Reproducibility in the absence of selective reporting : An illustration from large-scale brain asymmetry research

Altres ajuts: Max Planck Society (Germany).The problem of poor reproducibility of scientific findings has received much attention over recent years, in a variety of fields including psychology and neuroscience. The problem has been partly attributed to publication bias and unwanted practices such as p-hacking. Low statistical power in individual studies is also understood to be an important factor. In a recent multisite collaborative study, we mapped brain anatomical left-right asymmetries for regional measures of surface area and cortical thickness, in 99 MRI datasets from around the world, for a total of over 17,000 participants. In the present study, we revisited these hemispheric effects from the perspective of reproducibility. Within each dataset, we considered that an effect had been reproduced when it matched the meta-analytic effect from the 98 other datasets, in terms of effect direction and significance threshold. In this sense, the results within each dataset were viewed as coming from separate studies in an "ideal publishing environment," that is, free from selective reporting and p hacking. We found an average reproducibility rate of 63.2% (SD = 22.9%, min = 22.2%, max = 97.0%). As expected, reproducibility was higher for larger effects and in larger datasets. Reproducibility was not obviously related to the age of participants, scanner field strength, FreeSurfer software version, cortical regional measurement reliability, or regional size. These findings constitute an empirical illustration of reproducibility in the absence of publication bias or p hacking, when assessing realistic biological effects in heterogeneous neuroscience data, and given typically-used sample sizes

Long Pulse Technology Tokamak

The LPTT tokamak is a non-circular tokamak (R = 1.5 m, a = .45 m) proposed by ORNL for extended pulse operation at high ..beta.. (5%) and reactor level wall power loading (40 w/cm/sup 2/). The toroidal field coils are superconducting and a super-conducting bundle divertor is proposed for active impurity control. All systems are designed for continuous operation which will provide pulse lengths > 20 seconds with a 6 to 10 weber flux swing. Experimental access and flexibility in operation are primary design goals

Objectives of the tokamak magnetic fusion program

A brief description of the tokamak program as related to the national magnetic confinement program is given. Primary areas where the ISX and PDX tokamaks are contributing to the program are discussed. (MOW

ISX: a tokamak for surface and impurities studies

The ISX (Impurity Study Experiment) is a moderate size tokamak slightly larger than the ORMAK tokamak. ISX is being built explicitly for the study of impurities and plasma-wall interactions. It is scheduled to begin experiments in the spring of 1977. Several features have been deliberately designed into the ISX which make it particularly adaptable to surface studies. The first is a welded stainless steel vacuum system, bakeable to 400$sup 0$C, with a projected base pressure greater than or equal to 2 x 10$sup -9$ torr. Another feature is that of ''easy'' demountability of the vacuum system. Replacement of the entire vacuum system should take about two weeks. A third feature is diagnostic access to the edges of the plasma. The initial surface physics question to be answered is how best to keep surfaces clean: by baking, by direct or indirect wall bombardment discharges, or by gettering. Later experiments will involve using wall materials other than stainless steel to determine their effects on the plasma. (auth

Engineering considerations of the duoPIGatron ion source

From fifth symposium on engineering problems of fusion research; Princeton, New Jersey, USA (6 Nov 1973). In developing an injector system at ORNL with capabilities necessary for high-power injection into ORMAK, several engineering problems must be solved. Emphasis is given to the design and fabrication of the system to achieve electrical stability, power dissipation, beam optics, beam quality, high efficiency and reliability. (auth

Fueling efficiency of pellet injection on DIII-D

Pellet injection has been used on the DIII-D tokamak to study density limits and particle transport in H-mode and inner wall limited L-mode plasmas. These experiments have provided a variety of conditions in which to examine the fueling efficiency of pellets injected into DIIID plasmas. The fueling efficiency defined as the total increase in number of plasma electrons divided by the number of pellet fuel atoms, is determined by measurements of density profiles before and just after pellet injection. We have found that there is a decrease in the pellet fueling efficiency with increased neutral beam injection power. The pellet penetration depth also decreases with increased neutral beam injection power so that, in general, fueling efficiency increases with penetration depth. The fueling efficiency is generally 25% lower in ELMing H-mode discharges than in L-mode due to an expulsion of particles with a pellet triggered ELM. A comparison with fueling efficiency data from other tokamaks shows similar behavior