Study of channel sediments, James River & Hampton Roads area

Bottom sediment samples were collected from 3 locations transecting the channel in the lower James and Elizabeth rivers

Učinak Butadin-akrilnog umreživača na udarnu čvrstoću poli(metilmetakrilata)

A cross-linking agent, ethylene glycol dimethacrylate, which is added to poly (methyl methacrylate) (VMMA) denture base resins to improve crazing resistance, has little effect on the mechanical properties o f the resultant denture base. A poly functional cross-linking agent, butadiene acrylate (BDA), has been considered to have a greater cross-linking efficiency and thus altering the mechanical properties. The purpose o f this study was to investigate the effect o f BDA on the impact strength o f a PMMA specimens containing 0%, 1%, 4% and 12% BDA o f monomer volume which had been produced by a conventional dental dough-moulded technique as determined. Mean impact strengths were 1.789 KJ/m2 (SD 0.254), 1.720 KJ/m2 (SD 0.273); 1.715 KJ/m2 (SD 0.280) and 1.838 KJ/m2 (SD 0.244), respectively. These differences were not significant (p >0.05) as tested by the analysis o f variance. It was concluded that the cross-linking agent BDA did not affect the impact strength of the PMMA resin specimens.U svrhu povećanja otpornosti poli(metilmetakrilatnih) proteznih smola na lomove i stvaranje napuklina, monomer-kapljevini se tvornički dodaje tvar za umrežavanje, najčešće etilen-glikol-dimetakrilat (EGDMA), koji se u tome smislu nije pokazao učinkovitim. Ovo istraživanje je provedeno s pretpostavkom da bi polifunkcionalna tvar za umrežavanje, kao što je to butadin - akrilat (BDA), mogla imati veći učinak na umrežavanje i poboljšanje mehaničkih svojstava poli(metilmetakrilatnih) smola. Ispitivana je udarna čvrstoća Zwick-postupkom poli(metilmetakrilatnih) pripravaka, podijeljenih u četiri skupine s obzirom na količinu tvari za umreživanje (0%, 1%, 4% i 12%), te dobivenih uobičajenom kivetnom tehnikom oplopolimerizirajućeg postupka. Vrijednosti za udarnu čvrstoću pripravaka po skupinama iznosile su: 0% BDA - 1,789 KJ/m2 (SD 0,254); 1% BDA - 1,720 KJ/m2 (SD 0,273); 4% BDA - 1,715 KJ/m2 (SD 0,280) i 12% BDA - 1,838 KJ/m2 (SD 0,244), a razlike među skupinama nisu se pokazale statistički značajnim (p > 0,05). Zaključeno je da istraživana tvar za umrežavanje (BDA) nije doprinijela poboljšanju udarne čvrstoće poli(metilmetakrilatnih) pripravaka

The Effect Of Tropical Storm Agnes On Heavy Metal And Pesticide Residues In The Eastern Oyster From Southern Chesapeake Bay

The concentrations of cadmium, copper, and zinc in the eastern oyster, Crassostrea virginica, are compared for samples collected before and after Tropical Storm Agnes. The before samples consisted of 475 animals from 95 stations collected in January 1971 and the after samples of 285 animals from 57 stations collected in January 1973. Shifts in the areal concentrations distributions were observed, apparently due to Agnes. Analyses of hard clams, blue crabs and oysters for chlorinated hydrocarbon pesticides showed influx of these compounds to be minimal as reflected by the residue levels observed. Comparison of residue levels in oysters to pre-Agnes conditions revealed a decrease in pesticide body burden.https://scholarworks.wm.edu/vimsbooks/1069/thumbnail.jp

Methods for measuring ecosystem stress

If one looks back over the past twenty-five years, at the pollution crises which have made the headlines and influenced our decision making policies on both local and national levels, one may note a very interesting aspect. That is, the crises are often associated with the development of new and more sensitive types of analytical instrumentation. Several examples of this readily come to mind: for example, it wasn\u27t until the development of electron capture detection for gas chromatography that DDT really became a crisis. The reason is quite simple: the concentrations which were being accumulated by the organisms were below detection limits of most available instrumentation. Another example is mercury. The advent of atomic absorption spectrophotometry and the refinement of the the flameless method for mercury allowed the mercury problem to be investigated. New instrumentation doesn\u27t cause the crisis, it merely finds it.https://scholarworks.wm.edu/vimsbooks/1135/thumbnail.jp

Organic Chemicals in Sediments from the Lower Chesapeake Bay

Many of the toxic organic chemicals affecting the marine environment are hydrophobic and associate with sediments. Sediments can accumulate the substances over long intervals and store them after the original source of the toxic material has been eliminated. Contaminated sediments can provide small but damaging amounts of the to.xicant to the overlying water for decades. For example, more than 10 years after the discovery of Kepone in the James River, Virginia, much of the James\u27 fisheries ·is still closed because Kepone levels are above federal action levels.https://scholarworks.wm.edu/vimsbooks/1166/thumbnail.jp

Contaminants in Chesapeake Bay: The Regional Perspective

Industrial and municipal point sources of contaminants are scattered along the shores of Chesapeake Bay and its tributaries, but reach especially high density at Norfolk, Va., and Baltimore, Md. Sedimentation and various chemical processes in many cases conspire to restrict the water-borne transport of contaminant away from point source . Kepone, residual chlorine, volatile halogenated hydrocarbons, and anthropogenic trace metals are well-studied example of point-source contaminants. For the most part, their concentration in water and sediment drop to nearly immeasurable values within a distance of a few kilometers, or sometimes a few tens of kilometers, from their source . On the other hand, certain contaminants have now been shown to be truly regionally dispersed. Included are polychlorinated biphenyls, phthalate esters, anthropogenic trace metal (Cu, Zn, Pb), polycyclic aromatic hydrocarbons, herbicides and weapon derived radionuclides. Most of these enter the Bay in significant amount from the atmosphere. Thus their dispersion throughout the Bay is not dependent on aquatic tranport processes. Although it is tempting to link the existence of this regional contamination with well publicized regional biological problem , no link has yet been proven.https://scholarworks.wm.edu/vimsbooks/1058/thumbnail.jp

Long Term Culture of Hepatocytes of Some Fish Species of the Chesapeake Bay

The liver is an important site of metabolism and effects of toxic chemicals. This makes it an important organ for tumorigenesis studies. This study was aimed at investigating the optimal culture characteristics of liver cells derived from some indigenous Chesapeake Bay fish species. Hepatocytes from Atlantic -menhaden (Brevootia tyraMus), toadfish (Opsanus tau), croaker (Micropogonius undulatus), and hogchocker (Trinectes maculatus) were isolated using an enzymatic dispersion technique. The highest yield was obtained from toadfish livers (14.9±5. lx 1 o5 cells/g oflive weight) and the lowest was from the croaker (5.9±3. lx 1 o5 cells/g of live body weight). The percentage of hepatocytes in cell preparations exceeded 90% except for the toadfish liver cells preparation (82.3%). Freshly isolated hepatocytes were globular with irregular contour and occurred as individual cells or small clusters of 2-30 cells. A confluent monolayer of attached cells was obtained after two weeks of incubation. An osmolality of 325 m Osm/kg best supported the multiplication of hepatocytes of the four fish species. While the optimum temperature for hogchocker and toadfish hepatocytes appeared to be 33oC; it ranged from 21-27oC for menhaden and croaker. The medium that best supported the growth of culture The potential of long term hepatocyte culture using fish of Chesapeake Bay will enable further studies on the activation and detoxification processes of xenobiotics and, therefore, help in understanding pollution related neoplasia and diseaseshttps://scholarworks.wm.edu/vimsbooks/1181/thumbnail.jp

Properties of an ionization spectrometer exposed to 10, 20.5, and 28 GeV/c machine accelerated protons

Properties of ionization spectrometer exposed to 10, 20.5, and 28 GeV/c synchrotron accelerated proton