White participants were exposed to other-race or own-race faces to test the generalized mere exposure hypothesis in the domain of face perception, namely that exposure to a set of faces yields increased liking for similar faces that have never been seen. In Experiment 1, rapid supraliminal exposures to Asian faces increased White participants' subsequent liking for a different set of Asian faces. In Experiment 2, subliminal exposures to Black faces increased White participants' subsequent liking for a different set of Black faces. The findings are consistent with prominent explanations for mere exposure effects as well as with the familiar face overgeneralization hypothesis that prejudice derives in part from negative reactions to faces that deviate from the familiar own-race prototype.

Purpose To develop a novel 4-dimensional computed tomography (4D-CT) technique that exploits standard fast helical acquisition, a simultaneous breathing surrogate measurement, deformable image registration, and a breathing motion model to remove sorting artifacts. Methods and Materials Ten patients were imaged under free-breathing conditions 25 successive times in alternating directions with a 64-slice CT scanner using a low-dose fast helical protocol. An abdominal bellows was used as a breathing surrogate. Deformable registration was used to register the first image (defined as the reference image) to the subsequent 24 segmented images. Voxel-specific motion model parameters were determined using a breathing motion model. The tissue locations predicted by the motion model in the 25 images were compared against the deformably registered tissue locations, allowing a model prediction error to be evaluated. A low-noise image was created by averaging the 25 images deformed to the first image geometry, reducing statistical image noise by a factor of 5. The motion model was used to deform the low-noise reference image to any user-selected breathing phase. A voxel-specific correction was applied to correct the Hounsfield units for lung parenchyma density as a function of lung air filling. Results Images produced using the model at user-selected breathing phases did not suffer from sorting artifacts common to conventional 4D-CT protocols. The mean prediction error across all patients between the breathing motion model predictions and the measured lung tissue positions was determined to be 1.19 ± 0.37 mm. Conclusions The proposed technique can be used as a clinical 4D-CT technique. It is robust in the presence of irregular breathing and allows the entire imaging dose to contribute to the resulting image quality, providing sorting artifact–free images at a patient dose similar to or less than current 4D-CT techniques.

Purpose To report on a novel technique for providing artifact-free quantitative 4DCT image datasets for breathing motion modeling. Methods Commercial clinical four-dimensional computed tomography (4DCT) methods have trouble managing irregular breathing. The resulting images contain motion-induced artifacts that can distort structures and inaccurately characterize breathing motion. We have developed a novel scanning and analysis method for motion-correlated CT that utilizes standard repeated fast helical acquisitions, a simultaneous breathing surrogate measurement, deformable image registration, and a published breathing motion model. Results The motion model differs from the CT-measured motion by an average of 0.72 mm, indicating the precision of the motion model. The integral of the divergence of one of the motion model parameters is predicted to be a constant 1.11 and is found in this case to be 1.09, indicating the accuracy of the motion model. Conclusions The proposed technique shows promise for providing motion-artifact free images at user-selected breathing phases, accurate Hounsfield units, and noise characteristics similar to non-4D CT techniques, at a patient dose similar to or less than current 4DCT techniques.

Internally generated, spontaneous activity is ubiquitous in the cortex, yet it does not appear to have a significant negative impact on sensory processing. Various studies have found that stimulus onset reduces the variability of cortical responses, but the characteristics of this suppression remained unexplored. By recording multiunit activity from awake and anesthetized rats, we investigated whether and how this noise suppression depends on properties of the stimulus and on the state of the cortex. In agreement with theoretical predictions, we found that the degree of noise suppression in awake rats has a nonmonotonic dependence on the temporal frequency of a flickering visual stimulus with an optimal frequency for noise suppression ~2 Hz. This effect cannot be explained by features of the power spectrum of the spontaneous neural activity. The nonmonotonic frequency dependence of the suppression of variability gradually disappears under increasing levels of anesthesia and shifts to a monotonic pattern of increasing suppression with decreasing frequency. Signal-to-noise ratios show a similar, although inverted, dependence on cortical state and frequency. These results suggest the existence of an active noise suppression mechanism in the awake cortical system that is tuned to support signal propagation and coding.

The purpose of this study was to assess the feasibility of proton pencil beam scanning (PBS) for the treatment of mediastinal lymphoma. A group of 7 patients of varying tumor size (100-800 cc) were planned using a PBS anterior field. We investigated 17 fractions of 1.8 Gy(RBE) to deliver 30.6 Gy(RBE) to the internal target volume (ITV). Spots with σ ranging from 4 mm to 8 mm were used for all patients, while larger spots (σ = 6-16 mm) were employed for patients with motion perpendicular to the beam (⩾5 mm), based on initial 4-dimensional computed tomography (4D CT) motion evaluation. We considered volumetric repainting such that the same field would be delivered twice in each fraction. The ratio of extreme inhalation amplitude and regular tidal inhalation amplitude (free-breathing variability) was quantified as an indicator of potential irregular breathing during the scanning. Four-dimensional dose was calculated on the 4D CT scans based on the respiratory trace and beam delivery sequence, implemented by partitioning the spots into separate plans on each 4D CT phase. Four starting phases (end of inhalation, end of exhalation, middle of inhalation and middle of exhalation) were sampled for each painting and 4 energy switching times (0.5 s, 1 s, 3 s and 5 s) were tested, which resulted in 896 dose distributions for the analyzed cohort. Plan robustness was measured for the target and critical structures in terms of the percent difference between 'delivered' dose (4D-evaluated) and planned dose (calculated on average CT). It was found that none of the patients exhibited highly variable or chaotic breathing patterns. For all patients, the ITV D98% was degraded by <2% (standard deviations ∼ 0.1%) when averaged over the whole treatment course. For six out of seven patients, the average degradation of ITV D98% per fraction was within 5% . For one patient with motion perpendicular to the beam (⩾5 mm), the degradation of ITV D98% per fraction was up to 15%, which was mitigated to 2% by employing larger spots and repainting. Deviation of mean lung dose was at most 0.2 Gy(RBE) (less than 1% of prescribed dose, 30.6 Gy(RBE)), while the deviation of heart maximum dose and cord maximum dose could exceed 5% of the prescribed dose. No significant difference in either target coverage or normal tissue dose was observed for different energy switching times compared via two-sided Wilcoxon signed-rank tests (p < 0.05). This feasibility study demonstrates that, for mediastinal lymphoma, the impact of the interplay effect on the PBS plan robustness is minimal when volumetric repainting and/or larger spots are employed.

The observed problems of spirometry recording illustrate the challenges encountered when using spirometers as breathing surrogate for 4D CT acquisition. The high correlation between spirometry and bellows breathing signals and the verified factor of 1.11 between CT-based air content and tidal volume mean that the bellows measurement (or other equivalent surrogates) can be reliably converted to tidal volume using the CT-based air content, avoiding the need for a spirometer.

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As part of our continuing research on the nature of silicate liquids at high pressures and to provide insight into the flow properties of granitic magmas at depth, we determined the viscosity (η) of liquid KAlSi3O8, and the viscosities of liquids in the systems KAlSi3O8‐CO2 and KAlSi3O8‐H2O, as a function of pressure and temperature using the falling‐sphere method. At 1500°C, log η of KAlSi3O8 decreases from 5.0 at 1 bar to 4.36 and 3.96 at 15 and 20 kbar, respectively, consistent with the negative (∂η/∂P)T of other highly polymerized silicate liquids. However, log η isothermally increases to 4.23 at 25 kbar. Adding 0.50 wt % CO2 to the liquid produces an isothermal decrease in log η to 4.06, 3.79, and 3.41 at 15, 20, and 25 kbar and 1500°C. An equimolar amount of H2O (0.21 wt %) reduces log η to 3.45, 3.40, and 3.34 at the above conditions. At 25 kbar, 0.21 wt % H2O and 0.50 wt % CO2 produce nearly equal reductions in the viscosity of KAlSi3O8 at 1500° and 1600°C. These data indicate that H2O and CO2 disrupt the flow mechanism of KAlSi3O8 by breaking bridging‐oxygen bonds, either by reaction of the molecular volatile species with the tetrahedral network to form OH− and CO32−, or by CO2 reacting with a non‐bridging oxygen to form CO32−, which disrupts the network of the liquid by rearrangement of the local balance in charges. This is in accord with previous studies of the viscosities of H2O‐ and CO2‐bearing NaAlSi3O8 liquids. CO2 is more effective in reducing the viscosity of KAlSi3O8 relative to NaAlSi3O8 at 25 kbar, indicating that the former liquid may dissolve a larger percentage of total carbon as CO32−. This conclusion is consistent with our published feldspar‐CO2 phase equilibria. At 20 and 25 kbar and 1500°C, log η decreases to 2.30 as H2O increases to 2.00 wt %, with a highly positive (∂2(log η)/∂χ2)T,P. In contrast to KAlSi3O8‐H2O, KAlSi3O8‐CO2 exhibits a viscosity minimum between 0.50 and 1.00 wt % at 20 kbar and 1.00 and 1.50 wt % at 25 kbar, perhaps reflecting a concentration‐dependent speciation of the CO2 molecule similar to that for H2O, or a change toward non‐Newtonian, pseudoplastic behavior as the liquid becomes saturated with carbon.