Dynamics of cell–matrix mechanical interactions in three dimensions

The forces cells apply to their surroundings control biological processes such as growth, adhesion, development, and migration. In the past 20 years, a number of experimental techniques have been developed to measure such cell tractions. These approaches have primarily measured the tractions applied by cells to synthetic two-dimensional substrates, which do not mimic in vivo conditions for most cell types. Many cell types live in a fibrous three-dimensional (3D) matrix environment. While studying cell behavior in such 3D matrices will provide valuable insights for the mechanobiology and tissue engineering communities, no experimental approaches have yet measured cell tractions in a fibrous 3D matrix.

This thesis describes the development and application of an experimental technique for quantifying cellular forces in a natural 3D matrix. Cells and their surrounding matrix are imaged in three dimensions with high speed confocal microscopy. The cell-induced matrix displacements are computed from the 3D image volumes using digital volume correlation. The strain tensor in the 3D matrix is computed by differentiating the displacements, and the stress tensor is computed by applying a constitutive law. Finally, tractions applied by the cells to the matrix are computed directly from the stress tensor.

The 3D traction measurement approach is used to investigate how cells mechanically interact with the matrix in biologically relevant processes such as division and invasion. During division, a single mother cell undergoes a drastic morphological change to split into two daughter cells. In a 3D matrix, dividing cells apply tensile force to the matrix through thin, persistent extensions that in turn direct the orientation and location of the daughter cells. Cell invasion into a 3D matrix is the first step required for cell migration in three dimensions. During invasion, cells initially apply minimal tractions to the matrix as they extend thin protrusions into the matrix fiber network. The invading cells anchor themselves to the matrix using these protrusions, and subsequently pull on the matrix to propel themselves forward.

Lastly, this thesis describes a constitutive model for the 3D fibrous matrix that uses a finite element (FE) approach. The FE model simulates the fibrous microstructure of the matrix and matches the cell-induced matrix displacements observed experimentally using digital volume correlation. The model is applied to predict how cells mechanically sense one another in a 3D matrix. It is found that cell-induced matrix displacements localize along linear paths. These linear paths propagate over a long range through the fibrous matrix, and provide a mechanism for cell-cell signaling and mechanosensing. The FE model developed here has the potential to reveal the effects of matrix density, inhomogeneity, and anisotropy in signaling cell behavior through mechanotransduction.

Effect of nonuniform seismic input on arch dams

Standard earthquake analyses of civil engineering structures use uniform ground motions even though considerable variations in both amplitude and phase can occur along the foundation interface for long-span bridges and large dams. The objective of this thesis is to quantify the effect that these nonuniformities have on the structural response.

The nonuniform, free-field motions of the foundation interface are assumed to be caused by incident plane body waves. The medium in which these waves travel is a linear, elastic half-space containing a canyon of uniform cross section in which the structure is placed. The solutions for the free-field motions that are due to incident SH, P and SV waves are calculated using the boundary element method.

An analysis of Pacoima (arch) dam located near Los Angeles, California, is performed for both uniform and nonuniform excitations. The important effect of nonuniformities in the free-field motions, sometimes leading to a decrease in the dam response and sometimes to an increase, is quantified.

Legal dimensions of the Chinese experience in Los Angeles, 1860-1880

On October 24, 1871, a massacre of eighteen Chinese in Los Angeles brought the small southern California settlement into the national spotlight. Within a few days, news of this “night of horrors” was reported in newspapers across the country. This massacre has been cited in Asian American narratives as the first documented outbreak of ethnic violence against a Chinese community in the United States. This is ironic because Los Angeles’ small population has generally placed it on the periphery in historical studies of the California anti-Chinese movement. Because the massacre predated Los Angeles’ organized Chinese exclusion movements of the late 1870s, it has often been erroneously dismissed as an aberration in the history of the city.

The violence of 1871 was an outburst highlighting existing community tensions that would become part of public debate by decade’s close. The purpose of this study is to insert the massacre into a broader context of anti-Chinese sentiments, legal discrimination, and dehumanization in nineteenth century Los Angeles. While a second incident of widespread anti-Chinese violence never occurred, brutal attacks directed at Chinese small businessmen and others highlighted continued community conflict. Similarly, economic rivalries and concerns over Chinese prostitution that underlay the 1871 massacre were manifest in later campaigns of economic discrimination and vice suppression that sought to minimize Chinese influence within municipal limits. An analysis of the massacre in terms of anti-Chinese legal, social and economic strategies in nineteenth-century Los Angeles will elucidate these important continuities.

Relationship of dimensions and weight in freshwater planktonic crustaceans. [Translation from: Doklady Akademii Nauk SSSR 84(1) 153-156, 1952. ]

There is no doubt that determination of the biomass of zooplankton (primarily of crustaceans) will be taken into consideration in practice and limnological works, especially after the recent publication of fairly comprehensive tables of weights of a whole range of species of freshwater copepods and cladocerans. The usefulness of applying formulae of determining the biomass of marine crustaceans for freshwater copepods is discussed.

Analysis of a concrete arch highway bridge reinforced with structural steel

An article in the Engineering News-Record for March 30, 1923, describes a new concrete arch bridge across the Connecticut River between Springfield and West Springfield, Mass.

Observations on the physiological development of trout eggs [Translation from: Roux. Arch. f. Entwicklungsmechanik der Organismen, 114. 771, 1929]

The osmotic pressure of the perivitelline fluid and the yolk of trout (Salmo trutta) eggs were measured separately by the Drucker-Schrein method. The permeability of the egg membrane and the variations in the osmotic pressure of the eggs when placed in salt solutions were also investigated.

Aspects of the washout of salmonid eggs. 6. Information on gravel composition , redd sites, the dimensions of redds and the depth of egg burial

Sampling was concentrated on the North Moor region and the series of ditches which drained this area to the Bristol Channel. Although most ditches were not deep the mud substratum precluded sampling from within the habitat. All samples were taken with a pond net from the banks. Efforts were made to sample each part of the habitat although in some ditches the macrophyte growth was so intense as to make sampling difficult particularly of the sediments. Organisms were identified on the 10 sampling sites.

The relationship of shell dimensions and shell volume to live weight and soft tissue weight in the mangrove clam, Polymesoda erosa (Solander, 1786) from northern Australia

Shell dimensions (length, height, width) and shell volume were evaluated as estimators of growth for Polymesoda erosa in northern Australia. Each parameter was a good estimator when applied to live weight (r2 values of 76-96 percent), but not to soft tissue weight (wet, dry, or ash-free dry weight) (r2 values of 13-32 percent). The b value for shell volume to weight relationship of clams collected during the dry season (June to October) was signifi cantly different than for those collected in the wet season (February to April).

Changing traditions: first global look at the gender dimensions of fisheries

The Asian Fisheries Society and the WorldFish Center conducted the first ever Global Symposium on Gender and Fisheries in Penang, Malaysia, from 30 November to 4 December 2004. The two-day Symposium, held in conjunction with the 7th Asian Fisheries Forum, attracted 30 papers by over 100 authors and strong audience discussions that covered countries from Kiribati, through Asia Pacific, Africa, Europe and to the Arctic. The flavor of the Symposium was of changing traditions and recognition of the contributions of different groups to fisheries.

Human Dimensions of Marine Fisheries: Using GIS to Illustrate Land-Sea Connections in the Northeast U.S. Herring, Clupea harengus, Fishery

Geographic Information Systems can help improve ocean literacy and inform our understanding of the human dimensions of marine resource use. This paper describes a pilot project where GIS is used to illustrate the connections between fish stocks and the social, cultural, and economic components of the fishery on land. This method of presenting and merging qualitative and quantitative data represents a new approach to assist fishery managers, participants, policy-makers, and other stakeholders in visualizing an often confusing and poorly understood web of interactions. The Atlantic herring fishery serves as a case study and maps from this pilot project are presented and methods reviewed.