Fast Pulse Techniques Research Articles

B2LiVe, a label-free 1D-NMR method to quantify the binding of amphitropic peptides or proteins to membrane vesicles

Amphitropic proteins and peptides reversibly partition from solution to membrane, a key process that regulates their functions. Experimental approaches classically used to measure protein partitioning into lipid bilayers, such as fluorescence and circular dichroism, are hardly usable when the peptides or proteins do not exhibit significant polarity and/or conformational changes upon membrane binding. Here, we describe binding to lipid vesicles (B2LiVe), a simple, robust, and widely applicable nuclear magnetic resonance (NMR) method to determine the solution-to-membrane partitioning of unlabeled proteins or peptides. B2LiVe relies on previously described proton 1D-NMR fast-pulsing techniques. Membrane partitioning induces a large line broadening, leading to a loss of protein signals; therefore, the decrease of the NMR signal directly measures the fraction of membrane-bound protein. The method uses low polypeptide concentrations and has been validated on several membrane-interacting polypeptides, ranging from 3 to 54kDa, with membrane vesicles of different sizes and various lipid compositions.

A comparison of fast pulse and conventional LA-ICP-MS detrital zircon geochronology: A large n detrital zircon study from the Centralian Superbasin, northwestern Australia

Over ten thousand detrital zircon U–Pb analyses on thirty four samples were undertaken using a fast pulse laser ablation protocol from the Neoprotoerozoic rocks of the largely unexposed Yeneena and northwestern Officer Basins in Western Australia. In addition, conventional laser ablation detrital zircon U–Pb geochronology was carried out on three of the samples. A comparison of the two datasets demonstrated that no statistical significant difference was observed in the detrital zircon spectra between the two techniques.The results of the detrital zircon analyses reveal that after an intial pulse of material dominated by Archean detritus the sediment are dominated by Mesoproterozic sources. This indicates that there is little variation in source materials within and between the identified formations. The major age peaks coincide with magmatic rock ages from within Australia. The results indicate that either the Palaeoproterozoic and Mesoproterozoic terranes remained sources throughout the deposition of the Yeneena and northwestern Officer Basins during the Neoproterozoic, or that recycling of zircons occurred within a quasi-closed system for the duration of sedimentation. The remaining 10 % of grains are difficult to reconcile with magmatic suites of any significant volume within Australia. However, when considering the broader palaeogeographic context at the time the sediments are inferred to have been deposited, rocks from Dronning Maud Land and the Kalahari Craton can supply grains of appropriate ages and are consistent with the known paleocurrent directions.This work demonstrates that there is no significant disadvantage in the application of the fast pulse technique when applied to the collection of U–Pb detrital zircon datasets for the purpose of detrital zircon fingerprinting. However, there is a large upside related to the significant amount of data that can be collected for a given amount of time compared to other more conventional techniques.

Primary Structure of Glycans by NMR Spectroscopy.

Glycans, carbohydrate molecules in the realm of biology, are present as biomedically important glycoconjugates and a characteristic aspect is that their structures in many instances are branched. In determining the primary structure of a glycan, the sugar components including the absolute configuration and ring form, anomeric configuration, linkage(s), sequence, and substituents should be elucidated. Solution state NMR spectroscopy offers a unique opportunity to resolve all these aspects at atomic resolution. During the last two decades, advancement of both NMR experiments and spectrometer hardware have made it possible to unravel carbohydrate structure more efficiently. These developments applicable to glycans include, inter alia, NMR experiments that reduce spectral overlap, use selective excitations, record tilted projections of multidimensional spectra, acquire spectra by multiple receivers, utilize polarization by fast-pulsing techniques, concatenate pulse-sequence modules to acquire several spectra in a single measurement, acquire pure shift correlated spectra devoid of scalar couplings, employ stable isotope labeling to efficiently obtain homo- and/or heteronuclear correlations, as well as those that rely on dipolar cross-correlated interactions for sequential information. Refined computer programs for NMR spin simulation and chemical shift prediction aid the structural elucidation of glycans, which are notorious for their limited spectral dispersion. Hardware developments include cryogenically cold probes and dynamic nuclear polarization techniques, both resulting in enhanced sensitivity as well as ultrahigh field NMR spectrometers with a 1H NMR resonance frequency higher than 1 GHz, thus improving resolution of resonances. Taken together, the developments have made and will in the future make it possible to elucidate carbohydrate structure in great detail, thereby forming the basis for understanding of how glycans interact with other molecules.

SENSASS NMR: New NMR techniques for enhancing the sensitivity and the spectral resolution of polymer supported chemicals

The use of polyethylene glycols (PEGs) as organic polymer soluble supports for synthesis has been receiving growing interest. The main advantages of using PEGs as support are related to their non-toxicity, their commercial availability and their solubility properties allowing easy recovery and analysis of compounds linked to the polymer. The NMR characterization of PEG-branched products could however be difficult due to the presence of huge signals of the polymeric support. In order to overcome this problem, we developed new NMR experiments named SENSitivity increAsed and resolution enhanced by Signal Suppression or SENSASS NMR. These experiments implement either semi-selective pulses or Water Gate sequences for reducing signals of the polymer as well as fast pulsing techniques optimizing the recycling delay for enhancing the sensitivity of signals. They have been successfully implemented in classical NMR characterization experiments namely, COSY, HSQC and HMBC experiments.

Photoconductivity of the two polar surfaces of ZnO

Transient photoconductivity of the two polar surfaces of ZnO single crystal has been studied by using a fast-pulse technique. When ZnO crystal was irradiated by an ultraviolet (UV) light pulse, an obvious Dember effect was observed for both polar surfaces. The sign of the Dember effect indicated that the dominant photocarriers were electrons. Additionally, two distinct differences in UV photoconductivity were observed for the two polar surfaces. First, photocurrent Q was much larger for the O surface than for the Zn surface. The ratio of QO to QZn was about 100 when the applied electric field E was perpendicular to the c-axis and about 30 when E was parallel to it. Second, the excitation light intensity I dependence was quite different. While the photocurrent of the O surface was proportional to I, the photocurrent of the Zn surface was proportional to I1∕2. These results indicated that the recombination processes of photocarriers were quite different between O and Zn surfaces; namely, the direct recombination process was dominant at the Zn surface, while the recombination centers were dominant at the O surface.

Three-dimensional mapping of polarization profiles with thermal pulses

High-resolution, large-area three-dimensional mapping of polarization profiles in electret polymers was carried out by means of a fast thermal pulse technique with a focused laser beam. A lateral resolution of 38 μm and a near-surface depth resolution of less than 0.5 μm was achieved. At larger depths, fast thermal diffusion in the metal electrode rather than the laser spot size becomes the limiting factor for the lateral resolution.

Voltammetric studies of anthraquinone dyes adsorbed at a hanging mercury drop electrode using fast pulse techniques

Square wave voltammetric studies, involving adsorptive stripping methodology, of anthraquinone-based reactive dyes and of a typical anthraquinone dye Alizarin Red S are reported. The reduction of their anthraquinone moiety is reversible and fast and the sensitivity of these determinations can be improved if current sampling is made earlier after the pulse application. In order to try to modify the rate of the electrochemical process at the electrode, two approaches have been tested: the effect of adding surfactants and the influence of supporting electrolyte concentration. In both cases, a change in the results obtained is observed, owing, in the first case, to the modification of the electrode surface, and, in the second, to the importance of the resistance of the solution.

NQR detection using a meanderline surface coil

14N pure NQR detection in a thin-layer sample using a meanderline, or zig-zag, surface coil is reported. The RF magnetic field of the meanderline drops off approximately as exp− πh b ) , where b is the conductor spacing and h is the distance from the plane of the coil, and therefore is ideally suited for NQR detection in thin, planar samples. A meanderline with 11 conducting strips of 4 cm spacing was used to observe the 14N ν-resonance line in sodium nitrite at sample distances up to 1.6 cm, where the RF field has dropped to less than 1 e . The meanderline results are compared with those obtained using a solenoid of comparable dimensions. It is also shown that the sensitivity of NQR detection using surface coils is greatly enhanced by using fast-pulsing techniques such as the strong off resonance comb, which can produce an order-of-magnitude or better improvement in the signal-to-noise ratio over more conventional ( T 1-limited) techniques.

Voltammetric study of copper(I) thioacetamide complexes

The composition and stability of copper(I) complexes with thioacetamide (TAA) have been evaluated with the help of square-wave voltammetry using the fast pulse technique. Two species, namely Cu(I) (TAA) and Cu(I) (TAA)2, have been identified having the formation constants log β1=16.85; log β2=18.03. The complex is stable in highly acidic medium (pH≤1). The application for the determination of copper is pointed out.

A cometary and interplanetary dust experiment on the Vega spacecraft missions to Halley's Comet

An instrument from the University of Chicago which measures the mass and flux of dust particles as a function of time and position in the dust coma of Halley's Comet has been included in the two USSR Vega spacecraft launched 15 and 21 December 1984 for encounters with the comet on 6 and 9 March 1986 respectively. The dust measurements are based on the new detection principle reported by Simpson and Tuzzolino (Nucl. Instr. and Meth. 1985) which employs a polarized polyvinylidene fluoride polymer film (PVDF) and fast electronic pulse techniques. The instrument, called the dust counter and mass analyzer (DUCMA) is described along with its expected performance for the measurement of both cometary and interplanetary dust. Since the electronic PVDF detector signal, resulting from an impacting dust particle of mass m and relative velocity v, is a known function of m and v, measured detector signals at Halley's Comet encounter will directly determine dust particle masses, since v is the known (78 km/s) velocity of the spacecraft relative to the dust particles. DUCMA measures dust particle masses by making use of a single PVDF detector of area 75 cm 2. The dust mass thresholds selected for the encounter include 3 ranges between 1.5 × 10 −13 and 9 × 10 −11 g, and the integral mass flux above 9 × 10 −11 g. The dynamic range of the instrument counting rates exceeds 5 × 10 4 s −1 for each mass interval and, since the detector remains in calibration even when punctured by large particles, it is expected that the instrument should function properly under the most extreme dust bombardment conditions which could occur during the encounters. The two spacecraft travel around the sun before the March 1986 encounters. Therefore, a search will be undertaken after Venus encounter in June 1985 for possible enhanced streams of interplanetary dust crossing the spacecraft trajectories associated, for example, with known meteor or cometary showers. The opportunity to contribute the dust experiment built and tested by the University of Chicago for the Vega Halley's Comet missions was made possible through the invitation from the USSR Academy of Sciences, Space Research Institute (Moscow) and with assistance from the Max-Planck Institute (Lindau) and the Central Research Institute (Budapest) for arranging this cooperative venture.

An Automated Test System for MNOS Transistor Characterization

An automated and thorough characterization of MNOS transistors has been made possible by using a calculator-based instrumentation system. Fast pulse techniques are used to obtain maximum information and minimize reading disturbance during measurements. Device characteristics such as retention, endurance, and mobility can be obtained with minimal manual interaction.

A size effect on the mobility of slow electrons in microcrystalline AgBr

Measurements of galvanomagnetic effects on AgBr microcrystals dispersed in insulating gelatin layers (photographic emulsion grains) were performed at 4.2–40 K as a function of the grain size (50 nm–1.3 μm) using a fast pulse technique with blocking electrodes. The value of the mobility of slow electrons was determined to be about 103 cm2/V s for 400-nm cubic crystals at 4.2 K, much smaller than that in pure bulk crystals, and decreases with decreasing size of the microcrystals. Additional results obtained from various specimens eliminate the possibility that this size effect is due to differences of impurity concentration. Possible mechanisms of this size effect on the mobility of slow electrons are discussed from the point of view of surface effects.

Streaming motion and population inversion of hot electrons in silver halides at crossed electric and magnetic fields

Galvanomagnetic measurements on photocarriers in pure AgCl and AgBr have been extended to an intense electric field (${E}_{x}\ensuremath{\sim}5$ kV/cm) and high magnetic field (${H}_{z}\ensuremath{\sim}58$ kOe) at 4.2 K by using a fast-pulse technique. improved arrangements of blocking electrodes were adopted in order to detect simultaneously the three components of the transient photocurrent, ${Q}_{x}$, ${Q}_{y}$, and ${Q}_{z}$. Substantial roles of the LO-phonon emission in hot-electron kinetics have been revealed and clear pictures of the hot-electron phenomena in silver halides were obtained, for the first time, by a quantitative analysis of the results: (1) At ${H}_{z}=0$, the momentum distribution of electrons (or holes) forms a line connecting the two points $\stackrel{\ensuremath{\rightarrow}}{\mathrm{v}}=0$ and $\stackrel{\ensuremath{\rightarrow}}{\mathrm{v}}=(\ensuremath{-}{V}_{\mathrm{LO}},0,0)$, where $(\frac{1}{2}){m}^{*}{V}_{\mathrm{LO}}^{2}\ensuremath{\equiv}\ensuremath{\hbar}{\ensuremath{\omega}}_{\mathrm{LO}}$, and the electrons are ideally streaming on the trajectory repeatingly emitting LO phonons. Hence, the electron drift velocity at high ${E}_{x}$ at ${H}_{z}=0$ is saturated to $(\frac{1}{2}){V}_{\mathrm{LO}}$. (2) An anomalous distribution of hot electrons involving population inversion predicted by Maeda and Kurosawa, is realized by applying a moderately high ${H}_{z}$ such that $1<\ensuremath{\zeta}<2$, where $\ensuremath{\zeta}\ensuremath{\Xi}{(\frac{2\ensuremath{\hbar}{\ensuremath{\omega}}_{\mathrm{LO}}}{{m}^{*}})}^{\frac{1}{2}}{(\frac{c{E}_{x}}{{H}_{z}})}^{\ensuremath{-}1}$. The distribution consists of two groups of electrons; the first group of electrons are streaming and the second group are accumulated within a high-energy area $K$ in momentum space. Depending on the electron accumulation in the area $K$, the tangent of the Hall angle, $tan\ensuremath{\theta}\ensuremath{\equiv}\frac{{Q}_{y}}{{Q}_{x}}$ and also ${Q}_{z}$ increase abruptly with ${H}_{z}$. (3) It was found that the electron trapping lifetime varies with ${E}_{x}$ and ${H}_{z}$. The streaming motion is responsible for the variation in lifetime. The experimental results here afford, for the first time, a set of conclusive evidence for the streaming motion, the anomalous distribution, and the advent of population inversion of the polarons in momentum space.

Anomalous Transport Phenomena of Photoelectrons in the Ferromagnetic Semiconductor EuO

Anomalous transport phenomena of photoelectrons in pure EuO crystals have been studied over the temperature range from T =4.2 K to 80 K and in the magnetic fields up to H =50 kOe by using a fast-pulse technique with blocking electrodes. The Redfield geometry was used to determine directly the value of Hall mobility of photocarriers, µ H . Anomalous behaviours of photoconductivity such as an abrupt increase below the Curie temperature T c =69.5 K and a large negative-magnetoresistance effect around T c were observed. The value of µ H has been measured as a function of both the temperature and the magnetic field. It was directly found that the value of µ H varies with H around T c ; the µ H -value at T =63.5 K increases from 90 cm 2 /V. sec at H =0 to 160 cm 2 /V. sec at H =15 kOe. Thus, the anomalous transport phenomema in pure EuO crystals around T c have been experimentally confirmed, for the first time, to be mainly due to the mobility change. Experimental results are discussed in terms of the transport...

Magneto-photoconductivity of europous oxide near the Curie temperature

The magneto-photoconductivity of EuO near the Curie temperature T c has been studied as a function of temperature and of magnetic field by using a fast-pulse technique in order to obtain clearer information on the transport properties of ferromagnetic semiconductors. A sharp rise of photoconductivity below T c and large negative magneto-resistance effects around T c were observed. These results indicate that the spin-disorder scattering of photoelectrons is the dominant scattering mechanism ruling the magneto-photoconductivity near the Curie temperature in this ferromagnetic semiconductor.

Transmission line pulse transformers—Theory and applications

The advent of fast rise-time pulse techniques and their increasing importance brought on by high-speed microminiature circuits and the computer industry has resulted in an increased demand for pulse transformers of various types. The basic idea of constructing transmission line type transformers has been known and used for a number of years. However, such devices have not gained widespread usage, partly because their existence is not well known, but largely because of a lack of basic understanding of their operating principles in terms of elementary fundamentals as well as their capabilities and limitations. The purpose of this paper is twofold. One aim is to develop in step-by-step fashion the basic ideas of transmission line transformers from ordinary transmission line theory. The subject will be approached from the point of view of pulse response rather than ac excitation as is usually the case. Both impedance transformers and balanced-to-unbalanced (balun) transformers, including inverters, will be considered with physical insights into their operation. Several fundamental concepts will be developed and explored in detail (without mathematics), since they have a strong bearing on practical applications. The second purpose is to present new information and pulse measurements which will be useful in the design and applications of such devices, showing their capabilities and hitherto unexplored limitations, as derived from the fundamental concepts. Thus, this paper is partly supplementary to other published work and partly new work with the goal of providing a convenient fundamental understanding of these devices and their inherent potential and shortcomings. Although the intention is not to give a detailed design procedure, some approximate calculations and discussion of significant design criteria are included.

Nonlinear Transport Phenomena in AgCl and AgBr at High Electric Field

The mobility of electrons in zone-refined and impurity-doped AgCl and AgBr crystals at high electric fields has been investigated over the temperature range from $T={4}^{\ensuremath{\circ}}$ K to 77\ifmmode^\circ\else\textdegree\fi{}K in order to examine the energy-momentum relation and to clarify the scattering mechanisms of slow and fast electrons in ionic crystals. The highest-purity crystals were obtained from ingots zone-refined 300 times in halogen atmospheres. Several crystals containing known amounts of iron impurity were also investigated. A fast-pulse technique was used to observe both the transient photoconductivity and the Hall mobility of the photo-electrons. The electrode geometry of Redfield was used in the Hall-mobility measurements. At high electric fields, the photocurrent $Q(T,E)$ was found to be proportional to the square root of the electric field $E$ in pure AgCl and AgBr crystals at low temperatures. The Hall mobility ${\ensuremath{\mu}}_{H}(T,E)$ of fast electrons in pure crystals at low temperatures was observed to be a decreasing function of the electric field, thus explaining the $Q(T,E)$ data. Such nonlinear behavior is weaker in the impurity-doped crystals and gradually disappears even in pure crystals as the temperature rises, for the same range of the electric fields. These results are discussed in terms of the hot-electron theory. An energy-dissipation mechanism similar to the scattering due to the acoustical mode of lattice vibrations is suggested as effective for fast electrons in ionic crystals.

Louis Harold Gray: An American View

His appeal was to the intellect and to the heart and spirit of Everyman; so there are many persons in all parts of the world who will remember Dr. Gray. In America especially we feel a brotherly kinship with him. Many of us have come to know him very well, and among these people there is only one opinion concerning him—profound respect for his mind and its works, and love for him as a man. His work in the late ‘20’s on the “cavity ionisation” principle that is now the so-called Bragg-Gray principle is recognised widely as basic to presently used dosimetric methods. Not so well known, except by the experts, is the fact that questions he raised in the early papers, and reviewed in later papers, on the interactions between high energy photons and matter inspired the important experimental work on the value of “W” carried on in a number of laboratories in the United States. This work is required for an understanding of the transfer processes between high energy photons and matter. It might appear that after the early papers in physics, in which these questions on early events were examined, he then forsook them for radiation biology but I believe his efforts with Dr. Boag 15 years later on the development of fast pulse techniques in radiation chemistry and biology signified that he had not forsaken at all, but, rather, had redirected his interests in this difficult field.

Mobility of Electrons in Silver Chloride at High Electric Field

The mobility of electrons in specially purified AgCl crystals at high electric field has been investigated in order to clarify the scattering mechanism of fast electrons in ionic crystals. A fast-pulse technique was adopted to observe both the transient photoconductivity and the Hall mobility for photoelectrons. The experimental results show that the mobility of fast electrons at low temperatures is a decreasing function of electric field. An energy dissipation mechanism similar to the scattering due to the acoustical mode of lattice vibration is suggested for these fast electrons.

Electron and Hole Transport in CdS Crystals

Fast pulse techniques have been used to study the drift mobility of both electrons and holes in undoped CdS crystals of high resistivity over the temperature range from 500 ?K to 80 ?K. A short electron pulse generated free carriers near the top electrode and measurements of the transit time in a pulsed applied field led to a value for the drift mobility. The method is sensitive to the injection of additional carriers and the choice of electrodes is discussed. In the temperature range above about 160 ?K the electron drift mobility ?e is in good agreement with Hall mobility values. Below this temperature a transition takes place to a charge transport predominantly controlled by a level of states close to the conduction band. The depth of the centres depends on their density; at infinite dilution it is 0.049 ev. Calculated (?e, 1/T) curves agree well with the experimental values. It is shown that all the published electron mobility data lie suprisingly close to a mobility curve determined by acoustic mode scattering (? T-3/2) from 700 ?K to about 80 ?K. The experimental method provides the first direct evidence for the transport of holes in CdS. At room temperature the hole drift mobility ?h has a mean value of 15 cm2 sec-1 v-1 and the hole lifetime lies between 1 ? 10-7 sec and 3 ? 10-7 sec. In the lower temperature range all log ?h against 1/T curves decrease linearly with an activation energy of 0.019 + 0.002 ev. An attempt has been made to interpret the results in terms of a model of hole transport in the upper two valence bands of CdS.