Periodic Planar Disk Packings

Several conditions are given when a packing of equal disks in a torus is locally maximally dense, where the torus is defined as the quotient of the plane by a two-dimensional lattice. Conjectures are presented that claim that the density of any strictly jammed packings, whose graph does not consist of all triangles and the torus lattice is the standard triangular lattice, is at most $\frac{n}{n+1}\frac{\pi}{\sqrt{12}}$, where $n$ is the number of packing disks. Several classes of collectively jammed packings are presented where the conjecture holds.Comment: 26 pages, 13 figure

Charting New Ground: The Ethical Terrain of Nonprofit Journalism

A different kind of revenue, one that has nothing to do with advertising or subscriptions, is playing a larger role in journalism today. Nonprofit funding, once largely the province of public broadcasting, is becoming an important source of support for a new cohort of non-commercial news organizations -- many of them digital natives -- and a growing number of commercial news publishers, which are partnering with nonprofit media and in some cases accepting direct grants themselves. But the ethics of taking grants from foundations and gifts from donors to produce news is still evolving and not without controversy. In New York, a major public TV station returned a large journalism grant for a documentary series because of the donor's connection to the topic being covered. In New Orleans, a nonprofit media organization's reporting about a university president may have cost the organization's its office space at the school. In Texas, a nonprofit established new transparency rules after criticism that it was not revealing enough about donors and event backers. The role of nonprofit media outlets also seems likely to grow. In Philadelphia, the new owner of city's major newspapers is transferring ownership of the publications to a new nonprofit organization, a case being closely watched to see if it might become a model. This report, by the American Press Institute, explores the ethical terrain of nonprofit journalism by examining the kinds of grants made, the nature of communication between funders and grantees, the existence of journalistic firewalls, and the prevalence of written guidelines. The report is based on two main elements: surveys of funders, nonprofit news organizations and commercial partners about a range of funding and ethical issues; and five essays commissioned by people from various media and foundation stakeholder groups that explore different areas of ethical complexity. In a second phase, the study will be followed by recommendations for ethical guidelines

Establishment of a District Media Center in Ottawa School District 141

The study consisted primarily of an evaluation on the media program in the Ottawa Elementary School District 141 and recommendations for improving this program. A key element in improving the program is the establishment of a district media center. The study begins with a review of the literature concerning the role of the media in schools, the value of coordinating media programs, and the role played by district media centers. The paper explains the categories used in evaluating the schools and examines each in relationship to the established criteria set forth in Standards for Educational Media (Library and Audiovisual) Programs in Illinois. This chapter also examines the district media centers in Mattoon District Number 2 and Gillespie Unit Number 7 in order to provide comparison with existing programs in Ottawa. The Mattoon and Gillespie programs were compared with the guidelines suggested in Standards for Educational Media (Library and Audiovisual) Programs in Illinois for district media centers in an effort to provide uniformity of evaluative data for comparison with the Ottawa District. Each of the nine grade schools in District 141 was evaluated in terms of its individual media program. The criteria used in evaluating each program were: equipment, space, personnel, and software. Each of these categories was compared to the recommendations suggested by Standards for Educational Media (Library and Audiovisual) Programs in Illinois. The personal opinions of the administrator of each school were solicited in order to determine how they felt about the possible value of a district media center and its possible benefit to his particular school. Chapter III procedes to draw the conclusion that the individual media programs do not conform to the Standards for Educational Media (Library and Audiovisual) Programs in Illinois. Using the standards as a guide, the study made recommendations concerning steps each school should take to improve its media program. The study recommends the establishment of a district media center for an orderly upgrading of the media program. The study then recommends, what the structure of the district media center should be, using the guidelines suggested in the standards. The study makes recommendations concerning staffing of a district media center, altering the suggested standards to conform to local conditions. Also, a plan was developed for the establishment of a distribution service for the district. Chapter III also recommends a particular location for a district media center based on local conditions. Recommendations are also made concerning the type of equipment necessary to establish a district media center. The last element of Chapter III discusses how District 141 would benefit from establishing a district media center. It also reviews the literature to give support to the value of media

Scales of Variability in the Size Composition and Community Structure of Fishes in Estuarine Ecosystems

Fishing, other human activities, and natural perturbations can alter the species composition and size structure of fish communities in coastal ecosystems. Normalized biomass size spectra (NBSS) and other metrics based on size and abundance of fish communities are sensitive to effects of fishing and have been proposed as useful tools for ecosystem-based management. However, these approaches based on size and abundance are unevaluated at temporal and spatial scales relevant for management within estuaries. Because individual species have important ecological and economic value, tracking temporal and spatial changes in the species composition of the fish communities using multivariate analyses, such as principal component analysis (PCA), can facilitate interpretation of patterns observed in the NBSS. A goal of my dissertation was to determine if indicators suitable for ecosystem-based management can be derived from NBSS parameters and other metrics based on size and abundance for estuarine fish and plankton communities at relatively small temporal and spatial scales. Additionally, I sought to elucidate effects of temporal and spatial variability in species composition on community size structure of estuarine fish communities by combining multivariate and NBSS analyses. Analyzing data from multiple fisheries-independent surveys and water quality monitoring programs, the objectives of my dissertation were 1) to describe and quantify the size distribution and community composition of fish and plankton in Chesapeake Bay at temporal scales ranging from months to over a decade and at spatial scales ranging from 18 km to 100 km, 2) to evaluate long-term trends in abundance, size distribution, and species composition of fish communities in Chesapeake Bay and Pamlico Sound, and 3) to analyze environmental variables and their effects on community structure and size distribution of biological communities in the Chesapeake and Pamlico Sound estuaries. Results supported the conclusion that NBSS combined with traditional community analyses permits detection of changes in ecosystem status, facilitates identification the species associated with the observed variability, and provides a framework to establish management reference points

From Design To Denial- An Environmental Histroy Of The United States Chemical Weapons Program

In 1993, the affluent Washington D.C. neighborhood of Spring Valley was unaware of what lurked beneath their carefully manicured lawns and million-dollar homes. Contractors hired by a resident to build an inground pool suddenly found themselves short of breath and half the crew had to be rushed to the hospital suffering respiratory distress, internal blistering of the lungs, and vision problems. The symptoms they exhibited matched all the characteristics of the World War I era blister agent lewisite. This thesis is an environmental study of chemical weapons that aims to contribute to the overall history of these weapons and their disposal by looking beyond diplomacy and development and focusing on how production and disposal of chemical weapons have affected ecosystems, impacting both human and non-human actors in significant ways. Spring Valley is just one of the more prominent examples of negligent chemical weapons disposal by the military. Numerous other incidents have occurred across the United States since 1993 including a host of chemical agents produced both during and after the Great War including sulfur mustard, chloropicrin, phosgene, and VX gas. By looking at the deep and expansive footprint left by the American chemical weapons program, this study will show how disposal methods used during the twentieth century and continuing through the twenty-first century contributed to the disruption of delicate ecosystems and the continued marginalization of classes of citizens who have been denied agency in decisions regarding the locations and methods used for destruction of America’s aging chemical weapons arsenal

Potomac River Pound-Net Survey Summer 1996: 1996 annual report

This survey had the following goals: (1) collect length and weight data on fishes captured in pound nets in the Potomac River; (2) collect length data of fish captured and released or discarded at-sea; and (3) establish length weight relations in summary statistics to provide baseline data

Variable action potential backpropagation during tonic firing and low-threshold spike bursts in thalamocortical but not thalamic reticular nucleus neurons

Backpropagating action potentials (bAPs) are indispensable in dendritic signaling. Conflicting Ca2-imaging data and an absence of dendritic recording data means that the extent of backpropagation in thalamocortical (TC) and thalamic reticular nucleus (TRN) neurons remains unknown. Because TRN neurons signal electrically through dendrodendritic gap junctions and possibly via chemical dendritic GABAergic synapses, as well as classical axonal GABA release, this lack of knowledge is problematic. To address this issue, we made two-photon targeted patch-clamp recordings from rat TC and TRN neuron dendrites to measure bAPs directly. These recordings reveal that “tonic”’ and low-threshold-spike (LTS) “burst” APs in both cell types are always recorded first at the soma before backpropagating into the dendrites while undergoing substantial distance-dependent dendritic amplitude attenuation. In TC neurons, bAP attenuation strength varies according to firing mode. During LTS bursts, somatic AP half-width increases progressively with increasing spike number, allowing late-burst spikes to propagate more efficiently into the dendritic tree compared with spikes occurring at burst onset. Tonic spikes have similar somatic half-widths to late burst spikes and undergo similar dendritic attenuation. In contrast, in TRN neurons, AP properties are unchanged between LTS bursts and tonic firing and, as a result, distance-dependent dendritic attenuation remains consistent across different firing modes. Therefore, unlike LTS-associated global electrical and calcium signals, the spatial influence of bAP signaling in TC and TRN neurons is more restricted, with potentially important behavioral-state-dependent consequences for synaptic integration and plasticity in thalamic neurons