A Search for Optical Variability of Type 2 Quasars in SDSS Stripe 82

Hundreds of Type 2 quasars have been identified in Sloan Digital Sky Survey (SDSS) data, and there is substantial evidence that they are generally galaxies with highly obscured central engines, in accord with unified models for active galactic nuclei (AGNs). A straightforward expectation of unified models is that highly obscured Type 2 AGNs should show little or no optical variability on timescales of days to years. As a test of this prediction, we have carried out a search for variability in Type 2 quasars in SDSS Stripe 82 using difference-imaging photometry. Starting with the Type 2 AGN catalogs of Zakamska et al. (2003) and Reyes et al. (2008), we find evidence of significant g-band variability in 17 out of 173 objects for which light curves could be measured from the Stripe 82 data. To determine the nature of this variability, we obtained new Keck spectropolarimetry observations for seven of these variable AGNs. The Keck data show that these objects have low continuum polarizations (p<~1% in most cases) and all seven have broad H-alpha and/or MgII emission lines in their total (unpolarized) spectra, indicating that they should actually be classified as Type 1 AGNs. We conclude that the primary reason variability is found in the SDSS-selected Type 2 AGN samples is that these samples contain a small fraction of Type 1 AGNs as contaminants, and it is not necessary to invoke more exotic possible explanations such as a population of "naked" or unobscured Type 2 quasars. Aside from misclassified Type 1 objects, the Type 2 quasars do not generally show detectable optical variability over the duration of the Stripe 82 survey.Comment: 14 pages, 8 figures. Accepted for publication in A

Inertia compensation while scanning screw threads on coordinate-measuring machines

Usage of scanning coordinate-measuring machines for inspection of screw threads has become a common practice nowadays. Compared to touch trigger probing, scanning capabilities allow to speed up measuring process while still maintaining high accuracy. However, in some cases accuracy drasticaly depends on the scanning speed. In this paper a compensation method is proposed allowing to reduce the influence of some dynamic effects while scanning screw threads on coordinate-measuring machines

Early foetal development of the articular disc in the human temporomandibular joint

In foetuses of 9 and 10 weeks the articular disc presents a more cellular structure with bands of connective tissue fibres. It is connected with the articular capsule and lateral pterygoid muscle. During weeks 11 and 12 there is an increase in collagenous fibres and fusiform cells are located mainly close to the surface of the disc

Water and Fire – The History of a Mound of Ash: Water Management in Hellenistic Berenike, Its Environmental and Logistical Setting

Archaeological work since 2014 in the Hellenistic areas of Berenike, a key port on Egypt’s Red Sea coast, founded by Ptolemy II Philadelphus in c. 275 BC, has brought extensive evidence of water-related structures: a rock-cut well located inside a rebuilt early-Hellenistic gate and a nearby cistern with an associated rainwater-collection system, that has changed the way in which the sources and uses of water in Hellenistic Berenike is understood today. The research started with the excavation of an ash mound, a characteristic landmark in the western part of the site, which is now believed to be the rubbish dump from the furnace that heated a Hellenistic bathhouse. At this stage in the research, it can be argued that Hellenistic Berenike had sufficient water available on site not only for drinking (hence potable), and agricultural and industrial uses, but also for public bathing. This article summarises the current state of research, presenting recent discoveries of a Hellenistic date at the site within their archaeological, architectural and environmental contexts

Skeletal units of the human embryonic mandible

The development of the mandible was traced on serial sections of 20 human embryos aged 5-8 weeks (developmental stages 13-23). Special consideration was given to the differentiation of skeletal units proposed by Sperber. The first skeletal units, namely the mandibular body, the alveolar unit and the condylar unit, may be distinguished in the 7th week. The primordia of all units are identified by the end of the embryonic period (8 weeks)

Differentiation of the nuclear groups in the posterior horn of the human embryonic spinal cord

The formation of nuclear groups in the posterior horns of the human embryonic spinal cord was traced in serial sections of embryos of developmental stages 13 to 23 (32 to 56 postovulatory days). The following observations, new for the human, are presented: 1. The differentiation of the neural tube into 3 zones (germinal, mantle and marginal) is detected in the middle of the 5th week. 2. The primordia of the posterior horns are marked at stage 14 (33 days). 3. In the middle of the 7th week the nucleus proprius and substantia gelatinosa are discerned. 4. Differentiation of the nuclei within the posterior horns proceeds in the ventrodorsal and rostrocaudal gradients. (Folia Morphol 2011; 70, 4: 245&#8211;251

Schwann units in the human foetal phrenic nerve

In three human foetuses aged 15, 17, and 23 weeks the number of axons surrounded by single Schwann cells was counted. These Schwann cell/axon complexes form the Schwann units. The largest Schwann units in the foetus aged 15 weeks contained 232 axons, in the foetus of 17 weeks the number was 140 and in the foetus of 23 weeks the largest units contained 65 axons

Early development of the human palate in stages 16 and 17

A study was performed on 12 human embryos at developmental stages 16 and 17 (6th week). In the investigated embryos the primary palate is formed from medial nasal, lateral nasal, and maxillary processes. The medial and lateral nasal processes merge and form the nasal fin at stage 16. This fin regresses and at stage 17 and persists as the oronasal membrane. The primordia of the secondary palate appear at stage 17. (Folia Morphol 2011; 70, 1: 29-32

The Optical Gravitational Lensing Experiment. Monitoring of QSO 2237+0305

We present results from 2 years of monitoring of Huchra's lens (QSO 2237+0305) with the 1.3 m Warsaw telescope on Las Campanas, Chile. Photometry in the V band was done using a newly developed method for image subtraction. Reliable subtraction without Fourier division removes all complexities associated with the presence of a bright lensing galaxy. With positions of lensed images adopted from HST measurements it is relatively easy to fit the variable part of the flux in this system, as opposed to modeling of the underlying galaxy. For the first time we observed smooth light variation over a period of a few months, which can be naturally attributed to microlensing. We also describe automated software capable of real time analysis of the images of QSO 2237+0305. It is expected that starting from the next observing season in 1999 an alert system will be implemented for high amplification events (HAE) in this object. Time sampling and photometric accuracy achieved should be sufficient for early detection of caustic crossings.Comment: 8 pages (including 4 figures and table), latex, emulateapj, submitted to ApJ, revised version - minor change