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To be complete, the characterization of the photoionization process of atoms and molecules requires the extraction of all quantum-mechanical phases and amplitudes. So far, complete experiments have accessed only the ionization process of neutral atoms and molecules. Here we report the quantum-mechanically complete characterization of the single and double ionization of neon to yield doubly charged ions. The first ionization step by intense, polarized extreme ultraviolet light from a free-electron laser leaves the ion in a polarized state (that is, one in which the angular momentum of the ion is aligned in space). By controlling the polarization of the light, we determine the bound and continuum components of the system in the first and second ionization steps leading to the formation of doubly charged neon ions. We test the validity of our approach by characterizing the influence of autoionizing ionic states on the two-photon double-ionization mechanism. Our results are important for understanding the physics of the interaction of extreme ultraviolet radiation with ions.

Extreme ultraviolet and X-ray free-electron lasers (FELs) produce short-wavelength pulses with high intensity, ultrashort duration, well-defined polarization and transverse coherence, and have been utilized for many experiments previously possible only at long wavelengths: multiphoton ionization, pumping an atomic laser and four-wave mixing spectroscopy. However one important optical technique, coherent control, has not yet been demonstrated, because self-amplified spontaneous emission FELs have limited longitudinal coherence. Single-colour pulses from the FERMI seeded FEL are longitudinally coherent, and two-colour emission is predicted to be coherent. Here, we demonstrate the phase correlation of two colours, and manipulate it to control an experiment. Light of wavelengths 63.0 and 31.5 nm ionized neon, and we controlled the asymmetry of the photoelectron angular distribution by adjusting the phase, with a temporal resolution of 3 as. This opens the door to new short-wavelength coherent control experiments with ultrahigh time resolution and chemical sensitivity.

AbstractIn a multi-service IP/MPLS network, it is a key challenge to provide Quality of Service (QoS) to end-users applications while effectively using network resources and providing reliable services. In this framework, native TE mechanisms can be used to improve network performance, whereas a set of procedures that protects the traffic flows carried on different paths enforces resilience techniques. The paper presents the main functionalities of MTENS (MPLSTE network simulator), a new NS2-based simulator, specifically developed to facilitate the design of MPLS networks with TE support. Moreover, to highlight the effectiveness of MTENS in the design of MPLS-TE networks, the paper shows a case study concerning the performance evaluation of different recovery strategies when path computation algorithms with QoS constraints are used for primary and backup label switched paths.

KRb and Rb2dimers are formed on cold helium nanodroplets. Laser excitation and emission spectra from the transition (1)3?g-3?u+of Rb2and the transition (2)3?-3?+of KRb have been measured. A thorough analysis of the emission, which takes place after desorption of the dimers from the surface of the helium cluster, has been performed. It allows us to determine the redistribution of vibrational population on the droplet surface. A comparison of the experimental spectra with simulations, obtained with the potential energy curves and dipole moments calculated by Aymar and Dulieu, allows a test of the accuracy of the ab initiopotentials.

We investigated the effect of the transient neonatal hyperthyroid state on thermogenesis at birth by measuring rectal temperature, plasma free fatty acids, plasma catecholamines, and in vitrobrown adipose tissue respiration in thyroidectomized (n6) and sham operated (n5) fetal sheep. Surgery was performed at an average of 133 days of gestation followed by cesarean delivery at 146 days. Fetuses were delivered into a constant room temperature of 25° C. Serial measurements were made in uterobefore delivery and at timed intervals after birth. Serum 3,3',5 triiodothyronine and thyroxine concentrations in the neonatal period were normal in sham operated and nondetectable in thyroidectomized fetuses. Rectal temperatures and serum free fatty acid levels were reduced in thyroidectomized newborns. Plasma epinephrine concentrations were increased and the hypothyroid neonates were acidotic when compared to control animals. In vitrobasal and norepinephrine stimulated brown adipose tissue respiration were reduced in thyroidectomized compared to control animals. These results indicate that thyroid hormone deficiency impairs non shivering thermogenesis in brown adipose tissue and leads to hypothermia despite augmented plasma epinephrine values.

We exploit the high efficiency of Langmuir−Taylor surface ionization detectors to measure by beam depletion the electronic absorption spectra of alkali atoms attached to H2 and He clusters. Li, Na, and K atoms attached to large (H2)N and (D2)N clusters (N ≈ 10³−10⁴) have been studied at various ortho/para concentrations in an attempt to correlate the properties of the matrix to the observed spectral features. The results are compared to theoretical predictions and to measurements done by means of conventional matrix isolation spectroscopy in bulk hydrogen. While some similarities are found, several discrepancies remain and are discussed. In the case of helium clusters, beam depletion spectra are very similar to, and in one case identical with, the laser-induced fluorescence spectra measured previously in our laboratory, revealing the total absence of quenching processes. In contrast to this, for alkali atoms attached to hydrogen clusters, quenching processes appear to dominate, and beam depletion spectra are totally different from their laser-induced fluorescence counterparts.

Helium cluster isolation spectroscopy is a recently developed spectroscopic method that involves the formation of a beam of large helium clusters (10⁴ atoms per cluster), the capture by the clusters of the atoms or molecules of interest in a low-pressure pick-up cell, and the spectroscopic study of the isolated species. Here we exploit the unique feature of this method of allowing the selective preparation of high-spin molecular species (e.g., triplet dimers) over their low-spin (singlet) counterparts to measure the spectra of several alkali dimers in their triplet manifold. By probing via laser-induced fluorescence their lowest triplet-to-triplet transitions, Li2, Na2, K2, and NaK are found to reside on the surface of the helium clusters. Since the spectroscopic shifts induced by the helium cluster are minimal, vibrational analysis of the electronic transitions produces transition frequencies that can be compared to previous ab initio and experimental values. Both bound−bound and bound−free transitions have been observed. Emission spectra reveal the presence of vibrational relaxation and nonadiabatic intersystem crossings of the excited dimers that result from the proximity of the helium cluster surface. Through this study we improve our understanding of triplet alkali dimer potential energy curves, we test an efficient analytical model to represent them, and we provide input information for the study of nonadditive effects present in quartet (spin-polarized) alkali trimers which can be formed using the same method.

ABSTRACT.: We investigated the effect of the transient neonatal hyperthyroid state on thermogenesis at birth by measuring rectal temperature, plasma free fatty acids, plasma catecholamines, and in vitro brown adipose tissue respiration in thyroidectomized (n = 6) and sham operated (n = 5) fetal sheep. Surgery was performed at an average of 133 days of gestation followed by cesarean delivery at 146 days. Fetuses were delivered into a constant room temperature of 25° C. Serial measurements were made in utero before delivery and at timed intervals after birth. Serum 3,3',5 triiodothyronine and thyroxine concentrations in the neonatal period were normal in sham operated and nondetectable in thyroidectomized fetuses. Rectal temperatures and serum free fatty acid levels were reduced in thyroidectomized newborns. Plasma epinephrine concentrations were increased and the hypothyroid neonates were acidotic when compared to control animals. In vitro basal and norepinephrine stimulated brown adipose tissue respiration were reduced in thyroidectomized compared to control animals. These results indicate that thyroid hormone deficiency impairs non shivering thermogenesis in brown adipose tissue and leads to hypothermia despite augmented plasma epinephrine values.

The effect of perinatal changes in thyroid function on adaptation at birth as reflected in plasma free fatty acids (FFA's), catecholamines, glycerol and biophysical parameters was assessed in thyroidectomized (TX) (n=5) and sham (n=4) operated (control) fetal sheep. Surgery was done at 133±1 days gestation followed by cesarean delivery at 146±1 days gestation into a room held at 72°F. Measurements were made in utero before delivery and at timed intervals after birth. Blood gases, rectal temperature, pulse, respiratory rate, mean blood pressure, plasma glycerol and plasma norepinephrine levels were similar. Plasma epinephrine levels were markedly elevated after delivery in the TX animals with a mean (±SEM) peak level of 1849±593 pg/ml compared to a mean peak level of 263±129 pg/ml (p<0.01) in controls. FFA's were decreased in the TX animals with lower levels measured at 15 min (237±81 (SEM) μEq/L vs 688±79, p<0.01) and 30 min (439±66 vs 1026±230, p<0.01). T3 increased after delivery in controls (260-360 ng/dl) and was measurable but did not increase after delivery in the TX animals (8-45 ng/dl). Conclusions: 1) thyroid hormones play an important role in non-shivering thermogenesis after birth as reflected in decreased plasma FFA's in the TX animals; 2) altered thyroid status results in an augmented epinephrine response to birth; 3) absence of the perinatal T3 surge does not affect body temperature when the animal is exposed to a mild cold stress.

A marked increase in plasma catecholamines (CAT) at birth has been described in animals and man. This study was conducted to determine whether the magnitude and duration of the CAT surge are similar in preterm (130 days, n=4) and term lambs (145 days, n=6), and to correlate plasma CAT and plasma END levels in the acutely exteriorized fetal lamb. CAT were measured by radioenzymatic assay and END by specific radioimmunoassay. Preterm lambs were maintained physiologically stable by administration of natural sheep surfactant intratracheally prior to the first breath. Baseline CAT & END were similar in the term and preterm lambs. Following umbilical cord cutting there was a marked increase in circulating norepinephrine (NE) and epinephrine (E) levels. Peak preterm NE (2.2±0.6 ng/ml at 1 hr) was greater than peak term NE (1.0±0.2 ng/ml, at 5 min). Peak preterm E also later and greater than peak term E (2.9±0.9 ng/ml at 1 hr vs 0.9±0.2 ng/ml at 15 min, respectively p<.01). Similarly, peak plasma END in preterm animals (2.2±0.1 ng/ml at 3 hrs) was later and greater than at term (1.1±0.2 ng/ml at 15 min). END was positively correlated with NE and E in both term and preterm animals (p<.05).Conclusions: 1) Preterm animals have a delayed, exaggerated CAT surge following delivery, 2) The peak plasma END response parallels the peak of plasma CAT. Speculation: The CAT surge at birth is an important adaptive phenomenon and may be modulated by changes in the END system.