122 research outputs found
Holographic Methods as Local Probes of the Atomic Order in Solids
In the last fifteen years several techniques based on the holographic
principle have been developed for the study of the 3D local order in solids.
These methods use various particles: electrons, hard x-ray photons, gamma
photons, or neutrons to image the atoms. Although the practical realisation of
the various imaging experiments is very different, there is a common thread;
the use of inside reference points for holographic imaging. In this paper we
outline the basics of atomic resolution holography using inside reference
points, especially concentrating to the hard x-ray case. Further, we outline
the experimental requirements and what has been practically realized in the
last decade. At last we give examples of applications and future perspectives.Comment: 14 pages, 6 figure
Measurement of synchrotron-radiation-excited Kossel patterns
Kossel line patterns contain information on the crystalline structure, such as the
magnitude and the phase of Bragg reflections. For technical reasons, most of
these patterns are obtained using electron beam excitation, which leads to
surface sensitivity that limits the spatial extent of the structural information. To
obtain the atomic structure in bulk volumes, X-rays should be used as the
excitation radiation. However, there are technical problems, such as the need
for high resolution, low noise, large dynamic range, photon counting, twodimensional
pixel detectors and the small spot size of the exciting beam, which
have prevented the widespread use of Kossel pattern analysis. Here, an
experimental setup is described, which can be used for the measurement of
Kossel patterns in a reasonable time and with high resolution to recover
structural information
Imaging atom-clusters by hard x-ray free electron lasers
The ingenious idea of single molecule imaging by hard x-ray Free Electron
Laser (X-FEL) pulses was recently proposed by Neutze et al.
[Nature,406,752(2000)]. However, in their numerical modelling of the Coulomb
explosion several interactions were neglected and no reconstruction of the
atomic structure was given. In this work we carried out improved molecular
dynamics calculations including all quantum processes which affect the
explosion. Based on this time evolution we generated composite elastic
scattering patterns, and by using Fienup's algorithm successfully reconstructed
the original atomic structure. The critical evaluation of these results gives
guidelines and sets important conditions for future experiments aiming single
molecule structure solution.Comment: 8 pages, 4 figures, submitted to Europhysics Letter
3D atomic structure from a single XFEL pulse
X-ray Free Electron Lasers (XFEL) are the most advanced pulsed x-ray sources.
Their extraordinary pulse parameters promise unique applications. Indeed,
several new methods have been developed at XFEL-s. However, no methods are
known, which would allow ab initio atomic level structure determination using
only a single XFEL pulse. Here, we present experimental results, demonstrating
the determination of the 3D atomic structure from data obtained during a single
25 fs XFEL pulse. Parallel measurement of hundreds of Bragg reflections was
done by collecting Kossel line patterns of GaAs and GaP. With these
measurements, we reached the ultimate temporal limit of the x-ray structure
solution possible today. These measurements open the way for studying
non-repeatable fast processes and structural transformations in crystals for
example measuring the atomic structure of matter at extremely non-ambient
conditions or transient structures formed in irreversible physical, chemical,
or biological processes. It would also facilitate time resolved pump-probe
structural studies making them significantly shorter than traditional serial
crystallography.Comment: 16 pages of manuscript followed by 15 pages of supplementary
informatio
Citrobacter freundii infection after acute necrotizing pancreatitis in a patient with a pancreatic pseudocyst: a case report
<p>Abstract</p> <p>Introduction</p> <p>Infections are the most frequent and severe complications of acute necrotizing pancreatitis with a mortality rate of up to 80 percent. Although experimental and clinical studies suggest that the microbiologic source of pancreatic infection could be enteric, information in this regard is controversial.</p> <p>Case presentation</p> <p>We describe a <it>Citrobacter freundii </it>isolation by endoscopy ultrasound fine needle aspiration in a 80-year-old Caucasian man with pancreatic pseudocyst after acute necrotizing pancreatitis.</p> <p>Conclusion</p> <p>Our case report confirms that this organism can be recovered in patients with a pancreatic pseudocyst. On-site cytology feedback was crucial to the successful outcome of this case as immediate interpretation of the fine needle aspiration sample directed the appropriate cultures and, ultimately, the curative therapy. To the best of our knowledge, this is the first reported case of isolated pancreatic <it>C. freundii </it>diagnosed by endoscopy ultrasound fine needle aspiration.</p
EUS-derived criteria for distinguishing benign from malignant metastatic solid hepatic masses
Background
Detection of hepatic metastases during EUS is an important component of tumor staging.
Objective
To describe our experience with EUS-guided FNA (EUS-FNA) of solid hepatic masses and derive and validate criteria to help distinguish between benign and malignant hepatic masses.
Design
Retrospective study, survey.
Setting
Single, tertiary-care referral center.
Patients
Medical records were reviewed for all patients undergoing EUS-FNA of solid hepatic masses over a 12-year period.
Interventions
EUS-FNA of solid hepatic masses.
Main Outcome Measurements
Masses were deemed benign or malignant according to predetermined criteria. EUS images from 200 patients were used to create derivation and validation cohorts of 100 cases each, matched by cytopathologic diagnosis. Ten expert endosonographers blindly rated 15 initial endosonographic features of each of the 100 images in the derivation cohort. These data were used to derive an EUS scoring system that was then validated by using the validation cohort by the expert endosonographer with the highest diagnostic accuracy.
Results
A total of 332 patients underwent EUS-FNA of a hepatic mass. Interobserver agreement regarding the initial endosonographic features among the expert endosonographers was fair to moderate, with a mean diagnostic accuracy of 73% (standard deviation 5.6). A scoring system incorporating 7 EUS features was developed to distinguish benign from malignant hepatic masses by using the derivation cohort with an area under the receiver operating curve (AUC) of 0.92; when applied to the validation cohort, performance was similar (AUC 0.86). The combined positive predictive value of both cohorts was 88%.
Limitations
Single center, retrospective, only one expert endosonographer deriving and validating the EUS criteria.
Conclusion
An EUS scoring system was developed that helps distinguish benign from malignant hepatic masses. Further study is required to determine the impact of these EUS criteria among endosonographers of all experience
Inheriting library cards to Babel and Alexandria: Contemporary metaphors for the digital library
Librarians have been consciously adopting metaphors to describe library concepts since the nineteenth century, helping us to structure our understanding of new technologies. We have drawn extensively on these figurative frameworks to explore issues surrounding the digital library, yet very little has been written to date which interrogates how these metaphors have developed over the years. Previous studies have explored library metaphors, using either textual analysis or ethnographic methods to investigate their usage. However, this is to our knowledge the first study to use bibliographic data, corpus analysis, qualitative sentiment weighting and close reading to study particular metaphors in detail. It draws on a corpus of over 450 articles to study the use of the metaphors of the Library of Alexandria and Babel, concluding that both have been extremely useful as framing metaphors for the digital library. However, their longstanding use has seen them become stretched as metaphors, meaning that the fieldâs figurative framework now fails to represent the changing technologies which underpin contemporary digital libraries
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