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2011

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Articles 1 - 22 of 22

Full-Text Articles in Physical Sciences and Mathematics

Model For Amorphous Aggregation Processes, Samual Stranks, Heath Ecroyd, Steve Van Sluyter, Elizabeth J. Waters, John A. Carver, Lorenz Von Smekal Dec 2011

Model For Amorphous Aggregation Processes, Samual Stranks, Heath Ecroyd, Steve Van Sluyter, Elizabeth J. Waters, John A. Carver, Lorenz Von Smekal

Heath Ecroyd

The amorphous aggregation of proteins is associated with many phenomena, ranging from the formation of protein wine haze to the development of cataract in the eye lens and the precipitation of recombinant proteins during their expression and purification. While much literature exists describing models for linear protein aggregation, such as amyloid fibril formation, there are few reports of models which address amorphous aggregation. Here, we propose a model to describe the amorphous aggregation of proteins which is also more widely applicable to other situations where a similar process occurs, such as in the formation of colloids and nanoclusters. As first …

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Hydroclimatic Forecasting In The Western United States Using Paleoclimate Reconstructions And Data-Driven Models, Christopher Allen Carrier Dec 2011

Hydroclimatic Forecasting In The Western United States Using Paleoclimate Reconstructions And Data-Driven Models, Christopher Allen Carrier

UNLV Theses, Dissertations, Professional Papers, and Capstones

This thesis investigated climate variability and their associated hydrologic responses in the western United States. The western United States faces the problem of water scarcity, where the management and mitigation of available water supplies are further complicated by climate variability. Climate variability associated with the phases of oceanic-atmospheric oscillations has been shown to influence streamflow and precipitation, where predictive relationships have led to the possibility of producing long-range forecasts. Based on literature review, four oceanic-atmospheric oscillation indices were identified in having the most prominent influence over the western United States including the El Niño - Southern Oscillation (ENSO), Pacific Decadal …

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A Phishing Model And Its Applications To Evaluating Phishing Attacks, Narasimha Shashidhar, Lei Chen Aug 2011

A Phishing Model And Its Applications To Evaluating Phishing Attacks, Narasimha Shashidhar, Lei Chen

International Cyber Resilience conference

Phishing is a growing threat to Internet users and causes billions of dollars in damage every year. In this paper, we present a theoretical yet practical model to study this threat in a formal manner. While it is folklore knowledge that a successful phishing attack entails creating messages that are indistinguishable from the natural, expected messages by the intended victim, this concept has not been formalized. Our model captures phishing in terms of this indistinguishability between the natural and phishing message distributions. To the best of our knowledge, this is the first study that places phishing on a concrete theoretical …

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Modeling Wireless Networks For Rate Control, David C. Ripplinger Jul 2011

Modeling Wireless Networks For Rate Control, David C. Ripplinger

Theses and Dissertations

Congestion control algorithms for wireless networks are often designed based on a model of the wireless network and its corresponding network utility maximization (NUM) problem. The NUM problem is important to researchers and industry because the wireless medium is a scarce resource, and currently operating protocols such as 802.11 often result in extremely unfair allocation of data rates. The NUM approach offers a systematic framework to build rate control protocols that guarantee fair, optimal rates. However, classical models used with the NUM approach do not incorporate partial carrier sensing and interference, which can lead to significantly suboptimal performance when actually …

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Analysis Of Roms Estimated Posterior Error Utilizing 4dvar Data Assimilation, Joseph Patrick Horton Jun 2011

Analysis Of Roms Estimated Posterior Error Utilizing 4dvar Data Assimilation, Joseph Patrick Horton

Mathematics

The appropriateness of the approximate error calculated by the Regional Ocean Modeling System (ROMS) is analyzed using Four-Dimensional Data Assimilation (4DVAR) performed on a numerical model of the San Luis Obispo Bay. An effective method of sampling data to minimize the actual error associated with the assimilated numerical model is explored by using different data sampling methods. An idealized state of the SLO bay region ("Real Run") is created to be used as the real ocean, then a numerical model of this region is created approximating this Real Run; this is known as the "Simulated State". By taking samples from …

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Thermodynamics Of The Antiferromagnetic Heisenberg Model On The Checkerboard Lattice, Ehsan Khatami, Maros Rigol Apr 2011

Thermodynamics Of The Antiferromagnetic Heisenberg Model On The Checkerboard Lattice, Ehsan Khatami, Maros Rigol

Faculty Publications

Employing numerical linked-cluster expansions (NLCEs) along with exact diagonalizations of finite clusters with periodic boundary condition, we study the energy, specific heat, entropy, and various susceptibilities of the antiferromagnetic Heisenberg model on the checkerboard lattice. NLCEs, combined with extrapolation techniques, allow us to access temperatures much lower than those accessible to exact diagonalization and other series expansions. We show that the high-temperature peak in specific heat decreases as the frustration increases, consistent with the large amount of unquenched entropy in the region around maximum classical frustration, where the nearest-neighbor and next-nearest-neighbor exchange interactions (J and J′, respectively) have the same …

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Chiral Symmetry Breaking By Spatial Confinement In Tactoidal Droplets Of Lyotropic Chromonic Liquid Crystals, Luana Tortora, Oleg Lavrentovich Mar 2011

Chiral Symmetry Breaking By Spatial Confinement In Tactoidal Droplets Of Lyotropic Chromonic Liquid Crystals, Luana Tortora, Oleg Lavrentovich

Oleg Lavrentovich

In many colloidal systems, an orientationally ordered nematic (N) phase emerges fromthe isotropic (I) melt in the form of spindle-like birefringent tactoids. In cases studied so far, the tactoids always reveal a mirror-symmetric nonchiral structure, sometimes even when the building units are chiral. We report on chiral symmetry breaking in the nematic tactoids formed in molecularly nonchiral polymer-crowded aqueous solutions of low-molecular weight disodium cromoglycate. The parity is broken by twisted packing of self-assembled molecular aggregates within the tactoids as manifested by the observed optical activity. Fluorescent confocal microscopy reveals that the chiral N tactoids are located at the boundaries …

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A Financial Impact Assessment Of Ld 1725: Stream Crossings, New England Environmental Finance Center, Muskie School Of Public Service Jan 2011

A Financial Impact Assessment Of Ld 1725: Stream Crossings, New England Environmental Finance Center, Muskie School Of Public Service

Water

This report looks at the potential financial impact of LD 1725 on the estimated 30,000 stream crossings in the State of Maine that would be affected by the law. Our research for this report included the analysis of nearly 2000 stream crossings and the data collection necessary for the development of extensive stream crossing replacement cost models. We found that the 1.2 bankfull requirements in LD 1725 would result in a 75% ‐ 250% increase in structure widths for stream crossing projects across the state. An upsize of this magnitude would increase the cost of replacing stream crossings statewide by …

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A Financial Impact Assessment Of Ld 1725: Stream Crossings (Presentation), New England Environmental Finance Center, Muskie School Of Public Service Jan 2011

A Financial Impact Assessment Of Ld 1725: Stream Crossings (Presentation), New England Environmental Finance Center, Muskie School Of Public Service

Water

This report looks at the potential financial impact of LD 1725 on the estimated 30,000 stream crossings in the State of Maine that would be affected by the law. Our research for this report included the analysis of nearly 2000 stream crossings and the data collection necessary for the development of extensive stream crossing replacement cost models. We found that the 1.2 bankfull requirements in LD 1725 would result in a 75% ‐ 250% increase in structure widths for stream crossing projects across the state. An upsize of this magnitude would increase the cost of replacing stream crossings statewide by …

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Theory Of Gaussian Variational Approximation For A Poisson Mixed Model, Peter Hall, J T. Ormerod, M P. Wand Jan 2011

Theory Of Gaussian Variational Approximation For A Poisson Mixed Model, Peter Hall, J T. Ormerod, M P. Wand

Faculty of Informatics - Papers (Archive)

Likelihood-based inference for the parameters of generalized linear mixed models is hindered by the presence of intractable integrals. Gaussian variational approximation provides a fast and effective means of approximate inference. We provide some theory for this type of approximation for a simple Poisson mixed model. In particular, we establish consistency at rate m−1/2 +n−1, where m is the number of groups and n is the number of repeated measurements.

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Statistical Analysis Model Predicting Computer Use In Mathematics, Rebecca Hudson, Anne Porter, Mark Nelson Jan 2011

Statistical Analysis Model Predicting Computer Use In Mathematics, Rebecca Hudson, Anne Porter, Mark Nelson

Faculty of Informatics - Papers (Archive)

This paper is a report of a doctoral thesis that investigated the factors that were associated with the use of computers in secondary mathematics teaching, the choices made by teachers and learning theories guiding their teaching. Mixed methods approaches were used to triangulate the results of the study. The study was divided into three stages, the first a questionnaire completed by 114 teachers, the second was examination of current accredited courses in teacher preparation for mathematics teaching to identify what learning theories were included in subjects, and the third were interviews with 8 teachers in training and 6 experienced teachers. …

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Asymptotic And Numerical Results For A Model Of Solvent-Dependent Drug Diffusion Through Polymeric Spheres, Scott Mccue, Mike Hsieh, Timothy J. Moroney, Mark I. Nelson Jan 2011

Asymptotic And Numerical Results For A Model Of Solvent-Dependent Drug Diffusion Through Polymeric Spheres, Scott Mccue, Mike Hsieh, Timothy J. Moroney, Mark I. Nelson

Faculty of Informatics - Papers (Archive)

A model for drug diffusion from a spherical polymeric drug delivery device is considered. The model contains two key features. The first is that solvent diffuses into the polymer, which then transitions from a glassy to a rubbery state. The interface between the two states of polymer is modeled as a moving boundary, whose speed is governed by a kinetic law; the same moving boundary problem arises in the one-phase limit of a Stefan problem with kinetic undercooling. The second feature is that drug diffuses only through the rubbery region, with a nonlinear diffusion coefficient that depends on the concentration …

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A Mathematical Model For The Biological Treatment Of Industrial Wastewaters In A Cascade Of Four Reactors, Annette L. Worthy, Mark I. Nelson, Rubayyi Turki Alqahtani Jan 2011

A Mathematical Model For The Biological Treatment Of Industrial Wastewaters In A Cascade Of Four Reactors, Annette L. Worthy, Mark I. Nelson, Rubayyi Turki Alqahtani

Faculty of Informatics - Papers (Archive)

Many industrial processes, particularly in the food industry, produce slurriesor wastewaters containing high concentrations of biodegradable organicmaterials. Before these contaminated wastewaters can be dischargedthe concentration of these pollutants must be reduced. A method which has beenextensively employed to remove biodegradable organic matter is biologicaltreatment. In this process the wastewater (or slurry) is passed through abioreactor containing biomass which grows through consumption of thepollutants.The industrial treatment of wastewaters typically employs a reactor cascade.In a reactor cascade of n reactors the effluent stream from the ith reactor inthe cascade acts as the feed stream for the (i+1)th reactor, i.e. the nextreactor. The …

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A Preliminary Investigation Of Complex Adaptive Systems As A Model For Explaining Organisational Change Caused By The Introduction Of Health Information Systems, Kieren Diment, Ping Yu, Karin Garrety Jan 2011

A Preliminary Investigation Of Complex Adaptive Systems As A Model For Explaining Organisational Change Caused By The Introduction Of Health Information Systems, Kieren Diment, Ping Yu, Karin Garrety

Faculty of Informatics - Papers (Archive)

This paper documents the preliminary development of a framework for evaluating organisational change processes during the implementation of an electronic nursing documentation system in residential aged care facilities. It starts with a brief outline of organisational change processes. This is followed by a more detailed exposition of the principles underlying complex adaptive systems (CAS) theory, where we explain how mathematical concepts can be used to illuminate qualitative research approaches. Finally we present some preliminary findings on the facilitators and barriers for the introduction of the electronic documentation system, explained with reference to the CAS theory, based on analysis of interviews …

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Daily And 3-Hourly Variability In Global Fire Emissions And Consequences For Atmospheric Model Predictions Of Carbon Monoxide, M Mu, James Randerson, G R. Van Der Werf, L Giglio, Prasad Kasibhatla, D Morton, G J. Collatz, R S. Defries, E J. Hyer, E M. Prins, David W. Griffith, Debra Wunch, G C. Toon, V Sherlock, Paul O. Wennberg Jan 2011

Daily And 3-Hourly Variability In Global Fire Emissions And Consequences For Atmospheric Model Predictions Of Carbon Monoxide, M Mu, James Randerson, G R. Van Der Werf, L Giglio, Prasad Kasibhatla, D Morton, G J. Collatz, R S. Defries, E J. Hyer, E M. Prins, David W. Griffith, Debra Wunch, G C. Toon, V Sherlock, Paul O. Wennberg

Faculty of Science - Papers (Archive)

"Attribution of the causes of atmospheric trace gas and aerosol variability often requires the use of high resolution time series of anthropogenic and natural emissions inventories. Here we developed an approach for representing synoptic-and diurnal-scale temporal variability in fire emissions for the Global Fire Emissions Database version 3 (GFED3). We disaggregated monthly GFED3 emissions during 2003-2009 to a daily time step using Moderate Resolution Imaging Spectroradiometer (MODIS)-derived measurements of active fires from Terra and Aqua satellites. In parallel, mean diurnal cycles were constructed from Geostationary Operational Environmental Satellite (GOES) Wildfire Automated Biomass Burning Algorithm (WF_ABBA) active fire observations. Daily variability …

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Methane Observations From The Greenhouse Gases Observing Satellite: Comparison To Ground-Based Tccon Data And Model Calculations, Robert Parker, Hartmut Boesch, Austin Cogan, Annemarie Fraser, Liang Feng, Paul Palmer, Janina Messerschmidt, Nicholas M. Deutscher, David W. Griffith, Justus Notholt, Paul O. Wennberg, Debra Wunch Jan 2011

Methane Observations From The Greenhouse Gases Observing Satellite: Comparison To Ground-Based Tccon Data And Model Calculations, Robert Parker, Hartmut Boesch, Austin Cogan, Annemarie Fraser, Liang Feng, Paul Palmer, Janina Messerschmidt, Nicholas M. Deutscher, David W. Griffith, Justus Notholt, Paul O. Wennberg, Debra Wunch

Faculty of Science - Papers (Archive)

We report new short-wave infrared (SWIR) column retrievals of atmospheric methane (X CH4) from the Japanese Greenhouse Gases Observing SATellite (GOSAT) and compare observed spatial and temporal variations with correlative ground-based measurements from the Total Carbon Column Observing Network (TCCON) and with the global 3-D GEOS-Chem chemistry transport model. GOSAT X CH4 retrievals are compared with daily TCCON observations at six sites between April 2009 and July 2010 (Bialystok, Park Falls, Lamont, Orleans, Darwin and Wollongong). GOSAT reproduces the site-dependent seasonal cycles as observed by TCCON with correlations typically between 0.5 and 0.7 with an estimated single-sounding precision between 0.4-0.8%. …

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Retrieval Of Atmospheric Co2 With Enhanced Accuracy And Precision From Sciamachy: Validation With Fts Measurements And Comparison With Model Results, M Reuter, H Bovensmann, M Buchwitz, Jp Burrows, B Connor, Nicholas M. Deutscher, David W. Griffith, J Heymann, Gretchen Keppel-Aleks, Janina Messerschmidt, Justus Notholt, Christof Petri, J Robinson, O Schneising, V Sherlock, Voltaire A. Velazco, Thorsten Warneke, Paul O. Wennberg, Debra Wunch Jan 2011

Retrieval Of Atmospheric Co2 With Enhanced Accuracy And Precision From Sciamachy: Validation With Fts Measurements And Comparison With Model Results, M Reuter, H Bovensmann, M Buchwitz, Jp Burrows, B Connor, Nicholas M. Deutscher, David W. Griffith, J Heymann, Gretchen Keppel-Aleks, Janina Messerschmidt, Justus Notholt, Christof Petri, J Robinson, O Schneising, V Sherlock, Voltaire A. Velazco, Thorsten Warneke, Paul O. Wennberg, Debra Wunch

Faculty of Science - Papers (Archive)

The Bremen Optimal Estimation differential optical absorption spectroscopy (DOAS) (BESD) algorithm for satellite based retrievals of XCO 2 (the column-average dry-air mole fraction of atmospheric CO 2) has been applied to Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) data. It uses measurements in the O 2-A absorption band to correct for scattering of undetected clouds and aerosols. Comparisons with precise and accurate ground-based Fourier transform spectrometer (FTS) measurements at four Total Carbon Column Observing Network (TCCON) sites have been used to quantify the quality of the new SCIAMACHY XCO 2 data set. Additionally, the results have been compared to …

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The Australian Methane Budget: Interpreting Surface And Train-Borne Measurements Using A Chemistry Transport Model, A Fraser, C C. Miller, Paul Palmer, Nicholas M. Deutscher, Nicholas B. Jones, David W. Griffith Jan 2011

The Australian Methane Budget: Interpreting Surface And Train-Borne Measurements Using A Chemistry Transport Model, A Fraser, C C. Miller, Paul Palmer, Nicholas M. Deutscher, Nicholas B. Jones, David W. Griffith

Faculty of Science - Papers (Archive)

We investigate the Australian methane budget from 2005-2008 using the GEOS-Chem 3D chemistry transport model, focusing on the relative contribution of emissions from different sectors and the influence of long-range transport. To evaluate the model, we use in situ surface measurements of methane, methane dry air column average (XCH 4) from ground-based Fourier transform spectrometers (FTSs), and train-borne surface concentration measurements from an in situ FTS along the north-south continental transect. We use gravity anomaly data from Gravity Recovery and Climate Experiment to describe the spatial and temporal distribution of wetland emissions and scale it to a prior emission estimate, …

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Computational Network Analysis Of The Anatomical And Genetic Organizations In The Mouse Brain, Shuiwang Ji Jan 2011

Computational Network Analysis Of The Anatomical And Genetic Organizations In The Mouse Brain, Shuiwang Ji

Computer Science Faculty Publications

Motivation: The mammalian central nervous system (CNS) generates high-level behavior and cognitive functions. Elucidating the anatomical and genetic organizations in the CNS is a key step toward understanding the functional brain circuitry. The CNS contains an enormous number of cell types, each with unique gene expression patterns. Therefore, it is of central importance to capture the spatial expression patterns in the brain. Currently, genome-wide atlas of spatial expression patterns in the mouse brain has been made available, and the data are in the form of aligned 3D data arrays. The sheer volume and complexity of these data pose significant challenges …

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An Assessment Tool For E-Government System Performance: A Citizen-Centric Model, Shatha A. Al-Haddad, Peter Hyland, Geoffrey Hubona Jan 2011

An Assessment Tool For E-Government System Performance: A Citizen-Centric Model, Shatha A. Al-Haddad, Peter Hyland, Geoffrey Hubona

Faculty of Informatics - Papers (Archive)

Governments worldwide have, increasingly, implemented e-government initiatives for their potential significant benefits; among which, delivering better services to citizens through increasing citizens' convenience, satisfaction, and independence; and saving their time, effort, and cost. Achieving each benefit is an objective to these governments and fulfilling each objective is considered a critical success factors. Hence, governments need to assess the extent to which they were able to obtain their preset goals. This study merely focuses on the citizens' perspective of the evaluation. However, the literature seems to lack studies that propose such a sufficient evaluation tool that has been reliably validated. Therefore, …

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Early Season Depletion Of Dissolved Iron In The Ross Sea Polynya: Implications For Iron Dynamics On The Antarctic Continental Shelf, Peter N. Sedwick, C. M. Marsay, B. M. Sohst, A. M. Aguilar-Islas, M. C. Lohan, M. C. Long, K. R. Arrigo, R. B. Dunbar, M. A. Saito, W. O. Smith, G. R. Ditullio Jan 2011

Early Season Depletion Of Dissolved Iron In The Ross Sea Polynya: Implications For Iron Dynamics On The Antarctic Continental Shelf, Peter N. Sedwick, C. M. Marsay, B. M. Sohst, A. M. Aguilar-Islas, M. C. Lohan, M. C. Long, K. R. Arrigo, R. B. Dunbar, M. A. Saito, W. O. Smith, G. R. Ditullio

OES Faculty Publications

The Ross Sea polynya is among the most productive regions in the Southern Ocean and may constitute a significant oceanic CO2sink. Based on results from several field studies, this region has been considered seasonally iron limited, whereby a "winter reserve" of dissolved iron (dFe) is progressively depleted during the growing season to low concentrations (~ 0.1 nM) that limit phytoplankton growth in the austral summer (December-February). Here we report new iron data for the Ross Sea polynya during austral summer 2005-2006 (27 December-22 January) and the following austral spring 2006 (16 November-3 December). The summer 2005-2006 data show …

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Evaluation Of Satellite-Retrieved Extreme Precipitation Rates Across The Central United States, A. Aghakoucak, A. Behrangi, S. Sorooshian, K. Hsu, Eyal Amitai Jan 2011

Evaluation Of Satellite-Retrieved Extreme Precipitation Rates Across The Central United States, A. Aghakoucak, A. Behrangi, S. Sorooshian, K. Hsu, Eyal Amitai

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

Water resources management, forecasting, and decision making require reliable estimates of precipitation. Extreme precipitation events are of particular importance because of their severe impact on the economy, the environment, and the society. In recent years, the emergence of various satellite-retrieved precipitation products with high spatial resolutions and global coverage have resulted in new sources of uninterrupted precipitation estimates. However, satellite-based estimates are not well integrated into operational and decision-making applications because of a lack of information regarding the associated uncertainties and reliability of these products. In this study, four satellite-derived precipitation products (CMORPH, PERSIANN, TMPA-RT, and TMPA-V6) are evaluated with …

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