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排序方式: 共有118条查询结果,搜索用时 15 毫秒
21.
Rolf MP Hofman MB Kuijer JP Pai VM Greiser A van Rossum AC Heethaar RM 《Magnetic resonance imaging》2009,27(3):385-392
Multiecho phase-contrast steady-state free precession (PC-SSFP) is a recently introduced sequence for flow quantification. In this multiecho approach, a phase reference and a velocity-encoded readout were acquired at different echo times after a single excitation. In this study, the sequence is validated in vitro for stationary flow. Subsequently, the sequence was evaluated on cardiac output measurements in vivo for through-plane flow in comparison to regular single gradient echo velocity quantification [phase-contrast spoiled gradient echo (PC-GE)]. In vitro results agreed with regular flow meters (RMS 0.1 cm/s). Cardiac output measurements with multiecho PC-SSFP on 10 healthy subjects gave on average the same results as the standard PC-GE. However, the limits of repeatability of PC-SSFP were significantly larger than those of PC-GE (2 l/min and 0.5 l/min, respectively, P=.001). The multiecho approach introduced some specific problems in vivo. The difference in echo times made the velocity maps sensitive for water-fat shifts and B(0)-drifts, which in turn made velocity offset correction problematic. Also, the addition of a single bipolar gradient cancelled the flow compensated nature of the SSFP sequence. In combination with the prolonged TR, this resulted in flow artifacts caused by high and pulsatile through-plane flow, affecting repeatability. Given the significantly lower repeatability of PC-SSFP, cardiac output in turn is less reliable, thus impairing the use of multiecho PC-SSFP. 相似文献
22.
Fry AM Seibel HA Lokuhewa IN Woodward PM 《Journal of the American Chemical Society》2012,134(5):2621-2625
Na(1.5)Ag(1.5)MoO(3)F(3) and Na(1.5)Ag(1.5)WO(3)F(3) have been synthesized by solid state reactions and structurally characterized using synchrotron X-ray and neutron powder diffraction. Unlike the vast majority of salts containing [MO(3)F(3)](3-) anions (M = Mo, W) the oxyfluoride groups in Na(1.5)Ag(1.5)MoO(3)F(3) and Na(1.5)Ag(1.5)WO(3)F(3) are orientationally ordered, so that the Na(+) ions are coordinated by fluorine and the Ag(+) ions by oxygen. The resulting structure type, which has not previously been reported, is related to the LiNbO(3) structure, but the combination of Na/Ag ordering and orientational ordering of the [MO(3)F(3)](3-) anions produces a supercell that doubles the c-axis and changes the space group symmetry from R3 to R3. The use of hard (Na(+)) and soft (Ag(+)) cations to direct the orientational ordering of polar oxyfluoride building units provides a new approach to the design of polar materials. 相似文献
23.
A. Yu. Didyk R. Wiśniewski K. Kitowski V. Kulikauskas T. Wilczynska A. Hofman A. A. Shiryaev Ya. V. Zubavichus 《Physics of Particles and Nuclei Letters》2012,9(1):86-95
Pure metals (Cu, Ti, Zr, V, Pd) and diluted Pd alloys (Pd-Ag, Pd-Pt, Pd-Ru, Pd-Rh) were implanted by 25-keV deuterium ions
at fluences in the range (1.2–2.3) × 1022 m−2. The post-treatment depth distributions of deuterium ions were measured 10 days and three months after the implantation by
using Elastic Recoil Detection Analysis (ERDA) and Rutherford Backscattering (RBS). Comparison of the obtained results allowed
us to make conclusions about relative stability of deuterium and hydrogen gases in pure metals and diluted Pd alloys. Very
high diffusion rates of implanted deuterium ions in V and Pd pure metals and Pd alloys were observed. Small-angle X-ray scattering
revealed formation of nanosized defects in implanted corundum and titanium. 相似文献
24.
I. V. Amirkhanov A. Yu. Didyk E. V. Zemlyanaya I. V. Puzynin T. P. Puzynina N. R. Sarkar I. Sarkhadov V. K. Semina Z. A. Sharipov A. Hofman 《Physics of Particles and Nuclei Letters》2006,3(1):37-45
A system of equations for electron gas and lattice around and along the trajectory of a heavy uranium ion with an energy of 700 MeV in nickel at constant heat capacity and heat conduction taken at room temperature is solved numerically in an axially symmetric cylindrical coordinate system. On the basis of the lattice temperature obtained as a function of radius around the ion trajectory and depth, a conclusion is made that the ionization energy losses of a uranium ion in nickel are sufficient for melting and evaporating the material from the surface. The maximum radius and depth of the region in which melting and evaporation take place are estimated. 相似文献
25.
Jadwiga Skupiska Monika Karpiska Leszek Wachowski Magdalena Hofman 《Reaction Kinetics and Catalysis Letters》2004,82(2):311-316
A simple catalytic system containing metallic palladium, iron and iodine has been shown to be very active in the carbonylation
of nitrobenzene to carbamate. The influence of the components of the catalytic system studied on its selectivity and activity
has been established. It has been found that the catalytic activity of palladium supported on carbon (using both lignite coal
and bituminous coal) was not lower than the activity of metallic palladium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
26.
Thomas J Hofman D Kleint C Schumann J Wetzig K 《Analytical and bioanalytical chemistry》2002,374(4):695-698
Anomalies in the nanostructure evolution of ReSi(2+/-x) thin films have proved to be of large interest in connection with their thermoelectric properties. By means of electron microscopic methods the correlation between structural properties and transport behaviour has been studied. The short-range order of the amorphous state was characterised by reduced density functions calculated from diffuse electron diffraction diagram and is found to correlate with the temperature dependence of the electrical resistance. The crystallisation process observed in situ in the transmission electron microscope starts with the formation of relatively large ReSi(1.75) grains (up to 100 nm). In later stages, only smaller grains are growing. This leads to a decrease in the mean grain size and to the increase of the nanocrystalline volume fraction during the heat treatment. This behaviour allows the investigation of the thermopower as function of the nanocrystalline volume fraction. Thus, at a nanocrystalline content of about 35% the thermopower exhibits a maximum in accordance with calculations. 相似文献
27.
J.P. Seitz B.B. Back M.P. Carpenter I. Diszegi K. Eisenman P. Heckman D.J. Hofman M.P. Kelly T.L. Khoo S. Mitsuoka V. Nanal T. Pennington R.H. Siemssen M. Thoennessen R.L. Varner 《Nuclear Physics A》2005,750(2-4):245-255
The giant dipole resonance built on excited states was observed in very fissile nuclei in coincidence with evaporation residues. The reaction 48Ca + 176Yb populated evaporation residues of mass A=213–220 with a cross section of 200 μb at 259 MeV. The extracted giant dipole resonance parameters are in agreement with theoretical predictions for this mass region. 相似文献
28.
Rafał Bogel-Łukasik Dobrochna Matkowska Małgorzata E. Zakrzewska Ewa Bogel-Łukasik Tadeusz Hofman 《Fluid Phase Equilibria》2010
Solid–liquid, liquid–liquid and vapour–liquid equilibrium measurements for binary and ternary systems containing building blocks of biomass origin such as propionic acid, lactic acid and alternative solvents like carbon dioxide and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid have been carried out at 313.15 K. The binary solid–liquid and liquid–liquid equilibrium measurements were performed at ambient pressure. The vapour–liquid equilibrium was studied in the range of pressure from 3.54 to 12 MPa while ternary systems were examined at 9, 10 and 12 MPa. The samples from the coexisting phases were taken and the compositions of both liquid and vapour phases were determined experimentally. The three-phase system was observed for lactic acid + ionic liquid + CO2 as well. The achieved results were correlated using the Peng–Robinson equation of state with the Mathias–Klotz–Prausnitz mixing rule. The set of interaction parameters for the employed equations of state and the mixing rule for the investigated systems were obtained. 相似文献
29.
Alver B Back BB Baker MD Ballintijn M Barton DS Betts RR Bindel R Busza W Chai Z Chetluru V García E Gburek T Gulbrandsen K Hamblen J Harnarine I Henderson C Hofman DJ Hollis RS Hołyński R Holzman B Iordanova A Kane JL Kulinich P Kuo CM Li W Lin WT Loizides C Manly S Mignerey AC Nouicer R Olszewski A Pak R Reed C Richardson E Roland C Roland G Sagerer J Sedykh I Smith CE Stankiewicz MA Steinberg P Stephans GS Sukhanov A Szostak A Tonjes MB Trzupek A van Nieuwenhuizen GJ Vaurynovich SS Verdier R 《Physical review letters》2006,96(21):212301
We present transverse momentum distributions of charged hadrons produced in Cu + Cu collisions at square root of SNN = 62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25 < pT < 5.0 GeV/c at square root of SNN = 62.4 GeV and 0.25 < pT < 7.0 GeV/c at square root of SNN = 200 GeV, in a pseudorapidity range of 0.2 < eta < 1.4. The nuclear modification factor R(AA) is calculated relative to p + p data at both collision energies as a function of collision centrality. At a given collision energy and fractional cross section, R(AA) is observed to be systematically larger in Cu + Cu collisions compared to Au + Au. However, for the same number of participating nucleons, R(AA) is essentially the same in both systems over the measured range of pT, in spite of the significantly different geometries of the Cu + Cu and Au + Au systems. 相似文献
30.
Back BB Baker MD Ballintijn M Barton DS Betts RR Bickley AA Bindel R Busza W Carroll A Chai Z Decowski MP García E Gburek T George N Gulbrandsen K Halliwell C Hamblen J Hauer M Henderson C Hofman DJ Hollis RS Hołyński R Holzman B Iordanova A Johnson E Kane JL Khan N Kulinich P Kuo CM Lin WT Manly S Mignerey AC Nouicer R Olszewski A Pak R Reed C Roland C Roland G Sagerer J Seals H Sedykh I Smith CE Stankiewicz MA Steinberg P Stephans GS Sukhanov A Tonjes MB Trzupek A Vale C van Nieuwenhuizen GJ 《Physical review letters》2005,94(8):082304
We have measured transverse momentum distributions of charged hadrons produced in Au+Au collisions at sqrt[s(NN)]=62.4 GeV. The spectra are presented for transverse momenta 0.25
相似文献