A free-fall determination of the newtonian constant of gravity

Recent determinations of the Newtonian constant of gravity have produced values that differ by nearly 40 times their individual error estimates (more than 0.5%). In an attempt to help resolve this situation, an experiment that uses the gravity field of a one-half metric ton source mass to perturb the trajectory of a free-falling mass and laser interferometry to track the falling object was performed. This experiment does not suspend the test mass from a support system. It is therefore free of many systematic errors associated with supports. The measured value was G = (6.6873 +/- 0. 0094) x 10(-11) m3 kg-1 sec-2.     

Intestinal uptake of macromolecules: effect of oral immunization

Animals were orally immunized with horseradish peroxidase and bovine serum albumin, and absorption of these antigens was studied. In comparison with controls, a consistent and significant decrease in peroxidase uptake was noted in both germ-free and conventional rats immunized with peroxidase; a similar decrease in serum albumin uptake was also noted in animals immunized with serum albumin. There was no difference in the uptake of an unrelated macromolecule. These observations suggest that local immunization interferes specifically with the intestinal uptake of macromolecular antigens.     

Plasma membranes of rat liver: isolation of lipoprotein macromolecules

Three high-denisity lipoprotein classes and one protein were separated from rat-liver plasma in membranes that had been treated with mild sonic oscillation. The lipoproteinis were separated and identified by techniques in which ultracentrifugation was used. Enzyme markers and electron-microscopic examination revealed membrane preparations essentially free of contaminating cellular partictulates.     

DNA: a model compound for solution studies of macromolecules

Well-defined, monodisperse, homologous series of oligonucleotides and DNA restriction fragments may now be produced and used as models of rigid and semirigid rodlike molecules in solution. Information from optical experiments on these model systems aids in the formulation and testing of theories of macromolecular dynamics in both dilute and concentrated solution.     

Conformation of macromolecules in the gas phase: use of matrix-assisted laser desorption methods in ion chromatography

Conformational data for macromolecules in the gas phase have been obtained by the coupling of a matrix-assisted laser desorption ion source to an ion chromatograph. A series of polyethylene glycol (PEG) polymers "cationized" (converted to a cation) by sodium ions (Na(+)PEG9 to Na(+)PEG19) and a protonated neurotransmitter protein, bradykinin, were studied. Mobilities of Na(+)PEG9 to Na(+)PEG19 are reported. Detailed modeling of Na(+)PEG9 with molecular mechanics methods indicates that the lowest energy structure has the Na(+) ion "solvated" by the polymer chain with seven oxygen atoms as nearest neighbors. The agreement between the model and experiment is within 1 percent for Na(+)PEG9, Na(+)PEG13, and Na(+)PEG17, giving strong support to both the method and the deduced structures. Similar agreement was obtained in initial studies that modeled experimental data for arginine-protonated bradykinin.     

Zinc deposition in Acid lakes: the role of diffusion

Steep negative concentration gradients of dissolved zinc are present between the overlying waters and the anoxic pore waters of two acid lakes. In the anoxic pore waters, the low zinc concentrations can be explained as due to the formation of relatively insoluble zinc sulfide minerals. Downward diffusive fluxes of dissolved zinc account for at least 50 to 75 percent of the recent zinc deposition to the sediments of these lakes. This downward diffusion occurs to a depth of 2 to 3 centimeters below the sediment water interface, where pronounced maxima in total zinc are observed. These subsurface peaks in total zinc have been interpreted as an indication of recent lake acidification. The present observations indicate that such subsurface peaks may also result from a diagenetic activity unrelated to recent changes in lake acidity.     

Electrophoresis of flexible macromolecules: evidence for a new mode of transport in gels

Movement of macromolecules through low concentration agarose gels was investigated with linear poly(styrenesulfonate), linear DNA, star-shaped poly(styrenesulfonate), and circular DNA. Mobilities of weakly entangled flexible macromolecules were independent of molecular radius; within a homologous chemical sequence, electrophoretic separation at low field strengths depended solely on the degree of polymerization. These observations cannot be explained either by sieving or by reptation mechanisms; transport was apparently controlled by spatial variations of chain configurational entropy. Only when the chain was highly entangled did chain topology affect mobility. Evidence for entropically regulated transport clarifies how gel electrophoresis separates flexible macromolecules.     

Borehole measurement of the newtonian gravitational constant

It has been reported that the geophysically determined Newtonian gravitational constant is consistently larger than the laboratory value by 1 to 2% on the basis of gravity measurements in Australian mines. This discrepancy may have strong implications for the physics of gravitation. To test whether similar results can be observed in a different geological environment, gravity measurements in a Michigan borehole have been examined. Although these results cannot be taken as conclusive, owing to the large uncertainties involved in mass determination on a geophysical scale, these measurements are generally consistent with those of the Australian experiment.     

Farmer innovation diffusion via network building: a case of winter greenhouse diffusion in China

Farmer innovation diffusion (FID) in the developing world is not simply the adoption of an innovation made by farmers, but a process of communication and cooperation between farmers, governments, and other stakeholders. While increasing attention has been paid to farmer innovation, little is known about how farmers’ innovations are successfully diffused. To fill this gap, this paper aims to address the following questions: What conditions are necessary for farmers to participate in FID? How is a collaborative network built up between farmers and stakeholders for this purpose? And what roles can government play? The above questions are addressed through analysis of the diffusion of winter greenhouse technology in China. A framework for analyzing a FID system is developed, and the conclusion is drawn that building mutual trust and collaborative networks is crucial for the success of FID. Furthermore, this network building can be broken down into various levels with different scales, speeds and consequences for FID: informal networks among farmers themselves, farmer-led networks, and government-facilitated networks. The success of government intervention depends upon building and enhancing the collaborative networks in which farmer leadership is crucial.     

磁共振常规及弥散加权成像对预测宫颈癌淋巴结转移的价值

目的 探讨磁共振常规及弥散加权成像在宫颈癌淋巴结转移诊断中的敏感性、特异性.方法 113例ⅠB1至ⅡB期宫颈癌患者行术前MRI常规及弥散加权成像检查、根治性子宫切除术加盆腔或盆腔及腹主动脉旁淋巴结清扫术.结果 94例(83.2%)经术后病理学检查证实无淋巴结转移,19例(16.8%)有淋巴结转移.MRI常规及弥散加权成...     

Atom interferometer measurement of the newtonian constant of gravity

We measured the Newtonian constant of gravity, G, using a gravity gradiometer based on atom interferometry. The gradiometer measures the differential acceleration of two samples of laser-cooled Cs atoms. The change in gravitational field along one dimension is measured when a well-characterized Pb mass is displaced. Here, we report a value of G = 6.693 x 10(-11) cubic meters per kilogram second squared, with a standard error of the mean of +/-0.027 x 10(-11) and a systematic error of +/-0.021 x 10(-11) cubic meters per kilogram second squared. The possibility that unknown systematic errors still exist in traditional measurements makes it important to measure G with independent methods.     

Intracranial drug implants: an autoradiographic analysis of diffusion

Labeled crystalline atropine, administered to the hypothlalamus of rats, remainted strictly localized in a sphere, 1.0 to 1.8 millimeters in diameter, ditring the first 3 minutes. A similar distribution obtained after 1 hour. At intermediate times, slightly elevated radioactivity, reflecting concentrations 2,000 to 10,000 times below behaviorally effective doses, was observed several millimeters from the implantation site.     

Pressure dependence of the radioactive decay constant of beryllium-7

Diamond anvil presses of a new design were used to compress samples of beryllium-7 oxide to 120, 210, and 270 kilobars. The decay constant for the conversion of beryllium-7 to lithium-7 by electron capture was measured for compressed and uncompressed samples. A least-squares fit of the equation (lambda(c)-lambda)/lambda = KpP to the experimental data, where lambda(C) and lambda are the decay constants of the compressed sample and an uncompressed sample, respectively, and P is pressure, yields a value of (2.2 +/- 0.1) x 10(-5) kbar(-1) for the constant K(p).     

Efficiency of convection and time variation of the solar constant

Variations in the efficiency of convection resulting from its stochastic nature could be manifested as small ( less, similar1 percent) fluctuations in the solar constant. This could result in changes in the earth's climate with time scales of decades to centuries.