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1.
Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their
key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving
mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have
lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical
considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from
the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated
virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate
a Universe with a low value (≤ 0.3) for the Ω parameter. 相似文献
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Experimental study of the behavior of a valveless impedance pump 总被引:1,自引:0,他引:1
When a fluid-filled flexible tube is connected to tubing of different impedance, a net flow in either direction can be induced by periodically pinching the flexible section asymmetrically from the ends. We have experimentally demonstrated a variety of conditions under which pumping occurs; including changes in actuator position, size and pinching frequency, transmural pressure, systemic resistance and materials. Data collected includes dynamic pressure and flow-rate measurements at the inlet and outlet of the pump and ultrasound imaging of the tube walls. The net flow rate is highly sensitive to pinching frequency. The pump does not require a closed loop and can sustain a pressure head. We have also shown that a flexible, yet inelastic material is a sufficient condition for impedance-driven flow. A micro-scaled version of the pump was simultaneously tested demonstrating the feasibility of a miniature design.
An erratum to this article is avaliable at .
相似文献
An erratum to this article is avaliable at .
Anna Iwaniec HickersonEmail: Phone: +1-626-395-4758Fax: +1-626-577-5258 |
3.
Half life for the emission of exotic clusters like 8Be, 12C, 16O, 20Ne, 24Mg and 28Si are computed taking Coulomb and proximity potentials as interacting barrier and many of these are found well within the
present upper limit of measurement. These results lie very close to those values reported by Shanmugam et al using their cubic plus Yukawa plus exponential model (CYEM). It is found that 12C and 16O emissions from 116Ce and 16O from 118Ce are most favorable for measurement (T
1/2<1010 s). Lowest half life time for 16O emission from 116Ce stress the role of doubly magic 100Sn daughter in exotic decay. Geiger-Nuttall plots were studied for different clusters and are found to be linear. Inclusion
of proximity potential will not produce much deviation to linear nature of Geiger-Nuttall plots. It is observed that neutron
excess in the parent nuclei slow down the exotic decay process. These findings support the earlier observations of Gupta and
collaborators using their preformed cluster model (PCM). 相似文献
4.
Liu J Mendenhall MP Holley AT Back HO Bowles TJ Broussard LJ Carr R Clayton S Currie S Filippone BW García A Geltenbort P Hickerson KP Hoagland J Hogan GE Hona B Ito TM Liu CY Makela M Mammei RR Martin JW Melconian D Morris CL Pattie RW Pérez Galván A Pitt ML Plaster B Ramsey JC Rios R Russell R Saunders A Seestrom SJ Sondheim WE Tatar E Vogelaar RB VornDick B Wrede C Yan H Young AR;UCNA Collaboration 《Physical review letters》2010,105(18):181803
A precise measurement of the neutron decay β asymmetry A? has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science Center. Combining data obtained in 2008 and 2009, we report A? = -0.119?66±0.000?89{-0.001?40}{+0.001?23}, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon g{A}/g{V}=-1.275?90{-0.004?45}{+0.004?09}. 相似文献
5.
Dean Hickerson 《Inventiones Mathematicae》1988,94(3):639-660
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Shashwati Sen DK Aswal Ajay Singh TV Chandrasekhar Rao KP Muthe JC Vyas LC Gupta SK Gupta VC Sahni 《Pramana》2002,58(5-6):867-870
The MgB2 superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties.
The upper critical field, irreversibility line and critical current density have been determined using magnetization data.
The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition.
The surface analysis using X-ray photoelectron spectroscopy shows that MgB2 is sensitive to atmospheric degradation. 相似文献
10.
Zhe‐Yi Hu Bradley A. Boucher S. Casey Laizure Vanessa L. Herring Robert B. Parker William L. Hickerson 《Journal of mass spectrometry : JMS》2013,48(8):945-950
A hydrophilic interaction chromatography/mass spectrometry (HILIC‐MS)‐based assay for imipenem (IMP) and cilastatin (CIL) was recently reported. This orthogonal electrospray ion source‐based (ORS) assay utilized nonvolatile salt (unremovable) to stabilize IMI in plasma. Unfortunately, this method was not applicable to conventional MS with off‐axis spray (OAS‐MS) because MS sensitivity was rapidly deteriorated by the nonvolatile salt. Therefore, we aimed to find a nonvolatile salt‐ and ion suppression‐free approach to stabilize and measure the analytes in plasma using OAS‐MS. Acetonitrile and methanol were tested to stabilize the analytes in the plasma samples. The recoveries, matrix effects and stabilities of the analytes in the stabilizer‐treated samples were studied. The variations in MS signal intensities were used as the indicator of the assay ruggedness. The results show that a mixture of methanol and acetonitrile (1:1) is best for the storage and measurement of IMP and CIL in human plasma. Utilization of this precipitant not only blocked the hydrolysis of the analytes in plasma but also resulted in an ion suppression‐free, fast (120 s per sample) and sensitive detection. The sensitivity obtained using the less sensitive OAS‐MS (API3000, 4 pg on column) is much greater than that of the published ORS‐MS‐based assay (API4000, 77 pg on column). The ruggedness of the assay was demonstrated by its constant MS signal intensity. In conclusion, an improved HILIC/MS‐based assay for IMP and CIL was established. The approach presented here provides a simple solution to the challenge of analyzing hydrolytically unstable β‐lactam antibiotics in biological samples. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献