University of British Columbia

About: University of British Columbia is a education organization based out in Vancouver, British Columbia, Canada. It is known for research contribution in the topics: Population & Health care. The organization has 89939 authors who have published 209679 publications receiving 9226862 citations. The organization is also known as: UBC & The University of British Columbia.

Practical Non-Linear Energy Harvesting Model and Resource Allocation for SWIPT Systems

Abstract: In this letter, we propose a practical non-linear energy harvesting model and design a resource allocation algorithm for simultaneous wireless information and power transfer (SWIPT) systems. The algorithm design is formulated as a non-convex optimization problem for the maximization of the total harvested power at energy harvesting receivers subject to minimum required signal-to-interference-plus-noise ratios (SINRs) at multiple information receivers. We transform the considered non-convex objective function from sum-of-ratios form into an equivalent objective function in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. In each iteration, a rank-constrained semidefinite program (SDP) is solved optimally by SDP relaxation. Numerical results unveil a substantial performance gain that can be achieved if the resource allocation design is based on the proposed non-linear energy harvesting model instead of the traditional linear model.

In vivo visualization of myelin water in brain by magnetic resonance

Abstract: We exploit the intrinsic difference in magnetic resonance spin-spin relaxation time, T2, between water associated with myelin sheaths and water in other central nervous system tissue in order to measure myelin water content within any region of an image or to generate indirectly a myelin map of the brain. In normal volunteers, myelin water maps give the expected myelin distribution. In multiple sclerosis patients, lesions exhibit different myelin water contents providing insight into the demyelination process unavailable from conventional magnetic resonance images. In vivo myelin measurement has important applications in the clinical management of multiple sclerosis and other white matter diseases.

The Effect of Green Investment on Corporate Behavior

Abstract: This paper explores the effect of exclusionary ethical investing on corporate behavior in a risk-averse, equilibrium setting. While arguments exist that ethical investing can influence a firm's cost of capital, and so affect investment, no equilibrium model has been presented to do so. We show that exclusionary ethical investing leads to polluting firms being held by fewer investors since green investors eschew polluting firms' stock. This lack of risk sharing among non-green investors leads to lower stock prices for polluting firms, thus raising their cost of capital. If the higher cost of capital more than overcomes a cost of reforming (i.e., a polluting firm cleaning up its activities), then polluting firms will become socially responsible because of exclusionary ethical investing. A key determinant of the incentive for polluting firms to reform is the fraction of funds controlled by green investors. In our model, empirically reasonable parameter estimates indicate, that more than 20 % green investors are required to induce any polluting firmss to reform. Existing empirical evidence indicates that at most 10% of funds are invested by green investors.

Calcium transients in astrocyte endfeet cause cerebrovascular constrictions

Abstract: Cerebral blood flow (CBF) is coupled to neuronal activity and is imaged in vivo to map brain activation. CBF is also modified by afferent projection fibres that release vasoactive neurotransmitters in the perivascular region, principally on the astrocyte endfeet that outline cerebral blood vessels. However, the role of astrocytes in the regulation of cerebrovascular tone remains uncertain. Here we determine the impact of intracellular Ca(2+) concentrations ([Ca(2+)](i)) in astrocytes on the diameter of small arterioles by using two-photon Ca(2+) uncaging to increase [Ca(2+)](i). Vascular constrictions occurred when Ca(2+) waves evoked by uncaging propagated into the astrocyte endfeet and caused large increases in [Ca(2+)](i). The vasoactive neurotransmitter noradrenaline increased [Ca(2+)](i) in the astrocyte endfeet, the peak of which preceded the onset of arteriole constriction. Depressing increases in astrocyte [Ca(2+)](i) with BAPTA inhibited the vascular constrictions in noradrenaline. We find that constrictions induced in the cerebrovasculature by increased [Ca(2+)](i) in astrocyte endfeet are generated through the phospholipase A(2)-arachidonic acid pathway and 20-hydroxyeicosatetraenoic acid production. Vasoconstriction by astrocytes is a previously unknown mechanism for the regulation of CBF.