free expansion is not possible for the thin layers on the undeformed bulk material, compressive stresses occur which shield the crack-tip region from externally applied tensile load. The consequence is a fracture mechanics shielding stress intensity factor K<0. So far we only determined the shielding stress intensity factor from theoretical considerations on water diffusion und the high tensile stresses at crack tips. Since water concentration measurements on crack surfaces of uncritically driven cracks are available in literature, we determine the shielding term Ksh from experimental data. This evaluation is done with and without consideration of damaging the initial ring network by hydroxyl generation. It can be concluded that the shielding stress intensity factor is clearly overestimated, when crack-tip damage is ignored. Finally, it is illustrated in which way the shielding stress intensity factor influences the v-K-curve for subcritical crack growth
Mass Transfer of Water at Silica Surfaces - Extension of the data base to lower temperatures
In two previous reports we have dealt with the description of the time dependence of the water content at the surface of silicate glass by mass transfer (SWP 73 and SWP 94). Literature measurements in the range of 200°C100°C. Measurements by Helmich&Rauch serve as a basis.
A step change in the mass transfer coefficient is found at 200°
Evaluation of crack profiles by Bando et al. Analysis of crack opening displacements
The behavior of cracks in glass is discussed contrary for many years. Both purely elastic material behavior as well as plasticity and viscosity were discussed. One of the key results were the crack opening measurements of Bando which were considered for an indication of non-elastic behavior.
There are two effects of water, damage by breaking the ring structure due to chemical water reaction and swelling. In this short note, the effect of damage by the water-glass reaction is addressed. In this report we deal with a purely linear attempt by the J-integral
Romancelandia on Twitter: Designing a Digital Humanities Research Assignment for First-Year Writing Students
On Facebook, Instagram, and Tumblr, on blogs and Pinterest and Twitter, romance writers have embraced social media as a way to engage with their readers; they also use these platforms to foster community among romance authors, encouraging and promoting each other. This public presence provides a unique opportunity for scholars to witness the dynamics of the romance writing community in action. In Heather’s first-year writing class, Love and American Culture, in the primary goal is to introduce students to academic writing and research. Part of this entails helping students experience the excitement of writing a research paper when the topic is new and the questions are motivated by genuine interest. Heather has been collaborating with Ann, a research librarian, to develop an assignment sequence around original research on romance authors’ public social networks. The project uses Social Feed Manager and textual analysis tools to give students the opportunity to shape their own research questions and study the Twitter feed of the romance author of their choice. In-class activities will help students track down supplemental research and think through the ethical questions raised by studying individuals’ social media accounts. We are excited to be introducing a project the breaks free from the traditional writing program practice of privileging literary analysis (a quite distinctive research genre) as the prototype of academic research. In our presentation, we will discuss the successes and failures of our first semester’s efforts and, we hope, get good ideas on improving the project
Crack-tip models by Irwin and Dugdale for hydroxyl-damaged crack-tip zones
Due to the hydroxyl generation, the silica network ahead of crack tips is damaged. The consequence is a damaged crack-tip zone showing a reduced Young’s modulus. The linear-elastic fracture mechanical treatment by application of stress intensity factors becomes doubtful especially for large zones. In this report, we use a description via well-known models of Elastic-Plastic Fracture Mechanics, namely, the models by Irwin and Dugdale.
As an application we compared the results with experimental observations on crack profiles from literature. The computed and observed Crack-Tip Opening Displacements (CTOD) were found to be in good agreement
Validation of the swelling formalism via evaluation of bending moments from literature: Comparison of theoretical predictions and measurements
The volume of silica expands by the hydroxyl generation when silica surfaces react with water. These volume strains are proportional to the mass concentration of the hydroxyl. They were measured by Wiederhorn et al. by evaluating the curvature of disks undergoing this reaction on only one side. The obtained bending moments were found to be proportional to square-root of heat-treatment time.
In the present considerations we pay particular attention to global bending moments caused by swelling, which, in contrast to local swelling stresses, do not require assumptions about the type of stress distribution.
It can be stated that
• The bending moments from disk curvature and hydroxyl measurements via the IR-evaluation procedure by Libowitzky and Rossman are in excellent agreement.
• Predictions of moments M based on diffusivities and surface water concentrations by Helmich and Rauch also show good agreement with correlation coefficients R>0.95. Consequently, we can sufficiently write: M = M
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