Inhomogeneity

Comparison of medical images is frequently needed for diagnosis or evaluation of a progressive disease. The comparison is performed by alignment and registration of images or warping them with a transformation function. It is possible to compare images of the same patient, which have been taken at different time periods to detect or quantify the changes that might have taken place in-between acquisitions. Also, a comparison can be performed using images from different subjects. In a Magnetic Resonance Image (MRI), intensity values do not only depend on the underlying tissue type. They also depend on developmental processes, scanner-related intensity artifacts and disease progression. Therefore, spatial normalization, which brings an image into the coordinate system of a template using a coordinate transformation to make meaningful comparisons of spatially varying data, is required. In this work, an intensity normalization method based on spatially varying distribution matching is proposed. The efficiency of the proposed method has been shown on brain MRIs.

The crystallographic microtexture and microstructure of a β-titanium alloy (Ti–35 wt.% Nb–7 wt.% Zr–5 wt.% Ta) is studied after warm rolling and recrystallization. The main observations are the evolution of partially recrystallized microstructures during warm rolling and the formation of strong through-thickness texture and microstructure gradients at larger strains. Both, the recrystallized volume fraction and the texture depend on the thickness reduction. At small reductions (≤50%) texture gradients are also small showing some αbcc-fiber (crystallographic axis 〈1 1 0〉 parallel to the rolling direction) and γ-fiber (crystallographic axis 〈1 1 1〉 parallel to the normal direction) texture components. At larger strains (70–90%) the texture and microstructure gradients are characterized by shear texture components and dynamic recrystallization particularly close to the surface layers and plane strain texture components which are typical of recovered grains in the center layer.

The crystallographic microtexture and microstructure of a beta-titanium alloy (Ti–35wt.% Nb–7wt.% Zr–5wt.% Ta) is studied after warm rolling and recrystallization. The main observations are the evolution of partially recrystallized microstructures during warm rolling and the formation of strong through-thickness texture and microstructure gradients at larger strains. Both, the recrystallized volume fraction and the texture depend on the thickness reduction. At small reductions (≤50%) texture gradients are also small showing some bcc-alpha fiber (crystallographic axis
110 parallel to the rolling direction) and gamma-texture--fiber (crystallographic axis 111 parallel to the normal direction) texture components. At larger strains(70–90%) the texture and microstructure gradients are characterized by shear texture components and dynamic recrystallization particularly close to the surface layers and plane strain texture components which are typical of recovered grains in the center layer.

A group of activities, using digital technology which supports learning and facilitates student academic success, were compiled in a 28-item challenge for beginning General Education students, as a part of a Life and Study Skills course. Each challenge invited students to access some aspect of digital technology which had the potential to increase their academic competence. A convenience sample of 29 male students, from three different classes, was used for the intervention. Students were all taught by the same instructor, in the same semester. The main objective of the study was to increase students' digital academic literacy, exposing them to applications and ICT skills which would increase their efficiency, self-efficacy and accuracy in executing academic tasks. The efficacy of the intervention was assessed by comparing students' work to others who did not take part in the study. The technology tools used were aimed at accomplishing tasks such as group formation and communication, note-taking, information capture, summarization, synchronous and asynchronous collaboration on tasks, referencing, formatting, grammar check, plagiarism and assessment. Students were challenged to complete particular tasks using specific applications. Students were given 28 days to complete the tasks, after which they were required to do two quizzes, using Kahoot!, as a group and Nearpod, individually. A screenshot of each completed activity was submitted as evidence of task completion. A questionnaire was used to garner student perspective on the intervention. Throughout the semester academic output were analyzed to see if students continued to use the technology introduced. The results of the study showed that students were appreciative of the technology introduced and had no problems learning how to use the different applications. Faculty observed that student output improved over previous semesters, where the intervention was not carried out. Some students nearing the end of their academic careers expressed regret at not being introduced to the technology earlier. The study illuminated the inhomogeneity inside classrooms with regards to academic digital technology. It also showed the benefit of introducing the technology during the General Education program, at the beginning of students' academic careers, and how this knowledge contributes to development of 21 st century skills and workplace readiness of students. Plans are underway to introduce the technology to all students taking the Life and Study Skills course.

In the framework of the concordance cosmological model, the first-order scalar and vector perturbations of the homogeneous background are derived in the weak gravitational field limit without any supplementary approximations. The sources of these perturbations (inhomogeneities) are presented in the discrete form of a system of separate point-like gravitating masses. The expressions found for the metric corrections are valid at all (sub-horizon and super-horizon) scales and converge at all points except at the locations of the sources. The average values of these metric corrections are zero (thus, first-order backreaction effects are absent). Both the Minkowski background limit and the Newtonian cosmological approximation are reached under certain well-defined conditions. An important feature of the velocity-independent part of the scalar perturbation is revealed: up to an additive constant, this part represents a sum of Yukawa potentials produced by inhomogeneities with the same finite time-dependent Yukawa interaction range. The suggested connection between this range and the homogeneity scale is briefly discussed along with other possible physical implications.

We have numerically investigated the effects of helicity and inhomogeneities on DNA base pairs opening. The inhomogeneities are due to the site-dependent stacking and hydrogen bonding energies in DNA and protein molecules. We have considered a situation in which the active site of the RNA-polymerase molecule binds onto the promoter site of the spin-like model of the DNA molecule at the physiological temperature and creates a bubble. During the study, we have found that the helical coupling has to be very weak compared to intra-strand coupling in the real DNA molecule. Results show that inhomogeneities do not affect the general pattern of base pair opening, even as the periodic inhomogeneity introduces a train of periodic oscillations on the tail of the bubble; while the height of the bubble is an increasing function of the helical coupling parameter. The basic properties of breather-like modes, obtained here by taking into account helical structure and inhomogeneities, are essential for DNA functioning since such breathing-like modes are considered to be much better candidates for the nonlinear modes responsible for a locally open state where biological functioning takes place.

Physica Scripta. 89 085003
Issue 8 (August 2014)
Received 19 April 2013, accepted for publication 29 May 2014
Published 26 June 2014
doi:10.1088/0031-8949/89/8/085003
http://iopscience.iop.org/1402-4896/89/8/085003/