Measurement of the α-Particle Monopole Transition Form Factor Challenges Theory: A Low-Energy Puzzle for Nuclear Forces?

We perform a systematic study of the α-particle excitation from its ground state 0_{1}^{+} to the 0_{2}^{+} resonance. The so-called monopole transition form factor is investigated via an electron scattering experiment in a broad Q^{2} range (from 0.5 to 5.0 fm^{-2}). The precision of the new data dramatically supersedes that of older sets of data, each covering only a portion of the Q^{2} range. The new data allow the determination of two coefficients in a low-momentum expansion, leading to a new puzzle. By confronting experiment to state-of-the-art theoretical calculations, we observe that modern nuclear forces, including those derived within chiral effective field theory that are well tested on a variety of observables, fail to reproduce the excitation of the α particle.

New Insight in the Q

Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer Q^{2}: 0.10, 0.20, and 0.45 GeV^{2}, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions P_{LL}-P_{TT}/ε and P_{LT}, as well as the electric and magnetic generalized polarizabilities α_{E1}(Q^{2}) and ß_{M1}(Q^{2}). These new results show a smooth and rapid falloff of α_{E1}(Q^{2}), in contrast to previous measurements at Q^{2}=0.33 GeV^{2}, and provide for the first time a precise mapping of ß_{M1}(Q^{2}) in the low-Q^{2} region.

First Measurement of the Q

We report on the first Q^{2}-dependent measurement of the beam-normal single spin asymmetry A_{n} in the elastic scattering of 570 MeV vertically polarized electrons off ^{12}C. We cover the Q^{2} range between 0.02 and 0.05 GeV^{2}/c^{2} and determine A_{n} at four different Q^{2} values. The experimental results are compared to a theoretical calculation that relates A_{n} to the imaginary part of the two-photon exchange amplitude. The result emphasizes that the Q^{2} behavior of A_{n} given by the ratio of the Compton to charge form factors cannot be treated independently of the target nucleus.

Beam-Recoil Polarization Measurement of π

The helicity-dependent recoil proton polarizations P_{x}^{'} and P_{z}^{'} as well as the helicity-independent component P_{y} have been measured in the p(e[over →],e^{'}p[over →])π^{0} reaction at four-momentum transfer Q^{2}≃0.1 GeV^{2}, center-of-mass proton emission angle θ_{p}^{*}≃90°, and invariant mass W≃1440 MeV. This first precise measurement of double-polarization observables in the energy domain of the Roper resonance P_{11}(1440) by exploiting recoil polarimetry has allowed for the extraction of its scalar electroexcitation amplitude at an unprecedentedly low value of Q^{2}, establishing a powerful instrument for probing the interplay of quark and meson degrees of freedom in the nucleon.

Search at the Mainz Microtron for light massive gauge bosons relevant for the muon g-2 anomaly.

A massive, but light, Abelian U(1) gauge boson is a well-motivated possible signature of physics beyond the standard model of particle physics. In this Letter, the search for the signal of such a U(1) gauge boson in electron-positron pair production at the spectrometer setup of the A1 Collaboration at the Mainz Microtron is described. Exclusion limits in the mass range of 40 MeV/c^{2} to 300 MeV/c^{2}, with a sensitivity in the squared mixing parameter of as little as ε^{2}=8×10^{-7} are presented. A large fraction of the parameter space has been excluded where the discrepancy of the measured anomalous magnetic moment of the muon with theory might be explained by an additional U(1) gauge boson.

Cardiac death in mucocutaneous lymph node syndrome.

A 12 year old boy had 4 symptom-free years after hospitalization for acute febrile mucocutaneous lymph node syndrome before he died suddenly from extensive myocardial infarction. Current evidence suggests that many patients with this syndrome have coronary artery disease and that those with significant cardiac findings should be studied with coronary angiography. Serial studies are recommended because of the danger of sudden death.

The minimal repression domain of MBD2b overlaps with the methyl-CpG-binding domain and binds directly to Sin3A.

Different mechanisms mediating methylation-dependent repression have been demonstrated. Two of these mechanisms play a role in the context of the granulocyte/macrophage-specific lysozyme gene: direct interference with DNA binding of the transcription factor GA-binding protein and deacetylation of histones. Besides enhancement in the unmethylated state, and transcriptional repression upon DNA methylation, the lysozyme downstream enhancer confers tissue-specific demethylation. Because both demethylation activity and repression ability have been attributed to the methyl-CpG-binding domain-containing protein MBD2, we analyzed this protein. The short form MBD2b binds to the methylated lysozyme enhancer and mediates transcriptional repression. MBD2b is capable of binding to the transcriptional repressor Sin3A. The interaction domain of Sin3A required for binding to MBD2b contains the paired amphipathic helix 3. We identified a minimal functional domain that confers both transcriptional repression as well as the interaction to Sin3A. In contrast to the functionally related proteins MeCP2 and MBD1, the repression domain of MBD2b overlaps with the methyl-CpG-binding domain.

Thoracic coarctation associated with neurofibromatosis.

A child with neurofibromatosis and hypertension also demonstrated renal artery stenosis, the most common cause of hypertension in children with neurofibromatosis; abdominal coarctation, which has previously been described; and thoracic coarctation, which to our knowledge, has not been previously reported. Rib notching may appear in patients with uncomplicated nueorfibromatosis, but the possibility of associated thoracic coarctation must also be considered in these patients.

[Enlargement of the sella in primary hypothyroidism]. / Sellavergrösserung bei primärer Hypothyreose.

Length of the sella, depth of the sella and surface of the sella profile of 37 primary hypothyroids were compared with a normal group. All the three parameters were significantly different, though situated in the normal area. The results are discussed on the basis of literature. The reactive formation of hypophyseal tumours at adult age in primary myxoedema is relatively rare. However, in every enlargement of the sella also a primary hypothyreosis should be regraded differential-diagnostically. A therapeutic experiment with thyroid hormones should always be made.

Uso racional de medicamentos: ¿qué conocen losmédicos residentes sobre los fármacos de uso corriente? / Rational drug use: what do resident surgeons know about common medicines?

Introducción: el uso irracional de los medicamentos constituye un riesgo inadmisible para los pacientes y un continuo derroche de recursos. De los diversos factores que contribuyen a esta realidad,el hábito de prescripción de los médicos es uno de los más frecuentes. La prescripción es un proceso razonado que exige el uso de información actualizada e independiente sobre los medicamentos. Objetivo: conocer la información que tienen los médicos residentes ded pediatría y medicina interna sobre medicamentos de uso frecuente. Material y método: en diciembre de 2002 se encuestaron en forma personal y anónima, 69 médicos residentes (38 de pediatría y 31 de medicina interna). Se evaluó el conocimiento sobre nombre genérico, dosis, efectos adversos y contraindicaciones absolutas de medicamentos de uso frecuente en cada una de las disciplinas. Las respuestas fueron catalogadas como verdaderas o falsas usando un estándar elaborado por los autores. Resultados: los porcentajes de respuestas verdaderas entre los residentes de pediatría fueron: genérico 82 por ciento, dosis 42 por ciento, efectos adversos comunes 16 por ciento, efectos adversos graves 16 por ciento y contraindicaciones 32 por ciento. Entre los residentes de medicina interna: genérico 89 por ciento, dosis 53 por ciento, efectos adversos comunes 16 por ciento, efectos adversos graves 45 por ciento y contraindicaciones 46 por ciento. Se observó una proporción mayor de respuestas verdaderas estadísticamente significativa, entre resideentes de medicina interna en relación a las dosis, efectos adversos graves y contraindicaciones. Conclusiones: una elevada proporción de los residentes encuestados no tiene conocimientos suficientes en relación a las dosis, los efectos adversos y las contraindicaciones de estos medicamentos de uso frecuente. Esto constituye un factor determinante en la prescripción irracional de los medicamentos. Es necesario fortalecer la formación continua en farmacología y terapéutica de los médicos residentes para revertir este problema.