Search PubMed⌕ Search

Biomedical subjects

B Krauss

Publications and source records attributed to B Krauss.

At least 19 recordsLinked to original sources

Double-hadron leptoproduction in the nuclear medium.

The first measurements of double-hadron production in deep-inelastic scattering within the nuclear medium were made with the HERMES spectrometer at DESY HERA using a 27.6 GeV positron beam. By comparing data for deuterium, nitrogen, krypton, and xenon nuclei, the influence of the nuclear medium on the ratio of double-hadron to single-hadron yields was investigated. Nuclear effects on the additional hadron are clearly observed, but with little or no difference among nitrogen, krypton, or xenon, and with smaller magnitude than effects seen on previously measured single-hadron multiplicities. The data are compared with models based on partonic energy loss or prehadronic scattering and with a model based on a purely absorptive treatment of the final-state interactions. Thus, the double-hadron ratio provides an additional tool for studying modifications of hadronization in nuclear matter.

Journal Article↗

Measurement of the tensor structure function b1 of the deuteron.

The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.

Journal Article↗

Single-spin asymmetries in semi-inclusive deep-inelastic scattering on a transversely polarized hydrogen target.

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.

Journal Article↗

Flavor decomposition of the sea-quark helicity distributions in the nucleon from semiinclusive deep inelastic scattering.

Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.

Journal Article↗

Evidence for quark-hadron duality in the proton spin asymmetry A1.

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A1. Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q2 between 1.2 and 12 GeV2 and values of W2 between 1 and 4 GeV2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q2 above 1.6 GeV2.

Journal Article↗

Q2 dependence of nuclear transparency for exclusive rho0 production.

Exclusive coherent and incoherent electroproduction of the rho(0) meson from 1H and 14N targets has been studied at the HERMES experiment as a function of coherence length (l(c)), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon (-Q2). The ratio of 14N to 1H cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing l(c) for coherent (incoherent) rho(0) electroproduction. For fixed l(c), a rise of nuclear transparency with Q2 is observed for both coherent and incoherent rho(0) production, which is in agreement with theoretical calculations of color transparency.

Journal Article↗

Electromagnetic versus fluoroscopic mapping of the inferior isthmus for ablation of typical atrial flutter: A prospective randomized study.

BACKGROUND: Radiofrequency catheter ablation within the tricuspid annulus-inferior caval vein isthmus can cure typical atrial flutter. The target for ablation, nonetheless, is relatively wide, and standard ablation procedures may require significant exposure to radiation. METHODS AND RESULTS: A total of 50 patients (mean age, 58+/-11 years) with typical atrial flutter were prospectively randomized to receive isthmus ablation using conventional fluoroscopy for catheter navigation (group I, n=24) or electromagnetic mapping (group II, n=26). Complete bidirectional isthmus block was verified with double potential mapping. If complete isthmus block could not be achieved after 20 radiofrequency pulses or 25 minutes of fluoroscopy, the patients were switched to the other group. Eight patients from group I (33%) but only 1 patient from group II (4%) were switched. Overall, complete isthmus block was achieved in 47 of 50 patients (94%). The overall fluoroscopy time, including the placement of the diagnostic catheters, was 22.0+/-6.3 minutes in group I and 3.9+/-1.5 minutes in group II (P:<0.0001). The fluoroscopy time needed for isthmus mapping was 17.7+/-6.5 minutes in group I and 0.2+/-0.3 minutes in group II (P:<0.0001). CONCLUSIONS: Electromagnetic mapping during the induction of linear lesions for the ablation of atrial flutter permitted a highly significant reduction in exposure to fluoroscopy while maintaining high efficacy, and it allowed the time required for fluoroscopy to be reduced to levels anticipated for diagnostic electrophysiological studies.

Atrial Flutter↗

Combined stentless mitral valve implantation and radiofrequency ablation.

BACKGROUND: The aim of this study was to evaluate the results of combined stentless mitral valve (SMV) replacement and intraoperative radiofrequency ablation for chronic atrial fibrillation (IRAAF) to restore physiologic hemodynamic function. METHODS: Since July 1998 12 patients (72+/-4 years, 10 women, mitral stenosis/mitral incompetence 8/4, NYHA 3.3+/-0.4, CI 1.8+/-0.5) had SMV implantation and received additional IRAAF by inducing continuous left atrial lesion lines from the MV annulus to all four pulmonary veins and to the atriotomy. RESULTS: The flexible SMV was implanted at the papillary muscles and at the annulus using a conventional (n = 6) or a minimally invasive approach (n = 6). Sinus rhythm was successfully restored in 10 of 12 patients with 6- and 12-months' follow-up; 2 required DDD-pacemaker implantation. However, in the early postoperative period several interventions including medical treatment (sotalol or amiodarone) in 9 and electrical cardioversion in 7 patients was required. Two patients required reinterventions: 1 cardioversion and 1 amiodarone medication after 3 and 6 months, respectively. At echocardiography the SMV demonstrated good hemodynamic function and atrial contraction. CONCLUSIONS: Restoration of physiologic cardiac function by SMV implantation and IRAAF is advantageous and no further anticoagulation is required.

Aged↗

Accuracy of capnography with a 30 foot nasal cannula for monitoring respiratory rate and end-tidal CO2 in children.

We tested the accuracy of a low flow (50 cc/min) sidestream capnography system equipped with an experimental 30-foot nasal cannula to monitor ventilatory status in children. End-tidal CO2 and respiratory rate, both at room air and in the presence of supplemental oxygen, were recorded simultaneously from the experimental 30-foot nasal cannula and the standard, FDA approved, 10-foot nasal cannula. The 30-foot nasal cannula was as accurate as the 10-foot nasal cannula in measuring respiratory rate and end-tidal CO2 in children. When supplemental oxygen was delivered by face-mask, there was no dilutional effect on the respiratory rate or end-tidal CO2 recorded with either the 10-foot or 30-foot nasal cannulas in place.

Adolescent↗

Adverse events of procedural sedation and analgesia in a pediatric emergency department.

STUDY OBJECTIVE: To determine the adverse event and complication rate for the use of procedural sedation and analgesia for painful procedures and diagnostic imaging studies performed in a pediatric emergency department. METHODS: This prospective case series was conducted in the ED of a large, urban pediatric teaching hospital. Subjects were patients younger than 21 years seen between August 1997 and July 1998, who required intravenous, intramuscular, oral, rectal, intranasal, or inhalational agents for painful procedures or diagnostic imaging. All patients who underwent procedural sedation and analgesia were continually monitored. Adverse events and complications were recorded. The ED controlled substance log was checked weekly and all sedations were reviewed. Adverse events were defined as follows: oxygen desaturation less than 90%, apnea, stridor, laryngospasm, bronchospasm, cardiovascular instability, paradoxical reactions, emergence reactions, emesis, and aspiration. Complications were defined as adverse events that negatively affected outcome or delayed recovery. RESULTS: Of 1,180 patients who underwent procedural sedation and analgesia in the ED, 27 (2.3%) experienced adverse events, which included oxygen desaturation less than 90% requiring intervention (10 patients) [supplemental oxygen (9), bag-mask ventilation (1)], paradoxical reactions (7), emesis (3), paradoxical reaction and oxygen desaturation requiring supplemental oxygen (2), apnea requiring bag-mask ventilation (1), laryngospasm requiring bag-mask ventilation (1), bradycardia (1), stridor and emesis (1) and oxygen desaturation requiring bag-mask ventilation with subsequent emesis (1). There was no statistically significant difference in mean doses for all procedural sedation and analgesia medication regimens between those children who experienced adverse events and those who did not. No single drug or drug regimen was associated with a higher adverse event rate. In addition, there was no significant difference in the adverse event rate between males and females, among the different ages, or among the different indications for procedural sedation and analgesia. No patient required reversal of sedation with naloxone or flumazenil, endotracheal intubation, or hospital admission because of complications from procedural sedation and analgesia. CONCLUSION: The adverse event rate for procedural sedation and analgesia performed by pediatric emergency physicians was 2.3% with no serious complications noted.

Adolescent↗

Microstream capnograpy technology: a new approach to an old problem.

Significant technical limitations inherent in black-body infrared technology used in conventional sidestream and mainstream capnography have hindered the acceptance and growth of capnography as a monitoring tool outside the operating room environment. We describe a new technology (Microstream) for CO2 monitoring, based on molecular correlation spectroscopy, which results in a highly efficient and selective emission of a spectrum of discrete wavelengths exactly matching those for CO2 absorption. The CO2 specific emissions allow for an extremely small sample cell (15 microl), which in turn, permits the use of a very low sample flow rate (50 ml/min) without compromising waveform integrity or end-tidal CO2 accuracy. Design and technology features of the CO2 emission source, sample cell, and breath sampling circuits are described.

Absorption↗