248 research outputs found
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A high-resolution transmission-type x-ray spectrometer designed for observation of the KÎą transitions of highly charged high-Z ions
High-resolution reflection-type crystal spectrometers have been used for x-ray energies up to 13 keV, e.g., the K-shell radiation of heliumlike Kr. In order to extend crystal spectrometer measurements to higher energy x rays from higher-Z elements, we employ the crystal in transmission. The geometry we use is known as DuMond geometry. Using such a transmission-type crystal x-ray spectrometer, we have measured the K-shell radiation of various highly charged high-Z ions. In particular, we present a measurement of the 1s2pâ1P1â1s2â1S0 transition in heliumlike xenon, Xe52+. For this transition, we measure a linewidth of 34 eV, which demonstrates that the resolving power we achieved with the new spectrometer is on the order of 100
Hyponatremia revisited: Translating physiology to practice
The complexity of hyponatremia as a clinical problem is likely caused by the opposite scenarios that accompany this electrolyte disorder regarding pathophysiology (depletional versus dilutional hyponatremia, high versus low vasopressin levels) and therapy (rapid correction to treat cerebral edema versus slow correction to prevent osmotic demyelination, fluid restriction versus fluid resuscitation). For a balanced differentiation between these opposites, an understanding of the pathophysiology of hyponatremia is required. Therefore, in this review an attempt is made to translate the physiology of water balance regulation to strategies that improve the clinical management of hyponatremia. A physiology-based approach to the patient with hyponatremia is presented, first addressing the possibility of acute hyponatremia, and then asking if and if so why vasopressin is secreted non-osmotically. Additional diagnostic recommendations are not to rely too heavily of the assessment of the extracellular fluid volume, to regard the syndrome of inappropriate antidiuresis as a diagnosis of exclusion, and to rationally investigate the pathophysiology of hyponatremia rather than to rely on isolated laboratory values with arbitrary cutoff values. The features of the major hyponatremic disorders are discussed, including diuretic-induced hyponatremia, adrenal and pituitary insufficiency, the syndrome of inappropriate antidiuresis, cerebral salt wasting, and exercise-associated hyponatremia. The treatment of hyponatremia is reviewed from simple saline solutions to the recently introduced vasopressin receptor antagonists, including their promises and limitations. Given the persistently high rates of hospital-acquired hyponatremia, the importance of improving the management of hyponatremia seems both necessary and achievable. Copyrigh
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Measurement and interpretation of the polarization of the x-ray line emission of heliumlike Fe XXV excited by an electron beam
The linear polarization of the 1s2p 1P1â1s2 1S0 resonance line, the 1s2p 3P1,2â1s2 1S0 intercombination lines, and the 1s2s 3S1â1s2 1S0 forbidden line was measured in heliumlike Fe XXV excited near threshold by a monoenergetic electron beam. The measurement was carried out with a high-resolution x-ray spectrometer employing a set of two analyzing crystals that acted as polarizers by selectively reflecting the individual polarization components. A value of +0.56-0.08+0.17 was determined for the polarization of the 1P1 line, -0.53-0.02+0.05 for the 3P2 line, -0.22-0.02+0.05 for the 3P1 line, and -0.076-0.007+0.007 for the 3S1 line. The measurements were compared with results from a relativistic distorted-wave calculation, which was carried out for a number of mid-Z heliumlike ions (Mg10+âKr34+), and good agreement was found. By contrast, disagreement was noted with predictions based on Coulomb-Born calculations, allowing us to distinguish between theoretical approaches
High-resolution X-ray spectroscopy and imaging of supernova remnant N132D
The observation of the supernova remnant N132D by the scientific instruments
on board the XMM-Newton satellite is presented. The X-rays from N132D are
dispersed into a detailed line-rich spectrum using the Reflection Grating
Spectrometers. Spectral lines of C, N, O, Ne, Mg, Si, S, and Fe are identified.
Images of the remnant, in narrow wavelength bands, produced by the European
Photon Imaging Cameras reveal a complex spatial structure of the ionic
distribution. While K-shell Fe emission seems to originate near the centre, all
of the other ions are observed along the shell. A high O VII / O VIII emission
ratio is detected on the northeastern edge of the remnant. This can be a sign
of hot ionising conditions, or it can reflect relatively cool gas. Spectral
fitting of the CCD spectrum suggests high temperatures in this region, but a
detailed analysis of the atomic processes involved in producing the O VII
spectral lines leads to the conclusion that the intensities of these lines
alone cannot provide a conclusive distinction between the two scenarios.Comment: To appear in A&A Letters, 365 (2001
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Overview of the current spectroscopy effort on the Livermore electron beam ion traps
An overview is given of the current spectroscopic effort on the Livermore electron beam ion trap facilities. The effort focuses on four aspects: spectral line position, line intensity, temporal evolution, and line shape. Examples of line position measurements include studies of the K-shell transitions in heliumlike Kr34+ and the 2s-2p intrashell transitions in lithiumlike Th87+ and U89+, which provide benchmark values for testing the theory of relativistic and quantum electrodynamical contributions in high-Z ions. Examples of line intensity measurements are provided by measurements of the electron-impact excitation and dielectronic recombination cross sections of the heliumlike transition-metal ions Ti20+ through Co25+. A discussion of radiative lifetime measurements of metastable levels in heliumlike ions is given to illustrate our time-resolved spectroscopy techniques in the microsecond range. We also present a measurement of the spectral lineshape that illustrates the very low ion temperatures that can be achieved in an EBIT
Persistent elevation of urine aquaporin-2 during water loading in a child with nephrogenic syndrome of inappropriate antidiuresis (NSIAD) caused by a R137L mutation in the V2 vasopressin receptor
Nephrogenic Syndrome of Inappropriate Antidiuresis (NSIAD) is a novel disease caused by a gain-of-function mutation in the V2 vasopressin receptor (V2R), which results in water overload and hyponatremia. We report the effect of water loading in a 3-year old boy with NSIAD, diagnosed in infancy, to assess urine aquaporin-2 (AQP2) excretion as a marker for V2R activation, and to evaluate the progression of the disease since diagnosis. The patient is one of the first known NSIAD patients and the only patient with a R137L mutation. Patient underwent a standard water loading test in which serum and urine sodium and osmolality, serum AVP, and urine AQP2 excretion were measured. The patient was also evaluated for ad lib fluid intake before and after the test. This patient demonstrated persistent inability to excrete free water. Only 39% of the water load (20 ml/kg) was excreted during a 4-hour period (normal ⼠80-90%). Concurrently, the patient developed hyponatremia and serum hypoosmolality. Serum AVP levels were detectable at baseline and decreased one hour after water loading; however, urine AQP2 levels were elevated and did not suppress normally during the water load. The patient remained eunatremic but relatively hypodipsic during ad lib intake. In conclusion, this is the first demonstration in a patient with NSIAD caused by a R137L mutation in the V2R that urine AQP2 excretion is inappropriately elevated and does not suppress normally with water loading. In addition, this is the first longitudinal report of a pediatric patient with NSIAD diagnosed in infancy who demonstrates the ability to maintain eunatremia during ad lib dietary intake
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