Spin dependent point potentials in one and three dimensions

We consider a system realized with one spinless quantum particle and an array of $N$ spins 1/2 in dimension one and three. We characterize all the Hamiltonians obtained as point perturbations of an assigned free dynamics in terms of some ``generalized boundary conditions''. For every boundary condition we give the explicit formula for the resolvent of the corresponding Hamiltonian. We discuss the problem of locality and give two examples of spin dependent point potentials that could be of interest as multi-component solvable models.Comment: 15 pages, some misprints corrected, one example added, some references modified or adde

Small Angle X-ray Scattering From Lipid-bound Myelin Basic Protein In Solution

The structure of myelin basic protein (MBP), purified from the myelin sheath in both lipid-free (LF-MBP) and lipid-bound (LB-MBP) forms, was investigated in solution by small angle x-ray scattering. The water-soluble LF-MBP, extracted at pH 7.0. Under all conditions, the scattering from the two protein forms was different, indicating different molecular shapes. For the LB-MBP, well-defined scattering curves were obtained, suggesting that the protein had a unique, compact (but not globular) structure. Furthermore, these data were compatible with earlier results from molecular modeling calculations on the MBP structure which have been refined by us. In contrast, the LF-MBP data were in accordance with the expected open-coil conformation. The results represent the first direct structural information from x-ray scattering measurements on MBP in its native lipidic environment in solution.861 I455460Altschul, S.F., Madden, T.L., Schäffer, A.A.Z.J., Zhang, Z., Miller, W., Gapped, L.D.J., BLAST and PSI-BLAST: A new generation of protein database search programs (1997) Nucleic Acids Res., 25, pp. 3389-3402Alvord, E.C., Kies, M.W., Suckling, A.L., (1984) Experimental Allergic Encephalomyelitis: A Useful Model for Multiple Sclerosis, , Alan R. Liss Inc., New YorkBates, I.R., Harauz, G., Molecular dynamics exposes α-helices in myelin basic protein (2003) J. Mol. Mod., , published online 24 July 2003Beniac, D.R., Luckevich, M.D., Czamota, G.J., Tompkins, T.A., Ridsdale, R.A., Ottensmeyer, F.P., Moscarello, M.A., Harauz, G., Three-dimensional structure of myelin basic protein. I. Reconstruction via angular reconstitution of randomly oriented single particles (1997) J. Biol. 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Biochem., 2, pp. 139-165Deibler, G.E., Boyd, L.F., Kies, M.W., Proteolytic activity associated with purified myelin basic protein (1984) Experimental Allergic Encephalomyelitis: A Useful Model for Multiple Sclerosis, pp. 249-256. , E. C. Alvord Jr., M. W. Kies, and A. J. Suckling, editors. Liss, New YorkEpand, R.M., Moscarello, M.A., Zierenberg, B., Vail, W.J., The folded conformation of the encephalogenic protein of the human brain (1974) Biochemistry, 13, pp. 1264-1267Garavito, R.M., Ferguson-Miller, S., Detergents as tools in membrane biochemistry (2001) J. Biol. Chem., 276, pp. 32403-32406Glatter, O., Convolution square root of band-limited symmetrical functions and its applications to small-angle scattering data (1981) J. Appl. Crystallogr., 14, pp. 101-108Gow, A., Smith, R., The thermodynamically stable state of myelin basic protein in solution is a flexible coil (1989) Biochem. 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Lighting the fuse: Cultivating the masculine physics habitus – a case study of Victor aged 10-18

This chapter presents a longitudinal case study analysis of Victor, a young man who was interviewed from the ages of 10–19, together with his mother, Sam, and who went on to study for a degree in astrophysics. We apply a Bourdieusian conceptual lens to the data, to explore how interactions of capital, habitus and field combine to possibilise Victor and his trajectory to being/becoming a physicist. We also identify specific alignments of his habitus and capital with dominant notions of masculinity and ‘cleverness’ that are demanded and normalised within physics and which, we argue, are key to the reproduction of the elite nature of physics

An autonomous chemically fuelled small-molecule motor

Molecular machines are among the most complex of all functional molecules and lie at the heart of nearly every biological process. A number of synthetic small-molecule machines have been developed, including molecular muscles, synthesizers, pumps, walkers, transporters and light-driven and electrically driven rotary motors. However, although biological molecular motors are powered by chemical gradients or the hydrolysis of adenosine triphosphate (ATP), so far there are no synthetic small-molecule motors that can operate autonomously using chemical energy (that is, the components move with net directionality as long as a chemical fuel is present). Here we describe a system in which a small molecular ring (macrocycle) is continuously transported directionally around a cyclic molecular track when powered by irreversible reactions of a chemical fuel, 9-fluorenylmethoxycarbonyl chloride. Key to the design is that the rate of reaction of this fuel with reactive sites on the cyclic track is faster when the macrocycle is far from the reactive site than when it is near to it. We find that a bulky pyridine-based catalyst promotes carbonate-forming reactions that ratchet the displacement of the macrocycle away from the reactive sites on the track. Under reaction conditions where both attachment and cleavage of the 9-fluorenylmethoxycarbonyl groups occur through different processes, and the cleavage reaction occurs at a rate independent of macrocycle location, net directional rotation of the molecular motor continues for as long as unreacted fuel remains. We anticipate that autonomous chemically fuelled molecular motors will find application as engines in molecular nanotechnology.</p

Resonances in Models of Spin Dependent Point Interactions

In dimension $d=1,2,3$ we define a family of two-channel Hamiltonians obtained as point perturbations of the generator of the free decoupled dynamics. Within the family we choose two Hamiltonians, $\hat H_0$ and \hat H_\ve, giving rise respectively to the unperturbed and to the perturbed evolution. The Hamiltonian $\hat H_0$ does not couple the channels and has an eigenvalue embedded in the continuous spectrum. The Hamiltonian \hat H_\ve is a small perturbation, in resolvent sense, of $\hat H_0$ and exhibits a small coupling between the channels. We take advantage of the complete solvability of our model to prove with simple arguments that the embedded eigenvalue of $\hat H_0$ shifts into a resonance for \hat H_\ve. In dimension three we analyze details of the time behavior of the projection onto the region of the spectrum close to the resonance.Comment: Changes in the proof of theorem 3, few misprints corrected, 21 page

Immunogenicity of Fractional Doses of Tetravalent A/C/Y/W135 Meningococcal Polysaccharide Vaccine: Results from a Randomized Non-Inferiority Controlled Trial in Uganda

Meningitis are infections of the lining of the brain and spinal cord and can cause high fever, blood poisoning, and brain damage, as well as result in death in up to 10% of cases. Epidemics of meningitis occur almost every year in parts of sub-Saharan Africa, throughout a high-burden area spanning Senegal to Ethiopia dubbed the “Meningitis Belt.” Most epidemics in Africa are caused by Neisseria meningitidis (mostly serogroup A and W135). Mass vaccination campaigns attempt to control epidemics by administering meningococcal vaccines targeted against these serogroups, among others. However, global shortages of these vaccines are currently seen. We studied the use of fractional (1/5 and 1/10) doses of a licensed vaccine to assess its non-inferiority compared with the normal full dose. In a randomized trial in Uganda, we found that immune response and safety using a 1/5 dose were comparable to full dose for three serogroups (A, Y, W135), though not a fourth (C). In light of current shortages of meningococcal vaccines and their importance in fighting meningitis epidemics around the world, we suggest fractional doses be taken under consideration in mass vaccination campaigns