879 research outputs found
Submm-bright QSOs at z~2: signposts of co-evolution at high z
We have assembled a sample of 5 X-ray and submm-luminous z~2 QSOs which are
therefore both growing their central black holes through accretion and forming
stars copiously at a critical epoch. Hence, they are good laboratories to
investigate the co-evolution of star formation and AGN. We have performed a
preliminary analysis of the AGN and SF contributions to their UV-to-FIR SEDs,
fitting them with simple direct (disk), reprocessed (torus) and star formation
components. All three are required by the data and hence we confirm that these
objects are undergoing strong star formation in their host galaxies at rates
500-2000 Msun/y. Estimates of their covering factors are between about 30 and
90%. In the future, we will assess the dependence of these results on the
particular models used for the components and relate their observed properties
to the intrinsice of the central engine and the SF material, as well as their
relevance for AGN-galaxy coevolution.Comment: 6 pages, 2 figures, contributed talk to "Nuclei of Seyfert galaxies
and QSOs - Central engine & conditions of star formation" November 6-8, 2012.
MPIfR, Bonn, Germany. Po
Submm-bright X-ray absorbed QSOs at z~2: insights into the co-evolution of AGN and star-formation
We have assembled a sample of 5 X-ray-absorbed and submm-luminous type 1 QSOs
at which are simultaneously growing their central black holes
through accretion and forming stars copiously. We present here the analysis of
their rest-frame UV to submm Spectral Energy Distributions (SEDs), including
new Herschel data. Both AGN (direct and reprocessed) and Star Formation (SF)
emission are needed to model their SEDs. From the SEDs and their UV-optical
spectra we have estimated the masses of their black holes , their intrinsic AGN bolometric luminosities
, Eddington ratios
and bolometric corrections
. These values are common among optically and
X-ray-selected type 1 QSOs (except for RX~J1249), except for the bolometric
corrections, which are higher. These objects show very high far-infrared
luminosities (2 - 8) and Star Formation
Rates SFRy. From their and the shape of their
FIR-submm emission we have estimated star-forming dust masses of . We have found evidence of a tentative correlation between the
gas column densities of the ionized absorbers detected in X-ray (N)
and . Our computed black hole masses are amongst the most massive known.Comment: Accepted for publication in MNRAS, December 22, 2014, 17 pages, 5
figure
Covariance forecasting in equity markets
We compare the performance of popular covariance forecasting models in the context of a portfolio of major European equity indices. We find that models based on high-frequency data offer a clear advantage in terms of statistical accuracy. They also yield more theoretically consistent predictions from an empirical asset pricing perspective, and, lead to superior out-of-sample portfolio performance. Overall, a parsimonious Vector Heterogeneous Autoregressive (VHAR) model that involves lagged daily, weekly and monthly realised covariances achieves the best performance out of the competing models. A promising new simple hybrid covariance estimator is developed that exploits option-implied information and high-frequency data while adjusting for the volatility riskpremium. Relative model performance does not change during the global financial crisis, or, if a different forecast horizon, or, intraday sampling frequency is employed. Finally, our evidence remains robust when we consider an alternative sample of U.S. stocks
Herschel/HerMES: the X-ray–infrared correlation for star-forming galaxies at z ~ 1
For the first time, we investigate the X-ray/infrared (IR) correlation for star-forming galaxies (SFGs) at z ~ 1, using SPIRE submm data from the recently launched Herschel Space Observatory and deep X-ray data from the 2-Ms Chandra Deep Field-North survey. We examine the X-ray/IR correlation in the soft X-ray (SX; 0.5–2 keV) and hard X-ray (HX; 2–10 keV) bands by comparing our z ~ 1 SPIRE-detected SFGs to equivalently IR-luminous (L_(IR) > 10^(10) L_⊙) samples in the local/low-redshift Universe. Our results suggest that the X-ray/IR properties of the SPIRE SFGs are on average similar to those of their local counterparts, as we find no evidence for evolution in the L_(SX)/L_(IR) and L_(HX)/L_(IR) ratios with redshift. We note, however, that at all redshifts, both L_(SX)/L_(IR) and L_(HX)/L_(IR) are strongly dependent on IR luminosity, with luminous and ultraluminous IR galaxies (LIRGs and ULIRGs; L_(IR) > 10^(11) L_⊙) having up to an order of magnitude lower values than normal IR galaxies (L_(IR) < 10^(11) L_⊙). We derive a L_(SX)–L_(IR) relation and confirm the applicability of an existing L_(HX)–L_(IR) relation for both local and distant LIRGs and ULIRGs, consistent with a scenario where X-ray luminosity is correlated with the star formation rate
Local Guarantees in Graph Cuts and Clustering
Correlation Clustering is an elegant model that captures fundamental graph
cut problems such as Min Cut, Multiway Cut, and Multicut, extensively
studied in combinatorial optimization. Here, we are given a graph with edges
labeled or and the goal is to produce a clustering that agrees with the
labels as much as possible: edges within clusters and edges across
clusters. The classical approach towards Correlation Clustering (and other
graph cut problems) is to optimize a global objective. We depart from this and
study local objectives: minimizing the maximum number of disagreements for
edges incident on a single node, and the analogous max min agreements
objective. This naturally gives rise to a family of basic min-max graph cut
problems. A prototypical representative is Min Max Cut: find an cut
minimizing the largest number of cut edges incident on any node. We present the
following results: an -approximation for the problem of
minimizing the maximum total weight of disagreement edges incident on any node
(thus providing the first known approximation for the above family of min-max
graph cut problems), a remarkably simple -approximation for minimizing
local disagreements in complete graphs (improving upon the previous best known
approximation of ), and a -approximation for
maximizing the minimum total weight of agreement edges incident on any node,
hence improving upon the -approximation that follows from
the study of approximate pure Nash equilibria in cut and party affiliation
games
Central Serous Chorioretinopathy with Subretinal Deposition of Fibrin-Like Material and Its Prompt Response to Ranibizumab Injections
Purpose: Central serous chorioretinopathy (CSCR) manifests as neurosensory detachment of the macula and can be attributed to focal or multifocal leakage in the retinal pigment epithelium (RPE). Fibrin accumulation in the subretinal space is an unusual and heretofore unreported visually damaging manifestation of severe CSCR. Methods: The patient was followed up with the use of biomicroscopy, fluorescein angiography, and optical coherence tomography (OCT). Results: A 32-year-old woman was referred to our department complaining of metamorphopsia and decreased visual acuity in the right eye. Best-corrected visual acuity (BCVA) was 20/40 in the right eye and 20/20 in the left eye. Biomicroscopy revealed an irregularly shaped foveal elevation and wrinkling in the right eye. OCT showed a steep neurosensory retina elevation with a highly reflective material accumulation in the subretinal space, presumably fibrin. Our diagnosis was CSCR complicated by subretinal fibrin accumulation. Since most of these cases resolve spontaneously, the patient was kept under observation; 1 month later, the fibrin accumulation had expanded subfoveally (BCVA 20/200). The patient was offered 3 intravitreal ranibizumab injections. After the initial injection, BCVA improved to 20/50 and, after the 3 injections, to 20/30. Two months later (BCVA 20/30), fresh leakage was observed at the margin of the original lesion, and an additional intravitreal ranibizumab injection was performed. After another 2 months, BCVA stabilized at 20/25 and remained stable throughout the 12 months after the initial injection. Conclusions: Prompt recognition of CSCR complicated by subretinal fibrin and immediate intervention may result in recovery from this potentially devastating complication. Ranibizumab may be an alternative treatment option in the management of refractory CSCR complicated by subretinal fibrin accumulation
Peripapillary Neovascular Membrane in a Young Pregnant Woman and Prompt Response to Ranibizumab Injections following Uneventful Delivery
Purpose: Occurrence of choroidal neovascularization (CNV) during pregnancy has been reported as a complication of presumed ocular histoplasmosis syndrome or punctuate inner chorioretinopathy. To our knowledge, idiopathic CNV (ICNV) during pregnancy has only been reported once in the relevant literature. Bevacizumab has been used for the treatment of ICNV in small case series. However, there is limited experience regarding the use of ranibizumab for the management of ICNV. Case Report: A 31-year-old woman in the eighth month of her second pregnancy was diagnosed with mild macular and papillary edema. She was followed up using biomicroscopy, fluorescein angiography (FA), and optical coherence tomography (OCT). After 3 months, visual acuity further deteriorated and funduscopy, FA and OCT findings revealed a juxtapapillary choroidal neovascular membrane (CNVM). After two ranibizumab injections, best-corrected visual acuity increased significantly, physiological macular anatomy was restored and no subretinal fluid was observed. Discussion: In this case report, we present a young pregnant patient with peripapillary ICNV and neurosensory detachment involving the macula, and treatment of the eye with intravitreal ranibizumab following uneventful delivery. Increased angiogenic factor levels associated with pregnancy may contribute to the onset of CNV although this relationship has to be investigated experimentally. The rapid response to ranibizumab suggests that this anti-VEGF agent may be an alternative treatment option in the management of peripapillary ICNV
HERMES: Scalable, Secure, and Privacy-Enhancing Vehicle Access System
We propose HERMES, a scalable, secure, and privacy-enhancing system for users
to share and access vehicles. HERMES securely outsources operations of vehicle
access token generation to a set of untrusted servers. It builds on an earlier
proposal, namely SePCAR [1], and extends the system design for improved
efficiency and scalability. To cater to system and user needs for secure and
private computations, HERMES utilizes and combines several cryptographic
primitives with secure multiparty computation efficiently. It conceals secret
keys of vehicles and transaction details from the servers, including vehicle
booking details, access token information, and user and vehicle identities. It
also provides user accountability in case of disputes. Besides, we provide
semantic security analysis and prove that HERMES meets its security and privacy
requirements. Last but not least, we demonstrate that HERMES is efficient and,
in contrast to SePCAR, scales to a large number of users and vehicles, making
it practical for real-world deployments. We build our evaluations with two
different multiparty computation protocols: HtMAC-MiMC and CBC-MAC-AES. Our
results demonstrate that HERMES with HtMAC-MiMC requires only approx 1,83 ms
for generating an access token for a single-vehicle owner and approx 11,9 ms
for a large branch of rental companies with over a thousand vehicles. It
handles 546 and 84 access token generations per second, respectively. This
results in HERMES being 696 (with HtMAC-MiMC) and 42 (with CBC-MAC-AES) times
faster compared to in SePCAR for a single-vehicle owner access token
generation. Furthermore, we show that HERMES is practical on the vehicle side,
too, as access token operations performed on a prototype vehicle on-board unit
take only approx 62,087 ms
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