Convective-Dynamical Instability in Radiation-Supported Accretion Disks

We study radiation-hydrodynamical normal modes of radiation-supported accretion disks in the WKB limit. It has long been known that in the large optical depth limit the standard equilibrium is unstable to convection. We study how the growth rate depends on location within the disk, optical depth, disk rotation, and the way in which the local dissipation rate depends on density and pressure. The greatest growth rates are found near the disk surface. Rotation stabilizes vertical wavevectors, so that growing modes tend to have nearly-horizontal wavevectors. Over the likely range of optical depths, the linear growth rate for convective instability has only a weak dependence on disk opacity. Perturbations to the dissipation have little effect on convective mode growth rates, but can cause growth of radiation sound waves.Comment: 20 pages, AAS LaTe

The Inverse Compton Thermostat in Hot Plasmas Near Accreting Black Holes

The hard X-ray spectra of accreting black holes systems are generally well-fit by thermal Comptonization models with temperatures $\sim 100$ keV. We demonstrate why, over many orders of magnitude in heating rate and seed photon supply, hot plasmas radiate primarily by inverse Compton scattering, and find equilibrium temperatures within a factor of a few of 100 keV. We also determine quantitatively the (wide) bounds on heating rate and seed photon supply for which this statement is true. Plasmas in thermal balance in this regime obey two simple scaling laws, one relating the product of temperature and optical depth to the ratio of seed photon luminosity to plasma heating rate $l_s/l_h$, the other relating the spectral index of the output power-law to $l_s/l_h$. Because $\alpha$ is almost independent of everything but $l_s/l_h$, the observed power law index may be used to estimate $l_s/l_h$. In both AGN and stellar black holes, the mean value estimated this way is $l_s/l_h \sim 0.1$. As a corollary, $\Theta \tau_T$ must be $\simeq 0.1$ -- 0.2, depending on plasma geometry.Comment: 26 pages, AASLaTeX, to appear in July 10 Ap.J. Figures available in uuencoded form at ftp://jhufos.pha.jhu.edu/pub/put/jhk/comptfigs.u

The effect of radiation pressure on virial black hole mass estimates and the case of Narrow Line Seyfert 1 galaxies

We consider the effect of radiation pressure from ionizing photons on black hole (BH) mass estimates based on the application of the virial theorem to broad emission lines in AGN spectra. BH masses based only on the virial product V^2R and neglecting the effect of radiation pressure can be severely underestimated especially in objects close to the Eddington limit. We provide an empirical calibration of the correction for radiation pressure and we show that it is consistent with a simple physical model in which BLR clouds are optically thick to ionizing radiation and have average column densities of NH~10^23 cm^-2. This value is remarkably similar to what is required in standard BLR photoionization models to explain observed spectra. With the inclusion of radiation pressure the discrepancy between virial BH masses based on single epoch spectra and on reverberation mapping data drops from 0.4 to 0.2 dex rms. The use of single epoch observations as surrogates of reverberation mapping campaigns can thus provide more accurate BH masses than previously thought. Finally, we show that Narrow Line Seyfert 1 (NLS1) galaxies have apparently low BH masses because they are radiating close to their Eddington limit. After the radiation pressure correction, NLS1 galaxies have BH masses similar to other broad line AGNs and follow the same MBH-sigma/L relations as other active and normal galaxies. Radiation forces arising from ionizing photon momentum deposition constitute an important physical effect which must be taken into account when computing virial BH masses.Comment: To appear in the Astrophysical Journal, May 1 issu

A flexible SNP genotyping system to study allelic determinants of brain function

We developed a system for SNP-genotyping consisting of two ‘‘microchips’’, one investigating 40 SNPs in genes involved in the hepatic metabolism of antidepressant drugs, the other 100 SNPs in genes involved in brain response to antidepressants. Candidate genes were chosen by literature screening. SNPs were selected on HapMap data, using the pairwise algorithm combinedwith the ‘‘BestN’’ method; a few SNPs, reported as associated with treatment outcome, were added to the set. The main advantages of our experimental design are: a) simultaneous analysis of several genes (22) involved in distinct aspects of antidepressant response; b) a comprehensive search for common variability in candidate genes by HapMap ‘‘tag-SNPs’’. DNA samples are genotyped by ‘‘padlock probes’’, which specifically recognise the two variants of each SNP; padlock probes are amplified with universal primers, and contain unique tags for hybridisation to known positions on ad hoc designed micro-arrays, where the two alleles are distinguished by distinct fluorophores. Since reactions carried out on multiplex and signal intensities on microarrays are homogeneous, as they are not affected bySNPflanking sequences, tens of SNPsfrom tens of individuals can be analysed simultaneously on a single slide, with high accuracy and reproducibility. Considering that 100 SNPs from manygenes related to neural transmission, plasticity and neurogenesis are included in the secondmicrochip and that each of them can easily be substituted withothers if needed, our system represents a powerful tool for investigating genetic influence on normal and pathological brain function

Secretory phospholipase A2 pathway during pediatric acute respiratory distress syndrome: A preliminary study

Objective: To verify if secretory phospholipase A2 (sPLA2) is increased in pediatric acute respiratory distress syndrome (ARDS) triggered or not by respiratory syncytial virus infection and to clarify how the enzyme may influence the disease severity and the degree of ventilatory support. Design: Prospective pilot study. Setting: Two academic pediatric intensive care units. Patients: All infants <6 months old hospitalized for severe respiratory syncytial virus bronchiolitis, who developed ARDS (respiratory syncytial virus-ARDS group); all infants <6 months old diagnosed with ARDS secondary to other causes (ARDS group); and infants <6 months old who needed ventilation for reasons other than any lung disease (control group). Interventions: None. Measurements and Main Results: We enrolled six respiratory syncytial virus -ARDS babies, five ARDS babies, and six control infants. The sPLA2 activity and tumor necrosis factor (TNF)-\u3b1 were significantly higher in the bronchoalveolar lavage of ARDS infants. Worst oxygenation, ventilation, and longer pediatric intensive care unit stay and ventilation time were present in ARDS babies. No differences were found in Clara cell secretory protein and in serum cytokines levels. Because there is no correlation between bronchoalveolar lavage protein content (a marker of permeability) and sPLA2, the enzyme seems mainly produced in the alveoli. TNF-\u3b1, the main inductor of sPLA2 expression, significantly correlates with the enzyme level in the bronchoalveolar lavage. Significant positive correlations exist between sPLA2, TNF-\u3b1 and oxygen need, mean airway pressure, ventilatory index, and the Murray's lung injury score. Negative correlations were also found between sPLA2, TNF-\u3b1, and Pao2/Fio2 ratio. Conclusions: The sPLA2 and TNF-\u3b1 are increased in ARDS and seem correlated with clinical severity, higher oxygen requirement, and more aggressive ventilation. This correlation confirms findings from adult experience and should guide further investigations on pediatric ARDS pathophysiology

The modern perspective for long-acting injectables antipsychotics in the patient-centered care of schizophrenia

Schizophrenia is a chronic syndrome involving different clinical dimensions, and causes significant disability with a negative impact on the quality of life of patients and their caregivers. Current guidelines for the treatment of schizophrenia focus on maximizing a patient's adaptive functioning and quality of life in a recovery-oriented approach that encourages active collaboration among patients, caregivers, and mental health professionals to design and manage a customized and comprehensive care plan. In the present study, a panel of experts (psychiatrists, psychologists, nurse, and social worker) gathered to review and explore the need for contemporary use of second-generation antipsychotic long-acting injectables (SGA LAIs) in "recovery-oriented" and "patient-centered" care of schizophrenia. Starting from the available data and from sharing personal attitudes and experiences, the panel selected three clinical dimensions considered useful in characterizing each patient: phase of disease, adherence to treatment, and level of functioning. For each clinical dimension, perspectives of patients and caregivers with regard to needs, expectations, and personal experiences were reviewed and the role of SGA LAIs in achieving shared goals examined. The experts concluded that from today's modern perspectives, SGA-LAIs may play an important role in breaking the spiral of desocialization and functional decline in schizophrenia, thus favoring the recovery process