The Challenge of Functional Magnetic Resonance Imaging

Abstract

Functional magnetic resonance imaging of the human brain in action presents large statistical and computational challenges. Here we describe those challenges and provide references to a number of other papers where detailed methods developed to meet them are reported. The first seven sections of this paper were written in 1995 when our work was in its infancy. The last four sections were written more recently, to update the earlier sections and to show the directions we have gone and the directions we intend to go.     

Trace forms over finite fields of characteristic 2 with prescribed invariants

We determine the possible pairs of invariants of a trace form and construct forms with these invariants. We use this to construct new maximal Artin–Schreier curves.     

Design and fabrication of subwavelength nanogratings based light-emitting diodes

Linearly polarized light from InGaN green light emitting diode grown on (0001) oriented sapphire is demonstrated by using subwavelength metallic nanogratings. Polarization ratio can reach 7:1 (∼88%), the highest ever reported from a single light emitting device. We discuss the design and fabrication of this device in detail.     

Motion visualization and estimation for flapping wing systems

Studies of fluid-structure interactions associated with flexible structures such as flapping wings require the capture and quantification of large motions of bodies that may be opaque. As a case study, motion capture of a free flying Manduca sexta, also known as hawkmoth, is con-sidered by using three synchronized high-speed cameras. A solid finite element (FE) representation is used as a reference body and successive snapshots in time of the displacement fields are reconstructed via an optimization procedure. One of the original aspects of this work is the formulation of an objective function and the use of shadow matching and strain-energy regularization. With this objective function, the authors penalize the projection differences between silhou-ettes of the captured images and the FE representation of the deformed body. The process and procedures undertaken to go from high-speed videography to motion estimation are dis-cussed, and snapshots of representative results are presented. Finally, the captured free-flight motion is also characterized and quantified.     

‘Good enough’ performance measurement: a trade-off between activity and action

Performance measurement systems along the lines of the EFQM and the balanced scorecard have developed rapidly in recent years, and now occupy much management time and effort. There is limited evidence that performance improvement has received proportionate attention. Six organisations selected for their success were studied using a grounded theory approach based on interviews with management accountants and operations managers in each of the organisations. It is clear that they are all making strenuous efforts to use their performance measurement systems but with a focus on the ‘good enough’ rather than the detail. This gave managers in these organisations the time and space to concentrate on the use of performance measures on forward looking relevance, understanding and action, rather than retrospective and detailed control. This approach was promoted by senior managers and was based on their ability to see the business in simple terms and their understanding of the key drivers of business performance.     

Spin-dependent reaction mechanism in Ti(d, p)Ti from proton-γ correlation

The γ-decays of the states in ⁴⁷Ti at 157 keV and 1547 keV have been studied following the ⁴⁶Ti(d, p)⁴⁷Ti reaction at 5.0 MeV incident energy. Protons were detected at 0° with a semiconductor detector. The angular correlations of the γ-rays with the reaction protons were measured. The E2/M1 mixing ratios of the γ-decays and the population ratios of the to the substates were deduced. From the non-zero population of the substate it was concluded that a spin-flip mechanism exists in the ⁴⁶Ti(d, p)⁴⁷Ti stripping reaction.     

A perceptual learning investigation of the pitch elicited by amplitude-modulated noise

Noise that is amplitude modulated at rates ranging from 40 to 850 Hz can elicit a sensation of pitch. Here, the processing of this temporally based pitch was investigated using a perceptual-learning paradigm. Nine listeners were trained (1 hour per day for 6-8 days) to discriminate a standard rate of sinusoidal amplitude modulation (SAM) from a faster rate in a single condition (150 Hz SAM rate, 5 kHz low-pass carrier). All trained listeners improved significantly on that condition. These trained listeners subsequently showed no more improvement than nine untrained controls on pure-tone and rippled-noise discrimination with the same pitch, and on SAM-rate discrimination with a 30 Hz rate, although they did show some improvement with a 300 Hz rate. In addition, most trained, but not control, listeners were worse at detecting SAM at 150 Hz after, compared to before training. These results indicate that listeners can learn to improve their ability to discriminate SAM rate with multiple-hour training and that the mechanism that is modified by learning encodes (1) the pitch of SAM noise but not that of pure tones and rippled noise, (2) different SAM rates separately, and (3) differences in SAM rate more effectively than cues for SAM detection.     

New measurements of G using the measurement standards laboratory torsion balance

This Letter presents the results of a series of measurements of the Newtonian gravitational constant G using the compensated torsion balance developed at the Measurement Standards Laboratory. Since our last published result using the torsion balance in the compensated mode of operation [Meas. Sci. Technol. 10, 439 (1999)]], several improvements have been made to reduce the uncertainty in the final result. The new measurements have used both stainless steel and copper large masses. The values of G for the two sets of masses are in good agreement. After combining all of the measurements we get a value of G=6.673 87(0.000 27) x 10(-11) m3 kg(-1) s(-2). This new value is 5 parts in 10(5) smaller than our previous published values.     

Preliminary molecular replacement results for a crystalline gene 4 protein-deoxyoligonucleotide complex.

Complexes of the gene 5 protein from bacteriophage fd with a variety of oligodeoxynucleotides, ranging in length from two to eight and comprised of several different sequences, have been formed and crystallized for X-ray diffraction analysis. The crystallographic parameters of four different unit cells, all of which are based on hexagonal packing arrangements, indicate that the fundamental unit of the complex is composed of six gene 5 protein dimers. We believe this aggregate has 622 point group symmetry and is a ring formed by end-to-end closure of a linear array of six dimers. From our results we have proposed a double-helix model for the gene 5 protein-DNA complex in which the protein forms a spindle or core around which the DNA is spooled. Currently 5.0-A X-ray diffraction data from one of the crystalline complexes is being analyzed by molecular replacement techniques to obtain a direct image of the protein-nucleic acid complex.     

The effects of low molar mass diluents on the microstructure of ionomers

The effect of polar and nonpolar low molar mass diluents on the microstructure of lightly sulfonated polystyrene (SPS) ionomers was studied using electron spin resonance spectroscopy, small-angle x-ray scattering, and dynamic mechanical analysis. Nonpolar diluents primarily affected the hydrocarbon - rich phase, while polar diluents partitioned into the ion-rich regions and disrupted the supramolecular structure. The ionic clusters remained intact, even at elevated temperatures, upon the addition of nonpolar solvents such as dodecane and dioctylphthalate. More polar solvents such as methanol and glycerol swelled the ionic domains and promoted increased mixing of the two phases.