Life Test Based on Progressively Group-Censored Samples From Exponential Distribution With Periodic Change in Failure Rate

A life test experiment based on progressively group censored sample with periodic change in the failure rate of an exponential distribution is considered. Estimates of the two failure rates under different conditions of usage of an item together with their asymptotic standard error are obtained by the method of maximum likelihood. A numerical example is given using the data available in the form of grouped observations under two conditions of usage during alternate time intervals of fixed lengths T/Sub1 and T/Sub2

On Detecting Interstellar Scintillation in Narrowband Radio SETI

To date, the search for radio technosignatures has focused on sky location as a primary discriminant between technosignature candidates and anthropogenic radio frequency interference (RFI). In this work, we investigate the possibility of searching for technosignatures by identifying the presence and nature of intensity scintillations arising from the turbulent, ionized plasma of the interstellar medium (ISM). Past works have detailed how interstellar scattering can both enhance and diminish the detectability of narrowband radio signals. We use the NE2001 Galactic free electron density model to estimate scintillation timescales to which narrowband signal searches would be sensitive, and discuss ways in which we might practically detect strong intensity scintillations in detected signals. We further analyze the RFI environment of the Robert C. Byrd Green Bank Telescope (GBT) with the proposed methodology and comment on the feasibility of using scintillation as a filter for technosignature candidates.Comment: 17 pages, 8 figures, published by Ap

Setiburst: A Robotic, Commensal, Realtime Multi-Science Backend For The Arecibo Telescope

Radio astronomy has traditionally depended on observatories allocating time to observers for exclusive use of their telescopes. The disadvantage of this scheme is that the data thus collected is rarely used for other astronomy applications, and in many cases, is unsuitable. For example, properly calibrated pulsar search data can, with some reduction, be used for spectral line surveys. A backend that supports plugging in multiple applications to a telescope to perform commensal data analysis will vastly increase the science throughput of the facility. In this paper, we presen

A 4-8 GHz Galactic Center Search for Periodic Technosignatures

Radio searches for extraterrestrial intelligence have mainly targeted the discovery of narrowband continuous-wave beacons and artificially dispersed broadband bursts. Periodic pulse trains, in comparison to the above technosignature morphologies, offer an energetically efficient means of interstellar transmission. A rotating beacon at the Galactic Center (GC), in particular, would be highly advantageous for galaxy-wide communications. Here, we present blipss, a CPU-based open-source software that uses a fast folding algorithm (FFA) to uncover channel-wide periodic signals in radio dynamic spectra. Running blipss on 4.5 hours of 4-8 GHz data gathered with the Robert C. Byrd Green Bank Telescope, we searched the central 6' of our Galaxy for kHz-wide signals with periods between 11-100 s and duty cycles ($\delta$) between 10-50%. Our searches, to our knowledge, constitute the first FFA exploration for periodic alien technosignatures. We report a non-detection of channel-wide periodic signals in our data. Thus, we constrain the abundance of 4-8 GHz extraterrestrial transmitters of kHz-wide periodic pulsed signals to fewer than one in about 600,000 stars at the GC above a 7$\sigma$ equivalent isotropic radiated power of $\approx 2 \times 10^{18}$ W at $\delta \simeq 10\%$. From an astrophysics standpoint, blipss, with its utilization of a per-channel FFA, can enable the discovery of signals with exotic radio frequency sweeps departing from the standard cold plasma dispersion law.Comment: 20 pages, 11 figures, published in AJ, in press (http://seti.berkeley.edu/blipss/

The miR-17 similar to 92 cluster collaborates with the Sonic Hedgehog pathway in medulloblastoma

Medulloblastomas (MBs) are the most common brain tumors in children. Some are thought to originate from cerebellar granule neuron progenitors (GNPs) that fail to undergo normal cell cycle exit and differentiation. Because microRNAs regulate numerous aspects of cellular physiology and development, we reasoned that alterations in miRNA expression might contribute to MB. We tested this hypothesis using 2 spontaneous mouse MB models with specific initiating mutations, Ink4c(-/-); Ptch1(+/-) and Ink4c(-/-); p53(-/-). We found that 26 miRNAs showed increased expression and 24 miRNAs showed decreased expression in proliferating mouse GNPs and MBs relative to mature mouse cerebellum, regardless of genotype. Among the 26 overexpressed miRNAs, 9 were encoded by the miR-17 similar to 92 cluster family, a group of microRNAs implicated as oncogenes in several tumor types. Analysis of human MBs demonstrated that 3 miR-17 similar to 92 cluster miRNAs (miR-92, miR-19a, and miR-20) were also overexpressed in human MBs with a constitutively activated Sonic Hedgehog (SHH) signaling pathway, but not in other forms of the disease. To test whether the miR-17 similar to 92 cluster could promote MB formation, we enforced expression of these miRNAs in GNPs isolated from cerebella of postnatal (P) day P6 Ink4c(-/-); Ptch1(+/-) mice. These, but not similarly engineered cells from Ink4c(-/-); p53(-/-) mice, formed MBs in orthotopic transplants with complete penetrance. Interestingly, orthotopic mouse tumors ectopically expressing miR-17 similar to 92 lost expression of the wild-type Ptch1 allele. Our findings suggest a functional collaboration between the miR-17 similar to 92 cluster and the SHH signaling pathway in the development of MBs in mouse and man