On Universal Cycles for Multisets

A Universal Cycle for t-multisets of [n]={1,...,n} is a cyclic sequence of $\binom{n+t-1}{t}$ integers from [n] with the property that each t-multiset of [n] appears exactly once consecutively in the sequence. For such a sequence to exist it is necessary that n divides $\binom{n+t-1}{t}$, and it is reasonable to conjecture that this condition is sufficient for large enough n in terms of t. We prove the conjecture completely for t in {2,3} and partially for t in {4,6}. These results also support a positive answer to a question of Knuth.Comment: 14 pages, two figures, will appear in Discrete Mathematics' special issue on de Bruijn Cycles, Gray Codes and their generalizations; paper revised according to journal referees' suggestion

A Profile of Frail Older Americans and Their Caregivers

Provides a profile of older Americans and their caregivers, focusing on people age 65 and older who are not in nursing homes, and those with severe disabilities. Includes policy implications and recommendations for community-based home care options

NASA Magnetospheric MultiScale Mission TableSat 1C

The NASA Magnetospheric MultiScale (MMS) mission (to be launched in 2014) consists of four spin-stabilized spacecraft flying in precise formation. The MMS spacecraft, which have wire booms up to 60 m long, are analyzed using the UNH MMS TableSat IC, a limited 3-DOF rotation (full spin, limited nutation) table top prototype of the MMS spacecraft. A PID controller is implemented on TableSat IC to observe the effects of spin rate and nutation control on the experimental satellite bus and scaled booms. Nutation and spin are implemented independently and the behavior of the test bed with and without SDP booms is examined. The SDP booms are shown to increase the response time of the controlled platform

Receiving Basin Substrate Controls on Delta Morphodynamics

Deltas are inhabited by hundreds of millions of people and are critical for food security, coastal defence, carbon sequestration and ecological diversity. These intrinsically vulnerable systems are threatened by an array of anthropogenic pressures, such as accelerated sea level rise, enhanced subsidence due to sub-surface fluid extraction, retention of sediment within upstream reservoirs and levee construction isolating the delta floodplain from sediment deposition. This study investigates how delta morphodynamics are influenced by the resistance of the sediment making up the receiving basin substrate, and how these effects evolve in the face of anthropogenic forcing of relative sea level and sediment supply loss.Numerical modelling using Delft3d_flow found bed sediment erodibility w to be a strong driver of delta land area, elevation, distributary channel geometry and channel mobility, with the potential to overcome or modulate the effects of fluvial sediment. Substrate fine sediment content was found to be dominant in setting channel mobility, but the cohesive strength of the fine sediment was dominant in setting channel depth, width:depth ratio and subaerial land area. Fieldwork in the Wax Lake Delta, Louisiana, a sediment limited delta underlain by erosion resistant fine sediment, utilised multibeam echosounder and acoustic doppler current profiler to collect high resolution bathymetric and velocimetric data. This highlighted that substrate type and sediment supply could cause delta bifurcations to be stable under flow conditions different to those dictated to produce stable bifurcations by previous studies.This work highlights that the effects of substrate sediment on delta morphodynamics cannot be neglected if their reaction to current and future anthropogenic forcing is to be accurately predicted and demonstrates the desperate need for further work constraining the effects of channel bed erodibility on bifurcation dynamics, as well as field studies to quantify the properties of sediment underlying modern and ancient deltas

The impact of water column mixing in a salt wedge estuary

The Puget Sound is a complex estuarine system within the Salish Sea, fed by both high salinity water from the Pacific Ocean and freshwater from a number of rivers. The Snohomish River is one of the largest of these inputs, transporting freshwater from the Skykomish and Snoqualmie rivers to Port Gardner Bay off the coast of Everett. At its mouth, the higher density salt water from the Puget Sound intrudes into the freshwater, forming a salt wedge that causes a highly stratified water column which rapidly changes with the tidal cycle. In this highly stratified water column, little mixing occurs between the different layers of the water, resulting in a lack of nutrients near the surface. This study aims to quantify the amount of mixing occurring at this location in relation to tidal patterns and season, and analyze the effect varying levels of mixing have on related chemical properties. This research is being conducted at the Ocean Research College Academy (ORCA), a dual enrollment program through Everett Community College. In cooperation with Gravity Marine Consulting and the Port of Everett, ORCA has moored a SeaBird CTD two meters below the surface and a Nortek Aquadopp Profiler (ADCP) on the seafloor of the Snohomish River. The CTD captures temperature, salinity, chlorophyll, turbidity, and dissolved oxygen measurements at 30-minute intervals. The ADCP measures current speed, direction, and velocity in three dimensions through sound wave scattering. In addition, a chain of DS18B20 temperature sensors has been deployed at .3 meter increments to a depth of two meters in order to profile temperature gradients in the water column. This study will quantitatively define water column mixing in terms of vertical current velocity and sediment concentrations. Various chemical properties will then be correlated with this mixing, providing an overarching view of the water column

Long-Term Performance of Pavement Markings on Primary and Secondary Roads

This research analyzes waterbased and thermoplastic pavement markings on primary and secondary roads in South Carolina. The primary objective of this research was to develop retroreflectivity degradation models for these two pavement marking materials, as well as determine the expected useful life of the markings. Predicting retroreflectivity and marking life is important so that state DOTs may efficiently replace markings in order to reduce safety hazards as well as maintenance costs. Data collection for this research lasted 21 months, where retroreflectivity of pavement markings was measured on over 100 primary and secondary roads in South Carolina. Variables such as marking type, date of application, traffic volume, among others were collected during this data collection period. Stepwise regression was performed to determine which variables were significant. Simple and multiple linear regression was completed to develop degradation models. These models were enhanced with the addition of buffer zones, which reduces the frequency of model over-prediction. Final degradation models were then created for waterbased and thermoplastic markings, along with estimated marking lives based on an assumed minimum retroreflectivity. The result of this research is a set of fully-functional models that state DOTs and other governing agencies may use in their pavement marking management systems