1,641 research outputs found
On continuum modeling of sputter erosion under normal incidence: interplay between nonlocality and nonlinearity
Under specific experimental circumstances, sputter erosion on semiconductor
materials exhibits highly ordered hexagonal dot-like nanostructures. In a
recent attempt to theoretically understand this pattern forming process, Facsko
et al. [Phys. Rev. B 69, 153412 (2004)] suggested a nonlocal, damped
Kuramoto-Sivashinsky equation as a potential candidate for an adequate
continuum model of this self-organizing process. In this study we theoretically
investigate this proposal by (i) formally deriving such a nonlocal equation as
minimal model from balance considerations, (ii) showing that it can be exactly
mapped to a local, damped Kuramoto-Sivashinsky equation, and (iii) inspecting
the consequences of the resulting non-stationary erosion dynamics.Comment: 7 pages, 2 Postscript figures, accepted by Phys. Rev. B corrected
typos, few minor change
Infrared variability, maser activity, and accretion of massive young stellar objects
Methanol and water masers indicate young stellar objects. They often exhibit
flares, and a fraction shows periodic activity. Several mechanisms might
explain this behavior but the lack of concurrent infrared (IR) data complicates
to identify the cause. Recently, 6.7 GHz methanol maser flares were observed,
triggered by accretion bursts of high-mass YSOs which confirmed the IR-pumping
of these masers. This suggests that regular IR changes might lead to maser
periodicity. Hence, we scrutinized space-based IR imaging of YSOs associated
with periodic methanol masers. We succeeded to extract the IR light curve from
NEOWISE data for the intermediate mass YSO G107.298+5.639. Thus, for the first
time a relationship between the maser and IR variability could be established.
While the IR light curve shows the same period of ~34.6 days as the masers, its
shape is distinct from that of the maser flares. Possible reasons for the IR
periodicity are discussed.Comment: 4 pages, 3 figures, to be published in: Proceedings IAU Symposium 336
"Astrophysical Masers: Unlocking the Mysteries of the Universe", Editors: A.
Tarchi, M.J. Reid & P. Castangia, updated version with hyperlinks adde
Mid - infrared interferometry of massive young stellar objects II Evidence for a circumstellar disk surrounding the Kleinmann - Wright object
The formation scenario for massive stars is still under discussion. To
further constrain current theories, it is vital to spatially resolve the
structures from which material accretes onto massive young stellar objects
(MYSOs). Due to the small angular extent of MYSOs, one needs to overcome the
limitations of conventional thermal infrared imaging, regarding spatial
resolution, in order to get observational access to the inner structure of
these objects.We employed mid - infrared interferometry, using the MIDI
instrument on the ESO /VLTI, to investigate the Kleinmann - Wright Object, a
massive young stellar object previously identified as a Herbig Be star
precursor. Dispersed visibility curves in the N- band (8 - 13 {\mu}m) have been
obtained at 5 interferometric baselines. We show that the mid - infrared
emission region is resolved. A qualitative analysis of the data indicates a non
- rotationally symmetric structure, e.g. the projection of an inclined disk. We
employed extensive radiative transfer simulations based on spectral energy
distribution fitting. Since SED - only fitting usually yields degenerate
results, we first employed a statistical analysis of the parameters provided by
the radiative transfer models. In addition, we compared the ten best - fitting
self - consistent models to the interferometric observations. Our analysis of
the Kleinmann - Wright Object suggests the existence of a circumstellar disk of
0.1M\odot at an intermediate inclination of 76\circ, while an additional dusty
envelope is not necessary for fitting the data. Furthermore, we demonstrate
that the combination of IR interferometry with radiative transfer simulations
has the potential to resolve ambiguities arising from the analysis of spectral
energy distributions alone.Comment: 12 pages, 22 figures accepted for publication in A&
Dissecting Massive YSOs with Mid-Infrared Interferometry
The very inner structure of massive YSOs is difficult to trace. With
conventional observational methods we often identify structures still several
hundreds of AU in size. But we also need information about the innermost
regions where the actual mass transfer onto the forming high-mass star occurs.
An innovative way to probe these scales is to utilise mid-infrared
interferometry. Here, we present first results of our MIDI GTO programme at the
VLTI. We observed 10 well-known massive YSOs down to scales of 20 mas. We
clearly resolve these objects which results in low visibilities and sizes in
the order of 30 - 50 mas. Thus, with MIDI we can for the first time quantify
the extent of the thermal emission from the warm circumstellar dust and thus
calibrate existing concepts regarding the compactness of such emission in the
pre-UCHII region phase. Special emphasis will be given to the BN-type object
M8E-IR where our modelling is most advanced and where there is indirect
evidence for a strongly bloated central star.Comment: 8 pages, 6 figures, proceedings contribution for the conference
"Massive Star Formation: Observations confront Theory", held in September
2007 in Heidelberg, Germany; to appear in ASP Conf. Ser. 387, H. Beuther et
al. (eds.
A Newly Discovered Bordetella Species Carries a Transcriptionally Active CRISPR-Cas with a Small Cas9 Endonuclease
Background Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated genes (cas) are widely distributed among bacteria. These systems provide adaptive immunity against mobile genetic elements specified by the spacer sequences stored within the CRISPR. Methods The CRISPR-Cas system has been identified using Basic Local Alignment Search Tool (BLAST) against other sequenced and annotated genomes and confirmed via CRISPRfinder program. Using Polymerase Chain Reactions (PCR) and Sanger DNA sequencing, we discovered CRISPRs in additional bacterial isolates of the same species of Bordetella. Transcriptional activity and processing of the CRISPR have been assessed via RT-PCR. Results Here we describe a novel Type II-C CRISPR and its associated genes—cas1, cas2, and cas9—in several isolates of a newly discovered Bordetella species. The CRISPR-cas locus, which is absent in all other Bordetella species, has a significantly lower GC-content than the genome-wide average, suggesting acquisition of this locus via horizontal gene transfer from a currently unknown source. The CRISPR array is transcribed and processed into mature CRISPR RNAs (crRNA), some of which have homology to prophages found in closely related species B. hinzii. Conclusions Expression of the CRISPR-Cas system and processing of crRNAs with perfect homology to prophages present in closely related species, but absent in that containing this CRISPR-Cas system, suggest it provides protection against phage predation. The 3,117-bp cas9 endonuclease gene from this novel CRISPR-Cas system is 990 bp smaller than that of Streptococcus pyogenes, the 4,017-bp allele currently used for genome editing, and which may make it a useful tool in various CRISPR-Cas technologies
Антропоекосистема та духовні цінності – чи вдасться перетнути барьер сучасної кризи та чим небезпечна концепція лімітування (до питання транскрипції та перекладів наукових понять на кшталт "сталий розвиток")
Derangements in a Ferrers Board
The classic derangement question of counting the number of derangements for n objects from some initial permutation of the objects was first considered by de Montfort in 1708. A particular recasting of a permutation allows us to place any permutation onto an n x n board, from which certain properties of derangements may be understood. This research extends the classic derangement question to the more general Ferrers board, which is an n x n board with a missing section in the lower-right corner. Various properties of the derangement numbers for these more general boards are stated and proven in the course of this work
Avian Use of Rice-Baited Trays Attached to Cages with Live Decoy Blackbirds in Central North Dakota
For several decades, blackbird depredation of sunflower has been a continuous problem. Sunflower growers consistently place blackbirds in the top tier of problems associated with growing sunflower in the northern Great Plains. Many non-lethal tactics have been employed in an attempt to protect ripening sunflower from foraging flocks of blackbirds. Thinning cattail-choked wetlands to reduce roosting habitat, using pyrotechniques to frighten feeding birds, planting Wildlife Conservation Sunflower Plots to lure birds away from commercial plots, applying taste repellents, and adapting cultural methods such as block planting to synchronize ripening are just a few such tactics. Even so, the numbers of blackbirds migrating through the northern Great Plains can overwhelm non-lethal techniques. That is, in some circumstances there are too many blackbirds for non-lethal techniques to be effective. One avicide, DRC-1339, is registered for use as a lethal bait in the U.S. and North Dakota. The avicide is usually mixed with brown rice at a ratio of 1:25 (treated rice kernel to untreated rice kernels). Normally, the rice mixture is broadcast on the ground in the ripening or sprouting crop. Non-blackbirds are plentiful in ripening sunflower fields, causing a potential risk to these species with the use of DRC-1339. These granivorous non-blackbirds might eat treated rice, causing an unintentional loss. A number of species of songbirds and sparrows could be at risk. Also, ring-necked pheasants (Phasianus colchicus) and mourning doves (Zenaida macroura) are species of high concern. One potential method of avoiding non-blackbirds is to put live decoys (blackbirds) in cages in areas devoid of habitat to attract free-living blackbirds to bait trays attached to the top of the decoy cages. The intent is to reduce large concentrations of blackbirds that cannot be otherwise dispersed by non-lethal means. The objective of this study is to identify and quantify the avian species visiting the bait trays. Our goal is to develop an effective and environmentally-safe method for managing locally abundant blackbird populations
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