Showing papers on "Resolution (electron density) published in 1997"

Nonlinear scanning laser microscopy by third harmonic generation

Abstract: Third harmonic generation near the focal point of a tightly focused beam is used to probe microscopical structures of transparent samples. It is shown that this method can resolve interfaces and inhomogeneities with axial resolution comparable to the confocal length of the beam. Using 120 fs pulses at 1.5 μm, we were able to resolve interfaces with a resolution of 1.2 μm. Two-dimensional cross-sectional images have also been produced.

Clocking transient chemical changes by ultrafast electron diffraction

Abstract: With the advent of femtosecond (fs) time resolution in spectroscopic experiments, it is now possible to study the evolution of nuclear motions in chemical and photobiochemical reactions. In general, the reaction is clocked by an initial fs laser pulse (which establishes a zero of time) and the dynamics are probed by a second fs pulse; the detection methods include conventional and photoelectron spectroscopy and mass spectrometry. Replacing the probe laser with electron pulses offers a means for imaging ultrafast structural changes with diffraction techniques, which should permit the study of molecular systems of greater complexity (such as biomolecules). On such timescales, observation of chemical changes using electron scattering is non-trivial, because space-charge effects broaden the electron pulse width and because temporal overlap of the (clocking) photon pulse and the (probe) electron pulse must be established. Here we report the detection of transient chemical change during molecular dissociation using ultrafast electron diffraction. We are able to detect a change in the scattered electron beam with the zero of time established unambiguously and the timing of the changes clocked in situ. This ability to clock changes in scattering is essential to studies of the dynamics of molecular structures.

High spatial resolution quantitative microwave impedance microscopy by a scanning tip microwave near-field microscope

Abstract: A recently developed scanning tip microwave near-field microscope has been improved to achieve a spatial resolution of 100 nm (∼λ/106). Furthermore, explicit calculations of the field distribution using a simplified model allow quantitative microscopy of dielectric properties for dielectric materials. A detection sensitivity of δe/e∼6×10−4 has been achieved.

Survey of conflict detection and resolution modeling methods

Abstract: The design and evaluation of traffic conflict detection and resolution systems requires the use of analytical models that describe encounter dynamics and the costs and benefits of avoidance actions. A number of such models have been applied in the past to the problem, but there has been no cohesive discussion or comparative evaluation of these approaches. Each method has benefits and limitations, and future efforts may be facilitated by combining the best features of different techniques. This paper presents a summary of conflict detection and resolution modeling approaches. Modeling techniques are categorized and the fundamental assumptions, capabilities, and limitations of each approach are described. The methods are evaluated and compared based on their applicability to free flight traffic conflict situations.

Far-field fluorescence microscopy with three-dimensional resolution in the 100-nm range.

Abstract: We report three-dimensional (3D) microscopy with nearly isotropic resolution in the lambda/5-lambda/10 range. Our approach combines 4PI-confocal two-photon fluorescence microscopy with image restoration. The 3D resolution is demonstrated with densely clustered beads as well as with F-actin fibers in mouse fibroblast cells. A comparison with unrestored two-photon confocal images reveals a total reduction of the uncertainty volume up to a factor of 15.

Ab Initio Structure Solution from X-ray Powder Data at Moderate Resolution: Crystal Structure of a Microporous Layer Silicate

Abstract: The ab initio crystal structure solution of a layer silicate is presented. Since the crystallinity of the material is limited, the corresponding X-ray powder pattern shows only moderate resolution. Based on a new interpretation of the tangent formula, a general direct method strategy for the determination of the crystal structure of poorly crystalline materials from X-ray powder patterns is presented. The structure model derived from the interpretation of the E map was subsequently refined with the Rietveld technique using the whole diffraction pattern. This leads finally to a picture of the crystal structure of atomic resolution which explains in full detail the specific characteristics of the material.

Synchrotron Powder Diffraction using Imaging Plates: Crystal Structure Determination and Rietveld Refinement

Abstract: The combination of intense X-ray synchrotron radiation and an imaging-plate area detector makes it possible to extract real-time structural information using Rietveld refinement of individual time slices. Powder diffraction data from capillary samples were collected using a flat imaging plate mounted perpendicular to, or at an oblique angle to, the incoming beam. Owing to the geometry of the experiments, several factors must be taken into account when Rietveld refinement of powder diffraction data obtained using a flat imaging plate is performed: (i) nonequal step sizes are obtained when the diffraction profiles are extracted; (ii) the refined zero-point correction is different from that for conventional diffraction geometry; (iii) the sample-detector distance is not constant, requiring a modified geometric term in the Lorentz factor; (iv) the geometric contribution to the instrumental resolution function must be considered. The geometric factors have been derived and are discussed. The Rietveld program XRS-82 and the profile extraction program ALLHKL have been modified to allow flat imaging-plate powder diffraction data to be refined. The Rietveld refinement of powder diffraction data of α-quartz collected using a 30 s exposure is presented. LaB6 powder diffraction data were collected using various settings. The profile variation with angle and the resolution function are described. Data were collected up to sin θ/λ = 1.29 A−1 (d values down to 0.39 A) using high energy and with the imaging plate inclined at an angle to the incoming beam.

High resolution scanning raman microscope

Abstract: A method of obtaining high-resolution spectroscopic information from a scanning microscope. An optical beam is directed at a sample and light emitted from the sample (e.g., from Raman scattering or fluorescence) is collected. Resolution is improved by supporting a tiny conductive element (e.g., a silver particle) from a probe located within the optical beam area. The conductive element enhances the light emitted from molecules in the vicinity of the probe. The invention provides the high spatial resolution of microscopes such as the AFM with the high chemical detection sensitivity of surface enhanced Raman spectroscopy. This combination allows the isolation and differentiation of single molecules on surfaces of nanostructures.

The light yield nonproportionality component of scintillator energy resolution

Abstract: The scintillator energy resolution component which is due to light yield nonproportionality has been characterized for NaI(Tl) and LSO. Results are based on a discrete convolution of measured electron response data and the electron energy distribution resulting from full-energy absorption events. The behavior of this energy resolution component as a function of energy is observed to be strongly dependent on the shape of the electron response. Furthermore, in some energy regions, the light yield nonproportionality component is observed to be larger than the resolution predicted by assuming Poisson photoelectron statistics. Characterization of this energy resolution component will facilitate deconvolution of other components from the total energy resolution.

Phase contrast hard x-ray microscopy with submicron resolution

Abstract: In this letter we present a hard x-ray phase contrast microscope based on the divergent and coherent beam exiting an x-ray waveguide. It uses lensless geometrical projection to magnify spatial variations in optical path length more than 700 times. Images of a nylon fiber and a gold test pattern were obtained with a resolution of 0.14 μm in one direction. Exposure times as short as 0.1 s gave already visible contrast, opening the way to high resolution, real time studies.

Reflection scanning near-field optical microscopy with uncoated fiber tips: How good is the resolution really?

Abstract: We have investigated the optical resolution of a scanning near-field optical microscope in reflection collection mode using an uncoated fiber tip We demonstrate that the apparent resolution in the optical signal (better than 70 nm) is a topography-induced effect We believe that the purely optical resolution is only of the order of λ/2 and diffraction limited

Coordination of Ti (super 4+) in silicate glasses; a high-resolution XANES spectroscopy study at the Ti K edge

Abstract: Abstract The coordination environment of Ti in eight Ti-bearing glasses of the Na2Si4O9-Na2Ti4O9 join (NTS) and in six ATY2 glasses (A2O·TiO2·2YO2, with A = Na, K, or Rb and Y = Si or Ge) was determined using high-resolution, X-ray absorption near-edge structure (XANES) spectroscopy at the Ti K edge in ambient conditions. Fivefold-coordinated Ti ([5]Ti) is the dominant Ti species (≥50 ± 10% of the total Ti) in all the glasses studied. Sixfold-coordinated Ti was detected mostly in sodic glasses (NTS, NTS2, NTG2), and it increases with TiO2 content (as high as 40 ± 10% of the total of Ti in the most TiO2-rich NTS glasses) and in the order Si < Ge. Fourfold-coordinated Ti was detected only in nonsodic ATY2 glasses, and its content increases in the order Na < K < Rb and Ge < Si. Fivefold-coordinated Ti4+ is probably present as square pyramidal, titanyl-bearing moieties, or (|5]Ti=O)O4. A synthesis of Ti4+ coordination for oxide glasses derived using direct methods (X-ray absorption and neutron scattering) can be used, for instance, to help in the interpretation of Raman scattering spectra collected for Ti-bearing glasses and to estimate NBO/T ratios better for titanosilicate glasses and melts.

Direct observation of ferroelectric domains in litao3 using environmental scanning electron microscopy

Abstract: Direct observation of ferroelectric domain structures in LiTa${\mathrm{O}}_{3}$ crystal, without etching or surface coating, has been realized by using environmental scanning electron microscopy in secondary electron emission mode. The new method can nondestructively provide domain contrast image at submicron resolution, and the domain contrast image is very stable. Conditions for best domain contrast of LiTa${\mathrm{O}}_{3}$ crystals have been established.

Three-dimensional diffuse x-ray scattering from crystals of Staphylococcal nuclease (protein dynamicsyliquid-like motions)

Abstract: We have developed methods for obtainingand characterizing three-dimensional maps of the reciprocal-space distribution of diffuse x-ray scattering from proteincrystals, and have used the methods to study the nature ofdisorder in crystals of Staphylococcal nuclease. Experimen-tally obtained maps are 99.5% complete in the reciprocal-space resolution range of 10 A–2.5 A, show symmetry consis-tent with the P4 1 space group of the unit cell, and are highlyreproducible. Quantitative comparisons of the data withthree-dimensional simulations imply liquid-like motions ofthe protein [Caspar, D. L. D., Clarage, J., Salunke, D. M. &Clarage, M. (1988) Nature (London) 332, 659–662], with acorrelation length of 10 A and a root-mean-square displace-ment of 0.36 A. Biological macromolecules perform many important func-tions, including enzymatic catalysis, receptor recognition, andsignal transduction. Physical measurements from a variety ofsources suggest that a common feature in most biologicalprocesses is molecular flexibility and motion. In the solid state,this flexibility introduces crystalline disorder in the form of acollection of conformationally distinct states of the unit cell.In x-ray crystallography, disorder, even in a good crystal thatdiffracts to high resolution, can cause x-rays to be scatteredinto angles that do not satisfy the Bragg condition (1–7). This‘‘diffuse scattering’’ has been used to study the nature ofdisorder in protein crystals and has been shown to be a usefulexperimental technique for characterizing the fluctuations ofcrystalline proteins (8–16). A common feature of reportedstudies, however, is a limited sampling of reciprocal space fromusing, at most, a few x-ray exposures for analysis, and leavingmost of the accessible data unrecorded. Although simulationshave been successful in reproducing diffuse features observedin individual diffraction images, a full three-dimensional dataset provides more independent measurements and could beused to test models that are more complex than those thatalready have been proposed.We sought to obtain images of diffuse x-ray diffraction from