Strong neutrino cooling by cycles of electron capture and ß- decay in neutron star crusts.

The temperature in the crust of an accreting neutron star, which comprises its outermost kilometre, is set by heating from nuclear reactions at large densities, neutrino cooling and heat transport from the interior. The heated crust has been thought to affect observable phenomena at shallower depths, such as thermonuclear bursts in the accreted envelope. Here we report that cycles of electron capture and its inverse, ß(-) decay, involving neutron-rich nuclei at a typical depth of about 150 metres, cool the outer neutron star crust by emitting neutrinos while also thermally decoupling the surface layers from the deeper crust. This 'Urca' mechanism has been studied in the context of white dwarfs and type Ia supernovae, but hitherto was not considered in neutron stars, because previous models computed the crust reactions using a zero-temperature approximation and assumed that only a single nuclear species was present at any given depth. The thermal decoupling means that X-ray bursts and other surface phenomena are largely independent of the strength of deep crustal heating. The unexpectedly short recurrence times, of the order of years, observed for very energetic thermonuclear superbursts are therefore not an indicator of a hot crust, but may point instead to an unknown local heating mechanism near the neutron star surface.

Neutron single particle structure in 131Sn and direct neutron capture cross sections.

Recent calculations suggest that the rate of neutron capture by (130)Sn has a significant impact on late-time nucleosynthesis in the r process. Direct capture into low-lying bound states is expected to be significant in neutron capture near the N=82 closed shell, so r-process reaction rates may be strongly impacted by the properties of neutron single particle states in this region. In order to investigate these properties, the (d,p) reaction has been studied in inverse kinematics using a 630 MeV beam of (130)Sn (4.8 MeV/u) and a (CD(2))(n) target. An array of Si strip detectors, including the Silicon Detector Array and an early implementation of the Oak Ridge Rutgers University Barrel Array, was used to detect reaction products. Results for the (130)Sn(d, p)(131)Sn reaction are found to be very similar to those from the previously reported (132)Sn(d, p)(133)Sn reaction. Direct-semidirect (n,γ) cross section calculations, based for the first time on experimental data, are presented. The uncertainties in these cross sections are thus reduced by orders of magnitude from previous estimates.

Time-of-flight mass measurements for nuclear processes in neutron star crusts.

We present results from time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory that are relevant for neutron star crust models. The masses of 16 neutron-rich nuclei in the scandium-nickel range were determined simultaneously, with the masses of (61)V, (63)Cr, (66)Mn, and (74)Ni measured for the first time with mass excesses of -30.510(890) MeV, -35.280(650) MeV, -36.900(790) MeV, and -49.210(990) MeV, respectively. With these results the locations of the dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit super bursts are now experimentally constrained. We find the experimental Q value for the (66)Fe→(66)Mn electron capture to be 2.1 MeV (2.6σ) smaller than predicted, resulting in the transition occurring significantly closer to the neutron star surface.

Effects of inelastic neutrino-nucleus scattering on supernova dynamics and radiated neutrino spectra.

Based on the shell model for Gamow-Teller and the random phase approximation for forbidden transitions, we calculate cross sections for inelastic neutrino-nucleus scattering (INNS) under supernova (SN) conditions, assuming a matter composition given by nuclear statistical equilibrium. The cross sections are incorporated into state-of-the-art stellar core-collapse simulations with detailed energy-dependent neutrino transport. While no significant effect on the SN dynamics is observed, INNS increases the neutrino opacities noticeably and strongly reduces the high-energy tail of the neutrino spectrum emitted in the neutrino burst at shock breakout. Relatedly the expected event rates for the observation of such neutrinos by earthbound detectors are reduced by up to about 60%.

Neutrino-induced nucleosynthesis of A>64 nuclei: the nu p process.

We present a new nucleosynthesis process that we denote as the nu p process, which occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers A>64, , making this process a possible candidate to explain the origin of the solar abundances of (92,94)Mo and (96,98)Ru. This process also offers a natural explanation for the large abundance of Sr seen in a hyper-metal-poor star.

Consequences of nuclear electron capture in core collapse supernovae.

The most important weak nuclear interaction to the dynamics of stellar core collapse is electron capture, primarily on nuclei with masses larger than 60. In prior simulations of core collapse, electron capture on these nuclei has been treated in a highly parametrized fashion, if not ignored. With realistic treatment of electron capture on heavy nuclei come significant changes in the hydrodynamics of core collapse and bounce. We discuss these as well as the ramifications for the postbounce evolution in core collapse supernovae.

Electron capture rates on nuclei and implications for stellar core collapse.

Supernova simulations to date have assumed that during core collapse electron captures occur dominantly on free protons, while captures on heavy nuclei are Pauli blocked and are ignored. We have calculated rates for electron capture on nuclei with mass numbers A=65-112 for the temperatures and densities appropriate for core collapse. We find that these rates are large enough so that, in contrast to previous assumptions, electron capture on nuclei dominates over capture on free protons. This leads to significant changes in core collapse simulations.

Strength of the 18F(p,alpha)15O resonance at Ec.m. = 330 keV.

Production of the radioisotope 18F in novae is severely constrained by the rate of the 18F(p,alpha)15O reaction. A resonance at E(c.m.)=330 keV may strongly enhance the 18F(p,alpha)15O reaction rate, but its strength has been very uncertain. We have determined the strength of this important resonance by measuring the 18F(p,alpha)15O cross section on and off resonance using a radioactive 18F beam at the ORNL Holifield Radioactive Ion Beam Facility. We find that its resonance strength is 1.48+/-0.46 eV, and that it dominates the 18F(p,alpha)15O reaction rate over a significant range of temperatures characteristic of ONeMg novae.

Simulation of the spherically symmetric stellar core collapse, bounce, and postbounce evolution of a star of 13 solar masses with boltzmann neutrino transport, and its implications for the supernova mechanism.

With exact three-flavor Boltzmann neutrino transport, we simulate the stellar core collapse, bounce, and postbounce evolution of a 13M star in spherical symmetry, the Newtonian limit, without invoking convection. In the absence of convection, prior spherically symmetric models, which implemented approximations to Boltzmann transport, failed to produce explosions. We consider exact transport to determine if these failures were due to the transport approximations made and to answer remaining fundamental questions in supernova theory. The model presented here is the first in a sequence of models beginning with different progenitors. In this model, a supernova explosion is not obtained.

Management of AIDS-related pneumothorax.

BACKGROUND: Pneumothorax (PTX) occurs in 5% of patients with acquired immunodeficiency syndrome (AIDS) infected with Pneumocystis carinii pneumonia, and up to 50% of those will die during hospitalization. The treatment strategies for managing AIDS-related PTXs are often complex and ineffective at treating the PTX, and they can prolong hospitalization. METHODS: We reviewed our experience with 36 male patients with AIDS treated for 44 PTXs over a 2.5-year period to determine if a particular therapeutic approach could allow for an earlier recovery and effective treatment of the PTX. All patients had current or prior history of Pneumocystis carinii pneumonia infection, and the CD4+ T-lymphocyte counts were less than 100/microL in 100%. RESULTS: Twenty-seven patients with 31 PTXs were discharged from the hospital. Of these 31 PTXs, 21 had resolved at the time of the patient's discharge from the hospital, and the other 10 PTXs were converted from Pleurevac (Deknatel, Inc, Fall River, MA) drainage to a Heimlich valve for persistent bronchopleural fistula after more than 15 days of conventional treatment. The PTXs were effectively managed by tube thoracostomy alone in 18/44 PTXs (41%), tube thoracostomy plus sclerosing therapy in 2/8 PTXs (25%), and thoracotomy with blebectomy and pleurodesis in 1/3 PTXs (33%). Nine of 11 of the procedure-related PTXs responded to tube thoracostomy alone; the other 2 PTXs were converted from Pleurevac drainage to a Heimlich valve and allowed for patient discharge from the hospital in less than 10 days. Nine patients with 13 PTXs died during hospitalization. Four of these 9 patients (44%) had bilateral PTXs, and 8/9 (89%) were being treated by tube thoracostomy with Pleurevac suction for persistent bronchopleural fistula in the intensive care unit at the time of death. The 8 patients treated for 10 PTXs with a Heimlich valve had effective management of the PTX, had no morbidity associated with the Heimlich valve and no in-hospital mortality, and were discharged from the hospital to home or a hospice setting. CONCLUSIONS: The management of AIDS-related PTXs is complex and often associated with a destructive pulmonary process and other systemic disease conditions related to AIDS that result in ineffective resolution of the PTX, a prolonged hospitalization, and a high mortality. In our experience, there is a lesser role for managing the PTXs with sclerosing therapy or thoracotomy. Patients with advanced AIDS complicated by PTXs with bronchopleural fistula can be converted from a Pleurevac drainage system to a Heimlich valve with no apparent morbidity or mortality, and managed as an outpatient, thereby potentially shortening hospitalization and facilitating an earlier discharge from an acute care setting.

Repair of tracheogastric fistula after cervical exenteration.

A case of tracheogastric fistula after laryngopharyngoesophagectomy for cervical esophageal cancer is described. The surgical management of the tracheogastric fistula is detailed and accompanied by a pertinent review of the literature. The one-stage repair in this report can provide an effective palliation or definitive treatment for this debilitating and unusual complication.

Role of open lung biopsy in diagnosing pulmonary complications of AIDS.

Over a 4-year period, 25 patients with pulmonary complications of acquired immunodeficiency syndrome underwent open lung biopsy for diagnosis. Results of the biopsy led to a change in therapy in 15, and of this group, 8 patients improved clinically and were discharged. We believe that a select group of acquired immunodeficiency syndrome patients with pulmonary disease will benefit from open lung biopsy. Our indications for open lung biopsy are (1) a nondiagnostic bronchoscopy, (2) failed medical therapy after a diagnostic bronchoscopy, (3) failed empiric medical therapy after a nondiagnostic bronchoscopy or after a second nondiagnostic bronchoscopy, and (4) when any of the forementioned are accompanied with a worsening chest roentgenogram. Patients with acquired immunodeficiency syndrome who have a deteriorating respiratory status or require mechanical ventilation should not undergo open lung biopsy.

Solitary pulmonary nodule. What should be included in the workup?

Rapid, thorough diagnostic workup of patients with solitary pulmonary nodules is imperative. The optimal management for these patients is exploratory thoracotomy for biopsy and appropriate resection. Preliminary fiberoptic bronchoscopy and transthoracic needle aspiration do not rule out malignant tumors if negative and add only unnecessary complexity, delay, expense, and risk to the patient's management.

Malignant pleural effusion treated by tetracycline sclerotherapy. A comparison of single vs repeated instillation.

Fifty patients with malignant pleural effusion were randomized to receive one or two doses of tetracycline sclerotherapy. We found that a single sclerotherapy treatment with tetracycline at a dose of 20 mg/kg was as effective as two sclerotherapy treatments and provided symptomatic relief in 46 of the 50 patients.

Reexpansion pulmonary edema.

Unilateral reexpansion pulmonary edema (RPE) is a rare complication of the treatment of lung collapse secondary to pneumothorax, pleural effusion, or atelectasis. Although RPE generally is believed to occur only when a chronically collapsed lung is rapidly reexpanded by evacuation of large amounts of air or fluid, in this review 15 of 47 cases of RPE available for assessment occurred when the pulmonary collapse was of short duration or when the lung was reexpanded without suction. The pathogenesis of RPE is unknown and is probably multifactorial. Implicated in the etiological process of RPE are chronicity of collapse, technique of reexpansion, increased pulmonary vascular permeability, airway obstruction, loss of surfactant, and pulmonary artery pressure changes. Since the outcome of RPE was fatal in 11 of 53 cases reviewed (20%), physicians treating lung collapse must be aware of the possible causes and endeavor to prevent the occurrence of this complication.

Active specific immunotherapy with an autologous tumor cell vaccine in patients with resected non-small cell lung cancer.

Eighteen postoperative patients with non-small cell lung cancer were actively immunized with a vaccine that included autologous cryopreserved irradiated tumor cells admixed with bacillus Calmette-Guerin. Patients received three weekly intradermal immunizations beginning 1-3 months after surgery (15 patients) or after completion of postoperative radiotherapy (3 patients). There was marked heterogeneity in the relative proportion of tumor cells versus host infiltrating cells within individual vaccines (range of percent tumor cells 7-75%). Five patients exhibited positive delayed cutaneous skin test reactivity (DCR) to autologous irradiated tumor cells prior to immunization, whereas 8 of 13 converted from skin test negative to positive. There were no correlations between DCR reactivity and in vitro lymphoproliferative responses to autologous tumor cells or to clinical outcomes, i.e., freedom from relapse. Possible explanations for the heterogeneity of the lung cancer vaccine and approaches for improving its immunogenicity are discussed.

Toluidine blue staining of the esophagus. A useful adjunct in the panendoscopic evaluation of patients with squamous cell carcinoma of the head and neck.

Carcinoma of the esophagus has a much higher incidence among patients with squamous cell carcinoma of the head and neck than among the population at large. Esophageal cancer has a low cure rate, and the possibility for increased survival can be enhanced primarily through early detection. Toluidine blue has proved to be effective in demonstrating early malignant lesions that would not be detectable otherwise. A technique has been developed for toluidine blue staining of the esophagus during panendoscopy. In this initial series of 18 patients with squamous cell carcinoma of the upper aerodigestive tract, we found a 17% incidence of early carcinoma of the esophagus. We believe this technique to be an important adjunct to the evaluation of these patients at high risk for esophageal carcinoma.