Anticoagulant activity of a synthetic heparinoid in relation to molecular weight and N-sulfate content

Addition of chlorosulfonyl isocyanate to C=C bonds in cis-1,4-polyisoprene and reaction of the adduct with NaOH resulted in the formation of a water-soluble polyelectrolyte with N-sulfate and carboxylate groups. The polyelectrolyte showed anticoagulant activity and it was found, just as with heparin, that the activity was related to molecular weight and N-sulfate content

Notes sur l'organisation économique et sociale de la pêche artisanale, du fumage et de la commercialisation du poisson dans la ville de Conakry

Les premières enquêtes effectuées par le C.R.H.B. semblent montrer que les activités halieutiques artisanales constituent à Conakry un milieu ouvert à des producteurs et des commerçants issus de secteurs économiques étrangers à la pêche et originaires de régions parfois éloignées du littoral maritime. Ces enquêtes suggèrent également qu'une étude des dynamiques des activités halieutiques dans la capitale guinéenne ne peut valablement être conduite qu'à l'intérieur d'une étude plus générale des dynamismes urbains dans leur ensemble. (Résumé d'auteur

Local effective dynamics of quantum systems: A generalized approach to work and heat

By computing the local energy expectation values with respect to some local measurement basis we show that for any quantum system there are two fundamentally different contributions: changes in energy that do not alter the local von Neumann entropy and changes that do. We identify the former as work and the latter as heat. Since our derivation makes no assumptions on the system Hamiltonian or its state, the result is valid even for states arbitrarily far from equilibrium. Examples are discussed ranging from the classical limit to purely quantum mechanical scenarios, i.e. where the Hamiltonian and the density operator do not commute.Comment: 5 pages, 1 figure, published versio

Coherence of single spins coupled to a nuclear spin bath of varying density

The dynamics of single electron and nuclear spins in a diamond lattice with different 13C nuclear spin concentration is investigated. It is shown that coherent control of up to three individual nuclei in a dense nuclear spin cluster is feasible. The free induction decays of nuclear spin Bell states and single nuclear coherences among 13C nuclear spins are compared and analyzed. Reduction of a free induction decay time T2* and a coherence time T2 upon increase of nuclear spin concentration has been found. For diamond material with depleted concentration of nuclear spin, T2* as long as 30 microseconds and T2 of up to 1.8 ms for the electron spin has been observed. The 13C concentration dependence of T2* is explained by Fermi contact and dipolar interactions with nuclei in the lattice. It has been found that T2 decreases approximately as 1/n, where n is 13C concentration, as expected for an electron spin interacting with a nuclear spin bath.Comment: 4 pages, 4 figures, 1 movie (avi), 1 supplementary material (pdf

Estimate of vascular permeability and cerebral blood volume using Gd-DTPA contrast enhancement and dynamic T2*-weighted MRI

Purpose To develop a numerical approach for estimation of vascular permeability from dynamic T2*-weighted imaging, a technique routinely used to measure cerebral blood volume (CBV) and flow in gliomas. Materials and Methods This study describes a process for estimating both the gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) transvascular transfer constant and CBV from dynamic T2*-weighted images. The algorithm was applied to data from the brains of 12 patients with grade IV gliomas. The stability of the method was assessed. Estimates of CBV by this technique were compared to those of the conventional method. Results The algorithm was found to be insensitive to noise and to generate stable voxel-by-voxel estimates of permeability and CBV. Conclusion Using a single imaging acquisition, the three most important vascular properties, CBV, cerebral blood flow (CBF), and permeability, can be estimated. This approach may have potential in clinical evaluation of patients with brain tumor or acute ischemic stroke. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55796/1/20634_ftp.pd

The negatively charged nitrogen-vacancy centre in diamond: the electronic solution

The negatively charged nitrogen-vacancy centre is a unique defect in diamond that possesses properties highly suited to many applications, including quantum information processing, quantum metrology, and biolabelling. Although the unique properties of the centre have been extensively documented and utilised, a detailed understanding of the physics of the centre has not yet been achieved. Indeed there persists a number of points of contention regarding the electronic structure of the centre, such as the ordering of the dark intermediate singlet states. Without a sound model of the centre's electronic structure, the understanding of the system's unique dynamical properties can not effectively progress. In this work, the molecular model of the defect centre is fully developed to provide a self consistent model of the complete electronic structure of the centre. The application of the model to describe the effects of electric, magnetic and strain interactions, as well as the variation of the centre's fine structure with temperature, provides an invaluable tool to those studying the centre and a means to design future empirical and ab initio studies of this important defect.Comment: 24 pages, 6 figures, 10 table

Thermodynamics of quantum systems under dynamical control

In this review the debated rapport between thermodynamics and quantum mechanics is addressed in the framework of the theory of periodically-driven/controlled quantum-thermodynamic machines. The basic model studied here is that of a two-level system (TLS), whose energy is periodically modulated while the system is coupled to thermal baths. When the modulation interval is short compared to the bath memory time, the system-bath correlations are affected, thereby causing cooling or heating of the TLS, depending on the interval. In steady state, a periodically-modulated TLS coupled to two distinct baths constitutes the simplest quantum heat machine (QHM) that may operate as either an engine or a refrigerator, depending on the modulation rate. We find their efficiency and power-output bounds and the conditions for attaining these bounds. An extension of this model to multilevel systems shows that the QHM power output can be boosted by the multilevel degeneracy. These results are used to scrutinize basic thermodynamic principles: (i) Externally-driven/modulated QHMs may attain the Carnot efficiency bound, but when the driving is done by a quantum device ("piston"), the efficiency strongly depends on its initial quantum state. Such dependence has been unknown thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the temperature approaches absolute zero for certain quantized baths, e.g., magnons, thous challenging Nernst's unattainability principle. (iii) System-bath correlations allow more work extraction under periodic control than that expected from the Szilard-Landauer principle, provided the period is in the non-Markovian domain. Thus, dynamically-controlled QHMs may benefit from hitherto unexploited thermodynamic resources