Measurement Of Rapid Changes Research Articles

Quantitative Determination of Biogenic Volatile Organic Compounds in the Atmosphere Using Proton-Transfer Reaction Linear Ion Trap Mass Spectrometry

Although oxidation of biogenic volatile organic compounds (BVOCs) plays an important role in tropospheric ozone and secondary organic aerosol production, significant uncertainties remain in our understanding of the impacts of BVOCs on ozone, aerosols, and climate. To quantify BVOCs, the proton-transfer reaction linear ion trap (PTR-LIT) mass spectrometer was previously developed. The PTR-LIT represents an improvement over more traditional techniques (including the proton-transfer reaction mass spectrometer), providing the capability to directly quantify and differentiate isomeric compounds by MS/MS analysis, with better time resolution and minimal sample handling, compared to gas chromatography techniques. Herein, we present results from the first field deployment of the PTR-LIT. During the Program for Research on Oxidants: Photochemistry, Emissions and Transport (PROPHET) summer 2008 study in northern Michigan, the PTR-LIT successfully quantified isoprene, total monoterpenes, and isomeric isoprene oxidation products methyl vinyl ketone and methacrolein at sub-parts per billion (nmol/mol) levels in a complex forest atmosphere. The utility of the fast time response of the PTR-LIT was shown by the measurement of rapid changes in isoprene, methyl vinyl ketone, and methacrolein, concurrent with changing ozone mole fractions. Overall, the PTR-LIT was shown to be a viable field instrument with the necessary sensitivity, selectivity, and time response to provide detailed measurements of BVOC mole fractions in complex atmospheric samples, at trace levels.

Mechanical stretching forces oppose osmotic lens swelling

Mechanical stretching forces oppose osmotic lens swelling

Real-time glutamate measurements in the putamen of awake rhesus monkeys using an enzyme-based human microelectrode array prototype

Commonly used for research studies in the central nervous system, microdialysis has revealed a link between dysregulation of the excitatory neurotransmitter glutamate and ischemia and seizure, however limitations like slow temporal resolution have stalled the advancement of microdialysis as a diagnostic tool. We have developed and extensively characterized an enzyme-based microelectrode array technology for second-by-second in vivo amperometric measurements of glutamate in the mammalian CNS. The current studies demonstrated the ability of a human microelectrode array prototype (Spencer-Gerhardt-2 (SG-2)) to measure tonic and phasic glutamate neurotransmission in the putamen of unanesthetized non-human primates. We also showed that the SG-2 remains functional following sterilization. Ability to monitor dynamic changes in glutamate in real-time may assist the development of clinical algorithms to potentially alert care-providers prior to onset of overt ischemia or seizure, or provide neurosurgeons with second-by-second measurements of rapid changes in extracellular glutamate which could help guide surgical procedures or aid in interventional strategies.

Low-dose versus a Higher-dose Bupivacaine Spinal Anesthesia for Cesarean Delivery

Low-dose <i>versus</i> a Higher-dose Bupivacaine Spinal Anesthesia for Cesarean Delivery

Measurement of rapid changes in cell volume by forward light scattering.

Light scattering is an empirical technique employed to measure rapid changes in cell volume. This study describes a new configuration for the method of light scattering and its corroboration by measurements of cell height (as a measure of cell volume). Corneal endothelial cells cultured on glass cover-slips were mounted in a perfusion chamber on the stage of an inverted microscope. A beam of light was focused on the cells from above the stage at an angle of 40 degrees to the plane of the stage. The scattered light intensity (SLI), captured by the objective and referred to as forward light scatter (FLS), increased and decreased in response to hyposmotic and hyperosmotic shocks, respectively. The rapid increase and decrease in SLI corresponded to cell swelling and shrinkage, respectively. Subsequently, SLI decreased and increased as expected for a regulatory volume decrease (RVD) and increase (RVI), respectively. These data are in agreement with measurements of cell height, demonstrating that the method of light scatter in FLS mode is useful for monitoring rapid changes in cell volume of cultured cells. Changes in SLI caused by gramicidin were consistent with cell volume changes induced by equilibration of NaCl and KCl concentrations across the cell membrane. Similarly, an additional decrease in SLI was recorded during RVD upon increasing K+ conductance by valinomycin. Decreasing K+ conductance of the cell membrane with Ba2+ changed the time course of SLI consistent with the effect of the K+ channel blocker on RVD. Bumetanide and dihydro-ouabain inhibited increases in SLI during RVI. In conclusion, FLS is a valid method for qualitative analysis of cell volume changes with a high time resolution.

Development of Fast Charge Exchange Recombination Spectroscopy by Using Interference Filter Method in JT-60U

Recent developments and results of fast charge exchange recombination spectroscopy (CXRS) using interference filter method are reported. In order to measure the rapid change of the ion temperature and rotation velocity under collapse or transition phenomena with high-time resolution, two types of interference filter systems were applied to the CXRS diagnostics on the JT-60U Tokamak. One can determine the Doppler broadening and Doppler shift of the CXR emission using three interference filters having slightly different center wavelengths. A rapid estimation method of the temperature and rotation velocity without non-linear least square fitting is presented. The modification of the three-filters system enables us to improve the minimum time resolution up to 0.8 ms, which is better than that of 16.7 ms for the conventional CXRS system using the CCD detector in JT-60U. The other system having seven wavelength channels is newly fabricated to crosscheck the results obtained by the three-filters assembly, that is, to verify that the CXR emission forms a Gaussian profile under collapse phenomena. In a H-mode discharge having giant edge localized modes, the results obtained by the two systems are compared. The applicability of the three-filters system to the measurement of rapid changes in temperature and rotation velocity is demonstrated.

Modification of a whole room indirect calorimeter for measurement of rapid changes in energy expenditure

Whole room indirect calorimeters are among the most accurate devices for measurement of human energy expenditure and have provided useful data about determinants of total daily energy expenditure. However, a limitation of whole room indirect calorimeters has been the inability to detect acute (usually < 10-15 min) changes in energy expenditure. This precludes using these devices to study the acute effects of food, drugs, or exercise on energy expenditure. We describe modifications made to our whole room indirect calorimeter (respiratory chamber) to allow accurate measurement of energy expenditure over time periods as short as 1 min. The modifications involve changes in the system design and use of signal processing techniques. With these modifications, we can measure energy expenditure in 1-min intervals throughout the day. This allows accurate study of the acute effects of food, exercise, or drugs on energy expenditure in subjects moving freely inside the respiratory chamber. The ability to use respiratory chambers for these types of studies should improve our understanding of how body weight is regulated.

Dynamic temporal properties of effective connections in rat dorsal cochlear nucleus

In a prior report we presented evidence that functionally connected dorsal cochlear nucleus (DCN) neurons in close proximity can show differing peristimulus time histograms (PSTHs) in response to the same stimulus. We wished to further investigate how interconnections between such neurons might participate in the PSTH patterns. Methodology has recently been developed which permits measurement of rapid changes in effective connectivity between neuron pairs: the normalized joint PSTH. Using this technique we have observed that rapid changes in effective connectivity do occur in the DCN. These observations demonstrate that the effects of one DCN neuron on another cannot necessarily be understood by sequential recordings from single units, even if anatomical connectivity can be established.

A new method for carrier lifetime measurements in PIN diodes

Several existing methods of carrier lifetime measurements in PIN diodes give an effective carrier lifetime which depends on the measurement conditions. In this paper a new method for measurements of the carrier lifetime in the diode base region is presented. This method is based on the measurement of rapid changes of the voltage drop across a PIN diode, when successive rectangular pulses are applied to the diode under the condition that the diffusion current to end regions is negligibly small. However, contrary to the double-pulse method the voltage drop across heavily doped regions, ohmic contacts and the diode leakage are taken into account. Measured carrier lifetimes in BA379 diodes produced by different manufacturers are also given.

Superfusion and static culture techniques for measurement of rapid changes in prolactin secretion

This chapter describes a superfusion method for the cultured monolayers of anterior pituitary cells that permits the analysis of interactions among various regulatory factors, allows the monitoring of the temporal patterns of hormone release, and is compatible with the simultaneous determination of biochemical and structural changes correlated with secretion. The secretion of prolactin (PRL) is under the regulation of both inhibitory and stimulatory hypothalamic hormones. Dopamine (DA), a well characterized inhibitory hormone, tonically suppresses PRL secretion. The multifactorial regulation of PRL secretion represents a specific but not unique process, in which the sequence and duration of exposure to multiple hypothalamic hormones determine the secretory response. The culture/superfusion technique that is described for dissociated cells permits the unraveling of the hierarchy of the hypothalamic regulation of the secretion of anterior pituitary hormones. Both rapid changes in hormone secretion and cellular events––that is, events occurring within minutes––and slower modulatory effects––that is, effects taking days––can be correlated by the coupling of perifusion techniques with those of cell culture.

A venous outflow method for measurement of rapid changes of the cerebral blood flow and oxygen consumption in the rat.

A technique for continuous measurement of cerebral venous outflow in the rat is described. The method involves cannulation of one retroglenoid vein close to its exit from the skull, and diversion of cerebral venous blood through a closed extracorporal circuit with a drop recording device, the blood being returned to the central venous circulation via a catheter in the external jugular vein. Occlusion of the contralateral retroglenoid vein increases measured flow and minimizes extracerebral contamination of the diverted cerebral venous blood. The venous outflow system is not further isolated from cerebral or potential extracerebral collaterals. Thus, the mass of tissue drained cannot be exactly defined anatomically. However, the experiments involving changes of PP, arterial CO2 tension, and induction of epileptic seizure activity, and simultaneous indirect measurements with radioactive tracer technique, indicate that significant extracerebral contamination does not occur and that in short term measurements the venous outflow represents cerebral blood flow (CBF) in a constant mass of (dorsal and central, mainly forebrain) cerebral tissue. Measurement of arterial blood pressure and pressure in the cisterna magna allows calculation of cerebral perfusion pressure (PP). By simultaneous measurement of arterial and cerebral venous oxygen content changes in cerebral oxygen consumption (CMRO2) can be calculated. The method has been applied to document several situations of transient CBF and CMRO2 changes.

Measurements of Fast Time Evolutions of Plasma Potential Using Emissive Probe

We present a new method of measuring the floating potential of an emissive probe when the floating potential is very close to the plasma potential. The probe potential at which the probe current becomes zero in the current-voltage curve of the probe is automatically biased by a new probe circuit connected to a bipolar voltage source. This method enables direct measurement of rapid changes in the floating potential with a time resolution of ≃1 µs, giving a continuous data trace. The method was verified experimentally using a DP machine.

Improved fluorescent probes for the measurement of rapid changes in membrane potential

To improve the quality of fluorescent voltage-sensitive probes twenty new styryl dyes were synthesized. Some of the new probes are significantly better than any used in the past. A signal-to-noise ratio of 90 root mean square (rms) noise was obtained for an optical recording of action potentials from neuroblastoma cells maintained in monolayer culture. The fluorescence fractional change of the optical signal is as large as 14%/100 mV. Photodynamic damage and bleaching are much less significant with the new probes. These fluorescent probes can be used to measure small and rapid changes in membrane potential from single cells maintained in monolayer cultures, from single cells in invertebrate ganglia, from their arborization, and from other preparations. The optical measurement can be made with a standard fluorescent microscope equipped with DC mercury illumination. Guidelines for the design of even better fluorescent probes and more efficient instruments are suggested.

An intensity-monitoring technique for measuring ellipsometric transients

Intensity-monitoring techniques make possible the measurement of rapid changes in the ellipsometric parameters. Methods used hitherto have been suitable for measuring slight changes only and require prior knowledge of the Δ and Ψ values for the initial surface. It is shown that larger changes can also be measured and that the values of Δ and Ψ for the initial surface need not be known beforehand. To illustrate the method measurements are made relating to the anodising of a hanging mercury drop electrode in 1 mol dm −3 NaOH; under these conditions a thick oxide layer is known to be formed.

Contractlity in Spirostomum provides for nonelectrogenic calcium regulation through energy-dissipative metabolic processes in the absence of membrane excitability.

ATTEMPTS to carry out in vivo pharmacological analyses of the events leading to contraction in fast acting muscle systems have been hampered by problems due to, for example, intracellular diffusion, cell–cell interactions and extracellular control mechanisms, which arise in part because of the multicellular organisation of many vertebrate muscle systems. Their effect is to impede accurate measurement of rapid changes in the physiological and ultrastructural states throughout the system in response to specific stimuli. The most troublesome aspects of these problems can be bypassed through the use of single-celled models which have the same properties of excitability as do muscle systems.

Measurement of Rapid Changes of Odor Concentration by a Signal Detection Approach

For many odorous industrial gases, odor detecrability often involves such low concentrations that the sampling time factor makes physical-chemical methods of analysis impractical. However, a sensory detection method based on signal detection theory has shown itself to be well suited for such studies even at levels near the absolute threshold. Experiments undertaken to assess the method are described.

Measurement of coronary sinus blood flow by continuous thermodilution in man.

A technique was developed for measurement of blood flow in the coronary sinus in man by continuous thermodilution. For single determinations, 5% dextrose at room temperature is injected at a constant rate of 35 ml/min for a period of about 20 sec. In 14 subjects with normal coronary arteries the mean coronary sinus blood flow was 122 ± 25 ml/min (range, 83 to 159 ml/min). The blood flow computed per 100 g of left ventricle was 82 ± 16 ml/min, which is in the range of values obtained by nitrous oxide and coincidence counting methods. In 35 patients with arteriographically confirmed coronary artery disease the mean flow was similar (128 ± 20 ml/min; range, 92 to 167 ml/min). A special catheter was used for simultaneous measurement of blood flow in the coronary sinus and great cardiac vein. In eight normal subjects the mean great cardiac vein flow was 68 ± 11 ml/min (range, 51 to 78 ml/min) or 65 ± 10% of the coronary sinus blood flow. The method allowed continuous measurement of flow over a period of several minutes and, for the first time, measurement of rapid changes in myocardial perfusion.

Chemisorption of oxygen and hydrogen on nickel films — reconstitution of the adsorbate-adsorbent interface

Considerable detailed information may be obtained about the nature of the adsorbate phase and the changes that take place at the adsorbate-adsorbent interface subsequent to the chemisorption of a gas at a metal surface by measurement of rapid changes of the work function of the metal. Thus, the kinetics of the transformation of a covalently bonded oxygen adatom at the surface of an annealed nickel film to an ionic species within the surface layer have been elucidated; this theory should have general validity for the incorporation of any electronegative element into metal lattices. In systems, where the incorporated state is not ionic, incorporation is not expected although diffusion of the atomic species is still possible. Thus, with hydrogen on nickel, different information, namely, the nature and properties of the adspecies and the rate and activation energy for surface diffusion of one of the adspecies, has been obtained. Greater use of the results of work function changes simultaneously obtained in some LEED studies may therefore prove to be valuable.

Effect of endotoxin on renal function in the dog.

Studies were made on isolated and intact dog kidneys provided with a controlled renal arterial perfusion pressure. Renal function tests were performed for a period of 1–2 hours. Creatinine and PAH extraction ratios, clearance rates and TmPAH values were calculated. A procedure was devised for the calculation of renal clearances from simultaneously occurring values which obviated errors due to urinary dead space and permitted the measurement of rapid changes in extraction rates. Renal blood flows and urine flows were measured. After administration of endotoxin PAH extraction ratios and extraction rates declined. TmPAH values temporarily fell but within an hour returned to pre-endotoxin levels. Creatinine extraction ratios and rates and urine flow showed irregular changes after endotoxin. Renal hyperemia was observed if the arterial pressure was maintained and especially when smaller injections of endotoxin were administered. It is concluded that the effect of endotoxin on the kidney is primarily a vascular one. There is no evidence for the poisoning of renal tubule cells, and renal vascular occlusion is not observed.

A Sensitive Respirometer for the Measurement of Rapid Changes in Metabolism of Oxygen

A respirometer used to study the oxygen metabolism of peripheral nerve is described. The theory of its operation and its operating characteristics are given. The respirometer consists essentially of the nerve trunk itself, placed symmetrically across the tip of a polarized platinum microelectrode which is flush with the floor of the chamber. The sides of the nerve are exposed to moist gas of known oxygen content; the top surface of the nerve is covered. The current to the platinum electrode measures the concentration of oxygen in the nerve at the electrode tip. In the steady state the oxygen concentration near the electrode is determined by: (1) the configuration of the system, (2) the oxygen content of the gas phase, (3) the diffusion coefficient of oxygen in the tissue, and (4) the rate of oxygen consumption by the tissue. Starting from the steady state, any change in rate of oxygen uptake may be followed directly during the first 45 to 60 seconds of such a change; during this time the change is equal to the negative of the rate of change of oxygen concentration at the electrode tip. Slow, prolonged changes in respiratory rate may be followed, within limitations determined by the diffusion characteristics of the system and by slow drift in electrode calibration. It is estimated that changes in rate of oxygen uptake as small as 0.3 mm3 O2/cc hr (0.6 percent of the rate of uptake by resting frog nerve) can be reproducibly detected.