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91.
Larson KM Levine J 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1999,46(4):1001-1012
We have conducted several time-transfer experiments using the phase of the GPS carrier rather than the code, as is done in current GPS-based time-transfer systems. Atomic clocks were connected to geodetic GPS receivers; we then used the GPS carrier-phase observations to estimate relative clock behavior at 6-minute intervals. GPS carrier-phase time transfer is more than an order of magnitude more precise than GPS common view time transfer and agrees, within the experimental uncertainty, with two-way satellite time-transfer measurements for a 2400 km baseline. GPS carrier-phase time transfer has a stability of 100 ps, which translates into a frequency uncertainty of about two parts in 10(-15) for an average time of 1 day. 相似文献
92.
The activities of some enzymes of glycerolipid synthesis and fatty acid oxidation were measured in subcellular fractions of
the yolk sac membrane (YSM), an extra-embryonic tissue that mediates the transfer of lipid from the yolk to the circulation
of the chick embryo. The activities of monoacylglycerol acyltransferase and carnitine palmitoyl transferase-1 in the YSM (respectively,
284.8±13.2 nmol/min/mg microsomal protein and 145.6±9.1 nmol/min/mg mitochondrial protein; mean ±SE; n=4) at day 12 of development appear to be the highest yet reported for any animal tissue. Also, the carnitine palmitoyl transferase-1
of the YSM was very insensitive to inhibition by malonyl CoA. The maximal activities of glycerol-3-phosphate acyltransferase
and diacylglycerol acyltransferase in the YSM (respectively, 26.7±2.2 and 36.1±2.1 nmol/min/mg microsomal protein) were also
high compared with the reported values for various animal tissues. The very high enzymic capacity for glycerolipid synthesis
supports the hypothesis that the yolk-derived lipids are subjected to hydrolysis followed by reesterification during transit
across the YSM. The monoacylglycerol pathway appears to be the main route for glycerolipid resynthesis in the YSM. The results
also suggest that the YSM has the capacity to perform simultaneously β-oxidation at a high rate in order to provide energy
for the lipid transfer process. 相似文献
93.
94.
CR González FR Noriega S Huerta A Santiago M Vega J Paniagua V Ortiz-Navarrete A Isibasi MM Levine 《Canadian Metallurgical Quarterly》1998,16(9-10):1043-1052
Attenuated Salmonella typhi are attractive for use as live vector vaccines to express protozoal antigens and deliver them to the human immune system. The gene encoding the mature form of Leishmania mexicana mexicana gp63 under control of tac promoter was integrated into the delta aroC locus of the chromosome of attenuated delta aroC, delta aroD S. typhi strain CVD 908. After oral immunization of BALB/c mice with two 1 x 10(9) colony forming unit doses given 21 days apart, CVD 908 omega (delta aroC::Ptac-gp63) elicited a broad T cell-mediated immune response against L. m. mexicana gp63 as demonstrated by: (1) lymphoproliferative response to fixed whole L. m. mexicana promastigotes; (2) activation of IL-2 (but not IL-4)-producing lymphocytes; (3) appearance of cytotoxic T cells against mouse mastocytoma cells expressing gp63. This T-cell mediated immune response was associated with significant protection in F1 (BALB/cXC57Bl/6) mice challenged in their footpads with a wild type strain of L. m. mexicana. 相似文献
95.
96.
We previously reported early results of a new technique using a suture anchor to perform a modified Bankart reconstruction. That study included patients from two medical centers and had an average followup of only 1 year. This report includes patients from a single center with followup extended to a mean of 42 months (range, 33 to 61). Between April 1988 and August 1991, 53 patients with recurrent anterior glenohumeral instability underwent modified Bankart reconstruction with the use of a suture anchor. Thirty-two patients met inclusion criteria (identifiable Bankart lesion, open repair with suture anchors, and minimum followup of 2 years); 4 patients were lost to followup. There have been no complications as a result of this technique. Ninety-three percent of the patients in the study had objectively excellent or good results. There were 2 failures with recurrent anterior dislocation. The use of a suture anchor can simplify the Bankart reconstruction. At average followup of 3 years, 26 patients have returned to presurgery activity levels without recurrent dislocation or subluxation. However, careful attention to anchor placement at the junction of articular cartilage and the glenoid neck is necessary to avoid technical failure. 相似文献
97.
98.
The second harmonic coefficient d36 of HgGa2 S4 has been measured to be 5 times larger than d36 (LiNbO3 ). The birefringence is usefully large. 相似文献
99.
100.
Learning heuristics for an on-line controller are presented, and various aspects of the problem are discussed. The controller is required to achieve optimal regulator control for an unknown process in the face of random disturbances. A computer method of two-stage learning is employed in which the first stage is coarse and attempts to satisfy the terminal boundary conditions on the basis of subgoal learning. This yields an approximation to the optimum control law. Rote learning is also carried out during this time. The second, or tuning stage, improves on this result by a technique of reinforcement learning applied to the integral performance criterion. The effect of varying the parameters associated with the learning algorithm is studied. A discussion of a hybrid computer simulation of a second-order plant subject to one input with two possible levels is presented. 相似文献