20 research outputs found
The stochastic gravitational-wave background in the absence of horizons
Gravitational-wave astronomy has the potential to explore one of the deepest and most puzzling aspects of Einstein's theory: the existence of black holes. A plethora of ultracompact, horizonless objects have been proposed to arise in models inspired by quantum gravity. These objects may solve Hawking's information-loss paradox and the singularity problem associated with black holes, while mimicking almost all of their classical properties. They are, however, generically unstable on relatively short timescales. Here, we show that this 'ergoregion instability' leads to a strong stochastic background of gravitational waves, at a level detectable by current and future gravitational-wave detectors. The absence of such background in the first observation run of Advanced LIGO already imposes the most stringent limits to date on black-hole alternatives, showing that certain models of 'quantum-dressed' stellar black holes can be at most a small percentage of the total population. The future LISA mission will allow for similar constraints on supermassive black-hole mimickers
Superradiant instability of black resonators and geons
Abstract: Black resonators and geons in global AdS are rapidly rotating, low-energy solutions with a helical Killing field. We study the linear mode stability of equal angular momenta, five-dimensional black resonators and geons under scalar, electromagnetic, and gravitational perturbations. We find that black resonators are unstable to the superradiant instability, in agreement with previously known results. Perhaps surprisingly, many geons appear linearly stable, despite having an ergoregion. This apparent stability implies that geons are important long-lived, low-energy states in the dual gauge theory. However, we do find that geons are unstable within a certain range of parameter space. We comment on the nature of this instability and to its possible endpoints. We also report on new non-spinning oscillating geons, which we construct within a cohomogeneity two ansatz. Given the existing arguments that suggest our linear stability results may be extended nonlinearly, our findings indicate that most geons are generic and long-lived solutions
Analytical and clinical sensitivity of the Procleix Ultrio HIV-1/HCV/HBV assay in samples with a low viral load
Background and Objectives The Procleix Ultrio human immunodeficiency
virus type 1 (HIV-1)/hepatitis C virus (HCV)/hepatitis B virus (HBV)
(Ultrio) assay simultaneously detects HIV-1 RNA, HCV RNA and HBV DNA in
individual blood donations. The main objective of the study was to
assess the analytical and clinical sensitivity of the multiplex and
discriminatory probe assays in samples with a low viral load.
Material and Methods The VQC HIV RNA genotype B, HCV RNA genotype 1 and
HBV DNA genotype A standard dilutions were tested in 26 repeats. The
probability of detection by Ultrio was compared with previously obtained
data of the Procleix Duplex HIV-1/HCV assay on the same reference
panels. A selection of 121 anti-HIV-1, 138 anti-HCV and 190 HBsAg
positive samples from patients receiving antiviral therapy were tested.
The majority of patient samples had a viral load below the detection
limit of the diagnostic nucleic acid test assays, which made them
suitable to evaluate the performance of the multiplex and discriminatory
assays on yield cases with a similar low viral load.
Results The 95% and 50% detection end-points of the Ultrio assay along
with the corresponding 95% confidence intervals are 53.7 (32.9-117.2)
and 8.6 (6.2-12.1) geq/ml for HIV-1 RNA, 30.3 (19.0-62.4) and 5.2
(3.7-7.2) geq/ml for HCV RNA and 393.7 (147.9-6978) and 54.5
(22.4-143.8) geq/ml for HBV DNA. The analytical sensitivity of Ultrio
expressed as a potency factor relative to previously obtained Duplex
results on the same HIV-1 RNA and HCV-RNA standard dilutions was 1.09
(0.20-6.10) and 1.11 (0.21-5.89), respectively. The assay detected all
22 HIV-1 infected patients with viral load > 50 copies/ml, and 41 of 99
patients (41%) with viral load < 50 copies/ml, of which 23 (56%) were
detected by the discriminatory assay. All 47 patients with HCV RNA load
> 521 IU/ml and 10/91 polymerase chain reaction-negative patients with
viral load < 50 IU/ml tested positive in Ultrio assay of which five were
missed in the discriminatory test. The assay detected 53/55 HBV infected
patients (96%) with viral load > 250 copies/ml and 108/135 patients
(80%) with viral load < 250 copies/ml of which 17 (16%) were missed by
the discriminatory test.
Conclusions The new Procleix Ultrio assay is as sensitive as the
Procleix Duplex assay for HIV-1 and HCV detection meeting the
requirements of universal guidelines. The ability of the assay to detect
HBV DNA in low viral load samples could be useful for screening blood.
Inevitable negative results of discriminatory probe assays caused by
stochastic sample variation will reduce the chance of recognizing low
viraemic blood donors detected by individual donation nucleic acid test
Searching for West Nile virus (WNV) in Greece
West Nile virus (WNV), a mosquito-borne flavivirus, has increasingly
become a concern in both America and Europe due to its complex and
unpredictable lifecycle. Transfusion-associated transmission of the WNV
has been well documented during the last few years. This study aimed to
detect the presence of WNV in: (i) cerebrospinal fluid (CSF) specimens
derived from aseptic meningitis cases in Greece and (ii) Greek blood
donations. A total of 115 CSF specimens from patients suffering from
aseptic meningitis and 9590 blood samples were collected from seven
Greek hospitals during the periods June to October 2006 and 2007 and
tested for investigational purposes. Both blood and CSF samples were
tested for the presence of WNV RNA by using the PROCLEIX WNV assay. None
of 115 CSF and 9590 blood donor samples was found positive according to
our testing algorithms. Despite the presence of WNV in Balkan countries,
WNV has not reached significant levels in Greece