Pulse Injection Method Research Articles

Scanning tunneling microscopy imaging and manipulation of DNA oligomer adsorbed on Cu(111) surfaces by a pulse injection method

We have developed a pulse injection method of DNA oligomer aqueous solution onto Cu(111) surfaces as a new sample-preparation technique for scanning tunneling microscopy (STM) studies of biomolecules. The STM images revealed that the surface of Cu(111) retains its atomic flatness even after the injection of DNA-containing solution and that the deposition of intact DNA oligomers without aggregation is possible. The observed internal structure of deposited DNA suggests the promising possibility of sequencing DNA by means of STM. In order to examine the possibility of manipulation of DNA, translational positioning of DNA oligomer has been performed by a lateral pushing of the DNA with scanning tip.

Improvements in sample introduction for mass spectrometry using pulsed high-pressure fluid injection with resonant two-photon ionization detection

Pulsed supercritical fluid and pulsed high-pressure liquid injection are used as means of introducing thermally labile biological species into a time-of-flight mass spectrometer (TOFMS) system. The analyte species are then ionized by resonant two-photon ionization, which can produce either soft ionization or extensive fragmentation on the basis of laser power and wavelength. Since the solvent is transparent to the laser radiation, hard ionization can be produced without physical separation of the analyte from the effluent jet expansion. In addition, the pulsed liquid injection method allows introduction of the sample from high-pressure fluids at relatively low temperatures without the extensive clustering that normally occurs in liquid expansions unless a much higher temperature is utilized. Using this method, we have been able to study the laser-induced ionization mass spectrometry of several classes of small polar biological molecules in a TOFMS.

Pulsed High-Pressure Liquid Injection of Biological Molecules into Supersonic Beam/Mass Spectrometry with Resonant Two-Photon Ionization Detection

Pulsed high-pressure liquid injection is used as a means of introducing thermally labile biological species into a time-of-flight mass spectrometer (TOFMS) system. The analyte species are then ionized by resonant two-photon ionization (R2PI) in the near ultraviolet. This method serves as a means of producing soft ionization or extensive fragmentation on the basis of the laser power and wavelength, without physical separation of the analyte from the effluent jet expansion. In addition, the pulsed liquid injection method allows introduction of the sample in methanol at 80°C without the extensive clustering that normally occurs in continuous expansions unless much higher temperature is utilized. With the use of this method the R2PI of catecholamines and indoleamines, as well as their metabolites, is studied in a TOFMS. The ability to obtain some spectral selectivity from jet expansions of liquid methanol is also demonstrated.

Dynamic analysis of irreversible adsorption of protein on porous polymer resins as studied by pulse injection method

Irreversible adsorption of bovine serum albumin onto porous polymer resins is examined by a pulse injection method. The experimental results are theoretically analyzed by a model based on the assumption that there exist three kinds of binding sites with different binding rates, which are considered to exist in the vicinity of the outer periphery surface, the inner surface of macropore, and the micropore, or center part, of particles. The three kinds of adsorption rates are also evaluated by a batch method and are nearly equal to the corresponding kinetic parameters by this method. The amount of BSA bound irreversibly to the resins is independent of the protein concentration and the flow rate examined, which suggests that protein molecules penetrate into pores of resins and occupy almost all the effective binding sites in the resins. The total amount of bound BSA shows a pH dependence with a maximum near the isoelectric point of BSA, and the amount of BSA bound at the slowest rate is most largely influenced by pH.

Mass spectrometric transient study of dc plasma etching of Si in SF6/O2 mixtures

A thin wafer of polycrystalline Si was mounted on the cathode of a small cylindrical plasma cell which consisted of two flat stainless steel electrodes and a piece of alumina tubing. A discharge was supported by a slow flow of Ar, and short pulses of SF6 and O2 were injected simultaneously into the Ar stream. The contents of the plasma cell were sampled continuously, and analyzed by mass spectrometer. The concentration transients of various species resulting from the SF6 and O2 pulses were measured as a function of time. The maxima of the SiF+3 transients and thus the etching rates were found to depend on oxygen concentrations in the mixtures, but far less so than the atomic fluorine concentrations, as reported by others. By contrast, the maxima of several S–F and S–O–F species concentrations depended very strongly on O2 concentrations. It is concluded that neither atomic fluorine, nor any one of the other observed species can be the sole important reactive species in the etching reaction studied. The experimental results also bear on the fate of SiF2 initially formed and thus illustrate the potential of the pulse injection method used in mechanistic studies.

Pulsed-injection method for blood flow velocity measurement in intraarterial digital subtraction angiography.

The pulsed-injection method for measuring the velocity of blood flow in intraarterial digital subtraction angiography is described. With this technique, contrast material is injected at a pulsing frequency as high as 15 Hz, so that two or more boluses can be imaged simultaneously. The velocity of flow is determined by measuring the spacing between the boluses and multiplying it by the pulsing frequency. Results of tests with phantoms correlate well with flow measurements obtained with a graduated cylinder for velocities ranging from 8 to 60 cm/sec. The potential of the method for time-dependent velocity measurement has been demonstrated with simulated pulsatile flows.

Nature and reactivity of carbonaceous species deposited by ethylene on supported ruthenium catalysts

The species formed in the interaction of C 2H 4 with supported Ru catalysts have been investigated in the temperature range 296–650 K using a sequential pulse injection method. The time- and temperature-dependent reactivity of these species with hydrogen has been evaluated. The relative yields of the hydrogen-deficient dicarbon (C 2) and monocarbon (C 1) species formed at the catalyst surface depended on the temperature and the support material used, viz., molecular sieves, alumina, or glass beads. It was found that while the H 2 reacted with these species to give C 2H 6 and CH 4, in its absence, the C 2 species transformed with time to the C 1 form. Also, both the C 2 and C 1 species converted on standing to a form that was no more reactive to H 2, the rate of transformation depending on the catalyst temperature and the nature of support material. The kinetics of these transformations has been evaluated.

Ceria in automotive exhaust catalysts: I. Oxygen storage

Oxygen storage capacities of CeO 2, CeO 2 Al 2O 3 , and PM/CeO 2/Al 2O 3, measured by a pulse injection method, are affected by pretreatment temperature, pulsing temperature, partial pressure of CO, presence of precious metals (PM), and the concentration of CeO 2 on alumina. They are lowered by higher pretreatment temperature but increase with the pulsing temperature in the range of application. At a pulsing temperature ≤500 °C, the capacities are not affected by oxygen pressure but increase with partial pressure of CO. The presence of PM lowers the reduction temperature and increases the oxygen storage capacity of CeO 2. TPR was used to measure the oxygen removal at various temperatures. At 900 °C, the maximum amount of oxygen removed from unsupported or alumina-supported ceria is about 25%. The TPR traces of the unsupported ceria show two peaks at 500 and 750 °C which are associated with the reduction of surface capping oxygen and bulk oxygen anions, respectively. For alumina-supported ceria, the TPR traces show a third peak at 850 °C which is associated with the reduction of the shared oxygen anions at the interface. The presence of PM lowers only the reduction temperature of the capping oxygen anions but not of the other two oxygen species. Both oxygen chemisorption and TPR were used to measure the oxygen anion restoration at various temperatures following the reduction at 500 and 900 °C, respectively. Chemisorption data show that the oxygen uptake per CeO 2 is highest at the lowest CeO 2 concentration. The TPR traces show that a new oxygen species, probably a molecular oxygen anion, is formed at 25 °C which converts slowly at 500 °C to the capping oxygen anion. Complete restoration of all three types of oxygen anions is accomplished at 850 °C in air.

Corticotropin-releasing factor: pharmacokinetics in man.

Corticotropin-releasing factor (CRF), a 41-amino acid peptide isolated and sequenced from ovine hypothalami, has potential clinical application as a provocative test of the hypothalamic-pituitary-adrenal axis. To define its pharmacokinetic parameters in man, we measured the MCR and plasma half-life of immunoreactive CRF (IR-CRF) by the pulse injection and continuous infusion methods. Synthetic ovine CRF was given to 12 normal men as a bolus injection (1 microgram/kg; n = 6) or as a continuous infusion (0.51 +/- 0.05 micrograms/kg X h; n = 6) over 8 h. The disappearance curve of IR-CRF from plasma was biexponential. The plasma half-life of IR-CRF was 11.6 +/- 1.5 min (mean +/- SE) for the fast component and 73 +/- 8 min for the slow component. The MCR using the pulse injection technique was 95 +/- 11 liters/m2 X day, and the volume of distribution was 6.2 +/- 0.5 liters. Continuous infusion of CRF gave approximately the same MCR (88 +/- 7 liters/m2 X day). A small percentage of IR-CRF (approximately 0.03%) was found in the urine at the end of the continuous infusion. The relatively low MCR of CRF may explain its prolonged biological action in primates and man.

METABOLIC CLEARANCE RATE AND PLASMA HALF-LIFE OF RADIOIODINATED CORTICOTROPIN RELEASING FACTOR IN A PRIMATE

Corticotropin releasing factor (CRF) has recently been identified, purified and shown to be a 41-amino acid polypeptide that stimulates secretion of beta-endorphin and ACTH. The metabolic clearance rates (MCR) of I125-CRF and I125-TyroCRF were measured in cynomologus monkeys using the pulse injection and the continuous infusion methods. Hunter-Bolton reagent was used for iodination of CRF and the chloramine-T method for Tyro-CRF. Gel chromatography was used to separate free iodine (and radioiodinated small fragments) from iodinated CRF in plasma samples. Disappearance of I125-CRF or I125-Tyro-CRF could be modeled with two components (bi-exponential). Plasma half-life of I125-CRF was 17.1 +/- 2.44 min (mean +/- SE, n=4) for the fast component and 198 +/- 5.3 min for the slow component. The MCR of I125-CRF using the pulse injection technique was 0.44 +/- 0.06 L/Kg/d, n=4 and the volume of distribution 213.5 +/- 12 ml, n=4, roughly equal to the plasma volume. Continuous infusion of I125-CRF and of I125-Tyro-CRF gave MCR's ranging between 2.23 -= 5.08 L/Kg/d, n=4. I125-ACTH MCR, measured for comparison using the same technique, was 5-10 fold higher. Thus, the plasma half-life of CRF is longer than for all other known hypothalamic peptides and its metabolic clearance rate relatively low and considerably less all other known hypothalamic peptides and its metabolic clearance rate relatively low and considerably less than that of ACTH. Strong binding of CRF to plasma proteins may be responsible for the small volume of distribution and lower MCR values for the pulse injection method.

Sulphur poisoning of ruthenium/alumina methanation catalyst and hydrogenation of CS 2

Different species formed in the interaction of CS 2 with Ru/γ-alumina catalyst in the temperature range 425–625 K were examined using a pulse injection method and a flow microcatalytic reactor. In the presence of H 2 carrier flow, CS 2 reacts over the catalyst to form primarily CH 4 and small amounts of higher hydrocarbons. Prolonged treatment with CS 2 produced new products CO and H 2S from CS 2 and reduced drastically the catalytic methanation of CO. Under the inert atmosphere of He, CS 2 interaction over catalyst generated CO 2 in the initial stage and subsequent H 2 injections gave rise to CH 4. Further CS 2H 2 injections gave progressively reduced yields of CH 4. At the stage when no methane was formed on H 2 injections following a CS 2 pulse, further injections of CS 2 pulses produced new products, CO, SO 2, COS, and H 2S and subsequent H 2 injections again resulted in H 2S formation. The effect of a time gap between CS 2 and H 2 injections on the yields of CH 4 and H 2S has been studied. XPS studies indicated that CS 2 decomposes on the catalyst surface to give elemental carbon and sulphur. It is suggested that S atoms progressively block those Ru sites where carbon or carbon oxides are methanated. It has also been found that the nascent sulphur formed on decomposition of CS 2 loses its chemical reactivity with increasing temperature and time.

Protein Metabolism and Cold Adaptation in Antarctic Fishes

Protein synthetic rates have been determined in vivo at −1.5 C by the method of constant infusion in four species of Antarctic fish of McMurdo Sound of genus Trematomus (Nototheniidae) and Gymnodraco (Bathydraconidae). Parameters for liver protein synthesis were obtained by pulse injection and infusion methods in T. hansoni. Protein synthetic rates in liver averaged 6% of tissue protein per day. Synthetic rates in the other tissues studied fell in the following order: foregut > liver > gill = spleen = head kidney > trunk kidney > red muscle > white muscle. Rates in liver and white muscle are compared with data for temperate and tropical fishes at habitat temperatures and at reduced temperatures. The theoretical temperature dependency for protein synthetic reactions based on studies in temperate species is taken as Q10 = 2.5. The results indicate a twofold adaptation for liver protein synthesis and a threefold adaptation for white muscle in the Antarctic species relative to predicted values. Rates in white muscle of freshly caught T. hansoni and T. bernacchii averaged 0.22% of tissue protein per day, declining to 0.05% per day with 5–15 days starvation. The data suggest that as much as three-fourths of protein synthesis in white muscle of these species is directed toward growth under normal summer feeding conditions. The results are compared with growth data for T. bernacchii.

MIXING PERFORMANCE OF VIBRATING DISK TANK

The mixing time required to achieve 99.5% of homogeneous concentration in a vibratory disk tank has been measured by a pulse injection method of NaCI solution. The mixing time, tm has been well correlated by where D is the tank inside diameter, Pw, the power requirement per unit volume, V the tank volume, A the amplitude of disk vibration, f the frequency, p the liquid density and d the disk diameter. It is also found that liquid mixing in the vibratory disk tank is mainly controlled by turbulent mixing phenomena rather than by convective flow.

Thermal reemission of trapped electrons in SiO2

Electron trapping by neutral trap centers in SiO2 was studied at 77 K and at room temperature, using n-channel silicon-gate IGFET structures. The electrons were injected in the dark using the forward-bias pulsed injection method. The results show that electron trapping by the neutral centers was one to two orders of magnitude more efficient at 77 K than at room temperature; which may be compared with the previously reported electron trapping by Coulomb-attractive centers where the capture cross sections at room temperature and at 77 K were about the same. For injected electron concentrations of less than 1016 cm−2, more than 90% of the electron trapping at 77 K was due to shallow-level centers where the captured electrons were thermally reemitted as the samples were warmed to room temperature. The concentrations of these shallow-level traps in dry, wet, and HCl oxides were about the same, regardless of whether the aluminum evaporation was by electron-beam or by rf heating in a tantalum boat. The capture cross section of these traps at 77 K was estimated to be about 10−15 cm2 at Eox=1×106 V/cm, decreasing slowly with increases in the oxide field. Thermally stimulated reemission measurements were made by monitoring the gate voltage shifts at constant channel conductance. Analyses of the results indicated a broad energy distribution for these shallow-level traps, with a peak at 300±50 meV below the conduction-band edge of SiO2 and a half-width of about 200 meV. A small portion of the enhanced trapping at 77 K was attributable to deep-level centers where the captured electrons were not thermally reemitted at room temperature.