Gadolinium Concentration Analysis in Brain Phantom by X-ray Fluorescence

We have measured the X-ray fluorescence from gadolinium as a function of concentration and position in tumors of different sizes and shapes in a head phantom. The gadolinium fluorescence was excited with a 36 GBq Am-241 source. The fluorescence signal was detected with a CdTe detector and a multi-channel analyzer. The fluorescence peak was clearly separated from the scattered X-rays. Concentrations of 5.62–78.63 mg/ml of Gd ion were used in 1, 2, and 3 cm diameter spherical tumors and a 2 9 4 cm oblate spheroid tumor. The data show trends approaching saturation for the highest concentrations, probably due to reabsorption in the tumor. A comparison of X-ray photographic imaging and densitometer measurements to determine concentration is also presented

Teaching and Flexible Learning in Science and Entrepreneurship Courses Using Mobile Devices

Mobile devices, such as iPods and cell phones, are a ubiquitous part of our world today. Young people have particularly embraced this technology and it is an integral part of their daily lives. The Science and Entrepreneurship courses, SCIE301 and SCIE302, offered at the University of Canterbury, use this technology to introduce students to how an idea in the laboratory can be developed in a commercial environment. These courses are designed for students, either on- or off-campus (distance) learners, from a broad range of disciplines. We have incorporated the use of mobile devices into SCIE301 and SCIE302 as teaching and flexible learning tools. The lecture content is provided as downloadable mp3 or mp4 files (video podcasts or vodcast format) for students to view in their own time. This course material is a combination of lectures, videos and PowerPoint presentations. The students are also provided with DVDs containing video case studies of individuals discussing their experiences in the world of entrepreneurship. The face-to-face lecture time is spent interacting with guest entrepreneurs and discussing the case studies. In this workshop we will present our innovative teaching methods that are facilitating flexible learning and discuss our future plans for utilising mobile devices in teaching and learning

Physical dynamics of quasi-particles in nonlinear wave equations

By treating the centers of solitons as point particles and studying their discrete dynamics, we demonstrate a new approach to the quantization of the soliton solutions of the sine-Gordon equation, one of the first model nonlinear field equations. In particular, we show that a linear superposition of the non-interacting shapes of two solitons offers a qualitative (and to a good approximation quantitative) description of the true two-soliton solution, provided that the trajectories of the centers of the superimposed solitons are considered unknown. Via variational calculus, we establish that the dynamics of the quasi-particles obey a pseudo-Newtonian law, which includes cross-mass terms. The successful identification of the governing equations of the (discrete) quasi-particles from the (continuous) field equation shows that the proposed approach provides a basis for the passage from the continuous to a discrete description of the field.Comment: 10 pages, 3 figures (6 images); v2: revised and improved the presentation, updated the references, fixed typos; v3: corrected a few minor mistakes and typos, version accepted for publication in Phys. Lett.

Thermodynamics of RNA structures by Wang–Landau sampling

Motivation: Thermodynamics-based dynamic programming RNA secondary structure algorithms have been of immense importance in molecular biology, where applications range from the detection of novel selenoproteins using expressed sequence tag (EST) data, to the determination of microRNA genes and their targets. Dynamic programming algorithms have been developed to compute the minimum free energy secondary structure and partition function of a given RNA sequence, the minimum free-energy and partition function for the hybridization of two RNA molecules, etc. However, the applicability of dynamic programming methods depends on disallowing certain types of interactions (pseudoknots, zig-zags, etc.), as their inclusion renders structure prediction an nondeterministic polynomial time (NP)-complete problem. Nevertheless, such interactions have been observed in X-ray structures

Where Do Introns Come From?

The systems for mRNA surveillance, capping, and cleavage/polyadenylation are proposed to play pivotal roles in the physical establishment and distribution of spliceosomal introns along a transcript

Control of ligand binding to heme proteins: The role of the distal histidine

We have investigated the effect of the distal histidine on the recombination rates of CO and O2 to sperm whale myoglobin, separated beta chains of normal human hemoglobin and to the beta chains of hemoglobin Zurich. The recombination was measured using flash photolysis from 300 to 40 K, on a time scale of 100 ns to 300 s. Lowering the pH of the solution from 7.0 to S.O, we find a 3 kJ/mol and 1.S kJ/mol decrease in the final barrier for CO binding to myoglobin and the separated chains of human hemoglobin, respectively. The distal histidine, His E 7, is identified as the titratable group by observing no pH dependence in the rates when CO binds to the beta chains of hemoglobin Zurich, a mutant of hemoglobin lacking a distal histidine in the beta chains. We postulate a charge-dipole interaction between the CO and the protonated histidine, since the recombination of the symmetric ligand, O2, is pH independent. The temperature independent energy shift is then used to demonstrate the importance of the final barrier even at 300 K, support the sequential model used and finally to spectulate on the structural contributions to the final barrier for binding. The protein structure is shown to be the major contribution to the final barrier for myoglobin. We then show how the distribution of atomic positions from the X-ray scattering data at 80 K can result in the distribution of activation enthalpies observed between 60 and 160 K. Preliminary studies on the effect of pH on the CO recombination to chloroperoxidase show a reversed effect. The rates increase with increasing pH, unlike myoglobin and beta hemoglobin. However, the pK and energy difference between the protonated and unprotonated states suggest a distal histidine is also being protonated in chloroperoxidase.U of I OnlyThesi