40,447 research outputs found
The integral cohomology rings of some p-groups
We determine the integral cohomology rings of an infinite family of p-groups,
for odd primes p, with cyclic derived subgroups. Our method involves embedding
the groups in a compact Lie group of dimension one, and was suggested by P H
Kropholler and J Huebschmann
Flight parameters and vehicle performance for project fire flight 1, launched april 14, 1964
Flight parameters and spacecraft performance for Fire project flight
A Quasi-Global Presentation of TIROS III Radiation Data
The TIROS III meteorological satellite was equipped with a five-channel medium resolution radiometer to measure the reflected solar radiation as well as the infrared emission of the earth-atmosphere system in five different spectral regions (Reference 1). According to the initial design of this radiation experiment, one of the most useful applications of the infrared measurements was to be the derivation of day and nighttime cloudiness from Channel 2, which was sensitive within the atmospheric "window" region (8 to 12 microns). Several authors already have demonstrated and discussed the principal usefulness of these data for this particular purpose (References 2, 3, and 4). This present study was performed to investigate and demonstrate the utility of the TIROS radiation data for global synoptic analyses
Lensed CMB power spectra from all-sky correlation functions
Weak lensing of the CMB changes the unlensed temperature anisotropy and
polarization power spectra. Accounting for the lensing effect will be crucial
to obtain accurate parameter constraints from sensitive CMB observations.
Methods for computing the lensed power spectra using a low-order perturbative
expansion are not good enough for percent-level accuracy. Non-perturbative
flat-sky methods are more accurate, but curvature effects change the spectra at
the 0.3-1% level. We describe a new, accurate and fast, full-sky
correlation-function method for computing the lensing effect on CMB power
spectra to better than 0.1% at l<2500 (within the approximation that the
lensing potential is linear and Gaussian). We also discuss the effect of
non-linear evolution of the gravitational potential on the lensed power
spectra. Our fast numerical code is publicly available.Comment: 16 pages, 4 figures. Changes to match PRD version including new
section on non-linear corrections. CAMB code available at http://camb.info
Distributed memory in a heterogeneous network, as used in the CERN-PS complex timing system
The Distributed Table Manager (DTM) is a fast and efficient utility for distributing named binary data structures called Tables, of arbitrary size and structure, around a heterogeneous network of computers to a set of registered clients. The Tables are transmitted over a UDP network between DTM servers in network format, where the servers perform the conversions to and from host format for local clients. The servers provide clients with synchronization mechanisms, a choice of network data flows, and table options such as keeping table disc copies, shared memory or heap memory table allocation, table read/write permissions, and table subnet broadcasting. DTM has been designed to be easily maintainable, and to automatically recover from the type of errors typically encountered in a large control system network. The DTM system is based on a three level server daemon hierarchy, in which an inter daemon protocol handles network failures, and incorporates recovery procedures which will guarantee table consistency when communications are re-established. These protocols are implemented over a communications layer which performs the data conversions, packet splitting, error-correction with retry, and time out handling. The same communications layer is used to implement the application program interface which calls on the server daemon for client services. DTM is a registration based system, in which communications are established dynamically as needed, and tables are distributed only to the clients who have registered their interest in them. The registration protocols include mechanisms to recover from daemon re-launches, and clean up after aborted clients
Chern classes and extraspecial groups
The mod-p cohomology ring of the extraspecial p-group of exponent p is
studied for odd p. We investigate the subquotient ch(G) generated by Chern
classes modulo the nilradical. The subring of ch(G) generated by Chern classes
of one-dimensional representations was studied by Tezuka and Yagita. The
subring generated by the Chern classes of the faithful irreducible
representations is a polynomial algebra. We study the interplay between these
two families of generators, and obtain some relations between them
Events leading up to the June 2015 outburst of V404 Cyg
On 2015 June 15 the burst alert telescope (BAT) on board {\em Swift} detected
an X-ray outburst from the black hole transient V404 Cyg. We monitored V404 Cyg
for the last 10 years with the 2-m Faulkes Telescope North in three optical
bands (V, R, and i). We found that, one week prior to this outburst, the
optical flux was 0.1--0.3 mag brighter than the quiescent orbital modulation,
implying an optical precursor to the X-ray outburst. There is also a hint of a
gradual optical decay (years) followed by a rise lasting two months prior to
the outburst. We fortuitously obtained an optical spectrum of V404 Cyg 13 hours
before the BAT trigger. This too was brighter () than
quiescence, and showed spectral lines typical of an accretion disk, with
characteristic absorption features of the donor being much weaker. No He II
emission was detected, which would have been expected had the X-ray flux been
substantially brightening. This, combined with the presence of intense
H emission, about 7 times the quiescent level, suggests that the disk
entered the hot, outburst state before the X-ray outburst began. We propose
that the outburst is produced by a viscous-thermal instability triggered close
to the inner edge of a truncated disk. An X-ray delay of a week is consistent
with the time needed to refill the inner region and hence move the inner edge
of the disk inwards, allowing matter to reach the central BH, finally turning
on the X-ray emission.Comment: Accepted by ApJ Letter, 7 pages, 5 figure
Effective use of ERTS multisensor data in the Northern Great Plains
The author has identified the following significant results. ERTS imagery was used as a tool in the identification and refinement of soil association areas; to classify land use patterns between crop and fallow fields; to identify corn, soybeans, and oats; and to identify broad generalized range ecosystems. Various data handling techniques were developed and applied to accomplish these tasks. A map outlining soil associations and relative land values was completed on a base mosaic of ERTS imagery and is included as an appendix to the report
New Cepheid variables in the young open clusters Berkeley 51 and Berkeley 55
As part of a wider investigation of evolved massive stars in Galactic open clusters, we have spectroscopically identified three candidate classical Cepheids in the little-studied clusters Berkeley 51, Berkeley 55 and NGC 6603. Using new multi-epoch photometry, we confirm that Be 51 #162 and Be 55 #107 are bona fide Cepheids, with pulsation periods of 9.83±0.01 d and 5.850±0.005 d respectively, while NGC 6603 star W2249 does not show significant photometric variability. Using the period-luminosity relationship for Cepheid variables, we determine a distance to Be 51 of 5.3 +1.0 −0.8 kpc and an age of 44 +9 −8 Myr, placing it in a sparsely-attested region of the Perseus arm. For Be 55, we find a distance of 2.2±0.3 kpc and age of 63 +12 −11 Myr, locating the cluster in the Local arm. Taken together with our recent discovery of a long-period Cepheid in the starburst cluster VdBH222, these represent an important increase in the number of young, massive Cepheids known in Galactic open clusters. We also consider new Gaia (data release 2) parallaxes and proper motions for members of Be 51 and Be 55; the uncertainties on the parallaxes do not allow us to refine our distance estimates to these clusters, but the well-constrained proper motion measurements furnish further confirmation of cluster membership. However, future final Gaia parallaxes for such objects should provide valuable independent distance measurements, improving the calibration of the period-luminosity relationship, with implications for the distance ladder out to cosmological scales
Crystallization of the regulatory and effector domains of the key sporulation response regulator Spo0A
The key response-regulator gene of sporulation, spo0A, has been cloned from Bacillus stearothermophilus and the encoded protein purified. The DNA-binding and phospho-acceptor domains of Spo0A have been prepared by tryptic digestion of the intact protein and subsequently crystallized in forms suitable for X-ray crystallographic studies. The DNA-binding domain has been crystallized in two forms, one of which diffracts X-rays to beyond 2.5 Angstrom spacing. The crystals of the phospho-acceptor domain diffract X-rays beyond 2.0 Angstrom spacing using synchrotron radiation
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