Characterization of Real Time Platelet Deposition onto Opaque Surfaces under Clinically-Relevant Flow Conditions

Although the thrombogenic nature of the surfaces of cardiovascular devices is an important aspect of blood biocompatibility, few studies have examined platelet deposition onto opaque materials used for these devices in real time. This is particularly true for the metallic surfaces used in current ventricular assist devices (VADs). Using hemoglobin depleted red blood cells (RBC ghosts) and long working distance optics to visualize platelet deposition, we sought to perform such an evaluation. A titanium alloy (Ti6Al4V) and 5 alternative opaque materials were examined. Ti6Al4V had significantly increased platelet deposition relative to the majority of alternative materials. Blood flow patterns are of particular concern for devices such as blood pumps where shearing forces can be high, volumes are relatively large, and the flow fields can be complex. However, few studies have examined the effect of geometric irregularities on thrombus formation on clinically relevant opaque materials under flow. The second objective of this report was to quantify human platelet deposition onto titanium alloys, as well as positive and negative control surfaces, in the region of crevices (~50-150 µm in width) that might be encountered in many VADs. The results revealed that the largest crevice size was the least thrombogenic. At the higher shear rate, the most deposition occurred in the medium size crevice. A third challenge in assessing the hemocompatibility of a blood-wetted device is understanding the functional relationship between shear stress, biochemical agonists, and artificial surfaces. The final objective of this report was to investigate the effect of sub-threshold concentrations of ADP in conjunction with flow on platelet deposition onto clinically relevant opaque materials. To achieve this aim, a membrane-based agonist delivery system was designed to evenly introduce specific concentrations of agonists into a flowing blood analog. The results showed that that the addition of a sub-threshold level of ADP to the system resulted in nearly a 2.5 fold increase in deposition on the titanium surface. The data generated from this report could be used to improve the accuracy of a predictive model of thrombotic deposition in VADs

Entangling operations and their implementation using a small amount of entanglement

We study when a physical operation can produce entanglement between two systems initially disentangled. The formalism we develop allows to show that one can perform certain non-local operations with unit probability by performing local measurement on states that are weakly entangled.Comment: 4 pages, no figure

Comparison between the Cramer-Rao and the mini-max approaches in quantum channel estimation

In a unified viewpoint in quantum channel estimation, we compare the Cramer-Rao and the mini-max approaches, which gives the Bayesian bound in the group covariant model. For this purpose, we introduce the local asymptotic mini-max bound, whose maximum is shown to be equal to the asymptotic limit of the mini-max bound. It is shown that the local asymptotic mini-max bound is strictly larger than the Cramer-Rao bound in the phase estimation case while the both bounds coincide when the minimum mean square error decreases with the order O(1/n). We also derive a sufficient condition for that the minimum mean square error decreases with the order O(1/n).Comment: In this revision, some unlcear parts are clarifie

Unital Quantum Channels - Convex Structure and Revivals of Birkhoff's Theorem

The set of doubly-stochastic quantum channels and its subset of mixtures of unitaries are investigated. We provide a detailed analysis of their structure together with computable criteria for the separation of the two sets. When applied to O(d)-covariant channels this leads to a complete characterization and reveals a remarkable feature: instances of channels which are not in the convex hull of unitaries can return to it when either taking finitely many copies of them or supplementing with a completely depolarizing channel. In these scenarios this implies that a channel whose noise initially resists any environment-assisted attempt of correction can become perfectly correctable.Comment: 31 page

Continuous-variable Werner state: separability, nonlocality, squeezing and teleportation

We investigate the separability, nonlocality and squeezing of continuous-variable analogue of the Werner state: a mixture of pure two-mode squeezed vacuum state with local thermal radiations. Utilizing this Werner state, coherent-state teleportation in Braunstein-Kimble setup is discussed.Comment: 7 pages, 4 figure

Optimal Non-Universally Covariant Cloning

We consider non-universal cloning maps, namely cloning transformations which are covariant under a proper subgroup G of the universal unitary group U(d), where d is the dimension of the Hilbert space H of the system to be cloned. We give a general method for optimizing cloning for any cost-function. Examples of applications are given for the phase-covariant cloning (cloning of equatorial qubits) and for the Weyl-Heisenberg group (cloning of "continuous variables").Comment: 6 page