Exact solutions of n-level systems and gauge theories

We find a relationship between unitary transformations of the dynamics of quantum systems with time-dependent Hamiltonians and gauge theories. In particular, we show that the nonrelativistic dynamics of spin-$\frac12$ particles in a magnetic field $B^i (t)$ can be formulated in a natural way as an SU(2) gauge theory, with the magnetic field $B^i(t)$ playing the role of the gauge potential A^i. The present approach can also be applied to systems of n levels with time-dependent potentials, U(n) being the gauge group. This geometric interpretation provides a powerful method to find exact solutions of the Schr\"odinger equation. The root of the present approach rests in the Hermiticity property of the Hamiltonian operators involved. In addition, the relationship with true gauge symmetries of n-level quantum systems is discussed.Comment: LaTeX file, 5 pages, published versio

Measuring Pancharatnam's relative phase for SO(3) evolutions using spin polarimetry

In polarimetry, a superposition of internal quantal states is exposed to a single Hamiltonian and information about the evolution of the quantal states is inferred from projection measurements on the final superposition. In this framework, we here extend the polarimetric test of Pancharatnam's relative phase for spin$-{1/2}$ proposed by Wagh and Rakhecha [Phys. Lett. A {\bf 197}, 112 (1995)] to spin $j\geq 1$ undergoing noncyclic SO(3) evolution. We demonstrate that the output intensity for higher spin values is a polynomial function of the corresponding spin$-{1/2}$ intensity. We further propose a general method to extract the noncyclic SO(3) phase and visibility by rigid translation of two $\pi /2$ spin flippers. Polarimetry on higher spin states may in practice be done with spin polarized atomic beams.Comment: New title, minor corrections, journal reference adde

Calculation of the emission power distribution of microstructured OLEDs using the reciprocity theorem

S. Zhang, E.R. Martins, G.A. Turnbull and I.D.W. Samuel are grateful to the Scottish Universities Physics Alliance (SUPA) and the Engineering and Physical Sciences Research Council (EPSRC) for financial support.Integrating photonic microstructures into organic light-emitting diodes (OLEDs) has been a widely used strategy to improve their light out-coupling efficiency. However, there is still a need for optical modelling methods which quantitatively characterise the spatial emission pattern of microstructured OLEDs. In this paper, we demonstrate such rigorous calculation using the reciprocity theorem. The calculation of the emission intensity at each direction in the far field can be simplified into only two simple calculations of an incident plane wave propagating from the far field into a single cell of the periodic structure. The emission from microstructured OLED devices with three different grating periods was calculated as a test of the approach, and the calculated results were in good agreement with experiment. This optical modelling method is a useful calculation tool to investigate and control the spatial emission pattern of microstructured OLEDs.PostprintPeer reviewe

Búsqueda de grupos de galaxias y de galaxias peculiares

Las placas del SPM son óptimas para la búsqueda de galaxias puesto que unen a la escala de astrográfico (1': 1 mm) y al límite en brillo alcanzable (magnitud 19 en el azul con 2 horas de exposición), el hecho de que las placas se toman en dos colores y simultáneamente para cada centro cubriendo un área de 39,7 (°)²; finalmente se debe mencionar que como las mismas se toman con red de difracción se tiene una información directa sobre la emisión del núcleo.Asociación Argentina de Astronomí

Búsqueda de grupos de galaxias y de galaxias peculiares

Las placas del SPM son óptimas para la búsqueda de galaxias puesto que unen a la escala de astrográfico (1': 1 mm) y al límite en brillo alcanzable (magnitud 19 en el azul con 2 horas de exposición), el hecho de que las placas se toman en dos colores y simultáneamente para cada centro cubriendo un área de 39,7 (°)²; finalmente se debe mencionar que como las mismas se toman con red de difracción se tiene una información directa sobre la emisión del núcleo.Asociación Argentina de Astronomí

Búsqueda de grupos de galaxias y de galaxias peculiares

Las placas del SPM son óptimas para la búsqueda de galaxias puesto que unen a la escala de astrográfico (1': 1 mm) y al límite en brillo alcanzable (magnitud 19 en el azul con 2 horas de exposición), el hecho de que las placas se toman en dos colores y simultáneamente para cada centro cubriendo un área de 39,7 (°)²; finalmente se debe mencionar que como las mismas se toman con red de difracción se tiene una información directa sobre la emisión del núcleo.Asociación Argentina de Astronomí

Crystal structure of Mycobacterium tuberculosis FadB2 implicated in mycobacterial β-oxidation

The intracellular pathogen Mycobacterium tuberculosis is the causative agent of tuberculosis, which is a leading cause of mortality worldwide. The survival of M. tuberculosis in host macrophages through long-lasting periods of persistence depends, in part, on breaking down host cell lipids as a carbon source. The critical role of fatty-acid catabolism in this organism is underscored by the extensive redundancy of the genes implicated in β-oxidation (∼100 genes). In a previous study, the enzymology of the M. tuberculosisl-3-hydroxyacyl-CoA dehydrogenase FadB2 was characterized. Here, the crystal structure of this enzyme in a ligand-free form is reported at 2.1 Å resolution. FadB2 crystallized as a dimer with three unique dimer copies per asymmetric unit. The structure of the monomer reveals a dual Rossmann-fold motif in the N-terminal domain, while the helical C-terminal domain mediates dimer formation. Comparison with the CoA- and NAD + -bound human orthologue mitochondrial hydroxyacyl-CoA dehydrogenase shows extensive conservation of the residues that mediate substrate and cofactor binding. Superposition with the multi-catalytic homologue M. tuberculosis FadB, which forms a trifunctional complex with the thiolase FadA, indicates that FadB has developed structural features that prevent its self-association as a dimer. Conversely, FadB2 is unable to substitute for FadB in the tetrameric FadA–FadB complex as it lacks the N-terminal hydratase domain of FadB. Instead, FadB2 may functionally (or physically) associate with the enoyl-CoA hydratase EchA8 and the thiolases FadA2, FadA3, FadA4 or FadA6 as suggested by interrogation of the STRING protein-network database

Practical and ethical challenges of a North-South partnership

INTRODUCTION The Departments of Surgery at the University of North Carolina (UNC) and Kamuzu Central Hospital (KCH) in Lilongwe, Malawi, formed a partnership of service, training, and research in 2008. We report a case of recurrent pancreatitis leading to pancreatic necrosis treated at KCH. PRESENTATION OF CASE A 42 year-old male presented to KCH with his fourth episode of abdominal pain, nausea and vomiting. He had tachycardia, guarding, rebound tenderness, and free fluid on abdominal ultrasonography. He underwent laparotomy and had fat saponification with pancreatic necrosis. A large drain was placed, he was given antibiotics, and he recovered. He had normal lipids, no gallstones, and did not consume alcohol. He was encouraged to seek further evaluation with endoscopic retrograde cholangiopancreatography or computed tomography in South Africa, however this was prohibitively expensive. DISCUSSION This case illustrates the limitations that are often faced by surgeons visiting developing countries. What we consider standard resources and treatment algorithms in managing necrotizing pancreatitis in developed countries (such as serum lipase and percutaneous interventions) were not available. CONCLUSION Visiting surgeons and trainees must be both familiar with local resource limitations and aware of the implications of such limitations on patient care. To support training and promote advances in health care, local surgeons and trainees should understand optimal treatment strategies regardless of their particular resource limitations. North-South partnerships are an excellent means to uphold our professional obligation to humanity, promote health care as a right, and shape the future of health care in developing countries

Low field vortex matter in YBCO: an atomic beam magnetic resonance study

We report measurements of the low field structure of the magnetic vortex lattice in an untwinned YBCO single-crystal platelet. Measurements were carried out using a novel atomic beam magnetic resonance (ABMR) technique. For a 10.7 G field applied parallel to the c-axis of the sample, we find a triangular lattice with orientational order extending across the entire sample. We find the triangular lattice to be weakly distorted by the a-b anisotropy of the material and measure a distortion factor, f = 1.16. Model-experiment comparisons determine a penetration depth, lambda_ab = 140 (+-20) nm. The paper includes the first detailed description of the ABMR technique. We discuss both technical details of the experiment and the modeling used to interpret the measurements.Comment: 44 pages, 13 figures, submitted to Phys. Rev. B Revision includes Postscript wrapped figures + minor typo

The General Solution of Bianchi Type VIIhVII_h Vacuum Cosmology

The theory of symmetries of systems of coupled, ordinary differential equations (ODE) is used to develop a concise algorithm in order to obtain the entire space of solutions to vacuum Bianchi Einstein Field Equations (EFEs). The symmetries used are the well known automorphisms of the Lie algebra for the corresponding isometry group of each Bianchi Type, as well as the scaling and the time re-parametrization symmetry. The application of the method to Type VII_h results in (a) obtaining the general solution of Type VII_0 with the aid of the third Painlev\'{e} transcendental (b) obtaining the general solution of Type $VII_h$ with the aid of the sixth Painlev\'{e} transcendental (c) the recovery of all known solutions (six in total) without a prior assumption of any extra symmetry (d) The discovery of a new solution (the line element given in closed form) with a G_3 isometry group acting on T_3, i.e. on time-like hyper-surfaces, along with the emergence of the line element describing the flat vacuum Type VII_0 Bianchi Cosmology.Comment: latex2e source file, 27 pages, 2 tables, no fiure