1,302 research outputs found
Measurement of gut permeability using fluorescent tracer agent technology
Abstract The healthy gut restricts macromolecular and bacterial movement across tight junctions, while increased intestinal permeability accompanies many intestinal disorders. Dual sugar absorption tests, which measure intestinal permeability in humans, present challenges. Therefore, we asked if enterally administered fluorescent tracers could ascertain mucosal integrity, because transcutaneous measurement of differentially absorbed molecules could enable specimen-free evaluation of permeability. We induced small bowel injury in rats using high- (15 mg/kg), intermediate- (10 mg/kg), and low- (5 mg/kg) dose indomethacin. Then, we compared urinary ratios of enterally administered fluorescent tracers MB-402 and MB-301 to urinary ratios of sugar tracers lactulose and rhamnose. We also tested the ability of transcutaneous sensors to measure the ratios of absorbed fluorophores. Urinary fluorophore and sugar ratios reflect gut injury in an indomethacin dose dependent manner. The fluorophores generated smooth curvilinear ratio trajectories with wide dynamic ranges. The more chaotic sugar ratios had narrower dynamic ranges. Fluorophore ratios measured through the skin distinguished indomethacin-challenged from same day control rats. Enterally administered fluorophores can identify intestinal injury in a rat model. Fluorophore ratios are measureable through the skin, obviating drawbacks of dual sugar absorption tests. Pending validation, this technology should be considered for human use
Cone-beam CT reconstruction with gravity-induced motion.
Fixed-gantry cone-beam computed tomography (CBCT), where the imaging hardware is fixed while the subject is continuously rotated 360° in the horizontal position, has implications for building compact and affordable fixed-gantry linear accelerators (linacs). Fixed-gantry imaging with a rotating subject presents a challenging image reconstruction problem where the gravity-induced motion is coupled to the subject's rotation angle. This study is the first to investigate the feasibility of fixed-gantry CBCT using imaging data of three live rabbits in an ethics-approved study. A novel data-driven motion correction method that combines partial-view reconstruction and motion compensation was developed to overcome this challenge. Fixed-gantry CBCT scans of three live rabbits were acquired on a standard radiotherapy system with the imaging beam fixed and the rabbits continuously rotated using an in-house programmable rotation cradle. The reconstructed images of the thoracic region were validated against conventional CBCT scans acquired at different cradle rotation angles. Results showed that gravity-induced motion caused severe motion blur in all of the cases if unaccounted for. The proposed motion correction method yielded clinically usable image quality with <1 mm gravity-induced motion blur for rabbits that were securely immobilized on the rotation cradle. Shapes of the anatomic structures were correctly reconstructed with <0.5 mm accuracy. Translational motion accounted for the majority of gravity-induced motion. The motion-corrected reconstruction represented the time-averaged location of the thoracic region over a 360° rotation. The feasibility of fixed-gantry CBCT has been demonstrated. Future work involves the validation of imaging accuracy for human subjects, which will be useful for emerging compact fixed-gantry radiotherapy systems
Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence
The cross section for coherent pair production by linearly polarised photons
in the 20-170 GeV energy range was measured for photon aligned incidence on
ultra-high quality diamond and germanium crystals. The theoretical description
of coherent bremsstrahlung and coherent pair production phenomena is an area of
active theoretical debate and development. However, under our experimental
conditions, the theory predicted the combined cross section and polarisation
experimental observables very well indeed. In macroscopic terms, our experiment
measured a birefringence effect in pair production in a crystal. This study of
this effect also constituted a measurement of the energy dependent linear
polarisation of photons produced by coherent bremsstrahlung in aligned
crystals. New technologies for manipulating high energy photon beams can be
realised based on an improved understanding of QED phenomena at these energies.
In particular, this experiment demonstrates an efficient new polarimetry
technique. The pair production measurements were done using two independent
methods simultaneously. The more complex method using a magnet spectrometer
showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for
publicatio
Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons
We present the first experimental results on the use of a thick aligned Si
crystal acting as a quarter wave plate to induce a degree of circular
polarisation in a high energy linearly polarised photon beam. The linearly
polarised photon beam is produced from coherent bremsstrahlung radiation by 178
GeV unpolarised electrons incident on an aligned Si crystal, acting as a
radiator. The linear polarisation of the photon beam is characterised by
measuring the asymmetry in electron-positron pair production in a Ge crystal,
for different crystal orientations. The Ge crystal therefore acts as an
analyser. The birefringence phenomenon, which converts the linear polarisation
to circular polarisation, is observed by letting the linearly polarised photons
beam pass through a thick Si quarter wave plate crystal, and then measuring the
asymmetry in electron-positron pair production again for a selection of
relative angles between the crystallographic planes of the radiator, analyser
and quarter wave plate. The systematics of the difference between the measured
asymmetries with and without the quarter wave plate are predicted by theory to
reveal an evolution in the Stokes parameters from which the appearance of a
circularly polarised component in the photon beam can be demonstrated. The
measured magnitude of the circularly polarised component was consistent with
the theoretical predictions, and therefore is in indication of the existence of
the birefringence effect.Comment: 12 pages, 12 figures, 1 table, REVTeX4 two column, Version for
publicatio
Results on the Coherent Interaction of High Energy Electrons and Photons in Oriented Single Crystals
The CERN-NA-59 experiment examined a wide range of electromagnetic processes
for multi-GeV electrons and photons interacting with oriented single crystals.
The various types of crystals and their orientations were used for producing
photon beams and for converting and measuring their polarisation.
The radiation emitted by 178 GeV unpolarised electrons incident on a 1.5 cm
thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the
String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised
photon beams.
A new crystal polarimetry technique was established for measuring the linear
polarisation of the photon beam. The polarimeter is based on the dependence of
the Coherent Pair Production (CPP) cross section in oriented single crystals on
the direction of the photon polarisation with respect to the crystal plane.
Both a 1 mm thick single crystal of Germanium and a 4 mm thick multi-tile set
of synthetic Diamond crystals were used as analyzers of the linear
polarisation.
A birefringence phenomenon, the conversion of the linear polarisation of the
photon beam into circular polarisation, was observed. This was achieved by
letting the linearly polarised photon beam pass through a 10 cm thick Silicon
single crystal that acted as a "quarter wave plate" (QWP) as suggested by N.
Cabibbo et al.Comment: Presented at International workshop "Relativistic Channeling and
Related Coherent Phenomena", Frascati (Rome) 23-26 March 200
Coherent bremsstrahlung, boherent pair production, birefringence and polarimetry in the 20-170 GeV energy range using aligned crystals
The processes of coherent bremsstrahlung (CB) and coherent pair production
(CPP) based on aligned crystal targets have been studied in the energy range
20-170 GeV. The experimental arrangement allowed for measurements of single
photon properties of these phenomena including their polarization dependences.
This is significant as the theoretical description of CB and CPP is an area of
active theoretical debate and development. With the theoretical approach used
in this paper both the measured cross sections and polarization observables are
predicted very well. This indicates a proper understanding of CB and CPP up to
energies of 170 GeV. Birefringence in CPP on aligned crystals is applied to
determine the polarization parameters in our measurements. New technologies for
high energy photon beam optics including phase plates and polarimeters for
linear and circular polarization are demonstrated in this experiment. Coherent
bremsstrahlung for the strings-on-strings (SOS) orientation yields a larger
enhancement for hard photons than CB for the channeling orientations of the
crystal. Our measurements and our calculations indicate low photon
polarizations for the high energy SOS photons.Comment: 23 pages, 27 figures, 2 tables, REVTeX4 two column
Transdermal fluorescence detection of a dual fluorophore system for noninvasive point-of-care gastrointestinal permeability measurement
The intestinal mucosal barrier prevents macromolecules and pathogens from entering the circulatory stream. Tight junctions in this barrier are compromised in inflammatory bowel diseases, environmental enteropathy, and enteric dysfunction. Dual sugar absorption tests are a standard method for measuring gastrointestinal integrity, however, these are not clinically amenable. Herein, we report on a dual fluorophore system and fluorescence detection instrumentation for which gastrointestinal permeability is determined in a rat small bowel disease model from the longitudinal measured transdermal fluorescence of each fluorophore. This fluorophore technology enables a specimen-free, noninvasive, point-of-care gastrointestinal permeability measurement which should be translatable to human clinical studies
Pressure-induced valence anomaly in TmTe probed by resonant inelastic x-ray scattering
The pressure-induced valence transition in TmTe was investigated by resonant inelastic x-ray scattering at the Tm L(3) edge, a powerful probe of the rare-earth valent state. The data are analyzed within the Anderson impurity model which yields key parameters such as the Tm 4f-5d hybridization. In addition to the general tendency of the f electrons towards delocalization, we find a plateau in both the Tm valence and hybridization pressure dependences between 4.3 and 6.5 GPa which is interpreted in terms of an n-channel Kondo (NCK) screening process. This behavior is at odds with the usually continuous, single-channel Kondo-like f delocalization while being supported by the seminal calculations of the NCK temperature in Tm ion by Saso et al. Our study raises the interesting possibility that an NCK effect realized in a compressed mixed-valent f system could impede the concomitant electron delocalization
Black Holes as Effective Geometries
Gravitational entropy arises in string theory via coarse graining over an
underlying space of microstates. In this review we would like to address the
question of how the classical black hole geometry itself arises as an effective
or approximate description of a pure state, in a closed string theory, which
semiclassical observers are unable to distinguish from the "naive" geometry. In
cases with enough supersymmetry it has been possible to explicitly construct
these microstates in spacetime, and understand how coarse-graining of
non-singular, horizon-free objects can lead to an effective description as an
extremal black hole. We discuss how these results arise for examples in Type II
string theory on AdS_5 x S^5 and on AdS_3 x S^3 x T^4 that preserve 16 and 8
supercharges respectively. For such a picture of black holes as effective
geometries to extend to cases with finite horizon area the scale of quantum
effects in gravity would have to extend well beyond the vicinity of the
singularities in the effective theory. By studying examples in M-theory on
AdS_3 x S^2 x CY that preserve 4 supersymmetries we show how this can happen.Comment: Review based on lectures of JdB at CERN RTN Winter School and of VB
at PIMS Summer School. 68 pages. Added reference
Cardiac Potassium Channels: Physiological Insights for Targeted Therapy.
The development of novel drugs specifically directed at the ion channels underlying particular features of cardiac action potential (AP) initiation, recovery, and refractoriness would contribute to an optimized approach to antiarrhythmic therapy that minimizes potential cardiac and extracardiac toxicity. Of these, K(+) channels contribute numerous and diverse currents with specific actions on different phases in the time course of AP repolarization. These features and their site-specific distribution make particular K(+) channel types attractive therapeutic targets for the development of pharmacological agents attempting antiarrhythmic therapy in conditions such as atrial fibrillation. However, progress in the development of such temporally and spatially selective antiarrhythmic drugs against particular ion channels has been relatively limited, particularly in view of our incomplete understanding of the complex physiological roles and interactions of the various ionic currents. This review summarizes the physiological properties of the main cardiac potassium channels and the way in which they modulate cardiac electrical activity and then critiques a number of available potential antiarrhythmic drugs directed at them
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