Tweed in Martensites: A Potential New Spin Glass

We've been studying the ``tweed'' precursors above the martensitic transition in shape--memory alloys. These characteristic cross--hatched modulations occur for hundreds of degrees above the first--order shape--changing transition. Our two--dimensional model for this transition, in the limit of infinite elastic anisotropy, can be mapped onto a spin--glass Hamiltonian in a random field. We suggest that the tweed precursors are a direct analogy of the spin--glass phase. The tweed is intermediate between the high--temperature cubic phase and the low--temperature martensitic phase in the same way as the spin--glass phase can be intermediate between ferromagnet and antiferromagnet.Comment: 18 pages and four figures (included

Iodine waste form summary report (FY 2007).

This new program at Sandia is focused on Iodine waste form development for GNEP cycle needs. Our research has a general theme of 'Waste Forms by Design' in which we are focused on silver loaded zeolite waste forms and related metal loaded zeolites that can be validated for chosen GNEP cycle designs. With that theme, we are interested in materials flexibility for iodine feed stream and sequestration material (in a sense, the ability to develop a universal material independent on the waste stream composition). We also are designing the flexibility to work in a variety of repository or storage scenarios. This is possible by studying the structure/property relationship of existing waste forms and optimizing them to our current needs. Furthermore, by understanding the properties of the waste and the storage forms we may be able to predict their long-term behavior and stability. Finally, we are working collaboratively with the Waste Form Development Campaign to ensure materials durability and stability testing

Hysteresis and hierarchies: dynamics of disorder-driven first-order phase transformations

We use the zero-temperature random-field Ising model to study hysteretic behavior at first-order phase transitions. Sweeping the external field through zero, the model exhibits hysteresis, the return-point memory effect, and avalanche fluctuations. There is a critical value of disorder at which a jump in the magnetization (corresponding to an infinite avalanche) first occurs. We study the universal behavior at this critical point using mean-field theory, and also present preliminary results of numerical simulations in three dimensions.Comment: 12 pages plus 2 appended figures, plain TeX, CU-MSC-747

Disorder-Driven Pretransitional Tweed in Martensitic Transformations

Defying the conventional wisdom regarding first--order transitions, {\it solid--solid displacive transformations} are often accompanied by pronounced pretransitional phenomena. Generally, these phenomena are indicative of some mesoscopic lattice deformation that ``anticipates'' the upcoming phase transition. Among these precursive effects is the observation of the so-called ``tweed'' pattern in transmission electron microscopy in a wide variety of materials. We have investigated the tweed deformation in a two dimensional model system, and found that it arises because the compositional disorder intrinsic to any alloy conspires with the natural geometric constraints of the lattice to produce a frustrated, glassy phase. The predicted phase diagram and glassy behavior have been verified by numerical simulations, and diffraction patterns of simulated systems are found to compare well with experimental data. Analytically comparing to alternative models of strain-disorder coupling, we show that the present model best accounts for experimental observations.Comment: 43 pages in TeX, plus figures. Most figures supplied separately in uuencoded format. Three other figures available via anonymous ftp

Desalination of brackish ground waters and produced waters using in-situ precipitation.

The need for fresh water has increased exponentially during the last several decades due to the continuous growth of human population and industrial and agricultural activities. Yet existing resources are limited often because of their high salinity. This unfavorable situation requires the development of new, long-term strategies and alternative technologies for desalination of saline waters presently not being used to supply the population growth occurring in arid regions. We have developed a novel environmentally friendly method for desalinating inland brackish waters. This process can be applied to either brackish ground water or produced waters (i.e., coal-bed methane or oil and gas produced waters). Using a set of ion exchange and sorption materials, our process effectively removes anions and cations in separate steps. The ion exchange materials were chosen because of their specific selectivity for ions of interest, and for their ability to work in the temperature and pH regions necessary for cost and energy effectiveness. For anion exchange, we have focused on hydrotalcite (HTC), a layered hydroxide similar to clay in structure. For cation exchange, we have developed an amorphous silica material that has enhanced cation (in particular Na{sup +}) selectivity. In the case of produced waters with high concentrations of Ca{sup 2+}, a lime softening step is included

Spatial Representations Are Specific to Different Domains of Knowledge

There is evidence that many abstract concepts are represented cognitively in a spatial format. However, it is unknown whether similar spatial processes are employed in different knowledge domains, or whether individuals exhibit similar spatial profiles within and across domains. This research investigated similarities in spatial representation in two knowledge domains – mathematics and music. Sixty-one adults completed analogous number magnitude and pitch discrimination tasks: the Spatial-Numerical Association of Response Codes and Spatial-Musical Association of Response Codes tasks. Subgroups of individuals with different response patterns were identified through cluster analyses. For both the mathematical and musical tasks, approximately half of the participants showed the expected spatial judgment effect when explicitly cued to focus on the spatial properties of the stimuli. Despite this, performances on the two tasks were largely independent. Consistent with previous research, the study provides evidence for the spatial representation of number and pitch in the majority of individuals. However, there was little evidence to support the claim that the same spatial representation processes underpin mathematical and musical judgments

Abnormal neural responses to harmonic syntactic structures in congenital amusia

Harmonic syntactic structures are organized hierarchically through local and long-distance dependencies. The present study investigated whether the processing of harmonic syntactic structures is impaired in congenital amusia, a neurodevelopmental disorder of pitch perception. Harmonic sequences containing two phrases were used as stimuli, in which the first phrase ended with a half cadence and the second with an authentic cadence. In Experiment 1, we manipulated the ending chord in the authentic cadence to be either syntactically regular or irregular. Sixteen amusics and 16 controls judged the expectedness of these chords while their EEG waveforms were recorded. In comparison to the regular endings, irregular endings elicited an ERAN, an N5 and a late positive component in controls but not in amusics, indicating that amusics were impaired in perceiving harmonic syntactic structures induced by local dependencies. In Experiment 2, we manipulated the half cadence of the harmonic sequences to examine the processing of harmonic syntactic structures induced by long-distance dependencies. An ERAN-like response and an N5 were elicited in controls but not in amusics, suggesting that amusics were impaired in processing long-distance syntactic dependencies. Furthermore, for controls, the neural processing of local and long-distance syntactic dependencies was correlated in the late (as indexed by the N5) but not in the early stage. These findings indicate that amusics are impaired in the detection of syntactic violations and subsequent harmonic integration. The implications of these findings in terms of hierarchical music-syntactic processing are discussed

Dynamical Principles of Emotion-Cognition Interaction: Mathematical Images of Mental Disorders

The key contribution of this work is to introduce a mathematical framework to understand self-organized dynamics in the brain that can explain certain aspects of itinerant behavior. Specifically, we introduce a model based upon the coupling of generalized Lotka-Volterra systems. This coupling is based upon competition for common resources. The system can be regarded as a normal or canonical form for any distributed system that shows self-organized dynamics that entail winnerless competition. Crucially, we will show that some of the fundamental instabilities that arise in these coupled systems are remarkably similar to endogenous activity seen in the brain (using EEG and fMRI). Furthermore, by changing a small subset of the system's parameters we can produce bifurcations and metastable sequential dynamics changing, which bear a remarkable similarity to pathological brain states seen in psychiatry. In what follows, we will consider the coupling of two macroscopic modes of brain activity, which, in a purely descriptive fashion, we will label as cognitive and emotional modes. Our aim is to examine the dynamical structures that emerge when coupling these two modes and relate them tentatively to brain activity in normal and non-normal states

A historical review of Waste Isolation Pilot Plant backfill development

Backfills have been part of Sandia National Laboratories' [Sandia's] Waste Isolation Pilot Plant [WIPP] designs for over twenty years. Historically, backfill research at Sandia has depended heavily on the changing mission of the WIPP facility. Early testing considered heat producing, high level, wastes. Bentonite/sand/salt mixtures were evaluated and studies focused on developing materials that would retard brine ingress, sorb radionuclides, and withstand elevated temperatures. The present-day backfill consists of pure MgO [magnesium oxide] in a pelletized form and is directed at treating the relatively low contamination level, non-heat producing, wastes actually being disposed of in the WIPP. Its introduction was motivated by the need to scavenging CO{sub 2} [carbon dioxide] from decaying organic components in the waste. However, other benefits, such as a substantial desiccating capacity, are also being evaluated. The MgO backfill also fulfills a statutory requirement for assurance measures beyond those needed to demonstrate compliance with the US Environmental Protection Agency [EPA] regulatory release limits. However, even without a backfill, the WIPP repository design still operates within EPA regulatory release limits