Topical versus systemic fluoride: which is more effective in preventing dental caries in high risk population?

Dental caries is a multifactorial, bacterial, chronic infection that affects millions of people in the world and has become a public health problem. Also referred to as tooth decay, this disease is one of the most common disorders throughout the world, second only to the common cold. Dental caries is the most common chronic childhood disease in the United States and is 5 to 7 times more common than asthma. According to the World Oral Health Report in 2003, dental caries affect 60-80% of school children and a vast majority of adults. Dental caries is a chronic bacterial infection of the hard tissue of the tooth that is characterized by alternating phases of demineralization and remineralization. Dental decay can lead to significant pain and dysfunction that can interfere with basic functions such as eating, sleeping, and speaking. If left untreated, dental caries can result in cavities forming and eventually tooth loss. Although the prevalence and severity of dental caries has decreased over the years, this disease can be better controlled with proper fluoride exposure. Fluoride therapy has become the cornerstone strategy in the prevention of dental caries development and progression. With fluoride being available in various forms, fluoride exposure and/or treatment has greatly increased and has led to decreased incidences of dental caries. Fluoride has the ability to control the initiation and progression of carious lesions, mainly through the promotion of remineralization and the reduction in tooth enamel demineralization. Whether administered systemically or topically, the use of fluoride has proven to be effective in reducing the prevalence of dental caries. The aim of this review is to compare the topical methods of fluoride therapy with systemic applications. The goal is to evaluate the various forms of fluoride treatments based on cost effectiveness, safety, concentration and dosage of fluoride, ease of application, and accessibility to the community. This review will also identify the populations that are most susceptible to dental caries. The purpose of this review is to examine the benefits and risks of the various options of fluoride treatments in order to determine which would be the most the effective, safe, and efficient means of preventing dental caries in high risk populations. Based on the literature review, it was determined that the populations with the greatest risk for dental caries comprised of young children who were from lower socioeconomic backgrounds and elderly adults over the age of 65. After comparing the various forms of fluoride therapies, it was found that systemic fluoride treatments, mainly water fluoridation, would be the most effective in preventing dental caries in high caries risk populations

Identification of Air Traffic Flow Segments via Incremental Deterministic Annealing Clustering

Many of the traffic management decisions and initiatives in air traffic are based on "flows" of traffic in the National Airspace System (NAS), but the actual identification of the location and time of the flow segments are often left to interpretation based on observations of traffic data points over time. Having an automated method of identifying major flow segments can help to target traffic management initiatives, evaluate design of airspace, and enable actions to be taken on the collection of flights in a flow segment rather than on the flights individually. A novel approach is developed to identify the major flow segments of air traffic in the NAS that consists of a robust method for partitioning 4-dimensional traffic trajectories into a series of great circle segments, and clustering the segments using an Agglomerate Deterministic Annealing clustering algorithm. In addition, a very efficient algorithm to incrementally cluster the segments is developed that takes into account the spatial and temporal properties of the segments, and makes the method very suitable for real-time applications. Further, an enhancement to the algorithm is provided that requires only a small subset of the segments to be clustered, drastically reducing the run time. Results of the clustering technique are shown, highlighting various major traffic flow patterns in the NAS. In addition, organizing the traffic into the flow segments identified using the Incremental Clustering method is shown to have a potential reduction in the number of conflict points. An application of the flow information is presented in the form of a Decision Support Tool (DST) that aids traffic managers in establishing and managing Airspace Flow Programs. In addition, the flow segment information is applied to a low-level form of aggregated traffic management, showing that aggregating flights into the flow segments and rerouting the whole flow segment can be efficiently performed as compared to rerouting individual aircraft separately, and can reduce the number of conflict points. Considerations for implementing these techniques in real-time systems are also discussed

A Direct to Ground Architecture for Supporting Communications for the International Space Station

The deployment of the International Space Station (ISS) has opened new opportunities for research in space, providing a unique platform for tele-science, microgravity experiments, human physiology studies, and earth observation. In order to control, gain data from, and interact with these activities from the ground, a communications system that can support this broad range of applications needs to be established. In this thesis, three communications architectures for the ISS are discussed: 1) using NASA Tracking Data Relay Satellite System (TDRSS), 2) using emerging broadband commercial satellite systems to relay data to the ground, and 3) communicating directly to the ground ("DTG"). The thesis will focus on the latter option, DTG, and establish a methodology for determining the optimum placement of ground terminals for this type of service. A simulation model is developed for a large image file download application, and a detailed coverage analysis of the ISS communicating directly to these ground facilities is performed. In addition, a bottom-up cost estimate of this architecture is developed and compared to the costs of the other two architectures. The results show that the direct to ground architecture cost is competitive with that of the other architectures, and offers scalability for non-real-time applications. Coverage provided by commercial Ka-band satellite systems is about the same as that achieved by direct to ground, but its services will likely not be tailored to the needs of the ISS. The TDRS system provides complete coverage, and is therefore good for real-time applications such as videoconferencing

First-principle Study of Multiple Metastable Charge Ordering States in La1/3_{1/3}Sr2/3_{2/3}FeO3_{3}

La doped SrFeO$_{3}$, La$_{1/3}$Sr$_{2/3}$FeO$_{3}$, exhibits a metal-to-insulator transition accompanied by both antiferromagnetic and charge ordering states along with the Fe-O bond disproportionation below a critical temperature near 200K. Unconventionally slow charge dynamics measured in this material near the critical temperature shows that its excited charge ordering states can exhibit novel electronic structures with nontrivial energy profiles. Here, we reveal possible metastable states of charge ordering structures in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ using the first-principle and climbing image nudged elastic band methods. In the strong correlation regime, La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ is an antiferromagnetic insulator with a charge ordering state of the big-small-big pattern, consistent with the experimental measurement of this material at the low temperature. As the correlation effect becomes weak, we find at least two possible metastable charge ordering states with the distinct Fe-O bond disproportionation. Remarkably, a ferroelectric metallic state emerges with the small energy barrier of $\sim$7 meV, driven by a metastable CO state of the small-medium-big pattern. The electronic structures of these metastable charge ordering states are noticeably different from those of the ground-state. Our results can provide an insightful explanation to multiple metastable charge ordering states and the slow charge dynamics of this and related oxide materials.Comment: The paper has 8 pages and 6 figure

Extending IP Services to Future Space Missions

We outline the first steps of an effort to start defining the communication architecture for the next generation of space missions that will support NASA's "faster, better, cheaper" concept and will enable new types of collaborative science, where investigators can access their data from space "anytime, anywhere" via direct communication with the instruments on the spacecraft. We discuss the building blocks for a conceptual design of a network architecture that could support and take advantage of IP-capable spacecraft. We show that access from a large number of ground stations (that could be directly connected to the existing Internet infrastructure) could increase spacecraft availability time by a significant factor. We discuss possible multiple access techniques that could enable the transition to an on-demand operation, where spacecraft share space spectrum dynamically. We calso discuss the particular requirements of a next generation of missions consisting of constellations of several small spacecraft and introduce a number of new complex network control, scheduling, routing, data management and communication problems that need to be addressed for this topology

Using Commercial Satellites to Provide Communication Support for Space Missions

NASA is interested in using commercial satellites to provide broadband communications support for future space missions. In this paper, we describe a large-scale simulation model that we plan to use for detailed performance studies of critical parameters. We focus on the unique challenges we face and how we plan to use simulations to investigate:ﶴhe feasibility of using proposed commercial constellations to carry various classes of traffic between ground terminals and near-earth spacecraft.ﶴhe performance optimization of such systems.The research and scientific content in this material has been published inthe proceedings from the GLOBECOM2000 Symposium on Satellite Communications for the New Millennium, San Francisco, Nov, 2000

Using Commercial Communication Satellite Constellations for Supporting Traffic from NASA Missions

NASA is interested in using commercial satellites to provide broadband communications support for the International Space Station and other space missions. We describe a large-scale simulation model that we plan to use for detailed performance studies of critical parameters such as QoS guarantees for specific services, traffic routing schemes, transport protocol support, dynamic bandwidth allocation methods, queuing disciplines, and handoff strategies. In this paper we focus on the unique challenges we face and how we plan to use simulations to investigate:ﶴhe feasibility of using proposed commercial constellations to carry mission telemetry, command and control, and tele-science traffic between ground terminals and near-earth spacecraft.ﶴhe end-to-end performance optimization of such systems.The research and scientific content in this material has been published in the proceedings from the 18th AIAA International Conference on Satellite Systems & Communications, Oakland, CA, April 2000

Studying Inter-Cluster Galaxy Filaments Through Stacking GMBCG Galaxy Cluster Pairs

We present a method to study the photometric properties of galaxies in filaments by stacking the galaxy populations between pairs of galaxy clusters. Using Sloan Digital Sky Survey data, this method can detect the inter-cluster filament galaxy overdensity with a significance of $\sim 5 \sigma$ out to $z=0.40$. Using this approach, we study the $g-r$ color and luminosity distribution of filament galaxies as a function of redshift. Consistent with expectation, filament galaxies are bimodal in their color distribution and contain a larger blue galaxy population than clusters. Filament galaxies are also generally fainter than cluster galaxies. More interestingly, the observed filament population seems to show redshift evolution at $0.12<z<0.40$: the blue galaxy fraction has a trend to increase at higher redshift: a filament "Butcher Oemler Effect". We test the dependence of the observed filament density on the richness of the cluster pair: richer clusters are connected by higher density filaments. We also test the spatial dependence of filament galaxy overdensity: this quantity decreases when moving away from the inter-cluster axis between a cluster pair. This method provides an economical way to probe the photometric properties of filament galaxies and should prove useful for upcoming projects like the Dark Energy Survey.Comment: Submitted to Ap

Alternative Network Architectures for Supporting Communications from the International Space Station

In order to support the communications needs of the International Space Station (ISS), alternative communications architectures to provide broadband support need to be considered. We address three communications options and evaluate an architecture for the direct to ground option, which could serve as an intermediary solution to satisfy near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. We focus on a particular user requirements, and examine the system communications links, and coverage availability. These parameters, along with high-level cost estimates, are compared to using commercial relay satellites, and an enhanced TDRSS. The direct to ground option is viable for store-and-forward applications and cost comparable to commercial constellations, but TDRSS is the choice for real-time or continuous data applications

A direct-to-ground architecture for supporting Commercial Communications from the International Space Station

We outline the first steps of an effort to start defining a communications architecture for supporting broadband data communications from the International Space Station. We address three communications options and focus on a direct-to-ground architecture, which could serve as an intermediary solution to satisfy near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. A high-level analysis of the architecture for the direct to ground option is performed, focusing on a particular user requirements, communications links, and coverage availability. We also discuss system, mobility support and protocol issues that need to be addressed for this solution to be a feasible alternative