Sequential Nature of (p,3p) Two-Proton Knockout from Neutron-Rich Nuclei.

Twenty-one two-proton knockout (p,3p) cross sections were measured from neutron-rich nuclei at ∼250 MeV/nucleon in inverse kinematics. The angular distribution of the three emitted protons was determined for the first time, demonstrating that the (p,3p) kinematics are consistent with two sequential proton-proton collisions within the projectile nucleus. Ratios of (p,3p) over (p,2p) inclusive cross sections follow the trend of other many-nucleon removal reactions, further reinforcing the sequential nature of (p,3p) in neutron-rich nuclei.

Metastable States of

Here we present new information on the shape evolution of the very neutron-rich ^{92,94}Se nuclei from an isomer-decay spectroscopy experiment at the Radioactive Isotope Beam Factory at RIKEN. High-resolution germanium detectors were used to identify delayed γ rays emitted following the decay of their isomers. New transitions are reported extending the previously known level schemes. The isomeric levels are interpreted as originating from high-K quasineutron states with an oblate deformation of ß∼0.25, with the high-K state in ^{94}Se being metastable and K hindered. Following this, ^{94}Se is the lowest-mass neutron-rich nucleus known to date with such a substantial K hindrance. Furthermore, it is the first observation of an oblate K isomer in a deformed nucleus. This opens up the possibility for a new region of K isomers at low Z and at oblate deformation, involving the same neutron orbitals as the prolate orbitals within the classic Z∼72 deformed hafnium region. From an interpretation of the level scheme guided by theoretical calculations, an oblate deformation is also suggested for the ^{94}Se_{60} ground-state band.

Prominence of Pairing in Inclusive (p,2p) and (p,pn) Cross Sections from Neutron-Rich Nuclei.

Fifty-five inclusive single nucleon-removal cross sections from medium mass neutron-rich nuclei impinging on a hydrogen target at ∼250 MeV/nucleon are measured at the RIKEN Radioactive Isotope Beam Factory. Systematically higher cross sections are found for proton removal from nuclei with an even number of protons as compared to odd-proton number projectiles for a given neutron separation energy. Neutron removal cross sections display no even-odd splitting, contrary to nuclear cascade model predictions. Both effects are understood through simple considerations of neutron separation energies and bound state level densities originating in pairing correlations in the daughter nuclei. These conclusions are supported by comparison with semimicroscopic model predictions, highlighting the enhanced role of low-lying level densities in nucleon-removal cross sections from loosely bound nuclei.

Shape Evolution in Neutron-Rich Krypton Isotopes Beyond N=60: First Spectroscopy of

We report on the first γ-ray spectroscopy of low-lying states in neutron-rich ^{98,100}Kr isotopes obtained from ^{99,101}Rb(p,2p) reactions at ∼220 MeV/nucleon. A reduction of the 2_{1}^{+} state energies beyond N=60 demonstrates a significant increase of deformation, shifted in neutron number compared to the sharper transition observed in strontium and zirconium isotopes. State-of-the-art beyond-mean-field calculations using the Gogny D1S interaction predict level energies in good agreement with experimental results. The identification of a low-lying (0_{2}^{+}, 2_{2}^{+}) state in ^{98}Kr provides the first experimental evidence of a competing configuration at low energy in neutron-rich krypton isotopes consistent with the oblate-prolate shape coexistence picture suggested by theory.

Are There Signatures of Harmonic Oscillator Shells Far from Stability? First Spectroscopy of

The first measurement of the low-lying states of the neutron-rich ^{110}Zr and ^{112}Mo was performed via in-beam γ-ray spectroscopy after one proton removal on hydrogen at ∼200 MeV/nucleon. The 2_{1}^{+} excitation energies were found at 185(11) keV in ^{110}Zr, and 235(7) keV in ^{112}Mo, while the R_{42}=E(4_{1}^{+})/E(2_{1}^{+}) ratios are 3.1(2), close to the rigid rotor value, and 2.7(1), respectively. These results are compared to modern energy density functional based configuration mixing models using Gogny and Skyrme effective interactions. We conclude that first levels of ^{110}Zr exhibit a rotational behavior, in agreement with previous observations of lighter zirconium isotopes as well as with the most advanced Monte Carlo shell model predictions. The data, therefore, do not support a harmonic oscillator shell stabilization scenario at Z=40 and N=70. The present data also invalidate predictions for a tetrahedral ground state symmetry in ^{110}Zr.

Low-dimensional dynamics in sensory biology 2: facial cold receptors of the rat.

We report the results of a search for evidence of unstable periodic orbits in the sensory afferents of the facial cold receptors of the rat. Cold receptors are unique in that they exhibit a diversity of action potential firing patterns as well as pronounced transients in firing rate following rapid temperature changes. These characteristics are the result of an internal oscillator operating at the level of the membrane potential. If such oscillators have three or more degree of freedom, and at least one of which also exhibits a nonlinearity, they are potentially capable of complex activity. By detecting the existence of unstable periodic orbits, we demonstrate low-dimensional dynamical behavior whose characteristics depend on the temperature range, impulse pattern, and temperature transients.

Stimulus sensitivity and neuromodulatory properties of noisy intrinsic neuronal oscillators.

Intrinsic subthreshold oscillations in the membrane potential are a common property of many neurons in the peripheral and central nervous system. When such oscillations are combined with noise, interesting signal encoding and neuromodulatory properties are obtained which allow, for example, sensitivity adjustment or differential encoding of stimuli. Here we demonstrate that a noisy Hodgkin/Huxley-model for subthreshold oscillations, when tuned to maximum sensitivity, can be significantly modulated by even minor physiological changes in the oscillation parameters amplitude or frequency. Given the ubiquity of subthreshold oscillating neurons, it can be assumed that these findings reflect principle encoding properties which are relevant for an understanding of sensitivity and neuromodulation in peripheral and central neurons.

Heterogeneity in the mitotic checkpoint control of BALB/3T3 cells and a correlation with gene amplification propensity.

Chinese hamster ovary (and many rodent cell lines) transiently delay mitosis and progress into a second cell cycle without undergoing cytokinesis when treated with Colcemid, whereas HeLaS3 (and most human cell lines) arrest permanently in mitosis. We have discussed these differences and their consequences for cell survival under cell cycle-perturbing conditions within the context of mitotic checkpoint control (Schimke et al., Cold Spring Harbor Symp. Quant. Biol., 56: 417-425, 1991). Here, we report studies with mouse BALB/3T3 cell populations which, by the criterion of response to Colcemid, constitute a heterogeneous population with respect to mitotic checkpoint control. Clonal and subclonal populations retain population heterogeneity but with a bias for enrichment of cell populations that respond as do HeLaS3 cells. We have analyzed clones for their propensity for gene amplification as assessed by a stepwise increment selection protocol in methotrexate and report that there are significant differences in amplification propensities that correlate with differences in mitotic checkpoint control properties.

Production of pineapple plants in vitro.

In vitro culture of pineapple (Ananas comosus) was studied to determine the efficiency of axillary bud culture for rapid propagation of several cultivars. The technique used maximizes the success rate of various steps in the production of pineapple plants. Rapid mass multiplication of plantlets started 9 months after explanting with a significant log phase. The number of plantlets obtained from the culture of a single bud by the thirteenth month ranged from 210 to 380 for 'Perolera'; 300 to 350 for 'PR-1-67'; and 40 to 85 for 'Smooth Cayenne'. The method permits culture of a range of pineapple cultivars. Little morphological variation was observed in young regenerated plants.

[Value of echography in the diagnosis of hematomas of the digestive tract wall in rheumatoid purpura]. / Apport de l'échographie dans le diagnostic des hématomes des parois digestives au cours du purpura rhumatoïde.

Three cases of Henoch-Schönlein purpura with intramural hematoma of the duodenum, jejunum or colon are reported. In the first 2 cases, there was complete agreement between the X-ray and ultrasonographic data: multiple thumb print defects and irregular narrowing of the digestive lumen, and thickening of the intestinal wall, respectively. Ultrasonography was the only investigation performed in the third case. Finally, in 2 of 3 cases an exudative enteropathy of unclear mechanism was discovered.

[Urinary malformations in synostoses of the cervical vertebrae (Klippel-Feil syndrome). Apropos of 35 cases]. / Malformations urinaires dans les synostoses du rachis cervical (syndrome de Klippel-Feil). A propos de trente-cinq cas.

A study of 35 cases of congenital fusion of the cervical vertebrae demonstrated the high incidence of its association with urinary anomalies (52 per cent). More than half of these cases concerned unilateral kidney defects. The urinary anomalies are normally asymptomatic, but there is always the risk of chronic renal failure, and preventive surgery may be necessary. It is therefore advisable to make a systematic practice of obtaining ultrasound examinations and intravenous urograms. There are many other possible associated anomalies, which are often the first to be noted and lead to the discovery of the vertebral and urinary malformations. The authors define Klippel-Feil syndrome as the synostosis of two or more cervical vertebrae.

[Value of gastroesophageal scintigraphy for the detection of gastroesophageal reflux in infants]. / Valeur de la scintigraphie gastro-oesophagienne pour la détection du reflux gastro-oeophagien du nourrisson.

50 children with a strong clinical suspicion of gastroesophageal reflux and 10 control patients were evaluated with gastroesophageal scintiscans. 500 muCi à 1 mCi of Tc sulfur colloid mixed the patients' routine milk or formula feeding was administered and serial images of the abdomen and thorax were obtained. A positive scintiscan was found in 35 patients (sensitivity 70%) and none of the controls (specificity 100%). A comparison of findings in 34 patients referred for both radiographic and radionuclide studies showed that barium studies were positive in 38% and radionuclide in 64.7%. We found this examination to be more sensitive that the standard barium radiography particularly in patients with respiratory symptoms. We concluded that the GE scintiscan is complementary to barium studies in the diagnosis of GE reflux. Pulmonary aspiration of gastric contents was detected in only a case of the 35 patients with documented GE reflux. A T 1/2 emptying gastric longer than 90 minutes (linear calculation) or 105 minutes (exponential calculation) is an indirect GE reflux test. This procedure is simple, safe more physiologic than other available examinations.