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Biomedical subjects

J E Greene

Publications and source records attributed to J E Greene.

11 recordsLinked to original sources
PubMed2004

Dislocation-driven surface dynamics on solids.

Dislocations are line defects that bound plastically deformed regions in crystalline solids. Dislocations terminating on the surface of materials can strongly influence nanostructural and interfacial stability, mechanical properties, chemical reactions, transport phenomena, and other surface processes. While most theoretical and experimental studies have focused on dislocation motion in bulk solids under applied stress and step formation due to dislocations at surfaces during crystal growth, very little is known about the effects of dislocations on surface dynamics and morphological evolution. Here we investigate the near-equilibrium dynamics of surface-terminated dislocations using low-energy electron microscopy. We observe, in real time, the thermally driven nucleation and shape-preserving growth of spiral steps rotating at constant temperature-dependent angular velocities around cores of dislocations terminating on the (111) surface of TiN in the absence of applied external stress or net mass change. We attribute this phenomenon to point-defect migration from the bulk to the surface along dislocation lines. Our results demonstrate that dislocation-mediated surface roughening can occur even in the absence of deposition or evaporation, and provide fundamental insights into mechanisms controlling nanostructural stability.

Journal Article↗
PubMed2003

Self-organized superlattice formation during crystal growth from continuous beam fluxes.

Alloy superlattice structures consisting of alternating Si-rich and C-rich layers form spontaneously during gas-source molecular beam epitaxy of Si(1-y)C(y) on Si(001) from constant Si2H6 and CH3SiH3 precursor fluxes at T(s)=725-750 degrees C. The self-organized patterning is due to a complex interaction among competing surface reactions. During growth of the initial Si-rich layer, strain-driven C segregation to the subsurface results in charge transfer from surface Si atom dangling bonds to C backbonds. This decreases the Si2H6 sticking probability, and, hence, the instantaneous deposition rate, thereby enhancing C segregation. The Si-rich layer continues until a critical C coverage is reached allowing nucleation of a C-rich layer which grows until the excess subsurface C is depleted. The process then repeats with periods tunable through the choice of T(s) and y(avg).

Journal Article↗
PubMed2002

Size-dependent detachment-limited decay kinetics of two-dimensional TiN islands on TiN(111).

In situ high-temperature (T(a)=1050-1250 K) scanning tunneling microscopy was used to determine the coarsening and decay kinetics of two-dimensional TiN adatom and vacancy islands on atomically smooth TiN(111) terraces. We report the first observation of an abrupt decrease in decay rates, irrespective of T(a), of adatom islands with areas less than a critical value of 1600 A(2). However, no decay rate transition was observed for vacancy islands. We attribute the size-dependent island decay behavior, which is consistent with detachment-limited kinetics, to anisotropic attachment and detachment barriers.

Journal Article↗
PubMed2002

Absolute TiN(111) step energies from analysis of anisotropic island shape fluctuations.

In situ high-temperature (1165-1248 K) scanning tunneling microscopy was used to measure fluctuations around the equilibrium shape of two-dimensional vacancy islands on TiN(111) terraces. From the equilibrium shape, the ratio of the two <110> step energies was found to be 0.72 +/- 0.02. Combining this with the results of an exact approach for analysis of shape fluctuations, applicable to highly anisotropic islands, we obtain absolute values for step energies and step stiffnesses as a function of orientation.

Journal Article↗
PubMed1997

Role of epinephrine and norepinephrine in the metabolic response to stress hormone infusion in the conscious dog.

The role of epinephrine and norepinephrine in contributing to the alterations in hepatic glucose metabolism during a 70-h stress hormone infusion (SHI) was investigated in four groups of chronically catheterized (20-h-fasted) conscious dogs. SHI increased glucagon (approximately 5-fold), epinephrine (approximately 10-fold), norepinephrine (approximately 10-fold), and cortisol (approximately 6-fold) levels. Dogs received either all the hormones (SHI; n = 5), all the hormones except epinephrine (SHI-Epi; n = 6), or all the hormones except norepinephrine (SHI-NE; n = 6). In addition, six dogs received saline only (Sal). Glucose production (Ra) and gluconeogenesis were assessed after a 70-h hormone or saline infusion with the use of tracer ([3-(3)H]glucose and [U-(14)C]alanine) and arteriovenous difference techniques. SHI increased glucose levels (108 +/- 2 vs. 189 +/- 10 mg/dl) and Ra (2.6 +/- 0.2 vs. 4.1 +/- 0.3 mg x kg(-1) x min(-1)) compared with Sal. The absence of an increase in epinephrine markedly attenuated these changes (glucose and Ra were 140 +/- 6 mg/dl and 2.7 +/- 0.4 mg x kg(-1) x min(-1), respectively). Only 25% of the blunted rise in Ra could be accounted for by an attenuation of the rise in net hepatic gluconeogenic precursor uptake (0.9 +/- 0.1, 1.5 +/- 0.1, and 1.1 +/- 0.2 mg x kg(-1) x min(-1) for Sal, SHI, and SHI-Epi, respectively). The absence of an increase in norepinephrine did not blunt the rise in arterial glucose levels, Ra, or net hepatic gluconeogenic precursor uptake (they rose to 195 +/- 21 mg/dl, 3.7 +/- 0.5 mg x kg(-1) x min(-1), and 1.7 +/- 0.2 mg x kg(-1) min(-1), respectively). In summary, during chronic SHI, the rise in epinephrine exerts potent stimulatory effects on glucose production principally by enhancing hepatic glycogenolysis, although the rise in circulating norepinephrine has minimal effects.

Animals↗
PubMed1991

Do public cholesterol screenings really screen?

Two hospital-sponsored cholesterol-screening programs were evaluated to assess whether they detected individuals with undiagnosed high blood cholesterol. Surveys asking about prior testing, knowledge of cholesterol level, and participant characteristics were examined to test screening utilization. In both screenings 54% of participants reported having prior cholesterol testing, only 56% of whom knew their cholesterol level. Of previously untested participants, 8% had high blood cholesterol levels and 13% had borderline levels. Only 65% of participants with a personal or family history of heart attack were aware of their cholesterol level. To attract individuals without prior testing, screening planners should consider locations (eg, worksites and schools) and methods (eg, weekend screenings) to target underrepresented groups in community-wide cholesterol screenings. We encourage an increased emphasis on individualized exit education for participants, especially those who know their cholesterol level or have multiple risk factors for vascular disease. Physicians planning public screenings can utilize this data to develop parameters for referrals from the screenings.

Adult↗
PubMed1983

Ureteric stone extraction by a new double-balloon catheter: an experimental study.

An atraumatic double-ballooned catheter was designed to extract endoscopically ureteral calculi of relatively large size (1 to 1.5 cm.) arrested at any level of the ureter. This reduces the need for ureterolithotomy, eliminates the problems of stone basket manipulations, and reduces the need for prolonged waiting for spontaneous migration of stones.

Animals↗
PubMed1975

Spontaneous pyeloduodenal and renocolic fistulas.

Twenty-seven previously reported cases of pyeloduodenal fistulas are reviewed and the first case of a simultaneously occurring pyeloduodenal and renocolic fistula is reported. Pyeloduodenal fistulas appear to result from an inflammatory process originating in the kidney, frequently are associated with calculi, and are best managed surgically with nephrectomy and closure of the fistula.

Colonic Diseases↗