Influence of the photon orbital angular momentum on electric dipole transitions: negative experimental evidence.

We describe an experiment of atomic spectroscopy devoted to ascertaining whether the orbital angular momentum (OAM) of photons has the same property of interacting with atoms or molecules as occurs for the spin angular momentum (SAM). In our experiment, rubidium vapors are excited by means of laser radiation with different combinations of OAM and SAM, particularly selected to inhibit or enhance the fluorescence according to the selection rules for the electric dipole transitions between the fundamental state and the first excited doublet. Our results clearly show that an electric-dipole-type transition is insensitive to the OAM value, and provide an original validation of a problem long debated in theoretical works.

Black hole physics. Black hole lightning due to particle acceleration at subhorizon scales.

Supermassive black holes with masses of millions to billions of solar masses are commonly found in the centers of galaxies. Astronomers seek to image jet formation using radio interferometry but still suffer from insufficient angular resolution. An alternative method to resolve small structures is to measure the time variability of their emission. Here we report on gamma-ray observations of the radio galaxy IC 310 obtained with the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes, revealing variability with doubling time scales faster than 4.8 min. Causality constrains the size of the emission region to be smaller than 20% of the gravitational radius of its central black hole. We suggest that the emission is associated with pulsar-like particle acceleration by the electric field across a magnetospheric gap at the base of the radio jet.

Controlled tissue expansion in the initial management of the short bowel state.

The treatment of short gut syndrome has evolved dramatically during the past decade. The combination of surgical techniques and medical management in the context of a multidisciplinary approach has improved the outcomes of these children. The authors describe in detail their technique of controlled tissue expansion of the bowel before lengthening procedures. Monitoring of the child and troubleshooting actions during the controlled tissue expansion program also are discussed.

Chylopericardium in a child with impaired venous access following small bowel transplantation.

A 10-yr-old child with impaired venous access (bilateral occlusion of internal jugular veins, subclavian veins, and inominate veins) underwent an isolated small bowel transplant. He presented with lethargy, shortness of breath 13 months into his follow-up and was diagnosed to have chylopericardium. MR venography and lymphangiography could not demonstrate the site of lymphatic leak. His chyloperciardium was treated with pericardiocentesis and MCT diet. The most likely cause for the chylopericardium was venous occlusion of the subclavian veins with backpressure resulting in a lymphatic leak. A brief review of literature along with treatment options is discussed.

Liver transplantation in children using non-heart-beating donors (NHBD).

Selected livers from controlled NHBD are accepted for OLT in adults. Recent evidence has shown good medium-term outcome. The purpose of this study was to report our experience of pediatric OLT with whole and partial grafts from NHBD, analyzing complications and outcome. Retrospective review of all the recipients who underwent primary OLT between December 2005 and December 2008, using livers from NHBD. Four children (one male child) mean age was 9.5 yr (0.2-17), mean weight was 26 kg (range 2.6-48), underwent OLT using NHBD. Mean donor age was 14.2 yr, and mean WIT (systolic BP<50 mmHg to cold perfusion) 12.2 min (range 10-15). Two children received reduced grafts and two full grafts. Mean cold ischemia time was 7.18 h (range 6-8). Liver function tests one wk and nine months post-OLT confirmed a good graft function. One child was treated for two episodes of acute rejection. Post-transplant complications included two cases of mild ischemic cholangiopathy treated conservatively. Graft and patient survival was 100% with a mean follow-up of 19 months (range 8.1-43.4). Short- to medium-term follow-up suggests that liver grafts from young NHBD with short warm and cold ischemia times can be safely utilized in pediatric transplantation.

Full control of sodium vapor density in siloxane-coated cells using blue LED light-induced atomic desorption.

We propose and experimentally implement a method, based on light-induced atomic desorption, for controlled generation of large sodium densities in siloxane-coated cells, kept at room temperature. An array of blue LEDs is used to desorb sodium atoms from the cell walls. The required atomic vapor density is achieved and stabilized by controlling the LED power through the feedback given by the sodium fluorescence. We show that sodium densities corresponding to about 400 K can be obtained and kept stable for a long time with less than 6 mW of LED light power. Moreover, this technique allows for precise vapor density modulation with a frequency of tenths of hertz, which is not possible using traditional heating methods.

Diode laser spectroscopy of ammonia and ethylene overtones.

Some overtone absorption lines of ammonia and ethylene have been examined by using a tunable diode laser (TDL) spectrometer in the region around 12,650 and 11,800 cm(-1), respectively. The spectrometer sources are commercially available double heterostructure InGaAlAs and AlGaAs TDLs operating in the "free-running" mode. The high resolving power ( approximately 10(7) ) of the spectrometer permitted the detection and the study of the line positions of such molecules with a precision better than 0.01 cm(-1). In order to maximize the signal to noise ratio and to extract the necessary informations either on the line width and on the line position for the detected molecular resonances, the wavelength modulation spectroscopy (WMS) along with the second harmonic detection techniques have been applied. For this purpose, the fitting procedure took into account the instrumental effects and the amplitude modulation (AM) always associated with the frequency modulation (FM) of these type of sources. This technique permitted also the measurement of the collisional-broadening and -shifting coefficients by different buffer gases at room temperature.

Cold rubidium molecules formed in a magneto-optical trap

We report the first observation of translationally cold ( approximately 90 &mgr;K) Rb2 molecules. They are produced in a magneto-optical trap in their triplet ground state. The detection is performed by selective mass spectroscopy after two-photon ionization into Rb+2, resonantly enhanced through the intermediate a (3)Sigma(+)(u)-->2 (3)Pi(g) molecular band. The two rubidium isotopes present very different types of behavior that are interpreted in terms of their respective collisional properties.

Diode laser spectroscopy of methane overtone transitions.

With the aid of commercial room-temperature AlGaAs diode lasers, frequency modulation absorption spectroscopy was performed on the 7900 A and 8600 A rovibrational combination overtone bands of methane. Three weak transitions are reported in the range around 8610 A that, to our knowledge, have not yet been observed and measured. Self-broadening and pressure-broadening coefficients of one ofthese new absorption features (at 8608.93 A) were derived from CH(4) and for CH(4) immersed in N(2) and He buffer gases. An evaluation of the methane detection sensitivity is given for favorable laboratory conditions as well as for an open-path situation.