He\u27s Free in 5G Bail; Served 6 1/2 Years

Daily News, April 5, 197

Novel array representation methods in support of a microcomputer-based APL interpreter

Objective: To study novel ways of representing data arrays for potential application in a microcomputer-based APL interpreter. The goal is to find, for arrays containing mixed integers and real numbers, a way to improve both storage efficiency and thruput, over that obtainable using conventional APL interpreter array representations. Investigation: For the purposes of this study, three representative APL operators were chosen for implementation - dyadic addition, multiplication and selection. To establish a set of base cases from which to work, these three operators were implemented for two distinctly different data structures: Case-0: arrays containing only fixed length floating point data elements Case-1: arrays containing only fixed length integer data elements These two cases are termed homogeneous because all data elements within each array share a common data structure - the conventional approach for APL interpreters. Three additional heterogeneous cases were then built upon the homogeneous base cases: Case-2: arrays containing mixed floating point and integer fixed length data elements Case-3: arrays containing mixed floating point and integer data elements, with the integer elements having variable length Case-4: arrays containing fixed length pointers to variable length Case-3 data elements For all of these cases, space and time tradeoffs were studied and charted. Exerciser programs were written in BASIC to drive the 5 Case-n implementations to enable direct comparison of the 5 storage allocation approaches; these driver routines prepared test data, ran the addition/multiplication/selection exercises, retrieved time and space measurements, and performed data reduction for presentation in this report. The 5 Case-n implementors were written in 6502 CPU assembly language, and provided the functions of addition, multiplication, selection, timing, and data format conversion between BASIC and Case-n data structures. Fixed length floating point arithmetic was supported on the target microcomputer for which all code was written -an Atari 800. In support of multi-byte integer arithmetic, however, original addition and multiplication atomic functions required development. Conclusions: Of the 5 cases implemented, Case-3 (heterogeneous variable length data elements) showed the greatest promise for saving space without adversely affecting addition and multiplication thruput. However, the selection algorithm had to be modified from an address calculation scheme based upon the indices of the desired elements to a search algorithm more suited to the variable length data elements. This produced astonishingly fast selection thruput for some applications, and dismally poor selection performance for others. At the end of the report are suggestions for future development of the variable length data element selection algorithm. Case-4 (pointers to heterogeneous variable length data elements) was introduced to enable the conventional address calculation selection scheme for variable length elements. The addition of the pointers did not have much impact upon thruput, but the additional space required for the pointers erased the space savings achieved with variable length elements

Tests of Statistical Significance and Background Estimation in Gamma Ray Air Shower Experiments

In this paper we discuss several methods of significance calculation and point out the limits of their applicability. We then introduce a self consistent scheme for source detection and discuss some of its properties. The method allows incorporating background anisotropies by vetoing existing small scale regions on the sky and compensating for known large scale anisotropies. By giving an example using Milagro gamma ray observatory we demonstrate how the method can be employed to relax the detector stability assumption. Two practical implementations of the method are discussed. The method is universal and can be used with any large field-of-view detector, where the object of investigation, steady or transient, point or extended, traverses its field of view.Comment: 12 pages, 7 figures. Submitted to ApJ, submission number: 5833

Clinical applications of ultra-high field magnetic resonance imaging in multiple sclerosis

Introduction: Magnetic resonance imaging (MRI) is of paramount importance for the early diagnosis of multiple sclerosis (MS) and MRI findings are part of the MS diagnostic criteria. There is a growing interest in the use of ultra-high-field strength 127 Tesla- (7T) MRI to investigate, in vivo, the pathological substrate of the disease. Areas covered: An overview of 7T MRI applications in MS focusing on increased sensitivity for lesion detection, specificity of the central vein sign and better understanding of MS pathophysiology. Implications for disease diagnosis, monitoring and treatment planning are discussed. Expert commentary: 7T MRI provides increased signal-to-noise and contrast-to-noise-ratio that allow higher spatial resolution and better detection of anatomical and pathological features. The high spatial resolution reachable at 7T has been a game changer for neuroimaging applications not only in MS but also in epilepsy, brain tumors, dementia, and neuro-psychiatric disorders. Furthermore, the first 7T device has recently been cleared for clinical use by the food and drug administration

Laminar analysis of the cortical T1/T2-weighted ratio at 7T

Objective: In this observational study, we explored cortical structure as function of cortical depth through a laminar analysis of the T1/T2-weighted (T1w/T2w) ratio, which has been related to dendrite density in ex vivo brain tissue specimens of patients with MS. Methods: In 39 patients (22 relapsing-remitting, 13 female, age 41.1 ± 10.6 years; 17 progressive, 11 female, age 54.1 ± 9.9 years) and 21 healthy controls (8 female, , age 41.6 ± 10.6 years), we performed a voxel-wise analysis of T1w/T2w ratio maps from high-resolution 7T images from the subpial surface to the gray matter/white matter boundary. Six layers were sampled to ensure accuracy based on mean cortical thickness and image resolution. Results: At the voxel-wise comparison (p < 0.05, family wise error rate corrected), the whole MS group showed lower T1w/T2w ratio values than controls, both when considering the entire cortex and each individual layer, with peaks occurring in the fusiform, temporo-occipital, and superior and middle frontal cortex. In relapsing-remitting patients, differences in the T1w/T2w ratio were only identified in the subpial layer, with the peak occurring in the fusiform cortex, whereas results obtained in progressive patients mirrored the widespread damage found in the whole group. Conclusions: Laminar analysis of T1w/T2w ratio mapping confirms the presence of cortical damage in MS and shows a variable expression of intracortical damage according to the disease phenotype. Although in the relapsing-remitting stage, only the subpial layer appears susceptible to damage, in progressive patients, widespread cortical abnormalities can be observed, not only, as described before, with regard to myelin/iron concentration but, possibly, to other microstructural features

The Intrinsic Origin of Spin Echoes in Dipolar Solids Generated by Strong Pi Pulses

In spectroscopy, it is conventional to treat pulses much stronger than the linewidth as delta-functions. In NMR, this assumption leads to the prediction that pi pulses do not refocus the dipolar coupling. However, NMR spin echo measurements in dipolar solids defy these conventional expectations when more than one pi pulse is used. Observed effects include a long tail in the CPMG echo train for short delays between pi pulses, an even-odd asymmetry in the echo amplitudes for long delays, an unusual fingerprint pattern for intermediate delays, and a strong sensitivity to pi-pulse phase. Experiments that set limits on possible extrinsic causes for the phenomena are reported. We find that the action of the system's internal Hamiltonian during any real pulse is sufficient to cause the effects. Exact numerical calculations, combined with average Hamiltonian theory, identify novel terms that are sensitive to parameters such as pulse phase, dipolar coupling, and system size. Visualization of the entire density matrix shows a unique flow of quantum coherence from non-observable to observable channels when applying repeated pi pulses.Comment: 24 pages, 27 figures. Revised from helpful referee comments. Added new Table IV, new paragraphs on pages 3 and 1