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41.
Davies GR Lurie DJ Hutchison JM McCallum SJ Nicholson I 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,148(2):289-297
There is growing interest in the use of magnetic resonance imaging (MRI) to examine solid materials where the restricted motion of the probed spins leads to broad lines and short T(2) values, rendering many interesting systems invisible to conventional 2DFT pulsed imaging methods. In EPR T(2) seldom exceeds 0.1 mus and continuous-wave methods are adopted for spectroscopy and imaging. In this paper we demonstrate the use of continuous-wave MRI to obtain 2-dimensional images of short T(2) samples. The prototype system can image samples up to 50 mm in diameter by 60 mm long and has been used to image polymers and water penetration in porous media. Typical acquisition times range between 10 and 40 min. Resolution of 1 to 2 mm has been achieved for samples with T(2) values ranging from 38 to 750 mus. There is the possibility of producing image contrast that is determined by the material properties of the sample. 相似文献
42.
43.
H. Wu M. J. Kramer K. W. Dennis R. W. McCallum 《Physica C: Superconductivity and its Applications》1997,290(3-4):252-264
The lower solubility limits of Nd1+xBa2−xCu3O7 (Nd123ss) in 1 bar, 0.2 bar, 0.01 bar, and 0.001 bar oxygen partial pressure (PO2) were studed by differential thermal analysis (DTA) and X-ray diffraction (XRD). Large relative changes in stability with decreasing PO2 explain why sharp superconducting transitions can be achieved in PO2 ≤ 0.01 bar while processing in 0.2 to 1 bar PO2 tends to produce broad transitions. While the lower solubility limits in 0.01 bar and 0.001 bar PO2 remain at x = 0.00, the solubility limits in 0.2 bar and 1 bar PO2 show a narrowing with decreasing temperature. Because of the narrowing of the solubility range in 1 bar PO2, oxygen annealing of Nd123 initially processed in low PO2 will result in precipitation of second phases which act as flux pinning centers. 相似文献
44.
Phase transition in the superconducting state in Gd-rich pseudoternary compounds (La1-xGdx)1.0Mo6Se8
A pronounced lambda-type specific heat anomaly in the superconducting state is reported for Gd-rich pseudoternary compounds (La1-xGdx)1.0Mo6Se8. The anomaly is very similar to that previously reported for the compound Gd1.2Mo6Se8. Both the temperature of the lambda anomaly (≈ 3.5 K) and the Curie-Weiss temperature were found to be nearly independent of x. In addition, evidence for the occurence of magnetic ordering at 0.8 K in Gd1.2Mo6Se8 is presented. These observations support our earlier conjecture that the lambda anomaly at 3.5 K does not arise from magnetic ordering of the Gd3+ ions. The anomaly appears instead to be due to a different type of phase transition which is associated with the presence of the localized 4f electrons of the Gd3+ ions, but the exact nature of the transition remains to be established. 相似文献
45.
Megan M. McCallum Alan J. Pawlak William R. Shadrick Anton Simeonov Ajit Jadhav Adam Yasgar David J. Maloney Leggy A. Arnold 《Analytical and bioanalytical chemistry》2014,406(7):1867-1875
Herein, we describe the development of a fluorescence-based high throughput assay to determine the small molecule binding towards human serum albumin (HSA). This innovative competition assay is based on the use of a novel fluorescent small molecule Red Mega 500 with unique spectroscopic and binding properties. The commercially available probe displays a large fluorescence intensity difference between the protein-bound and protein-unbound state. The competition of small molecules for HSA binding in the presence of probe resulted in low fluorescence intensities. The assay was evaluated with the library of pharmacological active compounds (LOPAC) small molecule library of 1,280 compounds identifying known high protein binders. The small molecule competition of HSA?Red Mega 500 binding was saturable at higher compound concentrations and exhibited IC50 values between 3 and 24 μM. The compound affinity toward HSA was confirmed by isothermal titration calorimetry indicating that the new protein binding assay is a valid high throughput assay to determine plasma protein binding. Figure
A high throughput fluorescence-based serum protein binding assay 相似文献
46.
R.W. McCallum D.C. Johnston R.N. Shelton W.A. Fertig M.B. Maple 《Solid State Communications》1977,24(8):501-505
Low temperature specific heat and magnetic susceptibility measurements indicate that superconductivity and long-range antiferromagnetic order coexist in the compound ErxMo6Se8 (x = 1.0 and 1.2). 相似文献
47.
Zeng Z Patel J Lee SH McCallum M Tyagi A Yan M Shea KJ 《Journal of the American Chemical Society》2012,134(5):2681-2690
The interaction between synthetic polymer nanoparticles (NPs) and biomacromolecules (e.g., proteins, lipids, and polysaccharides) can profoundly influence the NPs fate and function. Polysaccharides (e.g., heparin/heparin sulfate) are a key component of cell surfaces and the extracelluar matrix and play critical roles in many biological processes. We report a systematic investigation of the interaction between synthetic polymer nanoparticles and polysaccharides by ITC, SPR, and an anticoagulant assay to provide guidelines to engineer nanoparticles for biomedical applications. The interaction between acrylamide nanoparticles (~30 nm) and heparin is mainly enthalpy driven with submicromolar affinity. Hydrogen bonding, ionic interactions, and dehydration of polar groups are identified to be key contributions to the affinity. It has been found that high charge density and cross-linking of the NP can contribute to high affinity. The affinity and binding capacity of heparin can be significantly diminished by an increase in salt concentration while only slightly decreased with an increase of temperature. A striking difference in binding thermodynamics has been observed when the main component of a polymer nanoparticle is changed from acrylamide (enthalpy driven) to N-isopropylacryalmide (entropy driven). This change in thermodynamics leads to different responses of these two types of polymer NPs to salt concentration and temperature. Select synthetic polymer nanoparticles have also been shown to inhibit protein-heparin interactions and thus offer the potential for therapeutic applications. 相似文献
48.
Y.L. Tang D.J. Branagan D.J. Miller M.J. Kramer R.W. McCallum 《Applied Physics A: Materials Science & Processing》2003,76(6):987-989
The microstructures of nanophase Pr-Co-C-(Ti) materials, which have improved magnetic properties, were investigated by means
of transmission electron microscopy (TEM) to reveal their phase assemblage and grain-boundary structure. The phase assemblage
was carefully controlled by the introduction of TiC nanoparticles and annealing. The optimal nanostructure contained uniformly
distributed PrCo5 and PrCo2 nanophases without any magnetically soft phases, resulting in high coercivity and the characteristics of a single, hard magnetic
phase. TEM analysis confirmed the presence of an amorphous grain-boundary phase surrounding the grains in alloys without TiC.
In contrast, alloys with added TiC showed no amorphous phase and also showed higher coercivity compared to Co-Pr-C. Therefore,
the variation of the grain boundary phases may be effective in changing the degree of exchange coupling. Controlling the formation
of a uniform nanoscale microstructure, leading to improved magnetic properties, is discussed.
Received: 5 September 2002 / Accepted: 10 September 2002 / Published online: 22 January 2003
RID="*"
ID="*"Corresponding author. Fax: +1-630/252-7777, E-mail: ytang@anl.gov 相似文献
49.
P. Allenspach B. W. Lee D. A. Gajewski V. B. Barbeta M. B. Maple G. Nieva S. -I. Yoo M. J. Kramer R. W. McCallum L. Ben-Dor 《Zeitschrift für Physik B Condensed Matter》1995,96(4):455-464
Low temperature heat-capacity measurements have been performed to study the magnetic ordering in NdBa2Cu3O
x
and DyBa2Cu3O
x
. In order to investigate the type of ordering, magnetic fields up to 6 T and hydrostatic pressures up to 4.5 kbar were applied. While for NdBa2Cu3O
x
and DyBa2Cu3O
x
both the fully oxidized and the fully oxygen reduced samples display long rang antiferromagnetic ordering, only magnetic short range interaction could be found for samples in an intermediate range of oxygen concentration. For NdBa2Cu3O
x
, where superexchange is believed to be the dominant magnetic interaction,T
N
is three times higher in the sample withx=6.26 compared to the one withx=6.98. In contrast,T
N
of DyBa2Cu3O
x
is almost oxygen independent as expected for this mainly dipolar interacting system. 相似文献
50.
Charles J McCallum 《Journal of Mathematical Analysis and Applications》1973,44(3):643-660
In an earlier paper, it was shown that the linear and quadratic programming problems in complex space could be unified in the “complex linear complementarity problem” (complex LCP). An existence theory for this problem was provided. The present paper addresses the problem of actually solving the complex LCP and hence complex linear and quadratic programs as well. Two solution procedures are described and an example is given. 相似文献