Geodesics in the static Mallett spacetime

Mallett has exhibited a cylindrically symmetric spacetime containing closed timelike curves produced by a light beam circulating around a line singularity. I analyze the static version of this spacetime obtained by setting the intensity of the light to zero. Some null geodesics can escape to infinity, but all timelike geodesics in this spacetime originate and terminate at the singularity. Freely falling matter originally at rest quickly attains relativistic velocity inward and is destroyed at the singularity.Comment: 5 page

Magnetic Resonance Imaging of a Natural Killer Cell Therapy in a Mouse Model of Prostate Cancer

Purpose: This thesis uses magnetic resonance imaging (MRI) techniques to study natural killer (NK) cell therapy in a nude mouse model of prostate cancer. Cellular MRI, anatomical MRI and hyperpolarized 13C spectroscopy were used to study various aspects of the model. Methods: The cells used were KHYG-1 NK cells and PC-3M prostate cancer cells. Imaging was performed on a clinical 3T GE MR 750 scanner, using a high-performance gradient insert for acquisition with the balanced steady state free precession (bSSFP) sequence, and using the built-in gradients for 13C pyruvate spectroscopy. Pyruvate was hyperpolarized by dynamic nuclear polarization. Results: KHYG-1 were toxic to PC-3M in vitro and were successfully labeled with MoldayRhodamine, a superparamagnetic iron oxide nanoparticle (SPIO). A subcutaneous PC-3M tumour model was used to investigate tracking of KHYG-1 in vivo using the bSSFP sequence. Four days after administration, KHYG-1 accumulation in the tumours was detected by histology but not by MRI, although labeled KHYG-1 at high density were visible in MR images. The bSSFP sequence was then optimized for imaging the mouse prostate and the whole mouse body. Tumour development in an orthotopic prostate cancer model was characterized by MRI and histology for tumour growth, metastasis and tumour metabolism. Tumours were visible by MRI day 9 after injection. Using histology, metastasis was detected in the lymph nodes and spleen of the mice. Necrotic regions in the tumours were detected on day 22 by both anatomical imaging and pyruvate spectroscopy and were confirmed by histology. Conclusions: KHYG-1 cell therapy shows promise as a treatment of prostate cancer. A mouse model that developed lymph node metastases was characterized. Based on the accumulation of KHYG-1 in SC tumours 4 days after administration, and the consistent presence of MRI-visible tumours on day 9-13, a treatment time point of 9-13 days is proposed for future NK cell tracking experiments

CAROTID THREE-DIMENSIONAL ULTRASOUND: LONGITUDINAL MEASUREMENT AND CARDIAC-GATED ACQUISITION

Carotid atherosclerosis is the main cause of stroke - the fourth leading cause of death in Canada - and can be quantified by ultrasound measurements. Intima-media thickness (IMT), total plaque area (TPA) and 3-dimensional ultrasound vessel wall volume (3DUS VWV) were compared in a longitudinal study of 71 patients with diabetic nephropathy randomized to vitamin B or placebo. Only 3DUS VWV was sensitive to a difference in change between treatment groups. We developed and tested cardiac-gated 3DUS acquisition for use in younger subjects with compliant arteries; images were acquired from 400 ms after the start of the cardiac cycle to the beginning of the next cardiac cycle. In healthy volunteers and rheumatoid arthritis patients, change in area over the cardiac cycle was reduced to below that seen in moderate atherosclerosis patients. 3DUS VWV can measure change in atherosclerosis and can now be used in younger patients at risk of atherosclerosis in future studies

Can a circulating light beam produce a time machine?

In a recent paper, Mallett found a solution of the Einstein equations in which closed timelike curves (CTC's) are present in the empty space outside an infinitely long cylinder of light moving in circular paths around an axis. Here we show that, for physically realistic energy densities, the CTC's occur at distances from the axis greater than the radius of the visible universe by an immense factor. We then show that Mallett's solution has a curvature singularity on the axis, even in the case where the intensity of the light vanishes. Thus it is not the solution one would get by starting with Minkowski space and establishing a cylinder of light.Comment: 5 pages, RevTe

Non-stationary rotating black holes: Entropy and Hawking's radiation

We derive a class of non-stationary embedded rotating black holes and study the Hawking's radiation effects on these embedded black holes. The surface gravity, entropy and angular velocity, which are three important properties of black holes, are presented for each of these embedded black holes.Comment: 36 pages, LaTe