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71.
We have found strong supporting evidence for the helical structures of single-stranded nucleic acids by stretching individual molecules of polyadenylic acid [poly(A)] and polycytidylic acid [poly(C)]. Analyzing the force versus extension data using a two-state elastic model in which random-coil domains alternate with rigid helical domains allows one to extract the thermodynamic and structural properties. In addition, it also yields moderate to low cooperativity of the helix-coil transition for poly(A) and poly(C), respectively. 相似文献
72.
Fiber optic illumination of a poly(dimethylsiloxane) sheath flow cuvette for diode laser induced fluorescence detection in capillary electrophoresis
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Cameron D. Skinner 《Electrophoresis》2015,36(4):502-508
A Tee configuration sheath flow cuvette with square cross‐section channels has been produced in PDMS for CE detection. The output of a 1.4 W laser diode operating at 450 nm was focused onto the 300 μm core of a 370 μm od fiber optic whose end was inserted into one arm of the Tee for LIF. The optimal configuration had the fiber optic positioned 500 μm downstream from the intersection and the end of the 35 cm 50 μm id 365 μm od capillary just outside the intersection and in the leg of the Tee, resulting in a 90° configuration. Detection limits of 50 and 3 pM and linear calibrations of at least three orders of magnitude were obtained for Lucifer Yellow and fluorescein, respectively. 相似文献
73.
Stoner-Ma D Skinner JM Schneider DK Cowan M Sweet RM Orville AM 《Journal of synchrotron radiation》2011,18(1):37-40
Three-dimensional structures derived from X-ray diffraction of protein crystals provide a wealth of information. Features and interactions important for the function of macromolecules can be deduced and catalytic mechanisms postulated. Still, many questions can remain, for example regarding metal oxidation states and the interpretation of `mystery density', i.e. ambiguous or unknown features within the electron density maps, especially at ~2 ? resolutions typical of most macromolecular structures. Beamline X26-C at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL), provides researchers with the opportunity to not only determine the atomic structure of their samples but also to explore the electronic and vibrational characteristics of the sample before, during and after X-ray diffraction data collection. When samples are maintained under cryo-conditions, an opportunity to promote and follow photochemical reactions in situ as a function of X-ray exposure is also provided. Plans are in place to further expand the capabilities at beamline X26-C and to develop beamlines at NSLS-II, currently under construction at BNL, which will provide users access to a wide array of complementary spectroscopic methods in addition to high-quality X-ray diffraction data. 相似文献
74.
Skinner OS McLafferty FW Breuker K 《Journal of the American Society for Mass Spectrometry》2012,23(6):1011-1014
The structural evolution of ubiquitin after transfer into the gas phase was studied by electron capture dissociation. Site-specific
fragment yields show that ubiquitin’s solution fold is overall unstable in the gas phase, but unfolding caused by loss of
solvent is slowest in regions stabilized by salt bridges. 相似文献
75.
Théberge R Connors LH Skinner M Costello CE 《Journal of the American Society for Mass Spectrometry》2000,11(2):172-175
In our continuing efforts to develop mass spectrometry-based methods for transthyretin (TTR) variant detection and characterization, we have sought to use matrix-assisted laser desorption/ionization (MALDI) bioreactive probes incorporating immobilized trypsin for screening purposes. These devices show good diagnostic potential as a clinical screening tool to detect amino acid substitutions in TTR. MALDI probes allow the on-probe generation of tryptic digests. The subsequent mass analysis of the on-probe digest yields the peptide map. The inherent advantages of this method include considerably reduced digestion times (minutes vs. hours), absence of autolysis products, minimized sample handling, and hence minimal sample loss. A further advantage is that the opportunity for loss of hydrophobic peptides is reduced because no sample transfer occurs. The method can be applied as a preliminary screen for TTR variants where TTR is isolated from patient serum through immunoprecipitation. This method should also be applicable to other proteins and suitable for automation. 相似文献
76.
Martin Donnelley Kaye S. Morgan Andreas Fouras William Skinner Kentaro Uesugi Naoto Yagi Karen K. W. Siu David W. Parsons 《Journal of synchrotron radiation》2009,16(4):553-561
Fine non‐biological particles small enough to be suspended in the air are continually inhaled as we breathe. These particles deposit on airway surfaces where they are either cleared by airway defences or can remain and affect lung health. Pollutant particles from vehicles, building processes and mineral and industrial dusts have the potential to cause both immediate and delayed health problems. Because of their small size, it has not been possible to non‐invasively examine how individual particles deposit on live airways, or to consider how they behave on the airway surface after deposition. In this study, synchrotron phase‐contrast X‐ray imaging (PCXI) has been utilized to detect and monitor individual particle deposition. The in vitro detectability of a range of potentially respirable particulates was first determined. Of the particulates tested, only asbestos, quarry dust, fibreglass and galena (lead sulfate) were visible in vitro. These particulates were then examined after delivery into the nasal airway of live anaesthetized mice; all were detectable in vivo but each exhibited different surface appearances and behaviour along the airway surface. The two fibrous particulates appeared as agglomerations enveloped by fluid, while the non‐fibrous particulates were present as individual particles. Synchrotron PCXI provides the unique ability to non‐invasively detect and track deposition of individual particulates in live mouse airways. With further refinement of particulate sizing and delivery techniques, PCXI should provide a novel approach for live animal monitoring of airway particulates relevant to lung health. 相似文献
77.
Sisyphus amplification, familiar from quantum optics, has recently been reported as a mechanism to explain the enhanced quality factor of a classical resonant (tank) circuit coupled to a superconducting flux qubit. Here we present data from a coupled system, comprising a quantum mechanical rf SQUID (flux qubit) reactively monitored by an ultrahigh quality factor noise driven rf resonator and excited by microwaves. The system exhibits enhancement of the tank-circuit resonance, bringing it significantly closer (within 1%) to the lasing limit, than previously reported results. 相似文献
78.
The distribution of solute arrival times, W(t;x), at position x in disordered porous media does not generally follow Gaussian statistics. A previous publication determined W(t;x) in the absence of diffusion from a synthesis of critical path, percolation scaling, and cluster statistics of percolation.
In that publication, W(t;x) as obtained from theory, was compared with simulations in the particular case of advective solute transport through a two-dimensional
model porous medium at the percolation threshold for various lengths x. The simulations also did not include the effects of diffusion. Our prediction was apparently verified. In the current work
we present numerical results related to moments of W(x;t), the spatial solute distribution at arbitrary time, and extend the theory to consider effects of molecular diffusion in
an asymptotic sense for large Peclet numbers, Pe. However, results for the scaling of the dispersion coefficient in the range 1<Pe<100 agree with those of other authors, while results for the dispersivity as a function of spatial scale also appear to explain
experiment. 相似文献
79.
Skinner TE Kobzar K Luy B Bendall MR Bermel W Khaneja N Glaser SJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,179(2):241-249
An optimal control algorithm for generating purely phase-modulated pulses is derived. The methodology is applied to obtain broadband excitation with unprecedented tolerance to RF inhomogeneity. Design criteria were transformation of Iz-->Ix over resonance offsets of +/-25 kHz for constant RF amplitude anywhere in the range 10-20 kHz, with a pulse length of 1 ms. Simulations transform Iz to greater than 0.99 Ix over the targetted ranges of resonance offset and RF variability. Phase deviations in the final magnetization are less than 2-3 degrees over almost the entire range, with sporadic deviations of 6-9 degrees at a few offsets for the lowest RF (10 kHz) in the optimized range. Experimental performance of the new pulse is in excellent agreement with the simulations, and the robustness of the excitation pulse and a derived refocusing pulse are demonstrated by insertion into conventional HSQC and HMBC-type experiments. 相似文献
80.
Wandering is a typical feature of wing-tip vortices and it consists in random fluctuations of the vortex core. Consequently, vortices
measured by static measuring techniques appear to be more diffuse than in reality, so that a correction method is needed.
In the present paper statistical simulations of the wandering of a Lamb-Oseen vortex are first performed by representing the
vortex core locations through bi-variate normal probability density functions. It is found that wandering amplitudes smaller
than 60% of the core radius are well predicted by using the ratio between the RMS value of the mean cross-velocity and its
slope measured at the mean vortex center. Furthermore, the principal axes of wandering can be accurately evaluated from the
opposite of the cross-correlation coefficient between the spanwise and the normal velocities measured at the mean vortex center.
The correction of the wandering smoothing effects is then carried out through four different algorithms that perform the deconvolution
of the mean velocity field with the probability density function that represents the wandering. The corrections performed
are very accurate for the simulations with wandering amplitudes smaller than 60% of the core radius, whereas errors become
larger with increasing wandering amplitudes. Subsequently, the whole procedure to evaluate wandering and to correct the mean
velocity field is applied to static measurements, carried out with a fast-response five-hole pressure probe, of a tip vortex
generated from a NACA 0012 half-wing model. It is found that the wandering is predominantly in the upward-outboard to downward-inboard
direction. Furthermore, the wandering amplitude grows with increasing streamwise distance from the wing, whereas it decreases
with increasing angle of attack and free-stream velocity. 相似文献