Electronic and optical properties of electromigrated molecular junctions.

Electromigrated nanoscale junctions have proven very useful for studying electronic transport at the single-molecule scale. However, confirming that conduction is through precisely the molecule of interest and not some contaminant or metal nanoparticle has remained a persistent challenge, typically requiring a statistical analysis of many devices. We review how transport mechanisms in both electronic and optical measurements can be used to infer information about the nanoscale junction configuration. The electronic response to optical excitation is particularly revealing. We briefly discuss surface-enhanced Raman spectroscopy on such junctions, and present new results showing that currents due to optical rectification can provide a means of estimating the local electric field at the junction due to illumination.

Further observations on mesenteric vasoconstriction, survival and the clotting defect after endotoxin administration.

1. The initial response after endotoxin administration (3 mg/kg) in cats involved pulmonary vasoconstriction. This was not seen when endotoxin was given by slow infusion and it could be prevented after a bolus injection of endotoxin by pretreatment of the cats with aspirin (10 mg/kg). Intense mesenteric vasoconstriction occurred in all the cats.2. The mesenteric vasoconstriction was a specific response of the mesenteric blood vessels. At the time the mesenteric bed constricted, the renal bed dilated, the hepatic arterial bed remained unchanged and the smooth muscle of the intestinal wall relaxed.3. Arterial blood from cats with a fully developed mesenteric vasoconstriction after endotoxin administration was perfused through a normal intestine. No immediate vasoconstriction developed but the perfused intestine constricted slowly over 60 minutes. This suggests that mesenteric constriction was not due to circulating vasoconstrictor factors or the intestinal innervation, but involved a slow local mechanism within the intestine. It could not be prevented or reversed by a variety of pharmacological agents.4. These observations suggest that endotoxin caused a unique type of mesenteric vasoconstriction in cats by a local mechanism which took up to 60 min to develop, was sufficiently potent to reduce mesenteric flow to <30% control, and was maintained until death of the cats. Blood from these animals did not clot when placed in a glass tube.5. The mesenteric constriction and the clotting defect could be prevented by repeated administration of aminophylline and dextran solution before and after a bolus intravenous injection of endotoxin. Arterial pressure and mesenteric flow were maintained for at least 10 h in these experiments. Inadequate treatment intensified rather than reduced the intestinal mucosal damage.6. Cats were treated with aspirin, endotoxin and the optimal regimen for prevention of the mesenteric constriction and allowed to recover from the anaesthetic agent. In this series, 63% survived indefinitely compared to 25% after aspirin and endotoxin treatment and 0% after endotoxin alone.7. The possible mechanisms of action of aspirin and aminophylline-dextran solution are discussed. Our failure to obtain 100% survival is probably due to pulmonary damage which develops 10-24 h after endotoxin administration. This delayed pulmonary action of endotoxin is not prevented by aspirin treatment and it seems unlikely that aspirin will be of any value in the treatment of the pulmonary lesion in man.

NMR probing of spin excitations in the ring structure of a two-subband system.

Resistively detected nuclear magnetic resonance (NMR) is observed inside the ringlike structure, with a quantized Hall conductance of 6e(2)/h, in the phase diagram of a two-subband electron system. The NMR signal persists up to 470 mK and is absent in other states with the same quantized Hall conductance. The nuclear spin-lattice relaxation time T1, is found to decrease rapidly towards the ring center. A strong dynamic nuclear polarization by the biasing current has also been observed only inside the ring. These observations are consistent with the assertion of the ringlike region being a ferromagnetic state that is accompanied by collective spin excitations.

The newly released prisoner.

This paper deals with the problems faced by offenders in a category of short-term, bit-term and long-term incarceration. Each group has characteristics which mitigate against unassisted rehabilitation. In a country burdened by unemployment of skilled and well-educated people, the criminal releasee is at a great disadvantage and often finds the freedom of prison more comfortable than the captivity of society. The bleak and forlorn futures of offenders vary in intensity. Certain recommendations are made in this paper which could prevent future criminal involvement.

Quantitative integration of the cardiovascular system and synthesis of drug actions: another attempt.

This article describes the latest version of a computer program, first published in 1982, that attempts to integrate quantitatively the physiological and pharmacological knowledge of the cardiovascular system. This new version incorporates pressure-induced autoregulation of arterioles, distensibility of venous and pulmonary resistances, and some aspects of pericardial constraint on cardiac function. The program allows the researcher or student to explore the complex interactions resulting from changes in a wide variety of cardiovascular parameters and to synthesize the cardiovascular actions of drugs in the human, dog, or cat. The program can be run on an IBM-compatible computer with math coprocessor and with DOS as the operating system. The program can be modified by licensed users of QuickBasic. The program is available on diskette from the authors. This model represents our attempt to put together some of the complex interactions within the cardiovascular system. Every relationship, every initialized parameter, and every drug action can be questioned and alternatives can be proposed. However, the model allows these alternatives to be tested and their consequences to be predicted. We believe that the value of the model lies in the thought, discussion, and experiments that can be generated by this process.

Attenuated total reflection angular spectra and associated resonant electromagnetic oscillations of a dielectric slab bounded by Ag films.

The attenuated total reflection (ATR) angular spectra of a layered system of Ag-MgF(2)-Ag, sandwiched between glass and air, have been measured at three different wavelengths in the visible region. Resonant electromagnetic (EM) oscillations are detected as narrow minima in the reflectance and sometimes as accompanying maxima in the transmittance of both p- and s-polarized light. Detailed calculations of the resonant EM fields illustrate the nature of the oscillations. Discrepancies between theory and experiment are thought to be due largely to the surface roughness of evaporated MgF(2) films. A cermet layer is imagined to form at the MgF(2)-Ag interface, and also an induced roughness layer at the Ag-air interface. When the optical constants of the cermet and roughness layers are evaluated by the Maxwell Garnett theory, the discrepancies for both polarizations can be accounted for in a consistent manner at all three wavelengths.

Attenuated total reflection angular spectra of a system of alternating plasma-dielectric layers.

The attenuated total reflection (ATR) angular spectra of a five-film system have been observed. Successive layers of Ag-LiF-Ag-LiF-Ag are evaporated onto the base of a glass prism. Surface plasma wave resonances corresponding to coupled oscillations at the plasma-dielectric interfaces were found for p-polarization. Guided light modes coupled between the two dielectric layers were observed in both p- and s-polarized spectra. If guided mode reflectance resonances occur at less than the critical angle they have associated with them resonance transmissions. In general the ATR resonances of the five-film system occur as doublets, which form a splitting of the resonances of a single dielectric slab bounded by Ag layers. The resonant oscillations are demonstrated by detailed calculations of the Poynting vector field and electric field oscillations, which also help in understanding the source of discrepancies between experimental and calculated ATR spectra. These discrepancies are thought to be due largely to the surface roughness of evaporated LiF films. The roughness is modeled as thin cermet layers at the LiF-Ag interfaces, and the optical constants of the cermets are calculated by the Maxwell Garnett theory. When the ATR spectra are then computed with the pseudolayers inserted, much improved agreement with experiment can be obtained.

Sites of autoregulatory escape of blood flow in the mesenteric vascular bed.

1. Stimulation of the sympathetic nerves to the intestinal vascular bed results in an initial decrease in blood flow followed by a recovery towards the control level. This recovery was termed autoregulatory escape by Folkow and his co-workers and they suggested it was associated with a redistribution of blood flow within the intestinal wall. This theory has been examined in cats anaesthetized with pentobarbitone sodium. 2. The sympathetic nerves to the intestinal vascular bed were stimulated for 4 min periods at a submaximal frequency (4 Hz). The blood flows to individual parts of the superior mesenteric arterial bed (whole intestine, mucosal and submucosal layer, muscle layer of intestine, mesentery and lymph nodes, appendix and colon) were measured using radioactive microspheres before, at the peak of the vasoconstriction (30 sec), after autoregulatory escape had occurred (3-5 min) and during the hyperaemia after cessation of nerve stimulation. 3. All parts of the mesenteric vascular bed showed a significant initial vasoconstriction followed by a recovery in the flow to a level not significantly different from the pre-stimulation control flow. All parts showed a significant hyperaemia after cessation of stimulation. The distribution of the superior mesenteric flow at the peak of the vasoconstriction, after autoregulatory escape had occurred and during the hyperaemia after cessation of nerve stimulation was not significantly different from that during the control period. 4. It is concluded that all parts of the mesenteric vascular bed show autoregulatory escape and that this phenomenon is not associated with a redistribution of blood flow within the intestinal wall. Autoregulatory escape must involve relaxation of the same vessels which were originally constricted and various theories on the mechanism of the escape are discussed.

Optical properties of aggregated gold on aluminum.

The optical reflectances of evaporated deposits of gold on aluminum have been measured in the visible and IR regions. Aggregation of the gold and diffusion of the aluminum into the gold by heat treatment produces surfaces with high absorptance in the visible and high reflectance in the infrared, characteristics required of selective solar absorbers. The effects of prolonged heating at 350 degrees C are shown to be slight.

Venoconstriction of hepatic capacitance vessels during hemorrhage in cats: efferent mechanisms.

Cats anesthetized with pentobarbital sodium were hemorrhaged (1 ml.min-1.kg body wt-1) until arterial pressure declined to 55 mmHg. Hepatic volume was recorded by plethysmography. In controls, 20 +/- 5 (SD) ml/kg was removed and hepatic volume decreased 3.6 +/- 0.8 ml/kg. Splanchnic nerve section or administration of hexamethonium-atropine reduced hemorrhage volumes (to 10.3 +/- 2.3 and 4.8 +/- 1.8 ml/kg, respectively) and liver volume changes (to 1.5 +/- 0.5 and 0.7 +/- 0.3 ml/kg, respectively). Section of only the hepatic nerves had no effect on hemorrhage volume or the decrease in hepatic volume. Section of the hepatic nerves after removal of the adrenals and kidneys also had no significant effect on hemorrhage volume or the decrease in liver volume. We conclude that the hepatic capacitance response to hemorrhage does not require direct sympathetic venoconstriction of the hepatic capacitance vessels. Changes in inferior vena caval pressure play a significant but small role. The splanchnic nerves (excluding hepatic nerves) play a major role, possibly by splanchnic arteriolar constriction. Whereas the liver comprises only 2.5% of the body weight, it contributed 18% of the hemorrhage volume.

Pre- and post-sinusoidal origin of hepatic exudate in anesthetized cats.

In cats anesthetized with pentobarbital, hepatic venous pressure was increased to cause drops of exudate to appear on the surface of the liver. These drops were collected during steady-state infusions of small doses of ethanol and galactose when there was a large arteriovenous gradient across the liver. Comparison of the concentrations of these substances in arterial, portal, and hepatic venous blood and exudate showed that the exudate concentrations were slightly higher than the hepatic venous concentrations but markedly lower than arterial and portal blood concentrations. We conclude that the exudate cannot be entirely formed in the space of Mall (presinusoidal) but a substantial part is postsinusoidal in origin. If the exudate is a mixture of fluids equilibrated with inflowing and outflowing blood, then 75-80% of the exudate is postsinusoidal and 20-25% is presinusoidal in origin.

Venoconstriction of hepatic capacitance vessels during hemorrhage in cats: afferent mechanisms.

Cats anesthetized with pentobarbital sodium were hemorrhaged (1 ml.min-1.kg body wt-1) until arterial pressure declined to 55 mmHg. Hepatic volume was recorded by plethysmography. Hemorrhage volume was 21.1 +/- 4.7 (SD) ml/kg, and hepatic volume declined by 4.0 +/- 1.7 ml/kg. These responses were markedly reduced by four procedures that prevented decreases in carotid arterial and central venous pressures and eliminated vagal conduction. When any three of these four procedures were carried out, the remaining stimulus caused a significant increase in the size of the hepatic volume decrease. The results suggest that arterial receptors (baro- and/or chemoreceptors) in the carotid arterial bed or brain and venous baroreceptors in the right atrium and superior and inferior venae cavae are involved in hepatic capacitance responses to hemorrhage. The responses were linearly related to the stimuli, and hepatic blood volume changed by 1.7 +/- 1.1 and 0.030 +/- 0.016 ml/kg for each 1-mmHg change in venous and carotid arterial pressures, respectively. The maximal responses to these afferent stimuli applied individually were not significantly different (-4.2 +/- 1.8 ml/kg) and were not additive, suggesting overlapping redundant systems. The possibility of baroreceptors in superior vena cava has not previously been documented.

Plasma catecholamines in normal pregnancy and in pregnancies complicated by mild chronic hypertension.

Plasma epinephrine and norepinephrine were measured throughout pregnancy in an ambulatory population of normal and untreated chronically hypertensive pregnant women. There was no significant difference between trimesters for plasma epinephrine, norepinephrine, or the ratio epinephrine/norepinephrine in either the normal or chronically hypertensive group. In the first trimester of pregnancy, women with chronic hypertension demonstrated a significantly higher plasma norepinephrine and a significantly lower epinephrine/norepinephrine ratio than normal women.

Changes in hepatic blood volume on galactose and indocyanine green uptake by cat liver.

The liver has important functions as a blood volume reserve and in uptake and metabolism of many substrates. This study examines whether changes in hepatic blood volume modify the uptakes of model substrates galactose and indocyanine green (ICG) in cats anesthetized with pentobarbital sodium. A hepatic venous long-circuit technique with an extracorporeal reservoir was used to control hepatic flow and venous pressure and to allow repeated sampling of arterial, portal, and hepatic venous blood without depletion of the cat's blood volume. Hepatic blood volume was measured by plethysmography. Galactose and ICG were infused intravenously at constant rates for 200 min in each of three series of experiments. The first series were time controls. In the second series, hepatic blood volume was increased by raising hepatic venous pressure. In the third series hepatic blood volume was decreased by hepatic nerve stimulation and infusions of norepinephrine and angiotensin. Hepatic congestion resulted in small increases in blood galactose levels, suggesting mild impairment of hepatic galactose metabolism. Decreases in liver blood volume did not modify hepatic galactose metabolism. Increases in hepatic blood volume facilitated while decreases inhibited ICG uptake, but the effects were small. Sinusoidal velocity and transit time have minor effects on uptake even for protein-bound substrates. In summary, large changes in hepatic blood volume had minor effects on galactose and ICG blood concentrations, suggesting that the metabolic functions of the liver are essentially independent of the blood reservoir function.

The effects of hydrocortisone on the development of the amine systems in the fetal brain.

Human and animal studies suggest impaired central nervous system (CNS) development due to corticoid use in the perinatal period. In this study, hydrocortisone was given to pregnant rats and the development of the fetal dopamine (DA) and norepinephrine (NE) systems in the CNS was investigated. In the fetal rat brain DA and NE systems develop between days 12 and 17 of gestation. Hydrocortisone (HC), 57 mg/kg/day, or saline (SAL) was given intraperitoneally at day 12 or 15 of gestation. The offspring were studied at days 20 to 21 of gestation and days 12 to 13 in the neonatal period. Brain amine systems were visualized using a modified cryostat glyoxylic acid histofluorescence method, and DA and NE levels were determined in whole brains by means of a radioenzymatic assay. The visualized amine systems were evaluated semiquantitatively for distribution and fluorescence intensity without previous knowledge of the administered drug. The amine systems of the HC and SAL groups showed an equal maturation. In both groups cell bodies were demonstrable in areas A1 to A13 and axon terminals in all examined final regions. The distribution and the fluorescence intensity did not show consistent differences for the HC and SAL brains. The concentrations of DA and NE were similar in the offspring of the SAL- and HC-treated animals. The results indicate that HC given during pregnancy does not influence the proliferation of amine cell bodies or the arrival of axon terminals in the regions where the synapses form.