Free-breathing 2D time-of-flight pulmonary MRA at 3T

This study aims to optimize and evaluate a free-breathing 2D TOF PMRA protocol at 3T. The protocol was based on a T1-weighted turbo field echo sequence with static tissue suppression using magnetization transfer plus selective inverse recovery, spectral fat saturation, cardiac gating, respiratory navigator gating, and parallel imaging. Satisfactory pulmonary MRAs were demonstrated in volunteer subjects (N=12). The proposed protocol is clinically relevant for patients who are unable to provide long breath-holds during MRI scans.published_or_final_versio

MOTSA TOF-MRA using multi-oblique-stacks acquisition (MOSA)

One of the intrinsic advantages of current TOF MRA techniques is their insensitivity to in-plane blood flow or turbulent flow, causing hypointense signal or discontinuity in blood vessels in MRA images. To overcome this problem, a multi-oblique-stacks acquisition (MOSA) technique is proposed to improve the visualization of in-plane blood flows in MRA. The results showed that TOF-MRA obtained from MOSA was improved as compared to that of conventional MOTSA for the same amount of scan time.published_or_final_versio

Accretion Disks Around Black Holes: Twenty Five Years Later

We study the progress of the theory of accretion disks around black holes in last twenty five years and explain why advective disks are the best bet in explaining varied stationary and non-stationary observations from black hole candidates. We show also that the recently proposed advection dominated flows are incorrect.Comment: 30 Latex pages including figures. Kluwer Style files included. Appearing in `Observational Evidence for Black Holes in the Universe', ed. Sandip K. Chakrabarti, Kluwer Academic Publishers (DORDRECHT: Holland

MRI characterization of trabecular bone structure by exploring bone microscopic susceptibility effect

Bone strength depends on bone mineral density (BMD) as well as properties related to bone quality, such as the microarchitecture of trabecular bone. Structural parameters, such as trabecular thickness, can also critically influence the mechanical competence and thus resistance to fracture of bone. Complex bone structure can induce microscopic susceptibility effect and alter the bone transverse relaxation properties, which are expected to become more prominent at high field. This study aims to examine such susceptibility effect at 3T and explore the possibility of using bone as an endogenous contrast agent to derive the structural information in human trabecular bone.published_or_final_versio

Quantum mechanics/molecular mechanics minimum free-energy path for accurate reaction energetics in solution and enzymes: Sequential sampling and optimization on the potential of mean force surface

To accurately determine the reaction path and its energetics for enzymatic and solution-phase reactions, we present a sequential sampling and optimization approach that greatly enhances the efficiency of the ab initio quantum mechanics/molecular mechanics minimum free-energy path (QM/MM-MFEP) method. In the QM/MM-MFEP method, the thermodynamics of a complex reaction system is described by the potential of mean force (PMF) surface of the quantum mechanical (QM) subsystem with a small number of degrees of freedom, somewhat like describing a reaction process in the gas phase. The main computational cost of the QM/MM-MFEP method comes from the statistical sampling of conformations of the molecular mechanical (MM) subsystem required for the calculation of the QM PMF and its gradient. In our new sequential sampling and optimization approach, we aim to reduce the amount of MM sampling while still retaining the accuracy of the results by first carrying out MM phase-space sampling and then optimizing the QM subsystem in the fixed-size ensemble of MM conformations. The resulting QM optimized structures are then used to obtain more accurate sampling of the MM subsystem. This process of sequential MM sampling and QM optimization is iterated until convergence. The use of a fixed-size, finite MM conformational ensemble enables the precise evaluation of the QM potential of mean force and its gradient within the ensemble, thus circumventing the challenges associated with statistical averaging and significantly speeding up the convergence of the optimization process. To further improve the accuracy of the QM/MM-MFEP method, the reaction path potential method developed by Lu and Yang [Z. Lu and W. Yang, J. Chem. Phys. 121, 89 (2004)] is employed to describe the QM/MM electrostatic interactions in an approximate yet accurate way with a computational cost that is comparable to classical MM simulations. The new method was successfully applied to two example reaction processes, the classical SN 2 reaction of Cl- + CH3 Cl in solution and the second proton transfer step of the reaction catalyzed by the enzyme 4-oxalocrotonate tautomerase. The activation free energies calculated with this new sequential sampling and optimization approach to the QM/MM-MFEP method agree well with results from other simulation approaches such as the umbrella sampling technique with direct QM/MM dynamics sampling, demonstrating the accuracy of the iterative QM/MM-MFEP method. © 2008 American Institute of Physics.published_or_final_versio

Development of stable marker-free nuclear transformation strategy in the green microalga Chlorella vulgaris

Although microalgae have valuable resources with great necessity in many biotechnological applications, no tools have been developed yet for a stable genetic transformation without antibiotic marker genes in these organisms. Chlorella is one of the most useful genus for biotechnological applications. The transfer of foreign DNA (vector or linear DNA cassette) into Chlorella by electroporation has very low stability and it is hard to screen the transformants without antibiotic marker genes. However, the marker genes have some disadvantages to host cells. To avoid the negative effects caused by the marker genes, we tried to develop a stable marker-free nuclear transformation system in Chlorella. For this, linear gene expression cassettes (LGEC) were constructed with functional domains, which are responsible for transformation, of SV40 large T antigen. The LGECs were transferred into Chlorella via electroporation and durability of the LGECs were confirmed in transgenic Chlorella. Transcription levels of the LGECs were also determined at different cell cycle sates. The LGECs integrated into the chromosomal DNA of Chlorella were stably replicated and were expressed successfully at G0-, G1-, and G2-phases. This study presents a stable marker-free nuclear transformation system with potential for biotechnological applications.Key words: Chlorella vulgaris, marker-free nuclear transformation, SV40 large T antigen, microalga

An Efficient Representation of Euclidean Gravity I

We explore how the topology of spacetime fabric is encoded into the local structure of Riemannian metrics using the gauge theory formulation of Euclidean gravity. In part I, we provide a rigorous mathematical foundation to prove that a general Einstein manifold arises as the sum of SU(2)_L Yang-Mills instantons and SU(2)_R anti-instantons where SU(2)_L and SU(2)_R are normal subgroups of the four-dimensional Lorentz group Spin(4) = SU(2)_L x SU(2)_R. Our proof relies only on the general properties in four dimensions: The Lorentz group Spin(4) is isomorphic to SU(2)_L x SU(2)_R and the six-dimensional vector space of two-forms splits canonically into the sum of three-dimensional vector spaces of self-dual and anti-self-dual two-forms. Consolidating these two, it turns out that the splitting of Spin(4) is deeply correlated with the decomposition of two-forms on four-manifold which occupies a central position in the theory of four-manifolds.Comment: 31 pages, 1 figur

Effects of L-arginine on intestinal development and endogenous arginine-synthesizing enzymes in neonatal pigs

This study aimed to investigate the effects of dietary L-arginine supplementation on the intestinal development of neonatal piglets and the underlying mechanisms. 36 neonatal piglets were randomly allocated into three diet groups: control group (supplemented with 0% L-arginine), 0.4 and 0.8% Larginine groups. When compared with the control, dietary supplementation with L-arginine decreased (P<0.05) blood urea nitrogen (BUN), and improved (P<0.05) serum T3 and insulin level of the piglets on day 11. Arginine and its metabolites (citrulline and ornithine) were elevated, additionally, dietary supplementation with 0.8% L-arginine markedly enhanced jejunal villus height, villus area on day 11 and D-xylose absorption rate on day 19. Dietary supplementation with 0.8% L-arginine increased (P<0.05) activities of maltose and lactose on day 18, respectively. This effect correlated with profound change in enzyme activities as inducible nitric oxide synthetase (iNOS), glutamine synthetase (GS) and ornithine decarboxylase (ODC) were elevated on day 18. The concentrations of spermine was increased (P<0.05) by L-arginine supplementation on day 18. These results collectively suggest that dietary  Larginine supplementation improves protein synthesis and intestinal development of the neonatal pigs, the underlying mechanism includes dietary L-arginine supplementation which regulated the productions of intestinal polyamine in jejunum, and stimulated endogenous arginine-synthesizing enzymes in neonatal piglets.Key words: Neonatal pig, L-arginine, intestinal development, arginine-synthetases

Collaborative Gaze Channelling for Improved Cooperation During Robotic Assisted Surgery

The use of multiple robots for performing complex tasks is becoming a common practice for many robot applications. When different operators are involved, effective cooperation with anticipated manoeuvres is important for seamless, synergistic control of all the end-effectors. In this paper, the concept of Collaborative Gaze Channelling (CGC) is presented for improved control of surgical robots for a shared task. Through eye tracking, the fixations of each operator are monitored and presented in a shared surgical workspace. CGC permits remote or physically separated collaborators to share their intention by visualising the eye gaze of their counterparts, and thus recovers, to a certain extent, the information of mutual intent that we rely upon in a vis-à-vis working setting. In this study, the efficiency of surgical manipulation with and without CGC for controlling a pair of bimanual surgical robots is evaluated by analysing the level of coordination of two independent operators. Fitts' law is used to compare the quality of movement with or without CGC. A total of 40 subjects have been recruited for this study and the results show that the proposed CGC framework exhibits significant improvement (p<0.05) on all the motion indices used for quality assessment. This study demonstrates that visual guidance is an implicit yet effective way of communication during collaborative tasks for robotic surgery. Detailed experimental validation results demonstrate the potential clinical value of the proposed CGC framework. © 2012 Biomedical Engineering Society.link_to_subscribed_fulltex